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Unformatted text preview: y in ceramics Ore Minerals Most ore minerals of the scarce metals are found as sulphides (e.g. ZnS, PbS, CuFeS2) A few, such as the ore minerals of tin and tungsten, are oxides Ore minerals rarely occur alone They are mixed with other non-valuable minerals, collectively termed “gangue” (e.g. quartz, calcite, feldspar, mica) 3 Location of important metallic resources in Canada What makes an ore deposit? 4 350 years of serious thinking about ore deposits .... De Re Metallica, A gricolla (1556) Mineral Deposits, Lindgren (1913) Origins of Mineral Deposits Minerals become concentrated in 5 ways: 1) Concentration by hot, aqueous solutions flowing through fractures and pore spaces in rock to form hydrothermal mineral deposits 2) Concentration by magmatic processes within a body of igneous rock to form magmatic mineral deposits Origins of Mineral Deposits 3) Concentration by precipitation from modified sea water to form sedimentary mineral deposits 4) Concentration by flowing surface water in streams or along the shore, to form placers 5) Concentration by weathering processes to form residual or supergene mineral deposits 5 A simple set of rules ... Source Trap Transport rocks or magma enriched in metals that can be supplied to the “ ore-forming” system melt or fluid that can carry metals from a source to a site of deposition physical or chemical process that concentrates the metals into an ore deposit A simple set of rules ... Trap Transport Source Layered m afic intrusions Fractional crystallization Sulphide settling A simple set of rules ... Source Volcanic eruptions Transport Trap Geothermal fluids Hydrothermal precipitation 6 A simple set of rules ... Source Erosion of a source Transport Fluvial Transport Trap Gravity concentration Where are Mineral Deposits Found? Mineral deposits are found in a variety of plate tectonic settings depending on where these processes operate Continents Oceans 7 Metallic Mineral Deposits Magmatic ore deposits • Some of the most important accumulations of metals are associated with magma that forms igneous rocks • Different metals are naturally enriched in different types of magma (e.g. Cu and Au in felsic magmas, Ni in mafic magmas), and they are further concentrated during cooling and crystallization of the magma I. Magmatic deposits: 1) gravitational settling • heavy minerals that crystallize early, settle and concentrate on the bottom of the magma chamber High-density minerals, such as chromite, sink to the bottom of the magma chamber (Bushveld Complex, South Africa) I. Magmatic deposits: 2) immiscibility • segregation of metal-rich (sulphide) liquid from the crystallizing magma (e.g. Sudbury, Ontario and Voisey’s Bay, Labrador) • dense, metal-sulfide melt settles to the bottom of the crystallizing magma chamber At Voisey’s Bay, Nisulphides crystallized out of a large gabbroic body… 8 Sudbury Basin I. Magmatic deposits: 3) pegmatites • melt remaining in last stages of crystallization of graniti...
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