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Li N.,Xinjiang Institute of Ecology and Geography | Li N.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | Li N.,University of Aarhus | Pirajno F.,University of Western Australia
Ore Geology Reviews | Year: 2016

As one of the most important Mo provinces in the world, the Qinling Orogen is host to mainly Late Mesozoic (Late Jurassic-Early Cretaceous) porphyry Mo systems. Recently, additional Early Mesozoic (mainly Triassic plus minor Early Jurassic) Mo deposits have been identified, which occur as fault-controlled quartz veins or as carbonatite veins and as such, they are fundamentally different from the commonly observed porphyry systems. Furthermore, Early Mesozoic porphyry systems are also present but they are different from those of Late Mesozoic age. Thus, Early Mesozoic Mo systems not only offer a new and comprehensive view of the Mo metallogenesis, but also provide unique insight into the tectonic evolution of the Qinling Orogen taking into consideration the role of mineral deposits as ideal probes of the geodynamic evolution.The known Early Mesozoic Mo deposits in Qinling can be classified into three types based on their geological and geochemical features: porphyry, carbonatite, and orogenic systems. Porphyry Mo systems, including porphyry, porphyry-skarn and intrusion-related veins, are spatially and genetically associated with granitic porphyries. They display typical porphyry type alterations and are formed by magmatic water. Carbonatites are considered as mantle-derived igneous rocks, and Mo mineralization is associated with magmatic fluids. Orogenic Mo systems occur as fault-controlled quartz lodes, and the ore-forming fluids are medium-high temperature, CO2-rich metamorphic fluids. Spatially, Early Mesozoic porphyry Mo systems are concentrated in the western and middle part of the Qinling Orogen, whereas carbonatite veins and orogenic Mo systems are located in the northeastern part. Temporally, orogenic Mo deposits were the earliest (mainly between 220 and 250Ma), followed by carbonatite veins (mainly between 205 and 225Ma) and porphyry Mo systems (mainly between 190 and 205Ma). With some exceptions, there is generally a trend of decreasing deposit ages toward the western part of the orogen. Detailed comparison reveals that the Early Mesozoic porphyry Mo systems in the Qinling Orogen are different from the Late Mesozoic ones in terms of their economic importance, spatial distribution, ore-causative intrusions, hydrothermal alteration and the ore-forming fluids.To explain the above geological and geochemical features, the Triassic Qinling is considered as an active continental margin caused by the northward subduction of the Mian-Lue oceanic plate. A transition from continental arc to back-arc basin is suggested for the formation of Triassic orogenic and carbonatite vein Mo deposits, whereas continental arc is host to the Early Mesozoic porphyry Mo systems. © 2016. Source

Zhang C.,Zijin Mining Group Co. | Zhang C.,Peking University | Li N.,Xinjiang Institute of Ecology and Geography | Li N.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | Li N.,University of Aarhus
Ore Geology Reviews | Year: 2016

In this contribution, the largest porphyry Mo deposit in NE China, Chalukou, is selected to provide insights into the tectonic evolution of NE China. The deposit was considered to be rift-related (or Climax-type) porphyry Mo deposit developed in an extensional setting, while other researchers attributed its formation to the subduction of the Paleo-Pacific Ocean. In view of different granite petrogenesis between rift-type and subduction-type porphyry Mo deposits, geochronological and zircon Lu-Hf isotope studies have been carried out on granitic rocks associated with the Chalukou deposit. Zircon grains from the ore-host monzogranite and ore-causative granite porphyry yield weighted mean 206Pb/238U ages of 166±2Ma and 152±2Ma, with molybdenite samples yielding a Re-Os isochron age of 150±2Ma, indicating a Jurassic age for both granitic intrusion and Mo mineralization. Zircon εHf(t) values of monzogranite and granite porphyry range from 0.9 to 3.0 and from -1.4 to 0.5, respectively. When integrated with published zircon Lu-Hf isotopic data, our data suggest that the barren granites (both pre- and post-ore) were mainly derived from mantle-derived juvenile rocks, whereas the syn-ore granite requires additional involvement of old continental crust. Thus, a contribution of continental crust to Mo mineralization is suggested. The petrogenesis and geochemical data reveal that the Chalukou deposit is a subduction-related porphyry Mo deposits and not rift-related. Integrated evidence links its formation to the southeastward subduction of the Mongol-Okhotsk Ocean, instead of the westward subduction of the Paleo-Pacific Ocean. © 2016 Elsevier B.V. Source

Zhang N.,Xinjiang Institute of Ecology and Geography | Zhang N.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | Zhou K.,Xinjiang Institute of Ecology and Geography | Zhou K.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology
Journal of Intelligent and Fuzzy Systems | Year: 2015

