Fluid Inclusion Characteristics Research Articles

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

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

The superlarge Tyrnyauz skarn W-Mo and stockwork Mo(-W) to Au(-Mo, W, Bi, Te) deposit in the Northern Caucasus, Russia: Geology, geochemistry, mineralization, and fluid inclusion characteristics

The Tyrnyauz deposit (>850 Kt WO3, >220 Kt Mo, ~60 t Au, with additional ~140 t Au at a satellite deposit) is the largest W skarn deposit in Russia and the FSU. It comprises large mineralized (molydoscheelite) skarn zones of the intermediate-redox type, followed by overprinting and much wider systems of post-skarn quartz-garnet-pyroxene, quartz-garnet, quartz-wollastonite, quartz-feldspar and quartz veins with molybdenite and minor scheelite. Younger quartz-molybdenite (±scheelite) stockworks in zones of propylitic (quartz-amphibole-chlorite) alteration are typically more distal, and so are the complex W-Au-Bi-As-Te-Sb quartz-sulfide stockworks occurring in zones of phyllic (carbonate-phyllic) alteration. The mineralization appears to be associated with at least two separate igneous suites, possibly a Late Paleozoic low-K “trondhjemite” plutonic suite (quartz diorite, tonalite-granodiorite, and plagiogranite) followed by the formation of mineralized skarns, and a Neogene moderate- to high-K, plutonic to subvolcanic suite (leucocratic granite, biotite granite, rhyolite to rhyolite-dacite, vitroandesite, to trachyandesite-trachybasalt). The Neogene intrusions exhibit a reverse (toward less silicic rocks) overall differentiation trend, cut skarns, and alternate with the post-skarn hydrothermal stages.Prograde calcic skarn was formed from a carbonic-free aqueous, low-salinity (~3 wt% NaCleq.), high-pressure (~1.3 kbar), hot fluid, which could be sourced from crystallizing magma. As the magma degassing progressed, a Na-K-Ca-chloride, high salinity (~50 wt% NaCleq.), but still high-pressure (~1.4 kbar) fluid formed mineralized (with molybdoscheelite) retrograde skarn. After the Neogene leucocratic granite emplacement, the molybdenite (±scheelite) stockworks were formed from a boiling aqueous-carbonic fluid at decreasing (from 420 to 390 °C to 370–350 °C) temperatures and much lower (~0.5 kbar) pressures. A short (?) episode of the late quartz-pyroxene-fluorite-calcite veins with scheelite occurred after the rhyolite emplacement, and a corresponding influx of boiling high-temperature (600–650 °C), Na-K-Ca-chloride, high-salinity (>50 wt% NaCleq.), methane-rich fluid interrupted the generally low- to moderate-salinity carbonic-aqueous fluid supply. A moderate- to low-salinity (22 to 4–9 wt% NaCleq.), aqueous Na-K-chloride fluids formed the late Cu-Zn sulfide to W-Au-Bi-As-Te-Sb mineralization. The superposition of different fertile igneous suites and related mineralization styles may have been the key reason for the giant metal endowment.

Ore genesis and tectonic implication of the Daeheung-Ryongyang magnesite deposits in the East Jiao-Liao-Ji Belt, North Korea

The Daeheung and Ryongyang magnesite deposits in the Dancheon Mineralized Belt (DMB) of South Hamgyong Province, North Korea, have attracted wide attention because of their large reserves and geological similarity with a number of magnesite deposits in the Dashiqiao magnesite belt of Liaoning Province, China. The study of the magnesite deposits in the DMB was performed to analyze and compare the genetic and geotectonic implications between the two districts. The Daeheung and Ryongyang deposits comprise sedimentary and metamorphic rocks of the Paleoproterozoic Bugdaecheon Series and intrusive and extrusive rocks of diverse ages. Magnesite ores comprise magnesite, talc, chlorite, quartz, calcite, and apatite, and based on the mineralogy, ores can be divided into four groups: pure magnesite, chlorite-magnesite, talc-magnesite, and chlorite-talc-magnesite. Rare earth element (REE) patterns can be classified into three types: middle REE-enriched, heavy REE-enriched, and light REE-enriched, implying multiple events in the formation of magnesite deposits in the DMB. The carbon and oxygen isotope compositions of magnesite ores and dolostones in the DMB range from −1.0 to 1.0‰ and from 8.7 to 23.0‰, respectively. The results suggest that the mineralization proceeded under low fluid/rock ratios at low XCO2 or large input of freshwater into hydrothermal fluids. Salinity and homogenization temperature of fluid inclusions in magnesites range from 0.5 to 34.1 wt% NaCl eq. and from 112 to 290 °C, respectively, which are similar to those of the Dashiqiao magnesite belt. Considering the ore mineralogy, REE patterns, stable isotope composition, and fluid inclusion characteristics, magnesite ores may have been formed by various processes involving the inflow of Mg-enriched brines into carbonate rocks and then hydrothermal fluid infiltration related to granitoid intrusions. These results indicate that the Daeheung and Ryongyang magnesite deposits in the DMB belong to the Veitsch-type sedimentary-metamorphic deposits and are genetically correlated with mineralization in the Dashiqiao magnesite belt of Liaoning Province in China.

