The giant mid-Miocene Cerro de Pasco Cordilleran polymetallic (Zn-Pb-Ag-Cu-Bi) deposit in central... more The giant mid-Miocene Cerro de Pasco Cordilleran polymetallic (Zn-Pb-Ag-Cu-Bi) deposit in central Peru formed during three successive mineralization stages resulting in low- to high-sulfidation mineral associations emplaced at a paleodepth from <500 to 1,500 m: (1) pyrrhotite pipes grading outward to sphalerite and galena replacement bodies (stage A), (2) deep quartz-pyrite veins (stage B1) and a funnel-shaped massive replacement body of pyrite-quartz (stage B2) with quartz-sericite ± kaolinite alteration, and (3) well-zoned Zn-Pb-(Bi-Ag- Cu) carbonate-replacement orebodies (stage C1) and E-W–trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins (stage C2); stages C1 and C2 are accompanied by advanced argillic alteration. Field evidence indicates that the epithermal polymetallic mineralization has formed in the shallow part of a porphyry system. A detailed microthermometric and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) study of fluid inclusions hosted in gangue and, using near-infrared microscopy, opaque ore minerals from the different mineralization stages as well as available bulk and in situ secondary ion mass spectrometry (SIMS) stable isotopic data allow reconstruction of the evolution and tracing of the source(s) of the mineralizing fluids. Fluid inclusions are two phase (L + V), homogenize to liquid at moderate temperatures (~220°–280°C in stages A, B1, B2, and C2 and down to 150°C in stage C1), and show a wide salinity range (1.2–19 wt % NaCl equiv) with no evidence of phase separation. Fluids during mineralization stages A, B1, B2, and C1 are the result of mixing between a moderate-salinity metal-rich magmatic fluid and a low-salinity fluid at the (shallow) site of deposition. The moderate-salinity metal-rich magmatic fluid cannot be interpreted as an evolved intermediate-density fluid or its boiling product due to its salinity (up to 19 wt % NaCl equiv), its high base metal concentration (>1 wt % Mn, Fe, Zn, and Pb), and its high Li, B, As, and Sb contents (up to several thousands of ppm). The obtained results suggest that the moderate-salinity metal-rich magmatic fluid results from mixing at depth between metal-rich hypersaline fluids and low-salinity magmatic fluids exsolved late in the lifetime of the magmatic-hydrothermal system. The moderate-salinity metal-rich magmatic fluid resulting from this deep mixing rose to the epithermal environment, where it in turn mixed with low-salinity fluids that were stored below the paleowater table and had similar temperatures to the moderate-salinity fluid. In contrast, enargite-pyrite veins of stage C2 were formed by the ascent of CO2-bearing, contracted vapor-like fluids that subsequently mixed with cold meteoric water. No interaction with the moderate-salinity, metal-rich magmatic fluids has been registered in stage C2. The similarity between fluid compositions and evolution during stages A, B1, B2, and C1 contrasts with their significantly different mineral assemblages that are rather controlled by changing fO2, pH, fS2, and temperature. Trace element LA-ICP-MS analyses of sphalerite, pyrite, and enargite also reveal important compositional differences. The trace elements in the measured minerals reside to a significant extent in micro- to nanoscale solid sulfide and/or sulfosalt inclusions. A direct correlation between fluid composition recorded in the studied fluid inclusion assemblages and the measured trace element composition of sphalerite, pyrite, and enargite has not been found in most cases. The cyclic rise of metal-rich, moderately saline fluids that issued from dilution of hypersaline fluids stored at depth by low-salinity magmatic fluids is a major process in the formation of stages A, B1, B2, and C1 of the giant epithermal polymetallic deposit of Cerro de Pasco. Such a mechanism may also explain moderate-salinity fluids (≈20 wt % NaCl equiv) recorded in other magmatic-related polymetallic epithermal deposits worldwide.
The large Cerro de Pasco Cordilleran base metal deposit in central Peru is the result of three su... more The large Cerro de Pasco Cordilleran base metal deposit in central Peru is the result of three successive mineralizing stages comprising both low-and high-sulfidation mineral associations: (A) several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies, (B) a massive, funnel-shaped pyrite-quartz replacement orebody, and (C) E-W-trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins and well-zoned Zn-Pb-(Bi-Ag-Cu) carbonate-replacement orebodies. This superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships. A detailed study of the textures and mineral composition of the up to 15-m-wide replacement front existing between the pyrrhotite pipes and the pyrite-quartz body allows for clarification of the relative chronology of the hydrothermal events. The results show that, in contrast to previous interpretations, the emplacement of the pyrrhotite pipes and their Zn-Pb mineralized rims precedes that of the pyrite-quartz body. The replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fS 2 , fO 2 , and pH of the mineralizing fluids. Two steps of pyrrhotite replacement have been recorded. The first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite. The second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite. Subsequently, marcasite is partly replaced by fine-grained euhedral nonporous pyrite. LA-ICP-MS trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolutionreprecipitation as the main mechanism for replacement. Positive correlations between some of the elements (e.g., Pb-Sb, Pb-Ag) are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements; however, coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded. The obtained As, Sb, Pb, and Bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems. Nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation, the initial trace element content of replaced minerals, and the subsequently dissolved neighboring phases. The results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals. This study leads to a simpler interpretation of the fluid evolution than previously proposed, with a progressive increase of fS 2 , fO 2 , and pH as a result of decreasing wall-rock buffering during the three successive mineralizing stages at Cerro de Pasco.
