Types Of Fluid Inclusions Research Articles

Sources of metals and fluids for the Taijiying gold deposit on the northern margin of the North China Craton

Recognition of the sources of metals and fluids is crucial to determine the genesis of gold deposits, especially in distinguishing the orogenic and magmatic hydrothermal deposits. There is no consensus on the source and genetic style of the Mesozoic gold deposits in the North China Craton (NCC). The Taijiying gold deposit in the Chifeng-Chaoyang gold district on the northern margin of the NCC is a medium-sized gold deposit and worth studying for its sources of metals and fluids. It is hosted by amphibole- to granulite-facies metamorphic rocks and Mesozoic intrusions, and controlled by NNE-, NE-trending compressional reverse faults and NW-trending extensional normal faults. The gold mineralization types include auriferous quartz veins and wall rock alterations of phyllic mineralization, pyritization, chloritization, and carbonatization. According to the crosscutting relationships of the veins and the mineral textures within the ore-bearing veins, four mineralization stages are recognized: clouded-white quartz ± pyrite (stage I), gray quartz + pyrite (stage II), quartz + polymetallic sulfides (stage III), and calcite ± quartz (stage IV), among which the stages II and III represent the main gold mineralization stages. The timing of the gold mineralization is constrained to the Middle Triassic by zircon U-Pb ages of a pre-metallogenic diorite (258.0 ± 1.9 Ma) and a ore-related granitic porphyry dike (241.5 ± 2.2 Ma). Three types of fluid inclusions (FIs) in the quartz veins of four stages are identified: vapor-rich (type 1), CO2-H2O three-phase (type 2), and liquid-rich FIs (type 3). Their trapping temperatures gradually decrease from 352 ℃ (stage I) to 124 ℃ (stage IV), with salinities decreasing from 9.8 to 2.0 wt% NaCl eqv., indicating that the ore-forming fluids belong to a H2O-NaCl-CO2 system. The first three stages were characterized by moderate-high temperatures, a large variation in salinities, akin to those of the magmatic hydrothermal fluids. The H-O isotope compositions from the stage II (δ18Ow = 4.1–4.8‰ and δD = -110 to −87‰) to the stage III (δ18Ow = 3.5 to 3.7‰ and δD = -101 to −98‰), indicate that the ore-forming fluids were mainly magmatic fluids. The δ34SV-CDT (1.7–2.1‰), Pb isotopes (206Pb/204Pb = 15.09–15.90, 207Pb/204Pb = 15.00–15.15, 208Pb/204Pb = 35.76–37.97), and Os isotopes (initial 187Os/188Os = 2.3 ± 1.0) of the Au-bearing pyrite samples at the stages II and III, similar to those of the crust-derived magma, suggest that the gold and other metals were extracted from the partial melting of the lower crust. Accordingly, the Taijiying gold deposit is probably a magmatic hydrothermal deposit. The areas recording the Triassic batholith with a developed fault system would be prospective targets for gold mineralization in the Chifeng-Chaoyang district on the northern margin of the NCC.

Geology, geochemistry and genesis of Keyue: A newly discovered Pb-Zn-Sb-Ag polymetallic deposit associated with magmatic center in Southern Tibet, China

The Keyue Pb-Zn-Sb-Ag polymetallic deposit is located within the North Himalayan Metallogenic Belt (NHMB). This study aims to clarify whether the Keyue deposit has close association in time and space with magmatism, and discuss the significance for further exploration. Orebodies are hosted by the Lower Jurassic Ridang Formation black carbonaceous slate and controlled by the NE-trending faults. Keyue is characterized by multiple stages of hydrothermal veins, including Mn-Fe Carbonate-sulfide (I), quartz-sulfide-sulfosalt mineral (II) and quartz-calcite-stibnite veins (III).Hydrothermal minerals contain six types of fluid inclusions, including H2O-rich bi-phase aqueous (type I), pure CO2 (type II), CO2-rich H2O-CO2-NaCl tri-phase (type III), H2O-rich H2O-CO2-NaCl tri-phase (type IV), halite-bearing tri-phase (type V) and halite-bearing H2O-CO2-NaCl multiphase inclusions (type VI). All six types of inclusions were observed in stage II quartz, whereas only types I and III inclusions in stage I siderite and sphalerite and type I inclusions in stage III quartz and calcite. Type I inclusions in stage I display total homogenization temperatures (Th, total) ranging from 250.1 to 289.3 °C, with salinities of 9.6–16.3 wt% NaCleq. Types I, III, IV and V inclusions in stage II yield Th, total of 175.5–282.7 °C, 188.8–286.3 °C, 214.3–287.5 °C and 198.3–266.0 °C, with corresponding salinities of 4.0–21.5 wt% NaCleq, 0.6–2.9 wt% NaCleq, 0.0–11.0 wt% NaCleq and 30.1–33.2 wt% NaCleq, respectively. Type I inclusions in stage III have Th,total values of 172.3–240.7 °C and salinities of 3.1–12.6 wt% NaCleq. Fluid phase separation occurred in stages I and II, resulting in CO2 and H2S release, pH increase and rapid Pb-Zn-Ag precipitation, whereas mixing of magmatic fluids and meteoric water in stage III caused the cooling, dilution and stibnite precipitation.Fluid inclusion analysis and C-H-O isotopic compositions indicate that the initial hydrothermal fluids were magmatic water, with increasing input of meteoric water with time. The δ34SCDT values of sulfides from three stages are similar and range from 4.8 to 10.3 ‰ (average 7.7 ‰), showing characteristics of mixture of magmatic and sedimentary sulfur. The Pb isotopic compositions of sulfides are closely consistent with those of Cenozoic leucogranite and Precambrian metamorphic crystalline basement in the NHMB, suggesting that the ore-forming metals were sourced from the hidden causative Himalayan leucogranite formed by the decompression melting of metamorphic crystalline domains.Combining evidence from geochronology, fluid inclusions, isotopes suggest that the Keyue Pb-Zn-Sb-Ag and Cuonadong W-Sn-Be mineralization at different locations around the Cuonadong Dome constitute an integrated magmatic-hydrothermal system, with the distal end-member Pb-Zn-Sb-Ag veins centered on the Cuonadong leucogranites-related W-Sn-Be mineralization. Pegmatite-skarn-type W-Sn-Be polymetallic mineralization may occur at deeper sites beneath the Keyue area, and the distal Pb-Zn-Sb-Ag veins controlled by faults within strata also need more attention around these leucogranite domes in the NHMB.

