Buckhornite

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Formula: (Pb₂BiS₃)(AuTe₂)
Sulphosalt, bismuth- and tellurium- bearing mineral
Crystal System: Orthorhombic
Specific gravity: 8.43 calculated
Hardness: 2½
Streak: Grey
Colour: Black
Common impurities: Cu
Environments

Hydrothermal environments

Buckhornite occurs in hydrothermal gold- and tellurium- bearing deposits (HOM).

Localities

At the Bohuliby deposit, Bohuliby, Petrov, Prague-West District, Central Bohemian Region, Czech Republic, nagyágite occurs as lamellar subhedral crystals in intimate intergrowth with buckhornite in a quartz gangue containing pyrite, tellurobismuthite, altaite, galena, calaverite and native gold (AM 80.188).

The type locality, the Buckhorn Mine, Jamestown, Jamestown Mining District, Boulder County, Colorado, USA, was mined for lead and silver in the nineteenth century. The mine was sunk in Cambrian (538.8 to 485.4 million years ago) granite near its contact with a sodic granite - quartz - monzonite porphyry of Tertiary age (66 to 2.6 million years ago). The ore consisted of pyrite, chalcopyrite and galena, together with some copper and sphalerite, gold included in the pyrite and chalcopyrite, and silver included in the galena and copper.
In hand specimens, buckhornite occurs as bladed, free-standing crystals and clusters within cavities and vugs in pyrite. The buckhornite crystals are black, have a splendent metallic lustre, and vary considerably in size, the larger crystals being up to 1.5 x 0.2 x 0.01 mm³.
SEM photomicrographs of a typical buckhornite cluster in a pyrite vug reveal aikinite crystals, shorter and stouter than buckhornite, and heavily striated along their length, intergrown with buckhornite in some of the vugs. Sericite dusts the vug contents in some vugs and completely fills others. Native gold also was observed on blades of buckhornite.
Several vugs containing buckhornite were exposed in a polished section, associated and intergrown with aikinite, tetradymite and gold, and minor amounts of chalcopyrite and covellite.
Within the pyrite, inclusions are abundant, including anhedral grains of aikinite, buckhornite, bornite, chalcopyrite, chalcocite, calaverite, galena, sphalerite and tetradymite, and euhedral crystals of hematite and tetradymite (CM 30.1039-1047).

At the Golden Sunlight Mine, Whitehall Mining District, Jefferson County, Montana, USA, buckhornite is associated with pyrite, melonite and tetradymite (HOM).

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