Microthermometric Measurements Research Articles

Hydrothermal evolution and ore genesis of the Jiamante Au deposit in Western Tianshan, Xinjiang, China: Evidence from the geology, fluid inclusions, and C–H–O–S–Pb isotopes

The Jiamante Au deposit is one of the important deposits in the Axi ore cluster of the Western Tianshan, Xinjiang. The orebodies occurring mainly as quartz‐sulphide veins are hosted in Late Devonian volcanoclastic rocks and granitic porphyries, and structurally controlled by a group of NNW‐ and NNE‐ trending extensional faults and volcanic breccias. Primary metallic minerals are chalcopyrite, galena, pyrite, sphalerite, and native gold, with minor amounts of bismuthinite and bismuth. Nonmetallic minerals are dominated by quartz, sericite, chlorite, and calcite. Medium to low temperature hydrothermal alterations are well developed and characterized by silicification, beresitization, phyllic alteration, and chloritization. Two hydrothermal stages were identified: (a) the main‐ore quartz‐sulphide stage; and (b) the post‐ore quartz‐calcite stage. Microthermometric measurements indicate that the primary biphase liquid‐rich aqueous fluid inclusions within quartz of the main‐ore stage homogenize at temperatures (Th) of 176 to 251°C and have salinities of 2.1 to 7.4 wt% NaCleqv. A lower range of homogenization temperatures (169 to 212°C) and salinities (1.6 to 5.2 wt% NaCleqv) were obtained in calcite of the post‐ore stage. The fluid characteristics of moderate to low temperatures and salinities imply that the ore‐forming process occurred in an epithermal environment. In addition, there is a positive relationship between Th and salinities consistent with the fluid mixing trend. Together with H–O isotopic data (δDH2O = −118 to −97‰ and δ18OH2O = −5.5 to −1.6‰) and fluid characteristics, it is suggested that the ore‐forming fluids were a mixture of magmatic and meteoric waters. The δ13C values for CO2 in the hydrothermal fluids range from −3.2 to −2.7‰, and the sulphides have δ34S values of −5.2 to 2.9‰ with relatively uniform Pb isotopic compositions (206Pb/204Pb = 18.228 to 18.287, 207Pb/204Pb = 15.574 to 15.617, and 208Pb/204Pb = 38.151 to 38.251), indicating that the ore‐forming materials were magmatic sources that were derived directly from magmatic fluids and/or leached from volcanic‐subvolcanic rocks by hydrothermal fluids. Combined with the evidence from the mineralization and alteration, fluid inclusions, and C–H–O–S–Pb isotopes suggest that the Jiamante deposit is an intermediate‐sulphidation epithermal Au deposit. A combination of fluid mixing and fluid–rock interactions is inferred as the important factors causing ore deposition. According to the close spatial and temporal relationship between intermediate‐epithermal deposits and porphyry deposits, it is further suggested that porphyry‐type mineralization should have a good potential at the deep sites of the Jiamante deposit and its vicinity.

Origin of Middle-Upper Cambrian dolomites in eastern Laurentia: A case study from Belle Isle strait, western Newfoundland

The Middle and Upper Cambrian Port au Port Group of western Newfoundland consists mainly of mixed carbonates and siliciclastics and is composed of the March Point, Petit Jardin, and Berry Head formations. Samples were collected from the core NF-02 that spans the uppermost Hawke Bay (40 m), the March Point (~83 m thick) and the lowermost Petit Jardin (~47 m). Petrographic examination of carbonates of the March Point and Petit Jardin carbonates reveals three generations of dolomite: (i) micritic to near-micritic (D1, 4 μm −35 μm) fabric-retentive dolomite, (ii) coarse crystalline sucrosic (D2, 60 μm−150 μm) fabric-destructive dolomite (sub-to euhedral zoned rhombs with clear rim and cloudy core), and (iii) coarse anhedral (D3, >0.5 mm) fracture-filling saddle dolomite. The microthermometric measurements of primary two-phased fluid inclusions retained in D2, and D3 samples yielded homogenization temperatures (Th) showing a general increase with burial. The mean values of Th and salinity are 89.1 ± 6.4 °C vs 21.2 ± 2.2 eq. wt% NaCl, and 110 ± 8.2 °C vs 21.1 ± 4.7 eq. wt% NaCl, respectively. The investigated dolomites show a decrease of Sr from D1 (102 ± 49 ppm) to D3 (47 ± 15 ppm) which reflects the influence of progressive burial. The mean δ18O values decrease from D1 (−6.3 ± −1.1‰ VPDB), to D3 (−9.7 ± 1.7‰ VPDB) where D2 (−7.6 ± 1.2‰ VPDB) is in the middle. The estimated δ18O values of the D1 parent fluid (−5 to −10‰ VSMOW) are bracketed by those suggested for the Middle Cambrian meteoric and seawaters. The fluid-inclusion gas analyses provided CO2/CH4 and N2/Ar ratios coherent with the conclusions from the petrographic examination and geochemical compositions.

