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摘要
The noble gas (Ar, Kr, Xe) and halogen (Cl, Br, I) composition of fluid inclusions in hydrothermal quartz and calcite related to the hypogene iron oxide-copper-gold (IOCG) mineralization at Mantoverde and Candelaria, Chile, have been investigated to provide new insights of fluid and salinity sources in Andean IOCG deposits. A combination of mechanical extraction by crushing and thermal decrepitation methods was applied and collectively indicate that fluid inclusions with salinities ranging from 3.4 up to 64 wt% NaCl equivalent have molar Br/Cl and I/Cl ratios of between 0.5 x 10(-3) and 3.0 x 10(-3) and I/Cl of between 8 x 10(-6) and 25 x 10(-6) in the majority of samples, with maximum values of 5.2 x 10(-3) obtained for Br/Cl and 64 x 10(-6) for I/Cl in fluid inclusions within individual samples. The fluid inclusions have age-corrected Ar-40/Ar-36 ratios ranging from the atmospheric value of 296 up to 490 +/- 45, indicating the presence of crustal- or mantle-derived excess Ar-40 in the fluid inclusions of most samples. The fluid inclusions have Kr-84/Ar-36 and Xe-130/Ar-36 ratios intermediate of air and air-saturated water. However, Ar-40/Ar-36 is not correlated with either Kr-84/Ar-36 or Xe-130/Ar-36, and the fluid inclusion Ar-36 concentrations of 0.2-3.5 x 10(-10) mol/g (calculated from measured Cl/Ar-36 and thermometric salinity measurements) extend below the seawater value of 0.34 x 10(-10) mol/g, suggesting that contamination with modern air is a minor artifact. The range of fluid inclusion Br/Cl and I/Cl ratios overlap those previously documented for the mantle and magmatic-hydrothermal ore deposits, and the fluids' unusually low Ar-36 concentration is consistent with the involvement of magmatic-hydrothermal fluids. Input of additional non-magmatic fluid components is suggested by the spread in Br/Cl and I/Cl to values characteristic of bittern brine sedimentary formation waters and near atmospheric Ar-40/Ar-36. These data are compatible with mixing of magmatic-hydrothermal fluids and evaporated seawater, which was modified by interaction with back-arc basin sediments as the major control on ore formation. Low Br/Cl (< 0.5 x 10(-3)) and I/Cl (< 5.0 x 10(-6)) values that would provide evidence for evaporite dissolution as an important source of fluid salinity were not detected.
- 出版日期2015-3
