Sequences, Synsedimentary Structures, and Sub-Basins: the Where and When of SEDEX Zinc Systems in the Southern McArthur Basin, Australia
Published:January 01, 2010
Peter McGoldrick, Peter Winefield, Stuart Bull, David Selley, Robert Scott, 2010. "Sequences, Synsedimentary Structures, and Sub-Basins: the Where and When of SEDEX Zinc Systems in the Southern McArthur Basin, Australia", The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries, Richard J. Goldfarb, Erin E. Marsh, Thomas Monecke
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The late Paleoproterozoic upper McArthur Group (River Supersequence) is a dominantly shallow marine carbonate platform sequence. Deeper water shaley rocks of the Barney Creek Formation of this Supersequence host the supergiant HYC Zn-Pb-Ag deposit. Three higher order sequences, the Emmerugga Depositional Sequence, the Barney Creek Depositional Sequence, and the Lynott Depositional Sequence, make up the River Supersequence in the southern McArthur basin. Within the Barney Creek Depositional Sequence, there are 26 lithofacies that can be grouped into seven facies associations, each representing specific and coeval sedimentary environments.
This complex facies mosaic formed in response to a sinistral transpression event during regional north-south extension. Basin architecture was controlled by major meridional strike-slip structures, such as the Emu, Tawallah, and Hot-Springs faults. Although these structures have a later, postsedimentation history, they also controlled the distribution of the different facies of the Barney Creek Depositional Sequence. North- to northwest-trending segments of these structures were transtensional, whereas structures oriented east of north were transpressional. Transtension resulted in the development of significant local accommodation and sub-basin development and allowed substantial thicknesses of deeper water, fine-grained sediments, which are potential hosts to Zn-Pb-Ag SEDEX deposits, to accumulate. Locally, in platform and slope facies of the Barney Creek Depositional Sequence, the orientation and vergence of kinematic indicators, such as neptunian dikes and intrafolial folds, may indicate the direction to deeper shaley facies.
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The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries
VOLCANIC-ASSOCIATED and sedimentary-exhalative massive sulfide deposits on land account for more than one-half of the world's total past production and current reserves of zinc and lead, 7 percent of the copper, 18 percent of the silver, and a significant amount of gold and other by-product metals (Singer, 1995). A new source of these metals is now being considered for exploitation from deep-sea massive sulfide deposits. Because the oceans cover more than 70 percent of the Earth's surface, many expect the ocean floor to host a proportionately large number of these deposits. However, there have been few attempts to estimate the global mineral potential. Significant accumulations of metals from hydrothermal vents have been documented at some locations (e.g., 91.7 Mt of 2.06% Zn, 0.46% Cu, 58.5 g/t Co, 40.95 g/t Ag, and 0.51 g/t Au in the Atlantis II Deep of the Red Sea: Mustafa et al., 1984; Nawab, 1984; Guney et al., 1988). Even more metal is contained in deep-sea manganese nodules. Current estimates in the U.S. Geological Survey (USGS) mineral commodities summaries indicate a global resource of copper in deep-sea nodules of about 700 Mt. In the Pacific "high-grade" area, an estimated 34,000 Mt of nodules contain 7,500 Mt of Mn, 340 Mt of Ni, 265 Mt of Cu, and 78 Mt of Co (Morgan, 2000; Rona, 2003). A number of countries, including China, Japan, Korea, Russia, France, and Germany, are actively exploring this area.