The Inner Carpathians comprise several distinct Neogene late-stage orogenic Pb-Zn-Cu-Ag-Au ore di... more The Inner Carpathians comprise several distinct Neogene late-stage orogenic Pb-Zn-Cu-Ag-Au ore districts. The mineral deposits in these districts are closely related to volcanic and subvolcanic rocks, and represent mainly porphyry and epithermal vein deposits, which formed within short periods of time in each district. Here, we discuss possible geodynamic and structural controls that suggest why some of the Neogene volcanic districts within the Carpathians comprise abundant mineralization, while others are barren. The Neogene period has been characterized by an overall geodynamic regime of subduction, where primary roll-back of the subducted slab and secondary phenomena, like slab break-off and the development of slab windows, could have contributed to the evolution, location and type of volcanic activity. Structural features developing in the overlying lithosphere and visible in the Carpathian crust, such as transtensional wrench corridors, block rotation and relay structures due to extrusion tectonics, have probably acted in focusing hydrothermal activity. As a result of particular events in the geodynamic evolution and the development of specific structural features, mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation. In the Slovakian ore district of the Western Carpathians, Neogene volcanism and associated mineralization were localized by sinistral, NE-trending wrench corridors, which formed part of the extruding Alcapa block. The Baia Mare ore district, in the Eastern Carpathians, reflects a transtensional wrench setting on distributed oversteps close to the termination of the Dragos Voda fault. There, mineralization was spatially controlled by the transtensional Dragos Voda master fault and associated crossfault systems. The Golden Quadrangle Cu-Au ore district of the Southern Apuseni Mountains reflects an unusual rotated transtensional/extensional setting close to the termination of a graben system. There, fluid flow was probably localized by fault propagation at the inner tip of the graben system. The spatial and temporal evolution of the magmatism and its changing geochemical signature from (N)W to (S)E strongly suggests a link with the contemporaneous northeastward roll-back of the subducted slab and a progressive southeastward detachment during accelerating roll-back. This geodynamic evolution is further supported by the present-day overall and
Porphyry-related Cordilleran polymetallic mineralization in the Morococha district, central Peru,... more Porphyry-related Cordilleran polymetallic mineralization in the Morococha district, central Peru, displays a deposit-scale base metal zonation, a common feature observed in many ore deposits of this type. The distinct pattern of zonation consists of Cu-rich ores in the core area and increasingly Zn-, Pb-, and Ag-rich ores in more distal veins and replacement orebodies. We investigated the changing composition of key ore minerals throughout these zones. They are important indicators for the conditions of mineral precipitation and evolving hydrothermal fluid. The mineral species stannoidite Cu8(Fe,Zn)3Sn2S12, vinciennite Cu10Fe4Sn(As,Sb) S16, and tennantite-tetrahedrite have variable Cu content and Fe2+/Fe3+ values between the different base metal zones. Controlled by coupled substitution mechanisms, they show Cu-excess and predominantly ferric Fe compositions in the central areas (Cu and Zn-Cu zones), whereas stoichiometric Cu values and mixed Fe3+ and Fe2+ compositions are typical in the more distal zones (Zn-Pb-Ag and Ag-Pb). These compositional changes are interpreted to reflect decreasing oxidation state of the cooling and evolving fluid and increasing reaction with the host rock toward outer parts of the deposits. Initially high Cu, Fe, and S values in the fluid decrease with precipitation of Cu- and Fe-sulfides. As result of decreasing oxidation state and Fe and Cu values in the fluid, Fe in tennantite-tetrahedrite is increasingly substituted by competing Zn, and Cu by Ag. These data show that compositions of major and even minor ore-forming minerals reflect metal content, oxidation and sulfidation state, and degree of buffering of an evolving hydrothermal fluid by the host rock on a district-scale.
Manganilvaite, CaFe 2+ Fe 3+ (Mn,Fe 2+)(Si 2 O 7)O(OH), is a new mineral species, the Mn end-memb... more Manganilvaite, CaFe 2+ Fe 3+ (Mn,Fe 2+)(Si 2 O 7)O(OH), is a new mineral species, the Mn end-member of the ilvaite group of minerals. It was found in the Pb-Zn-(Mn) skarn deposits of the central Rhodope Mountains, Bulgaria, and especially in the Ossikovo and Mogilata deposits (Madan ore district) and the Govedarnika deposit (Laki district). In the marble-hosted distal skarn-type orebodies, it is closely associated with Mn-rich clinopyroxene (hedenbergite-johannsenite) ± rhodonite, and with the products of their retrograde alteration (manganoan amphiboles and chlorites, bustamite, manganoan carbonates, quartz). The mineral is black, with a vitreous luster, brittle, with a distinct cleavage. It has Mohs hardness of 5½-6 and a micro-indentation hardness (VHN 100) of 868 kg/mm 2. The measured density D x is 3.92 g/cm 3. In refl ected light, it is opaque with moderate pleochroism, from bluish gray to grayish brown, strongly anisotropic in grayish blue to pale reddish brown colors and with red internal refl ections. It is homogeneous in BSE images and in thin sections under the IR microscope, where it is transparent. The refl ectance is low, in the range 8.3-5.7% for R min (// c) and 10.0-9.3% for R max (// a). In some cases, well-shaped dipyramidal crystals occur, with a prismatic habit along c and forms r{011}, m{110}, s{210} and o{111}. The average results of 62 and 17 electron-microprobe analyses of manganilvaite from Ossikovo and Govedarnika, respectively, are (in wt.%): MgO 0.48, 0.45;
The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an ... more The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations...
