Large- scale porphyry- type mineralization in the Central Asian metallogenic domain: tectonic background, fluid feature and metallogenic deep dynamic mechanism
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1.Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing;2.Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing;3.State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences (Beijing);4.College of Earth Sciences,Jilin University;5.School of Earth and Space Sciences,Peking University;6.Institute of Geology and Geophysics,Chinese Academy of Sciences;7.School of Earth Sciences and Engineering,Nanjing University

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    Abstract:

    A series of porphyry- type Cu(- Au), Mo, and Cu(- Mo) deposits occur in the Central Asian metallogenic domain (CAMD), the outline of which almost overlaps with that of the most typical accretionary orogenic belt with Phanerozoic crustal growth in the world—the Central Asian Orogenic Belt (CAOB) and is located between the East Europe, Siberia, Tarim and North China cratons. The characteristics of porphyry- type mineralization in the CAMD vary distinctly from the west to the east and can be summarized as having the feature of “Paleozoic copper deposits occurring in the western segment and Mesozoic molybdenum deposits in the east”. On the basis of the systematic studies on Precambrian basements, metallogenic tectonic backgrounds and porphyrytype mineralization characteristics,the CAMD can be subdivided into three metallogenic provinces according to tectonic line boundaries:the Kazakhstan Cu(- Au- Mo), the Mongolia Cu(- Au) and the Northeast China Mo(- Cu) metallogenic provinces.The Kazakhstan metallogenic province has definite Neo- Archean to Paleo- Proterozoic crystalline basements. And, four large- sized porphyry Cu deposits were formed during the Early Paleozoic accretionary orogenic process (481 to 440 Ma). However, most of deposits were produced by the Late Carboniferous (~330 to 295 Ma) clustering mineralization. The porphyry- type metallogenesis was dominated by the linear Paleozoic magmatic arc system extending from the Chinese Central Tianshan- Southern Yili- Kyrgyz Northern Tianshan- Central Kazakhstan- Kokchetav to Chingiz and the Kazakhstan orocline tectonic jointly in the western segment of the Paleo- Asian Ocean. The clustering porphyry- type mineralization occurred during the transformation from the accretionary orogeny to the oroclinal bending. The ~370 Ma and ~240 Ma porphyry- type mineralization of the Mongolia metallogenic province, which also has Neo- Archean to Paleo- Proterozoic crystalline basements, sporadically and locally happened during the evolution of the Tuva- Mongolia orocline. The earlier mineralization is related to the subductional and accretionary event of the Paleo- Asian Ocean under the South Gobi micro- continent and the later mineralization may be resulted from the subduction of the Mongol- Okhotsk Ocean. The Neo- Proterozoic crystalline basement and the petrological record of Pan- African events have been preserved widespread in the Northeast China metallogenic province. The Ordovician porphyry- type mineralization (482~440 Ma) was controlled by the subductional accretionary event of the Paleo- Asian Ocean in early Paleozoic. Whereas, the Mesozoic clustering mineralization of porphyry Mo deposits was dominated by different geodynamic processes that were associated with the post- collisional process of the Paleo- Asian Ocean (~250 Ma), the syn- subductional tectonics of the Mongol- Okhotsk Ocean (248~204 Ma), the syn- subductional process of the Paleo- Pacific Ocean (195~145 Ma) and the lithospheric thinning in eastern China (145~106 Ma). In general, the alteration and fluid characteristics of porphyry- type deposits in the CAMD are following the classic model summarized by Lowell and Guibert. The substantial exclusion of high oxidized magmatic fluids had triggered the formation of large to super large- sized porphyry deposits. The rock type of ore- forming porphyries related to copper deposits in the CAMD resembles to that of the Circum- Pacific metallogenic domain and has a calc- alkaline to high- K calc- alkaline composition predominantly. Granite, monzonitic granite, granodiorite and quartz monzodiorite occur most commonly. The Mo ore- forming porphyry is more felsic with a higher SiO2 content, compared with that of Cu deposits. Some of porphyries have a trace element geochemical signature resembling to that of adakitic rocks while others have geochemical compositions similar to that of normal arc volcanic rocks. Even though the prevalent ‘MASH’, ‘slab melting’ and ‘post- collisional break- off and melting of juvenile lower crust’ models can be employed to interpret the genesis of some porphyry Cu deposits in the CAMD, a here newly suggested model, which is based on ‘the subduction of a relictic mid- oceanic ridge and the melting of pre- enriched mafic lower crust’, is thought to explain the deep mechanism of large- scale porphyry copper mineralization in the Balkhash- West Junggar metallogenic belt of the Kazakhstan metallogenic province. Furthermore, the Mo mineralization in the CAMD has no genetic relationship with the melting of ancient crust or lithosphere mantle. Whereas, it may be genetically associated with the deep event causing the genesis of felsic magmas as a result of the melting of juvenile lower crust. The juvenile crust in the Kazakhstan province of the western segment of the CAMD was generated by the arc accretion event associated with the evolution of the Paleo- Asian Ocean in Paleozoic while that in the Northeast China province of the eastern segment of the CAMD may be produced by the event related to the assembly and the break- up of the Rodinia in Neo- Proterozoic. The ‘Mo- mineralization resulting from the partial melting of juvenile lower crust’ model has innovated the Mo metallogenic theory which is related to the melting of ancient crust and can explain the deep dynamic mechanism of mineralization in the Northeast China, the largest Mo metallogenic province in the world, successfully.

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GAO Jun, ZHU Mingtian, WANG Xinshui, HONG Tao, LI Guangming, LI Jilei, XIAO Wenjiao, QIN Kezhang, ZENG Qingdong, SHEN Ping, XU Xingwang, ZHANG Zhaochong, ZHOU Jianbo, LAI Yong, ZHANG Xiaohui, SUN Jinggui, WAN Bo, WANG Bo.2019. Large- scale porphyry- type mineralization in the Central Asian metallogenic domain: tectonic background, fluid feature and metallogenic deep dynamic mechanism[J]. Acta Geologica Sinica,93(1):24-71

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History
  • Received:November 10,2018
  • Revised:January 02,2019
  • Adopted:January 03,2019
  • Online: January 08,2019
  • Published: