Sylvanite
specimen number:
2262315
location:
Portland Mine, Cripple Creek, Colorado, USA
description: The Portland mine, situated on Battle Mountain in the Cripple Creek district of Teller County, Colorado, was one of the most prolific and deep underground gold operations in North America. Geologically, the deposit is located within the roots of a Tertiary-age alkaline volcanic caldera complex, where intense brecciation and fracturing of Precambrian granites and metamorphic rocks accommodated rich epithermal vein systems. Mineralization consists predominantly of gold-telluride species, particularly calaverite and sylvanite, hosted in dolomite-quartz veins alongside pyrite, fluorite, and celestine, which required specialized metallurgical roasting to process. Historically, the property was discovered and staked in July 1892 by James F. Burns and James Doyle, rapidly expanding into the cornerstone asset of the Portland Gold Mining Company. Industrial development involved the sinking of three primary vertical shafts (No. 1, No. 2, and No. 3) to depths exceeding 900 meters, utilizing extensive pumping systems to manage the deep water table. The corporate underground operation maintained continuous, large-scale production through the late nineteenth and early twentieth centuries, serving as a major regional employer until changing macroeconomic conditions, rising labor costs, and ore depletion forced a transition to lease-operator extraction and eventual closure of the primary shafts by the mid-1950s, though the site was later enveloped by modern regional surface heap-leach operations.
Metallic sylvanite across the top of matrix. Nice for the species and locality. The specimen comes with several all labels as seen at the end of the video. This is pre-1960.
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