The Deva copper-gold deposit represents the richest porphyry-type ore deposit in the Miocene Sout... more The Deva copper-gold deposit represents the richest porphyry-type ore deposit in the Miocene South Apuseni Mountains metallogenic district, West Romania. It consist of cylindrical 0.5 km diameter breccia hosted subvolcanic stock, that is mineralized over more than 1 km vertically, most of which is mined to date. The mineralisation is associated with the latest Hbl-Bt andesite and consists of bornite-cpy-mgt stringers and impregnations, producing ore grades as high as 2 wt-% Cu. Detailed petrography together with field observations have allowed to define the evolutionary sequence of events. This forms the basis to constrain the chemical evolution of this magmatic-hydrothermal system on the basis of EMP, microthermometric and LA-ICPMS analyses of phenocrysts, hydrothermal mineral parageneses and silicate and sulphide melt and fluid inclusion assemblages that are currently in progress. These data will be used to reconstruct the magmatic to hydrothermal evolution of the rich Deva porphyry-Cu-Au deposit and help in determining the key-processes responsible for the genesis of highly economic porphyry-type ore deposits.
Objekttyp: Article Zeitschrift: Schweizerische mineralogische und petrographische Mitteilungen = ... more Objekttyp: Article Zeitschrift: Schweizerische mineralogische und petrographische Mitteilungen = Bulletin suisse de minéralogie et pétrographie Band (Jahr): 84 (2004) Heft 1-2: Geodynamics and Ore Deposit Evolution of the Alpine-Carpathian-Balkan-Dinaride Orogenic System
The Rosia Poieni porphyry Cu-Au and Rosia M ontana epithermal Au-Ag deposits are the largest oper... more The Rosia Poieni porphyry Cu-Au and Rosia M ontana epithermal Au-Ag deposits are the largest operating mines in the South Apuseni mineral district, Romania. Rosia M ontana is a breccia-hosted low-to intermediatesulfidation 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 M ontana, is a porphyry copper system with a high-sulfidation epithermal overprint. This study provides the first high-precision U-Pb dating of M iocene magmatic and hydrothermal events in the South Apuseni M ountains. Together with the existing 40 Ar-39 Ar data the new results show clearly that the two deposits belong to two separate magmatichydrothermal systems, the porphyry copper system of Rosia Poieni being about 3 M a younger than the neighbouring Rosia M ontana epithermal deposit. The timing of the porphyry mineralization at Rosia Poieni has been bracketed by dating the main Poieni diorite intrusion (9.42 ± 0.14 M a) and a later intra-mineralization dike (9.16 ± 0.10 M a), cutting a mineralized porphyry stockwork and cut by later porphyry veins. Whereas the magmatism at Rosia M ontana is dated at 13.15-13.61 M a by U-Pb dating on zircons and the epithermal mineralization there-at 12.71-12.85 M a by 40 Ar-39 Ar dating on hydrothermal adularia.
Porphyry Cu-Au mineralisation with associated potassic and phyllic alteration and low-sulphidatio... more Porphyry Cu-Au mineralisation with associated potassic and phyllic alteration and low-sulphidation epithermal quartz-sulphide-gold-carbonate veins, are telescoped within a vertical interval of >400 m in the Valea Morii deposit, Romania. The deposit is located in the eastern part of the Barza magmatic structure – the richest goldbearing magmatic-hydrothermal system of the South Apuseni Mountains Miocene metallogenic district. It consists of a steeply dipping intrusion of quartz diorite crosscut by a younger quartz microdiorite subvolcanic body. The field observations and time relationships between the porphyry and epithermal styles of mineralisation and host rocks in both intrusions give evidence for successive development of alternating porphyry-style veining and igneous breccias, followed by several porphyry and epithermal stage hydrothermal breccias. Detailed petrographic study allowed reconstruction of the complex scenario of magmatic and hydrothermal events. EMP and LA-ICPMS ...