Evidence of gas plume model in porphyry copper deposits based on anatomy, fluid inclusions and H-O isotopes: Insight from Kahang deposit, Iran

The Kahang deposit (100 Mt at 0.6% Cu) is one of the important porphyry copper deposits in the central part of Urumieh-Dokhtar Magmatic Arc (UDMA), Iran. The mineralization occurs as chalcopyrite and molybdenite in quartz and anhydrite -bearing veinlets or breccias and is closely associated with sericitic and phyllic alterations. Through comprehensive studies of the deposit's anatomy, some previously overlooked evidence raised new questions about the ore-forming process in the Kahang deposit. The coexistence of sulfate and sulfide minerals as veinlets and breccias, pore space breccias, could not be justified solely based on a previously introduced concept (i.e., mixing high temperature-high salinity magmatic water with low temperature-low salinity meteoric water). Fluid inclusions were examined in quartz veinlets of the A1, A2, and B types, anhydrite veinlets, and sphalerite of the L type veinlets. There are three types of fluid inclusions: liquid-rich (L-type), vapor-rich (V-type), and hypersaline (H-type). According to microthermometry of fluid inclusions, the fluids associated with anhydrite veinlets have relatively high temperatures (390–495 °C, mean = 455 °C) and low salinities (12.8–20.9 wt% NaCl equiv.) On the contrary, temperatures below 400 °C justified the coexistence of sulfate and sulfide minerals. The low solubility of anhydrite in high-temperature waters, on the other hand, demonstrates the gas–solid reaction of SO2 (g) and plagioclase at such temperatures, as evidenced by fluid inclusions. Additionally, the fluid inclusions in quartz veinlets generated temperatures (290 to >600 °C) higher than those in the majority of other porphyry copper deposits. H-O isotopes indicated that magmatic fluids dominated, and meteoric waters played an insignificant role. These findings and observations supported the formation of the Kahang porphyry copper deposit as a result of a gas plume and the reactions of gas species with plagioclase to form anhydrite and sulfide minerals, as well as the formation of sericitic alteration in the host rock as a novel scenario.

Fluid evolution of the Zhunuo porphyry Cu-Mo deposit in Gangdese Tract, Tibet, China: A fluid-inclusion investigation

The Zhunuo porphyry Cu-Mo deposit in the western part of south Gangdese porphyry copper belt (GPCB), Tibet, is a large porphyry system. The Cu-Mo mineralization of this deposit is mainly associated with a weakly aluminous I-type Miocene granite porphyry pluton that formed in a post-collisional extensional tectonic setting. Field observations and petrographic studies demonstrate that emplacement of the pluton took place in several intrusive pulses, each with associated hydrothermal activities. Early hydrothermal alteration produced a potassic assemblage, overprinted by later phyllic alteration. At least three main stages of mineralization have been identified: (1) early A stage quartz + K-feldspar + minor sulfide veins; (2) middle stage B1-subtype veins composed of quartz + molybdenite + sporadic sulfide and B2-subtype quartz + pyrite + chalcopyrite veins; and (3) late stage pyrite + quartz D veins.Three types of fluid inclusions (FIs) in quartz were identified in the early and middle stages (i.e., CO2 bearing-aqueous vapor (V)-type and liquid (L)-type, and solid (S)-type); only aqueous L-type FIs were observed in the late stage minerals. S-type FIs contain variable solid particles, including halite, calcite, anhydrite (or gypsum), and chalcopyrite, hematite, and an unidentified transparent crystal. Only halite was dissolved during heating. Halite-bearing S-type FIs were mainly homogenized by halite dissolution at 300–470°C (S2-type), corresponding to salinities of 38.9–56.3 wt% NaCl equiv.; and minor halite bearing S-type FIs were homogenized to liquid at 360–520°C via vapor disappearance (S1-type), with salinities of 31.9–56.7 wt% NaCl equiv. Other FIs in minerals of A, B1, B2 and D veins were homogenized at temperatures of 350–550°C, 303–500°C, 305–460°C, and 250–347°C with salinities of 3.4–20.9, 2.6–22.4, 4.8–21.8, and 4.7–18.2 wt% NaCl equiv., respectively. These data suggest that the ore fluids forming the Zhunuo deposit changed from high-temperature, low-moderate salinity, CO2-bearing magmatic fluids to low-temperature, low-salinity and CO2-poor meteoric fluids. Phase separation and cooling caused the precipitation of the abundant chalcopyrite in the middle stage B2-subtype veins. The molybdenite mineralization was caused mainly by the decrease of pressure due to the release of CO2, and by phase separation of fluid in the middle stage as recorded in the B2-subtype veins. This hydrothermal ore-forming system is different from other magmatic-hydrothermal systems in GPCB, but is similar to the typical Cu-Mo porphyry systems, which were initially CO2-bearing as indicated by the presence of abundant CO2-bearing, low-moderate salinity FIs and calcite-bearing S-type FIs.

