Fluid Inclusions In Quartz Research Articles

Fluid evolution and genesis of the Zhuanghuhe Au–Sb mineralization in the Duobaoshan orefield, Northeast China: Evidence from fluid inclusions and H–O–C isotopes

The newly discovered Zhuanghuhe Au–Sb occurrence is located 20 km north of the famous Duobaoshan Cu–Mo deposit, it is the first gold–antimony deposit discovered in the Duobaoshan orefield. The hydrothermal quartz vein-type orebodies occur in the Middle Ordovician Duobaoshan Formation and are controlled by NNW and ENE compressional faults. Four mineralization stages are identified: stage I quartz + pyrite + arsenopyrite, stage II quartz + polymetallic sulfides, stage III quartz + stibnite, and stage IV quartz + calcite. Fluid inclusions (FIs) in quartz and calcite veins include six types: types I (two-phase aqueous), IIa (aqueous–carbonic; the volume of the carbon phase <50 %), IIb (aqueous–carbonic; the volume of the carbon phase >50 %, with more CO2 than CH4), IIc (aqueous–carbonic; the volume of the carbon phase >50 %, with more CH4 than CO2), IIIa (carbonic, with more CO2 than CH4) and IIIb (carbonic, with more CH4 than CO2). FIs of stage I are types I, IIa, IIb and IIIa, with homogenization temperatures of 279–311 °C and salinities of 4.87–11.84 wt%, indicating a medium-temperature low-salinity immiscible NaCl–H2O–CO2 fluid system. Stage II contains all FI types with final homogenization temperatures of 233–288 °C and salinities of 4.94–8.67 wt%, indicating a medium- to low-temperature low-salinity NaCl–H2O–CO2–CH4 system. FIs of stage III contain types I and IIa with homogenization temperatures of 193–240 °C and salinities of 3.85–6.63 wt%, belong to a low-temperature low-salinity NaCl–H2O–CO2 ± CH4 system. FIs of stage IV contain only type I with homogenization temperatures of 158–212 °C and salinities of 2.56–4.01 wt%, indicating a NaCl–H2O system. The H–O–C isotope data show that the NaCl–H2O–CO2 fluids of stage I (δD = −98 to −105.7 ‰, δOH2O = 5.7 to 6.9 ‰, δ13CCO2 = −11.9 to −11.1 ‰) were derived from a magmatic system, the fluids of stage II (δD = −85.7 ‰, δOH2O = 2.8 ‰, δ13CCO2 = −14.2 ‰, δ13CCH4 = −32.5 to −31.9 ‰) were characterized by the addition of CH4, which might have come from the reaction between the original ore-forming fluids and carbonaceous slate of the Duobaoshan Formation. The fluids in stage III (δD = −90.2 to −89.6 ‰, δOH2O = −9.1 to −6.1 ‰) and stage IV (δD = −110.6 to −96.3 ‰, δOH2O = −13.0 to −12.6 ‰) were characterized by mixing of meteoric water. According to the geology, fluid inclusion and H-O-C stable isotope evidences, the initial magma-derived NaCl-H2O-CO2 fluids were immiscible in stage I and then the process of mixing with CH4-bearing fluids in stage II, resulting in the gold precipitation; the precipitation of antimony was mainly related to the temperature drop and the mixing of meteoric water in stage III.

Magma-related origin for Pb–Zn–Ag vein formation at the Aerhada deposit, Inner Mongolia, NE China: Constraints from fluid inclusion, C–H–O–S–Pb isotopic compositions, and geochronological studies

The Aerhada Pb–Zn–Ag deposit is on the western margin of the Great Xing’an Range in NE China. Prior studies on this deposit lack information regarding precise mineralization age and convincing genetic interpretation, which limits both the prospecting at Aerhada and the reconstruction of the regional metallogenic evolution. Based on a detailed field investigation and microscopic observation, in this study, our aim was to determine the origin and evolution of the hydrothermal system and the timing of magmatism and mineralization, as well as to develop a possible metallogenic model, by revealing information regarding the mineralization paragenetic relationship, fluid inclusions, H–O–C–S–Pb isotopes, and sphalerite Rb–Sr and zircon U–Pb ages. Three successive mineralization stages were recognized: stage I quartz-arsenopyrite-pyrite, stage II quartz-sphalerite-galena, and stage III fluorite-calcite-pyrite. Four types of fluid inclusions were also identified in host minerals: CH4-rich two-phase, halite-bearing, vapor-rich two-phase, and liquid-rich two-phase. Fluid inclusion and microthermometric results showed that the homogenization temperatures were 287–341 °C for stage I, 237–291 °C for stage II, and 162–230 °C for stage III, with respective salinities of 1.7–40.2 wt%, 6.7–10.9 wt%, and 4.2–8.8 wt% NaCl equivalent. The δ18Ofluid and δDfluid values of quartz in stage I (δ18Ofluid = 8.6–10.3 ‰, δDfluid = -126.6 to −124.3 ‰) indicated that initial magmatic water interacted with organic strata, while decreasing the values of quartz in stage II (δ18Ofluid = 3.9–6.8 ‰, δDfluid = -129.1 to −127.6 ‰) and calcite in stage III (δ18Ofluid = -3.5 to −1.0 ‰, δDfluid = -115.5 to −113.4 ‰), showing a trend of dilution and cooling by meteoric water. The negative δCfluid values (δCfluid = -15.9 to −12.6 ‰) of quartz fluid inclusions from stages I and II emphasize that organic carbon was added to the hydrothermal system through water–rock interactions. The δ34S values (δ34Ssulfides = 1.2–7.5 ‰) and lead isotope data of sulfides (206Pb/204Pb = 18.153–18.684, 207Pb/204Pb = 15.370–15.750, 208Pb/204Pb = 37.653–39.301), coupled with those of the hidden biotite granite and Devonian strata, indicate that the ore-forming material was primarily derived from magma and wall rocks. The sphalerite samples produced a Rb–Sr isochron age of 154.1 ± 3.5 Ma (2σ, MSWD = 0.82, n = 8), which was like the zircon U–Pb age of biotite granite (156.3 ± 1.4 Ma, 2σ, MSWD = 0.89, n = 14). Combining the alteration pattern, fluid inclusions, and isotopic and geochronological studies, it was concluded that Aerhada is a magma-related hydrothermal Pb–Zn deposit formed under the post-collision extension setting following the Mongol–Okhotsk Ocean closure during the Late Jurassic period. The proposed metallogenic model is expected to assist in the exploration and development of polymetallic mineralization in the Great Xing’an Range.

