Oxygen Isotope Composition Of Quartz Research Articles

Fluid origin and critical ore-forming processes for the giant gold mineralization in the Jiaodong Peninsula, China: Constraints from in situ elemental and oxygen isotopic compositions of quartz and LA–ICP–MS analysis of fluid inclusions

The Jiaodong Peninsula, China, is one of the largest gold provinces in the world. During a short time interval in the Early Cretaceous, over 5000 t of gold were accumulated there. The mechanisms controlling the focused Au deposition and the origins of massive amounts of auriferous fluids are still controversial. Quartz–sulfide lode mineralization (Linglong-type) and disseminated/stockwork mineralization (Jiaojia-type) are the two major mineralization styles in the Jiaodong Peninsula. Herein, we conducted in situ textural, elemental and oxygen isotopic analyses using scanning electron microscopy (SEM), laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) and secondary ion mass spectrometry (SIMS) on quartz from different hydrothermal stages and depths for three representative Linglong-type (Linglong deposit) and Jiaojia-type (Xiadian and Jiangjiayao deposits) gold deposits in the northwestern Jiaodong Peninsula, with the aim to constrain the ore-forming processes. The LA–ICP–MS analysis of individual fluid inclusions was also conducted to unravel the origin of the auriferous fluids. The results show that from the pre-mineralization to the ore-forming stages in the Linglong-type mineralization, the homogenization temperatures and salinities of fluid inclusions and the δ18Oquartz values change slightly, but the Al concentrations of quartz decrease continuously. Combined with the coexistence of CO2- and H2O-rich fluid inclusion endmembers, these trends indicate the increase of pH induced by CO2 degassing (fluid–fluid unmixing), which led to focused Au deposition. The quartz grains from the Jiaojia-type mineralization typically show a homogeneous texture with well-correlated lithophile elements (e.g., K, Al and Rb), which are distinct from those of the Linglong-type that are characterized by oscillatory zoning with much higher Al concentrations and δ18Oquartz values. These phenomena indicate that enhanced fluid–rock interaction occurred in the Jiaojia-type mineralization. In addition, the δ18Oquartz values show an increase from deep to shallow depths. In combination with thermodynamic modelling, it suggests decreasing fluid–rock interaction with decreasing depth. The above results corroborate that multiple mechanisms led to the efficient Au deposition in the Jiaodong Peninsula. Fluid–fluid unmixing typically occurred in the Linglong-type mineralization, while fluid–rock interaction was dominant in the Jiaojia-type mineralization. The different mechanisms might render mining challenging due to the changeable locations of favorable Au unloading.The LA–ICP–MS results of fluid inclusions suggest that the ore-forming fluids are metamorphic fluids rather than magmatic–hydrothermal fluids. In combination with the isotopic compositions of ores showing considerable mantle affinities and large-scale mafic underplating occurring beneath the study region, we propose a new genetic model that accounts for the origin of the auriferous fluids. The new model invokes the devolatilization of previously emplaced H2O- and Au-rich amphibole cumulates through amphibolite- to granulite-facies metamorphism in the middle–lower crust. It suggests an alternative way to generate the ‘orogenic-like’ gold deposits.

Geochronology and Ore Genesis of the Niujuan-Yingfang Pb-Zn-Ag Deposit in Fengning, Northern North China Craton: Constraints from Fluid Inclusions, H-O-S Isotopes and Fluorite Sr-Nd Isotopes

The Niujuan-Yingfang Pb-Zn-Ag deposit in northern North China Craton (NCC) is hosted at the contact zone between Permian biotite monzogranite and Hongqiyingzi Group migmatitic gneiss. The orebodies are structurally controlled by NE-trending F1 fault. Mineralization can be divided into three stages: (1) siliceous-chlorite-pyrite stage, (2) quartz-Ag-base metal stage, and (3) fluoritecalcite stage. Four types of fluid inclusions were identified, including: (1) liquid-rich aqueous inclusions, (2) vapor-rich inclusions, (3) liquid-rich, solid-bearing inclusions, and (4) CO2-bearing inclusions. Microthermometric measurements reveal that from stage I to III, the homogenization temperatures range from 317 to 262 °C, from 297 to 192 °C, and from 248 to 151 °C, respectively, and the fluid salinities are in the ranges from 1.1 wt.% to 6.5 wt.%, 1.2 wt.% to 6.0 wt.% and 0.7 wt.% to 4.0 wt.% NaCl equivalents, respectively. Fluid boiling and cooling are the two important mechanisms for ore precipitation according to microthermometric data, and fluid-rock interaction is also indispensable. Laser Raman spectroscopic analyses indicate the fluid system of the deposit is composed of CO2-NaCl-H2O±N2. Metallogenic fluorites yielded a Sm-Nd isochron age of 158±35 Ma. The δ34SV-CDT values of sulfides range from −1.3‰ to 6.3‰, suggesting that the sulfur may be inherited from the basement metamorphic igneous rocks. Hydrogen and oxygen isotopic compositions of quartz indicate a metamorphic origin for the ore-forming fluid, and the proportion of meteoric water increased during the ore-forming processes. Sr-Nd isotopes of fluorites show a crustal source for the ore-forming fluid, with primary metamorphic fluid mixed with meteoric water during ascent to lower crustal levels. Combined with the geological, metallogenic epoch, fluid inclusions, H-O-S and Sr-Nd isotopes characteristics of the deposit, we suggest that the Niujuan-Yingfang deposit belongs to the medium-low temperature hydrothermal vein-type Pb-Zn-Ag polymetallic deposit, with ore-forming fluids dominantly originated from metamorphic fluids.

