1,720,988 research outputs found
Hydrothermal sulfur geochemistry on molybdenite deposition of the Questa Mo-deposit, New Mexico, USA
No full textWe conducted combined microthermometry and LA-ICP-MS microanalysis in the several brine inclusion assemblages of the Questa porphyry Mo deposits, USA and the nearby cogenetic Rito del Medio granitoid to study the hydrothermal geochemistry responsible for a molybdenite deposition in the Climax-type Mo deposit. We analyzed S concentrations in the fluid inclusions by using a recent technique on S quantification in the singly-targeted fluid inclusions. We found plenty of S in the fluid inclusions adequate to precipitate molybdenite, and the molybdenite might be precipitated in the tight temperature range of 350-450 A degrees C in the Questa. A fractional crystallization in the causative magma would enrich Mo in the evolving magmatic-hydrothermal fluids from the early-stage hydrothermal breccias (MHBX) to the postdating stockwork veinlets (STW), while maintaining S to precipitate molybdenite in the Questa.N
Selective copper diffusion into quartz-hosted vapor inclusions: Evidence from other host minerals, driving forces, and consequences for Cu-Au ore formation
No full textISSN:0016-7037ISSN:1872-9533ISSN:1872-953
Fractionation of Cl/Br during fluid phase separation in magmatic-hydrothermal fluids
No full textISSN:0016-7037ISSN:1872-9533ISSN:1872-953
The role of sulfur in the formation of magmatic-hydrothermal copper-gold deposits
No full textEssential resources of many rare metals including copper, zinc, molybdenum, silver and gold occur in natural sulfide mineral deposits. Understanding the origin of these metal resources has been limited by a lack of data about the geochemistry of sulfur, the most important and abundant element of ore deposits. We report the first directly measured sulfur concentrations in high-temperature fluids, together with their ore-metal contents, using a new method for sulfur quantification in fluid inclusions by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Co-genetic brine and vapor inclusions from magmatic-hydrothermal ore deposits and granitic intrusions show an excess of sulfur over ore metals, as required for efficient ore-mineral precipitation. The results demonstrate that S, Cu and Au are highly enriched in vapor-like magmatic fluids, implying that such low-salinity fluids are the key agent for the formation of porphyry copper and epithermal gold deposits. (C) 2009 Elsevier B.V. All rights reserved.Y
Quantum chemical calculations of equilibrium copper(I) isotope fractionations in ore-forming fluids
No full textWe calculated the equilibrium isotope fractionation of Cu (I) complexes in hydrothermal ore-forming fluids using quantum chemical calculations (based on the density functional theory and Hartree-Fock approximations) of molecular structures and vibrational frequencies to gain insights into the CU isotope (Cu-63, Cu-65) composition in natural systems. The calculated molecular structures of liquid - (copper chlorides and copper hydrosulfides) and vapor-phase (CuCl(H2O) and Cu3Cl3) CU complexes are largely consistent with the experimental data. The predicted vibrational frequencies are dependent on the energy levels of theory and basis sets used in the calculations. The vibrational frequency shift due to isotopic substitution is most prominent in the stretching (for linear molecules such as CuCl) and bending (for [CuCl2](1-) and [CuCl3](2-)) modes of vibration. The calculated reduced partition function ratio (i.e. 10(3) center dot 1n(beta(65-63))) of each copper isotopomer depends on the Cu coordination environments and types of ligands. The Cu complexes with a longer bond length (e.g., Cu-Cl or Cu-S) and larger