Fluid Regime of Crystallization of the Calcite–Quartz Carbonatitoids of the Murun Massif

Abstract —Primary melt and fluid inclusions in quartz and dalyite of calcite–quartz carbonatitoids of the Murun massif have been studied. They contain CO2, N2, CH4, C2H6, C3H8, H2, and H2S as well as sulfates and hydrocarbonates as solid daughter phases. The inclusion solutions contain HS- and chlorides. In addition, disordered carbon and bitumen are present. It is concluded that the magmatic fluid phase that was in equilibrium with quartz was characterized by a predominantly H2O–CO2–H2S composition and a reduced state. This explains the appearance of sulfides at the magmatic stage of crystallization of calcite–quartz carbonatitoids of the Murun massif. We substantiate the hypothesis that the sulfates, hydrocarbons, and H2 detected in the inclusions form at decreasing temperature as a result of shift of the redox equilibrium.

Multiphase-solid fluid inclusions in HP-LT eclogite facies rock (Zavkhan Terrane, Western Mongolia): evidence for the evolution from saline to hypersaline fluids during metamorphism in subduction zone

Fluid inclusions in high- and ultrahigh-pressure metamorphic rocks provide direct information on the composition of the fluids that evolved during metamorphism and fluid-rock interactions in deep subduction zones. We investigate the fluid inclusions in the Khungui eclogite of the Zavkhan Terrane, Central Asian Orogenic Belt. Fluid inclusions are observed in garnet and quartz in the eclogite samples that underwent metamorphism during subduction. The primary fluid inclusions in quartz are composed of liquid and vapor with high salinities (15.7–16.4 wt.% NaCl eq.), whereas the secondary fluid inclusions in quartz are classified as: relatively high salinity (Type I:12.5–16.3 wt.% NaCl eq.) and low salinity (Type II:6.7–10.6 wt.% NaCl eq.). The garnet shows compositional zoning from Ca-poor cores to Ca-rich rims, and the rims that grew during the eclogite-stage metamorphism (2.1–2.2 GPa at 580–610 °C) preferentially contain numerous primary fluid inclusions. The primary fluid inclusions in garnet are commonly bi-phases (liquid and vapor); however, some are multiphase-solid fluid inclusions composed of fluids (liquid and vapor) and combinations of several minerals (halite, quartz, apatite, calcite, biotite, chlorite, and actinolite). Bi-phase fluid inclusions preferentially occur in the inner parts of the Ca-rich garnet rim, whereas multiphase-solid fluid inclusions occur along the margins of the Ca-rich rim. We hypothesize that the multiphase-solid fluid inclusions are formed via interactions between trapped fluids, trapped minerals, and the host garnet during exhumation. By combination of FIB–SEM and synchrotron X-ray CT analyses, the detailed occurrences, volumes, and compositions of the solid phases in the fluid inclusion was analyzed. We then conduct mass balance analysis to reconstruct accurate fluid compositions using data from the FIB–SEM and synchrotron X-ray CT images of the multiphase-solid fluid inclusion. The results of these analyses reveal that (1) fluid changed from an H2O-dominated saline fluid (13–16 wt. % NaCl eq.) at the prograde to the earlier eclogite stage to H2O–CO2-dominated hypersaline fluid at later eclogite stage (~ 32 wt. % NaCl eq., 7.3 wt. % CO2 and ~ 19 molal dissolved cations); (2) a variety of mineral assemblages in multiphase-solid fluid inclusions are produced by post-entrapment reactions between the trapped hypersaline fluid, trapped minerals and the fluid host mineral. The evolution of fluids from saline to hypersaline during the eclogite facies stage is probably caused by the formation of hydrous minerals (i.e., barroisite) under a near-closed system.

Sulfide Mineralization of Carbonate–Silicate Veins in Early Proterozoic Metabasites of North Karelia: Mineral Assemblages, Mineral Forms of Silver, and Fluid Inclusions