Geology, geochemistry, fluid inclusions and O–H stable isotope constraints on genesis of the Lake Siah Fe-oxide ± apatite deposit, NE Bafq, Central Iran

The Lake Siah iron ± apatite deposit is situated in the Bafq Mining District (BMD), Central Iran. The iron ± apatite orebodies are hosted by a succession of rhyolite, rhyolitic tuff, trachyandesite, and andesite of Lower Cambrian age. The host rock has undergone widespread alteration and mineralization stages including Na (albite–quartz), followed by Na–Ca (albite–calcite–amphibole–magnetite ± quartz ± epidote), magnetite–apatite, K (biotite ± K-feldspar), hydrolytic (sericite–quartz), and argillic (kaolinite–montmorillonite ± dickite), respectively. Electron microprobe analyses (EPMA) from magnetite and hematite show significant variations of trace elements. Based on Ni/Cr + Mn and Ca + Al + Mn versus Ti + V diagrams, the majority of magnetite samples belong to Kiruna-type deposits. At least, three generations of fluid inclusions, including solid-bearing (L + V + S) (Type I), liquid-rich (L + V) (Type II-A), vapor-rich (L + V) (Type II-B), and liquid or vapor mono-phase (Type III), are recognized in quartz and apatite. The solid-bearing fluid inclusions in quartz completely homogenized at temperatures of 150 to > 530 °C with salinities of 30–58 wt% NaCl equiv. Liquid-rich fluid inclusions in apatite homogenized to a liquid phase at 175–210 °C, whereas the vapor-rich fluid inclusions homogenized to a vapor at 335–350 °C. Oxygen isotope analysis was carried out on quartz and magnetite. The hydrogen and oxygen isotopic compositions of quartz (δ18Ofluid values of 7.57–11.04‰) show that with progress in time the ore-forming solutions gradually evolved from a magmatic to meteoric-dominated source.

Fluid inclusion and H–O isotope study of the Jiguanshan porphyry Mo deposit, Xilamulun Metallogenic Belt: implications for characteristics and evolution of ore-forming fluids

We studied the fluid inclusions of the Jiguanshan Mo deposit in China, which is a large porphyry deposit located in the southern Xilamulun Metallogenic Belt. The irregular Mo ore body with various types of hydrothermal veinlets is hosted by Late Jurassic granite porphyry. Intense hydrothermal alterations in the deposit from the core to margin are silicification–potassium feldspar alteration, pyrite–quartz–sericite–fluorite alteration, and propylitic alteration. Based on the mineral assemblages and crosscutting relationships of ore veins, the ore-forming process were divided into three stages and two substages: quartz–pyrite veins (stage I) associated with potassic alteration; quartz–molybdenite–chalcopyrite–pyrite veins (substage II-1) and quartz–molybdenite–fluorite veins (substage II-2) associated with phyllic alteration; and fluorite–quartz–carbonate veins (stage III) with carbonation. Five major fluid inclusions (FIs) types were distinguished in the quartz associated with oxide and sulfide minerals, i.e. polyphase brine (Pb-type), opaque-bearing brine (Ob-type), solid halite (S-type), two-phase aqueous (A-type), and vapor (V-type) inclusions. The FIs of stage I were composed of liquid-rich S-, A-, and V-type FIs with homogenization temperatures and salinities of 490 to 511 °C and 8.9 to 56.0 wt% NaCl equiv., respectively. The FIs of substage II-1 are composed of Pb-, Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 352 to 460 °C and 3.7 to 46.1 wt% NaCl equiv, respectively. The FIs of substage II-2 are Ob-, S-, A-, and V-type FIs with homogenization temperatures and salinities of 234 to 309 °C and 3.7 to 39.2 wt% NaCl equiv, respectively. The FIs of stage III are A-type FIs with homogenization temperatures and salinities of 136 to 172 °C and 1.1 to 8.9 wt% NaCl equiv, respectively. Fluid boiling, which resulted in the precipitation of sulfides, occurred in stages I and II. The initial ore-forming fluids of the Jiguanshan deposit had high temperature, high salinity, and belonged to an F-rich NaCl ± KCl–H2O system. The fluids gradually evolved to low temperature, low salinity, and belonged to a NaCl–H2O system. Studies of the hydrogen and oxygen isotope compositions of quartz (δ18OH2O = − 7.3 to 6.3‰, δDH2O = − 104.3 to − 83.3‰) show that the ore-forming fluids gradually evolved from magmatic water to meteoric water.

