Fluid Inclusions In Quartz Research Articles

Generalized <i>Р—Т</i> path and fluid regime of exhumation of metapelites of the central zone of the Limpopo complex, south Africa

The P–T paths of exhumation of Precambrian granulite complexes at the craton boundaries usually include two stages: sub-isothermal decompression and a decompression–cooling stage with a more gentle P–T path. Our goal is to understand the possible causes of the change in the slope of the P–T path of exhumation of the Central Zone (CZ) of the Limpopo granulite complex (South Africa), located between the Kaapvaal and Zimbabwe cratons. For this purpose, rocks (mainly, metapelites) from various structural positions within the Central Zone, i.e. dome structures, regional crossfolds, local and regional shear-zones, were studied. Metapelites are gneisses of similar bulk composition. Relics of leucosomes composed of quartz-feldspar aggregates with garnet and biotite are variously manifested in rocks, and melanocratic areas enriched in cordierite usually mark micro-shear-zones that envelope and/or break garnet porphyroblasts. Study of polymineral (crystallized melt and fluid) inclusions in garnet, its zoning with respect to the major (Mg, Fe, Ca) and some trace (P, Cr, Sc) elements, fluid inclusions in quartz, as well as phase equilibria modeling (PERPLE_X) showed that rocks coexisted with granite melts and aqueous-carbonic-salt fluids (aH2O = 0.74–0.58) at the peak of metamorphism at 800–850°C and 10–11 kbar. Partial melting initiated sub-isothermal exhumation of rocks to 7.5–8 kbar during diapirism of granitic magmas in the Neoarchean (2.65–2.62 Ga). This is reflected in the specific zoning of garnet grains in terms of the grossular content. A change in the rheology of rocks as a result of partial removal and crystallization of the melt activated shear-zones during further exhumation to 6–5.5 kbar along the P–T decompression–cooling path of 95–100°/kbar, reflecting a slower uplift of rocks in the middle crust. This process was resumed due to thermal effects and interaction of rocks with aqueous fluids (aH2O 0.85) in the Paleoproterozoic (~2.01 Ga). Such a scenario of metamorphic evolution implies that the Limpopo granulite complex, in general, and its Central Zone, in particular, are the result of the evolution of an ultra-hot orogen, where vertical tectonic movements associated with diapirism were conjugate with horizontal tectonic processes caused by the convergence of continental blocks.

Amazarkan gold deposit: conditions of formation, sources of ore substance (Eastern Transbaikalia)

Relevance. The need to clarify the sources and conditions of formation of gold mineralisation of the Amarzakan gold deposit. The characteristic feature of the deposit is the spatial combination of gold mineralisation and small intrusions of the middle and basic composition of the Amudzhikan complex. Aim. Determination of physico-chemical conditions and nature of the source of the ore substance of the Amazarkan deposit. Methods. ICP-MS method and standard chemical analysis were used to determine the elemental composition of rocks. Sulfur isotope composition of sulfides was obtained using gas-source mass-spectrometry and fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and by FTIR spectroscopy at the Centre for Collective Use of Multi-element and Isotope Studies of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). The oxygen isotope composition was determined at the Geological Institute of the Siberian Branch of the Russian Academy of Sciences (Ulan-Ude) using the MIR 10-30 laser heating system with a 100-watt CO2 laser and a wavelength of 10.6 µm in the infrared region in the presence of BrF5 reagent. Results. The authors have established the spatial confinement of ore zones to Mesozoic dikes of the Amudzhikan complex (J2-3). The Eu/Sm and Eu/Eu* ratios in the dikes indicate fractionation of magmatic melts in the sources at the level of the lower continental crust and low degree of their differentiation. The character of REE distribution in the rocks of dikes of the Amudzhikan complex is similar to the distribution of REE in the ores of the deposit. Eu/Sm–Eu/Eu* figurative points of compositions of ore veins and granodiorites of the Amudzhikan complex form a single trend. Dykes of the Amuzhikan complex are characterized by increased Au content from 0.026 to 1.171 g/t. These data suggest a paragenetic link between Au mineralization and rocks of the Amudzhikan complex. Ore veins of productive stages of ore formation were formed at temperatures ranging from 125 to 410°C. The calculated S and O isotopic composition of the ore-forming fluid in equilibrium with pyrite and quartz, as well as the Co/Ni>1 ratio in the ores indicate the presence of a magmatic component in its composition.

The Sources of Ore-Forming Materials and Fluids for the Jinqingding Gold Deposit in the Mouping–Rushan Metallogenic Belt, Jiaodong Peninsula: Evidence from S-H-O Isotopes and Trace Elements in Pyrite

The Jinqingding gold deposit, characterized as an extra-large quartz-vein-type deposit, is located in the middle of the Mouping–Rushan metallogenic belt in the Jiaodong Peninsula, and there is still controversy over its sources of ore-forming materials and fluids. This paper divides the mineralization of Jinqinding gold deposits into four stages, based on a field geological investigation and indoor petrographic observations: (1) coarse-grained pyrite–quartz stage, (2) quartz–fine-grained pyrite stage, (3) quartz–polymetallic sulfide stage, and (4) quartz–carbonate stage. The quartz fluid inclusions showed δD values of −96.0 to −81.8‰ and δOV-SMOW values of 0.70 to 6.32‰, indicating that the ore-forming fluids were mainly magmatic water, with some metamorphic water and atmospheric precipitation. The in situ δ34S values in different subzones of the pyrites of the Jinqingding gold deposit range from 6.69 to 10.86‰. The δ34S value range of the Jinqingding gold deposit is basically consistent with the contemporaneous intermediate–basic dikes in the region, suggesting a shared material source. In situ LA-ICP-MS geochemical analyses of the pyrites show large variations of Co/Ni ratios (0.21 to 99.5), which suggest a hydrothermal origin for the gold deposit. We infer that the ore-forming fluid of the Jinqingding gold deposit originated from the magma from the upper mantle and the mantle–crust transition zone.

