Lecture 10 - Ore Deposits PDF

Lecture 10 Ore Deposits Definition of Terms ■ Ore - rocks or minerals that are mined 1 processed & delivered at a profit ► Categories - metallic non-metallic energy and water Gangue - non-valuable minerals in the ore 1 eg. silicaclay in Au veins Proto re - mineralized rock that is too lean in ore...

Lecture 10 Ore Deposits Definition of Terms ■ Ore - rocks or minerals that are mined 1 processed & delivered at a profit ► Categories - metallic non-metallic energy and water Gangue - non-valuable minerals in the ore 1 eg. silicaclay in Au veins Proto re - mineralized rock that is too lean in ore minerals to yield a profit Waste - non-valuable portion of ore Mineral Deposit - concentration of minerals Ore Deposit (or Orebody) - concentration of minerals which certain elements can be recovered economically Cut-off Grade - lowest grade1 or quality1 of mineralized material that qualifies as economically mineable and available in a given deposit Clarke of Concentration - average content of an 1 element in the earth s crust 1 ■ ■ ■ ■ ■ ■ ■ 1 Definition of Terms ■ ■ ■ ■ ■ ■ 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 Definition of Terms ■ Resource Geology- the study of geologic materials used by man to facilitate his task. ■ Economic mineral - any geological material which is of commercial value to human society. Ex. Fossil fuels, construction and industrial materials, metals, gemstones, etc. ■ Mineral deposit - accumulations or concentrations of one or more useful substances, metalliferous or non-metalliferous, that are for the most part sparsely distributed in the earth's outer crust. ■ Geologic resource - naturally occurring solids, liquids or gases known or thought to exist in or on the Earth's crust in concentrations which make extraction economically feasible either at present or sometime in the future. ■ Geologic reserve - a subset of a geologic resource; that portion of an identified resource which can be extracted economically using current t echnology. HISTORICAL BACKGROUND ■ Neptunism vs. Plutonism ► Plutonism (Magmatists) ✓ James Hutton (1788-1795 ), Brunner (1801 ), S. Breisla k (1811) ✓ Ores are direct magmatic product or are formed as products if differentiation. ► Neptunism (Syngeneticists) ✓ Abraham Werner (1791), C. Anderson (1809) ✓ Basalt, sandstone, limestone, and ore deposits were formed from sediments in a primival ocean. Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 (DENR), 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 (DTI). 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 Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reserves" ► 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" Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves" Exploration Results Mineral Resources Ore Reserves Inferred r--------- ------- ----- ------ ------ ------ -----, Increasing level of geological knowledge and confidence 1 Indicated Measured • -~ -- _ ~ Probable : -- II I Proved : --------------------------------------------Consideration of mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors ----11 ►► (the "Modifying Factors") ► I I Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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. Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 Reser ves & (2) Proved Ore Reserves. Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 prefeasibility study have been carried out, and include consideration of, and modification by realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors Philippine Mineral Reporting Code (PMRC) ■ PMRC of 2007 - "Philippine Mineral Reporting Code for Reporting of Exploration Results~ Mineral Resources and Ore Reservesn ► 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 prefeasibility study have been carried out, and include consideration of, and modification by, realistically assumed mining, metallurgical, economic, marketing, legal, environmental, social and governmental factors Fundamentals of Ore Deposits Ore ► What is ore ? ■ ■ ■ ■ Rock or mineral that can be mined, processed, and delivered to the market-place or to technology at profit. Rock or mineral with economic value. Rock with a concentration of metal-rich mineral. Sub divided into categories ✓ ✓ ✓ ✓ ✓ Metallic Non-metallic Metal-bearing minerals Energy Water Cl10!Copyrtte molochlle cnrysocolla ozurtte bomife cuprite copper Ore ► Metals ■ ■ ■ ■ Opaque, solid, shiny, smooth, and conductive Metal properties from metallic chemical bonds □ Delocalized electrons move from atom to atom easily □ Electron fluidity creates electrical conductivity Property due to crystal structure and bonding □ May be extremely hard or soft □ Ductile □ Malleable 3 categories of metal □ Native metals - naturally occurs in pure form (ex. Cu, Au, Ag) □ Precious metals - rare and economically important (ex. Au, Ag, Pt) □ Base metals - commonly used in industry (ex. Fe, Pb, Zn, Sn) Ore ► Smelting ■ Process of releasing metal from minerals ► Slag ■ Non metallic wastes •!• Steel is made from iron smelted with carbon •!• Bronze - An alloy of Cu and Sn •!• Brass - Cu alloyed with Zn NAME COMBINATION NAME COMBINATION AL-LI aluminum, lithium, sometimes mercury MAGNOX magnesium oxide, aluminum ALNICO aluminum, nickel, copper NAMBE aluminum plus seven other unspecified metals DURALUMIN copper, aluminum SILUMIN aluminum, silicon MAGNALIUM aluminum, 5% magnesium ZAMAK zinc, aluminum, magnesium, copper ♦ ffiDLDwJDUJ[D[D] ffi~DillV~ ♦ NAME COMBINATION NAME COMBINATION BERYLLIUM COPPER copper, beryllium TUMBAGA copper, gold BILLON copper, silver HEUSLERALLOY copper, manganese, tin BRASS copper, zmc CUPRONICKEL copper, nickel BRONZE copper, tin, aluminum or any other element DEVARDA•S ALLOY copper, aluminum, zinc CONSTANTAN copper, nickel ELECTRUM copper, gold, silver COPPERTUNGSTEN copper, tungsten HEPATIZON copper, gold, silver CORINTHIAN BRONZE copper, gold, silver NICKEL SILVER copper, nickel CUNIFE copper, nickel, iron NORDIC GOLD copper, aluminum, zinc, tin ELECTRUM gold, silver, copper TUMBAGA gold, copper