Mineral Systems & Ore Deposits

Mineral Systems & Ore Deposits

• Ore involves a metalliferous mineral, mixed with gangue, able to be won at a profit by miners or treated at a profit by metallurgists
• A byproduct refers to a subsidiary material ore mineral worked from ore deposits where other materials are dominant.
• Ore definitions emphasize the material from which a metal is extracted must be a profit-making operation
• Economically mineable aggregates or ore minerals form orebodies, ore shoots, ore deposits, or ore reserves
• Clarke Value or Approximate Crustal Abundance signifies the relative abundance of a chemical element in Earth's crust
• Typical Exploitable Grade indicates the average grade of a metal needed to become ore
• Approximate Concentration Factor refers to the level of enrichment needed compared to crustal abundance

Requirements for Ore Deposit Formation

• Four geological requirements for ore deposit formation include:
• A source for ore components (metals and ligands)
• A transport mechanism for these components to the ore deposit site
• A depositional mechanism (trap) to fix the components as minerals and associated gangue
• A preservation process or geological setting
• Ore deposits are classified based on the deposit’s composition, form(size, shape, orientation, ore mineral distribution), host rocks/geological structures, and genesis
• Syngenetic deposits form with the enclosing rocks and are commonly stratabound or layered
• Epigenetic deposits are introduced into pre-existing rocks
• The distribution of a particular ore depends on geological processes, specific sources, transport modes with carrier-agents, traps and precipitation mechanisms, and other pressure-temperature conditions

Earth Systems

• Processes generating metals usually start within the mantle and/or core
• Solid earth divides into the core of iron and related elements, mantle of ultramafic rocks (Cr, Co, Ni), and crust
• Oceanic crust is 0-10 km thick (mafic rocks – basalts) where deposits such as black smokers can form
• Continental Crust: 20–70 km thick felsic igneous, metamorphic, and sedimentary rocks (Mn)
• Earth consists of the atmosphere, hydrosphere, biosphere, and lithosphere, with mineral deposits located in the lithosphere

Geological Processes Forming Mineral Deposits

• Magma is naturally occurring mobile rock material
• As magma cools, it crystallizes/separates into fractions through fractional crystallization or igneous differentiation
• Metallic elements concentrate by rock-forming mechanisms in resulting igneous assemblages
• Subsurface magmatic and hydrothermal processes involve chemical changes in rocks/minerals resulting in the concentration of dispersed compounds into ore minerals

Hydrothermal Processes

• Water and magmas are effective agents for chemical changes, dissolving elements and crystallizing minerals.
• Hydrothermal solutions exist as hot, mineral rich fluids in the Earth's crust.
• The metal source is from magmatic, metamorphic devolatilization, and/or leaching of rocks.
• Fluids are transported through metamorphic, meteoric, and/or seawater.
• Fluid movement facilitates formation of massive, disseminated veins, stockwork breccia, and replacement orebodies.
• Hydrothermal fluids alter surface rocks referred to as hydrothermal alteration, which is looked for during exploration.
• Precipitation mechanisms involve cooling, boiling, decompression, fluid mixing, and redox-p/fluid-rock reactions.
• Hydrothermal ore deposits can be broken into:
• Vein or stockwork systems where solutions deposit ore minerals in brittle structures or cavities
• Replacement deposits where solutions react with host rocks, replacing silicates and carbonates with new gangue and ore minerals

Magmatic Processes

• Primary dispersion patterns associated with hydrothermal fluid movement through host rocks.
• Magmatic ore formation involves crystallization of ore minerals in silicate melt or sulphide-oxide phases with separation and concentration of ore minerals.
• The process initializes with mantle/crustal melting forming silicate or sulphide-oxide phases
• The magma is emplaced within a shallow crust, intrudes, and crystallizes as a silicate melt
• Pressure and temperature then segregates sulphides and oxides via mineralizers
• Eventually magmatic ore injection happens, until the orebody extrudes through surface
• Ore bearing magmas and fluids include:
• Silicate-dominated magmas
• Hydrothermal fluids (meteoric waters, seawater and connate waters
• Surface ore forming processes involve water (hydrothermal) and magmas.

