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Presentation on theme: "BACKGROUND: FORMATION AND CLASSIFICATION OF MINERAL DEPOSITS."— Presentation transcript:


2 database Predictor maps Favorability map MINERAL POTENTIAL MAP MODEL Mineralization processes Conceptual models Knowledge-base Mappable exploration criteria Spatial proxies Processing Overlay Validation Systematic Application of GIS in Mineral Exploration

3 Remote Sensing Geophysics Geochemistry Geology Garbage In, Garbage Out Mineral potential maps GIS Analyse / Combine Good Data In, Good Resource Appraisal Out Mineral potential maps GIS Analyse / Combine Remote Sensing Geophysics Geochemistry Geology

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 TERMS Hydrothermal : 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 water Meteoric Connate Metamorphic Juvenile - Source of heat Intrusion of magma into the crust Radioactive heat generated by cooled masses of magma Heat from the mantle Hydrothermal circulation, particularly in the deep crust, is a primary cause of mineral deposit formation and a cornerstone of most theories on ore genesis.


7 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 as minerals or metals contained, the shape or size of the deposit, host rocks (the rocks which enclose or contain the deposit) or the 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. CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS


9 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS MAGMATIC Magmatic 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 Deposits 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. SEDIMENTARY DEPOSITS CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS

11 HYDROTHERMAL These deposits form by precipitation of metals from hydrothermal fluids generated in a variety of environments Example: Orogenic Gold Deposits (e.g., Kolar, Kalgoorlie)

12 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS MAGMATIC – HYDROTHERMAL Deposits 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 a type of metal sulfide ore deposit, mainly Cu-Zn-Pb, which are associated with and created by volcanic-associated hydrothermal events in submarine environments.

13 CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS SEDIMENTARY HYDROTHERMAL These deposits form by precipitation of metals from fluids generated in sedimentary environments. Example: SEDEX Deposits (e.g., Pb-Zn deposits of Rajasthan)


15 FORMATION OF MINERAL DEPOSITS COMPONENTS Ligand source Metal source Deposit Model I Trap Region Energy (Driving Force) Transporting fluid Residual Fluid Discharge No Deposits Mineral System (≤ 500 km) Deposit Halo Deposit (≤ 10 km) (≤ 5 km) 1. Energy2. Ligand 3. Source4. Transport5. Trap 6. OutflowINGREDIENTS Deposit Model II Deposit Model III




19 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 – C Major deposits form close to: – Fault deflections – Dilational jogs – Fault intersections – Regions of low mean stress and high fluid flow (permeable regions) – Greenschist facies metamorphism (low-grade metamorphism, low temperature-pressure conditions)

20 Source of fluids and metals FLUID SOURCES – Devolatilization: Magmatic devolatilization – magmatic underplating by mantle-derived magma – Devolatilization of individual batches of magma Metamorphic devolatilization – Mantle degassing (CH4, CO2) METAL SOURCES - Crustal rocks LEGEND SOURCES – Crustal sulfur/sulfate deposits

21 Leaching of Gold in Source Areas By hydrothermal fluids that contain suitable ligands for complexing gold as Au(HS) 2 –, HAu(HS) 2 0 and Au(HS) 0 Hydrothermal fluids are: – aqueous (H 2 O)-CO 2 -CH 4 – dilute – carbonic – having low salinity (<3 Wt% NaCl) – Source rocks – typically crustal rocks (granites) – Low Cl but high S indicating that the fluids are generated in crust with low Cl (~200 ppm) but high S (~1 %) – S isotope ranges (0 to +9 ‰) consistent with magmatic Sulphur, desulfidation or dissolution of magmatic sulfides or average crustal sulphur.

22 Alteration High Au (> 1 PPM) and Ag; Au/Ag ≈ 5 Hydrolysis of feldspars, Fe, Mg, Ca silicates (muscovite/paragonite-chlorite+/-Albite/K-Felspars) Carbonization of minerals (Ca, Mg,Fe carbonates) Sulfidation of Fe-silicates and oxides to sulfides (pyrite etc) Enrichment of semi-metals (K, Rb, Ba, Cs, As, Sb) and volatiles (H 2 O, CO 2, CH 4, H 2 S) Depletion of base and transition metals (Zn, Cu, Pb)

23 Transportation of Gold Gold is transported in the form of sulfide complex Au(HS) 2 –, HAu(HS) 2 0 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.

