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1.
The Qianfanling Mo deposit, located in Songxian County, western Henan province, China, is one of the newly discovered quartz-vein type Mo deposits in the East Qinling–Dabie orogenic belt. The deposit consists of molybdenite in quartz veins and disseminated molybdenite in the wall rocks. The alteration types of the wall rocks include silicification, K-feldspar alteration, pyritization, carbonatization, sericitization, epidotization and chloritization. On the basis of field evidence and petrographic analysis, three stages of hydrothermal mineralization could be distinguished: (1) pyrite–barite–quartz stage; (2) molybdenite–quartz stage; (3) quartz–calcite stage.Two types of fluid inclusions, including CO2-bearing fluid inclusions and water-rich fluid inclusions, have been recognized in quartz. Homogenization temperatures of fluid inclusions vary from 133 °C to 397 °C. Salinity ranges from 1.57 to 31.61 wt.% NaCl eq. There are a large number of daughter mineral-CO2-bearing inclusions, which is the result of fluid immiscibility. The ore-forming fluids are medium–high temperature, low to moderate salinity H2O–NaCl–CO2 system. The δ34S values of pyrite, molybdenite, and barite range from − 9.3‰ to − 7.3‰, − 9.7‰ to − 7.3‰ and 5.9‰ to 6.8‰, respectively. The δ18O values of quartz range from 9.8‰ to 11.1‰, with corresponding δ18Ofluid values of 1.3‰ to 4.3‰, and δ18D values of fluid inclusions of between − 81‰ and − 64‰. The δ13CV-PDB values of fluid inclusions in quartz and calcite have ranges of − 6.7‰ to − 2.9‰ and − 5.7‰ to − 1.8‰, respectively. Sulfur, hydrogen, oxygen and carbon isotope compositions show that the sulfur and ore-forming fluids derived from a deep-seated igneous source. During the peak collisional period between the North China Craton and the Yangtze Craton, the ore-forming fluids that derived from a deep igneous source extracted base and precious metals and flowed upwards through the channels that formed during tectonism. Fluid immiscibility and volatile exsolution led to the crystallization of molybdenite and other minerals, and the formation of economic orebodies in the Qianfanling Mo deposit. 相似文献
2.
The Eocene (ca. 55–38 Ma) Bear Lodge alkaline complex in the northern Black Hills region of northeastern Wyoming (USA) is host to stockwork-style carbonatite dikes and veins with high concentrations of rare earth elements (e.g., La: 4140–21000 ppm, Ce: 9220–35800 ppm, Nd: 4800–13900 ppm). The central carbonatite dike swarm is characterized by zones of variable REE content, with peripheral zones enriched in HREE including yttrium. The principle REE-bearing phases in unoxidized carbonatite are ancylite and carbocernaite, with subordinate monazite, fluorapatite, burbankite, and Ca-REE fluorocarbonates. In oxidized carbonatite, REE are hosted primarily by Ca-REE fluorocarbonates (bastnäsite, parisite, synchysite, and mixed varieties), with lesser REE phosphates (rhabdophane and monazite), fluorapatite, and cerianite. REE abundances were substantially upgraded (e.g., La: 54500–66800 ppm, Ce: 11500–92100 ppm, Nd: 4740–31200 ppm) in carbonatite that was altered by oxidizing hydrothermal and supergene processes. Vertical, near surface increases in REE concentrations correlate with replacement of REE(±Sr,Ca,Na,Ba) carbonate minerals by Ca-REE fluorocarbonate minerals, dissolution of matrix calcite, development of Fe- and Mn-rich gossan, crystallization of cerianite and accompanying negative Ce anomalies in secondary fluorocarbonates and phosphates, and increasing δ18O values. These vertical changes demonstrate the importance of oxidizing meteoric water during the most recent modifications to the carbonatite stockwork. Scanning electron microscopy, energy dispersive spectroscopy, and electron probe microanalysis were used to investigate variations in mineral chemistry controlling the lateral complex-wide geochemical heterogeneity. HREE-enrichment in some peripheral zones can be attributed to an increase in the abundance of secondary REE phosphates (rhabdophane group, monazite, and fluorapatite), while HREE-enrichment in other zones is a result of HREE substitution in the otherwise LREE-selective fluorocarbonate minerals. Microprobe analyses show that HREE substitution is most pronounced in Ca-rich fluorocarbonates (parisite, synchysite, and mixed syntaxial varieties). Peripheral, late-stage HREE-enrichment is attributed to: 1) fractionation during early crystallization of LREE selective minerals, such as ancylite, carbocernaite, and Ca-REE fluorocarbonates in the central Bull Hill dike swarm, 2) REE liberated during breakdown of primary calcite and apatite with higher HREE/LREE ratios, and 3) differential transport of REE in fluids with higher PO43−/CO32− and F−/CO32− ratios, leading to phosphate and pseudomorphic fluorocarbonate mineralization. Supergene weathering processes were important at the stratigraphically highest peripheral REE occurrence, which consists of fine, acicular monazite, jarosite, rutile/pseudorutile, barite, and plumbopyrochlore, an assemblage mineralogically similar to carbonatite laterites in tropical regions. 相似文献
3.