Primary & Secondary Dispersion

• Primary ore dispersion occurs during the formation of the deposit, either above or below the Earth's surface
• Primary dispersion patterns include the sub-ore grade portion and related zones of non-ore element enrichment/depletion.
• The primary dispersion patterns are a function of the ore-forming process, host rock types, and controlling structures, and are critical in exploration
• Secondary ore dispersion occurs after deposit formation, resulting in larger dispersion halos
• A dispersion halo is a zone around a mineral deposit with lower metal values than the deposit but higher than background values in surrounding country rocks

Hydrothermal Fluid Types

• Hydrothermal fluids are a major transport medium in ore systems
• Hydrothermal fluids are derived from seawater, connate waters, meteoric waters, and metamorphic fluids
• Water is the principle mobile constituent in all magmas

Meteoric Waters

• Meteoric water is water that has passed through and equilibrated with the atmosphere such as rainwater or river water.
• Downward penetrating surface water meets the upward flowing magmatic water, creating deposits
• Meteoric waters have low amounts of ions and metals, however, causes processes such as boiling, creating metals to precipitate
• Seawater is described in the context of evaporates, phosphorites, and submarine exhalates
• It is associated with VHMS and sedimentary iron deposits
• Black smokers are rich in metals and are magmatic fluid which penetrates the seafloor and mixes with the seawater, creating metal precipitation and sedimentation processes
• Connate Waters are water trapped in sediments at deposition and are associated with Pb-Zn MVT Type Deposits
• Metamorphic fluids are the fluids released during metamorphism
• Volatile and mobile metal constituents are activated during metamorphism and migrate towards fault zones

Surface Processes

• Weathering creates laterite deposits or Nickel, Bauxite, Gold and Clay
• Physical sedimentation creates placer deposits of Gold, Platinum, Diamond, Ilmenite, Rutile, Zircon, Sand and Gravel, and Dune Deposits Sand
• Chemical Sedimentation creates Evaporite Deposits (Halite, Sylvite, Borax, Trona), Chemical Deposits of Iron, VHMS, and SEDEX deposits
• Organic Sedimentation creates Hydrocarbon Deposits(Oil, Natural Gas, Coal) and other deposits like Sulphur and Phosphate

Primary Geochemical Dispersion Around Major Ore Deposit Types

• Magmatic Deposits have gradational ore element concentrations, which reflect incomplete ore mineral segregation

• Skarn Deposits have distinctive mineral zoning related to thermal and chemical gradient, plus ore element patterns related to prograde vs retrograde evolution

• Hydrothermal Stockwork/Porphyry Deposits possess broad, diffuse patterns of element dispersion with metal zoning, together with wall rock alteration

• Hydrothermal Vein Deposits show narrow patterns of element dispersion, which depends on host rock permeability and chemistry

• As well, wall rock alteration may be distinctive or extensive

Classification Of Metallic Ore Deposits

• Metallic ore deposits are classified by descriptive classification (structure, alteration), genetic classification, Commodity-Based Classification, plate tectonics, fluid classification, and mineral system classification

Genetic Classification

• A metalloid is a chemical element that shares properties with metals and non-metals
• Orthomagmatic deposits are mineral deposits formed directly from the crystallization of mafic or ultramafic magmas. This magma can be:
• Mafic Magmas, rock rich in magnesium and iron
• Ultramafic Magmas, rock richer in magnesium and iron with lower silica content
• Felsic magmatic deposits are mineral deposits associated with silica-rich, felsic magmas. For example, felsic magma include granite
• A hydrothermal deposit is a mineral deposit formed by the precipitation of minerals from hot, mineral-rich fluids that flows through fractures and porous rocks

Ore Deposit Types

• VHMS yields Cu, Pb, Zn from Seawater
• SEDEX yields Pb-Zn from Basinal Brines
• BHT yields Pb, Zn during metamorphism
• MVT yields Pb-Zn-Ag from Basinal Brines
• BIF yields Fe from Basinal Brines and meteoric activity
• Orogenic yields Au from magmatic, metamorphic, and meteoric conditions
• Porphyry yields Cu-Mo-Au from magmatic and meteoric conditions
• Epithermal yields Au-Ag from magmatic and meteoric conditions
• Skarn yields Cu, Au from magmatic and meteoric conditions
• Komatiite-Hosted yields Ni
• Layered Intrusions yield PGE
• Diamonds originate from C
• Carbonatites yield P, Cu, Fe, etc.
• Greisen yields Sn-W
• Pegmatites yield Li
• Industrial minerals are mined geological materials for commercial value, not fuel or metal
• Deposit models derive from deposit-scale observations:
• Often focus on one aspect of a system
• Often include too many variations on a theme making applications impractical

Mineral Systems Approach

• Ore deposits derive from geological processes at larger scales than the depositional site
• When mapped out the mineral system provides a larger exploration target that can extend 10-100's of km around the deposit.
• A mineral system encompasses all geological factors that control the generation and preservation of mineral deposits
• The mineral system stems from the “petroleum system,” where oil and gas had a much larger success rate than mining.
• Compared to petroleum systems the processes forming economic concentrations in mineral systems differ and seals are not applicable, necessitating passages of large fluid volumes through the trap site which is more complex.

