Fluid Inclusions In Quartz Veins Research Articles

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.

ФЛЮИДНЫЙ РЕЖИМ ФОРМИРОВАНИЯ ОРОГЕННЫХ ЗОЛОТОРУДНЫХ МЕСТОРОЖДЕНИЙ ЯНО-КОЛЫМСКОГО ПОЯСА

The microthermometric and bulk analysis data on fluid inclusions in vein quartz of 16 orogenic gold deposits located in various parts of the Yana-Kolyma belt are presented. The deposits were found to have formed in the temperature range 350–220°C with weakly mineralized carbon dioxide-aqueous fluids (&lt; 5 wt. % NaCl-eq.) typical for orogenic ore-forming systems. The composition of the salts is dominated by sodium bicarbonate, and trace elements are K, B, As, Sb, Rb, and Cs. The molar fraction of CO2 varies from 0.19 to 0.03 depending on the RTX conditions. The molar fraction of methane in carbon dioxide does not exceed 0.1. Intense degassing of solutions in the range between 320° and 270°C could be one of the reasons for ore deposition. Gold–bearing quartz veins and veinlets were formed at depths of 6–3 km with a decrease in pressure from 1.5–1.0 to 0.9–0.8 kbar while the orogeny dynamic regime evolved. At the final stage, the opening of fractures led to a change of the lithostatic regime to hydrostatic with a pressure drop to 0.5–0.1 kbar. At the final stages of mineral formation, fluid systems are characterized by increased salinity and the gas phase comprising essentially nitrogen and methane, which indicates their supply from another source. Thus, the parameters of fluid inclusions in quartz reflect a long history of evolution of the processes involved in mineral and ore formation that associated with the orogen development.

Vývoj metamorfních fluid pozdního stádia regionální metamorfózy v keprnické klenbě silezika

Neo-Proterozoic rocks (Brunovistulian Unit) are dominant in the studied area of Silesicum, which have complex nappe, thick-skinned and thrust sheet geological structures. The Keprník Dome (Keprník nappe) represents the easternmost part of crystalline complexes of the Silesian domain and is dominated by various types of orthogneiss, gneiss, mica schist and phyllite, with a small occurrence of calc-silicate rocks. These rocks are affected by pre-Variscan and Variscan metamorphism, dominantly staurolite-sillimanite and garnet zone and late Variscan to Cenozoic brittle deformation. Hydrothermal Variscan quartz veins and surrounding rocks (biotite-bearing paragneiss and orthogneiss) were studied in the Keprník dome geological unit to confront the type of fluids enclosed in fluid inclusions and the intensity of metamorphism that affected the host rocks. The study of fluid inclusions in quartz veins was supplemented by Raman spectrometry and microscopic study of rocks, EMPA and mineral thermometry. Temperatures 616 to 643 °C obtained by the Ti-in-biotite method for biotite paragneisses are compatible with the peak metamorphic conditions estimated by previous authors. Thermometer for orthogneiss provided temperatures between 688 to 699 °C using the Ti-in-biotite thermometer. The lower temperatures (483 to 529 °C) obtained using magnetite-ilmenite thermometer document later retrogression. Three types of fluids were found in the quartz of the Variscan hydrothermal veins based on the phases present, respectively components: I. L+V, H2O–NaCl ± K+ ± Mg2+ ± Ca2+, II. L+V+S±S2, H2O–NaCl–CaCl2 ± K+ ± Mg2+, III. L1+L2+V, H2O–NaCl–CO2 ± CH4 ± K+ ± Mg2+ ± Ca2+ (L – liquid, V – vapour, S – solid). Type II inclusions contain aqueous fluids with high salinities, which would correspond to the post-Variscan systems found (Slobodník et al. 2010a, 2020) in the Silesicum area. On the other hand, they have high Th temperatures, reaching values of over 300 °C. Only results from type I could be used to calculate isochores and derive P-T conditions for the formation of Variscan veins, because in type III often occur fluid inclusion decrepitation and the impossibility of measuring total homogenization. Types I and III according to the structural position of fluid inclusion (uncertain or primary and pseudosecondary inclusions), microthermometric data and composition, they are considered to be metamorphic types of fluids generated by Variscan metamorphism. The evaluation of isochores of the first type of fluids using a lithostatic thermobaric gradient (50 °C/270 bar/km) indicates the entrapment of fluids, or formation of inclusions under conditions of 190–300 °C and 90–160 MPa. This type of fluid was very likely captured at a later stage of metamorphism, after the crystallization of magnetite and ilmenite, and represents a retrograde stage of metamorphism.

