BACKGROUND:

FORMATION AND CLASSIFICATION OF MINERAL DEPOSITS

Remote SensingGeophysics

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 SensingGeophysics

Geochemistry

Geology

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

SOME TERMSMagmatic - 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.

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 water• Meteroric• Connate• Metamorphic• Juvenile (Magmatic)

- 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.

FUMNDAMENTAL PROCESSES OF FORMATION OF ECONOMIC MINERAL DEPOSITS

PRIMARY PROCESSES• MAGMATISM• SEDIMENTARY (includes biological)• HYDROTHERMAL• COMBINATIONS OF ABOVE

SECONDARY PROCESSES• MECHANICAL CONCENTRATION• RESIDUAL CONCENTRATION

 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

CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS

• MAGMATIC

• MAGMATIC HYDROTHERMAL• Porphyry 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 HYDROTHERMAL• SEDEX 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)

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)

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 atype of metal sulfide ore deposit, mainly Cu-Zn-Pb, which are associated with and created by volcanic-associated hydrothermal events in submarine environments.

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

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)

CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS

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)

SECONDARY DEPOSITS:

Formed by concentration of pre-existing deposits

• MECHANICAL CONCENTRATION• RESIDUAL CONCENTRATION

CLASSIFICATION OF ECONOMIC MINERAL DEPOSITS

FORMATION OF MINERAL DEPOSITS

COMPONENTS

Ligand source

Metal source

Model I

Model III

Trap Region

Energy(Driving Force)

Transporting fluid

ResidualFluid Discharge

No Deposits

Mineral System

(≤ 500 km)Deposit Halo

Deposit(≤ 10 km)

(≤ 5 km)

1. Energy 2. Ligand 3. Source 4. Transport 5. Trap 6. OutflowIN

GRED

IEN

TS

GOLD DEPOSIT FORMATION

DistalMagmaticFluid

Fluid from Subcreted Oceanic Crust

Metamorphic Fluid

Metamorphic Fluid

SOURCE

FLUID PATHWAY

TRAP

Granulite

Amphibolite

Mid -Greenschist

Volcanic Rock

Dolerite

Sedimentary Sequence

Granite I

GraniteII

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 – 200-400 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)

Orogenic gold deposits characteristics

• High Au (> 1 PPM) and Ag; Au/Ag ≈ 5 • Associated with

– hydrated 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)

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)0

• Hydrothermal fluids are:– aqueous (H2O)-CO2-CH4

– dilute– carbonic– having low salinity (<3 Wt% NaCl)– Source rocks – typically crustal rocks (granites)

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.

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

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

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

LEAD-ZINC SULFIDE DEPOSITS

100m

60 km 10-100 km

LEAD-ZINC SULFIDE DEPOSITS – SEDEX or Sedimentary Exhalative Deposits

PbClx(2-x) + H2S PbS +2H+ + xCl-

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 plumbingsystem

Deep level magma chamber

CSIRO, Australia Slide

30-40 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.

Uranium deposit formation

Uranium deposit

Uranium Ore

Transported as U+6(uranyl)

Deposited as U+4

(uraninite)

Coal, Oil And Natural Gas FormationThe 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.

Difference between coal and oilCrude 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

Oil And Natural Gas Formation

Kerogen

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)

• http://www.sciencelearn.org.nz/Contexts/Future-Fuels/Sci-Media/Animations-and-Interactives/Oil-formation

Cross Section Of A Petroleum System

Overburden Rock

Seal Rock

Reservoir Rock

Source Rock

Underburden Rock

Basement RockTop Oil WindowTop Gas Window

Geographic Extent of Petroleum System

Petroleum Reservoir (O)

Fold-and-Thrust Belt(arrows indicate relative fault motion)

EssentialElements

ofPetroleum

System

(Foreland Basin Example)

(modified from Magoon and Dow, 1994)

O O

Sedi

men

tary

Bas

in F

ill

O

Stratigraphic Extent of

PetroleumSystem

Pod of ActiveSource Rock

Extent of Prospect/FieldExtent of Play

Hydrocarbon Traps

• Structural traps

• Stratigraphic traps

Structural Hydrocarbon Traps

SaltDiapir

Oil/WaterContact

GasOil/GasContact

Oil

ClosureOilShale Trap

Fracture Basement

(modified from Bjorlykke, 1989)

Fold Trap

Seal

OilSalt

Dome

Oil

Sandstone Shale

Hydrocarbon Traps - Dome

Gas

Water

Fault Trap

Oil / GasSand

Shale

Oil/Gas

Stratigraphic Hydrocarbon Traps

Uncomformity

(modified from Bjorlykke, 1989)

Unconformity