Types Of Fluid Inclusions Research Articles

Insights into the Ore Genesis of the Harla Gold Deposit in Eastern Tianshan, NW China: Evidence from Geology, Fluid Inclusions, and H-O-C-S-Pb Isotopes

The Harla gold deposit is located on the eastern segment of the Kanggur-Huangshan ductile shear belt in Eastern Tianshan, on the southern margin of the Central Asian Orogenic Belt. The orebodies show close spatial association with NEE-trending faults and are hosted in volcanic rocks of the Lower Carboniferous Xiaorequanzi Formation. Three mineralization stages were recognized: an early stage characterized by specularite–pyrite–quartz mineralization, an intermediate stage with pyrite–chalcopyrite–gold–quartz genesis, and a late stage defined by sulfide-poor calcite and quartz veins. Three types of fluid inclusions (FIs) were recognized: daughter mineral-bearing triphase FIs (S-type), liquid-dominated biphase FIs (LV-type), and liquid-only monophase FIs (L-type). S- and LV-type FIs entrapped in the early stage show similar homogenization temperatures (Th) at 216–229 °C and 199–222 °C. However, they display contrasting salinities of 32.2–33.4 and 6.7–8.9 wt.% NaCl eqv., respectively. LV-type FIs entrapped in the intermediate stage display Th of 163–191 °C, with salinities of 5.6–7.4 wt.% NaCl eqv. LV-type FIs occur in the late stage display Th of 135–258 °C and salinities of 3.7–5.6 wt.% NaCl eqv. Insights from hydrogen, oxygen, and carbon isotope analyses (δ18OH2O = −10.7 to 3.3‰, δDH2O = −88.1 to −61.4‰, δ13CH2O = −8.9 to −6.2‰), combined with FI characteristics, indicate that the ore-forming fluids were derived from a hybrid source of magmatic and meteoric water, with the latter becoming dominant in the later stage. Sulfide and lead isotopic compositions (δ34Spyrite = 0.2 to 2.5‰, 206Pb/204Pb = 17.709–18.273, 207Pb/204Pb = 15.483–15.569, 208Pb/204Pb = 37.533–37.754) suggest that ore-forming materials were mainly derived from wall rocks (Xiaorequanzi Formation rocks and plagiogranite). By integrating geological background work and fluid inclusion analyses, as well as isotope data, we conclude that the Harla gold deposit is an epithermal-type deposit.

Origin of the Dongbulage Mo–Pb–Zn deposit in the Great Hinggan Range, northeast China: Geological, molybdenite Re–Os dating, fluid inclusion, and C–H–O–S–Pb isotope constraints

The Dongbulage porphyry Mo–Pb–Zn deposit is located in the Huanggang–Ganzhuermiao polymetallic district (HGD) in the southern part of the Great Hinggan Range in northeast China. The Dongbulage deposit is hosted by granite porphyry, and the wall rock alteration can be divided into quartz–potassic, quartz–sericite, and propylitic zones. The hydrothermal activity in the deposit can be divided into five stages, with molybdenite and Pb–Zn ore occurring mainly as veins and veinlets in stages II and III, respectively. The fluid inclusion (FI) types include liquid-rich (L-type), vapor-rich (V-type), and daughter mineral-bearing (S-type) FIs. Based on the combination of FI types and their temperatures and salinities, it is inferred that fluid boiling and incorporation of meteoric water were key factors in the precipitation of Mo and Pb–Zn, respectively. Hydrogen and O isotope data for quartz, and C and O isotope data for calcite indicate that the ore-forming fluids were primarily magmatic in origin, and were mixed with meteoric waters during their evolution. The S and Pb isotope data, along with the mineral paragenesis, suggest that molybdenite and chalcopyrite which precipitated during stage II were derived mainly from magmatic–hydrothermal fluids, whereas arsenopyrite, sphalerite, and pyrite that precipitated during stage III were strongly affected by the incorporation of surrounding strata materials. Rhenium–Os dating of molybdenite indicates that mineralization in the Dongbulage deposit occurred at 162.1 ± 1.3 Ma (n = 6; MSWD = 1.4). The results, combined with data from other deposits in the region of this age, indicate that important mineralization occurred in the HGD during 165–155 Ma.

A study of iron carbonates and clay minerals for understanding the origin of marine ooidal ironstone deposits

