Geology,mineralogy and fluid inclusion data of the Kizilcaören fluorite–barite–REE deposit,Eskisehir, Turkey

The Kizilcaören fluorite–barite–Rare Earth Element (REE) deposit occurs as epithermal veins and breccia fillings in altered Triassic metasandstones and Oligocene–Miocene pyroclastics adjacent to alkaline porphyritic trachyte and phonolite. This deposit is the only commercial source of REE and thorium in Turkey. Most of the fluorite–barite–REE mineralisation at Kizilcaören has been formed by hydrothermal solutions, which are thought to be genetically associated with alkaline volcanism. The occurrence of the ore minerals in vuggy cavities and veins of massive and vuggy silica indicate that the ore stage postdates hydrothermal alteration. The deposit contains evidence of at least three periods of hypogene mineralisation separated by two periods of faulting. The mineral assemblage includes fluorite, barite, quartz, calcite, bastnäsite, phlogopite, pyrolusite and hematite as well as minor amounts of plagioclase feldspar, pyrite, psilomelane, braunite, monazite, fluocerite, brockite, goethite, and rutile. Fluid inclusion microthermometry indicates that the barite formed from low salinity (0.4–9.2 equiv. wt% NaCl) fluids at low temperatures, between 105 and 230 °C, but fluorite formed from slightly higher salinity (<12.4 equiv. wt% NaCl) fluids at low and moderate temperatures, between 135–354 °C. The depositional temperature of bastnäsite is between 143–286 °C. The local coexistence of liquid- and vapour-rich inclusions suggests boiling conditions. Many relatively low-salinity (<10.0 equiv. wt% NaCl), low and moderate temperature (200–300 °C) inclusions might be the result of episodic mixing of deep-saline brines with low-salinity meteoric fluids. The narrow range of δ³⁴S (pyrite and barite) values (2.89–6.92‰ CDT)suggests that the sulphur source of the hydrothermal fluids are the same and compatible with a volcanogenic sulphate field derived from a magmatic sulphur source.     

Fluid inclusions,muscovite Ar–Ar age,and fluorite trace elements at the Baiyanghe volcanic Be–U–Mo deposit,Xinjiang, northwest China: Implication for its genesis

The Baiyanghe Be–U–Mo deposit is located in the Late Paleozoic Xuemisitan–Kulankazi island arc of the northwestern margin of the Junggar plate, Northwest China. It is the largest Be deposit (2.2 M tons of ore with grades ranging from 0.2% to 1.4%) in Asia. Orebodies in the deposit occur as fractures along contact zones between the Yangzhuang granite porphyry intrusion and Devonian pyroclastic country rocks and within the porphyry itself. Muscovite–fluorite veins are closely associated with the Be–U–Mo mineralization. A new Ar–Ar dating of the muscovite in this study yields a plateau age of 303.0 ± 1.6 Ma, which constrains the timing of the Be–U–Mo mineralization of the deposit. Three stages of fluorite of different colors have been identified at the deposit, with the earliest dark-purple fluorite more closely associated with the mineralization. Microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature (120–150 °C) hydrothermal fluids with salinity ranging from 4.7 to 19.7 wt.% NaCl eqv. Based on the trace elemental concentrations and REE patterns of the fluorite, the style of veining, and the low salinity and low temperature characters of the fluid inclusions, it is suggested that Be and U were most likely transported as fluoride complexes and Mo as hydroxyl complexes. Pb isotopic compositions of the ores and country rocks, as well as O and H isotopic characters of the ore-related muscovite, indicate mixing between magmatic and meteoric waters; both contributed to formation of the ore-forming fluids. Metallic Be, U, and Mo were most likely leached out from the granite porphyry by the fluids. The fluid mixing led to the reduction of U, Mo, and Be and their precipitation at the deposit.     

Physicochemical parameters of crystallization of melts in intermediate suprasubduction chambers (by the example of Tolbachik and Ichinskii Volcanoes,Kamchatka Peninsula)

In study of plagioclases, amphiboles, and melt inclusions, we have determined the physicochemical parameters of crystallization of melts in the intermediate suprasubduction chambers of volcanoes representing different types of subduction magmatism on the Kamchatka Peninsula: the young basaltic systems of Tolbachik Volcano (Klyuchevskaya group) and ancient Ichinskii Volcano (Sredinnyi Ridge) with alternating basaltic and felsic eruptions. For Tolbachik Volcano, we have found that plagioclase lapilli formed from basaltic melts at 1075-1115 °C and low (< 1 kbar) pressures at depths of 2-3 km. Andesite minerals crystallized within a wider range of temperatures and pressures (1220-1020 °C and 3.3-1.6 kbar) in an intermediate chamber at depths of < 10 km. The melts were generated in basaltic magma chambers (detected well by geophysical methods at depths of 18-20 km) with minimum temperatures of ~ 1290 °C. For Ichinskii Volcano, three levels of intermediate chambers are distinguished. Andesites formed at depths of < 23 km at < 1225 °C. Dacitic melts were generated from an intermediate chamber (14 km) at 1135-1045 °C as a result of differentiation of andesitic magmas. Dacites formed in the uppermost horizons (9-3 km) at 1130-1030 °C. Despite the similarity between differentiation processes in the intermediate chambers of the Kamchatka volcanoes, each volcano is characterized by specific magmatism. The lavas of basaltic volcanoes (Tolbachik) and those of andesitic volcanoes (Ichinskii) differ in genesis and differentiation.     