Genesis of the Baimadong carbonate-hosted uranium deposit, Guizhou, SW China: Constrains from geology, fluid inclusions, and C-O isotopes

The Baimadong uranium deposit is situated in the Yangtze Craton, SW China, and is one of the most representative carbonate-hosted uranium deposits in China. Uranium mineralization has spatial and genetical relationships with black and red alterations that has been documented by previous studies. However, the signature, source, and evaluation of ore-forming fluids producing the alterations and mineralization remain poorly understood. Fluid inclusions hosted in different generations of hydrothermal calcite have been analyzed in this study, including Cal 1 (pre-ore stage), Cal 2 (early ore stage), and Cal 3 (main ore stage). Three types of fluid inclusions were identified: liquid-dominated biphase, vapor-dominated biphase, and vapor-only monophase. Based on fluid inclusion microthermometry using the FIA method, the fluids associated with Cal 2 are characterized by relatively higher temperature (∼243 ℃) and salinity (5.3 wt% NaCl equiv.) compared with fluids associated with Cal 1 (Th = ∼221 ℃; Salinity = 1.9 wt% NaCl equiv.) and Cal 3 (Th = ∼144 ℃; Salinity = 2.5 wt% NaCl equiv.). The results of stable isotopes (C, O, and S) indicate that the carbon in pre-ore stage fluids was dominantly originated from host marine carbonate rocks (δ13Cfluid-PDB = −3.0 to 0.5 ‰; δ18Ofluid-SMOW = 4.8 to 11.3 ‰), the carbon and sulfur in early ore-forming fluids were mainly derived from the Niutitang Formation with minor from deep crust (δ13Cfluid-PDB = −11.2 to −8.4 ‰; δ18Ofluid-SMOW = 7.9 to 11.4 ‰; δ34Sv-CDT = −11.3 to + 2.1 ‰), whereas the main ore-forming fluids were sourced from meteoric fluids (δ13Cfluid-PDB = −8.6 to −4.9 ‰; δ18Ofluid-SMOW = 0.4 to 8.6 ‰). These results reveal that redox reaction as well as fluid-rock reaction are key factors controlling the large-scale uranium mineralization at Baimadong. Combined with these observations, geological setting, and previous geochemical features, we suggest that tectonic system together with overprinting zone of black and red alterations are indicators for exploration of carbonate-hosted uranium deposit in South China and elsewhere worldwide.

Genesis of the Heiyanshan Tungsten Skarn Deposit in the East Tianshan, NW China: Insights From Geology, Fluid Inclusion, Isotopic Geochemistry and Geochronology

The eastern Tianshan Terrane is a highly prospective zone that contains several porphyry Cu–Mo, VMS Cu–Zn, magmatic Cu–Ni, epithermal and orogenic Au deposits. However, few attention has been paid to tungsten deposits. Of these, the source and evolution of the mineralising fluids related to the skarn W deposits are poorly understood. The Heiyanshan W deposit is hosted by metamorphosed clastic and carbonate beds in the Mesoproterozoic Jianshanzi Formation deposited on a continental margin tectonic setting. The Jianshanzi Formation is intruded by biotite monzogranite that yield weighted206Pb/238U age of 326.9 ± 1.6 Ma, which suggest that the Heiyanshan W deposit was formed in the Carboniferous. The mineralisation is hosted by a prograde hydrothermal altered zone represented by a garnet (–pyroxene) skarn, and retrograde skarn characterised by fine-grained scheelite. The paragenesis of the Heiyanshan mineralisation can be subdivided into prograde skarn stage, retrograde skarn stage, quartz-sulphide stage and quartz-calcite vein stage. The types of fluid inclusions recognised in the various minerals in the deposits are liquid-rich aqueous, vapour-rich aqueous, and daughter mineral-bearing. The homogenisation temperatures of fluid inclusions from the Heiyanshan deposit decrease from 290 ± 28°C in garnet, through 232 ± 31°C in scheelite, to 232 ± 36°C in quartz and 158 ± 15°C in non-mineralised calcite, which is typical of W-bearing skarn deposits worldwide. The δ18Owatervalues from the Heiyanshan deposit range from +4.7 to +6.6‰ in garnet, +1.3 to +1.9‰ in quartz and −6.1 to −4.4‰ in calcite. We have measured δD in fluid inclusions from different minerals, although these bulk analyses are just a mixture of the different FIA’s present in the sample. The δD values of fluid inclusions in garnet, quartz, and calcite are from −121 to −71‰, −84 to −75‰ and −101 to −82‰, respectively, also indicative of deep-sourced magmatic fluids mixed with meteoric water. The decrease in the homogenisation temperatures for the fluid inclusions at the Heiyanshan deposit is accompanied by a drop in salinity indicating that tungsten-bearing minerals precipitated during fluid mixing between magmatic fluids and meteoric water. We conclude that eastern Tianshan Terrane contains two pulse of tungsten metallogenic events of Late Carboniferous and Early Triassic.

Evolution of pegmatite ore-forming fluid: The Lijiagou spodumene pegmatites in the Songpan-Garze Fold Belt, southwestern Sichuan province, China