Gold Mineralization at the Syenite-Hosted Anwangshan Gold Deposit, Western Qinling Orogen, Central China

The Anwangshan gold deposit is located in the northwestern part of the Fengtai Basin, Western Qinling Orogen (WQO). The gold ore is hosted within quartz syenite and its contact zone. The U–Pb weighted mean age of the quartz syenite is 231 ± 1.8 Ma. It is characterized by high potassium (K2O = 10.13%, K2O/Na2O > 1) and high magnesium (Mg# = 55.31 to 72.78) content, enriched in large ion lithophile elements (Th, U, and Ba) and light rare earth elements (LREE), with a typical “TNT” (Ti, Nb, and Ta) deficiency. The geochemical features and Hf isotope compositions (εHf(t) = −6.68 to +2.25) suggest that the quartz syenite would form from partial melting of an enriched lithospheric mantle under an extensional setting. Three generations of gold mineralization have been identified, including the quartz–sericite–pyrite (Py1) stage I, the quartz–pyrite (Py2)–polymetallic sulfide–early calcite stage II, and the epidote–late calcite stage III. In situ sulfur isotope analysis of pyrite shows that Py1 (δ34S = −1.1 to +3.8‰) possesses mantle sulfur characteristics. However, Py2 has totally different δ34S (+5.1 to +6.7‰), which lies between the typical orogenic gold deposits in the WQO (δ34S = +8 to +12‰) and mantle sulfur. This suggests a mixed source of metamorphosed sediments and magmatic sulfur during stage II gold mineralization. The fluid inclusions in auriferous quartz have three different types, including the liquid-rich phase type, pure (gas or liquid)-phase type, and daughter-minerals-bearing phase type. Multiple-stage fluid inclusions indicate that the ore fluids are medium-temperature (concentrated at 220 to 270 °C), medium-salinity (7.85 to 13.80% NaCleq) CO2–H2O–NaCl systems. The salinity is quite different from typical orogenic gold deposits in WQO and worldwide, and this is more likely to be a mixture of magmatic and metamorphic fluids as well. In summary, the quartz syenite should have not only a spatio-temporal but also a genetical relationship with the Anwangshan gold deposit. It could provide most of the gold and ore fluids at the first stage, with metamorphic fluids and/or gold joining in during the later stages.

Source of Ore-Forming Fluids and Ore Genesis of the Batailing Au Deposit, Central Jilin Province, Northeast China: Constraints from Fluid Inclusions and H-O-C-S-Pb Isotopes

The Batailing Au deposit is a vein-type deposit in central Jilin Province, situated in the southern sector of the Lesser Xing’an–Zhangguangcai Range within the eastern Central Asian Orogenic Belt. NE-trending fault-controlled orebodies occur in the Upper Permian Yangjiagou Formation and quartz diorite–porphyrite. The mineralisation process was delineated into three stages: (I) quartz–arsenopyrite–pyrite, (II) quartz–polymetallic sulphides (main Au mineralisation stage), and (III) quartz–pyrite–carbonate. Fluid inclusions (FIs) in quartz were identified as four types: PC-type (pure CO2), C1-type (CO2-bearing), C2-type (CO2-rich), and W-type (aqueous two-phase). Raman spectroscopy analysis revealed that the vapor components of the FIs predominantly comprised CO2 with minor quantities of CH4 in stages I–II. Stages I and II encompassed four types of FIs with homogenisation temperature ranging from 264 to 332 °C and 213 to 292 °C and salinity spanning from 4.7 to 11.2 wt% and 1.8 to 11.6 wt%, respectively. Stage III exclusively contained W-type FIs with homogenisation temperature ranging from 152 to 215 °C and salinity spanning from 1.4 to 6.4 wt%. H-O isotopic values (δD = −84 to −79.6‰, δ18OH2O = 6.2 to 6.4‰ in stage I and δD = −96.4 to −90.4‰, δ18OH2O = 2.8 to 4.4‰ in stage II) and microthermometric data indicated that the ore-forming fluids are initially from a magmatic source, with later meteoric water input. Low C isotopic data from CO2 in FIs in quartz (−24.4 to −24.3‰ in stage I and −23.7 to −22.6‰ in stage II) indicated an organic carbon source. Ore precipitation is mainly attributable to fluid immiscibility. S-Pb isotopic data (δ34S = −3.5 to −1.6‰; 206Pb/204Pb = 18.325–18.362, 207Pb/204Pb = 15.523–5.562, 208Pb/204Pb = 38.064–38.221) revealed that ore metals primarily originated from magma. Based on this research, the origin of the Batailing Au deposit is of the mesothermal magmatic–hydrothermal lode type.