An Early Cretaceous carbonate replacement origin for the Xinqiao stratabound massive sulfide deposit,Middle-Lower Yangtze Metallogenic Belt,China

Stratabound massive sulfide deposits are widespread along the Middle-Lower Yangtze Metallogenic Belt (MLYMB) and serve as an important copper producer in China. Two contrasting genetic models have been proposed, interpreting the stratabound massive sulfide deposits as a Carboniferous SEDEX protore overprinted by Cretaceous magmatic-hydrothermal system or an Early Cretaceous carbonate replacement deposit. These two contrasting models have been applied to the Xinqiao stratabound Cu-Au sulfide deposit, which is dominated by massive sulfide ores hosted in marine carbonates of the Carboniferous Chuanshan and Huanglong Formations, with minor Cu-Au skarn ores localized in the contact zone between the Cretaceous diorite Jitou stock and the Carboniferous carbonate rocks. New SIMS zircon U-Pb dating suggests that the Jitou stock formed at 138.5 ± 1.1 Ma (2σ, MSWD = 0.6). Pyrite Re-Os dating yields an imprecise date of 142 ± 47 Ma (2σ, MSWD = 7.8). The geochronological data thus constrain the mineralization of the Xinqiao deposit at Early Cretaceous.Fluid inclusions in prograde skarn diopside have homogenization temperatures of 450–600 °C and calculated salinities of 13–58 wt.% NaCl equiv. Quartz from the stratabound ores and pyrite-quartz vein networks beneath the stratabound ores have homogenization temperatures of 290–360 and 200–300 °C, with calculated salinities of 5–12 and 2–10 wt.% NaCl equiv., respectively. Quartz from the skarn ores and veins beneath the stratabound ores have δ¹⁸O values of 12.32 ± 0.55 (2 SD, n = 22) and 15.57 ± 1.92‰ (2 SD, n = 60), respectively, corresponding to calculated δ¹⁸O values of 6.22 ± 1.59 (2σ) and 6.81 ± 2.76‰ (2σ) for the equilibrated ore-forming fluids. The fluid inclusion and oxygen isotope data thus support a magmatic-hydrothermal origin rather than a SEDEX system for the stratabound ores, with the hydrothermal fluids most likely being derived from the Jitou stock or associated concealed intrusion. Results from this study have broad implications for the genesis and exploration of other stratabound massive sulfide deposits along the MLYMB.     

Fluorite (U–Th)/He thermochronology: Constraints on the low temperature history of Yucca Mountain,Nevada

Fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at Yucca Mountain, Nevada. The authors have conducted (U–Th)/He dating of this fluorite in an attempt to constrain the temperature and timing of paleo-fluid flux into the site. Repeated analysis of colourless fluorite yielded a weighted average age of 9.7 ± 0.15 Ma (2σ), younger than previously determined sanidine ⁴⁰Ar/³⁹ Ar ages (12.8 Ma) for deposition of the tuff.Laboratory He-diffusion experiments conducted on the Yucca fluorite yield a preliminary He closure temperature (T_c) of 90 ± 10 °C (cooling rate of 10 °C/Ma) and previous studies have determined that the fluorite precipitated from warm fluids (65–80 °C) at depths of <400 m. However, minerals can experience partial He loss at temperatures well below the T_c and therefore the (U–Th)/He age of 9.7 Ma is interpreted to be a cooling age. This result implies that the last period of elevated temperature fluid circulation through the Yucca site was approximately 9.7 Ma ago.It was observed that the purple coloured outer portion of the fluorite nodule yielded non-reproducible and invariably older ages than colourless fluorite. Several possible reasons are suggested.     

Spatial–temporal evolution of ore-forming fluids and related mineralization in the western Lanping basin,Yunnan Province,China

The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt in the Sanjiang Tethyan metallogenic province. A series of sediment-hosted Himalayan Cu–Ag–Pb–Zn polymetallic deposits have been discovered in the western part of the basin, controlled by a thrust–nappe system. In the thrust–nappe system, the Cu orebodies mainly occur in the western and relatively deep part of the mineralization system (the root zone), whereas the Pb–Zn–Ag (± Cu) orebodies occur in the eastern and relatively shallow part of the system (the front zone), both as vein-type mineralization.In this paper we present new data, combined with existing data on fluid inclusions, isotopes and geologic characteristics of representative deposits, to provide the first study that contrasts mineralizing fluids in the Cu–Ag (Mo) and Pb–Zn–Ag (Cu) polymetallic deposits.Fluid inclusion and isotope studies show that the Cu–Ag (Mo) mineralization in the root zone formed predominantly from deep crustal fluids, with the participation of basinal brines. The deep crustal fluids are marked by high CO₂ content, relatively high temperatures (280 to 340 °C) and low salinities (1 to 4 wt.% NaCl equivalent), whereas the basinal brine shows relatively low temperatures (160 °C to 220 °C) and high salinities (12 to 22 wt.% NaCl equivalent), containing almost no CO₂. In comparison, hydrothermal activity associated with the Pb–Zn–Ag (± Cu) deposits in the front zone is characterized by basinal brine, with relatively low temperatures (130 °C to 180 °C), high salinities (9 to 24 wt.% NaCl equivalent), and low CO₂ concentrations. Although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids, magmatic and metamorphic components cannot be completely excluded. The basinal brine was predominantly derived from meteoric water.The δ³⁴S values of sulfides from the Cu–Ag (Mo) deposits and Pb–Zn–Ag (± Cu) deposits range from − 17.9 to 16.3‰ and from 2.5 to 11.2‰, respectively. These ranges may relate to variations in physicochemical conditions or compositional variation of the sources. Lead isotope compositions indicate that the ore-forming metals were predominantly derived from sedimentary rocks of the Lanping basin.     

