The petrogenesis of the Koperberg suite in the jubilee mine, Namaqualand.

[摘要] The Koperberg Suite intrusion at Jubilee, Namaqualand varies in composition fromanorthosite, through mica diorite to pyroxene leucodiorite and pyroxene diorite. Detailedmapping and petrological studies of these rocks indicate that they were sequentially emplacedinto the Concordia Granite country rocks, and that each of the rock types represent discretemagmatic events. The sequence of intrusion is from more acidic to more basic.Whole-rock geochemical analyses indicate that these rocks represent cumulates involvingvariable proportions of plagioclase, orthopyroxene, mica, quartz, oxides and immisciblesulphides. These cumulate phases intruded into the Concordia Granite at the time of peak ofmetamorphism and deformation in the Okiep Copper District, i.e, about 1030Ma ago, At thetime of intrusion, the country rocks were under going partial melting under high grade(granulite facies) metamorphic conditions. and granitic anatects were present in the crust.Hybridisation of basic magma and granitic melts occurred within the shear zones along whichthe basic magmas ascended. The En content of orthopyroxene in the Koperberg Suite exceedsthe An content of plagioclase. This is atypical of basic intrusions and is a consequence of thismixing. Mixing calculations based on the initial 87Sr/86Srratio (Ru) of the Jubilee samples at1030Ma, imply high levels of assimilation (as much as 80% assimilation in the case ofanorthositic rocks) between a granitic component, similar in composition to the NababeepGneiss and a mantle-derived basic magma.Sulphide mineralisation was initiated by the assimilation process, which caused the separationof immiscible sulphides from the hybridised magma. Subsequent oxidation of the originalsulphide assemblage produced bornite, chalcopyrite and Ti-poor magnetite.

[发布机构] University of the Witwatersrand