The Kriván 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 refl ected light it is isotropic with low refl ectivity 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 fi lled by oxidation products of Sb and Fe. Compositionally it does not conform with stibian mustard gold from Yakutia and Bolivia, approximately AuSb_1.4O_2.1, 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.