The late to post-tectonic Lijiagou spodumene pegmatites are located in the Ke’eryin orefield, which lies in the Triassic central Songpan-Garze Fold Belt (SGFB) in southwestern Sichuan Province, China. Fluid inclusion petrography, microthermometry and Raman spectroscopic analyses were carried out on quartz and spodumene in granites and four types of pegmatite in the Ke’eryin orefield. A Hydrothermal Diamond Anvil Cell (HDAC) was used to observe the microthermometric behavior of crystal-rich inclusions. Five types of fluid inclusions were identified. Crystal-rich inclusions (Type 1) in spodumene pegmatites were trapped at high temperature (658 to 741 °C) and high pressure (>4.7 kbar). Other inclusion types were found in granite and all types of pegmatite. Triphase CO2-H2O (CO2 + V + L, Type 2) inclusions show medium homogenization temperatures (324 to 339 °C), medium trapping pressures (2.09 to 2.54 kbar) and low to moderate salinities (3.1 to 11.3 wt% NaCl equiv). Biphase aqueous inclusions (L + V, Type 3) show similar homogenization temperatures (319 to 347 °C), and low to moderate salinities (5.5 to 18.0 wt% NaCl equiv). Monophase liquid CO2 (Type 4) inclusions have very low homogenization temperatures (15.4 to 19.1 °C). Monophase liquid H2O (Type 5) inclusions have moderate ice melting temperatures (–18.6 to –9.8 °C), and moderate salinities (18.4 to 18.5 wt% NaCl equiv). The various types of fluid inclusion reveal the P–T conditions of pegmatite formation, which records the transition from a magmatic to a hydrothermal environment and indicate that the ore-forming fluid resulted from the unmixing of magmatic melt. Fluid immiscibility is the key mechanism responsible for formation of the Lijiagou spodumene pegmatites and lithium mineral precipitation occurred from a high to medium temperature CO2-rich fluid. The absence of temperature and salinity gradients between granite and progressively more distal and evolved pegmatite compositions is inconsistent with formation of pegmatite magmas by fractional crystallization of granitic magmas, but consistent with separate anatectic origins of each type of pegmatite magma.

Geological, fluid inclusion, and O–C–S–Pb–He–Ar isotopic constraints on the genesis of the Honghuagou lode gold deposit, northern North China Craton

The Honghuagou Au deposit is located in the Chifeng-Chaoyang region within the northern margin of the North China Craton. The auriferous quartz veins are mainly hosted in the mafic gneiss and migmatite of the Neoarchean Xiaotazigou Formation along NNW- and NE-striking faults, with pyrite as the predominant ore mineral. The gold mineralization process can be divided into two stages, involving stage I quartz-pyrite and stage II quartz-calcite-polymetallic sulfide. Three types of fluid inclusions (FIs) have been identified in the Honghuagou deposit, namely, carbonic inclusions, aqueous‑carbonic inclusions, and aqueous inclusions. Quartz of stage I contains all types of FIs, whereas only aqueous inclusions are evident in stage II veins. The FIs of stages I and II yield homogenization temperatures of 275–340 °C and 240–290 °C with salinities of 3.4–10.7 wt% and 1.4–9.7 wt% NaCl eqv., respectively. The ore-forming fluids are characterized by medium temperature and low salinity, belonging to the H2O–NaCl–CO2 system. The δ18OH2O values of the ore fluids are between 2.1‰ and 5.9‰, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ13CPDB = −4.4‰ to −4‰) are also similar to mantle carbon. He-Ar isotope data (3He/4He = 0.38–0.44 Ra; 40Ar/36Ar = 330–477) of fluid inclusions in pyrite indicate a mixed crustal and mantle source for the ore-forming fluids. Whereas, S-Pb isotope compositions of sulfides reveal that ore metals are principally derived from crustal rocks. On the basis of available geological and geochemical evidence, we suggest that the Honghuagou deposit is an orogenic gold deposit.

First characterization of the cooling of the paleo-geothermal system of Terre-de-Haut (Les Saintes archipelago, Guadeloupe): Application of fluid inclusion and chlorite thermometry

Due to its geodynamic location in the Lesser Antilles arc, Basse-Terre of Guadeloupe displays an active volcanism which is favourable to the development of high-enthalpy geothermal energy. An exhumed analogue of the Bouillante geothermal reservoir has been recently characterized in Terre-de-Haut island (Les Saintes archipelago), giving an opportunity to study the cooling of a natural geothermal system and the related alterations.By coupling chlorite geothermometry and primary fluid inclusions in associated zoned quartz crystals located in N70 trending fractures, new insights on the Terre-de-Haut paleo-geothermal evolution can be inferred by distinguishing three new different episodes during functioning and cooling of this system: (i) a temperature of at least 240–270 °C in fluid inclusions trapped in the quartz core, (ii) chlorite formation at about 120 °C, and (iii) temperatures of ~50 °C - or less - in fluid inclusions of the quartz outer growth zones. Fluid inclusions also reveal that the hydrothermal fluid is of low salinity (2 wt% NaCl), probably of meteoric and sea water origin. Additionally, a second type of fluid inclusions observed in a banded quartz vein indicates at least an episode of a CO2-(H2O) fluid, with traces of H2S. Hence, some similarities can be highlighted between Terre-de-Haut and the Bouillante active geothermal systems in term of the highest temperatures of circulation events and gas composition, despite a difference in fluid origin. This study shows that some alteration episodes also occur at low temperature during the cooling of the geothermal system. Moreover, the N70 trending fractures, that have been identified as drains for the hot temperature fluids, have to be considered for future geothermal exploration.

The high-grade Fe skarn deposit of Jinling, North China Craton: Insights into hydrothermal iron mineralization