The Dalucao deposit, located in western Sichuan Province, southwestern China, in the western part of the Yangtze Craton, is one of the largest and most extensive rare earth element (REE) deposits in the Himalayan Mianning–Dechang REE belt. Moreover, the Dalucao deposit is the only deposit identified in the southern part of the belt. The Dalucao deposit contains the No. 1, 2, and 3 orebodies; the No. 1 and 3 orebodies are both hosted in two breccia pipes, located in syenite–carbonatite host rocks. Both pipes have elliptical cross-sections at the surface, with long-axis diameters of 200–400 m and short-axis diameters of 180–200 m; the pipes extend downwards for > 450 m. No. 1 and No. 3 have total thickness varying between 55 and 175 m and 14 to 58 m respectively. The REE mineralization is associated with four brecciation events, which are recorded in each of the pipes. The ore grades in the No. 1 and 3 orebodies are similar, and consist of 1.0%–4.5% rare earth oxides (REOs). The No. 1 orebody is characterized by a Type I mineral assemblage (fluorite + barite + celestite + bastnäsite), whereas the No. 3 orebody is characterized by a Type II assemblage (fluorite + celestite + pyrite + muscovite + bastnäsite + strontianite). Argon (40Ar/39Ar) dating of hydrothermal muscovite intergrown with REE minerals in typical ores from the No. 1 and 3 orebodies yielded similar ages of 12.69 ± 0.13 and 12.23 ± 0.21 Ma, respectively, which suggest that both mineral assemblages formed coevally, rather than in paragenetic stages. Both ages are also similar to the timing of intrusion of the syenite–carbonatite complex (12.13 ± 0.19 Ma). The ore-mineral assemblages occur in breccias, veinlets, and in narrow veins. The ore veinlets, which usually show a transition to mineralized breccia or brecciated ores, are commonly enveloped by narrow veins and stringer zones with comparable mineral assemblages. The brecciated ores form 95% of the volume of the deposit, whereas brecciated ores are only a minor constituent of other deposits in the Mianning–Dechang REE belt. The carbonatite in the syenite–carbonatite complexes contains high concentrations of S (0.07–2.32 wt.%), Sr (16,500–20,700 ppm), Ba (3600–8400 ppm), and light REEs (LREE) (2848–10,768 ppm), but is depleted in high-field-strength elements (HFSE) (Nb, Ta, P, Zr, Hf, and Ti). The syenite is moderately enriched in large-ion lithophile elements (LILE), Sr (155–277 ppm), and Ba (440–755 ppm). The mineralized, altered, and fresh syenites and carbonatites exhibit similar trace element compositions and REE patterns. Brecciation events, and the Dalucao Fault and its secondary faults around the deposit, contributed to the REE mineralization by facilitating the circulation of ore-forming fluids and providing space for REE precipitation. Some hydrothermal veins composed of coarse-grained fluorite and quartz are distributed in the syenite–carbonatite complex. The oxygen isotope compositions of ore-forming fluids in equilibrium with quartz at 215 °C are − 4.95‰ to − 7.45‰, and the hydrogen isotope compositions of fluid inclusions in coarse-grained quartz are − 88.4‰ to − 105.1‰. The syenite–carbonatite complex and carbonatite are main contributors to the mineralization in the geological occurrence. Thus, the main components of the ore-forming fluids were magmatic water, meteoric water, and CO2 derived from the decarbonation of carbonatite. According to the petrographic studies, bastnäsite mineralization developed during later stages of hydrothermal evolution and overprinted the formation of the brecciated fluorite–quartz hydrothermal veins. As low-temperature isotope exchange between carbonates of the carbonatite and water-rich magmatic fluids will lead to positive shifts in δ18O values of the carbonates, C–O isotopic compositions from the bulk primary carbonatite to hydrothermal calcite and bastnäsite changed (δ18OV-SMOW from 8.0‰ to 11.6‰, and δ13C V-PDB from − 6.1 to − 8.7‰). According to the chemical composition of syenite and carbonatite, REE chloride species are the primary complexes for the transport of the REEs in the hydrothermal fluids, and the presence of bastnäsite and parisite means the REE were precipitated as fluorocarbonates. High contents of Sr, Ba and S in the syenite–carbonatite complex led to the deposition of large amount of barite and celestite. 相似文献
4.
The Devonian (ca. 385–360 Ma) Kola Alkaline Province includes 22 plutonic ultrabasic–alkaline complexes, some of which also contain carbonatites and rarely phoscorites. The latter are composite silicate–oxide–phosphate–carbonate rocks, occurring in close space-time genetic relations with various carbonatites. Several carbonatites types are recognized at Kola, including abundant calcite carbonatites (early- and late-stage), with subordinate amounts of late-stage dolomite carbonatites, and rarely magnesite, siderite and rhodochrosite carbonatites. In phoscorites and early-stage carbonatites the rare earth elements (REE) are distributed among the major minerals including calcite (up to 490 ppm), apatite (up to 4400 ppm in Kovdor and 3.5 wt.% REE2O3 in Khibina), and dolomite (up to 77 ppm), as well as accessory pyrochlore (up to 9.1 wt.% REE2O3) and zirconolite (up to 17.8 wt.% REE2O3). Late-stage carbonatites, at some localities, are strongly enriched in REE (up to 5.2 wt.% REE2O3 in Khibina) and the REE are major components in diverse major and minor minerals such as burbankite, carbocernaite, Ca- and Ba-fluocarbonates, ancylite and others. The rare earth minerals form two distinct mineral assemblages: primary (crystallized from a melt or carbohydrothermal fluid) and secondary (formed during metasomatic replacement). Stable (C–O) and radiogenic (Sr–Nd) isotopes data indicate that the REE minerals and their host calcite and/or dolomite have crystallized from a melt derived from the same mantle source and are co-genetic. 相似文献
5.
