Continental Margin Evolution and Fluid-involving Mineralization Processes
Solid Mineral Resources
---Continental Margin Evolution and Fluid-involving Mineralization Processes

Our research groups focus on the structure-magmatism-fluid-mineralization process along the ancient and juvenile active continental margins (volcanic arc, interplate rift zone, collision belt). Combining with the isotopic dating, geochemistry, fluid inclusions and structure geology, construct the evolutions of the continental margins and discuss the origin of hydrothermal deposits (porphyry Cu-Mo deposits, orogenic gold deposits, giant REE deposits). Groups produce numerous scientific achievements from researches of the Jiaodong gold deposits district east margin of North China craton, the Bayan Obo giant REE-Nb-Fe deposits north margin of NCC, the Zhongtiao Mountains copper district central south of NCC and the Tianshan orogenic belt. 

1. Magmatic-hydrothermal evolution and origin of Jiaodong Au deposit 

The Jiaodong Peninsula which experienced the process of craton destruction during Mesozoic is located in the eastern margin of the North China Craton. This area has produced several world-class (>100t), dozens of large ones and many small and medium sized gold deposits, making it the largest and most important gold producing district of China. Our research group has made a lot of original research on the genesis of the Jiaodong granites and gold deposits (including the northwestern Zhaoyuan-Laizhou, eastern Penglai-Qixia and southern Muping-Rushan gold belts) in recent ten years. 

1.1 Evolution of the lithospheric mantle beneath the southeastern North China Craton 

The mafic-intermediate dike swarms are like “the pulse of the Earth” and typically associated with extensional tectonic regimes in the post-collisional or intraplate settings. Investigations on dike swarms have provided important information on tectonic evolution, mantle source characteristics, geodynamic setting and genesis of associated mineralization in various terranes. 

Through detailed field studies, we identified two stages of mafic-intermediate dikes in the Jiaodong Peninsula. In combination with the results of zircon U-Pb LA-ICPMS dating, major and trace elements, Sr-Nd-Pb isotopic compositions and zircon Hf isotopic data, we investigate the petrogenesis of Jiaodong mafic-intermediate dikes, evaluate their mantle source, and constrain the evolution of lithospheric mantle beneath the southeastern North China Craton (NCC). Also, we present a detailed petrographic and geochemical study, microthermometric data and major and trace element composition through LA-ICPMS analysis of SMIs hosted in clinopyroxene phenocrysts of dolerite dikes from the Jiaojia gold deposit in the NCC. We quantify the compositions of the SMIs, and attempt to investigate the petrogenesis and mantle source of the dolerite dikes in order to understand the formation and evolution of the parental melt. 

Two stages of mafic-intermediate dikes with ages as ~117–108 Ma and ~95–87 Ma, respectively, are identified in the Jiaodong Peninsula based on zircon U-Pb ages. The Early Cretaceous mafic-intermediate dikes (ECMDs) and Late Cretaceous mafic dikes (LCMDs) show distinct geochemical and isotopic features. The ECMDs are enriched in large ion lithophile elements (LILE, Rb, Sr, Ba, U and Th) and light rare earth elements (LREE, La, Ce, Pr, Nd, Sm and Eu) with a strong depletion in high field strength elements (HFSE, Nb, Ta, Ti and P). They show uniformly high (87Sr/86Sr)i, low εNd(t) values, positive (206Pb/204Pb)i and negative εHf(t) values. These rocks were derived from partial melting of an enriched lithospheric mantle, and the enrichment of the mantle source resulted from source metasomatism imparted by the melts generated from remelting of the subducted lower crust of the Yangtze Craton (YC). In contrast, the LCMDs show lower SiO2, lack of HFSE depletion and are depleted in whole rock Nd and zircon Hf isotope. They are interpreted to have sourced from a newly accreted depleted lithospheric mantle generated through continuous erosion of older enriched lithospheric mantle by asthenospheric upwelling, leaving out minor remnants of the older mantle in the newly accreted lithospheric mantle. 