Fluid inclusion and stable isotope constraints on the source and evolution of ore-forming fluids in the Bailongshan pegmatitic Li-Rb deposit, Xinjiang, western China

The newly discovered Bailongshan pegmatitic lithium–rubidium (Li–Rb) deposit in West Kunlun–Karakorum (western China) is a world-class Li deposit. In this paper, we present detailed field observations and fluid inclusion (FI) data for four major mineral zones at Bailongshan; i.e., the fine albite (FAZ), blocky feldspar (BFZ), quartz–muscovite (QMZ), and spodumene–quartz (SQZ) zones. FIs are abundant in quartz and spodumene, and include four types: (1) two-phase L-type, (2) two-phase V-type, (3) three-phase S-type, and (4) three-phase (CO2–H2O–NaCl) or two-phase (CO2-rich) C-type. Quartz contains all four FI types, whereas spodumene contains mainly C-type FIs. Microthermometric measurements show that the L-type FIs in the FAZ, BFZ, and SQZ homogenised at 283–338, 156–224, and 223–421 °C, respectively, with corresponding salinities of 15.4–26.5, 4.4–10.4, and 10.5–30.6 wt% NaCl equivalent. The S-type FIs in the FAZ and SQZ homogenised at 183–285 and 214–298 °C, respectively. The C-type FIs in spodumene and quartz homogenised at 256–321 and 234–286 °C, with corresponding salinities of 4.4–18.1 and 4.4–12.6 wt% NaCl equivalent, respectively. The ore-forming fluids were of medium–low-temperature and medium–low-salinity, and no systematic fluid compositional variations were identified in each zone. The average CO2 densities and trapping pressures were estimated at 0.72–0.91 g/cm3 and 3.00–3.75 kb, respectively, corresponding to mineralisation depths of 9–11 km. Supercritical fluids likely contributed to the concentration of ore-forming elements in the fluids, and fluid boiling may have led to CO2 degassing and Li ore deposition. H–O isotope data show that quartz grains from all four zones have δ18OV-SMOW values of 8.6‰–10.2‰ and δDV-SMOW values of −38‰ to 107‰. The ore-forming fluids were likely sourced from pegmatitic magmas.

The Lotsberg Salt Formation in Central Alberta (Canada)—Petrology, Geochemistry, and Fluid Inclusions

The Lotsberg Salt Formation (LSF) of the Lower Devonian age occupies a large area in Alberta (Canada). It has been used for brine production, disposal, and storage purposes since the 1950s. Its petrological and geochemical features remain poorly understood up to now. Previous studies showed that these salt rocks are large crystalline and distinguishable by a very low bromine content (2–5 ppm). Our studies reveal that the main impurity is dolomite with an addition of haematite. It showed, also, a lack of sulphate minerals (anhydrite). Manganite also occurs within the halite crystals. Microthermometric measurements of primary fluid inclusions in halite show a large range of homogenization temperatures from 32.4 °C to 357.0 °C with the highest temperature in the upper part of the salt profile. Geochemical analysis confirms the low bromine contents, which is between 0.67–12.74 ppm. Potassium contents (166–3651 ppm) seem to be in the normal range for salt rocks, but magnesium content (25–177 ppm) is much lower than potassium. Rubidium is, as well, within the normal range, with values between <0.01 ppm and 3.13 ppm, while caesium contents (5.07–211.22 ppm) are almost sixty times higher in comparison to those of rubidium. The high concentration of Cs, Mn, Rb, and the high homogenization temperatures of the host minerals suggest that the LSF underwent extensive ion exchange related to hydrothermal inflow. These hydrothermal solutions originated from the basement of the LSF.

