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1.
Limu W–Sn–Nb–Ta mining district is located in the Nanling Range W–Sn poly‐metallic mineralization belt in south China. The district includes a number of Sn–Nb–Ta and W–Sn ore occurrences; all of them are spatially associated with granite stocks of a largely‐unexposed pluton, the Limu granitic pluton. A granite sample collected from the Sn–Nb–Ta‐bearing Jinzhuyuan granite stock yields a zircon SHRIMP U–Pb age of 218.3 ± 2.4 Ma, a muscovite 40Ar/39Ar plateau age of 212.4 ± 1.4 Ma, and a muscovite 40Ar/39Ar isochron age of 213.2 ± 2.2 Ma. Another granite sample collected from the W–Sn‐bearing Sangehuangniu granite stock yields a zircon SHRIMP U–Pb age of 214 ± 5 Ma. The geochronological data provide new constraints on the age of the Limu granite pluton and the timing of the associated W–Sn–Nb–Ta mineralization—at least it sets a reasonable upper age limit for the mineralization of the W–Sn–Nb–Ta ores. The reported ages suggest an active Late Triassic granitic magmatism in Limu area which is part of a regional magmatic event near the end of the Indosinian orogeny in south China.  相似文献   

2.
Whole‐rock geochemistry, zircon U–Pb and molybdenite Re–Os geochronology, and Sr–Nd–Hf isotopes analyses were performed on ore‐related dacite porphyry and quartz porphyry at the Yongping Cu–Mo deposit in Southeast China. The geochemical results show that these porphyry stocks have similar REE patterns, and primitive mantle‐normalized spectra show LILE‐enrichment (Ba, Rb, K) and HFSE (Th, Nb, Ta, Ti) depletion. The zircon SHRIMP U–Pb geochronologic results show that the ore‐related porphyries were emplaced at 162–156 Ma. Hydrothermal muscovite of the quartz porphyry yields a plateau age of 162.1 ± 1.4 Ma (2σ). Two hydrothermal biotite samples of the dacite porphyry show plateau ages of 164 ± 1.3 and 163.8 ± 1.3 Ma. Two molybdenite samples from quartz+molybdenite veins contained in the quartz porphyry yield Re–Os ages of 156.7 ± 2.8 Ma and 155.7 ± 3.6 Ma. The ages of molybdenite coeval to zircon and biotite and muscovite ages of the porphyries within the errors suggest that the Mo mineralization was genetically related to the magmatic emplacement. The whole rocks Nd–Sr isotopic data obtained from both the dacite and quartz porphyries suggest partial melting of the Meso‐Proterozoic crust in contribution to the magma process. The zircon Hf isotopic data also indicate the crustal component is the dominated during the magma generation.  相似文献   

3.
On the basis of internal structures, laser ablation U–Pb ages and trace element compositions, the origin of zircon in jadeitite in the Nishisonogi metamorphic rocks was examined. The zircon comprises euhedral zoned cores overgrown by euhedral rims. The cores contain inclusions of muscovite, quartz, albite and possibly K‐feldspar, yield 238U–206Pb ages of 126 ± 6 Ma (±2 SD, n = 45, MSWD = 1.0), and have Th/U ratios of 0.48–1.64. The rims contain inclusions of jadeite, yield 238U–206Pb ages of 84 ± 6 Ma (±2 SD, n = 14, MSWD = 1.1), and have Th/U ratios of <0.06. The cores are richer in Y, Th, Ti and rare earth elements (REEs), but the rims are richer in Hf and U. Chondrite‐normalized REE patterns of the cores indicate higher SmN/LaN ratios, lower YbN/GdN ratios and larger positive Ce anomalies compared with those of the rims. Thus, the cores and rims have different 238U–206Pb ages and trace element compositions, suggesting two stages of zircon growth. Although the 238U–206Pb ages of the rims are consistent with the reported 40Ar/39Ar spot‐fusion ages of matrix muscovite in the jadeitite, the 238U–206Pb ages of the cores are older. The mineral inclusions and high Th/U ratios in the cores are best explained by crystallization from felsic magma. Therefore, the cores are considered relicts from igneous precursor rocks. The rims surrounding the inherited cores possibly precipitated from aqueous fluids during jadeitite formation. The elevated U concentrations in the rims suggest that infiltration of external fluids was responsible for the precipitation. This study provides an example of jadeitite formation by metasomatic replacement of a protolith.  相似文献   

