Authors / CoAuthors
Direen, N.G. | Lyons, P.
Abstract
We propose a geodynamic model for the generation of Fe oxide Cu-Au deposits in the eastern Gawler Craton. Rifting during the early Calymnian Period, at 1.59 Ga, produced steep geothermal gradients, active magmatism, regional-scale faulting, and immature clastic sedimentation. Major NNW?SSE-trending, dextral transtensional faults exerted fundamental structural controls on several elements of the mineral system: the geometry of intrusion of magmas of the Hiltaba Suite; the provision of fluid pathways for magnetite- and haematite-buffered fluids; creation of basinal space for the effusive lavas of the Gawler Range Volcanics and the overlying terrigeneous sediments of the Pandurra Group; and propagation of near-surface fault tips giving rise to fault-bound hydrothermal breccias. We demonstrate that faults active at 1.59 Ga were of sufficient dimension and seismic longevity to have acted as fluid pumps within the mineral system. Their size and location imply multiple sources for metals in the Olympic Dam deposit and other Fe oxide Cu-Au occurrences in the region. Multiple sources would have resulted in some of the anomalous features of the mineralisation, such as non-magmatic Br:Cl ratios, and magmatic and juvenile, mafic isotopic signatures, all noted by previous workers. Isostatic footwall uplift in the actively extending system may have compressed the regional geothermal gradients, and brought rock volumes altered by hot, reduced fluids into contact with circulating cooler, oxidised fluids. In general, fluid circulation and deposition was enhanced by deformation-induced permeabilities and hydrofracture. In the time-span of the mineral system, say 3 million years, mineralisation cycles (source-transport-deposition) may have repeated 102 to 106 times, depending on the hydraulic conductivity of the source rocks. Some associations at the Olympic Dam deposit, such as granite and maar-like volcanism, are fortuitous and are not essential elements of the mineral system. In the light of the geodynamic model, geophysical. geochemical, and petrological data may be examined for evidence of likely source rocks, fluid pathways, and suitably oxidised magnetite deposits that may contain ore.
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48506
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- External PublicationScientific Journal Paper
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- AU-SA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2003-06-26T00:00:00
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[-32.58, -29.88, 135.97, 138.22]
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