Genesis of the Abbasabad epithermal base metal deposit, NW Iran: Evidences from ore geology, fluid inclusion and O–S isotopes

The Abbasabad epithermal Pb–Zn–Cu deposit is located in the Tarom–Hashtjin Metallogenic Belt (THMB), northwest Iran. Mineralization occurs as quartz-base metal sulfide veins and breccias mainly hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four mineralization stages are recognized: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz-calcite I-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) late stage barite veins and veinlets, and (4) barren post-ore calcite II veinlets. The primary metallic minerals, in order of abundance, are galena, sphalerite, chalcopyrite, and pyrite; gangue minerals are mainly quartz, barite, calcite, sericite/illite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonatization, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz, sphalerite and barite show that the ore-forming fluids belong to the low- to moderate-temperature (170–315 °C), moderate-salinity (3.6–7.1 wt% NaCl equiv.), low-density H2O–NaCl system. Estimated trapping hydrostatic pressures are 60 to 100 bars, corresponding to entrapment depths of 614 to 1022 m below the paleowater table. Oxygen isotopic data (δ18OH2O of + 7.6 to + 0.6‰) indicate that the ore-forming fluid was derived largely from magmatic fluid, with the addition of meteoric water in the later stage. δ34SH2S values of sulfides vary over a narrow range from –17.4‰ to –15.4‰, (averaging − 16.3‰), indicate that sulfur might be derived from a relatively homogeneous magmatic source which oxidized by meteoric water through fluid mixing. The Abbasabad deposit is interpreted as an intermediate-sulfidation epithermal mineralization derived from a mixed source during a phase change in temperature and pressure interpreted as being related to fluid mixing and boiling. Our data suggest that mineralization at Abbasabad and other epithermal deposits in the THMB are related to late Eocene (~40 to 36 Ma) post-collisional magmatism, which is a useful concept for local and regional epithermal base metal exploration targeting.

Stable-isotope and fluid inclusion constraints on the timing of diagenetic events in the dolomitized Dolomia Principale inner platform (Norian, Southern Alps of Italy)

The petrographic, cathodoluminescence (CL), stable isotope, and microthermometry investigation of inner platform facies of the pervasively dolomitized carbonate platform of the Norian (Upper Triassic) Dolomia Principale (Southern Alps, N Italy) identified two major dolomite phases. An early replacement fabric-retentive dolomite (D1 and D2, respectively replacing the sedimentary facies - from fenestral mudstone/wackestone to bioclastic packstone and mudstone and stromatolites- and early marine cements) is followed by a later, vug- and fracture-filling dolomite cement phase (D3, planar-s texture).The fabric-retentive dolomitized carbonates (<4 μm−30 μm, D1) and marine fibrous cements (30 μm−250 μm, D2) exhibit dull luminescence under CL whereas the burial dolomite cement (200 μm−500 μm, D3) exhibits zoned luminescence. Microthermometric measurements of the primary two-phase fluid inclusions in D3 yielded a mean homogenization temperature of 112.4 ± 8.2 °C. Supposing a surface seawater temperature of at least 20–25 °C and a geothermal gradient of about 40 °C/km during the Early Jurassic rifting that led to the opening of the Alpine Tethys, such temperature might be reached at reasonable burial depth ranging from 2.0 km to about 2.5 km. According to the subsidence curve this depth, compatible with the temperature recorded by the fluid inclusions, was reached during the Early Jurassic, with D3 cement precipitation causing a significant reduction of the porosity.The δ13C values of the investigated dolomites (D1, D2, and D3) show a narrow range of variation (2.0–3.1‰ VPDB), pointing toward a fluid-buffered system. Differently, the δ18O values largely varies, ranging from −12.8 to +1.9‰ VPDB. In this range, D3 values cluster distinctively between −6.0 to −12.8‰ VPDB with respect to D1 and D2, which cluster from about −4 to +1.9‰ VPDB. The estimated oxygen isotope composition of the parent fluid of D1 and D2 (~0 to −5‰ VSMOW) suggests possible contributions from marine to slightly evaporated seawater, which is consistent with the arid climate and some basin restrictions suggested by earlier studies, whereas that of D3 (+1 to +5‰ VSMOW) is consistent with burial fluids.The followed integrated approach highlights the possibility to better characterize the occurrence of multiple diagenetic events in time and space, as well as their feedback effects on the porosity evolution of dolomitized carbonate reservoirs, framing the diagenetic events at regional scale.