The work presents the first data on sulfide mineralization in carbonate–silicate veins, which are widespread on the islands and coast of the White Sea (North Karelia), associating with Early Proterozoic metamorphosed gabbroid bodies. The veins with Fe–Cu sulfide mineralization up to ore occurrences are localized within metabasite bodies and along their contacts with host gneisses. During the study of the mineral composition of the veins, the main assemblages of sulfide minerals were identified: chalcopyrite –bornite ± chlorite ± selenides and Pb–Ag tellurides (B1); digenite–bornite ± selenides and Pb, Ag, and Pd tellurides (B2); pyrite–bornite ± chalcopyrite (B3); marcasite–pyrite–bornite–chalcopyrite (B4); and siegenite–chalcopyrite ± acanthite ± chlorargyrite. The development of sulfide associations, as well as quartz–chlorite aggregates, was related to the late stage of vein formation. Inductively coupled plasma and laser ablation mass spectrometry analyses showed that bornite from association B1 has the highest silver content (up to 675 ppm) and, in terms of Ag, Se, and Bi contents, is closest to bornite from low-temperature epithermal, skarn, and high-temperature vein deposits. In general, bornite is the main Ag carrier in the studied associations, while digenite containing up to 1000 ppm Ag, as well as discrete silver minerals (selenides, tellurides, acanthite, and chlorargyrite), occur in subordinate quantities. Fluid inclusions in quartz from sulfide associations, as well as from a sulfide-free carbonate–silicate vein, were studied by cryo- and thermometric methods. It is established that mineralization at the late stages of vein formation was related to heterogeneous CO2–H2O–NaCl metamorphic fluid. Carbon dioxide fluid inclusions were captured by vein quartz at temperature of 253–314°C and pressure of 2 ± 1 kbar. Water–salt inclusions were captured in a wider temperature range of 100–500°С. The highest temperature fluid inclusions with temperatures of homogenization 300°С are characteristic of quartz veinlets of the siegenite–chalcopyrite association with Ag sulfide and chlorargyrite.

Geology, fluid inclusions and C−O−S−Pb isotopic compositions of the Chahmileh Pb-Zn deposit, Central Iran: Implications for ore genesis

AbstractThe Chahmileh Pb–Zn deposit, located northwest of the Central Iran Zone, is a sediment-hosted Pb–Zn deposit in the ‘Yazd-Anarak Metallogenic Belt’. It is hosted in Middle Triassic carbonate rocks and is mainly controlled by NW-trending faults. The main ore minerals are galena and sphalerite with minor chalcopyrite, pyrite, and quartz, dolomite, along with minor calcite and baryte as gangue minerals. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the main non-sulphide ore minerals. The main styles of mineralization are vein-veinlet, breccia, disseminated and replacement in association with silicification and dolomitization. Microthermometry of fluid inclusions in dolomite and quartz indicates that the ore precipitated from a warm to hot basin-derived saline fluid. Dolomite samples have δ13CVPDB and δ18OVSMOW values of −0.99 to +1.99‰ and +20.74 to +25.48‰, respectively, and are plotted in the marine carbonate rocks field. These isotopic values suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rock. The δ34S values range from +6.3 to +8.2‰ for galena, +5.9 to +6.2‰ for sphalerite, +1.4 to +3.4‰ for chalcopyrite and +15.0 to +17.4‰ for bayite are compatible with a predominant thermochemical sulphate reduction process, and with sulphur sourced from Triassic seawater. Galena samples have a homogeneous Pb isotopic composition that is indicative of a continental crustal reservoir as the main source of lead and probably for the other ore metals. Based on geology, mineralogy, texture and fluid characteristics, the Chahmileh deposit is classified as a carbonate-hosted Mississippi Valley-type deposit.

The evolution of the majiang paleoreservoir, west margin of xuefeng uplift: Insights from in situ calcite U–Pb dating and bitumen and shale trace element analysis

The Majiang Reservoir, situated within the Yangtze Block, is the largest paleoreservoir in the region. Employing a comprehensive methodology involving the analysis of trace and rare earth elements in bitumen and shale, in situ U–Pb dating of hydrocarbon-associated calcite, and incorporating previously published data on oil-source correlation and significant stages of reservoir development, we successfully reconstructed the complete evolution of the Majiang Reservoir quantitatively. The bitumen trace elements data show the ratio of V/(V + Ni) ranging from 0.64 to 0.82, Ni/Co exceeding 7.0 and Zr/Cr below 1.0. PAAS-normalized rare earth element distribution patterns of both bitumen and Cambrian shales present zig-zags distributions. In addition, biomarker distribution acquired by catalytic hydropyrolysis and bulk δ13C values of both bitumen and Cambrian shales (−29.1‰ to −34.7‰ vs −30.2‰ to −32.3‰) also show similarity. All the geochemical parameters together indicate that the primary source of bitumen stems from Early Cambrian shales. Integrating fluid inclusion analysis, specifically examining two Th groups with temperatures of 97.2 °C and 142.6 °C, and U–Pb dating on hydrocarbon-bearing calcite (∼300 Ma), referencing prior Re–Os dates on bitumen (∼430 Ma) and pyrobitumen (∼80 Ma) and quartz fluid inclusion Ar–Ar dating (∼225 Ma), we successfully reconstructed the entire hydrocarbon evolution. The findings reveal that initial oil generation occurred during the Caledonian event, followed by secondary continuous oil and gas generation and migration, influenced by the Indosinian event. The combination of fluid inclusion analysis and isotopic geochronology data exemplifies immense potential in precisely determining the progression of petroleum evolution.