Pyrite (FeS 2), arsenopyrite (FeAsS) and löllingite (FeAs 2) are exceptional gold concentrators o... more Pyrite (FeS 2), arsenopyrite (FeAsS) and löllingite (FeAs 2) are exceptional gold concentrators on Earth; yet the exact redox and structural state of this "invisible" gold and the forces driving its intake and release by these minerals remain highly controversial. Here we applied high resolution X-ray absorption spectroscopy to Au-bearing pyrite and iron sulfarsenides from hydrothermal deposits and their synthetic analogues. We show that Au preferentially enters octahedral Fe structural sites [Au(As,S) 6 ] enriched in As, by forming respectively [AuAs 1-3 S 5-3 ], [AuAs 3 S 3 ⋯AuAs 6 ] and [AuAs 6 ] atomic units in arsenian pyrite (>0.1-1.0 wt. % As), arsenopyrite and löllingite, implying a formal oxidation state of Au II in the minerals. In contrast, in As-poor pyrite, Au is dominantly chemisorbed as [Au I S 2 ] moieties in much lower concentrations. Combined with experimental data on Au mineral-fluid partitioning, our findings imply a universal control exerted by arsenic on gold incorporation in iron sulfides and sulfarsenides via coupled Au-As redox reactions. These reactions account for the observed variations in invisible gold contents in the minerals from different hydrothermal deposit types and enable quantitative prediction of iron sulfarsenide ability in controlling gold concentration and distribution in hydrothermal systems.
Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry-and epitherm... more Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry-and epithermal styles playing a major role in its total gold endowment. These deposit types are mainly clustered in two areas, the Rhodope-and Attico-Cycladic massifs, and formed from about 33 Ma to the Pleistocene, as a result of back-arc extension in the Aegean Sea, metamorphic core complex formation, and contemporaneous post-subduction and arc magmatism. In the Serbo-Macedonian massif, porphyry Cu-Carlin-style mineralization in Greece. Several factors played a role to the metal endowment of the Aegean porphyry-epithermal systems: magma fertility in the source regions, depth of emplacement of causative intrusives, relative contribution of mantle versus crustal material, redox state of subductionrelated magmas, and physico-chemical fluid conditions at the site of ore deposition.
Fluid inclusion studies give unique insights into physical conditions and composition of fluids i... more Fluid inclusion studies give unique insights into physical conditions and composition of fluids involved in geological processes. Most studies to date are performed on transparent minerals. Near-infrared (NIR) microscopy allows also microthermometry to be performed on minerals that are opaque to the visible light such as pyrite, hematite, wolframite, enargite and stibnite. The main drawback of this technique is the underestimation of the recorded phase-change temperatures with increasing light intensity, up to several hundred percent in the case of ice-melting temperatures. Although this issue has been known for a decade, it is poorly understood. We address this problem based on a systematic study of synthetic fluid inclusions in a variety of opaque minerals. For the first time, fluid inclusions have been co-synthetized with success in quartz and opaque minerals. Fracturing the host minerals by in-situ quenching allowed for fluid–mineral equilibration prior to fluid inclusion formation. In this study, we assess the impact of mineral intrinsic parameters, mainly absorption and thermal-conductivity, and experimental settings (light source operative power, diaphragms aperture, and the use of filters) on recorded phase-change temperatures. We show that these are underestimated due to local overheating of the sample caused by radiative heating from the light source. It affects all minerals and the extent of the temperature shift of the observed phase-changes depends on sample thickness, mineral characteristics, and the amount of light reaching the sample. Thus, any calibration of the temperature shift as a function of the amount of light is complicated and in most cases impracticable. However, we demonstrate, based on co-generated inclusions in opaque minerals and quartz that yield similar values during NIR-microthermometry that for any mineral, there is a range of light power and microscope settings for which no shift is noticeable within the thermal stage accuracy. These are defined as "ideal measuring conditions" ensuring reliability of acquired microthermometry data.
magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting... more magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting for Li. By contrast, heated hydrothermal quartz shows enrichment up to several hundreds of ppm in Cu, Li, and Na, which substitute for originally present H. This study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments, leading to erroneous quantification of elemental concentrations. In addition, each quartz crystal also becomes significantly enriched in Cu in the sub-surface layer during heating. We propose that sub-surface Cu enrichment is a direct indication of Cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device. Our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations.