ROSE GOLD gold, copper WHITE GOLD gold, nickel, palladium, or platinum mornrn~ ruDffiVS) NAME COMBINATION NAME COMBINATION ALUMEL nickel, manganese, aluminum, silicon MONELMETAL copper, nickel, iron, manganese CHROMEL nickel, chromium MU-METAL nickel, iron CUPRONICKEL nickel, bronze, copper NI-C nickel, carbon GERMAN SILVER nickel, copper, zinc NICHROME chromium, iron, nickel HASTELLOY nickel, molybdenum, chromium, sometimes tungsten NICROSIL nickel, chromium, silicon, magnesium INCONEL nickel, chromium, NISIL nickel, silicon lfOn NAME COMBINATI ON NAME COMBINATI ON ARGENTIUM STERLING SILVER silver, copper, . germanium GOLOID silver, copper, gold BILLON copper or copper bronze, sometimes with silver PLATINUM STERLING silver, platinum BRITANNIA SILVER silver, copper SHIBUICHI silver, copper ELECTRUM silver, gold STERLING SILVER silver, copper NAME COMBINATION ANTIMONIAL LEAD lead, antimony MOLYBDOCHALKOS lead, copper SOLDER lead, tin TERNE lead, tin TYPE METAL lead, tin, antimony NAME COMBINATION WOOD'S METAL bismuth, lead, tin, cadmium ROSE METAL bismuth, lead, tin ]M[JEffiCClIJJffiY AJLJL(Q)Y§ NAME COMBINATION AMALGAM mercury with just about any metal except platinum NAME COMBINATION BRASS zinc, copper ZAMAK zinc, aluminum, magnesium, copper . ~IlIRlCC CO)NilTIJMI AJLJLCO)¥§ NAME COMBINATION ZIRCALOY zirconium and tin, sometimes with niobium, chromium, iron, nickel uom lffiDillV~ NAME COMBINATION BRITANNIUM tin, copper, antimony PEWTER tin, lead, copper SOLDER tin, lead, antimony M[ACGNIE§JIUJIM[ AILIL(O)Y§ MAGNOX magnesium, aluminum I NAME COMBINATION (WITH IRON) NAME COMBINATION STAINLESS STEEL chromium, nickel INVAR nickel SILICON STEEL silicon KOVAR cobalt TOOL STEEL tungsten or manganese SPIEGELEISEN manganese, carbon, silicon CHROMOLY chromium, molybdenum ANTHRACITE IRON carbon FERROBORON FERROMOLYBDENUM FERNICO nickel, cobalt FERROMAGNESIUM FERROPHOSPHORUS ELINVAR nickel, chromium FERROMANGANESE FERROTITANIUM I FERROALLOYS Ore ► Formation of ore via geologic processes; Lava spine ■ ■ ■ ■ ■ ■ Magmatic Activity Hydrothermal Alteration Secondary Enrichment Sedimentary Processes Weathering Processes Hydraulic Sorting Om S02 flux 40000t/d Separation of magmatic volatiles End of amphlbole crystallization psc " a degassing broic cumulate(3.0 g/cm3) oof col lapse - - 2•3 ~,m' - - - - - - 3---lkm? Nt,utnlbu,;,}11ncyo(oon••·t liculJ1ti! mapu:i 3 2.7g cm B Leached zone AficrJuoe 27 OI C "iii ~lagrna intrusion 2 CuSO.,.. • :J H•,CO- Dyke not buoyant 1 Cu,CCO.>,IOH), ♦ - Hp - Cu,(co.>40H>, ♦ 2 H~SO- •- CO, J C1.1,lc:o,)(OH), -+ CO, native copper Cu - . , Cu,(CO,XOHh =5 .§ .,.... Cu~CO,),(OH~ """',. Cu,O CuSlO,>i,O ch<y$000la 5 r.51 + 1,060, ♦ U H,0 - cur.s, + cuso, ~S+O,,S04 - 7 Cu,S +5 f:60• • U H,SO. 2 CuS • Ft50, chalcoateCu,S CuS-+PldO, Enrichment zone coveliet CuS Fig. 2 Shcmatic iUus1ration of dK: ~liyakcjima magm:itic processes I Primary mineralisation, Protore C Bastian Asmus 2013 Ore ► Common Ore Minerals Metal Cu Fe Sn Pb Hg Zn Mineral Chalcocite Chalcopyrite Bornite Azurite Malachite Magnetite Hematite Cassiterite Galena Cinnabar Sphalerite Metal Al Cr Ni Ti w Mo Mg Mn Mineral Kaolinite Corundum Chromite Pentlandite Ilmenite Rutile Sheelite Molybdenite Dolomite Magnesite Pyrolusite Rhodochrosite ~ - Ore ► Four most important considerations in the formation of ore deposits • • • • Source and character of the ore bearing fluids Source of the ore constituents and how they were obtained in solution Migration of ore-bearing fluids Manner of deposition 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 im miscibility • Ultramafics - enriched in Cr, Ni, PGE ✓ I-type Granites - enriched in Cu-Mo-Zn-Pb-Ag-Au (Igneous) ✓ S-type Granites - enriched Sn-W-Be-U-Li (Sediment/ Continental Crust Derived) ✓ A-type Granites- Alkali/ Atectonic ✓ M-type Granites- Mantle-derived Ore Bearing Fluids ► Magmatic Fluids • Highest temperature for each magma ✓ 625 degrees Celsius for felsic ✓ 1200 degrees Celsius for mafic ✓ 1600 degrees Celsius for ultramafic • Filter Pressing ✓ A process where a partly crystallized magma is subjected to stress, the fluid fraction is squeezed off from the residual crystalline mush. ✓ Metallic elements may be concentrated in either the crystalline residual mush or in more fluid fraction. If either of these materials is forced into the surrounding rocks, the process is called magmatic injection. If ore is present, it is called magmatic injection deposit. • Oxides or sulfides dominated magma or magmatic fractions that solidify directly as ore are called ore magma. Ore Bearing Fluids ► 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, CO2, H2O (1- 15% of magma), F, P ■ Trapped in fluid inclusions - contains gases and/or liquids during time of ore formation Ore Bearing Fluids ► Hydrothermal fluids • • • A hot-water solution carrying dissolved mineral substance It is rich in mineral and bacteria emanates from hydrothermal vents known as chimneys or smokers Associated with magmatic water or juvenile water WHITE SMOKER BLACK SMOKER Ore Bearing Fluids ► Meteoric Waters • • • • • Any water that passed thru & equilibrated with the atmosphere Temperature and consequently solubility of mineral increases as this water percolates down Meteoric water contains lower percentage of the heavy isotopes of S2 and 02 than magmatic waters. Contains large amount of crustal elements ✓ Na, Ca, Mg, S02-, N, 0, CO2, (HC03)-, H+ and traces of rare gases Important in ✓ Supergene processes ✓ Mixing with magmatic hydrothermal fluids due to downdraw by convective circulation Ore Bearing Fluids ► Sea Water • involved in formation of evaporites, phosphorites, submarine exhalatives, Mn nodules & oceanic crust deposits • A medium of dispersion of dissolved ions, molecules, and suspended particles. Sea salts Sea water Chloride 55 % (19 .25 g) Sulfate 7.711o (2.7g) Water 96 .5 % (965 g) Sodium 30.6 't6 (10 .7 g) Magnesium 12 96 ('0.42 g) S.796 (lJ g) __Minor constituents Potassium........... 