Ores Principally we discuss ores as sources of

Ores • Principally we discuss ores as sources of metals • However, there are many other resources bound in minerals which we find useful • How many can we think of?

Ore Deposits • A deposit contains an unusually high concentration of particular element(s) • This means the element(s) have been concentrated in a particular area due to some process • What sort of processes might concentrate these elements in one place?

Gold Au • Distribution of Au in the crust = 3. 1 ppb by weight 3. 1 units gold / 1, 000, 000 units of total crust = 0. 00000031% Au • Concentration of Au needed to be economically viable as a deposit = few g/t 3 g / 1000 kg = 3 g/ 1, 000 g = 0. 00031% Au • Need to concentrate Au at least 1000 -fold to be a viable deposit • Rare mines can be up to a few percent gold (extremely high grade)!

Ore minerals • Minerals with economic value are ore minerals • Minerals often associated with ore minerals but which do not have economic value are gangue minerals • Key to economic deposits are geochemical traps metals are transported and precipitated in a very concentrated fashion – Gold is almost 1, 000 times less abundant than is iron

Economic Geology • Understanding of how metalliferous minerals become concentrated key to ore deposits… • Getting them out at a profit determines where/when they come out

Ore deposit environments • Magmatic – Cumulate deposits – fractional crystallization processes can concentrate metals (Cr, Fe, Pt) – Pegmatites – late staged crystallization forms pegmatites and many residual elements are concentrated (Li, Ce, Be, Sn, and U) • Hydrothermal – Magmatic fluid - directly associated with magma – Porphyries - Hot water heated by pluton – Skarn – hot water associated with contact metamorphisms – Exhalatives – hot water flowing to surface – Epigenetic – hot water not directly associated with pluton

Geochemical Traps • Similar to chemical sedimentary rocks – must leach material into fluid, transport and deposit ions as minerals… • p. H, redox, T changes and mixing of different fluids results in ore mineralization • Cause metals to go from soluble to insoluble • Sulfide (reduced form of S) strongly binds metals many important metal ore minerals are sulfides!

Hydrothermal Ore Deposits • Thermal gradients induce convection of water – leaching, redox rxns, and cooling create economic mineralization

Ore deposit environments • Sedimentary – Placer – weathering of primary mineralization and transport by streams (Gold, diamonds, other) – Banded Iron Formations – 90%+ of world’siron tied up in these (more later…) – Evaporite deposits – minerals like gypsum, halite deposited this way – Laterites – leaching of rock leaves residual materials behind (Al, Ni, Fe) – Supergene – reworking of primary ore deposits remobilizes metals (often over short distances)

Ore Deposit Types I • • • • Placer uranium gold Stratiform phosphate Stratiform iron Residually enriched deposit Evaporites Exhalative base metal sulphides Unconfornity-associated uranium Stratabound clastic-hosted uranium, lead, copper Volcanic redbed copper Mississippi Valley-type lead-zinc Ultramafic-hosted asbestos Vein uranium Arsenide vein silver, uranium Lode Gold

Ore Deposit Types II • • • • Clastic metasediment-hosted vein silver-lead-zinc Vein Copper Vein-stockwork tin, tungsten Porphyry copper, gold, molybdenum, tungsten, tin, silver Skarn deposits Granitic pegmatites Kiruna/Olympic Dam-type iron, copper, uranium, gold, silver Peralkaline rock-associated rare metals Carbonatite-associated deposits Primary diamond deposits Mafic intrusion-hosted titanium-iron Magmatic nickel-copper-platinum group elements Mafic/ultramafic-hosted chromite