Mineralogical and chemical evolution of ochreous precipitates from the Libiola Fe–Cu-sulfide mine (Eastern Liguria,Italy)

The mineralogical and chemical evolution of ochreous precipitates forming from acid mine drainage (AMD) from the abandoned Libiola Fe–Cu-sulfide mine (Eastern Liguria, Italy) was followed through a multianalytical approach (XRD, TEM, XRF, ICP) applied to surface precipitates and associated waters collected from several mine adits. The mineralogy of the precipitates changed significantly as a consequence of the variations of the chemical parameters of the circulating solutions (mainly pH, Eh, and sulfate concentrations) which, in turn, were mainly controlled by mixing with unpolluted stream and rill waters of the mining area. A progressive transition from jarosite-, to schwertmannite-, to goethite-, to ferrihydrite-, to amorphous-dominated precipitates was observed, mainly as a consequence of an increase in the pH of the associated solutions. This mineralogical evolution agrees well with the aqueous speciation and Eh–pH stability calculations performed on the waters associated with the different precipitate types. Furthermore, TEM analysis indicated that metastable pristine phases (schwertmannite) tend to transform progressively to well-crystallized more stable species, here represented by goethite. The comparison of the water chemistry and the crystal chemistry of the different precipitates showed a significant decrease in the Zn, Cu, Ni, Co contents in waters where the coexisting precipitates were almost exclusively composed of goethite. The distribution of V, Sr, As concentrations within the different precipitates showed that the most efficient scavenging phase for these elements was jarosite, whereas ferrihydrite efficiently took up Pb ions, and schwermannite acted as a natural sink for Cr.     

Different types of fine-grained sediments associated with acid mine drainage in the Libiola Fe–Cu mine area (Ligurian Apennines,Italy)

Different types of fine-grained chemical precipitates were characterized in the surroundings of the pyrite-chalcopyrite mine of Libiola (Northern Italy). Both water chemistry and sediment composition were used to investigate metal mobility near the mine area. Local drainage waters were very acidic (with a pH as low as 2.5) and were rich in dissolved metals (Fe, Al, Cu, Zn, Mn, Ni). Sediments associated with low pH water (pH <4.5) were ochreous mixtures of schwertmannite and goethite with traces of jarosite. Their chemistry was dominated by Fe and they had, compared to other sediments investigated, low concentrations of other metals. When the acidity decreased gradually, other precipitates formed. At a pH of approximately 5, a poorly crystalline, whitish, Al-rich precipitate occurred. At a pH between 6 and 7, a poorly crystalline, blue, Cu (Zn) rich phase was present. These “sequential” precipitation events progressively reduced the metal loading typical of the acidic mine water when there was a gradual mixing with normal water. When a sudden mixing between normal waters (pH ∼8, Ca–HCO₃, low metal bearing) and acidic waters took place, a rapid flocculation occurred of mixed precipitates containing Fe, Al and trace elements.     

Mineralogical and geochemical investigation of layered chromitites from the Bracco–Gabbro complex, Ligurian ophiolite, Italy

The Bracco–Gabbro Complex (Internal Liguride ophiolite), that intruded subcontinental mantle peridotite, contains layers of chromitite that are associated with ultramafic differentiates. The chromitites and disseminated chromites in the ultramafics have Al contents similar to the Al-rich podiform chromitites [0.40 < Cr# = Cr/(Cr + Al) < 0.55]. TiO₂ contents of the chromitites are unusually high and range up to 0.82 wt%. The calculated Al₂O₃ and TiO₂ content of the parental melt suggest that the melt was a MORB type. Geothermobarometrical calculations on few preserved silicate inclusions revealed formation temperatures between 970 and 820 °C under a relatively high oxygen fugacity (ΔlogfO₂ at +2.0–2.4). Chromitites were altered during the post-magmatic tectono-metamorphic uplift and the final exposure at the seafloor, as evidenced by the formation of ferrian chromite. The PGE contents of the chromitites and associated ultramafics are unusually low (PGEmax 83 ppb). The chondrite-normalized PGE spidergrams show positive PGE patterns and to some extent similarities with the typical trend of stratiform chromitites. No specific PGM have been found but low concentrations of PPGE (Rh, Pt, and Pd) have been detected in the sulphides that occur interstitially to or enclosed in chromite. Recently, it has been shown that the Internal Liguride gabbroic intrusions have formed by relatively low degrees of partial melting of the asthenospheric mantle. We conclude that the low degree of partial melting might be the main factor to control the unusual low PGE contents and the rather unique PGE distribution in the Bracco chromitites.     