4.
Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite facies zones of the Higo low‐P/high‐T metamorphic terrane. Here, we report data from an outcrop in the highest grade part of the granulite facies zone, in which diatexite occurs as a 3 m thick layer between 2 m thick layers of stromatic‐structured metatexite within pelitic gneiss. The migmatites and gneiss contain the same peak mineral assemblage of biotite + plagioclase + quartz + garnet + K‐feldspar with retrograde chlorite ± muscovite and some accessory minerals of ilmenite ± rutile ± titanite + apatite + zircon + monazite ± pyrite ± zinc sulphide ± calcite. Calculated metamorphic P–T conditions are 800–900 °C and 9–12 kbar. Zircon in the diatexite forms elongate euhedral crystals with oscillatory zoning, but no core–rim structure. Zircon from the gneiss and metatexite forms euhedral–subhedral grains comprising inherited cores overgrown by thin rims. The overgrowth rims in the metatexite have lower Th/U ratios than zircon in the diatexite and yield a 206Pb/238U age of 116.0 ± 1.6 Ma, which is older than the 110.1 ± 0.6 Ma 206Pb/238U age derived from zircon in the diatexite. Zircon from the diatexite has variable REE contents with convex upward patterns and flat normalized HREE, whereas the overgrowth rims in the metatexite and gneiss have steep HREE‐enriched patterns; however, both types have similar positive Ce and negative Eu anomalies. 176Hf/177Hf ratios in the overgrowth rims from the metatexite are more variable and generally lower than values from zircon in the diatexite. Based on U–Pb ages, trace element and Hf isotope data, the zircon rims in the metatexite are interpreted to have crystallized from a locally derived melt, following partial dissolution of inherited protolith zircon during anatexis, whereas the zircon in the diatexite is interpreted to have crystallized from a melt that included an externally derived component. By integrating zircon and petrographic data for the migmatites and pelitic gneiss, the metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source, whereas the diatexite migmatite included an externally derived juvenile component. The Cretaceous high‐temperature metamorphism of the Higo metamorphic terrane is interpreted to reflect emplacement of mantle‐derived basalts under a volcanic arc along the eastern margin of the Eurasian continent and advection of heat via hybrid silicic melts from the lower crust. Post‐peak crystallization of anatectic melts in a high‐T region at mid‐crustal depths occurred in the interval c. 116–110 Ma, as indicated by the difference in zircon ages from the metatexite and diatexite migmatites.  相似文献   

5.
First comprehensive investigations of the Cuonadong leucogranite exposed in North Himalayan gneiss dome of southern Tibet are presented in this study. The SIMS U–Pb ages of oscillatory zircon rims scatter in a wide range from 34.1 to 16.0 Ma, and the Cuonadong leucogranite probably emplaced at 16.0 Ma. High-precision 40Ar/39Ar dating on a muscovite sample yields an essentially flat age spectrum with consistent plateau and isochron ages, indicating that the Cuonadong leucogranite cooled below 450 °C at 14 Ma. Based on the youngest zircon U–Pb age and muscovite 40Ar/39Ar age, the Cuonadong leucogranite experienced rapid cooling with a rate of 119 °C/Myr from 16 to 14 Ma. The geochronological data of this undeformed leucogranite also suggest that the ductile extension of the South Tibetan Detachment System in the eastern Himalaya ceased by ca. 14 Ma. Furthermore, the initial Sr–Nd isotopic compositions and Nd model ages demonstrate that the leucogranite was derived from metapelitic source within the Greater Himalayan Crystalline Complex. The distinct Ba depletion with high Rb/Sr ratios and negative Eu anomalies make it clear that the leucogranite melts were generated by breakdown of muscovite under fluid-absent conditions.  相似文献   