Fluid inclusions in vein quartz as a reflection of the deformation stages of the junction area of Baikal-Muisk and Barguzin-Vitim structural-formation zones (Western Transbaikalia)

Research subject. Fluid inclusions in quartz of three vein systems associated with tectonic cracks occurred during the development of thrust and shear deformations of the Western Transbaikalia. Vein systems localized in volcanic, terrigenous and granite rocks. Methods. The composition of fluid inclusions was studied by microthermometry, Raman spectroscopy and gas chromatography-mass spectrometry. Results. The quartz under study was formed by high-density medium-temperature NaCl-KCl and a low- and medium-salinity water-carbon dioxide fluid (2-5 wt % NaCl eq.). A distinctive feature of quartz of different vein systems was found to be the gas phase composition of inclusions associated with the composition of host rocks. The minimum temperatures of vein quartz formation were determined to range from 180 to 450°C under the minimum fluid pressure values of 0.7-2.9 kbar. Conclusions. Complex vein systems of the junction zone of the Baikal-Muiskaya and Barguzino-Vitimskay SFZ, confined to different host rocks and having different structural positions, are characterized by a similar fluid composition and a common thermodynamic history reflecting the change of deformation aggregates. The metamorphogenic-hydrothermal nature of the fluid involved in the formation of quartz vein systems was established. The development of the hydrothermal system was accompanied by its influence on the host rocks, which was manifested in the variations of fluid composition. The evolution of a single hydrothermal system is associated with tectonic deformation processes, which can be described by three dynamic stages corresponding to three quartz generations.

Gold Mineralization at the Maletoyvayam Deposit (Koryak Highland, Russia) and Physicochemical Conditions of Its Formation

Microthermometry study of fluid inclusions in quartz veins of the Maletoyvayam deposit (Koryak Highland, Russia) was carried out. This epithermal gold deposit contains unique Au compounds including maletoyvayamite, which has not been reported anywhere else. Two paragenetic mineral associations (pyrite-quartz and maletoyvayamite-quartz) with quartz of different generations corresponding to different pulses were also described. Only early generations of quartz (Q1) include ore minerals: pyrite for the first mineral assemblage, and in Au-bearing minerals, sulfosalts, bismuthinite, and others—for the second assemblage. A study on fluid inclusions in quartz showed a salinity (mainly NaCl + KCl) range from 0.2 to 4.3 wt.% NaCl eq., increasing from the first mineral association to the second due to boiling fluids. The obtained temperature variations for quartz crystallization were 295–135 °C, the fluid pressure ranged from 79 to 4 bar. On the other hand, the range of conditions obtained for the gold productive ore association is more narrow: salinity of the fluid inclusions is 4.3 wt.% NaCl eq., the temperatures vary from 255 °C to 245 °C, and the pressure from 39 to 32 bar. These physicochemical characteristics of the Maletoyvayam ore deposit greatly coincide with other HS-type epithermal deposits; however, within the Central Kamchatka Volcanic Belt it is so far the only deposit of this type reported.

Geochemical characteristics of gold mineralization of the Huai Kham On deposit, Sukhothai Fold Belt, Northern Thailand

AbstractThe Huai Kham On gold deposit is located in the central part of the Sukhothai Fold Belt, northern Thailand. The Sukhothai Fold Belt represents an accretionary complex formed by subduction and collision between the Indochina and Sibumasu Terranes. There are many small gold deposits in the Sukhothai Fold Belt; however, the styles and formation environments of those gold deposits are not clear. The geology of the Huai Kham On deposit consists of volcanic and volcanosedimentary rocks, limestone, and low‐grade metamorphic rocks of Carboniferous to Triassic age. Gold‐bearing quartz veins are hosted by volcanic and volcanosedimentary rocks. The quartz veins can be divided into four stages. The mineral assemblage of the gold‐bearing quartz veins of Stages I and II comprises quartz, calcite, illite, pyrite, native gold, galena, chalcopyrite, and sphalerite. Quartz veins of Stage III consist of microcrystalline quartz, dolomite, calcite, pyrite, native gold, and chalcopyrite. Veins of Stage IV consist of calcite, dolomite, chlorite, and quartz. Fluid inclusions in quartz veins are classified into liquid‐rich two‐phase (Types IA and IB), carbonic‐aqueous (Type II), and carbonic (Type III) fluid inclusions. The homogenization temperatures of Types IA and II fluid inclusions that are related to the gold‐bearing quartz veins from Stages I to III ranged from 240° to 280°C. The δ18O values of quartz veins of Stages I to III range from +12.9 to +13.4‰, suggesting the presence of a homogeneous hydrothermal solution without temperature variation such as a decrease of temperature during the formation of gold‐bearing quartz veins from Stages I to III in the Huai Kham On gold deposit. Based on the calculated formation temperature of 280°C, the δ18O values of the hydrothermal solution that formed the gold‐bearing quartz veins range from +3.2 to +3.7‰, which falls into the range of metamorphic waters. The gold‐bearing quartz veins of the Huai Kham On deposit are interpreted to be the products of metamorphic water.