Skarn-type Fe deposits constitute a major source of iron in the world, and 57% of the high-grade iron ores in China are hosted by skarn deposits. Most researchers agree that skarn-type Fe deposits are genetically linked with the associated magmas and precipitate from hydrothermal fluids, however, whether these ore-forming fluids are mainly derived from magmas or some other external sources is controversial. Besides, the detailed process of iron concentration in the high-grade ores in skarn Fe deposits has not been well constrained. To better understand these issues, we investigated the petrological, mineral chemical, geochronological, fluid inclusion and oxygen isotope characteristics of the Jinling Fe deposit, which is a typical high-grade skarn-type Fe deposit in the North China Craton. Zircon grains in these skarns were demonstrated to result from completely modification of magmatic zircons by the later hydrothermal fluids and they yield a weighted mean 206Pb/238U age of 126.7 ± 2.0 Ma (2σ) constraining the timing of the skarn iron formation, which is consistent with that of the ore-hosting Jinling complex. The similarity in chondrite-normalized REE patterns of the zircons in skarns and magmatic zircons suggests that the ore-forming hydrothermal fluids might mainly be derived from magmas. Additionally, the oxygen isotopes of the hydrothermal fluids in various stages as estimated based on δ18O values of representative hydrothermal minerals show relatively constant values during the evolution of hydrothermal system, suggesting that there was no significant involvement of external fluids. Three types of fluid inclusions, namely, high-salinity Type 1 with daughter minerals (homogenizing into liquid phase, with salinity of 42–71 wt% NaCl equivalent), vapor-rich Type 2 (homogenizing into vapor, with salinity ≤23 wt% NaCl equivalent), and relatively low-salinity Type 3 (homogenizing into liquid, with salinity ≤23 wt% NaCl equivalent) were identified in the various skarn minerals (garnet, clinopyroxene, epidote, and anhydrite). Among these, only Type 3 fluid inclusions occur in the clinopyroxene within the dominant massive ores, implying that the relatively low-salinity fluids were the predominant ore-forming hydrothermal fluids from which the magnetite ores precipitated. The high-salinity Type 1 fluids which might have resulted from phase separation (or boiling) of the primary magmatic hydrothermal fluids due to pressure drop, were believed to be responsible for the Fe-rich rims of zoned clinopyroxenes (with Fe-poor cores) in the thin magnetite-clinopyroxene interbedding layers between skarns and the massive magnetite orebodies. Thus, this zoned texture also implies an Fe re-enrichment event after formation of magnetite ores. The process of multiple Fe enrichment may significantly contribute to the formation of high-grade skarn-type Fe deposits.

Geological and geochemical characterization of the Nanlia and Makorongo gold prospects, Mozambique Belt, northeastern Mozambique

Northern Mozambique hosts numerous occurrences of gold mineralization in metamorphic terranes, which are little known because of the insufficient studies. In this work, we describe the main geological and geochemical characteristics of the Nanlia and Makorongo gold prospects located in the Namuno district, northeastern Mozambique. We report the mode of occurrence of gold, petrography and mineralogy of the host rocks and ores, fluid inclusion characteristics and stable isotope data, to understand the genesis of gold mineralization in the study area. The gold mineralization in the Nanlia and Makorongo prospects is hosted by the Neoproterozoic Xixano Metamorphic Complex in the Mozambique Belt, which is composed of mafic granulite, amphibolite, paragneiss and marble. The host rock amphibolite consists mainly of amphibole, plagioclase, biotite and minor quartz, titanite and sulfides. The gold mineralization is associated with E-W to ENE-WSW trending quartz veins, oriented parallel to low angle to the foliation of the host rock amphibolite. The ore mineralogy consists of pyrite, pyrrhotite, chalcopyrite, magnetite, galena and sphalerite, with minor tellurides, xilingolite, electrum and native gold. Mineralized quartz veins in the Nanlia and Makorongo prospects host two types of fluid inclusions which locally coexist in the same assemblage: type 1, one-phase CO2 inclusions with final melting temperature between −58 and −52 °C; and type 2, two-phase H2O + NaCl (±CO2 ± N2 ± CH4) inclusions with homogenization temperature ranging from 246 to 370 °C and 239 to 382 °C in the Nanlia and Makorongo prospects, respectively, and salinity of 12–21 wt% NaCl eq. Pressure and temperature (P-T) conditions of ore-formation were estimated from fluid inclusions and sphalerite geobarometry at 420–620 °C and 160–280 MPa, and 330–440 °C and 150–200 MPa in the Nanlia and Makorongo prospects, respectively. The Nanlia and Makorongo gold prospects are classified as orogenic-type gold deposits. We suggest that gold mineralization was caused by an aqueous-carbonic fluid with low-moderate salinity originated by devolatilization during prograde metamorphism of underlying rocks. The gold mineralization post-dates the peak of metamorphism of the host rocks, thus formed during the retrograde metamorphism of the host rocks. The precipitation of gold in the Nanlia and Makorongo prospects was caused by fluid phase separation induced by pressure drop as the mineralizing fluid migrated to shallower depths.

Fluid inclusions, isotopes and mineralogy of the Kuruer epithermal Cu-Au deposit, Chinese Western Tianshan: Implications for ore genesis and exploration

The Kuruer Cu-Au deposit is located in the Wusun Range of Yili Block, Chinese Western Tianshan, where numerous epithermal Au, skarn Fe-Cu and porphyry Mo-Cu deposits have been recognized. Petrography, fluid inclusions, S-Pb-H-O isotopes, field emission-scanning electron microscopy (FE-SEM) plus energy dispersive spectrometer (EDS) and electron microprobe analysis (EMPA) have been carried out to constrain the genesis of the Kuruer deposit and its implication for further exploration. The minerlization is hosted by volcanic rocks and occur as veins and veinlets structurally controlled by NW-trending faults. Three ore-forming stages were recognized, including quartz-sulfides-bismuth-gold stage (I), quartz-chalcopyrite stage (II) and calcite-chlorite-chalcopyrite stage (III).Six types of fluid inclusions were identified in stage I quartz, including monophase vapor inclusions (type 1), liquid-rich biphase inclusions (type 2), vapor-rich biphase inclusions (type 3), H2O-rich CO2-H2O triphase inclusions (type 4), CO2-rich CO2-H2O triphase inclusions (type 5) and solid halite-bearing triphase inclusions (type 6), whereas only type 2 inclusions were recognized in stage II quartz and stage III calcite. Types 2, 3, 4 and 6 inclusions in stage I have homogenization temperature (Th) ranges of 184–359 °C, 209–252 °C, 250–319 °C and 229–263 °C, with salinity ranges of 4.1–8.5 wt% NaCleq, 5.9–6.9 wt% NaCleq, 1.0–6.0 wt% NaCleq and 32.7–33.9 wt% NaCleq, respectively. Type 2 inclusions in stages II and III have Th varying from 144 to 212 °C and 114 to 163 °C, with salinities of 0.2–6.7 wt% NaCleq and 0.1–3.1 wt% NaCleq, respectively.The in-situ δ34S values of sulfides in stage I range from −4.66 to 0.34‰. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of stage I chalcopyrite vary from 18.295 to 18.954, 15.568 to 15.673 and 38.109 to 38.817, respectively, which are consistent with those of Early Carboniferous Dahalajunshan Formation volcanic rocks and granitoids from the Wusun Range. The values of δ18OH2O-VSMOW calculated from δ18Oquartz and δDH2O-VSMOW of stage I quartz range from 0.0 to 2.4‰ and −118.6 to −109.3‰, respectively. These isotopic compositions indicate that both metals and sulfur were sourced from the hosting volcanic rocks and hidden causative pluton, while the initial ore-forming fluids were magmatic in origin, with increasing involvement of meteoric water with time.Evidence from mineralogy, mineral geochemistry and fluid inclusions indicates that the initial fluid phase separation triggered the precipitation of “invisible” gold within pyrite and chalcopyrite during stage I. Subsequently, the decrease of fS2 due to the escape of H2S(g) and sulfide precipitation and cooling caused the formation of liquid bismuth from solutions. The bismuth melts have scavenged Au in situ from the residual solutions, resulting in the formation of Bi-Au inclusions within the fractures and intergranular spaces of earlier pyrite. For stages II and III, dilution and cooling due to input of meteoric water facilitated the chalcopyrite precipitation. The Kuruer Cu-Au deposit is classified as a subepithermal mineralization associated with porphyries. Porphyry Cu-Au mineralization could have developed beneath the Kuruer and its vicinity.