The use of equations of state of pure components in pore fluid and fluid inclusion research: Computer program Pures (software package FLUIDS)

Fluid inclusions and pore fluids seldomly contain pure fluids, i.e. single component, and the properties of these natural fluids must be investigated with complex equations of state for fluid mixtures. However, the properties of nearly-pure fluids can be modelled with equations of state for pure gas components, including an insignificant error. Occasionally, fluid inclusions are observed that can be modelled according to these considerations. The program “Pures” has been developed to calculate properties of pure gases: H2O, CO2, CH4, N2, C2H6, O2, NH3, CO, H2, D2O, Ar, C3H8, SO2, H2S, and He. These fluid components belong to the most abundant volatile species that are observed in fluid inclusions in quartz and other host minerals in rock. The thermodynamic properties of these fluids are calculated with highly accurate Helmholtz energy functions that cover both the liquid and vapour. Viscosity and surface tension are calculated with additional purely- and semi-empirical equations. Stand-alone applications can be operated in Macintosh-, Windows-, and Linux-based operated computer systems, and contain algorithms that are designed with BASIC language within the XOJO programming environment. A series of twelve self-instructive interfaces (modules) are leading the user through the complex calculation procedures. The modules include the calculation of pressure, temperature, molar volume, isochores, isotherms, fugacity, homogenization conditions, liquid-vapour equilibria, thermodynamic state properties, viscosity, and surface tension. Fluid densities in quartz-confined inclusions can be corrected for temperature- and pressure-dependent volume changes of the host crystal. Fluid modelling in the program “Pures” is not restricted to fluid inclusion research, and can also be applied to other research fields that involve a fluid phase. “Pures” is included in the software package FLUIDS.

Conditions of Formation of Epithermal Mineralization of the Kyplatap Volcanic Field (Central Chukotka)

The article considers the geochemical features and conditions of the formation of substantially silver mineralization of the Kyplatap volcanic field (KVF), of the Chaunsky zone, of the Central Chukchi Sector, of the Okhotsk-Chukchi volcanic belt (OChVB). New data on the composition, distribution and grade of trace elements, including REE in ores, are presented. The noticeable enrichment REE of the studied samples, the predominance of light lanthanides over heavy ones, very low Eu/Sm ratios (\( \ll {\kern 1pt} 1\)), weakly inclined near–chondrite spectra with obvious Eu minima are typical for the epithermal ore-forming system of the KVF. The Ce/Ce* vary from slightly negative to moderately positive values (from 0.81 to 1.38), and the Eu/Eu* vary from 0.28 to 0.7. This combination of Ce/Ce* and Eu/Eu* indicates the oxidative conditions prevailing during ore formation. The results of thermo- and cryometric studies of fluid inclusions in quartz allowed us to establish that the ore-forming fluid contained Na, Mg and K chlorides, epithermal mineralization was deposited by homogeneous hydrothermal fluids with salt concentrations (0.3–6.2 wt. %-eq. NaCl), fluid density – 0.60–0.87 g/cm3, at temperatures from 203 to 343°C, water vapor pressure varied from 40 to 140 bar. The obtained geochemical and thermometric data confirm the assumption put forward earlier – that the studied mineralization of KVF belongs to the intermediate sulfidation epithermal class. These data point to andesite magmas and meteoric waters as the most likely sources of fluids. The information in the article is of practical importance for regional predictive metallogenic constructions, prospecting and evaluation of epithermal Au–Ag deposits.

Formation of barite in the Ab Torsh deposit, Kerman province, Iran: Insights from rare earth elements, O and S isotopes, and fluid inclusions

Barite can form in a variety of geological environments, as it occurs in a wide range of mineral deposits. To determine the origin and physicochemical conditions under which the Ab Torsh barite deposit formed, an extensive study was conducted using petrographic, Rare Earth Element (REE) geochemical, O and S isotopic, and fluid inclusion methods. Barite mineralization occurs at Ab Torsh as a stratabound vein in the Senonian carbonate rock units. Barite-quartz is accompanied by subordinate malachite, chrysocolla, Fe-Mn oxide-hydroxides, galena, azurite, fluorite, pyrite, and bornite. The ∑REE values are very low in barite (5.32–14.56 ppm), with chondrite-normalized patterns showing enrichment of Light Rare Earth Elements (LREE) relative to Heavy Rare Earth Elements (HREE). The low ∑REE content and REE element ratios (Ce/La, (La/La*)N, and (Gd/Gd*)N) indicate that seawater with a highly altered geochemical signature (connate water) acted as a Ba ore-forming fluid. The δ18O and δ34S values in barite (+10.4–+11.1 ‰ and +27.3–+27.8 ‰, respectively) and the δ34S values in galena (+6.3 and + 7.9 ‰) indicate that the sulfate (and thus sulfur) originated from sulfate-bearing connate waters and/or evaporites. Thermochemical Sulfate Reduction (TSR) was the most likely mechanism for the formation of the reduced sulfur in galena. The salinity and homogenization temperatures in the aqueous fluid inclusions of barite and quartz (2.7–19.3 wt% NaCl equivalent and 110–275 °C, respectively) indicate that basinal fluids containing a meteoric water component were the source of the mineralizing solutions. The fluid inclusion data demonstrate that two fluid mixing have occurred: one between the hot basinal brines and cold meteoric waters, and another between heated and cold meteoric waters. It is estimated that the hot fluids derived from a maximum depth of about 9 km. The Ab Torsh deposit is classified here as a structure (unconformity)-related barite deposit. It is concluded that intense faulting and brecciation of the host rocks caused by post-Cretaceous compressional tectonics probably provided the channels necessary for the upward migration of deep mineralizing fluids from a basinal brine source. Barite formed where these ascending hot, Ba-bearing hydrothermal fluids encountered cooler, sulfate-bearing connate waters trapped in the overlying Senonian strata and/or the descending cold meteoric waters that dissolved evaporite-bearing rock units.