Formation and genesis of Paleozoic sediment-hosted barite deposits in Turkey

Most barite deposits in Turkey are sediment-hosted deposits which are located in different lithologies within passive margin sediments from the Paleozoic. The Şarkikaraağaç, Hüyük and Tordere deposits occur in the western part of the Tauride-Anatolide tectonic unit, whereas the Şekeroba and Önsen region deposits located in the eastern part of Turkey occur on both Arabian and Tauride-Anatolide microplates. While the former deposits occur as both concordant and discordant bodies within Early Paleozoic carbonates, the latter deposits are found as discordant, fracture filling and replacement-type ore bodies.O, D, S, Sr and Pb isotope studies were used to determine and correlate the formation conditions of these deposits. δ18OSMOW mean values of the Tordere barite deposit are slightly higher (mean 16.2‰) than the mean values for the Şekeroba (10.8‰) and Önsen (11.3‰) deposits. The δ18OSMOW (mean 15.83‰) and δDSMOW (mean −67‰) values obtained from fluid inclusions in quartz veins in the Şekeroba barite deposit correspond to metamorphic or deep circulation hydrothermal waters. Mean δ34 SCDT values from Şekeroba, Tordere and Önsen deposits are 31.7, 33.8 and 20.6‰, respectively, which are compatible with the early Paleozoic seawater, except for the Önsen deposit.87Sr/86Sr mean values for the barite deposits of Turkey are defined as follows (‰); Şekeroba: 0.713, Önsen: 0.711, and Tordere: 0.711, which are higher 87Sr/86Sr isotope ratios than Paleozoic seawater. The Pb isotope values in Şekeroba and Tordere deposits are similar and mean is 206Pb/204Pb = 18.28, 207Pb/204Pb = 15.67 and 208Pb/204Pb = 38.50. High radiogenic Sr and Pb isotope data from the deposits indicate that Ba was generated from thick Paleozoic clastics or the older crust beneath them.Sr, S, and O isotopes and the positive Gd anomaly in the barites are very similar to those of Paleozoic stratiform cold-seep barites. The primary stratiform-stratabound barite deposits, like Şarkikaraağaç-Hüyük deposit, could have formed either by cold seep or diagenetic processes at the sediment–seawater interface or within the sediment related to sulfate-methane boundary. Although there are similar Sr and Pb isotopic signatures between the western and eastern region deposits, the eastern region Şekeroba, Önsen and Tordere barite deposits show discordant ore geometry and highly radiogenic isotope values indicating that primary stratabound-stratiform barite was dissolved and remobilized along deep-seated fault zones during the Hercynian orogenesis and deposited in different Paleozoic lithologies related to cooling and/or increase in Eh.

Geology, geochemistry, geochronology and genesis of the late Miocene porphyry Cu-Au-Mo mineralization at Afyon-Sandıklı (AS) prospect, western Anatolia, Turkey

Afyon-Sandıklı ‘AS’ is an example of a porphyry Cu-Au-Mo systems hosted in post-collisional late Miocene magmatic rocks within the Afyon-Ören Zone of Turkey. The systems were generated by multi-phase intrusions emplaced into early stage volcanic and volcanoclastic rocks of the Afyon volcanics. The REE and radiogenic isotope data from these rocks suggest a magma source containing residual garnet with a low hydrous phase. These collectively, favor a metasomatized mantle source for magmas generated in either subduction or post-collisional environments.Four main alteration types have been identified in the AS porphyry Cu prospect; potassic, phyllic, epidote-chlorite and advanced argillic. The alteration zones are centered around monzonite porphyry intrusives. Chalcopyrite and bornite are the main copper minerals in the potassic alteration zone with subordinate molybdenite. All are replaced by pyrite.The U-Pb SHRIMP analyses on a post-mineral micromonzonite porphyry dike yielded an age of 10.97 ± 0.09 Ma, whereas the host monzonite porphyry yielded an age range between 10.5 and 12.5 Ma. Ar-Ar geochronology on alunite constrains the timing of the argillic alteration at 11.2 ± 0.5 Ma.Fluid inclusion studies were performed on primary inclusions in quartz veins from the potassic and phyllic alteration zones. The primary fluid inclusions in quartz veins in both zones were classified as Type 1, single-phase vapor (V); Type 2, two-phase liquid-vapor (L-V); and Type 3, three-phase liquid-vapor-solid (L-V-S). Type 3 inclusions in the potassic alteration zone with weak phyllic overprint have higher homogenization temperatures compared to those in pervasive phyllic alteration zones. The majority group of fluid inclusions in the AS prospect are Type 2 inclusions with variable vapor and liquid abundances. This suggests boiling (phase separation) of the hydrothermal fluids, and post boiling trapping of the vapor and liquid. The presence of abundant multiphase (Type 3) inclusions in the AS prospect marks the stage when phase separation took place. The phase separation appears to have resulted in intermediate to high-salinity multiphase brines and daughter crystals in the residual fluid. Additionally, we suggest that superposition of phyllic and potassic alteration zones with a variety of Type 2 and Type 3 inclusions in the AS prospect should mark the stage at which mixing by relatively cooler and dilute meteoric water coupled with phase separation occurred.The calculated δ18O(fluid) vs δD(fluid) values for the alteration minerals display a wide range between the primary magmatic field to the meteoric water line. The δ18O(fluid) vs δD(fluid) values for biotite suggest a strong magmatic water influence during the formation of potassic alteration. Likewise, a very narrow range of δ34S, close to the sulfur isotope values of magmatic sulfur indicate a magmatic source, and may suggest that potassic alteration was caused by a uniform magmatic fluid source. Additionally, the enrichment in the δD(fluid) from biotite suggests that phase separation (boiling) was also active during potassic alteration. The overlapping pattern of the δ18O(fluid) vs δD(fluid) compositions for biotite and sericite indicate an isotopic similarity, and may suggest that they have been formed from a similar, predominantly magmatic fluid mixed to some degree with the meteoric water.