Sulfide melts in ore deposits from low-grade metamorphic settings: Insights from fluid and Tl-rich sulfosalt microinclusions from the Monte Arsiccio mine (Apuan Alps, Tuscany, Italy)

Sulfide melting is increasingly recognized as an efficient ore remobilization process in several ore bodies deformed and metamorphosed under amphibolite to granulite facies conditions. Actually, sulfide melts may also occur at lower metamorphic conditions, provided the abundance of the so-called Low-Melting point Chalcophile Elements (LMCE). The Monte Arsiccio ore body (Apuan Alps, northern Tuscany, Italy) is strongly enriched in several LMCE, i.e., Ag, As, Hg, Pb, Sb, and Tl, and experienced greenschist facies metamorphism (T = 350–450 °C; P = 0.3–0.4 GPa) during the Alpine orogeny. Trails of polyphase sulfosalt inclusions (up to five phases), coexisting with fluid inclusions, were observed within quartz and baryte crystals found in late-stage veins. Sulfosalt assemblages are formed by LMCE-rich phases, the main being ferdowsiite, Ag8As3Sb5S16, chabournéite, Tl2Pb(Sb,As)10S17, and intermediate members of the arsiccioite/routhierite isotypic pair, (Ag1−xCux)Hg2TlAs2S6, along with minor realgar. Sulfosalt inclusions range between 200 nm and more than 100 µm in size, whereas larger inclusions, likely formed through the coalescence of smaller melt droplets, are up to 500 µm. Sulfosalt inclusions are associated with primary two-phase liquid-rich fluid inclusions (Type 1a), containing CO2 and N2, as revealed by microthermometric investigations and micro-Raman spectroscopy. Secondary two-phase liquid-rich fluid inclusions (Type 1b) were also identified. Microthermometric measurements carried out on Type 1a fluid inclusions gave homogenization temperatures (Th) in the range 265–296 °C, whereas Type 1b fluid inclusions showed lower Th, between 222 and 246 °C. As microthermometric heating experiments on sulfosalt inclusions revealed homogenization temperatures around 270 °C, it is very likely that sulfosalt inclusions were in the liquid state during their entrapment, in agreement with many Tl-bearing systems. These results are fully consistent with the occurrence of LMCE-rich sulfide melt during the formation of the sulfosalt assemblages observed at the Monte Arsiccio mine. In addition, the polyphase nature of most of the observed sulfosalt inclusions may be related to the unquenchable nature of sulfide melts. The formation of LMCE-rich sulfosalt assemblages could be related to the release of these elements from pyrite during its metamorphic recrystallization. Consequently, pyrite ores may produce sulfide melts, with potential implications in the change of speciation of LMCE, from trace to major elements.

Genesis of the Yujiadian F-Pb-Zn-Ag deposit, Inner Mongolia, NE China: Constraints from geochemistry, fluid inclusion, zircon geochronology and stable isotopes

The Yujiadian F-Pb-Zn-Ag deposit in the South Great Xing’an Range (SGXR) consists of vein-type fluorite and F-Pb-Zn-Ag mineralization associated with granitoid. The orebodies occur in NS-trending extensional faults. Wallrock alterations are characterized by a series of medium-low temperature hydrothermal alteration, including silification, kaolinization, chloritization, sericitization, pyritic and carbonate alteration. Four stages of primary paragenetic sequences are recognized: polymetallic sulfide stage (stage I), sulfide fluorite sub-stage (stage II-1), silver-fluorite sub-stage (stage II-2), pure fluorite stage (stage III) and late carbonate stage (stage IV). Silver mineralization primarily belongs to the stage II. The 139–135 Ma quartz syenite porphyry is metaluminous and peralkalic, and is classified as A-type granite that formed in a post-orogenic extensional setting. The δ34S (1.8‰) of hydrothermal fluid calculated from coeval minerals (barite and galena) is comparable with the majority of adjacent magmatic hydrothermal deposits in the SGXR, implying a magmatic source. Microthermometric measurements show that ore minerals were deposited at intermediate temperatures (109.7–320.1 °C) and had low salinities (0.18–5.62 wt% NaCl equive). Ore-forming fluid originated from post-magmatic hydrothermal fluid and mixed with heated meteoric water. Successive precipitation of base metals occurred with changing physicochemical conditions and boiling of ore fluid. The main precipitation mechanism for fluorite in the late stage is related to fluid-rock reaction. We propose that the A-type granite related to the fracture-controlled hydrothermal vein-type Yujiadian F-Pb-Zn-Ag deposit forms part of the magmatic response to Paleo-Pacific subduction and associated lithospheric thinning, extension and delamination processes. Furthermore, the deposit represents the terminal and distal member of the regional Mesozoic large-scale mineralization events.