Minerals of antimony: a newly found occurrence in the Karkonosze granitoid pluton and a review for Lower Silesia, Poland, with general background

The article describes assemblages of ore minerals of the size of tenths to a few millimetres, which occurred in small quartz veinlets and nests in 10 previously unknown sites. This mineralization was found in the north-eastern part of the Karkonosze granitoid pluton at the southern slope of the Wysoki Grzbiet (High Ridge) in Izera Mts. The studies concerned mainly 18 Sb minerals: antimony, Sb-bearing domeykite, getchellite, stibnite, willyamite, berthierite, boulangerite, bournonite, chalcostibite, falkmanite, famatinite, geocronite, robinsonite, semseyite, tetrahedrite-(Fe), cervantite, kermesite and schafarzikite; seven of them have been found in Poland for the first time. The parageneses, morphological features, XRD data and chemical composition of the Sb minerals are presented. Fluid inclusions in quartz adhering to the Sb minerals had generally homogenization temperature (Th) 108–341°C and total salinity ΣS 4.6–10.1 wt. %. The inclusion fluids were of the NaCO3- Ca(HCO3)2-NaCl-KCl type with minor F and S, and occasional CO2 presence. The parent granitoid contains Sb in trace amounts (0.18–0.36 ppm) and the rock was possibly a source of this (and other) element(s) for the ore minerals. Migration of meso-epithermal solutions with Sb etc. was probably stimulated by local reduction of pressure during the formation of fissures and cracks in granite, next filled by quartz with ore minerals. The features of the historical process of the recognition of Sb ores and previous studies of the minerals investigated in this research are included in the presentation and discussion. Special attention was paid to the listing of the occurreences of Sb minerals in Lower Silesia with appropriate references.

Unraveling the genesis of wolframite mineralization in the West Qinling Belt, China: Evidence from geochronology, geochemistry, and fluid inclusion study

The West Qinling Belt is a pivotal part of the Central China Orogenic Belt renowned for producing abundant Au-polymetallic deposits. Nonetheless, reports of wolframite mineralization within this region were absent. The Xuehuashan deposit is the premier documented quartz-vein type wolframite deposit in West Qinling, which has significant implications of W mineralizing potential in the West Qinling Belt. The ore bodies are predominantly composed of wolframite-quartz veins and/or veinlets which are proximal or within the Late Triassic Baijiazhuang granitoid. To elucidate the age and genesis of the Xuehuashan wolframite mineralization, we presented analyses of U-Pb dating and chemical composition on wolframite, fluid inclusion study, and hydrogen–oxygen isotopes on wolframite and quartz. The Xuehuashan wolframite U-Pb dating yielded an age of 213.0 ± 6.7 Ma, which is consistent with the age of the Baijiazhuang granitoid. The correlation among trace elements and the Y/Ho vs. Zr/Hf diagram suggests trace elements in wolframite were influenced by crystalline chemical factors and the geochemistry of parental ore-forming fluid. Homogeneous texture and stable chemical composition of wolframite, as well δD vs. δ18O isotopes, suggest a single magmatic fluid from the Baijiazhuang granitoid. Fluid inclusions in wolframite and quartz have high homogenization temperatures and varying salinities of 0.4 – 16.4 wt%, suggesting that intense decompression and fluid boiling during fracture open caused the wolframite precipitation. Compared with the Late Triassic granitoids in the Qinling Belt, the Baijiazhuang granitoid shows higher ratios of Rb/Sr and lower ratios of Zr/Hf, K/Rb, Nb/Ta, LREE/HREE, as well as negative Eu anomalies, which are consistent with the W-related highly evolved granitoids but distinct to W-barren granitoids. Hence, this study highlights W mineralization potential in the Qinling belt associated with the highly evolved Late Triassic granitoids.

Fluid Inclusion, Rare Earth Element Geochemistry, and Isotopic (O and S) Characteristics of the Ardakan Barite Deposit, Yazd Province, Iran

The stratabound barite mineralization occurs in the Ardakan deposit as patches and veins in the dolomites and limestones of the Middle Triassic Shotori Formation. Rare-earth element (REE) geochemistry, O and S isotopes, and fluid inclusion data were used to identify the mode of barite formation. Barite is associated with subordinate fluorite and quartz and, to a lesser extent, with sphalerite, malachite, chrysocolla, and iron and manganese oxide-hydroxides. Barite contains a very low ∑REE concentration (14.80–19.59 ppm) and is enriched in light rare-earth elements (LREEs) relative to heavy rare-earth elements (HREEs). The low ∑REE content and the Ce/La ratio (4.0–6.5) indicate a hydrothermal (terrestrial) origin of the barite. Similar to barite, the ∑REE content in fluorite is low (0.14–6.52 ppm) and suggests a sedimentary setting. The Tb/Ca versus Tb/La diagram also indicates a hydrothermal origin of fluorite. The δ34S values in the barite (+27.9 to +32.4‰) indicate that the sulfur most likely originates from evaporites and/or connate waters from the Late Precambrian to the Lower Cambrian. The δ18O values (+15.9 to +18.1‰) in the barite show that the oxygen originated either from Late Precambrian–Lower Cambrian evaporites or from basinal brines with slightly higher δ18O values than the evaporites. The salinity and homogenization temperature ranges of the aqueous fluid inclusions in barite, fluorite, and quartz (0.88–16.89 wt% NaCl equivalent and 90–270 °C, respectively) reveal that the mineralizing fluids were formed from basinal brines with the participation of heated meteoric water. From this, it is concluded that the Ardakan barite deposit was formed by the meeting of heated, ascending sulfate-bearing meteoric water and cooler, Ba-bearing connate water trapped in the overlying Middle Triassic dolomites and limestones. The Ardakan deposit belongs to the structure-related class and the unconformity-related subclass of barite deposits.

