Laserfiche WebLink
telluride belt, pyritic gold veins and lead-silver veins have also contributed appreciable <br />amounts of ore. <br />Wall Rock <br />Boulder Creek Granite is the chief wall rock of the veins in the telluride belt. It ranges in <br />composition from quartz monzonite through granodiorite to granite. According to the <br />U.S. Geological Survey, seven samples of Boulder Creek Granite had the following <br />average chemical composition: SiOZ (66.0%); A1z03 (16.0%); Fez03 (1.9%); Fe0 (2.0%); <br />MgQ (1.4%); Ca0 (4.8%); Na203 (3.3%); K20 (2.5%); Mn0 (0.1%); HZO (0.7%); Ti02 <br />(0.7%); and, PZOs (0.6%). The mineralogical composition is typically from 20 to 40 <br />percent quartz, about 20 percent microcline, 25 to 30 percent plagioclase (oligoclase or <br />andesine), and 15 to 35 percent biotite. Acoarse-grained porphyritic granodiorite is the <br />main wall rock in the Gold Hill mining district. It has a mineralogical composition of 46 <br />percent plagioclase, 24 percent quartz, 11 percent microcline, 15 percent biotite, and 3 <br />percent hornblende. <br />There have been several studies of the hydrothermal wall rock alteration associated with <br />the telluride mineralization of the ore deposits of the Boulder Country telluride belt. The <br />wail rocks of the telluride veins are commonly altered for 6 to 36 inches from the veins; <br />with an inner zone that is sericitized, silicified, and pyritized for several inches into the <br />bordering wall rock, and an outer zone of complex azgillic alteration that may extend for <br />several feet beyond the sericitic casing. Wall rock caught up in the networks of <br />interlacing horn quartz seams that comprise the telluride veins is moderately to strongly <br />silicified. In places, the silicification extends several inches into the surrounding wall <br />rock. Disseminations of fine-grained pyrite are found in the altered wall rocks close to <br />the ore minerals in association with quartz and sericite. <br />Ore Minerals <br />The size of the ore bodies within the veins generally range from 100 to 400 feet in length, <br />from 50 to 300 feet in breadth, and from 1 to 5 feet in thickness. Most of the ore shoots <br />aze elliptical in shape, with the vertical dimension exceeding the horizontal. The size of <br />2 <br />