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991.
The Changjiang uranium ore field, which contains >10,000 tonnes of recoverable U with a grade of 0.1–0.5%, is hosted by Triassic two-mica and Jurassic biotite granites, and is one of the most important uranium ore fields in South China. The minerals associated with alteration and mineralization can be divided into two stages, namely syn-ore and post-ore. The syn-ore minerals are primarily quartz, pitchblende, hematite, hydromica, chlorite, fluorite, and pyrite; the post-ore minerals include quartz, calcite, fluorite, pyrite, and hematite. The fluid inclusions of the early syn-ore stage characteristically contain O2, and those of the late syn-ore and post-ore stage contain H2 and CH4. The fluid inclusions in quartz of the syn-ore stage include H2O, H2O–CO2, and CO2 types, and they occur in clusters or along trails. Homogenization temperatures (Th) for the H2O–CO2 and two-phase H2O inclusions range from 106 °C to >350 °C and cluster in two distinct groups for each type; salinities are lower than 10 wt% NaCl equiv. The ore-forming fluids underwent CO2 effervescence or phase separation at ∼250 °C under a pressure of 1000–1100 bar. The U/Th values of the altered granites are lowest close to the ore, increase outwards, but subsequently decrease close to unaltered granites. From the unaltered granites to the ore, the lowest Fe2O3/FeO values become lower and the highest values higher. The REE patterns of the altered granites and the ores are similar to each other. The U contents of the ores show a positive correlation with total REE contents but a negative correlation with LREE/HREE ratios, indicating the pitchblende is REE-bearing and selectively HREE-rich. The δEu values of the ore show a positive correlation with U contents, indicating the early syn-ore fluids were oxidizing. The δCe values show a negative correlation, indicating the later mineralization environment became reducing. The water–rock interactions of the early syn-ore stage resulted in oxidization of altered granites and reduction of the ore-forming fluids, and it was this reduction that led to the uranium mineralization. During alteration in the early syn-ore stage, the oxidizing fluids leached uranium from granites close to faults, and Fe2O3/FeO ratios increased in the alteration zones. The late syn-ore and post-ore alteration decreased the Fe2O3/FeO ratios in the alteration zones. The δ18OW–SMOW values of the ore-forming fluids range from −1.8‰ to 5.4‰, and the δDW–SMOW values range from −104.4‰ to −51.6‰, suggesting meteoric water. The meteoric water underwent at least two stages of water–rock interaction: the first caused the fluids to become uranium-bearing, and the second stage, which was primarily associated with ore-bearing faults, led to uranium deposition as pitchblende, accompanied by CO2 effervescence. 相似文献
992.
The Hadamengou-Liubagou Au-Mo deposit is the largest gold deposit in Inner Mongolia of North China. It is hosted by amphibolite to granulite facies metamorphic rocks of the Archean Wulashan Group. To the west and north of the deposit, there occur three alkaline intrusions, including the Devonian-Carboniferous Dahuabei granitoid batholith, the Triassic Shadegai granite and the Xishadegai porphyritic granite with molybdenum mineralization. Over one hundred subparallel, sheet-like ore veins are confined to the nearly EW-trending faults in the deposit. They typically dip 40° to 80° to the south, with strike lengths from hundreds to thousands of meters. Wall rock alterations include potassic, phyllic, and propylitic alteration. Four distinct mineralization stages were identified at the deposit, including K-feldspar-quartz-molybdenite stage (I), quartz-pyrite-epidote/chlorite stage (II), quartz-polymetallic sulfide-gold stage (III), and carbonate-sulfate-quartz stage (IV). Gold precipitated mainly during stage III, while Mo mineralization occurred predominantly in stage I. The δDH2O and δ18OH2O values of the ore-forming fluids range from −125‰ to −62‰ and from 1.4‰ to 7.5‰, respectively, indicating that