Origin of Monte Rosa whiteschist from in-situ tourmaline and quartz oxygen isotope analysis by SIMS using new tourmaline reference materials

Abstract A series of tourmaline reference materials are developed for in situ oxygen isotope analysis by secondary ion mass spectrometry (SIMS), which allow study of the tourmaline compositions found in most igneous and metamorphic rocks. The new reference material was applied to measure oxygen isotope composition of tourmaline from metagranite, meta-leucogranite, and whiteschist from the Monte Rosa nappe (Western Alps). The protolith and genesis of whiteschist are highly debated in the literature. Whiteschists occur as 10 to 50 m tube-like bodies within the Permian Monte Rosa granite. They consist of chloritoid, talc, phengite, and quartz, with local kyanite, garnet, tourmaline, and carbonates. Whiteschist tourmaline is characterized by an igneous core and a dravitic overgrowth (XMg > 0.9). The core reveals similar chemical composition and zonation as meta-leucogranitic tourmaline (XMg = 0.25, δ18O = 11.3–11.5‰), proving their common origin. Dravitic overgrowths in whiteschists have lower oxygen isotope compositions (8.9–9.5‰). Tourmaline in metagranite is an intermediate schorl-dravite with XMg of 0.50. Oxygen isotope data reveal homogeneous composition for metagranite and meta-leucogranite tourmalines of 10.4–11.3‰ and 11.0–11.9‰, respectively. Quartz inclusions in both meta-igneous rocks show the same oxygen isotopic composition as the quartz in the matrix (13.6–13.9‰). In whiteschist the oxygen isotope composition of quartz included in tourmaline cores lost their igneous signature, having the same values as quartz in the matrix (11.4–11.7‰). A network of small fractures filled with dravitic tourmaline can be observed in the igneous core and suggested to serve as a connection between included quartz and matrix, and lead to recrystallization of the inclusion. In contrast, the igneous core of the whiteschist tourmaline fully retained its magmatic oxygen isotope signature, indicating oxygen diffusion is extremely slow in tourmaline. Tourmaline included in high-pressure chloritoid shows the characteristic dravitic overgrowth, demonstrating that chloritoid grew after the metasomatism responsible for the whiteschist formation, but continued to grow during the Alpine metamorphism. Our data on tourmaline and quartz show that tourmaline-bearing white-schists originated from the related meta-leucogranites, which were locally altered by late magmatic hydrothermal fluids prior to Alpine high-pressure metamorphism.

Thermogenetic degradation of early zeolite cement: An important process for generating anomalously high porosity and permeability in deeply buried sandstone reservoirs?

Abstract Diagenetic explanations to anomalously high porosities and permeabilities in deeply buried sandstones have been presented for many reservoirs. For example, grain coatings of microquartz or chlorite can preserve porosity by preventing succeeding quartz overgrowths, and dissolution of grains or cement can generate secondary porosity. Anomalously high porosity and permeability (up to 25% and 500 mD, respectively) characterize the deeply buried (>5 km) Upper Jurassic shoreface sandstones of the Gert Member (Heno Formation) in the Hejre Field in the Danish Central Graben. Optical, cathodoluminescence and scanning electron microscopy were used to characterize the petrography and diagenetic changes that resulted in this high pressure and high temperature (HPHT) reservoir. This was supplemented by chemical analyses (ICP-OES and ICP-MS), mineralogical composition (XRD), and oxygen isotope composition of quartz and calcite cement (SIMS). The petrographic investigation shows that none of the known explanations for anomalously high porosity and permeability can be applied, hence a new hypothesis for deeply buried sandstones in contact with lavas and volcaniclastic lithologies is proposed. The new hypothesis includes reducing mechanical compaction due to early patchy zeolite cement, which was sourced from adjacent lavas and volcaniclastic rocks. Locally, stylolites developed where zeolite cement was less effective, hence the present overpressure formed at a later stage. Increased temperatures during burial resulted in thermal instability of the zeolite cement, which was dissolved and authigenic K-feldspar and quartz precipitated instead. This resulted in a reduction of the cement volume of up to 70% if the zeolite was K-heulandite and a corresponding relative porosity-increase. Thus, a reduction in cement-volume was generated by replacing zeolite of an open crystal structure with mineral phases, K-feldspar and quartz, of denser crystal structures. The thermogenetic breakdown of zeolite was forced by increased temperatures during burial. This process may explain previously enigmatic highly porous and permeable deeply buried sandstone reservoirs.

Triple oxygen and hydrogen isotopic study of hydrothermally altered rocks from the 2.43–2.41 Ga Vetreny belt, Russia: An insight into the early Paleoproterozoic seawater

Abstract The early Paleoproterozoic represents a period of rapid changes in Earth systems that could have affected the stable isotopic composition of seawater. The well-preserved pillow structures, hyaloclastites and komatiitic basalts of the 2.43–2.41 Ga Vetreny belt, Baltic Shield provide a record of high-temperature water-rock interaction induced by contemporaneous seawater. Here we present results of mineralogical, fluid inclusion, hydrogen, and triple oxygen isotopic analysis of hydrothermal alteration products. Emphasis is given to vein-filling quartz and epidote as they likely formed at high water-rock ratios. Ten minerals pairs, quartz-epidote and quartz-calcite, returned temperatures of isotopic equilibrium between 286 and 387 °C, which compares well to the homogenization temperatures measured for saline fluid inclusions hosted in vein quartz. The computed δD and δ18O values of equilibrium fluids range between −31 and +12‰, and −1.36 and +3.20‰, respectively, which overlap with the isotopic composition of ice-free world seawater and fluids generated at submarine hydrothermal systems. This is the earliest piece of evidence suggesting that early Paleoproterozoic seawater had a δD value close to 0‰. We also present triple oxygen isotopic composition of quartz and epidote that formed in similar facies of hydrothermal alteration from the relatively young (6–7 Ma) oceanic crust as sampled by the ODP Hole 504B in the eastern Pacific Ocean. These data show similarity to the triple oxygen isotope analyses of the Vetreny belt rocks indicating that the 2.43–2.41 Ga seawater had the Δ17O value close to that of modern-day seawater. Due to small fractionation at 300–390 °C (αepidote-water ≈ 1), epidotes present a strong evidence that equilibrium fluids had Δ′17O values close to 0‰. Based on the previously published quartz-water calibration, the computed Δ17O values of equilibrium fluids range between −0.11 and −0.03‰, significantly lower than that of seawater or inferred seawater-derived fluids at low water-rock ratios. This can be explained by multiple factors including phase separation of fluids or/and presence of low-temperature quartz overgrowths. Both are reflected in the fluid inclusion data and in situ δ18O measurements by ion microprobe (SIMS) presented here. Overall, our study suggests that the δ18O, Δ17O and δD values of the 2.43–2.41 Ga seawater were −1.7 ± 1.1, −0.001 ± 0.011 and 0 ± 20‰ respectively, similar to the modern values, which reflects the dominant role of submarine hydrothermal alteration in the stable isotopic budget of seawater throughout Earth’s history.

