Fluid Inclusions from Anhydrite Related to the Chicxulub Crater Impact Breccias,Yucatan, Mexico: Preliminary Report

Abstract, Results of a study of fluid inclusions in anhydrite from drill hole Y-6 in the Chicxulub crater, of northwestern Yucatan, Mexico, are reported in this work. The Chicxulub crater was formed at the Cretaceous-Tertiary boundary by a meteorite impact. The resulting ejection breccias are composed mostly of hydrothermally altered crystalline basement material. The mineral assemblage pyroxene + anhydrite + quartz is associated with the hydrothermal alteration. The analyzed fluid inclusions in the anhydrite show highly heterogeneous phase assemblages within the same crystal plane. Fluid inclusion types include liquid plus vapor inclusions (L+V), vapor-rich inclusions (V), and inclusions containing daughter crystals (L+V+S). The eutectic temperatures indicate a brine composition dominated by CaCl₂-NaCl. Both the salinity and the homogenization temperatures show a wide range (from 3.6 to 23 wt% NaCl equivalent for the L+V inclusions, and 36 to 42 wt% NaCl equivalent for the L+V+S inclusions). The homogenization temperatures range from 100° to 500°C. These data represent cooling and boiling trends. We assume that the impact breccias were ejected at high temperature in an aqueous environment (above 500°C). This caused boiling of sea water and precipitation of anhydrite with its inclusions.     

山东招远玲珑金矿床含金石英脉石英中流体包裹体特征及成矿温度

本文旨在通过对山东招远玲珑金矿床含金石英脉中流体包裹体特征的观察和测温,对矿床的成矿温度、压力和成矿介质的性质提出一些初浅的看法。     

Melt inclusions in basalts of Ross Island area,Antarctica

There are many melt and fluid inclusions (mainly CO₂-rich) in olivine and pyroxene phenocrysts in basalts from the Ross Island area. The melt inclusions can be classified as follows: (1) crystalline melt inclusions (type I), (2) fluid-melt inclusions (type II) and (3) glass inclusions (type III). The daughter minerals in type I include olivine, plagioclase, ilmenite, etc. Fluid-melt inclusions are a new type which represent the immiscibility of magma and fluid at a particular stage of evolution. Three types of fluid-melt inclusions were examined in this study: a) crystal + liquid + gas, b) inclusions coexisting with glass inclusions and fluid inclusions, and c) crystal + daughter mineral (dissolved salt) + gas. Both primary and secondary melt inclusions are recognizable in the samples. The secondary melt inclusions were formed during healing of fractures in the host minerals in the process of magma rise. The homogenization temperatures (both Leitz 1350 stage and quench method were used) of melt inclusions in basalts range from 1190 to 135°C at high pressure (about 7 kbars), indicating that the basalts may have come from the upper mantle. Melt-fluid immiscibility in basaltic magma shows that the CO₂-rich fluids may be the main fluid phase in the upper mantle, which are of significance in understanding the evolution of magma and various processes in the deep levels of the earth. The homogenization temperatures of melt and aqueous fluid inclusions in granites and metamorphic rocks in this area vary from 980 to 1100°C and 279 to 350°C, respectively.     

Hambergite-rich melt inclusions in morganite crystals from the Muiane pegmatite, Mozambique and some remarks on the paragenesis of hambergite

Raman spectroscopic studies of daughter crystals of hambergite [Be₂BO₃(OH, F)] in primary melt and secondary fluid inclusions in morganite crystals from the Muiane pegmatite, Mozambique, show that the inclusions have extremely high beryllium concentrations, corresponding to as much as 10.6% (g/g) in melt inclusions and 1.25% (g/g) BeO in fluid inclusions. These melt and fluid inclusions were trapped at about 610°C and 277°C, respectively. We propose two possible mechanisms for the formation of the hambergite crystals: (i) direct crystallization from a boron- and beryllium-rich pegmatite-forming melt or (ii) these are daughter crystals produced by the retrograde reaction of the boron-rich inclusion fluid with the beryl host, after release of boric acid from the primary trapped metastable volatile-rich silicate melt during cooling and recrystallization. Although we favor the second option, either case demonstrate the extent to which Be maybe concentrated in a boron-rich fluid at relatively high temperatures, and in which species of Be maybe transported. One important constraint on the stability of the hambergite paragenesis is temperature; at temperatures of ≥650°C (at 2 kbar) hambergite is not stable and converts to bromellite [BeO].     

