Hydrothermal Vein and Alteration Assemblages Associated with Low-Sulfide Footwall Cu-Ni-PGE Mineralization and Regional Hydrothermal Processes, North and East Ranges, Sudbury Structure, Canada
Györgyi Tuba, Ferenc Molnár, David H. Watkinson, Peter C. Jones, Aberra Mogessie, 2010. "Hydrothermal Vein and Alteration Assemblages Associated with Low-Sulfide Footwall Cu-Ni-PGE Mineralization and Regional Hydrothermal Processes, North and East Ranges, Sudbury Structure, Canada", 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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Among the Cu-Ni-PGE occurrences hosted by the footwall units of the Sudbury Igneous Complex, low-sulfide systems possess the lowest sulfide content while being significantly enriched in Pd and Pt. Although the contribution of hydrothermal processes to the formation of this type of mineralization has already been recognized, no detailed studies have previously focused on the mineralogy and zonation of mineralization-related silicate assemblages and their distinction from regional processes postdating ore formation. Here, the results of detailed alteration mapping carried out on two recently discovered low-sulfide occurrences in the footwall of the Wisner area in the North Range of the Sudbury Igneous Complex are described to address these questions.
In both areas, disseminated sulfides, S-shaped sulfide veins, and extensional silicate veins trending northwest-southeast to north-northwest−south-southeast formed from hydrothermal activity driven by the heat of the Sudbury Igneous Complex. Hydrothermal vein assemblages in mafic to intermediate host rocks are dominated by actinolite whereas epidote and quartz predominate in granitic host rocks. Compositional similarity (high Ni, low K, and relatively low Mg contents) of actinolite rims of vein-filling amphiboles and actinolite in ore-bearing assemblages, coupled with anomalous PGE contents of amphibole veins and their spatial proximity to mineralized zones, suggest a direct genetic relationship between silicate veining and low-sulfide mineralization. Shear-type epidote veining postdates the Sudbury Igneous Complex-related hydrothermal alteration and slightly redistributes metals from the low-sulfide footwall ores on a local scale. Both Sudbury Igneous Complex-related and regional hydrothermal assemblages of the Wisner area show characteristics identical to similar occurrences elsewhere in the Sudbury structure.
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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.