Silicate melt inclusions (SMIs) in magmatic minerals provide key information on the chemical and mineralogical evolution of source magmas. The widespread Cretaceous mafic dikes in the Jiaojia region of the eastern North China Craton contain abundant SMIs within clinopyroxene phenocrysts. The daughter minerals in these SMIs include amphibole, plagioclase, pyrite and ilmenite, together with CO2 + CH4and CH4 as the major volatile phase. The total homogenization temperatures of the SMIs range between 1280 and 1300 °C. The host clinopyroxene phenocrysts in these dolerite dikes are dominantly augite with minor diopside. From LA-ICPMS analyses of the SMIs, we identify two compositional groups: (1) low-MgO SMIs; (2) high-MgO SMIs. The Low-MgO group exhibits higher concentrations of TiO2, Al2O3, Na2O, P2O5 and lower CaO and CaO/Al2O3 ratio as compared to the high-MgO SMIs. The trace element patterns of the two types of SMIs are similar to those of the host mafic dikes. However, the low-MgO SMIs and host mafic dikes are clearly more enriched in all the trace elements as compared to the high-MgO type, especially with regard to the highly incompatible elements. The estimated capture temperatures and pressures are 1351–1400 °C and 16.2–21.0 kbar for the high-MgO SMIs and 1177–1215 °C and 5.5–10.9 kbar for the low-MgO type. The high-MgO and low-MgO SMIs were trapped at depths of ~51–68 km and ~20–35 km, respectively. Computations show that the parental melt is basic with SiO2 content 49.6 wt % and Mg# 80.0 with relatively low total alkali contents (1.35 wt % Na2O+K2O) and high CaO (15.2 wt %). Exploratory runs with the program MELTS and pMELTS show that the low-MgO and high-MgO SMIs were derived from the same parental melt through different degrees of crystallization. Clinopyroxene and a small amount of olivine were the fractionating phases during the evolution from parental melt to low MgO melt. While the low MgO melt experienced significant fractional crystallization of olivine and clinopyroxene. We postulate the newly accreted lithospheric clinopyroxenite as the major source for the Jiaojia dolerite dikes, with melting of the source at a depth of ~68–80 km. 
The representative papers: 

  1. Cai YC, Fan HR, Santosh M, Liu X, Hu FF, Yang KF, Lan TG, Yang YH, Liu YS. 2013. Evolution of the lithospheric mantle beneath the southeastern North China Craton: Constraints from mafic dikes in the Jiaobei terrain. Gondwana Research, 24: 601-621. 
  2. Cai YC, Fan HR, Santosh M, Hu FF, Yang KF, Hu ZC. 2015. Subduction-related metasomatism of the lithospheric mantle beneath the southeastern North China Craton: Evidence from mafic to intermediate dykes in the northern Sulu orogen. Tectonophysics, 659: 137151 
  3. Cai YC, Fan HR, Santosh M, Hu FF, Yang KF, Liu X, Liu YS. 2015. Silicate melt inclusions in clinopyroxene phenocrysts from mafic dikes in the eastern North China Craton: constraints on melt evolution. Journal of Asian Earth Sciences, 97: 150–168. 

1.2 Comparative study on deep and shallow part of Jiaodong gold mineralization 

Sanshandao gold deposit with abundant reserves (>1000t Au) is a respective altered rock type gold deposit in Jiaodong. In a short period of time, there was a large and intensive metal accumulation with multi-stages and strong hydrothermal alteration. The mineralization age is ~117Ma by the method of the Rb-Sr dating of the altered sericite. Detailed petrographic observation revealed that strong water / rock interactions have occurred during the formation of Sanshandao gold deposit. And the temporal sequence of these interactions is potassic alteration, sericitization, silicification, beresitization and carbonatization. The precipitation of gold has a close relationship with beresitization. In the process of water / rock interaction, a variety of main elements are brought into and taken out, and most of the large ion lithophile elements (LILEs) and light rare earth elements (LREEs) also showed a strong activity. Besides, it is worth noting that the heavy rare earth elements (HREEs) and high field strength elements (HFSEs) that are traditionally considered to have poor activity may also be gained and lossed strongly. Sr-Nd isotopes of altered minerals imply that the ore-forming fluids are mainly derived from the crustal fluids, such as the hydrothermal fluid of intermediate-acid magma, the meteoric water and so on, but with some contribution of mantle derived fluids. The altered minerals can be deposited directly from the ore forming fluids, or through the formation of water / rock interactions, so the physicochemical properties of the ore forming fluids can be inferred. 
The representative papers: 

  1. Fan HR, Zhai MG, Xie YH, Yang JH. 2003. Ore-forming fluids associated with granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong gold province, China. Mineralium Deposita, 38: 739-750 
  2. Hu FF, Fan HR, Jiang XH, Li XC, Yang KF, Mernagh. 2013. Fluid inclusions at different depths in the Sanshandao gold deposit, Jiaodong Peninsula, China. Geofluids, 13: 528-541 
  3. Li XC, Fan HR, Santosh M, Hu FF, Yang KF, Lan TG. 2013. Hydrothermal alteration associated with Mesozoic granite-hosted gold mineralization at the Sanshandao deposit, Jiaodong gold province, China. Ore Geology Reviews. 53: 403-421. 
  4. Wen BJ, Fan HR, Hu FF, Liu X, Yang KF, Sun ZF, Sun ZF. Fluid evolution and ore genesis of the giant Sanshandao gold deposit, Jiaodong gold province, China: Constrains from geology, fluid inclusions and H–O–S–He–Ar isotopic compositions. Journal of Geochemical Exploration, 