The Glafirinskoe and related skarn Cu-Au-W-Mo deposits in the Northern Altai, SW Siberia, Russia: Geology, igneous geochemistry, zircon U-Pb geochronology, mineralization, and fluid inclusion characteristics

The Glafirinskoe and related skarn Cu-Au (+Mo, W) deposits represent an Early Paleozoic (Late Cambrian to very early Ordovician) mineralization in the Altaid Belt, also known as the Central Asian Orogenic Belt. They are associated with multiphase plutons of high-K calc-alkaline to shoshonitic rocks that are related to a low-degree partial melting of metasomatically-enriched upper mantle, followed by amphibole fractionation in a deep (lower crustal ?) magma chamber and then by magma fractionation and emplacement at shallower crustal levels. Isotopic U-Pb zircon dating of the igneous rocks yields early Ordovician (ca. 480–478 Ma and 483 Ma) age. These rocks were emplaced in a continental magmatic arc after the Late Cambrian collision, in a post-collisional setting involving the stall and break-off of the subducting slab during the Late Cambrian to Early Ordovician.The deposits comprise prograde and retrograde skarns that are characterized by abundant andradite-rich garnet, which defines their oxidized type. Wider zones of potassic (quartz-K-feldspar) and calc-potassic (quartz-K-feldspar-calcite-garnet) alteration occur in the igneous rocks, with their further overprint by propylitic (with abundant scapolite) and phyllic (carbonate-phyllic) alteration. All these alteration assemblages bear abundant chalcopyrite and minor bornite. Phyllic alteration assemblages also contain various As, Sb, Pb, Zn, Co, Ni sulfides and sulfosalts, tellurides, Bi minerals, and native Au. Scheelite and/or molybdenite are locally present in some mineralized zones. The Cu-Au-Mo(-W) mineralization occurs as skarn orebodies that are spatially associated with porphyry-style alteration assemblages reflecting the high exploration potential for additional, but concealed, skarn-porphyry Cu-Au-Mo deposits in the vicinity.The retrograde skarn and potassic (calc-potassic) alteration assemblages were formed from high temperature (570–580 °C), high salinity, aqueous chloride magmatic-hydrothermal fluid, with its boiling and phase separation indicating hydrostatic conditions at a relatively deep (~6 km) skarn-porphyry environment. Propylitic alteration assemblages were formed at lower temperatures (~380–420 °C) from a Ca-Na-chloride, low salinity (~8 wt% NaCl-eq.) magmatic-hydrothermal fluid. Fluid inclusions in minerals from phyllic alteration assemblages indicate the influx of a CO2-rich fluid at about 270–290 °C and 1400 ± 50 bars and subsequent mixing with more saline (20 wt% NaCl-eq.) and cooler (~240 °C) hydrothermal fluids.