the fluids were dominated by magmatic water with a minor contribution of meteoric water. The δ13CPDB and δ18OSMOW values of hydrothermal carbonate minerals vary from −10.3‰ to −3.2‰ and from 3.7‰ to 15.3‰, respectively, suggesting a magmatic carbon origin. The δ34SCDT values of sulfides from the ores vary from −21.7‰ to 5.4‰ and are typically negative (mostly −20‰ to 0‰). The wide variation of the δ34SCDT values, the relatively uniform δ13C values of carbonates (typically −5.5‰ to −3.2‰), as well as the common association of barite with sulfides suggest that the minerals were precipitated under relatively high fo2 conditions, probably in a magmatic fluid with δ34SƩS ≈ 0‰. The Re-Os isotopic dating on molybdenite from Hadamengou yielded a weighted average age of 381.6 ± 4.3 Ma, indicating that the Mo mineralization occurred in Late Devonian. Collectively, previous 40Ar-39Ar and Re-Os isotopic dates roughly outlined two ranges of mineralizing events of 382–323 Ma and 240–218 Ma that correspond to the Variscan and the Indosinian epochs, respectively. The Variscan event is approximately consistent with the Mo mineralization at Hadamengou-Liubagou and the emplacement of the Dahuabei Batholith, whereas the Indosinian event roughly corresponds to the possible peak Au mineralization of the Hadamengou-Liubagou deposit, as well as the magmatic activity and associated Mo mineralization at Xishadegai and Shadegai. Geologic, petrographic and isotopic evidence presented in this study suggest that both gold and molybdenum mineralization at Hadamengou-Liubagou is of magmatic hydrothermal origin. The molybdenum mineralization is suggested to be associated with the magmatic activity during the southward subduction of the Paleo-Asian Ocean beneath the North China Craton (NCC) in Late Devonian. The gold mineralization is most probably related to the magma-derived hydrothermal fluids during the post-collisional extension in Triassic, after the final suturing between the Siberian and NCC in Late Permian. 相似文献
993.
The Jidetun deposit is a large porphyry Mo deposit that is located in central Jilin Province, northeast China. The Mo mineralization occurs mainly at the edge of porphyritic granodiorite, as well as the adjacent monzogranite. Field investigations, cross-cutting relationships, and mineral paragenetic associations indicate four stages of hydrothermal activity. To determine the relationships between mineralization and associated magmatism, and better understand the metallogenic processes in ore district, we have undertaken a series of studies incluiding molybdenite Re–Os and zircon U–Pb geochronology, fluid inclusions microthermometry, and C–H–O–S–Pb isotope compositions. The molybdenite Re–Os dating yielded a well-defined isochron age of 168.9 ± 1.9 Ma (MSWD = 0.34) that is similar to the weighted mean 206Pb/238U age of 173.5 ± 1.5 Ma (MSWD = 1.8) obtained from zircons from the porphyritic granodiorite. The results lead to the conclusion that Mo mineralization, occurred in the Middle Jurassic (168.9 ± 1.9 Ma), was spatially, temporally, and genetically related to the porphyritic granodiorite (173.5 ± 1.5 Ma) rather than the older monzogranite (180.1 ± 0.6 Ma). Fluid inclusion and stable (C–H–O) isotope data indicate that the initial H2O–NaCl fluids of mineralization stage I were of high-temperature and high-salinity affinity and exsolved from the granodiorite magma as a result of cooling and fractional crystallization. The fluids then evolved during mineralization stage II into immiscible H2O–CO2–NaCl fluids that facilitated the transport of metals (Mo, Cu, and Fe) and their separation from the ore-bearing magmas due to the influx of abundant external CO2 and heated meteoric water. Subsequently, during mineralization stage III and IV, increase of pH in residual ore-forming fluids on account of CO2 escape, and continuous decrease of ore-forming temperatures caused by the large accession of the meteoric water into the fluid system, reduced solubility and stability of metal clathrates, thus facilitating the deposition of polymetallic sulfides. 相似文献
994.
