PETROGRAPHIC, SULFIDE MINERAL CHEMISTRY, AND SULFUR ISOTOPE EVIDENCE FOR A HYDROTHERMAL IMPRINT ON MUSINA COPPER DEPOSITS, LIMPOPO PROVINCE, SOUTH AFRICA

The Musina copper deposits occur in the Central Zone of the Limpopo orogeny, Limpopo Province, South Africa. We studied samples from Artonvilla and Campbell copper deposits and a country rock granitic gneiss to the Artonvilla deposit to place constrains on the origin of these deposits.

Brecciated potassium feldspar, sericite, muscovite, chlorite, calcite, and amphibole at both deposits are consistent with sericitic or potassium silicate alteration. Amphibolites from Campbell Mine have S concentrations of chalcopyrite plotting in narrow ranges, from 30.1 - 34.1 wt. %, and Fe concentrations from 26.4 to 30.0 wt. %. However, in quartz vein samples from the Campbell deposit, sulfur concentrations of chalcopyrite have a somewhat wider range from 30.8 - 38.4 wt. %, whereas Fe concentrations show a narrow range from 26.8 - 29.8 wt. %. The occurrence of sulfides both as inclusions in, or as interstitial phases in silicates, suggest that hydrothermal alteration that affected these deposits may have helped concentrate the mineralization at the Musina copper deposits.

Quartz vein samples from the Campbell deposit yielded δ³⁴S_pyrite values of 0.5, 0.4, and 0.7 ‰, a δ³⁴S_bornite value of 0.4‰, and a δ³⁴S_chalcopyrite value of -0.3 ‰, consistent with a mantle source for the sulfur. Sulfur isotope thermometry for one Campbell Mine quartz vein sample with coexisting sulfides yielded a temperature of 359^oC (D³⁴S_{chalcopyrite-bornite} ). One sample from the Artonvilla Mine, however, has pyrite δ³⁴S values of 3.1 and 3.6 ‰, and chalcopyrite from the same sample yielded a δ³⁴S value of 3.9 ‰. A country rock granitic gneiss to the Artonvilla deposit yielded a δ³⁴S_pyrite value of 8.2 ‰. Contamination of the sulfur by sulfur derived from granitic country rocks likely occurred at the Artonvilla deposit.