What is an ore An ore is an aggregate of minerals from which one or more minerals can be extracted profitably Ore Deposits A deposit contains an unusually high concentration of particular elements ID: 1022283
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1. Ore Forming Processes and Rock Association What is an ore?An ore is an aggregate of minerals from which one or more minerals can be extracted profitably. 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 processThe processes that concentrate these elements in one place is called ore forming processes.
2. Gold AuDistribution of Au in the crust = 3.1 ppb by weight 3.1 units gold / 1,000,000,000 units of total crust = 0.00000031% Au Concentration of Au needed to be economically viable as a deposit = few g/t 3 g / 1000kg = 3g/ 1,000,000 g = 0.00031% AuNeed to concentrate Au at least 1000-fold to be a viable depositRare mines can be up to a few percent gold (extremely high grade)!
3. Some unusual process must: 1) remove specific elements, compounds or minerals from ordinary rock,2) transport these elements, compounds, or minerals3) concentrate the elements, compounds, or minerals preferentially at one spot or zone where the transport stops.
4. The primary mechanisms for concentrating minerals into ores involves either: (a) sorting by density (b) sorting by solubility. Ores concentrate in igneous, metamorphic or sedimentary rocks either during the time the rock forms or due to subsequent enrichment. 1. Syngenetic ore deposits represent primary mineralization wherein ores form at the same time – synchronous – as the rock. 2. Epigenetic ore deposits form by secondary mineralization wherein ore concentrates some time after the rock has formed. Epigenetic mineralization can postdate the host rock by hundreds of millions of years.
5. A. Hypogene enrichment is a primary or syngenetic process that occurs as deep, upwelling magmatic fluids concentrate ore synchronous with rock development. B. Supergene enrichmentoccurs as surface waters percolate downward, in so doing leaching near surface metals and concentrating them at deeper levels within Earth ’ s crust. Supergene enrichment is an epigenetic process that commonly develops in oxidizing zone.
6. Supergene enrichment
7. Ore deposit environments/ ore forming processes and rock assMagmatic deposits (ass with Ig rocks)Igneous ore - forming environmentsIgneous processes create large - scale ore deposits at convergent and divergent plate boundaries as well as within intraplate settings.
8. Magmatic/Related ores and Igneous Rock ass 1. Cumulate deposits/Crystal settling (mafic / ultramafic rock ass)2. Pegmatites Ass3. Kimberlite Ass4. Hydrothermal deposits5. Volcanogenic massive sulfide (VMS) deposits6. Porphyry deposits
9. Cumulate deposits/Crystal settling (mafic / ultramafic rock ass)– fractional crystallization processes, early form dense min like chromite, magnetite can settle at the magma bottom chamber, can concentrate metals (Cr, Fe, Pt)Pegmatites ass– late stage crystallization of a magma body forms pegmatites and many residual elements are concentrated (Li, Ce, Sn, and U)Kimberlite Ass – diamond form at great depth, at high P in mantle, brought up rapidly into the crust by kimberlite pipes. Kimberlites are fluid charged, emplaced rapidly
10. TopazAmethyst (Quartz)
11. Mineral deposits in layered Igneous complexes
12. Kimberlite pipe
13. 4. Hydrothermal depositsMagma has water and other fluids, at the last stage of xl, these fluids may escape from the cooling magma, seep through cracks, fractures, pores in the rocks, carries with dissolved salts, gases, metals, the warm fluid may leach additional metals from the rocks through which it passes, the fluids cools and deposits the dissolved minerals creating hydrothermal ores deposits, like copper, lead, zinc, gold, silver, platinum, uranium etc
14. Hydrothermal deposits
15. Mineral deposits at oceanic ridge
16. 5. Volcanogenic massive sulfide depositscopper – zinc – lead sulfide deposits concentrated on the ocean floor at divergent and convergent plate boundaries.Other VMS ores include silver, gold, cobalt, nickel, iron, tin, selenium, manganese, cadmium, bismuth, germanium, gallium, indium and tellurium.While plate margin magmatism at ocean spreading ridges or volcanic arcs is the driving force behind the development of VMS deposits, extensive hydrothermal alteration and metamorphism play critical roles in altering the igneous rocks and concentrating ores through both hypogene and supergene enrichment.