Geochemical, fluid inclusion and O–H–S isotope studies of the Milajerd Au-polymetallic prospect, Central Iran: Implications for ore genesis

The Milajerd Pb-Zn ± Au polymetallic prospect in Naein-Qom Magmatic Zone is a favorable target for exploration. Geological and geochemical characteristics such as setting, alteration assemblages, fluid inclusion microthermometry and stable isotopes are consistent with the Milajerd Pb-Zn ± Au polymetallic prospect being a typical low-sulfidation (LS) epithermal deposits. The Au-polymetallic mineralization occurs mainly as structurally controlled veins, and brecciated dikes, hosted by calc-alkaline volcanic rocks. Mineralization at the Milajerd prospect is controlled by an annular fault system. The sulfide mineralogy of the deposit includes sphalerite, galena, pyrite, arsenopyrite, and marcasite. The principal gangue minerals are quartz, calcite, sericite, and adularia. The alteration assemblages include quartz ± pyrite, quartz-sericite-pyrite and chlorite-calcite-epidote. Fluid inclusions in quartz-sulfide veins have homogenization temperatures (Th) of 158–255 °C and salinities of 4.7–7.7 wt% NaCl equiv., whereas those in barren quartz ± carbonate veins yield Th values of 135–176 °C and salinities of 1.1–4.3 wt% NaCl equiv. The H and O isotopic composition (δDwater = − 120 to − 92‰; inferred δ18Owater = − 6.2 to 3.5‰) of fluid inclusions in quartz veins imply that cooling a mixed magmatic and meteoric waters was the main mechanisms of ore deposition at Milajerd deposit. The δ34S values of ore sulfides are mostly close to zero (avg. − 0.1‰), indicating a magmatic source of sulfur, which could have emanated directly from magmatic activity or have been leached from the surrounding volcanic rocks.

In situ Raman spectroscopic quantification of CH4\u2013CO2 mixture: application to fluid inclusions hosted in quartz veins from the Longmaxi Formation shales in Sichuan Basin, southwestern China

We re-evaluate the Raman spectroscopic quantification of the molar ratio and pressure for CH4–CO2 mixtures. Firstly, the Raman quantification factors of CH4 and CO2 increase with rising pressure at room temperature, indicating that Raman quantification of CH4/CO2 molar ratio can be applied to those fluid inclusions (FIs) with high internal pressure (i.e., > 15 MPa). Secondly, the v1(CH4) peak position shifts to lower wavenumber with increasing pressure at constant temperature, confirming that the v1(CH4) peak position can be used to calculate the fluid pressure. However, this method should be carefully calibrated before applying to FI analyses because large discrepancies exist among the reported v1(CH4)-P curves, especially in the high-pressure range. These calibrations are applied to CH4-rich FIs in quartz veins of the Silurian Longmaxi black shales in southern Sichuan Basin. The vapor phases of these FIs are mainly composed of CH4 and minor CO2, with CO2 molar fractions from 4.4% to 7.4%. The pressure of single-phase gas FI ranges from 103.65 to 128.35 MPa at room temperature, which is higher than previously reported. Thermodynamic calculations supported the presence of extremely high-pressure CH4-saturated fluid (218.03–256.82 MPa at 200 °C), which may be responsible for the expulsion of CH4 to adjacent reservoirs.

