Was responsible for many vms deposits as old as 3

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Unformatted text preview: l vents in sedimentary basins • These deposits are sometimes referred to as sedimentary exhalative deposits (SEDEX) • A present-day example is the Atlantis II Deep of the Red Sea III. Hydrothermal ore deposits • Associated with sediments • SEDEX deposits form thin layers of metallic sulphide in the sedimentary rocks (e.g. Sullivan Mine, British Columbia) SEDEX deposits typically occur in the sediment that fills rift basins III. Hydrothermal ore deposits • Associated with sediments • Sediment-Hosted Stratiform Copper Oxidized copper-bearing brines moving through coarse-grained sedimentary rock are forced upward into reduced sediments, which promotes the precipitation of sulphide minerals • Unconformity-Associated Uranium Oxidized uranium-bearing brines moving through coarse-grained sedimentary rock are forced upward into reduced sediments, which promotes the precipitation of reduced uranium minerals 14 • Ore deposits in “aquifers” • Mississippi Valley-type Deposits Oxidized metal-bearing brines migrate toward a basin edge and infill cavities in limestone (karst e nvironments) Sedimentary ore deposits • Reducing conditions during much of the early history of the Earth allowed dissolved iron to accumulate in ocean basins • Eventually photosynthesizing bacteria generated enough oxygen to precipitate iron oxide minerals Banded Iron Formation 15 Sedimentary hosted deposits • Placer deposits – formed when heavy metals are mechanically concentrated by currents in rivers • gold, platinum, diamonds, tin Klondike 1902 Klondike 2002 More than half of the gold recovered historically came from placers Concentration of Placer Deposits in Stream Beds Sedimentary hosted deposits • South Africa’s fossil placer deposits • The largest concentration of gold on Earth is in the ancient placer deposits of the Witwatersrand Basin • Conglomerates deposited about 2.7 billion years ago 16 Deposits associated with weathering • Residual enrichment – concentrating metals into economically valuable concentrations • Laterite (enriched in Fe, Al, Ni) forms by deep weathering of the parent rock and leaching out elements such as silica • Forms in rainy tropical climates Bauxite – principal ore of aluminum • All of the very large bauxite deposits formed in the last 25 million years • Not found in glaciated regions Deposits associated with weathering • Supergene enrichment occurs when s oluble minerals are dissolved near the surface and reprecipitated a t depth near the water table • Low-grade primary ores in large porphyry Cu deposits are enriched by supergene processes (secondary ores) • Form in arid climates 17 Nonmetallic Resources Significant Industrial Mineral Deposits in Canada • P otash (KCl salts) is one of the most important mineral deposit types • Diamonds are a new deposit type in Canada! Diamonds • Most diamonds are found in rare u ltramafic igneous rocks called kimberlites • Kimberlite magma originates at g...
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This note was uploaded on 11/10/2012 for the course SCIENCE 1, 2, 3 taught by Professor All during the Spring '12 term at University of Ottawa.

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