Halite-bearing Fluid Inclusions Research Articles

Genesis of the Hajibolagh-Zalibolagh Cu-(Ag) intermediate-sulfidation epithermal deposit, Urumieh-Dokhtar magmatic arc, Iran: Evidence from ore geology, fluid inclusions, and stable isotopes

The Hajibolagh-Zalibolagh deposit located northeast of the city of Saveh in the central part of the Urumieh-Dokhtar magmatic arc of Iran, demonstrates vein and breccia vein style copper-(silver) mineralization hosted by Eocene volcano-sedimentary rocks. The main mineralization stage can be divided into four phases, respectively (1) jasperoid + quartz veins, chalcopyrite, and pyrite; (2) quartz veins along with chalcopyrite, bornite, chalcocite, arsenopyrite, and pyrite; (3) quartz-barite veins along with chalcopyrite, bornite, chalcocite and pyrite; and (4) veins of quartz, calcite, hematite, and oligist along with a small number of copper sulfides. The main stages of mineralization are cut by barren post-ore quartz and calcite veinlets. As a result of supergene processes, minerals are oxidized, and malachite, azurite, chrysocolla, chalcocite, covellite, goethite, and hematite are formed, presenting an important exploration guide. The hydrothermal alteration from the center of the vein-veinlets to the outside includes, respectively, silicification, sericitization, intermediate argillic, and propylitic. The average salinity and homogenization temperature (Th) of fluid inclusions is 14.2 wt% NaCl equiv. and 288 °C, respectively. The coexistence of the vapor phase, liquid-rich phase, and halite-bearing fluid inclusions is a sign of boiling in this hydrothermal system, which has contributed to copper saturation. Sulfur isotope values for pyrite, chalcopyrite, chalcocite, and bornite are mainly from –0.16 to 2.98 ‰, indicating a probable magmatic source for sulfur. Boiling, dilution, and mixing are the mechanisms for the ore deposition and facilitated the mineralization. The Hajibolagh-Zalibolagh deposit shows the highest similarity to intermediate-sulfidation epithermal deposits. The best environment for mineralization and fluid circulation in these epithermal deposits is the intersection of faults with the Eocene subvolcanic rocks.

A numerical model for the quantification of fluid inclusion property variations caused by heterogeneous entrapment and post-entrapment modifications in the H2O-NaCl system

The primary geological conditions for hydrothermal systems can be reconstructed using fluid inclusions, which generally requires that fluid inclusions trapped a single homogeneous phase and experienced no mass and volume changes after entrapment (Roedder's Rules). However, heterogeneous entrapment and post-entrapment modifications have been frequently identified in fluid inclusion studies, making the recovery of primary of fluid properties from fluid inclusion data challenging or impossible. In this study, we constructed a specific tool, FlincPro, for the calculations of ideal and nonideal Fluid inclusion Properties in the H2O-NaCl system (ideal here refers to fluid inclusions that adhere to Roedder's Rules). Multiple modules have been developed to quantify the variations of fluid inclusion properties caused by heterogeneous entrapment, volume contraction/expansion, and water loss. The developed software illustrates possibilities in the variation of fluid inclusions in a specific assemblage with the input of a certain starting point.We found that compositions of the vapor endmember fluid are more significantly affected by heterogeneous entrapment than the liquid endmember, as the latter has several orders of magnitude higher salinity and density. Homogenization pressure and temperature of halite-bearing fluid inclusions trapped on the halite liquidus will increase sharply with the addition of halite, but the homogenization behavior will not be changed. Volume contraction/expansion are effective ways to change the homogenization behaviors, especially for high salinity fluid inclusions. Water loss is not likely to cause the homogenization behavior change from total homogenization by vapor disappearance to total homogenization by halite dissolution for a halite-bearing fluid inclusion without additional volume contraction. Low-salinity and low-density fluid inclusions with total homogenization temperature around the critical temperature of water are least affected by post-entrapment modifications. Therefore, the interpretation of fluid inclusions formation depends on more parameters, e.g., petrographic observations, density and composition variations in fluid inclusion assemblages, and geological information, than only microthermometric data.

Genesis of the Dingjiashan and Fengyan Zn-Pb polymetallic deposits in central Fujian, SE China: Evidence from magnetite geochemistry