The Nanling Range in South China is characterized by extensive Mesozoic magmatism and coeval nonferrous and rare metal mineralization. Huangshaping is a world-class Pb-Zn-W-Mo polymetallic skarn deposit in the central Nanling Range. Magmatic rocks occurring in this ore district include quartz porphyry, granite porphyry, granophyre, dacite porphyry, and aplite, with only the first three granitoids genetically associated with polymetallic mineralization. Most of the orebodies are constrained within the contact zones as skarn and veins between these granitic stocks and the carbonate wall rocks.Since the age of the quartz porphyry is still controversial, and studies of the dacite porphyry and aplite are absent, we focus on these magmatic rocks first. LA-ICP-MS zircon U-Pb dating suggests that the crystallization ages of the quartz porphyry, dacite porphyry, and aplite are 154.3 ± 1.9 Ma, 158.1 ± 0.8 Ma, and 148.4 ± 3.4 Ma, respectively. Combined with previously published age data, we infer the evolutionary sequence of magmatic rocks should be dacite porphyry → quartz porphyry → granite porphyry (granophyre) → aplite. The quartz porphyry, dacite porphyry, and aplite yield high contents of high field strength elements (Zr + Nb + Ce + Y = 255–440 ppm), high ratios of 10,000 × Ga/Al (2.6–3.2), and prominent depletions in Ba, Sr, Eu, P, and Ti, indicating their crustal affinities to A-type granites. They have negative εNd(t) values (−9.4 to −7.0) and high initial Pb isotopic ratios (206Pb/204Pbi = 18.307–18.644, 207Pb/204Pbi = 15.689–15.742, 208Pb/204Pbi = 38.589–38.986), suggesting that they were probably derived by partial melting of ancient granulitic crustal materials.The sulfide minerals exhibit a wide range of δ34SV-CDT values from −22.6 to 24.2‰, with 206Pb/204Pb of 17.669–19.708, 207Pb/204Pb of 15.492–15.714, and 208Pb/204Pb of 37.880–39.789, indicating that sulfur, lead, and other associated metals were derived from a mixture of magmatic components and the Carboniferous wall rocks. Fluid inclusions in pyrrhotite, sphalerite, and marmatite samples have 3He/4He ratios of 0.12 to 1.53 Ra, with calculated mantle helium proportions of 1.3 to 18.9%, indicating a predominantly crustal origin for the ore fluids, with minor inputs from the mantle. The Huangshaping deposit is a typical example of the genetic relationship both spatially and temporally between Jurassic magmatism and polymetallic metallogeny in the Nanling Range. 相似文献
995.
The Yinchanggou Pb-Zn deposit, located in southwestern Sichuan Province, western Yangtze Block, is stratigraphically controlled by late Ediacaran Dengying Formation and contains >0.3 Mt of metal reserves with 11 wt% Pb + Zn. A principal feature is that this deposit is structurally controlled by normal faults, whereas other typical deposits nearby (e.g. Maozu) are controlled by reverse faults. The origin of the Yinchanggou deposit is still controversial. Ore genetic models, based on conventional whole-rock isotope tracers, favor either sedimentary basin brine, magmatic water or metamorphic fluid sources. Here we use in situ Pb and bulk Sr isotope features of sulfide minerals to constrain the origin and evolution of hydrothermal fluids. The Pb isotope compositions of galena determined by femtosecond LA-MC-ICPMS are as follows: 206Pb/204Pb = 18.17–18.24, 207Pb/204Pb = 15.69–15.71, 208Pb/204Pb = 38.51–38.63. These in situ Pb isotope data overlap with bulk-chemistry Pb isotope compositions of sulfide minerals (206Pb/204Pb = 18.11–18.40, 207Pb/204Pb = 15.66–15.76, 208Pb/204Pb = 38.25–38.88), and both sets of data plotting above the Pb evolution curve of average upper continental crust. Such Pb isotope signatures suggest an upper crustal source of Pb. In addition, the coarse-grained galena in massive ore collected from the deep part has higher 206Pb/204Pb ratios (18.18–18.24) than the fine-grained galena in stockwork ore sampled from the shallow part (206Pb/204Pb = 18.17–18.19), whereas the latter has higher 208Pb/204Pb ratios (38.59–38.63) than the former (208Pb/204Pb = 38.51–38.59). However, both types of galena have the same 207Pb/204Pb ratios (15.69–15.71). This implies two independent Pb sources, and the metal Pb derived from the basement metamorphic rocks was dominant during the early phase of ore formation in the deep part, whereas the ore-hosting sedimentary rocks supplied the majority of metal Pb at the late phase in the shallow part. In addition, sphalerite separated from different levels has initial 87Sr/86Sr ratios ranging from 0.7101 to 0.7130, which are higher than the ore formation age-corrected 87Sr/86Sr ratios of country sedimentary rocks (87Sr/86Sr200 Ma = 0.7083–0.7096), but are significantly lower than those of the ore formation age-corrected basement rocks (87Sr/86Sr200 Ma = 0.7243–0.7288). Again, such Sr isotope signatures suggest that the above two Pb sources were involved in ore formation. Hence, the gradually mixing process of mineralizing elements and associated fluids plays a key role in the precipitation of sulfide minerals at the Yinchanggou ore district. Integrating all the evidence, we interpret the Yinchanggou deposit as a strata-bound, normal fault-controlled epigenetic deposit that formed during the late Indosinian. We also propose that the massive ore is formed earlier than the stockwork ore, and the temporal-spatial variations of Pb and Sr isotopes suggest a certain potential of ore prospecting in the deep mining area. 相似文献
996.