A detailed study of cement and matrix of ooidal ironstones of the Bakchar deposit (Western Siberia) was carried out to assess the factors influencing ore-forming processes. This research focusses on a debated issue about iron sources for Phanerozoic ooidal ironstone. Siderite, the main cementing mineral in the ironstones, is of two varieties that differ in morphology, chemical and isotopic composition, and types of fluid inclusions. The first variety of siderite occurs either as veinlet or as anhedral cement, consisting of isotopically light carbon and oxygen (δ13C from −39.5 to −29.7‰ and δ18O from −15.2 to −5.1‰). Fluid inclusions show a relatively high homogenization temperature (170–320 °C) and methane in the gas phase, corresponding to methane-bearing hydrothermal fluids. The second variety of siderite occurs as aggregates of small crystals in the ironstone matrix and is relatively enriched in heavier stable carbon and oxygen isotopes (δ13C from −28.1 to −12.2‰ and δ18O from −28.4 to −2.1‰), suggesting its formation on the seafloor under the combined influence of methane flux and seawater. The zone of the ooidal ironstone most proximal to the most intense ore-mineralization, an area of intense diffusion of metals and methane through marine sediments, is marked by the first variety of siderite, with rare authigenic minerals, a low clay content (kaolinite, chlorite, nontronite) and a high Fe content of the smectites. The authigenic mineral associations reflect the transition from methanic (sulfate-methane transition zone) to ferruginous (iron reduction zone) through sulfidic environment. The intermediate zone is dominated by montmorillonite-illite-saponite-nontronite and the second variety of siderite. The distal zone of the ore deposit is relatively unaltered, and is marked by illite-montmorillonite (illite-smectite), with rare second variety of siderite. The ratio of 1 M phyllosilicates (kaolinite) to the main swelling 2 M phyllosilicates in the clay fraction (K/M mineral index) decreases from the proximal zone of the intense iron-mineralization to the distal zone. The trend of clay mineral changes reflects the decreasing alteration of sediment matrix away from the main iron-rich and/or carbonate-bearing fluid influx. This study shows the expected lateral and vertical variation in authigenic minerals associated with marine Phanerozoic ironstone deposits, related to variable flux of metal- and methane-bearing fluids.

Fluid evolution characteristics and ore genesis in the Jinqu Au deposit, Qinling Orogen, China: Implications for ore genesis

The Jinqu Au deposit is located in the central Xiaoqinling gold field along the southern margin of the North China Craton. Ore-bearing auriferous quartz veins in the deposit are controlled by E–W trending structures within amphibolite facies metamorphic rocks of the Archean Taihua Group. The ore-forming process in this deposit can be divided into four stages represented by feldspar-quartz, pyrite-quartz, polymetallic sulfide-quartz, and carbonate-quartz veins and veinlets. Here we present fluid inclusion and isotopic data of the Jinqu Au deposit. Four types of fluid inclusions in quartz and calcite are identified, including carbonic-aqueousinclusions (type-1), aqueousinclusions (type-2), solid-bearinginclusions (type-3) and pure carbonic inclusions (type-4) varieties, based on petrography and laser Raman spectroscopy. Quartz in stage I contains type-1 fluid inclusions (FIs) which homogenized to aqueous or carbonic phase at temperature 361 to 406 ℃ and 385 to 400 ℃ respectively, and have salinities of 10.3 to 17.9 wt% NaCl equiv. Type-2 FIs show homogenization temperatures of 347 to 410 ℃ into the liquid phase, with high salinities of 11.6 to 18.6 wt% NaCl equiv. Quartz in stage II is the major host of type-1 FIs, with minor type-4 FIs, the former showing homogenization at temperatures of 305 to 390 ℃ into the carbonic phase and 280 to 410 ℃ into the aqueous phase, with variable salinities of 4.5 to 19.8 wt% NaCl equiv. The stage III quartz contains all the four types of FIs (homogenizing to carbonic or aqueous phase at temperature 309 to 360 ℃ and 295 to 400 ℃, with salinities of 6.6 to 19.9 wt% NaCl equiv for type-1, and homogenizing to liquid at temperature 308 to 326 ℃ with salinities of 12.5 to 13.2 wt% for type-2 Fls). In stage IV, type-2 FIs are the major type in quartz and calcite with total homogenization temperatures of 213 to 280 ℃ into the liquid phase and variable salinities of 5.3 to 18.6 wt% NaCl equiv. Our data show that the ore-forming fluids of the Jinqu Au deposit are generally characterized by moderate to high homogenization temperatures and variable salinities, belonging to the CO2-H2O-NaCl ± CH4 system. Based on fluid inclusion data, we infer that fluid immiscibility occurred in stages II and III, and the estimated trapping pressures for stages II and III fluids are between 81 and 275 MPa.The CHO isotopic values of fluids (δ18Owater = 1.2 to 6.4 ‰; δDV-SMOW = − 68.5 to − 56.0 ‰; δ13CCO2 = − 12.4 to − 3.4 ‰) in stage I to IV and δ13CV-PDB values for calcite (δ13CV-PDB = − 7.6 to − 4.3 ‰) in stage IV suggest that the ore-forming fluids were composed of a mixture of metamorphic water and mantle-derived fluids with minor involvement of meteoric water. Fluid inclusions in pyrite of stage II and III yield 3He/4He ratios of 0.88 to 1.39 Ra, and considerable 40Ar/36Ar ratios range from 2287.6 to 5669.9, suggesting the mixing of mantle and crustal components. The δ34SV-CDT values of sulfide samples in stages II and III range from − 5.8 to 4.5 ‰ (except for a pyrite grain within calcite that shows − 28.5 ‰). The values of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of pyrite samples in stages II and III are from 16.919 to 17.321, 15.340 to 15.539, and 37.303 to 37.971 respectively. Our data suggest that the Taihua Group was possibly a major source for the ore-forming metals of the Jinqu Au deposit. Integrating the data from ore geology, fluid inclusions, isotope geochemistry and regional setting, we propose that the Jinqu Au deposit is an orogenic-type deposit which formed within the continental collision setting of the North China and Yangtze Cratons.