Formation of epigenetic graphite inclusions in diamond crystals: experimental data

To elucidate the conditions of formation of epigenetic graphite inclusions in natural diamond, we carried out experiments on high-temperature treatment of natural and synthetic diamond crystals containing microinclusions. The crystal annealing was performed in the CO–CO₂ atmosphere at 700–1100 °C and ambient pressure for 15 min to 4 h. The starting and annealed diamond crystals were examined by optical microscopy and Raman spectroscopy. It has been established that the microinclusions begin to change at 900 °C. A temperature increase to 1000 °C induces microcracks around the microinclusions and strong stress in the diamond matrix. The microinclusions turn black and opaque as a result of the formation of amorphous carbon at the diamond–inclusion interface. At 1100 °C, ordered graphite in the form of hexagonal and rounded plates is produced in the microcracks. A hypothesis is put forward that graphitization in natural diamond proceeds by the catalytic mechanism, whereas in synthetic diamond it is the result of pyrolysis of microinclusion hydrocarbons. The obtained data on the genesis of graphite microinclusions in diamond are used to evaluate the temperature of kimberlitic melt at the final stage of formation of diamond deposits.     

DISTINCTIVE FEATURES OF THE HEALING OF A CRACK IN A CRYSTAL UNDER CONDITIONS OF DECLINING TEMPERATURE

The concentrations of aqueous solution from which quartz, feldspar, topaz, tourmaline and other minerals crystallize during the hydrothermal stage, is important to an understanding of pegmatite formation. Two opposing theories have been advanced on solution concentration: 1) Pegmatitic minerals separate from highly concentrated solution, without marked change in concentration, by gradual cooling. 2) Pegmatitic minerals separate as a result of flow and of renovation of the exhausted contents of solutions; this need is based on low solubility of silica in pure water. Study of liquid inclusions in minerals reveals that separation of hydrothermal minerals is known to occur from aqueous solutions heavily saturated with alkaline-halide salts, carbonates, borates, and free carbonic acid. From observations made on secondary liquid inclusions in topaz samples from pegmatites, it was found that one-third of the inclusion-cavity volume was occupied by the gas bubble and the remainder of the volume, largely, by small crystals of several solid phases. Inclusion contents could not be completely homogenized, because they exploded at 400° - 450° C; homogenization required temperatures above 500° C. Flattened inclusions, formed by healing of cracks parallel to the (001) cleavage plane, were examined. At room temperature, the included bubble was disk like; on heating to temperatures of 180° - 200° C, the bubble contracted revealing beneath it a circular crescent-shaped depression, probably an indication that crystal substance had been deposited on inclusion-cavity walls. Accordingly, crystal substance precipitated out after entrapment of solution in the cavity because redeposition occurred around the bubble; this could have been possible only after the solution had been completely enclosed and subsequently cooled. To determine the original amount of substance entrapped, measurements were made of inclusion-cavity volume, thickness of substance deposited within the cavity (found to be about 2 percent of inclusion-cavity height), and depth of crescent-shaped depression. From these data it was found that up to 2 percent volume of the topaz substance remained in dissolved state at relatively low temperatures. Deposition traces were found on walls of sufficiently flat inclusions where a large part of the wall surface was blocked by a flattened bubble; presence of these conditions was required in order to detect the deposited layer and measure its height.     

Genesis and mineralization of gold-bearing quartz veins in the Xiao Qinling area, central China

Gold-bearing quartz veins of the Taihua Group consisting of Archean metavolcanic rocks are a main gold deposit type in the Xiao Qinling area,one of the three biggest gold production areas in China.The quartz veins experienced strong alteration characterized by a typical mesothermal hydrothermal altered mineral assemblage.The grade of gold is affected by the contents of sulphides,e.g.galena,pyrite and chalcopyrite.Results of minor elements analysis for the of gold-bearing quartz veins indicate higher contents of Au and high contents of Ag,Pb,Cu,Cd,W,and Mo.Abundant fluid inclusions were found in the gold-bearing quartz veins.Three types of fluid inclusions were identified:(1) aqueous inclusions;(2) CO 2-bearing inclusions;and(3) daughter crystal-bearing fluid inclusions.Homogenization temperatures ranged from 110 to 670℃ with low and high peaks appearing at 160 180℃ and 280 300℃,respectively.The salinity of aqueous inclusions varies between 1.8 wt% and 38.2 wt% NaCl.The homogenization temperature and salinity show a positive correlation.The H and O isotopes of fluid inclusions in the gold-bearing quartz veins indicate that magmatic solution and metamorphic hydrothermal solution,together with meteoric water,were involved in the formation of gold-bearing fluid.Mesozoic magma activities related to granite intrusions should be the main source of CO 2 fluid with higher temperature and salinity.     