The Montviel 250 Mt carbonatite-hosted REE–Nb deposit is hosted in a Paleoproterozoic alkaline suite located in the Sub-Province of Abitibi, in the Archean Province of the Superior. The alkaline intrusion consists of biotite clinopyroxenites, melano- to leucosyenites, a melteigite–ijolite–urtite series, riebeckite granite, a series of carbonatites and a carbonatite polygenic breccia. The carbonatite series includes silicocarbonatites, calciocarbonatites, rare magnesiocarbonatites, ferrocarbonatites and mixed carbonatites and are cut by a late, high-energy carbonatite polygenic breccia. Diamond drill hole assays and microscope observations indicate that Nb is hosted in pyrochlore from silicocarbonatite whereas the REE mineralization is mainly hosted in ferrocarbonatite, late mixed carbonatites and polygenic breccia, in REE-bearing carbonates and fluorocarbonate minerals. Diamond drill hole underground mapping and systematic assays have shed light on zones enriched in Nd and LREE with preferential Ba and Sr hydrothermal precipitation and zones enriched in Dy, Y and HREE displaying preferential F and P bearing hydrothermal precipitation. Petrographic observations, electron microprobe analyses, LA-ICPMS and X-ray diffraction were used to study the mineralization processes and to identify and quantify the REE-bearing burbankite–(Ce), carbocernaite–(Ce), ewaldite–(Y), huanghoite–(Nd), cordylite–(Ce), cordylite–(Nd), kukharenkoite–(Ce) and synchysite–(Ce). Most minerals are enriched in total LREE with values around 19.3 wt.%, have total MREE values around 2.2 wt.% and extremely variable total HREE values, with very high contents of Dy and Y averaging around 0.3 wt.% and 1.0 wt.%, respectively, and with total HREE reaching up to 10.0 wt.%. A paragenetic sequence is proposed that consists of: (1) a silicocarbonatite Nb stage, and (2) a calciocarbonatite stage, dominated by magmatism but accompanied by hydrothermal fluids, (3) a main ferrocarbonatite stage, dominated by episodes of Ba- and Sr-hydrothermalism and LREE mineralization, F- and P-hydrothermalism and HREE mineralization and evolved ferrocarbonatitic magmatism, (4) a renewed, mixed carbonatite magmatic stage with minor but increasing hydrothermalism, and (5) a terminal stage of fluid pressure buildup and explosion, leading to the creation of a HREE-enriched polygenic breccia. Globular melt inclusions of Ba–Cl–F (± Si–O) may indicate the presence and contribution of barium-bearing chlorofluoride melts during hydrothermal activity and mineralization of the carbonatite. 相似文献
6.
F. J. Nie 《Mineralium Deposita》1994,29(6):488-498
Located in the Luonan county, Shaanxi Province, northwest China, Jinduicheng, Shijiawan and Huanglongpu molybdenum deposits constitute the most important molybdenum mineralized district in China. Among these three deposits, the Jinduicheng and Shijiawan molybdenum deposits are connected spatially and genetically with granitoid porphyry (124 ± 6 Ma, K-Ar biotite), and consist of disseminated-veinlet ores. Geochemical studies of rare earth elements (REE) furnish further evidence for understanding the rock- and ore-forming processes of these two porphyry molybdenum deposits and their related granitoid rocks. The REE distribution in molybdenum ore, granitoids and their Middle Proterozoic meta-volcanic wall rocks is discussed. The similarities between the REE signatures of the Shijiawan molybdenum-bearing monzogranite porphyry and the neighbouring Laoneushan monzogranite (130 ± 5 Ma, K-Ar biotite) show that they were produced at the same evolutional stage of granitoid magma derived mainly from crustal anatexis. The Shijiawan biotite monzogranite porphyry may be an apophysis of the Laoneushan granitoid batholith. Compared to the Shijiawan monzogranite porphyry, the Jinduicheng molybdenum-bearing granite porphyry is characterized by a high content of HREE, and depletion in LREE. The unique REE patterns indicates that the molybdenum-bearing granite porphyry was formed by thermogravitation diffusion of a granitoid magma. The slight depletion of REE abundance in the altered granitoid porphyry and meta-volcanic wall rocks shows that leaching of REE occurred during breakdown of the primary mineral assemblage, and crystallization of secondary minerals. The high REE content of molybdenum ore represented re-deposition of the mobilized molybdenum and REE. 相似文献
7.
The Hongcheon area in the central Gyeonggi massif is a unique carbonatite locality in South Korea. The age and petrogenesis of this uncommon rock type and associated rare earth element (REE) mineralization still remain uncertain. The NNE trending, 20–50 m wide and ~ 2 km long Fe-REE ore bodies are hosted within a swarm of carbonatite dykes intruding Precambrian basement gneisses. The intrusive nature of the dykes, fenite alteration halos, exsolution intergrowths of constituent minerals and stable isotope data in the literature collectively attest to the ore formation by crystallization of carbonatite magma. The carbonatites are composed primarily of dolomite, ankerite, siderite, magnetite, monazite, apatite, strontianite and pyrite with subordinate quartz, barite, columbite, fergusonite and calcite. The principal carrier phase of REEs is monazite. The REE contents of monazite vary narrowly (TREO = 66.1–69.4 wt.%) irrespective of the textural occurrence. Although the monazite shows a sample-to-sample variation in La/Nd ratio, the textural varieties from each rock sample are similar with respect to this ratio. Thorium contents in monazite are consistently low (average = ca. 2500 ppm) with unusually high (average = ca. 2200) Th/U ratios. Sensitive high-resolution ion microprobe (SHRIMP) dating of monazite yielded a weighted mean 208Pb/232Th age of 232.9 ± 1.6 Ma, which agrees with a weighted mean 206Pb/238U age of 227.2 ± 8.3 Ma within uncertainties. This age, coupled with comparable intrusion ages documented for kimberlites and monzonite-syenite-gabbro-mangerite suite from central Korea, demonstrates the occurrence of mantle-derived alkaline igneous activities and associated REE mineralization following the North and South China collision. The intrusion of the Hongcheon carbonatite and potassic or ultrapotassic suite in central Korea may have resulted from the post-collisional detachment of the subducted slab and consequent upwelling of hot asthenosphere and melting of the overriding lithospheric mantle. Initial Nd‐Sr isotopic ranges of the Hongcheon carbonatite (εNd = ca. − 26, 87Sr/86Sr = 0.703–0.706) and previous trace element data deny a petrogenetic linkage with the coeval silicate magmas. The metasomatism in the lithospheric mantle source of the Hongcheon carbonatite must have occurred in the distant past (> 1.7 Ga) to generate significantly negative εNd values. 相似文献
8.