1l961U9g) 0.796111.259) Salt 3.5 96 (35 g) O•lllllles ll 1<lot10nlll 1111 orllll< ofst~-·- Ore Bearing Fluids ► Connate Water ■ ■ ■ ■ 11 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-HC03 & many contains Sr-Ba-N Important in Mississippi Valley-type Pb-Zn ores Ore Bearing Fluids ► Metamorphic Fluids • Connate 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. ✓ Can also derived from the breaking down of hydrous minerals. Ore Bearing Fluids ► Other ore-bearing fluids • Thermal Hot Spring ✓ Most ore deposits are formed by complex processes rather than by simple end-member ones. ✓ The ore-bearing fluids of base-metal deposits ara Na-Ca-Cl brines ✓ The ratio of total dissolved metals to dissolved sulfides in the ore fluid was very high, and the metal were transported as chloride complexes in the presence of small amount of sulfides. • Mine Water ✓ Ground water in deep mines ✓ Most have no relation to the fluid deposited the ore, except in areas of volcanism ✓ Dominated by Na and CaS04 which were probably products of hydrotherma I mineralization. Movement of Ore Bearing Fluids ► Type of movement of ore bearing fluids • Migration of Magmas ✓ Magmas move, it's not a 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 Movement of Ore Bearing Fluids ► Type of movement of ore bearing fluids ■ Migration of Magmas ✓ What causes magma to moves up? □ Expansion of gases and the resultant decrease in Spg. □ Tectonic stresses squeezing the magma or fraction of magmatic differentiates into overlying or adjacent rocks. □ Movement through stoping. Magma works its way upward engulfing blocks of overlying country rock □ Stoping - the process by which country rock is broken up and removed by the upward movement of magma. Alteration Wall-rock alteration ► Alteration Zoning • • • • Although mineral zoning patterns are not uncommonly developed around ore deposits, they are not always present or obvious. The patterns can be caused by changes in temperature, fluid chemistry or gas content. The change in parameters over time, such as decreasing temperature of the fluids, can cause overprinting of lower temperature minerals by higher temperature minerals. Structural deformation, such as when a rock shattering or faulting event affects the host rocks, can cause more complexity. Wall-rock alteration ► Alteration • An irreversible water-rock interaction • It affects the density, chemical composition, magnetic property, permeability, porosity, and resistivity • Factors to be considered in hydrothermal alteration ✓ Temperature ✓ Pressure ✓ Permeability ✓ Rock Type • Does not actually matters at higher temperature, mineral alteration would be the same at certain higher temperature ✓ Fluid Chemistry (pH) ✓ Duration of Activity (Reaction or interarction) Wall-rock alteration ► Alteration ■ Factors to be considered in hydrothermal alteration ✓ Temperature • From High to Low •!• Biotite / K-feldspar (>250) •!• Epidote ("'250) •!• Quartz •!• IIlite "'(200) •!• lnterlayared lllite-chlorite •!• Interlaya red II lite-smectite •!• Montmorillonite ("'100) •!• Calcite Wall-rock alteration ► Alteration ■ Factors to be considered in hydrothermal alteration ✓ Permeability • minerals indicating good permeability: •!• quartz, anhy, wairakite, illite, adularia, pyrite, calcite • poor permeability indicators: •!• low intensity of alteration of host rocks •!• absence of above minerals •!• prehnite, pumpellyite, pyrrhotite and abundant titanite and laumontite Intensity vs. rank of alteration Wall-rock alteration ► Alteration ■ Factors to be considered in hydrothermal alteration ✓ Fluid Chemistry (pH) •!• A neutral pH alteration suite formed by the water-rock interaction involving hot, near-neutral pH alkali-chloride fluids □ montmorillonite □ calcite •!• An acid-alteration suite involves low pH high sulfurbearing fluids □ kaolinite (low temperature) □ pyrophyllite (high temperature) □ alunite □ illite Wall-rock alteration ► Alteration Assemblage --------------------- Common Alteratlon Mlneralogy In Hydrothermal Systems ------INCIIEASINGr,t-------.. D - ,_.bl Oullr/Mft..,,. - lbm . ,.,.i.. o w- 0 1111,ae - ~_. lllnll'IIAblnvllllonl : I Q Q I - •.._Jd- Kllcila;M•....._ Al •lllllllr; Ml• ll!ldullli Bio• 11111111; Cb-caN•{Cl.lllln.'-Cll•. . _ - -~dllelll ••--C.-~ Olll■da; Cpl· ...,,...Nii Q • allli, 1■1. Q•~Dl- d11l It.Ill•. _ Dp-dllpani; r, .... Ftp. 11111-■ I ._........... ' a.-..-Hltt~- ..... •-- ~ . . - · - tr-lllallll; lll•--- ■• • •; - -- - - -•--Op•GpllntllDI; , , • ...,....Q . . . . . . . . . . - .. Group, ... 1--,...a,;11-•11s r..1;-.-w...._ - ¥11 ~:mellA; W -• •· Wt,- walbl!IIM; l'.IO•..._ Lid Wall-rock alteration ► Alteration Types ■ Propylitic: (Chlorite1 Epidote1 Actinolite) ✓ Propylitic alteration turns rocks green, because the new ✓ ✓ ✓ ✓ ✓ minerals formed are green. characterized by the assemblage chlorite + epidote + calcite. Albite as well as other carbonates may be present. They usually form from the decomposition of Fe-Mg-bearing minerals, such as biotite, amphibole or pyroxene, although they can aIsa replace feldspar. Propylitic alteration occurs at relatively low temperatures. Propylitic alteration will generally form in a distal setting relative to other alteration types. This zone seems to represent the addition of cations. Wall-rock alteration ► Alteration Types ■ Sericitic: {Sericite) ✓ Sericitic alteration alters the rock to the mineral sericite, which is a very fine-grained white mica. It typically forms by the decomposition of feldspars, so it replaces feldspar. ✓ In the field, its presence in a rock can be detected by the softness of the rock, as it is easily scratchable. It also has a rather greasy feel (when present in abundance), and its color is white, yellowish, golden brown or greenish. ✓ Sericitic alteration implies /ow pH (acidic) conditions. ✓ Alteration consisting of sericite + quartz is called "phyllic" alteration. Wall-rock alteration ► Alteration Types ■ Potassic: (Biotite~ «-feldspar, Adu/aria) ✓ Potassic alteration is a relatively high temperature type of alteration which results from potassium enrichment. ✓ This style of alteration can form before complete crystallization of a magma, as