The Spatial and Temporal Evolution of the Sadisdorf Li-Sn-(W-Cu) Magmatic-Hydrothermal Greisen and Vein System, Eastern Erzgebirge, Germany

Abstract The Sadisdorf Li-Sn-(W-Cu) prospect in eastern Germany is characterized by vein- and greisen-style mineralization hosted in and around a small granite stock that intruded into a shallow crustal environment. The nature and origin of this mineral system are evaluated in this contribution by a combination of petrography and fluid inclusion studies, complemented by Raman spectroscopy and whole-rock geochemical analyses. The early magmatic-hydrothermal evolution is characterized by a single-phase low-salinity (7.0 ± 4 wt % NaCl equiv), high-temperature (>340°C), CO2-CH4–bearing aqueous fluid, which caused greisen alteration and mineralization within the apical portions of the microgranite porphyry. The bimodal distribution of brine and vapor fluid inclusions, and the formation of a magmatic-hydrothermal breccia associated with the proximal vein mineralization are interpreted to mark the transition from lithostatic to hydrostatic pressure. The vein- and stockwork-style mineralization (main stage) displays lateral zonation, with quartz-cassiterite-wolframite-molybdenite mineral assemblages grading outward into base-metal sulfide-dominated assemblages with increasing distance from the intrusion. Late fluorite-bearing veinlets represent the waning stage in the evolution of the mineral system. The similarity in the homogenization temperature (250°–418°C) of fluid inclusions in quartz, cassiterite, and sphalerite across the Sadisdorf deposit suggests that cooling was not a significant factor in the mineral zonation. Instead, fluid-rock interaction along the fluid path is considered to have controlled this zonation. In contrast to quartz-, cassiterite- and sphalerite-hosted fluid inclusions, which have a salinity of 0.0 to 10.0 wt % NaCl equiv, the fluid inclusions in late fluorite veins that overprint all previous assemblages have a salinity of 0.0 to 3.0 wt % NaCl equiv and homogenize at temperatures of 120° to 270°C, thus indicating cooling with or without admixture of meteoric fluids during the waning stage of the mineral system. The Sadisdorf deposit shares similar characteristics with other deposits in the Erzgebirge region, including a shallow level of emplacement, similar mineralization/alteration styles, and a hydrothermal evolution that includes early-boiling, fluid-rock interaction, and late cooling. In contrast to most systems in the region, both proximal and distal mineralization are well preserved at Sadisdorf. The recognition of such spatial zoning may be a useful criterion for targeting greisen-related Li and Sn resources.

Fluid source and ore-forming process of the Lishupo Au deposit, NE Hunan: Constraints from fluid inclusions, SIMS oxygen isotope, LA-ICP-MS pyrite trace elements and fsLA-ICP-MS quartz trace elements

The Lishupo Au deposit (4.3 t @ 4.76 g/t) is located in the central Jiangnan Orogen. The processes and origins of regional gold mineralization, as well as the characteristics of the ore-forming fluids, continue to be poorly understood. This study integrates field geology, fluid inclusions, secondary ion mass spectrometry (SIMS) O isotope, femtosecond laser ablation inductively coupled plasma mass spectrometry (fsLA-ICP-MS) trace elements analysis for quartz, and LA-ICP-MS for trace elements study of pyrite to constrain the nature and source of ore-forming fluids, mechanism of gold precipitation, and ore genesis. Field investigations and microscopic observations reveal three mineralization stages at Lishupo: (1) the quartz-pyrite (Qtz1-Py1) stage; (2) the quartz-dolomite-polymetallic sulfides-gold (Qtz2-Py2) stage; and (3) the quartz-carbonate-pyrite (Qtz3-Py3) stage.Cathodoluminescence (CL) observations reveal that Qtz1 and Qtz2 have a homogeneous texture, while Qtz3 exhibits oscillatory zoning. Fluid inclusions in quartz suggest a CO2-H2O-NaCl ± N2 ± CH4 fluid system, which comprise H2O-CO2-NaCl, CO2-rich, and aqueous types. Microthermometry of fluid inclusions indicates low salinity (stage 1: 3.7–7.9 wt% NaCl equiv.; stage 2: 2.2–7.5 wt% NaCl equiv.; stage 3: 1.4–3.9 wt% NaCl equiv.) and medium to low temperature (stage 1: 313–341 °C; stage 2: 209–286 °C; stage 3: 139–198 °C) for ore-forming fluids, consistent with the low Ti content (<10 ppm) found in the quartz. The low Al content (7.99–20.7 ppm) of Qtz1 suggests that the ore-forming fluids were saturated with CO2 and had a near-neutral pH. The Al contents are higher and more variable in Qtz2 (10.7–1959 ppm) and Qtz3 (21.6–713 ppm), which may imply fluctuations in fluid pH. δ18OFluid values for various types of quartz (Qtz1: 9.02–10.95 ‰, Qtz2: 6.30–7.68 ‰, Qtz3: 3.45–3.94 ‰) indicate a metamorphic fluid origin for stages 1 and 2 fluids, which were mixed with the meteoric water during stage 3. The highest concentrations of Au and As in Py2 suggest that the Qtz2-Py2 stage is the primary ore stage. The Co/Ni ratios of all types of pyrite are less than 1, indicating that the ore-forming materials are derived from metamorphic sedimentary rocks. Fluid inclusion microthermometry suggests that fluid immiscibility was responsible for the gold deposition during the Qtz2-Py2 stage. Fluid immiscibility destabilizes Au(HS)2-, leading to the precipitation of native gold. These data strongly suggest that the Lishupo gold deposit is classified as an orogenic-type deposit. Integrating the existing geochronology data and geological context, we emphasize the presence of the Late Triassic orogenic gold deposit in the Jiangnan orogen. This highlights a significant exploration target area within this zone for future gold prospecting.