The recently-discovered Wenquan porphyry Mo deposit hosted in the Wenquan granite of the West Qinling Orogen has been recognized as a product of the Indosinian metallogenesis. Three generations of mineral assemblage for the deposit are identified as follows: (1) quartz–biotite–K-feldspar; (2) quartz–sulfide and (3) sulfide–calcite. Geochemical study shows that the mafic microgranular enclaves (MMEs) in the ore-bearing Wenquan granite have lower SiO2, and higher Mg# and Nb/Ta ratios than the host granite itself. Different from the granite which have zircon εHf(t) values of − 3.6–3.0 and TDM2 of 1234–890 Ma, the MMEs are characterized by the εHf(t) values of − 10.1–10.8 and TDM1 of 865–441 Ma. This can be interpreted to indicate a mixture origin of the Meso- and Neoproterozoic crust-derived component and Neoproterozoic SCLM-derived materials for the formation of the Wenquan granite, which played an essential role in the Mo mineralization. Comparative Pb isotopic data between ores and K-feldspar suggest that the Wenquan granitic magma originated from the middle-lower crust of the South China Block and the ore-forming materials were incorporated by hydrothermal fluid differentiated from the Triassic magmatic system, with minor contribution of sedimentary rocks. The δ34S values of 5.0–11.7‰ with a pronounced mode at 5.0 to 6.1‰ for the ores probably represent the sulfur incorporation of a typical magmatic hydrothermal fluid contaminated by heavy sulfur of Devonian sediments. The granite yielded the zircon U–Pb ages of 218 ± 2.4 Ma and 221 ± 1.3 Ma, as the same as the ages of 217 ± 2.0 Ma and 218 ± 2.5 Ma obtained for the MMEs. These ages are indistinguishable with the molybdenite Re–Os isochron age of 219 ± 5.2 Ma which is the timing for the Mo mineralization. Tectonically, the magmatic mixture processes of the Wenquan granite and the Mo mineralization to form the Wenquan Mo deposit contemporaneously occurred during the transition of tectonic regime from syn- to post-collision orogeny in the Qinling Orogen in the Late Triassic. 相似文献
9.
The Bayan Obo deposit in North China contains the largest rare-earth element (REE) resources in the world, but its forming time remains controversial. Nearly one hundred carbonatite dykes occur around the Bayan Obo deposit, including dolomite, calcite and calcite–dolomite carbonatite varieties. Zircons from a REE-rich carbonatite dyke and wallrock quartz conglomerate at Bayan Obo have been analyzed for U–Pb to determine the age of the dyke. Zircon from the carbonatite dyke, analyzed by conventional isotope dilution thermal ionization mass spectrometry (ID-TIMS), yielded an upper intercept age of 1417 ± 19 Ma. This age is confirmed by SHRIMP U–Pb analysis of zircon from the same carbonatite dyke, which gave a 207Pb/206Pb weighted mean age of 1418 ± 29 Ma. In situ Nd isotope measurements of monazite collected from the carbonatite dyke gave an isochron age of 1275 ± 87 Ma. These results demonstrate that the dyke intruded ~ 1400 Ma. In view of predecessor's results, it is clarified that the REE mineralization at Bayan Obo occurred at ca. 1400 Ma, consistent with the timing of carbonatite dyke intrusion in the region. The youngest detrital zircons from the quartz conglomerate yielded a 207Pb/206Pb weighted mean age of 1941 ± 7 Ma using LA ICP-MS U–Pb method. Detrital zircons in the carbonatite dyke also gave a mean apparent age of 1932 ± 3 Ma using ID-TIMS U–Pb method and 1914 ± 14 Ma using SHRIMP U–Pb method. These ages constrain the beginning active time of the Zha'ertai–Bayan Obo rift in the northern margin of the North China Craton after ~ 1900 Ma. 相似文献
10.
Flat rare earth element patterns as an indicator of cumulate processes in the Lesser Qinling carbonatites, China 总被引：1，自引：0，他引：1
Cheng Xu Ian H. Campbell Charlotte M. Allen Zhilong Huang Liang Qi Huan Zhang Guishan Zhang 《Lithos》2007,95(3-4):267-278
The Lesser Qinling carbonatite dykes are mainly composed of calcites. They are characterized by unusually high heavy rare earth element concentrations (HREE; e.g. Yb > 30 ppm) and flat to weakly light rare earth element (LREE) enriched chondrite-normalized patterns (La/Ybn = 1.0–5.5), which is in marked contrast with all other published carbonatite data. The trace element contents of calcite crystals were measured in situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Some crystals show reduced LREE from core to rim, whereas their HREE compositions are relatively constant. The total REE contents and chondrite-normalized REE patterns from the cores of carbonate crystals are similar to those of the whole rock. The carbon and oxygen isotopic compositions of calcites fall within the range of primary, mantle-derived carbonatites. The initial Sr isotopic compositions (0.70480–0.70557) of calcites are consistent with an EM1 source or mixing between HIMU and EM1 mantle sources. However these sources cannot produce carbonatite parental magmas with a flat or slightly LREE enrichment pattern by low degrees of partial melting. Analyses of carbonates from other carbonatites show that carbonates have nearly flat REE pattern if they crystallize from a LREE enriched carbonatite melt. This implies that when carbonates crystallize from a carbonatite melt the calcite/melt partition coefficients (D) for HREE are much greater than the D for the LREE. The nearly flat REE patterns of the Lesser Qinling carbonatites can be explained if they are carbonate cumulates that contain little trapped carbonatite melt. Strong enrichment of HREE in the carbonatites may require their derivation by small degrees of melting from a garnet-poor source. 相似文献
11.