Central Fujian is an important polymetallic (Zn-Pb-Ag-Cu-Mo-Au) mineral province in southeastern (SE) China, yet its mineralization is still disputed between Proterozoic volcanogenic massive sulfide (VMS) or Mesozoic skarn-type. The Dingjiashan and Fengyan are two representative of them, with the ores mainly hosted in the Meso-Neoproterozoic Longbeixi Formation marble and schists. For the magnetite from Dingjiashan and Fengyan, their hydrothermal mineral assemblage and their low V, Al, Cr, Ni, Ga, and HFSEs contents (cf. igneous magnetite) are all typical of hydrothermal origin. LA-ICP-MS time-resolved depth profile and inter-element correlation suggest that: 1) Mn, Ti, V, Ni, and Cr are mainly present in solid solution; 2) Na, Mg, Al, K, Si, and Ca occur both as solid solution and the micro-silicate inclusions and/or halite-bearing fluid inclusions; and 3) Zn, Co, Cu, Ag, Pb, and Bi are intimately associated with sulfide micro-inclusions. For both Dingjiashan and Fengyan magnetite, the Ti, V, Al, Ga, and Mn contents are temperature-controlled, whilst Ti, V, Cr, and Sn contents are redox-controlled. Meanwhile, the Ca and Mg contents are controlled by fluid-rock interactions, and the Mn enrichment is inherited from the fluid composition. Coexisting mineral phases have likely exerted major geochemical control on the magnetite samples. We compiled a large published geochemical dataset on magnetite from well-studied VMS and skarn deposits worldwide. Compared with VMS-hosted magnetite, skarn-hosted magnetite has relatively high median contents for Ca, Al, Ge, Sn, Mn, and Mg, and low median contents for Si, Ga, Ti, V, Ni, and Cr. Overall, the Dingjiashan and Fengyan magnetite samples have similar trace element compositions (esp. Mn and V) to those of skarn-hosted (rather than VMS-hosted) magnetite. Magnetite geochemistry thus suggests that both the Dingjiashan and Fengyan are best classified as stratabound, distal Zn-Pb skarn deposits. Our findings highlight the effectiveness of magnetite trace element geochemistry in differentiating ore deposit types, which contributes to regional Zn-Pb ore exploration and research.

Metallogeny of the Dagangou Au-Ag-Cu-Sb Deposit in the Eastern Kunlun Orogen, NW China: Constraints from Ore-Forming Fluid Geochemistry and S-H-O Isotopes

A study of ore-forming fluid geochemistry and S-H-O isotopes has been conducted to reveal the metallogeny of the Dagangou Au-Ag-Cu-Sb deposit, NW China. Three mineralization stages are identified within Dagangou, including ankerite-quartz-pyrite (Ank-Qz-Py), quartz-Au-sulfide (Qz-Au-Sul), and quartz-calcite (Qz-Cal) stages. Four types of primary fluid inclusions (FIs) and various fluid inclusion assemblages (FIAs) are identified by petrographic observations, including pure CO2, CO2-bearing, vapour-liquid and halite-bearing FIs, most of which are distributed randomly or along growth zones. Raman spectroscopy suggests that the fluid vapour is mainly H2O and CO2 with minor N2, CH4, and C2H6. The homogenization temperatures of primary FIs from the Ank-Qz-Py to Qz-Au-Sul to Qz-Cal stages are 208.7–313.4°C, 184.3–251.7°C, and 167.3–224.2°C, with salinities of 3.4–13.4 wt.%, 5.4–39.5 wt.% and 4.9–11.4 wt.% NaClequiv.. Sulfide S isotopes show a predominant source of sedimentary sulfur with minor magmatic sulfur, as evidenced by δ34S values of -1.4–5.1‰. The FI H-O isotopes reveal that the primary fluid was derived from magmatic waters mixed with minor sedimentary water (δD=−90.0to -86.8‰,δ18OH2O=6.7–7.4‰) and then was significantly diluted by meteoric water in the Qz-Cal stage (δD=−97.2to -95.7‰,δ18OH2O=3.9–4.3‰). Thus, the ore-forming fluid geochemistry and S-H-O isotopes indicate that fluid boiling occurred in the Qz-Au-Sul stage due to a pressure reduction from 85 MPa to 70 MPa, which led to the phase separation of fluid, loss of CO2, increase in residual fluid salinity, and formation of immiscible FIAs and halite-bearing FIs in the Qz-Au-Sul stage. This indicates a system moving away from a primary equilibrium, resulting in the deposition of metallic elements. The Dagangou Au-Ag-Cu-Sb deposit, therefore, is an orogenic gold-polymetallic deposit with a mesozonal depth of 5.9–7.5 km.

Formation and evolution of the calcic-magnesian Saheb Fe (Cu) skarn deposit from the Sanandaj-Sirjan Belt, NW Iran: Evidence for multistage boiling in episodes of magnetite saturation

