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Zhuzhou, China

Zhou Y.,CAS Guangzhou Institute of Geochemistry | Zhou Y.,Guilin University of Technology | Liang X.,CAS Guangzhou Institute of Geochemistry | Wu S.,416 Geological Team | And 5 more authors.
Journal of Asian Earth Sciences

Zircon U-Pb geochronological, geochemical and petrological analyses have been carried out on the Xitian granite emplaced in the middle part of Shi-Hang zone, which is closely related to the economically important Xitian tungsten-tin deposit in Hunan Province, Southeast China. LA-ICP-MS zircon U-Pb dating of two representative samples yielded weighted means 206Pb/238U age of 151.7±1.2Ma and 151.8±1.4Ma. These granites are comprised mainly of K-feldspar, quartz, plagioclase, Fe-rich biotite and minor fluorite, and are characterized by enrichments in Rb, Th, REEs (total REE=159-351ppm), and HFSEs (e.g., Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. They are metaluminous to weakly peraluminous and show a clear A-type granite geochemical signature with high SiO2 (73.44-78.45wt.%), total alkalis (Na2O+K2O=2.89-8.98wt.%), Fe2O3*/MgO ratios and low P2O5, CaO, MgO and TiO2 contents. In-situ zircon Hf isotope analysis suggests their εHf(t) values ranging from -7.43 to -14.69. Sr-Nd isotope data show their εNd(t) values in the range of -9.2 to -7.3, with corresponding TDM2 ages of 1.72-1.56Ga. These characteristics indicate that the Xitian granite originated from partial melting of metamorphic basement rocks with a certain amount of mantle-derived materials. Combined with previous geochemical and isotopic data, it is derived that mantle-crust interaction was gradually enhanced from the early to late stages of magmatism. The ore-forming materials and fluids of the Xitian W-Sn deposit are mainly produced by the Early Yanshanian granitic magmatism, which is also responsible for the Late Jurassic (ca. 152Ma) A-type granitic rocks that host the W-Sn polymetallic deposits distributed along the Shi-Hang zone, implying a significant Mesozoic extensional event in Southeast China likely caused by the subduction of the Paleo-Pacific plate. © 2015 Elsevier Ltd. Source

Ni Y.,CAS Guangzhou Institute of Geochemistry | Ni Y.,University of Chinese Academy of Sciences | Shan Y.,CAS Guangzhou Institute of Geochemistry | Wu S.,416 Geological Team | And 6 more authors.
Geotectonica et Metallogenia

Different viewpoints exist about the formation age, slip sense and displacement of the Laoshan'ao fault, the most important fault in the Xiangdong tungsten deposit, southeast Hunan province, China. Structural observations within the fault zone and nearby, comparison in mineral composition, structure and horst deformation between ore sets in the walls, and the type and distribution of alteration in the area reveal a post-metallogenic, normal nature of the fault. Considering both the north and south-south ore sets have a contact-parallel, banded structure, an alternation of black and white bands, we believe that they should have come from a single ore set before the fault formation. Accordingly, the Laoshan'ao fault would have a horizontal throw of 1.5-2.0 km. Both single and connected ore veins have aspect ratios of no less than 0.01. The ratios are much larger than the measurements made at the outcrop scale, implying the influence in aspect ratio of vein size. Based upon the above analysis, we suggest that future ore prospecting in the area should focus on the footwall for vein sets corresponding with the middle and south ore sets and in the hanging wall for a vein set corresponding with the north ore set. ©, 2015, Science Press. All right reserved. Source

Ni Y.,CAS Guangzhou Institute of Geochemistry | Ni Y.,University of Chinese Academy of Sciences | Shan Y.,CAS Guangzhou Institute of Geochemistry | Wu S.,416 Geological Team | And 6 more authors.
Geotectonica et Metallogenia

In an Indosinian porphyritic granite that comprises a majority of the Mesozoic Dengfuxian-Xitian granite batholith in eastern Hunan, central South China, there exist two types of foliations, flow foliation and tectonic gneissosity. Their discrimination hinges on the configuration of plagioclase phenocrysts: they appear euhedral in the former and flattened in the latter. Flow foliations tend to parallel the contact between the pluton and the wall rocks, and they are non-developed, underdeveloped, and developed towards the center. On this point, the ballooning model can best explain the emplacement of the pluton. Owing to the dramatic decrease in magma supply at the final pulse, the strain intensity tends to increase towards the center, as is different from the strain distribution observed in classic ballooning plutons. Tectonic gneissosity is much more locally distributed, but strikes towards northeast in general, indicating that it should have formed in the subsolidus or solidus state during the NW-SE regional compression. Source

Liang X.,CAS Guangzhou Institute of Geochemistry | Dong C.,CAS Guangzhou Institute of Geochemistry | Dong C.,University of Chinese Academy of Sciences | Jiang Y.,CAS Guangzhou Institute of Geochemistry | And 10 more authors.
Ore Geology Reviews

The Xitian tungsten-tin (W-Sn) polymetallic deposit, located in eastern Hunan Province, South China, is a recently explored region containing one of the largest W-Sn deposits in the Nanling W-Sn metallogenic province. The mineral zones in this deposit comprise skarn, greisen, structurally altered rock and quartz-vein types. The deposit is mainly hosted by Devonian dolomitic limestone at the contact with the Xitian granite complex. The Xitian granite complex consists of Indosinian (Late Triassic, 230-215 Ma) and Yanshanian (Late Jurassic-Early Cretaceous, 165-141 Ma) granites. Zircons from two samples of the Xitian granite dated using laser ablation-inductively coupled mass spectrometer (LA-ICPMS) U-Pb analysis yielded two ages of 225.6±1.3 Ma and 151.8±1.4 Ma, representing the emplacement ages of two episodic intrusions of the Xitian granite complex. Molybdenites separated from ore-bearing quartz-veins yielded a Re-Os isochron age of 149.7±0.9 Ma, in excellent agreement with a weighted mean age of 150.3±0.5 Ma. Two samples of muscovites from ore-bearing greisens yielded 40Ar/39Ar plateau ages of 149.5±1.5 Ma and 149.4±1.5 Ma, respectively. These isotopic ages obtained from hydrothermal minerals are slightly younger than the zircon U-Pb age of 151.8±1.4 Ma of the Yanshanian granite in the Xitian area, indicating that the W-Sn mineralization is genetically related to the Late Jurassic magmatism. The Xitian deposit is a good example of the Early Yanshanian regional W-Sn ore-forming event (160-150 Ma) in the Nanling region. The relatively high Re contents (8.7 to 44.0 ppm, average of 30.5 ppm) in molybdenites suggest a mixture of mantle and crustal sources in the genesis of the ore-forming fluids and melts. Based upon previous geochemical studies of Early Yanshanian granite and regional geology, we argue that the Xitian W-Sn polymetallic deposit can be attributed to back-arc lithosphere extension in the region, which was probably triggered by the break-off of the flat-slab of the Palae-Pacific plate beneath the lithosphere. © 2016 Elsevier B.V. Source

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