An Early Cretaceous gold metallogenesis in the Wuhe area, Eastern Anhui province: Constraints from geology, fluid inclusion, H-O isotope and geochronology on the Hekou gold deposit

The Wuhe area in eastern Anhui province, hosting 23 metric tons of gold, has been recognized as a new gold ore cluster in the North China Craton (NCC) since the Hekou gold deposit was discovered in 2017. Its metallogenic setting and ore-forming process remain unclear. In this contribution, we perform a combined geology, cathodoluminescence, fluid inclusion, H-O isotope and pyrite Rb-Sr geochronologic studies on the Hekou gold deposit of the Wuhe area. In order to perform detailed fluid inclusion petrography study, we used scanning electron microscope-cathodoluminescence (SEM-CL) on a well preserved sulfides-bearing quartz grain from the auriferous quartz vein. In this quartz grain, generation A barren quartz in the core zone (QA, CL-white), minor sulfides bearing generation B (QB, CL-light gray) in intermediate zone and sulfides rich generation C (QC, CL-dark gray) in the distal zone and fractures were revealed. Only in QC, the higher carbonic proportion (50–80 vol%) inclusions (CC) coexist with the two-phase liquid-rich aqueous fluid inclusions (LC) and sulfides, meanwhile the CC and the LC show a similar Th of 258–313 °C and 249–308 °C, but different salinities of 1.4–5.3 wt% NaCl equivalent and 6.0–10.9 wt% NaCl equivalent, respectively. It suggests that dominating fluid immiscibility recorded in QC is responsible for the prime deposition of gold and sulfide minerals. The δ18O (-4.1 to −6.5‰) and δD (-67.1 to −81.3‰) values of fluid inclusions in quartz suggest that ore-forming fluids were mainly derived from magmatic water which could related to mantle source. Gold-bearing pyrites yield an Rb-Sr isochron age of 128.1 ± 2.7 Ma, which is 8 m.y. earlier than the peak value of gold mineralization ages (ca. 120 Ma) at Jiaodong in response to the Early Cretaceous lithospheric thinning of the NCC and the reactivation of the Tan-Lu Fault zone (TLFZ). The Wuhe area shares similar characteristics of geology, fluid inclusions, H-O isotopes, and ore-forming ages with the Jiaodong gold ore cluster, highlighting the exploration potential in this region.

Mineralization and fluid inclusion characteristics of Pb-Zn-Fe-Ba (Cu, F, Sr) ore-deposits in northern east of Algeria

The northern east of Algeria represents the most important metallogenic zone for Pb-Zn-Fe-Ba (Cu, F, Sr) ore-deposits. The mineral association consists of galena, sphalerite, barite, and celestite with gray copper, pyrite, chalcopyrite, and marcasite associated with a carbonate (dolomite and calcite) matrix. Quartz, siderite, fluorite, and oxidation products like hematite, limonite, magnetite, smithsonite, and hydrozincite are also abundant. The ore-bodies are hosted in carbonate sedimentary rocks of lower Cretaceous, from Hauterivian to Aptian. Mineralization is mainly in vein fillings in fractures and in epigenetic lenticular or strata-bound ores. Most of the ore-bodies are structurally controlled by NE-SW-, NW-SE-, and E-W-trending faults, localized along the margins of subsiding sedimentary basins and diapiric zones, either inside hinges or on the flanks of anticlinal structures. Micro-thermometric data from sphalerite, dolomite, fluorite, quartz, calcite, and barite samples show relatively high temperatures, varying between 90 and 160°C. Salinity is variable, generally with high values (between 10 and 29.92 wt% NaCl equiv). These results combined to geological and metallogenic observations suggest an epigenetic origin for these mineral deposits. The saline fluids responsible for mineralization are related to basin fluids (formation water), which are classified as Mississippi Valley type (MVT), diluted locally by meteoric water. Eutectic temperatures measured in the fluid inclusions indicate an H2O-NaCl-CaCl2 system. The presence and variability of Na+ and Ca++ in the aqueous solutions suggest interaction with host rocks (contamination by dissolution respectively of Triassic gypsum and carbonate formations).

Mineralogy, petrochronology, geochemistry, and fluid inclusion characteristics of the Dardvay skarn iron deposit, Sangan mining district, NE Iran

