Pokhodyashinite, CuTlSb 2 (Sb 1- x Tl x )AsS 7- x , a new thallium sulfosalt from the Vorontsovskoe gold deposit, Northern Urals, Russia

[摘要] Pokhodyashinite CuTlSb2(Sb1–xTlx)AsS7–x, is a new sulfosalt from the Vorontsovskoe gold deposit, Sverdlovsk Oblast’,Northern Urals, Russia. It forms anhedral grains up to 0.1×0.05 mm in size in calcite and is associated with major orpiment, pyrite, realgar and minor baryte, clinochlore, As-bearing fluorapatite, harmotome, prehnite, native gold and a richspectrum of sulfosalts. Pokhodyashinite is black, opaque, and has a metallic luster and a black streak. It is brittle, withan uneven fracture and poor cleavage on {100}. The Vickers hardness (VHN, 20 g load) is 55 kg/mm2, correspondingto a Mohs hardness of 2. The calculated density is 5.169 g/cm3. In reflected light, pokhodyashinite is grayish-white,bireflectance is distinct. In crossed polars, it is strongly anisotropic; rotation tints vary from dark brownish gray to lightbluish-gray. No internal reflections are observed. The reflectance values for wavelengths recommended by the Commissionon Ore Mineralogy of the IMA are (Rmin/Rmax, %): 28.9/34.6 (470 nm), 27.6/33.4 (546 nm), 26.7/32.4 (589 nm), 26.1/31.1(650 nm). The empirical formula of pokhodyashinite based on ΣMe = 6 apfu is Cu0.700Ag0.340Tl1.320Pb0.020Sb2.630As0.990S6.625.Pokhodyashinite is monoclinic, space group C2/m, a = 23.431(5), b = 3.996(2), c = 14.070(3) Å, β = 110.23(3)°,V = 1236.1(8) Å3 and Z = 4. Its structure can be described as wavy slabs of a complex structure based on double-rodsof Sb-coordination pyramids and lone-electron-pair interspaces/micelles, separated by wavy interlayers consisting ofpaired columns of Tl and rods of paired Cu-coordination polyhedra. A small amount of Tl-for-Sb substitution results inpartial anion vacancies in one sulfur site. The new mineral is named in honor of Maxim Mikhailovitch Pokhodyashin,a pioneer of mining engineering and smelting works in the Northern Urals of the 18th century.

[学科分类] 自动化工程

[关键词] pokhodyashinite;new mineral;copper;thallium;sulfosalt;crystal structure;Vorontsovskoe gold deposit;Northern Urals