24 Gold trapping – (precipitation) At the Golden Mile (Kalgoorlie) deposit: Total Gold – 1300 Tonnes 150 Km 3 volume of fluids in 2 Km 3 volume! That is, the fluid has to be focussed through to a very small part of the crust very efficiently. Accumulation of fluids followed by catastrophic fracturing!

25 Gold trapping – (precipitation) Inter-seismic-Seismic events ductile deformation, pressure solution and dislocation glide Increase in pore-fluid pressure, accumulation of fluids in pore spaces, slow development of supra-hydrostatic pore-fluid pressures Co-seismic episode Supra-hydrostatic pore-fluid pressures trigger seismic episodes Catastrophic hydraulic fracturing Massive fluid flow through the fractures

26 Gold trapping – (precipitation) Key precipitation process: -break soluble gold sulfide complexes (Au(HS) -1 ) How? - Take sulfur out of the system How? - by changing physical conditions - by modifying chemical compositions

27 Gold trapping – (precipitation) Physical mechanism: - Fluid boiling through pressure release - Catastrophic release of volatiles, particularly, SO 2 - 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

28 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

29 Sediment-hosted Pb-Zn Deposits Types Clastic Dominated (CD) Hosted in shale, sandstone, siltstone, or mixed clastic rocks, or occur as carbonate replacement, within a CD sedimentary rock sequence Occur in passive margins, back- arcs and continental rifts, and sag basins. Mississippi Valley Type (MVT) Hosted by dolostone and limestone in platform carbonate sequences Form in passive-margin tectonic settings. Tectonic setting of sediment-hosted Pb- Zn deposits in passive margins. Figure 1

30 SEDEX vs VMS SEDEX and MVT deposits occur within or in the platforms to a thick sedimentary basin and are the results of the migration of basinal saline fluids, whereas VMS deposits occur in submarine volcanic- sedimentary regions and are formed from convective hydrothermal fluids which are driven by magmatic fluids from a sub-volcanic intrusion (Goodfellow and Lydon, 2007). So the key difference is in the origin of the ore-fluids – basinal vs magmatic origin of the fluids.

31 LEAD-ZINC SULFIDE DEPOSITS – SEDEX or Sedimentary Exhalative Deposits PbCl x (2-x) + H 2 S  PbS +2H + + xCl -

32 Continental Rift/sag basins If rifting stops short of sea-floor spreading, then thermally driven subsidence becomes dominant and rift-related strata and structures are blanketed, similar to passive margins. The result is a sag basin which can host CD deposits

33 Tectonic Settings of Sediment Hosted Pb-Zn deposits Most sediment-hosted Pb-Zn deposits are in strata that were deposited in rift or passive- margin settings. These settings are related: passive margins form when continental rifts succeed Rifts Rifts are fault-bounded elongate troughs, under or near which the entire thickness of the lithosphere has been reduced in extension during their formation. Coarse, immature clastic sediments are shed off the bounding highlands and deposited in alluvial fans along basin-bounding growth faults. Sedimentation along the rift axis may either be marine or nonmarine. Rapid subsidence leads to deep-water environments which favour CD Pb-Zn deposits. A : A single continent is extended asymmetrically. B: Rifting has succeeded, and an ocean has begun to open which is bordered by a young passive margin on both sides. C: The ocean widens. D: Some time later, an arc approaches from the west, consuming the oceanic part of the plate that also includes the continent on the east. E: Arc and passive margin collide and the distal passive margin enters the trench. F: Arc-passive margin collision is nearly complete.

34 Continental rifting (Fig. 2A) may or may not proceed all the way to sea-floor spreading. If it does, then the axial valley of a rift evolves into a midoceanic ridge and, over time, the continents on either side drift apart. Passive margins develop on the rifted edges of the two diverging continents (Fig. 2B,C) Passive Margin Setting Water depth, distance from shore, sea level, and climate control the character of sediments deposited. Compositionally mature sandstones and siltstones are typical of shelf environments at high latitudes. Platform carbonates, the classic assemblage of passive margins, and the eventual host of most MVT deposits, are dominant at low latitudes. Finer grained and shale equivalents are deposited farther offshore on the slope and rise, the prime site for syngenetic or diagenetic CD Pb-Zn deposition. Ancient passive margins ended their tenure by colliding with an arc (Fig. 2E, F) Tectonic Settings of Sediment Hosted Pb-Zn deposits continued

