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Ore Deposits and Mantle Plumes, 2000

2006

The transport, deposition and zoning of hydrothermal ores are controlled by three main factors: the crystal chemistry and stability of the mineral phase, the physicochemical properties of aqueous electrolyte solutions at high T and P, and the thermodynamic and molecular properties of aqueous species of metals. Recent solubility and spectroscopic data permit the following generalizations on the chemistry of transition-metal complexes at elevated temperatures. Bonding changes from primarily ionic to covalent from left to righi across each transition row. The d10 transition-metals behave more as Pearson soft acids, preferentially complexing with soft bases (electron donors) such as HS-, whereas metals to the left show increasing "hardness", bonding to moderately soft electron-donors such as Cl-. The Pearson rule successfully describes speciation to about 250oC, but breaks down at higher T as all metals become harder, and electrostatic interaction increases. Recently recognize...

2011

A modern state of the following problems of magmatogene hydrothermal mineralization are considered in this paper: Dependence of ore types from a redox state of ore producing magmas; D.S. Korzhinskii's principle of acid-base interaction as a possible variety of Le Chatelier's principle; the structural features of zonal near-ore alkaline and acidic metasomatites and related revised formula of the mineralogical phase rule; dependence of acidity-alkalinity of fluids from NaCl and KCl hydrolysis at different P-T environments, as well as from subcritical fluid's heterogenization; the features and reason of general evolution of mineralization within a single metallogenic cycle; mineralization from heterophase fluids at the postorogenic deposits of W, Sn, Au, Ag, Cu, Pb, Zn, and Hg related to acidic metasomatites; evidence and reason of intermittent (multi-stage) mineralization on the background of general evolution of composition and properties of fluids; as well as (8) some guidelines for local ore prediction based on above analysis.

2015

Quantitative evaluation of the distribution of a variable within a solid by a method using constitution and distribution heterogeneities of P. Gy, application to textural study of ores.

2015

Abstract. The Rosia Poieni porphyry Cu-Au and Rosia Montana epithermal Au-Ag deposits are the largest operating mines in the South Apuseni mineral district, Romania. Rosia Montana is a breccia-hosted low- to intermediate-sulfidation epithermal system, related to strong phreatomagmatic activity due to shallow emplacement of a dacitic dome structure. The Rosia Poieni deposit, situated about 4 km NE of Rosia Montana, is a porphyry copper system with a high-sulfidation epithermal overprint. This study provides the first high-precision U-Pb dating of Miocene magmatic and hydrothermal events in the South Apuseni Mountains. Together with the existing 40Ar-39Ar data, the new results show clearly that the two deposits belong to two separate magmatic-hydrothermal systems, the porphyry copper system of Rosia Poieni being about 3 Ma younger than the neighbouring Rosia Montana epithermal deposit. The timing of the porphyry mineralization at Rosia Poieni has been bracketed by dating the main Poie...

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sedimenthosted Au deposits in increasingly peripheral locations; and superjacent high-and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas carbonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal-or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediatesulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sulfides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the lithocaps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during porphyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeability. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with Sand metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatichydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hypersaline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low-to moderatesalinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineralization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace. Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the porphyry Cu environment, early-formed features commonly, but by no means always, give rise to the best orebodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in porphyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sedimenthosted Au deposits in increasingly peripheral locations; and superjacent high-and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer.

BASICS OF ECONOMIC GEOLOGY AND MINING PRACTICES Chapter 3b: Mineral Deposit Types

Mineral deposit types are usually named or described on the basis of a classification scheme using defined criteria. However, the determination of what type a deposit belongs to is not a casual affair but based on a combination of field observations and rigorous laboratory studies that often include mineralogical examination of the ores, stable isotope geochemistry and fluid inclusion study. There are many ways of grouping mineral deposits, but some geological criteria have been accepted and used for classification including; (1) metal content (commodity); (2) shape or form of deposits (morphology); (3) host rock association; (4) ore forming processes, (5) conditions of deposition (temperature, pressure), (6) tectonic setting, and (7) origin (genesis). Table 1.1 summarizes the important classification schemes and identified groupings. Among these classifications, the most widely accepted by economic geologists is the genetic classification which is broadly based on the supposed origin of the mineral deposits and ore-forming processes. The genetic types include deposits associated with magmatic, hydrothermal, sedimentary, metamorphic and surficial ore-forming processes as described in earlier sections of this book (Table 2.10).