Tectonic setting, fluid inclusion and gold mineralization of the southwest Poli region (northern Cameroon Domain)

This paper documents original petrographic and structural data on metamorphic and magmatic rocks as well as the occurrence of gold mineralization in the Dourou Tchaga area (SW Poli) in the northwestern Cameroon domain. The study area is dominated by high-grade gneisses derived from a volcanic-sedimentary series alternating with orthogneiss and magmatic rocks. Four main deformation stages were distinguish comprising the early D1 and D2 deformations showing ductile behavior under amphibolite to granulite facies, followed by retrogression into greenschist facies. D3 and D4 are characterized by ductile-brittle and late brittle structures. Gold mineralization is hosted in laminated quartz veins in steeply dipping, ENE–WSW-trending, sinistral shear zone developed during D3. Host rocks are high-grade metamorphic paragneiss and orthogneiss. Ore minerals include native gold, galena, sphalerite, pyrite and chalcopyrite; wall rock alteration assemblage includes stable pyrite, magnetite and hematite. This assemblage together with specific quartz microstructures indicate gold mineralization at lower greenschist facies conditions. Gold is disseminated in quartz veins and wall rock alteration zones, where it occurs as free grains but also as inclusions in pyrite and sphalerite. Two types of fluid inclusions are distinguished: aqueous-carbonic CO2–H2O and aqueous (H2O), both with low to moderate (2.0–13.9 wt% NaCleq) salinity and variable CO2 content of 13–23 mole% for the aqueous-carbonic fluid inclusions. Fluid inclusions data and alteration assemblage provide evidence that gold precipitation in quartz veins occurred in response to an increase in fO2 caused by fluid pressure fluctuations in the shear zone. Gold mineralization in the northern Cameroon domain was formed during post-collisional stage and retrograde exhumation of the terrane in the greenschist facies toward the end of the Panafrican Orogeny.

Age and genesis of the Lamahanshan Ag-Pb-Zn deposit, southern Great Xing'an Range, northeastern China: Constraints from sphalerite Rb-Sr dating, fluid inclusions and H-O-S-Pb isotopes

The Lamahanshan deposit in the eastern Central Asian Orogenic Belt (CAOB) is a newly-discovered Ag-Pb-Zn vein deposit in the southern Great Xing'an Range (GXR). Vein-type Ag-Pb-Zn orebodies are mainly hosted in the fracture zones of gneissic plagiogranite, granite porphyry, and quartz porphyry. Mineralization comprises four stages: (I) quartz-magnetite, (II) quartz-pyrite-chalcopyrite, (III) quartz-polymetallic sulfides, and (IV) quartz ± sphalerite. Sphalerite Rb-Sr dating yielded an isochron age of 137.7 ± 6.1 Ma, coeval with the regional Late Jurassic-Early Cretaceous Pb-Zn polymetallic mineralization. Three types of fluid inclusions (FIs), namely vapor-rich two-phase (LV-type), liquid-rich two-phase (VL-type), and daughter mineral-bearing three-phase (SL-type), are distinguished at Lamahanshan. Stage I and II contain all FI types with homogenization temperatures (Th) of 383–418 °C and 350–392 °C and salinities of 0.9–38.1 wt% and 0.7–35.0 wt%, respectively, whereas stage III contain VL- and LV-type FIs with Th = 318–349 °C and salinity = 0.7–10.5 wt%. Only VL-type FIs occur in stage IV, with Th of 271–320 °C and salinities of 4.3–7.8 wt%. The microthermometric and H-O isotope data (δ18OH2O = −9.4 to 0.9‰ and δD = −137.0 to −124.7‰) indicate that the ore-forming fluids were initially magmatic with later meteoric water incursion. Fluid boiling, cooling, fluid-rock reactions, and meteoric water mixing were the major ore precipitation mechanisms at Lamahanshan. The sulfide S (δ34S = 4.0–6.7‰), Sr ((87Sr/86Sr)i = 0.698957–0.700069), and Pb (206Pb/204Pb = 17.230–18.193, 207Pb/204Pb = 15.440–15.627, and 208Pb/204Pb = 37.664–38.407) isotopes also support that the metals were magmatic-derived. Integrating the available geological, mineralization, fluid inclusion, and H-O-S-Sr-Pb isotope evidence, we propose that the Lamahanshan deposit shares many similar features with distal magmatic-hydrothermal vein-type ores, and was formed in an extensional setting related to the Early Cretaceous Paleo-Pacific subduction rollback.