The Sangan mining district, with a proven reserve of 1 Gt of 35 to 60% iron, is a world-class iron ore district in Iran, and located in the far eastern part of the Cenozoic Alborz Magmatic Arc. The east–west trending Sangan mining district consists of fourteen iron deposits, spatially associated with the Eocene Sarnowsar composite intrusion (syenite to syenogranite and granite), subvolcanic (quartz monzonite and syenite) and volcanic rocks (andesite and rhyolite). Syenogranite and quartz monzonite rocks in the Dardvay skarn are classified as oxidized I-type granites, with an average SiO2 content of 69.25–65.91 wt%, Al2O3 content of 13.71–13.98 wt%, total alkali (Na2O + K2O) content of 8.55–8.02 wt%, respectively. LA-ICP-MS zircon U-Pb dating on three syenogranite samples yield U-Pb ages of 39.6 ± 0.7 Ma, 39.3 ± 0.3 Ma, and 39.1 ± 0.4 Ma, whereas two zircon samples from skarn zones yield U-Pb ages of 39.7 ± 0.4 Ma and 39.5 ± 0.4 Ma, indicating a Middle Eocene mineralization event closely related to the Sarnowsar syenogranite. Zircon grains from a host rhyolite yield a U-Pb isochron age of 40.2 ± 0.4 Ma and previous published age for quartz monzonite is 42.3 ± 0.8 Ma. The Dardvay deposit is developed along the contact of the Sarnowsar syenogranite with dolomitic limestone with distinct exoskarn and endoskarn zones. The endoskarn zone is limited in extent, whereas the exoskarn is more extensive and includes pyroxene and garnet skarn zones close to the Sarnowsar syenogranite and epidote-phlogopite-actinolite skarn distal to it. The composition of clinopyroxenes plot along the diopside-hedenbergite join in the diopside and augite fields. The garnet composition ranges from Ad60Gr38 to Ad40Gr59. Three main paragenetic stages of skarn formation and ore deposition have been recognized at the Dardvay deposit: (1) a prograde stage developed at 380° to >550 °C with a fluid salinity between 16 and 66 wt% NaCl equivalent, (2) a retrograde stage which formed at 175°–325 °C with fluid salinity of 2.3 and 33.4 wt% NaCl equivalent, and (3) a post-ore-stage with quartz veins that developed at 180°–300 °C with salinity range of 8.3 to 17.7 wt% NaCl equivalent. Oxygen isotope analyses were conducted on magnetite from retrograde stage, resulting in a narrow variation of δ18O between 1.2 and 1.6 per mil with δ18O fluid of 10.3 to 10.7 per mil. Fluid inclusion and oxygen isotope analyses suggest that a possible mechanism for magnetite deposition is boiling and dilution with surface (meteoric) fluids, which together with increasing pH and decreasing T explains iron ore formation.

Characteristics of fluid inclusions in and metallogensis of the Zhuanshanzi gold deposit in Inner Mongolia

Characteristics of fluid inclusions in and metallogensis of the Zhuanshanzi gold deposit in Inner Mongolia

Paleo-Temperature and -Pressure Characteristics of Fluid Inclusions in Composite Veins of the Doushantuo Shale (Yichang Area, South China): Implications for the Preservation and Enrichment of Shale Gas

The Sinian Doushantuo Formation has been identified as a promising shale gas reservoir in South China and potentially worldwide. This study aims to restore the paleo-temperature and paleo-pressure ...

Characteristics of fluid inclusions in the Alqal Copper-Lead-Zinc deposit, Xinjiang

The Alqal Copper-lead-zinc deposit isl ocated in the Tarim plate of the Xinjiang. It has undergone multiple stages of tectonic mineralization and is an important deposit in the Kuslafu metallogenic belt of the West Kunlun area. Based on the analysis of the metallogenic geological conditions of the deposit, The composition of fluid inclusions in mining area was studied, The characteristics of metallogenic fluid are discussed. The results show that the uniform temperature of gas-liquid two-phase fluid inclusions in the Alqal deposit is between 145°C and 267°C, the average uniform temperature is 191°C; the salinity is 0.71% to 14.87%, and the average salinity is 6.33%. The estimated metallogenic pressure is about 135MPa, and the capture temperature is concentrated around 320°C. The ore-forming fluid has undergone multi-stage superimposed transformation, which is inconsistent with the characteristics of the typical MVT deposit, and it is a sedimentary transformation type deposit.

