Mineralogical, Petrological and Geochemical Study of a Suite of Rocks from the Damara Orogenic Belt South West Africa

摘要

This work was a pilot study in which the petrology, mineralogy and geochemistry of a suite of rocks from the Khan/Swakop area of the Damara Orogen were investigated. Petrographic and mineralogical data are presented for about 140 samples. This data (1) assisted in the selection of suitable samples for chemical analysis; (2) aided in the classification of the samples as a basis for geochemical classification; (3) allowed the samples to be correlated with the regional geology of the area. It was found that petrographic examination alone cannot be used to distinguish between mineralised and unmineralised alaskites. Certain features although not exclusive to mineralised and unmineralised alaskites are nevertheless in general characteristic of these rocks types. the X-ray diffraction analysis indicated that mineralised alaskites, even from different localites, produced characteristic X-ray diffractograms which separated them from the rest of the rock-types including the unmineralised alaskites. The geochemical interpretation of the data showed that it was possible to distinguish between the main rock groups using both the major and trace elements. With using the trace elements only this distinction was not possible. Mineralogical relationships within the rock groups could be inferred from the geochemical results thereby complementing the petrographic investigation. It was established that in the main, mineralised alaskites are K-feldspar rich with biotite and no muscovite and that the thorium and rare-earth contents should be high. (Atomindex citation 10:490816)