The giant mid-Miocene Cerro de Pasco Cordilleran polymetallic (Zn-Pb-Ag-Cu-Bi) deposit in central... more The giant mid-Miocene Cerro de Pasco Cordilleran polymetallic (Zn-Pb-Ag-Cu-Bi) deposit in central Peru formed during three successive mineralization stages resulting in low- to high-sulfidation mineral associations emplaced at a paleodepth from <500 to 1,500 m: (1) pyrrhotite pipes grading outward to sphalerite and galena replacement bodies (stage A), (2) deep quartz-pyrite veins (stage B1) and a funnel-shaped massive replacement body of pyrite-quartz (stage B2) with quartz-sericite ± kaolinite alteration, and (3) well-zoned Zn-Pb-(Bi-Ag- Cu) carbonate-replacement orebodies (stage C1) and E-W–trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins (stage C2); stages C1 and C2 are accompanied by advanced argillic alteration. Field evidence indicates that the epithermal polymetallic mineralization has formed in the shallow part of a porphyry system. A detailed microthermometric and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) study of fluid inclusions hosted in gangue and, using near-infrared microscopy, opaque ore minerals from the different mineralization stages as well as available bulk and in situ secondary ion mass spectrometry (SIMS) stable isotopic data allow reconstruction of the evolution and tracing of the source(s) of the mineralizing fluids. Fluid inclusions are two phase (L + V), homogenize to liquid at moderate temperatures (~220°–280°C in stages A, B1, B2, and C2 and down to 150°C in stage C1), and show a wide salinity range (1.2–19 wt % NaCl equiv) with no evidence of phase separation. Fluids during mineralization stages A, B1, B2, and C1 are the result of mixing between a moderate-salinity metal-rich magmatic fluid and a low-salinity fluid at the (shallow) site of deposition. The moderate-salinity metal-rich magmatic fluid cannot be interpreted as an evolved intermediate-density fluid or its boiling product due to its salinity (up to 19 wt % NaCl equiv), its high base metal concentration (>1 wt % Mn, Fe, Zn, and Pb), and its high Li, B, As, and Sb contents (up to several thousands of ppm). The obtained results suggest that the moderate-salinity metal-rich magmatic fluid results from mixing at depth between metal-rich hypersaline fluids and low-salinity magmatic fluids exsolved late in the lifetime of the magmatic-hydrothermal system. The moderate-salinity metal-rich magmatic fluid resulting from this deep mixing rose to the epithermal environment, where it in turn mixed with low-salinity fluids that were stored below the paleowater table and had similar temperatures to the moderate-salinity fluid. In contrast, enargite-pyrite veins of stage C2 were formed by the ascent of CO2-bearing, contracted vapor-like fluids that subsequently mixed with cold meteoric water. No interaction with the moderate-salinity, metal-rich magmatic fluids has been registered in stage C2. The similarity between fluid compositions and evolution during stages A, B1, B2, and C1 contrasts with their significantly different mineral assemblages that are rather controlled by changing fO2, pH, fS2, and temperature. Trace element LA-ICP-MS analyses of sphalerite, pyrite, and enargite also reveal important compositional differences. The trace elements in the measured minerals reside to a significant extent in micro- to nanoscale solid sulfide and/or sulfosalt inclusions. A direct correlation between fluid composition recorded in the studied fluid inclusion assemblages and the measured trace element composition of sphalerite, pyrite, and enargite has not been found in most cases. The cyclic rise of metal-rich, moderately saline fluids that issued from dilution of hypersaline fluids stored at depth by low-salinity magmatic fluids is a major process in the formation of stages A, B1, B2, and C1 of the giant epithermal polymetallic deposit of Cerro de Pasco. Such a mechanism may also explain moderate-salinity fluids (≈20 wt % NaCl equiv) recorded in other magmatic-related polymetallic epithermal deposits worldwide.
The large Cerro de Pasco Cordilleran base metal deposit in central Peru is the result of three su... more The large Cerro de Pasco Cordilleran base metal deposit in central Peru is the result of three successive mineralizing stages comprising both low-and high-sulfidation mineral associations: (A) several pyrrhotite pipes grading outward to sphalerite and galena replacement bodies, (B) a massive, funnel-shaped pyrite-quartz replacement orebody, and (C) E-W-trending Cu-Ag-(Au-Zn-Pb) enargite-pyrite veins and well-zoned Zn-Pb-(Bi-Ag-Cu) carbonate-replacement orebodies. This superposition of hydrothermal events leads to complex replacement textures and crosscutting relationships. A detailed study of the textures and mineral composition of the up to 15-m-wide replacement front existing between the pyrrhotite pipes and the pyrite-quartz body allows for clarification of the relative chronology of the hydrothermal events. The results show that, in contrast to previous interpretations, the emplacement of the pyrrhotite pipes and their Zn-Pb mineralized rims precedes that of the pyrite-quartz body. The replacement textures affecting pyrrhotite and arsenopyrite and the nature of the newly formed minerals have been used as a qualitative way to track the evolution of fS 2 , fO 2 , and pH of the mineralizing fluids. Two steps of pyrrhotite replacement have been recorded. The first one takes place under moderate acidity and relatively reduced to moderately oxidized conditions and is marked by replacement of pyrrhotite by euhedral nonporous pyrite. The second step occurs under more acidic and oxidized conditions and is characterized by replacement of pyrrhotite by porous marcasite and replacement of arsenopyrite by pyrite. Subsequently, marcasite is partly replaced by fine-grained euhedral nonporous pyrite. LA-ICP-MS trace element analyses of the replaced pyrrhotite and arsenopyrite and of the newly formed marcasite and pyrite support dissolutionreprecipitation as the main mechanism for replacement. Positive correlations between some of the elements (e.g., Pb-Sb, Pb-Ag) are indicative of the possible presence of nanoscale solid inclusions as main carriers for those elements; however, coupled substitutions and incorporation of some of the elements at a ppm level into the pyrite and marcasite structures cannot be excluded. The obtained As, Sb, Pb, and Bi values in pyrite are systematically higher than published data of pyrite in epithermal and porphyry systems. Nature and trace element content of the newly formed minerals yield information on the physicochemical conditions during their precipitation, the initial trace element content of replaced minerals, and the subsequently dissolved neighboring phases. The results show that the metal concentration of the fluid is locally influenced by the composition of the dissolved minerals. This study leads to a simpler interpretation of the fluid evolution than previously proposed, with a progressive increase of fS 2 , fO 2 , and pH as a result of decreasing wall-rock buffering during the three successive mineralizing stages at Cerro de Pasco.
