Presentation on theme: "FORMATION AND CLASSIFICATION OF MINERAL DEPOSITS"— Presentation transcript:
1 FORMATION AND CLASSIFICATION OF MINERAL DEPOSITS BACKGROUND:FORMATION AND CLASSIFICATION OF MINERAL DEPOSITS
2 Mineral potential maps Garbage In,Garbage OutGood Data In, GoodResource Appraisal OutMineral potential mapsGISAnalyse / CombineRemote SensingGeophysicsGeochemistryGeologyRemote SensingGeophysicsGeochemistryGeologyGISAnalyse / CombineMineral potential maps
3 CONCEPTUAL GIS Systematic Application of GIS in Mineral Exploration databaseMineralization processesConceptual modelsKnowledge-baseMappable exploration criteriaSpatial proxiesProcessingPredictor mapsOverlayCONCEPTUALGISMODELFavorability mapValidationMINERAL POTENTIAL MAP
4 SOME TERMS Magmatic - Related to magma A complex mixture of molten or (semi-molten) rock, volatiles and solids that is found beneath the surface of the Earth.Temperatures are in the range 700 °C to 1300 °C, but very rare carbonatite melts may be as cool as 600 °C, and komatiite melts may have been as hot as 1600 °C.most are silicate mixtures .forms in high temperature, low pressure environments within several kilometers of the Earth's surface.often collects in magma chambers that may feed a volcano or turn into a pluton.
5 SOME TERMSHydrothermal : related to hydrothermal fluids and their circulation- Hydrothermal fluids are hot (50 to >500 C) aqueous solutions containing solutes that are precipitated as the solutions change their physical and chemical properties over space and time.- Source of water in hydrothermal fluids:Sea waterMeteroricConnateMetamorphicJuvenile (Magmatic)- Source of heatIntrusion of magma into the crustRadioactive heat generated by cooled masses of magmaHeat from the mantleHydrothermal circulation, particularly in the deep crust, is a primary cause of mineral deposit formation and a cornerstone of most theories on ore genesis.
6 FUMNDAMENTAL PROCESSES OF FORMATION OF ECONOMIC MINERAL DEPOSITS PRIMARY PROCESSESMAGMATISMSEDIMENTARY (includes biological)HYDROTHERMALCOMBINATIONS OF ABOVESECONDARY PROCESSESMECHANICAL CONCENTRATIONRESIDUAL CONCENTRATION
7 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS In order to more readily study mineral deposits and explore for them more effectively, it is helpful to first subdivide them into categories.This subdivision, or classification, can be based on a number of criteria, such asminerals or metals contained,the shape or size of the deposit,host rocks (the rocks which enclose or contain the deposit) orthe genesis of the deposit (the geological processes which combined to form the deposit).It is useful to define a small number of terms used in the classification which have a genetic connotation.
8 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS MAGMATICMAGMATIC HYDROTHERMALPorphyry deposits (e.g., porphyry copper deposits)Volcanogenic massive sulfide (e.g., VMS deposits – Zn and Pb deposits)SEDIMENTARY (e.g., banded iron deposits, most types of uranium deposits)SEDIMENTARY HYDROTHERMALSEDEX Deposits (e.g., Pb-Zn deposits of Rajasthan)HYDROTHERMAL (e.g., Orogenic gold deposits – Kolar, Kalgoorlie)MECHANICAL CONCENTRATION (Gold placers, Tin)RESIDUAL CONCENTRATION (Bauxite deposits)
9 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS MAGMATICMagmatic Deposits are so named because they are genetically linked with the evolution of magmas emplaced into the crust (either continental or oceanic) and are spatially found within rock types derived from the crystallization of such magmas.The most important magmatic deposits are restricted to mafia and ultramafic rocks which represent the crystallization products of basaltic or ultramafic liquids. These deposit types include:Disseminated (e.g., diamond in ultrapotassic rocks called kimerlites)Early crystallizing mineral segregation (e.g., Cr, Pt deposits)Immiscible liquid segregation (Ni deposits)Residual liquid injection (Pegmatite minerals, feldspars, mica, quartz)
10 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS MAGMATIC – HYDROTHERMALDeposits formed by precipitation of metals from hydrothermal fluids related to magmatic activity.Porphyry deposits (e.g., porphyry copper deposits) are associated with porphyritic intrusive rocks and the fluids that accompany them during the transition and cooling from magma to rock. Circulating surface water or underground fluids may interact with the plutonic fluids.Volcanogenic massive sulfide (e.g., VMS deposits – Zn and Pb deposits) are atype of metal sulfide ore deposit, mainly Cu-Zn-Pb, which are associated with and created by volcanic-associated hydrothermal events in submarine environments.
