Lectture-2-Metalliferous-Deposits.pdf

METALLIFEROUS ORE DEPOSITS INTRODUCTION Knowledge in metalliferous ore deposits is a key tool in mineral exploration & metal mining Philippines is a key study center for ore deposits Cu-Au systems ❑Porphyry Cu, skarn & epithermal Au-base metal Podiform chromite Ni lateri...

METALLIFEROUS ORE DEPOSITS INTRODUCTION Knowledge in metalliferous ore deposits is a key tool in mineral exploration & metal mining Philippines is a key study center for ore deposits Cu-Au systems ❑Porphyry Cu, skarn & epithermal Au-base metal Podiform chromite Ni laterites Minor in VMS OUTLINE Introduction – definitons, role of mineral resources, history & dev’t of study of ore deposits Exploration-mining stages, PMRC code, resources/reserves estimation Fundamentals Classification of Ore Deposits DEFINITIONS DEFINITIONS Ore – rocks or minerals that are mined, processed & delivered at a profit Categories – metallic, non-metallic, energy and water Gangue – non-valuable minerals in the ore, eg. silica-clay in gold veins Protore – mineralized rock that is too lean in ore minerals to yield a profit Waste - non-valuable portion of ore DEFINITIONS – CON’T Mineral Deposit – concentration of ore minerals Ore Deposit (or Orebody) – concentration of ore minerals which certain elements can be recovered economically Cut-off Grade – lowest grade, or quality, of mineralized material that qualifies as economically mineable and available in a given deposit Clarke of Concentration – average content of an element in the earth’s crust DEFINITIONS – CON’T Syngenetic ore – ore formed as the same time as the host rock Epigenetic ore – ore formed after the host rock Hypogene ore – ore formed within the earth Supergene ore – ore formed at the earth surface Primary ore – ore formed from either magmas or fluids Secondary ore – ore formed as a consequence of alteration of pre-existing minerals DEFINITIONS – CON’T Syngenetic ore – ore formed as the same time as the host rock Epigenetic ore – ore formed after the host rock Hypogene ore – ore formed within the earth Supergene ore – ore formed at the earth surface Primary ore – ore formed from either magmas or fluids Secondary ore – ore formed as a consequence of alteration of pre-existing minerals DEFINITIONS – CON’T Hydrothermal Deposita Orogenic Goldb Temp (oC) Pressure Type Type Depths (km) Temp (oC) 50-200 Moderate Epithermal Epizonal 12 >475 a Lingren (1933). Epithermal Type currently increased to 300oC b Goldfarb et al. (2005) ROLE OF MINERAL RESOURCES ROLE OF MINERAL RESOURCES Fundamental in modern society – “When it can’t be grown, it must be mined” National development – self-sufficiency in resources is a key strategy of governments In the 1980s, Philippines was in the top 10 countries in Au, Cu, Cr and Ni production Today, Philippines is no longer a strong mineral producer EXPLORATION – MINING STAGES  EXPLORATION STAGES (1) GRASSROOT TARGET TARGET DELINEATION FEASIBILITY EXPLORATION GENERATION TESTING DISCOVERY!! DRILLING STUDY REMOTE PROPERTY DETAILED OREBODY BULK SENSING GENERATION GEOSCIENCE MODELING METALLURGICAL SURVEYS TESTING >1:5,000 SCALE AIRBORNE PROPERTY RESOURCE GEOTECHNICAL GEOPHYSICS ACQUISITION TRENCHING / ESTIMATION STUDY TEST PITTING REGIONAL SEMI- “AT LEAST 3 INITIAL MINING / GEOSCIENCE DETAILED HOLES METALLURGICAL PROCESSING SCOUT HITTING ORE SURVEYS GEOSCIENCE DRILLING TESTING STUDY 1:50,000 SCALE SURVEYS OVER ~1:10,000 SCALE ECONOMIC WIDTHS” MINING ENVIRONMENTAL ADITING / SCOPING EIA / EIS / EMP SHAFTING STUDY (optional) ECONOMIC ENVIRONMENTAL STUDY BASELINE STUDY GOVERNMENT / COMMUNITY PERMITING  MINING STAGES (2) DEVELOPMENT MINING MINE CLOSURE 1-4 years 3 - >10 years 5 - 10 years MINERAL RESOURCES & ORE RESERVES - CODE, CATEGORIES & ESTIMATION PMRC CODE PMRC Code of 2007 – “Philippine Mineral Reporting Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves” an initiative of the Philippine Minerals Development Institute Foundation (PMDIF) together with The Philippine Stock Exchange, Inc. (PSE), Mines and Geosciences Bureau (MGB) of the Department of Environment and Natural Resources, Chamber of Mines of the