Pyrite

specimen number:
9273006

location:
Black Cloud Mine, Lake Co., Colorado, USA

description:

A superb large somewhat distorted complete crystal of golden lustrous pyrite. This is in really good condition all around with no points of attachment. Exceptionally fine for the species and locality.

The Black Cloud mine, situated in the Leadville mining district along the continental divide of Lake County near Leadville, Colorado, United States, was a premier underground base-metal and silver operation and the last major active mine in that legendary district. Geologically, this deposit is classified as a classic Mississippi Valley-type and intrusion-related replacement ore body, where mid-Tertiary porphyritic quartz monzonite intrusions drove intense hydrothermal fluids into receptive Paleozoic sedimentary carbonate rocks, specifically the Mississippian-age Leadville Limestone. This chemical reaction generated extensive, high-grade replacement blankets (mantos) and structural veins rich in lead, zinc, silver, copper, and gold sulfides, yielding exceptional mineral specimens of crystallized galena, sphalerite, and pyrite, alongside of sharp, amber-colored barite crystals. Historically, while the surrounding Leadville district had been heavily exploited since the 1860s gold and silver rushes, the modern Black Cloud shaft was formally sunk by the Asarco corporate joint venture starting in 1968, with commercial underground production officially commencing in April 1971. The highly mechanized operation served as the economic backbone of Lake County for nearly three decades, producing millions of tons of ore until dropping international metal commodity prices and the exhaustion of easily accessible, high-grade replacement zones forced Asarco to permanently cease all commercial mining extraction and deactivate the deep pumps in late November 1999.

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