Petrology of Precambrian metaultramafites of the Gridino high-pressure complex (Karelia)

Along with eclogitized gabbro and gabbronorite bodies, boudinaged metaultramafites such as garnet-pyroxene rocks and orthopyroxenites were revealed in the Archean plagiogneiss strata of the Gridino complex. The garnet-pyroxene rock crope out as a boudin on Vysokii Island. The early stage of the rock evolution is documented by inclusions of diabantite (Fe-Si chlorite), a mineral that occurs in metasomatized peridotites. Diabantite was found in all rock-forming minerals in paragenesis with mineral phases enriched in REE (Ce, Nd, La, etc.), U, and Th. The confinement of ore phases to the inclusion rims and the development of two systems of cracks, radial and concentric, around the inclusions in pyroxenes point to the transformation of the inclusions after their trapping. Thermobarometric studies of the crystal cores revealed that the anhydrous paragenesis garnet + orthopyroxene + clinopyroxene, which replaced the chlorite-bearing rock, formed at ~690 ºC and ~17 kbar. The rims of the rock-forming minerals reflect isothermal decompression to ~12 kbar, which was followed by decompression cooling to ~650 ºC and ~9 kbar with the formation of regressive amphibole-garnet-pyroxene paragenesis. The giant-grained orthopyroxenites compose chains of boudinaged bodies on Izbnaya Luda Island. The orthopyroxene crystals host abundant amphibole, quartz, biotite, and pyrite inclusions pointing to amphibolite metamorphism at the early stage of the rock evolution. There are two types of amphibole: magnesian hornblende and anthophyllite. The hornblende is a primary mineral, whereas the low-temperature anthophyllite forming rims around the quartz inclusions was produced at the regressive stage of metamorphism. There are no indicators of the PT-conditions of the peak metamorphism in the orthopyroxenite. The reaction enstatite + quartz + H₂O = anthophyllite allows deciphering water activity of anthophyllite formation, a ≤ 0.5.     

Geology and inclusion studies on the genesis of the Baolun gold deposit in Hainan Province,South China

The late Triassic Baolun gold deposit hosted by Silurian phyllites is a large‐scale high‐grade gold deposit in Hainan Island, South China. The ores can be classified into quartz‐vein dominated type and less altered rock type. Three mineralization stages were recognized by mineral assemblages. The early stage, as the most important mineralization stage, is characterized by a quartz–native gold assemblage. The muscovite?quartz?pyrite?native gold assemblage is related to the intermedium mineralization stage. In late mineralization stage, native gold and Bi‐bearing minerals are paragenetic minerals. Microthermometry analyses show that the early mineralization stage is characterized by two types of fluid inclusions, including CO₂‐rich inclusions (C‐type) and aqueous inclusions (W‐type). C‐type inclusions homogenize at 276–335°C with an averaged value of 306°C and have salinities of 1.0–10.0 wt% NaCl equivalent (mean value of 4.9 wt% NaCl equivalent). W‐type inclusions homogenize at 252–301°C (mean value of 278°C) with salinity of 4.0–9.7 wt% NaCl equivalent (mean value of 7.4 wt% NaCl equivalent). In intermedium mineralization stage, C‐type and W‐type inclusions homogenize at 228–320°C (mean value of 283°C) and 178–296°C (mean value of 241°C), with salinities of 2.4–9.9 wt% NaCl equivalent (mean value of 6.5 wt% NaCl equivalent) and 3.7–11.7 wt% NaCl equivalent (mean value of 7.7 wt% NaCl equivalent), respectively. No suitable mineral, such as quartz or calcite, was found for fluid inclusion study from late mineralization stage. In contrast, only aqueous inclusions were found from post‐ore barren veins, which yielded lower homogenization temperatures ranging from 168–241°C (mean value of 195°C) and similar salinities (2.6–12.6 wt% NaCl equivalent with averaged value of 7.2 wt% NaCl equivalent). The different homogenization temperatures and similar salinities of C‐type and W‐type from each mineralization stage indicate that fluid immiscibility and boiling occurred. The Baolun gold deposit was precipitated from a CO₂‐bearing mesothermal fluid, and formed at a syn‐collision environment following the closure of the Paleo‐Tethys.     