Detachment fault fluid composition, temperature, and pressure from fluid inclusion analysis in the central Grouse Creek Mountains, Utah

Fluid inclusions were trapped in sealed microfractures in quartz in quartz-muscovite veins in and near the Red Butte pluton. The pluton lies in the footwall of the Ingham Pass detachment fault in the Grouse Creek Mountain portion of the Raft River-Albion-Grouse Creek metamorphic complex. The veins crosscut all metamorphic fabrics in the country rock and the pluton and postdate the pluton intrusion. The aqueous fluids determined from temperature measurements contain 1.8 to 5.6 wt percent salt as NaCl and 5–21 mol percent CO2. The inclusions homogenized at 185 °C–290 °C though many of the inclusions leaked or decrepitated before homogenization was reached. Pressure estimates made from the CO2 content of the fluids ranged from a high of 210 Mpa near lithostatic pressure to 60 Mpa near hydrostatic pressure. Thermal history determined by Ar-Ar dating of K-feldspar, biotite, and muscovite show that the temperature cooled to 315 °C by 21 Ma near the upper fluid inclusion temperature. Basin and Range normal faulting is dated at 13.4 Ma. The fluid inclusion characteristics compared to lithostatic pressure gradients indicate that the upper plate of the detachment fault had thinned from the maximum of near 15 km at the inception of the fault to about 8 km by the time of entrapment of the fluid inclusions. Pressure as high as lithostatic could have facilitated detachment faulting if the elevated fluid pressure was present during detachment fault displacement.

Porphyry-type mineralization associated with epithermal deposits in the Tarom metallogenic belt of NW Iran: Constraints from fluid inclusions

Research is conducted to investigate whether or not, apart from the Chodarchay deposit, there are other examples of porphyry-type mineralization associated with epithermal deposits in the Tarom metallogenic belt of the Alborz zone, NW Iran. Homogenization temperature, final ice-melting, and salinity values are determined for fluid inclusions in mostly quartz and partly calcite, fluorite, sphalerite, and barite samples from eight epithermal ore deposits to unravel the enigma on porphyry-type mineralization in Tarom. The homogenization temperatures and salinities of the fluid inclusions range from 82 to 520 °C and 0.2 to 37 wt% NaCl equiv., respectively. The fluid inclusions show varying densities from 0.4 to ~1.2 g/cm3 with most values between 0.7 and 0.95 g/cm3. Tarom epithermal deposits in order of maximum mineralization depth are Chargar (520 m), Zajkan (640 m), Goloujeh (770 m), Lohneh (1075 m), Nikoueieh (1150 m), Khalifelou (1500 m), Aghkand (1690 m), and Chodarchay (1900 m). It seems that magmatic water played an important role in the Tarom epithermal deposits except for Chargar where mixing magmatic and meteoric waters is considered as the main mechanism for ore deposition. The physicochemical variations suggest differences among epithermal deposits in the Tarom district. Chodarchay, Lohneh, Khalifelou, and Goloujeh have some fluid inclusion features of porphyry mineralization associated with an epithermal part. Minerals from Tarom contain fluid inclusions indicative of porphyry mineralization beneath some intermediate- and high-sulfidation epithermal deposits. The findings of this study are instrumental in the exploration of deeper porphyry parts of the Tarom epithermal deposits.

Trace element and fluid inclusion geochemistry constraint for genesis of gold-polymetallic mineralization in the Songhung deposit, DPR Korea