evidenced by the typically sinuous, and rather discontinuous vein patterns. ✓ Potassic alteration can occur in deeper plutonic environments, where orthoclase will be formed, or in shallow, volcanic environments where adularia is formed. ✓ Pyrite and minor chalcopyrite and molybdenite are the only ore minerals associated with this alteration. Wall-rock alteration ► Alteration Types ■ Albitic: (A/bite) ✓ Albitic alteration forms al bite, or sodic plagioclase. ✓ Its presence is usually an indication of Na enrichment. ✓ This type of alteration is also a relatively high temperature type of alteration. ✓ The white mica paragonite (Na-rich) is also formed sometimes. saussuritization is a process by which calcium-bearing plagioclase feldspar is altered to a characteristic assemblage of minerals called saussurite; the typical assemblage formed includes zoisite, chlorite, amphibole, and carbonates. Wall-rock alteration ► Alteration Types ■ Uralitization ✓ The development of amphibole from pyroxene; specific at late-magmatic or metamorphic process of replacement whereby uralitic amphibole results from alteration of primary pyroxene. ✓ Also, the alteration of an igneous rock in which pyroxene is changed to amphibole; e.g., the alteration of gabbro to greenstone by pressure metamorphism. Wall-rock alteration ► Alteration Types ■ Silicification: (Quartz) ✓ Silicification is the addition of secondary silica (Si02). ✓ Silicification is one of the most common types of alteration, ✓ ✓ ✓ and it occurs in many different styles. One of the most common styles is called "silica flooding which results form replacement of the rock with microcrysta 11 ine quartz (chalcedony). Greater porosity of a rock will facilitate this process. Another common style of silicification is the formation of close-spaced fractures in a network, or "stockworks which are filled with quartz. Silica flooding and/or stockworks are sometimes present in the wall rock along the margins of quartz veins. Silicification can occur over a wide range of temperatures 11 , 11 , ✓ Wall-rock alteration ► Alteration Types ■ Silication: {Silicate Minerals +/- Quartz) ✓ Silication is a general term for the addition of silica by forming any type of silicate mineral. These are commonly formed in association with quartz. Examples include the formation of biotite or garnet or tourmaline. ✓ Silication can occur over a wide range of temperatures. The classic example is the replacement of limestone (calcium carbonate) by silicate minerals forming a "skarn", which usually form at the contact of igneous intrusions. ✓ A special subset of silication is a style of alteration called "greisenization". This is the formation of a type of rock called "greisen", which is a rock containing parallel veins of quartz+ muscovite+ other minerals (often tourmaline). The parallel veins are formed in the roof zone of a pluton and/or in the adjacent country rocks (if fractures are open). With intense veining, some wallrocks can become completely replaced by new minerals similar to the ones forming the veins Wall-rock alteration ► Alteration Types ■ Carbonatization: {Carbonate Minerals} ✓ Carbonitization is a general term for the addition of any type of carbonate mineral. ✓ The most common are calcite, ankerite, and dolomite. ✓ Carbonatization is also usually associated with the addition of other minerals, some of which include talc, chlorite, sericite and albite. ✓ Carbonate alteration can form zonal patterns around ore deposits with more iron-rich types occurring proximal to the deposit Wall-rock alteration ► Alteration Types ■ Alunitic: (A/unite) ✓ Alunitic alteration is closely associated with certain hot springs environments. ✓ Alunite is a potassium aluminum sulfate mineral which tends to form massive ledges in some areas. ✓ The presence of alunite suggests high 504 gas contents were present, which is thought to result from the oxidation of sulfide minerals Wall-rock alteration ► Alteration Types ■ Argillic: (Clay Minerals) ✓ Argillic alteration is that which introduces any one of a wide variety ✓ ✓ ✓ ✓ of clay minerals, including kaolinite, smectite and illite. Argillic alteration is generally a low temperature event, and some may occur in atmospheric conditions. The earliest signs of argillic alteration includes the bleaching out of feldspars. A special subcategory of argillic alteration is "advanced argillic". This consists of kaolinite+ quartz+ hematite+ limonite. feldspars leached and altered to sericite. The presence of this assemblage suggests low pH {highly acidic) conditions. At higher temperatures, the mineral pyrophyllite {white mica) forms in place of kaolinite Wall-rock alteration ► Alte ration Types ■ Advanced Argil/ic: {Clay Minerals) steam-heated blanket acid sulphate cap silica sinter • ✓ Characterized by the clays dickite, kaolinite and pyrophyllite (all hydrated aluminum silicates) and quartz. '/ high sulphidation eptthermal Au mineralisation ✓ Sericite may be present as well as alunite and tourmaline. ✓ Alteration involves the extreme leaching of cations, especially the difficult to leach alkalis and calcium, and the concentration of H+. Atg/1/ic t advanced Blgi/1ic - Mvanced arg,lbc ~ Sillcal9dges Wall-rock alteration ► Alteration Types ■ Zeolitic: (Zeolite Minerals) ✓ Zeolitic alteration is often associated with volcanic environments, but it can occur at considerable distances from these. ✓ In volcanic environments, the zeolite minerals replace the glass matrix. ✓ Zeolite minerals are low temperature minerals, so they are generally formed during the waning stages of volcanic activity, in near-surface environments Wall-rock alteration ► Alteration Types ■ Serpentinization and Talc Alteration: (Serpentine, Talc) ✓ ✓ ✓ ✓ ✓ ✓ Serpentinization forms serpentine, which recognized softness, waxy, greenish appearance, and often massive habit. This type of alteration is only common when the host rocks are mafic to ultramafic in composition. These types of rocks have relatively higher iron and magnesium contents. Serpentine is a relatively low temperature mineral. Talc is very similar to the mineral serpentine, but its appearance is slightly different (pale to white). Talc alteration indicates a higher concentration of magnesium was available during crystallization ~ &c:~ !t2 • ••-. ,/ t~~-~,. ~ :. ·_ ._-:- r-',~ .,i ~ . ' t;. • 1/ (;t-1 ..,b_ './, _; ' er '.~·::- ~ ··""- . - r.~~ Wall-rock alteration ► Alteration Types ■ Oxidation: (Oxide Minerals) ✓ ✓ ✓ ✓ ✓ Oxidation is simply the formation of any type of oxide mineral. The most common ones to form are hematite and limonite (iron oxides), but many different types can form, depending on the metals which are present. Sulfide minerals often weather easily because they are susceptible to oxidation and replacement by iron oxides. Oxides form most easily in the surface or near surface environment, where oxygen from the atmosphere is more readily available. The temperature range for oxidation is variable. It can occur at surface or atmospheric conditions, or it can occur as a result of having low to moderate fluid temperatures Wall-rock alteration ► Alteration Types • Feldspathization - kspar + albite, • Greisenization - tourmaline+ topaz+ cassiterite + various tu ngste n-bea ring min era Is. • Fenitization - characterized by nepheline, alkali feldspar and Nabearing amphiboles. Hematization - characterized by secondary hematite. • Bleaching - not characterized by any specific mineral assemblage, but rather a color change between altered and unaltered rock. Generally the result of oxidation of Fe. Deposits Related to Mafic Igneous Rocks Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits • Use to all kind of ore that is being deposited through direct crystallization of magma. Excluding pegmatites, porphyry base-metal deposits, and other that involves hydrothermal transport. • Usually form in the magma chamber, and thus are deep-seated intusive bodies, but differentiated or immiscible melts and crystal mushes can be derived into magma chamber walls or roofs to orebodies that are dikes, sills, and even extrusive flows. • May constitute an entire intrusive rock mass or a single compositional layer within such a body, or it may be defined by the presence of valuable accessory minerals in an otherwise normal igneous rock • The ore is a product of early or late fractionation due to gravitative settling, immiscibility, and or filter pressing. Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits ■ Layered Mafic Intrusions (LMI) ✓ is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions can be many kilometres in area covering from around 100 km2 to over 50,000 km2 and several hundred metres to over a kilometre in thickness. PG~-3 Skaergaard _an~ PGE-1 waterburg-type S n u Lake miner llzat1on . . t· ....cu minera1Iza I0n C ·---------------------------- PGE-1_ Merensk_y and J-M _Reefs-------------------------------·- en E~ PGE-1 marginal mineralization in Bushveld (Platreef 0 (.) "'O 0 or-i=. 1 1Ir-.? c:::• ilfirlp_ and PGE-2 intrusions in Finland and Ontario I I... (.) --~---~'-'--~~WM•••••••••••••••••••••••••••••••• i.+= ,_.....__....._ earing chromitite cu PGE-1 dunite pipes ~ Appearance of cumulus plagiocla~--------------------"'O (1) (.) i.+= cu en E~ cu (.) I... 0 :!:= => I... • D D Sulfide-dominated mineralization Ultramafic cumulates Alternating ultramafic, mafic and plagioclase cumulates PGE-1 chromitites rich in Ir, Os, Ru Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits • Layered Cr-Pt Mafic-Ultramafic Complexes ✓ General Setting □ Occur in a plutonic igneous setting and appear to be intruded into a more or less stable craton. □ Most economically important LMls are Proterozoic in age. □ All are layered with the average composition of a gabbro. ✓ Distribution □ Only eight known layered igneous complexes in the world, and of these only three have significant chromium. □ Two of those have been mined for chromium (Bushveld Igneous Complex, South Africa and the Great Dyke, Zimbabwe) and only one for platinum (BIC). Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits ■ Layered Cr-Pt Mafic-Ultramafic Complexes ✓ Bushveld, South Africa □ Largest Cr resource i.e ~1 BT @ 45% Cr2O3- 70% of the world resource □ Largest Pt-Pd-Os-Ir-Rh-Ru (PGE) resource - i.e. Merensky Reef+ UG-2 ~ 2B oz PGE □ Huge Fe-Ti-Vn-Sn resource □ Age - 2.06 billion Ma (Proterozoic) :-'.:""':~ ;:--,-,,. -~~~ c:::J Overburden =--~ ... -c:::J Upper Post RLS J!. zone Mainzone C ] Bastard Menmsky c::J Merensky Reef c::J Psuedo reef/ UG3 c:::J Psuedo reef!UG3 Footwall C]UG2 c::::::J UG2 Footwal - UG1 E c:::J Middle Group Chromatite c:::J Lower Group Chroma.tit• c:::J LOMrZone - c:::J M.-gina)Zone Pr►Bushveld/Transvaal System - / __ 7 /. Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits ■ ■ Cu-Ni-Pt Segregation Sudbury, Canada ✓ Largest Ni resource Ni ~ 1.6 BT @ 1.2% Ni & 1% Cu plus Co-PG E □ complete melting of the continental crust due to large meteorite impact N i 9 flD .~ lD I Proterozoic Granophyre D Quartz-rich gabbrO Onwat,n Formation Norite D Sublayer - Chemsford Formation Onaping Formation Creighton. Murray granites - D D Greywacke. volcanic rocks D Granite gneiss and plutons Quartzite Archean -~--~Ohv,nedoabase dykes----0 Nl-Cu-PGE deposits Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits • Anorthosite - Titanium o 90% or more of intermediate to calcic plagioclase o Source of almost all "hard rock" sources of Ti o Ilmenite (FeTiO3) and Rutile (TiO2) - Titaniferous ores ✓ 2 Types □ Layered mafic intrusions, eg. Bushveld, formed by gravitational stratification in ultramafic-mafic complexes characterized by anorthite (An 70-100) □ Proterozoic "massifs" or plutons containing plagioclase ranging from andesine to labradorite (An35-65) Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits • Anorthosite - Titanium Segregation of Fe-Ti-rich interstitial melt from uprising anorthosite mush HydrothermaJ remobilization of Source: https: //www. sciencedirect. com/science/artic lelpii/S0012825 21400203 71 Fe and Tl from plagioclase Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits • Kimberlites - Diamond o Kimberlites was first recognized in Kimberly, South Africa. Now, they are known in all continents except Antartica ✓ Definition - kimberlite is a volatile-rich, potassic ultramaficrelated phreatomagmatic breccia pipe or igneous dike dominated by olivine, with subordinate minerals of mantle derivation □ Variable amounts of monticellite ( Ca olivine), phlogopite (Mg biotite), diopside, serpentine w/ minor amounts of apatite, chromite, garnet, diamond etc □ Contains xenoliths of upper mantle materials, eg. Garnet lherzolite, eclogite & harzburgite ✓ Other sources of "hard rock" diamonds - minettes, lamproites (Krich Mg-lamprophyres), diabases. ✓ Age- most productive pipes are 80-100, 250, & 1000-1100 Ma ► Deposits Related to Mafic Igneous Rocks Magmatic Segregation Deposits ■ Kimberlites - Diamond o Distribution ✓ Kimberlites occur in continental settings and range in age from late Proterozoic to Recent. The greatest concentration, however, is in rocks of Mesozoic age. Kimberlites have been found on all continents, but the largest concentration is along the East African Rift System. Surprisingly, diamond pipes also occur in North America in Arkansas and WyomingColorado. Deposits Related to Mafic Igneous Rocks ► Magmatic Segregation Deposits ■ Kimberlites - Diamond o Alteration ✓ Kimberlites are surprisingly free of alteration assemblages. Serpentinization is common in near surface environments, but is attributed to meteoric water circulation. The absence of alteration is rather remarkable given the fact that kimberlites are thought to represent mantle rocks that have somehow been emplaced in the upper crust. 1' 0 l 111 1111 1111 l 1 jllll llllll llllll lltttilll l l11 jlll llll l111111/lll!llllljl!llllll1/1111itlll/llll/111l/lllljll!l/111ljllll/llll/lll 2 3 4 5 6 7 8 9 10 11 12 ► Deposits Related to Mafic Igneous Rocks Magmatic Segregation Deposits ■ Kimberlites - Diamond o Diamonds in kimberlites occur as sparse xenocrysts and within diamondiferous xenoliths hosted by intrusives em placed as subvertical pipes or resedimented volcaniclastic and pyroclastic rocks deposited in craters. Economic concentrations of diamonds occur in approximately 1% of the kimberlites throughout the world. o Alteration: Diamonds can undergo graphitization or resorption. ❖ Graphitization is a form of material degradation occurring when the microstructure of some carbon and low alloy steels breaks down after long exposure to elevated temperatures (825 - 1300 F), causing the metal to weaken and be susceptible to cracking failures ❖ Resorption is the partial or complete remelting or dissolution of a mineral by magma, resulting from changes in temperature, pressure, or magma composition ► Deposits Related to Mafic Igneous Rocks Magmatic Segregation Deposits • Kimberlites- Diamond o Extraction of diamond ✓ Diamonds are recovered from the ore by heavy-liquid separation in ferosilicon, by the property unique to diamond that it adhere to greased surface. ✓ Sortex method, a jet of air activated by photocells that perceive visible light fluorescence included in diamond by an X-ray beam as concentrates move along a V belt, the air jet popping the diamonds and adjacent particles off the belt. - B UHLER f _,, Vibrator I _ - - - ,- T- I~- • •• ...;. - - 1111... • ... t=:; ~ . ► Deposits Related to Mafic Igneous Rocks Magmatic Segregation Deposits • Ca rbonatites o o o o Since 1940s, 100s have been recognized Cylindrical pipelike bodies of calcite, dolomite and/or siderite Most are prominently concentrically zoned; some are irregularly shaped Age - early Proterozoic to Phanerozoic to recent times o 2 General Types ✓ Magnetite-apatite-rich, eg. Palabora, South Africa ✓ REE-Fl-Ba-rich, eg. Mountain Pass, USA o Mined for REE, Nb-Ta, Zr-Hf, Fe-Ti-V, U-Th & industrial minerals, eg. apatite, vermiculite & barite (BASTNASITE, MONAZITE and LOPARITE) o Some are highly differentiated rocks, occurring near & with syenites & other alkalic rocks, but others appear to be undifferentiated, occurring with diopside-olivine pyroxenite-harzburgite intrusives Deposits Related to Oceanic Crust Deposits Related to Oceanic Crust ► Podiform Chromite • Also known as "Alpine-type" Chromite • Ophiolite-related which formed in mid-oceanic ridges or back-arc basin spreading centers & tectonically obducted onto continental or island arc margins • <1.2 Ba Age (Proterozoic) to Phanerozoic • From top down, Ophiolite has 3 layers (sometimes considered as 4) ✓ Layer 1- deep sea siliceous or ocherous sediments w/ radiolarian cherts (few cm - few m) ✓ Layer 2 - layered pillow basalts cut by sheeted diabase dikes ( 100s to 1000s m) ✓ Layer 3 - gabbros/norites + serpentinized mafic to ultramafic rocks (~1Q-1Skms) •!• Contains podiform smeared-out bodies of chromite in dunite harzburgite sequences ❖ ocherous - an earthy usually red or yellow and often impure iron ore used as a pigment Deposits Related to Oceanic Crust ► Podiform Chromite □ Associated rock types include: ✓ ( 1) an overlying sedimentary section typically including ribbon cherts, thin shale interbeds, and minor limestones; ✓ (2) podiform bodies of chromite generally associated with dunite ✓ (3) Sodic felsic intrusive and extrusive rocks. o Faulted contacts between mappable units are common. Whole sections may be missing. An ophiolite may be incomplete, dismembered, or metamorphosed ophiolite. o Although ophiolite generally is interpreted to be oceanic crust and upper mantle, the use of the term should be independent of its supposed origin. - Anonymous, 1972 Reference: 6 - Ophiolites by Payot, B. (Lecture slide) Deposits Related to Oceanic Crust ► Podiform Chromite • Distribution ✓ ✓ occur in all the major Paleozoic or younger tectonic belts of the world close association with convergent plate boundaries and/or major crustal ✓ sutures most important producing districts are in the Philippines, New Caledonia, ✓ Turkey and Cuba. within any one district the actual number of chromite deposits might number in the thousands, but usually only a few are large enough to be economic. .... 