1.3 Geochronology of Guilaizhuang Au deposit, Luxi 

Numerous gold deposits occur along the eastern margin of the North China Craton (NCC), most of which are distributed in the Jiaodong Peninsula. These gold deposits, with ages mostly in the range of 130-110 Ma, are mainly located within or proximal to Mesozoic granitoids, especially those with Late Jurassic-Early Cretaceous age, and characterized by quartz lode (Linglong-type) or disseminated (Jiaojia type) styles of mineralization with extensive alteration of wall rocks. However, a unique class of gold mineralization with typical Au-Te association was discovered in the southwestern Shandong Province (Luxi Block) near the Tan-Lu Fault, in which the Guilaizhuang gold de- posit is the most significant one with gold resource of 35 metric tons and an average grade of 8.1 ppm. The Guilaizhuang gold deposit is located near the Tongshi intrusive complex which is composed of syenites and quartz monzonites with intrusive ages of ~181 Ma. 

The Guilaizhuang gold deposit is composed of limestone- and breccia-type ores. In the limestone ores, gold is hosted by pyrite, As-bearing pyrite and arsenopyrite, whereas in the breccia ores, tellurides are the main gold carriers. Selenium often isomorphously substitutes for sulfur in sulfides in the limestone ores, but occurs as selenides in the breccia ores. Hematite is the only oxide in the breccia ores, associated with barite and other tellurides. Based on EPMA results and thermodynamic calculations, we propose that gold has been transported as [Au(HS,HSe)2]-, and released during rapid formation of pyrite, As-pyrite and arsenopyrite, at logfS2(g) between -12.8 and -11.4 (250 °C). In the breccia ores, logfTe2(g) and logfSe2(g) are constrained within -12.9 to -9.4, and -12.4 to -6.9 (250 °C), respectively, based on the mineral assemblages observed in the ores.  

Besides, in order to illuminate the geochronology schedule of the Guilaizhuang gold deposit, we systematically dated the intrusions and gold mineralization related minerals. The intrusive age of the syenite should mark the lower limit of the gold mineralization age, whereas the formation age of the fluorite and calcite would represent the upper limit. In this study, we analyzed zircons from the altered syenite in the open-pit, and the results show U-Pb ages of 179-180 Ma consistent with those of the Tongshi intrusive complex. We also present a Sm-Nd isochron age from the fluorite–calcite mineral pair that shows 181 Ma. Based on those results, we infer the timing of gold mineralization to be approximately 180 Ma, coeval with the intrusion of the Tongshi complex. A correlation with the regional tectonic milieu shows that the Guilaizhuang gold deposit was located in a post-collision setting at this time, following the amalgamation between the North China Craton and the Yangtze Craton. Thus, the Guilaizhuang deposit should mark an important alkaline rock-related gold-forming event within the eastern margin of the North China Craton in a post-collisional setting associated with the collision of the North China Craton and Yangtze Craton during late Triassic to Early Jurassic, and is obviously different from the Early Cretaceous intensive gold mineralization in the adjacent Jiaodong Peninsula.  

Since there are two different intrusive rocks in the area, it is necessary to distinguish their differential role in gold mineralization. The oxygen fugacity of the syenite and monzonite calculated by apatite Mn content indicate that high oxidization state of the syenite magma can enhance the metallic mineralization potential. In contrast, the lower oxygen fugacity of the monzonite melt was unfavorable for metal enrichment, thus leading to insignificant mineralization. Our study recommends more focus for gold exploration in the rocks with syenitic affinities in this region. 
The representative papers: 

  1. Xu WG, Fan HR, Hu FF, Santosh M, Yang KF, Lan TG. 2014. Gold mineralization in the Guilaizhuang deposit, southwestern Shandong Province, China: Insights from phase relations among sulfides, tellurides, selenides and oxides. Ore Geology Reviews, 56: 276-291. 
  2. Wen BJ, Fan HR, Santosh M., Hu FF, Pirajno F, Yang KF. 2015. Genesis of two different types of gold mineralization in the Linglong gold field, China: Constrains from geology, fluid inclusions and stable isotope. Ore Geology Reviews, 65: 643–658. 
  3. Xu WG, Fan HR, Hu FF, Santosh M, Yang KF, Lan TG, Wen BJ. 2015. Geochronology of the Guilaizhuang gold deposit, Luxi Block, eastern North China Craton: Constrains from zircon U-Pb and fluorite-calcite Sm-Nd dating. Ore Geology Reviews, 65: 390–399. 