6.
Granitic pegmatites are commonly thought to form by fractional crystallization or by liquid immiscibility of granitic magma;however,these proposals are based mainly on analyses of fluid and melt inclusions.Here,we use the Jiajika pegmatite deposit,the largest spodumene deposit in Asia,as a case study to investigate ore forming processes using isotope dating.Dating of a single granite sample from the Jiajika deposit using multiple methods gave a zircon U-Pb SHRIMP age of 208.4±3.9 Ma, an 40Ar/39Ar age for muscovite of 182.9±1.7 Ma,and an 40Ar/39Ar age for biotite of 169.9±1.6 Ma. Based on these dating results and the 40Ar/39Ar age of muscovite from the Jiajika pegmatite,a temperature-time cooling track for the Jiajika granite was constructed using closure temperatures of the different isotope systems.This track indicates that the granite cooled over～40 m.y.,with segregation of the pegmatite fluid from the granitic magma at a temperature of～700℃.This result suggests that the Jiajika pegmatite formed not by fractional crystallization,but by segregation of an immiscible liquid from the granitic magma.When compared with fractional crystallization,the relatively early timing of segregation of an immiscible liquid from a granitic magma can prevent the precipitation of ore-forming elements during crystallization,and suggests that liquid immiscibility could be an important ore-forming process for rare metal pegmatities.We also conclude that isotope dating is a method that can potentially be used to determine the dominant ore-forming processes that occurred during the formation of granite-related ore deposits,and suggest that this method can be employed to determine the formation history of the W-Sn ore deposits found elsewhere within the Nanling Metallogenic Belt.  相似文献   

7.
The Tengchong-Lianghe tin district in northwestern Yunnan, China, is an important tin mineralization area in the Sanjiang Tethyan Metallogenic Domain. There are three N–S trending granite belts in the Tengchong-Lianghe area, with emplacement ages ranging from Early Cretaceous to Late Cretaceous and Early Cenozoic. Tin mineralization is spatially associated with these granitic rocks. However, the petrogenetic link between the tin deposits and the host granites is not clear because of the lack of age data for the tin mineralization. We investigate the possibility of direct dating of cassiterite from three typical tin deposits in the Tengchong-Lianghe tin district, using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). In situ LA-MC-ICP-MS dating of seven cassiterite samples from the Lailishan (LLS-1 and LLS-2), Xiaolonghe (XLH, WDS, DSP, and HJS), and Tieyaoshan (TYS) tin deposits yielded well-defined 206Pb/207Pb–238U/207Pb isochron ages. To assess the accuracy of the in situ U/Pb dating of cassiterite, 40Ar/39Ar dating of coexisting muscovite (in samples LLS-1, DSP, and TYS) was also performed. The cassiterite in situ U/Pb ages (47.4?±?2.0, 71.9?±?2.3, and 119.3?±?1.7 Ma, respectively) are in excellent agreement with the coexisting muscovite 40Ar/39Ar ages (48.4?±?0.3, 71.9?±?1.4, and 122.4?±?0.7 Ma, respectively). The U/Pb ages of cassiterite combined with the 40Ar/39Ar ages of muscovite indicate that there are three tin mineralization events in this district: the Lailishan tin deposit at 47.4?±?2.0 to 52?±?2.7 Ma, the Xiaolonghe tin deposit at 71.6?±?2.4 to 3.9?±?2.0 Ma, and the Tieyaoshan tin deposit at 119.3?±?1.7 to 122.5?±?0.7 Ma. These ages are highly consistent with the zircon U/Pb ages of the host granites. It is su.ggested that the Cretaceous tin mineralization might have taken place in a subduction environment, while the Early Tertiary tin metallogenesis was in a postcollisional geodynamic setting.  相似文献   