35 SEDEX Deposits Source of fluids and ligands: Sea water? Sedex brines: Highly saline 10-30% TDS, but the normal sea water salinity is 3-5% How are the salts concentrated and huge amounts of fluids of high salinity are required ??? Halites are typically absent in SEDEX sequences Generation of near-saturated brines through evaporation in near isolated basins next to the main sedex basin in carbonate shelf; tropical environment Gravity-driven influx of these saturated brines in the rift-fill clastics through marginal normal faults, mixing with connate brines as well as sea water would produce large amounts of brines of the required salinity

36 SEDEX Deposits Source of metal: Rift-fill clastic sediments Brines circulate through rift-fill sediments over prolonged periods (~70 my) and leach out metals Basinal brines can be oxidized (SO 4 -2 rich) or reduced (H 2 S rich) Nature of brines is a function of rift-fill sediments – fluvial-deltaic and shallow marine clastic having high reactive Fe produce oxidized brines; shales/carbonates produce reduced brines Oxidized brines are preferred - PbCl x (2-x) +H 2 S PbS + 2H + + xCl - Reactive Fe tends to remove H 2 S as pyrite – hence clastic sediments rich in Fe are good source of metals

37 SEDEX Deposits Source of driving energy Brines circulate over prolonged periods (~70 my) in the rift-fill clastic sediments – what drives the circulation? Sag-fill sediments have typically low thermal conductivity as well as low permeability No dewatering and heat-loss during compaction =>> development of geopressurized hot brines in the rift-fill sediments Geothermal gradient/proximity to mantle/mafic dykes at depth create thermal gradient =>> generation of convectional currents

38 SEDEX Deposits Transportation pathways to the traps for fluids Normal rift faults reactivated Breaching of sag-fill cap (aquitard) and gushing of geopressurized brines as exhalations on the sea floor

39 SEDEX Deposits Precipitation of metals: Chemical Traps PbCl x (2-x) + H 2 S  PbS +2H + + xCl - A column H2S rich anoxic waters required near the sea-floor

40 SEDEX Deposits Why no SEDEX deposits prior to 1.85 Ga???

41 Great Oxygenation Event The atmosphere and the hydrosphere, were reduced prior to about 2.4 Ga. During the time period from about 2.4 and 1.8 Ga, the atmosphere became progressively oxygenated as the result of the loss of H 2 to space and/or the evolution of O 2 -producing organisms. This led to oxygenation of the hydrosphere by addition of sulfates derived from oxidative weathering of sulfides. The change in oceanic composition was most rapid in shallow marginal seas and shelf environments, which resulted in oxidized, relatively sulfate rich shallow seawater in these basins. Bacteriogenic reduction of sulfate in deep basins was nearly complete, leading to the persistence of deep, anoxic ocean waters perhaps into the Neoproterozoic The presence of abundant Fe 2+ in these deep waters would have limited the amount of reduced sulfur, leading, at least prior to ~1.8 Ga, to reduced and relatively sulfide poor deep seawater. Only after the oceans were scrubbed of Fe 2+ during extensive deposition of iron formations between 1.95 and 1.85 Ga would sulfide contents of the deep oceans have increased. The mid-Proterozoic maximum in SEDEX mineralization and the absence of Archean deposits reflect a critical threshold in the accumulation of oceanic sulfate and thus sulfide within anoxic bottom waters and pore fluids—conditions that favored both the production and preservation of sulfide mineralization at or just below the sea floor. Consistent with these evolving global conditions, the appearance of voluminous SEDEX mineralization ca Ma coincides generally with the disappearance of banded iron formations—marking the transition from an early iron-dominated ocean to one more strongly influenced by sulfide availability.

42 Nickel deposit formation Nickel-rich source magma (ultramafic) Transportation of the source magma through active pathways Deposition of nickel- sulfide through sulphur saturation Shallow sills and dyke complexes Mid-crustal magma chamber Magma plumbing system Deep level magma chamber CSIRO, Australia Slide Km Sub-volcanic staging chambers 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.