2. Genesis of Bayan Obo REE-Nb-Fe deposits 

Bayan Obo giant REE-Nb-Fe deposit in the northern margin of the North China Craton (NCC) is well known in the world for its abundant rare earth element resources. The NCC once was one of the most active zone for mineralization, especially the Mesoproterozoic continental rift event and of related tectonic and magmatic movement created favorable conditions for enrichment of huge amount of rare earth element. Recent research shows that the Bayan Obo ore deposit likely resulted from the carbonatitic magma activity, which is a favorable factor for REE accumulation. 

High precision Sm-Nd isochron data shows that the intrusion age of carbonatite veins was at 1319±48Ma. Moreover, the REE mineralization age in calcite carbonatite veins was around 1275±87Ma that is consistent with the intrusion age in error range. According to these data the abundant REE already existed in the carbonatite magma before intrusion and result in the earlier ore mineralization. The average age of mineralized dolomite was at 1353±100Ma, and the mineralization age of apatite in coarse grain dolomite was around 1329±150Ma. These data is consistent with carbonatite. Considering the coincident rare, trace element and isochron composition between them, it is presumed that mineralized dolomite was also the carbonatite intrusion and was the mainly factor for huge REE enrichment. 

Evidence from petrological and geochemical data suggests that abundant alkaline-basic magma resulted from enhancement of continental breakup activity, that separated into carbonatite veins and mafic dykes by melt immiscibility mechanism, intruded in Bayan Obo margin rifts at the late stage of extension movement. Carbonatite veins can be divided into three main types by mineral composition: dolomite carbonatite, dolomite-calcite coexistent carbonatite and calcite carbonatite. Intrusion relationship between different types of carbonatite veins show that the calcite carbonatite veins were formed latter than the dolomite type as well as the coexistent type. Moreover, geochemical data also reveals successive and evolutive character between them. The content of REE increases together with the calcite minerals component. Through continuous evolution (crystal fractionation), abundant LREE accumulation occurred in the terminal calcite carbonatite magma, which was then superposed on the early dolomite carbonatite pluton, thus resulting in the formation of the giant Bayan Obo REE deposit. 
The representative papers: 

  1. Fan HR, Yang KF, Hu FF, Liu S, Wang KY. 2015. The giant Bayan Obo REE-Nb-Fe deposit, China: Controversy and ore genesis. Geoscience Frontiers, 7: 335-344. 
  2. Fan HR, Hu FF, Yang KF, Pirajno F, Liu X, Wang KY. 2014. Integrated U-Pb and Sm-Nd geochronology for a REE-rich carbonatite dyke at the giant Bayan Obo REE deposit, Northern China. Ore Geology Reviews, 63: 510–519. 
  3. Yang KF, Fan HR, Santosh M, Hu FF, Wang KY. 2011. Mesoproterozoic carbonatitic magmatism in the Bayan Obo deposit, Inner Mongolia, North China: Constraints for the mechanism of super accumulation of rare earth elements. Ore Geology Reviews, 40: 122-131. 
  4. Yang KF, Fan HR, Santosh M, Hu FF, Wang KY. 2011. Mesoproterozoic mafic and carbonatitic dykes from the northern margin of the North China Craton: Implications for the final breakup of Columbia supercontinent. Tectonophysics, 498: 1-10. 
  5. Hu FF, Fan HR, Liu S, Yang KF, Chen F. 2009. Sm-Nd and Rb-Sr isotopic dating of veined REE mineralization for the Bayan Obo REE-Nb-Fe deposit, northern China. Resource Geology, 59: 407-414. 

3. Tectonic evolution of Tienshan orogen, subduction metamorphism and fluids 

3.1 Accretional orogenisis of Southwestern Tianshan 

Integrated the evidences from eclogite, ophiolite and ancient metamorphic basement, we reconstructed a tectonic model with multiple oceanic evolutions in west segments of CAOB. Based on geochemical and geochronological data we conclude that the Central Tianshan Arc Terrane has undergone three global tectonothermal events, namely 2.5 Ga continental crustal growth, 1.8 Ga collision related to the Columbia assembly and 785 Ma crustal reworking due to the Rodinia breakup. The Neoproterozoic open of old Asian Ocean is believed to be a direct consequence of the breakup of Rodinia. Accretional orogenisis is closely related to multiple ocean evolution and multi-polarized subduction. It is suggested that the Tianshan Orogen has undergone early Paleozoic Terskey ocean subduction, early Paleozoic-late Paleozoic South Tianshan Ocean subduction and late Paleozoic North Tianshan Ocean subduction, and believed that Paleozoic is a complex period of multiple ocean evolution and multi-polarized subduction. In addition, the final ocean disappears happened at late Carboniferous to Permian, during which the syn-collisional southwards thrust deformation occurred at late Carboniferous, while the large-scale strike-slip shearing at Permian. Our innovative work significantly contributes to the architecture of the new accretional orogenisis model characterized by “multiple ocean evolution, multi-polarized subduction and archipelagos with multiple microcontinents”. 