Metallogenesis at the Carris W–Mo–Sn deposit (Gerês,Portugal): Constraints from fluid inclusions,mineral geochemistry,Re–Os and He–Ar isotopes

The Carris orebody consists of two partially exploited W–Mo–Sn quartz veins formed during successive shear stages and multipulse fluid fillings. They cut the Variscan post-D3 Gerês I-type granite. The most important ore minerals are wolframite, scheelite, molybdenite and cassiterite. There are two generations of wolframite. The earlier generation of wolframite is rare and has the highest WO₄Mn content (91 mol%) and the most common wolframite contains 26–57 mol% WO₄Mn. Re–Os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 ± 1.2 Ma and 280.3 ± 1.2 Ma, respectively which are in very good agreement with the previous ID-TIMS U–Pb zircon age for the Carris granite (280 ± 5 Ma).³He/⁴He ratio of pyrite ranging between 0.73 and 2.71 Ra (1 Ra = 1.39 × 10^− 6) and high ³He/³⁶Ar (0.8–5 × 10^− 3) indicate a mixture of a crustal radiogenic helium fluid with a mantle derived-fluid.The fluid inclusion studies on quartz intergrown with wolframite and scheelite, beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit. The first was a low to medium salinity aqueous carbonic fluid (CO₂ between 4 and 14 mol%) with less than 1.95 mol% N₂, which was only found in quartz associated with wolframite. The other was a low salinity aqueous fluid found in all the four minerals. The homogenization temperatures indicate minimum entrapment temperatures of 226–310 °C (average 280 °C) for the H₂O–CO₂–N₂–NaCl fluid and average temperatures of 266 °C for scheelite and 242 °C, 190 °C and 160 °C for the last generations of beryl, fluorite and quartz, respectively. It was estimated that wolframite was deposited ~ 7 km depth, assuming a lithostatic pressure, probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event. Precipitation of scheelite and sulphides took place later, at the same depth, but under a hydrostatic or suprahydrostatic pressure regime, and probably caused by mixing between the magmatic–hydrothermal fluid and meteoric waters that deeply penetrated the basement during post-Variscan decompression.     

Fluorite solubility in hydrous haplogranitic melts at 100 MPa

Fluorite is the most common fluoride mineral in magmatic silicic systems and its crystallization can moderate or buffer fluorine concentrations in these settings. We have experimentally determined fluorite solubility and speciation mechanisms in haplogranitic melts at 800–950 °C, 100 MPa and aqueous-fluid saturation. The starting haplogranite compositions: peraluminous (alumina saturation index, ASI = 1.2), subaluminous (ASI = 1.0) and peralkaline (ASI = 0.8) were variably doped with CaO or F₂O₋₁ in the form of stoichiometric mineral or glass mixtures. The solubility of fluorite along the fluorite–hydrous haplogranite binaries is low: 1.054 ± 0.085 wt.% CaF₂ (peralkaline), 0.822 ± 0.076 wt.% (subaluminous) and 1.92 ± 0.15 wt.% (peraluminous) at 800 °C, 100 MPa and 10 wt.% H₂O, and exhibits a minimum at ASI ∼ 1. Fluorite saturation isotherms are strongly hyperbolic in the CaO–F₂O₋₁ space, suggesting that fluorite saturation is controlled by the activity product of CaO and F₂O₋₁, i.e., these components are partially decoupled in the melt structure. The form of fluorite liquidus isotherms implies distinct roles of fluorite crystallization: in Ca-dominant systems, fluorite crystallization is controlled by the fluorine concentration in the melt only and remains nearly independent of calcium contents; in F-rich systems, the crystallization of fluorite is determined by CaO contents and it does not buffer fluorine concentration in the melt. The apparent equilibrium constant, K, for the equilibrium CaO + cF₂O₋₁ = CaF₂ (+ associates) is log K= − (2.449 ± 0.085)·Al₂O₃^exc + (4.902 ± 0.066); the reaction-stoichiometry parameter varies as follows: c= − (0.92 ± 0.11)·Al₂O₃^exc + (1.042 ± 0.084) at 800 °C, 100 MPa and fluid saturation where Al₂O₃^exc are molar percent alumina in excess over alkali oxides. The reaction stoichiometry, c, changes at subaluminous composition: in peralkaline melts, competition of other network modifiers for excess fluorine anions leads to the preferential alkali–F short-range order, whereas in peraluminous compositions, excess alumina associates with calcium cations to form calcioaluminate tetrahedra. The temperature dependence of fluorite solubility is described by the binary symmetric Margules parameter, W = 36.0 ± 1.4 kJ (peralkaline), 39.7 ± 0.5 kJ (subaluminous) and 32.8 ± 0.7 kJ (peraluminous). The strong positive deviations from ideal mixing imply the occurrence of CaF₂–granite liquid–liquid immiscibility at temperatures above 1258 °C, which is consistent with previous experimental data. These experimental results suggest very low solubilities of fluorite in Ca-rich melts, consistent with the lack of fluorine enrichment in peralkaline rhyolites and calc-alkaline batholiths. On the other hand, high CaO concentrations necessary to crystallize fluorite in F-rich peraluminous melts are not observed in nature and thus magmatic crystallization of fluorite in topaz-bearing silicic suites is suppressed. A procedure for calculating fluorite solubility and the liquidus isotherms for a whole-rock composition and temperature of interest is provided.     

Cenozoic high-K alkaline magmatism and associated Cu–Mo–Au mineralization in the Jinping–Fan Si Pan region,southeastern Ailao Shan–Red River shear zone,southwestern China–northwestern Vietnam

The Jinping–Fan Si Pan (JFP) Cenozoic magmatic and Cu–Mo–Au metallogenic belt in the southeastern part of the Ailao Shan shear zone host the Tongchang, Chang′an, Habo, and Chinh Sang Cu–Mo–Au deposits. These deposits form an integrated epithermal-porphyry regional mineralization system associated with 40–32 Ma high-K alkaline magmatism. The magmatic rocks in the belt have relatively low TiO₂ (<0.73 wt%), P₂O₅ (<0.29 wt%), and FeO^* (<4.99 wt%), and high Na₂O (2.86–4.75 wt%) and K₂O (4.01–7.98 wt%). They also have high contents of incompatible trace elements, and are enriched in LILE (Rb, Ba, K, Sr) and LREE. They have marked Nb, Ta, Ti and P depletion in primitive mantle-normalized spidergrams, and plot close to the EMII mantle field in the Sr–Nd isotopic diagram. These characteristics are similar to those of the Eocene high-K alkaline rocks along the northern Ailao Shan belt, eastern Tibet plateau. The sulfur and lead isotope analyses of sulfide minerals from both the ores and related magmatic rocks confirm the involvement of a magmatic ore fluid. The Cenozoic alkaline intrusions and Cu–Mo–Au mineralization in the JFP were formed prior to the initiation of left-lateral shearing along the Ailao Shan shear zone. The magmas appear to have been derived from enriched mantle, possibly with mixing of materials from the buried Tethyan oceanic lithosphere, and/or crust.     

