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Late Cretaceous and Tertiary igneous rocks
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altered altitude andesite base-metal Basin beds belt biotite blocks bodies Boulder County breccia reefs caldera Camp Bird Canyon chalcopyrite channels chimney Colo Colorado contain Creek crosscut Denver depth dikes drift east fault zone feet wide Figure fissures fluorspar formation formed fractures galena gangue gneiss Gold Hill Gold Hill district granite Gray porphyry Gulch porphyry Hoosier reef igneous intrusive Iowa Gulch junction leaching Leadville Leadville district Leadville limestone locally lode Magnolia miles Mineral Point Mosquito Range nearly northeast northwest Old Lout oreshoots ounces Ouray outcrops pegmatite places Poorman porphyry pre-Cambrian productive prospecting pyrite quartz latite radial Red Mountain region rhyolite rocks San Juan Mountains San Juan tuff shaft shear shoots silicified silver Silverton slope Sneffels sphalerite strike structural sulphides surface Telluride Tertiary tion trend tuff tunnel U. S. Geol Uncompahgre upper vein vertical volcanic pipes volcanic series wall width