Quartz fluid inclusions and trace elements in the Lailisigaoer porphyry Mo deposit, Western Tianshan, Xinjiang: Fluid evolution and metallogenic mechanism in magmatic-hydrothermal system

The Lailisigaoer deposit is a typical porphyry Mo deposit located in the late Paleozoic Boluokenu metallogenic belt of Western Tianshan, NW China. This study aims to understand molybdenum mineralization and the dynamics of magmatic-hydrothermal fluid within the porphyry system, focusing on fluid inclusion, cathodoluminescence textures, and trace elemental composition in various generations of quartz. Six vein types in the Lailisigaoer deposit are classified as comb quartz veins with unidirectional solidification texture (UST, QI), actinolite/biotite ± quartz veinlets (M-type, QII), quartz-chalcopyrite vein (A-type, QIII), quartz-molybdenite vein (B-type, QIV), quartz-pyrite vein (D-type, QV) and quartz-carbonate vein (E-type, QVI). Micro thermometry data indicate decreasing homogenization temperatures in primary fluid inclusions from UST to E-type veins. The magmatic-hydrothermal fluids associated with UST and M-, A-, B-, D-, E-type veins underwent a transition from high temperature (342–495℃), high-pressure (∼1.25 kb), and variable salinity (6.7–41.1 wt%NaCl) in the H2O-CO2-NaCl system to low-temperature (142–238℃), low-pressure (∼0.25 kb), and low-salinity (1.6–5.1 wt%NaCl) in the H2O-NaCl system. This evolution is reflected in the proportion of quartz with oscillatory zones decreasing and irregular quartz increasing, indicating a shift from turbulent to stable fluid conditions. Furthermore, a gradual reduction in Ti concentration (from 79 ppm in UST to 1.4 ppm in E-type quartz) suggests a decrease in fluid temperature during the magmatic-hydrothermal evolution. Mineralization primarily occurs in A- and B-type veins, with molybdenum precipitation attributed to fluid immiscibility in a medium–high temperature (240–368 ℃) and high pressure (∼0.95 kb) environment. The A-type veins (mean 31 ppm in Ti concentrations) consist of equigranular (dark-core) (QIII-1) and patchy inhomogeneous CL-gray quartz (QIII-2). The B-type veins (mean 24 ppm in Ti concentrations) are characterized by equigranular (bright-core) inhomogeneous quartz (QIV-1) with growth zones that are cemented by later mosaic homogeneous CL-gray quartz (QIV-2). Based on the quartz-Ti thermometer, the mineralized veins (A- and B-type) were confined to be formed at depths of 2.8–3.6 km, with molybdenum mineralization occurring at 3.4–3.6 km. Molybdenum mineralization initiates during the QIV-1 crystallization period in magmatic-hydrothermal fluids and terminates in the QV-2 generation.

Fluid inclusions in quartz of the gold-ore occurrences and gold-quartz intergrowths from placers in the Sololi uplift of the Olenyok arch (Yakutia)

Fluid inclusions have been studied in vein quartz with gold sulfide mineralization from metamorphosed sandstones of the Eekite series and metarhyolites of the Early Proterozoic, in quartz breccia from the zone of overlapping gold mineralization on the Early and Middle Permian sandstones, as well as in the gold quartz intergrowths from the Sololi River placer. It has been revealed that formation of quartz breccias occurred within a wide temperature interval from 230 to 425 ºC, with predominance of carbon dioxide and nitrogen in the vapor phase. It is suggested that the increased nitrogen content may be associated with a chemical reaction between the fluid and ammonium-containing silicates of host rocks, in which nitrogen in the form of NH4+ isomorphically replaces potassium at the regressive stage of metamorphism. At the same time, it is possible that mantle nitrogen, which was transported along the Anabar-Eekite deep fault, participated in formation of the studied breccias. The close homogenization temperatures and similar nature of the water-salt composition for the fluid inclusions of quartz veins that inject the Eekite series meta-rocks and meta-rhyolites indicate the synchronism of their formation and attribute them to the common stage of ore formation. Quartz veins with gold sulfide mineralization were the primary sources of pebbles with gold-quartz intergrowths from the Sololi River, this is evidenced by similarity of principal characteristics of fluid inclusions. Oxidizing conditions of the mineralization serve as favorable factor for the Au deposition, it is indicated by the predominant CO2 content in fluid inclusions, keeping role of a geochemical barrier and leading to an elevated gold content in quartz veins.