Evidence for shear heating,Musgrave Block,central Australia

The phenomenon of shear-heating is generally difficult to recognise from petrologic evidence alone. Establishing that shear zones attain higher temperatures than the surrounding country rocks requires independent evidence for temperature gradients. In the Musgrave Block, central Australia, there is a clear spatial association between shear zones and interpreted elevated temperatures. Eclogite facies shear zones that formed at ∼550 Ma record temperatures of ∼650–700°C. Outside the high-pressure shear zones, minerals with low closure temperatures such as biotite (∼450°C in the ⁴⁰Ar–³⁹Ar and Rb–Sr systems), preserve ages >800 Ma, suggesting that these rocks did not experience temperatures greater than about 450°C at ∼550 Ma for any extended period. Thus, the shear zones record temperatures that are ∼200°C higher than the surrounding country rocks. Simple calculations show that the combination of relatively high shear stresses (∼100 MPa) and high strain rates (∼10⁻¹¹ s⁻¹) for short durations (<1 Ma) can account for the observed apparent temperature variations. The evidence indicates that shear heating is the dominant mechanism for localised temperature increases in the shear zones, while the country rock remained at relatively lower temperatures.     

Origin of the inconsistent apparent Re–Os ages of the Jinchuan Ni–Cu sulfide ore deposit,China: Post-segregation diffusion of Os

Apparent Re–Os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite U–Pb ages which are interpreted as the formation age of the host intrusions. The Jinchuan Ni–Cu–PGE deposit of China, the world's third largest, is such a case. We report apparent Re–Os isochron ages of 1117 ± 67 Ma, 1074 ± 120 Ma and 867 ± 75 Ma with initial ¹⁸⁷Os/¹⁸⁸Os ratios of 0.120 ± 0.012, 0.162 ±0.017 and 0.235 ± 0.027 for disseminated ores, sulfides from the disseminated ores and massive ores from Jinchuan, respectively. Using these data and Re–Os ages from the literature, we find that the oldest apparent Re–Os age and lowest initial Os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals, the highest initial Os isotope ratios and youngest apparent Re–Os ages, consistent with the zircon and baddeleyite U–Pb ages, are from massive ores containing 90–100 modal% sulfide, and net-textured ores with about 25 modal% sulfides yield apparent Re–Os ages and initial Os ratios intermediate between those of the disseminated and massive ores.Because Os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures, re-equilibration did not occur in the disseminated ore and the samples retained the Os ratios of the contaminated magma, leading to geologically meaningless ages that are older than the formation age of the rocks. While Os-bearing sulfide minerals and magnetite show low closure temperatures of Os diffusion and the sulfide minerals in the massive ore are closely connected with each other, facilitating fast diffusion of Os, re-equilibration of Os was achieved during cooling of the ore from about 850 °C after the segregation to about 400 °C. Thus, an age corresponding to the formation time and an elevated initial Os ratio were yielded by the massive ore. Os isotopes in the net-textured ore behave in the way intermediate between the disseminated and massive ores. Pb isotope data support the Os results. Disseminated ores have heterogeneous Pb isotope ratios whereas Pb in the massive ores is more uniform, consistent with Pb isotopic equilibration in the massive ores, but not in the disseminated ores.     

Metallogeny of the Shilu Fe–Co–Cu deposit,Hainan Island,South China: Constraints from fluid inclusions and stable isotopes

The Shilu deposit is a world-class Fe–Co–Cu orebody located in the Changjiang area of the western part of Hainan Island, South China. The distribution of Fe, Co, and Cu orebodies is controlled by strata of the No. 6 Formation in the Shilu Group and the Beiyi synclinorium. Based on a petrological study of the host rocks and their alteration assemblages, and textural and structural features of the ores, four mineralization stages have been identified: (1) the sedimentary ore-forming period; (2) the metamorphic ore-forming period; (3) the hydrothermal mineralization comprising the skarn and quartz–sulfide stage; and (4) the supergene period. The fluid inclusions in sedimentary quartz and/or chert indicate low temperatures (ca. 160 °C) and low salinities from 0.7 to 3.1 wt.% NaCl_eq, which corresponds to densities of 0.77 to 0.93 g/cm³. CO₂-bearing or carbonic inclusions have been interpreted to result from regional metamorphism. Homogenization temperatures of fluid inclusions for the skarn stage have a wide range from 148 °C to 497 °C and the salinities of the fluid inclusions range from 1.2 to 22.3 wt.% NaCl_eq, which corresponds to densities from 0.56 to 0.94 g/cm³. Fluid inclusions of the quartz–sulfide stage yield homogenization temperatures of 151–356 °C and salinities from 0.9 to 8.1 wt.% NaCl_eq, which equates to fluid densities from 0.63 to 0.96 g/cm³.Sulfur isotopic compositions indicate that sulfur of the sedimentary anhydrite and Co-bearing pyrite, and the quartz–sulfide stage, was derived from seawater sulfate and thermochemical sulfate reduction of dissolved anhydrite at temperatures of 200 °C and 300 °C, respectively. H and O isotopic compositions of the skarn and quartz–sulfide stage demonstrate that the ore-forming fluids were largely derived from magmatic water, with minor inputs from metamorphic or meteoric water. The Shilu iron ore deposit has an exhalative sedimentary origin, but has been overprinted by regional deformation and metamorphism. The Shilu Co–Cu deposit has a hydrothermal origin and is temporally and genetically associated with Indosinian granitoid rocks.     