The Saheb Fe (Cu) skarn deposit is located along the northwestern end of the Sanandaj-Sirjan Zone. This deposit occurs over an approximately 2 km distance along the contact zone between the Upper Cretaceous causative granite and the Upper Permian calcareous host rock, with several iron orebodies occurring as high-grade lenticular massive magnetite bodies (with a length of up to 90 m and a width of 25 m).Following the formation of pyroxene hornfels facies, four main stages of skarn formation have been recognized: (I) early prograde stage (type I garnet + clinopyroxene + olivine): fluid inclusions in the type I garnet yielded a high temperature and salinity (average of 506 °C and 57 wt% NaCl equiv.), which may represent the composition of initial magmatic fluids. Higher salinities at this early stage can be associated with orthomagmatic differential fluid exsolution. (II) late prograde stage (type II and III garnets ± clinopyroxene ± disseminated magnetite): the coexistence of vapour-rich and halite-bearing fluid inclusions in type II garnet and their similar homogenization temperatures (420°–480 °C) presumably signify that fluid immiscibility from a supercritical fluid occurred at lithostatic pressures of 300 to 500 bar, corresponding to a depth of 1.5–2.0 km. (III) early retrograde stage (massive magnetite + pyrite + chalcopyrite + epidote + quartz + type I calcite + amphibole + serpentine + talc): hypersaline liquid and low-salinity vapour phases trapped within the epidote, quartz, and type I calcite are coexisting, indicating phase separation of hydrothermal fluids at temperatures of 300°–400 °C and pressures ranging from 310 to >100 bar under hydrostatic conditions, equivalent to a depth of 1.5 to 2.0 km. Hypersaline inclusions in the quartz and type I calcite show Td(NaCl) > Th(L-V), deduced to have been trapped by the over-saturated fluids or under over-pressured conditions before the hydrofracturing (up to 2200 bars). (IV) Late retrograde stage (type II calcite ± quartz ± chlorite), which is characterized by moderate temperature and salinity and non-boiling fluid inclusion assemblage (with average of 172 °C and 17 wt% NaCl equiv.).The first boiling event is documented in the type II garnet of the late prograde stage and provoked the ore-bearing fluids to precipitate the disseminated iron ore. The main deposition of magnetite has plausibly been triggered by the second episode of fluid boiling, recorded in epidote, quartz, and type I calcite during the early retrograde stage. Two boiling events mean producing more fractured and brecciated zones, which can act as conduits for the iron-bearing hydrothermal fluids. This seems to be why there are dozens of isolated magnetite orebodies in the Saheb skarn deposit, which extend over an area of greater than two kilometers (in an E-W direction). Comparably higher salinities even in the type II calcite of the late retrograde stage (25 wt% NaCl equiv.) may reveal that significant mixing of saline magmatic fluids with external, dilute, and cold fluids is almost implausible, despite the presence of brecciated zones. Boiling, therefore, can be pondered as the most salient factor in controlling the ore precipitation at the Saheb Fe (Cu) skarn deposit. However, mixing with meteoric fluids and shifting in pH values could also facilitate the alteration and mineralization.

Multi-Stage Fluid System Responsible for Ore Deposition in the Ossa-Morena Zone (Portugal): Constraints in Cu-Ore Deposits Formation

The Mociços Cu-deposit is part of a cluster of ancient copper mines in the Sousel-Barrancos metallogenic belt in the Ossa-Morena Zone at the SW Iberia. The orebodies develop along NNW-SSE quartz-carbonate-sulfides veins with pyrite and chalcopyrite as the main sulfide phases, and ore emplacement has been attributed to copper remobilization from the metasedimentary host-rocks, though no detailed studies were conducted. A novel multi-stage fluid circulation model is hereby proposed, supported by petrography and fluid inclusion data evidencing the P–T–V-x evolution of the deposit. Stage (i) is an early metamorphic stage with a predominance of carbonic fluids, identified in highly deformed milky quartz (QzI), with estimated pressures between 338 and 486 MPa compatible to the regional metamorphic events (greenschist facies). Stage (ii) corresponds to a late-metamorphic manifestation of H2O–NaCl–CO2 fluids, with low-salinity (eq. w(NaCl) from 0.4 to 5.0%) and CO2 dominated. Stage (iii) in which ore emplacement took place and is characterized by dominant multisolid H2O–NaCl hypersaline, halite-bearing fluid inclusions (eq. w(NaCl) from 29.3 to 44.3%) with an H2O–NaCl–CO2 endmember and features indicative of magmatic-hydrothermal brines. Many of these inclusions homogenize by halite dissolution, with pressures as high as 320 MPa, and the coexistence of both fluids in the same fluid inclusion assemblages (FIA) could indicate phase separation caused by fluid pressure variations. Although there is no direct evidence of the magmatism responsible for these fluids, the geodynamic settings could favor deep-seated magmatism. Stage (iv) is characterized by low-salinity (eq. w(NaCl) from 0.18 to 15.57%) and low-temperature (68 to 160°C) primary two-phase fluid inclusions hosted by late-stage quartz (QzIV), suggesting a late-meteoric fluid circulation phase responsible for the leaching, oxidation and supergene enrichment observed at surficial levels. Throughout the P–T evolution of the system a decrease in pressure and temperature was registered, especially in fluid inclusions hosted in quartz from the sulfide bearing veins, suggesting that the transition from ductile to brittle regimes might have favored ore deposition.