The Wulaga gold deposit, located in Heilongjiang province, NE China, is a subvolcanic rock-hosted, low-sulfidation epithermal gold deposit, and has an Au reserve of about 84 tons. The gold mineralization occurs in a crypto-explosive breccia, and is spatially and temporally associated with an Early Cretaceous granodioritic porphyry. Three individual stages of mineralization have been identified in the Wulaga gold deposit: an early white quartz-euhedral vein stage, a fine-grained pyrite–marcasite–stibnite–chalcedony stage, and a late calcite–pyrite stage. The sulfur isotopic values of sulfide minerals vary in a wide range from − 4 to 4.9‰, but are concentrated in the range of − 3 to 0‰, implying that sulfur in the hydrothermal fluids was derived from magmatic volatiles. Lead isotopic results of the granodioritic porphyry (206Pb/204Pb = 18.341–18.395, 207Pb/204Pb = 15.507–15.523, 208Pb/204Pb = 38.174–38.251) and sulfide minerals (206Pb/204Pb = 18.172–18.378, 207Pb/204Pb = 15.536–15.600, 208Pb/204Pb = 38.172–38.339) are comparatively consistent and clustered together between the orogenic and upper mantle lines, indicating the lead in the ores is closely related to the parent magma of the granodioritic porphyry. The REE patterns of fluid inclusions trapped in sulfides are similar to those of the granodioritic porphyry, which confirms the magmatic origin of the REE in the hydrothermal fluids. The characteristics of S and Pb isotopes and REE suggest that the ore-forming materials of the Wulaga gold deposit are partly magmatic in origin, and related to a high-level hydrous granodioritic magma. 相似文献
12.
Lai-min Zhu Guo-wei Zhang Yan-jing Chen Zhen-ju Ding Bo Guo Fei Wang Ben Lee 《Ore Geology Reviews》2011,39(1-2):46-62
East Qinling is the largest porphyry molybdenum province in the world; these Mo deposits have been well documented. In West Qinling, however, few Mo deposits have been discovered although granitic rocks are widespread. Recently, the Wenquan porphyry Mo deposit has been discovered in Gansu province, which provides an insight into Mo mineralization in West Qinling. In this paper we report Pb isotope compositions for K-feldspar and sulfides, S isotope ratios for sulfides, the results obtained from petrochemical study and from in situ LA-ICP-MS zircon U-Pb dating and Hf isotopes. The granitoids are enriched in LILE and LREE, with REE and trace element patterns similar to continental crust, suggesting a crustal origin. The Mg# (40.05 to 56.34) and Cr and Ni contents are high, indicating a source of refractory mafic lower crust. The εHf(t) values of zircon grains from porphyritic monzogranite range from ? 2.9 to 0.6, and from granitic porphyry vary from ? 3.3 to 1.9. The zircons have TDM2 of 1014 to 1196 Ma for the porphyritic monzogranite and 954 to 1224 Ma for the granitic porphyry, implying that these granitoids were likely derived from partial melting of a Late Mesoproterozoic juvenile lower crust. The Pb isotope compositions of the granitoids are similar to granites in South China, showing that the magma was sourced from the middle–lower crust in the southern Qinling tectonic unit. The Pb isotopic contrast between the Mo-bearing granitoids and ores shows that the Pb in the ore-forming solution was derived from fractionation of a Triassic magmatic system. δ34S values of sulfides are between 5.02 and 5.66‰, similar to those associated with magmatic-hydrothermal systems. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 216.2 ± 1.7 and 217.2 ± 2.0 Ma for the granitoids, consistent with a previously reported molybdenite Re-Os isochron age of 214.4 ± 7.1 Ma. This suggests that the Mo mineralization is related to the late Triassic magmatism in the West Qinling orogenic belt. In view of these geochemical results and known regional geology, we propose that both granitoid emplacement and Mo mineralization in the Wenquan deposit resulted from the Triassic collision between the South Qinling and the South China Block, along the Mianlue suture. Since Triassic granitoid plutons commonly occur along the Qinling orogenic belt, the Triassic Wenquan Mo-bearing granitoids highlight the importance of the Triassic tectono-magmatic belt for Mo exploration. In order to apply this metallogenic model to the whole Qinling orogen, further study is needed to compare the Wenquan deposit with other deposits. 相似文献
13.