These studies were published on international journals like Precambrian Research, Tectonophysics, International Journal of Earth Sciences.
The representative papers are: 

  1. Gao, J., Wang, X.-S., Klemd, R., Jiang, T., Qian, Q., Mu, L.-X., Ma, Y.-Z., 2015. Record of assembly and breakup of Rodinia in the Southwestern Altaids: Evidence from Neoproterozoic magmatism in the Chinese Western Tianshan Orogen. Journal of Asian Earth Sciences 113: 173–193. 
  2. Wang, X.S., Gao, J., Klemd, R., Jiang, T., Li, J.L., Zhang, X., Tan, Z., Li, L., Zhu, Z.X., 2014. Geochemistry and geochronology of the Precambrian high-grade metamorphic complex in the Southern Central Tianshan ophiolitic mélange, NW China. Precambrian Research, 254: 129–148. 
  3. Jiang, T., Gao, J., Klemd, R., Qian, Q., Zhang, X., Xiong, X.M., Wang, X.S., Tan, Z., Chen, B.X., 2014. Paleozoic ophiolitic mélanges from the South Tianshan Orogen, NW China: Geological, geochemical and geochronological implications for the geodynamic setting. Tectonophysics, 612: 106–127. 
  4. Gao, J., Klemd, R., Qian, Q., Zhang, X., Li, J.L., Jiang, T., Yang, Y.Q., 2011. The collision between the Yili and Tarim blocks of the Southwestern Altaids: geochemical and age constraints of a leucogranite dike crosscutting the HP-LT metamorphic belt in the Chinese Tianshan Orogen. Tectonophysics, 499: 118–131. 
  5. Qian, Q., Gao, J., Klemd, R, He, G.Q., Xiong, X.M., Long, L.L., Liu, D.Y., Xu, R.H., 2009. Early Paleozoic tectonic evolution of the Chinese South Tianshan Orogen: constraints from SHRIMP zircon U–Pb geochronology and geochemistry of basaltic and dioritic rocks from Xiate, NW China. International Journal of Earth Sciences, 98: 551–569. 
  6. Gao, J., Li, M.S., He, G.Q., Xiao, X., Tang, Y., 1998. Paleozoic tectonic evolution of the Tianshan Orogen, northwestern Chica. Tectonophysics, 287:213–231. 
  7. Gao, J., He, G.Q., Li, M.S., Tang, Y., Xiao, X., Zhou, M., Wang, J., 1995. The mineralogy, petrology, metamorphic PTDt trajectory and exhumaion mechanism of blueschists, South Tianshan, northwestern China. Tectonophysics, 250: 151–168. 
  8. Gao, J., Long, L.L., Qian, Q., Huang, D.Z., Su, W., Klemd, R., 2006. South Tianshan: a Late Paleozoic or a Triassic Orogen? Acta Petrologica Sinica 22: 1049-1061 (in Chinese with English abstract).   

3.2 Mechanism of continental growth in Western Tianshan 

We reconstructed a “two-stage” model for the Phanerozoic continental growth of the western segment of the CAOB through geochemical and geochronological studies of granitoid rocks from the Western Tianshan Orogen. During oceanic subduction, continental growth occurred as a result of several combined processes, i.e. by addition of oceanic crustal melts (adakites), the intrusion of basaltic magmas derived by partial melting of the metasomatized depleted mantle wedge and the upwelling of granitic magma derived from a mixed source of basaltic magmas and old continental basement. However, during the post-collisional period, vertical accretion of underplated juvenile mantle material may have been accomplished during ‘slab breakoff’ delamination. This study suggests a two stage model of continental growth of ‘syn-subduction lateral accretion of arc complexes’ and ‘post-collisional vertical accretion of underplated mantle material’, which may also be relevant for the western segment of the CAOB in the Phanerozoic. This “two-stage” model gets more and more acceptances from international colleague, and becomes the guiding ideology of State Key Project for Basic Research of China “Central-Asia type orogenesis and metallogenesis in western China”. 

