Gold- and associated ore minerals of the Waaikraal Deposit, northwest of Brits, Bushveld Complex
Verryn, Sabine M.C.; Merkle, Roland K.W.; Von Gruenewaldt, Gerhard
European Journal of Mineralogy Volume 3 Number 2 (1991), p. 451 - 466
published: Apr 18, 1991
manuscript accepted: Nov 15, 1990
manuscript received: Aug 20, 1990
ArtNo. ESP147050302014, Price: 29.00 €
Abstract The Waaikraal Gold Deposit 25 km northwest of Brits is a sill-like body of alternating layers and lenses of pyroxenite and magnetite-rich rock, hosted in sediments belonging to the Rayton Formation of the Transvaal Sequence. The sediments are situated between the magnetite gabbros of the Upper Zone of the Bushveld Complex and the granites of the Lebowa Granite Suite. Two assemblages of ore minerals can be distinguished in the sill-like ore body, viz. (i) earlier pyrrhotite, pentlandite, pyrite, chalcopyrite and sphalerite and (ii) later safflorite, arsenopyrite, cobaltite, joseite, bismuthinite, native bismuth, chalcopyrite and gold. Apart from native gold, two gold bearing compounds, maldonite (Au2Bi) and CuAu3, were identified. Bismuth-bearing minerals are joseite-B (Bi4Te2S), bismuthinite (Bi2S3) and native bismuth. Safflorite varies in composition from loellingite to safflorite rich members with up to 8 mole per cent NiAs2. Cobaltite and arsenopyrite are the only sulfarsenides. The temperature range of formation of the ore minerals associated with the gold and the mode of occurrence of the gold as small grains and in veinlets suggest a hydrothermal origin of the gold. The concentration of PGE is very low. It is assumed that the gold, together with some PGE, was mobilized from the Upper Zone of the Bushveld Complex at the postmagmatic stage by hydrothermal fluids and was locally enriched in the roof of the Complex.