The Yinjiagou Mo–Cu–pyrite deposit of Henan Province is located in the Huaxiong block on the southern margin of the North China craton. It differs from other Mo deposits in the East Qingling area because of its large pyrite resource and complex associated elements. The deposit’s mineralization process can be divided into skarn, sulfide, and supergene episodes with five stages, marking formation of magnetite in the skarn episode, quartz–molybdenite, quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite, and calcite–galena–sphalerite in the sulfide episode, and chalcedony–limonite in the supergene episode. Re–Os and 40Ar–39Ar dating indicates that both the skarn-type and porphyry-type orebodies of the Yinjiagou deposit formed approximately 143 Ma ago during the Early Cretaceous. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst, various quartz veins, and calcite vein. Based on petrographic observations and microthermometric criteria the FIs include liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The homogenization temperature of FIs in quartz phenocrysts of K-feldspar granite porphyry ranges from 341 °C to >550 °C, and the salinity is 0.4–44.0 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite veins is 382–416 °C, and the salinity is 3.6–40.8 wt% NaCl eqv. The homogenization temperature of FIs in quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite ranges from 318 °C to 436 °C, and the salinity is 5.6–42.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite stockworks is in a range of 321–411 °C, and the salinity is 6.3–16.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–sericite–pyrite is in a range of 326–419 °C, and the salinity is 4.7–49.4 wt% NaCl eqv. The ore-forming fluids of the Yinjiagou deposit are mainly high-temperature, high-salinity fluids, generally with affinities to an H2O–NaCl–KCl ± CO2 system. The δ18OH2O values of ore-forming hydrothermal fluids are 4.0–8.6‰, and the δDV-SMOW values are between −64‰ and −52‰, indicating that the ore-forming fluids were primarily magmatic. The δ34SV-CDT values of sulfides range between −0.2‰ and 6.3‰ with a mean of 1.6‰, sharing similar features with deeply sourced sulfur, implying that the sulfur mainly came from the lower crust composed of poorly differentiated igneous materials, but part of the heavy sulfur came from the Guandaokou Group dolostone. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of sulfides are in the range of 17.331–18.043, 15.444–15.575, and 37.783–38.236, respectively, which is generally consistent with the Pb isotopic signature of the Yinjiagou intrusion, suggesting that the Pb chiefly originated from the felsic–intermediate intrusive rocks in the mine area, with a small amount of lead from strata. The Yinjiagou deposit is a porphyry–skarn deposit formed during the Mesozoic transition of a tectonic regime that is EW-trending to NNE-trending, and the multiepisode boiling of ore-forming fluids was the primary mechanism for mineral deposition. 相似文献
14.
L. G. Gwalani K. A. Rogers A. Demény D. I. Groves R. Ramsay A. Beard P. J. Downes A. Eves 《Mineralogy and Petrology》2010,98(1-4):123-141
The Yungul carbonatite dykes at Speewah in the Kimberley region of Western Australia were emplaced along a north-trending splay from the northeast-trending Greenvale Fault located at the western boundary of the Halls Creek Orogen. The Yungul carbonatite dykes intrude a thick composite sill of the Palaeoproterozoic Hart Dolerite (~1,790 Ma), consisting of tholeiitic dolerite and gabbro with its felsic differentiates that form the Yilingbun granophyres and associated granites. The carbonatite dykes consist of massive, calcite carbonatite that host very coarse, pegmatitic veins and pods of calcite, and have largely replaced (carbonatitized) and fenitized the country rock Hart Dolerite suite in a zone up to 150 m wide. Dykes of red-brown siliceous fluidized-breccia and epithermal-textured veins consisting of bladed quartz, adularia and fluorite are closely associated with the carbonatite dykes. The Yungul carbonatites are closely associated with fluorite occurrences with resources currently reported as 6.7 Mt at 24.6% CaF2. The precise age of the Yungul carbonatite is not known, although it is believed to be post early Cambrian. The total REE content of the Yungul carbonatite is low (174.0–492.8 ppm; La/Yb 2.28–10.74) and thus atypical for calciocarbonatite. Chondrite-normalized REE patterns for the carbonatite are relatively flat compared to average calciocarbonatite, and show small negative Eu anomalies. These unusual geochemical features may have been acquired from the Hart Dolerite suite during emplacement of the carbonatite, a process that involved extensive replacement and fenitization of country rocks. Carbon and oxygen isotope compositions of massive calcite carbonatite and the coarse calcite veins and pods from the carbonatite suggest a deep-seated origin. The C and O isotope compositions show an overall positive correlation that can be attributed to both magmatic and magmatic-hydrothermal processes in their evolution. The magmatic δ13C-δ18O trend is also indicative of crustal contamination and/or low-temperature water/rock exchange. The carbon isotopic compositions have δ13C values that range from about ?5.2‰ to ?6.3‰ that support a mantle-derived origin for the Yungul carbonatites and are consistent with earlier conclusions based on whole-rock geochemistry and radiogenic isotopes studies. 相似文献
15.
白云鄂博含矿碱性火山岩建造及其地球化学 总被引：3，自引：1，他引：2
白云鄂博矿床历经几十年的研究,主要集中在矿区H8岩性段矿化白云岩成因的认识,许多研究显示含矿白云岩是岩浆碳酸岩,本文主要从岩石学和地球化学方面进一步分析其属于火山喷发环境形成的火山碳酸熔岩。H8含矿白云岩段和H9板岩段作为一套含矿岩系主要由含矿白云岩、霓闪钠长岩、钾长板岩3类岩石组成,白云岩和霓闪钠长岩都具有的碎屑结构及角砾状构造、条带构造,显示为火山熔岩和火山碎屑岩特征,而钾长板岩则主要显示致密微晶火山熔岩特征。工业矿物主要是磁铁矿、赤铁矿、稀土矿物和铌铁矿物,其重要特征是出现大量原生赤铁矿,反映岩石氧化系数高,与火山喷发环境一致。霓闪钠长岩、钾长板岩岩石化学显示碱性特征,稀土元素与CaO、F相关系数在0.7以上,并与Fe2O3高氧化物相关,而与硅酸盐矿物组分反相关,表示碳酸岩与稀土成矿密切相关,并显示为表生氧化环境形成。稀土地球化学特征显示白云岩∑REE最高,钾长板岩∑REE最低,相应的岩脉∑REE低于喷发岩。各种岩石均表现为明显的轻重稀土分异,但是以白云岩LREE/HREE比值最大,霓闪钠长岩LREE/HREE比值最小,而纯钠长石岩脉和含稀土磁铁矿LREE/HREE明显高于其他岩石。白云岩和霓闪钠长岩均表现出不同的铕、铈负异常,但是碳酸岩脉和钾长板岩则显示弱正铈异常,霓闪钠长岩和钾长板岩铕异常不明显。矿化白云岩和碳酸岩脉的δ18O、δ13C值介于沉积灰岩与已知碳酸岩的δ18O、δ13C值之间,碳酸岩中白云石的δ18O低于方解石的δ18O,而δ13C高于方解石的δ13C,稀土矿物的δ13C、δ18O与碳酸岩脉δ13C、δ18O接近。归纳这些特征,含矿白云岩与霓闪钠长岩、钾长板岩是碱性火山岩组合,与一系列同期的碳酸岩、霓闪钠长岩碱性岩脉一起,构成一套完整碱性火山岩系。 相似文献
16.
