Geology and diatremes of Desert Mountain, Utah

The Desert Mountains and the Allison Knolls make up a group of isolated peaks which rise from part of the Bonneville lake plain. The area is in Juab County and is located about 24 miles west of Jericho and about 35 miles north of Delta. Sedimentary rocks are exposed in the northeast part of the area. They consist of Precambrian Sheeprock Series and Ordovician Fish Haven Dolomite. The older rock has been thrust on top of the dolomite by what is probably the Sheeprock Thrust. Most of the bed rock exposed in the area is intrusive. Two distinct intrusive rocks are present. The older is a very dark colored granodiorite. The other, is a light colored granite. Aplite, pegmatite and lamprophyre dikes cut the granite. A diatreme complex is located east of Desert Mountain The complex is characterized by an igneous matrix which ha fragments and large blocks of dolomite, quartzite, slate, jasperoid, and igneous rocks suspended in it. Extrusive rocks occur mainly in the eastern part of the area. All the volcanics are thought to be equivalents of the Keg Mountain Ignimbrites. Two volcanic units are altered and apparently correlate with the older recks of the Keg Mountain Ignimbrites. The structure is dominated by three shear directions, sheeting, and thrust fault mentioned above. The three shear directions form a pattern similar to patterns produced by model work from strike-slip stresses. The pattern is also similar to rock fracture patterns under compression. These similarities together with the general east-west alignment of intrusions and volcanic vents, suggests that there is deep-seated structure control with left-lateral movement. Hydrothermal alteration occurs in many areas but generally is weak. Locally the alteration is moderately strong. Some small copper deposits occur in the western part of the area but they are too small to be of economic Interest.