Fluid Characteristics and Evolution of the Zhawulong Granitic Pegmatite Lithium Deposit in the Ganzi‐Songpan Region,Southwestern China

The Zhawulong granitic pegmatite lithium deposit is located in the Ganzi-Songpan orogenic belt. Fluid inclusions in spodumene and coexisting quartz were studied to understand the cooling path and evolution of fluid within albite–spodumene pegmatite. There are three distinguishable types of fluid inclusions: crystal-rich, CO2–NaCl–H2O, and NaCl–H2O. At more than 500°C and 350~480 MPa, crystal-rich fluid inclusions were captured during the pegmatitic magma-hydrothermal transition stage, characterized by a dense hydrous alkali borosilicate fluid with a carbonate component. Between 412°C and 278°C, CO2–NaCl–H2Ofluid inclusions developed in spodumene (I) and quartz (II) with a low salinity (3.3–11.9 wt%NaCl equivalent) and a high volatile content, which represent the boundary between the transition stage and the hydrothermal stage. The subsequentNaCl–H2Ofluid inclusions from the hydrothermal stage, between 189°C and 302°C, have a low salinity (1.1–13.9 wt%NaCl equivalent). The various types of fluid inclusions reveal the P–T conditions of pegmatite formation, which marks the transition process from magmatic to hydrothermal. The ore-forming fluids from the Zhawulong deposit have many of the same characteristics as those from the Jiajika lithium deposit. The ore-forming fluid provided not only materials for crystallization of rare metal minerals, such as spodumene and beryl, but also the ideal conditions forthe growth of ore minerals. Therefore, this area has favorable conditions for lithium enrichment and excellent prospecting potential.     

The nature, origin and physicochemical controls of hydrothermal Mo-Bi mineralization in the Cadillac deposit, Quebec, Canada

Mo-Bi mineralization occurs in subvertical and subhorizontal quartz-muscovite-± K-feldspar veins surrounded by early albitic and later K-feldspathic alteration halos in monzogranite of the Archean Preissac pluton, Abitibi region, Québec, Canada. Molybdenite is intergrown with muscovite in the veins or associated with K-feldspar in the alteration halos. Mineralized veins contain five main types of fluid inclusions: aqueous liquid and liquid-vapor inclusions, aqueous carbonic liquid-liquid-vapor inclusions, carbonic liquid and vapor inclusions, halite-bearing aqueous liquid and liquid-vapor inclusions, trapped mineral-bearing aqueous liquid and liquid-vapor inclusions. The carbonic solid in frozen carbonic and aqueous-carbonic inclusions melts in most cases at −56.7 ± 0.1 °C indicating that the carbonic fluid consists largely of CO₂. All aqueous inclusion types and the aqueous phase in carbonic inclusions have low initial melting temperatures (≥70 °C), requiring the presence of salts other than NaCl. Leachate analyses show that the bulk fluid contains variable proportions of Na, K, Ca, Cl, and traces of Mg and Li. The following solids were identified in the fluid inclusions by SEM-EDS analysis: halite, calcite, muscovite, millerite (NiS), barite and antarcticite (CaCl₂ · 6H₂O). All are interpreted to be trapped phases except halite which is a daughter mineral, and antarcticite which formed during sample preparation (freezing). Aqueous inclusions homogenize to liquid at temperatures between 75 °C and 400 °C; the mode is 375 °C. Aqueous-carbonic inclusions homogenize to liquid or vapor between 210 °C and 400 °C. Halite-bearing aqueous inclusions homogenize by halite dissolution at approximately 170 °C. Aqueous inclusions containing trapped solids exhibit liquid-vapor homogenization at temperatures similar to those of halite-bearing aqueous inclusions. Temperatures of vein formation, based on oxygen isotopic fractionation between quartz and muscovite, range from 342 °C to 584 °C. The corresponding oxygen isotope composition of the aqueous fluid in equilibrium with these minerals ranges from 1.2 to 5.5 per mil with a mean of 3.9 per mil, suggesting that the liquid had a significant meteoric component. Isochores for aqueous fluid inclusions intersect the modal isotopic isotherm of 425 °C at pressures between 590 and 1900 bar. A model is proposed in which molybdenite was deposited owing to decreasing temperature and/or pressure from CO₂-bearing, moderate to high salinity fluids of mixed magmatic-meteoric origin that were in equilibrium with K-feldspar and muscovite. These fluids resulted from the degassing of a monzogranitic magma and evolved through interaction with volcanic (komatiitic) and sedimentary country rocks. Received: 6 February 1997 / Accepted: 28 January 1998     