Knowledge-and data-driven approaches are two major methods used to integrate various evidential maps for mineral prospectivity mapping (MPM). Geological maps, geochemical samples and data from known gold deposits were collected in the western Junggar area, Xinjiang Province. The geological and a spatial database for geological and mineral occurrences were constructed for the studied region. A weights-of-evidence model and a fuzzy logic model were employed for MPM, and the results were compared. Results indicate that favorable sedimentary rocks, fault density, fault distance and concentration of Au were the primary factors affecting Au mineralization. Arsenic (AS), Stibium (Sb), fault direction, quartz veins and intrusive rocks were secondary factors affecting Au mineralization. Conditional independence exerted a major influence on the weights-of-evidence model. However, posterior probability would be very high if the conditional independence was disregarded, which impaired results. Combining the quantification results provided by weights-of-evidence and the fuzzy membership values determined by expert knowledge, the mineral prospectivity mapping according to the fuzzy logic method was proved to be valid. For the study area, which had a large number of deposits, data-driven approaches for MPM are generally considered to be appropriate. However, if sufficient data are not collected, the knowledge-driven approaches, for example, the fuzzy logic method used in the present study, usually achieves a better result. © 2015 - IOS Press and the authors. All rights reserved. Source

Wu Y.-S.,Xinjiang Institute of Ecology and Geography | Wu Y.-S.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | Zhou K.-F.,Xinjiang Institute of Ecology and Geography | Zhou K.-F.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | And 3 more authors.
Ore Geology Reviews | Year: 2016

The giant Donggebi porphyry Mo deposit is located in the Jueluotage metallogenic belt of Eastern Tianshan, Xinjiang, Northwest China. Mo mineralization mainly occurs as numerous veinlets in the altered sandstone wall-rocks, with the development of potassic, phyllic, argillic and propylitic alteration assemblages outward from a buried porphyritic granite stock. Zircon crystals from the buried porphyritic granite yield a weighted average 206Pb/238U age of 236±2.2Ma (MSWD=1.2, 1σ, n=17), slightly older than the molybdenite Re-Os isotope ages of 231-234Ma, suggesting that the Donggebi porphyry Mo deposit was formed in the Triassic, post-collisional tectonism subsequent to termination of the Paleo-Asia Ocean. The samples from porphyritic granite show high contents of SiO2, K2O and Al2O3, low contents of TiO2, MgO and CaO, and peraluminous high-K calc-alkaline to shoshonite affinity, with obvious LREE enrichment and negative Eu anomalies. They have high initial 87Sr/86Sr ratios of 0.70618 to 0.70821, εNd(t) values of 0.60 to 1.62, and T DM2(Nd) ages of 0.88 to 0.96Ga. Their (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t values are 17.122-18.577, 15.493-15.574, and 37.887-38.006, respectively. Zircons from the porphyritic granite yield εHf(t) values of -1.58 to 4.82, and T DM2(Hf) ages of 0.96-1.36Ga. These geochemical and isotopic data imply that the Donggebi porphyritic granite originated mainly from partial melting of lower continental crust derived from a depleted mantle. The Donggebi Mo deposit is unique based upon the crustal source for the causative porphyry, the distal position of mineralization, and the previously revealed CO2-rich ore-forming fluids, and thus belongs to the collisional- or Dabie-type porphyry deposits as exemplified by the Qiane'chong and Yaochong deposits in Dabie Shan, the Donggou deposit in Qinling Orogen, China. © 2016 Elsevier B.V. Source

Zhang N.,Xinjiang Institute of Ecology and Geography | Zhang N.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | Zhou K.,Xinjiang Institute of Ecology and Geography | Zhou K.,Xinjiang Key Laboratory of Mineral Resources and Digital Geology | And 2 more authors.
Xinan Shiyou Daxue Xuebao/Journal of Southwest Petroleum University | Year: 2016

Extraction of information in geochemical anomalies has long been geologists' concerns. In this paper, we use the collected 1:20 millions of geochemical data of the western Junggar area to analyze spatial variability of the Au elements, and interpolate it. By using the C-A model of fractal and the traditional method, we obtain different anomaly threshold values. We compare the method of extracting geochemical anomalies information based on the traditional method and fractal technique. The result proves that the spatial distribution of Au elements is characteristic of isotropic with medium correlation;the fractal method is better than the traditional one. Fractal technology and known gold deposits agree better, as it can avoid the omission of abnormal information. The result has certain guiding significance for further prospection works in this area. © 2016, Science Press. All right reserved. Source

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