The Songhung deposit is located in the southwestern part of the Yangdok metamorphic core complex (YMCC) in the northern portion of the Pyongnam Basin, the eastern part of the Sino-Korean Craton. In this paper, we present a detailed study on the magma sources of the granitoids (Yangdok and Hoechang graintic intrusions), genesis of pyrite and fluid inclusion characteristics for sufficient and additional understanding of tectonic events, petrogenesis of the granitoids and mineralization in the study deposit. The Yangdok granite has lower Al2O3/TiO2 ratios (mean value of 60.58) than the Hoechang granite (mean value of 994.46), indicating the higher temperature magma source of the former. On the Rb/Ba vs. Rb/Sr and CaO/(TFeO + MgO + TiO2) vs. (CaO + TFeO + MgO + TiO2) discriminant diagrams, the magma source of the Yangdok granite belongs in the plagioclase-rich and clay-poor source rocks, while those of the Hoechang granite plots either in the plagioclase-rich and clay-poor source rocks (for granite and fine-grained granite) or in the plagioclase-poor and clay-rich source rocks (for granite porphyry and felsite). On the Nb vs. Y, Ta vs. Yb, Rb vs. Y + Nb and Rb vs. Yb + Ta tectonomagmatic discrimination diagrams, these two granites are connected with the volcanic arc-related setting and plot in post-collision setting. Moreover, some data of the Hoechang granite fall in WPG field, suggesting that the volcanic arc setting may be changed to an intraplate setting from Middle Cretaceous.The pyrite trace element geochemistry, showing the high Co/Ni ratio than one with an average of 8.2 and high Co content and low Ni content, suggests that its formation was closely linked with I-type granitic magma-derived hydrothermal fluid mixed with meteoric water. It could also be assumed by the Co and As contents in pyrite, indicating a certain degree of meteoric water in the ore forming fluid. It is consonant to the Pb, S, C and O isotope geochemistry in the previous study, suggesting that ore-forming fluids and metals could be derived from both the Yangdok granite and the Proterozoic and Paleozoic meta-sedimentary rocks exposed in the study area. All of the pyrite grains have not compositional zoning and the similar distribution patterns of Co and Ni are appeared in single pyrite grain (from core to rim), suggesting the stable crystallization environment of pyrites and same ore forming fluid source. In pyrite grains, the positive correlation between gold and arsenic is appeared. The Au exists either as a micro- and nano-size inclusion in pyrite and other minerals or as a solid solution in pyrite lattice. Based on the petrological and microthermometric characteristics of the fluid inclusions in ore-bearing quartz, we suggest that the ore-forming fluid is represented as NaCl + H2O or NaCl + KCl + H2O systems with low salinity. The absence of CO2-enriched phase and vapor-only or liquid-only primary inclusions in quartz indicates the homogenous magma-derived ore forming fluids and a lack of boiling during ore-forming process. The formation temperature and pressure of this deposit approximately vary from 317 to 326 °C and from 105.46 to 111.69 × 105 Pa, respectively, exhibiting the hydrothermal deposit origin. In conclusion, the Songhung deposit is originated from I-type granitic magma source-derived hydrothermal fluid which was mixed with meteoric water.

Gold composition and conditions of Southern Ak-Dag gold-sulfide-quartz ore occurrence formation (Western Tuva)

Research subject. The paper presents data on the mineralogical, geochemical and fluid inclusion features of the Southern Ak-Dag gold-sulphide-quartz ore occurrence in Western Tuva.Methods. Mineral formation temperatures, salt composition and fluid salinity were examined using a Linkam TMS-600 cryostage and an Olympus BX 51 microscope. The chemical composition of samples was identified using a MIRA 3 LMU (Tescan Orsay Holding) scanning electron microscope equipped with INCA Energy 450+XMax 80 and INCA Wave 500 microanalysis systems; BSE photos were taken by Tescan Vega 3 and Hitachi ТМ-1000 SEM instruments.Results. The ores under study were found to contain both high-grade and medium-grade gold with an Ag content of up to 17.05 wt %. The average gold fineness comprised 904 ‰, ranging from 830 to 928 ‰. According to fluid inclusion data, gold-sulphide-quartz veins were formed at temperatures of 280–240 °C and pressures of 0.8–1.2 kbar from aqueous fluids having a salinity of 8.6–6.4 wt % NaCl eq. The narrow range of fluid salinity at decreasing temperatures and the prevalence of high-grade gold in sulphide-quartz veins indicate a relatively high rate of mineral formation in a narrow permeable zone without any significant interaction with host rocks or mixing with meteoric waters.Conclusions. Gold mineralization in the Southern Ak-Dag ore occurrence, which was formed within one ore substage, corresponds to the type of gold-galena-chalcopyrite with barite. The established similarity of native gold in the Southern Ak-Dag occurrence and other deposits in the Aldan-Maadyr ore cluster in terms of P-T parameters of ore formation and mineralogical and geochemical features, as well as association of the ore mineralization with beresites, indicate the possibility of discovering industrial ore deposits in the region and confirm its paragenetic relation with Devonian magmatic activity.

The Ultramicrochemical Analyses (UMCA) of Fluid Inclusions in Halite and Experimental Research to Improve the Accuracy of Measurement

Fluid inclusions in halite are widely used in research to determine the conditions of sedimentation in salt basins and reconstruct the chemical composition of seawater during a specific geological period. However, previous preliminary studies of the genetic types of inclusions, considered in the present research project, have not received due attention. Consequently, we decided to take into account the main distinguishing features of fluid inclusions in halite, belonging to various genetic types. The ultramicrochemical analysis (UMCA) method is one of the several methods that are used for the quantitative determination of the chemical composition of the primary fluid inclusions in halite. We have upgraded that technique, and that allowed us to reduce the analytical error rates of each component determination. The error rates were calculated in the study of Ca-rich and SO4-rich types of natural sedimentary brines.