These studies were published on international journals like Lithos, International Journal of Earth Sciences.
The representative papers are: 

  1. Jiang, T., Gao, J., Klemd, R., Qian, Q., Zhang, X., Wang, X., Tan, Z., Zhu, Z., 2015. Genetically and geochronologically contrasting plagiogranites in South Central Tianshan ophiolitic mélange: Implications for the breakup of Rodinia and subduction zone processes. Journal of Asian Earth Sciences 113: 266–281. 
  2. Long, L.L., Gao, J., Klemd, R., Beier, C., Qian, Q., Zhang, X., Wang, J.B., Jiang, T., 2011. Geochemical and geochronological studies of granitoid rocks from the Western Tianshan Orogen: implications for continental growth in the southwestern Central Asian Orogenic Belt. Lithos, 126: 321–340. 
  3. Gao, J., Long, L.L., Klemd, R., Qian, Q., Liu, D. Y., Xiong, X. M., Su, W., Liu, W., Wang, Y. T., Yang, F. Q., 2009. Tectonic evolution of the South Tianshan Orogen, NW China: geochemical and age constraints of granitoid rocks. International Journal of Earth Sciences, 98: 1221–1238. 

3.3 Southwestern Tianshan HP-UHP belt 

The eclogite in Chinese SW Tianshan Orogen was firstly found by Jun Gao in 1997, and the subsequent significant researches on high-pressure metamorphism promote the SW Tianshan HP-UHP belt to be a international window on studying subduction processes. The detailed mineralogical, petrological, geochemical and isotopic investigations have been performed on HP rocks. The protoliths of eclogitic rocks show E-MORB, N-MORB and OIB affinities, indicating an oceanic slab subduction. The peak metamorphic age is constrained at late Paleozoic (ca. 320 Ma). Based on evidences of field occurrences, P-T conditions, peak metamorphic ages and poly-cyclic metamorphism of eclogite rocks, a sedimentary “subduction channel”model is proposed for the exhumation mechanism of SW Tianshan HP-UHP rocks. 

These studies were published on international journals like Journal of Petrology, Earth and Planetary Science Letters, Journal of Metamorphic Geology, Lithos, American Mineralogist. One paper was selected as the “Highlight and Breakthrough” paper by Journal American Mineralogist.
The representative papers are: 

  1. Li, J.L., Klemd, R., Gao, J., John, T., 2016. Poly-cyclic Metamorphic Evolution of Eclogite: Evidence for Multistage Burial–Exhumation Cycling in a Subduction Channel. Journal of Petrology 57: 119-146. 
  2. Li, J.L., Klemd, R., Gao, J., Jiang, T., Song, Y.H., 2015. A common high-pressure metamorphic evolution of interlayered eclogites and metasediments from the ‘ultrahigh-pressure unit’ of the Tianshan metamorphic belt in China. Lithos 226: 169-182. 
  3. Klemd, R., Gao, J., Li, J.L., Meyer, M., 2015. Metamorphic evolution of (ultra)-high-pressure subduction-related transient crust in the South Tianshan Orogen (Central Asian Orogenic Belt): Geodynamic implications. Gondwana Research 28: 1-25. 
  4. Li, J.L., Klemd, R., Gao, J., Meyer, M., 2014. Compositional zoning in dolomite from lawsonite-bearing eclogite (SW Tianshan, China): Evidence for prograde metamorphism during subduction of oceanic crust. American Mineralogist, 99: 206–217. 
  5. Li, J.L., Klemd, R., Gao, J., Meyer, M., 2012. Coexisting carbonate-bearing eclogite and blueschist in SW Tianshan, China: Petrology and phase equilibria. Journal of Asian Earth Sciences, 60: 174–187. 
  6. Klemd, R., John, T., Scherer, E.E., Rondenay, S., Gao, J., 2011. Changes in dip of subducted slabs at depth: Petrological and geochronological evidence from HP-UHP rocks (Tianshan, NW-China). Earth and Planetary Science Letters 310: 9-20. 
  7. Su, W., Gao, J., Klemd, R., Li, J.L., Zhang, X., Li, X.H., Chen, N.S., Zhang, L., 2010. U–Pb zircon geochronology of Tianshan eclogites in NW China: implication for the collision between the Yili and Tarim blocks of the southwestern Altaids. European Journal of Mineralogy, 22: 473–478. 
  8. Gao, J. and Klemd, R., 2003. Formation HP-LT rocks and their tectonic implications in the western Tianshan Orogen, NW China: geochemical and age constraints. Lithos, 66: 1–22. 
  9. Klemd, R., Schroter, F., Will, T., Gao, J., 2002, PT-evolution of glaucophane- clinozoisite bearing HP-LT rocks in the western Tianshan orogen, NW China. Journal of Metamorphic Geology, 20: 239–254. 
  10. Gao, J., Klemd, R. and Zhang, L., 1999.  P-T path of high pressure-low temperature rocks and tectonic implications in the western Tianshan Mountains (NW China). Journal of Metamorphic Geology, 17: 621–636. 
  11. Gao, J., 1997. The discovery of eclogites and its tectonic implication, Southwest Tianshan. Chinese Science Bulletin 42: 737-740.   