SEM-CL Study of Quartz Containing Fluid Inclusions in Wangjiazhuang Porphyry Copper (-Molybdenum) Deposit, Western Shandong, China

The Wangjiazhuang porphyry copper (-molybdenum) deposit is located at Zouping volcanic basin in Shandong Province, East China and hosted in the Wangjiazhuang intrusive complex emplaced along a late volcanic conduit. There are two types of ores in this deposit: early disseminated and stockwork ores in the ore-bearing intrusion, and late massive sulfide-quartz veins above brecciated quartz monzonite. The ore minerals are mainly pyrite, chalcopyrite, and subordinately magnetite, tennantite, molybdenite with minor bornite, enargite, galena and sphalerite, etc., and gangue minerals including K-feldspar, biotite, quartz, muscovite-sericite, chlorite and calcite. Combined with fluid inclusion study, the scanning electron microscope-cathodoluminescence (SEM-CL) study of quartz in the deposit and wall rocks shows significant differences between the two types of quartz in the ores. In addition, four types of primary-pseudosecondary fluid inclusions in the quartz have been recognized. They are one- or two-phase aqueous inclusions with vapor/liquid ratios less than 30% to 40% (type I); gas-rich inclusions with vapor/ liquid ratios more than 50% (type II), some of which contain some small opaque minerals, probably chalcopyrite; multiphase fluid inclusions with daughter minerals of halite±anhydrite±opaque (chalcopyrite)± sylvite±hematite±unknown crystal (type III); and mica-bearing fluid inclusions (type IV). Quartz containing abundant muscovite-bearing and halite-bearing fluid inclusions in the mineralized quartz monzonite with potassic-silicic alteration, have better oscillatory growth zoning with CL-colors from bright in the core to darker in the rim, indicating variations of element concentrations in the fluid media from which quartz grew during the later period of magmatic-hydrothermal process. In contrast, the quartz in the sulfide-quartz veins contains mainly fluid inclusions of low-to-medium salinities and does not show oscillatory zoning, indicating that there was less fluctuation in composition and element concentrations of the hydrothermal fluids. However, the quartz containing halite-bearing fluid inclusions and being associated with copper-molybdenum mineralization in the sulfide-quartz veins shows zoning in its rims, indicating variations in composition and element concentrations of the hydrothermal fluids.

Fluid inclusion and stable isotope constraints (C, O, H) on the Dağbaşı Fe–Cu–Zn skarn mineralization (Trabzon, NE Turkey)

The Dağbaşı Fe–Cu–Zn skarn mineralization developed along the contact between the block and lens shaped limestones of the Lower Cretaceous Berdiga Formation and the Upper Cretaceous Dağbaşı Granitoid. The exoskarn-type mineralization is characterized by prograde stage garnet and pyroxene, while the retrograde stage is characterized by epidote, tremolite, actinolite, and chlorite. Quartz and calcites were observed in both stages of the skarn development. The ore minerals mainly consist of magnetite and hematite, with a lesser amount of pyrrhotite, pyrite, chalcopyrite, sphalerite, and minor galena. The homogenization temperatures (Th) and salinity values of the prograde stage halite-bearing fluid inclusions are in the range of 412–514 °C and 48.8–61.8 wt% NaCl equ., respectively. The second stage liquid- and vapor-rich fluid inclusion assemblage reveals that boiling at temperatures of 353–458 °C took place after the formation of halite-bearing fluid inclusions. Final stage liquid-rich fluid inclusions were characterized by low Th (160 and 327 °C) and salinity values (0.5 and 6.2 wt% NaCl equ.). The decreasing salinity trend of the fluid inclusions versus Th indicated that meteoric water was involved in the hydrothermal solutions. Eutectic temperatures (Te) of the prograde stage fluid inclusions were found to be CaCl2 dominated, while retrograde stage inclusions contained different salt combinations rather than a specific salt type. The minimum trapping pressures of the early stage brine fluid inclusions were calculated to be between 710 and 884 bar, while later stage inclusions had much lower trapping pressures between ~195 and 445 bar. The δ18O isotopes of prograde stage quartz, garnet, and pyroxenes are close to the composition of the hydrothermal solutions of magmatic sources. Moreover, retrograde stage quartz, epidote, tremolite-actinolite, and calcite minerals and their equilibrated solutions were found to be highly depleted by δ18O isotopes. Therefore, the fluid inclusion and stable isotope constraints suggest that the hydrothermal solutions of magmatic origin were responsible for the prograde skarn stage, while a mixture of magmatic and meteoric solutions were responsible for the ore formation in a shallow skarn environment.

Genesis of the Dachang Sn-polymetallic and Baoshan Cu ore deposits, and formation of a Cretaceous Sn-Cu ore belt from southwest China to western Myanmar

Large scale Cretaceous magmatism and SnCu mineralization occurred in an E-W-trending ore belt from southwest China to western Myanmar. We investigated the genesis of the world-class Dachang Sn-polymetallic and newly discovered Baoshan Cu deposit in Guangxi Province, southwest China, and the tectonic setting of this belt. The Dachang ore field contains a giant vein ore body (No. 100) and stratiform ore bodies (No. 91 and 92). The cassiterite U-Pb age (92.5 ± 4.4 Ma) of the No. 100 ore body is similar to the zircon U-Pb age of the Longxianggai biotite granite (90.8 ± 1.0 Ma), suggesting the vein ore body was related to Cretaceous magmatism. The fluid inclusions in the No. 92 ore body are similar to those in the No. 100 ore body, and contain CO2-H2O, liquid-rich and halite-bearing fluid inclusions, with homogenization temperatures of 300–410 °C. These data further suggest that mineralization was related to Cretaceous magmatism. The mineralization in the Baoshan Cu deposit occurs as veins in the Baoshan porphyry and adjacent country rocks. The Baoshan porphyry yielded a zircon U-Pb age of 90.6 ± 1.3 Ma, EuN/Eu* = 0.05, CeN/Ce* = 12.2 and εHf(t) = −11.39 to −7.37. These data indicate that the porphyry magma was reduced and crustally derived. Low Sr/Y ratios (<0.1) and large negative Eu anomalies (EuN/Eu* = 0.03–0.06), along with rare earth element tetrad effects further imply the porphyry magma was highly fractionated. The Baoshan porphyry was genetically associated with Cu mineralization, but is distinct from the typical Cu-mineralizing porphyry magmas.This Cretaceous Sn-Cu ore belt was likely related to subduction and roll-back of the Neo-Tethys Plate rather than northwestward subduction of the Paleo-Pacific Plate.