Metallogeny of the Dagangou Au-Ag-Cu-Sb Deposit in the Eastern Kunlun Orogen, NW China: Constraints from Ore-Forming Fluid Geochemistry and S-H-O Isotopes

A study of ore-forming fluid geochemistry and S-H-O isotopes has been conducted to reveal the metallogeny of the Dagangou Au-Ag-Cu-Sb deposit, NW China. Three mineralization stages are identified within Dagangou, including ankerite-quartz-pyrite (Ank-Qz-Py), quartz-Au-sulfide (Qz-Au-Sul), and quartz-calcite (Qz-Cal) stages. Four types of primary fluid inclusions (FIs) and various fluid inclusion assemblages (FIAs) are identified by petrographic observations, including pure CO2, CO2-bearing, vapour-liquid and halite-bearing FIs, most of which are distributed randomly or along growth zones. Raman spectroscopy suggests that the fluid vapour is mainly H2O and CO2 with minor N2, CH4, and C2H6. The homogenization temperatures of primary FIs from the Ank-Qz-Py to Qz-Au-Sul to Qz-Cal stages are 208.7–313.4°C, 184.3–251.7°C, and 167.3–224.2°C, with salinities of 3.4–13.4 wt.%, 5.4–39.5 wt.% and 4.9–11.4 wt.% NaClequiv.. Sulfide S isotopes show a predominant source of sedimentary sulfur with minor magmatic sulfur, as evidenced by δ34S values of -1.4–5.1‰. The FI H-O isotopes reveal that the primary fluid was derived from magmatic waters mixed with minor sedimentary water (δD=−90.0to -86.8‰,δ18OH2O=6.7–7.4‰) and then was significantly diluted by meteoric water in the Qz-Cal stage (δD=−97.2to -95.7‰,δ18OH2O=3.9–4.3‰). Thus, the ore-forming fluid geochemistry and S-H-O isotopes indicate that fluid boiling occurred in the Qz-Au-Sul stage due to a pressure reduction from 85 MPa to 70 MPa, which led to the phase separation of fluid, loss of CO2, increase in residual fluid salinity, and formation of immiscible FIAs and halite-bearing FIs in the Qz-Au-Sul stage. This indicates a system moving away from a primary equilibrium, resulting in the deposition of metallic elements. The Dagangou Au-Ag-Cu-Sb deposit, therefore, is an orogenic gold-polymetallic deposit with a mesozonal depth of 5.9–7.5 km.

Ore-Forming Fluid Evolution in the Giant Gejiu Sn–Cu Polymetallic Ore Field, SW China: Evidence From Fluid Inclusions

The giant Gejiu Sn–Cu polymetallic ore deposit is one of the largest Sn producers in the world, and is related in time and space to highly evolved S type granitic intrusion. The mineralization processes can be divided into four stages: (I) skarnization; (II) greisenization; (III) cassiterite–sulfid; and (IV) cassiterite–tourmaline–quartz. Five types of fluid inclusions were recognized using optical petrography, microthermometry, and Raman spectroscopy. The results of microthermometry revealed the evolution of the ore-forming fluid, from a high temperature with low–to–high salinity to a low temperature with low–to–intermediate salinity. Stage I, skarn Sn–Cu ores were formed by bimetasomatism between the granitic intrusion and the surrounding rock under near–critical conditions with the help of ore-forming fluid. Stage II, the fluid was separated into the coexisting liquid and vapor phases in equilibrium condition, and a large amount of cassiterite–scheelite–beryl–lithium muscovite minerals were formed during greisenization. Stage III, mixing, boiling and immiscibility of different types of fluid solutions took place with a decline in temperature and pressure as well as a change in the Eh–pH, which caused amounts of cassiterites and sulfides to precipitate. Stage IV, stockwork ores characterized by cassiterite–tourmaline–quartz minerals were formed associated with the low temperature and low salinity hydrothermal liqiud activity. The laser Raman spectra identified CH4 in all ore-forming stages, indicating that the ore deposits might have been formed in a relatively reduced environment. CO2 appeared in all stages in addition to Stage I, and might have been formed due to both immiscibility of fluid solutions with dropping pressure as well as temperature and mixing of different types of fluid solutions. In conclusion, the bimetasomatism, mixing, and immiscibility of fluid solutions should have been responsible for the formation of giant Sn–Cu polymetallic deposits.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