11 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS SEDIMENTARY DEPOSITSDeposits formed by (bio-)sedimentary processes, that is, deposition of sediments in basins.The term sedimentary mineral deposit is restricted to chemical sedimentation, where minerals containing valuable substances are precipitated directly out of water.Examples:Evaporite Deposits - Evaporation of lake water or sea water results in the loss of water and thus concentrates dissolved substances in the remaining water. When the water becomes saturated in such dissolved substance they precipitate from the water. Deposits of halite (table salt), gypsum (used in plaster and wall board), borax (used in soap), and sylvite (potassium chloride, from which potassium is extracted to use in fertilizers) result from this process.Iron Formations - These deposits are of iron rich chert and a number of other iron bearing minerals that were deposited in basins within continental crust during the Early Proterozoic (2.4 billion years or older), related to great oxygenation event.
12 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS SEDIMENTARY HYDROTHERMALThese deposits form by precipitation of metals from fluids generated in sedimentary environments.Example: SEDEX Deposits (e.g., Pb-Zn deposits of Rajasthan)
13 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS HYDROTHERMALThese deposits form by precipitation of metals from hydrothermal fluids generated in a variety of environmentsExample: Orogenic Gold Deposits (e.g., Kolar, Kalgoorlie)
14 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS SECONDARY DEPOSITS:Formed by concentration of pre-existing depositsMECHANICAL CONCENTRATIONRESIDUAL CONCENTRATION
17 Orogenic gold deposits Close to trans-lithospheric structures (vertically extensive plumbing systems for hydrothermal fluids)Related to accretionary terranes (collisional plate boundaries)Temperature of formation – CMajor deposits form close to:Fault deflectionsDilational jogsFault intersectionsRegions of low mean stress and high fluid flow (permeable regions)Greenschist facies metamorphism (low-grade metamorphism, low temperature-pressure conditions)
18 Orogenic gold deposits characteristics High Au (> 1 PPM) and Ag; Au/Ag ≈ 5Associated withhydrated minerals (micas, chlorite, clay)Carbonate minerals (calcite, dolomite)Sulfides (pyrite etc)Enrichment of semi-metals (As, Sb, Bi, Sn)Depletion of base and transition metals (Zn, Cu, Pb)
19 Leaching of Gold in Source Areas By hydrothermal fluids that contain suitable ligands for complexing gold as Au(HS)2– , HAu(HS)20 and Au(HS)0Hydrothermal fluids are:aqueous (H2O)-CO2-CH4dilutecarbonichaving low salinity (<3 Wt% NaCl)Source rocks – typically crustal rocks (granites)
20 Transportation of Gold Gold is transported in the form of sulfide complex Au(HS)2– , HAu(HS)20 or Au(HS)0 Low Cl and high S in hydrothermal fluids account for high Au and low Zn/Pb in hydrothermal solutions Transportation pathways – permeable structures such as faults, shear zones, fold axes focus vast volumes of gold-sulfide bearing fluids into trap areas.