Microthermometric behavior of crystal-rich inclusions in spodumene under confining pressure

Abstract A hydrothermal diamond anvil cell (HDAC) was used to observe the microthermometric behavior of solid + liquid + vapor inclusions in spodumene from the Tanco pegmatite, Manitoba, under confining pressure. At 25 °C, these inclusions commonly contain a carbonate mineral (zabuyelite, rarely calcite or nahcolite), quartz, a phyllosilicate (cookeite), and an aqueous carbonic fluid phase. Heating spodumene-hosted inclusions to temperatures between 600 and 680 °C in a HDAC resulted in total or partial dissolution of the contained solid phases, followed by homoepitaxial growth of new spodumene on the inclusion walls, which reduced the inclusion volume by up to 31%. At room temperature, the homogenized inclusions contain only an aqueous fluid phase, CO2 liquid, and CO2 vapor. Inclusions that failed to homogenize at 680 °C, or leaked during heating, contain partially dissolved minerals with or without an aqueous carbonic fluid. The volume of spodumene formed within an inclusion during experimental re-heating, as determined by the difference in inclusion size before and after total dissolution of the contained solid phases, was used to estimate the volume of zabuyelite, quartz/cristobalite, and cookeite produced by the reaction The relative volumes of the calculated reaction products approximate the proportions of zabuyelite, quartz/cristobalite, and cookeite in inclusions prior to heating. The absence of silicate glass in the quenched homogenized inclusions indicates that they do not represent the crystallized products of an entrapped hydrous silicate melt that wetted the surface of spodumene during its growth. Large changes in inclusion volume and composition during experimental re-heating shows that the inclusions are neither isochoric nor isoplethic systems and as such are unsuitable for estimating the P-T conditions of trapping. Readers should therefore exercise caution when using thermobaric estimates of pegmatite crystallization inferred from microthermometric measurements of presumably primary melt inclusions in spodumene.

Fluid Inclusion and Oxygen Isotope Characteristics of Vein Quartz Associated with the Nabeba Iron Deposit, Republic of Congo: Implications for the Enrichment of Hypogene Ores

The Nabeba iron ore deposit is located at the northern part of Congo Craton, Republic of Congo. The ore deposit consists of supergene and hypogene ores, both of which are hosted in the Precambrian Nabeba banded iron formation (BIF). This study focuses on the hypogene iron ore mineralization associated with quartz veins in the Nabeba deposit, for which two hypogene ore stages have been recognized based on geologic and petrographic observations: early-stage high‐grade hematite‐rich ore (HO‐1) and late-stage magnetite‐rich ore (HO‐2). Based on microthermometric measurements and laser Raman spectroscopy of the fluid inclusions, the H2O‐NaCl ± CO2 fluids interacting with the Nabeba BIF at the HO‐1 stage evolve from high‐to‐moderate temperatures (203–405 °C) and contrasting salinities (moderate-to-low: 1–15 wt. % NaCl equiv.; high: 30–35 wt. % NaCl equiv.) to H2O‐NaCl fluids of moderate‐to‐low temperatures (150–290 °C) and salinities (1–11 wt. % NaCl equiv.) for the HO‐2 ore stage. Assuming equilibrium oxygen isotopic exchange between quartz and water, the δ18Ofluid values range from 4.7–8.1‰ for the HO‐1 stage and −2.3‰ to −1.5‰ for the HO‐2 stage. This implies the ore‐forming fluid of initially-mixed metamorphic–magmatic origin, later replenished by seawater and/or meteoric water during the formation of the HO‐2 stage. These mixtures of different fluids, coupled with their interaction with the BIF lithology followed by phase separation, are responsible for the enrichment of hypogene iron ore in the Nabeba deposit.

Ore Forming Fluid of Epithermal Quartz Veins at Cisuru Prospect, Papandayan District, West Java, Indonesia

The Cisuru area is located in Talegong Sub-district, Garut Regency, West Java, Indonesia which is belongs to the central part of Southern Mountain Slope. The aim of this research is to understand the nature and characteristic of fluid inclusion from quartz veins (especially drill core samples) in the study area. Rock units in the area are characterized by Tertiary volcanic rocks and volcaniclastic sequence which is mainly composed of andesite, andesitic breccia, volcanic breccia, lapilli tuff, dacite and related to the intrusion of diorite. The Cisuru epithermal mineralization is dominantly hosted by andesite, dacite, breccia and lapilli tuff, and would probably be controlled by both permeable rocks and NS and NE-SW trending strike-slip faults. The mineralization is shown as void filling and replacement within the silica zone, veinlets along with the open space/fractures and dissemination. Fluid inclusion from quartz veins was studied to know nature, characteristics and origin of hydrothermal fluids. Microthermometric measurements of fluid inclusions were realized by using a Linkam THMSG 600 combined freezing and heating stages. Homogenization temperature and final ice melting temperature were measured for primary two-phase inclusion from quartz veins. Base on the study of the fluid inclusion, the value of homogenization temperature (Th) range from 200 ºC to 395 °C and ice melting temperature range from -0.1 to - 4.5 where salinity range from 0.2 to 7.2 wt. % NaCl equivalent. Fluid inclusion petrography and microthermometric measurement data exhibit that fluid mixing, dilution and boiling were main processes during the hydrothermal evolution. The formation temperature of each quartz vein is 260 ºC to 290 ºC and also their formation depth is estimated between 560m to 925m respectively. Combination of fluid inclusions petrography, microthermometric measurement, and estimate paleo depth from Cisuru area were suggested under the epithermal environment.