Mineralogical and geochemical studies on the Gowd-e-Morad (Ni,Co, As–Cu) mineral deposit,Anarak (central Iran)

The Ni, Co, As, and Cu deposit of Gowd-e-Morad is located 20 km northwest of Anarak in Central Iran. In this hydrothermal deposit, mineralization occurs as veins in a fault breccia zone hosted by the Chahgorbeh (schist and metabasite) complex. The main ores are made up of Ni, Co, and Cu arsenides. Petrologic studies and results obtained from geochemical analyses have indicated that the Ni, Co, As, and Cu are derived from ultramafic rocks while Pb and Zn are likely to be derived from schist. Based on the geochemical evidence, particularly the high correlation between Ni, Co, and As, it is proposed that this deposit be categorized as a “five elements” mineral deposit. Fluid inclusion studies have shown homogenization temperatures (T_H) in the range 113?206 ?C and salinity 3?13.5 % wt eq. NaCl. Therefore this “five elements” mineral deposit has been determined as a low temperature, epithermal deposit type. It is proposed that the low fluid temperatures are a result of an environment of formation which was distal to a volcanogenic source systems and the major influence of meteoric waters in the hydrothermal system.     

Integrated geophysical and geochemical study on AMD generation at the Haveri Au–Cu mine tailings,SW Finland

The Haveri tailings area contains 1.5 Mt of sulfide-bearing waste from the Au–Cu mine that operated during 1942–1961. Geophysical and geochemical methods were used to evaluate and characterize the generation of acid mine drainage (AMD). Correlations were examined among the electrical resistivity tomography (ERT) data, the total sulfide content and concentrations of sulfide-bound metals (Cu, Co, Fe, Mn, Ni, Pb and Zn) of tailings samples, and the resistivity and geochemistry of surface water. The resulting geophysical–geochemical model defines an area in the vadose tailings, where a low resistivity anomaly (<10 Ohm m) is correlated with the highest sulfide content, extensive sulfide oxidation and low pH (average 3.1). The physical and geochemical conditions, resulting from the oxidation of the sulfide minerals, suggest that the low resistivity anomaly is associated with acidic and metal-rich porewater (i.e., AMD). The lower resistivity values in the saturated zone of the central impoundment suggest the formation of a plume of AMD. The natural subsoil layer (silt and clay) and the bedrock surface below the tailings area were well mapped from the ERT data. The detected fracture zones of the bedrock that could work as leakage pathways for AMD were consistent with previous geological studies. The integrated methodology of the study offers a promising approach to fast and reliable monitoring of areas of potential AMD generation and its subsurface movement over large areas (ca. 9 ha). This methodology could be helpful in planning drill core sampling locations for geochemical and mineralogical analysis, groundwater sampling, and choosing and monitoring remedial programs.     

Mineralogical,petrological, and geochemical studies of the Limahe mafic–ultramatic intrusion and associated Ni–Cu sulfide ores,SW China

The Limahe Ni–Cu sulfide deposit is hosted by a small mafic–ultramafic intrusion (800 × 200 × 300 m) that is temporally associated with the voluminous Permian flood basalts in SW China. The objective of this study is to better understand the origin of the deposit in the context of regional magmatism which is important for the ongoing mineral exploration in the region. The Limahe intrusion is a multiphase intrusion with an ultramafic unit at the base and a mafic unit at the top. The two rock units have intrusive contacts and exhibit similar mantle-normalized trace element patterns and Sr–Nd isotopic compositions but significantly different cumulus mineralogy and major element compositions. The similarities suggest that they are related to a common parental liquid, whereas the differences point to magma differentiation by olivine crystallization at depth. Sulfide mineralization is restricted to the ultramafic unit. The abundances of sulfides in the ultramafic unit generally increase towards the basal contacts with sedimentary footwall. The δ ³⁴S values of sulfide minerals from the Limahe deposit are elevated, ranging from +2.4 to +5.4‰. These values suggest the involvement of external S with elevated δ ³⁴S values. The mantle-normalized platinum-group element (PGE) patterns of bulk sulfide ores are similar to those of picrites associated with flood basalts in the region. The abundances of PGE in the sulfide ores, however, are significantly lower than that of sulfide liquid expected to segregate from undepleted picrite magma. Cr-spinel and olivine are present in the Limahe ultramafic rocks as well as in the picrites. Mantle-normalized trace element patterns of the Limahe intrusion generally resemble those of the picrites. However, negative Nb–Ta anomalies, common features of contamination with the lower or middle crust, are present in the intrusion but absent in the picrites. Sr–Nd isotopes suggest that the Limahe intrusion experienced higher degrees of contamination with the upper crust than did the picrites. The results of this study permit us to suggest that the parental magma of the Limahe intrusion was derived from picritic magma by olivine fractionation and contamination in a staging chamber at mid-crustal levels. Depletion of PGE in the sulfide ores in the Limahe intrusion is likely due to previous sulfide segregation of the parental magmas in the staging chamber. Sulfide mineralization in the Limahe intrusion is related to second-stage sulfide segregation after the fractionated magmas acquired external S from pyrite-bearing country rocks during magma ascent to the Limahe chamber. The abrupt change in mineralogical and chemical compositions between the ultramafic unit and the overlying unit suggests that at least two separate pulses of magma were involved in the development of the Limahe intrusion. We propose that the Limahe intrusion was once a wider part of a dynamic conduit that fed magma to the overlying subvolcanic dykes/sills or lavas. The ultramafic unit formed by the first, relatively more primitive magma, and the mafic unit formed by the second, relatively more fractionated magma. Immiscible sulfide droplets that segregated from the first magma settled down with olivine crystals to form the sulfide-bearing, olivine-rich rocks in the base of the intrusion. The overlying residual liquids were then pushed out of the chamber by the second magma. Critical factors for the formation of an economic Ni–Cu sulfide deposit in such a small intrusion include the dynamic petrologic processes involved and the availability of external sulfur. The Limahe deposit reminds us that small, multiphase, mafic–ultramafic intrusions in the region should not be overlooked for the potential of economic Ni–Cu sulfide deposits.     

