Alteration and trace elements of volcanics in the San Francisco Mountains

Alteration and trace elements of volcanics in the San Francisco Mountains

ALTERATION AND TRACE ELEMENTS OF VOLCANICS IN THE SAN FRANCISCO MOUNTAINS by JOHN PERCIVAL BROOKE A t h e s i s s u b m i t t e d t o t h e f a c u l t y of t h e U n i v e r s i ty o f U t a h i n p a r t i a l f u l f i l l m e n t of t h e r e q u i r e m e n ts f o r t h e d e g r e e of D o c t o r of P h i l o s o p hy D e p a r t m e n t of M i n i n g a n d G e o l o g i c a l E n g i n e e r i ng U n i v e r s i t y of U t ah J u n e 9 1964 UNIVERSITY OF UTAH LIBRARIES T h i s T h e s i s f o r t h e PhoDo D e g r ee by J o h n P e r c i v a l B r o o ks h a s b e e n a p p r o v ed A p r i l o 1964 a i r m a r i y - o u p © r v I s o r y Commi 1 1 e e S u p e r v i s o r y C o m m i t t ee a d e r 9 S u p e r v is arrr^^^K i aMPBM ; 1 HU -B Wi 11 .' - g a d e r 9 S u p e r v i s o r y C o m m i t t ee a d e r 9 S u p e r v i s o r y C o m m i t t ee 7 a d M a j o r D e p a r t m e nt 5 3 2 S 7 9 ACKNOWLEDGMENTS T h e a u t h o r w i s h e s t o e x p r e s s h i s a p p r e c i a t i o n t o t h o se i n d i v i d u a l s who h e l p e d c o m p l e t e t h i s t h e s i s 0 Drc Ho P c N a c k o w s kl s u g g e s t e d t h e t o p i c and g u i d e d t h e r e s e a r c h * , Dr0 W i l l i a m P a r ry a n d Mr0 B r e n t H a m i l made h e l p f u l s u g g e s t i o n s and c o n s t r u c t i ve c r i t i c i s m s t h r o u g h o u t t h e p r o j e c t , -, T h e f i n a n c i a l a s s i s t a n c e of s e v e r a l o r g a n i s a t i o n s is a c k n o w l e d g e d o The B e a r C r e e k M i n i n g Company g r a n t e d a i d f o r a p o r t i o n of t h e f i e l d r e s e a r c h 0 The two s o u t h e r n m o s t a r e a s w e re m a p p e d i n c o n j u n c t i o n w i t h Dr<> Brmmon S t r i n g f c a m w i t h f u n ds s u p p l i e d by t h e U n i f o r m S c h o o l Fund of t h e s t a t e of U t a h o A p o r t i o n of t h e s u p p l i e s w e r e p u r c h a s e d w i t h m o n i e s f r om t he K e n n e e o t t R e s e a r c h Fundo S e v e r a l o t h e r I n d i v i d u a l s h e l p s w i t h t h e e x p e r i m e n t al s t u d i e s o P r o f e s s o r H a r o l d B r a d f o r d a i d e d i n t h e s p e c t r o c h e m i c al a n a l y s e s o MrD Don L i v i n g s t o n a s s i s t e d w i t h t h e f i e l d m a p p i ng a n d s a m p l e c o l l e c t i n g d u r i n g on© f i e l d s e a s o n0 TABLE OF CONTENTS CHAPTER PAGE l o INTRODUCTION O O O O O O O O 6 O O O O O O O O O •i* T h e P r o b l e m 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 T h e F i e l d S t u d y „ 0 O O O O O O O O O O O O O *» The L a b o r a t o r y S t u d y 0 0 0 0 0 0 0 0 0 0 0 0 0 3 L o c a t i o n of t h e A r e a 0 0 0 0 0 0 0 0 0 0 0 0 0 5 I I o THEORETICAL BACKGROUND OF ALTERATION 0 0 0 0 0 0 8 D e f i n i t i o n s of H y d r o t h e r m a l A l t e r a t i o n 0 a 0 o 8 P h y s i c a l ^ C h e m i c a l 9 and M i n e r a l C h a n g e s 0 0 « 9 M e c h a n i s m s of A l t e r a t i o n o o 0 0 0 o o o o o o 13 L a b o r a t o r y A l t e r a t i o n S t u d i e s 0 0 0 0 0 0 o a I? F i e l d A l t e r a t i o n S t u d i e s 0 0 0 0 0 0 0 0 0 0 0 2^ Summary of P r e v i o u s A l t e r a t i o n S t u d i e s 0 „ o o 2? I I I o THEORETICAL GEOCHEMICAL BASIS FOR TRACE ELEMENT CONTENT 0 0 0 0 0 0 0 0 0 0 0 0 29 T r a c e E l e m e n t O c c u r r e n c e 0 o 0 o o o o B 0 o 0 29 G e o c h e m i c a l D i s p e r s i o n 0 0 0 0 0 0 0 0 0 0 0 0 30 G e o c h e m i c a l M o b i l i t y 0 0 0 0 0 0 0 0 0 0 0 0 0 31 G e o c h e m i s t r y of C o p p e r 0 0 0 0 0 0 0 0 0 0 0 0 32 G e o c h e m i s t r y of Lead „ 0 0 0 0 0 0 0 0 0 0 0 0 j j G e o c h e m i s t r y of Z i n c 0 D o 0 o 0 o o P 9 o 0 o 35 G e o c h e m i s t r y of A r s e n i c 0 0 0 0 0 0 0 0 0 0 0 J f ( i ) CHAPTER PAGE IVo VOLCANIC ROCK UNITS OF THE SAN FRANCISCO MOUNTAIN AREA 0 9 o o o 0 o . » <, « o 0 o ? o 39 G e n e r a l S t a t e m e n t 0 o » 0 o 0 0 » o 0 o o o o 39 Rock U n i t s I n D e t a i l e d A r e a s 0 0 o o o o o o o 39 Vo HYDROTHERMAL ALTERATION IN THE SAN FRANCISCO MOUNTAINS F i e x d S t u d i e s o o o o o o o o o o o o o o o o ^6 D e s c r i p t i o n of t h e A r e a s Mapped I n D e t a i l 0 0 52 D e s c r i p t i v e P e t r o g r a p h y of A l t e r ed "VOlC a n I C S O O O O O O O O O O O O O O O O O 6 i r a r a g e n e s i s O O O O O O O O O O O O O O O O ffc» VIo ALTERATION MINERALS FROM THE SAN FRANCISCO MOUNTAINS O O O O O O O O O O O O O O O O OO V I I o TRACE ELEMENTS OF VOLCANICS 0 o • o • • • • , 0 83 I n t r o d u c t i o n S p e c t r o c h e m l c a l A n a l y s i s of S a m p l es V I I I o X-RAY FLUORESCENCE SPECTROGRAPHIC ANALYSES 0 o 0 96 T h e o r y of X ~ r a y F l u o r e s c e n c e S p e c t r o g r a p h y 0 0 96 P r e s e n t a t i o n of S p e c t r o g r a p h l c D a t a 0 ° e o 0 98 S t a t i s t i c a l A n a l y s i s of X - r a y F l u o r e s c e nt S p e c t r o g r a p h l c D a t a 0 o « o o a o © o o o *> 102 IXo INTERPRETATIONS o o o o o o o o o o o o o o o o 10? An A n a l y s i s of t h e N a t u r e and D i s t r i b u t i on o f t h e S e c o n d a r y M i n e r a l S u i t e 0 O O O O O O O O O O O O O O O O O O O o o o O O o o o o I I CHAPTER PAGE An A n a l y s i s of S p e e t r o e h e m l c a l D a t a 0 o © 0 © 110 Xo CONCLUSIONS 0 0 0 0 „ 0 0 0 0 0 0 0 . 8 0 6 0 . u6 BIBLIOGRAPHY o o o o o © © © o © o o © © © •, o © © © © 119 ( i i i ) L I S T OF TABLES TABLES PAGE 1, A r e a s and M i n i n g D i s t r i c t s S h o w i ng S I X i f i c a t i o n i> 6 4 z'::« a-.i e: ;©: ' •© ' © © # • • £ • • • • • • * • > * 11 2o A r e a s and M i n i n g D i s t r i c t s S h o w i ng S e r i c i t i z a t l o n o © © © © ©. © o o © o © ©© © © o 1^ 3 , A r e a s and M i n i n g D i s t r i c t s S h o w i ng A r g l n i d a t i o n © o » o © ©' © © o o © o © © © © © 13 4o M o b i l i t y of T r a c e E l e m e n t s 8 © « © © © © ' © © © © 0 J2 5© C o n c e n t r a t i o n of C o p p e r i n I g n e o u s R o c k s © © © © © 33 6© C o n c e n t r a t i o n of L e a d I n I g n e o u s B o c k s © © © © © © 3^ 7© C o n c e n t r a t i o n of Z i n c i n I g n e o u s R o c k s © © © © © © 3b 8© G e n e r a l i z e d S e q u e n c e of V o l c a n i c s i n t he S q u a w P e a k A r e a o o o © © © o « © © © © © 6 © © 9e G e n e r a l i z e d S e q u e n c e of V o l c a n i c s i n t he E a s t and West W h i t e M o u n t a i n A r e a s © © © © © © © 10© X - r a y D i f f r a c t i o n P e a k s of A l u n l t e . © © © © © © © 7^ I I o X - r a y D i f f r a c t i o n P e a k s of C r l s t o b a l i t e © © © © © ?6 12© X - r a y D i f f r a c t i o n P e a k s of J a r o s i t e © © © © © © © 78 13o X - r a y D i f f r a c t i o n P e a k s of K a o l i n i t e © © © © © © » 79 l ^ o P h y s i c a l P r o p e r t i e s of Copper,.. L e a d 9 and I n d i u m © 87 15© S p e c t r o g r a p h l c A r c i n g C o n d i t i o n s and L i n es A n a l y z e d f o r Cu a n d Pb © © © © © © © © © © © © • 88 16© A l t e r a t i o n Type a n d S p e c t r o c h e m i c a l R e s u l ts f o r t h e S a m p l e s A n a l y z e d © o o o o o o o o o o o TABLE PAGE S t a t i s t i c a l F u n c t i o n f o r Cu a n d Pb A n o m a l i e s 0 0 o 95 iSo Cu2 P b 9 Z n 9 and As C o n t e n t and A l t e r a t i on T y p e of S a m p l e s o o o o o o o o o o o o o o o o 98 19„ S t a t i s t i c a l X - r a y S p e c t r o g r a p h l c D a t a 0 o » 0 0 « .103 20o R e s u l t s of t h e F a n d H t " T e s t 9 Where t he H o r n S i l v e r A r e a T r a c e E l e m e n t V a l u es Were C o m p a r e d W i t h T h o s e of O t h e r A r e a s 0 <, 0 0 106 2 1 o Means a n d S t a n d a r d D e v i a t i o n s of Cu C o n t e n ts o f t h e F o u r A l t e r a t i o n A r e a s 0 o & © » o o 0 o o 112 22o Means and S t a n d a r d D e v i a t i o n s of Pb C o n t e n ts o f t h e F o u r A l t e r a t i o n A r e a s o o o o o o o o o o 113 2 3 0 Means and S t a n d a r d D e v i a t i o n s of Zn C o n t e n ts o f t h e F o u r A l t e r a t i o n A r e a s o o o o o o o o o o 114 2 ^ 0 Means and S t a n d a r d . D e v i a t i o n s of A r s e n ic C o n t e n t s of t h e F o u r A l t e r a t i o n A r e a s © © © 0 © 115 { v ) o o o o o o o o o o o o o o o o o o o o o o o o o o L I S T OP PLATES PLATE PAGE %0 I n d e x Map S h o w i n g A r e a s S t u d i ed 2o S o l u b i l i t y of S I 0 2 i n HCiD H g S O ^ HgOg NaCO^ a n d NaOH a t V a r i o u s T e m p e r a t u r e s 0 o o o Jo F i e l d s of F o r m a t i o n of Some Common H y d r o t h e r m a l M i n e r a ls 4 0 A p p r o x i m a t e P r e s s u r e - T e m p e r a t u r e D i a g r a ms f o r S 1 0 ^ M i n e r a l s 0 0 0 0 * « 0 0 & 0 Q o o 0 «. 23 5o X - r a y P a t t e r n s of A r g l l l l c A l t e r a t i o n 0 o 0 0 «, o 48 60 Z o n i n g of A l t e r a t i o n M i n e r a l s In T h e Squaw P e a k A r e a 0 0 0 0 0 0 0 0 0 0 0 0 0 0 53 7e A r g i l l i e A l t e r a t i o n W i t h I r o n S t a i n i n g In T h e Squaw P e a k A r ea 80 A l t e r a t i o n I n The W h i t e M o u n t a i n A r e a 0 0 0 0 0 0 58 9o Views of t h e H o r n S i l v e r Mine 0 O O O O O O O O O WW lOo A r g i l l i e A l t e r a t i o n 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 63 H o A r g i l l i e A l t e r a t i o n W i t h S a n i d i n e C r y s t a ls 12o A r g i l l l z a t i o n From T h e Squaw P e a k A r ea 13o Z e o X I t i o A l t e r a t i o n 0 -o. »: « « * o 9 « <o- « • « o o 71 1 4 0 M u l t i p l e F r a c t u r e s 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 73 15o A l t e r a t i o n Map of The Squaw P e a k A r e a 0 0 0 0 0 P o c k et l 6 o A l t e r a t i o n Map of West Whit© M o u n t a i n A r e a o « o P o c k et 17o A l t e r a t i o n Map of The E a s t W h i t e M o u n t a i n A r e a 0 P o c k et 0 0 0 0 0 0 0 0 0 0 PLATE PAGE 1 8 0 X= r a y P a t t e r n of A l u n i t e Prom t he S a n F r a n c i s c o M o u n t a i n s © o o o o o o o o o o o 75 1 9 e X - r a y P a t t e r n of C r l s t o b a l l t e Prom t he S a n F r a n c i s c o M o u n t a i n s 0 0 0 0 0 0 0 0 0 0 0 0 77 20o X - r a y P a t t e r n of J a r o s l t e From t he S a n F r a n c i s c o M o u n t a i n s o o o 0 o o 0 0 o o o o 78 21o X - r a y P a t t e r n of K a o l l n i t e From t he S a n F r a n c i s c o M o u n t a i ns 22o X - r a y S t u d y of Q u a r t z - K a o l i n l t e M i x t u r e s 0 ZJo Sample L o c a t i o n Map o f t h e S o u t h e rn S a n F r a n c i s c o M o u n t a i n s 0 0 0 0 0 0 * 0 0 0 0 P o c k et 2k* W o r k i n g C u r v e s F o r Cu a n d Pb 0 o o « 25» D i a g r a m of X - r a y S p e c t r o g r a ph 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 o o o o o o o o o o o o o o o o ( T i l ) CHAPTER I INTRODUCTION S e v e r a l a r e a s of h y d r o t h e r m a l a l t e r a t i o n e x i s t s o u th of t h e H o r n S i l v e r m i n e i n t h e S a n F r a n c i s c o M o u n t a i n s of Utah© I o THE PROBLEM S t a t e m e n t of t h e p r o b l e m 0 I t was t h e p u r p o s e of t h is s t u d y ( 1 ) t o d e s c r i b e t h e n a t u r e of a l t e r a t i o n m i n e r a l s i n t he S a n F r a n c i s c o M o u n t a i n s n e a r a n d s o u t h of t h e H o r n S i l v e r m i n e; ( 2 ) t o d e t e r m i n e t h e t r a c e e l e m e n t c o n t e n t of f r e s h a n d a l t e r ed v o l c a n i c r o c k s ; a n d ( 3 ) t o s t u d y i n d e t a i l t h e a l t e r a t i on c h a r a c t e r i s t i c s of t h r e e s e l e c t e d a l t e r a t i o n a r e a s„ c o n d u c t i n g t h e f o l l o w i n g f i e l d and l a b o r a t o r y s t u d i e s c o n ­c u r r e n t l y o v e r a p e r i o d of f o u r f i e l d s e a s o n s f r o m 1 9 5 9 to 1963© A r e a s of a l t e r e d v o l c a n i c s f i r s t w e r e d e l i n e a t e d on a e r i a l p h o t o g r a p h s , w h e r e t h e y a p p e a r e d a s b l e a c h e d p a t c h e s 0 T h e y w e r e t h e n e x a m i n e d i n t h e f i e l d a n d t h e i r c h a r a c t e r was v e r i f i e d © Rock s a m p l e s w e r e c o l l e c t e d f r om t h e s e p a t c h e s and f r om f r e s h o r u n a l t e r e d v o l c a n i c r o c k s f o r l a b o r a t o r y s t u d y© Maps of t h e t h r e e a r e a s s t u d i e d i n d e t a i l w e r e p r e p a r e d by s k e t c h i n g z o n e s of s e c o n d a r y m i n e r a l s on a e r i a l p h o t o g r a p h s0 A l t e r a t i o n m i n e r a l s w e r e i d e n t i f i e d i n t h e l a b o r a t o r y by x - r a y d i f f r a c t i o n and i n f r a r e d s p e c t r o s c o p y a n a l y s e s © The ( 1 ) t r a c e l e a d , c o p p e r s z i n c , and a r s e n i c c o n t e n t of a l t e r e d and f r e s h r o c k s a m p l e s was d e t e r m i n e d by x - r a y f l u o r e s c e n t s p e c t r p - c h e m i c a l a n a l y s i s . The t r a c e l e a d and c o p p e r c o n t e n t of some a l t e r e d a n d f r e s h r o c k s a m p l e s was a l s o d e t e r m i n e d by e m i s s i on s p e c t r o g r a p h y . The t r a c e e l e m e n t d a t a w e r e a n a l y z e d s t a t i s ­t i c a l l y t o d e t e r m i n e t h e p r e s e n c e of g e o c h e m i c a l a n o m a l i e s© I I o THE FIELD STUDY F i e l d s t u d y . The f i e l d s t u d y c o n s i s t e d of ( l ) d e l i n e ­a t i n g a n d s t u d y i n g a r e a s of h y d r o t h e r m a l a l t e r a t i o n s (2) c o l ­l e c t i n g s p e c i m e n s f o r l a b o r a t o r y a n a l y s i s ! a n d ( 3 ) s t u d y i ng t h r e e s e l e c t e d a r e a s i n d e t a i l © A l t e r a t i o n a r e a s w e r e l o c a t ed a n d p l o t t e d on a e r i a l p h o t o g r a p h s a t a s c a l e of 2 " = 1 m i l e . S a m p l e s of a l t e r e d r o c k w e r e o b t a i n e d f r om e a c h a r e a . G e o l o g ic maps of t h e t h r e e a r e a s w e r e p r e p a r e d © These w e r e t h e Squaw P e a k 9 West W h i t e M o u n t a i n a n d E a s t W h i t e M o u n t a i n a r e a s. a r e a a n d s t u d i e d i n d e t a i l * T h e s e i n c l u d e d z o n e s of a l u n l t e 9 s i l i c a 9 k a o l i n l f c a , h e m a t i t e 9 a n d c h l o r i t e © A e r i a l p h o t o g r a p hs a t a s c a l e of 1 H « 4 0 0 6 w e r e u s e d a s b a s e maps f o r p l o t t i ng t h e s e d a t a © From t h e s e a n a l t e r a t i o n map of e a c h a r e a was p r e p a r e d© v o l c a n i c r o c k s w e r e o b t a i n e d f o r l a b o r a t o r y a n a l y s i s . Rock f r a g m e n t s w e r e b r o k e n f r o m t h e o u t c r o p s a n d t h e s a m p le M a p p i n g . S e v e r a l m i n e r a l z o n e s w e r e m a p p e d i n e a ch ( 2 ) l o c a t i o n s w e r e n o t e d on t h e a e r i a l p h o t o g r a p h s . A w r i t t en d e s c r i p t i o n of e a c h s a m p l e l o c a t i o n a n d r o c k t y p e was r e c o r d e d. The s a m p l e s w e r e s t o r e d i n c l o t h s a m p l e b a g s w i t h e x t e r i or l a b e l s a n d t r a n s p o r t e d t o t h e l a b o r a t o r y f o r a n a l y s i s . A p p r o x i ­m a t e l y 250 s a m p l e s w e r e c o l l e c t e d a n d s t u d i e d© I I I . THE LABORATORY STUDY L a b o r a t o r y s t u d y . The l a b o r a t o r y s t u d y c o n s i s t e d of m i n e r a l i d e n t i f i c a t i o n - p e t r o g r a p h i c a n a l y s i s , a n d t r a c e e l e m e nt d e t e r m i n a t i o n . A l t e r a t i o n m i n e r a l s w e r e i d e n t i f i e d by x - r ay d i f f r a c t i o n a n d i n f r a r e d s p e c t r o s c o p i c t e c h n i q u e s . F r a g m e n ts a n d t h i n s e c t i o n s of r o c k s w e r e o b s e r v e d w i t h t h e p e t r o g r a p h ic m i c r o s c o p e . The t r a c e l e a d . c o p p e r 9 z i n c a n d a r s e n i c c o n t e nt of f r e s h a n d a l t e r e d r o c k s w e r e d e t e r m i n e d by e m i s s i o n and x - r a y s p e c t r o g r a p h l c t e c h n i q u e s. X - r a y d i f f r a c t i o n © A l t e r a t i o n m i n e r a l s w e r e i d e n t i f i ed by x - r a y d i f f r a c t i o n a n a l y s i s . T h r e e h u n d r e d x - r a y p o w d er p a t t e r n s w e r e p r e p a r e d u s i n g a N o r e l c o x - r a y d i f f r a c t o m e t er w i t h a s t r i p c h a r t r e c o r d e r © O r i e n t e d s m e a r s a n d r a n d o m o r i e n t a ­t i o n d i f f r a c t i o n p a t t e r n s w e r e r e c o r d e d a n d a n a l y z e d © A q u a n t i ­t a t i v e x - r a y s t u d y t o d e t e r m i n e d e t e c t i o n l i m i t s of s i l i c a and k a o l i n i t e was c o m p l e t e d© I n f r a r e d a n a l y s i s . M i n e r a l I d e n t i f i c a t i o n s were v e r i f i e d by i n f r a r e d s p e c t r o s c o p i c a n a l y s i s . I n f r a r e d a b s o r p ­t i o n p a t t e r n s of a l t e r a t i o n m i n e r a l s w e r e o b t a i n e d u s i n g a ( 3 ) p e r k i n - E l m e r Model 4 2 1 i n f r a r e d s p e c t r o p h o t o m e t e r © These w e r e c o m p a r e d w i t h p a t t e r n s of known a l t e r a t i o n m i n e r a l s and i d e n t i f i e d by m a t c h i n g d i a g n o s t i c m i n e r a l a b s o r p t i o n peaks© One h u n d r e d i n f r a r e d d i a g r a m s w e r e a n a l y z e d© P e t r o g r a p h i c a n a l y s i s © A p e t r o g r a p h i c s t u d y of t he a l t e r a t i o n u n i t s was c o m p l e t e d © The p a r a g e n e s i s and p o s ­s i b l e m e c h a n i s m s of a l t e r a t i o n w e r e d e t e r m i n e d © P r e v i o us p e t r o g r a p h i c s t u d i e s of t h e f r e s h r o c k u n i t s by E a s t and B u t l e r w e r e r e v i e w e d - T r a c e e l e m e n t s t u d i e s © Q u a n t i t a t i v e t r a c e e l e m e nt c o n t e n t s of some r o c k s a m p l e s w e r e d e t e r m i n e d b o t h by x - r ay a n d e m i s s i o n s p e c t r o g r a p h l c t e c h n i q u e s © One h u n d r e d and e i g h t y s a m p l e s , i n c l u d i n g a l l a l t e r a t i o n t y p e s a n d f r e sh r o c k s , w e r e a n a l y z e d g e o c h e m l c a l l y w i t h a n x - r a y s p e c t r o ­g r a p h© The t r a c e l e a d 9 z i n c 9 c o p p e r 9 and a r s e n i c c o n t e n t of e a c h s a m p l e was d e t e r m i n e d © The s a m p l e s w e r e a n a l y z e d on a N o r e l c o x - r a y d l f f r a c t o m e t e r w i t h a f l u o r e s c e n t a t t a c h m e n t© Some of t h e s e r e s u l t s w e r e v e r i f i e d by e m i s s i o n s p e c t r o c h e m l c al a n a l y s i s © The t r a c e l e a d a n d c o p p e r c o n t e n t of e i g h t y r o ck s a m p l e s was d e t e r m i n e d s p e c t r o c h e m i c a l l y © S p e c t r o g r a m s w e re p r e p a r e d on a n A p p l i e d R e s e a r c h L a b o r a t o r y g r a t i n g e m i s s i on s p e c t r o g r a p h u s i n g t h e de c © a r c method© F i l m s w e r e r e a d on a p r o j e c t i o n c o m p a r a t o r d e n s i t o m e t e r© ( 4 ) I V . LOCATION OP THE AREA S a n P r a n c i s e o M o u n t a i n s 0 The S a n F r a n i s o © M o u n t a i ns a r e l o c a t e d a b o u t 170 m i l e s s o u t h w e s t of S a l t L a k e C i t y in B e a v e r C o u n t y 9 Utaho P l a t e 1 9 a n i n d e x map of t h e a r e a 9 shows t h e l o c a t i o n of t h e S a n F r a n c i s c o M o u n t a i n s 0 It a l s o shows t h e a r e a s a m p l e d g e o c h e m i c a l l y and t h e t h r e e s e l e c t e d a r e as s t u d i e d i n d e t a i l„ A r e a of g e o c h e m i c a l s t u d y o The a r e a f r om w h i c h s a m p l es f o r g e o c h e m i c a l a n a l y s i s w e r e o b t a i n e d i s l o c a t e d i n t h e San F r a n c i s c o M o u n t a i n s a b o u t t e n m i l e s w e s t of M l l f o r d 9 Utah© It i s r e c t a n g u l a r a n d e x t e n d s t e n m i l e s i n a n e a s t - w e s t d i r e c t i on a n d s e v e n t e e n m i l e s i n a n o r t h - s o u t h d i r e c t i o n , , P l a t e 1 shows t h e o u t l i n e of t h e a r e a s t u d i e d g e o c h e m i c a l l y0 S q u a w P e a k a r e a 0 The Squaw P e a k a l t e r a t i o n a r e a 9 w h i ch was s t u d i e d i n d e t a i l , i s l o c a t e d a b o u t t h r e e m i l e s s o u t h of t he H o r n S i l v e r M i n e 0 It i s a p p r o x i m a t e l y 20 m i l e s w e s t of M i l f o r d9 Utah© The a r e a o c c u p i e s a p o r t i o n of s e c t i o n s 2 9 3$> 1 0 , a n d 11 of R 13 W9 T 28 S 0 An u n i m p r o v e d g r a v e l r o a d 9 known a s Squaw S a d d l e 9 r u n s f r om s t a t e h i g h w a y 21 t o t h e n o r t h e r n f r i n g e of t h e a r e a a n d m a k e s i t a c c e s s i b l e t o a u t o m o b i l e s 0 P l a t e 1 shows t h e l o c a t i o n of t h e Squaw P e a k a r e a 0 West W h i t e M o u n t a i n a r e a 0 The West W h i t e M o u n t a in a l t e r a t i o n a r e a 9 w h i c h was a l s o s t u d i e d i n d e t a i l , o c c u r s in ( 5 ) I N D E X MAP S H O W I N G A R E A S S T U D I ED i n t h e s o u t h e r n p a r t of t h e S a n F r a n c i s c o M o u n t a i n s , It is l o c a t e d a b o u t 12 m i l e s s o u t h of t h e H o r n S i l v e r Mine a n d c o n ­s i s t s of a n e a s t - w e s t t r e n d i n g s t r i p of a l t e r a t i o n 3 m i l es l o n g a n d 1 m i l e i n t h e n o r t h - s o u t h d i r e c t i o n , . The a r ea o c c u p i e s a p o r t i o n of s e c t i o n s 7, 8, a n d 9 of R 13 W, T 28 S a n d s e c t i o n s 1 a n d 12 of R 14 W, T 29 S Q An u n i m p r o v e d g r a v el r o a d r u n n i n g a l o n g t h e w e s t s i d e of t h e S a n F r a n c i s c o M o u n t a in r a n g e m a k e s t h e r e g i o n a c c e s s i b l e t o j e e p t r a v e l , P l a t e 1 shows t h e a p p r o x i m a t e l o c a t i o n a n d e x t e n t of t h e West W h i te M o u n t a i n a r e a. E a s t W h i t e M o u n t a i n a r e a . The E a s t W h i t e M o u n t a in a l t e r a t i o n a r e a , w h i c h was s t u d i e d i n d e t a i l , i s i n t h e s o u t h ­e a s t e r n p a r t of t h e S a n F r a n c i s c o M o u n t a i n s . It i s 20 m i l es w e s t of M i l f o r d 9 U t a h a n d c o n s i s t s of a n e a s t - w e s t t r e n d i ng s t r i p of a l t e r a t i o n 2 m i l e s l o n g a n d 1 m i l e i n t h e n o r t h - s o u th d i r e c t i o n 0 The a r e a o c c u p i e s a p o r t i o n of s e c t i o n s 1, 2 , 3 , 10 1 1 , and 12 of R 13 W, T 29 S . A g r a v e l r o a d r u n n i n g d i r e c t l y t M i l f o r d m a k e s i t a c c e s s i b l e t o j e e p t r a v e l o P l a t e 1 s h o w s t he l o c a t i o n a n d e x t e n t of t h e E a s t W h i t e M o u n t a i n a l t e r a t i o n a r e a© ( ? ) CHAPTER 11 THEORETICAL BACKGROUND OF ALTERATION Much h a s b e e n w r i t t e n a b o u t h y d r o t h e r m a l a l t e r a t i o n *, t h e c h e m i s t r y a n d p h y s i c s of a l t e r a t i o n m i n e r a l s and c h a n g e s 9 a n d t h e a s s o c i a t i o n of m e t a l d e p o s i t s a n d a l t e r a t i o n g b u t o n ly a b r i e f summary of t h e e x p e r i m e n t a l and t h e o r e t i c a l b a c k g r o u nd of t h e work on p r o b l e m s v e r y c l o s e l y r e l a t e d t o t h e one at h a n d w i l l be g l v e n0 i o DEFINITIONS OF RTDROTEERMAL ALTERATION H y d r o t h e r m a l a l t e r a t i o n I n c l u d e s p h a s e c h a n g e s I n r o c ks r e s u l t i n g f r om t h e r e a c t i o n of h y d r o t h e r m a l f l u i d s w i t h p r e ­e x i s t i n g m i n e r a l s o The f l u i d s a r e g e n e r a l l y h o t a s c e n d i ng w a t e r s a n d g a s e s ©f unknown © r l g i n 0 The p h a s e ( m i n e r a l ) c h a n g es t a k e s p l a c e a s t h e f l u i d s m i g r a t e a n d d i f f u s e t h r o u g h i n t e r s t i c es o f t h e c o u n t r y r o c k s 0 Along w i t h t h e m i n e r a l c h a n g e s c e r t a in p h y s i c a l a n d b u l k c h e m i c a l c h a n g e s I n r o c k s a r e n o t e d a s a r e ­s u l t of a l t e x a t l o n .o T h e p h y s i c o - c h e m i c a l p r o c e s s e s c a u s i n g t h e m i n e r a l, c h a n g e s a r e a l s o r e f e r r e d t o a s a l t e r a t i o n These I n v o l ve b r i n g i n g t h e r e a g e n t t o t h e m i n e r a l 9 f o r m i n g a new m i n e r a l 9 a n d t a k i n g away t h e s o l u b l e p r o d u c t s of t h e r e a c t i o n © This i s one f o rm of m e t a s o m a t i s m © M e t a s o m a t i s m was d e f i n e d by L i n d g r e n a s " t h e p r o c e s s of p r a c t i c a l l y s i m u l t a n e o u s c a p i l l a ry s o l u t i o n a n d d e p o s i t i o n by w h i c h a new m i n e r a l of w h o l ly ' ( 8) d i f f e r i n g c o m p o s i t i o n may g r o w i n t h e b o d y of a n o l d m i n e r al o f m i n e r a l a g g r e g a t e ©H H e PHYSICALo CHEMICAL9 AND MINERAL CHANGES P h y s i c a l C h a n g e s, R o c k s u n d e r g o p h y s i c a l c h a n g e s a s a r e s u l t of h y d r o - t h e r m a l a l t e r a t i o n © The a l t e r e d r o c k s a r e g e n e r a l l y more p e r m e a b l e a n d p o r o u s t h a n t h e f r e s h r o c k s© The c o h e r e n c e or t e x t u r e of t h e o r i g i n a l r o c k may b e d e s t r o y e d © A p r o n o u n c ed d e c r e a s e i n g r a i n s i z e a c c o m p a n i e s t h e f o r m a t i o n of c l ay m i n e r a l s © A c h a n g e i n c o l o r may b e o b s e r v e d © G e n e r a l ly a r e a s t h a t h a v e b e e n h y d r o t h e r m a l l y a l t e r e d a p p e a r l i g ht c o l o r e d o r b l e a c h e d © A s e q u e n c e of c o l o r z o n e s i s commonly formed© C h e m i c a l Changes© B u l k c h e m i c a l c o m p o s i t i o n c h a n g e s a r e o b s e r v e d In r o c k s a s a r e s u l t of h y d r o t h e r m a l a l t e r a t i o n © They a re u s u a l l y r e p o r t e d i n r e f e r e n c e t o t h e c o m p o s i t i o n of t h e u n ­a l t e r e d r o c k a n d r e f e r t o a c o n c e n t r a t i o n o r d e p l e t i o n of e a c h c o m p o n e n t i n t e r m s of w e i g h t p e r c e n t of t h e o r i g i n al b u l k c o m p o s i t i o n © The c o m p o n e n t s t h a t f r e q u e n t l y u n d e r go m e a s u r a b l e c h a n g e s i n c l u d e calcium©, s o d i u m s p o t a s s i u m c a l u ­minum 9 s u l f u r 9 i r o n 9 magnesiums, w a t e r a n d c a r b o n d i o x i d e© C a l c i u m g s o d i u m 9 m a g n e s i u m 9 and c a r b o n d i o x i d e a r e d e p l e t ed d u r i n g h y d r o t h e r m a l a l t e r a t i o n ; w h i l e r o c k s s u r r o u n d i ng ( 9 ) a l t e r a t i o n c e n t e r s show e n r i c h m e n t of s u l f u r 9 i r o n , p o t a s s i u m, a l u m i n u m , a n d w a t e r© M i n e r a l Changes© A w i d e v a r i e t y of s e c o n d a r y m i n e r a l s h a v e b e e n o b s e r v ed ( 3 9 ) i n n u m e r o u s a l t e r a t i o n s t u d i e s © Some of t h e new m i n e r a ls r e p o r t e d i n c l u d e s e r i e i t e , q u a r t z , e p i d o t e , c h l o r i t e , a l u n i t e, c a r b o n a t e s , f e l d s p a r s a n d c l a y m i n e r a l s © The m i n e r a l s formed d e p e n d u p o n t h e c o m p o s i t i o n a n d t e m p e r a t u r e of t h e h y d r o t h e r m al s o l u t i o n s , t h e c o m p o s i t i o n of t h e o r i g i n a l r o c k , t h e p r e s s u re a t t h e r e a c t i o n s i t e , a n d t h e t i m e a l l o t t e d f o r t h e m i n e r al c h a n g e s t o t a k e p l a c e © S o m e t i m e s d i v e r s e r o c k t y p e s w i l l be a l t e r e d t o s i m i l a r m i n e r a l a s s e m b l a g e s© Z o n i n g of m i n e r a l a s s e m b l a g e s I s o f t e n o b s e r v e d In a l t e r a t i o n a r e a s . The f o r m a t i o n of one o r m o r e a l t e r a t i on m i n e r a l s i n a n a r e a o r z o n e i s u s u a l l y d e s i g n a t e d o r d e s c r i b ed b y a f f i x i n g a t e r m s u c h a s s i l i c i f i c a t i o n , e h l o r i t i z a t i o n, a l u n i t i z a t i o n , a r g l l l i z a t i o n , c a r b o n a t i z a t i o n , f e l d s p a t h i z a - t i o n , or p r o p y l i t i z a t i o n t o t h e a l t e r a t i o n © The t e r m u s ed g e n e r a l l y I n d i c a t e s t h e d o m i n a n t a l t e r a t i o n m i n e r a l p r e s e nt i n t h e zone© S i l i c i f i c a t i o n © S i l i c i f I c a t i o n i s t h e f o r m a t i o n of o n e o r m o r e s i l i c a m i n e r a l s d u r i n g h y d r o t h e r m a l a l t e r a t i o n© T h e p o s s i b l e new s i l i c a m i n e r a l s f o r m e d i n c l u d e q u a r t z , c h a l - c e d o n i c q u a r t z , j a s p e r , s i l i c e o u s s i n t e r , t r i d y m i t e, ( 1 0 ) c r i s t o b a l i t e , o p a l , a n d o t h e r v a r i e t i e s © All v a r i e t i e s h a ve a c o m p o s i t i o n of SiOg e x c e p t o p a l w h i c h I s h y d r a t e d S i 0 2 © The s o u r c e of s i l i c a i n t h e a l t e r e d r o c k s may b e o r i g i n a l h i g h ly s i l i c e o u s m i n e r a l s , s i l i c a f r om m a g m a t i c s o u r c e s 9 o r s i l i ca o b t a i n e d by t h e f l u i d s w h i l e i n t r a n s i t © The s i l i c a m a t e r i al may r e s u l t f r om l e a c h i n g of a l l t h e o r i g i n a l r o c k c o m p o n e n ts e x c e p t s i l i c a r e s u l t i n g i n i t s c o n c e n t r a t i o n ^ or f r om t he d e p o s i t i o n of s i l i c a by h y d r o t h e r m a l s o l u t i o n s 0 T a b l e 1 shows some of t h e common l o c a l i t i e s w h e r e s i l i c i f I c a t i o n h a s b e en r e p o r t e d ( 3 9 9 4 0 ) 0 S e r i c i t l z a t l o n © S e r i c i t l z a t l o n i s t h e m o s t a b u n d a nt t y p e of h y d r o t h e r m a l a l t e r a t i o n ( ? 