Yong Zhang Shu–Wen Xing Chao Li Shi–Fu Liang Zheng–Tao Yu Xiao–Hui Du 《International Geology Review》2017,59(2):185-203
The Changfagou Cu deposit is a newly discovered porphyry deposit located in the southern Jilin Province of Northeastern China, on the northeastern margin of the North China Craton. To better understand the formation of the Cu deposit, we report the zircon U–Pb and molybdenite Re–Os dating, and Sr-, Nd-, and Hf- isotopic data of the granite porphyry. LA-ICP-MS dating of zircon grains from two mineral zones in the granite porphyry yield ages of 115.7 ± 0.8 and 115.3 ± 0.6 Ma, which is interpreted as the emplacement age of the granite porphyry. The molybdenite Re–Os model ages of 112.5 to 113.8 Ma, an isochron age of 113.3 ± 1.3 Ma, and a weighted mean model age of 113.0 ± 0.7 Ma, which represents the age of the Cu mineralization quite well. The Changfagou granite porphyry samples lack amphibole and muscovite, and are compositionally characterized by high SiO2, high Na2O+K2O, and low P2O5, enriched in some Rb, Th, U, and Pb, and depleted in Nb, Ta, Ti, P, and Eu. Mineralogical and geochemical features suggest that the Changfagou granite porphyry samples are slightly peraluminous and are of highly fractionated I-type granitoids. The granitic rocks also have relatively high (87Sr/86Sr)i (0.71199 to 0. 71422), and both low εNd(t) (?14.56 to ?13.19) and εHf(t) values (?14.916 to ?8.644), which suggest that Changfagou granite porphyry are derived from mixed sources of crustal and mantle, and diagenesis and mineralization were possibly related to the switch in subduction direction of the Palaeo-Pacific Plate in the late phase of Early Cretaceous. 相似文献
997.
The northwest Zhejiang Province is a key domain for providing deep insight into the crust–mantle interaction and tectonic evolution of the South China block. In this paper, we collect geochemical, geochronological, and isotopic data of the Jurassic porphyries in this region, and investigated the Huangbaikeng ore-bearing porphyry in the Tongcun Mo–Cu deposit, using it as an example to uncover the porphyry petrogenesis and evaluate their metallogenic potential. Two varieties of the Huangbaikeng porphyry were distinguished: the medium- to coarse-grained type and medium- to fine-grained type. Zircon Sensitive High-Resolution Ion Microprobe U–Pb dating indicates that they were emplaced at 161.8 ± 2.8 and 162.7 ± 3.5 Ma, respectively, which are consistent with the molybdenite Re–Os ages of 163.9–161.8 Ma. The inherited zircons age spectrum significantly recorded a series of geological events, for example, assembly and breakup of the Columbia and Rodinia supercontinent, and the Triassic collision of Yangtze and North China blocks. Whole rock Sr–Nd and Jurassic zircon Hf isotopic data yield mostly negative εHf(t) values (0.5 to ?8.4) and εNd(t) values (?0.79 to ?4.82). Besides the Huangbaikeng porphyry, all the Jurassic porphyries in the northwest Zhejiang Province have a wide range of SiO2 contents (76.78–60.91 wt.%). They do not contain typical aluminous minerals (e.g. cordierite and garnet), and are mainly metaluminous to weakly peraluminous with high Na2O, low FeOT/MgO, and Zr + Nb + Ce + Y concentrations in composition. They thus fit the I-type granite definition. Some major and trace elements show strong correlations with SiO2, possibly indicating extensive fractional crystallization during their magma evolution. Tectonic discriminations imply that these plutons were likely formed in a volcanic arc regime possibly related to subduction of the Palaeo-Pacific plate. Sr–Nd–Hf isotopic data suggest a mixed source of the Mesoproterozoic crust and 30–50% mantle components. Compared with the adjacent Dexing Cu-bearing porphyies, which have more positive εHf(t) and εNd(t) values with more significant mantle components (55–70%), the Jurassic porphyries in the northwest Zhejiang Province probably lack metallogenic potential to form a giant porphyry copper deposit as Dexing. 相似文献
998.