The Nature of Tungstenite of the Bystrinskoe Porphyry-Skarn Au–Fe–Cu Deposit (Eastern Transbaikalia,Russia)

Doklady Earth Sciences - Tungstenite of unusual shapes (spheroids, rings, threads, spirals, etc.) was found in scheelite of gold-bearing quartz–carbonate–pyrite–chalcopyrite...     

Listvenite–lode association at the Barramiya gold mine,Eastern Desert,Egypt

Several occurrences of gold-bearing quartz veins are situated along the east–northeast-trending Barramiya–Um Salatit ophiolitic belt in the central Eastern Desert of Egypt. In the Barramiya mine, gold mineralization within carbonaceous, listvenized serpentinite and adjacent to post-tectonic granite stocks points toward a significant role of listvenitization in the ore genesis. The mineralization is related to quartz and quartz–carbonate lodes in silicified/carbonatized wallrocks. Ore minerals, disseminated in the quartz veins and adjacent wallrocks are mainly arsenopyrite, pyrite and trace amounts of chalcopyrite, sphalerite, tetrahedrite, pyrrhotite, galena, gersdorffite and gold. Partial to complete replacement of arsenopyrite by pyrite and/or marcasite is common. Other secondary phases include covellite and goethite. Native gold and gold–silver alloy occur as tiny grains along micro-fractures in the quartz veins. However, the bulk mineralization can be attributed to auriferous arsenopyrite and arsenic-bearing pyrite (with hundreds of ppms of refractory Au), as evident by electron microprobe and LA-ICP-MS analyses.The mineralized quartz veins are characterized by abundant carbonic (CO₂ ± CH₄ ± H₂O) and aqueous-carbonic (H₂O–NaCl–CO₂ ± CH₄) inclusions along intragranular trails, whereas aqueous inclusions (H₂O–NaCl ± CO₂) are common in secondary sites. Based on the fluid inclusions data combined with thermometry of the auriferous arsenopyrite, the pressure–temperature conditions of the Barramiya gold mineralization range from 1.3 to 2.4 kbar at 325–370 °C, consistent with mesothermal conditions. Based on the measured δ³⁴S values of pyrite and arsenopyrite intimately associated with gold, the calculated δ³⁴S_Σs values suggest that circulating magmatic, dilute aqueous-carbonic fluids leached gold and isotopically light sulfur from the ophiolitic sequence. As the ore fluids infiltrated into the sheared listvenite rocks, a sharp decrease in the fluid fO₂ via interaction with the carbonaceous wallrocks triggered gold deposition in structurally favorable sites.     