9 38)9 a n d r e f e r s t o t he f o r m a t i o n of h y d r o t h e r m a l s e r i c i t e 0 S e r l c l t e9 i s a r e l a t i v e l y h i g h t e m p e r a t u r e m i n e r a l a n d f o r m s I n a n a c id e n v i r o n m e n t © Numerous f i e l d s t u d i e s h a v e shown t h a t d i v e r se r o c k t y p e s f r om a n d e s i t e t o a l a s k i t e h a v e b e e n a l t e r e d t o h y ­d r o t h e r m a l s e r i c i t e © T h i s i s n o t o n l y a r e s u l t of t h e a l t e r a ­t i o n of p o t a s h - b e a r i n g m i n e r a l s s u c h a s o r t h o c l a s e a n d a d u l a r ia TABLE 1 AREAS AND MINING DISTRICTS SHOWING SILICIFICATION C l i m a x 9 C o l o r a do B l a c k h i l l s 9 S o u t h D a k o ta M e t a l l i n e D i s t r i ct L i b e r t y M i n i n g D i s t r i c t G o l d f i e l d 9 Nevada T i n t i c , U t ah ( 1 1 ) b u t a l s o d u e i n p a r t t o t h e c o n t r i b u t i o n of p o t a s h t o p r e ­e x i s t i n g m i n e r a l s by t h e h y d r o t h e r m a l s o l u t i o n s ( ? ) « Some of t h e m o r e i m p o r t a n t a r e a s a n d m i n i n g d i s t r i c t s w h e r e s e r i e i t i z a - t i o n h a s b e e n d e s c r i b e d ( 4 0 ) a r e l i s t e d i n T a b l e 2© AREAS AND MINING DISTRICTS SHOWING SERICITIZATION B o u l d e r C o u n t y 9 C o l o r a do B u t t e 9 M o n t a na T i n t i e 9 U t ah E l y 9 Nevada B i s b e e 9 A r i z o na B i n g h a m , U t ah B a g d a d 9 A r i z o na S a n M a n u e l C o p p e r D i s t r i c t A r g l l l l z a t i o n © A r g i l l l z a t i o n i s a c o l l e c t i v e t e rm r e f e r r i n g t o t h e f o r m a t i o n by a l t e r a t i o n p r o c e s s of one or m o r e c l a y m i n e r a l s © The m o s t common of t h e s e a r e k a o l i n i t e 9 d i c k l t e 9 m o n t m o r i l l o n i t e o A l u n i t e g e n e r a l l y a c c o m p a n i es a r g i l l l z a t i o n * However, many o t h e r m i n e r a l s may b e i n c l u d ed i n t h i s t y p e of a l t e r a t i o n © A r g i l l i e a l t e r a t i o n i s commonly o b s e r v e d i n z o n e s a r o u n d many p r e s e n t d a y h o t s p r i n g s © L e v e r ­i n g ( 2 8 ) h a s o b s e r v e d t h a t m o s t r o c k t y p e s when s u b j e c t e d to l e a c h i n g by warm w a t e r s of a c i d h o t s p r i n g s a l t e r t o a r g i l l ie m i n e r a l s © T a b l e 3 s h o w s some common l o c a l i t i e s w h e r e a r g i l l l ­z a t i o n h a s b e e n d e s c r i b e d ( 3 9 )* TABLE 2 ( 1 2 ) TABLE 3 AREAS AND MINING DISTRICTS SHOWING ARGILLIZATION L a s s e n P e a k , C a l i f o r n ia S o l f a t a r a s I t a ly Y e l l o w s t o n e P a r k , M o n t a na B o u l d e r C o u n t y , C o l o r a do T i n t i c 9 Utah B i n g h a m , U t ah G o l d f i e l d g Nevada C h l o r l t i z a t l o n © C h l o r i t i z a t i o n i s t h e f o r m a t i o n of h y d r o t h e r m a l c h l o r i t e by a l t e r a t i o n p r o c e s s e s 0 The m i n e r a ls p e n n l n e , c l i n o e h l o r e 9 and p r o c h l o r l t e h a v e a l l b e e n r e p o r t ed a s s e c o n d a r y c h l o r i t e m i n e r a l s © T h i s t y p e of a l t e r a t i on r e s u l t s f r om s u b j e c t i n g f e r r o m a g n e s i u m m i n e r a l s t o a t t a c k by d i l u t e a c i d w a t e r s a t t e m p e r a t u r e s b e l o w 3 0 0 ° C 0 H y d r o t h e r m al c h l o r i t e i s commonly i n t h e b o r d e r o r f r i n g e a l t e r a t i o n zone a n d d i s a p p e a r s i n t h e z o n e s of i n t e n s e a l t e r a t i o n © S c h w a r tz ( 3 8 ) h a s s t a t e d t h a t " c h l o r i t l c a l t e r a t i o n c a n n o t be s a i d to b e a d i r e c t g u i d e t o o r e © H A l t e r a t i o n c h l o r i t e h a s b e e n r e ­p o r t e d ( 4 0 ) I n t h e J e r o m e d i s t r i c t ? A j o 9 A r i z o n a ? C e r r o de P a s c o , P e r u ? C h u q u i c a m a t a 9 C h i l e ? G o l d f i e l d 9 N e v a d a ? G r a ss V a l l e y , C a l i f o r n i a ? and many o t h e r a r e a s© C a r b o n a t 1 z a t I o n © C a r b o n a t i z a t i o n i s t h e f o r m a t i o n of s e c o n d a r y c a r b o n a t e m i n e r a l s a n d i s a common v a r i e t y of h y d r o - t h e r m a l a l t e r a t i o n i n some a r e a s © S e c o n d a r y c a r b o n a t e s r e p o r t ed a s a l t e r a t i o n p r o d u c t s i n c l u d e c a l c i t e , d o l o m i t e , m a g n e s i t e, s i d e r i t e , a n k e r i t e a n d m a n g a n o c a l c i t e © C a r b o n a t e s a p p e a r to f o rm i n a l k a l i n e s o l u t i o n s o v e r a w i d e t e m p e r a t u r e range© ( 1 3 ) C a r b o n a t i z a t l o n h a s b e e n r e p o r t e d ( 4 0 ) a t T i n t i c , U t a h ? t he M i c h i g a n C o p p e r d e p o s i t s ? T e l l u r i d e , C o l o r a d o ? and many o t h er a r e a s 0 a t i o n t y p e c o n s i s t i n g of c h l o r l t e 9 e p i d o t e 9 z o i s i t e 9 c a r b o n a t e s9 s u l f i d e s a n d s e v e r a l o t h e r m i n e r a l s . I t c o n s t i t u t e s a f r i n ge a l t e r a t i o n z o n e a n d g r a d e s i n t o m o r e i n t e n s e a l t e r a t i o n © U s u a l ly i t i s c h a r a c t e r i z e d by t h e p r e s e r v a t i o n of o r i g i n a l r o c k t e x ­t u r e s , b u t t h e r o c k s a p p e a r v e r y d u l l w i t h a g r e e n c a s t © The a s s o c i a t e a l t e r a t i o n m i n e r a l s ( k a o l i n i t e a n d s e r i c i t e ) i n d i c a te t h a t t h i s t y p e of a l t e r a t i o n may f o rm by t h e a t t a c k of s l i g h t ly a c i d warm w a t e r s on a l m o s t a n y r o c k s . The m o s t f a m o u s e x a m p le of p r o p y l i t i z a t i o n I s I n t h e M i c h i g a n C o p p e r D i s t r i c t a l t h o u gh s e v e r a l o t h e r a r e a s show ( 4 0 ) t h i s t y p e of a l t e r a t i o n© A l u n i t i z a t i o n © A l u n i t i z a t i o n i s t h e f o r m a t i o n of a l u n i te by h y d r o t h e r m a l a l t e r a t i o n of p r e - e x i s t i n g r o c k s© A l u n i t e, K A l y ~ ( S 0 ^ ) 2 ( O H ) 6 9 I s f o r m e d by t h e a t t a c k of a c i d s on p o t a sh b e a r i n g r o c k s , U s u a l l y a l u n i t e I s i n t i m a t e l y m i x e d w i th k a o l i n i t e i n t h e a r g i l l i e a l t e r a t i o n z o n e s , b u t r a r e l y a l u n i te f o r m s i n q u a n t i t i e s l a r g e e n o u g h t o c o n s t i t u t e a d i s t i n c t map­p i n g u n i t © E x t e n s i v e a l u n i t e a r e a s h a v e b e e n r e p o r t e d ( 4 0 ) at M a r y s v a l e 9 U t a h ? T l n t i c , U t a h ? G o l d f i e l d 9 N e v a d a ? The San F r a n c i s c o M o u n t a i n s of U t a h ? a n d many o t h e r a r e a s© ( 1 4 ) F e l d s p a t h l z a t l o r i c F e l d s p a t h i z a t i o n , t h e f o r m a t i on o f s e c o n d a r y f e l d s p a r s , i s a r e l a t i v e l y uncommon t y p e of h y d r o t h e r m a l a l t e r a t i o n ( 3 3 ) « O r t h o c l a s e a n d a l b i t e a r e t he f e l d s p a r s f o r m e d m o s t o f t e n © S e c o n d a r y o r t h o c l a s e h a s b e en d e s c r i b e d a t A j o , A r i z o n a a n d a t C l i m a x , C o l o r a d o © The o c ­c u r r e n c e of s e c o n d a r y a l b i t e h a s b e e n r e p o r t e d a t T o n o p a h, N e v a d a a n d a t A j o , A r i z o n a© I I I o MECHANISMS OF ALTERATION H y d r o t h e r m a l a l t e r a t i o n r e s u l t s from, a c o m b i n a t i o n of o n e o r m o r e of t h r e e p h y s i c o - c h e m i c a l p r o c e s s e s © The p r o c e s s es a r e c h e m i c a l a d d i t i o n , c h e m i c a l s u b t r a c t i o n a n d a t o m i c r e a r r a n g e ­ment © C h e m i c a l s u b t r a c t i o n i s t h e s o l u t i o n a n d r e m o v a l of o n e o r m o r e c o m p o n e n t s f r om t h e h o s t r o c k by f l u i d s © The m a t e r i a l i s t r a n s p o r t e d away f r om t h e f l u i d s o u r c e by d i f f u s i o n and c o n ­v e c t i o n © A c o n c e n t r a t i o n g r a d i e n t a n d a t h e r m a l g r a d i e n t a c t as d r i v i n g m e c h a n i s m s © The f o r m a t i o n of s o l u t i o n c a v i t i e s i n l i m e ­s t o n e i s a n e x a m p l e of c h e m i c a l s u b t r a c t i o n © Carbon d i o x i de d i s s o l v e d i n w a t e r r e a c t s w i t h c a l c i u m c a r b o n a t e t o f o r m c a l c i um h y d r o g e n c a r b o n a t e © T h i s i n t u r n i s c a r r i e d away i n s o l u t i o n by s u b s u r f a c e w a t e r a l o n g p r e - e x i s t i n g f r a c t u r e s i n t h e l i m e s t o n e© A s m a l l c a v i t y i n t h e l i m e s t o n e may u l t i m a t e l y become l a r g e as m o r e a n d m o r e l i m e s t o n e i s c a r r i e d away© C h e m i c a l a d d i t i o n t a k e s p l a c e when m i n e r a l s a r e p r e ­c i p i t a t e d i n o p e n s p a c e s s u c h a s f i s s u r e s o r p o r e s © The ( 1 5 ) c e m e n t a t i o n of s a n d s t o n e a n d t h e p r e c i p i t a t i o n of s u l f i d e s in a f i s s u r e o r o t h e r o p e n i n g s a r e e x a m p l e s of t h i s p r o c e s s © P r e ­c i p i t a t i o n of m i n e r a l s i n o p e n s p a c e s i s b r o u g h t a b o u t by c h a n g es i n t e m p e r a t u r e , p r e s s u r e a n d c h e m i c a l c h a r a c t e r of t h e h y d r o - t h e r m a l f l u i d s © Changes i n t e m p e r a t u r e a n d p r e s s u r e of t he f l u i d s c h a n g e s t h e s o l u b i l i t y of m a t e r i a l s i n s o l u t i o n © In g e n e r a l a d e c r e a s e i n t e m p e r a t u r e o r p r e s s u r e p r o m o t e s ( 5) p r e c i p i t a t i o n of m i n e r a l s f r om s o l u t i o n © V a r i a t i o n s i n t he c h e m i s t r y of t h e h y d r o t h e r m a l f l u i d s w i l l a l s o c a u s e ( 3 1 ) many m i n e r a l s t o p r e c i p i t a t e f r om s o l u t i o n . The s u l p h i d e s C u S 9 HgS, P b S , a n d CdS a r e p r e c i p i t a t e d ( 3 1 ) i n a n a c i d s o l u t i o n ? w h i le ZnS a n d MnS a r e p r e c i p i t a t e d i n a n a l k a l i n e s o l u t i o n© A t o m i c r e a r r a n g e m e n t i s t h e c o n v e r s i o n of a compound f r om one c r y s t a l s t r u c t u r e t o a n o t h e r by t h e a d d i t i o n o r s u b ­t r a c t i o n of h e a t© The c h a n g e s may o r may n o t i n v o l v e t he b r e a k i n g of c h e m i c a l b o n d s . The t r a n s i t i o n l o w q u a r t z = h i gh q u a r t z i s a n e x a m p l e of a t o m i c r e a r r a n g e m e n t w i t h o u t b r e a k i ng t h e bonds© While t h e t r a n s f o r m a t i o n s , q u a r t z = t r l d y m i t e = c r i s t o b a l i t e , a r e e x a m p l e s r e q u i r i n g t h e r e a r r a n g e m e n t of c o v a l e n t o r i o n i c l i n k a g e s a n d a r e u s u a l l y s l u g g i s h i n p r o ­c e e d i n g © O f t e n t h e y r e q u i r e t h e p r e s e n c e of a s o l v e n t i n o r d er t o f o r m a n a p p r e c i a b l e r a t e . While a t o m i c r e a r r a n g e m e n t is c h a r a c t e r i s t i c of t h e r m a l m e t a m o r p h i s o n , i t i s o n l y of m i n or i m p o r t a n c e i n a l t e r a t i o n s t u d i e s . However, t h e c r i s t o b a l i te r e p o r t e d ( 1 ? ) a t S u l p h u r B a n k , C a l i f o r n i a and t h e S a n F r a n c i s co ( 1 6 ) M o u n t a i n s of U t a h may b e d u e t o t h i s mechanism© V a r i o u s c o m b i n a t i o n s of t h e t h r e e f u n d a m e n t a l p r o c e s s es commonly a r e o p e r a t i v e i n t h e h y d r o t h e r m a l a l t e r a t i o n © These i n c l u d e c h e m i c a l a d d i t i o n w i t h a t o m i c r e a r r a n g e m e n t a n d c h e m i c al s u b t r a c t i o n w i t h s i m u l t a n e o u s a d d i t i o n. C h e m i c a l a d d i t i o n w i t h a t o m i c r e a r r a n g e m e n t i s s o m e ­t i m e s e x h i b i t e d when f l u i d p h a s e s r e a c t w i t h s o l i d p h a s e s © The f o r m a t i o n of h e m a t i t e f r o m m a g n e t i t e a n d t h e f o r m a t i o n of h y d r a t ed s u l p h a t e s a r e e x a m p l e s of t h i s m e c h a n i s m of a l t e r a t i o n © The r e a c t i o n , m a g n e t i t e t o h e m a t i t e , ( 3 1 ) t a k e s p l a c e by h e a t i ng m a g n e t i t e i n a i r © S e v e r a l h y d r a t e s of c o p p e r s u l p h a t e may be f o r m e d ( 3 1 ) by a d d i n g w a t e r a t v a r i o u s t e m p e r a t u r e s , a l t h o u gh t h e y a l l e f f l o r e s c e a t room t e m p e r a t u r e © A n h y d r i t e f o r m s gypsum ( 3 1 ) u p o n t h e a d d i t i o n of w a t e r a t t e m p e r a t u r e s up t o 200°C© C h e m i c a l s u b t r a c t i o n w i t h s i m u l t a n e o u s a d d i t i o n f r e ­q u e n t l y i s o b s e r v e d i n h y d r o t h e r m a l a l t e r a t i o n s t u d i e s © The p r o c e s s of l e a c h i n g f o r m s c a v i t i e s , w h i c h s e r v e a s r e c e p t a c l es f o r s i m u l t a n e o u s p r e c i p i t a t i o n of t r a n s p o r t e d m a t e r i a l © I o n ic s u b s t i t u t i o n i s a n e x a m p l e of s u b t r a c t i o n w i t h s i m u l t a n e o us a d d i t i o n of m a t e r i a l © An e x a m p l e of i o n s u b s t i t u t i o n w o u l d be c a t i o n b a s e e x c h a n g e by z e o l i t e s© IVo LABORATORY ALTERATION STUDIES A l t e r a t i o n p r o c e s s e s a n d m i n e r a l s h a v e b e e n s t u d i e d in t h e l a b o r a t o r y by s e v e r a l i n v e s t i g a t o r s • A r t i f i c i a l m i n e r a ls h a v e b e e n s y n t h e s i z e d © M i n e r a l s t a b i l i t i e s h a v e b e e n s t u d i ed ( 1 7 ) I n e n v i r o n m e n t s t h a t w e r e t h e r m © d y n a m i c a l l y u n s t a b l e » The d a t a f r om t h e s e s t u d i e s h a s h e l p e d e l u c i d a t e t h e m e c h a n i sm of h y d r o t h e r m a l a l t e r a t i on s t a b i l i t y of M i n e r a l s i n A c i d E n v i r o n m e n t s0 S e v e r a l i n v e s t i g a t o r s h a v e s u b j e c t e d m i n e r a l s t o a t t a ck by a c i d s o l u t i o n s , , The G o l d i c h m i n e r a l s t a b i l i t y s e r i e s g i v es t h e a p p r o x i m a t e s u s c e p t i b i l i t y of m i n e r a l s t o a c i d a t t a c k © The r e l a t i v e s u s c e p t i b i l i t i e s of m i n e r a l s i n a q u a r t z l a t i t e or q u a r t z m o n z o n i t e t o a c i d a t t a c k i s ( i n o r d e r of d e c r e a s i n g s u s ­c e p t i b i l i t y ) a u g i t e a n d h o r n b l e n d e , , p l a g i o c l a s e ^ b i o t i t e 9 a p a ­t i t e s g r o u n d m a s s c o n s t i t u e n t s s p o t a s s i u m f e l d s p a r a n d q u a r tz ( w h i c h i s a l m o s t c h e m i c a l l y i n e r t )© S m i t h 2 J o h n s t o n e „ S e s t i n i 9 D a u b r e e 9 B l a n c h and P a s s a r a g e 9 and n u m e r o u s o t h e r w o r k e r s h a v e s t u d i e d t h e r e ­s i s t a n c e of m i n e r a l s t o a t t a c k by d i l u t e a c i d o r n e u t r a l s o l u t i o n s o S m i t h a n d J o h n s t o n e h a v e s u b j e c t e d m i n e r a l s to t h e a t t a c k of a c i d s © S m i t h ( 2 8 ) l i s t s l 4 l m i n e r a l s t h a t a re a t t a c k e d by HCi? 29 a t t a c k e d by HNO- a n d n o t HC1? 