Ore-forming material sources of the Pakbeng gold deposit, Laos: Evidence from fluid inclusions, H-O-S isotopes, and trace elements

The Pakbeng gold deposit, located at the junction of the eastern Tethys and western Pacific tectonic domains, is part of the Phôngsali-Luang Prabang-Sayaboury polymetallic metallogenic belt. Its gold ore bodies are predominantly governed by fault structures, being vein-like and short-axis-veined in shape. The Pakbeng gold deposit primarily exhibits two types of mineralized alterations: the quartz-vein type and the schistositized altered rock type. The ore bodies are primarily distributed within cataclastic granites and altered andesite plutons, near their contact zone. The ore-forming process can be divided into four stages: quartz + rutile + pyrite (stage I), quartz + pyrite + coarse-grained arsenopyrite (stage II), quartz + polymetallic sulfides + native gold (stage III), and calcite + quartz (stage IV). Native gold primarily occurs as invisible gold in the quartz and pyrite of stages I and II, and as enclosed, intergranular, and interstitial gold within the quartz, pyrite, and other metal sulfides of stage III. The ore-forming materials of the Pakbeng gold deposit primarily originate from plagioclase granites and altered andesites, as indicated by investigations of gold-bearing quartz fluid inclusions, hydrogen and oxygen isotopes, the trace-element composition of pyrite, and in situ sulfur isotopes. The sulfur in the deposit is mainly derived from metamorphic sources, supplemented by late magmatic sulfur. The ore-forming fluids in the deposit were dominated by metamorphic fluids in the early stage, with magmatic fluids participating in the late stage. While ascending, the temperature of the ore-forming fluids decreased due to fluid boiling and mixing, but their salinity increased slightly. The ore-forming fluids exhibited a consistent decrease in homogenization temperatures from stages I to IV, with salinity initially increasing and then decreasing. This suggests that the ore-forming fluids are low-temperature, medium to low-salinity and low-density fluids.

Genesis of sediment‐hosted copper and silver mineralization at the Omatapati prospect, Kaoko Belt, Opuwo district, Kunene region, Namibia

AbstractThe Omatapati copper and silver prospect within the Kaoko Belt is located in the Opuwo district, Kunene region, Namibia. The prospect is hosted by dolomite and interbedded argillites of the Neoproterozoic Devede Formation, the Ombombo Subgroup. An ore body is exposed in shallow artisanal mining pits and drill‐cores of the prospect have grades of 0.4 to 5.2 wt% Cu, and 23 to 312 g/t Ag. The prospect was formed by both hypogene and supergene mineralization processes. The hypogene mineralization occurred in three stages. Stage 1 is represented by calcite veins containing chalcopyrite, bornite, sphalerite and galena. Stage 2 consists of quartz and calcite veins with chalcopyrite and bornite. Stage 3 consists of quartz‐calcite‐barite veins with chalcopyrite. The veins of stages 1 and 2 are subparallel or discordant to the foliation of argillites, and those of Stage 3 are NE‐striking and steeply dipping in the brecciated dolostone and argillite. The mineralization stages 1, 2, and 3 are overprinted by supergene chalcocite, digenite, annite, covellite, malachite, delafossite, hematite, and goethite. The supergene process forms a semi‐massive chalcocite‐covellite zone, which extends from the surface to ~50 m depth. The veins show average concentrations of 2.1 wt% Cu, 80 ppm Ag, and 532 ppm Pb for the stage 1, 3.1 wt% Cu, 118 ppm Ag, and 66 ppm Pb for the stage 2, and 18.6 wt% Cu, 675 ppm Ag, and 565 ppm Pb for the Stage 3 with supergene overprinting. Silver occurs as impurity in supergene chalcocite (6303 ppm Ag), digenite (4425 ppm Ag), and covellite (3060 ppm Ag). Fluid inclusions in quartz and calcite revealed that the hypogene mineralization occurred under a pressure &gt;7–8 MPa. Temperatures of ore formation of the stages 1, 2, and 3 were &gt;145–155 °C, &gt;290–300 °C, and &gt;190–230 °C, respectively. Large variation of salinities in each fluid inclusion assemblage suggests fluid mixing and dilution processes. Fluid inclusion gas compositions in the Stage 3 have weighted means of 98.98 mol% H2O, 0.75 mol% N2, 0.52 mol% CO2, 0.02 mol% CH4, 0.0021 mol% Ar, 0.0009 mol% H2S, and 0.00006 mol% He and indicate a signature of magmatic fluids mixed with meteoric waters or seawater. δ34SCDT values of sulfides in the stages 1, 2, and 3 in the prospect have three data clusters, (1) near 0 ‰ of chalcopyrite in the stages 1 and 2, (2) near −11 ‰ of bornite in the stage 2, and (3) +5 to +11 ‰ of the supergene chalcocite and covellite. Modes of occurrence of ores, fluid inclusions and sulfur isotope data show that the prospect is likely the same type as sediment‐hosted copper‐silver deposits with veining found in the Central African Copperbelt.

The formation mechanism of the Xilekuduke porphyry Mo‐Cu deposit, NW China, revealed by the fluid inclusions and H‐O‐S isotopes

