Title:
Geochemical and mineralogical distribution of germanium in the Khusib Springs Cu–Zn–Pb–Ag sulfide deposit, Otavi Mountain Land, Namibia
Publication Year:
2006
Abstract:
The Khusib Springs deposit in the Otavi Mountain Land, Namibia, is a small though high-grade carbonate-hosted Cu-Zn-Pb-Ag-(As-Sb-Ge) deposit of the "Tsumeb-type" containing approximately 300,000 t of ore grading 10% Cu, 1.8% Pb and 584 ppm Ag. A lens-shaped sulfide orebody, up to 10 m thick and elongated parallel to bedding, replaces limestone, locally brecciated, of the lower Tsumeb Subgroup (Damara Supergroup) in the northern limb of a large NE-trending synclinal structure. A prominent zone of dolomite alteration surrounds the orebody. In a drill core through the orebody, the uppermost 2 m are enriched in Zn (up to 5%) and Ag (up to 3350 ppm), but lower in Ge ( 30 ppm) than the central and lower parts of the orebody, which are in turn enriched in Ge (up to 200 ppm) and Pb (up to 7%). Massive ore consists of a texturally complex mineral assemblage dominated by Zn-rich tennantite, enargite, galena and pyrite. Fe-poor sphalerite is abundant only in the uppermost part of the orebody and in the footwall where it forms a prominent zone of disseminated sphalerite-chalcopyrite-galena-pyrite. The upper zone of the massive ore is further characterized by a general lack of enargite, and the occurrence of a variety of late-stage phases including tetrahedrite, Ag-bearing tennantite, pearceite-polybasite and native silver. The central and lower parts of the orebody are composed of tennantite-enargite-galena ore with variable proportions of pyrite, but lacking sphalerite. Most Ge is hosted in Ge-bearing colusite [Cu26V2(As,Ge)6S32] forming small (usually 50 μm in size) grains along the margins of ore layers and veinlets. With the notable exception of enargite, the major sulfides contain only trace amounts of Ge ( 100 ppm). Trace element analyses reveal a wide range of Ge concentrations in enargite, averaging to 500 ppm. Frequently, colusite is associated with deformed trails of phengitic, F-rich muscovite, rutile, apatite, tourmaline, dolomite and pyrite. Such trails are interpreted as former stylolites in the carbonate host rock, which has been replaced by sulfide ore. Colusite carries on average 4.0 wt.% Ge, up to 4.7 wt.% W and up to 4.4 wt.% Sn, and is occasionally accompanied by small amounts of Mo-W sulfides. Additional minerals identified in the ore include W-bearing germanite, Ge-bearing stannoidite, chalcopyrite, bornite, stromeyerite, minerals of the chalcocite-group, and covellite. Keywords: Germanium mineralization, Otavi Mountainland, Namibia, Colusite, Tennantite, Tsumeb-type deposit.
Publication Title:
Ore Geology Reviews
Volume:
28
Issue:
1
Pages:
32-56
Item Type:
Journal Article
Language:
en