8.
The Xinlu Sn‐polymetallic ore field is located in the western Nanling Polymetallic Belt in northeastern Guangxi, South China, where a number of typical skarn‐, hydrothermal vein‐type tin deposits have developed. There are two types of Sn deposits: skarn‐type and sulfide‐quartz vein‐type. The tin mineralizations mainly occur on the south side of the Guposhan granitic complex pluton and within its outer contact zone. To constrain the Sn mineralization age and further understand its genetic links to the Guposhan granitic complex, a series of geochronological works has been conducted at the Liuheao deposit of the ore field using high‐precision zircon SHRIMP U‐Pb, molybdenite Re‐Os, and muscovite Ar‐Ar dating methods. The results show that the biotite‐monzogranite, which is part of the Xinlu intrusive unit of the Guposhan complex pluton, has a SHRIMP U‐Pb zircon age of 161.0 ± 1.5 Ma. The skarn‐type ore has a 40Ar‐39Ar muscovite plateau age of 160 ± 2 Ma (same as its isochron age), and the sulfide‐quartz vein‐type ore yields an Re‐Os molybdenite isochron age of 154.4 ± 3.5 Ma. The magmatic‐hydrothermal geochronological sequence demonstrated that the hydrothermal mineralization took place immediately following the emplacement of the monzogranite, with the skarn metasomatic mineralization stage predating the sulfide mineralization stage. Geochronologically, we have compared this ore field with 26 typical Sn deposits distributed along the Nanling Polymetallic Belt, leading to the suggestion of the magmatic‐metallogenic processes in the Xinlu ore field (ca. 161–154 Ma) as a component of the Early Yanshanian large‐scale Sn‐polymetallic mineralization event (peaked at 160–150 Ma) in the Nanling Range of South China. Petrogenesis of Sn‐producing granite and Sn‐polymetallic mineralization were probably caused by crust–mantle interaction as a result of significant lithospheric extension and thinning in South China in the Late Jurassic.  相似文献   

9.
The Guposhan–Huashan district is an important W–Sn–Sb–Zn–(Cu) metallogenic area in South China. It is located in the middle‐west segment of the Nanling Range. Granitoids in the Guposhan–Huashan district possess certain properties of A‐type or I‐type granites. The W–Sn–Sb–Zn mineralization in the district is closely associated with magma emplacement. Two igneous biotite and seven hydrothermal muscovite samples from skarn, veins and greisenization ores were analyzed by Ar–Ar methods. Two igneous biotite samples from fine‐grained quartz monzodiorite and fine‐grained biotite granite show plateau ages of 168.7 ± 1.9 Ma and 165.0 ± 1.1 Ma, respectively. Seven hydrothermal muscovite samples from ores yield plateau ages as two groups: 165 Ma to 160 Ma and 104 Ma to 100 Ma. These data suggest that the emplacement of fine‐grained granitoids in this district is coeval with the main phase magma emplacement, different from previous studies. The W–Sn–Sb–Zn mineralization took place in two stages, i.e. the Middle–Late Jurassic and early Cretaceous. W–Sn mineralization in the Guposhan–Huashan district is closely related to the magmatism, which was strongly influenced by underplating of asthenospheric mantle along trans‐lithospheric deep faults and related fractures.  相似文献   

10.
Jilin Province in NE China lies on the eastern edge of the Xing–Meng Orogenic Belt. Mineral exploration in this area has resulted in the discovery of numerous large, medium, and small sized Cu, Mo, Au, and Co deposits. To better understand the formation and distribution of both the porphyry and skarn types Cu deposits of the region, we examined the geological characteristics of the deposits and applied zircon U–Pb and molybdenite Re–Os isotope dating to constrain the age of the mineralization. The Binghugou Cu deposit yields a zircon U–Pb age for quartz diorite of 128.1 ± 1.6 Ma; the Chang'anpu Cu deposit yields a zircon U–Pb age for granite porphyry of 117.0 ± 1.4 Ma; the Ermi Cu deposit yields a zircon U–Pb age for granite porphyry of 96.8 ± 1.1 Ma; the Tongshan Cu deposit yields molybdenite Re–Os model ages of 128.7 to 130.2 Ma, an isochron age of 129.0 ± 1.6 Ma, and a weighted mean model age of 129.2 ± 0.7 Ma; and the Tianhexing Cu deposit yields molybdenite Re–Os model ages of 113.9 to 115.2 Ma, an isochron age of 114.7 ± 1.2 Ma, and a weighted mean model age of 114.7 ± 0.7 Ma. The new ages, combined with existing geochronology data, show that intense porphyry and skarn types Cu mineralization was coeval with Cretaceous magmatism. The geotectonic processes responsible for the genesis of the Cu mineralization were probably related to lithospheric thinning. By analyzing the accumulated molybdenite Re–Os, zircon U–Pb, and Ar–Ar ages for NE China, it is concluded that the Cu deposits formed during multiple events coinciding with periods of magmatic activity. We have identified five phases of mineralization: early Paleozoic (~476 Ma), late Paleozoic (286.5–273.6 Ma), early Mesozoic (~228.7 Ma), Jurassic (194.8–137.1 Ma), and Cretaceous (131.2–96.8 Ma). Although Cu deposits formed during each phase, most of the Cu mineralization occurred during the Cretaceous.  相似文献   