Constraints on ore formation conditions at the Mazra’eh Shadi epithermal deposit, NE Tabriz, Iran: evidences from geochemistry, sulphur isotope, quartz textures and fluid inclusion studies

The Mazra’eh Shadi deposit is one of the most representative gold deposits in the Ahar-Arasbaran Belt. The main minerals are galena, sphalerite, pyrite and chalcopyrite. Concentrations of Au-Ag occur mainly within quartz veins. Five textures (crustiform, comb, microcrystalline, cockade, and mosaic) are distinguished by field reconnaissance and hand specimen observations. The d 34 S values suggest an increasing role of meteoric water from the deepest levels to the shallow level and surface. Fluid inclusion data show that the mineralisation at the Mazra’eh Shadi deposit can be classified as a volcanic-rock-hosted intermediate-sulphidation epithermal deposit. Fluid inclusions in vein quartz can be distinctly divided into three types according to interpretation of petrographic features: intense boiling, gentle boiling and non-boiling conditions. The presence of intense and gentle boiling among different substages at the same level in the Mazra’eh Shadi deposit indicates that the base of the boiling zone likely shifted upward and downward during vein formation. The concentrations of Au-Ag occur mainly within quartz veins in the shallow level with gentle boiling (max. 813 ppb Au) and with intense boiling (max. 2420 ppb Au), whereas lower Au-Ag concentrations are associated with base metal-rich (Pb-Zn) in the deepest levels with non-boiling fluids (max. 52 ppb Au).

Gold-Bearing Pyrrhotite Ores in East Sayan: Composition and Formation Conditions (by the Example of the Ol’ginskoe Ore Occurrence)

Abstract —We present results of study of the chemical composition, formation conditions, and genesis of gold-bearing pyrite–pyrrhotite ores widespread within the ophiolite belts in the southeast of East Sayan. The study was performed at the Ol’ginskoe ore occurrence localized in the Ol’gino gold ore zone. Sulfide mineralization zones are composed of lenticular interbeds and bodies subconfoimable with the bedding of the enclosing schist strata. The ores are carbonaceous siliceous garnet–biotite schists variably enriched in sulfide minerals, mainly pyrrhotite, with impurities of other silicate minerals: tremolite, chlorite, albite, plagioclase, diopside, and epidote. In addition, sphalerite, chalcopyrite, pyrite, and arsenopyrite are present in small amounts in the ores. The established Р–Т conditions of ore metamorphism (T = 430–540 °C, P ~ 5 kbar) correspond to the lower boundary of the epidote–amphibolite facies. Thermobarogeochemical studies of fluid inclusions in vein quartz showed close temperatures (536–340 °C) but lower pressures, 200–800 bars, which indicates that the quartz vein formation was related to a pressure drop. The predominant salts of the fluid inclusions are Fe and Mg chlorides with Na and K impurities. The geologic location, structures, textures, and mineral, geochemical, and isotope compositions of the studied sulfide ores indicate their formation in submarine deep-water environments as a result of the activity of hydrothermal systems, analogues of “black smokers”, later subjected to metamorphism. During metamorphism, primary ores underwent mineral and chemical transformations: pyrrhotitization of pyrite, appearance and coarsening of native gold particles, and redistribution of components (Mn, As, etc). The low contents of gold and some ore-forming elements (Zn, Cu, and Pb) in pyrrhotite ores testify to the removal of these elements with a metamorphogenic fluid. The removed ore-forming components might have been a source of material for later gold–sulfide–quartz deposits of the Urik–Kitoi zone in East Sayan.

Gold Mineralization in Izu Peninsula, Central Japan, during Crustal Extension in Response to Double Subduction

AbstractIzu Peninsula in central Japan, the northern tip of the Izu‐Bonin arc, hosts numerous epithermal Au–Ag vein deposits of low‐sulfidation style. All have similar vein textures, mineralogy, and alteration. Geochemical data from fluid inclusions in vein quartz, the mineralogy and mineral chemistry of alteration, and stable isotope data indicate that auriferous hydrothermal activity occurred under subaerial conditions. The K–Ar ages of auriferous vein minerals are &lt;1.5 Ma, indicating that the mineralization took place after extensive submarine volcanism for the host rocks. These observations suggest that Au–Ag mineralization was synchronous with the development of an extensional regime of the Izu block after its collision with the Honshu arc after 1.5 Ma. This collision resulted in the shifting of the Izu block far from the trench to the rear position, and the subduction of the Izu block along the Suruga trough to the west and along the Sagami trough to the east. The reararc position of the Izu block and double subduction resulted in crustal extension, upwelling of asthenospheric mantle, and tholeiitic magmatism reflected by mafic dyke swarms and subsequent monogenetic volcanic activity in the Izu peninsula. The timing of the Au mineralization in the Izu Peninsula during the beginning of lithospheric extension is similar to that of the Sado Au–Ag deposit on Sado island in the Japan Sea. Two mineralization events coincide with extensive tholeiitic mafic volcanism and injections of dyke swarms related to the back‐arc opening of the Japan Sea. The geological setting of the Au–Ag mineralization in Izu and Sado is also similar to that of the epithermal Au–Ag deposits in northern Nevada, where mineralization was contemporaneous with crustal extension and tholeiitic mafic magmatism derived from the asthenospheric mantle. This study suggests that epithermal Au mineralization at shallow crustal depths is a product of large‐scale lithospheric evolution.