43 Geology of Petroleum Systems

44 Petroleum System - A Definition A Petroleum System is a dynamic hydrocarbon system that functions in a restricted geologic space and time scale. A Petroleum System requires timely convergence of geologic events essential to the formation of petroleum deposits. These Include: Mature source rock Hydrocarbon expulsion Hydrocarbon migration Hydrocarbon accumulation Hydrocarbon retention (modified from Demaison and Huizinga, 1994)

45 Background: Geological terminology and concepts Stratigraphic Relationships Angular Unconformity Igneous Sill A B C D E F G H I J K Igneous Dike

46 Disconformity – An unconformity in which the beds above and below are parallel Angular Unconformity – An unconformity in which the older bed intersect the younger beds at an angle Nonconformity – An unconformity in which younger sedimentary rocks overlie older metamorphic or intrusive igneous rocks Background: Geological terminology and concepts - Types of Unconformities

47 Correlation Establishes the age equivalence of rock layers in different areas Methods: – Similar lithology – Similar stratigraphic section – Index fossils – Fossil assemblages – Radioactive age dating

48 Cryptozoic (Precambrian) Phanerozoic Quaternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian Millions of years ago Billions of years ago Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Recent Quaternary period Tertiary period EonEraPeriod Epoch Geologic Time Chart Paleozoic Mesozoic Cenozoic Era

49 Classification of Rocks SEDIMENTARY Rock-forming process Source of material IGNEOUS METAMORPHIC Molten materials in deep crust and upper mantle Crystallization (Solidification of melt) Weathering and erosion of rocks exposed at surface Sedimentation, burial and lithification Rocks under high temperatures and pressures in deep crust Recrystallization due to heat, pressure, or chemically active fluids


51 Siltstone, mud and shale ~75% Sedimentary Rock Types Relative abundance Sandstone and conglomerate ~11% Limestone and dolomite ~13% Carbonate ~13%

52 Average Detrital Mineral Composition of Shale and Sandstone Mineral CompositionShale (%)Sandstone (%) Clay Minerals Quartz Feldspar Rock Fragments Carbonate Organic Matter, Hematite, and Other Minerals <5 3 < <1 (modified from Blatt, 1982)

53 The Physical and Chemical Characteristics of Minerals Strongly Influence the Composition of Sedimentary Rocks Quartz Feldspar Calcite Mechanically and Chemically Stable Can Survive Transport and Burial Nearly as Hard as Quartz, but Cleavage Lessens Mechanical Stability May be Chemically Unstable in Some Climates and During Burial Mechanically Unstable During Transport Chemically Unstable in Humid Climates Because of Low Hardness, Cleavage, and Reactivity With Weak Acid

54 Some Common Minerals Silicates Oxides Sulfides Carbonates SulfatesHalides Non-Ferromagnesian (Common in Sedimentary Rocks) Anhydrite Gypsum Halite Sylvite Aragonite Calcite Dolomite Fe-Dolomite Ankerite Pyrite Galena Sphalerite Ferromagnesian (not common in sedimentary rocks) Hematite Magnetite Quartz Muscovite (mica) Feldspars Potassium feldspar (K-spar) Orthoclase Microcline, etc. Plagioclase Albite (Na-rich - common) through Anorthite (Ca-rich - not common) Olivine Pyroxene Augite Amphibole Hornblende Biotite (mica) Red = Sedimentary Rock- Forming Minerals

55 Sandstones: The Four Major Components Framework – Sand (and Silt) Size Detrital Grains Matrix – Clay Size Detrital Material Cement – Material precipitated post-depositionally, during burial. Cements fill pores and replace framework grains Pores – Voids between above components

56 Norphlet Sandstone, Offshore Alabama, USA Grains are About =< 0.25 mm in Diameter/Length PRF KF P KF = Potassium Feldspar PRF = Plutonic Rock Fragment P = Pore Potassium Feldspar is Stained Yellow With a Chemical Dye Pores are Impregnated With Blue-Dyed Epoxy CEMENT Sandstone Composition Framework Grains

57 Scanning Electron Micrograph Norphlet Formation, Offshore Alabama, USA Pores Provide the Volume to Contain Hydrocarbon Fluids Pore Throats Restrict Fluid Flow Pore Throat Porosity in Sandstone

58 Diagenesis Carbonate Cemented Oil Stained Diagenesis is the Post- Depositional Chemical and Mechanical Changes that Occur in Sedimentary Rocks Some Diagenetic Effects Include Compaction Precipitation of Cement Dissolution of Framework Grains and Cement The Effects of Diagenesis May Enhance or Degrade Reservoir Quality Whole Core Misoa Formation, Venezuela

59 Fluids Affecting Diagenesis

60 Thin Section Micrograph - Plane Polarized Light Avile Sandstone, Neuquen Basin, Argentina Dissolution of Framework Grains (Feldspar, for Example) and Cement may Enhance the Interconnected Pore System This is Called Secondary Porosity Pore Quartz Detrital Grain Partially Dissolved Feldspar (Photomicrograph by R.L. Kugler) Dissolution Porosity

61 Hydrocarbon Generation, Migration, and Accumulation

62 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.