Geological Factors Defining Mineral Systems

• Sources of mineralizing fluids/transporting ligands
• Sources of metals and other ore components
• Migration pathway
• Thermal gradient
• Energy sources
• Mechanical and structural focusing mechanism
• Chemical/physical traps

Mineral System Elements

• Metal and Fluid mobilization by an energy source, Magmatism and metamorphism
• Migration of metal rich fluids through fluid pathways
• Deposition, metals precipitate due to fluid mixing or fluid-rock interactions, forming ore deposits at camp-scale or deposit scale.
• Outflow where residual fluids exit the system which potentially causes further phase separation.
• Mineral system types are subdivided into orthomagmatic (mafic-ultramafic), felsic magmatic, hydrothermal, sedimentary environment types

Critical Elements of a Mineral System

• Trigger in a mineral system involves tectonic events that trigger and define temporal windows for mineralizing events
• Source involves geochemical and tectonic processes that produce source regions enriched in metals and hydrothermal fluids/magmas
• Pathways are processes that produce conduits act as pathways that provides conduits for hydrothermal fluid
• Driver involves processes that cause fluid flow
• Throttle are mechanisms that concentrates the flow of fluids/magmas onto depositional sites
• Trap/Depositional Sites involve geochemical (fluid/magma mixing, fluid-rock interaction, etc) processes that operate at the trap that deposit metals out of fluids
• Dispersion is the geochemical process that operates during and after deposition of hydrothermal alteration of minerals to produce detectable anomalies
• Preservation/Upgrading are processes that exhume, enhance preservation, and upgrade mineralized material after deposition
• Advantages of the mineral system approach are: Focuses on critical geological processes, not restricted to descriptive elements, explains the spatial and temporal occurrence of deposits and is applicable to mineral systems of the same age
• Challenges of the mineral system approach are: defining targeting criteria, uncertainty in exploration, modeling mutual dependencies

Recent Developments in Mineral Systems

• Scale dependency of systems
• Whole-of-lithosphere composition/tectonic architecture as factors
• Long-lived deep crustal domain boundaries
• Uncertainty
• Self-organized criticality

Knowledge Gaps in Mineral Systems

• The application of mineral system approach extends to sediment-hosted mineral deposits, sedimentary mineral systems, constraint on geodynamic setting, definition on overprinting, translation on exploration, and exploration targeting.

Mineral System Types and Elements

• Orthomagmatic triggers arise from mantle plumes/early rift zones
• Orthomagmatic sources are magma that originated deep in the convective mantle
• Orthomagmatic pathways are transcrustal faults
• Orthomagmatic drivers is the buoyancy of the magma column
• Orthomagmatic throttles are transcrustal dykes and magma emplacement in the crust
• The hydrothermal trigger are tectonic events
• Hydrothermal sources involve mantle/magmas
• Hydrothermal pathways involve any open and permeable zone
• Hydrothermal throtttles involve structures that causes seismic pumping coupled with fault valve behaviour
• Traps occurs through magma emplacement with redox and disequilibrium process

Dispersion

• In orthomagmatic systems dispersion includes platinum group element (PGE) enrichment in host komatiites
• In hydrothermal systems dispersion includes hydrothermal alteration, which is influenced by temperature, pressure, host rock and fluid composition
• Preservation/Upgrading and Magmatism
• A dyke is a vertical or steeply inclined sheet of intrusive igneous rock that cuts across pre-existing rock layers

Scales Within the Mineral Systems Approach

• Regional Scale (Data Mining and Testing Remote Sensing) encompasses large areas on tectonic settings
• District Scale focuses on smaller regions
• Camp/Deposit Scale 3D Visualization and Studying Structural Controls & Alteration represents deposits within a district
• Sample Scale (Petrography, Geochemical Anomalies, Mass Balance)
• Deposit Scale focuses on individual orebodies
• Mineral Scale (Mineral Chemistry, Elementary Mapping)

Application of Mineral Systems

• The mineral system approach considers deposits driven by regional-scale geological processes with generic identification of mineral provinces:
• Larger scales (Relationships between tectonism and metallogeny)
• Smaller scales (Relationships between deposits and anomalies)
• Gold deposits geometry controlled by folds and faults

