The stibian mustard gold from the Krivan Au deposit, Tatry Mts., Slovak Republic
Makovicky, Emil; Chovan, Martin; Bakos, Frantiek
published: Oct 31, 2007
ArtNo. ESP154018402008, Price: 29.00 €
The Kriváň Au-Sb mineralization is hosted in several subhorizontal variscan mylonite zones located in granitoid rocks. Ore minerals occur in thin lens-shaped quartz veinlets. Albite, chlorite, calcite, muscovite and tourmaline are minor gangue minerals. Four mineral assemblages have been recognized - (1) pyrite-arsenopyrite-gold, (2) stibnite-sulfosalts-sphalerite, (3) tetrahedrite-chalcopyrite-electrum, (4) supergene minerals. Isometric and irregular grains of mustard gold are 0.X mm in size. In reflected light it is isotropic with low reflectivity and orange-red or brown-yellow color. Porosity produces different shades of grey color in BSE image and low microprobe totals. The compositions of different textural varieties of mustard gold studied lie between the atomic Au:Sb ratio of 66.9:33.1 and almost pure Au+Ag. It is a composite material consisting of a submicroporous sponge of gold with pores more or less filled by oxidation products of Sb and Fe. Compositionally it does not conform with stibian mustard gold from Yakutia and Bolivia, approximately AuSb1.4O2.1, derived from decomposition of aurostibite, but it conforms with mustard gold from Krásná Hora, Czech Republic. For this type of mustard gold a precursor with approximate composition Au2Sb is required. Physical chemistry and natural conditions of formation of stibian mustard gold are discussed in detail.