Geology, fluid inclusions and S-Pb-C-O isotopes of the Kuokuqueke Fe-Cu skarn deposit in Western Tianshan, China

The late Paleozoic Boluokenu island arc belt, located on the northern margin of Western Tianshan, Xinjiang, hosts a series of epithermal Au, hydrothermal vein-type Pb-Zn and porphyry-skarn Fe-Cu polymetallic deposits and is one of the most important metallogenic belts in China. The Kuokuqueke skarn deposit is located in the middle of the Boluokenu metallogenic belt. Skarn and Fe-Cu orebodies crop out along the contact between the lower Silurian Nilekehe Formation and the Kenaxia-Kekeqiaoke granitic intrusions. Based on field investigations and petrographic observations, four main paragenetic stages of skarn formation and ore deposition are identified: the prograde skarn stage (I), retrograde skarn stage (II), quartz-sulfide stage (III), and quartz-calcite stage (IV). Ore minerals mainly consist of magnetite and hematite, with lesser amounts of pyrite, chalcopyrite, sphalerite and galena. Four types of fluid inclusions were identified in garnet, epidote, quartz, and calcite at different stages, i.e., bi-phase (liquid and vapor) aqueous inclusions (L-dominated homogenized to liquid phase and V-dominated homogenized to vapor phase), tri-phase (liquid, vapor and solid) aqueous inclusions (S-bearing) and liquid-only aqueous inclusions. From the early to late stages, ore-forming fluids show an evolutionary trend from high temperature and medium–high salinity to low temperature and low salinity. The fluid inclusions were trapped at pressures of 400∼600 bars and 100∼300 bars for the prograde and retrograde skarn stage, respectively, corresponding to depths of 1.6∼2.4 km (under lithostatic conditions) and 1∼2 km (under hydrostatic conditions), respectively. The δ34S values of sulfides range from −5.2 to 0.5‰, indicating a magmatic origin of the sulfur in ore-forming fluids. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of the sulfides vary from 17.893 to 18.242, 15.550 to 15.591 and 37.996 to 38.175, respectively, indicating that lead was derived from a mixed crust-mantle source of subduction; the δ13CV-PDB values and δ18OV-SMOW values of calcite range from −0.6 to 2.4 and 8.1 to 13.3, respectively, indicating that carbon in fluids was mainly sourced from the mixture of ore-related granite and host carbonate rocks. Comprehensive studies indicate that the Kuokuqueke deposit is a typical skarn deposit, in which fluid boiling occurred locally in the pre-ore stage (I) and boiling in the main ore stage (II∼III) was the main cause of ore mineral deposition, while meteoric water may have been involved in the post-ore stage (IV).

Beryl Mineralogy and Fluid Inclusion Constraints on the Be Enrichment in the Dakalasu No.1 Pegmatite, Altai, NW China

The Dakalasu No.1 pegmatitic rare-element deposit is a representative of Be-Nb-Ta pegmatites in Altai, Xinjiang, China. Beryl is the most important beryllium-carrying mineral in Dakalasu No.1 pegmatite. To constrain the concentration mechanism of Be, we conducted a study of the textural relationships and chemical compositions (major and trace elements) of beryl, along with microthermometry and Raman spectroscopy on beryl-hosted fluid inclusions. Two generations of beryl were recognized. The early beryl I was formed in the magmatic stage, whereas the late beryl IIa and IIb were formed in the magmatic-hydrothermal stage. Lithium and Cs contents increased from beryl I, beryl IIa, to beryl IIb, whereas Mg and Rb contents decreased. Scandium, V, and Ga contents of beryl IIa are similar to beryl IIb, but different in beryl I. Titanium is enriched in beryl IIa. The high FeO contents and Na/Cs ratios of beryl (I, IIa, and IIb) reveal the low degree of differentiation evolution of the Dakalasu No.1 pegmatite. Two types of melt inclusions and four types of fluid inclusions were identified in beryl IIa, IIb, and associated quartz. The microthermometry results indicated that beryl II is formed at 500 °C–700 °C, and 200 MPa–300 MPa. The Dakalasu No.1 pegmatite melt is enriched in volatiles, such as B, F, and CO2, evidenced by a large amount of tourmaline in the wall zone, the occurrence of a variety of tiny cryolite (Na3AlF6) inclusions, and CO2-rich fluid inclusions in beryl IIa. The enrichment mechanism of Be may be related to the crystallization of beryl at highly undercooled states of melt, and melt–melt–fluid immiscibility during the evolution and differentiation of the melt.

Genesis of the Maoling gold deposit in the Liaodong Peninsula: Constraints from a combined fluid inclusion, C-H-O-S-Pb-He-Ar isotopic and geochronological studies