Fluorite REE-Y (REY) geochemistry of the ca. 850 Ma Tumen molybdenite–fluorite deposit,eastern Qinling,China: Constraints on ore genesis

The Tumen molybdenite–fluorite vein system is hosted by carbonate rocks of the Neoproterozoic Luanchuan Group, located on the southern margin of the North China Craton (NCC) in central China. Previous studies divided the mineralization into four stages according to the crosscutting relationships between veinlets and their mineral assemblages. In this contribution, two distinctive types of fluorite mineralization are recognized: 1) the first type (Type 1) includes colourless, white or green fluorite grains present in Stage 1 veins; and 2) the second type includes Type 2a purple fluorite present in Stage 2 veins and does not coexist with sulfides, and Type 2b purple fluorite crystals associated with sulfides in Stage 2 veins. The rare earth element (REE) content in the fluorite ranges between 13.8 and 27.9 ppm in Type 1, 16.9 and 27.2 ppm in Type 2a, and 42.5 and 75.1 ppm in Type 2b, which suggests that the fluorite was precipitated from acidic fluids (given that REEs are mobile in saline HCl-bearing fluids at high temperature (~ 400 °C)). Comparing the REE chemistry of the Stage 1 against Stage 2 fluorite, the LREE/HREE ratios decrease from 9.8 to 4.0, La/Yb ratios decrease from 16.0 to 6.9 and La/Ho ratios decrease from 10.2 to 3.0, indicating that the hydrothermal process was at high-T and low-pH conditions. The Eu/Eu* ratios in the fluorite decrease from 1.11 ± 0.35 for Type 1 through 0.89 ± 0.19 for Type 2a to 0.75 ± 0.17 for Type 2b, suggesting a gradual increase in oxygen fugacity (fO₂) and pH of the mineralising fluid. The Tb/Ca, Tb/La and Y/Ho ratios of the fluorite types indicate that they were formed from the interaction between magmatic fluids and carbonate wallrocks. The fluorite samples show similar REE + Y (REY) patterns to those of dolostone units in the Luanchuan Group and the nearby Neoproterozoic syenite, suggesting that the REY in the fluorite was mainly sourced from the host-rocks, although the syenite could be an additional minor source.     

Recognition of Yanshanian magmatic-hydrothermal gold and polymetallic gold mineralization in the Laowan gold metallogenic belt,Tongbai Mountains: New evidence from structural controls,geochronology and geochemistry

The Laowan metallogenic belt in China is an important metallogenic belt within the Tongbai orogenic belt, and contains the medium-sized Laowan and Shangshanghe gold deposits, the small Huangzhuyuan lead–zinc–silver–gold deposit and some gold and Cu–Pb occurrences. These deposits are hosted in Mesoproterozoic plagioclase amphibolite (or schist) and mica-quartz schist. The gold ores are mainly quartz veins and veinlets and disseminated altered ores. Subordinate ore types include massive sulfides and breccias. The Laowan gold deposit is characterized by three right-stepping en-echelon fracture-controlled alteration zones that dip gently to the south and includes disseminated, sheeted and stockwork ores. These lodes were formed by the interaction of ore-forming fluid with foliated-to laminated cataclasite within the transpressional faults. The Shangshanghe gold deposit is characterized by parallel ore lodes that dip steeply to the north, and includes quartz veins and breccias in addition to ores in altered wallrocks. These lodes were formed by focusing of fluids into transtensional faults. These ore controlling faults displaced early barren quartz veins 10 m horizontally with a dextral sense of motion. The ore-hosting structures at the Laowan and Shangshanghe deposits correspond to the P and R-type shears of a brittle dextral strike-slip fault system, respectively, which make angles of about 15° and − 15° to the Laowan and Songpa boundary faults. The ore-controlling fault system post-dated formation of a ductile shear zone, and peak regional metamorphism. This precludes a genetic relationship between hydrothermal mineralization and regional metamorphism and ductile shear deformation. These gold deposits are not typical orogenic gold deposits. The metallogenic belt displays district-scale-zoning of Mo → Cu–Pb–Zn–Ag → Au relative to Songpa granite porphyry dike zone, suggesting the mineralization may be closely related to the granite porphyry. Measured δ³⁴S of sulfides and δ¹⁸O and δD of fluid inclusion waters in auriferous quartz also are consistent with a magmatic source for sulfur and ore fluids. The similarity of Pb isotope ratios between the ores and Yanshanian granitoids suggests a similar source. As the age (139 ± 3 Ma) of granite porphyry obtained by zircon U–Pb isotope overlaps the mineralization age (138 ± 1 Ma: Zhang et al., 2008a), the gold and polymetallic metallogenesis of the Laowan gold belt has close spatial, temporal and possibly genetic relationships with Yanshanian high level magmatism.     

Mineralogy and mineral chemistry of Bi-minerals: Constraints on ore genesis of the Beiya giant porphyry-skarn gold deposit,southwestern China

The Beiya deposit, located in the Sanjiang Tethyan tectonic domain (SW China), is the third largest Au deposit in China (323 t Au @ 2.47 g/t). As a porphyry-skarn deposit, Beiya is related to Cenozoic (Himalayan) alkaline porphyries. Abundant Bi-minerals have been recognized from both the porphyry- and skarn- ores, comprising bismuthinite, Bi–Cu sulfosalts (emplectite, wittichenite), Bi–Pb sulfosalts (galenobismutite, cosalite), Bi–Ag sulfosalt (matildite), Bi–Cu–Pb sulfosalts (bismuthinite derivatives), Bi–Pb–Ag sulfosalts (lillianite homologs, galena-matildite series), and Bi chalcogenides (tsumoite, the unnamed Bi₂Te, the unnamed Ag₄Bi₃Te₃, tetradymite, and the unnamed (Bi, Pb)₃(Te, S)₄). Native bismuth and maldonite are also found in the skarn ores. The arsenopyrite geothermometer reveals that the porphyry Au mineralization took place at temperatures in the range of 350–450 °C and at log fS₂ in the range of − 8.0 to − 5.5, respectively. In contrast, the Beiya Bi-mineral assemblages indicate that the skarn ore-forming fluids had minimum temperatures of 230–175 °C (prevailing temperatures exceeding 271 °C) and fluctuating fS₂–fTe₂ conditions. We also model a prolonged skarn Au mineralization history at Beiya, including at least two episodes of Bi melts scavenging Au. We thus suggest that this process was among the most effective Au-enrichment mechanisms at Beiya.     