Laser-Raman spectral analysis of the Baoxingchang Cu-Mo deposit, Yunnan Province, SW China

Baoxingchang Cu-Mo deposit is one of several Cu-Mo-(Au) polymetallic deposits have been found in the Tethys metallogenic province. Laser-Raman spectral analysis shows that the vapour-phase components of fluid inclusions in quartz are mainly composed of water vapour and a little CO2, while the fluid-phase components contain Na+ and Cl− metallogenic fluid, which generally belongs to a NaCl-H2O system. In conclusion, the characteristics of fluid inclusions in porphyry-type Cu-Mo polymetallic deposits in Baoxingchang are closely related to multi-stage intrusions along the Jinshajiang-Red River shear zone.

Epithermal Mineralization in the Busang Southeast Zone, Indonesia: New Insight into the Au Prospect at the Center of the Bre-X Fraud

The Busang mineral prospect in Kalimantan, Indonesia, was reported to host a large Au resource until 1997 when it was revealed that drill core samples had been deliberately and systematically contaminated (“salted”) with extraneous Au to falsify resource estimates. One month before the fraud was uncovered, Dr. G. Milligan, then professor emeritus of geology, visited the site to collect a suite of core samples for academic study that was deemed representative of the host rocks, alteration, and mineralization of the Busang Southeast Zone. These samples were re-examined here by optical microscopy, electron microprobe (EMPA), whole-rock geochemistry, and fluid inclusion microthermometry to characterize the subsurface geology and hydrothermal mineralization, and to assess reasons why the system is of uneconomic character. The host rocks were variably altered calc-alkaline porphyritic subvolcanic diorites, typical of the lithological units along the mineralized trend in the Kalimantan Gold Belt. Early hydrothermal mineralization with quartz-sulfide (pyrite, chalcopyrite, Cu-sulfosalts) stockwork veinlets associated with pervasive phyllic and propylitic alteration was overprinted by crudely banded quartz-carbonate-sulfide/sulfosalt (pyrite, sphalerite, chalcopyrite, galena, tennantite-tetrahedrite, bournonite-seligmannite) veins. The stockwork veins were associated with up to 140 ppb bulk rock Au, some of which was hosted by Cu-sulfosalts. Microthermometry on quartz-hosted aqueous fluid inclusion assemblages (FIA; n = 13) and single inclusions (non-FIA; n = 20) in quartz-carbonate-sulfide/sulfosalt veins yielded an overall range in homogenization temperatures (Th) between 179 °C and 366 °C and bulk salinities between 1.1 wt.% to 8.6 wt.% NaCl equivalent, with much smaller data ranges for individual FIA (e.g., FIA 3; 239.1 °C to 240.5 °C and 0.5 wt.% to 1.4 wt.% NaCl equivalent). Primary FIA along growth zones in quartz were identified, providing constraints on fluid characteristics at the time of quartz growth. Carbonate-hosted FIA (n = 3) and single inclusions (non-FIA; n = 3) in the same veins yielded Th between 254 °C and 343 °C and bulk salinities of 1.1 wt.% to 11.6 wt.% NaCl equivalent. Likewise, data ranges for individual FIA were much smaller. Many of the geological characteristics of the Busang Southeast Zone were compatible with a telescoped, intermediate-sulfidation epithermal system, having formed from diluted magmatic fluids that precipitated weak base metal mineralization. However, the system was unproductive with respect to Au and Ag, at least within the studied area. Of note, vein textures and fluid inclusion characteristics indicative of boiling or efficient fluid mixing—processes both considered critical for the formation of economic lode gold deposits—were absent in the samples.