Fluid and ore sources of the tungsten mineralisation in the Yangbishan iron–tungsten deposit, Heilongjiang Province, North‐eastern China: Constraints from fluid inclusions, sulphide S–Pb isotopes and scheelite C–H–O–Sm–Nd isotopes

The Yangbishan iron–tungsten deposit, located in the central part of the Jiamusi Massif, Heilongjiang Province, NE China, is the oldest tungsten deposit in NE China to date. Both ore‐forming conditions and mineralisation characteristics indicate that tungsten mineralisation belongs to the skarn type. Petrography, microthermometric measurements and laser Raman spectroscopy of fluid inclusions in quartz grains associated with scheelite indicate that the ore‐forming fluid of the tungsten mineralisation in Yangbishan deposit belonged to the moderate‐temperature NaCl–H2O–CH4±N2 system. Fluid inclusion analyses indicate that ore‐forming fluid experienced decreasing temperatures and fluid degassing, inducing scheelite precipitation. Analysis of C, H and O isotopes of fluid inclusions within scheelite grains show δ13C values varying from −20.7 to −24.9‰, δD from −109.9 to −119.9‰, δ18O from 6.8 to 10.0‰ and δ18OH2O from 8.7 to 11.9‰. These data, together with C, H and O isotope compositions of the quartz associated with scheelite in tungsten ores, imply that ore‐forming fluid was derived dominantly from magma but influenced by organic material (reducing carbon) derived from wall rocks. Sm/Nd ratios of scheelite vary from 0.15 to 0.21, εNd (t = 520 Ma) values from −5.64 to −17.95 (average of −10.21) and TDM2 values from 702 and 2693 Ma (average of 2070 Ma), indicating the ores were sourced from ancient crustal rocks. The compositions of C–H–O–S–Pb and Nd isotopes support the fact that interaction between crust‐derived magma and strata rich in organics played an important role in the tungsten mineralisation of the Yangbishan deposit.

Origin and evolution of hydrothermal fluids in the Marshoun epithermal Pb–Zn–Cu (Ag) deposit, Tarom-Hashtjin metallogenic belt, NW Iran

The Marshoun epithermal Pb–Zn–Cu (Ag) deposit is located in the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran. The epithermal base metal veins are mainly hosted in Eocene volcanic and volcaniclastic rocks of the Karaj Formation, and late Eocene pyroxene quartz monzodiorite. The mineralization process can be divided into five stages: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz (calcite)-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) barren post-ore quartz veinlets, (4) barren post-ore calcite veinlets, and (5) supergene mineral assemblages. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, and galena; gangue minerals are mainly quartz, calcite, sericite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonate, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 °C from fluids with salinities between 3.4 and 6.3 wt% NaCl equiv. Coexisting LV, VL, and V inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of bladed calcite as well as plumose and colloform/crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling. Obtained oxygen and sulfur isotope compositions (δ18Owater = +9.2‰ to +1.5‰; δ34SH2S = –10.0‰ to –5.7‰) indicate there was a major contribution from a magmatic component to metallogenesis. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Marshoun. The Marshoun deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the epithermal mineralization in the THMB are related to late Eocene (ca. 36–37 Ma) shallow magmatic–hydrothermal activity. The altered Eocene volcanic-subvolcanic rocks, particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at THMB.

Ore-forming fluids and ore genesis of the large Bayanbaolege Ag polymetallic deposit, Southern Great Xing’an Range, NE China