11.
The Yuchiling Mo deposit is a recently discovered giant porphyry system in the East Qinling Mo belt, China. Its apparent causative intrusion, i.e., the Yuchiling granite porphyry, is the youngest intrusion (phase 4) of the Heyu multiphase granite batholith, which was emplaced between 143 and 135 Ma. New robust constraints on the formation of the Yuchiling porphyry Mo system are provided by combined zircon U–Pb, biotite 40Ar/39Ar, and molybdenite Re–Os dating. Zircon grains from the Mo-mineralized granite porphyry yield weighted 206Pb/238U age of 134.0?±?1.4 Ma (n?=?19, 2σ error, MSWD?=?0.30). Magmatic biotite from the same sample yield a 40Ar/39Ar plateau age of 135.1?±?1.4 Ma (2σ error), and an inverse isochron age of 135.6?±?2.0 Ma (n?=?7, 2σ error, MSWD?=?10.8), which are effectively coincident with the zircon U–Pb age within analytical error. Three pulses of mineralization can be deduced from the molybdenite Re–Os ages, namely: ～141, ～137, and ～134 Ma, which agree well with the zircon U–Pb ages of granitic phases 1, 2, and the Yuchiling porphyry (phase 4), respectively. These well-constrained temporal correlations indicate that Mo mineralization was caused by pulses of granitic magmatism, and that the ore-forming magmatic-hydrothermal activity responsible for the Yuchiling porphyry Mo system lasted about 8 Ma. The Yuchiling Mo deposit represents a unique style of porphyry Mo system formed in a post-collision setting, and associated with F-rich, high-K calc-alkaline intrusions, which differ from convergent margin-associated porphyry Mo deposits.  相似文献   

12.
The Yinshan deposit in the Jiangnan tectonic belt in South China consists of Pb‐Zn‐Ag and Cu‐Au ore bodies. This deposit contains approximately 83 Mt of the Cu‐Au ores at 0.52% Cu and 0.8 g/t Au, and 84 Mt of the Pb‐Zn‐Ag ores at 1.25% Pb, 1.02% Zn and 33.3 g/t Ag. It is hosted by low‐grade metamorphosed sedimentary rocks and mafic volcanic rocks of the lower Mesoproterozoic Shuangqiaoshan Group, and continental volcanic rocks of the Jurassic Erhuling Group and dacitic subvolcanic rocks. The ore bodies mainly consist of veinlets of sulfide minerals and sulfide‐disseminated rocks, which are divided into Cu‐Au and Pb‐Zn‐Ag ore bodies. The Cu‐Au ore bodies occur in the area close to a dacite porphyry stock (No. 3 stock), whereas Pb‐Zn‐Ag bodies occur in areas distal from the No. 3 stock. Muscovite is the main alteration mineral associated with the Cu‐Au ore bodies, and muscovite and chlorite are associated with the Pb‐Zn‐Ag ores. A zircon sensitive high‐resolution ion microprobe U‐Pb age from the No. 3 dacite stock suggests it was emplaced in Early Jurassic. Three 40Ar‐39Ar incremental‐heating mineral ages from muscovite, which are related to Cu‐Au and Pb‐Zn‐Ag mineralization, yielded 179–175 Ma. These muscovite ages indicate that Cu‐Au mineralization occurred at 178.2±1.4 Ma (2σ), and Pb‐Zn‐Ag mineralization at 175.4±1.2 Ma (2σ) and 175.3±1.1 Ma (2σ), which supports a restricted period for the mineralization. The Early Jurassic ages for the mineralization at Yinshan are similar to that of the porphyry Cu mineralization at Dexing in Jiangnan tectonic belt, and suggest that the polymetallic mineralization occurred in a regional transcompressional tectonic regime.  相似文献   

