V007-0007
Zinc on the edge: lithospheric controls on the distribution of basin-hosted zinc deposits

Tuesday, 8 December 2020
Poster
David Huston1, David C Champion2, Karol Czarnota1, Matthew Hutchens3, Mark Hoggard4, Bryant Douglas Ware5, Fred Richards6, Svetlana Tessalina5, George M Gibson7 and Graham Richard Carr8, (1)Geoscience Australia, Canberra, ACT, Australia, (2)Geoscience Australia, Canberra, Australia, (3)Northern Territory Geological Survey, Darwin, Australia, (4)University of Cambridge, Cambridge, United Kingdom, (5)Curtin University, Applied Geology, Perth, WA, Australia, (6)Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA, United States, (7)Australian National University, Canberra, Australia, (8)CSIRO, North Ryde, NSW, Australia
Abstract:
Basin-hosted (excluding Mississippi Valley-type) mineral systems, including the North Australian Zinc Belt (NAZB), are major global sources of zinc (38%) and lead (48%). Although the local controls on the distribution of these deposits are reasonably well known, regional to global controls, essential for area selection during early exploration, are not as well known. Our work in the NAZB and other major global basin-hosted zinc provinces indicates that a fundamental control on these deposits is the edge of thick lithospheric blocks. Geochemical and geophysical datasets may be further used to identify these margins and, thereby, enable area selection at the global to province scales.

The first evidence of this control is the association of major deposits in the NAZB with a gradient in μ (238U/204Pb) that marks the boundary between a more isotopically evolved cratonic block and adjacent deeper basins. A similar relationship was observed in the Western Cordillera of North America. The second evidence is the association of deposits with gradients in the depth of the lithosphere-asthenosphere boundary (LAB), as mapped using calibrated surface wave tomography models. This dataset not only mapped these edges in Australia and North America, but mapped the location of most basin-hosted deposits around the world. The third dataset marking the edge is upward-continued gravity data. Deposits in the NAZB coincide with gradients in 15-, 30-, 50- and 100-km upward-continued datasets.

The change from thicker to thinner lithosphere is interpreted to localize prospective basins for zinc-lead (and copper-cobalt) mineralization, a change that is also thought to control the gradients observed in lead isotope and gravity data. In terms of area selection, gradients in the LAB provide the best continental-scale dataset as it is global in nature. The coarseness of the data and grids, however, limit the utility of the data at finer scales. Gravity and lead isotope data, in combination with other local scale data (e.g. magnetic, geological, stratigraphic), provide criteria that can be used at the province to district scales. Very high resolution data sets (detailed geological, geochemical and geophysical, and drill hole) are then essential for more detailed exploration.

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