Genesis of massive sulfide deposits in the Verkhneural’sk ore district, the South Urals, Russia: Evidence for magmatic contribution of metals and fluids

Melt inclusions and aqueous fluid inclusions in quartz phenocrysts from host felsic volcanics, as well as fluid inclusions in minerals of ores and wall rocks were studied at the Cu-Zn massive sulfide deposits in the Verkhneural’sk ore district, the South Urals. The high-temperature (850–1210°C) magmatic melts of volcanic rocks are normal in alkalinity and correspond to rhyolites of the tholeiitic series. The groups of predominant K-Na-type (K₂O/Na₂O = 0.3–1.0), less abundant Na-type (K₂O/Na₂O = 0.15–0.3), and K-type (K₂O/Na₂O = 1.9–9.3) rhyolites are distinguished. The average concentrations (wt %) of volatile components in the melts are as follows: 2.9 H₂O (up to 6.5), 0.13 Cl (up to 0.28), and 0.09 F (up to 0.42). When quartz was crystallizing, the melt was heterogeneous, contained magnetite crystals and sulfide globules (pyrrhotite, pentlandite, chalcopyrite, bornite). High-density aqueous fluid inclusions, which were identified for the first time in quartz phenocrysts from felsic volcanics of the South Urals, provide evidence for real participation of magmatic water in hydrothermal ore formation. The fluids were homogenized at 124–245°C in the liquid phase; the salinity of the aqueous solution is 1.2–6.2 wt % NaCl equiv. The calculated fluid pressure is very high: 7.0–8.7 kbar at 850°C and 5.1–6.8 kbar at 700°C. The LA-ICP-MS analysis of melt and aqueous fluid inclusions in quartz phenocrysts shows a high saturation of primary magmatic fluid and melt with metals. This indicates ore potential of island-arc volcanic complexes spatially associated with massive sulfide deposits. The systematic study of fluid inclusions in minerals of ores and wall rocks at five massive sulfide deposits of the Verkhneural’sk district furnished evidence that ore-forming fluids had temperature of 375–115°C, pressure up to 1.0–0.5 kbar, chloride composition, and salinity of 0.8–11.2 (occasionally up to 22.8) wt % NaCl equiv. The H and O isotopic compositions of sericite from host metasomatic rocks suggest a substantial contribution of seawater to the composition of mineral-forming fluids. The role of magmatic water increases in the central zones of the feeding conduit and with depth. The dual nature of fluids with the prevalence of their magmatic source is supported by S, C, O, and Sr isotopic compositions. The TC parameters of the formation of massive sulfide deposits are consistent with the data on fluid inclusions from contemporary sulfide mounds on the oceanic bottom.     

Experimental study of the interaction of mineral-forming hydrothermal solutions with oil and their joint migration

Interaction between oil and hydrothermal solutions of different compositions was experimentally studied in a wide range of temperature (260–490°C) and pressures (8–150 MPa). This study was based on a new technique involving simultaneous occurrence of water-hydrocarbon interaction and growth of quartz, calcite, and fluorite crystals with fluid inclusions from the same solution. Fluid inclusions were studied to characterize the behavior of oil and aqueous solutions at elevated and high temperatures and pressures. It was shown that, owing to interaction with hydrothermal solutions, oil is intensely removed from the source rock and accumulated in the frontal part of hydrothermal convective flow. During this process, the oil is partially transformed into hydrocarbons, light oil, semiliquid and solid bitumens. At temperatures of 300–350°C and pressures of 50–100 MPa, oil and its fractionation products migrate in hydrothermal solution mainly in a drop-liquid state. At higher temperatures (360–395°C), when the oil/water ratio in the initial mixture is no higher than 1/70–1/35, liquid and gaseous hydrocarbons are completely dissolved in hydrothermal solutions forming a complex homogenous water-hydrocarbon fluid. The fluid can exist and migrate in this state, but it becomes heterogeneous with decreasing P-T parameters. Under favourable structural and lithological conditions, this can lead to the formation of displaced oil-and-gas deposits, with oil enriched in light components. The experiments unambiguously confirmed the concept that bitumen inclusions in minerals can serve as indicators of hydrocarbon migration paths in the Earth’s crust.     