Temporal and spatial variations in characteristics of fluid inclusions in epizonal magmatic-hydrothermal systems: Applications in exploration for porphyry copper deposits

Temporal and spatial variations in the room temperature phase relations of fluid inclusions serve as a proxy for the PTX properties of fluids associated with emplacement and crystallization of a shallow epizonal intrusion following the “Burnham Model”. Accordingly, during magma ascent, hydrous magmas approach and achieve volatile saturation in response to decreasing pressure (“first boiling”) and/or as a result of cooling and crystallization of anhydrous mineral phases (“second boiling”). In both cases, a magmatic aqueous fluid phase will exsolve from the volatile-saturated silicate melt. Fluid inclusions that trap the exsolved magmatic fluid show predictable room temperature phase relations, compositions, and microthermometric characteristics indicative of the pressure and temperature conditions of the trapping environment.We model aqueous phase equilibria as a function of temperature, pressure, and fluid composition. The composition and phase behavior of the magmatic aqueous fluid phase is adequately approximated by the system H2O-NaCl, and the PVTX characteristics of the magmatic fluids may be determined at any temperature and pressure using phase equilibrium data for this binary system. Then, PVTX data for the system H2O-NaCl are used to predict the room temperature phase relations and homogenization temperatures of fluid inclusions that trap the magmatic fluid at various times and locations in the magmatic-hydrothermal system. The temperature at any position in the system is based on established numerical models of conductive and convective cooling of shallow plutons, and the pressure at any depth is calculated assuming that hydrostatic conditions apply at temperatures <400 °C, and that lithostatic conditions are applicable at higher temperatures.We apply the model to four different stages during the crystallization of a shallow, intermediate composition magma, beginning in the early stages of crystallization and immediately following initial volatile saturation, and ending with complete crystallization of the melt. Mapping the stable fluid phase fields onto a cross-section of the pluton allows us to predict the characteristics of fluid inclusions trapped at various times and locations in the overall system. The fluid inclusion characteristics are predicted along five depth profiles that extend from the center of the pluton to the periphery. The results show good agreement with numerous studies that describe the distribution of halite-bearing, vapor-rich, and two-phase, liquid-rich inclusions in porphyry copper deposits.The results of this study may be applied in exploration for porphyry copper mineralization, as well as other magmatic-hydrothermal porphyry deposits in which the magmatic fluids can be approximated by the system H2O-NaCl. Importantly, halite-bearing fluid inclusions occur only within the pluton and in the immediately surrounding wallrocks, which represents the part of the system that often hosts mineralization. Similarly, fluid inclusion assemblages comprised of only vapor-rich inclusions occur in the near-surface, sub-volcanic part of the system, whereas coexisting halite-bearing and vapor-rich inclusions characterize the deeper parts of the system. The distribution of fluid inclusion types constrains the vertical and lateral position within the overall magmatic-hydrothermal system and, thus, develops vectors towards the magmatic center of the system that is most likely to host economic mineralization.

Fluid inclusion and H–O–S–Pb isotopic evidence for the Dongxiang Manto-type copper deposit, South China

The Dongxiang copper deposit is located in northeastern Jiangxi Province, South China. Ore bodies in the Zishan Formation of this province are primarily stratoid and lentiform and show a close spatial association with Jurassic intrusive rocks. The current debates generally concentrate on whether the Dongxiang copper deposit is a Carboniferous sedimentary deposit or, alternatively, a Jurassic porphyry–skarn deposit. Three stages of mineralization can be observed in this deposit: the pre-ore, main ore, and post-ore stages. The massive sulfide ore bodies are identified as the main ore stage, whereas the pyrite-quartz veins and barren quartz veins are identified as pre-ore and post-ore stages, respectively. Three fluid inclusion types were recognized: two-phase vapor-rich fluid inclusions (type 1), two-phase liquid-rich fluid inclusions (type 2), and halite-bearing fluid inclusions (type 3). All three of these types of inclusions are present in the main copper mineralization stage, but only type 2 inclusions occur in both the pre-ore and post-ore stages. Type 2 inclusions in the pre-ore stage display homogenization temperatures (Th) of 349–392°C, with salinities of 1.4–8.1wt.% NaCl equivalent. In the main ore stage, types 1 and 3 inclusions show similar Th at 289–346°C and 273–348°C but contrasting salinities of 0.4–4.5 and 29.4–41.9wt.% NaCl equivalent, respectively. In the post-ore stage, type 2 inclusions have Th of 144–228°C and salinities of 0.4–6.0wt.% NaCl equivalent. The coexisting types 1 and 3 inclusions in the main ore stage have similar Th ranges but contrasting salinities, which indicates that fluid boiling occurred. The determined hydrogen and oxygen isotopic values for these fluids (δD from −42‰ to −69‰; δ18OH2O 5.04‰ to 9.01‰), based on analysis of fluid inclusions and host quartz, imply that the inferred ore fluids were principally derived from magmatic water. The lead isotopic compositions of sulfides from the ores and plagioclases from the adjacent porphyry indicate that they share a common origin. The sulfides from the ores show δ34S values of 0.3–3.2‰, also suggests a magmatic source. As the fluid inclusions and isotopic compositions strongly suggest a magmatic origin, this argues against a SEDEX origin for this deposit. In addition, the presence of stratoid and lentiform ore bodies and the absence of skarn alteration minerals suggest that the Dongxiang copper deposit is best described as a Manto-type rather than a porphyry–skarn deposit.

