Geological Survey Bulletin, Edição 1434

2M sericite 2M>1M sericite abundant alteration mineral assemblage aphanitic arsenopyrite base-metal stage biotite bismuth brecciated rocks chalcopyrite chemical Chicago Basin stock chlorite Columbine Pass comb quartz compatibility diagram concentrated copper deposits detected dickite dike distribution east-trending eastern Eolus Granite feet fine-grained fluorite galena geochemical data groundmass highly anomalous amounts inclusions indicate K₂O kaolinite least altered samples locally Mesa metal anomalies metallized veins molybdenite Molybdenum muscovite Na₂O Needle Creek Needle Mountains district older body older intrusive body older intrusive rocks older porphyry oxidized oz of gold Paleozoic percent phenocrysts plagioclase polytypes potassium feldspar Precambrian pyrite pyrophyllite quartz quartzite Rapid rock analyses rhyolite rhyolite porphyry rock samples samples contain samples taken sanidine sanidine phenocrysts seen microscopically SiO2 southwestern Colorado spectrographic methods sphalerite sphene structural Tertiary tetrahedrite trusive U.S. Geol U.S. Geological Survey Vallecito Basin west side western younger body younger intrusive body younger intrusive rocks younger porphyry