Genesis and tectonic setting of the Bulage Pb–Zn deposit, Inner Mongolia, China: Evidence from geology, fluid inclusions, EMPA, H–O isotope systematics, zircon U–Pb geochronology, and geochemistry

The recently discovered Bulage Pb–Zn deposit is located in the central part of the Erlianhot–Dongwuqi Metallogenic Belt (eastern Central Asian Orogenic Belt) in Inner Mongolia, China. The ore bodies of the deposit are hosted in alkali feldspar granite and in dacitic crystal tuff within Unit 2 of the Carboniferous Baoligaomiao Formation. The Bulage deposit is a low to moderate temperature hydrothermal vein‐type deposit and is controlled by fractures. The hydrothermal mineralization can be divided into three stages: early (quartz + specularite ± magnetite), middle (quartz + sphalerite + galena ± chalcopyrite ± pyrite), and late (calcite ± quartz + sphalerite + galena). The deposit contains liquid‐rich two‐phase (VL‐type) and pure‐liquid (L‐type) fluid inclusions. The initial ore‐forming fluids are attributed to the low to moderate temperature and low salinity of a NaCl–H2O system. Hydrogen and oxygen isotopic compositions of quartz and calcite indicate that the ore‐forming fluids were dominated by meteoric water with minor contributions of magmatic water. The quartz diorite, monzonite porphyry, and alkali feldspar granite in the deposit yield LA–ICP–MS zircon U–Pb ages of 305–300 Ma. These high‐K calc‐alkaline I‐type granitoids are enriched in large‐ion lithophile elements (LILEs; e.g., Rb, Cs, and K) and light rare earth elements (LREEs) and are depleted in high‐field‐strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The primary magma of these granitoids was derived from the partial melting of lower crust. The parental magma of the quartz diorite may have provided part of the ore‐forming material and acted as a heat source for mineralization. Therefore, we infer that the Bulage Pb–Zn deposit was formed as a result of the southward subduction of the Paleo–Asian Ocean beneath the North China Craton during the Late Carboniferous.

Hydrothermal evolution and ore genesis of the Zhaiping Ag-Pb-Zn deposit in Fujian Province of Southeast China: Evidence from stable isotopes (H, O, C, S) and fluid inclusions

The Zhaiping Ag-Pb-Zn deposit (204 t Ag, average grade: 221.8 g/t) is located in the coastal area of the Cathaysia Block, Southeast China. Vein-type Ag-Pb-Zn orebodies are mainly hosted in the early Cretaceous volcanic and subvolcanic rocks, and structurally controlled by a group of NW-trending extensional faults. Ore-related hydrothermal alteration is well developed on both sides of the veins, dominated by silicic, phyllic, propylitic, and carbonate alteration. Mineralization can be divided into three stages: (1) the pre-ore quartz-pyrite stage, (2) syn-ore quartz-Ag-base metal stage, and (3) post-ore quartz-calcite stage. Microthermometric measurements of fluid inclusion assemblages in quartz, fluorite, sphalerite, and calcite from various hydrothermal stages reveal that from the pre-ore, syn-ore to post-ore stages, the homogenization temperatures range from 365 to 319 °C, from 317 to 222 °C, and from 233 to 172 °C, respectively. Fluid salinities range from 1.7 to 10.8 wt% NaCl equivalent. The microthermometric data indicate that the fluid cooling and fluid-rock interaction are two important mechanisms for ore precipitation. The δ34SV-CDT values of sulfide minerals (pyrite, sphalerite, galena, pyrrhotite and tetrahedrite) range from −1.9 to 6.2‰, and mostly between 1.0 and 4.5‰, consistent with a deep-seated magmatic sulfur source. Hydrogen and oxygen isotopic compositions of quartz indicate a primarily magmatic origin for the ore-forming fluids, and the proportion of meteoric water increased during the ore-forming processes. Post-ore stage calcite has δ13CV-PDB values of −2.8 to −0.8‰ and δ18OV-SMOW values of 4.2–6.4‰, corresponding to calculated values of fluids of −3.2 to −1.1‰, and −4.9 to −2.8‰, respectively. The carbon isotopes indicate a magmatic source for carbon but the oxygen isotopes indicate a significant contribution of meteoric water during calcite precipitation. We therefore proposed that the Zhaiping deposit is a typical mesothermal deposit that formed in an extensional environment related to the early Cretaceous subduction of the paleo-Pacific plate.

