TY - JOUR
T1 - Origin of mineralizing fluids of the sediment-hosted Navachab gold mine, Namibia: Constraints from stable (O, H, C, S) isotopes
AU - Wulff, Katharina
AU - Dziggel, Annika
AU - Kolb, Jochen
AU - Vennemann, Torsten
AU - Böttcher, Michael E.
AU - Meyer, F. Michael
PY - 2010/3
Y1 - 2010/3
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=78149295594&partnerID=8YFLogxK
U2 - 10.2113/gsecongeo.105.2.285
DO - 10.2113/gsecongeo.105.2.285
M3 - Article
VL - 105
SP - 285
EP - 302
JO - Economic Geology
JF - Economic Geology
SN - 0361-0128
IS - 2
ER -