Brodtkorbite

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Formula: Cu₂HgSe₂
Valence: Cu¹⁺₂Hg²⁺Se^2-₂
Selenide of copper and mercury
Crystal System: Monoclinic
Specific gravity: 7.77 calculated for the ideal formula
Hardness: 2½ to 3
Streak: Dark grey
Colour: Dark grey
Luminescence:
Solubility:
Common impurities:
Environments

Hydrothermal environments

Brodtkorbite is an uncommon mineral occurring in telethermal (formed at shallow depth and relatively low temperatures, with little or no wall-rock alteration, presumably far from the source of hydrothermal solutions - Wiki) selenium-rich hydrothermal polymetallic deposits, in calcite veins in amphibolites, formed below 112°C (HOM).

Localities

At the type locality, the Tumiñico Mine, Sierra de Cacho, Villa Castelli, General Lamadrid Department, La Rioja Province, Argentina, the host rocks of the selenide mineralisation consist of marble intercalated with thin layers of amphibolite, intensely stained with hematite in the vicinity of the selenium-bearing ores. The selenide mineralisation occurs as a network of veinlets and disseminations with a calcite gangue. Angular to slightly rounded graphite-bearing fragments of hematite-stained amphibolite also are present in the veins.
The first stage of selenide mineralisation involved the formation of Fe, Cu–Fe as well as Co–Cu-Ni selenides and arsenides. The crystallisation of ferroselite was followed by tyrrellite and Co-rich members of the trogtalite–kru'taite solid-solution series, and ended with several as yet undetermined (Co,Ni,Cu)–As–Se mineral species.
The second stage commenced with the formation of hakite, cadmoselite and several as yet undefined Cd-Hg–Se phases, and terminated with the deposition of bukovite and chaméanite. The latter two minerals replace the earlier-formed cadmoselite, but, in turn, were replaced by umangite, the dominant copper selenide of the third stage.
The third stage involves the precipitation of various copper selenides, which represent more than 90% of the total selenide assemblage. Umangite is the most widespread species and is generally associated with klockmannite. Berzelianite and bellidoite are less common, and their intergrowth textures with umangite point to an overlapping period of crystallisation. Crookesite is very rare and is commonly found embedded within berzelianite. Brodtkorbite is generally intimately associated with berzelianite.
Cross-cutting veinlets of tiemannite in brodtkorbite grains mark the beginning of the fourth stage of mineralisation, during which Ag–(Cu) and Hg selenides were deposited. These include eucairite, naumannite and the bulk amount of the tiemannite. A very rare Ag–Hg compound, probably related to luanheite, is assumed to have formed during this stage.
The fifth and last stage of ore formation involved the precipitation of sulphides in negligible amounts, particularly chalcopyrite, bornite, chalcocite and covellite. Secondary minerals, such as malachite in reniform and radiating masses, chalcomenite, schmiederite and connellite, are usually observed in vugs and cavities of the calcite gangue.
Brodtkorbite occurs as individual anhedral grains that range in size from 10 x 20 μm up to 50 x 100 μm, and as aggregates of composite grains approaching 150 x 250 μm in size. The most common associated phase is berzelianite, followed by tiemannite, umangite and clausthalite (CM 40.1.225-237).

At the Uranium Mine No. 11A, Bytíz, Příbram, Příbram District, Central Bohemian Region, Czech Republic, brodtkorbite occurs as anhedral aggregates up to 150 μm across, in intergrowths with tiemannite and eucairite in a calcite gangue. Other associated minerals include berzelianite, umangite and uraninite. In reflected light, brodtkorbite is cream-white, somewhat darker than the associated tiemannite. (EJM 29.4.663-672).

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