Microchemistry and stable isotope systematics of gold mineralization in a gabbro-diorite complex, SE Egypt

Electron probe micro-analysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) data of ore minerals from the Um Eleiga deposit (SE Egypt) suggest that primary Au was sequestered within Ni-pyrrhotite and Co-Ni-Fe sulfarsenide, while refined, free-milling gold grains (~. 93. wt.% Au) are associated with late pyrite, or occur along micro-fractures in quartz veins. A magmatic source of gold is most likely, yet endowment by circulating metasomatic fluid was crucial for Au concentration.Sulfur stable isotope values (δ ³⁴S) of sulfide minerals disseminated in the quartz veins (pyrite: -0.5 to 1.5‰, chalcopyrite: -0.3 to 0.6‰, and sphalerite: -0.1 to -0.4‰), indicate a generally light sulfur source. Similarly, measured δ ¹³C of vein calcite (-3.1 to -1.8, n=9) and calculated fluid δ ¹³C _CO2 values (-0.6 to 0.6‰, for the temperature range 350-375°C of associated hydrothermal chlorite) cluster around 0‰, consistent with a magmatic source for carbon. Oxygen isotope data for vein calcite (10.3-13‰, n=9) and quartz (11.7-14.3‰, n=10) indicate average fluid δ ¹⁸O _H2O values of 7.4 and 7.8‰, respectively, which implicate fluids similar to those in intrusion-related systems.