Characteristics of fluid inclusions in the Cenozoic volcanic-hosted Kushk-e-Bahram Manto-type Cu deposit of central Iran

Abstract The Kushk-e-Bahram Manto-type Cu deposit is located in central Iran, within Eocene to Oligo–Miocene volcanic strata which occur in the central part of the Uremia-Dokhtar Magmatic Arc (UDMA). Propylitization, silicification, argillization and carbonatization are the main types of alteration to have affected the pyroclastic and volcanic rocks. There are high amounts of oxide minerals, including malachite, azurite, hematite, magnetite and goethite. Three types of primary FIs have been determined in the Kushk-e-Bahram deposit, namely; I: two-phase liquid-rich FIs (L+V), II: mono-phase liquid FIs, III: two-phase vapour-rich FIs which have been identified based on petrographical studies. Based on FI studies of co-existing quartz and calcite, homogenization temperatures (Th) must have been between 67 and 228°C, with an average of 158°C. Moreover, salinity is between 14.0–30.3 wt% NaCl, equivalent to a 19.6% average. Fluid density values vary from 0.8 to 1.1 gr/cm3. Based on FI data and related diagrams, the depth of their trapping was estimated to be <200 m and ore formation occurred at pressures of <50 bars. Consequently, mineralogy, host rock and FIs characteristics in the Kushk-e-Bahram deposit are similar to the Manto-type Cu deposits in Mesozoic-Cenozoic volcanic belts of Iran and South America.

A Manto-type Cu deposit in the Central Asian Orogenic Belt: The Hongguleleng example (Xinjiang, China)

Manto-type Cu deposits with relatively high grade (up to >8 wt% Cu) occurred widely around the Pacific Rim Belt and along the Himalayan–Tibetan Belt. However, so far, Manto-type Cu deposits have not been reported in the Central Asian Orogenic Belt (CAOB). Hongguleleng (also called Armuqiang), located in the West Junggar, Xinjiang, China, is the first recognized Manto-type Cu deposit. It is hosted in the Late Silurian–Early Devonian volcano-sedimentary sequence and associated with pale-volcanic apparatus. The Cu bodies are restricted to particular porous units (e.g. andesitic volcanic breccias, amygdale basalt and andesite) and are mostly controlled by the steep dipping fault zones.The host volcanic rocks have been overprinted by three alteration assemblages and associated copper mineralization. An early barren propylitic (chlorite-calcite) assemblage is widespread and is overprinted by epidote-chlorite assemblage associated with ores. They are cut by barren calcite veins. The major copper sulfides are chalcopyrite, bornite, and chalcocite that show disseminated, amygdale filling, breccias, vein-veinlet, massive and replacement textures. Only two fluid inclusion types were recognized in quartz, calcite and epidote: liquid-rich and vapor-rich inclusions. They have homogenization temperatures in the range 140–280 °C. Sulfur isotope compositions from ores have a positive δ34S values range from +0.5‰ to +3.4‰, suggesting a magma source. From the geology, alteration, mineralization, and fluid inclusion characteristics and sulfur isotopic compositions, we propose that the Hongguleleng deposit is classified as a typical Manto-type copper deposit.

Quartz-Hosted Fluid Inclusions Characteristics and Their Implications for Fluvial Deposits along the Changjiang River

The characteristics of quartz-hosted fluid inclusions in fluvial sediments from five locations in the upstream, midstream, and estuary of the Changjiang River, China, are analyzed. The sources of sediments are discussed concerning their differences in the shape, size, number, gas percentage and genetic type of quartz-hosted fluid inclusions. From upstream to downstream, the characteristics of quartz-hosted fluid inclusions in sediments are different. The fluid inclusion types in the samples from upstream to estuary are gradually enriched. The sediment influx from the tributaries of the Changjiang River makes new types of quartz-hosted fluid inclusions in the downstream and estuary. In terms of the number and size, most quartz-hosted fluid inclusions are concentrated in the range of 2–4 µm in diameters and 10–150 in number per 10−3 mm3. The number and size ranges of the fluid inclusions from different positions are also different. The fluid inclusions in the sample collected from the Shigu, upstream of the Changjiang River, are 2–18 µm in size, with the number of 2–166 per 10−3 mm3. Among the samples collected from Yibin, Yichang and Wuhan, the sizes of fluid inclusions are 2–15, 2–10, 2–12 µm, with the number of 1–270, 2–220, and 1–308 per 10−3 mm3, respectively. The proportion of primary fluid inclusions in the sample of the upstream (14%) is higher than that of the midstream (6%–8%) and the estuary (5%), suggesting that different types of source rocks have been input into the river by the tributaries. The characteristics of quartz-hosted fluid inclusions in the fluvial sediments could offer a new perspective for exploration of the source of sediments.