Genesis of the Bianbianshan Cu-polymetallic deposit of the Xilamulun Cu-Mo metallogenic belt, Inner Mongolia, China: A fluid inclusion and O–H–S–Pb isotope study

The Bianbianshan Cu-polymetallic deposit is located in the Xilamulun Cu-Mo belt of Inner Mongolia, NE China, and occurs within Late Jurassic andesite, rhyolite and tuff. Cu mineralization is observed in various types of hydrothermal disseminated veins exhibiting siliciification, sericitization and chloritization. The ore-forming process occurred in four stages: (1) chalcopyrite-pyrite-quartz, (2) pyrite-chalcopyrite-quartz-vein, (3) sphalerite-galena-quartz-vein, (4) and quartz-calcite-vein. Three types of fluid inclusions were identified in the deposit, including C-type (CO2-NaCl-H2O) as well as V- and L-type (NaCl-H2O) inclusions, where only L-type inclusions are observed in the fourth stage. Homogenization temperature of fluid inclusions in the four stages are 325–365 °C, 282–335 °C, 268–312 °C, and 195–259 °C, respectively, all of which exhibit salinities lower than ∼ 13 wt% NaCl equiv. Trapping pressure estimated from C, V- and L-fluid inclusions are between 550 and 900 bars, corresponding to minimum depths of 2.5–3.7 km. Hydrogen and oxygen isotopic compositions of quartz from different stages (δD = −109.7 ~ –107.6‰, δ18O = 7.6–9.6‰, V-SMOW) suggest that the mineralizing fluid gradually evolved from a magmatic to a meteoric origin. Sulfur (δ34SV-CDT = −0.7 to 0.4‰) and lead isotopes (208Pb/204Pb = 37.746–38.137‰; 208Pb/204Pb = 15.52–15.56%; 206Pb/204Pb = 17.75–18.36%) indicate that ore-forming materials were derived from mantle with minor additional participation of crustal reservoirs. Our data suggests the ore-forming fluids of the Bianbianshan Cu-polymetallic deposit are attributed to a moderate temperature, moderate-low salinity, and moderate density system, where decreases in pressure, phase separation and local mixing with meteoric water drove precipitation of metals.

Ore genesis and hydrothermal evolution of the Wulandele Mo deposit, Inner Mongolia, Northeast China: Evidence from geology, fluid inclusions and H–O–S–Pb isotopes

The newly identified Wulandele Mo deposit is located in the western part of the Great Xing’an Range, Northeast China. Molybdenum mineralization generally occurs as veins or disseminations hosted in Permian to Cretaceous granitic intrusions, associated with potassic alteration, silicification, greisenization and propylitic alteration. The ore-forming process can be divided into four stages: quartz ± K-feldspar ± biotite ± pyrite (stage I), quartz + molybdenite ± K-feldspar ± pyrite (stage II), quartz + chalcopyrite ± bornite (stage III), and quartz + carbonate (stage IV). Combined fluid inclusion microthermometry and stable and Pb isotopic compositions are used to constrain the hydrothermal processes and ore genesis of the Wulandele Mo deposit. Fluid inclusion data show four types of fluid inclusion assemblages (FIAs), i.e., L0 (liquid-rich two-phase FIAs), V0 (vapour-rich two-phase FIAs), C (CO2-rich FIAs), and rare L1 (liquid-rich three-phase FIAs with one transparent mineral), but only the former three types of FIAs were analysed. Aqueous and carbonic fluid inclusions occur in quartz veins of stages I and II, and only aqueous inclusions are observed in stages III and IV. Hydrogen and oxygen isotopic compositions of quartz indicate a primarily magmatic origin, and the proportion of meteoric water increased during the ore-forming process. Sulfur (δ34SVCDT = 1.90–4.19‰) and lead isotopes suggest that the ore-forming materials came predominantly from magmatic fluids. The Wulandele Mo deposit was formed by an initially high-temperature, high-oxygen fugacity and CO2-rich fluid system at an estimated depth of ∼0.4 to 3.3 km. Decreases in temperature and fO2 as well as the input of meteoric water were critical factors for sulfide precipitation. Combining the integrated analysis of deposit geology, the fluid evolutionary process, and the ore-forming environment, we suggest that the Wulandele deposit should be classified as a porphyry Mo deposit that was formed in a continental collision orogen during post-collisional extension associated with the consumption of the Mongol–Okhotsk ocean in NE China.

Geology, geochemistry, and geochronology of the East Bay gold trend, Red Lake, Ontario, Canada

The Red Lake greenstone belt is situated in northwestern Ontario within the Uchi Subprovince, Superior Province. Most gold deposits therein are associated with major deformation corridors; the east-west oriented “Mine trend” hosts most of the large deposits and the northeast-southwest “East Bay trend” hosts several small deposits and showings. Gold along the East Bay trend typically occurs in quartz replacement veins that were emplaced into pre-existing quartz-carbonate veins. Gold can occur as free gold or along vein margins associated with pyrite and pyrrhotite. Most primary fluid inclusions, preserved in relatively undeformed portions of veins, are carbonaceous with lesser quantities of aqueous inclusions. The average homogenization temperature of aqueous fluids is ~250 °C; however, the abundance of three-phase inclusions, variation in liquid-vapor ratios, and a wide range in homogenization temperatures indicate that immiscibility, effervescence, and fluid mixing are mechanisms associated with gold deposition. The age (~2550 Ma) of alteration minerals in the Abino area is considerably younger (by ~100 Myr) than alteration minerals in other deposits in the Red Lake district, indicating that the mineralizing fluid history was more protracted than previously thought. Along the East Bay trend, barren veins generally have lower δ18OVSMOW values (0.0 to 8.5‰) relative to auriferous veins (9.6 and 13.1‰). Consequently, the oxygen isotopic composition of quartz could be used as a vector for gold mineralization. The genetic model for the East Bay trend involves several stages of vein formation. Auriferous veins formed near the upper boundary of the mesozonal regime (depth of ~5–6 km).

