A mineralogical and geochemical study of the tin deposit at NAD-mine in the Rooiberg tin field

[摘要] ENGLISH ABSTRACT:The NAD deposit forms part of the A-Mine Complex in the Rooiberg tin field inthe north-western Transvaal. Mining started in 1986 and the mine was closedrecently following a decline of tin prices and metallurgical problems with orerecovery.The deposit is hosted by the Boschoffsberg Quartzite Member of the PretoriaGroup sediments and is structurally controlled within the so-called Tin Zone.Extensive alteration of the original host rocks occurred during themineralisation event. Potassic remobilisation and redistribution appear tohave taken place pervasively. The nature of the original host rock wasaltered to such an extent that it cannot be classified correctly. Previousworkers refer to the host rock as an arkose because of its feldspathic nature.Wall rock alteration in the hanging- and foot wall of the different ore lodes(fractures) is generally similar. Very little change is observed in whole rockchemistry away from the lodes.The mineral chemistry of the ore lode minerals is indicative of fluidcomposition and mineralising conditions in the NAD deposit. The FeO/(FeO +MgO) ratio of tourmalines indicates deposition at a distance from the sourceof the mineralising fluids. Pyrite trace element chemistry differs from that ofthe Leeuwpoort deposit, indicating changing fluid chemistry. Contrary toprevious assumptions that the carbonate present is ankerite, abundantsiderite occurrences were found. Pyrite may co-precipitate with siderite underspecific physico-chemical conditions. Cassiterite is generally trace elementpoor and relatively enriched in Fe.Hydraulic brecciation of the fractures as well as the tourmaline chemistry arestrong indicators of a hydrothermal origin for the NAD deposit. However, theorigin of the hydrothermal fluids is still uncertain.

[发布机构] Stellenbosch University