Mineralogical, fluid inclusion, and stable isotope constraints on mechanisms of ore deposition at the Samgwang mine (Republic of Korea)—a mesothermal, vein-hosted gold–silver deposit

The Samgwang mine is located in the Cheongyang gold district (Cheonan Metallogenic Province) of the Republic of Korea. It consists of eight massive, gold-bearing quartz veins that filled NE- and NW-striking fractures along fault zones in Precambrian granitic gneiss of the Gyeonggi massif. Their mineralogy and paragenesis allow two separate vein-forming episodes to be recognized, temporally separated by a major faulting event. The ore minerals occur in quartz and calcite of stage I, associated with fracturing and healing of veins. Hydrothermal wall-rock alteration minerals of stage I include Fe-rich chlorite (Fe/(Fe+Mg) ratios 0.74-0.81), muscovite, illite, K-feldspar, and minor arsenopyrite, pyrite, and carbonates. Sulfide minerals deposited along with electrum during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, argentite, pyrargyrite, and argentian tetrahedrite. Only calcite was deposited during stage II. Fluid inclusions in quartz contain three main types of C–O–H fluids: CO₂-rich, CO₂–H₂O, and aqueous inclusions. Quartz veins related to early sulfides in stage I were deposited from H₂O–NaCl–CO₂ fluids (1,500–5,000 bar, average 3,200) with T _htotal values of 200°C to 383°C and salinities less than about 7 wt.% NaCl equiv. Late sulfide deposition was related to H₂O–NaCl fluids (140–1,300 bar, average 700) with T _htotal values of 110°C to 385°C and salinities less than about 11 wt.% NaCl equiv. These fluids either evolved through immiscibility of H₂O–NaCl–CO₂ fluids as a result of a decrease in fluid pressure, or through mixing with deeply circulated meteoric waters as a result of uplift or unloading during mineralization, or both. Measured and calculated sulfur isotope compositions (δ³⁴S_H2S = 1.5 to 4.8‰) of hydrothermal fluids from the stage I quartz veins indicate that ore sulfur was derived mainly from a magmatic source. The calculated and measured oxygen and hydrogen isotope compositions (δ¹⁸O_H2O = −5.9‰ to 10.9‰, δD = −102‰ to −87‰) of the ore-forming fluids indicate that the fluids were derived from magmatic sources and evolved by mixing with local meteoric water by limited water–rock exchange and by partly degassing in uplift zones during mineralization. While most features of the Samgwang mine are consistent with classification as an orogenic gold deposit, isotopic and fluid chemistry indicate that the veins were genetically related to intrusions emplaced during the Jurassic to Cretaceous Daebo orogeny.     

Geology and ore genesis of the late Paleozoic Heijianshan Fe oxide–Cu (–Au) deposit in the Eastern Tianshan,NW China

The Heijianshan Fe–Cu (–Au) deposit, located in the Aqishan-Yamansu belt of the Eastern Tianshan (NW China), is hosted in the mafic–intermediate volcanic and mafic–felsic volcaniclastic rocks of the Upper Carboniferous Matoutan Formation. Based on the pervasive alteration, mineral assemblages and crosscutting relationships of veins, six magmatic–hydrothermal stages have been established, including epidote alteration (Stage I), magnetite mineralization (Stage II), pyrite alteration (Stage III), Cu (–Au) mineralization (Stage IV), late veins (Stage V) and supergene alteration (Stage VI). The Stage I epidote–calcite–tourmaline–sericite alteration assemblage indicates a pre-mineralization Ca–Mg alteration event. Stage II Fe and Stage IV Cu (–Au) mineralization stages at Heijianshan can be clearly distinguished from alteration, mineral assemblages, and nature and sources of ore-forming fluids.Homogenization temperatures of primary fluid inclusions in quartz and calcite from Stage I (189–370 °C), II (301–536 °C), III (119–262 °C) and V (46–198 °C) suggest that fluid incursion and mixing probably occurred during Stage I to II and Stage V, respectively. The Stage II magmatic–hydrothermal-derived Fe mineralization fluids were characterized by high temperature (>300 °C), medium–high salinity (21.2–56.0 wt% NaCl equiv.) and being Na–Ca–Mg–Fe-dominated. These fluids were overprinted by the external low temperature (<300 °C), medium–high salinity (19.0–34.7 wt% NaCl equiv.) and Ca–Mg-dominated basinal brines that were responsible for the subsequent pyrite alteration and Cu (–Au) mineralization, as supported by quartz CL images and H–O isotopes. Furthermore, in-situ sulfur isotopes also indicate that the sulfur sources vary in different stages, viz., Stage II (magmatic–hydrothermal), III (basinal brine-related) and IV (magmatic–hydrothermal). Stage II disseminated pyrite has δ³⁴S_fluid values of 1.7–4.3‰, comparable with sulfur from magmatic reservoirs. δ³⁴S_fluid values (24.3–29.3‰) of Stage III Type A pyrite (coexists with hematite) probably indicate external basinal brine involvement, consistent with the analytical results of fluid inclusions. With the basinal brines further interacting with volcanic/volcaniclastic rocks of the Carboniferous Matoutan Formation, Stage III Type B pyrite–chalcopyrite–pyrrhotite assemblage (with low δ³⁴S_fluid values of 4.6–10.0‰) may have formed at low fO₂ and temperature (119–262 °C). The continuous basinal brine–volcanic/volcaniclastic rock interactions during the basin inversion (∼325–300 Ma) may have leached sulfur and copper from the rocks, yielding magmatic-like δ³⁴S_fluid values (1.5–4.1‰). Such fluids may have altered pyrite and precipitated chalcopyrite with minor Au in Stage IV. Eventually, the Stage V low temperature (∼160 °C) and low salinity meteoric water may have percolated into the ore-forming fluid system and formed late-hydrothermal veins.The similar alteration and mineralization paragenetic sequences, ore-forming fluid sources and evolution, and tectonic settings of the Heijianshan deposit to the Mesozoic Central Andean IOCG deposits indicate that the former is probably the first identified Paleozoic IOCG-like deposit in the Central Asian Orogenic Belt.     

