Determining the absolute timing of mineralization is a critical, but problematic, aspect for understanding the origin of metallic ore deposits—the ore minerals in these deposits are not amenable to direct isotope dating using common methods.
Morelli et al used radioactive isotope dating, using the rare elements rhenium and osmium (Re-Os) in arsenopyrite, to establish the age of gold mineralization at the giant Muruntau gold deposit, Uzbekistan (>5100 metric tons gold) to be 287.5 ± 1.7 Ma (millions of years before present). These results suggest a possible link between gold mineralization and intrusion into the crust of ca. 290 Ma regional granitoid magmas. This temporal association was previously clouded because commonly used geochronometers are unable to accurately and/or precisely date the gold mineralizing event directly. Isotopic compositions of Os and helium provide important new constraints on potential metal and fluid sources to the deposit, including a small but detectable mantle contribution to the ore system. These new results provide a more comprehensive understanding of one of Earth’s giant gold accumulations, and rule out several current hypotheses for its origin.-Geological Society of America
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