The large tonnage Maoling gold deposit (25 t @ 3.2 g/t) is located in the southwest Liaodong Peninsula, North China Craton. The deposit is hosted in the Paleoproterozoic metamorphic rocks. Four stages of mineralization were identified in the deposit: (stage I) quartz-arsenopyrite ± pyrite, (stage II) quartz-gold- arsenopyrite-pyrrhotite, (stage III) quartz-gold- polymetallic sulfide, and (stage IV) quartz-calcite-pyrrhotite. In this paper, we present fluid inclusion, C-H-O-S-Pb-He-Ar isotope data, zircon U-Pb, and gold-bearing sulfide (i.e. arsenopyrite and pyrrhotite) Rb-Sr age of the Maoling gold deposit to constrain its genesis and ore-forming mechanism. Three types of fluid inclusions were distinguished in quartz-bearing veins, including liquid-rich two-phase (WL type), gas-rich two-phase (GL type), and daughter mineral-bearing fluid inclusions (S type). Fluid inclusions data show that the homogenization at temperatures 197 to 372 °C for stage I, 126 to 319 °C for stage II, 119 to 189 °C for stage III, and 115 to 183 °C for stage IV, with corresponding salinities of 3.7 to 22.6 wt.%, 4.7 to 23.2 wt.%, 5.3 to 23.2 wt.%, and 1.7 to 14.9 wt.% NaCl equiv., respectively. Fluid boiling was the critical factor controlling the gold and associated sulfide precipitation at Maoling. Hydrogen and oxygen stable isotopic analyses for quartz yielded δ18O = −5.0‰ to 9.8‰ and δ D = −133.5‰ to −77.0‰. Carbon stable isotopic analyses for calcite and ankerite yielded δ13C = −2.3‰ to −1.2‰ and O = 7.9‰ to 14.1‰. The C-H-O isotope data show that the ore-forming fluids were originated from magmatic water with meteoric water input during mineralization. Hydrothermal inclusions in arsenopyrite have 3He/4He ratios of 0.002 Ra to 0.054 Ra, and 40Ar/36Ar rations of 1225 to 3930, indicating that the ore-forming fluids were dominantly derived from crustal sources almost no mantle input. Sulfur isotopic values of Maoling fine-grained granite range from 6.‰1 to 9.8‰, with a mean of 7.7‰, δ34S values of arsenopyrite from the mineralized phyllite (host rock) range from 8.9‰ to 10.6‰, with a mean of 10.0‰, by contrast, δ34S values of sulfides from ore vary between 4.3‰ and 10.6‰, with a mean of 6.8‰, suggesting that sulfur was mainly originated from both the host rock and magma. Lead radioactiveisotopic analyses for sulfides yielded 206Pb/204Pb = 15.830–17.103, 207Pb/204Pb = 13.397–15.548, 208Pb/204Pb = 35.478–36.683, and for Maoling fine-grained granite yielded 206Pb/204Pb = 18.757–19.053, 207Pb/204Pb = 15.596–15.612, and 208Pb/204Pb = 38.184–39.309, also suggesting that the ore-forming materials were mainly originated from the host rocks and magma. Zircon U-Pb dating demonstrates that the Maoling fine-grained granite was emplaced at 192.7 ± 1.8 Ma, and the host rock (mineralized phyllite) was emplaced at some time after 2065.0 ± 27.0 Ma. Arsenopyrite and pyrrhotite give Rb–Sr isochron age of 188.7 ± 4.5 Ma, indicating that both magmatism and mineralization occurred during the Early Jurassic. Geochronological and geochemical data, together with the regional geological history, indicate that Early Jurassic magmatism and mineralization of the Maoling gold deposit occurred during the subducting Paleo-Pacific Plate beneath Eurasia, and the Maoling gold deposit is of the intrusion-related gold deposit type.

Fluid inclusion and isotopic constraints on the origin of the Ag-Pb-Zn polymetallic mineralization at Biliya, Great Xingan Range, NE China

The Biliya Ag-Pb-Zn polymetallic (SLZP) deposit (16.5 Mt, @ 52.9 g/t Ag, 2.6% Pb and 2.3% Zn) lies in the Great Xing’an Range, Northeast China. Breccia-, veinlet- and vein-type Ag-Pb-Zn ore bodies are primarily hosted in the quartz porphyry, trachyandesite and rhyolitic tuff. They are spatially and temporally related to andesitic porphyry. Three mineralization processes are identified: stage I: grey quartz - pyrite + tawny sphalerite (high Cd2+), stage II: grayish white quartz - pyrite + grey sphalerite (high Fe2+) + galena + argentite + tetrahedrite, stage III: white quartz-pyrite. The alterations consist of quartz + sericite, illite + quartz, fluorite + calcite + opal and chlorite zone. The silver-lead–zinc mineralization primarily corresponds to stage II. Five sulfide samples from stage II yielded a well-fitted isochron age of 131.3 ± 2.4 Ma (MSWD = 2.4), marking the timing of Ag-Pb-Zn polymetallic mineralization. CO2-bearing NaCl-H2O (C), gaseous CO2 (V); vapour-liquid H2O-NaCl (WL) and fluid-phase H2O-NaCl (L)-type of fluid inclusions were distinguished. Their petrographic and microthermometric features and H-O isotopic data suggest that the hydrothermal fluids were initially originated from magmatic source, with intensive mixing with meteoric water and that their temperatures and salinities are 254–130 ℃ and 7.15–1.22 wt% NaCl eqv, respectively, belonging to a reduced fluid (CO2-H2O-NaCl ± CH4) system. In-situ S and bulk Pb isotope analyses indicate that the metal materials were related to andesitic magma from the lower crust. The deposit geology, fluid inclusions, stable isotopes and chronology results suggest that the Biliya deposit belongs to a low-sulfidation (LS) epithermal SLPZ deposit. Boiling and fluid immiscibility coupled with suddenly decreasing in temperature, pressure, logfS2 of the hydrothermal fluids are likely to play important roles in Biliya SLPZ ore deposition.