Titanite (sphene, CaTiSiO5) is sensitive to changes in temperature, oxygen and water fugacity, and fluid composition. In order to understand formation processes and the nature of hydrothermal fluids, various types of titanite from Cu ores at the Baogutu reduced porphyry Cu deposit were chosen for detailed study. Magmatic titanite is associated with biotite, plagioclase and K-feldspar, whereas hydrothermal titanite occurs with K-feldspar, chlorite, actinolite and calcite. The formation of hydrothermal titanite was related to hydration of igneous minerals under high fH2O, whereas the widespread replacement of ilmenite by titanite (without magnetite) indicates a relatively low oxygen fugacity. Magmatic titanite has low Al, high Fe, Y, Sn, Zr, Nb and REE contents, relative to hydrothermal titanite. On the basis of the Zr-in-titanite and Al-in-chlorite geothermometers, formation temperatures for magmatic and hydrothermal titanite are estimated to be 687–739 °C and 250–670 °C, respectively. The gradual decrease in REE, Y and Sn contents from magmatic to late hydrothermal titanite was probably caused by precipitation of REE-bearing minerals. Magmatic and hydrothermal titanites have similar chondrite-normalized REE patterns with negative Eu anomalies and relatively flat HREE. Randomly selected titanites have Nd isotopic compositions similar to the host rocks. Thus, both magmatic and hydrothermal titanite are believed to have been predominantly derived from a mantle source. 相似文献
17.
The Urals can be regarded as a significant Cu-Mo-porphyry province, hosting over 30 porphyry deposits. Although their geological structure and ore-forming processes have been studied in great detail, uncertainty remains about their age and related geotectonic setting. In this contribution we report for the first time the Re-Os dating of molybdenites from three Cu-Mo porphyry deposits, namely Kalinovskoe, Mikheevskoe and Talitsa. Three molybdenite samples from the Kalinovskoe deposit yield Silurian Re-Os ages ranging from 427.1 Ma to 431.7 Ma (mean 429.8 ± 4.8 Ma; 2σ standard deviation), and a Re–Os isochron age of 430.7 ± 1.3 Ma (MSWD = 0.63), which coincides with previous U-Pb zircon dating of ore-hosting diorites from the same ore field (427 ± 6 Ma). The molybdenite from the Mikheevskoe deposit gives Re-Os ages of 357.8 ± 1.8 Ma and 356.1 ± 1.4 Ma (mean 357.0 ± 2.4 Ma; Carboniferous/Tournaisian), which corresponds to previous U-Pb dating of zircons from the diorite hosting porphyry deposit (356 ± 6 Ma). The molybdenite from Talitsa Mo-porphyry deposit yields the youngest Re-Os ages of 298.3 ± 1.3 and 299.9 ± 2.9 Ma (mean 299.1 ± 2.3 Ma) at Carboniferous-Permian boundary. Thus, the studied Cu and Mo porphyry deposits are not synchronous and belong to distinct tectonic events of the Urals. 相似文献
18.
The Yangla Cu deposit is the largest Cu skarn deposit in the Jinshajiang tectonic belt. Based on the detailed observation of crosscutting relationships, three mineralization stages (i.e., pre-ore, ore and supergene) have been identified in the Yangla deposit. The pre-ore stage is dominated by prograde skarn. The ore stage is characterized by the precipitation of hydrous silicate minerals, Fe-oxides, Fe-Cu-Mo-sulfides, quartz and calcite, whose mineral assemblages were formed in the early and late sub-ore stages. The early sub-ore stage is marked by retrograde alteration with the deposition of hydrous silicate minerals (e.g., actinolite, epidote and chlorite), Fe-oxides, abundant Fe-Cu-Mo-sulfides, quartz and minor calcite. Whilst, the late sub-ore stage, associated with silicic and carbonate alteration, is represented by widespread thick quartz or calcite veins with disseminated pyrite, chalcopyrite, galena and sphalerite. We present new carbon-oxygen (C-O) isotopic compositions of the ore-hosting marble and hydrothermal calcite of this deposit. The hydrothermal calcite in the Yangla deposit was precipitated from both the early and late sub-ore stages. Calcite I from the early sub-ore stage is anhedral, and occurs as spot in the skarn or locally replaces the skarn minerals. Calcite II from the late sub-ore stage is distinguished by being coarse-grained, subhedral to euhedral and its occurrence in thick veins. Calcite I contains lower δ13CPDB (−7.0‰ to −5.0‰) and δ18OSMOW (7.2‰ to 12.7‰) than Calcite II (δ13CPDB = −4.5‰ to −2.3‰; δ18OSMOW = 10.7‰ to 19.4‰). In the δ13CPDB vs. δ18OSMOW diagram, the Calcite I and Calcite II data fall close to the igneous carbonatite field and between the fields of igneous carbonatite and marine carbonates, respectively. This suggests a dominantly magmatic origin for the early sub-ore fluids, and there might have been increasing carbonate wall rock involvement towards the late sub-ore stage. The ore-hosting marble (δ13CPDB = −4.8‰ to −0.3‰; δ18OSMOW = 10.2‰ to 23.9‰) also shows a positive δ13CPDB vs. δ18OSMOW correlation, which is interpreted to reflect the decreasing alteration intensity during the interactions between the hydrothermal fluids and ore-hosting carbonates. Simulated calculation suggests that both the Calcite I and Calcite II precipitated at 350 °C to 250 °C and 250 °C to 150 °C, respectively. We proposed that CO2 degassing and water/rock interactions were likely the two major processes that precipitated the calcite and led to the observed C-O isotopic features of the Yangla Cu deposit. 相似文献
19.