Phase separation,fluid mixing,and origin of the greisens and potassic episyenite associated with the Água Boa pluton,Pitinga tin province,Amazonian Craton,Brazil

Based on petrographical data, three types of greisen have been characterized at the western border of Água Boa pluton: siderophyllite–topaz–quartz greisen (greisen 1), fluorite–phengite–quartz greisen (greisen 2) and quartz–chlorite–phengite greisen (greisen 3). Episyenites were also identified.Two fluids of independent origin interacted with the same protolith – a hornblende-biotite alkali feldspar granite – and produced both the greisens and potassic episyenite: (1) an acid, low-salinity (4–12 wt.% NaCl eq.), F-rich, relatively hot (400–350 °C) reduced aqueous-carbonic fluid (CH₄–H₂O–NaCl–FeCl₂ ± KCl), which by immiscibility gave rise to fluid IA (aqueous) and IC (carbonic); and (2) a lower salinity (2–4 wt.% NaCl eq.) and temperature (200–150 °C) aqueous fluid (H₂O–NaCl), which was responsible for all dilution processes. Fluid 1 seems to have had a magmatic-hydrothermal origin, while fluid 2 is probably surface-derived (meteoric water?). An alkaline, F-poorer and diluted equivalent of fluid IA was interpreted to have caused the episyenitization of the granite host rock as well as the formation of phengite-rich greisen 3. The continuos interaction of this fluid with the potassic episyenite produced a moderate- to high-salinity (20–24 wt.% NaCl eq.), low-temperature (200–100 °C) fluid (H₂O–NaCl–CaCl₂ ± KCl), leading to the formation of chlorite-rich zone of greisen 3 and late silicification of potassic episyenite.In the greisen 1, decreasing F-activity and increasing oxygen fugacity, as the system cooled down, favored the formation of a topaz-rich inner zone, which grades into a siderophyllite-rich zone outwardly. Greisen 2 was formed under more oxidizing conditions by fluids poorer in F than those trapped in the siderophyllite-rich zone.The oxidation of aqueous-carbonic fluid took place at three distinct stages: (i) below the FMQ buffer; (ii) between the FMQ and NNO buffers; and (iii) above the NNO buffer.The dissolution cavities generated during the episyenitization process increased the permeability of the altered rocks, resulting in an increase of the fluid/rock ratios at the potassic episyenite and greisen 3 sites.All these fluids were trapped under pressure conditions of <1.0 kbar, representing shallow crustal levels and are consistent with those that have been estimated for the Pitinga tin–granites.The oxygen fugacity, F-activity gradients and salinity variations that occurred during the cooling of the hydrothermal system, in addition to differences in permeability, were important factors in the formation of distinct greisens. They not only controlled the fluid compositional changes, but also caused the cassiterite and sulfide precipitation at the greisen sites.     

Mineralogical and fluid characteristics of the fluorite-rich Monakoff and E1 Cu–Au deposits,Cloncurry region,Queensland, Australia: Implications for regional F–Ba-rich IOCG mineralisation

