Origin of mineralizing fluids of the sediment-hosted Navachab gold mine, Namibia: Constraints from stable (O, H, C, S) isotopes

Katharina Wulff, Annika Dziggel, Jochen Kolb, Torsten Vennemann, Michael E. Böttcher, F. Michael Meyer

Publikation: Bidrag til tidsskriftArtikelForskningpeer review

18 Citationer (Scopus)

Abstrakt

The Navachab gold mine in the Damara belt of central Namibia is characterized by a polymetallic Au-Bi-As-Cu-Ag ore assemblage, including pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, bismuth, gold, bismuthinite, and bismuth tellurides. Gold is hosted by quartz sulfide veins and semimassive sulfide lenses that are developed in a near-vertical sequence of shelf-type metasedimentary rocks, including marble, calcsilicate rock, and biotite schist. The sequence has been intruded by abundant syntectonic lamprophyre, aplite, and pegmatite dikes, documenting widespread igneous activity coeval with mineralization.

The majority of quartz from the veins has δ18O values of 14 to 15 per mil (V-SMOW). The total variations in δ18O values of the biotite schist and calcsilicate rock are relatively small (12–14‰), whereas the marble records steep gradients in δ18O values (17–21‰), the lowest values being recorded at the vein margins. Despite this, there is no correlation between δ18O and δ13C values and the carbonate content of the rocks, indicating that fluid-rock interaction alone cannot explain the isotopic gradients. In addition, the marble records increased δ13C values at the contact to the veins, possibly related to a change in the physicochemical conditions during fluid-rock interaction. Gold is interpreted to have precipitated in equilibrium with metamorphic fluid (δ18O = 12–14‰ δD = −40 to −60‰) at peak metamorphic conditions of ca. 550°C and 2 kbars, consistent with isotopic fractionations between coexisting calcite, garnet, and clinopyroxene in the alteration halos. The most likely source of the mineralizing fluid was a midcrustal fluid in equilibrium with the Damaran metapelites that underwent prograde metamorphism at amphibolite- to granulite-facies grades. Although there is no isotopic evidence for the contribution of magmatic fluids, they may have been important in contributing to the overall hydraulic regime and high apparent geothermal gradients (ca. 80°C/km−1) in the mine area.

OriginalsprogEngelsk
Sider (fra-til)285-302
Antal sider18
TidsskriftEconomic Geology
Vol/bind105
Udgave nummer2
DOI
StatusUdgivet - mar. 2010

Programområde

  • Programområde 4: Mineralske råstoffer

Fingeraftryk

Dyk ned i forskningsemnerne om 'Origin of mineralizing fluids of the sediment-hosted Navachab gold mine, Namibia: Constraints from stable (O, H, C, S) isotopes'. Sammen danner de et unikt fingeraftryk.

Citationsformater