coordination number apparently have greater isotope fractionation among the monomer complexes. A significant copper isotope fractionation has been predicted for each Cu complex: Cu3Cl3 (vapor phases) contain the most enriched C-65(u) isotopes, whereas [CuCl3]2(liquid phase) is the most depleted. The calculated 665 Cu range [maximum delta Cu-65 for CuCl3-minimum delta Cu-65 for [CuCl3](2-)] increases with a decrease in the temperature; the ranges are 0.76-0.89 parts per thousand at 500 degrees C, 1.00-1.17 parts per thousand at 400 degrees C, 1.37-1.61 parts per thousand at 300 degrees C, 2.01-2.35 parts per thousand. at 200 degrees C, and 2.50-2.92 parts per thousand at 150 degrees C. These ranges around 150-500 degrees C are somewhat larger than the observed isotopic compositions in sea-floor hydrothermal vents (approximately 0.8-1.3 parts per thousand) and porphyry copper deposits (0.7 parts per thousand). While detailed information about phase equilibria (stability fields) among both vapor and liquid copper complexes as function of composition, temperature and pressure should be known to better discuss the origin of the Cu isotope composition in natural systems, current theoretical prediction shows the effect of temperature could contribute to a variation in isotopic composition in the natural system. Our calculation indicates that temperature and types of ligands affect the copper isotope fractionation in the ore-forming fluids, and also imply that the liquid-vapor equilibrium (e.g., volcanic degassing) could lead to significant copper isotope fractionation. On the other hands, Cu isotope fractionations of [CuCl2](1-) and [Cu(HS2)](1-), the major copper-bearing species in hydrothermal conditions, are rather similar; thus, the fractionation without a change in the oxidation states may not fully account for the natural isotopic variation unless the concentrations of both Cu3Cl3 and for [CuCl3]2- are significant in the hydrothermal fluids. (c) 2007 Elsevier B.V. All rights reserved.N
Magmatic–hydrothermal processes in Sangdong W–Mo deposit, Korea: Study of fluid inclusions and 39 Ar– 40 Ar geochronology
No full textThe Sangdong scheelite-molybdenite deposit in northeast South Korea consists of strata-bound orebodies in intercalated carbonate-rich layers in the Cambrian Myobong slate formation. Among them, the M1 layer hosts the main orebody below which lie layers of F1-F4 host footwall orebodies. Each layer was first skarnized with the formation of a wollastonite + garnet + pyroxene assemblage hosting minor disseminated scheelite. The central parts of the layers were subsequently crosscut by two series of quartz veining events hosting minor scheelite and major scheelite-molybdenite ores, respectively. The former veins associate amphibole-magnetite (amphibole) alteration, whereas the latter veins host quartz-biotite-muscovite (mica) alteration. Deep quartz veins with molybdenite mineralization are hosted in the Cambrian Jangsan quartzite formation beneath the Myobong formation. In the Sunbawi area, which is in close proximity to the Sangdong deposit, quartz veins with scheelite mineralization are hosted in Precambrian metamorphic basement. Three muscovite Ar-39-Ar-40 ages between 86.6 +/- 0.2 and 87.2 +/- 0.3 Ma were obtained from M1 and F2 orebodies from the Sangdong deposit and Sunbawi quartz veins. The Upper Cretaceous age of the orebodies is concordant with the published ages of the hidden Sangdong granite, 87.5 +/- 4.5 Ma. This strongly suggests that the intrusion is causative for the Sangdong W-Mo ores and Sunbawi veins. Fluid inclusions in the quartz veins from the M1 and F2 orebodies, the deep quartz-molybdenite veins, and the Sunbawi veins are commonly liquid-rich aqueous inclusions