19 a t t a c k ed by H2S0^ b u t n o t HC1 o r HNO^© J o h n s t o n e ( 2 4 ) s u b j e c t e d s e v e r al m i n e r a l s t o c a r b o n a t e d w a t e r a t t a c k a n d o b s e r v e d S i O ^ s hl^Qy a n d b a s e s w e r e t a k e n i n t o s o l u t i o n © E x p e r i m e n t a l work by D a u b r e e ( 1 3 ) h a s shown t h a t p o t a s s i u m f e l d s p a r y i e l d s a l a r ge a m o u n t of p o t a s h a n d v e r y l i t t l e AlgO^ a n d S i 0 2 when a g i t a t ed i n f r e s h w a t e r © The p r e s e n c e of a c i d s i n c r e a s e t h e s o l u b i l i ty o f t h e b a s e s © With I n c r e a s i n g a c i d i t y ( l e s s t h a n pH 3 ) 9 ( 1 8 ) a l u m i n a shows m a r k e d s o l u b i l i t y and t h e d e c o m p o s i t i o n of s i l i c a t e s i s i n c r e a s e d , , S e s t i n i ( 4 2 ) s u b j e c t e d a u g i t e to a t t a c k by c a r b o n i c a c i d a n d n e u t r a l w a t e r s 0 and o b s e r v e d t h at SiO^o Fe«0^j> a n d MgG r e m o v a l was a c c e l e r a t e d i n a n a c i d s o l u - t i o n 0 B l a n c h a n d P a s s a r a g e ( 4 ) b o i l e d g r a n i t e i n a c o n c e n ­t r a t e d HCL s o l u t i o n f o r one h o u r 9 and o b s e r v e d t h a t a ll o x i d e s e x c e p t TiOg w e r e p a r t l y o r c o m p l e t e l y t a k e n i n to s o l u t i o n T h e s o l u t i o n of s i l i c a i n v a r i o u s e n v i r o n m e n t s I s a s i g n i f i c a n t f a c t o r i n a l t e r a t i o n s t u d i e s b e c a u s e ( 1 ) h y d r o - t h e r m a l s i l i c a i s a common a l t e r a t i o n m i n e r a l g and ( 2 ) t he r a t e of d e s t r u c t i o n of s i l i c a t e s by a c i d s o l u t i o n s i s p a r t ly d e t e r m i n e d by t h e s o l u t i o n a n d r e m o v a l of s i l i c a 0 In c o n d i ­t i o n s n o t f a v o r i n g t h e s o l u t i o n of s i l i c a . , , t h e s o l u t i o n and r e m o v a l of b a s e s I s impeded© S i l i c a d i s s o l v e d by h y d r o t h e r m al s o l u t i o n s i s h y d r a t e d s i l i c a and n o t q u a r t z © P l a t e 2 ( 2 8) s h o w s t h e s o l u b i l i t y of h y d r a t e d s i l i c a u n d e r v a r i o u s e x p e r i ­m e n t a l pHs c o m p o s i t i o n ^ and t e m p e r a t u r e r a n g e s 0 The s o l u b i l i ty o f s i l i c a i n w a t e r i n c r e a s e s f r om lOOppn to 3500ppm a s t he w a t e r t e m p e r a t u r e I n c r e a s e s f r om G°C t o 4 0 0 ° C 0 In HCi s o l u ­t i o n s a t 90 Cs, t h e s o l u b i l i t y of s i l i c a d e c r e a s e s f r om 420ppm t o 50ppm a s t h e s o l u t i o n c o n c e n t r a t i o n I n c r e a s e s f r om 0% to 20% HCljj b u t a t 25°C s i l i c a s o l u b i l i t y d e c r e a s e s f r om I50ppm t o 20ppm w i t h t h e same i n c r e a s e I n s o l u t i o n c o m p o s i t i o n © The s o l u b i l i t y i n a n RgSQ^ s o l u t i o n a t 90°C d e c r e a s e s f r om 420ppm ( 1 9 ) t o l80ppm a s t h e c o n c e n t r a t i o n c h a n g e s f r om 0% t o 20% H^SCko S i l i c a s o l u b i l i t y i n NagCO^ I n c r e a s e s f r om 500ppm t o 109 0 0 0 p pm a s t h e c o n c e n t r a t i o n c h a n g e s f r om 0% t o 7i% a t 100 C 8 w h i le t h e s o l u b i l i t y I n NaOH I n c r e a s e s f r om 500ppm t o 159 0 0 0 p p m as t h e c o n c e n t r a t i o n s l i g h t l y I n c r e a s e s f r om 0 t o 0 I N Na0Ho In g e n e r a l t h e d a t a on t h e g r a p h I n d i c a t e t h a t s i l i c a I n c r e a s es i n s o l u b i l i t y a s t h e t e m p e r a t u r e of t h e s o l u t i o n I n c r e a s e s and a s t h e pH I n c r e a s e s 0 PLATE 2 200 300 SILICA, IN PARTS PER MILLION 500 600 700 600 900 1000 2000 2500 .3000 3500 4000 SOLUBILITY OF S 1 0 2 9 IN HC1, R ^ S O ^ H £ 0 9 N a C 0 3 AND NaOH AT VARIOUS TEMPERATURES L a b o r a t o r y S y n t h e s i s of A r g i l l i e and R e l a t e d M i n e r a l s 0 N u m e r o u s m i n e r a l s h a v e b e e n f o r m e d i n l a b o r a t o r y e x ­p e r i m e n t s a t v a r y i n g t h e r o d y n a m i c c o n d i t i o n s 0 Among t h e se a r e q u a r t z 9 c a r b o n a t e s 9 k a o l i n i t e 9 d i c k i t e s a l l o p h a n e , z e o ­l i t e s 9 a n d m o s t o t h e r a l t e r a t i o n m i n e r a l s (33)<> G r u n e r ( 2 8) h a s d e c o m p o s e d o r t h o c l a s e and a l b i t e i n t e n t h n o r m a l HG1 s o l ­u t i o n s a t h i g h t e m p e r a t u r e s a n d p r e s s u r e s 9 p r o d u c i n g k a o l i n i te p y r o p h y l l i t e 9 b o e h m i t e 2 and m u s c o v i t e 0 S t e p h e n s o n ( 4 3 ) h as c o n v e r t e d b o t h a l b i t e and a d u l a r i a t o z e o l i t e s w i t h a 0o 5N HCO^ s o l u t i o n a t 183° a n d 233°C„ H y d r o t h e r m a l s y n t h e s i s of m i n e r a l s i n t h e l a b o r a t o r y h e l p s t o d e t e r m i n e t h e r o d y n a m ic s t a b i l i t y f i e l d s of v a r i o u s m i n e r a l s « T h e s e d a t a may b e u s ed t o e l u c i d a t e t h e c o n d i t i o n s u n d e r w h i c h a l t e r a t i o n h a s f o r m e d0 The f o l l o w i n g summary of p h y s i c a l c o n d i t i o n s g o v e r n i n g t he f o r m a t i o n of k a o l i n i t e , p y r o p h y l l i t e 9 s e r l c i t e a a n a l c i t e . , and m o n t m o r i l l o n i t e i s t a k e n f r om E s k o l a ( i 6 )s K a o l i n o r i g i n a t e s f r om SiCU o r A l ^ O ^ - g e l s i n n e u t r al s o l u t i o n s f r e e f r om a l k a l i m e t a l s o r i n a c i d s o l u t i o ns c o n t a i n i n g a l k a l i m e t a l s 9 a t t e m p e r a t u r e s b e l o w 4 0 0 ° C o? o n t h e o t h e r h a n d , m o n t m o r i l l o n i t e f o r m s i n a l k a l i ne s o l u t i o n s of t h e a l k a l i m e t a l s , and a t h i g h e r c o n c e n t r a ­t i o n s of p o t a s h j s e r i c i t e a p p e a r s 0 At v e r y h i g h c o n c e n ­t r a t i o n s of a l k a l i o z e o l i t e s , , e s p e c i a l l y a n a l c i t e 9 a p p e a r o P y r o p h l l l t e o r i g i n a t e s i n s i l i c a - r i c h s y s t e ms u n d e r c o n d i t i o n s o t h e r w i s e t h e same a s f o r k a o l i n , o n l y, I n c o n t r a s t t o t h i s l a t t e r a t t e m p e r a t u r e s u p w a r d from 4 0 G ° C o G e o l o g i c a l e x p e r i e n c e c o n f i r m s t h e c o n c l u s i on t h a t p y r o p h y l l i t e i s a h i g h - t e m p e r a t u r e h y d r o t h e r m al form,, Also s e r i c i t e h a s o f t e n b e e n f o r m e d a t t h e e x p e n se o f f e l d s p a r s o At l o w e r t e m p e r a t u r e s ( b e l o w 4 G G 0 C ) it d e p e n d s u p o n t h e a l k a l i c o n c e n t r a t i o n of t h e a c t i v e s o l u ­t i o n s w h e t h e r z e o l i t e s 9 s e r i c i t e 9 or k a o l i n a r e formed« F r om t h e p r o v i n c e of h y d r o t h e r m a l m e t a s o m a t i s m of f e l d ­s p a r s t h e s e p r o c e s s e s p a s s o v e r t o t h e h y d r c l y t i c b r e a k ­i n g u p of s i l i c a t e m i n e r a l s i n w e a t h e r i n g 0 ( 2 1 ) A l l e x p e r i m e n t a l a n d o b s e r v e d d a t a c o n c e r n i n g m i n e r a l s y n t h e s is u p t o 1951 h a v e b e e n t a b u l a t e d by S t r i n g h a m ( 4 6 ) a n d t h e s e a re shown I n P l a t e 3o PLATE 3 °C 600 - 550 - 500 - 450 - 400 - 350 300 - 250 - 200 - J50 - 100 - 50 - 0 - Acid pH7 Alkaline Biofite Pvrophvllitq Sericite Apatite Rutile ? EyiaRijyilllfi Dickite Koolinitc Endsilite Allophone i Albite Epidote. iBeideliite ChiII loiiir ite Hydrobiotite Sericite lllite Group Alunite Nontronite Gibbsite Underlined Minerals: Fairly Oefinite Field Established Wollastonite Tremolite - Actinolite Brucite Adularia Talc? Calcite a Other Carbonates Montmor-illor. ite Zeolites Chlorite Field: Sericite Field: i FIELDS OF FORMATION OF SOME COMMON HYDROTHERMAL MINERALS The S t a b i l i t y and S y n t h e s i s of S i l i c a M i n e r a l s 0 S i l i c a c a n f o r m ( 1 8 ) a n u m b e r of d i f f e r e n t p o l y m o r p hs a t v a r i o u s t e m p e r a t u r e a n d p r e s s u r e r a n g e s 0 T h e s e i n c l u d e t he m i n e r a l s q u a r t z 9 h i g h q u a r t z P l o w t r l d y m i t e , m i d d l e t r i d y m i t e, h i g h t r i d y m l t e 9 l o w c r i s t o b a l i t e 0 Each f o r m h a s I t s own ( 2 2 ) s t a b i l i t y f i e l d © At a t m o s p h e r i c p r e s s u r e s P t h e a p p r o x i m a te 8 6 7 ° C 1470°C s t a b i l i t y r e l a t i o n s h i p s a r e q u a r t z * t r i d y m i t e * 1 7 2 3 °C c r i s t o b a l i t e * l i q u i d s i l i c a © P l a t e 4 shows f o r m a t i on f i e l d s of t h e s e m i n e r a l s a s a f u n c t i o n of t e m p e r a t u r e and p r e s s u r e . The c h a n g e s f r om a h i g h t e m p e r a t u r e t o a l o w t e m ­p e r a t u r e m i n e r a l a r e e x t r e m e l y s l u g g i s h © As a r e s u l t c r i s t o b a* l i t e a n d t r i d y m i t e may e x i s t a t l o w t e m p e r a t u r e s m e t a s t a b l e ly a s t h e l o w p o l y m o r p h v a r i e t y of e a c h m i n e r a l© PLATE k APPROXIMATE PRESSURE-TEMPERATURE DIAGRAMS FOR S i O g MINERALS S e v e r a l of t h e p o l y m o r p h s f o r m m e t a s t a b l e l y d u e t o t he e f f e c t of a d d i n g HgO o r o t h e r i m p u r i t i e s t o t h e system© The ( 2 3 ) h i g h - l o w q u a r t z i n v e r s i o n t e m p e r a t u r e i s i n c r e a s e d by t h e s u b ­s t i t u t i o n of Ge f o r S i a n d d e c r e a s e d w i t h t h e s u b s t i t u t i o n of Al f o r Si© C r i s t o b a l i t e f o r m s t r i d y m i t e when h e a t e d i n t h e 5 7 3° t o 8 0 0 ° r a n g e i n t h e p r e s e n c e of a f l u x * S i l i c a f o r m e d ( 1 8 ) by c h e m i c a l m e t h o d s i n a w a t e r s o l u t i o n a t n o r m a l t e m p e r a t u r e and p r e s s u r e s i s a p o o r l y c r y s t a l l i z e d c r i s t o b a l i t e g l a s s* S t a b i l i t y a n d S y n t h e s e of Some I r o n M i n e r a l s© S e v e r a l i r o n m i n e r a l s h a v e b e e n s y n t h e s i z e d © T h e s e I n ­c l u d e m a g n e t i t e g h e m a t i t e 9 p y r l t e 9 a n d l i m o n l t e © M a g n e t i t eg Fe^O^p f o r m s ( 3 1 ) by b u r n i n g i r o n i n o x y g e n o r by h e a t i n g i r on t o r e d n e s s i n steam© H e m a t i t e ^ F e g O ^ h a s b e e n p r e p a r e d (31) b y h e a t i n g t h e p r e c i p i t a t e d h y d r o x i d e 0 l o w e r o x i d e s 9 o r f e r r ic s u l p h a t e © P y r i t e 9 w h i c h i s F e S g 9 h a s b e e n f o r m e d ( 3 1 ) by p a s s i ng h y d r o g e n s u l p h i d e o v e r r e d - h o t f e r r i c o x i d e o r c h l o r i d e 9 or by h e a t i n g a m i x t u r e of f e r r i c o x i d e 9 s u l p h u r a n d ammonium c h l o r i d e© L i m o n l t e ( w h i c h I s e i t h e r g o e t h l t e o r l e p l d o c r o c i t e ) p r o b a b l y is FeO(OH) w i t h a b s o r b e d w a t e r (31)© I t h a s b e e n s y n t h e s i z e d by o x i d i z i n g p r e c i p i t a t e d f e r r o u s h y d r o x i d e u n d e r s p e c i a l c o n d i t i o n s© V© FIELD ALTERATION STUDIES I n v e s t i g a t o r s h a v e m a p p e d a l t e r a t i o n h a l o s a r o u n d some m i n i n g d i s t r i c t s i n g r e a t d e t a i l a n d h a v e a l s o s t u d i e d a l t e r a t i on f o r m i n g a r o u n d p r e s e n t d a y h o t s p r i n g s © The a l t e r a t i o n h a l o s a re t h e end p r o d u c t i n a l a r g e s c a l e c h e m i c a l r e a c t i o n a n d t h e h ot s p r i n g s r e p r e s e n t t h e r e a c t i o n i n p r o g r e s s © These o f f e r l a r g er (2k) a n d m o r e c o m p l e t e e x a m p l e s t h a n I s p o s s i b l e i n t h e l a b o r a t o r yQ • • O b g e r j a t l o n s a t P r e s e n t Day; H o t ' S p r i n g s o A n d e r s o n ( 3 ) a n d R l t t m a n ( 2 8 ) h a v e o b s e r v e d a l t e r a t i on f o r m i n g a r o u n d p r e s e n t d a y h o t s p r i n g s t h a t i s s i m i l a r t o t he a l t e r a t i o n a t t h e H o r n S i l v e r m l n e 0 A n d e r s o n h a s s u b j e c t e d a f r a g m e n t of d a c i t e t o a l t e r a t i o n by t h e warm ( 9 5 * ) a c i d w a t e rs o f L a s s e n P e a k o A z o n i n g s e q u e n c e of a l t e r a t i o n m i n e r a l s was o b s e r v e d i n t h e r o e k o The m i n e r a l z o n e s i n c l u d e d ( 1 ) a f r e sh c o r e ? ( 2 ) a t h i n a r g i l l i e z o n e of k a o l i n i t e 9 a l u n i t e a n d s e c o n d a ry s i l i c a ^ a n d ( 3 ) a n o u t e r s i l i c i c s h e l l two c e n t i m e t e r s t h i c k Q The s i l i c i c s h e l l c o n s i s t e d of o p a l 9 t r i d y m i t e $> a n d m i n o r k a o l i n i te a n d p y r i t e 0 S i m i l a r a l t e r a t i o n h a s b e e n o b s e r v e d a t S o l f a t a r a 9 I t a l y w h e r e a n a l k a ' l l c t r a c h y t e h a s b e e n a l t e r e d by a s t e am f u m a r o l e c o n t a i n i n g s u l p h u r g a s e s a n d CO^o The a l t e r a t i o n h as b e e n d e s c r i b e d by R i t t m a n 0 The t e m p e r a t u r e of t h e s t e a m f u m a r o le was 1 4 6 ° C 0 The m i n e r a l z o n e s o b s e r v e d w e r e ( 1 ) a z o n e of f r e sh r o c k | ( 2 ) a p a r t l y a l t e r e d z o n e of o p a l 9 b r o w n i r o n o x i d e s and h a l l o y s l t e ^ and ( 3 ) a c o m p l e t e l y a l t e r e d z o n e c o n s i s t i n g p r e ­d o m i n a n t l y of o p a l w i t h m i n o r g r a i n s of l i m o n l t e 9 gypsum a nd s u l p h u r o The g e n e r a l t e r m " S o l f a t a r i e A l t e r a t i o n " may b e u s ed t o d e s c r i b e t h i s t y p e of a l t e r a t i on F i e l d M a p p i n g S t u d l e s 0 I n some m i n i n g d i s t r i c t s 9 z o n e s of h y d r o t h e r m a l a l t e r a ­t i o n a r e I n c l o s e p r o x i m i t y t o m i n e r a l d e p o s i t s „ T h i s h as ( 2 5 ) s e r v e d a s a s t i m u l u s t o p r o m o t e m a p p i n g of a l t e r e d a r e a s © A s y m m e t r i c s e q u e n c e of a l t e r a t i o n z o n e s s u r r o u n d i n g s u l f i d e o r e - b o d i e s h a s b e e n o b s e r v e d by s e v e r a l I n v e s t i g a t o r s 0 S a l e s and M e y e r s ( 3 ? ) f o u n d s y m m e t r i c z o n e s of a l t e r a ­t i o n m i n e r a l s s u r r o u n d i n g f i s s u r e - t y p e o r e b o d l e s a t B u t t e 9 M o n t a n a o Here f i s s u r e s c o n t r o l v e i n s i n q u a r t z m o n z o n l t e 0 Con-c e t r i c e n v e l o p e s of s e r i c i t l z e d and a r g i l l l z e d q u a r t z m o n z o n i te a l w a y s a c c u p y t h e same r e l a t i v e p o s i t i o n s w i t h r e s p e c t t o e a ch s t r u c t u r e © A s e r i c i t e zone o c c u r s a d j a c e n t t o o r e b e a r i n g v e i n s© T h i s i s s u r r o u n d e d by a n a r g i l l i e z o n e c o n s i s t i n g of k a o l i n i te a n d m o n t m o r l l l o n i t e 0 A d j a c e n t t o t h e a r g i l l i e z o n e i s a p r o p y - l i t i e zones, w h i c h g r a d e s i n t o f r e s h rock© L o v e r i n g h a s mapped a l t e r a t i o n a r e a s a t B o u l d e r C o u n t y9 C o l o r a d o a n d a t T i n t i c 9 Utah© At B o u l d e r C o u n t y ( 2 ? ) D s e r i c i te z o n e s a r e a d j a c e n t t o t h e o r e v e i n s © An a r g i l l l z e d z o n e b o r d e rs t h e s e r i c i t e a n d g r a d e s i n t o f r e s h rock© At T i n t i e 9 U t a h L o v e r ­i n g ( 2 6 ) r e c o g n i z e d z o n e s of d o l o m i t e a n d j a s p e r © i d s u r r o u n d i ng some of t h e o r e b o d l e s 9 -but a z o n a l a r r a n g e m e n t of t h e o t h er a l t e r a t i o n p r o d u c t s was n o t n o t e d 0 At T l n t l c 9 L o v e r i n g ( 2 6) r e c o g n i z e d a t i m e s e q u e n c e w i t h f i v e d i f f e r e n t s t a g e s of a l t e r a ­t i o n© N u m e r o u s f i e l d s t u d i e s of o t h e r a l t e r a t i o n a r e a s h a ve b e e n c o m p l e t e d ( 3 8 ) ° The f o l l o w i n g e x a m p l e s h a v e a l t e r a t i on s i m i l a r t o t h a t i n t h e S a n F r a n c i s c o M o u n t a i n s © K e r r ( 2 5 ) h as m a p p e d t h e M a r y s v a l e a l t e r a t i o n a r e a 0 S c h w a r t z ( 4 l ) h a s mapped ( 2 6 ) t h e a l t e r a t i o n a t S a n Manuel© S t r i n g h a m ( 4 5 ) and B u r n h am ( 1 0) h a v e s t u d i e d t h e a l t e r a t i o n a t B i n g h a m 9 Utah© VIo SUMMARY OP PREVIOUS ALTERATION STUDIES A l t e r a t i o n a r e a s i n many m i n i n g d i s t r i c t s h a v e b e en s t u d i e d © A n u m b e r of g e n e r a l i z a t i o n s may b e d r a w n f r om p r e v i o us s t u d i e s t h a t may b e a p p l i c a b l e t o f u t u r e a r e a s of i n t e r e s t© T h e s e i n c l u d e t h e a s s o c i a t i o n of m e t a l l i z a t i o n a n d a l t e r a t i o n^ t h e o c c u r r e n c e a n d n a t u r e of a l t e r a t i o n z o n e s , a n d t h e s t a b i l i ty of a l t e r a t i o n m i n e r a l s© A l t e r a t i o n and M e t a l l i z a t i o n© O f t e n o r e o r m e t a l l i c m i n e r a l i z a t i o n i s a s s o c i a t e d w i th h y d r o t h e r m a l a l t e r a t i o n © C e r t a i n p h a s e s of a l t e r a t J . c n a r e " c o n t e m p o r a n e o u s w i t h m e t a l l i c m i n e r a l i z a t i o n © The e x c e p t i o n s to t h e r u l e a r e o r e w i t h o u t a l t e r a t i o n a n d a l t e r a t i o n w i t h o u t ore© L o v e r i n g ( 2 6 ) h a s r e p o r t e d a n o r e b o d y i n t h e T i n t l c d i s t r i ct n o t a s s o c i a t e d w i t h a l t e r a t i o n ^ a l t h o u g h m o s t o r e b o d l e s i n t he d i s t r i c t a r e a s s o c i a t e d w i t h a l t e r a t i o n © Many m i n i n g d i s t r i c ts e x h i b i t a l t e r a t i o n a r e a s t h a t a r e b a r r e n© • i t e r a t i o n Zones© Z o n e s of a l t e r a t i o n t y p e s a r e o f t e n o b s e r v e d i n a p a r t i c u l a r m i n i n g d i s t r i c t © Each z o n e may b e l a r g e e n o u g h to c o n s t i t u t e a u n i q u e m a p p i n g u n i t © The a l t e r a t i o n z o n e s I n a w a l l r o c k of q u a r t z m o n z o n i t e s e t a p a t t e r n a p p l i c a b l e t o o t h er w a l l r o c k t y p e s © The z o n i n g i n a r e a s w h e r e a r g i l l i e a l t e r a t i on (2?) g r a d e s f r om t h e p e r i p h e r y t o w a r d a c e n t e r I s c h l o r i t e 9 i l l i t e 9 a l u n i t e 9 k a o l i n i t e 9 s e r i c i t e 9 and q u a r t z i n t h e o r d e r named© The g e o m e t r i c s h a p e of t h e a l t e r a t i o n p a t t e r n i s u s e f u l a s a g u i d e t o p o t e n t i a l f o c a l p o i n t s of m e t a l l i c m i n e r a l i z a t i on Two c o n c e p t s of m i n e r a l z o n i n g h a v e e m e r g e d a s a r e s u lt of t h e v a r i o u s a l t e r a t i o n s t u d i e s © L o v e r i n g (26) and S c h w a r tz (kl) d e s c r i b e d o c c u r r e n c e s I n w h i c h t h e v a r i o u s z o n e s of a l t e r a ­t i o n r e p r e s e n t t h e e f f e c t s of p e r i o d i c f l o w of h y d r o t h e r m al s o l u t i o n s of d i f f e r e n t c o m p o s i t i o n A t i m e i n t e r v a l of d e ­c r e a s e d a c t i v i t y o c c u r r e d b e t w e e n t h e s t a g e s of s o l u t i o n flow© A s e c o n d c o n c e p t d u e t o S a l e s a n d M e y e r s ( 3 7 ) I n d i c a t e s t h a t t he v a r i o u s c l a y z o n e s a r o u n d t h e v e i n s r e p r e s e n t c h a n g e s by a h y d ro t h e r m a l s o l u t i o n w h i c h c h a n g e d i n c o m p o s i t i o n by w a l l r o ck r e a c t i o n s a s I t m i g r a t e d f r om t h e f i s s u r e© The R e s l s t a n . e e of A l t e r a t i o n M i n e r a l s To C h e m i c a l W e a t h e r i n g© T h e a r g i l l i e and s e r l c i t l c m i n e r a l s f o i m e d by h y d r o - t h e r m a l a l t e r a t i o n a r e u s u a l l y u n c h a n g e d by s u b s e q u e n t s u p e r - g e n e a l t e r a t i o n © S u r f a c e w e a t h e r i n g may s u p e r i m p o s e h e m a t i te a n d l i m o n l t e on t h e c l a y m i n e r a l s 9 b u t t h e m i n e r a l s a r e r e l a ­t i v e l y s t a b l e u n d e r s u r f a c e c o n d i t i o n s© ( 2 8 ) CHAPTER I II THEORETICAL GEOCHEMICAL BASIS FOR TRACE ELEMENT CONTENT G e o c h e m i s t r y i s t h e s t u d y of t h e r e l a t i v e and a b s o l u te a b u n d a n c e s of t h e e l e m e n t s of t h e e a r t h * . Some a s p e c t s of g e o ­c h e m i s t r y i n c l u d e t h e s t u d y of t h e d i s t r i b u t i o n a n d m i g r a t i on of t h e i n d i v i d u a l e l e m e n t s 9 V a r i a t i o n s i n r o c k and m i n e r al c h e m i c a l c o m p o s i t i o n m u s t be d e t e r m i n e d t o map i n d i v i d u a l e l e ­ment m i g r a t i o n E l e m e n t s may e x i s t a s b o t h m a j o r o r t r a ce c o n s t i t u e n t s . The d i s t r i b u t i o n of t r a c e e l e m e n t s may f r e q u e n t ly be u s e d t o e l u c i d a t e t h e g e o l o g i c h i s t o r y of a l o c a l i t y* I . TRACE ELEMENT OCCURRENCE M o s t of t h e l e s s common e l e m e n t s c a n b e i n c o r p o r a t ed i n t o one o r m o r e r o c k - f o r m i n g m i n e r a l s 0 One m e t h o d of i n c o r ­p o r a t i o n i s by a t o m i c s u b s t i t u t i o n ^ In a d d i t i o n e l e m e n t s may o c c u r t h r o u g h o u t a r o c k by s e v e r a l o t h e r m e t h o d s • These i n c l u de a d m i x e d l i q u i d i n c l u s i o n s , s o l i d i n c l u s i o n s , and e x - s o l u t i on p r o d u c t s o DeVore (1*0 h a s s u g g e s t e d t h a t t h r o u g h t h e m e c h a n i sm of a d s o r p t i o n , t r a c e e l e m e n t s o c c u r on g r o w t h s u r f a c e s , i m p e r ­f e c t i o n s , d i s l o c a t i o n s , and v a r i o u s i n t e r f a c e s w i t h i n c r y s t a ls a n d r o c k so T r a c e e l e m e n t s may e x i s t i n a l a t t i c e p o s i t i o n i n a m i n e r a l t h a t i s o r d i n a r i l y o c c u p i e d by a p r i n c i p a l c o n s t i t u e n t0 The a b i l i t y of a t r a c e e l e m e n t t o s u b s t i t u t e i n t o a c r y s t al l a t t i c e f o r a c o n s t i t u e n t e l e m e n t i s g o v e r n e d by i t s I o n ic ( 2 9 ) p o t e n t i a l o . The I o n i c p o t e n t i a l a s d e f i n e d by G e l d s e h m l d t is e q u a l t o t h e v a l e n c e of t h e I o n d i v i d e d by t h e r a d i u s 0 E l e m e n t s w i t h s i m i l a r I o n i c p o t e n t i a l s r e a d i l y s u b ­s t i t u t e f o r on® a n o t h e r i n a c r y s t a l l a t t i c e 0 T h e i r m i n e r a - l o g i c a l e n v i r o n m e n t may b e p r e d i c t e d f r o m t h e p r i n e l p 2 . e s of c a m o u f l a g e 9 c a p t u r e 9 and a d m i s s i o n a s s e t f o r t h by G o l d s c h m i d to C a p t u r e i s d e f i n e d a s t h e s u b s t i t u t i o n of a n i o n w i t h a h i g h er c h a r g e a n d I d e n t i c a l r a d i u s f o r an I o n n o r m a l l y p r e s e n t I n t he m i n e r a l o A d m i s s i o n o c c u r s when a n i o n of l o w e r c h a r g e a n d of a p p r o x i m a t e l y t h e same r a d i u s s u b s t i t u t e s f o r an I o n p r e s e nt I n a m i n e r a l 0 C a m o u f l a g e i s t h e s u b s t i t u t i o n f o r one I o n by a n I o n of a n o t h e r e l e m e n t h a v i n g t h e same c h a r g e a n d r a d i u s 0 A t r a c e I o n may b e t a k e n I n t o a m i n e r a l s t r u c t u r e u n d e r t h e se r u l e s 9 w h i c h d e p e n d u p o n t h e f u n d a m e n t a l c o n s i d e r a t i o n s of t he e l e c t r o v a l e n t c h a r g e a n d t h e I o n i c ' r a d i u s of the e l e m e n t0 H o GEOCHEMXCAL DISPERSION D i s p e r s i o n of t r a c e e l e m e n t s may p r o d u c e g e o e h e m l c ai h a l o s i n r o c k s o r s o i l s s u r r o u n d i n g o r e b o d l e s 0 D i s p e r s i o n Is d e f i n e d a s a s p r e a d i n g o u t of c h e m i c a l c o n s t i t u e n t s due t o t he I n t e r a c t i o n of m e c h a n i c a l a n d c h e m i c a l d i s p e r s i o n p r o c e s s e s 0 H a l o s may f o rm a t t h e s u r f a c e of t h e e a r t h d u e t o p r i m a r y and s e c o n d a r y d i s p e r s i o n p r o c e s s e s 0 F r a c t u r e s of n e a r s u r f a ce r o c k s a n d p o r e s p a c e s of o v e r b u r d e n s e r v e a s c h a n n e l w a y s in t h e f o r m a t i o n of d i s p e r s i o n p a t t e r n s 0 1 3 0 ) M e c h a n i c a l d i s p e r s i o n p r o c e s s e s I n c l u d e i n j e c t i o n or e x t r u s i o n of magma a n d movement of s u r f l c i a i m a t e r i a l by g r a v i t y 9 w i n d 9 o r g l a c i a l a c t l o n 0 The m a i n t y p e s of c h e m i c a l d i f f e r e n t i a ­t i o n p r o d u c e d by m e c h a n i c a l p r o c e s s e s a r e a l l u v i a l s a n d s 9 c l a ys a n d p l a c e r d e p o s i t s 0 C h e m i c a l d i s p e r s i o n p r o c e s s e s p l a y a more I m p o r t a n t r o l e 0 C h e m i c a l d i s p e r s i o n p r o c e s s e s a c t i n g a s s o r t i n g a g e n ts d i v i d e t h e m a t e r i a l i n t o f r a c t i o n s of d i f f e r i n g m o b i l i t y 0 The m o r e m o b i l e p h a s e s w i l l l e a v e - t h e s o u r c e a r e a i f a d e q u a t e c h a n - n e l w a y s a n d a c h e m i c a l o r p h y s i c a l p o t e n t i a l g r a d i e n t a r e a v a i l ­a b l e o R e y n o l d s ( 3 ^ ) h a s d e p i c t e d t h e Newry G r a n o d l o r l t e as h a v i n g f o r m e d d u e t o c h e m i c a l d i s p e r s i o n p r o c e s s e s 0 X I I o GEOCHEMICAL MOBILITY T h e m o b i l i t y of a n e l e m e n t g o v e r n s i t s r e s p o n s e to d i s p e r s i o n p r o c e s s e s 0 T h e - m o b i l i t y i s t h e e a s e w i t h w h i c h an e l e m e n t may b e moved i n a n y g i v e n e n v i r o n m e n t 0 The m o b i l i ty o f a n e l e m e n t v a r i e s w i t h i t s I o n i c p o t e n t i a l 0 Ions w i t h h i gh I o n i c p o t e n t i a l a r e r e l a t i v e l y i n e r t and d i f f i c u l t t o d l s p e r s e D T h e s i l i c o n I o n i n q u a r t z I s a n e x a m p l e of a n I m m o b i l e l o n0 T h e S I ' I o n h a s a n I o n i c p o t e n t i a l of 10 a n d q u a r t z i s a chem­i c a l l y I n e r t s u b s t a n c e0 T h e r e l a t i v e m o b i l i t y of some m i n o r e l e m e n t s I n r o c ks h a s b e e n t a b u l a t e d by Hawkes a n d Webb (22)0 These i n c l u de ( 1 ) B r 9 Ig Mos B 9 and S e 9 w h i c h a r e v e r y m o b i l e § ( 2 ) Z n 9 Ba a n d U8 w h i c h a r e m o d e r a t e l y m o b i l e s ( 3 ) N i 9 Co9 Cu a n d P b 9 ( 3 D w h i c h a r e m o b i l e a n d § (*0 C r 9 S i a n d T i 9 w h i c h a r e v e r y Immobil< T h e s e d a t a w e r e d e t e r m i n e d f r om c o n c e n t r a t i o n s of, e l e m e n t s In n a t u r a l w a t e r s i n r e l a t i o n t© t h e i r c o n c e n t r a t i o n I n t h e r o c ks I n t h e d r a i n a g e a r e a of t h e n a t u r a l w a t e r s 0 T a b l e 4 shows t he r e l a t i v e m o b i l i t y of m i n o r e l e m e n t so MOBILITY OP TRACE ELEMENTS V e r y M o b i l e Br9 I 9 Mo9 B 9 Se M o d e r a t e l y M o b i l e Zn9 Ba9 U I m m o b i l e Nl9 Coe Cu9 Pb V e r y I m m o b i l e Gr9 S i 9 Ti IVo GEOCHEMISTRY OP COPPER C o p p e r i s t h e t w e n t y - f i f t h m o s t a b u n d a n t e l e m e n t In t h e c r u s t of t h e e a r t h w i t h a n a v e r a g e c o n c e n t r a t i o n of 70 p a r t s p e r m i l l i o n 0 S a n d e l l and G o l d l c h (J6) have d e t e r m i n ed t h e c o p p e r c o n t e n t of a n u m b e r of r o c k s 0 They o b s e r v e d t h at t h e a m o u n t of s i l i c a a n d c o p p e r a r e i n v e r s e l y p r o p o r t i o n a l In I g n e o u s r o c k s o Rocks w i t h h i g h s i l i c a c o n t e n t h a v e a l o w c o p ­p e r c o n t e n t o The c o n c e n t r a t i o n of c o p p e r i s ( 1 ) l49ppm in b a s i c i g n e o u s r o c k s % ( 2 ) 38ppm i n I n t e r m e d i a t e i g n e o u s r o c ks a n d ( 3 ) i6ppm I n a c i d I g n e o u s r o c k s Q T a b l e 5 g i v e s t h e a v e r a ge Cu i n i g n e o u s r o c k s 0 In c o n t r a s t t o t h e c o p p e r - s i l i c a v a r i a ­t i o n t h e a m o u n t of c o p p e r i n I g n e o u s r o c k s I n c r e a s e s d i r e c t ly w i t h I n c r e a s e s i n t h e s u l p h u r c o n t e n t of t h e r o c k s0 TABLE 5 CONCENTRATION OP COPPER IN IGNEOUS ROCKS Rock Cu J P P M) B a s i c I g n e o u s R o c k s 1^9 I n t e r m e d i a t e I g n e o u s R o c k s 38 A c i d I g n e o u s R o c k s 16 T h e c h a l c o p h i l e c h a r a c t e r of c o p p e r a n d I t s h i gh a f f i n i t y f o r s u l p h u r g o v e r n s i t s o c c u r r e n c e i n I g n e o u s r o c k s0 C o p p e r u s u a l l y i s p r e s e n t - i n I g n e o u s r o c k s a s s u l f i d e m i n e r a l s 0 Among t h e m o s t i m p o r t a n t a r e c h a l c o p y r I t e 9 CuFeS § b o r n i t e 9 C u . F e S , j c h a l c o c i t e 9 Cu^Sj and t e t r a h e d r i t e 9 Cu .SbS 0 S u l f a te 3 /f • £ 3 3 a n d c a r b o n a t e m i n e r a l s of c o p p e r o f t e n f o r m a s a l t e r a t i o n s of p r i m a r y m i n e r a l s 0 T h e m o b i l i t y of c o p p e r v a r i e s f r om h i g h t o l o w Q I t h as a h i g h g e o c h e m i c a l m o b i l i t y when t h e t r a n s p o r t i n g s o l u t i o n s h a ve a pH b e l o w 5o5° In s o l u t i o n s w h e r e t h e pH i s s l i g h t l y a c i d to n e u t r a l 9 t h e m o b i l i t y i s l o w c The m o b i l i t y I n s o i l s i s l i m i t ed b y s o r p t i o n t o o r g a n i c m a t t e r a n d c l a y m i n e r a l s 0 \To GEOCHEMISTRY OF LEAD L e a d g w i t h a c o n c e n t r a t i o n of 16 p a r t s p e r m i l l i o n , is t h e t h i r t y - s i x t h m o s t a b u n d a n t e l e m e n t ( 2 0 ) i n t h e c r u s t of t he e a r t h o S a n d e l l a n d G o l d l c h ( 3 6 ) h a v e d e t e r m i n e d t h e l e a d c o n t e nt ( 3 3 ) of i g n e o u s r o c k s 0 The c o n c e n t r a t i o n of l e a d was o b s e r v e d to c l o s e l y f o l l o w t h a t of p o t a s s i u m . , A d i s t i n c t c o r r e l a t i o n b e ­t w e e n l e a d and s i l i c a was a l s o o b s e r v e d 0 The m o r e s i l i c ic m a g m a t i e r o c k s a r e t h e r i c h e s t i n l e a d o The c o n c e n t r a t i on v a r i e s f r om 5ppm i n u l t r a b a s i c s t o 19ppm i n a c i d i g n e o us r o c k s 0 T a b l e 6 shows t h e a b u n d a n c e of l e a d i n i g n e o u s r o c k s 0 TABLE 6 CONCENTRATION OF LEAD IN IGNEOUS ROCKS R o c k s Pb (PPM) U l t r a b a s i c s 5 B a s i c I g n e o u s Rocks 9 A c i d I g n e o u s Rocks 19 L e a d i s b o t h a c h a l c o p h i l e a n d l i t h o p h i l e e l e m e n t 0 I e x i s t s m o s t commonly a s s u l p h i d e s a n d s u l p h o s a l t s 0 The m o st i m p o r t a n t l e a d m i n e r a l s i n c l u d e g a l e n a , PbS^ c e r u s s i t e 9 PbCO^ a n d a n g l e s i t e 9 P b S 0 ^ o Of t h e s e , g a l e n a i s t h e m o s t I m p o r t a nt l e a d m i n e r a l o In a d d i t i o n ^ I t i s a l s o a n i m p o r t a n t s i l v er m i n e r a l ( c o n t a i n i n g up t o 2 p e r c e n t s i l v e r ) a C e r u s s i t e, a n g l e s ! t e s and o t h e r s u l f a t e s a n d c a r b o n a t e s of l e a d a re f o r m e d a s a l t e r a t i o n p r o d u c t s of g a l e n a i n t h e s u p e r f i c i al p a r t s of l e a d o r e b o d i e s 0 Lead h a s a l s o b e e n d e t e c t e d i n a l a r g e n u m b e r of r o c k - f o r m i n g m i n e r a l s . The i o n i c r a d i u s of o d i v a l e n t l e a d i s 10JJA and t h i s i s v e r y s i m i l a r t o t h e r a d ii ( 3 4 ) o f K9 Ba9 S r 9 and C a 0 I t r e a d i l y r e p l a c e s s t r o n t i u m ^ b a r i u m9 c a l c i u m , and p o t a s s i u m i n t h e m i n e r a l s of s i l i c a t e r o c k s 0 It-i s m o s t common i n p o t a s s i u m m i n e r a l s s u c h a s p o t a s s i u m f e l d s p a rs a n d m i c a s• L e a d i s v e r y i m m o b i l e , The m o b i l i t y i s l i m i t e d by p r e c i p i t a t i o n w i t h o r g a n i c m a t t e r a n d l i m o n i t e 0 Hawks ( 2 2) d e s c r i b e s a h i g h e r m o b i l i t y f o r l e a d i n a c h l o r i d e ( s e m i - a r i d) e n v i r o n m e n t , , VIo GEOCHEMISTRY OF ZINC Z i n c i s t h e t w e n t y - t h i r d m o s t a b u n d a n t e l e m e n t ( 2 0 ) in t h e c r u s t of t h e e a r t h w i t h a n a v e r a g e c o n c e n t r a t i o n of 23ppm* C l a r k e a n d W a s h i n g t o n r e p o r t e d 40ppm a s t h e c o n c e n t r a t i o n in t h e u p p e r l i t h o s p h e r e 0 A c o n c e n t r a t i o n of 51ppm i n A m e r i c an m a g m a t i c r o c k s was r e p o r t e d by C l a r k e a n d S t e i g e r * S a n d e l and G c l d i c h (36) found 80ppm a s t h e a v e r a g e a b u n d a n c e i n N o r th A m e r i c a n r o c k s Q The c o n c e n t r a t i o n i s ( l ) 90ppm i n g a b b r o? ( 2 ) 120ppm i n q u a r t z d i o r i t e ? (3) 200ppm i n g r a n o d i o r i t e; ( 4 ) 150ppm i n p l a g l o e l a s e g r a n i t e ? and ( 5 ) 3Qppm i n m i c r o c l l ne g r a n i t e e T a b l e 7 s h o w s t h e a v e r a g e a b u n d a n c e of z i n c I n I g n e o us r o c k s o T h e g e o c h e m i s t r y of z i n c i s d e t e r m i n e d p a r t l y by t he s i m i l a r i t y of r a d i i b e t w e e n d i v a l e n t z i n c 9 i r o n 9 m a g n e s l u m9 o 4-2 0 +2 a n d n i c k e l o The r a d i i a r e 0e 8 3 A f o r Zn , 0o 7 8 A f o r Mg , 0 . 