ABSTRACTThe Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions.The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

Genesis of the Shiyaogou porphyry Mo deposit at East Qinling, China: Evidence from geochronological, fluid inclusion, geochemical whole-rock and isotope studies

The Shiyaogou deposit in Luanchuan County, China, is a large concealed porphyry Mo deposit within the East Qinling metallogenic belt (EQMB). Major and trace element analyses reveal that the host granite is defined by high silica (SiO2 = 71.56 to 75.25%) and alkali (Na2O + K2O = 6.91 to 7.88%) contents and has typical I-type characteristics. Zircons derived from the pluton yield U–Pb ages of 133.2 ± 1.1 Ma, indicating an early Cretaceous magmatic event in the EQMB. The εHf (t) values and TDM2 ages range from − 15.1 to − 11.2 and from 2.1 to 1.9 Ga, respectively, suggesting that the granite mainly originated from the lower crust melting with the involvement of mantle components. The mineralization process can be divided into three stages: (1) quartz + K-feldspar + pyrite + molybdenite; (2) quartz + pyrite + molybdenite; and (3) quartz + calcite veins. Three different types of fluid inclusions (FIs) are present in quartz veins: NaCl–H2O (W-type), CO2–H2O (C-type), and daughter mineral-bearing (S-type). Hematite is recognized as a daughter mineral in S-type inclusions of stage 1, whereas the daughter sulfide and reducing CH4 gases can be observed in the stage 2 quartz, suggesting that the ore-forming fluids were initially oxidizing and then evolved to more reducing conditions. The FIs in stages 1 mainly display Th above 428 °C with salinities up to 57.62 wt% NaCl eqv; in stage 2, the FIs display Th of 132–423 °C and salinities of 3.23–50.03 wt% NaCl eqv; in stage 3, the FIs homogenized in the range of 117–247 °C with low salinities of 2.74–8.95 wt% NaCl eqv. The coexisting W-, S- and/or C-type inclusions homogenized at similar temperatures, but contain different salinities during stages 1 and 2, suggesting that the fluids boiled during both stages. Our study reveals that the ore-forming fluids are magmatic in origin. These high-temperature magmatic fluids gradually evolved from high salinities and high CO2 contents to a mixture of magmatic and meteoric water with lower temperature, lower salinity, and lower CO2 content. The precipitation of Mo mainly resulted from the decreasing temperature and salinity. Additionally, the changes in pH and CO2 content due to boiling and the water–rock reaction could have contributed toward the precipitation of Mo.

Fluid diversity in the gold-endowed Archean orogenic systems of the Abitibi greenstone belt (Canada) I: Constraining the PTX of prolonged hydrothermal systems

Although many aspects of orogenic gold systems are well understood, considerable debate surrounds the chemistry of the ore-forming fluids and their relevance to mineralization. This may in part relate to the lack of both regional-scale studies and a uniform approach in studying fluid inclusions in these complex and protracted hydrothermal ore systems. In order to address this problem, over 30 orogenic-type deposits covering a variety of geological settings were systematically studied using the fluid inclusion assemblage (FIA) protocol integrated with microthermometry in the gold-endowed Abitibi greenstone belt, Canada. A diversity of fluid inclusion types are documented (i.e., carbonic CO2-CH4, aqueous-carbonic, aqueous), in addition to complex textural features, in particular decrepitation clusters which are rarely reported in the literature or the deposits studied; together these data provide new insight to these ore systems. Furthermore, we note that the fluid composition is significantly affected by the proximity of carbon-rich sedimentary units which are capable of producing a carbonic-only fluid. In later stages of hydrothermal evolution, variable XCO2 in aqueous-carbonic inclusions reflects variable degrees of fluid-rock interaction. Pressure cycling is an integral part of these systems, but petrographic evidence of in situ fluid unmixing is lacking, and cannot be accounted for gold mineralization. Vein-style gold is not related to fluid chemistry and, where best constrained with petrography (i.e., visible Au near fluid inclusions), P-T estimates based on fluid inclusion microthermometry link the mineralization to the later, low-pressure (<1.5 kbar) stages of deposit evolution. Accordingly, gold is coeval with quartz vein formation in epizonal deposits whereas it postdates quartz in the ore dominant mesozonal ore systems.

Fluid evolution and ore genesis of the Chaobuleng skarn Fe[sbnd]Zn polymetallic deposit, Northeast China: Evidence from fluid inclusions, C[sbnd]O[sbnd]S[sbnd]Pb isotopes, and geochronology

The Chaobuleng skarn deposit, located in the Erlian–East Ujimqin region, Northeast China, is a medium-sized FeZn polymetallic deposit. Iron-polymetallic mineralization occurs mainly as stratiform, lenticular, and vein types hosted in the contact zone between the Chaobuleng syenogranite and the Devonian Taerbagete Formation. The Chaobuleng deposit is a calcic skarn deposit dominated by a grossular-rhodonite-allanite-epidote assemblage. The ore minerals mainly consist of magnetite, pyrite, sphalerite, chalcopyrite, and bismuthinite, with lesser amounts of molybdenite, arsenopyrite, and pyrrhotine. Four mineralization stages have been identified: (I) a prograde skarn stage; (II) a retrograde skarn stage; (III) a quartz-minor calcite-polymetallic sulfide stage; and (IV) a quartz-calcite-minor pyrite stage. Three types of fluid inclusions (FIs) in garnet, quartz and calcite were classified: vapor-rich two-phase FIs (V-type), liquid-rich two-phase FIs (L-type), and daughter mineral-bearing three-phase FIs (S-type). The homogenization temperatures of FIs from stages I, II, III, and IV are 446–547, 411–519, 279–415, and 147–217 °C, respectively, with corresponding salinities of 0.87–59.47, 0.52–51.52, 0.70–13.25, and 3.05–7.85 wt% NaCl equiv., respectively. The results suggest that mineralization in the Chaobuleng deposit occurred at a depth of 1.0–2.8 km, with fluid boiling and mixing with meteoric water likely being responsible for ore precipitation. The CO isotope data suggest the early ore-forming fluids were mainly related to felsic rocks and were accompanied by intense water/rock reactions during the fluid migration. The SPb isotopic compositions indicate that ore materials were derived from the mixing between magma and wall rocks. Zircon UPb dating yields a weighted mean 206Pb/238U age of 135.9 ± 0.8 Ma (MSWD = 1.03), which represents the crystallization time of the syenogranite. Together, these data suggest that the Chaobuleng deposit is a skarn ore system that is spatially, temporally, and genetically related to syenogranite and formed in an extensional environment resulted from the roll back of the subducted Paleo-Pacific Plate.