Geological and fluid inclusion studies of the Dongpo tungsten skarn ore deposit,China

The Dongpo tungsten ore deposit, the largest scheelite skarn deposit in China, is located at the contact of a 172-m. y. biotite granite with a Devonian marble. The mineralization associated with the granite includes W, Bi-Mo, Cu-Sn and Pb-Zn ores. Several W mineralization stages are shown by the occurrence of ore in massive skarn deposits and in later cross-cutting veins. The high garnet/pyroxene ratio, the hedenbergite and diopside-rich pyroxene and the andradite-rich garnet show the deposit belongs to the oxidized skarn type. Detailed fluid inclusion studies of granite, greisen, skarn and vein samples reveal three types of fluid inclusion: (1) liquid-rich, (2) gas-rich and (3) inclusions with several daughter minerals. Type (3) is by far the most common in both skarn and vein samples. The dominant daughter mineral in fluid inclusions is rhembic, highly birefringent, and does not dissolve on heating even at 530°C. We assume that this mineral is calcite. The liquid phase in most of the fluid inclusions has low to moderate salinities: 0–15 wt. %; in a few has higher salinities (30–40 wt. % NaCl equivalent). The homogenization temperatures of inclusions in the skarn stage range from 350°C to 530°C, later tungsten mineralization-stage inclusions homogenize between 200°C and 300°C, as do inclusions in veins. Fluid inclusions in granite and greisen resemble those of the late tungsten mineralization stage, with low salinity and homogenization temperatures of 200°–360°C. The tungsten-forming fluids are probably a mixture that came from biotite granite and the surrounding country rocks.     

The fidelity of melt inclusions as records of melt composition

A series of experiments created melt inclusions in plagioclase and pyroxene crystals grown from a basaltic melt at 1,150°C, 1.0 GPa to investigate diffusive fractionation during melt inclusion formation; additionally, P diffusion in a basaltic melt was measured at 1.0 GPa. Melt inclusions and melts within a few 100 microns of plagioclase–melt interfaces were analyzed for comparison with melt compositions far from the crystals. Melt inclusions and melt compositions in the boundary layer close to the crystal–melt interface were similar, but both differ significantly in incompatible element concentrations from melt found greater than approximately 200 microns away from the crystals. The compositional profiles of S, Cl, P, Fe, and Al in the boundary layers were successfully reproduced by a two-step model of rapid crystal growth followed by diffusive relaxation toward equilibrium after termination of crystal growth. Applying this model to investigate possible incompatible element enrichment in natural melt inclusions demonstrated that at growth rates high enough to create the conditions for melt inclusion formation, ∼10⁻⁹–10⁻⁸ m s⁻¹, the concentration of water in the boundary layer near the crystal was similar to that of the bulk melt because of its high diffusion coefficient, but sulfur, with a diffusivity similar to major elements and CO₂, was somewhat enriched in the boundary layer melt, and phosphorus, with its low diffusion coefficient similar to other high-field strength elements and rare earth elements, was significantly enriched. Thus, the concentrations of sulfur and phosphorus in melt inclusions may over-estimate their values in the bulk melt, and other elements with similar diffusion coefficients may also be enriched in melt inclusions relative to the bulk melt. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Geology,Fluid Inclusion,and Sulfur Isotope Studies of the Chehugou Porphyry Molybdenum–Copper Deposit,Xilamulun Metallogenic Belt,NE China