The Inner Carpathians comprise several distinct Neogene late-stage orogenic Pb-Zn-Cu-Ag-Au ore di... more The Inner Carpathians comprise several distinct Neogene late-stage orogenic Pb-Zn-Cu-Ag-Au ore districts. The mineral deposits in these districts are closely related to volcanic and subvolcanic rocks, and represent mainly porphyry and epithermal vein deposits, which formed within short periods of time in each district. Here, we discuss possible geodynamic and structural controls that suggest why some of the Neogene volcanic districts within the Carpathians comprise abundant mineralization, while others are barren. The Neogene period has been characterized by an overall geodynamic regime of subduction, where primary roll-back of the subducted slab and secondary phenomena, like slab break-off and the development of slab windows, could have contributed to the evolution, location and type of volcanic activity. Structural features developing in the overlying lithosphere and visible in the Carpathian crust, such as transtensional wrench corridors, block rotation and relay structures due to extrusion tectonics, have probably acted in focusing hydrothermal activity. As a result of particular events in the geodynamic evolution and the development of specific structural features, mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation. In the Slovakian ore district of the Western Carpathians, Neogene volcanism and associated mineralization were localized by sinistral, NE-trending wrench corridors, which formed part of the extruding Alcapa block. The Baia Mare ore district, in the Eastern Carpathians, reflects a transtensional wrench setting on distributed oversteps close to the termination of the Dragos Voda fault. There, mineralization was spatially controlled by the transtensional Dragos Voda master fault and associated crossfault systems. The Golden Quadrangle Cu-Au ore district of the Southern Apuseni Mountains reflects an unusual rotated transtensional/extensional setting close to the termination of a graben system. There, fluid flow was probably localized by fault propagation at the inner tip of the graben system. The spatial and temporal evolution of the magmatism and its changing geochemical signature from (N)W to (S)E strongly suggests a link with the contemporaneous northeastward roll-back of the subducted slab and a progressive southeastward detachment during accelerating roll-back. This geodynamic evolution is further supported by the present-day overall and
Porphyry-related Cordilleran polymetallic mineralization in the Morococha district, central Peru,... more Porphyry-related Cordilleran polymetallic mineralization in the Morococha district, central Peru, displays a deposit-scale base metal zonation, a common feature observed in many ore deposits of this type. The distinct pattern of zonation consists of Cu-rich ores in the core area and increasingly Zn-, Pb-, and Ag-rich ores in more distal veins and replacement orebodies. We investigated the changing composition of key ore minerals throughout these zones. They are important indicators for the conditions of mineral precipitation and evolving hydrothermal fluid. The mineral species stannoidite Cu8(Fe,Zn)3Sn2S12, vinciennite Cu10Fe4Sn(As,Sb) S16, and tennantite-tetrahedrite have variable Cu content and Fe2+/Fe3+ values between the different base metal zones. Controlled by coupled substitution mechanisms, they show Cu-excess and predominantly ferric Fe compositions in the central areas (Cu and Zn-Cu zones), whereas stoichiometric Cu values and mixed Fe3+ and Fe2+ compositions are typical in the more distal zones (Zn-Pb-Ag and Ag-Pb). These compositional changes are interpreted to reflect decreasing oxidation state of the cooling and evolving fluid and increasing reaction with the host rock toward outer parts of the deposits. Initially high Cu, Fe, and S values in the fluid decrease with precipitation of Cu- and Fe-sulfides. As result of decreasing oxidation state and Fe and Cu values in the fluid, Fe in tennantite-tetrahedrite is increasingly substituted by competing Zn, and Cu by Ag. These data show that compositions of major and even minor ore-forming minerals reflect metal content, oxidation and sulfidation state, and degree of buffering of an evolving hydrothermal fluid by the host rock on a district-scale.
