Tracking fluid sources for skarn formation using scapolite geochemistry: an example from the Jinshandian iron skarn deposit, Eastern China
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δ34S
Fluorapatite
Isotope Geochemistry
Magmatic water
Halite
Metasomatism
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Fluid inclusions in quartz from the mineralized quartz veins from the Mosabani and Rakha copper deposits were investigated. On the basis of petrography, two distinct types of primary inclusions were identified. These are low saline aqueous biphase inclusions and high saline halite-bearing polyphase inclusions. The halite-bearing inclusions mostly homogenized by halite dissolution, barring instances where homogenization was manifest by disappearance of the vapour bubble. Minimum entrapment pressure values were estimated by intersection of the halite liquid with the corresponding inclusion isochores. The ranges in P-T at the temperatures of halite dissolution are: 2.6 kb / 370°C - 0.8 kb / 263°C for Mosabani and 2.1 kb / 270°C - 0.65kb / 217°C for Rakha. Temperature-salinity plots for both the deposits is suggestive of restricted mixing (and simple cooling) of a hot saline magmatic fluid with cooler low saline meteoric water that caused precipitation of sulphide minerals. Stable isotope data ( δ 18 O and δD) from Changkakoti et al. (1987) are re-interpreted in the present study, leading to the conclusion that the main fluid component for Mosabani mineralization was either of magmatic/ metasomatic parentage or an evolved meteoric water at a low water/rock ratio, after its interaction with a granitic pluton. The observed high saline nature of fluids in both the deposits compels us to choose an initial magmatic/metasomatic fluid that evolved by restricted mixing and simple cooling.
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Halite
Scheelite
Magmatic water
Wolframite
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The Sakaerde copper deposit is a mesothermal-epithermal deposit. The δ13CPDB values of quartz and calcite samples in the deposit vary in a narrow range of-17.3‰~-0.7‰. The δ18OSMOW values range from 16.2‰ to 22.4‰, their corresponding δ 18OH2 O values are between 6.9‰ and 12.5‰, and the δD values of fluid inclusions vary from-73.8‰ to-52.4‰. These data imply that the ore-forming fluids of the ore deposit were mainly derived from the heated formation water mixed with a small amount of magmatic water and metamorphic water. The carbon in ore-forming fluids mainly came from formation water or atmosphere precipitation, with the addition of some deep magmatic water at the late stage. The δ34S values range from 0.2‰ to 6.1‰, implying that the sulfur in ore fluids mainly came from the magma or the upper mantle.
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Magmatic water
Mesothermal
Isotope Geochemistry
Ore genesis
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The post-collisional Qulong porphyry Cu-Mo deposit is the largest in the Gangdese Cu belt, southern Tibet. Despite many previous studies, the evolution of ore-forming fluids in the Qulong deposit remains controversial. Pyrite-bearing veins at Qulong can be divided into seven subclasses, including Mt-type, Bt-type, A-type, B-type, C-type, D-type, and E-type veins. To decipher the evolution of magmatic-hydrothermal fluids at Qulong, in situ LA-ICP-MS trace element and sulfur isotope compositions of pyrites from different veins were analyzed. The δ34S values (+1.01‰ to +4.28‰) for pyrites indicate a magmatic sulfur source and the high Se/S ratios of pyrite at Qulong are consistent with hydrothermal fluids being mainly magma-derived. The low Co/Ni ratio (0.01-0.1) of pyrite in Mt-type vein suggests that the earliest magmatic-hydrothermal fluids may have contributed from mafic magma injection. From Mt- to Bt- to A-type veins, the δ34S values in the hydrothermal fluids decrease as the temperature decreases, whereas the Cu and Co contents increase and the As and Ni contents decrease. In B- and C-type veins, the relatively high and stable Co and Ni contents and the range of δ34S isotope values in pyrite indicate the existence of multiple-stages of magmatic-hydrothermal fluids during the main mineralization period. During the late stages of mineralization, the decrease of Co, Ni and As contents and increase of Cu in pyrite in D- and E-type veins, as well as the narrow range of δ34S values, may be due to decreasing temperature as a result of fluid dilution caused by mixing with meteoric waters. The slightly negative δ34S fluid values for chalcopyrite (-1.56‰ to -0.75‰) in sample Q711-1968 also suggests the addition of external water at Qulong.
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Isotopic signature
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The Hutouya Zn-Pb deposit is located in western Qimantag of East Kunlun Mountains, Qinghai Province. The layered,quasi-lamellar, lenticular and veined ore bodies are controlled by the Langyashan Formation of Jixianian Period. Two stages of mineralization are recognized based on cross-cutting relationships. The late stage is represented by the galena-bearing calcite veins, which cut the banded ores. Sphalerite is characterized by higher content of Fe(2.255%~5.579%), lower content of Ga, Ge, and Zn/Cd ratios(146~198), and the content of Ag in galena is lower(0.015%~0.038%). These data indicate that the metallic minerals were probably formed in close relation to magmatic fluid. δD and δ18OH2O values of fluid inclusion water in calcite vary from-92.7‰ to-76‰ and-11.58‰ to-2.27‰ respectively, and parts of the values are between the range of magmatic water and atmospheric water. The oreforming fluid of the early stage was magamtic fluid with components of CO2, CH4, N2 and H2. All these data show that the ore-forming fluid was mainly magmatic water at the early stage, with the addition of atmospheric water at the late stage. The ore-forming fluid of the early stage was characterized by middle-lower temperature, high salinity and middle density. At the late stage, the salinity and density of ore-forming fluid decreased because of the continuous mixing with atmospheric water. The values of δ34S vary from 1.6‰ to 9.9‰, which indicate that sulfur in sulfides was mainly from the mixing of magma and wall rocks. The sulfides have206Pb/204Pb ratios from 18.533 to 18.580,207Pb/204Pb ratios from 15.606 to 15.669, and208Pb/204Pb ratios from 38.344 to 38.522, which suggest that ore-forming metals might have come from deep magmatic activity, with a little crust mixing. In summary, the Hutouya Zn-Pb deposit may be a layered skarn type deposit related to Indosinian magmatic activity.
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This study investigates for the first time the subsurface Miocene evaporite facies (Gachsaran Formation) in Abu Dhabi, United Arab Emirates. Forty-five evaporite rock samples were selected for petrographic, mineralogical, and geochemical investigations and stable isotope analyses to decipher their origin and constrain their age. Secondary gypsum with anhydrite relics dominates the investigated evaporitic rocks, with minor amounts of clays, dolomicrite, Fe/Ti oxides, and celestite. These samples are characterized by their excellent purity and low variability in geochemical composition. The distribution of trace element concentrations is significantly influenced by continental detrital intake. The main focus of the study is to determine the strontium, sulfur, and oxygen stable isotope compositions. The measured 87Sr/86Sr values of 0.708411–0.708739 are consistent with Miocene marine sulfates and indicate ∼21.12–15.91 Ma (Late Aquitanian-Burdigalian). The δ34S and δ18O values are 17.10‰–21.59‰ and 11.89‰–19.16‰, respectively. These values are comparable to those of Tertiary marine evaporites. The relatively low values of δ34S suggest that non-marine water possesses little influence on S distribution. The geochemical composition and Sr, S, and O isotope distributions of the Abu Dhabi gypsum facies from the Gachsaran Formation reveals that their source brines were marine (coastal saline/sabkha) with subordinate continental input.
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Sabkha
Anhydrite
Isotope Geochemistry
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δ34S
Lode
Mesothermal
Isotope Geochemistry
Overprinting
Arsenopyrite
δ18O
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