Nadezhda Priyatkina William J. Collins Andrei Khudoley Dmitry Zastrozhnov Victoria Ershova Kevin Chamberlain 《International Geology Review》2017,59(13):1632-1656
Identifying the cratonic affinity of Neoproterozoic crust that surrounds the northern margin of the Siberian Craton (SC) is critical for determining its tectonic evolution and placing the Craton in Neoproterozoic supercontinental reconstructions. Integration of new U–Pb–Hf detrital zircon data with regional geological constraints indicates that distinct Neoproterozoic arc-related magmatic belts can be identified within the Taimyr orogen. Sedimentary rocks derived from 970 to 800 Ma arc-related suites reveal abundant Archean and Paleoproterozoic detritus, characteristic of the SC. The 720–600 Ma arc-related zircon population from the younger Cambrian sedimentary rocks is also complemented by an exotic juvenile Mesoproterozoic zircon population and erosional products of older arc-related suites. Nonetheless, numerous evidences imply that both arcs broadly reworked Siberian basement components. We suggest that the early Neoproterozoic (ca. 970–800 Ma) arc system of the Taimyr orogen evolved on the active margin of the SC and probably extended along the periphery of Rodinia into Valhalla orogen of NE Laurentia. We also suggest the late Neoproterozoic (750–550 Ma) arc system could have been part of the Timanian orogen, which linked Siberia and Baltica at the Precambrian/Phanerozoic transition. 相似文献
999.
J. Pertille L. A. Hartmann J. O. S. Santos N. J. McNaughton R. Armstrong 《International Geology Review》2017,59(12):1532-1560
The Neoproterozoic geotectonic triad of the Brasiliano Orogen is reconstructed in southern Brazil from studies focused on the Porongos fold and thrust belt. We integrate field geology with isotopic studies of zircon U–Pb SHRIMP and Lu–Hf–O laser determinations in seven metasedimentary and three metavolcanic rock samples. The results indicate that the Porongos palaeo-basin was derived from mixed sources (3200–550 Ma), with major contributions from Rhyacian (2170 Ma) and Ediacaran (608 Ma) sources. Minor contributions from Archaean to Tonian sources are also registered. The maximum depositional age of the Porongos palaeo-basin is established by the age range of 650–550 Ma with TDM model ages between 2.5 and 1.3 Ga. The reworked signature (εHf values = ?34 to ?4) and the characteristic crustal magma reservoirs (δ18O ≥5.3 ‰) indicate that these sediments are equivalent to Neoproterozoic granites of the Dom Feliciano Belt. The episodic depositional history started in the Cryogenian (650 Ma) and lasted until the Ediacaran (most likely 570 Ma). A magmatic event of Tonian age is recorded in rhyodacite samples interleaved with the metasedimentary rocks and dated at 773, 801, and 809 Ma. The crustal evolution of the Sul-Riograndense Shield included mountain building, folding and thrusting and flexural subsidence in the foreland. An orogenic triad is revealed as the Pelotas Batholith, the Porongos fold and thrust belt and the Camaquã Basin, all part of the Dom Feliciano Belt. 相似文献
1000.
Gang Liu Shu-Wen Dong Zheng-Le Chen Shu-Qin Han Yi Yang 《International Geology Review》2017,59(9):1053-1081
ABSTRACTThe Balkhash metallogenic belt (BMB) in Kazakhstan is a famous porphyry Cu–Mo metallogenic belt in the Central Asian Orogenic Belt (CAOB). The late Palaeozoic granitoids in the BMB are mainly high-K calc-alkaline and I-type granites, with shoshonite that formed during a late stage. Geochemical analyses and tectonic discrimination reveal a change in the tectonic environment from syn-collision and volcanic arcs during the Carboniferous to post-collision during the Permian. The late Palaeozoic granitoids from the Borly porphyry Cu deposit formed in a classical island-arc environment, and those from the Kounrad and Aktogai porphyry Cu deposits and the Sayak skarn Cu deposit are adakitic. The εNd(t) values for the late Palaeozoic granitoids are between ?5.87 and +5.94, and the εSr(t) values range from ?17.16 to +51.10. The continental crustal growth histories are different on either side of the Central Balkhash fault. On the eastern side, the εNd(t) values of the granitoids from the Aktogai and Sayak deposits are very high, which are characteristic of depleted mantle and suggest that crustal growth occurred during the late Palaeozoic. On the western side, the εNd(t) values of the granitoids from the Borly and Kounrad deposits are slightly low, which suggests the presence of a Neoproterozoic basement and the mixing of crust and mantle during magmatism. The granitoids have initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.335–20.993, 15.521–15.732, and 38.287–40.021, respectively, which demonstrate an affinity between the late Palaeozoic magmatism in the BMB and that in the Tianshan, Altai, and Junggar orogens. 相似文献