Manganilvaite, CaFe 2+ Fe 3+ (Mn,Fe 2+)(Si 2 O 7)O(OH), is a new mineral species, the Mn end-memb... more Manganilvaite, CaFe 2+ Fe 3+ (Mn,Fe 2+)(Si 2 O 7)O(OH), is a new mineral species, the Mn end-member of the ilvaite group of minerals. It was found in the Pb-Zn-(Mn) skarn deposits of the central Rhodope Mountains, Bulgaria, and especially in the Ossikovo and Mogilata deposits (Madan ore district) and the Govedarnika deposit (Laki district). In the marble-hosted distal skarn-type orebodies, it is closely associated with Mn-rich clinopyroxene (hedenbergite-johannsenite) ± rhodonite, and with the products of their retrograde alteration (manganoan amphiboles and chlorites, bustamite, manganoan carbonates, quartz). The mineral is black, with a vitreous luster, brittle, with a distinct cleavage. It has Mohs hardness of 5½-6 and a micro-indentation hardness (VHN 100) of 868 kg/mm 2. The measured density D x is 3.92 g/cm 3. In refl ected light, it is opaque with moderate pleochroism, from bluish gray to grayish brown, strongly anisotropic in grayish blue to pale reddish brown colors and with red internal refl ections. It is homogeneous in BSE images and in thin sections under the IR microscope, where it is transparent. The refl ectance is low, in the range 8.3-5.7% for R min (// c) and 10.0-9.3% for R max (// a). In some cases, well-shaped dipyramidal crystals occur, with a prismatic habit along c and forms r{011}, m{110}, s{210} and o{111}. The average results of 62 and 17 electron-microprobe analyses of manganilvaite from Ossikovo and Govedarnika, respectively, are (in wt.%): MgO 0.48, 0.45;
The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an ... more The world-class San Rafael tin (-copper) deposit (central Andean tin belt, southeast Peru) is an exceptionally large and rich (>1 million metric tons Sn; grades typically >2% Sn) cassiterite-bearing hydrothermal vein system hosted by a late Oligocene (ca. 24 Ma) peraluminous K-feldspar-megacrystic granitic complex and surrounding Ordovician shales affected by deformation and low-grade metamorphism. The mineralization consists of NW-trending, quartz-cassiterite-sulfide veins and fault-controlled breccia bodies (>1.4 km in vertical and horizontal extension). They show volumetrically important tourmaline alteration that principally formed prior to the main ore stage, similar to other granite-related Sn deposits worldwide. We present here a detailed textural and geochemical study of tourmaline, aiming to trace fluid evolution of the San Rafael magmatic-hydrothermal system that led to the deposition of tin mineralization. Based on previous works and new petrographic observations...
The Deva copper-gold deposit represents the richest porphyry-type ore deposit in the Miocene Sout... more The Deva copper-gold deposit represents the richest porphyry-type ore deposit in the Miocene South Apuseni Mountains metallogenic district, West Romania. It consist of cylindrical 0.5 km diameter breccia hosted subvolcanic stock, that is mineralized over more than 1 km vertically, most of which is mined to date. The mineralisation is associated with the latest Hbl-Bt andesite and consists of bornite-cpy-mgt stringers and impregnations, producing ore grades as high as 2 wt-% Cu. Detailed petrography together with field observations have allowed to define the evolutionary sequence of events. This forms the basis to constrain the chemical evolution of this magmatic-hydrothermal system on the basis of EMP, microthermometric and LA-ICPMS analyses of phenocrysts, hydrothermal mineral parageneses and silicate and sulphide melt and fluid inclusion assemblages that are currently in progress. These data will be used to reconstruct the magmatic to hydrothermal evolution of the rich Deva porphyry-Cu-Au deposit and help in determining the key-processes responsible for the genesis of highly economic porphyry-type ore deposits.
Objekttyp: Article Zeitschrift: Schweizerische mineralogische und petrographische Mitteilungen = ... more Objekttyp: Article Zeitschrift: Schweizerische mineralogische und petrographische Mitteilungen = Bulletin suisse de minéralogie et pétrographie Band (Jahr): 84 (2004) Heft 1-2: Geodynamics and Ore Deposit Evolution of the Alpine-Carpathian-Balkan-Dinaride Orogenic System
The Rosia Poieni porphyry Cu-Au and Rosia M ontana epithermal Au-Ag deposits are the largest oper... more The Rosia Poieni porphyry Cu-Au and Rosia M ontana epithermal Au-Ag deposits are the largest operating mines in the South Apuseni mineral district, Romania. Rosia M ontana is a breccia-hosted low-to intermediatesulfidation 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 M ontana, is a porphyry copper system with a high-sulfidation epithermal overprint. This study provides the first high-precision U-Pb dating of M iocene magmatic and hydrothermal events in the South Apuseni M ountains. Together with the existing 40 Ar-39 Ar data the new results show clearly that the two deposits belong to two separate magmatichydrothermal systems, the porphyry copper system of Rosia Poieni being about 3 M a younger than the neighbouring Rosia M ontana epithermal deposit. The timing of the porphyry mineralization at Rosia Poieni has been bracketed by dating the main Poieni diorite intrusion (9.42 ± 0.14 M a) and a later intra-mineralization dike (9.16 ± 0.10 M a), cutting a mineralized porphyry stockwork and cut by later porphyry veins. Whereas the magmatism at Rosia M ontana is dated at 13.15-13.61 M a by U-Pb dating on zircons and the epithermal mineralization there-at 12.71-12.85 M a by 40 Ar-39 Ar dating on hydrothermal adularia.
Porphyry Cu-Au mineralisation with associated potassic and phyllic alteration and low-sulphidatio... more Porphyry Cu-Au mineralisation with associated potassic and phyllic alteration and low-sulphidation epithermal quartz-sulphide-gold-carbonate veins, are telescoped within a vertical interval of >400 m in the Valea Morii deposit, Romania. The deposit is located in the eastern part of the Barza magmatic structure – the richest goldbearing magmatic-hydrothermal system of the South Apuseni Mountains Miocene metallogenic district. It consists of a steeply dipping intrusion of quartz diorite crosscut by a younger quartz microdiorite subvolcanic body. The field observations and time relationships between the porphyry and epithermal styles of mineralisation and host rocks in both intrusions give evidence for successive development of alternating porphyry-style veining and igneous breccias, followed by several porphyry and epithermal stage hydrothermal breccias. Detailed petrographic study allowed reconstruction of the complex scenario of magmatic and hydrothermal events. EMP and LA-ICPMS ...