0cNnic awe Distribution of important Alpine-type chromite deposits Deposits Related to Oceanic Crust ► Podiform Chromite • Setting ✓ Occur in structurally complex setting with extensive post-ore deformation. Extensive alteration and chaotic nature of the host rocks has made further understanding of the geology of these deposits a matter of much speculation until quite recently, along with the recognition of ophiolites. IDEALIZED CROSS- SECTION OF AN OPHIOLITE ROCK TYPES chert , limestone, etc. basalt DESCRIPTION pelagic sediments pillcrw lavas s1-1eetecl cHkes 8. sills E 11) ::L. ~co ~ ro +-' ~ non-cumulates I > ~ ro i.Jj g-abbro w C -i5 ultrarnafic cumulates :c ....... har7burgite lherzolite ... cumulates _ geoplNsical Mot10 - petrologic !Jase of crust depleted mantle fertile mc1ntle Modified from Coleman ("1 977) anq Ehlers ,;;nd Blatt ("1 982) Deposits Related to Oceanic Crust ► Podiform Chromite Origin • Origin of podifonn chromitites Podiform chromitite with a dunite envelope can be interpreted to be a product of interaction between mantle harzburgite and an exotic magma, combined with magma mixing. (Mg.Fe}O • The secondary Si- and Crrich melt which is produced by the selective dissolution of orthopyroxene can be mixed with a subsequently supplied primitive melt with the mixed melt oversaturated with spinel to effectively precipitate chromitite. • The dunite envelope is of replasive origin. chromite olivine Olivine - . Chromite A Fig. 2. A model of the podiform chromititc formation during the mantle-melt interaction modified from A raj and Yurimoto (1994), Th.e secondary Si-rich melt {B), whicJ1 is formed by interaction beiwoen harzburgile and an exotic mel1 (A}, can be mixed with subs.equently supplied melt (A) to form a spincl-overra.turated melt (C). The hybrid melt (C) ca.o precipitate only s.pinel to form ehromitite. Deposits Related to Intermediate to Felsic Intrusions Deposits Related to Intermediate to Felsic Intrusions ► The relationship between mountain building and ore deposits has of course long been recognized, and mountain terrains have attracted prospectors and geologist from our emergence from the stone age into ages of bronze, iron, steel, and now energy. ► Great mountain belts involving calc-alkaline rocks are generally young. ~ do!posu -~ :=... ~ Pl~ - - • ,i.,• Tr- _,,, ,__.,,. _,, _ , t i ~ ~~l~I _,, _,eihyl(~ Ma,«1a!AUI --....-....ilor_,I • !No-• ._,... ,,._,...,. ~ 2000km "" Deposits Related to Intermediate to Felsic Intrusions ► Igneous Iron Deposit • 2 types 1. Volcano-sedimentary or sedimentary deposits (Rare but significant eg. El Loco Chile, Iron Mountain district, Missouri) 2. Intrusive Magmatic Segregation Ore (eg. Larap, Philippines) ✓ Important resource come from sedimentary deposit and 1 to 2 % of world's Fe is being mined from Intrusive magmatic segregation ore ✓ Both results from segregation of magma fluid rich in iron, with 4 to 5% of phosphorus. ✓ The difference is based whether the ferruginous melt is injected as an intrusive body forming podlike magnetite or it vents to surface as statabound iron-rich deposit. Deposits Related to Intermediate to Felsic Intrusions ► Igneous Iron Deposit • Kiirunavaara Mine in Kiruna, Sweeden is the most important intrusive iron ore because the final determination has not yet been made. ✓ Most productive iron deposit in the world (magmatic segregation) ✓ Has high phosphorus content of greater than 2% due to the apatite ✓ Kiruna Type Ore - Universally refers to high-phosphorus iron ores Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Large low- to medium-grade deposit, primarily of chalcopyrite & molybdenite, which exhibits hypogene sulphide & alteration silicate zoning, & is temporally and spatially related to an epizonal calc-alkaline porphyritic intrusion. • Porphyry Cu Deposit (PCD) ✓ 50 MT to 3BT covering <1-2 km2 of rock (/ts most sticking feature) ✓ 0.2 to >1% Cu w/ Au, Ag± Mo credits ✓ Chalcopyrite is dominant economic Cu-Fe-S mineral, subordinate to nil bornite, covelite, cuprite, chacocite, rare but ubiquitous molybdenite (<100 to 300ppm) □ Others - magnetite, pyrite (predominated silfide), specularite, galena, sphalerite, Cu sulphosalts (enargite, tennantite) Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) ✓ Prograde & Retrograde alteration stages □ Prograde - Potassic to Propylitic / Disseminations-Vein let-Veins □ Retrograde- Phyllic & Advanced Argillic / Vein let ✓ Cale-alkaline porphyritic intrusion - 1 to 2 kbar pressure, 1.5 to 4km depth. Rocks formed at 750-850oC and mineralization at >250 to <500 degree C ✓ Supergene Cu enrichment is important for a lot of deposits to make them economic or substantially higher in Cu grade Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) ✓ Almost all known porphyry copper deposits are Tertiary in age (Mesozoic to Cenozoic) □ PCD in the Philippines a. Cebu - Cretaceous (Oldest) b. SW Negros and Nueva Vizcaya - Oligocene c. Luzon and Eastern Mindanao - M-L Miocene d. Western Luzon to Cotabato - Plio-Pleistocene ✓ They are thought to have formed in island or continental igneous arc settings associated with a subduction zone. ✓ Their composition ranges from tonalite to monzonite. ✓ PCD deposits usually form in relatively fine-grained intrusions of felsic composition. ✓ Where formed in differentiated intrusive sequences, they tend to be formed in the finest-grained and most felsic end members of the suite. Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) ✓ The ores consist of concentrated swarms of quartz-sulfide stockworks and sometimes as sulfide disseminations. ✓ Some deposits have a zone of secondary enrichment at the surface caused by groundwater leaching and redepositing the Cu at a lower elevation. ✓ Characteristic alteration includes potassic (Biot. + K-feldspar), sericitic (Py+ Seri cite), and propyllitic ( Chlorite, Epidote) ✓ With the study conducted by Moore et, al porphyry base-metal deposits have been found to be truly mesothermal, with ore deposition from strongly saline fluids up to 30 to 60% NaCl ranging from 250 to 500 degree C, rarely 600 to 700 degree C. Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • adul = adularia Ag -.. silver alb = atite Porphyry Cu Deposit (PCD) Models ✓ Lowell & Gilbert {1970) am = anhydrite Au = gold b = blotile car1:) caibonate chi - chlorlte op = chalcopyrtl e gpi = epidots gal = galena ✓ First Model (static) - ✓ ✓ ✓ ✓ ✓ based on San Appro)cimate 1 km Manuel/Kalamazoo, Arizona (200MT @ I I ft 0 3000 0. 75% Cu & 0.015% Mo: Spatial relations only w/o temporal relations ?·_ 1 _ ; , _ . , Intrusive vs Host rocks Pettphetal __,,.,....._.._ not elucidated f9u-'I WW No tops & bottoms ( ~~ Supergene Argillic PY mistaken to be ~ PY 1 cp 0.1 hypogene mb No Advance Argillic fi!<lte1atio 11 ' Kao! q = quartz ser serlolte sl " ~ (bl kaolinite K-lald - !<,feldspar mag u frni9S:,elrle tnb = molybdeMe f1'I = pyrite 1-?- sphalerite ?_ Vems Peripheral '%J'~ Velnlel Velnl~ Veinlets > 71ed rnfnaled l.ow grade f.. elnt,ei:$ C0l'8 total sulfide - -mb Vi di$s~mln \ (C) Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) Models ✓ Alteration types in Porphyry-Epithermal system Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Mo Deposit (PMD) ✓ Porphyry molybdenum PMD are large, low grade molybdenum deposits ✓ ✓ ✓ ✓ ✓ ✓ and the exclusive source of Mo. As with the PCD, PMD tend to form in the most differentiated members of an intrusive suite. Unlike PCD, in PMD there is usually only one ore mineral containing Mo, which is the mineral molybdenite. Many PMD contain some tin and tungsten minerals which are recovered from the ores for additional credits. There is often a great deal of faulting associated with these types of deposits. Multiple, overlapping mineralizing events are not uncommon. Typically ore grades are in the range of 0.1-. 0.5 percent MoS2. Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu-Au Deposit ✓ Commonly in island arcs but a few found in continental arc, characteristically contain more magnetite (3-10%) than Cu-Mo systems (<1-2%), ✓ eg. Grasberg - reserves of S00MT @ 0.9% Cu, 0.98 g/t Au • Climax-type Moly deposits ✓ Relatively high grade with 0.3 to 0.5% Mo52 ✓ Has low grade Cu ✓ Occurs in atectonic to tensional rift environments w/ A-type (Atectonic or anorogen ic) high-silica porphyritic granitic al ka lie intrusives, high F/CI, ✓ eg. Climax - 300MT @ 0.2% Mo • Porphyry Tin deposits ✓ Extensive igneous-related hydrothermal vein system Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) Models ✓ Sillitoe~ 1972 up to present ✓ Plate tectonic model for the origin of porphyry Cu (1972) □ Located at calc-alkaline magmatic arcs as a result of partial melting of oceanic crust at subduction zones ✓ Introduced "Tops & Bottoms" concept ( 1973) ✓ Conceptualized the Porphyry Cu Model for the Philippines ( 1984) Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) Model Porphyry systems Intermediate sulfidation Au-Ag (Pb-Zn - Base of advanced argillic lithocap . related ; IS veins, f polymetal / / f ..! I : ~ :! .. -r . Porphyry Cu-Au \ • •· • • ~ Proximal CuAu skarn 1km Sillitoe, 201 O 1m Economic Geology Deposits Related to Intermediate to Felsic Intrusions ► Porphyry Base-Metal Deposit • Porphyry Cu Deposit (PCD) Models ✓ Porphyry-Epithermal Connection (Arc-type) eg. Biga Deposit, Atlas Mine ,Cebu (World class El Indio deposit)"Telescoped" An~jfg..d:Jei'ta volcanic edifice ____.___ Ootor limit of advancgd at gtll ic Ill ho;;ap AileQSyrtace ISAU~AQ b0&a metal / Early acidic magma1ic _ggsos t 1· ___________ xx _ sa.ms Later IS fluid Later evolved HS fluid Parental ganodiorite magma ehomber xx ....,_ 00 nden 5 ikm (Sillitoe and Hedenquist, 2003 Deposits Related to Intermediate to Felsic Intrusions ► Skarn Deposit • Also known as replacement deposits ✓ They form by the replacement of limestone, calcareous rocks (marl or ca le-schist), or dolomite. ✓ A wide variety of minerals can form in skarn deposits, but the most common include oxide minerals such as magnetite, sulfide minerals such as chalcopyrite, silicate minerals such as epidote, or the tungstate mineral Scheelite. ✓ Gold is also mined from skarn deposits. ✓ Skarn deposits are a result of the invasion of the country rock by hydrothermal fluids carrying the high metal concentrations outward from the intrusion. Deposits Related to Intermediate to Felsic Intrusions ► Skarn Deposit • • • • • • • Characterized by alteration assemblage of Garnet (Andradite) and Pyroxene (Diopside) Forms at high temperature (350 to 800 degree Celsius) Happens when silicic magma intruded a country rock (Carbonates) Important source for W, Fe, Mo, Zn, Pb, Cu, and Au Mineral assemblage - Magnetite, Molybdenite, Sphalerite, Galena, Scheelite, Hematite, Garnet, Epidote, and Pyroxene Ca and CO2 high activity becomes an effective buffering solution Types of deposits depends of the depths and settings Legend ~Marble .----, Calc-sllicate u:_Jmarble Qj Limestone □ Silty D D Calc-ellicate homfels limestone D oh.lie D □ Cak:-eilicote D C;:ilcareous homlele D Calcareous sandstone Homfele Voklanice Metaeomatlc el<arn DJ] okorn Ae1rograde _,.,}If' Tranter of heat '-.. Exsolution of ~ magmatic ftuido .#Oeaoendnig tfY meteoric wntere ~ Upwelling m.igmanc mineralized fluids ~age I : laoch&mical Sl<0rn (Conttlct Metumorphlsm) • Stages in skarn deposit Corbett & Leach ( 1998) Deposits Related to Intermediate to Felsic Intrusions ► Skarn Deposit • Stages in skarn deposit • Higher temperature waters (called "prograde" minerals), lower fluid temperatures (called "retrograde" minerals). Exoskarn - within the pluton (Retrograde; Gar>Pyx) Endoskarn - Within the country rock (Prograde: Pyx>Gar) • • • ~ '7~~-'-' QMGrtlo □ =,_ 18 [Tiumae- 0:z._ El =:co.. D liorntels OS:-"" □~ □ Cillc«lmNo~.m: homtela obm D Stage II : Metasomatic Skarn (Magmolic Fluid Exsolution) Stage Ill : Retrograde Skarn and Minerahzabon Caloa,.,,.,. enndaton& D "",,.._ mm Deposits Related to Intermediate to Felsic Intrusions ► Skarn Deposit • As function of depth emplacement and setting OAMING ENVIRONM NTS w (} Q OM Deposits Related to Intermediate to Felsic Intrusions ► Cordilleran Vein Type D