Abstract:The Oilian eugeosyncline is an important metallogenic province of massive sulfide ore deposits in northwest China; Based on its history of development and evolution as well as the volcanism, the mineralizations can be mainly assigned in time to three epochs, i.e., middle (early-middle) Ordovician and late Ordovician ages, and spatially to two metallogenic belts in concordance with north and south eugeosynclinic belts respectively. According to petrological and petrochemical characteristics, the volcanic rocks might be classified into tholeiitic (Th) +calc-alkalic (CA) assemblage (south belt) and tholeiitic (Th) +calc-alkalic (CA) +alkalic (A) assemblage (north belt). The major massive sulfide deposits are found mostly occurring in calc-alkalic terrains with few important ore deposits observed in the tholeiitic terrains. Judging from the relationship of the ore deposits to the facies of volcanic country rocks and to the ancient volcanic center in time and space, the Baiyinchang Zn-Cu deposit should occur in a near-vent sequence consisting of lava, agglomerate, breccia and tuff, supposedly located proximal to an ancient volcanic vent. The neighboring Xiaotieshan Cu-Pb-Zn deposit, lying in volcanic sedimentary sequence some distance away from the volcanic center, has a ratio of volcanic rocks to sedimentary rocks of l:0.4 as compared with l:0 of the Baiyinchang deposit, suggesting a distal occurrence. Pertaining to this type are also the Shiqingtong Cu-Pb-Zn deposit and the Xitieshan Pb-Zn deposit. Occurring in spilitic basic lava, the Honggou copper deposit bears more resemblance in ore-forming environment to the Besshi type deposit in Japan than to Cyprus type deposit: in that its mafic lava is interbedded with large thickness of graywacke sediments of flysh facies. Its ore features, however, are quite similar to those of Cyprus type deposit. In some sulfide ore deposits, the host rocks are frequently seen to be associated with carbonaceous rocks (black shale and black slate) along or near the sulfide-mineralized layers. The Xitieshan deposit, for example, roughly have the same distribution as the ore bed, implying a deposition environment of marine facies depression. The presence of red or ferruginous chert layers at the top of the ore-bearing volcanic sequence suggests the transition from a reduction environment to an oxidation environment in sedimentary facies. The fluid inclusion data obtained from minerals of the Baiyinchang and Xitieshan ore deposits as shown in the following table reveal a high salinity and hot brine nature of the ore-forming fluids. The late stage geosynclinal orogeny caused deformation and metamorphism of most known ore deposits and their enclosing rocks, resulting :in the simultaneous folding and dislocation of ore bodies and ore-bearing rock sequence and giving rise to such metamorphic features as recrystallization of sulfides and remobilization of minor amounts of substances.
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宋志高.1984.祁连优地槽区块状硫化物矿床形成地质环境的初步对比研究和探讨[J].矿床地质,3(2):11~20.1984.A Preliminary Investigation Into The Ore-Forming Environment Of The Massive Sulfide Deposits In The Qilian Eugeosyncline[J].Mineral Deposits3(2):11~20
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