having bubble sizes of 10-30 vol%, apparent salinities of 2-8 wt% NaCl eqv., and homogenization temperatures of 180-350 degrees C. The densities of the aqueous inclusions are 0.70-0.94 g/cm(3). No indication of fluid phase separation was observed in the vein. To constrain the formation depth in the Sangdong deposit, fluid isochores are combined with Ti-in-quartz geothermometry, which suggests that the M1 and F2 orebodies were formed at depths of 1-3 km and 5-6 km below the paleo-surface, respectively. The similarity of the Cs (cesium) concentrations and Rb/Sr ratios in the fluid inclusions of the respective orebodies indicate an origin from source magmas having similar degrees of fractionation and enrichment of incompatible elements such as W and Mo. High S concentrations in the fluids and possibly organic C in the sedimentary source likely promoted molybdenite precipitation in the Sangdong orebodies, whereas the scheelite deposition in the deep quartz-molybdenite veins hosted in the quartzite is limited by a lack of Ca and Fe in the hydrothermal fluids. The molybdenite deposition in the Sunbawi quartz-molybdenite veins hosted in the Precambrian metamorphic basement rocks was possibly limited by a lack of reducing agents such as organic C.N
Studies on Fluid Inclusion and Pyrite Geochemistry in the Moisan Au-Ag Deposit, Haenam District, Korea
No full text금-은 천열수 광상의 유체 환경의 재구성을 위하여, 해남 일대에 위치한 모이산 광상에서 획득한 심도별 맥상 시료에 대하여, 변질-조직 양상, 유체포유물 microthermometry, 그리고 황철석 LA-ICP-MS 분석을 실시하였다. 맥상 시료에서 모암은 규화 및 석영-일라이트 변질양상이 확인되며, 석영맥은 모암으로부터 초기의 옥수-미립 석영-황철석에서 후기 맥 중심의 자형 석영으로 발달된다. 일부 시료에서는 황철석과 함께 텔루라이드 광물이 함께 나타난다. 유체포유물은 염도가 0.18-2.24wt% 가량의 액상 수용액 포유물들이 주로 발견되며 일부 기체상 포유물 또한 발견된다. 유체포유물의 균질화 온도는 141-384oC 범위에서 나타나며, 대체로 깊어질수록 균질화온도가 높아진다. 특히 금-은 침전이 집중된 고품위 구간에서는 얕아질수록 유체의 염도 및 균질화 온도가 낮아지며 또한 범위가 넓어지는 것을 볼 수 있다. 이를 통하여 함 금-은 유체의 압력하강으로 인한 열수의 비등 그리고 천수와의 혼합이 금-은 침전과 함께 이루어진 것으로 생각된다. 황철석의 LA-ICP-MS 분석을 통하여, 황철석 광물 내의 금-은 치환은 이루어지지 않음을 발견하였다. 하지만, 황철석 내의 금-은은 대부분 텔루라이드 혹은 에렉트럼 등 함 금은 광물의 포유물에 저장이 됨을 알 수 있었다.
깊이별 황철석 내 포획된 함 금-은 광물은 차이가 없었고, 포유물의 금-은 비율 또한 차이가 없음을 확인하였다.N
Sphalerite geochemistry of the Zn-Pb orebodies in the Taebaeksan metallogenic province, Korea
No full textThe Taebaeksan region, located in the northeastern part of South Korea, is an important metallogenic province which hosts numerous Zn-Pb-W-Mo-Fe-Cu (-Au-Ag) mineral systems. The Zn-Pb orebodies in the region (inclusive of skarn, carbonate replacement, and vein-breccia ore types) are hosted on the early Paleozoic carbonate sequences and they are associated with late Cretaceous to early Paleogene magmatic-hydrothermal activities. We collected Zn-Pb orebodies from 15 areas including non-metal deposits, such as high-Ca calcite marble, as well as exploration sites in the Taebaeksan metallogenic province. Thereafter, we studied the geochemistry of the sphalerite present in them to understand the regional Zn-Pb mineralization process and to establish an exploration strategy. The sphalerites collected from the region contained detectable amounts of Fe, Mn, Cd, Co, Cu, Ga, Ge, Mo, Ag, In, Sn, Sb, W, Tl, Pb, and Bi which were identified using microbeam techniques like EPMA and LA-ICP-MS. Sphalerites from economically significant Zn-Pb deposits characteristically have high Mn and low Cd content, while W (-Mo)-bearing deposits have remarkably high Cd content. Correlation trends between trace elements demonstrate the coupled substitution mechanisms such as 3 Zn2+ <-> 2 (Cu+ or Ag+) + Sn4+ and 2 Zn2+ <-> Cu+ + In3+, occurring in the sphalerite. High-temperature ores such as skarn and vein-breccia are relatively enriched with Co and In, while Ga, Ag, and Sn tend to be concentrated in the relatively low-temperature ores, such as carbonate