21 Gold trapping – (precipitation) Key precipitation process:break soluble gold sulfide complexes (Au(HS)-1)How?- Take sulfur out of the systemHow?- by changing physical conditions- by modifying chemical compositions
22 Gold trapping – (precipitation) Physical mechanism: - Fluid boiling through pressure release - Catastrophic release of volatiles, particularly, SO2 - Removal of sulfur breaks gold sulfide complexes leading to the precipitation of gold - Pressure release could be by seismic pumping or by brittle failure of competent rock
23 Gold trapping – (precipitation) Chemical mechanism: - Gold-sulfide complexes react with iron, forming pyrite and precipitating gold - Rocks such as dolerite, banded iron formations are highly enriched in iron and therefore form good host rocks for trapping gold
26 Nickel deposit formation Magmatic nickel sulfide deposits form due to saturation of nickel-rich, mantle-derived ultramafic magmas with respect to sulfur, which results in formation and segregation of immiscible nickel sulfide liquid.Sub-volcanic staging chambersShallow sills and dyke complexesNickel-rich source magma (ultramafic)Transportation of the source magma through active pathwaysDeposition of nickel-sulfide through sulphur saturationMid-crustal magma chamberKmMagma plumbing systemDeep level magma chamberCSIRO, Australia Slide
27 Uranium deposit formation Transported as U+6(uranyl)Deposited as U+4 (uraninite)Uranium OreUranium deposit
28 Coal, Oil And Natural Gas Formation The carbon molecules (sugar) that a tree had used to build itself are attacked by oxygen from the air and broken down.This environment that the tree is decaying in is called an aerobic environment. All this means is that oxygen is available.If oxygen is not available (anaerobic environment), the chains of carbon molecules that make up the tree are not be broken down.If the tree is buried for a long time (millions of years) under high pressures and temperatures, water, sap and other liquids are removed, leaving behind just the carbon molecule chains. Depending on the depth and duration of burial, peat, lignite, bitumen and anthracite coal is formed.
29 Difference between coal and oil Crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface.Like coal, forms by anerobic decay and break down of organic material.However, while coal is solid, crude oil is liquid.Coal contains massive molecules of carbon rings derived from plant fibres that can be very long, sometimes metres long or more.The carbon chains in oil are tiny by comparison. They are the structural remains of microscopic organisms and so they are ALL very small
31 Oil and Natural Gas System An oil and natural gas system requires timely convergence of geologic processes essential to the formation of crude oil and gas accumulations.These Include:Mature source rockHydrocarbon expulsionHydrocarbon migrationHydrocarbon accumulationHydrocarbon retention(modified from Demaison and Huizinga, 1994)
33 Cross Section Of A Petroleum System (Foreland Basin Example)Geographic Extent of Petroleum SystemExtent of PlayExtent of Prospect/FieldOOOStratigraphicExtent ofPetroleumOverburden RockSystemEssentialElementsSeal RockofReservoir RockBasin FillPetroleumSedimentaryPod of ActiveSystemSource RockSource RockUnderburden RockPetroleum Reservoir (O)Basement RockFold-and-Thrust BeltTop Oil Window(arrows indicate relative fault motion)Top Gas Window(modified from Magoon and Dow, 1994)
34 Geology of Petroleum Systems 34 Hydrocarbon TrapsStructural trapsStratigraphic trapsStructural traps are caused by structural features. They are usually formed as a result of tectonics.Stratigraphic traps are usually caused by changes in rock quality.Combination traps that combine more than one type of trap are common in petroleum reservoirs.Other types of traps (such as hydrodynamic traps) are usually less common.
35 Geology of Petroleum Systems 35 Structural Hydrocarbon TrapsGasOilShaleTrapFracture BasementClosureOil/GasContactOil/WaterContactSealOilFold TrapSaltDiapirSaltDomeOil(modified from Bjorlykke, 1989)
36 Geology of Petroleum Systems 36 Hydrocarbon Traps - DomeGasOilWaterThe dome above shows gravity separation of fluids. Shale comprises the upper and lower confining beds.SandstoneShale
37 Geology of Petroleum Systems 37 Fault TrapOil / GasSandShaleIn this normal fault trap, oil-bearing sandstone is juxtaposed against impervious shale.
38 Geology of Petroleum Systems 38 Stratigraphic Hydrocarbon TrapsUnconformityUncomformityStratigraphic hydrocarbon traps occur where reservoir facies pinch into impervious rock such as shale, or where they have been truncated by erosion and capped by impervious layers above an unconformity.Oil/Gas(modified from Bjorlykke, 1989)