Pinos Altos Mine, Pinos Altos Mining District, Grant County, New Mexico, USAi

Regional Level Types
Pinos Altos Mine	Mine
Pinos Altos Mining District	Mining District
Grant County	County
New Mexico	State
USA	Country

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A copper-zinc mine owned by Cyprus Minerals Co.
Alteration: Outer 10 to 20 ft Of quartz monzonite pluton is a selvage of propylitic or argillic alteration. Diorite stocks on margin of quartz monzonite pluton Are Pervasively potassic-altered. Lake Valley, Oswaldo and Syrena Limestones Metamorphosed to marble. Clastics in Syrena Fm metamorphosed To Wollastonite-Diopside-Tremolite Hornfels. Beartooth Sandstone Annealed To Quartzite.

Deposit: Deposit consists of two types of skarn occurring as 25,000 to 500,000 short ton orebodies. Early (stage 1) skarns consist of retrograde calcite-rhodonite-pyrite-sphalerite-magnetite-hematite mineralization overprinting prograde garnet skarns in Syrena Fm. limestone associated with potassic-altered diorite intrusives. Late (stage 2) skarns consist of chlorite-pyrite-quartz-chalcopyrite-sphalerite-barite retrograde mineralization overprinting prograde garnet skarns in Oswaldo and Lake Valley Fms. limestone and As veins in Beartooth Fm quartzite associated with propylitic-altered quartz monzonite intrusives. Stage 2 skarn, rich in cu, bi, and as, overprints earlier stage 1 zn skarn mineralization. Wall rock between orbodies is barren of mineralization. Early zn skarns are located at transition from garnet skarn to marble in three favorable beds in the Syrena Fm. Late cu skarn overprints on early zn skarns occur along ne-sw fracture sets. Cu skarns also occur along base of Oswaldo Fm/top of Lake Valley Fm. and along ne-sw/nw-se trending conjugate fault sets in Beartooth Fm. Beartooth quartzite ores are cu-silica flux ores.

Deposit type: Skarn Cu

Development: Hole drilled 1948 by U.S. Smelting, Refining and Mining Co. cut a zn orebody. Discovery not pursued due to high holding costs. Early 1970's property acquired by Exxon Minerals Co., rediscovered ore 1973, Exxon drilled 213 diamond drill holes totaling 331,375.5 cumulative feet drilling. Some 7 million tons ore delineated, all as high grade orebodies separated by unmineralized rock. Project shelved in 1978. In 1982 Boliden Minerals, Inc. leased property, did 7,950 ft underground development, conducted pilot mill tests on ore, and drilled 135 diamond drill holes with a cumulative footage of 77,311 feet. Reserves recalculated As about 1 million tons ore. About $25 million spent by Exxon and Boliden. In 1987 Cyprus assumed Boliden lease in a joint venture agreement with St. Cloud Mining, a subsidiary of Goldfield. Mining began October, 1987 with St. Cloud as operator. In late 1989 joint venture was terminated and Cypurs took over. In 1992 Cyprus converted from mining zn-cu ore to mining cu ores. Reserves depleted early 1995.

Rock formation(s): Pinos Altos quartz monzonite stock;
Lake Valley;Oswaldo;Syrena;Beartooth


Ore(s): Mineralization localized in favorable host rocks adjacent to intrusive rocks.

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

24 valid minerals.

Rock Types Recorded