Philippines (COMP), Philippines- Australia Business Council (PABC) and the Board of Investments (BOI) of the Department of Trade and Industry. The formulation of the technical provisions of the code was undertaken by the Professional Regulation Commission’s (PRC) accredited professional organizations of the minerals industry which are the Philippine Society of Mining Engineers (PSEM), Geological Society of the Philippines (GSP), Society of Metallurgical Engineers of the Philippines (SMEP) and chaired by the PMDIF  PMRC CODE – CON’T Provides the guidelines on the Reporting for all deposit types except petroleum & gas to the Philippine Stock Exchange (PSE) Main principles Transparency – sufficient information, clear & unambiguous presentation of data, not misleading to the readers of the “Public Report” Materiality – Report contains all relevant info for the readers to make reasoned & balanced judgement of the Public Report Competence – Public Report is based on work of “Competent Persons”  PMRC CODE – CON’T Public Reports – are the responsibility of the public company thru its Board of Directors & based on info & supporting documentations prepared by “Competent Person(s)” Competent Person – is a member of PSEM, GSP or PSME, duly accredited by the professional organization to w/c he/she belongs or a “ROPO” included in the list promulgated as the need arises ROPO – Recognized Overseas Professional Organization RESOURCES/RESERVES CATEGORIES Exploration Results Mineral Resources Ore Reserves Inferred Increasing level of Indicated Probable geological knowledge and confidence Measured Proved Consideration of mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors (the “Modifying Factors”) General relationship between Exploration Results, Mineral Resources and Ore Reserves EXPLORATION RESULTS / MINERAL RESOURCES - DEFINITIONS Exploration Results – data, information & reports generated by exploration programmes that may be of use to investors &/or their financial advisers Mineral Resource – a concentration or occurrence of material of intrinsic economic interest in or on the Earth’s crust in such form, quality and quantity that there are reasonable prospects for eventual economic extraction The location, quantity, grade, geological characteristics and continuity of a Mineral Resource are known, estimated or interpreted from specific geological evidence, sampling and knowledge 3 Categories in order of increasing geological confidence – Inferred, Indicated & Measured categories MINERAL RESOURCES - DEFINITIONS Inferred Mineral Resource - tonnage, grade and mineral content can be estimated with a low level of confidence It is inferred from geological evidence, sampling and assumed but not verified geological and/or grade continuity It is based on information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes which may be limited or of uncertain quality and reliability MINERAL RESOURCES - DEFINITIONS Indicated Mineral Resource - tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a reasonable level of confidence It is based on exploration, sampling and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes The locations are too widely or inappropriately spaced to confirm geological and/or grade continuity but are spaced closely enough for continuity to be assumed MINERAL RESOURCES - DEFINITIONS Measured Mineral Resource - tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a high level of confidence It is based on detailed and reliable exploration, sampling and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes The locations are spaced closely enough to confirm geological and grade continuity. ORE RESERVES - DEFINITIONS Ore Reserve - economically mineable part of a Measured and/or Indicated Mineral Resource It includes diluting materials and allowances for losses, which may occur when the material is mined Appropriate assessments to a minimum of a pre-feasibility study have been carried out, and include consideration of, and modification by, realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors In the case of integrated mining operations, the pre-feasibility study will