The Monakoff iron oxide–Cu–Au (IOCG) deposit, located to the north east of Cloncurry within the Eastern Succession of the Mount Isa Inlier, Queensland, Australia, is characterised by high concentrations of F and Ba, with a host of other enriched elements including Co, Ag, Mn, REE, U, Pb, Zn and Sr. This gives the deposit a characteristic gangue assemblage dominated by fluorite, barite and calcite. The nearby E1 deposit, located 25 km to the NNE of Monakoff, and the large Ernest Henry deposit, 3 km to the west of E1, also contain abundant fluorite, barite and calcite in late stage assemblages. The three deposits, therefore, constitute a distinct group of IOCG deposits within the district, based on their F-rich geochemical and mineralogical affinities.The Monakoff ore zone is hosted in dilational openings along a shear zone developed within metasediments and metavolcanic rocks at the boundary between competent hangingwall rocks of the Toole Creek Volcanics and footwall rocks of the Mount Norna Quartzites. Four stages of alteration and mineralisation are recognised: Stage 1 garnet–biotite alteration; Stage 2 biotite–magnetite alteration; Stage 3 main F–Ba-ore mineralisation; and a Stage 4 pyrite–alloclasite Au–Co–As overprint. The E1 deposit has a more complex history, but Stage 5 has veins of fluorite–barite–carbonate that are comparable to Monakoff's main stage. The Stage 3 assemblage at Monakoff comprises a sheared groundmass of fluorite, barite, manganoan calcite, magnetite, chalcopyrite, pyrite, galena and sphalerite, with coarser grained pods of the same mineralogy interpreted to be dilational structures infilled during syn-ore deformation. Accessory minerals include U–Pb-oxides, REE–F-carbonates and Ag–Pb–Bi-sulfosalts, with no discrete Au minerals. The sulfosalts are interpreted to have formed from an immiscible Bi-melt within the mineralising fluid at temperatures higher than the melting point of Bi. The Stage 4 overprint at Monakoff contains pyrite and alloclasite. Laser ablation analyses of the sulphide minerals at Monakoff reveal that Stage 3 sulphides contain only trace amounts of Au (0.04 ppm in pyrite), although galena and chalcopyrite contain significant concentrations of Ag. Stage 4 pyrite and alloclasite, however, contain ~ 1 ppm Au in solid solution and mass balance calculations indicate the majority of bulk rock Au to be present in these minerals, although the majority of bulk Ag is present in Stage 3 sulphides. The Stage 5 veins at E1 have an identical gangue and accessory mineralogy to Stage 3 at Monakoff and differ in the sulphide mineralogy only in the lack of galena and sphalerite.Four fluid inclusion populations are identified within the fluorite at Monakoff: Group 1 is CO₂ rich; Group 2 is complex solid–liquid–vapour inclusions, with two groups based on homogenisation temperature (> 450 °C and 300–375 °C). Laser ablation-ICP-MS analyses indicate that these inclusions contain Cu, Pb, Zn, Fe, Mn, Mg, Ag, REE, U and Ba, but significantly no S, Se or Au; Group 3 are solid–liquid–vapour inclusions with a T_h of 200–275 °C, and contain Ba, Na, Mg, K and Br; and Group 4 are low salinity liquid–vapour inclusions. Group 1, 2 and 4 inclusions are also present in fluorite at E1. The REE geochemistry of fluorite from Monakoff and E1 is comparable and is characterised by a distinct positive Eu anomalies in all analyses, interpreted to indicate oxidising conditions at the time of high temperature ore deposition. The presence of abundant fluorite and barite is indicative of fluid mixing due to the insolubility of barite and fluorite and thus Ba and S, and Ca and F must have been introduced via different fluids. We propose that the oxidised fluid represented by the Group 2 inclusions and containing F, Ba, REE, U and base metals, mixed with a reduced, S-bearing fluid in a zone of dilation in the host shear zone that acted as a conduit for fluid flow during D₃ deformation. The source of the metal and F-rich fluid is likely to be the nearby granitic intrusions of the Williams–Naraku batholith, probably the Malakoff granite. This granite is also likely to be the source of the CO₂ represented by Group 1 fluid inclusions, and the REE, U, base metals and possibly Au, although the high Pb and Zn content of Monakoff and not E1 may suggest a local input of those elements at Monakoff. Stage 4 mineralisation overprints the F–Ba stage and is characterised by a Co–As–Au signature. At present it is unclear if this is a late stage, more reduced, evolution of the main ore fluid, or a separate mineralising event entirely.The presence of this F–Ba-metal-rich fluid has produced a distinctive style of IOCG mineralisation in the area to the north of Cloncurry. The probable link to the Malakoff granite implies that similar deposits may be present within several kilometres of the granite in suitable structural traps. Monakoff illustrates that although structurally controlled, the presence of Na–Ca alteration and ‘red rock’ K-alteration and brecciation are not key exploration criteria for these deposits. In addition, the presence of the overprinting As–Co–Au assemblage may indicate that this is a separate mineralising episode that may be present at other localities in the district. This study has also shown that fluorite can provide a powerful tool for determining ore forming conditions in F-rich IOCG systems.     

A combined fluid inclusion and S–Pb isotope study of the Neoproterozoic Pingshui volcanogenic massive sulfide Cu–Zn deposit,Southeast China

The Pingshui Cu–Zn deposit is located in the Jiangshan–Shaoxing fault zone, which marks the Neoproterozoic suture zone between the Yangtze block and Cathaysia block in South China. It contains 0.45 million tons of proven ore reserves with grades of 1.03 wt.% Cu and 1.83 wt.% Zn. This deposit is composed of stratiform, massive sulfide ore bodies, which contain more than 60 vol.% sulfide minerals. These ore bodies are hosted in altered mafic and felsic rocks (spilites and keratophyres) of the bimodal volcanic suite that makes up the Neoproterozoic Pingshui Formation. Metallic minerals include pyrite, chalcopyrite, sphalerite, tennantite, tetrahedrite and magnetite, with minor galena. Gangue minerals are quartz, sericite, chlorite, calcite, gypsum, barite and jasper. Three distinct mineralogical zones are recognized in these massive sulfide ore bodies: a distal zone composed of sphalerite + pyrite + barite (zone I); an intermediate zone characterized by a pyrite + sphalerite + chalcopyrite assemblages (zone II); and a proximal zone containing chalcopyrite + pyrite + magnetite (zone III). A thin, layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone. The volcanic rocks of the Pingshui Formation are all highly altered spilites and keratophyres, but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting. Homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 °C, and their salinities range from 3.2 to 5.7 wt.% NaCl equivalent. Raman spectroscopy of the fluid inclusions showed that water is the dominant component, with no other volatile components. Fluid inclusion data suggest that the ore-forming fluids were derived from circulating seawater. The δ³⁴S values of pyrite from the massive sulfide ores range from − 3.6‰ to + 3.4‰, indicating that the sulfur was primarily leached from the arc volcanic rocks of the Pingshui Formation. Both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions, implying that the lead was also derived from the Pingshui Formation. The low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many VMS Cu–Zn deposits in Canada (e.g., Noranda) and thus can be classified as belonging to the bimodal-mafic subtype. The presence of magnetite and the absence of jaspilite and barite at the − 505 m level in the Pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies. If this interpretation is correct, the deep part of the Pingshui Cu–Zn deposit may have significant exploration potential.     

Evidence of fluid inclusions for two stages of fluid boiling in the formation of the giant Shapinggou porphyry Mo deposit,Dabie Orogen,Central China

