Mesoproterozoic base metal sulphide deposits in the Namaqua Sector of the Namaqua-Natal Metamorphic Province, South Africa: a review

摘要

The Mesoproterozoic Namaqua Sector of the east-west trending Namaqua-Natal Metamorphic Province (NNMP) located in the Northern Cape Province is underlain by supracrustal rocks and abundant felsic intrusive rocks that have been subjected to medium to high grade metamorphism and polyphase deformation. It is the host to world class base metal sulphide resources that have been mined for more than a century. Most of these mines are no longer in production such that the Cu-Pb-Zn-Ag mines in the Aggeneys-Gamsberg Ore District (A-GOD), with a total output of 1.8 million ton (Mt) per annum, are the only current significant producers. Development of the supergiant Gamsberg zinc deposit commenced in 2015 and will add a further 4 Mt per annum (250 000t of zinc) to the output with the mine eventually becoming one of the larger zinc producers in the world. The Namaqua Sector of the NNMP has been subdivided into several lithologically distinct, structural discontinuity bounded Subprovinces and Terranes, each with its characteristic base metal sulphide deposits. The most extensive and best mineralized of these is the Bushmanland Subprovince where the ?1300 Ma stratabound polymetallic Broken Hill-type meta-SEDEX deposits contain total resources exceeding 500 Mt of Zn-Pb-Cu-Ag ore. Further east much smaller and subeconomic stratabound deposits occur at Putsberg (Cu-Zn-Pb-Ag) and Adjoining Geelvloer (Zn-Cu-Pb-Ag-Au). Magmatic ore deposits include minor magnetite-copper skarn/iron-oxide-copper-gold (IOCG) deposits associated with syntectonic granitoids (?1200 Ma) in the east and small syntectonic gabbro-norite hosted Ni-Cu-(Co) occurrences at Hondekloof (?1170 Ma) to the southwest. The mined-out Okiep Copper District in the west hosts an abundance of small, syn- to late-tectonic mafic cupriferous intrusions (?1030 Ma), which collectively contributed some 100 Mt of ore yielding ?2 Mt of blister copper. The Areachap Terrane in the far eastern part of the Namaqua sector of the NNMP has a