The Chehugou Mo–Cu deposit, located 56 km west of Chifeng, NE China, is hosted by Triassic granite porphyry. Molybdenite–chalcopyrite mineralization of the deposit mainly occurs as veinlets in stockwork ore and dissemination in breccia ore, and two ore‐bearing quartz veins crop out to the south of the granite porphyry stock. Based on crosscutting relationships and mineral paragenesis, three hydrothermal stages are identified: (i) quartz–pyrite–molybdenite ± chalcopyrite stage; (ii) pyrite–quartz ± sphalerite stage; and (iii) quartz–calcite ± pyrite ± fluorite stage. Three types of fluid inclusions in the stockwork and breccia ore are recognized: LV, two‐phase aqueous inclusions (liquid‐rich); LVS, three‐phase liquid, vapor, and salt daughter crystal inclusions; and VL, two‐phase aqueous inclusions (gas‐rich). LV and LVS fluid inclusions are recognized in vein ore. Microthermometric investigation of the three types of fluid inclusions in hydrothermal quartz from the stockwork, breccia, and vein ores shows salinities from 1.57 to 66.75 wt% NaCl equivalents, with homogenization temperatures varying from 114°C to 550°C. The temperature changed from 282–550°C, 220–318°C to 114–243°C from the first stage to the third stage. The homogenization temperatures and salinity of the LV, LVS and VL inclusions are 114–442°C and 1.57–14.25 wt% NaCl equivalent, 301–550°C and 31.01–66.75 wt% NaCl equivalent, 286–420°C and 4.65–11.1 wt% NaCl equivalent, respectively. The VL inclusions coexist with the LV and LVS, which homogenize at the similar temperature. The above evidence shows that fluid‐boiling occurred in the ore‐forming stage. δ³⁴S values of sulfide from three type ores change from ?0.61‰ to 0.86‰. These δ³⁴S values of sulfide are similar to δ³⁴S values of typical magmatic sulfide sulfur (c. 0‰), suggesting that ore‐forming materials are magmatic in origin.     

Textural history of recent basaltic-andesites and plutonic inclusions from Merapi volcano

Mt. Merapi in Central Java is one of the most active stratovolcanoes on Earth and is underlain by a multistage plumbing system. Crystal size distribution analyses (CSD) were carried out on recent Merapi basaltic-andesites and co-eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales. The basaltic-andesites exhibit log-linear, kinked-upwards CSD curves for plagioclase and clinopyroxene that can be separated into two main textural populations. Large plagioclase phenocrysts (≥1.6 mm) make up one population, but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid-crustal levels. This population was subsequently influenced by crystal accumulation and the onset of crustal assimilation, including the incorporation of high-Ca skarn-derived xenocrysts. Textural re-equilibration is required for these crystals to form a single population in CSD. A second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals <1.6 mm in size. Crustal assimilation is indicated by, for example, oxygen isotopes and based on the CSD data, crystallisation combined with contamination is likely semi-continuous in these upper crustal storage chambers. The CSD data observed in the basaltic-andesite samples are remarkably consistent and require a large-volume steady state magmatic system beneath Merapi in which late textural equilibration plays a significant role. Plagioclase CSDs of co-eruptive magmatic and plutonic inclusions may contain a third crystal population (<1 mm) not found in the lavas. This third population has probably formed from enhanced degassing of portions of basaltic-andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic-andesite mush inclusions. A suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep Merapi plumbing system, as deduced from CSD patterns and mineral assemblages.     

Geochemistry and Fluid Inclusions Analysis of Vein Quartz in the Multiple Hydrothermal Systems of Mankayan Mineral District,Philippines

Several high‐sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry‐type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold‐bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite‐rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry‐type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high‐temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite‐rich epithermal veins. In particular, the Ti content of quartz of the porphyry‐type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry‐type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.     

Magmatic-Hydrothermal Evolution in the “Bottoms” of Porphyry Copper Systems: Evidence from Silicate Melt and Aqueous Fluid Inclusions in Granitoid Intrusions in the Gyeongsang Basin,South Korea

The Gyeongsang Basin of southeastern Korea contains numerous Cretaceous-early Tertiary (120–40 Ma) granitoid intrusions formed at a convergent plate boundary. The geotectonic setting is similar to that associated with porphyry-type mineralization elsewhere in the Circumpacific region. However, erosion has removed higher-level economic mineralization and exposed deeper levels of the granitoids, representing the poorly mineralized “bottoms” of porphyry copper systems. The intrusions of the Gyeongsang Basin thus provide a unique opportunity to advance our understanding of magmatic-hydrothermal evolution in the roots of porphyry-type systems, below the level of economic mineralization.

The physical and chemical environment during crystallization of the magmas has been characterized through studies of silicate melt and aqueous fluid inclusions in the granitoids. Two different types of silicate melt inclusions were recognized based on occurrence and room-temperature appearance. Type-I inclusions contain one or more crystalline phases and vapor; type-II inclusions consist of a cluster of small crystals, partially devitrified glass, and vapor. Petrographic and Raman analyses indicate that most silicate melt inclusions contain muscovite daughter crystals. Some also contain feldspar. Solidus temperatures of type-I inclusions in quartz phenocrysts range from ≈630to 650°C, whereas solidus temperatures of type-I and type-II inclusions in vug quartz are slightly higher (640–670°C). Liquidus temperatures span a much wider range compared to solidus temperatures, with maximum liquidus temperatures of melts in phenocrysts being slightly higher (≤930°C) than those in vug quartz (≤910°C).