Geology, fluid inclusions, and isotope signatures reveal hydrothermal evolution and genesis of the Aqishan Pb-Zn deposit in Eastern Tianshan and implications for exploration of skarn mineralization

The Aqishan deposit (1.97 Mt at 1.05 % Pb + Zn) is located in the Aqishan-Yamansu arc, on the southwest section of the Eastern Tianshan, Northwest China. Pb-Zn mineralization is mainly hosted by garnet skarn and the volcaniclastic rocks of the Yamansu Formation. To decipher the evolution of ore fluids and source(s) of ore-forming components, and constrain the ore genesis, a combination of geological work, fluid inclusions, and C-O-S-Pb isotope systematics is presented. Detailed field and microscopic observations reveal that the skarn alteration and ore formation at Aqishan could be divided into four hydrothermal stages, consisting of prograde skarn (I), retrograde skarn (II), quartz–sulfides (III), and carbonate stage (IV). Sphalerite and galena are the dominant ore minerals generally occurring as disseminations and veins with locally laminated ores in stage III. Fluid inclusion data show that the fluids responsible for prograde skarn are high-temperature (342–518 °C) and high-salinity (7.3–44.2 wt% NaCl equiv.), and recorded fluid phase separation from an intermediate-salinity supercritical fluid, which was exsolved from crystallizing granitic magma. Microthermobarometry results limit the retrograde alteration within the temperature range of 313 to 388 °C and trapping pressures of 98 to 241 bars (1.0–2.5 km), with pressure dropping from lithostatic to hydrostatic regimes associated with a phase separation event. The boiling fluid inclusions in ore stage quartz show that the Pb-Zn mineralization formed at 205–357 °C, with a decrease in temperature facilitating the precipitation of ore-forming metals from hydrothermal system. Carbon and oxygen isotope compositions of calcite indicate a predominantly magmatic source for ore fluids at Aqishan with later meteoric water involved. Bulk and in situ sulfur values of sulfides range from −6.4 to −0.7 ‰, consistent with a dominantly magmatic origin. Sulfides together with the granite porphyry and tuff, show relatively homogeneous Pb isotope compositions, indicating that abundant ore-forming metals were sourced from a magmatic reservoir with contribution from country rocks. Fluid inclusion study and available calcite C-O isotopes suggest that significant decrease in temperature and fluid-rock interactions remarkably contributed to the metal deposition at Aqishan. The skarn alteration with typical alteration assemblages of garnet–diopside is proposed as an effective mineral exploration target of skarn(–like) ores in Eastern Tianshan.

Fluid properties and ore-forming process of the giant Jiajika pegmatite Li deposit, western China

The world class Jiajika lithium deposit in the Songpan-Ganze orogenic belt, western China is related to Late Mesozoic S-type granitic pegmatite. More than 500 pegmatite veins have been discovered in the Jiajika deposit and they show well defined zonal mineral pattern, including microcline pegmatite zone (Ⅰ), microcline-albite pegmatite zone (Ⅱ), albite pegmatite zone (III), albite-spodumene pegmatite zone (IV), and albite-lepidolite pegmatite zone (Ⅴ) from the center outward. Pegmatite Li orebodies are primarily hosted in zones III, IV and V. Barren samples of zones I and II were collected from the recent Jiajika Scientific Drilling (JSD) project performed in the years of 2020–2021 and ore samples of zones III, IV and V were collected from outcrop pegmatite veins No. 308, No. 134, and No. 528, respectively. Fluid inclusions in quartz from the Jiajika deposit include intermediate density CO2-bearing inclusions (type A), high density aqueous inclusions (type B), and low density CO2-rich inclusions (type C). Type A inclusions are predominant in zones I and II, whereas coexisting type B and C inclusions are prevailing in zones III, IV and V. Fluid inclusion microthermometry indicates that type A inclusions in zones I and II show homogenization temperatures ranging from 328 to 362 °C and salinities from 1.2 to 4.5 wt%. Type B inclusions and coexisting type C inclusions in the zones III, IV and V show homogenization temperatures of 278 to 336 °C and 301 to 358 °C, respectively. Their salinity values are 8.1 to 11.6 wt% and 0.8 to 3.6 wt%, respectively. The estimated pressures of type A inclusions are 310 to 424 Mpa, and those of immiscible type B and C inclusions are 151 to 239 Mpa. The change of fluid types with decreasing pressure indicates that extensive fluid immiscibility occurred during the formation of Li pegmatite veins in zones III, IV and V. Moreover, the LA-ICP-MS microanalysis demonstrates that chemical composition of fluid inclusions in this deposit is relatively simple, mainly containing Li, Na, K, Rb, Cs, B, and As. Such enrichment of alkaline elements (Li, Na, K, Rb and Cs) and volatile elements (B and As) is a typical geochemical index for lithium pegmatite. We suggest that the high-degree fractionated of parent magma and strong fluid immiscibility promoted the formation of the giant Jiajika Li deposit. This study highlights that immiscible fluid inclusions and strong enrichment of alkaline elements in inclusions can be an excellent tool for explorations of lithium pegmatites like Jiajika.

Fluid inclusions, H-O-S-Pb isotopes, and Rb-Sr geochronology of the Augaro gold deposit, West Eritrea, NE Africa: Implications for ore genesis

Northeast Africa is an emerging world-class gold province due to the numerous lode gold deposits with Au resources of over 43 Moz discovered in the Nubian Shield. The Augaro gold deposit, located in the Adobha-Augaro Cu-Au belt of west Eritrea, is composed of several auriferous quartz veins. The orientations of the auriferous quartz veins in this deposit are strictly controlled by NE-trending shear zones and nearly E-trending fractures. The most common metallic mineral is pyrite, and gold has been identified as native gold, electrum, and calaverite. Fluid inclusion study, H-O-S-Pb isotope analysis, and Rb-Sr dating were carried out in the Augaro gold deposit. A petrographic investigation revealed that fluid inclusions of type W (Liquid-rich aqueous), type C (CO2-rich), and type S (halite-bearing) are prevalent in auriferous quartz veins. The H2O, NaCl, and CO2 are the main components of the metallogenic fluids, which are medium-low temperatures (150–360 °C) and medium to low salinities (<34 wt% NaCl eqv.). The physicochemical features of fluid inclusions indicate that magmatic fluids experienced phase separation earlier in their evolution and mixed with meteoric water subsequently. Rb-Sr dating of fluid inclusions in auriferous quartz suggests that the Augaro gold deposit formed during the post-orogenic stage (543 ± 14 Ma) of East African orogeny in the Late Neoproterozoic, which is a new metallogenic epoch for the lode gold deposits in Nubian Shield. Geological and Geochemical features refer to the Augaro gold deposit being an intrusion-related gold deposit (IRGD).

