Gold mineralization in the Mazowe area, Harare-Bindura-Shamva greenstone belt, Zimbabwe: II. Genetic relationships deduced from mineralogical, fluid inclusion and stable isotope studies, and the Sm-Nd isotopic composition ofscheelites

In the Mazowe area some 40 km NW of Harare in Zimbabwe, gold mineralization is hosted in a variety of lithologies of the Archean Harare-Bindura-Shamva greenstone belt, in structures related to the late Archean regional D2/3 e vent. Conspicuous mineralzogical differences exist between the mines; the m ainly granodiorite-hosted wet-kings at Mazowe mine are on pyrite-rich reefs , mines of the Bernheim group have metabasalt host rocks and are characteri zed by arsenopyrite-rich ores, and Stori's Golden Shaft and Alice mine, bot h in metabasalts, work sulfide-poor quartz veins. in contrast to the minera logical diversity, neari-dentical fluid inventories were found at the diffe rent mines. Both H2O-CO2-CH4 fluids of low salinity, and highly saline flui ds are present and are regarded to indicate fluid mixing during the formati on of the deposits. Notably, these fluid compositions in the Mazowe gold fi eld markedly contrast to ore fluids " typical" of Archean mesothermal gold deposits on other cratons. Stable isotope compositions of quartz from the v ariousdeposits (delta(18)O = 10.8 to 13.2 parts per thousand SMOW), calcite (delta(18)O = 9.5 to 11.9 parts per thousand SMOW and delta(13)C = 3.2 to -8.0 parts per thousand PDB), inclusion water (delta D = -28 to -40 parts p er thousand SMOW) and sulfides (delta(34)S = 1.3 to 3.2 parts per thousand CDT) are uniform within the range typical for Archean lode gold deposits wo rldwide. The fluid and stable isotope compositions support the statement th at the mineralization in the Mazowe gold field formed from relatively reduc ed fluids with a "metamorphic'' signature during a single event of gold min eralization. Microthermometric data further indicate that the deposits form ed in the PT range of 1.65-2.3 kbar and 350-380 degrees C. Ages obtained by using the Sm/Nd and Rb/Sr isotope systems on scheelites an 2604 +/- 84 Ma for the mineralization at Stori's Golden Shaft mine, and 2.40 +/- 0.20 Ga f or Mazowe mine. The Archean age at Stori's is regarded as close to the true age of gold mineralization in the area, whereas the Proterozoic age at Maz owe mine probably reflects later resetting.