Abstract

Paleoproterozoic rocks with ages from 2100 to 1800 Ma are recognized as belonging to one of the three main periods in Earth history that host orogenic gold deposits. In contrast to older Archean orogenic gold deposits, which are hosted predominantly in greenstone terranes, supracrustal sedimentary rocks became increasingly important as hosts in the Paleoproterozoic. Unusually iron rich 1840 Ma marine mudstones in the Tanami region host one world-class gold deposit and many other large gold deposits. Fluid-rock modelling at 300° and 325°C suggests a strong correlation between gold grade and these iron-rich, fine-grained sedimentary rocks. New regional stratigraphic correlations for similar iron-rich rocks to those in the Tanami region are suggested with ~1860 Ma gold-bearing stratigraphy in the Pine Creek region. These northern Australian Paleoproterozoic iron-rich sedimentary rocks could be linked globally to iron-rich and gold-bearing sedimentary rocks deposited between 2100 to 1800 Ma in Homestake, South Dakota (United States), and in Ghana, and Brazil. Worldwide, from about 2400 to 1800 Ma, the Paleoproterozoic is also marked by the deposition of mainly Superior style BIFs, which are attributed to the progressive oxygenation of the deep oceans resulting in the global scrubbing of iron from the oceans. The high iron concentrations noted in pre-1800 Ma marine sediments in northern Australia could also be related to this same process occurring globally and help explain a worldwide peak in orogenic Au deposits hosted in rocks aged from 2100 to 1800 Ma.

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