Paleoenvironmental conditions across the Cretaceous–Paleogene transition at the Apennines sections (Italy): An integrated geochemical and ichnological approach

Two distal Cretaceous–Paleogene (K/Pg) boundary sections in the Central Apennine region (Italy) have been studied: Bottaccione Gorge and Contessa Highway. Geochemical and carbon isotope analyses on the infilling of trace fossils and on the host sedimentary rocks were performed to determine paleoenvironmental conditions during the Cretaceous–Paleogene transition. Major and trace element contents were measured in a 63 cm-thick interval at Bottaccione Gorge (from 22 cm below to 41 cm above the K/Pg boundary) and in a 72 cm-thick interval at Contessa Highway (from 43 cm below to 29 cm above the K/Pg boundary). Even though the K/Pg ejecta layer is now depleted at these sections due to continuous oversampling, the uppermost Maastrichtian and lowermost Danian deposits record the paleoenvironmental conditions prior to and after the K/Pg event. We used redox-sensitive element ratios (V/Al, Cr/Al, Co/Al, Ni/Al Cu/Al, Zn/Al, Mo/Al Pb/Al and U/Mo) and detrital element ratios (K/Al, Rb/Al, Zr/Al and ƩREE/Al) as proxies of certain environmental parameters, used for paleoenvironmental reconstruction. In general, similar values for elemental ratios are registered within Maastrichtian and Danian deposits, which supports similar paleoenvironmental conditions prior to and after the K/Pg event as well as the rapid reestablishment of the pre-impact conditions (i.e., oxygenation, nutrient availability, and/or sedimentary input). An enrichment in certain redox-sensitive elements above the K/Pg at the Bottaccione Gorge section suggests lower oxygenation, as also evidenced by the tracemaker community. Carbon isotope composition data from the infilling material of trace fossils furthermore reveals values similar to those of the host rocks at the corresponding depth, which supports an active infilling by nearly contemporaneous bioturbation during sediment deposition.     

Mineralogical and geochemical characterization of the Riópar non-sulfide Zn-(Fe-Pb) deposits (Prebetic Zone,SE Spain)

The present paper reports the first detailed petrological and geochemical study of non-sulfide Zn–(FePb) deposits in the Riópar area (Prebetic Zone of the Mesozoic Betic Basin, SE Spain), constraining the origin and evolution of ore-forming fluids. In Riópar both sulfide and non-sulfide Zn–(FePb) (“calamine”) ores are hosted in hydrothermally dolomitized Lower Cretaceous limestones. The hypogene sulfides comprise sphalerite, marcasite and minor galena. Calamine ores consist of Zn-carbonates (smithsonite and scarce hydrozincite), associated with abundant Fe-(hydr)oxides (goethite and hematite) and minor Pb-carbonates (cerussite). Three smithsonite types have been recognized: i) Sm-I consists of brown anhedral microcrystalline aggregates as encrustations replacing sphalerite; ii) Sm-II refers to brownish subhedral aggregates of rugged appearance related with Fe oxi-hydroxides in the surface crystals, which replace extensively sphalerite; and iii) Sm-III smithsonite appears as coarse grayish botryoidal aggregates in microkarstic cavities and porosity. Hydrozincite is scarce and appears as milky white botryoidal encrustations in cavities replacing smithsonite. Also, two types of cerussite have been identified: i) Cer-I cerussite consists of fine crystals replacing galena along cleavage planes and crystal surfaces; and ii) Cer-II conforms fine botryoidal crystals found infill porosity. Calcite and thin gypsum encrustations were also recognized. The field and petrographic observations of the Riópar non-sulfide Zn–(FePb) revealed two successive stages of supergene ore formation under meteoric fluid processes: i) “gossan” and “red calamine” formation in the uppermost parts of the ore with deposition of Fe-(hydr)oxides and Zn- and Pb-carbonates (Sm-I, Sm-II and Cer-I), occurring as direct replacements of ZnPb sulfides; and ii) “gray calamine” ore formation with deposition of Sm-III, Cer-II and hydrozincite infilling microkarst cavities and porosity. The stable isotope variation of Riópar smithsonite is very similar to those obtained in other calamine-ore deposits around the world. Their CO isotope data (δ¹⁸O: + 27.8 to + 29.6‰ V-SMOW; δ¹³C: − 6.3 to + 0.4‰ V-PDB), puts constrains on: i) the oxidizing fluid type, which was of meteoric origin with temperatures of 12 to 19 °C, suggesting a supergene weathering process for the calamine-ore formation under a temperate climate; and ii) the carbon source, that resulted from mixing between two CO₂ components derived from: the dissolution of host-dolomite (¹³C-enriched source) and vegetation decomposition (¹³C-depleted component).     