Pyrite (FeS 2), arsenopyrite (FeAsS) and löllingite (FeAs 2) are exceptional gold concentrators o... more Pyrite (FeS 2), arsenopyrite (FeAsS) and löllingite (FeAs 2) are exceptional gold concentrators on Earth; yet the exact redox and structural state of this "invisible" gold and the forces driving its intake and release by these minerals remain highly controversial. Here we applied high resolution X-ray absorption spectroscopy to Au-bearing pyrite and iron sulfarsenides from hydrothermal deposits and their synthetic analogues. We show that Au preferentially enters octahedral Fe structural sites [Au(As,S) 6 ] enriched in As, by forming respectively [AuAs 1-3 S 5-3 ], [AuAs 3 S 3 ⋯AuAs 6 ] and [AuAs 6 ] atomic units in arsenian pyrite (>0.1-1.0 wt. % As), arsenopyrite and löllingite, implying a formal oxidation state of Au II in the minerals. In contrast, in As-poor pyrite, Au is dominantly chemisorbed as [Au I S 2 ] moieties in much lower concentrations. Combined with experimental data on Au mineral-fluid partitioning, our findings imply a universal control exerted by arsenic on gold incorporation in iron sulfides and sulfarsenides via coupled Au-As redox reactions. These reactions account for the observed variations in invisible gold contents in the minerals from different hydrothermal deposit types and enable quantitative prediction of iron sulfarsenide ability in controlling gold concentration and distribution in hydrothermal systems.
Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry-and epitherm... more Greece hosts a variety of magmatic-hydrothermal ore deposits/prospects with porphyry-and epithermal styles playing a major role in its total gold endowment. These deposit types are mainly clustered in two areas, the Rhodope-and Attico-Cycladic massifs, and formed from about 33 Ma to the Pleistocene, as a result of back-arc extension in the Aegean Sea, metamorphic core complex formation, and contemporaneous post-subduction and arc magmatism. In the Serbo-Macedonian massif, porphyry Cu-Carlin-style mineralization in Greece. Several factors played a role to the metal endowment of the Aegean porphyry-epithermal systems: magma fertility in the source regions, depth of emplacement of causative intrusives, relative contribution of mantle versus crustal material, redox state of subductionrelated magmas, and physico-chemical fluid conditions at the site of ore deposition.
Fluid inclusion studies give unique insights into physical conditions and composition of fluids i... more Fluid inclusion studies give unique insights into physical conditions and composition of fluids involved in geological processes. Most studies to date are performed on transparent minerals. Near-infrared (NIR) microscopy allows also microthermometry to be performed on minerals that are opaque to the visible light such as pyrite, hematite, wolframite, enargite and stibnite. The main drawback of this technique is the underestimation of the recorded phase-change temperatures with increasing light intensity, up to several hundred percent in the case of ice-melting temperatures. Although this issue has been known for a decade, it is poorly understood. We address this problem based on a systematic study of synthetic fluid inclusions in a variety of opaque minerals. For the first time, fluid inclusions have been co-synthetized with success in quartz and opaque minerals. Fracturing the host minerals by in-situ quenching allowed for fluid–mineral equilibration prior to fluid inclusion formation. In this study, we assess the impact of mineral intrinsic parameters, mainly absorption and thermal-conductivity, and experimental settings (light source operative power, diaphragms aperture, and the use of filters) on recorded phase-change temperatures. We show that these are underestimated due to local overheating of the sample caused by radiative heating from the light source. It affects all minerals and the extent of the temperature shift of the observed phase-changes depends on sample thickness, mineral characteristics, and the amount of light reaching the sample. Thus, any calibration of the temperature shift as a function of the amount of light is complicated and in most cases impracticable. However, we demonstrate, based on co-generated inclusions in opaque minerals and quartz that yield similar values during NIR-microthermometry that for any mineral, there is a range of light power and microscope settings for which no shift is noticeable within the thermal stage accuracy. These are defined as "ideal measuring conditions" ensuring reliability of acquired microthermometry data.
magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting... more magmatic quartz records only small, up to a few ppm, enrichment in Cu and Na, mostly substituting for Li. By contrast, heated hydrothermal quartz shows enrichment up to several hundreds of ppm in Cu, Li, and Na, which substitute for originally present H. This study reveals that the composition of both quartz and its hosted melt inclusions may be significantly modified upon heating experiments, leading to erroneous quantification of elemental concentrations. In addition, each quartz crystal also becomes significantly enriched in Cu in the sub-surface layer during heating. We propose that sub-surface Cu enrichment is a direct indication of Cu diffusion in quartz externally sourced from both the surrounding sulfides as well as the copper pins belonging to the heating device. Our study shows that the chemical compositions of both heated quartz and its hosted inclusions must be interpreted with great caution to avoid misleading geological interpretations.
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Papers by K. Kouzmanov