Fluid inclusion geochemistry and ore genesis of the Longmendian Mo deposit in the East Qinling Orogen: Implication for migmatitic-hydrothermal Mo-mineralization

The 1.85Ga Longmendian Mo deposit in East Qinling is the oldest Mo system recognized in China. It is unique for three reasons: (1) quartzofeldspathic orebodies are away from any intrusion or fault, (2) it is closely associated with migmatitic rocks, and (3) it has remarkably high Re content in molybdenite (504 to 1660ppm). The origin of the deposit is poorly constrained.In the Longmendian deposit, strong Mo mineralization is always associated with hydrothermally altered migmatitic amphibolites. To probe into ore genesis, detailed fluid inclusion studies are carried out on both mineralized migmatitic amphibolites and ore-barren rocks. Four compositional types of fluid inclusions are observed, including CO2±CH4 (PC-type), CO2–H2O (C-type), daughter mineral-bearing (S-type) and H2O–NaCl (W-type). Quartz in mesosome and melanosome of mineralized migmatitic amphibolites contains all of the four types of inclusions. Measurements of immiscible inclusion assemblages in the ores constrain the Mo-mineralization temperatures and pressures to be 225–390°C and 114–265MPa, respectively. Primary fluid inclusions in barren migmatitic gneisses are dominated by S-type, and minor of C- and PC-types which are identical to those in the leucosome of migmatitic amphibolites. These inclusions yield lower homogenization temperatures than those in the mineralized mesosome and melanosome of migmatitic amphibolites, suggesting that the ore-causative, injected melts should have higher temperatures and originated from depths. Such features of the ore-forming fluids indicate that the Longmendian deposit was a migmatitic-hydrothermal system caused by high-temperature melt injection. This interpretation can also be supported by the observations below: (1) tourmaline is abundant in melanosome, but absent in mesosome; (2) the consistent quartzofeldspathic composition of leucosome is independent of mesosome; (3) leucosome in migmatitic amphibolite crosscuts each other; (4) halite-bearing fluid inclusions are prevalent in studied samples, which is the feature of granitic rocks, instead of the scenarios of in situ migmatites; and (5) the trapping temperatures of fluid inclusions in mineralized migmatitic amphibolite are much lower than those required for partial melting, but higher than those obtained from barren migmatitic rocks.

Mineralogy, geochemistry and petrogenesis of igneous inclusions within three inactive diapirs, Zagros belt, Shahre-kord, Iran

AbstractThe Kaj-Rostam Abad, Dashtak and Doab diapirs are part of the Precambrian–Cambrian Hormuz series that are rich in igneous inclusions concentrated by dissolution of diapiric salt. They are situated in the Iran–Pakistan salt range and commonly associated with inclusions of basalt, trachyte, andesite, micro-gabbro, gypsum and anhydrite, with lesser amounts of carbonate rocks. The mineral assemblage in these inclusions developed in three stages: (I) magmatic stage (diopside, Ti-augite, kaersutite, plagioclase, apatite, biotite and opaque minerals), (II) late magmatic stage (biotite, quartz, chlorite, albite, calcite, titanite, epidote, actinolite and opaque minerals) and (III) vein mineralization (quartz, chlorite, albite, calcite, garnet, epidote, opaque minerals and actinolite). Clinopyroxene is diopside to Ti-augite. Actinolite, kaersutite, albite and pycnochlorite are constituents of the metasomatic rocks of the area. Chlorite geothermometry yielded a temperature of 330–500 °C for chlorite formation. Clinopyroxene thermobarometry ranges from 960 ≤T≤ 1440 °C and 1 ≤P≤ 10 kbar. The presence of halite-bearing fluid inclusions in hydrothermal quartz veins with homogenization temperatures between 320 and 350 °C points to strong evidence of hydrothermal events. The salinity of these fluids is 39.8–42.7 wt% NaCl. δ18O data on hydrothermal quartz veins range from 14.89 to 22.09 ‰ (SMOW), indicating that the studied samples were affected by fluids originated from sedimentary-evaporitic rocks. Meteoric water that penetrated the evaporitic rocks likely mixed with late magmatic fluids while subjected to magmatic heat, when buried to depths of several kilometres by the Phanerozoic cover sequence. Whole-rock geochemistry data for the studied rocks emphasize their alkaline to sub-alkaline affinities, in a transitional magmatic series.