AbstractThe Xilekuduke porphyry Mo‐Cu deposit is located in the Altay‐East Junggar region of the Central Asian Orogenic Belt, northwest China. The orebodies occurring as vein type are host within the monzogranite and granite porphyry. Ore minerals include mainly molybdenite, pyrite, and chalcopyrite, whilst the major alteration include potassic, sericite, carbonate, and silicic. Mineralization can be divided into three stages: quartz‐K‐feldspar–polymetallic stage (Stage I), quartz‐polymetallic stage (Stage II), and quartz–calcite–pyrite (minor) stage (Stage III). Three types of fluid inclusion are present in the Mo‐Cu sulfide–calcite–quartz veins: CO2‐bearing (C‐type), aqueous (W‐type), and daughter mineral‐bearing (S‐type). Petrographic and microthermometric analyses of the fluid inclusions yielded homogenization temperatures for Stage I, II, and III to be 402–499°C, 214–391°C, and 136–254°C, respectively, with corresponding salinities of 39.2–59.6, 3.7–44.9 and 4.1–14.4 wt% NaCl equivalent. The δ18OH₂O and δD values of fluid inclusions in quartz are determined to be 5.3–6.0 ‰ and −76 to −60 ‰ (Stage I), 1.7–3.2 ‰ and −96 to −90 ‰ (Stage II), and −2.6 to −2.4 ‰ and −106 ‰ (Stage III), respectively. These results indicate that the primary ore‐forming fluids (stages I and II) were derived from granitic magma and were mixed with meteoric water in stage III. For the sulfide and sulfate (anhydrite), their δ34S values are of 0.4–5.8 ‰, 13.9–14.4 ‰, respectively, also that suggest a magmatic source. Fluid immiscibility, meteoric water interaction, and ore fluid‐wallrock interactions may have been critical for molybdenum precipitation.

Origin and evolution of gold-bearing fluids in a carbon-rich sedimentary basin: A case study of the Algamarca epithermal gold-silver-copper deposit, northern Peru

Sediment-hosted gold deposits account for the major part of economic gold in the Earth's crust. However, the origin of the gold-bearing fluid and its evolution in sedimentary basins in the presence of organic carbon and its metamorphosed products such as graphite are poorly known. In an attempt to clarify these issues, we performed an integrated mineralogical, geochemical, and fluid-inclusion study of the Algamarca epithermal Au-Ag-Cu deposit, hosted by Mesozoic sediments corresponding to an over-mature petroleum system within the Marañón fold and thrust belt (northern Peru). Results show that mineralization started with a pre-gold stage characterized by quartz veins containing gold-poor pyrite and chalcopyrite. Most gold was deposited afterwards, during the main gold stage in an “invisible” form within arsenian pyrite, followed by minor visible native gold with sulfosalts and chalcopyrite at a later stage. Fluid inclusions in quartz from the pre-gold and gold stages show features analogous to those observed in porphyry Cu-Au systems such as vapor–liquid immiscibility, enrichment in K, Rb, Cu, As, and Sb, a wide range of salinity (5–35 wt% NaCl eq.), and similar elemental (atomic) ratios (Zn/Pb ∼ 4, 0.1 < K/Na < 5, Br/Cl ∼ 0.06), all consistent with a fluid of magmatic origin. In addition, the fluid inclusions from the pre-gold stage are highly enriched in CO2 (∼60 mol% in gas phase), CH4 (∼10 mol%) and H2S (∼30 mol%). Such high volatile contents are rather unusual for typical porphyry-epithermal systems and likely reflect reactions between the magmatic fluid and carbon-bearing sediments. This conclusion is independently supported by the temperature values of graphite metamorphic peak determined by Raman spectroscopy, which are similar to those derived by fluid-inclusion microthermometry in quartz veins. Our findings imply that strong interactions of magmatic fluid with carbonaceous matter favored gold transport through the sedimentary basin and its subsequent concentration in arsenian pyrite. Furthermore, our results point to a possible presence of porphyry-style mineralization beneath the sedimentary sequence hosting the epithermal Algamarca deposit, thereby providing new potential for exploration.

Capitana mine, Tignamar district, a unique tin – bismuth concentration in the Chilean Central Andes, 250 km west of the Bolivian Tin Belt: Link to the Proterozoic-Paleozoic basement Belen inlier and the Arequipa-Antofalla terrane, a probable remnant of Laurentia

The Capitana mine, Tignamar District, is a unique Sn-Bi concentration in the highlands of Arica, in the Chilean Central Andes. Tin deposits associated with Triassic to Pliocene age igneous rocks are plentiful in the Tin Belt of Peru, Bolivia, and NW Argentina, but have not been reported in Chile, where contemporaneous rocks formed metallogenic belts rich in Fe, Cu, Mo, Ag and Au. We describe vein ore from Capitana mine, a small but exceptional Sn-bearing Pb-Bi-Ag-Cu-Sb-As epithermal deposit in the Tignamar (or Ticnamar) district in the high Andes of Arica, Chile, ca. 250 km west of the Bolivian Tin Belt. Fluid inclusions in vein quartz trapped a non-boiling, low salinity (<∼4 wt% NaCl equiv.), moderate T fluid (minimum T ∼ 220 °C) prior to metal precipitation. Flashing of this fluid, likely due to rapid changes in confining P, was synchronous with metal deposition; sulfosalt textures show evidence of syn-deformational growth. Although located within a district considered a porphyry copper system of Early Miocene age, it is likely that the Capitana deposit formed later, mainly as a result of regional hydrothermal activity related to compressive and transpressional tectonics as young as Pliocene. Common lead is 206Pb/204Pb 18.18; 207Pb/204Pb 15.61; and 208Pb/204Pb 38.53, significantly less radiogenic than that of Bolivian Sn deposits, and has a Paleozoic model lead age. These values point to affinities with a tectonically-emplaced inlier of crystalline basement of Proterozoic – Early Paleozoic age known as the Belen Metamorphic Complex, and with the Arequipa-Antofalla basement terrane, a probable remnant of Laurentia (North America), left behind during the dismemberment of the Rodinia Supercontinent. The complex mineralogy of Capitana vein, unlike other Chilean deposits, includes various sulphides and sulphosalts with Cu, Fe, Zn, Pb, Bi, Sn, Ag, As, Sb, Ga and In, and is exceptionally rich in U.

