Wei S.-G.,China University of Geosciences |
Tang J.-X.,Chinese Academy of Geological Sciences |
Song Y.,Chinese Academy of Geological Sciences |
Liu Z.-B.,Chinese Academy of Geological Sciences |
And 2 more authors.
Journal of Asian Earth Sciences | Year: 2017
We report new zircon U–Pb ages and Hf isotope compositions, and whole-rock major and trace element and Sr–Nd isotope data for the Meiriqiecuo Formation (MF) bimodal volcanic rocks collected from the Duolong Cu mining district (DCMD) in the western Qiangtang terrane (QT), western Tibet. These data provide important constraints on the petrogenetic evolution and geodynamic setting of Early Cretaceous magmatism in the DCMD. The MF bimodal volcanic rocks are mainly basaltic andesite and andesite, with subordinate rhyolite. Four mafic samples yielded zircon U–Pb ages of ca. 108.2–113.0 Ma, and one silicic sample has an age of 109.3 ± 2.2 Ma, indicating that the mafic and silicic eruptions were contemporaneous. The MF bimodal volcanic rocks belong to the medium-K calc-alkaline to shoshonite series. The rocks show arc-type affinities characterized by significant enrichment in light rare earth (LaN/YbN = 7.74–12.60) and large-ion lithophile elements (Rb, Cs, K, and Pb), but depletions in the high-field-strength elements (Nb, Ta, and Ti), which geochemically resemble Andean arc basalts. Therefore, the MF bimodal volcanic rocks were likely emplaced at an Andean-type active continental margin and represent an Early Cretaceous magmatic arc that was located at the western QT margin. Moreover, the mafic volcanic rocks have high initial Sr isotopic ratios (0.705269–0.705413) and negative εNd(t) values of −1.5 to −0.6 compared with the silicic volcanic rocks ((87Sr/86Sr)i = 0.704770–0.704903; εNd(t) = +1.2 to +1.3). Zircons from silicic samples have significantly higher εHf(t) values (+11.6 to +15.5) and predominantly lower Paleoproterozoic Hf crustal model ages (TDMC = 180–428 Ma) than the mafic samples, which have variable εHf(t) values of +3.4 to +13.0 and TDMC ages of 346–952 Ma. These results indicate that the mafic and silicic end-members of the MF bimodal suite were generated from mantle and crustal sources, respectively. The basaltic andesite and andesite may have been derived from mantle enriched by the metasomatism of subducted fluids, whereas the rhyolite could have been derived by partial melting of mafic juvenile crust that originated from an older and more depleted mantle. In light of the geochemical characteristics and field relationships, we propose that breakoff of the Bangong–Nujiang oceanic lithosphere was responsible for the generation and emplacement of the MF bimodal volcanic rocks. The fact that the MF bimodal volcanic arc magmatism was active at ca. 108–113 Ma indicates that it was associated with closure of the Bangong–Nujiang Ocean via an arc-arc “soft” collision during the Early Cretaceous. © 2016 Elsevier Ltd
Sun X.-G.,Tibet Jinlong Mining Co. |
Sun X.-G.,Chinalco Tibet Mining Co. |
Sun X.-G.,Chinalco Resources Co. |
Feng D.-Y.,Tibet Jinlong Mining Co. |
And 8 more authors.
Geology in China | Year: 2014
Based on detailed analysis of regional metallogenic geological background and conditions, it is held that the Duolong ore district of the West Bangong Lake arc has metallogenic prospecting and resources potential for porphyry Cu-Au deposits. Through the exploration in 2013, the authors made a breakthrough in Tiegelongnan. Copper reserves of the Tiegelongnan ore district has reached a superlarge ore deposit, and this deposit has thus become the largest porphyry Cu(Au) ore deposit in the Duolong ore district as well as the major exploration breakthrough in 2013. The deposit is located in early Cretaceous Meiriqiecuo formation of the middle Duolong ore district, and has a close temporal relationship with early Cretaceous intrusive granodiorite porphyry, granite porphyry and concomitant hydrothermal mineralization breccia. The orebodies mainly occur in the lower middle Jurassic Sewa Formation feldspar quartz sandstone, lithic sandstone intercalated with dark gray to deep black silty slate and mineralized porphyry. Orebodies exhibit concealed dome and are characterized by great downward extension in the forms of network veins, veinlets, and disseminations. Hydrothermal alteration is well developed, with obvious zonation, strong silicification, sericitization, and widely superimposed advanced argillic alteration. The denudation degree of the ore district is very low. The surface only develops limonite and clay, with no copper mineralization. Alteration and mineralization increased gradually downward, and the mineralization extension reaches one thousand kilometers at depth without closure. The upper copper mineralization is of chalcocite-digeniteenargite association, exhibiting characteristics of the Cu-S system, which gradually changes into bornite and chalcopyrite characteristics of the Cu-Fe-S system. Copper mineralization is associated with Au, Ag mineralization and assumes positive correlation. Compared with other porphyry Cu-Au ore deposits in the Duolong ore district, this deposits is poor in gold. The exploration breakthrough of the deposit provides a good example for the exploration work of the mining company and also has significance for regional ore-prospecting.
The telescoped porphyry-high sulfidation epithermal Cu (-Au) mineralization of Rongna deposit in Duolong ore cluster at the southern margin of Qiangtang Terrane, Central Tibet: Integrated evidence from geology, hydrothermal alteration and sulfide assemblages.
Li G.,CAS Institute of Geology and Geophysics |
Li G.,Chinese Academy of Sciences |
Zhang X.,CAS Institute of Geology and Geophysics |
Zhang X.,University of Chinese Academy of Sciences |
And 8 more authors.
Acta Petrologica Sinica | Year: 2015
Rongna telescoped porphyry-high sulfidation epithermal Cu-Au deposit within Duolong ore cluster, located at the southern margin of Qiangtang terrane, is an exploration breakthrough made by Chinalco Tibet Company and No. 5 Geological Party of Tibet Bureau of Geology and Exploration in recent years. Its inferred resource has reached a superlarge scale, but the genetic type is still controversy. Based on detailed geological drills records, combined with the observation of microscope, scanning electron microscope and EPMA analysis of sulfides, it is evident that the ore-forming porphyry is granodiorite porphyry. The ore bodies mainly occur in the Lower-Middle Jurassic Sewa Formation feldspathic quartz sandstone and ore-forming porphyry. The W-E trending blind orebodies dip to the south, and are characterized by great downward extension. The metallic metal is copper, associated with mineralization of Au, Ag, and molybdenite mineralization can be seen seldomly. The hydrothermal alteration has two stages, which is biotitization, hornfelsic alteration, silicification-sericitization, silicification-illitization-chloritization, that are related with porphyry, and telescoped advanced argillic alteration in shallow part. The alteration zones are obvious and they are, respectively, veinlet disseminated mineralization formed by porphyry and the other one which is characterized by enargite induced by high sulfidation epithermal hydrotherm. Cu-Bearing mineral assemblages can be divided into 4 zones, which mainly correspond to alteration zones: Bornite-chalcopyrite are major ore minerals in depth, while bornite-covellite in transition area, digenite-tennatite-enargite in upper-middle part and chalcocite-digenite on top. On the whole, mineralization is Cu-S system in shallow part and Cu-Fe-S system in depth. Contrasted with other similar deposits, the characteristic of Rongna's mineralization is rich in zinc and poor in gold. As mentioned above, Rongna is a typical example of telescoped porphyry-high sulfidation epithermal Cu-Au deposit, and the exploration breakthrough supplies an important way for exploration in volcanic rock area and coverage area at southern margin of Qiangtang terrane.