7 8 A f o r N i + 2 9 and O083& f o r F e + 2 D Z i n c r e a d i l y s u b s t i t u t es f o r t h e a b o v e e l e m e n t s i n s i l i c a t e s o S p h a l e r i t e , Z n S9 ( 3 5 ) TABLE ? CONCENTRATION OP ZINC IN IGNEOUS ROCKS Rock Zn (P?M) G a b b r o ;: Q u a r t z D i o r i t e 120 G r a n o d l o r l t e 200 P l a g i o c l a s e g r a n i t e 150 M I c r o c l i n e g r a n i t e Jd f r e q u e n t l y c a r r i e s lone, m a g n e s i u m a n d n i c k e l a s t r a c e e l e m e n t s, T h e c h a l c o p h i l e n a t u r e of z i n c g o v e r n s I t s o c c u r r e n ce a s m i n e r a l s I n t h e c r u s t of t h e e a r t h 0 The c h a l c o p h i l e e l e ­m e n t s i n a magma a s s o c i a t e w i t h s u l p h u r ( , The m o s t a b u n d a nt z i n c m i n e r a l i s s p h a l e r i t e ^ ZnS„ O t h e r common z i n c m i n e r a ls a r e w u r t z i t e 9 ZnS^ z i n c i t e i Z n 0 9 s m i t h s o n i t e 9 Z n C O ^ and c a l a m i n e o Z i n c b e c o m e s s t r o n g l y e n r i c h e d I n h y d r o t h e r m a l r o c ks f o r m i n g a t r e l a t i v e l y l o w t e m p e r a t u r e s 0 It i s a m o r e s u b s t a n ­t i a l c o n s t i t u e n t of t h o s e p a r t s of s u l p h i d e w h i c h a r e t h e l a st t o c r y s t a l i z e a n d o f t e n I n t r u d e t h e s u r r o u n d i n g r o c k s a s a p o ­p h y s e s o In h y d r o t h e r m a l d e p o s i t s z i n c e x i s t s a l m o s t e x c l u s i v e: a s t h e s u l p h i d e s p h a l e r i t e a n d I s u s u a l l y a s s o c i a t e d w i th g a l e n a o In a few c a s e s z i n c s i l i c a t e s s u c h a s h e m i m o r p h i t e or c a l a m i n e h a v e b e e n f o r m e d by t h e a c t i o n of h y d r o t h e r m a l or m e t e o r i c s o l u t i o n s u p o n p r e - e x i s t i n g s p h a l e r i t e d e p o s i t so Z i n c h a s a h i g h g e o c h e m i c a l m o b i l i t y „ The m o b i l i ty i s l i m i t e d by o r g a n i c a c t i v i t y and c o p r e c i p l t a t i o n w i t h l i m o n - i t e 0 I t s h i g h m o b i l i t y makes z i n c a s u i t a b l e g e o c h e m i c al i n d i c a t o r e l e m e n t f o r b a s e m e t a l p r o s p e c t i n g 0 V I I o GEOCHEMISTRY Op ARSENIC A r s e n i c , w i t h a n a v e r a g e c o n c e n t r a t i o n of 5ppJ&9 I s t he f o r t y - s e v e n t h m o s t a b u n d a n t e l e m e n t ( 2 0 ) I n t h e c r u s t of t he e a r t h o C l a r k e a n d W a s h i n g t o n e s t i m a t e d t h e a b u n d a n c e s of a r s e ­n i c i n r o c k s of t h e u p p e r l i t h o s p h e r e t o be I - I 0 p p m o S t e i g er f o u n d a n a v e r a g e c o n c e n t r a t i o n of 5o6ppm I n a c o m p o s i t e of 329 A m e r i c a n r o c k s 0 A r s e n i c shows a c l o s e g e o c h e m i c a l and c r y s t a l l o c h e m i e al r e l a t i o n s h i p w i t h t h e p h o s p h a t e s a n d v a n a d a t e s 0 A r s e n i c i n i ts h i g h e s t v a l e n c e s t a t e A s + ^ e x h i b i t e d by a r s e n a t e s f o r m e d from ASgO^ i s i s o m o p h o u s t o t h e p h o s p h o r o u s i n p h o s p h a t e s 0 The r a d ii a r e 0„ for As a n d 0o for P+ ^ c , a n d As r e a d i l y s u b s t i t u t es f o r P i n p h o s p h a t e m i n e r a l s 0 T h e c h a l c o p h i l e n a t u r e of a r s e n i c g o v e r n s i t s o c c u r r e n ce a s a m i n e r a l a n d t r a c e e l e m e n t i n m a g m a t i c r o c k s „ The s u l p h o - 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g r a p h i c s t u d i e s of t h e v o l e a n l c s 0 The r e g i o n a l v o l c a n i c s t r a t i - g r a p h y h a s b e e n d e s c r i b e d by Mae&ln(29-)© I o GENERAL STATEMENT T h e r o c k u n i t s I n t h e a l t e r e d a r e a s c o n s i s t of e a r l y to m i d d l e T e r t i a r y a c i d i g n l m b r i t e s a n d f l o w s 9 w h i c h I n c l u d e p e r l l te r h y o l i t e 9 l a t l t e 9 a n d e s i t e a n d l e u c o b a s a l t c , and l a t e T e r t i a ry a n d e s i t e a n d b a s a l t e T a b l e 8 I s a l i t h o i o g l e c o l u m n f o r t he Squaw p e a k a l t e r a t i o n a r e a a n d T a b l e 9 I s a l l t h o l o g i e c o l u mn f o r t h e West W h i t e M o u n t a i n a n d E a s t W h i t e M o u n t a i n a l t e r a t i on a r e a s o The f o l l o w i n g d e s c r i p t i o n s of t h e v o l c a n i c r o c k s a re p r e s e n t e d i n o r d e r t o m o r e r e a d i l y v i s u a l i z e t h e d i v e r s © c h e m i c al c o m p o s i t i o n s of t h e r o c k s p r i o r t o a l t e r a t i o n 0 I I o ROCK UNITS IN DETAILED AREAS S q u aw P e a k A r e a0 T h e v o l c a n i c r o c k u n i t s of t h e Squaw P e a k a l t e r a t i on a r e a h a v e b e e n d e s c r i b e d by E a s t ( 1 5 ) > Nine s e p a r a t e r o c k u n i ts f r om a t y p e s e c t i o n n o r t h of Squaw S a d d l e h a v e b e e n r e c o g n i z ed a n d d e s c r i b e d e U n i t s 7 9 3s ^9 a n & 1 a r e p r e s e n t i n t he C 3 9 ) TABLE 8 GENERALIZED SEQUENCE OP VOLCANICS IN THE SQUAW PEAK AREA Age Unit Rock Type Thickness Character Quaternary Alluvium Variable Unconsolidated mixtures of gravel, sand, s i l t , and clay. Lake beds, stream wash and deep soil cover are included. Pleistocene Basalt Variable Black aphanitic basalt, occa­sionally vesicular and amyg-daloidal. Oligocene 9 Andesite 1100 f t. Dark gray porphyritic andesite with a glomeroporphyritic texture. A massive flow that approaches a porphyry. CO Latite Light purplish-brown porphy­r i t i c l a t i t e. Tuff 250 f t. White rhyolitic v i t r i c and l i t h i c tuff that is bedded and weakly resistant to ero­sion. A porous friable rock with numerous fragments. 6 Tuff 250 f t. Brownish-stray rhyolitic crystal tuff. It is very r e s i s t a n t and massive in outcrop. 5 Perlite 250 f t. Mottled gray, blue, and green r h y o l i t i c p e r l i t e. 4 Tuff 230 f t. Red rhyoitic v i t r i c tuff. The unit i s dense and dull resembling unglazed porcelain. Leucobasalt 875 f t. Light purplish brown leuco­basalt. 2 Leucobasalt 1000 f t. Reddish brown leucobasalt with no apparent flow banding. 1 Tuff 875 f t. Grayish green crystal tuff with fragments of the under­lying Ely limestone. a l t e r a t i o n a r e a a n d t h e f o l l o w i n g p e t r o g r a p h i c d e s c r i p t i o n of t h e s e r o c k u n i t s i s p r e s e n t e do C r y s t a l t u f f • A g r a y g r e e n c r y s t a l t u f f i s t h e b a s al u n i t of t h e s e q u e n c e a n d i t l i e s on t h e E l y l i m e s t o n e • It is u n i f o r m l y f i n e g r a i n e d a n d c o n t a i n s a b u n d a n t c r y s t a l s and c r y s ­t a l f r a g m e n t s . It i s c o m p o s e d p r e d o m i n a n t l y of a n g u l a r , b r o k en a n d e u h e d r a l p h e n o c r y s t s of p l a g i o c l a s e a n d q u a r t z i n a g r e en c h l o r i t i c m a t r i x . P l a g i o c l a s e c o n s t i t u t e s 55 p e r c e n t of t he r o c k . About 25 p e r c e n t of t h e r o c k i s a p h a n i t i c m a t r i x . F r a g ­m e n t s of b i o t i t e , h o r n b l e n d e , a n d v o l c a n i c r o c k a r e p r e s e n t in l e s s e r a m o u n t s . The h o r n b l e n d e i s g r e e n a n d a l t e r s t o c h l o r i t e. The t u f f h a s a f r a g m e n t a l t e x t u r e and i s p a r t l y i n d u r a t e d . In t h e Squaw P e a k a l t e r a t i o n a r e a , t h e t u f f o c c u r s a s a n a s h w i th f ew f r a g m e n t s . It i s o b s e r v e d i n t h e g u l l e y s, L e u c o b a s a l t o A r e d d i s h - b r o w n l e u c o b a s a l t i s u n i t 2C M e g a s c o p i c a l l y i t l o o k s l i k e an a n d e s i t e . The u n i t i s m a s s i ve w i t h n o a p p a r e n t f l o w b a n d i n g . The r o c k i s p o r p h y r i t i c , b u t t he p h e n o c y r s t s a r e d i f f i c u l t t o d i s t i n g u i s h f r o m t h e m a t r i x . The c o m p o n e n t s of t h e r o c k a r e 30 p e r c e n t l a b r a d o r i t e p h e n o c r y s t s, 5 p e r c e n t m a g n e t i t e p h e n o c r y s t s , 5 p e r c e n t a u g i t e p h e n o c r y s ts a n d 50 p e r c e n t g l a s s . P h e n o c r y s t s of b i o t i t e and b a s a l t ic h o r n b l e n d e a r e m i n o r c o n s t i t u e n t s of t h e r o c k . E a s t h a s c l a s ­s i f i e d t h e r o c k a s a t h o l e i t i c l e u c o b a s a l t . It o c c u r s i n t he c e n t e r of t h e Squaw P e a k a l t e r a t i o n a r e a. L e u c o b a s a l t . Unit 3> a l i g h t p u r p l e - b r o w n l e u c o b a s a l t, i s d i s t i n g u i s h e d f r om u n i t 2 by t h e p r e s e n c e of a b u n d a n t h o r n ­b l e n d e p h e n o c r y s t s . Unit 3> w h i c h h a s a p u r p l e t o g r a y m a t r i x, l o o k s l i k e a n a n d e s i t e i n t h e h a n d s p e c i m e n * . Even f l o w l a y e rs f r om o n e i n c h t o s e v e r a l i n c h e s i n t h i c k n e s s o c c u r t h r o u g h o ut t h e r o c k . The r o c k i s p o r p h y r i t i c w i t h ^ 5 p e r c e n t p h e n o c r y s t s, L a b r a d o r i t e p h e n o c r y s t s c o n s t i t u t e 25 p e r c e n t of t h e f l o w. B a s a l t i c h o r n b l e n d e i s t h e d o m i n a n t m a f i c p h e n o c r y s t a n d c o n ­s t i t u t e s 10 p e r c e n t of t h e r o c k . M a g n e t i t e a n d b i o t i t e a re m i n o r a c c e s s o r i e s . The m a t r i x i s d e v i t r i f i e d g l a s s a n d c o n ­s t i t u t e s 55 p e r c e n t of t h i s r o c k, R h y o l i t i c t u f f . Unit 7 i s a w h i t e r h y o l i t i c v i t r ic a n d l i t h i c t u f f . I t i s u n i f o r m l y m a s s i v e l y b e d d e d a n d is w e a k l y r e s i s t a n t t o e r o s i o n . The t u f f i s p o r o u s , f r i a b l e and h a s a l o w s p e c i f i c g r a v i t y . The r o c k h a s a f r a g m e n t a l t e x t u r e. B r o k e n p h e n o c r y s t s of q u a r t z , b i o t i t e , p l a g i o c l a s e a n d s a n i d i ne a r e embedded i n a g l a s s y a s h m a t r i x . The m a t r i x i s p a r t l y d e ­v i t r i f i e d , P l a g i o c l a s e p h e n o c r y s t s c o m p o s e 10 p e r c e n t of t he r o c k , Q u a r t z , s a n i d i n e a n d b i o t i t e e a c h c o m p o s e 7 p e r c e n t of o f t h e r o c k o About 15 p e r c e n t of t h e t u f f i s c o m p o s e d of r o ck f r a g m e n t s . I t o c c u r s a l o n g t h e s o u t h w e s t e r n m a r g i n of t h e Squaw P e a k a l t e r a t i o n a r e a. The W h i t e M o u n t a i n A r e a s, A l t h o u g h t h e r o c k s s u r r o u n d i n g t h e W h i t e M o u n t a in a l t e r a t i o n a r e a s h a v e n o t b e e n s t u d i e d i n d e t a i l , Makin ( 2 9) ( 4 2 ) TABLE 9 GENERALIZED SEQUENCE OF VOLCANICS IN THE EAST AND WEST WHITE MOUNTAIN AREA Age Unit Formation or Rock Type Thickness Character Quaternary Alluvium Variable Unconsolidated mixtures of gravel, sand, s i l t and clay. Lake beds, stream wash and deep soil cover are included. Pleistocene 6 Basalt Variable Dense black basalt at places vesicular. 5 Andesite Gray to black porphyritic andesite. Oligocene Quichapa 400- 500 f t. White or light purple l i t h ic tuff with a large number of fragments of red f e l s i t e and underlying tuffs. Isom Black-brown ignimbrite with a small number of fragmental inclusions, and crystal inclusions. 2 Needles tuff Dark reddish brown ignimbrite with many inclusions. 