Raman spectroscopic characterization of the CO2-N2 gaseous system at 24–300°C and 2–40 MPa and applications

ABSTRACT CO2 and N2 are important gas components of deep-sourced geological fluids. To establish a quantitative method for the study of these fluids, we used a high-pressure optical cell, a heating–cooling stage, and a laser Raman spectrometer to examine pure CO2 and N2 gases and nine CO2-N2 gaseous mixtures at 24–300°C and 2–40 MPa. The results show that the CO2 Fermi diad split and the peak area ratios of the ν 1 band of N2 to the upper band of CO2 are considered to be the best for determining pressure and composition, respectively. The quantitative Raman analysis method developed in this study for the determination of the C N2/C CO2 molar ratio was verified by measuring those in synthetic N2-CO2-H2O fluid inclusions. The developed method has also been applied to the analysis of natural fluid inclusions in quartz from Donghai for the determination of both the C N2/C CO2 molar ratio and pressure.

Geochemistry, Fluid Inclusions and Sulfur Isotopes of the Goshgarchay Cu‐Au Deposit (Western Azerbaijan) in Lesser Caucasus: Implications for the Origins of Ore‐forming Fluids

AbstractThe Goshgarchay Cu‐Au deposit is located in the central part of the northwest flank of the Murovdagh region in the Lesser Caucasus. The Goshgarchay Cu‐Au deposit is associated with Middle Jurassic volcanic and Late Jurassic–Early Cretaceous high‐K calc‐alkaline intrusive rocks. The Cu‐Au mineralization is commonly related to quartz‐sericite‐chlorite alteration dominantly composed of chalcopyrite, gold, sphalerite, pyrite, bornite, hematite, covellite, chalcocite, malachite, and azurite. The Goshgarchay copper‐gold deposit, which is 600 m wide and approximately 1.2 km long, is seen as a fault‐controlled and vein‐, stockwork– and disseminated type deposit. The Goshgarchay Cu‐Au deposit predominantly comprises Cu (max. 64500 ppm) and Au (max. 11.3 ppm), while it comprises relatively less amounts Zn (max. 437 ppm), Mo (max. 47.5 ppm), Pb (max. 134 ppm), and Ag (max. 21 ppm). The homogenization temperatures and salinities of fluid inclusions in quartz for stage I range from 380°C to 327°C, and 6.9 wt% to 2.6 wt% NaCl eq., respectively. Th and salinities in quartz for stage II range from 304°C to 253°C, and 7.6 wt% to 3.2 wt% NaCl eq., respectively. The calculated δ34Sh2s values (–1.5‰ to 5.5‰) of sulfides and especially the narrow range of δ34Sh2s values of chalcopyrite and bornite (between –0.07‰ and +0.7‰) indicate that the source of the Goshgarchay Cu‐Au mineralization is magmatic. Based on the mineralogical, geochemical, fluid inclusion, and sulfur isotopic data, the Goshgarchay Cu‐Au deposit represents a late stage peripheral magmatic‐hydrothermal mineralization probably underlain by a concealed porphyry deposit.

Epithermal Deposits of Kamchatka, Russia

The results of studying the epithermal deposits of Kamchatka, one of the most promising gold-mining provinces of the Russian Federation, are generalized. The deposits are divided into acid–sulfate (Ac-Sul) and adularia–sericite (Ad-Ser) types (Heald et al., 1987). The disadvantages of the scheme, which is the most popular in the English-language literature and is based on the sulfidation state of mineral parageneses in ores (LS, IS, and HS types), are shown. The classification that we proposed includes differences in mineral associations in circum–ore metasomatites, which are determined by the acidity–alkalinity and an oxidation state of mineral-forming fluids, and are clearly diagnosed at the first stages of studying the deposits. Kamchatka epithermal deposits of the Ad-Ser-type are associated with andesite volcanism of the volcanic belts. Gold ore associations are concentrated in quartz, carbonate–quartz, and adularia–quartz veins, as well as in sericitized metasomatites, which are replaced by argillizites and propylites towards the periphery. The Ad-Ser-type is characterized by combination with polysulfide (Pb, Zn) (Amethyst, Kumroch, Vilyuchinskoe deposits), sulfosalt (Ag, Sb, As, Bi, Sn) (Ozernovskoe, Baranyevskoe), and selenide (Ag, Se) (Amethyst, Asachinskoe, Rodnikovoe) assemblages. Low-fineness native gold (220–310‰) is typical of the early polysulfide assemblage. With an increase in the fugacity of Te and Se, the gold fineness increases to 510–740‰, and with the progressive activity of Sb, As and Bi and the formation of sulfosalt associations, it reaches 998‰. The homogenization temperatures of primary fluid inclusions in quartz from gold-bearing associations of the Ad-Ser-type are 260–250°C; the minerals crystallize from solutions containing no more than 3 wt % NaCl eq. Maletoyvayam, the only Ac-Sul-type deposit in Kamchatka, is localized in quartz, secondary quartzites, and alunite–sericite–kaolinite–quartz metasomatites. Gold-bearing parageneses indicate the leading role of selenium in mineral formation, contain high-fineness native gold, sulfoselenotellurides, tellurides, and selenides of Au, which crystallize from acidic fluids with salinity of 1–5 wt % NaCl eq. at temperatures of 290–175°C.