13.
Both oceanic and continental HP rocks are juxtaposed in the Huwan shear zone in the western Dabie orogen, and thus provide a window for testing the buoyancy‐driven exhumation of dense oceanic HP rocks. The HP metamorphic age of the continental rocks in this zone has not been well constrained, and hence it is not known if they are of the same age as the exhumation of the HP oceanic rocks. In situ laser ablation (multiple collector) inductively coupled plasma mass spectrometry (LA‐(MC‐)ICP‐MS), U–Pb, trace element and Hf isotope analyses were made on zircon in a granitic gneiss and two eclogites from the Huwan shear zone. U–Pb age and trace element analysis of residual magmatic zircon in an eclogite constrain its protolith formation at 411 ± 4 Ma. The zircon in this sample displays εHf (t) values of +6.1 to +14.4. The positive εHf (t) values up to +14.4 suggest that the protolith was derived from a relatively depleted mantle source, most likely Palaeotethyan oceanic crust. A granitic gneiss and the other eclogite yield protolith U–Pb ages of 738 ± 6 and 700 ± 14 Ma, respectively, which are both the Neoproterozoic basement rocks of the Yangtze Block. The zircon in the granitic gneiss has low εHf (t) values of ?14.2 to ?10.5 and old TDM2 ages of 2528–2298 Ma, suggesting reworking of Palaeoproterozoic crust during the Neoproterozoic. The zircon in the eclogite has εHf (t) values of ?1.0 to +7.4 and TDM1 ages of 1294–966 Ma, implying prompt reworking of juvenile crust during its protolith formation. Metamorphic zircon in both eclogite samples displays low Th/U ratios, trace element concentrations, relatively flat heavy rare earth element patterns, weak negative Eu anomalies and low 176Lu/177Hf ratios. All these features suggest that the metamorphic zircon formed in the presence of garnet but in the absence of feldspar, and thus under eclogite facies conditions. The metamorphic zircon yields U–Pb ages of 310 ± 3 and 306 ± 7 Ma. Therefore, both the oceanic‐ and continental‐type eclogites share the same episode of Carboniferous eclogite facies metamorphism. This suggests that high‐pressure continental‐type metamorphic rocks might have played a key role in the exhumation and preservation of oceanic‐type eclogites through buoyancy‐driven uplift.  相似文献   

14.
Understanding convergent margin processes requires determination of the onset and the termination of subduction, the duration of subduction‐zone metamorphism, and the subduction zone polarity. Garnet growth and intracrystalline zonation can be used to constrain the timing, duration and kinetics of tectonometamorphic processes. An eclogite from the Huwan shear zone in the Hong'an orogen was investigated with combined pseudosection analysis and multiple geochronologies. The pseudosection analysis illustrates that garnet growth is continuous and along an early near‐isothermal trajectory followed by a near‐isobaric heating path from 1.9 GPa/500 °C to 2.4 GPa/575 °C and subsequent near‐isothermal decompression. 40Ar/39Ar dating of an amphibole inclusion in garnet from the eclogite yielded an age of 310 ± 5 Ma, which is consistent with a U–Pb age of 305 ± 3 Ma for the metamorphic zircon within uncertainty. Garnet core and rim material produced Lu–Hf ages of 296.9 ± 3.8 and 256.9 ± 3.9 Ma respectively; the latter is consistent with its Sm–Nd age of 254.3 ± 4.6 Ma for the same aliquots. Similarly, limited zircon U–Pb ages of c. 257 Ma were obtained in zircon rims with garnet inclusions. These ages were interpreted to bracket the period of garnet growth and the difference of up to c. 40 Ma is best explained by protracted garnet growth. We propose that the rocks represent detachment of part of the downgoing slab and remained free of significant compression/decompression or heating/cooling close to the subduction channel, most likely underplating the mantle wedge, for a long time. These rocks were incorporated into the following subduction channel due to the successive entry of the buoyant materials, and exhumed at some time later than c. 254 Ma. The increasing observations of protracted garnet growth and long‐lived subduction in various orogens worldwide demand more sophisticated geodynamic models.  相似文献   

15.
A typical HP/MT (high pressure/medium temperature) eclogite from Xiongdian, northwestern Dabie Mountains, has been geochronologically studied using the single-zircon U-Pb, 40Ar-39Ar and Sm-Nd methods. Prismatic zircons occurring as inclusions within garnets define a minimum crystallization age of 399.5±1.6 Ma. 40Ar-39Ar dating on amphibole gives a plateau age.of 399.2 ± 4 Ma, which is interpreted as a retrogression age of amphibolite facies. This integrated study enables us to conclude that the age of high-pressure metamorphism is older than 399.5 ± 1.6 Ma, suggesting Caledonian collision between the North China and Yangtze plates. Round zircon within the aggregate of quartz and muscovite gives a concordant age of 301± 2 Ma, reflecting a later retrogression event. An age profile of post-eclogite metamorphism is documented, including amphibolite facies metamorphism at 399.2 Ma shortly after eclogitization and later retrogressive metamorphism at 301 Ma. Sm-Nd mineral isochron of garnet+omphacite gives  相似文献   

16.

