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Show Tourmaline Compositions: A Guide To Copper Mineralization Mineral-Chemistry Of Tourmaline Occurances In Sonora, Northern Mexico Tourmaline, (Na,Ca)(Mg,Fe, Mn,Li,Al)3(Al,Mg,Fe)6(Si6O18)(BO3)3(O,OH)3(OH,F), is a mineral with a complex chemical composition, allowing it to form in numerous geological/geochemical environments. Thirty-six occurrences of tourmaline in the Cannanea-Milpillas district of Sonora, Mexico were characterized on the basis of rock type (granodiorite, feldspar porphyry, quartz-feldspar porphyry, volcanic), texture (breccia, vein, massive, disseminated), and geography. Following classification, occurrences were characterized based on composition using electron microprobe analysis. The goal of this study was to determine the geochemical characteristics of tourmaline in each setting and the role of boron metasomatism and copper mineralization. Wide variations in chemical composition occur with respect to molar ratios in XNa, XMg, XFe3+, Aliv, and XF. Our data shows differentiable chemical populations, and spatial correlation in both rock type and texture. Each sample has a distinct chemical range. The compositions of some gravel samples match that of known hard rock locations. There are, however, samples that are not represented by presently sampled hard rocks. Our interpretation is that they could represent eroded or concealed hard rock occurrences. The fact that the compositions in the Cannanea-Milpillas district are not homogeneous throughout the district may make it possible to obtain the source and transport direction of tourmaline clasts, indicating the presence of possible undiscovered economic copper mineralization. Jessica J. Moore Class Standing: Senior Major: Geology E-mail: jessica.moore@m.cc.utah.edu Faculty Sponsor: Erich U. Petersen Department of Geology and Geophysics E-mail: eupeters@mines.utah.edu |