Fluid–rock interaction across the South Tibetan Detachment,Garhwal Himalaya (India): Mineralogical and geochemical evidences

The Malari Leucogranite in the Garhwal Himalaya is cut across by a continental-scale normal fault system called the South Tibetan Detachment (STD). A mineralogical, geochemical and fluid inclusion study of samples from the fault zone of the Malari Granite was performed to reveal the imprints of fluid–rock interaction. Fluid inclusion assemblages observed in the alteration zone indicate the presence of NaCl-dominated aqueous fluids with varied salinity of 6–16 wt.% of NaCl equivalent. Mineralogical changes include the alteration of feldspar to muscovite and muscovite to chlorite. This alteration took place at temperatures of 275°–335°C and pressures between 1.9 and 4.2 kbars as revealed by the application of chlorite thermometry, fluid isochores, and presence of K-feldspar+muscovite+chlorite+quartz mineral assemblage. Geochemical mass-balance estimates predict 32% volume loss during alteration. An estimated fluid/rock ratio of 82 is based on loss of silica during alteration, and reveals presence of a moderately low amount of fluid at the time of faulting.     

Geodynamic evolution of the Eastern Sierras Pampeanas (Central Argentina) based on geochemical, Sm–Nd, Pb–Pb and SHRIMP data

Whole-rock geochemical analyses using major and trace elements in combination with the Sm–Nd and Pb–Pb isotope systems, together with SHRIMP age dating on metasedimentary rocks from the Sierras de Chepes, the Sierras de Córdoba, the Sierra Norte and the San Luis Formation in the Sierra de San Luis, have been carried out to unravel the provenance and the geodynamic history of the Eastern Sierras Pampeanas, Central Argentina. The geochemical and the Sm–Nd data point to a slightly stronger mafic and less-fractionated material in the provenance area of the Sierras de Córdoba when compared to the other units. The T_DM model ages from the Sierras de Chepes (~1.82 Ga) and the Sierra Norte (~1.79 Ga) are significantly older than the data from the Sierras de Córdoba (1.67 Ga). The Pb data are homogeneous for the different units. Only the ²⁰⁸Pb/²⁰⁴Pb ratios of some samples from the Sierras de Córdoba are higher. A late Pampean detrital zircon peak around 520 Ma from the Sierras de Chepes is in accordance with the new data from the San Luis Formation. This is similar to the literature data from the Famatina Belt located to the northwest of the Sierras de Chepes and also fits the detrital zircon peaks in the Mesón group. These maximum depositional ages were also reported from some locations in the Puncoviscana Formation but are absent in the Sierras de Córdoba. An improved model for the development of the Eastern Sierras Pampeanas in the area between the Sierras de Córdoba and the Puncoviscana Formation is provided. This gives new insights into the late Pampean development of the Sierra de San Luis and the complex development of the Eastern Sierras Pampeanas. This new model explains the younger detrital ages in the Puncoviscana Formation compared with the older ages of the Sierras de Córdoba. Another model of the Sierra de San Luis explains the younger depositional ages of the Pringles Metamorphic Complex and the San Luis Formation when compared to the Nogolí Metamorphic Complex and the Conlara Metamorphic Complex. Additionally, the rather fast change of the high-grade metamorphic conditions in the Pringles Metamorphic Complex and the low-grade metamorphic conditions in the San Luis Formation is explained by extension, the ascent of (ultra) mafic material and later folding and erosion.     