The large Bayanbaolege Ag polymetallic deposit is one of the newly discovered deposits in the Tuquan-Linxi Fe (Sn)-Cu-Pb-Zn-Ag-Nb (Ta) metallogenic belt of the Southern Great Xing’an Range, NE China. Its major ore bodies, sulfide-quartz veins, are distributed within granodiorite porphyry and in adjacent Late Permian strata. According to ore-forming geological conditions, mineralization and alternation characteristics, source and features of ore-forming fluid, as well as metallogenic depth (<1.45 km), the Bayanbaolege deposit belongs to the mesothermal vein type, and has a genetic relationship with the granodiorite porphyry. Three mineralization stages have been recognized, namely, arsenopyrite-pyrite-quartz (stage I), chalcopyrite-pyrite-sphalerite-quartz (stage II) and calcite-galena-silver minerals (stage III). The zircon U-Pb age of the granodiorite porphyry (130 ± 1 Ma, MSWD = 1.8), indicates that the Ag polymetallic mineralization took place in the Early Cretaceous period. Microthermometric measurements and laser Raman analyses of four types of fluid inclusions that formed in the three stages show that the ore-forming fluid belongs to the H2O-CO2-NaCl system, with medium temperatures (mean temperatures, stage I: 368 °C; stage II: 286 °C; stage III: 206 °C) and medium-low salinities (mean salinities, stage I: 2.1–7.6 wt% NaCl equivalent; stage II: 1.6–11.6 wt% NaCl equivalent; stage III: 1.2–8.4 wt% NaCl equivalent). C-H-O isotope data indicate that ore-forming fluid was derived largely from magmatic fluid, with the addition of meteoric water in the later stage.

Microthermometric evidence for the formation of Permian VHMS deposits in Tasik Chini area, Central Belt of Peninsular Malaysia

The VHMS deposits of Tasik Chini area are located in the Pahang State of Central Belt, Peninsular Malaysia. The deposits occur in a package of Permian volcanics within mixed volcano-sedimentary sequence, and have been exploited from the Bukit Botol and Bukit Ketaya deposits. They have many similarities with Kuroko-style massive sulfide deposits. The host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition. Mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers (Fe + Mn ± Si ore) at the stratigraphic top. The sulfide phases are characterized by pyrite as the major sulfide mineral, with subordinate chalcopyrite, sphalerite and rare galena; traces of gold, silver- and Sn-bearing minerals occur in the massive sulfide and barite ores. Primary fluid inclusions within quartz and barite occur as two types: (1) type I: two phase, liquid-vapour inclusions without daughter minerals, and (2) type II: three phase, liquid CO2-bearing carbonic inclusions. These three phase inclusions include liquid H2O, liquid CO2 and vapour CO2, with variable CO2 content, and often decrepitate before complete homogenization. Microthermometric measurements of the type I inclusions show that the temperature of homogenization (Th) varies between 180 °C and 310 °C with salinities ranging from 1.0 to 15.0 wt% NaCl equivalent in the quartz samples. Homogenization temperatures (Th) of 190 °C to 300 °C and salinities between 1.0 and 13.0 wt% NaCl equivalent are recorded from the barite samples. Type II inclusions have an initial melting temperature range of −57.1 °C to −57.5 °C, clathrate melting temperature (Tmclathrate) of 7.4 °C to 8.0 °C and CO2 homogenization temperature (ThCO2) between 30.1 °C and 30.3 °C, and salinity ranging from 4.0 to 5.1 wt% NaCl equivalent. Densities, pressure and depth of ore forming fluids range from 0.711 to 0.970 g/cm3, 12 to 93 bars, and ∼1500 m depth of seawater. Laser Raman spectroscopic analysis shows the presence of CO2 in the carbonic inclusions. The fluid inclusion results suggest that the main ore fluid during the formation of the Tasik Chini VHMS deposit is a seawater-dominated fluid, but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater (3.2 wt% NaCl) and the presence of CO2. Taking into account the regional geodynamic evolution, it is also concluded that the formation of VHMS deposits in the Tasik Chini area occurred in a back-arc geotectonic setting.

Fluid inclusion and stable isotope constraints on ore genesis of the Zajkan epithermal base metal deposit, Tarom–Hashtjin metallogenic belt, NW Iran

In the Zajkan Pb–Zn–Cu (Au–Ag) deposit of the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran, mineralization occurs as quartz-base metal sulfide veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four stages of ore formation are identified at Zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, galena, and trace amounts of hematite; gangue minerals are mainly quartz, sericite, chlorite, and calcite. The main wall-rock alteration is silicification, and intermediate argillic, and propylitic alteration. The coexistence of different types of fluid inclusions (LV, VL, and V) in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping. Excluding the heterogeneously entrapped fluid inclusions, the microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 °C from fluids with salinities between 1.7 and 6.4 wt% NaCl equiv. The oxygen isotopic compositions (δ18Owater-VSMOW of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. Sulfur isotopic values of sulfide minerals vary over a narrow range from −5.0 to −0.9‰VCDT (averaging −2.2‰VCDT), suggesting that sulfur was derived from a homogeneous magmatic source. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Zajkan. Our data suggest that the Zajkan deposit is an intermediate-sulfidation style epithermal mineralization. The estimated ore formation depth of Zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the THMB.