Listvenite-related gold deposits of the South Urals (Russia): A review

The Urals is a complex fold belt, which underwent long geological evolution. The formation of most gold deposits in the Urals is related to the collision stage. In this paper, we review some relatively small listvenite-related gold deposits, which are confined to the large Main Uralian fault zone and some smaller faults within the Magnitogorsk zone. The Mechnikovskoe, Altyn-Tash, and Ganeevskoe deposits are studied in detail in this contribution. They comprise the ore clusters along with other numerous small gold deposits, and constituted the sources for the gold placers exploited in historical time. The gold is hosted by metasomatites (listvenites, beresites) and quartz veins with economic gold grades (up to 20g/t Au). Listvenites are developed after serpentinites and composed of quartz, fuchsite, and carbonates (magnesite, dolomite)±albite. Volcanic and volcanoclastic rocks are altered to beresites, consisting of sericite, carbonates (dolomite, ankerite), quartz and albite. Pyrite and chalcopyrite are major ore minerals associated with gold; pyrrhotite, Ni sulfides, galena, sphalerite, arsenopyrite and Au-Ag tellurides are subordinate and rare. Gold in these deposits is mostly high-fineness (>900‰). The lower fineness (∼800‰) is typical of gold in assemblage with polymetallic sulfides and tellurides. The ores have been formed from the NaCl–CO2–H2O±CH4 fluids of low (∼2wt% NaCl-equiv.) to moderate (8–16wt% NaCl-equiv.) salinity at temperatures of 210–330°C. The oxygen isotopic composition of quartz (δ18O) varies from 14.7 to 15.4‰ (Mechnikovskoe deposit), 13.2 to 13.6‰ (Altyn-Tash deposit) and 12.0 to 12.7‰ (Ganeevskoe deposit). The oxygen isotopic composition of albite from altered rocks of the Ganeevskoe deposit is 10.1‰. The calculated δ18OH2O values of the fluid in equilibrium with quartz are in a range of 5.7–6.3, 4.2–4.6 and 6.3–6.7‰ respectively, and most likely indicate a magmatic fluid source.

Genesis of the Fuxing porphyry Cu deposit in Eastern Tianshan, China: Evidence from fluid inclusions and C–H–O–S–Pb isotope systematics

The Fuxing porphyry Cu deposit is a recently discovered deposit in Eastern Tianshan, Xinjiang, northwestern China. The Cu mineralization is associated with the Fuxing plagiogranite porphyry and monzogranite, mainly presenting as various types of hydrothermal veins or veinlets in alerted wall rocks, with potassic, chlorite, phyllic, and propylitic alteration developed. The ore-forming process can be divided into four stages: stage I barren quartz veins, stage II quartz–chalcopyrite–pyrite veins, stage III quartz–polymetallic sulfide veins and stage IV quartz–calcite veins. Four types of fluid inclusions (FIs) can be distinguished in the Fuxing deposit, including hypersline (H-type), vapor-rich two-phase (V-type), liquid-rich two-phase (L-type), and trace amounts of pure vapor inclusions (P-type), but only the stage I quartz contains all types of FIs. The stages II and III quartz have two types of FIs, with exception of H- and P-types. In stage IV quartz minerals, only the L-type inclusions can be observed. The FIs in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 357–518°C, 255–393°C, 234–322°C and 145–240°C, with salinities of 1.9–11.6wt.% NaCl equiv., 1.6–9.6wt.% NaCl equiv., 1.4–7.7wt.% NaCl equiv. and 0.9–3.7wt.% NaCl equiv., respectively. The ore-forming fluids of the Fuxing deposit are characterized by high temperature, moderate salinity and relatively oxidized condition. Carbon, hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magma source. The Cu mineralization in the Fuxing deposit occurred at a depth of ~1km, and the changes of oxygen fugacity, decompression boiling, and local mixing with meteoric water were most likely critical for the formation of the Fuxing Cu deposit.

Fluid inclusions and H–O–S–Pb isotope systematics of the Baishan porphyry Mo deposit in Eastern Tianshan, China

