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

Naude, Karin (1994-12)

Thesis (MSc.)--Stellenbosch University, 1994.

Thesis

ENGLISH ABSTRACT: The NAD deposit forms part of the A-Mine Complex in the Rooiberg tin field in the north-western Transvaal. Mining started in 1986 and the mine was closed recently following a decline of tin prices and metallurgical problems with ore recovery. The deposit is hosted by the Boschoffsberg Quartzite Member of the Pretoria Group sediments and is structurally controlled within the so-called Tin Zone. Extensive alteration of the original host rocks occurred during the mineralisation event. Potassic remobilisation and redistribution appear to have taken place pervasively. The nature of the original host rock was altered to such an extent that it cannot be classified correctly. Previous workers 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 rock chemistry away from the lodes. The mineral chemistry of the ore lode minerals is indicative of fluid composition and mineralising conditions in the NAD deposit. The FeO/(FeO + MgO) ratio of tourmalines indicates deposition at a distance from the source of the mineralising fluids. Pyrite trace element chemistry differs from that of the Leeuwpoort deposit, indicating changing fluid chemistry. Contrary to previous assumptions that the carbonate present is ankerite, abundant siderite occurrences were found. Pyrite may co-precipitate with siderite under specific physico-chemical conditions. Cassiterite is generally trace element poor and relatively enriched in Fe. Hydraulic brecciation of the fractures as well as the tourmaline chemistry are strong indicators of a hydrothermal origin for the NAD deposit. However, the origin of the hydrothermal fluids is still uncertain.

AFRIKAANSE OPSOMMING: Die NAD- tinafsetting vorm dee/ van die A-Myn-kompleks in die Rooiberg tinveld in die noord-wes Transvaal. Die myn is in 1986 geopen en is onlangs gesluit weens swak tinpryse en metallurgiese ertsherwinningsprobleme. Die tinafsetting kom voor in die Boschoffsberg Kwartsiet lid van die Pretoria Groep sedimente. Dit is strukturee/ gekontroleer binne die sogenaamde Tin Sone. Vorige navorsers het na die waardgesteente as 'n arkose verwys op grand van die hoe veldspaat-inhoud. lntensiewe en uitgebreide verandering van die oorspronklike waardgesteentes het plaasgevind tydens mineralisasie. Deurdringende kalium-hermobilisering en -herverspreiding het plaasgevind. Die aard van die oorspronklike waardgesteente is egter tot so 'n mate verander, dat dit chemies nie korrek gek/assifiseer kan word nie. Wandrotsverandering van die verskil/ende ertsskeute in beide die voet- en dakgesteentes is baie soortge/yk. Die heelrotsgeochemie van die wandgesteentes verskil baie min weg van die ertsskeute af. Die mineraalchemie van die ertsskeut-minerale is aanduidend van die v/oeistofsamestelling en mineralisasietoestande van die NAD-tinafsetting. Die FeO/(FeO + MgO) verhouding van toermalyne dui daarop dat afsetting op 'n afstand vanaf die bron van die mineralisasie-vloeistowwe plaasgevind het. Die spoor-elementchemie van die NAD-piriete verskil van die piriete van die Leeuwpoort tinafsetting, wat verandering in vloeistofsamestelling aandui. In teenstelling met vorige aannames dat die karbonate in die Rooiberg tinafsettings as ankeriet bekend staan, is daar volop sideriet gevind. Piriet kristalliseer dikwels saam met sideriet onder spesifieke fisiese en chemiese toestande. Kassiteriet is meestal arm aan spoor-elemente, maar is relatief verryk in Fe. Hidroliese breksiering van die skeute en die toermalyn-chemie dui sterk op 'n hidrotermale oorsprong vir die NAD afsetting. Die bron van die vloeistowwe is nog nie definitief vasgestel nie.

Digitized at 300 dpi Colour PDF format (OCR), using ,KODAK i 1220 PLUS scanner. Digitised, Ricardo Davids on request from IBL 10 September 2013

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/58243
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