1 Pre Needles tuff (Claren) Blue-white ignimbrite. h a s d e s c r i b e d t h e r e g i o n a l v o l c a n i c s t r a t i g r a p h y . The v o l c a n ic r o c k s p r e s e n t i n t h e W h i t e M o u n t a i n a r e a s r o u g h l y c o r r e l a t e w i th t h e s t r a t i g r a p h y a s g i v e n by M a k i n . The f o l l o w i n g l i t h o l o g ic d e s c r i p t i o n of t h e r o c k u n i t s p r e s e n t i n t h e a r e a i s c o n d e n s ed f r om M a k i n a n d S t r i n g h a m ( 4 7 ). I s om f o r m a t i o n . The b a s a l u n i t i n t h e a l t e r a t i o n a r ea i s a member of t h e I s om f o r m a t i o n and i t l i e s on t h e N e e d l es f o r m a t i o n . At t h e t y p e s e c t i o n n e a r M i n e r s v i l l e , U t a h i t c o n ­s i s t s of a s e q u e n c e of v o l c a n i c s made up of i g n i m b r i t e s a n d l a va f l o w s w i t h i n t e r c a l c a t e d s e d e m e n t a r y r o c k s . The p r i n c i p a l mem­b e r c o n s i s t s of a l a t i t e p o r p h r y . I t h a s a g l a s s y t e x t u r e and i s d a r k r e d w i t h a s t r o n g p l a t y p a r t i n g . The u p p e r m o s t member i s a l s o l a t i t e p o r p h r y . It i s l i t h o i d a l i n t e x t u r e . It h a s a p u r p l e g r a y c o l o r w i t h l i g h t g r a y l e n t i c u l e s . Near t h e a l t e r a ­t i o n a r e a t h e I s om f o r m a t i o n i s a d e n s e , g l a s s y t o a p h a n i t i c, r e d d i s h - b l a c k r o c k w i t h o r a n g e p l a g i o c l a s e f e l d s p a r p h e n o c r y s ts up t o 5mm i n d i a m e t e r. Q u i c h a p a t u f f . The Q u i c h a p a r h y o l i t i c t u f f l i e s on t op of t h e I s om f o r m a t i o n . It i s a w h i t e o r p u r p l e c r y s t a l and l i t h i c t u f f w i t h i n c l u d e d f r a g m e n t s of d a r k r e d f e l s i t e , l i g ht g r a y p u m i c e , and o t h e r r o c k s . F r a g m e n t s c o m p o s e 10 p e r c e n t of t h e r o c k . A s q u a r e f o o t of e x p o s u r e commonly c o n t a i n s 5 t o 10 v i s i b l e f r a g m e n t s . E u h e d r a l c r y s t a l p h e n o c r y s t s of q u a r t z, f e l d s p a r , b i o t i t e and o t h e r m i n e r a l s o c c u r i n a g l a s s y m a t r ix ( 4 4 ) w i t h t h e t e x t u r e of u n g l a z e d p o r c e l a i n * P y r o g e n i c m i n e r a ls make up 25 p e r c e n t of t h e r o c k o The b a s e of t h e f o r m a t i on c o n s i s t s of a z o n e of i n t e r l e n s i n g b l a c k 9 g r a y o r n o n c o n s o l i< d a t e d t u f f w i t h few f r a g m e n t s. 4 5 CHAPTER V HYDROTHERMAL ALTERATION IN THE SAN FRANCISCO MOUNTAINS T h e a l t e r a t i o n n e a r and s o u t h of t h e H o r n S l i v e r mine was s t u d i e d a n d i d e n t i f i e d 0 In a d d i t i o n t h r e e a r e a s s o u t h of t h e m i n e w e r e mapped I n d e t a i l 0 M i n e r a l z o n e s w e r e m a p p e d on t h e b a s i s of m e g a s c o p i c c h a r a c t e r i s t i c s of t h e r o c k s 0 The m i n e r a l s w e r e i d e n t i f i e d by x - r a y 9 I n f r a r e d 9 and m i c r o s c o p ic t e c h n i q u e s o An a p p r o x i m a t e p a r a g e n e s l s was d e t e r m i n e d from f i e l d o b s e r v a t i o n s a n d t h i n s e c t i o n a n a l y s e s 0 l o FIELD STUDIES N u m e r o u s a l t e r a t i o n a r e a s w e r e d e l i n e a t e d by o b s e r v i ng t h e i r c o l o r c o n t r a s t w i t h t h e s u r r o u n d i n g f r e s h v o l c a n i c s 0 The a l t e r a t i o n a p p e a r s a s p a t c h e s of w h i t e b l e a c h i n g s u r r o u n d e d by d a r k b r o w n u n a l t e r e d r o c k s 0 C h e m i c a l w e a t h e r i n g h a s s u p e r i m p o s ed r e d a n d b r o w n i r o n o x i d e s t a i n s u p o n t h e b l e a c h e d a r e a s 0 The c o l o r c o n t r a p o s i t i o n w i t h t h e f r e s h r o c k s m a k e s t h e a l t e r a t i on a r e a s r e a d i l y a p p a r e n t f r om t h e a i r a n d g r o u n d o The s e q u e n ce o f p a t t e r n o b s e r v e d e v e r y w h e r e was p a r t l y e x p r e s s e d by m i n e r al c o l o r v a r i a t i o n so G@njyral A l t e r a t i o n C o n f i & u r a 1 1 o n0 S y m m e t r i c z o n e s of a l t e r a t i o n m i n e r a l s a r e a p p a r e n t In e a c h a r e a 0 Zones of a r g i l l l c a l t e r a t i o n s u r r o u n d s i l i c a r e e fs i n t h e f l o w s a n d t u f f s Q These g r a d e f r om i n t e n s e w h i t e k a o l l n l t lc ( 4 6 ) a d j a c e n t t o t h e s i l i c a r e e f s t o a g r e e n m o n t m o r l l l o n i t e - c h l o r i t e s u b z o n e 9 w h i c h g r a d e s i n t o b r o w n o r b l a c k f r e s h r o c k0 N u m e r o u s m i n e r a l s u i t e s w e r e i d e n t i f i e d by a n a l y z i n g s a m p l es f r om a l l a r e a s„ T h e d o m i n a n t f o rm of h y d r o t h e r m a l a l t e r a t i o n i n t he S a n F r a n c i s c o M o u n t a i n s i s a r g l l l i z a t i o n 9 b u t s e v e r a l o t h er t y p e s w e r e o b s e r v e d 0 These i n c l u d e d s i l l c l f i c a t i o n , c h l o r i t l z a - t i © n 9 c a r b o n a t i z a t l o n 9 and z e o l l t i z a t i o n 0 An x ^ r a y p a t t e r n of e a c h s u i t e s e r v e d t o " f i n g e r p r i n t " or i d e n t i f y t h e m i n e r a ls p r e s e n t o P l a t e 5 s h o w s x - r a y p a t t e r n s of some t y p i c a l a r g i l - l l z a t i o n 0 K a o l i n i t e i s t h e m o s t a b u n d a n t s e c o n d a r y m l n e r a lo A l u n i t e and s i l i c a commonly a r e a s s o c i a t e d w i t h k a o l i n i t eo C h a p t e r VI c o n t a i n s a l i s t of a l l s e c o n d a r y m i n e r a l s t h at w e r e i d e n t i f i e d .. D e t a i l e d M a p p i n g S t u d i e s Q Maps of t h e v a r i o u s a l t e r a t i o n f e a t u r e s of t h r e e a r e as h a v e b e e n p r e p a r e d I n o r d e r t o e s t a b l i s h t h e s i g n i f i c a n c e of t he h y d r o t h e r m a l a l t e r a t i o n , , P l a t e 15 i s a map of Squaw P e a k A l t e r ­a t i o n A r e a c P l a t e 16 i s a map of t h e West W h i t e M o u n t a i n A l t e r - a t i o n A r e a Q P l a t e 1? i s a map of t h e E a s t W h i t e M o u n t a i n A l t e r ­a t i o n A r e a 0 The c o n c e p t of s t a g e s ( m i n e r a l z o n e s o r m a p p i ng u n i t s ) u s e d a t M a r y s v a l e 9 U t a h by K e r r ( 2 5 ) was f o l l o w e d i n t he m a p p i n g o T h e t y p e a n d a b u n d a n c e of c l a y m i n e r a l s a t a g i v e n s t a ge d e p e n d s u p o n t h e m i n e r a l o g y p r i o r t o t h e a l t e r a t i o n s t h e n a t u re ( 4 ? ) PLATE 5 F i g u r e 1 : X - r ay p a t t e r n of m i x ed q u a r t z - k a o l i n i t e a l t e r a t i o n F i g u r e 2 : X - r ay p a t t e r n of m i x ed c r i s t o b a l i t e - k a o l i n i t e a l t e r a t i o n F i g u r e 3 : X - r ay p a t t e r n s h o w i n g h y d r o - t h e r m a l c a l c i t e - q u a r t z m i x t u re F i g u r e 4 : X - r ay p a t t e r n s h o w i n g q u a r t z, c r i s t o b a l i t e , a l u n i t e, a n d k a o l i n ! te a l t e r a t i o n m i x t u re X-RAY PATTERNS OF ARGILLIC ALTERATION a n d i n t e n s i t y of t h e o r i g i n a l h y d r o t h e r m a l s o l u t i o n s , and on s u c h f a c t o r s a s t e m p e r a t u r e of s o l u t i o n s , p r e s s u r e i n t h e r e ­a c t i o n s i t e 9 and o x i d a t i o n a f t e r a l t e r a t i o n 0 The l i m i t s e s t a b ­l i s h e d f o r a p a r t i c u l a r s t a g e a r e a r b i t r a r y , and w e r e p i c k e d to f a c i l i t a t e f i e l d m a p p i n g o In t h e i d e a l p a t t e r n s , c l a y m i n e r al z o n e s o c c u p y s y m m e t r i c z o n e s on 'both s i d e s of t h e a l t e r a t i on c h a n n e l s ( q u a r t z r e e f s ) e However, i n a n y p a r t i c u l a r l o c a l i ty m i n e r a l r e v e r s a l s a r e common a n d t h e s y m m e t r i c p a t t e r n Is a b s e n t o T h e b o u n d a r i e s a d o p t e d f o r a l t e r a t i o n m a p p i n g u t i l i z ed m e g a s c o p i c c r i t e r i a , , These I n d i c a t e t h e p r o g r e s s i v e a s p e c t of t h e a l t e r a t i o n . , Seven s t a g e s w e r e r e c o g n i z e d , and f r om t h e se t h e f o l l o w i n g c o n v e n t i o n of m i n e r a l z o n e s was a d o p t e d f o r t he m a p p i n g s Z o n e J. - U n a l t e r e d o The f l o w s a r e h a r d 2 c o m p a c t 2 and r e t a i n t h e i r p r i m a r y t e x t u r e s o The t u f f s h a v e s u f f e r e d more r a p i d s u r f a c e w e a t h e r i n g a l t h o u g h t h e y t o o r e t a i n t h e i r p r i m a ry t e x t u r e s o The f e l d s p a r s a r e l u s t r o u s a n d Fe-Mg m i n e r a l s a re f r e e f r om c h l o r i t e ( e x c e p t i n u n i t 1 t u f f ) 0 Where s h e a r e d and f r a c t u r e d s t h e m i n e r a l s a r e b r o k e n and n o t r e p l a c e d 0 C h e m i c al w e a t h e r i n g h a s p r o d u c e d s m a l l a m o u n t s of s e r i c i t e 9 m o n t m o r l l - l o n i t e 9 and c h l o r i t e i n z o n e l e Z o n e 2 - S l i g h t a r g i l l l c a l t e r a t i o n . , The p l a g i o c l a se a n d b l o t i t e s a r e d u l l o B i o t i t e may s h o w c h l o r l t i z a t l o n o r may b e f r e s h o S a n i d i n e p h e n o c r y s t s a r e f r e s h 0 The o r i g i n al ( 4 9 ) t e x t u r e s a r e p r e s e r v e d 0 The g r o u n d m a s s may b e b l e a c h e d0 L i m o n i t e a n d h e m a t i t e s t a i n i n g may b e s u p e r i m p o s e d on t he a r g i l l l ^ e d r o e k o ' J a r o s i t e f o r m s a l o n g f r a c t u r e s a s a w e a t h e r ­i n g p r o d u c t of p y r i t e 0" g o n e J a - M o d e r a t e t o I n t e n s e a r g l l l i c a l t e r a t i o n 0 The Ca f e l d s p a r s and Fe«Mg m i n e r a l s a r e a l t e r e d t o c l a y 0 S a n i d i ne p h e n o c r y s t s may b e a l t e r e d or may b e f r e s h 0 The o r i g i n a l r o ck t e x t u r e may b e p r e s e r v e d o r may b e c o m p l e t e l y d e s t r o y e d 0 The m a t r i x I s w h i t e t o p i n k w i t h l i t t l e o r no h e m a t i t e s t a i n i ng p r e s e n t 0 Z o n e J b - M o d e r a t e t o I n t e n s e a r g i l l l s , a l t e r a t i o n w i th h e m a t i t e o The r o c k I s I d e n t i c a l t o 3 a e x c e p t t h a t a m o d e r a te a m o u n t of h e m a t i t e s t a i n i n g i s p r e s e n t 0 The m a t r i x c o l o r v a r i es f r om p i n k t o p u r p l e d e p e n d i n g upon t h e amount of h e m a t i t e p r e s e nt I n t h e r o c k o The h e m a t i t e o c c u r s m a i n l y a s c o a t i n g s a l o n g f r a c ­t u r e s a n d a s s m a l l c l o t s t h r o u g h t h e g r o u n d m a s so Z o n e 1c => M o d e r a t e t o i n t e n s e a r g d l i i c a l t e r a t i o n w i th h e a v y h e m a t i t e 0 Heavy h e m a t i t e s t a i n i n g o c c u r s a l o n g f r a c t u r es a n d t h r o u g h o u t t h e g r o u n d m a s s 0 The t e x t u r e i s i d e n t i c a l to t y p e 3aQ Z o n e J d - M o d e r a t e t o i n t e n s e , a r g i l l i e a l t e r a t i o n w i th AIJS£IlAJLS s t a i n l n g o The r o c k I s I d e n t i c a l t o 3a e x c e p t t h a t it I s s t a i n e d w i t h l i m o n i t e a n d j a r o s l t © 0 The l i m o n i t e may be o b s e r v e d t o w e a t h e r f r om f i n e g r a i n s of p y r i t e 9 and i s most common a l o n g f r a c t u r e s « The l i m o n i t e g i v e s t h e r o c k a brown a p p e a r a n c e o C50) Z o n e 4 - S l l l c l f l e a t l o n 0 S i l i c a r e p l a c e m e n t i s e x t e n ­s i v e o The p r i m a r y t e x t u r e h a s "been d e s t r o y e d 0 The r o c k may DS g r a y 9 y e l l o w o r r e d d e p e n d i n g u p o n t h e a m o u n t of h e m a t i te of l i m o n i t e s t a l n i n g o The . s i l i c a i s q u a r t z 9 e r i s t o b a l l t e 9 c h a l c e d o n y o r s i l i c e o u s s i n t e r 0 Z o n e Al •»,; A l u n l t e 0 A l u n i t e I s t h e m a i n a l t e r a t i o n c o n ­s t i t u e n t g b u t c l a y 9 q u a r t z 9 c r y s t o b a l i t e 9 and h e m a t i t e a re a s s o c i a t e s o P r i m a r y t e x t u r e s h a v e b e e n d e s t r o y e d 0 The r o ck h a s a s m o o t h w h i t e p o r c e l a l n - l l k e a p p e a r a n d e0 Z o n e Ch - C h l o r l t e 0 C h l o r i t e a l t e r a t i o n o c c u r s i n t he f r i n g e a r e a s a d j a c e n t t o f r e s h r o e k o C e l a d o n i t e 9 m o n t m o r l l - l o n i t e 9 q u a r t z 9 and l i m o n i t e a r e a s s o c i a t e d m i n e r a l s 0 P r i m a ry t e x t u r e s a r e p r e s e r v e d 0 The r o c k h a s a d u l l g r & e n i s h a p p e a r ­a n c e e v e n t h o u g h o n l y a s l i g h t amount of c h l o r i t e i s p r e s e n t 0 Z o n e Z - Z e o i l t i c A l t e r a t i o n 0 Z e o l i t e s a r e a s s o c i a t ed w i t h q u a r t z i n t h e Squaw P e a k a r e a 0 The p r i m a r y t e x t u r e s h a ve b e e n d e s t r o y e d 0 The m a t r i x v a r i e s f r om p i n k t o w h i t e o L i m o n i te s t a i n i n g o c c u r s a l o n g f r a c t u r e s 0 S u s c e p t i b i l i t y of R o c k ^ U n l t s , t o A l t ® r a t l o n 0 T h e t u f f s I n t h e a l t e r a t i o n a r e a s e x h i b i t w i d e s p r e ad a l t e r a t i o n e f f e c t s w i t h m o r e l i m i t e d a l t e r a t i o n shown by t he d e n s e f l o w s 0 In t h e Squaw P e a k a r e a 9 t h e a l t e r a t i o n e f f e c ts a r e w i d e l y d i s p e r s e d i n t h e b a s a l t u f f ( u n i t l ) a n d i n t he Q u l c h a p a t u f f ( u n i t 7)9 w h i l e t h e a n d e s i t e f l o w s ( u n i t s 2 and 3) show m o r e l i m i t e d e f f e c t s „ The r e l a t i v e s u s c e p t i b i l i t y of ( 5 15 t h e r e c k u n i t s t o a l t e r a t i o n I n o r d e r of d e c r e a s i n g s u s c e p t i ­b i l i t y i s u n i t 1 ( c r y s t a l t u f f ) 9 u n i t ? ( r h y o l i t i c t u f f ) 9 and u n i t s 2 a n d 5 ( l e u c o b a s a l t s } „ The s u s c e p t i b i l i t y of t h e d i f ­f e r e n t r o c k u n i t s ' v a r i e s w i t h t h e c o m p o s i t i o n ^ g r a i n s i z e 9 p o r o s i t y g and p e r m e a b i l i t y 0 It i n c r e a s e s w i t h i n c r e a s i ng p o r o s i t y a n d p e r m e a b i l i t y a n d a l s o w i t h d e c r e a s i n g g r a in s i z e 0 In g e n e r a l t h e s u s c e p t i b i l i t y of rock, u n i t s I n any a r e a i s d i f f i c u l t t o p r e d i c t 0 I I o DESCRIPTION OF THE AREAS MAPPED IN DETAIL E a c h l o c a l i t y s t u d i e d i n d e t a i l h a s a g e n e r a l a l t e r a ­t i o n p a t t e r n a n d m i n e r a l s u i t e I n a d d i t i o n t o I n d i v i d u al s p e c i f i c o r d i a g n o s t i c f e a t u r e s 0 The f o l l o w i n g d e s c r i p t i o ns c o n t a i n t h e g e n e r a l p a t t e r n a n d c e r t a i n a n o m a l o u s f e a t u r e s 0 The c o m p l e t e p a t t e r n i s p r e s e n t e d on t h e a r e a m a p s 0 In a d d i ­t i o n a s h o r t d e s c r i p t i o n of a l t e r a t i o n f r om t h e H o r n S i l v er p i t i s p r e s e n t e d i n o r d e r t o show I t s s i m i l a r i t y w i t h t he r e s t of t h e a r e a s 0 The Sffuaw P e a k A r e a0 T h e Squaw P e a k a l t e r a t i o n a r e a c o n s i s t s m a i n l y of a r g i l l i c a l t e r a t i o n w i t h h e m a t i t e s t a i n i n g p and I s a b o u t one m i l e i n t h e n o r t h - s o u t h d i r e c t i o n a n d on© h a l f of a m i l e in t h e e a s t - w e s t d i r e c t i o n A s y m m e t r i c s e q u e n c e of m i n e r al z o n e s f o r t h e e n t i r e a r e a was n o t o b s e r v e d 9 h o w e v e r B many s m a l l l o c a l a l t e r a t i o n c h a n n e l s show a p a t t e r n of z o n i n g t h at ( 5 2 ) P l a t e 6 Z o n i n g of A l t e r a t i o n M i n e r a l s i n t he S q u a w P e a k A r ea F i g u r e I - A r g i i l i c A l t e r a t i o n W i t h a n d W i t h o u t H e m a t i t e0 T h e l o w h i l l i n t h e m i d d l e f o r e g r o u n d shows a e o n t a c t "between a l t e r a t i o n z o n e s 3a 9 t he w h i t i s h a l t e r a t i o n on t h e l e f t 9 and z o n e 3 c9 t h e d a r k e r a l t e r a t i o n on t h e r i g h t o Q u a r tz r e e f s p r o t r u d e a t t h e t o p of t h e h i l l o The p i c t u r e was t a k e n l o o k i n g n o r t h 0 The h i l l is i n t h e n o r t h e r n f r i n g e of t h e Squaw P e a k A r ea j u s t n o r t h of Squaw S a d d l e 9 t h e d i r t r o ad r u n n i n g a c r o s s t h e l o w e r h a l f of t h e p i c t u r e 0 T h e d a r k c o l o r e d r o c k s s o u t h of t h e r o a d a re f r e s h v o l c a n i c S o The w h i t e a l t e r a t i o n s o u th o f t h e r o a d i s z o n e 2 a l t e r a t i o n F i g u r e 2 - H y d r o t h e r m a l g y p s u m 0 The h i l l I n t h e m i d d le f o r e g r o u n d shows h y d r o t h e r m a l gypsum w i th t y p e 3© a r g i i l i c a l t e r a t i o n j u s t a b o v e 0 The d a r k h i l l on t h e l e f t i s f r e s h v o l e a n i c s 0 The