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sediment-hosted Au deposits in increasingly peripheral locations; and superjacent high-and intermediate-sulfidation epi-thermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons, at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of mineralization generated in porphyry Cu systems. Individual systems have life spans of ~100,000 to several million years, whereas deposit clusters or alignments as well as entire belts may remain active for 10 m.y. or longer. The alteration and mineralization in porphyry Cu systems, occupying many cubic kilometers of rock, are zoned outward from the stocks or dike swarms, which typically comprise several generations of intermediate to felsic porphyry intrusions. Porphyry Cu ± Au ± Mo deposits are centered on the intrusions, whereas car-bonate wall rocks commonly host proximal Cu-Au skarns, less common distal Zn-Pb and/or Au skarns, and, beyond the skarn front, carbonate-replacement Cu and/or Zn-Pb-Ag ± Au deposits, and/or sediment-hosted (distal-disseminated) Au deposits. Peripheral mineralization is less conspicuous in noncarbonate wall rocks but may include base metal-or Au-bearing veins and mantos. High-sulfidation epithermal deposits may occur in lithocaps above porphyry Cu deposits, where massive sulfide lodes tend to develop in deeper feeder structures and Au ± Ag-rich, disseminated deposits within the uppermost 500 m or so. Less commonly, intermediate-sulfidation epithermal mineralization, chiefly veins, may develop on the peripheries of the lithocaps. The alteration-mineralization in the porphyry Cu deposits is zoned upward from barren, early sodic-calcic through potentially ore-grade potassic, chlorite-sericite, and sericitic, to advanced argillic, the last of these constituting the lithocaps, which may attain >1 km in thickness if unaffected by significant erosion. Low sulfidation-state chalcopyrite ± bornite assemblages are characteristic of potassic zones, whereas higher sulfidation-state sul-fides are generated progressively upward in concert with temperature decline and the concomitant greater degrees of hydrolytic alteration, culminating in pyrite ± enargite ± covellite in the shallow parts of the litho-caps. The porphyry Cu mineralization occurs in a distinctive sequence of quartz-bearing veinlets as well as in disseminated form in the altered rock between them. Magmatic-hydrothermal breccias may form during por-phyry intrusion, with some of them containing high-grade mineralization because of their intrinsic permeabil-ity. In contrast, most phreatomagmatic breccias, constituting maar-diatreme systems, are poorly mineralized at both the porphyry Cu and lithocap levels, mainly because many of them formed late in the evolution of systems. Porphyry Cu systems are initiated by injection of oxidized magma saturated with Sand metal-rich, aqueous fluids from cupolas on the tops of the subjacent parental plutons. The sequence of alteration-mineralization events charted above is principally a consequence of progressive rock and fluid cooling, from >700° to <250°C, caused by solidification of the underlying parental plutons and downward propagation of the lithostatic-hydrostatic transition. Once the plutonic magmas stagnate, the high-temperature, generally two-phase hyper-saline liquid and vapor responsible for the potassic alteration and contained mineralization at depth and early overlying advanced argillic alteration, respectively, gives way, at <350°C, to a single-phase, low-to moderate-salinity liquid that causes the sericite-chlorite and sericitic alteration and associated mineralization. This same liquid also causes mineralization of the peripheral parts of systems, including the overlying lithocaps. The progressive thermal decline of the systems combined with synmineral paleosurface degradation results in the characteristic overprinting (telescoping) and partial to total reconstitution of older by younger alteration-mineral-ization types. Meteoric water is not required for formation of this alteration-mineralization sequence although its late ingress is commonplace. Many features of porphyry Cu systems at all scales need to be taken into account during planning and execution of base and precious metal exploration programs in magmatic arc settings. At the regional and district scales, the occurrence of many deposits in belts, within which clusters and alignments are prominent, is a powerful exploration concept once one or more systems are known. At the deposit scale, particularly in the por-phyry Cu environment, early-formed features commonly, but by no means always, give rise to the best ore-bodies. Late-stage alteration overprints may cause partial depletion or complete removal of Cu and Au, but metal concentration may also result. Recognition of single ore deposit types, whether economic or not, in por-phyry Cu systems may be directly employed in combination with alteration and metal zoning concepts to †

Developments in Precambrian Geology, 2009