Microthermometry and Raman spectroscopy of fluid inclusions from El Vapor gold mineralizations, Colombia

Epigenetic El Vapor gold mineralization is hosted by the Segovia batholith and sedimentary rocks at both sides of El Nús fault, in the eastern flank of the Colombian Andes central cordillera. Gold mineralization is composed by continuous and discontinuous sigmoidal and stockwork veins and veinlets from a few centimeters to two meters of thickness and by hydrothermal breccias. Ore mineralogy includes Pyrite + Galena + Sphalerite + Chalcopyrite + Pyrrhotite + Proustite - Pyrargyrite. Gold is recognized as inclusions within pyrite, between quartz crystals and as fractures filled within pyrite at a late stage of mineralization. The fluid inclusions in quartz veins occur as clusters of primary inclusions and alignments of secondary and pseudo-secondary inclusions. Based on petrography and Raman spectroscopy, four types of fluid inclusions could be recognized: (1) Type I inclusions, biphasic, liquid-rich, with CO2 (v) + N2 (v) + CH4 (v) + KCl + NaCl + H2O(L), primary inclusions, (2) Type II inclusions, multi-volatile, CO2(V) + CO2(L) + N2(V) + CH4(V) + KCl + NaCl + H2O(L), primary to pseudo-secondary inclusions, (3) biphasic, liquid-rich inclusions, composed of H2O(v) +H2O(L)+KCl+NaCl with secondary origin and two different times of formation (IIIA and IIIB) (4) Type IV inclusions, very rare, three-phasic, secondary inclusions and composed by S+H2O(V)+H2O(L)+KCl+ NaCl. The microthermometric and spectroscopic analysis of fluid inclusions indicates that fluids associated with the first event of mineralization identified in El Vapor have low to moderate salinities (3.5-9.2 wt%NaCl equiv.), with trapping temperatures between 214°C and 350°C and pressures between 0.5kbar and 2.9kbar. There is evidence of the isothermal fluid mixture, and fO2 changes per reaction of fluids in the carbonaceous shales of the Segovia sedimentary rocks could influence the process of gold deposition. Hydrothermal fluids from El Vapor were near neutrality and reduced; similar features have been found in orogenic deposits hosted by turbidite sequences around the world.

The Bairendaba silver polymetallic deposit in Inner Mongolia, China: characteristics of ore-forming fluid and genetic type of ore deposit

Bairendaba silver-polymetallic deposit is located in the middle south of the Xing Meng orogenic belt, and in the silver-polymetallic metallogenic belt on the west slope of the southern of Great Xing’an Range. Based on studying of the fluid inclusion, we discuss the characteristics of ore-forming fluid and the metallic genesis of the Bairendaba silver-polymetallic deposit. By means of the analysis of the fluid inclusions, homogenization temperature, salinity and composition were studied in quartz and fluorite. The result is as the follows: with homogenization temperatures of fluid inclusions in quartz veins being 196∼312 °C, the average 244.52 °C, and fluid salinity 2.90∼9.08 wt%NaCl; with homogenization temperatures of fluid inclusions in fluorite being 127∼306 °C, the average 196.92 °C, and fluid salinity 2.90∼9.34 wt% NaCl. The ore-forming fluid is mainly composed of water and the gas. The results of laser Raman analysis show that the gas phase is mainly CH4. It shows that the ore-forming fluid is characterized by medium-low temperature and low-salinity system. The temperature of ore-forming fluid is from high to low, and the salinity from high to low, and the meteoric water or metamorphic water is added during deposit. According to the geological characteristics of the mining area, it is considered that the genetic type of the ore deposit should be the fault-controlled and the medium-low temperature hydrothermal deposit related to magmatic hydrothermal activities.

The study of mineralogy, geochemistry and fluid inclusions in quartz veins at the Mazreh Shadi gold deposit, northeastern Tabriz

The study of mineralogy, geochemistry and fluid inclusions in quartz veins at the Mazreh Shadi gold deposit, northeastern Tabriz

Petrology, geochemistry and fluid inclusion analysis of altered komatiites of the Mendon Formation in the BARB4 drill core, Barberton greenstone belt, South Africa

