The Central Asian Orogenic Belt,as one of world-class gold economic belts,preserves a number of giant,large black shale-hosted gold deposits,while it is still debated for origin of sulfides and gold mainly due to lack of identification for multiple stages of sulfides.The Haoyaoerhudong gold deposit is hosted in a sequence of Mesoproterozoic carbonaceous and pyritic slate,phyllite,and schist that form a tight syncline along the north margin of the North China Craton.Detailed petrography of the host rocks and mineralization have defined five stages of pyrites.The earliest form of pyrite(Py_(1))occurs as fine-grained dispersed pyrite in black carbonaceous slate and medium-to coarse-grained disseminated pyrite in pyrite-rich layers,contains relative low gold and high arsenic content,indicating a syn-sedimentary or diagenetic in origin.Stage Ⅱ pyrite(Py_(2))occurs with garnet and quartz inclusions and Py_(3) occurs as pyrite veins,contains higher gold and lower As content,and are interpreted to have formed from the dissolution-reprecipitation of Py_(1) during the peak metamorphism or post-peak metamorphism.Stage Ⅳ pyrite(Py_(4))from the pyrite-quartz veins crosscut the metamorphic garnet,contains the highest gold concentrations and other trace elements,and is considered to have formed post-peak metamorphism.Abundant native gold,electrum,and maldonite occur as inclusions within Py_(4) and monazite and in fractures that crosscut garnet.While,Py_(5) with typical remobilized feature is thought to be a product of melting of former pyrites(Py_(1) to Py_(4))triggered by the large-scale Hercynian magmatism.The sedimentary/diagenetic Py_(1) have δ^(34)S values that range from +12.4‰to +16.2‰.Later generations of sulfides,including Py_(2) to Py_(5),and Ccp_(2) to Ccp_(3),have δ^(34)S values from +9.5‰to +12.7‰.Monazite with maldonite inclusions from quartz-pyrite veins yielded an intercept age of 341.3±6.6 Ma,while coarse grained monazite associated biotite along fractures in the reefs yielded an intercept age of
The giant Central Asian Orogenic Belt is an extensive accretionary orogen,of which the Solonker suture,as a major regional suture,coincides closely with an early Permian paleobiogeographical boundary.This suture is considered to mark the location of the final closure of the Paleo-Asian Ocean between the North China Craton and the Mongolian Terrane.Although the closure time of the Paleo-Asian Ocean along the Solonker suture has generally been regarded as Late Permian-Early Triassic,uncertainty remains because of a lack of typical collisionrelated features(e.g.,high-grade regional metamorphism and well-developed fold-thrust structures)and a scarcity of outcrops.The present study reports Early Permian foliated gabbros and dikes(288-275 Ma)and Middle-Late Permian undeformed layered gabbros,strongly peraluminous granites,and I-type granites(265-254 Ma)in the Xinhure area along the northern margin of the North China Craton.The Early Permian foliated intrusions have a subduction-related geochemical signature and were derived from partial melting of lithospheric mantle modified by subduction-related melts or fluids at the active margin of the North China Craton.In contrast,the Late Permian undeformed layered gabbros and strongly peraluminous granites were derived from partial melting of lithospheric mantle and middle-upper crust,respectively,triggered by asthenospheric upwelling.Therefore,a transition from an end-compressional to an extensional environment according to a transition from collision termination to postcollision of the North China Craton and Mongolian Terrane may have occurred between 275 Ma and 262 Ma.This time span can be considered as the final closure time of the Paleo-Asian Ocean along the Solonker suture.
Haidong ZhangJianchao LiuJinkun YangJiakun GeJinya WangZhen Li
The Mesoproterozoic Bayan Obo Group located along the northern margin of the North China Craton(NMNCC)hosts a world’s largest known rare-earth element(REE)deposit(Bayan Obo Fe-REE-Nb deposit)[1,2]and a number of large gold deposits(eg.,Haoyaoerhugong and Zhulazhaga gold deposits;Fig.1a)[3],and has a long and protracted thermal history spanning from1.3 Ga to 250 Ma[1].The tectonic history was associated with Proterozoic rifting with carbonatite magmatism at1.3 Ga[4]and subsequent subduction-accretion processes of the Paleo-Asian Ocean[5,6].The Paleo-Asian oceanic subduction beneath the North China Craton(NCC)initiated in the Middle Silurian[7,8]and the ocean was closed in the Permian to induce the accretion of arcs and terranes with the NCC[2].This long and protracted tectonic history increases the difficulties both in dating and understanding the genesis of the Bayan Obo REE deposit and black shale-hosted gold deposits(e.g.,Haoyaoerhudong deposit).Thus,it is important to understand the thermal history of the hosting strata in order to constrain the tectonic drive and timing of polymetallic mineraliza-tion.There have been few attempts to date the multistage thermal events which the Bayan Obo Group has witnessed,predominantly because of greenschist facies overprint of the host rocks and lack of reliable geochronometers[9,10].
Haidong ZhangMingguo ZhaiDequan WangMostafa FayekJianchao Liu