New data on the formation conditions of the Drazhnoye deposit gold mineralization (Republic Sakha, Yakutia)

New results of thermal, baric, and geochemical studies indicate that quartz veins within the deposit were formed in mesozonal conditions at depths 3–9 km from heterogeneous CO2–H2O fluids containing water and carbon dioxide with low concentrations of salts and high concentrations of CO2, which is typical for ore-forming fluids of orogenic vein gold deposits. According to the phase composition, there are three types of fluid inclusions: 1) carbon dioxide- water; 2) gas-filled with dense carbon dioxide; 3) biphasic gas-liquid water-salt solutions. There are Na, Mg, and Fe chlorides predominated in the ore-forming fluids. It is assumed that the fluids migrated along the regional Adycha-Taryn shear zone, uplifting to the Earth’s surface at supra-lithostatic pressures, followed by the deposition of ore elements and the vein quartz formation during tectonic movements along shear zones.

Geological, mineralogical and ore fluid characteristics of the Tagun‐Khin‐Dan gold mineralization in Mogok‐Mandalay‐Mergui Belt, Central Myanmar

AbstractThe Tagun‐Khin‐Dan gold deposit in the Mogok‐Mandalay‐Mergui Belt, Central Myanmar, is characterized by an array of quartz‐veins hosted in mudstone of the Kogwe Formation of the Carboniferous Mergui Group. Two major deformational stages were recorded in the area; (1) N‐S shortening and (2) uplifting and emplacement of various dykes and quartz veinlets. The N‐S shortening within the area lead the development of km‐scale faults, determined largely by the presence of a zone of major WNW‐ESE trending dextral strike‐slip faulting. Quartz veins in the deposit include: (1) type‐A quartz veins, parallel to the dextral NW‐SE trending major fault; and (2) type‐B quartz veins which occur as isolated parallel veins. Gold in the type‐A quartz vein is present as native gold and electrum locked within pyrite and associated with pyrite and galena and in the type‐B quartz veins as electrum associated with sulfide minerals such as pyrite, chalcopyrite, galena and sphalerite. The mineralization stages can be classified into the type‐A quartz vein stage and the type‐B quartz vein stage. Two type of fluid inclusions; liquid‐rich aqueous inclusions (L‐type) and vapor‐rich aqueous inclusions (V‐type) are identified in the type‐A quartz veins. The homogenization temperature of L‐type fluid inclusions of the type‐A quartz veins ranges from 203 to 321°C and salinity of the fluid inclusions varies from 0.4 to 1.6 wt% NaCl equiv. The homogenization temperature of V‐type fluid inclusions of type‐A quartz veins ranges from 290 to 340°C with a salinity ranging from 0.4 to 1.9 wt% NaCl equivalent. In the type‐B quartz veins, only liquid‐rich aqueous inclusions (L‐type) are identified. The type‐B quartz veins yielded low homogenization temperatures from 160 to 220°C, with low salinities from 0.2 to 1.9 wt% NaCl equiv. compared with those of the type‐A veins. The depth range of ore formation is estimated to be a shallow depth of less than 0.2 km based on fluid inclusion microthermometry. Fluid boiling is evident during the type‐A quartz vein stage, and fluid cooling and mixing in the later type‐B quartz vein stage. Precipitation of pyrite in the ore zone occurred as four recognized types: arsenic‐rich pyrite‐1, 2, 3 in the type‐A quartz veins and pyrite‐4 in the type‐B quartz veins. A positive relation between Au and As contents of pyrites suggests that the gold is present together with arsenic in the structure of pyrites of the type‐A quartz veins as solid solution in addition to as nanoparticle inclusions. The high Co and Ni contents of pyrites of both the type‐A and the type‐B quartz veins, with no evidence of CO2 in the system indicate that the ore‐forming fluids were epizonal magmatic‐hydrothermal fluids rather than metamorphic fluid. The hydrothermal fluids of the Tagun‐Khin‐Dan deposit were driven by faulting to form the mudstone‐hosted epithermal gold mineralization and related to continuing northwards movement of the Indian Plate that initiated the displacement on the strike‐slip Sagaing Fault.

High‐sulfidation epithermal–porphyry transition in the Kumbokarno Prospect, Trenggalek district, East Java, Indonesia: Constraints from mineralogy, fluid inclusion, and sulfur isotope studies