3.4 Subduction fluids 

The rutile- and/or sulfide-bearing eclogite-facies veins were discovered by our group, from which we reported the transport of HFSE (Ti-Nb-Ta) and metal elements (Fe, Cu) in subduction fluids. Primary fluids entrapped at blueschist to eclogite transition were distinguished from the Tianshan meta-subduction complex in northwestern China, and this provides an important insight to understand the fluid process during subduction of oceanic crust. The primary fluid inclusions in omphacite from eclogitic veins are Si-Na-rich with low salinity. The veins consist of two types, an internal dehydrated in-situ vein and an external transport vein. The composition of fluids liberated by subducted oceanic crust varies significantly, including LILE-rich, HFSE-poor aqueous fluids and HFSE-rich aqueous fluids. This finding changes the traditional knowledge of subduction fluids that are always LILE-rich and HFSE-poor, and has significant implications to study the global element cycling and crust-mantle interactions. The occurrence of sulfide in eclogite veins suggest that the subduction fluids could infiltrate metal elements like Fe, Cu from subducted crust and transport them to overlying mantle wedge. It is most likely that slab fluids strongly contribute to the metal flux into the arc magma systems finally resulting in giant arc-related ore deposits. These researches stand at the frontier of metamorphic fluids. 

These studies were published on international journals like Geochimica et Cosmochimica Acta, Contribution to Mineralogy and Petrology, Lithos, Chemical Geology.
The representative papers are: 

  1. Li, J.L., Gao, J., John, T., Klemd, R., Su, W., 2013. Fluid-mediated metal transport in subduction zones and its link to arc-related giant ore deposits: Constraints from a sulfide-bearing HP vein in lawsonite eclogite (Tianshan, China). Geochimica et Cosmochimica Acta, 120: 326–362. 
  2. Beinlich, A., Klemd, R., John, T., Gao, J., 2010. Trace-element mobilization during Cametasomatism along a major fluid conduit: eclogitization of blueschist as a consequence of fluid-rock interaction. Geochimica et Cosmochimica Acta 74, 1892-1922. 
  3. John, T., Klemd, R., Gao, J., Garbe-Schönberg, C., 2008. Trace-element mobilization in slabs due to non-steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China). Lithos, 103:1–24. 
  4. van der Straaten, F., Schenk, V., John, T., Gao, J., 2008. Blueschist-facies rehydration of eclogites (Tian Shan, NW-China): Implications for fluid-rock interaction in the subduction channel. Chemical Geology 255, 195-219. 
  5. Gao, J., John, T., Klemd, R., Xiong, X., 2007. Mobilisation of Ti-Nb-Ta during subduction: evidence from rutile-bearing segregations and veins hosted in eclogites, Tianshan, NW China. Geochimica et Cosmochimica Acta, 71: 4974–4996. 
  6. Gao, J. and Klemd, R., 2001. Primary fluids entrapped at blueschist to eclogite transition: evidence from the Tianshan meta-subduction complexes in northwestern China. Contribution to Mineralogy and Petrology, 142:1–14. 

4. Origin of Zhongtiaoshan Cu deposits 

The Zhongtiao Mountain located in the central south of North China craton provides a good example to investigate the Paleoproterozoic rifting-subduction-accretion-collision tectonic cycles. This district contains voluminous outcrops of Paleoproterozoic strata and magmatic rocks and copper deposits. Intensified TTG magmatism, formation of granite-greestone belts and deposition of rift-type sedimentary-volcanic sequences witnessed the early history of this ancient craton. Meanwhile, large quantities of economic elements (Fe, Au Cu and B etc.) were concentrated. All of the significant copper deposits are hosted in the Paleoproterozoic lithological units ranging from graphite schist (Hubi type), micaschist (Henglingguan type) and meta-volcanic porphyry (Tongkuangyu type). The chronotectonic framework of this district was constructed throug the detrital zircon study from sedimentary rocks, the SIMS U-Pb dating of key magmatic rocks and intercalated amphibolite. The oreforming process, fluid evolution and timing of copper mineralization were delineate based on the research of the giant Tongkuangyu copper deposit and the sedimentary rock hosted copper depoists. 