Genesis of the Kuh-Panj porphyry copper deposit, Kerman, Iran: Constraints from mineralization, geochemistry, fluid inclusion, and zircon U[sbnd]Pb isotope systematics

The Miocene Kuh-Panj porphyry copper deposit, with reserve estimated at about 100 Mt. at 0.21 % Cu, is located 120 km SW of Kerman in the southern part of the Urumieh-Dokhtar magmatic arc. The Eocene host rocks consist of tuff, lithic tuff, breccia tuff, and lava flows, ranging in composition from rhyodacite to andesite. A late Miocene granodiorite porphyry stock (8.57 ± 0.49 Ma, U/Pb zircon) intruded into the Eocene sequence. Subvolcanic dykes cut the Eocene rocks and porphyry stock. The Kuh-Panj porphyry system has an extensive and typical hydrothermal alteration zoning pattern, which is comprised of potassic, phyllic, argillic, and propylitic alteration types from inner proximal to outer distal zones. Copper mineralization occurs in potassic and to some extent in phyllic zones. Mineralization is mostly observed as disseminated, stockwork, and vein-veinlets forms in the porphyry stock. Vein paragenesis includes barren quartz, M-type (magnetite+biotite), A1-type (quartz+magnetite+chalcopyrite±chlorite±biotite), A2-type (quartz+chalcopyrite±pyrite), D-type (quartz+pyrite±chalcopyrite), and L-type (galena+sphalerite±chalcopyrite±pyrite) veins. The I-type granitoids with calc-alkaline affinity have enrichments of LILE (Pb, K, U, Sr, and Cs), depletion of HFSE (P, Nb, Ta, Zr, and Ti), and enrichment in LREE displaying geochemical similarity to arc-related magmatic rocks. The high SiO2 (ave. 68.9 wt%), high Al2O3 (ave. 14.5 wt%), low MgO (ave. 1.3 wt%), low P2O5 (< 0.2 wt%), high Sr (ave. 365 ppm), high Sr/Y (ave. 45), relatively high LaN/YbN (ave. 28), relatively high Th (ave. 8 ppm), low Y (ave. 8 ppm), and low Yb (0.5 ppm) contents are similar to those of fertile porphyries and lower crust-derived adakites. The most dominant type of fluid inclusions in quartz from mineralized veins are liquid-vapor-halite-solid (LVHS), liquid-vapor-halite (LVH), liquid-vapor (LV), and vapor-liquid (VL) fluids. Homogenization temperatures of LVHS, LVH, LV, and VL fluids range from 306 to 574 °C, 141–566 °C, 215–422°, and 349–571 °C, respectively. Salinities of LVHS, LVH, LV, and VL fluid inclusions range from 30 to 69, 29.0–65.5, 0.35–22.0, and 0.7–13.0 wt% NaCl eq., respectively. The extreme variations in salinities of fluid inclusions represent the combined effects of varying salinity of the magmatic fluid, aqueous fluid-phase immiscibility (boiling), and mixing with lower salinity meteoric water later in the cooling history of the porphyry system. Normal cooling, water-rock interaction, surface fluid dilution, and boiling are dominant factors that control both the distribution and abundance of mineralization. Zircon from the Kuh-Panj system has high Th/U (0.53 to 0.83), low Dy/Yb (<0.3) ratios, positive Eu/Eu* (1.28–1.85), strong positive Ce/Ce* (1.36 to 197) reflecting high Ce4+/Ce3+ ratios, and enrichment in HREEs relative to LREEs, which indicate the magmatic origin of zircon, oxidized, and hydrous conditions of the primary magma. This magma with adakitic affinities is favorable for producing fertile porphyry systems. Based on these multidisciplinary studies, the Kuh-Panj deposit is classified as a continental arc-related porphyry copper system hosted predominantly at the transition zone between potassic and phyllic alteration zones due to decreasing temperature, boiling, and fluid-rock reaction that all enhance CuFe sulfide saturation.

Controls on metal fertility of dioritic intrusions in the Laiwu district, North China Craton: Insights from whole-rock geochemistry and mineral compositions