The Baishan porphyry Mo deposit formed in the Middle Triassic in Eastern Tianshan, Xinjiang, northwestern China. Mo mineralization is associated with the Baishan monzogranite and granite porphyry stocks, mainly presenting as various types of hydrothermal veinlets in alerted wall rocks, with potassic, phyllic, propylitic, and fluorite alteration. The ore-forming process can be divided into four stages: stage I K-feldspar–quartz–pyrite veinlets, stage II quartz–molybdenite±pyrite veinlets, stage III quartz–polymetallic sulfide veinlets and stage IV barren quartz–calcite veins. Four types of fluid inclusions (FIs) can be distinguished in the Baishan deposit, namely, liquid-rich two-phase (L-type), vapor-rich two-phase (V-type), solid-bearing multi-phase (S-type) and mono-phase vapor (M-type) inclusions, but only the stage I quartz contains all types of FIs. The stages II and III quartz have three types of FIs, with exception of M-type. In stage IV quartz minerals, only the L-type inclusions can be observed. The FIs in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 271–468°C, 239–349°C, 201–331°C and 134–201°C, with salinities of 2.2–11.6wt.% NaCl equiv., 1.1–10.2wt.% NaCl equiv., 0.5–8.9wt.% NaCl equiv. and 0.2–5.7wt.% NaCl equiv., respectively. The ore-forming fluids of the Baishan deposit are characterized by high temperature, moderate salinity and relatively reduced condition, belonging to a H2O–NaCl±CH4±CO2 system. Hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials came predominantly from a deep-seated magma source from the lower continental crust. The Mo mineralization in the Baishan deposit is estimated to have occurred at a depth of no less than 4.7km, and the decrease in temperature and remarkable transition of the redox condition (from alkalinity to acidity) of ore-forming fluids were critical for the formation of the Baishan Mo deposit.

Fluid inclusion and stable isotope study of the Khalyfehlou copper deposit, Southeast Zanjan, Iran

The Khalyfehlou deposit is one of volcanic-hosted vein-type Cu deposits located in the Tarom metallogenic zone, NW Iran. The host rocks are part of an Eocene volcano-sedimentary sequence formed into a NE–SW trending anticline with the Khalyfehlou deposit in its axis. The main ore minerals are chalcopyrite, bornite, chalcocite, and covellite and the gangue minerals are quartz, sericite, and calcite. This paper attempts to identify the source of the mineralizing fluids by using sulfur and oxygen isotope data and fluid inclusion studies. Two-phase liquid-rich fluid inclusions in the quartz gangue associated with the sulfide veins were studied and interpreted. Homogenization temperatures for these inclusions range from 159 to 293 °C and salinities are between 14 and 19.3 wt% NaCl equivalent. The sulfur isotope values for the chalcopyrite range from −2.0 to −5.3 ‰. Negative sulfur isotopes values and the occurrence of framboidal pyrite in the tuffaceous sandstone host rocks suggest a sedimentary origin for the sulfur. The oxygen isotope composition of quartz from the veins ranges from 12.3 to 14.3 ‰. The δ18Ofluid values calculated from the oxygen isotope data and the mean value of the homogenization temperatures range from 0.6 to 3.6 ‰. The constant fluid salinities at the whole range of temperature values and the H–O isotopic characteristics indicate that the ore-forming fluid for the Khalyfehlou deposit was relatively high salinity recirculating Ca–Na-rich meteoric-formational water. This study suggests that mineralization at the Khalyfehlou deposit is similar to cordilleran vein-type deposits. As such and based on the fluid inclusion data and other geological data, the cordilleran-type Khalyfehlou deposit would have been emplaced by a mesothermal system.

Geological characteristics and genesis of the Jurassic No. I porphyry Cu–Au deposit in the Xiongcun district, Gangdese porphyry copper belt, Tibet

The Xiongcun district, located in the western segment of the Gangdese porphyry copper belt (GPCB), hosts the only known Jurassic mineralization in the GPCB, Tibet, PRC. The No. I deposit in the Xiongcun district is related to the Middle Jurassic quartz diorite porphyry (167–161Ma) and the mineralization was formed at ca. 161.5±2.7Ma. Ore-bearing Middle Jurassic quartz diorite porphyry emplaced into the Early Jurassic volcano-sedimentary rock sequences of the Xiongcun Formation. Veinlets and disseminated mineralization developed within the Middle Jurassic quartz diorite porphyry and the surrounding metamorphosed tuff, hosting a measured and indicated resource of 1.04Mt copper, 143.31t gold and 900.43t silver with an average grade of 0.48% copper, 0.66g/t gold, and 4.19g/t silver. The mineralization can be assigned to four stages, including three main stages of hypogene mineralization and one epigenetic stage. The main alteration associated with mineralization is potassic. Seven mineralization-related hydrothermal veins have been recognized, including quartz–sulfide, biotite–sulfide, magnetite–sulfide, quartz–molybdenite–sulfide, chalcopyrite–pyrite–pyrrhotite, pyrite and polymetallic veins. The S and Pb isotopic compositions of the ore sulfides and the Re contents of the molybdenite suggest a mantle source for the ore-forming materials with minor contamination from the subducted sediments. Hydrogen and oxygen isotope compositions of quartz in the ores suggest that both magmatic and meteoric waters were involved in the ore-forming process. The ore-bearing porphyry (167–161Ma) and ore-forming (161.5±2.7Ma) ages of the No. I deposit correspond to the time of northward subduction of Neo-Tethys oceanic slab. The geochemical data of the ore-bearing porphyry indicate that the No. I deposit formed in an intra-oceanic island arc setting and the ore-bearing porphyry originated from the partial melting of mantle with limited contribution of subducted sediments. The genesis of the ore-bearing porphyry and No. I deposit is interpreted as being related to northward intra-oceanic subduction of Neo-Tethys oceanic slab in the Middle Jurassic time (167–161Ma).