Mineral Chemistry and In Situ Dating of Allanite, and Geochemistry of Its Host Rocks in the Bagjata Uranium Mine, Singhbhum Shear Zone, India--Implications for the Chemical Evolution of REE Mineralization and Mobilization

The present study combines textures, compositions, and in situ dating of allanite and whole-rock geochemistry from the Bagjata uranium deposit in the Singhbhum shear zone, the most important uranium-producing belt in India, to investigate the chemical evolution of rare earth element (REE) mineralization. Allanite, volumetrically the most important sink of light rare earth elements (LREEs) in this deposit, occurs as disseminated grains, pockets, veins, and stringers in biotite schist and chlorite schist. Metasomatic addition of LREEs in the rock was associated with Ca-K-Fe ± B metasomatism, as evident from the vein mineralogy. The allanite-bearing metasomatized rocks are locally extremely enriched in REEs, reaching up to ~4.8 wt percent ∑REEs. The textures and compositions of allanite demonstrate that early REE-rich allanite was replaced by later, relatively less REE bearing allanite-epidote, and this alteration followed a substitution scheme of REE +3 + (Fe +2 , Mg +2 ) → Ca +2 + (Al, Fe +3 ). The presence of halite-bearing fluid inclusions in associated tourmaline, high Cl content of biotite, and other circumstantial evidence indicate that a high-salinity, Cl-rich fluid was likely responsible for initial LREE metasomatism. A later hydrothermal event altered preexisting allanite and removed REEs. The more oxidized nature of altered allanite and the presence of unidentified secondary REE minerals in association with sulfide might indicate the involvement of oxidized, sulfate-rich fluid in the alteration of allanite and the removal of REEs. Alternatively, fluoride complexing of REEs and selective removal of HREEs during this alteration are possible. In situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of allanite and monazite indicates that LREE metasomatism took place at ~1.88 Ga. The next hydrothermal event, which altered existing allanite, removed some REEs, and perhaps was associated with U (+HREE) addition, is dated at ~1.66 Ga. The youngest age determined from the thin rim of allanite is ~1.02 Ga. These three different ages, determined from allanite, overlap with the known thermotectonic events in and around the Singhbhum shear zone. Comparison between the calculated ∑REE content of allanite-rich rock prior to allanite alteration and whole-rock ∑REE composition of the same rock suggests that the addition of a large quantity of REEs was followed by significant REE removal. Strong variations in the modal abundances of the constituent minerals and in whole-rock compositions, including REEs, indicate open-system behavior. The whole-rock REE pattern suggests that decoupling between LREEs and HREEs might be possible during superimposed alteration. Therefore, petrogenetic modeling using an REE-based discrimination diagram and REE patterns should be done with caution for rocks that underwent multiple events of hydrothermal fluid flux.

Henderson Porphyry Molybdenum System, Colorado: II.Decoupling of Introduction and Deposition of Metals during GeochemicalEvolution of Hydrothermal Fluids

Henderson Porphyry Molybdenum System, Colorado: II.Decoupling of Introduction and Deposition of Metals during GeochemicalEvolution of Hydrothermal Fluids

Analysis of individual fluid inclusions using synchrotron X-ray fluorescence microprobe: progress toward calibration for trace elements

A critical problem for conducting quantitative analysis of individual fluid inclusions using Synchrotron X-Ray Fluorescence (SXRF) technique relates to the standardization and the calibration of the X-ray spectra. In this study, different approaches have been tested for calibration purposes: (a) the use of chlorine when Cl content can be estimated either from melting point depressions of undersaturated fluid inclusions or from saturation limits for halite-bearing fluid inclusions, (b) the use of calcium from synthetic fluid inclusions of known CaCl2 content as an external standard. SXRF analysis was performed on individual fluid inclusions from the Chivor and Guali emerald deposits, Columbia. These well-known samples contain a single fluid inclusion population for which detailed crush-leach analyses are available, thus providing a relevant compositional reference frame. Concentration estimates were also compared to Particle Induced X-ray Emission (PIXE) analysis carried out independently on the same fluid inclusions.Results of the calibration tests indicate that major (Cl, K, Ca, Fe, Mn) and trace element (Cu, Zn, As, Br, Rb, Sr, Ba, Pb) concentration estimates can be performed without precise knowledge of the analytical volume and the inclusion’s 3D geometry. Although the standard deviation of the SXRF results can be relatively high depending on the calibration mode used, mean concentration estimates for most elements are in good agreement with PIXE and crush-leach analysis. Elemental distributions within single fluid inclusions were also established. Associated correlation diagrams argue for the homogeneous distribution of most elements in the fluid inclusion. In contrast, Br shows a bimodal distribution interpreted to reflect a significant enrichment of the vapor portion of the inclusion fluid.