63 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

64 Oil And Natural Gas Formation Kerogen


66 Organic Matter in Sedimentary Rocks Reflected-Light Micrograph of Coal Kerogen Disseminated Organic Matter in Sedimentary Rocks That is Insoluble in Oxidizing Acids, Bases, and Organic Solvents.

67 Interpretation of Total Organic Carbon (TOC) (based on early oil window maturity) Hydrocarbon Generation Potential TOC in Shale (wt. %) TOC in Carbonates (wt. %) Poor Fair Good Very Good Excellent > >2.0

68 Schematic Representation of the Mechanism of Petroleum Generation and Destruction (modified from Tissot and Welte, 1984) Organic Debris Kerogen Carbon Initial Bitumen Oil and Gas Methane Oil Reservoir Migration Thermal Degradation Cracking Diagenesis Catagenesis Metagenesis Progressive Burial and Heating

69 Reservoir rock Seal Migration route Oil/water contact (OWC) Hydrocarbon accumulation in the reservoir rock Top of maturity Source rock Fault (impermeable) Generation, Migration, and Trapping of Hydrocarbons

70 Cross Section Of A Petroleum System Overburden Rock Seal Rock Reservoir Rock Source Rock Underburden Rock Basement Rock Top Oil Window Top Gas Window Geographic Extent of Petroleum System Petroleum Reservoir (O) Fold-and-Thrust Belt (arrows indicate relative fault motion) Essential Elements of Petroleum System (Foreland Basin Example) (modified from Magoon and Dow, 1994) OO Sedimentary Basin Fill O Stratigraphic Extent of Petroleum System Pod of Active Source Rock Extent of Prospect/Field Extent of Play

71 Hydrocarbon Traps Structural traps Stratigraphic traps Combination traps

72 Structural Hydrocarbon Traps Salt Diapir Oil/Water Contact Gas Oil/Gas Contact Oil Closure Oil Shale Trap Fracture Basement (modified from Bjorlykke, 1989) Fold Trap Seal Oil Salt Dome

73 Oil Sandstone Shale Hydrocarbon Traps - Dome Gas Water

74 Fault Trap Oil / Gas Sand Shale

75 Oil/Gas Stratigraphic Hydrocarbon Traps Uncomformity (modified from Bjorlykke, 1989) Unconformity Pinch out

76 Uranium deposit formation Uranium deposit Uranium Ore Transported as U +6 (uranyl) Deposited as U +4 (uraninite)

77 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 rock Hydrocarbon expulsion Hydrocarbon migration Hydrocarbon accumulation Hydrocarbon retention (modified from Demaison and Huizinga, 1994)

78 Cross Section Of A Petroleum System Overburden Rock Seal Rock Reservoir Rock Source Rock Underburden Rock Basement Rock Top Oil Window Top Gas Window Geographic Extent of Petroleum System Petroleum Reservoir (O) Fold-and-Thrust Belt (arrows indicate relative fault motion) Essential Elements of Petroleum System (Foreland Basin Example) (modified from Magoon and Dow, 1994) OO Sedimentary Basin Fill O Stratigraphic Extent of Petroleum System Pod of Active Source Rock Extent of Prospect/Field Extent of Play

79 Hydrocarbon Traps Structural traps Stratigraphic traps

80 Structural Hydrocarbon Traps Salt Diapir Oil/Water Contact Gas Oil/Gas Contact Oil Closure Oil Shale Trap Fracture Basement (modified from Bjorlykke, 1989) Fold Trap Seal Oil Salt Dome

81 Oil Sandstone Shale Hydrocarbon Traps - Dome Gas Water

82 Fault Trap Oil / Gas Sand Shale

83 Oil/Gas Stratigraphic Hydrocarbon Traps Uncomformity (modified from Bjorlykke, 1989) Unconformity


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