The 40Ar/39Ar dating of alteration muscovite from the Peak Au mine in the Early Devonian Cobar Basin, New South Wales, has distinguished two major episodes of mineralization. Veined (Pb‐Zn‐Cu‐Au) mineralization was broadly synchronous with cleavage formation during the post‐inversion, shortening deformation of the basin sedimentary rocks, and replacive Ag‐Pb‐Zn mineralization significantly postdates the latter event. Veined base metals (Pb‐Zn‐Cu) and Au associated with silicification were coeval with three stages of cleavage formation (D1, D2 and D3) after basin inversion. The Cu‐Au phase of mineralization at the Peak Au mine which was broadly contemporaneous with the culmination of the cleavage‐forming events (D3) and with the local development of high‐strain zones occurred at 401.5 ± 1.0 Ma (40Ar/39Ar on muscovite). This date is essentially coeval with known fossil constraints on the age of basin formation, and indicates that basin inversion and deformation rapidly followed sedimentation. In contrast, replacive Ag‐Pb‐Zn mineralization occurred at 384.0 ± 1.4 Ma (40Ar/39Ar on muscovite) during an extended period of relaxation characterized by normal faulting (D4) which followed the shortening deformation. This mineralization was associated with desilicification and chlorite‐muscovite replacement assemblages which cross‐cut the cleavages, and which may have been broadly contemporaneous with the deposition of part of the Mulga Downs Group which unconformably overlies the Cobar Supergroup. Rhyolite exposed in the core of the Peak Au mine largely contains inherited zircons that range in age from ～430–1500 Ma. A few euhedral zircons have an age of ～430 Ma and this is interpreted as a maximum date for the rock. Zircons from a syn‐D3 chlorite‐muscovite replacement zone within the deposit have 206Pb/238U ages of ～410–650 Ma and are apparently inherited.  相似文献   

17.
The Tiegelongnan Cu (Au) deposit is the largest copper deposit newly discovered in the Bangong–Nujiang metallogenic belt. The deposit has a clear alteration zoning consisting of, from core to margin, potassic to propylitic, superimposed by phyllic and advanced argillic alteration. The shallow part of the deposit consists of a high sulphidation‐state overprint, mainly comprising disseminated pyrite and Cu–S minerals such as bornite, covellite, digenite, and enargite. At depth porphyry‐type mineralization mainly comprises disseminated chalcopyrite, bornite, pyrite, and a minor vein molybdenite. Mineralization is disseminated and associated with veins contained within the porphyry intrusions and their surrounding rocks. The zircon U–Pb ages of the mineralized diorite porphyry and granodiorite porphyry are 123.1 ± 1.7 Ma (2σ) and 121.5 ± 1.5 Ma (2σ), respectively. The molybdenite Re–Os age is 121.2 ± 1.2 Ma, suggesting that mineralization was closely associated with magmatism. Andesite lava (zircon U–Pb age of 111.7 ± 1.6 Ma, 2σ) overlies the ore‐bodies and is the product of post‐mineralization volcanic activity that played a critical role in preserving the ore‐bodies. Values of ?4.6 ‰ to + 0.8 ‰ δ34S for the metal sulfides (mean ? 1.55 ‰) suggest that S mainly has a deep magmatic source. The H and O isotopic composition is (δD = ?87 ‰ to ?64 ‰; δ18OH2O = 5.5 ‰ to 9.0 ‰), indicating that the ore‐forming fluids are mostly magmatic‐hydrothermal, possibly mixed with a small amount of meteoric water. The zircon εHf(t) of the diorite porphyry is 3.7 to 8.3, and the granodiorite porphyry is 1.8 to 7.5. Molybdenite has a high Re from 382.2 × 10?6 to 1600 × 10?6. Re and Hf isotope composition show that Tiegelongnan has some mantle source, maybe the juvenile lower crust from crust–mantle mixed source. Metallogenesis of the Tiegelongnan giant porphyry system was associated with intermediate to acidic magma in the Early Cretaceous (~120 Ma). The magma provenance of the Tiegelongnan deposit has some mantle‐derived composition, possibly mixed with the crust‐derived materials.  相似文献   

