Silver Cloud Mine, San Juan County, Colorado, USAi

Regional Level Types
Silver Cloud Mine	Mine
San Juan County	County
Colorado	State
USA	Country

The Silver Cloud Mine is a cordilleran vein-hosted hydrothermal ore deposit that developed within the Red Mountain mining district from 30 to 20 million years ago. Mineralizaton is confined to radial and concentric ring faulting from the collapse of the San Juan and Silverton calderas adjacently east of the mine. Detailed field and analytical studies establish that the mine contains three primary veins that are dominated by mesothermal lead-zinc-copper mineralization with minor silver and gold. Mineralization exhibits textures of open-space filling along fractures that are mantled by proximal phyllic and regionally pervasive propyllitic alteration assemblages. The association of ore minerals, exsolution products and alteration assemblages in these deposits indicate that mineralization formed under early conditions of 300°C- 600°C and moderate pressures consistent with formative conditions of the mesothermal category. Vein types in this deposit vary from massive quartz-calcite hosted veins with abundant base-metal sulfides (vein 1), to finely disseminated silver-rich sulfides (vein 2) and zones of anastomosing bull quartz dominated veins with minor pyrite (vein 3). Grade and tonnage estimates on these veins indicate that vein-type 1 has the highest potential for development with 19,419 tons assaying about 0.19% copper, 12.80% zinc, 6.90% lead, 1.11 ounces of silver, and 0.43 grams of gold per ton of ore. A comparison of selected geochemical signatures indicates a poor overall correlation of trace elements (As, Sb, etc) with mineralization. This implies that mineralization does not have a strong association with any given mineral or combination of minerals in the system to serve as exploration tools. Results of laboratory analysis and field work indicate a significant orebody at the Silver Cloud with base metals comprising most of the value. Vein 1 is the only mineralized structure of considerable value with a gross value of $7.14 million at $367.82/ton. While lateral and vertical expression of vein 1 are limited to a single drift level, exploration drilling at two specified sites will help to identify the extent of mineralization and zoning beyond current exposure. The economic viability of producing metals from the Silver Cloud will ultimately be determined by the profit margin that production costs afford.