New Mexico Mineral Symposium — Abstracts

In 1960 Pb-Cu-Zn replacement ore was discovered in the Eocene Telluride Conglomerate adjacent to the Argentine vein in the Idarado mine, San Miguel County, Colorado. Production of the first replacement ore was from the 2422 stope at the base of the Telluride Conglomerate and continued along the vein until the early 1970s. From 1964 through 1968 additional replacement ore-bodies were located on the Cross, Basin, Ajax, Black Bear, Pandora, and Subsidiary veins. Production ended in 1978 when the Idarado Mining Company ceased operations. During this period approximately 1,285,000 tons of ore were mined from the replacement orebodies.

In 1968 Camp Bird Colorado, Inc. discovered economic replacement ore along the northwest- trending Orphan vein. Subsequent drilling along the Camp Bird vein from the 14th level disclosed low-grade mineralization but no orebodies of economic importance. Once mining progressed on the 21th level of the Orphan vein, additional ore was discovered adjacent the parallel Gordon vein. The replacement orebodies were mined from 1970 through 1978 and produced 381,589 tons of ore that averaged Au-trace, Ag-0.8 ounces/ton, Pb-4.8 %, Cu-0.6 %, Zn-6.8 %.

During the 1980s when the Revenue mine, located in Yankee Boy Basin, was being operated, the Telluride Conglomerate was diamond drilled and replacement ore was encountered but no mining has taken place.

Most of the orebodies occurred at the base of the Telluride Conglomerate just above the unconformity with the Permian Cutler Shale. The ore boundary was so sharp in the Camp Bird mine that a pencil point could be put on the contact between ore and waste. The replacement ore could range from 10 to 60 feet thick and extend out from the vein for a distance of 40 feet and along the strike of the vein for thousands of feet. The ore from the Idarado and Camp Bird mines is almost identical and cannot be told apart when samples are placed next to each other.

Mineralogically, the main ore minerals were galena, chalcopyrite, and sphalerite. The gangue minerals consisted of green epidote, quartz, and pyrite. The ore minerals replaced the pebbles, cobbles, and boulders and formed pods of ore in the conglomerate. When replacement was not complete, beautiful vugs containing crystals of sphalerite, galena, chalcopyrite, quartz, calcite, pyrite, and barite were encountered in the mining of the orebodies. Probably some of the best mineral specimens that were produced in the 1970s came from these two deposits.

With the price of base metals still rising, there may be renewed of mining in the San Juans that will once again supply beautiful mineral specimens to the collector world.