AbstractAn indication of high‐sulfidation epithermal–porphyry transition was observed in the Kumbokarno prospect, East Java, Indonesia. The prospect is composed of two Middle Miocene intrusions with tonalitic and dioritic compositions. Tonalite, the main host‐rock was subjected to argillic, advanced argillic, and vuggy quartz alteration, whereas the juxtaposing diorite was subjected to peripheral propylitic alteration. Three types of vein exist in the research area, which are massive quartz, comb quartz, and stockwork vein. In addition, supergene alteration represented by goethite and hematite pervasively superimposed both the hydrothermal alteration and mineralization. Fluid inclusion petrography and microthermometry analysis on three types of quartz veins distinguished primary fluid inclusions into two groups, that is, V30 group composed of vapor (30 vol%)–liquid (70 vol%), and the second group V30H group composed of vapor (30 vol%)–halite (30 vol%)–liquid (40 vol%). The homogenization temperatures of both the groups show a similar range of ca. 350–480°C, but the V30H group has significantly higher salinity (35–50 wt% NaCl eq.) compared to the V30 group (10–20 wt% NaCl eq.). In terms of the vein types, the massive quartz vein has the highest homogenization temperatures, followed by the comb quartz vein and lastly the stockwork veins. The presence of alunite and its sulfur isotope compositions, δ34S = 19.6 (σ = 2.1‰), indicate acidic pH and presence of SO42− in the hydrothermal fluids. The prospect is an intrusion‐centered magmatic‐hydrothermal system reflecting the porphyry‐epithermal transition. The fluid inclusions with high homogenization temperatures up to 480°C and high salinity up to 50 wt% NaCl eq. also support the transition of porphyry to high‐sulfidation epithermal mineralization. The presence of two different types of primary fluid inclusions suggests that boiling process occurred and separated the original magmatic fluid into the liquid and vapor phases. More, this fluid underwent dilution and mixing with meteoric waters. The migration of both the fluids were likely unrelated to the formation of the advanced argillic–argillic alteration halo because the quartz veins cut across this alteration. The prospect was later subjected to intensive weathering process that altered most of the sulfides into iron oxides and hydroxides. Small amounts of copper and minor gold were detected, especially in the iron oxides and hydroxides ones with colloform and bladed textures. The Kumbokarno prospect evidences the potential for high‐sulfidation to porphyry deposits at the Southern Mountain Arc, Indonesia.

Fluid Inclusion Study of Epithermal Quartz Veins from the Kyaukmyet Prospect, Monywa Copper-Gold Ore Field, Central Myanmar

The Kyaukmyet prospect is located near the main ore bodies of the Kyisintaung and Sabetaung high-sulfidation Cu-Au deposits, Monywa copper-gold ore field, central Myanmar. Lithologic units in the research area are of mainly rhyolite lava, lapilli tuff and silicified sandstone, mudstone and siltstone units of Magyigon Formation which hosted to be polymetallic mineralization. Our field study recorded that epithermal quartz veins are hosted largely in rhyolite lava and lapilli tuff units. Those quartz veins show crustiform, banded (colloform), lattice bladed texture and comb quartz. The main objectives of the present research in which fluid inclusion studies were considered to conduct the nature, characteristics and hydrothermal fluids evolution from the epithermal quartz veins. In this research, there are three main types of fluid inclusions are classified according to their phase relationship (1) two-phase liquid-rich inclusions, (2) the coexisting liquid-rich and vapor-rich inclusions, and (3) only vapor-rich inclusions. Microthermometric measurements of fluid inclusions yielded homogenization temperatures (Th) of 148–282 °C and final ice-melting temperature (Tm) of -0.2°C to -1.4°C . The value of (Tm) are equal to the salinities reaching up 0.35 to 2.07 wt % NaCl equiv. respectively. Estimation formation temperature of the quartz veins provide 190°C and 210°C and paleo-depth of formation are estimated to be between 130m and 210m. Petrography of fluid inclusion and microthermometric data suggest that fluid boiling as well as mixing processes were likely to be happened during the hydrothermal fluid evolution at the Kyaukmyet prospect. According to the characteristics of many parameters including petrography of fluid inclusion, microthermometric data, paleo-depth, evidence of quartz vein textures and types of hydrothermal alteration from the Kyaukmyet prospect allows to interpret these data to be the low-sulfidation epithermal system.

Fluid-inclusion petrography in calcite stalagmites: Implications for entrapment processes

ABSTRACT Fluids trapped in speleothems have an enormous potential in frontier fields of paleoclimate and paleohydrological research. This potential is, however, hampered by diverse scientific and technical limitations, among which the lack of a systematic methodology for genetically characterizing fluid inclusions is a major one, as these can have different origins, and thus, the trapped fluid (usually water), different meanings. In this work, we propose a systematic petrological classification of fluid inclusions, based on: 1) the temporal relation between fluid inclusions and the host calcite, 2) the spatial relation between fluid inclusions and the “crystallites” and crystals aggregates, and 3) the phases (water, air) trapped inside fluid inclusions. The first criterion allows dividing fluid inclusions in two main categories: primary and secondary, whose identification is critical in any research based on trapped fluids. The other two criteria allow the definition of eight types of primary and four types of secondary fluid inclusions. Primary fluid inclusions contain the drip water that fed stalagmites at the time of crystal growth, and can be intercrystalline, i.e., located between adjacent crystallites, or intracrystalline, i.e., with the fluid trapped within crystallites. We differentiate six main types among the intercrystalline fluid inclusions (elongate, thorn-shaped, down-arrow, interbranch, macro-elongate, and bucket) and other two among intracrystalline inclusions (pyriform and boudin). In primary inclusions, water is the main phase, while gas is much less abundant. The presence of gas could be related to slow drip rates or degassing in the cave, but also to later leakage due to changes in temperature and humidity often occurring during inadequate handling of speleothem samples. Secondary fluid inclusions were clearly related to younger water inlet through stratigraphic disruptions or unconformities. They are formed after water infiltration, but sealed before the renewed crystal growth. We differentiate four main types of secondary inclusions: interconnected, rounded, triangular, and vertical fluid inclusions. The identification of primary and secondary fluid inclusions in speleothems is a key for interpretation in paleoclimate studies. Integration of petrological results allow establishment of three different genetic scenarios for the formation of fluid inclusions, whose identification can be relevant because of their predictive character.