18.
The Great Xing'an Range (GXR), Northeast (NE) China, is a major polymetallic metallogenic belt in the eastern segment of the Central Asian Orogenic Belt. The newly discovered Xiaokele porphyry Cu (–Mo) deposit lies in the northern GXR. Field geological and geochronological studies have revealed two mineralization events in this deposit: early porphyry‐type Cu (–Mo) mineralization, and later vein‐type Cu mineralization. Previous geochronological studies yielded an age of ca. 147 Ma for the early Cu (–Mo) mineralization. Our 40Ar/39Ar dating yielded 40Ar/39Ar plateau ages of 124.8 ± 0.4 to 124.3 ± 0.4 Ma on K‐feldspar in altered Cu‐mineralized diorite porphyrite dikes that represent the overprinting vein‐type Cu mineralization, consistent with zircon U–Pb ages of the diorite porphyrite (126.4 ± 0.5 to 125.0 ± 0.5 Ma). The Cr and Ni contents and Mg# of the Xiaokele diorite porphyrites are high. The diorite porphyrites at Xiaokele are enriched in light rare‐earth elements (REEs), and large‐ion lithophile elements (e.g., Rb, Ba, and K), are depleted in heavy REEs and high‐field‐strength elements (e.g., Nb, Ta, and Ti), and have weak negative εHf(t) values (+0.29 to +5.27) with two‐stage model ages (TDM2) of 1,164–845 Ma. Given the regional tectonic setting in Early Cretaceous, the ore‐bearing diorite porphyrites were likely formed in an extensional environment related to lithospheric delamination and asthenospheric upwelling induced by subduction of the Paleo‐Pacific Plate. These tectonic events caused large‐scale magmatic activity, ore mineralization, and lithospheric thinning in NE China.  相似文献   

19.
The Karamay porphyry Mo–Cu deposit, discovered in 2010, is located in the West Junggar region of Xinjiang of northwest China. The deposit is hosted within the Karamay granodiorite porphyry that intruded into Early Carboniferous sedimentary strata and its exo‐contact zone. The LA‐ICPMS U–Pb method was used to date the zircons from the granodiorite samples of the porphyry. Analyses of 12 spots of zircons from the granodiorite samples yield a U–Pb weighted mean age of 300.8 ± 2.1 Ma (2σ). Re–Os dating for five molybdenite samples obtained from two prospecting trenches and three outcrops in the deposit yield a Re–Os isochron age of 294.6 ± 4.6 Ma (2σ), with an initial 187Os/188Os of 0.0 ± 1.1. The isochron age is within the error of the Re–Os model ages, demonstrating that the age result is reliable. The Re–Os isochron age of the molybdenite is consistent with the U–Pb age of the granodiorite porphyry, which indicates that the deposit is genetically related with an Early Permian porphyry system. The ages of the Karamay Mo–Cu deposit and the ore‐bearing porphyry are similar to the ages of intermediate‐acid intrusions and Cu–Mo–Au polymetallic deposits in the West Junggar region. This consistency suggests the same geodynamic process to the magmatism and related mineralization.  相似文献   

20.
The Yunmengshan Geopark in northern Beijing is located within the Yanshan range. It contains the Yunmengshan batholith, which is dominated by two plutons: the Yunmengshan gneissic granite and the Shicheng gneissic diorite. Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U–Pb ages from 145 to 141 Ma, whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma. Dikes that cut the Yunmengshan diorite record SHRIMP zircon U–Pb age of 162±2 and 156±4 Ma. The cumulative plots of zircons from the diorites show a peak age of 155 Ma, without inherited zircon cores, and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton, whose igneous zircons contain inherited zircon cores. The data presented here show that there were two pulses of magmatism: early diorites, followed c13 Ma later by true granites, which incorporated material from an older continental crust.  相似文献   

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