replacement type ores. Lead isotope compositions of the sphalerites show a well-defined, positive, linear trend with those of the local Cretaceous intrusions and the sedimentary sequence of the Taebaeksan region. Major economic Zn-Pb deposits show relatively more signatures of non-radiogenic Pb isotope closer to the intrusions, as compared to the minor and sub-economic Zn-Pb orebodies. The Pb isotope signature suggests that Cretaceous magmatic-hydrothermal fluids with a minimal degree of fluid-rock interactions are required for economic Zn-Pb mineralization in the Taebaeksan metallogenic province.N
Periodically released magmatic fluids create a texture of unidirectional solidification (Ust) in ore-forming granite: A fluid and melt inclusion study of w-mo forming sannae-eonyang granite, korea
No full textISSN:2075-163
Fluid Inclusion Evidence for Subseafloor Magmatic-Hydrothermal Processes at Brothers Volcano, Kermadec Arc, New Zealand
No full textAbstract
Brothers volcano is a submarine dacitic caldera located on the southern Kermadec arc. It is host to the NW Caldera vent field (Site U1530 and Hole U1530A) that locally discharges more focused, metal-rich fluids, and the Upper Cone hydrothermal vent field (Site U1528 and Hole U1528D) that discharges predominantly diffuse, acidic fluids (pH 1.9). These two active vent sites were drilled in 2018 by the International Ocean Discovery Program (IODP) Expedition 376. Fluid inclusions hosted in anhydrite, quartz, barite, and alunite recovered from drill core samples were studied by microthermometry, Raman spectroscopy, and laser ablation-inductively coupled plasma-mass spectrometery (LA-ICP-MS) to obtain detailed depth profiles of temperature, salinity, and composition of the hydrothermal fluids. These analyses allow for a better understanding of complex hydrothermal processes such as phase separation and an assessment of magmatic-hydrothermal contributions while making reference to the dynamics of the deep hydrothermal fluid that rises beneath the hydrothermal vents at Brothers.
The fluid inclusions have homogenization temperatures (Th) ranging from 149° to 358°C and salinities between 0.7 and 10.0 wt % NaCl equiv at the Upper Cone site and Th of 254° to 394°C and salinities between 0.7 and 9.8 wt % NaCl equiv at the NW Caldera site. Microthermometry of fluid inclusions hosted in sulfate minerals from the NW Caldera site indicates subseafloor mixing between hydrothermal fluids and seawater. The enrichment of vapor-partitioning elements B and As in the fluid inclusions suggests phase separation subseafloor, which may be accompanied by halite dissolution and precipitation. Highly diverging Cl/Br values provide indirect evidence for halite dissolution that occurred via subseafloor convection of seawater. Petrographic observations made of the fluid inclusions, such as the recognition of combined liquid-rich and vapor-rich “boiling assemblages” and the occurrence of CO2 in the inclusions, indicate phase separation of hydrothermal fluids.
The CO2 and the content of trace elements and metals in the fluid inclusions are significantly higher than that reported for Brothers vent fluid values, which reflects a magmatic-hydrothermal contribution. At the NW Caldera site, relatively high-temperature hydrothermal fluids with high Cu (max 560 ppm) and Zn (max 740 ppm) mixed with seawater before discharging at the sea floor. Depth profiles of the fluid inclusion data identify a few specific depths of channelized (focused) hydrothermal fluid flow. We suggest that the hydrothermal fluids are mainly focused along lithological contacts which act as permeable pathways, enhancing subseafloor hydrothermal fluid flow.</jats:p
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