Chemical and sulphur isotope compositions of pyrite in the Jaduguda U (–Cu–Fe) deposit,Singhbhum shear zone,eastern India: Implications for sulphide mineralization

The Jaduguda U (–Cu–Fe) deposit in the Singhbhum shear zone has been the most productive uranium deposit in India. Pyrite occurs as disseminated grains or in sulphide stringers and veins in the ore zone. Veins, both concordant and discordant to the pervasive foliation, are mineralogically either simple comprising pyrite ± chalcopyrite or complex comprising pyrite + chalcopyrite + pentlandite + millerite. Nickel-sulphide minerals, though fairly common in concordant veins, are very rare in the discordant veins. Pyrite in Ni-sulphide association is commonly replaced by pentlandite at the grain boundary or along micro-cracks.     

Structural controls,temperature–pressure conditions and fluid evolution of orogenic gold mineralisation at the Betam mine,south Eastern Desert,Egypt

The Betam gold deposit, located in the southern Eastern Desert of Egypt, is related to a series of milky quartz veins along a NNW-trending shear zone, cutting through pelitic metasedimentary rocks and small masses of pink granite. This shear zone, along with a system of discrete shear and fault zones, was developed late in the deformation history of the area. Although slightly sheared and boudinaged within the shear zone, the auriferous quartz veins are characterised by irregular walls with a steeply plunging ridge-in-groove lineation. Shear geometry of rootless intra-folial folds and asymmetrical strain shadows around the quartz lenses suggests that vein emplacement took place under a brittle–ductile shear regime, clearly post-dating the amphibolite-facies regional metamorphism. Hydrothermal alteration is pervasive in the wallrock metapelites and granite including sericitisation, silicification, sulphidisation and minor carbonatisation. Ore mineralogy includes pyrite, arsenopyrite and subordinate galena, chalcopyrite, pyrrhotite and gold. Gold occurs in the quartz veins and adjacent wallrocks as inclusions in pyrite and arsenopyrite, blebs and globules associated with galena, fracture fillings in deformed arsenopyrite or as thin, wire-like rims within or around rhythmic goethite. Presence of refractory gold in arsenopyrite and pyrite is inferred from microprobe analyses. Clustered and intra-granular trail-bound aqueous–carbonic (L_CO2 + L_aq ± V_CO2) inclusions are common in cores of the less deformed quartz crystals, whereas carbonic (L_CO2 ± V_CO2) and aqueous H₂O–NaCl (L + V) inclusions occur along inter-granular and trans-granular trails. Clathrate melting temperatures indicate low salinities of the fluid (3–8 wt.% NaCl eq.). Homogenisation temperatures of the aqueous–carbonic inclusions range between 297 and 323°C, slightly higher than those of the intra-granular and inter-granular aqueous inclusions (263–304°C), which are likely formed during grain boundary migration. Homogenisation temperatures of the trans-granular H₂O–NaCl inclusions are much lower (130–221°C), implying different fluids late in the shear zone formation. Fluid densities calculated from aqueous–carbonic inclusions along a single trail are between 0.88 and 0.98 g/cm³, and the resulting isochores suggest trapping pressures of 2–2.6 kbar. Based on the arsenopyrite–pyrite–pyrrhotite cotectic, arsenopyrite (30.4–30.7 wt.% As) associated with gold inclusions indicates a temperature range of 325–344°C. This ore paragenesis constrains f _S2 to the range of 10⁻¹⁰ to 10^−8.5 bar. Under such conditions, gold was likely transported mainly as bisulphide complexes by low salinity aqueous–carbonic fluids and precipitated because of variations in pH and f _O2 through pressure fluctuation and CO₂ effervescence as the ore fluids infiltrated the shear zone, along with precipitation of carbonate and sericite. Wallrock sulphidation also likely contributed to destabilising the gold–bisulphide complexes and precipitating gold in the hydrothermal alteration zone adjacent to the mineralised quartz veins.     

Deciphering a multistage history affecting U–Cu(–Fe) mineralization in the Singhbhum Shear Zone,eastern India,using pyrite textures and compositions in the Turamdih U–Cu(–Fe) deposit