The Siah-Kamar porphyry Mo deposit, located in the western Alborz-Azarbayjan magmatic belt, is the first and largest Mo deposit in the Iran. This deposit is mainly hosted by an I-type, shoshonitic quartz monzonite to monzonite intrusion and also extends in the surrounding lower to middle Eocene volcanic rocks. The geochemical features of the Siah-Kamar intrusion show enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and significant negative anomalies of Nb, Ta and Ti analogues to the magmas derived from metasomatized sub-continental mantle. Porphyry molybdenum mineralization is associated with potassic, sericitic, argillic, and propylitic alteration zones. Mineralization occurs in disseminated form, in veins/veinlets and in hydrothermal breccias. The main ore minerals comprise molybdenite, chalcopyrite and bornite. The Microthermometric analyses at Siah-Kamar deposit showed that the halite-bearing inclusions contain high salinity (30.9–60.7 wt% NaCl eq.) with homogenization temperature ranging from 226 °C to 397 °C. The homogenization temperature of two phase liquid-rich inclusions range between 224 °C and 375 °C. The salinity of this type inclusions range from 0.6 to 7.5 wt% NaCl equivalent. The two-phase vapor-rich fluid inclusions homogenized at 270 °C to 397 °C. The salinity of this type fluid inclusions lie within the range of 0.6 to 4.24 wt% NaCl equivalent. Coexisting two phase V-rich and L-rich fluid inclusions in quartz associated with molybdenite provide evidence for boiling at 270 °C to 400 °C. The δ18Owater values of quartz in the molybdenite-bearing veins vary from +2.16 to +4.05‰, suggesting a magmatic origin for the ore-forming fluids. Re-Os isotopic dating of molybdenite indicated a mineralization age of 41.9 ± 3.6 Ma. The Re concentration in molybdenite suggests incorporation of mantle derived melt with crustal materials. The late Eocene magmatism along the western Alborz-Azarbayjan magmatic zone resulted from the Neo-Tethys subduction beneath the Iranian plateau. The Siah-Kamar monzonitic intrusion hosting the Mo deposit, could be considered as an example among the late Eocene intrusions within the western Alborz-Azarbayjan magmatic zone for any further exploration in this zone. 相似文献
20.
The Bayan Obo Fe–REE–Nb deposit is the world's largest rare earth element (REE) resource and with the increasing focus on critical metal resources has become a focus of global interest. The deposit is hosted in the Palaeoproterozoic Bayan Obo Group, mainly concentrated in the H8 dolomite marble. The ores consist of light REE enriched monazite and bastnäsite, with a wide array of other REE minerals. Niobium mineralisation is hosted primarily in aeschynite and pyrochlore, although there are a wide range of other Nb-minerals. The origin of the host dolomite and ore bodies has been a subject of intense debate. The host dolomite has been proposed to be both of sedimentary origin and an igneous carbonatite. Carbonatite dykes do occur widely in the area, and consideration of the textural, geochemical and isotopic composition of the dolomite suggests an origin via intrusion of magmatic carbonatite into meta-sedimentary marble, accompanied by metasomatism. The origin of the ore bodies is complex, indicated most strongly by an ~ 1 Ga range in radiometric age determinations. Compilation of available data suggests that the ores were originally formed around 1.3 Ga (Sm–Nd isochron ages; Th–Pb ages of zircon), close in time to the intrusion of the carbonatite dykes. The ores were subsequently subjected to several stages of deformation and hydrothermal overprint, culminating in deformation, metamorphism and fluid flow related to the Caledonian subduction of the Mongolian Plate under the North China Craton from ~ 450 to 420 Ma (Th–Pb ages of monazite). This stage resulted in the formation of the strong foliation (‘banding’) of the ore. The presence of undeformed veins with alkali mineral fills, and the overprinting of the foliation by Nb minerals suggest that secondary fluid flow events may also have contributed to the metal endowment of the deposits, as well as remobilising the original Fe and REE mineralisation. The alteration mineralogy and geochemistry of the ores are comparable to those of many REE mineralised carbonatites. Initial Nd isotope ratios at 450 Ma, however, suggest crustal sources for the metals. These conflicting lines of evidence can be reconciled if a (at least) two stage isotopic evolution is accepted for the deposits, with an original mantle-sourced, carbonatite-related metal accumulation forming around 1.3 Ga with εNd close to 0. The ore was remobilised, with associated re-equilibration of Th–Pb isotope systematics during deformation at ~ 450 Ma. A further stage of alkaline hydrothermal fluid was responsible for Nb mineralisation at this stage. The complex geological history, with multiple stages of alkaline, high field strength element-rich, metasomatic fluid flow, is probably the main reason for the exceptional metal endowment of the Bayan Obo area. 相似文献