The largest Tongkuangyu copper deposit is hosted by Paleoproterozoic meta-volcanic rocks. Genesis of this giant deposit has been subject to debate for over half century. Secondary ion mass spectrometer (SIMS) and laser ablation ICPMS zircon U–Pb dating show that the meta-monzogranitic porphyry was emplaced contemporaneous with the surrounding lithologies at 2180–2190 Ma as a sill, and that the basic volcanic rocks erupted slightly earlier at ~2220 Ma. The Re–Os geochronological data on molybdenite from the deposit constrain the timing of copper mineralization to 2122 ± 12 Ma. Ti in zircon thermometer reveals a crystallization temperature of 676±12 °C. Cerium anomalies in zircons indicated that the porphyry magmas have low oxygen fugacity ranging from 1.5 log units above and 4 log units below the fayalite-agnetite-quartz (FMQ) buffer. Zircons are slightly more enriched in 18O than that of mantle zircons, with δ18O values of 5.2−5.9 ‰. Geochemical modeling suggests that the porphyry magmas can be derived from remelting of the 2.7 Ga diorite (> 80 %) with minor (< 20%) juvenile materials from depleted mantle. The reducing nature of these magmas makes them incapable of sequestering sufficient Cu and S, thus rendering them unsuitable for porphyry-style copper mineralization. By tentative inference, we suggest that the reduced porphyries may have acted as a reductant to unload copper from oxidizing, ore-forming fluids. 

The Hujiayu Cu deposit, one of the typical “Hubi-type” copper deposits, is hosted by graphite schist and dolomitic marble with disseminated to veinlet (stage I) and thick vein (stage II) mineralization. Stage I mineralization, characterized by stratabound, disseminated pyrite and chalcopyrite within the graphite schist host rock, formed at the syn-metamorphic stage. Graphite geothermometry showed that the host rock was subjected to an upper-greenschist to lower amphibolite metamorphism at a temperature range of 486 to 596 °C, averaging of 546 ± 35 °C (1 σ, n=19). Stage II mineralization, consisting of brecciated dolomitic thick veins cemented by quartz-sulfide assemblages, was a product of metamorphic hydrothermal activity. Fluid inclusions study showed that gas species in fluid inclusions are mainly CO2 with minor CH4, and the solids are dominated by calcite and halite through the Laser Raman and SEM-EDS analyses. Microthermometry results indicated that the ore-forming fluids underwent phase separation at 1.41.8 kbar and 230240 °C after peak metamorphism. The calcite in the hosting marble and dolomite in the hydrothermal veins have δ13CV-PDB values of -0.2 to 1.2 ‰ and -1.2 to -6.3 ‰, and δ18OV-SMOW values of 14.0 to 20.8 ‰ and 13.2 to 14.3 ‰, respectively. The carbon-oxygen data suggested that the ore-forming fluids were probably derived from metamorphic fluids, which had reacted with organic matter in sedimentary rocks or graphite. Four chalcopyrite samples yielded a weighted model age of 1952 ± 39 Ma (1 σ, MSWD=1.5), suggesting that the copper mineralization formed synchronously with regional metamorphism (1970–1850 Ma) and hence a Paleoproterozoic metamorphogenic copper mineralization is implicated. Therefore, we envisaged disseminated-veinlet mineralization formed during a metamorphic peak and the major hydrothermal copper mineralization occurred during the retrograde cooling. 
The representative papers are: 

  1. Liu X, Fan HR, Yang KF, Qiu ZJ, Hu FF. 2016. Zhu XY. Geochronology, redox-state and origin of the ore hosting porphyry in the Tongkuangyu Cu deposit, North China Craton: implications for metallogenesis and tectonic evolution, Precambrian Research, 276: 211–232. 
  2. Liu X, Fan HR, Santosh M, Yang KF, Qiu ZJ, Hu FF, Wen BJ. 2016. Geological and geochronological constraints on the genesis of the giant Tongkuangyu Cu deposit (Palaeoproterozoic), North China Craton. International Geology Review, 58: 155-170. 
  3. Qiu ZJ, Fan HR, Liu X, Yang KF, Hu FF, Xu WG, Wen BJ. 2016. Mineralogy, chalcopyrite Re-Os geochronology and sulfur isotope of the Hujiayu Cu deposit in the Zhongtiao Mountains, North China Craton: implications for a Paleoproterozoic metamorphogenic copper mineralization. Ore Geology Reviews, 
  4. Qiu ZJ, Fan HR, Liu X, Wen BJ, Hu FF, Yang KF, Guo SL, Zhao FC. 2015. Fluid inclusion and carbon-oxygen isotope studies of the Hujiayu Cu deposit, Zhongtiao Mountains, China: implications for syn-metamorphic copper remobilization. Acta Geologica Sinica, 89(3): 726–745. 
Head of Group

Prof. Fan Hongrui

Division of Solid Mineral Resources
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