The ～200-km-long intensely deformed Singhbhum Shear Zone (SSZ) in eastern India hosts India’s largest U and Cu deposits and related Fe mineralization. The SSZ separates an Archaean cratonic nucleus to the south from a Mesoproterozoic fold belt in the North and has a complex geologic history that obscures the origin of the contained iron-oxide-rich mineral deposits. This study investigates aspects of the history of mineralization in the SSZ by utilizing new petrographic and electron microprobe observations of pyrite textures and zoning in the Turamdih U–Cu(–Fe) deposit. Mineralization at Turamdih is hosted in intensively deformed quartz–chlorite schist. Sulfides and oxides include, in inferred order of development: (a) magmatic Fe(–Ti–Cr) oxide and Fe–Cu(–Ni) sulfide minerals inferred to be magmatic (?) in origin; followed by (b) uranium, Fe-oxide, and Fe–Cu(–Co) sulfide minerals that predate most or all ductile deformation, and are inferred to be of hydrothermal origin; and (c) Fe–Cu sulfides that were generated during and postdating ductile deformation. These features are associated with the formation of three compositionally and texturally distinct pyrites. Pyrite (type-A), typically in globular–semiglobular composite inclusions of pyrite plus chalcopyrite in magnetite, is characterized by very high Ni content (up to 30,700 ppm) and low Co to Ni ratios (0.01–0.61). The textural and compositional characteristics of associated chalcopyrite and rare pyrrhotite suggest that this pyrite could be linked to the magmatic event via selective replacement of magmatic pyrrhotite. Alternatively, this pyrite and associated sulfide inclusions might be cogenetic with hydrothermal Fe-oxide. Type-B pyrite that forms elongate grains and irregular relics and cores of pyrite with high Co contents (up to 23,630 ppm) and high Co to Ni ratios (7.2–140.9) are interpreted to be related to hydrothermal mineralization predating ductile deformation. A third generation of pyrite (type C) with low Co, low Ni, and moderate Co to Ni ratios (0.19–13.93) formed during and postdating the ductile deformation stage overgrowing, replacing, and surrounding type-B pyrite. The textural evolution of pyrite parallels the tectonometamorphic evolution of the shear zone demonstrating grain elongation during progressive ductile deformation and prograde metamorphism, annealing at the peak metamorphic condition, porphyroblastic growth at the retrograde path and cataclasis following porphyroblastic growth. Compositional characteristics of hydrothermal pyrite and available geological information suggest that the U–Cu(–Fe) deposit at Turamdih might be a variant of the Fe oxide (–Cu–U–rare earth elements) family of deposits.     

Mineral Deposit Model of Cu–Fe–Au Skarn System in the Edongnan Region,Eastern China

Cu and Fe skarns are the world’s most abundant and largest skarn type deposits, especially in China, and Au-rich skarn deposits have received much attention in the past two decades and yet there are few papers focused on schematic mineral deposit models of Cu–Fe–Au skarn systems. Three types of Au-rich deposits are recognized in the Edongnan region, Middle–Lower Yangtze River metallogenic belt: ～140 Ma Cu–Au and Au–Cu skarn deposits and distal Au–Tl deposits. 137–148 Ma Cu–Fe and 130–133 Ma Fe s...     

Zircon geochronology of the Koraput alkaline complex: Insights from combined geochemical and U–Pb–Hf isotope analyses,and implications for the timing of alkaline magmatism in the Eastern Ghats Belt,India

Zircon formation and modification during magmatic crystallization and high-grade metamorphism are explored using TIMS and LA-ICP-MS U–Pb geochronology, Lu–Hf isotope chemistry, trace element analysis and textural clues on zircons from the Koraput alkaline intrusion, Eastern Ghats Belt (EGB), India. The zircon host-rock is a granulite-facies nepheline syenite gneiss with an exceptionally low Zr concentration, prohibiting early magmatic Zr saturation. With zircon formation occurring at a late stage of advanced magmatic cooling, significant amounts of Zr were incorporated into biotite, nearly the only other Zr-bearing phase in the nepheline syenite gneisses. Investigated zircons experienced a multi-stage history of magmatic and metamorphic zircon growth with repeated solid-state recrystallization and partial dissolution–precipitation. These processes are recorded by complex patterns of internal zircon structures and a wide range of apparently concordant U–Pb ages between 869 ± 7 Ma and 690 ± 1 Ma. The oldest ages are interpreted to represent the timing of the emplacement of the Koraput alkaline complex, which significantly postdates the intrusion ages of most of the alkaline intrusion in the western EGB. However, Hf model ages of TDM = 1.5 to 1.0 Ga suggest an earlier separation of the nepheline syenite magma from its depleted mantle source, overlapping with the widespread Mesoproterozoic, rift-related alkaline magmatism in the EGB. Zircons yielding ages younger than 860 Ma have most probably experienced partial resetting of their U–Pb ages during repeated and variable recrystallization events. Consistent youngest LA-ICP-MS and CA-TIMS U–Pb ages of 700–690 Ma reflect a final pulse of high-grade metamorphism in the Koraput area and underline the recurrence of considerable orogenic activity in the western EGB during the Neoproterozoic. Within the nepheline syenite gneisses this final high-grade metamorphic event caused biotite breakdown, releasing sufficient Zr for local saturation and new subsolidus zircon growth along the biotite grain boundaries.