Geochemistry

Gold Goes with the Flow

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Science  08 Dec 2000:
Vol. 290, Issue 5498, pp. 1859
DOI: 10.1126/science.290.5498.1859a

Gold can be found in ore deposits in and around igneous intrusions in magmatic arcs. Fluid flow and reactions of fluids with host rocks concentrate gold in these deposits, but the origin of the gold itself has been debated widely. It could originate in the mantle and be carried upward in the magma, as seems to be the case for copper, which is often associated with gold in this setting; it could also, however, be derived from crustal rocks.

Mathur et al. measured osmium isotopes in sulfides in the world's largest porphyry copper-gold deposit, the Grasberg Mine in central Irian Jaya. Their data imply that the gold was derived from shale near the deposit and not from the mantle or the magma. Fluid flow driven by intrusion of the hot magma apparently extracted the gold from the shale. -BH

Earth Planet. Sci. Lett. 183, 7 (2000).

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