have determined an ore treatment plan that is technically and commercially viable and from which the mineral recovery factors are estimated. These assessments demonstrate at the time of reporting that extraction could reasonably be justified 2 Categories in order of increasing confidence – (1) Probable Ore Reserves & (2) Proved Ore Reserves. ORE RESERVES - DEFINITIONS Probable Ore Reserve - the economically mineable part of an Indicated, and in some circumstances, a Measured Mineral Resource Includes diluting materials and allowances for losses which may occur when the material is mined Appropriate assessments to a minimum of pre-feasibility study have been carried out, and include consideration of and modification by realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors ORE RESERVES - DEFINITIONS Proved Ore Reserve - economically mineable part of a Measured Mineral Resource Includes diluting materials and allowances for losses which may occur when the material is mined Appropriate assessments to a minimum of pre-feasibility study have been carried out, and include consideration of, and modification by, realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors STEPS IN MINERAL RESOURCES/ ORE RESERVES ESTIMATION RESOURCE/ RESERVE ESTIMATION PROCESS Geological Modeling – data consolidation & interpretation to explain the geology and mineralization controls Production of cross sections and level plans Production of schematic sections showing the geology-mineralization w/ respect to time  RESOURCE/ RESERVE ESTIMATION PROCESS Estimation Methods Polygonal estimation – polygons drawn around individual data points ❑ By plan or levels ❑ By cross sections Block modeling – dividing the deposit into series of rectilinear blocks ❑ Averaging of data points inside a block ❑ Rolling mean approach ❑ Inverse distance weighting RESOURCE/ RESERVE ESTIMATION PROCESS Estimation Methods (Con’t) Geostatistics – branch of statistics focusing on spatiotemporal data sets ❑Variograms – “basic tool” providing a statistical measure of maximum distance that can be used in inverse distance weighting at any given direction ❑Kriging – “elegant class of inverse-distance weighting” ❖ Using weighing factors determined from the mathematical expression of the variogram model equations ❖ Provides a value for the estimation variance which conventional estimation can not do – “Standard Error” FUNDAMENTALS OF METALLIFEROUS DEPOSITS FUNDAMENTALS Ore-bearing Fluids Movements of Ore-bearing Fluids Ore Deposition Wallrock Alteration Paragenesis & Zoning Geothermometry, Geobarometry & Isotope Studies ORE-BEARING FLUIDS  ORE-BEARING FLUIDS Transporting media are liquids or gases All ore-formation processes are intimately associated with the movement of fluids Confirmed by examination of the ores themselves, the accompanying gangue, lab studies of synthetic systems, fluid inclusion, isotopic & geochemical studies  TYPES OF ORE-BEARING FLUIDS Magmatic Fluids Hydrothermal Fluids Meteoric Waters Sea Water Connate Waters Metamorphic Fluids ORE-BEARING FLUIDS Magmatic Fluids Magma is a high-temperature rock melt of liquid and crystals. Solidification produces igneous rocks Magma is not homogeneous, composition is constantly changing, subjected to continuous conventive overturn and mixing, it fractionates upon cooling, metallic minerals can be concentrated by rock-forming mechanisms such as fractionation, crystal settling, filter pressing, liquid immiscibility ❑Ultramafics - enriched in Cr, Ni, PGE ❑I-type Granites – enriched in Cu-Mo-Zn-Pb-Ag-Au ❑S-type Granites – enriched Sn-W-Be-U-Li ORE-BEARING FLUIDS – CON’T Hydrothermal fluids – formed from continuous cooling, differentiation and crystallization of intermediate to silisic magmas Accumulate at the top of the magma chamber Consists of lighter, more alkalic, and more hydrous volatile fractions along with compounds that crystallize at lower temperature Addition of Cl to water increases dramatically the metal concentrations in solution, eg. 10s of ppms of metals ❑ Chalcophile elements – Cu, Pb, Zn, Ag, Au, As, S etc ❑ LIL (Large Ion Lithophile) – Li, Be, B, Rb & Cs ❑ Alkalies, alkali earths & volatiles – Na, K, Ca, Cl, CO 2, H2O (1-15% of magma), F, P Trapped in fluid inclusions – contains gases and/or liquids during time of ore  ORE-BEARING FLUIDS – CON’T Meteoric Waters – any water that passed thru & equilibrated with the atmosphere Contains N, O, CO 2 , (HCO3)-, H+ and traces of rare gases Important in – ❑ Supergene processes ❑ Mixing with magmatic hydrothermal fluids due to downdraw by convective circulation ORE-BEARING FLUIDS – CON’T Sea Water – involved in formation of evaporites, phosphorites, submarine exhalatives, Mn nodules & oceanic crust deposits Connate Water – “fossil water” trapped in sediments at the time they were deposited Out of contact with atmosphere for an appreciable part of a geologic period Rich in Na & Cl, contain Ca-Mg-HCO3 & many contains Sr-Ba- N Important in Mississippi Valley-type Pb-Zn ores ORE-BEARING FLUIDS – CON’T Metamorphic Fluids – connote and meteoric waters enclosed in rocks buried below the surface of the earth & subjected to heat and pressure accompanying magmatic intrusion or low- to moderate-grade regional metamorphism Volatile & mobile constituents are activated during metamorphism and forced from the rock to migrate toward cooler and, in general, less deformed regions. Contains water, soluble salts, Cl and can remove and transport metals from the host rocks. MOVEMENT OF ORE-BEARING FLUIDS MOVEMENT OF ORE-BEARING FLUIDS Knowledge of the paths traveled by the ore fluids and the mode of ore emplacement is fundamental Obeys precepts of geohydrology governed by avenues of net permeability to the fluid dictated by its viscosity & density, the abundance of interconnected pores, fractures or fault planes, pressure gradients, & time. Obeys the rules of igneous petrology TYPES OF MOVEMENT OF ORE-BEARING FLUIDS Migration of Magmas Migration of Hydrothermal Fluids MIGRATION OF MAGMA Magmas move – not static bodies Bouyant & emplacement guided by major structures Important modes of movement for ore formation filter pressing – partly crystallized magma, subjected to differential external stresses, can cause the fluid fraction to be squeezed away from the crystalline mush late-liquid gravitative accumulation – sinking of globules of a heavy liquid formed by immiscibility within and from a parent liquid after some differentiation magmatic injection – residual liquid is squeezed out into the surrounding rocks, eg. magnetite-apatite dike MIGRATION OF HYDROTHERMAL FLUIDS Porosity vs. Permeability Concept Porosity – refers to the ratio of pore volume to total volume, whether these pores are interconnected or not Permeability – capacity to transmit a fluid through the rock across a pressure gradient → important for movement of ore fluids ❑Primary – intrinsic to the rock, eg. conglomerate vs. volcanic flow ❑Secondary – superimposed on the rocks, eg. fault, fold, breccia, foliation, chemical MIGRATION OF HYDROTHERMAL FLUIDS – CON’T Ground Preparation – any process that increases permeability, causes a favorable chemical change, or induces brittleness in the rocks may localize precipitation from ore-bearing fluids → heat, fluids, tectonics or combination Contact metamorphism and ore emplacement may occur sequentially in a limestone section around a cooling pluton, eg. skarn Silicification, dolomitization, recrystallization, decalcification, eg. Carlin-style Au Structural control – very important for epigenetic deposits which are emplaced during a tectonic activity Breccias due to phreatomagmatic, phreatic and hydrothermal processes, eg. breccia pipe-hosted Au-base metal HYDROTHERMAL FLUIDS AT SHALLOW DEPTH At shallow depth, secondary permeability in rocks such as faults is more significant to ore transport and deposition than primary permeability, eg. epithermal Au Aqueous fluids given off by a shallowly intruded stock can also wedge open fractures around it HYDROTHERMAL FLUIDS AT DEPTH Permeability & Porosity decrease with depth because the lithostatic pressure tends to close any opening Given time, ore fluids in large amounts do move through rocks. Secondary permeability features (eg. fault) increase fluid flow at