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18. On the basis of their genetic origin,VMS deposits have been classified as 1. Cyprus type2. Besshi type3. Kuroko type
19. 1. Cyprus typeForm in ocean ridge (East Pacific Rise) or backarc basin.Cyprus - type VMS are basalt - dominated deposits associated with ophiolites and enriched in copper, zinc, nickel, chromium and manganese and with minor amounts of silver and gold2. Besshi typeJuvenile, nascent, newly formed volcanic arc.Besshi - type VMS are early formed convergent margin deposits containing basalt, rhyolite and greywacke rocks. Besshi deposits are notable for their ore concentrations of copper and cobalt and only minor concentrations of zinc.
20. 3. Kuroko typeMature volcanic arc, or backarc basinKuroko - type VMS are dominated by silicic rocks such as rhyolite. Kuroko deposits are enriched in copper, zinc and lead and may also contain substantial gold and silver
21. 6. Porphyry deposits: occurs in subduction zone form as silica - rich magma intrudes and fractures the host rock and subsequently crystallizes. Forces associated with magma injection, coupled with hydrothermal fluid pressures, result in the diffuse infiltration of ore - bearing fluids into complex network of fractures and pore spaces of the surrounding rock. Cooling and crystallization results in massive, low concentration deposits of copper, molybdenum, gold, zinc, mercury, silver, lead, lithium
22. Sedimentary dep : formed by sed process1. Placer2. BIF3. Sedex4. Evaporite5. Residual deposit ass with weathering
23. Placerplacers: deposits of heavy mineral particles in stream bed. streams often deposit sed that are well sorted by size and density, such are placer dep (Gold, diamonds, cassiterite (tin ore)Steps for making a placer1. weathering removes mineral particles from country rock.2. kinetic energy of high velocity stream transports mineral particles. 3. where kinetic energy drops suddenly, high density particles stop, lower density particles continue
24. Placer Deposit
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26. 2. Banded Iron Formations 90% of world’s iron come from these. Confined in the Precam, oxygen deficient env in Archaean, reaction in weathering take place in reduced condition, reduced iron is soluble, iron goes to ocean, through time as photosynthetic org evolved and oxygen evolved, oxygen reacted with dissolved iron to ppt BIF. BIF unlike to form today, laterite form today.
27. Banded iron deposits: classified1. Superior Type BIF2. Algoma Type BIF Superior - type BIFconsist of alternating iron - rich and silica - rich layers. These shallow marine deposits formed in the Early Proterozoic when iron - rich, deep sea-water mixed with shallow oxygenated shelves.
28. 2. Algoma - type deposits contain iron ore concentrations that occur in metasedimentary deposits, most of which are Archean ( 2.5 Ga) in age. The Algoma ironstones contain hematite and magnetite interbedded with volcanic rocks, graywackes, turbidites and pelagic sedimentary rocks. Algoma ironstones form in deep abyssal basins heated by submarine volcanic activity.
29. 3. Sedimentary exhalative (sedex) deposits Hydrothermal fluids containing dissolved metals rise upward and are “ exhaled ” into clastic sedimentary basins releasing metal – rich brine solutions into the surrounding country rock.4. Evaporiteminerals like gypsum, halite deposited this way. Form in shallow marine setting with restricted water flow, evaporation leads to evaporate deposit.
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31. Evaporite
32. 5. Depo ass with Weathering/ Residual DepositWeathering alone can produce ores by leaching unwanted min leaving a residue enriched in valuable metals. Extreme leaching in tropical climate gives rise to bauxite/laterite, require Tropical climate, chemical weathering, tectonically stable region.Metamorphic deposit: ass with met rocks Graphite, asbestos, talc, garnet
33. Residual deposit: Laterite
34. Mineral Deposits and Plate Tectonics
35. Ancient smelting site Zawar, Udaipur
36. Retrots near Zawar, Udaipur. Indicators of historical smelting/ metallurgy in India