p i n k h i l l on t h e m i d d l e r i g h t i s z o n e 3© a l t e r a t i o n The v i e w i s l o o k i n g w e s t i n t he n o r t h e r n p a r t of t h e Squaw P e a k A r e a 0 i PLATE 6 g r a d e s f r om i n t e n s e a r g i l l i z a t i o n t o f r e s h r o e k o P l a t e 6 shows m i n e r a l z o n l n g o In a d d i t i o n t o t h e a r g i l l i z a t i o n m i n e r a l s 9 z e o ­l i t e s a n d g y p s um a r e s e c o n d a r y p h a s e s i n t h e a r e a Q An i r r e g u l a r p a t t e r n of m i n e r a l z o n e s was o b s e r v e d 0 A s i n g l e c e n t e r of a l t e r a t i o n was n o t a p p a r e n t 9 b u t m o r e I n t e n se a l t e r a t i o n e x i s t s i n t h e n o r t h e r n , h a l f of t h e a r e a c A p p r o x i ­m a t e l y 20 z o n e s of s i l i c a v a r y i n g f r om 2 f e e t t o 4 0 0 f e e t in l e n g t h a r e s c a t t e r e d t h r o u g h o u t t h e a r e a 0 These r e p r e s e nt a l t e r a t i o n c e n t e r s o r c h a n n e l s a r o u n d w h i c h a s y m m e t r i c s e q u e n ce of m i n e r a l z o n e s I s a p p a r e n t 0 The s e q u e n c e I s a q u a r t z ( or e r i s t o b a l i t e ) r e e f f o r m i n g a t o p o g r a p h i c h i g h s u r r o u n d e d by an a r g i i l i c z o n e 0 The a r g i i l i c z o n e s g r a d e s I n t o f r e s h r o e k o A f r i n g e a l t e r a t i o n a r e a e x i s t s i n some of t h e g u l l i e s w h e r e t he u n i t 1 t u f f h a s b e e n p a r t l y a r g i l l i z e d o H e m a t i t e a n d l i m o n i te s t a i n i n g a r e s u p e r i m p o s e d e r r a t i c a l l y on t h e a r g i i l i c a l t e r a t i o n ,, P l a t e ? shows t h e a r g i i l i c a l t e r a t i o n w i t h i r o n s t a i n i n g ,, S e v e r a l s m a l l z o n e s of e h l o r i t l c a l t e r a t i o n w e r e o b s e r v e d0 They v a r y I n s i z e f r om a b o u t 5 f e e t t o one z o n e 400 f e e t l o n g a U s u a l l y t h e y w e r e o b s e r v e d I n t o p o g r a p h i c d e p r e s s i o n s a n d c o n s t i ­t u t e d a f r i n g e a l t e r a t i o n z o n e , b u t 2 s m a l l s e c t i o n s w e r e l o c a t ed on a h i l l i n t h e c e n t e r of t h e z e o l i t i e zone© U n i t s I ( c r y s t al t u f f ) 9 2 ( l e u c o b a s a l t ) ' , 3 ( l e u c o b a s a l t ) , and ? ( r h y o l i t i c t u f f) h a v e b e e n e h l o r l t i z e d a l t h o u g h t h i s t y p e of a l t e r a t i o n i s most common i n u n i t 1„ ( 5 4 ) One l a r g e z o n e of z e o l i t i e a l t e r a t i o n was mapped in t h e n o r t h w e s t p o r t i o n of t h e a r e a Q I t i s a b o u t 400 f e e t in d i a m e t e r a n d f o r m s a t o p o g r a p h i c h i g h o P l a t e 12 shows p h o t o ­m i c r o g r a p h s of s p e c i m e n s f r om t h i s z o n e0 H y d r o t h e r m a l gypsum o c c u r s I n t h e Squaw P e a k a r e a In a p a r t i a l l y a r g i l l l z e d f r i n g e a r e a b o r d e r i n g f r e s h r o c k s0 M o n t m o r i l l o n i t e i s a n a s s o c i a t e m i n e r a l 0 P l a t e 6 shows t he gypsum a l t e r a t i o n z o n e0 Two p r e f e r r e d d i r e c t i o n s of o r i e n t a t i o n of t h e m i n e r al g o n e s w e r e d l s c e r n e d o These a r e a n o r t h - s o u t h a n d a n e a s t - w e st a l i g n m e n t o T h i s i s m a n i f e s t by a n a l i g n m e n t of z o n e s of s i m i l ar c o m p o s i t i o n a n d a l s o by t h e s t r i k e of t h e l o n g a x i s of i n d i v i d u al z o n e s o The e a s t - w e s t a l l g n e m n t i s d e m o n s t r a t e d by ( i ) t h e o r i ­e n t a t i o n of 4 o r 5 s e p a r a t e p a t c h e s of Jc a l t e r a t i o n a t t he n o r t h e r n e x t e n t of t h e a r e a ? ( 2 ) a g o n e of Jb a l t e r a t i o n j u st s o u t h of a n d p a r a l l e l t o ( l ) ^ and ( 3 ) t h e s t r i k e of t h e e l o n g a ­t i o n of many I n d i v i d u a l p a t c h e s 0 The n o r t h - s o u t h o r i e n t a t i o n is e x h i b i t e d by t h e a l i g n m e n t of s e v e r a l p a t c h e s of t y p e 2 a l t e r a ­t i o n a l o n g t h e w e s t e r n b o r d e r 0 The West W h i t e M o u n t a i n A r e a 0 T h e West W h i t e M o u n t a i n a r e a i s a n a r g i l l l z e d s t r ip e x t e n d i n g t h r e e m i l e s i n a n e a s t - w e s t d i r e c t i o n and a b o u t one h a l f m i l e i n a n o r t h - s o u t h d i r e c t i o n In a d d i t i o n t o t he a r g i i l i c m i n e r a l s 9 an a n o m a l o u s a r e a of a l u n i t e a n d a d e p o s it o f n a t i v e s u l p h u r e x i s t i n t h e a r e a G C o n c e n t r i c m i n e r a l z o n es ( 5 5 ) P l a t e ? A r g i i l i c A l t e r a t i o n W i t h I r o n S t a i n i ng i n t h e Squaw P e a k A r ea F i g u r e 1 - A r g i i l i c A l t e r a t i o n W i t h H e m a t l t i c S t a i n i n go T h e r e d h i l l i n t h e m i d d l e of t h e p i c t u re a b o v e t h e t r e e l i n e c o n s i s t s of a l t e r a t i on z o n e 3©9 a r g i i l i c a l t e r a t i o n w i t h h e m a t i te s t a i n i n g o A s i l i c a r e e f p r o t r u d e s a t t he t o p of t h e h i l l o The v i e w i s l o o k i n g s o u th f r om Squaw S a d d l e 0 F i g u r e 2 - S l i g h t A r g i i l i c A l t e r a t i o n W i t h L i m o n i te S t a i n i n g o L l e s e g a n g b a n d i n g o c c u r s I n t he s o u t h w e s t c o r n e r of t h e Squaw P e a k A r e a 0 T h e r o c k i s s l i g h t l y a r g i l l l z e d t u f f w i th l i m o n i t e b a n d i n g d u e t o s u r f a c e w e a t h e r i n g0 T h e l i m o n i t e b a n d s a r e p a r a l l e l t o f r a c t u r es i n t h e r o c k s 0 PLATE ? F i g u r e 20 ARGILLIC ALTERATION WITH IRON STAINING IN THE SQUAW PEAK AREA ( 5 6 ) on a n a r e a w i d e e x t e n t w e r e n o t a p p a r e n t , b u t l o c a l z o n i ng a r o u n d p a t c h e s of i n t e n s e a l t e r a t i o n was o b s e r v e d o An a l i g n ­ment of m u l t i p l e z o n e s a n d t h e l o n g a x i s of i n d i v i d u a l z o n es I n t h e two p r e f e r r e d d i r e c t i o n s e a s t - w e s t and n o r t h - s o u th was c o n s p i c u o u so T h e d i s t r i b u t i o n of m i n e r a l z o n e s o r p a t c h e s i s e r r a t ic a n d a r e g u l a r a r e a w i d e p a t t e r n d o e s n o t e x i s t 0 However, a g e n e r a l t r e n d of d e c r e a s i n g i n t e n s i t y of a r g i l l i z a t i o n t o w a rd t h e w e s t i s e v l d e n t o The e a s t e r n p o r t i o n c o n s i s t s of a one m i l e z o n e of I n t e n s e a r g i l l i z a t I o n 0 This Is b o r d e r e d on t he w e s t by a n o n e h a l f m i l e z o n e of a l u n i t e o The w e s t e r n m a r g in i s a n one h a l f m i l e z o n e of s l i g h t a r g l i l l z a t l o n o In a d d i t i on t o t h e a r e a p a t t e r n a v e r y l o c a l z o n i n g was d i s p l a y e d by e a ch h i l l o S y m m e t r i c z o n e s of a l t e r a t i o n m i n e r a l s e x i s t i n t he a r e a G The z o n i n g c o n s i s t s of a q u a r t z r e e f c o n s t i t u t i n g a t o p o g r a p h i c h i g h w h i c h i n t u r n I s s u r r o u n d e d by a n a r g i l l l z ed z o n e 0 The a r g i l l l z e d z o n e , w h i c h c o n s i s t s of k a o l i n ! t . e 9 a l u - n l t e , q u a r t z and c r i s t o b a l l t e , e x t e n d s t o f r e s h r o c k s 0 Dense h e m a t i t e s t a i n i n g on t o p of t h e h i l l s g r a d e s i n t o l i g h t hema­t i t e s t a i n i n g i n t h e p a r t l y a r g i l l l z e d a r e a s 0 Two a n o m a l o u s m i n e r a l o c c u r r e n c e s i n t h e a r e a a r e a l u - n i t e a n d n a t i v e s u l p h u r 0 The a l u n l t e d e p o s i t i s l a r g e e n o u gh t o c o n s t i t u t e a d i s t i n c t m a p p i n g u n i t e It was o b s e r v e d I n t he c e n t e r of t h e a l t e r a t i o n s t r i p , w h e r e t h e Q u i c h i p a t u f f h a s b e en (57) P l a t e 8 A l t e r a t i o n i n t h e W h i t e M o u n t a in A r e a F i g u r e 1 - N a t i v e S u l p h u r D e p o s i t 0 The o p e n i n g i n t he p i c t u r e i s a s m a l l w o r k i n g i n s i l i c e o us s i n t e r on t h e w e s t e r n end of t h e W h i te M o u n t a i n A l t e r a t i o n Zone,, The w o r k i n g s w e re c o n s t r u c t e d p r i o r t o i 9 3 0o F i g u r e 2 - A r g i i l i c A l t e r a t i o n i n t h e West W h i t e M o u n t a in A r e a c The l o w h i l l s I n t h e m i d d l e of t h e p i c° t u r e a r e w h i t e a r g i i l i c a l t e r a t i o n * The v i ew I s l o o k i n g e a s to PLATE 8 a l u n i t i z e d o A d e p o s i t of n a t i v e s u l p h u r 0 s i l i c e o u s s i n t e r, a n d c h a l c e d o n y , w e r e n o t e d i n t h e w e s t e r n p a r t of t h e a l t e r - a t l o n a r e a 0 P l a t e 8 s h o w s t h e s u l p h u r d e p o s i to T h e z o n e s s t r i k e I n two p r e f e r r e d d i r e c t i o n s , n o r t h - s o u t h a n d e a s t - w e s t o T h i s i s shown by t h e a l i g n m e n t of s i m i l a r m i n e r a l z o n e s s e p a r a t e d g e o g r a p h i c a l l y and t h e s t r i ke of t h e l o n g a x i s of s i n g l e z o n e s 0 The e a s t - w e s t a l i g n m e n t is d e m o n s t r a t e d by ( l ) t h e s t r i k e of l o n g a x i s of s e v e r a l i n d i v i d ­u a l s i l i c a r i d g e s | ( 2 ) t h e s t r i k e of a l i n e c o n n e c t i n g I s o l a t ed z o n e s of s i m i l a r c o m p o s i t i o n s and ( 3 ) t h e d i r e c t i o n of t he m a j o r a x i s of t h e e n t i r e a l t e r a t i o n s t r i p 0 The n o r t h - s o u th a l i g n m e n t i s e x h i b i t e d by s e v e r a l z o n e s of s i l i c a a n d h e m a t i te a l o n g t h e w e s t e r n m a r g i n , and a l s o by a s a l i e n t of a l t e r a t i o n, w h i c h e x t e n d s one m i l e n o r t h , a l o n g t h e w e s t e r n m a r g i n of t he s t r i p o The E a s t W h i t e M o u n t a i n A r e aQ T h e E a s t W h i t e M o u n t a i n a r e a i s a n a r g i l l l z e d s t r ip e x t e n d i n g 1-J- m i l e s I n a n e a s t - w e s t d i r e c t i o n a n d J of a m i le i n a n o r t h - s o u t h d i r e c t i o n It I s I n t e r m i t t e n t w i t h a r g i l l l z ed a r e a s i s o l a t e d from e a c h o t h e r by f r e s h r o c k s 0 A l a r g e c h l o r i te z o n e o c c u r s i n t h e c e n t e r of t h e a r e a 0 The a r e a p a t t e r n Is e r r a t i c , b u t l o c a l z o n i n g o r g r a d a t i o n I n a l t e r a t i o n I n t e n s i ty e x i s t s o T h e z o n i n g c o n s i s t s of I n t e n s e a r g l l l a t i o n a s t o p o ­g r a p h i c h i g h s s u r r o u n d e d by s l i g h t a r g i i l i c a l t e r a t i o n , w h i ch ( 5 9 ) P l a t e 9 V i e w s of t h e H o r n S i l v e r Mine F i g u r e 1 - D i s t a n t View of t h e H o r n S i l v e r W o r k i n g s0 T h e o p e n p i t j u s t a b o v e t h e t r e e t o p of t he t o w e r c e n t e r of t h e p i c t u r e i s t h e Horn S i l v e r Hinoo The v i e w i s l o o k i n g w e s t from S t a t e Highway 2 1 0 The r o c k s w e s t of t h e p it a r e l i m e s t o n e 0 and t h e r o c k s e a s t of t h e p it a r e v o l c a n i c s G F i g u r e 2 - W o r k i n g F a c e of t h e H o r n S i l v e r M i n e e A c l o s e v i e w of t h e w e s t end of t h e o p e n p l to T h e w h i t e s p o t s i n t h e w o r k i n g f a c e a r e f i ne g r a i n e d a r g i i l i c a l t e r a t i o n The brown s t a i n s a r e m i x t u r e s of l i m o n i t e a n d j a r o s i t e 0 PIATE 9 F i g u r e 2 VIEWS OF THE HORN SILVER MINE ( 6 0 ) g r a d e s i n t o f r e s h r o c k s 0 H e m a t i t e s t a i n i n g i s s u p e r i m p o s ed u p o n t h e a r g i i l i c a l t e r a t i o n * , The h e m a t i t e s t a i n i n g g r a d es f r om d e n s e t o m o d e r a t e h e m a t i t e s t a i n i n g o Two c h l o r i t e z o n es w e r e mapped i n t h e c e n t e r of t h e a r e a and t h e y a r e a l e ss i n t e n s e p h a s e of a r g i l l l z a t l o no 2 M g a m S i l v e r Mingo S e v e r a l s a m p l e s of a l t e r a t i o n w e r e o b t a i n e d f r o m t he H o r n S i l v e r p i t o T h e s e w e r e i d e n t i f i e d a s C1) a f i n e g r a i n ed m i x t u r e of q u a r t z 9 a l u n i t e a n d k a o l l n l t e , w h i c h was w h i t e or s t a i n e d r e d w i t h h e m a t i t e 5 ( 2 ) gypsum§ (J ) l i m o n i t e § (k) j a r o~ s i t e s and ( 5 ) c h l o r i t e © These s a m p l e s w e r e o b t a i n e d f o r com­p a r i s o n s w i t h t h e a l t e r a t i o n f r o m t h e r e s t of t h e d i s t r i c t 0 P l a t e 9 shows a r g i l l i z a t i o n I n t h e H o r n S i l v e r mine© XIXo DESCRIPTIVE PETROGRAPHY Op ALTERED VOLCANICS S e v e r a l r o c k s f r om t h e H o r n S l i v e r m i n e a n d S q u a w P e ak a r e a s w e r e a n a l y z e d p e t r o g r a p h l c a l l y 0 M i n e r a l o g y a n d t e x t u r es w e r e n o t e d 0 The c h a r a c t e r of a l t e r a t i o n was s t u d i e d a n d c e r t a in p a r a g e n e t - i c r e l a t i o n s h i p s w e r e o b s e r v e d 0 A b r i e f summary of some r o c k d e s c r i p t i o n s a l o n g w i t h s e l e c t e d p h o t o m i c r o g r a p h s Is p r e s e n t e d b e l o w * The t e x t u r a l t e r m s u s e d a r e t h o s e d e f i n e d by G r o u t ( 2 1 )o S a m p l e 6 6 a 0 C a l c i t i c a l t e r a t i o n was i d e n t i f i e d i n a l l a r e a s o The t y p e s p e c i m e n was o b t a i n e d two m i l e s n o r t h - e a s t of Long L i c k M o u n t a i no ( 6 1 ) T h e r o c k i s p i n k i n c o l o r a n d h a s a n a p h a n i t i c t e x t u r e0 The h a n d s p e c i m e n i s e x t r e m e l y p o r o u s a n d n o n c o h e r e n t 0 Small s p e c k s of h e m a t i t e a r e v i s i b l e t h r o u g h o u t« I n t h i s s e c I o n t h e g r o u n d m a s s i s c r y p t o c r y s t a l l i ne w i t h a n u n i f o r m g r a i n s i z e of a b o u t 0.005mmo It i s c o m p o s ed of a m i x t u r e of c a l c i t e a n d k a o l i n l t e 0 A n h e d r a l l a t h s of p l a g i o c l a s e p h e n o c r y s t s (0o2mm t o 2mm l e n g t h ) form 5% o f t he r o c k a n d t h e s e a r e e t c h e d w i t h c a l c i t e . About 5% of t h e r o ck c o n s i s t s of v o i d s f o r m e d by t h e r e m o v a l of f e l d s p a r s 0 Horn­b l e n d e I s a n a c c e s s o r y o F i g u r e 1, P l a t e 10, s h o w s a p h o t o ­m i c r o g r a p h of t h e s p e c i m e n ,, S a m p l e 6 6 c 0 A s a m p l e of a r g i l l i z a t i o n was o b t a i n ed 10 f e e t from s a m p l e 66a„ The s p e c i m e n i s r e d i n c o l o r and h as a b r e e e i a t e d p o r p h y r l t i c t e x t u r e 0 A n g u l a r 0 o 2 5 H t o 2t t f r a g - m e n t s of w h i t e a n d p u r p l e a p h a n i t e form 50% of t h e r o e ko S m a l l ( 0 o 0 2 w ) a n h e d r a l p h e n o c r y s t s of w h i t e a l t e r a t i o n o c c ur t h r o u g h o u t a n d t h e s e a r e s p o t t e d w i t h h e m a t i t e 0 I n t h i n s e c t i o n t h e g r o u n d m a s s i s g l a s s y and h e a v i ly s t a i n e d w i t h h e m a t i t e 0 The p h e n o c r y s t s I n c l u d e ( l ) 0o5mm l a t h s of m i l k y w h i t e g