Magmatic-Hydrothermal Processes of Vein-Type Haman-Gunbuk-Daejang Copper Deposits in the Gyeongnam Metallogenic Belt in South Korea

Haman, Gunbuk, and Daejang deposits are neighboring vein-type hydrothermal Cu deposits located in the SE part of the Korean Peninsula. These three deposits are formed by magmatic-hydrothermal activity associated with a series of Cretaceous granodioritic intrusions of the Jindong Granitoids, which have created a series of veins and alterations in a hornfelsed shale formation. The copper deposits have common veining and alteration features: 1) a pervasive chlorite-epidote alteration, cut by 2) Cu-Pb-Zn-bearing quartz veins with a tourmaline-biotite alteration, and 3) the latest barren calcite veins. Chalcopyrite, pyrite, and pyrrhotite are common ore minerals in the three deposits. Whereas magnetite is a dominant mineral in the Haman and Gunbuk deposits, no magnetite is present, but sphalerite and galena are abundant in the Daejang deposit. Ore-bearing quartz veins have three types of fluid inclusions: 1) liquid-rich, 2) vapor-rich, and 3) brine inclusions. Hydrothermal temperatures obtained from the brine inclusion assemblages are about 340–600, 250–500, and 320–460°C in the Haman, Gunbuk, and Daejang deposits, respectively. The maximum temperatures (from 460 to 600°C) recorded in the fluid inclusions of the three deposits are higher than those of the Cu ore precipitating temperature of typical porphyry-like deposits (from 300 to 400°C). Raman spectroscopy of vapor inclusions showed the presence of CO2 and CH4 in the three deposits, which indicates relatively reduced hydrothermal conditions as compared with typical porphyry deposits. The Rb/Sr ratios and Cs concentrations of brine inclusions suggest that the Daejang deposit was formed by a later and more fractionated magma than the Haman and Gunbuk deposits, and the Daejang deposit has lower Fe/Mn ratios in brine inclusions than the Haman and Gunbuk deposits, which indicates contrasting redox conditions in hydrothermal fluids possibly caused by an interaction with a hosting shale formation. In brines, concentrations of base metals do not change significantly with temperature, which suggests that significant ore mineralization precipitation is unlikely below current exposure levels, especially at the Haman deposit. Ore and alteration mineral petrography and fluid inclusions suggest that the Haman deposit was formed near the top of the deep intrusion center, whereas the Gunbuk deposit was formed at a shallower intrusion periphery. The Daejang deposit was formed later at a shallow depth by relatively fractionated magma.

Fluid Evolution and Ore Genesis of the Juyuan Tungsten Deposit, Beishan, NW China

The newly discovered Juyuan tungsten deposit is hosted in Triassic granite in the Beishan Orogen, NW China. The tungsten mineralization occurred as quartz veins, and the main ore minerals included wolframite and scheelite. The age, origin, and tectonic setting of the Juyuan tungsten deposit, however, remain poorly understood. According to the mineralogical assemblages and crosscutting relationships, three hydrothermal stages can be identified, i.e., the early stage of quartz veins with scheelite and wolframite, the intermediate stage of quartz veinlets with sulfides, and the late stage of carbonate-quartz veinlets with tungsten being mainly introduced in the early stage. Quartz formed in the two earlier stages contained four compositional types of fluid inclusions, i.e., pure CO2, CO2-H2O, daughter mineral-bearing, and NaCl-H2O, but the late-stage quartz only contained the NaCl-H2O inclusions. The inclusions in quartz formed in the early, intermediate, and late stages had total homogenization temperatures of 230–344 °C, 241−295 °C, and 184−234 °C, respectively, with salinities no higher than 7.2 wt.% NaCl equiv (equivalent). Trapping pressures estimated from the CO2-H2O inclusions were 33−256 MPa and 36−214 MPa in the early and intermediate stages, corresponding to mineralization depths of 3–8 km. Fluid boiling and mixing caused rapid precipitation of wolframite, scheelite, and sulfides. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition and from magmatic to meteoric, as indicated by decreasing δ18Owater values from early to late stages. The sulfur and lead isotope compositions in the intermediate-stage suggest that the Triassic granite was a significant source of ore metals. The biotite 40Ar/39Ar age from the W-bearing quartz shows that the Juyuan tungsten system was formed at 240.0 ± 1.0 Ma, coeval with the emplacement of granitic rocks at the deposit. Integrating the data obtained from the studies including regional geology, ore geology, biotite Ar-Ar geochronology, fluid inclusion, and C-H-O-S-Pb isotope geochemistry, we conclude that the Juyuan tungsten deposit was a quartz-vein type system that originated from the emplacement of the granites, which was induced by collision between the Tarim and Kazakhstan–Ili plates. A comparison of the characteristics of tungsten mineralization in East Tianshan and Beishan suggests that the Triassic tungsten metallogenic belt in East Tianshan extends to the Beishan orogenic belt and that the west of the orogenic belt also has potential for the discovery of further quartz-vein-type tungsten deposits.

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.