The 3.33 to 3.26 Ga Mendon Formation in the Palaeoarchaean Barberton greenstone belt, South Africa, forms the uppermost unit of the Onverwacht Group. It is dominated by ultramafic volcanic rocks interbedded with thin layers of cherty sediments that show pervasive alteration, including widespread serpentinisation, silicification and chert and quartz veining. The BARB4 drill core of the ICDP Barberton drilling project exposes a unique section through the Mendon Formation in the Manzimnyama Syncline. The komatiites are pervasively altered to an assemblage comprising quartz, chlorite, carbonate, talc, biotite, and, locally, plagioclase, K-feldspar, muscovite, amphibole, stilpnomelane and ankerite. The overlying sediments are made up of banded iron formations and rare beds of siliciclastic rocks. Though the altered komatiites are pervasively silicified, SiO 2 contents do not exceed 58 wt.%, and their major and trace element geochemistry is similar to other komatiitic rocks of the Mendon Formation, particularly those of the M2v-member. Quartz veins and, less commonly, quartz-carbonate and quartz-carbonate-plagioclase veins are found throughout the core. Overall, composition and texture of the veins differ from primary and early diagenetic veins found in silicified komatiites elsewhere in the Barberton greenstone belt. In the BARB4 drill core, the veins are generally coarse-grained, and the immediate wall rocks are locally foliated along the vein margins. In addition, the δ 18 O values of vein quartz range from 14.1 to 15.3‰, significantly lower than the values typically found in veins on the modern seafloor that formed during low temperature hydrothermal seafloor alteration (~22 to 32‰). Fluid inclusions in vein quartz are homogeneous two-phase (L+V) aqueous inclusions that occur in trans- and intragranular trails and clusters. Intragranular and isolated fluid inclusions have a similar homogenisation temperature (T h ) of 130 to 200°C, with most data ranging between 145 and 175°C. Salinities cluster in three different groups of high (20 to 27wt.% NaCl equiv.), medium (10 to 15wt.% NaCl equiv.) and low salinity (0.3 to 1.5wt.% NaCl equiv.). The composition and microthermometric characteristics of the fluid inclusions analysed within the drill core show similarities to those found in quartz veins in silicified komatiites of the Mendon Formation, which are interpreted to have been entrapped during metamorphism. P-T calculations based on fluid inclusion microthermometry reveal conditions of 230 to 400 MPa and 250 to 400°C. Similar conditions of 240 to 270°C have been obtained using oxygen isotope thermometry, assuming a metamorphic fluid with a δ 18 O value of 6‰. Collectively, the δ 18 O values, together with the texture and composition of the veins, are interpreted to indicate a metamorphic origin of the veins. The presence of high salinity inclusions indicates the occurrence of a highly saline fluid that locally mixed with the dominant lower salinity fluids. The high salinity might have been derived from fluid circulation through evaporites.

The synorogenic pegmatitic quartz veins of the Guacha Corral Shear zone (Sierra de Comechingones, Argentina): A textural, chemical, isotopic, cathodoluminescence and fluid inclusion study

The quartz veins and pegmatites of the Sierra de Comechingones (Sierras de Córdoba, NE Argentina) belong to the Comechingones Pegmatite field (CPF). For the quartz veins and the zoned pegmatites related parental granites are missing. The country rock of the quartz veins are mylonitic augengneisses in granulite to upper amphibolite facies. Field relations, microscopy, cathodoluminescence, radiometric age data, fluid inclusion, chemical and isotopic composition and literature define the quartz veins as synorogenic formed during the high-temperature phase of the Famatinian (480–460Ma) event. During the Famatinian up to the Achalian (382–366Ma) event the synorogenic quartz veins were subjected to high temperature ductile deformation documented by folding, boudinage and finally brittle shearing. K-Ar ages of illite from the shear zones of about 166Ma document the final cooling of the Sierras Pampeanas below 100°C. The long lasting thermal and deformational history of the study area is reflected by very different populations of fluid inclusions in vein quartz with remarkably high contents of thermogenic hydrocarbons in the early-formed fluid inclusions. LA–ICP–MS analysis reveals very low lattice-bound trace element contents, i.e. high purity quartz.

Pyrophyllite formation in the thermal aureole of a hydrothermal system in the Lower Saxony Basin, Germany