Ore genesis and fluid evolution of the Daheishan giant porphyry molybdenum deposit, NE China

The Daheishan giant porphyry Mo deposit is located at the eastern segment of the CAOB, NE China. The ore-bearing intrusion of Daheishan deposit is a Jurassic granitic complex that includes Changgangling biotite granodiorite, Qiancuoluo seriate granodiorite, and Qiancuoluo granodioritic porphyry. Mineralization consists of disseminated, breccia and veined types. The hydrothermal fluids show significant magmatic signatures, as evidenced by the hydrogen and oxygen isotopic compositions of quartz and sulfur isotopic characteristics of ores. Consistence of lead isotopic compositions of the sulfides and the Daheishan intrusive complex further indicate a close relationship between the mineralization and magma. The fluid inclusions in quartz comprise of predominant aqueous two-phase as well as gas-rich fluid inclusions and a small number of daughter mineral-bearing inclusions. The gas species in the fluid inclusions are H2O, CO2, N2, CH4, C2H6, Ar∗ and minor H2S; the liquid compositions are SO42−, Cl−, Na+, K+, Ca2+ and Mg2+. Raman spectroscopy on individual fluid inclusions reveals a main gaseous composition of H2O, minor H2S and CO2. The fluid system in Daheishan Mo deposit can be described as NaCl–KCl–H2O type. Fluid inclusion microthermometry reveals subsolidus homogenization temperatures for fluid inclusions in the magmatic quartz phenocrysts (Th=400–450°C, salinities=∼21eq. wt.%), suggesting an obliteration of higher temperature history of the porphyry system by the superimposed processes. Most of the mineralization occurred at temperature range of 220–360°C, or higher. The temperature and salinity decreased to 100–170°C and 0–15eq. wt.%, respectively, when the hydrothermal fluid activities were gradually ending. No distinct evolution pattern based on the homogenization temperature or stable isotopic analyses is observed among the different mineralization stages. Mineralization was supposed to be related to the multi-phased boiling of fluids, instead of the gradual cooling of fluids. Pressure may be more critical than temperature in controlling the precipitation of molybdenite.

Oxygen isotope signatures of quartz from major Asian dust sources: Implications for changes in the provenance of Chinese loess

We present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions (<16 and 16–63μm) from major dust source regions in East Asia, including the Mongolian Gobi, the northern Chinese deserts, the Taklimakan desert, and the Qaidam Basin. The results demonstrate that the quartz oxygen isotope ratios of the Taklimakan desert and the Mongolian Gobi are more heterogeneous compared with the other areas. The quartz δ18O values of both the fine and coarse fractions from the various sources are overlapped to varying degrees, thus making it difficult to differentiate them. Nevertheless, the quartz δ18O values of both fractions exhibit an increasing trend from the Mongolian Gobi, to the northern Chinese deserts, and then to the Taklimakan desert. This implies that the geological settings of the source areas are different, which in turn results in differing contributions of high-temperature igneous rocks. The combination of quartz δ18O results with other quartz-based provenance tracers can clearly differentiate the three major source areas, i.e., the Taklimakan desert, the Mongolian Gobi, and the northern Chinese deserts. In addition, comparison of our results with previous δ18O measurements of fine-grained quartz from the Luochuan loess sequence suggests the likely glacial–interglacial fluctuations in dust provenance. Finally, we suggest that the combination of quartz δ18O signatures and other dust provenance tracers can potentially improve the recognition of long-term fluctuations in the provenance of Chinese loess-red clay deposits.

Sulfur- and oxygen-isotope constraints on the sedimentary history of apparent conglomerates from the Nuvvuagittuq Greenstone Belt (Nunavik, Québec)

Mafic igneous rocks of the Nuvvuagittuq Greenstone Belt (NGB) crystallized before 3.8Ga and possibly as early as 4.3Ga, potentially making the belt the oldest known supracrustal sequence on Earth. However, detrital zircons from a rare quartz-biotite schist in the NGB yield significantly younger ages of ≈3.77Ga or less. These appear to be inconsistent with the ages of the mafic igneous rocks, as the quartz-biotite schist has been interpreted as a metaconglomerate, formed by the dismantling of preexisting lithologies. In order to assess this genetic interpretation, we performed a sulfur and oxygen isotope study of the quartz-biotite schist. Sulfide grains found in quartz clasts and the matrix show significant mass-independent fractionation of sulfur isotopes (+0.2‰≤Δ33S‰≤+1.0‰; mean Δ33S=+0.5±0.1‰). Secondary sulfides from crosscutting veins do not show mass-independent fractionation of sulfur isotopes (−0.1‰≤Δ33S≤+0.3‰; mean Δ33S=+0.1±0.1‰). Oxygen isotope compositions of quartz from clasts, matrix and a fine-grained lens are highly enriched in 18O (16.9‰≤δ18O≤26.7‰). Non-zero Δ33S values indicate a surficial origin for sulfur, probably the Eoarchean atmosphere, while high δ18O values suggest a low-temperature (65±18°C) origin for the quartz, likely as chemical precipitation of a chert precursor from Si-saturated seawater. Therefore, the coupled S- and O-isotope measurements show that primary isotopic signatures characteristic of surficial environments survived the protracted metamorphic history of the NGB, and suggest that the quartz-biotite schist contains material that originated as chemical metasediments. The near mono-mineralic compositions of the clasts (quartz) and their shared 18O-enrichment suggest that they had a common protolith, which was deposited prior to the formation of the schist, and subsequently reworked. Whether the quartz-biotite schist represents a metaconglomerate or a structural melange, it preserves remnants of some of the oldest chemical sediments on Earth.