The Cobalt Mining District: Silver Sources, Transport and Deposition

Cobalt, Ontario, is renowned for the 12.6 billion grams (445 million ounces) of silver produced from the area since discovery in 1903 by workers of the Timiskaming and Northern Ontario Railway. Native silver generally occurs with cobalt arsenides and sulfosalts in near-vertical carbonate veins cutting the Huronian sedimentary rocks of the Gowganda Formation, the Archean metavolcanics and/or the Nipissing diabase. All major deposits have been found within a few hundred meters of the unconformity between the Archean and Huronian rocks in general proximity to the Nipissing diabase and volcanogenic sulfide mounds within the Archean meta-volcanics. Silver has been mobilized from one or more of the local country rocks by hyper-saline brines and deposited in or near zones of mixing where the saline brines encounter paleometeoric water transported to depth along the unconformity or local structures. Previous work has shown that chloride complexes are the dominant ligands responsible for silver transport. These hypersaline brines, represented as halite-bearing fluid inclusions at room temperature, have been trapped as primary fluid inclusions within vein minerals. Pressure-temperature conditions of vein formation have been derived from mineral equilibria, maximum lithostat and fluid-inclusion studies. These data are consistent with vein formation occurring over the temperature range 300°C to 350°C, with pressures constrained between 60 Mpa and 136 Mpa (600 bars and 1360 bars).

Cracking at the magma–hydrothermal transition: evidence from the Troodos Ophiolite, Cyprus

The nature of the magma–hydrothermal transition in oceanic hydrothermal systems is poorly understood, in part because the geological relations in this critical region have rarely been observed in modern ocean crust. Detailed mapping was conducted in the Troodos Ophiolite, Cyprus, where a gabbronorite sequence intrudes the sheeted dyke complex, which is truncated at its base by a thin contact aureole composed of massive hornfels. Geothermometric data for hornblende and pyroxene hornfels show that hydrated sheeted dykes were recrystallized at amphibolite to granulite facies conditions (778–986°C). Quartz diorite veins and apophyses, and monomineralic amphibole veins cross-cut the contact aureole and show no preferred age relationships. Geothermometric data indicate that quartz diorite was injected at 817–919°C and that fractures were filled with amphibole at 575–750°C. Phase relations of quartz-hosted, halite-bearing fluid inclusions in quartz diorite veins constrain minimum entrapment temperatures of 225–520°C (average 402°C) and minimum pressures that span lithostatic and hydrostatic conditions. We believe that these characteristics are indicative of a conductive boundary layer that separates an active hydrothermal system from the heat source that drives it. Field and petrological data indicate that transient fracturing caused oscillations in temperature and pressure conditions within the conductive boundary layer, and mixing of hydrothermal and magmatic fluids at the magma–hydrothermal interface. Cross-cutting relations between magmatic and hydrothermal vein networks show that fracturing occurred prior to the cessation of magmatic activity. We explore plausible models for the causes and consequences of fracturing that consider the role of dyke injection, thermoelastic stresses, and volatile build-up.

Magmatic and hydrothermal history of the porphyry-style deposits of the Ardlethan tin field, New South Wales, Australia

The cassiterite-sulfide deposits of the Ardlethan tin field are classified as porphyry-style Sn deposits on the basis of the intimate spatial and temporal relationships of the breccia pipes and Sn deposits with the Ardlethan Granite, and in particular, the Mine porphyry; the continuum of salinity and temperature conditions from high-temperature and high-salinity fluids in the Ardlethan Granite to lower temperature and less saline fluids in the breccia pipes in the Mine granite; and the isotopic character of the ore fluids which is consistent with a magmatic fluid source characterized by primitive isotopic signatures for carbon and sulfur. The deposits occur in breccia pipes in the Siluro-Devonian Mine granite (417 + or - 2.5 Ma) close to its contacts with the Ardlethan Granite (410 + or - 2.5 Ma) and Ordovician metasediments. The Ardlethan Granite and related phases are moderately to strongly fractionated and enriched in Rb, Th, U, Nb, Y, Li, As, Ta, W, F, and Sn. Tourmaline nodules occur within the Ardlethan Granite and halite-bearing fluid inclusions found in quartz from the nodules homogenized between 250 degrees and 485 degrees C. One of the most fractionated phases of the Ardlethan Granite--the Mine porphyry-- was emplaced into the major breccia pipe of the Mine granite following the onset of brecciation. Brecciation and mineralization are linked to the release of magmatic volatiles and saline brines from the Ardlethan Granite. The vug-filling minerals in all the deposits show a paragenetic sequence from cassiterite, wolframite, arsenopyrite, milky quartz, and tourmaline to pyrite, chalcopyrite, sphalerite, galena, tourmaline, and clear quartz to late-stage toothy quartz, fluorite, and cookeite. Fluid inclusion data from quartz show that the deposition of milky quartz and cassiterite occurred between 300 degrees and 370 degrees C, sulfide and clear quartz between 210 degrees and 2800C, and toothy quartz, fluorite, and cookeite between 105 degrees and 245 degrees C. Fluid salinities ranged..