A combined clay mineralogical, fluid inclusion, and K-Ar study of Upper Jurassic metasediments at the Gehn (Lower Saxony Basin, Germany) provides evidence for a transient hydrothermal event during Upper Cretaceous basin inversion centered on a prominent gravimetric anomaly. Kaolinite and smectite in Oxfordian pelitic parent rocks that cap a deltaic sandstone unit were locally transformed into pyrophyllite, 2M1 illite, R3 illite–smectite, chlorite, and berthierine at the Ueffeln quarry. The pyrophyllite-bearing metapelites lack bedding-parallel preferred orientation of sheet silicates and experienced peak temperatures of about 260–270°C consistent with microthermometric data on quartz veins in the underlying silicified sandstones. The presence of expandable layers in illite–smectite and high Kubler Index values indicate that the thermal event was rather short-lived. K-Ar dating of the <0.2 μm fraction of the pyrophyllite-bearing Ueffeln metapelite yields a maximum illitization age of 117 ± 2 Ma. Lower trapping temperatures of aqueous fluid inclusions in quartz veins and the absence of pyrophyllite in metapelites of the Frettberg quarry in a distance of about 2.5 km from the Ueffeln quarry infer maximum paleotemperatures of only 220°C. The highly localized thermal anomaly at Ueffeln suggests fault-controlled fluid migration and heat transfer that provided a thermal aureole for pyrophyllite formation in the metapelites rather than metamorphism due to deep burial. A pH neutral hydrothermal fluid that formed by devolatilization reactions or less likely by mixing of meteoric and marine waters that interacted at depth with shales is indicated by the low salinity (3–5 wt. % NaCl equiv.) of aqueous inclusions, their coexistence with methane–carbon dioxide-dominated gas inclusions as well as carbon, hydrogen, and oxygen isotope data. The upwelling zone of hydrothermal fluids and the thermal maximum is centered on a gravimetric anomaly interpreted as an igneous intrusion (‘Bramsche Massif’) providing the heat source for the intrabasinal hydrothermal system.

Metal source and fluid–rock interaction in the Archean BIF-hosted Lamego gold mineralization: Microthermometric and LA-ICP-MS analyses of fluid inclusions in quartz veins, Rio das Velhas greenstone belt, Brazil

The Lamego orogenic gold deposit (440,742oz gold measured reserves and 2.4milliont measured resources, with an average grade of 5.71g/t Au and a cut-off grade of 2.15g/t Au; AngloGold Ashanti Córrego do Sítio Mineração S/A (AGA) personal communication, 2014) is located in the 5km-long trend that includes the world-class Cuiabá deposit. It is hosted in the Neoarchean metavolcano–sedimentary rocks of the Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil. Mineralization is associated mainly with metachert–banded iron formation (BIF) and carbonaceous phyllites in the reclined Lamego fold, in which the Cabeça de Pedra orebody represents the hinge zone. Mineralization is concentrated in silicification zones and their quartz veins, as well as in sulfide minerals, product of BIF sulfidation. Hydrothermal alteration varies according to host rock, with abundant sulfide–carbonate in BIF, and sericite–chlorite in carbonaceous phyllite. Quartz vein classification according to structural relationships and host rocks identified three vein systems. The V1 system, mainly composed of smoky quartz (Qtz I) and pyrite, is extensional, crosscuts the bedding plane S0 of BIF, and is parallel to the fold axis. The V2 system, of the same composition, is represented by veins that are parallel to the S1–2 foliation and S0. This system is also characterized by silicification zones in the BIF–carbonaceous phyllite contact that has its maximum expression in the hinge zone of folds. The V3 system has milky quartz (Qtz II) veins, which result from the recrystallization of smoky quartz, located mainly in shear zones and faults; these veins form structures en echelon and vein arrays. The most common ore minerals are pyrite, As-pyrite and arsenopyrite. Fluid inclusion-FI trapped in all quartz veins present composition in the H2O–CO2±CH4–NaCl system. Fluid evolution can be interpreted in two stages: i) aqueous–carbonic fluid trapped in Qtz I, of low salinity (~2% equiv. wt.% NaCl), and ii) carbonic–aqueous fluid, of moderate salinity (average 9eq.wt.% NaCl) hosted in Qtz II. Both stages are characterized by decrepitation temperatures in the range of 200 to >300°C, and suggest a fluid of metamorphic origin. Applying an arsenopyrite geothermometer, the calculated formation temperature for the Cabeça de Pedra orebody is 300 to 375°C. The vertical intersection of the isochors allows a minimum pressure calculation of 2.6kbar. The composition of individual FIs of this orebody, obtained by LA-ICP-MS analyses, compared with results of FIs for the Carvoaria Velha deposit, Córrego do Sítio lineament, highlights a standard composition typical of metamorphic fluids with Na>K>Ca>Mg, which increase or decrease in concentration as a function of salinity in both deposits. Trace elements vary according to fluid–rock reactions, and are directly related to the host rock composition. The comparison of data sets of the two deposits shows that the Cabeça de Pedra FIs have a higher enrichment in Zn, while Cu, As and Sb are richer in Carvoaria Velha, suggesting influence of the host rock geochemistry. The suggested mechanisms for gold precipitation at the Cabeça de Pedra orebody, Lamego gold deposit are: i) hydrolysis of the carbonaceous matter of phyllite and BIF, affecting fO2, destabilizing sulfur complexes and enhancing gold precipitation; ii) replacement of BIF iron carbonates by sulfides; and iii) continuous pressure changes that lead to silica precipitation and free gold. Other than playing the long-recognized role of the carbonaceous phyllites as a fluid barrier, the data highlight their importance as a source of metals.