Several large high-grade iron skarn deposits in the Laiwu district of Shandong Province (North China Craton) are developed along the contact zone between the Early Cretaceous Kuangshan diorite pluton and Middle Ordovician dolomitic limestone. In sharp contrast, no iron skarn mineralization has been recognized in association with other contemporaneous dioritic intrusions (Jiaoyu, Jinniushan, Tietonggou) in this district. The reason for this contrast remains elusive. Here we present a comparative study of the ore-related Kuangshan pluton and its barren equivalents using whole-rock and mineral (zircon, apatite) geochemistry combined with existing Sr-Nd isotope data to provide new insights into the critical controls on iron skarn mineralization and shed light on future mineral exploration. Geochemical and Sr-Nd isotope data suggest that both the ore-related and barren intrusions were derived from a common enriched lithospheric mantle source following variable degrees of fractional crystallization and crustal assimilation. Modeling based on whole-rock Sr-Nd isotopes implies that the magmas responsible for the Kuangshan and Jinniushan diorite plutons assimilated significant quantities of the Ordovician evaporite-bearing carbonates. Both the fertile and barren diorites show high whole-rock Sr/Y ratios, high zircon Eu/Eu* and Eu/Eu*/Y ratios, and low zircon Dy/Yb ratios. These data, combined with high magmatic water contents (4.4−8.0 wt%) calculated from amphibole compositions, indicate that those four plutons crystallized from hydrous magmas. High whole-rock Fe2O3/FeO, and high ΔFMQ values (mostly &amp;gt;1; fayalite-magnetite-quartz oxygen buffers) estimated from zircon, apatite, and amphibole suggest that the magmas from which the diorite intrusions crystallized were all oxidized. Using available partitioning coefficients for Cl between apatite and magma, the parental melts of the Kuangshan and Jinniushan diorite are estimated to have had higher Cl contents (0.15−0.77 wt%) than the Jiaoyu and Tietonggou diorites (0.06−0.34 wt%). Two types of apatite from the intrusions studied are recognized based on their paragenetic relations: Type 1 apatite (Ap1) is an early-formed phase enclosed in euhedral amphibole, plagioclase, and biotite, whereas type 2 (Ap2) is a late-formed variety hosted in, or intergrown with, anhedral K-feldspar (± anhedral amphibole ± subhedral to anhedral quartz). In the fertile Kuangshan diorite, Cl and OH contents of apatite decrease, but Sr contents increase from Ap1 to Ap2. However, those parameters show reverse trends or remain constant from Ap1 to Ap2 in barren diorites. Such distinctive apatite geochemical signatures are best interpreted as reflecting more efficient fluid exsolution from the parental magma of the Kuangshan diorite than from the barren intrusions. This view is supported by the presence of abundant fluid inclusions in apatite and quartz exclusively from the mineralized intrusion, indicating its crystallization from volatile oversaturated melts. The results presented here indicate that elevated magma Cl contents and efficient separation of magmatic hydrothermal fluid from cooling magmas have been the critical factors controlling iron skarn mineralization in the Laiwu district. Mass balance constraints on Cl budget indicate that a minimum of 44−60 km3 of magma was required to form the Fe deposits associated with the Kuangshan pluton. Our preliminary results suggest that decreasing OH and Cl contents from early to late apatite in intermediate rocks can be used as an indicator for efficient fluid exsolution and consequently metal fertility of those rocks.

Fluid evolution and metallogenesis of the Zhangjiapingzi gold deposit in mianning, Sichuan province: constraints from fluid inclusion studies

Introduction: The Zhangjiapingzi gold deposit, located at the western margin of the Yangtze Craton and controlled by the Jinhe-Chenghai deep fault, is a newly discovered super-large gold deposit in the Danba-Mianning metallogenic belt. The gold ore bodies are hosted in the Middle Triassic (T2) altered dolomite (Dm), and have two types of mineralization: altered rock type and quartz vein type. Previous studies on this deposit are rare, especially on the ore-fluid characteristics, which limit the understanding on the ore genesis.Methods: This study focused on fluid inclusions in quartz from altered rocks, and used microthermometry and laser Raman spectroscopy to investigate the properties and sources of ore-forming fluids, and to determine the ore genetic type.Results and discussion: The results show that the fluid inclusions are mainly CO2-H2O-NaCl inclusions, with medium temperature (220–300°C), low salinity (&amp;lt;10%), medium-low density (0.79–1.01 g/cm3) and high contents of CO2 and CH4, resembling typical orogenic gold ore fluids. We suggest that the Zhangjiapingzi is best classified as orogenic type, and our findings provide new insights into the fluid origin and metallogenesis of orogenic gold deposits in the Danba-Mianning metallogenic belt.

Sb-As LOJAN DEPOSIT (REPUBLIC OF NORTH MACEDONIA): ORE TYPES, CONDITIONS OF ORE TYPES LOCALIZATION AND GEOCHEMICAL FEATURES

This article discusses the results of comprehensive studies of Sb-As ores of the Lojan deposit, located in the north-east of the Republic of North Macedonia (RSM), near the border with Serbia. 5 types of Sb-As ores have been identified: breccated realgar-auripigment ores, realgar breccias, breccated antimonite ores, massive, almost monomineral realgar ores, as well as realgar-antimonite nest-shaped ores. The ores are characterized not only by an unusual paragenesis of nickel, arsenic and antimony minerals, but also by a very close fusion of antimonite, realgar and collomorphic quartz. A wide range of elements in ores (As, Sb, Cr, Ti, Mn, Ni, Mo, Co, Ag, Tl, U, etc.) is apparently due to the combination of mineralization in ores of several different-time parageneses. As a result of thermometric studies of fluid inclusions in quartz, Thom vary from 180 OC to 220 OC (the average value is 201 OC). Studies of the isotopic composition of sulfur in antimonite and realgar have shown rather narrow ranges of δ34S values from -5.19 to -0.26 and from -4.80 to 1.92, respectively, which indicates an endogenous source of sulfur. The results obtained allow us to attribute the Lojan deposit to the epithermal class

Условия образования кварцевожильной минерализации Кыввожского золотороссыпного поля на Среднем Тимане (по данным изучения флюидных включений)

We present a novel study of fluid inclusions in the vein quartz of the Kyvvozh gold placer field and in the quartz of gold-quartz intergrowths from the placer (methods of homogenization, cryometry, and Raman spectroscopy were used). We determined that in vein quartz the homogenization temperature of fluid inclusions fluctuated in the range of 220–425 °C, the liquid phase was represented by aqueous solutions, predominantly sodium and magnesium chloride. The homogenization temperature of fluid inclusions in quartz of gold–quartz intergrowths is 220–330 °C, and an aqueous solution of sodium chloride predominates in the liquid phase. Mineral formation proceeded in two stages: at the first stage, the fluid was enriched with nitrogen, at the second stage — with carbon dioxide.