Study on the PTX Parameters and Fractal Characteristics of Ore-Forming Fluids in the East Ore Section of the Pulang Copper Deposit, Southwest China

In this paper, the east ore section of the Pulang porphyry copper deposit is selected as the research object. The micro-thermometer and laser Raman spectroscopic technique are utilized to study the parameters of ore-forming fluids such as pressure, temperature, and compositions. In the meantime, the fractal models, including the perimeter-area (P-A) model and number-size (N-S) model, are introduced to quantify the shape of fluid inclusions, and distinguish the stages of ore-forming fluids, respectively. The results show that the types of fluid inclusions are diversified, namely two-phase liquid-rich type, two-phase vapor-rich type, three-phase CO2-rich type, three-phase halite-bearing type and pure liquid type. The fluids of main mineralization stage are characterized by medium-high temperature (170.2–421.4 °C), medium-high salinity (9.3 wt.%–33.3 wt.%), and low density (0.73–1.06 g/cm3). With the migration and evolution, the temperature, salinity, and pressure of ore-forming fluids gradually decrease, while the density of fluids increases. The liquid-phase compositions mainly include H2O, and the vapor-phase compositions consist of H2O, CH4, N2, and CO2, indicating the characteristics of reducing fluids and the mixing of atmospheric precipitation. In general, the characteristics of ore-forming fluids in the east ore section are similar to those of the first mining area, suggesting that the ore-forming fluids in the east ore section may not migrate from the first mining area. And the east ore section may be a relatively independent metallogenic system. Moreover, the fractal analysis results demonstrate that the shape of fluid inclusions formed in the same hydrothermal activity features self-similarity. The DAP values of fluid inclusions in B veins, ED veins, and D veins are 1.04, 1.06 and 1.10, respectively, showing a gradually increasing trend from the main stage to the late stage of mineralization. Meanwhile, the shape of fluid inclusions ranging from B veins to D veins becomes increasingly irregular. It also reveals that the homogenization temperature satisfies fractal distribution with four scale-invariant intervals, suggesting that all B veins, ED veins, and D veins have experienced at least four hydrothermal activities. Compared with histogram, the N-S fractal model is able to describe the distribution characteristics of the ore-forming fluids’ homogenization temperature more precisely. Therefore, it presents a potential tool for the stage division of ore-forming fluids. This research provides information about the characteristics of ore-forming fluids in the east ore section of the Pulang porphyry copper deposit, which is beneficial for further exploration in this region, and the extension of the application of fractal models in the study of fluid inclusions. However, further testing of fractal models on the fluid inclusion study is warranted to fully determine the universality.

Fluid inclusion evidence for hydrothermal evolution of the Sadaigoumen porphyry Mo deposit on the northern margin of the north China Craton

The Sadaigoumen porphyry Mo deposit is located on the northern margin of the North China Craton (NCC). In this study, in situ fluid-inclusion analyses including microthermometry, laser Raman spectroscopy, and LA–ICP–MS microanalysis, as well as Quartz H–O isotopes are present to precisely constrain the hydrothermal evolution of the Sadaigoumen deposit. Five stages of hydrothermal activity are identified, with Stage 1 characterized by the development of magnetite with rare sulfide minerals; Stage 2 by K-feldspar as the typical vein mineral; Stage 3 by molybdenite mainly in veins; Stage 4 by the development of fluorite–quartz and quartz–pyrite veins; and Stage 5 by barren carbonate–quartz veins. Fluid inclusion types were distinguished based on petrographic observations and microthermometric analysis, and fluid compositions were detected by LA–ICP–MS. Microthermometric analyses indicate decreasing homogenization temperatures in primary fluid inclusions from Stage 1 to Stage 3. Intermediate-density fluids of stages 1 and 2 are characterized by high homogenization temperatures (420 °C–470 °C), moderate salinities (6.3–11.2 wt%), and high Mo contents (52–541 ppm). Hydrothermal evolution during Mo mineralization in Stage 3 is characterized by immiscible inclusion assemblages that formed through phase separation from intermediate-density fluid. Fluid inclusions of Stage 3 were trapped at pressures fluctuating around the two-phase fluid surface, leading to at least two fluid immiscible phases (373 °C–414 °C and 311 °C–341 °C). The Mo contents of fluid inclusions vary greatly in Stage 3, with Mo tending to be enriched in brine. In stages 4 and 5, fluids display characteristics that indicate mixing with meteoric water, with homogenization temperatures (<299 °C) and salinities (<5.8 wt%) decreasing together with Mo content. The Cs/(Na + K + Mn + Fe) ratios of fluid inclusions are stable from stages 1 to 4, indicating a constant supply of ore-forming fluids from an underlying, geochemically uniform magma chamber. The fluid inclusion data suggest that Mo and Cu in the initial exsolved fluids of the Sadaigoumen porphyry Mo deposit display different migration and precipitation progresses, which is of great significance to the study of the delicate ore-forming progress of porphyry Mo (–Cu) deposits in the northern NCC.