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the ore shoots varies fibm one mine to another, and economic factors determined the <br />actual size of the ore bodies as much as geology did in some instances. <br />Gold-silver tellurides are the most important ore minerals in the district, although free <br />gold (Au) is abundant in many of the veins. Among the tellurides found in the district are <br />calaverite (AuTeZ), petzite (AuA$3Te2), sylvanite (AuAgTey), krennerite [(AuAg)Te2], <br />hessite (Ag2Te), altaite (PbTe), and coloradoite (HgTe). Free gold is associated with the <br />telluride minerals in places, and can contribute significantly to the value of the ore. <br />Pyrite (FeSZ) can be found finely disseminated throughout the telluride veins along with <br />very small amounts of galena (PbS) and sphalerite [(Zn,Fe)S]. The chief gangue mineral <br />is horn quartz (Si02) which grades into sugary quartz in places. <br />The gold-silver telluride veins are characterized by interlacing dark-grey to neazly white <br />horn quartz seams enclosing breceia fragments and lenticulaz bodies of altered and <br />sheared wall rock, which is usually granite. Within the veins' fissures, the distribution of <br />ore seems to have been dependent on local structural conditions which favored the <br />formation of openings during mineralization. <br />Metallic Sulfide Occurrences <br />In order to produce significant quantities of acidic waters from a mine, either the wall <br />rock or the vein material must contain substantial quantities of metallic sulfides. These <br />metallic sulfides include sulfides of copper (chalcopyrite, bomite, enazgite, and <br />tennanfite) and of iron (mazcasite, pyrrhotite, and pyrite). Lead sulfide (galena) forms <br />very insoluble sulfate (anglesite) and does not lower the pH of the water that wmes into <br />contact with it. Zinc sulfide (sphalerite) does not contribute to the formation of acid mine <br />waters because the oxidation reaction of sphalerite does not result in the liberation of free <br />acidity. The copper and iron sulfides identified by myself and others in polished sections <br />in the telluride veins and altered wall rock are listed below: <br />• Chalcopyrite (CuFeS~J: Small, but widespread quantities of chalcopyrite were <br />deposited during the telluride stages of mineralization, commonly in close association <br />3 <br />