The Shapinggou porphyry Mo deposit, one of the largest Mo deposits in Asia, is located in the Dabie Orogen, Central China. Hydrothermal alteration and mineralization at Shapinggou can be divided into four stages, i.e., stage 1 ore-barren quartz veins with intense silicification, followed by stage 2 quartz-molybdenite veins associated with potassic alteration, stage 3 quartz-polymetallic sulfide veins related to phyllic alteration, and stage 4 ore-barren quartz ± calcite ± pyrite veins with weak propylitization. Hydrothermal quartz mainly contains three types of fluid inclusions, namely, two-phase liquid-rich (type I), two- or three-phase gas-rich CO₂-bearing (type II) and halite-bearing (type III) inclusions. The last two types of fluid inclusions are absent in stages 1 and 4. Type I inclusions in the silicic zone (stage 1) display homogenization temperatures of 340 to 550 °C, with salinities of 7.9–16.9 wt.% NaCl equivalent. Type II and coexisting type III inclusions in the potassic zone (stage 2), which hosts the main Mo orebodies, have homogenization temperatures of 240–440 °C and 240–450 °C, with salinities of 34.1–50.9 and 0.1–7.4 wt.% NaCl equivalent, respectively. Type II and coexisting type III inclusions in the phyllic zone (stage 3) display homogenization temperatures of 250–345 °C and 220–315 °C, with salinities of 0.2–6.5 and 32.9–39.3 wt.% NaCl equivalent, respectively. Type I inclusions in the propylitization zone (stage 4) display homogenization temperatures of 170 to 330 °C, with salinities lower than 6.5 wt.% NaCl equivalent. The abundant CO₂-rich and coexisting halite-bearing fluid inclusion assemblages in the potassic and phyllic zones highlight the significance of intensive fluid boiling of a NaCl–CO₂–H₂O system in deep environments (up to 2.3 kbar) for giant porphyry Mo mineralization. Hydrogen and oxygen isotopic compositions indicate that ore-fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials at Shapinggou are magmatic in origin. Re–Os dating of molybdenite gives a well-defined ¹⁸⁷Re/¹⁸⁷Os isochron with an age of 112.7 ± 1.8 Ma, suggesting a post-collisional setting.     

The genesis of metal zonation in the Weilasituo and Bairendaba Ag–Zn–Pb–Cu–(Sn–W) deposits in the shallow part of a porphyry Sn–W–Rb system,Inner Mongolia,China

The Weilasituo and Bairendaba Zn–Pb–Ag–Cu–(Sn–W) sulphide deposits are located in the southern part of Great Xing'an Range of Inner Mongolia in China. The deposits are located at shallow depths in the newly discovered Weilasituo porphyry hosting Sn–W–Rb mineralization. The mineralization at Weilasituo and Bairendaba consist of zoned massive sulphide veins within fractures cutting the Xilinhot Metamorphic Complex and quartz diorite. The Weilasituo deposit gradually zones from the Cu-rich Zn–Cu sulphide mineralization in the west to Zn-rich Zn–Cu sulphide mineralization in the east. The Bairendaba deposit has a Cu-bearing and Zn-rich core through a transitional zone devoid of copper to an outer zone of Zn–Pb–Ag mineralization. Three main veins contain more than 50 wt.% of the contained metal in the two deposits with their metal ratios displaying a systematic and gradual increase in Zn/Cu, Pb/Zn and Ag/Zn ratios from the western part of Weilasituo to the eastern part of Bairendaba.Three stages of vein-type mineralization are recognized. Early, sub-economic mineralization consists of a variable proportion of euhedral arsenopyrite, pyrite, quartz, and rare wolframite, scheelite, cassiterite, magnetite and cobaltite. This was succeeded by main stage mineralization with economic concentration of zoned Cu, Zn, Pb and Ag sulphide minerals along strike within the veins. The zones consist of the assemblages: (1) pyrrhotite–Fe-rich sphalerite–chalcopyrite(–quartz–fluorite) at west Weilasituo; (2) pyrrhotite–Fe-rich sphalerite–chalcopyrite(–galena–tetrahedrite–quartz–fluorite) at east Weilasituo; (3) pyrrhotite–Fe-rich sphalerite–chalcopyrite(–galena–tetrahedrite–quartz–fluorite) in the centre of Bairendaba; (4) pyrrhotite–Fe-rich sphalerite–galena(–chalcopyrite–tetrahedrite–quartz–fluorite) in the transition zone of Bairendaba; and (5) pyrrhotite–Fe-rich sphalerite–galena–tetrahedrite(–chalcopyrite–falkmanite–argentite–pyrargyrite–quartz–fluorite) in the outer zone at Bairendaba. Post-main ore stage is devoid of sulphides and characterized overprinting of fluorite, sericite, chlorite, illite, kaolinite and calcite.Zircon SHRIMP U–Pb dating, Zircon LA–ICP–MS U–Pb dating, molybdenite Re–Os isochron dating, and muscovite Ar–Ar dating indicate the Beidashan granitic batholith was intruded at 140 ± 3 Ma (MSWD = 3.3), the porphyritic monzogranite from marginal facies of the Beidashan batholith was intruded at 139 ± 2 Ma (MSWD = 0.75), the mineralized quartz porphyry was intruded at 135 ± 2 Ma (MSWD = 0.91), the greisen mineralization occurred at 135 ± 11 Ma (MSWD = 7.2), and the post-main ore stage muscovite deposited at 129.5 ± 0.9 Ma. The new geochronology data show the porphyry Sn–W–Rb and vein-type sulphide mineralization are contemporaneous with granitic magmatism in the region.The metal zonation at the Weilasituo and Bairendaba deposits is a result of progressive metal deposition. This was during the evolution of a metal-bearing fluid along the strike of the veins and during the main stage of ore formation at the upper part of the deep-seated porphyry Sn–W–Rb system. This progressive zonation indicates that the deposits represent end-numbers formed from one ore-forming fluid, which moved from west to east from the porphyry. The metal zonation patterns of the major veins are consistent with metal-bearing fluid entering the system with the precipitation of chalcopyrite proximally and sphalerite, galena and Ag-bearing minerals more distally. We show that the mechanism of metal deposition is therefore controlled by thermodynamic conditions resulting in the progressive separation of sulphides from the metal-bearing fluid. The temperature gradient between the inflow zone and the outflow zone appears to be one of the key parameters controlling the formation of the metal zonation pattern. The sulphide precipitation sequence is consistent with a low fS₂ and low fO₂ state of the acidic metal-bearing fluid. The metal zonation pattern provides helpful clues from which it is possible to establish the nature of fluid migration and metal deposition models to locate a possible porphyry mineralization at depth in the Great Xing'an Range, which is consistent with the geology of the newly discovered porphyry Sn–W–Rb system.