Mineralogy, fluid inclusions and stable isotope study of epithermal Au-Ag-Bi-Te mineralization from the SE Afar Rift (Djibouti)

In this paper, the mineralogy, fluid inclusions and stable isotopes of hydrothermal veins from the SE part of the Afar Rift (Djibouti) were studied. Mineralization occurs as gold-silver in quartz/carbonate veins and is mainly associated with felsic volcanism. The morphologies and textures of quartz show crustiform colloform banding, massive and breccias. Microthermometric measurements were made on quartz-hosted two phases (liquid + vapor) inclusions. Mean homogenization temperature ranges from 150 °C to 340 °C and ice-melting temperatures range from −0.2 °C to − 1.6 °C indicating that inclusion solutions contain 0.35 to 2.7 eq. wt% NaCl. Furthermore, δ18O and δ13C values from calcite range from 3.7 to 26.6‰ and −7.5 to −0.3‰, respectively. The presence of platy calcite and adularia are consistent with boiling conditions. Our study shows that the deposit of precious-metal occurred at around 250 °C and is linked to a fluid generated by the mixture of magmatic fluid, hydrothermal fluid and seawater.

Ore geology, fluid inclusions and O-S stable isotope characteristics of Shurab Sb-polymetallic vein deposit, eastern Iran

The Shurab Sb-polymetallic mineralization is a subvolcanic rock-hosted epithermal deposit and located in north Lut Block, eastern Iran. It is one of the most important deposits of the Iranian East Magmatic Assemblage (IEMA) in which numerous Middle-Cenozoic precious and base metals deposits occur. The main lithological units in the area are Paleogene subvolcanic intrusions and minor Jurassic sedimentary rocks. Mineralization occurs as veins in a series of NW-SE and E-W trending faults and fractures in the Eocene-Oligocene dacite and andesite subvolcanic rocks. Mineralization at the Shurab deposit can be subdivided into four stages: pre-ore stage, Cu-Zn-Pb ore stage, Sb-Ag ± As ore stage and post-ore stage. The total sulfide content of the veins in the area is variable, ranging from 1 to 50%, and is dominated by stibnite, chalcopyrite, galena, Fe-poor sphalerite and pyrite with minor chalcostibite, Ag-tetrahedrite and bournonite; gangue minerals are mainly quartz and calcite. Silicic, argillic, propylitic, and sericitic, are the most obvious wall rock alterations. Microthermometric measurements of primary liquid-rich fluid inclusions in quartz and sphalerite indicate that the veins were formed at temperatures between 115 and 290 °C from fluids with salinities between 0.7 and 16.2 wt% NaCl eq., suggesting an epithermal origin. The δ34S values of pyrite, chalcopyrite and galena vary between -2.5 and 0.8‰, and δ18O values of quartz range between 12.5 and 14.8‰. It is inferred that the Shurab mineralization is of epithermal origin, related to an Eocene-Oligocene magmatic geothermal system involving fluids of magmatic and meteoric origin.

Evolution of fluorite-mica-feldspar veins: Evidences of a fossil geothermal system in the são Gabriel terrane and consequences for Pb-Zn-Cu metallogeny

Fluorite-mica-feldspar hydrothermal veins and stockworks host Pb-Zn-Cu sulphides in the São Gabriel Terrane, Southern Brazil. The veins fill second- and third-order structures in Neoproterozoic calcitic marbles on the Cambaizinho Complex. Veins are mostly symmetrically zoned showing, from borders to the centre, fluorite and sericite, muscovite, adularia and albite (minor quartz, calcite and iron oxides). Galena, sphalerite, chalcopyrite, pyrite and minor cassiterite are disseminated in the veins and concentrated in ore pockets. Vein petrography, mineral chemistry and microthermometric measurements in fluorite fluid inclusions indicate that the hydrothermal veins were formed in a shallow crust environment from epithermal fluids near 140 °C. Their origin is attributed to a fossil geothermal system related to the post-collisional alkaline volcanism and caldera system of the Acampamento Velho Formation (574-549 Ma). This hydrothermal system is interpreted as genetically associated to fluorite and Pb-Zn-Cu occurrences on rhyolites and miarolitic cavities of related alkaline granitoids, Pb-Zn-Cu anomalies on stream sediment and soil analyses and Au quartz veins hosted by alkaline granitoids accompanied by pyrite, sericite and fluorite alteration halos in the same region. Although there is no mineral deposit discovered so far, the studied veins linked to the other base metal occurrences would indicate that the northwestern São Gabriel Terrane may host a poorly preserved mineralized epithermal system.

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

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