Die Verandering van die wangesteentes in die omgewing van die ertsliggame van Rosh Pinah

Abstract

The Rosh Pinah zinc-lead sulphide deposit is situated in the south western part of South West Africa/Namibia, near the Orange River. The ore deposit was discovered by Dr MD McMillan of Cape Town University in 1964, while involved in geological mapping in the area. Production started during May 1969 and at present approximately 600 000 tons are produced per annum. The ore deposit is stratabound and occurs in the lower part of the late Precambrian Rosh Pinah Formation which in turn forms part of the lower sequence of the Gariep Complex. The wall rocks of the ore zone consist mainly of arkosic and quartzitic rocks, with subordinate argillite, limestone, dolomite, conglomerate, chert and felsite. The ore zone consists of sulphide bearing chemical and fine-grained elastic sediments. Geochemical alteration tendencies are identified in the arkosic wall= rocks in the vicinity of the ore-bodies. In the hanging wall arkosites the elements FezO3, MnO, Zn, Pb, Cu, Ba and Zr increase significantly towards the ore-body, while in the foot wall arkosi tes FezO3, Zn, Cu, Ba, Sr and Cd show the same tendency as the former. In the foot wall arkosites the lithophile elements (Ti Oz, MnO, KzO, Rb, Zr, Nb and Y), and also Co, Ni and organic carbon, decrease significantly towards the ore-body. SiOz and the chalcophile elements (Zn, Pb, Cu, Ag and Cd) tend to increase towards the ore-body in the breccia wall rocks. FezO3 and MnO increase towards the ore-body in the hanging wall breccia. The other wall rocks (argillite, carbonate rocks and microquartzite) also show alteration tendencies relatively closer and farther away from the ore-body. MnO, MgO and CaO and the chalcophile elements decrease with distance from the ore-body, while the other lithophile elements increase. Three types of altered arkosite are present around the ore-body. Chemical comparison of the different altered arkosites was done using suitable diagrams and the conclusion was made that the mineralization is related to the alteration processes of silicification, alteration (sericitisation) and carbonatization. These potassium alteration processes have also had an influence on the foot wall as well as the hanging wall arkosites, especially the silicification- and carbonatization processes. No simple relationship between ore occurrences and wall rock alteration that can be helpful in exploration, could be identified. Fumarolic activity within a marine miogeosynclinal and sedimentary environment, contributed to ore genesis.