Fluid evolution and genesis of the Sankuanggou Fe[sbnd]Cu skarn deposit, Duobaoshan ore field, Northeast China: Evidence from fluid inclusions and H-O-S-Pb isotopes

The Sankuanggou FeCu skarn deposit is located in the Duobaoshan ore field in the northern Great Xing'an Range, Notheast China. The ore bodies occurred in the skarn of the contact zone between the Yanshanian granodiorite and the middle Ordovician Duobaoshan Formation marble. According to the field investigations and mineral crosscutting relationships, five paragenetic stages were identified: the anhydrous skarn (Stage I); hydrous skarn (Stage II); chalcopyrite-pyrite-quartz-molybdenite (Stage III); sphalerite-quartz stage (Stage IV) and quartz-calcite (Stage V). In the Stage I and II, the assemblage of fluid inclusions (FIs) in quartz is characterized by the development of daughter mineral-bearing three-phase FIs (S-type), vapor-rich two-phase aqueous FIs (LV-type) and liquid-rich two-phase aqueous FIs (VL-type). VL- and LV-type FIs were found in the Stage III quartz, whereas only VL-type FIs were present in the Stage IV quartz and Stage V calcite. The homogeneous temperatures of the FIs in Stages I to V were 364–495, 295–405, 243–360 and 135–207 °C, respectively, with salinities of 4.16–58.42, 4.17–47.99, 3.37–14.2, 1.03–11.11 and 3.53–8.4 wt% NaCl eqv., respectively. In general, the ore-forming fluids changed from high-temperature NaCl-H2O system fluids, that contained negligible amounts of CO2 and CH4 and exhibited obvious boiling, to a medium- to low-temperature and low-salinity NaCl–H2O system with fluid mixing. According to the HO isotopic analysis of Stages I and II (δ18OH2O = 0.3–6.3 ‰, δ18D = −112.6 to −79.9 ‰), the ore-forming fluid was identified as magmatic fluid. In contrast, the δ18OH2O and δ18D values in Stages III and IV gradually decreased (δ18OH2O = −9.6 to −2.3 ‰, δ18D = −133.1 to −118.9 ‰), implying a gradual meteoric water input into the fluid. The S isotopic analysis (δ34S range from −4 to −0.8 ‰) revealed that S mainly originates from the magma during the mineralization process. Further, the Pb isotopic (208Pb/204Pb = 37.64–38.725, 207Pb/204Pb = 15.45–15.606 and 206Pb/204Pb = 18.115 to 19.786) investigations indicated that the ore-forming materials of this deposit are derived from the crust-mantle mixing. Based on the previously reported geochronologic and geodynamic data, we can conclude that the Sankuanggou deposit is a typical FeCu skarn deposit and formed during the Early Jurassic Paleo-Pacific Plate subduction.

Molecular mechanism of metamorphic alteration on traces of early life in banded iron formations

It is well-known that multi-stage metamorphism can result in the alteration of indigenous biological molecules, limiting our understanding of early life on Earth. However, the physiochemical mechanisms involved in these processes are still poorly understood. In this study, we present petrographic observations and micro- to nano-geochemical investigations on the carbonaceous matter (CM) in representative Neoarchean banded iron formations (BIFs) from North China, which have undergone significant alteration during lower amphibolite-facies prograde metamorphism, and subsequent retrograde alteration. The CM is in paragenetic equilibrium with prograde mineral phases, and is often associated with apatite that occurs in Fe-rich bands parallel to layering. This implies that the CM is most likely inherited from syn-depositional biomass, as confirmed by the nanoscale infrared spectroscopy, which shows the presence of CC, CH, and CN/NH bonds. Raman spectroscopic analyses reveal that the maximum metamorphic temperature of CM is 479 ± 50°C, which is consistent with the metamorphic peak conditions of the host BIFs from petrographic constraints (i.e., garnet-bearing amphibolite-face metamorphism). The BIFs possess average bulk δ13Corg values of −20.0 ± 0.9‰ (1σ) and δ13Ccarb values of −12.9 ± 1.8‰ (1σ), further indicating syngenetic biomass graphitization during prograde metamorphism. This thermal cracking process may have released gaseous hydrocarbons, as shown by secondary CH4 fluid inclusions in quartz. We further use quantum mechanical simulations to constrain dissociative tendencies for functional groups (CC, CH, CO, and CN) of original organic molecules to assess the stability of organic chemical bonds during prograde metamorphism (0–600°C, 0–15 kbar). The relatively high thermal durability of CH and the armoring effects of primary organic-phyllosilicate complexes may account for CH preservation in BIFs. Furthermore, the electron microscopy combined with elemental analysis reveals widespread nano-chlorite infiltration into CM during retrograde metamorphism (i.e., partial replacement of garnet by chlorite). The pervasive CM alteration is likely responsible for the absence of CO bonds, where nanopore-scale reactions might have played a key role. Altogether, we suggest that multi-stage metamorphic processes, involving mineral-organic reactions and nanoscale interface interactions, may have governed the preservation of ancient biosignatures in BIFs. Our findings highlight the importance of evaluating metamorphic effects when using molecular signals to reconstruct early life behaviors, and shed new light on the study of primordial microorganisms, particularly those found in iron-rich sediments on early Earth.