Three types of aqueous inclusions were observed based on occurrence and room temperature phase proportions. Type-A inclusions are liquid rich and low to moderate in salinity; type-B inclusions are vapor rich and low in salinity; type-C inclusions are liquid rich and contain a halite daughter mineral. Some type- A inclusions with a salinity of approximately 25 wt% NaCl equivalent are spatially associated with silicate melt inclusions in phenocrysts, where they occur as three-dimensional clusters of tiny inclusions surrounding the silicate melt inclusion. Type-A inclusions also occur along fractures in quartz phenocrysts. Non-fracture-controlled type-C inclusions are rare in phenocryst quartz, but are common in vug quartz, where they are associated with silicate melt inclusions. Type-C inclusions that coexist with silicate melt inclusions generally homogenize by halite dissolution after the vapor bubble and show a wide range in salinity, from about 30 to >60 wt% NaCl equivalent. Coexisting halite-bearing (Type-C) and vapor-rich (Type-B) inclusions in phenocryst quartz suggest local immiscibility in the late-or post-magmatic fluid.

Pressure-temperature conditions during the final stages of magmatic-hydrothermal activity associated with the granitoid intrusions of the Gyeongsang Basin were approximately 630° to 670° C and 1.9 to 2.5 kbars. These results suggest that the granitoids do not contain economic porphyry coppertype mineralization because the magmas crystallized at high pressures (relative to typical porphyry copper magmas) and did not become saturated in water until a relatively late stage in the crystallization history. Failure to reach water saturation resulted in most of the copper in the original melt being sequestered as a trace component in earlier-crystallizing silicate and sulfide phases to produce anomalous but subeconomic copper grades. Furthermore, owing to the depth of emplacement, less energy was available to fracture the rocks when water did exsolve from the magma, and the pressure remained too high for aqueous fluid immiscibility to be an important metal-concentrating or depositing mechanism. Geological, petrographic, and geochemical characteristics suggest that the granitoid rocks of the Gyeongsang Basin represent ethroot zones of porphyry-type systems, and any higher-grade mineralization that may have been present higher in the system has since been removed by erosion.     

Typomorphic Characteristics of Molybdenite from the Bystrinsky Cu–Au Porphyry–Skarn Deposit,Eastern Transbaikal Region,Russia

The paper presents pioneering data on the composition, texture, and crystal structure of molybdenite from various types of molybdenum mineralization at the Bystrinsky Cu–Au–Fe porphyry–skarn deposit in the eastern Transbaikal region, Russia. The data were obtained using electron microprobe analysis (EMPA), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS), and high-resolution transmission electron microscopy (HRTEM). Molybdenite found at the deposit in skarn, sulfide-poor quartz veins, and quartz–feldspar alteration markedly differs in the concentrations of trace elements determined by their species in the mineral, as well as in its structural features. Molybdenite-2H from skarn associated with phyllosilicates occurs as ultrafine crystals with uniform shape and texture; no dislocations or inclusions were found but amorphous silica was. The molybdenite composition is highly contrasting in the content and distribution of both structure-related (Re, W, and Se) and other (Mn, Co, Ni, Cu, Zn, As, Ag, Cd, Sb, Te, Ag, Pd, Au, Hg, Pb, and Bi) metals. In the sulfide-poor quartz veins, highly structurally heterogeneous (2H + 3R) molybdenite microcrystals with abundant defects (dislocations and volumetrically distributed inclusions) are associated with illite, goethite, and barite. Some single crystals are unique three-phase (2H + 3R polytypes + amorphous MoS₂). The mineral has a low concentration of all trace elements, which are uniformly distributed. However, individual domains with uniquely high Pd, Te, Ni, Hg, and W concentrations caused by mineral inclusions are found in some grains. Molybdenite from quartz–feldspar alteration is characterized by low concentrations of all trace elements except for Re and Se, which enrich some domains of the grains. Our data indicate that the compositional and structural heterogeneity of molybdenite from the Bystrinsky deposit are its crucial features, which obviously correlate with the types of Mo mineralization.