Gold Mineral Systems

• Magmatic-Meteoric Hydrothermal Systems include Porphyry, Skarn, Epithermal, Carbonate, Replacement, and Carlin Type Au
• Magmatic-Connate/Brine Hydrothermal Systems include Iron-Oxide-Copper-Gold (IOCG)
• Multiple Hydrothermal Systems include Orogenic.
• Seafloor Hydrothermal Systems includes VHMS
• Biogene/Sedimentary Hydrothermal Systems are Witwatersrand-Type
• Types include Orogenic, Epithermal, Porphyry, Skarn, Carlin-Type, Placer, and VHMS-SEDEX
• Orogenic gold systems are structurally controlled deposits formed from hydrothermal fluids
• They are controlled by the epigenetic type and formed from regional metamorphism precipitating gold due to pressure drops and fluid-rock interactions
• They are commonly located along major fault zones and are most common in WA.
• Pre-Cambrian times had the potential for orogenic gold systems which is dependant on depth and contains minimal base metals .

Orogenic Gold System Characteristics

• Located at or near terrane boundaries
• Hosted in volcano-sedimentary rocks and granites
• Changes from compression to transpression
• Has strong structural control
• Large vertical extent
• Upper to mid-crustal level
• Additions of SiO2, K, Na, CO2
• Low salinity ore fluid
• Mixed / multiple fluid source
• Mesothermal refers to a moderate temperature climate
• Porphyry gold deposits are large, low-grade formed by magmatic fluids when released into rock
• As fluids cool, gold and other metals precipitate along fractures creating low-grade deposits
• Archean were the shallow surface
• Skarn is mineralization between a granite and carbonate-rich unit at elevated temperatures
• Endo-skarn deposits are inside the intrusive contact
• Exo-skarn deposits are outside the intrusive contact

Skarn Classification

• Reduced Gold Skarns are Gold-bearing skarn deposits associates with mafic plutons in a reducing environment subdivided into outer deposits and inner deposits
• Gold Skarns in metamorphic terrains stable in high temperature, reduced FeO2 conditions and are rich in sulphur
• Oxidized skarn gold deposits are gold-rich deposits interacting with sediments in a oxidizing environment

Epithermal Gold Systems

• Epithermal gold systems are shallow deposits formed at low temperatures because of conditions in metal-rich fluids
• High Sulfidation, deposits are low grade, high tonnage sulphide (enargite) with zoned veins in andesite arcs and adjacent porphyries
• Intermediate Sulfidation, contains high grade with bonanzas
• Volcanogenic hosted massive sulphide gold systems are formed by the deposition of gold where fluid vent through floor and form sulphide-rich deposits located at plate boundaries.
• Carlin gold systems are sediment-hosted
• Iron-Oxide-Copper-Gold (IOCG) are deposits formed by fluids in fault-controlled settings
• Placer systems are eroded from primary systems
• Supergene systems are weathered from primary systems and are formed in long-lived land surfaces

Gold System Trap Sites At Various Scales

• At the Camp scale, trap sites are commonly linked to faults, inhomogeneities with sources originating from carbon with metamorphism
• At the Deposit scale, control includes rock behavior
• Depsite Scale: epizoal, mesozonal and hypozonal are at different depths within the crust
• Extention viens, Obique extention viens and fault fll veins
• Stockworks are veins
• Ovre shoots

Types of Geometry

• Includes complexity, rock formation, rhelogical
• Hydrothermal mineral systems are igneous rock characterized by crystal

Hydrothermal Mineral Systems

A porphyry is an igneous rock containing crystals that go through the processes of slow colling at dept, followed by rapid cooling near the surface characterized by extensive hydrothermal rock altheration. Scattered or restricted to quartz veins. Porphyrys hosts at intrusion. Stockwork more imporation. It associated with multipule intrusions creating alteration zones.

Porphyry Characteristics

• They include a capacity to absolue metal which is dependant on emplacement with certain veint types (A, B and D) Tin deposits occur without postassium

Stratiform Systems

• Formed of sediment and volcanolic environment. MVT are formed of basnial brines through fractures carbonate dominattion

Orthomagmatic Deposits

• Genesis the function of orthomagmatic occurs in matic and ultramafic. Comes in different types include chromoum nicel and cupersd and the only srounce of ge

Sulphide Systems

Occrus through enrichment Forms when magma accends Magenetic mineral process happens through the scregation of liquid Then bracken depending on material Come from plunes and from zones containing thin lithosphere

• Eaglekaltonke

They include komatle, and are the result of eruptions With the formation with suflier There is serpentine in kamblee

magments with magmatic nickel deposit , are formed at the base of chambers the commonty is related to kamattite Sudburg forms a mafic system from a meteor.