摘要:
陕西银硐子 -大西沟特大型菱铁银多金属矿床赋存于中泥盆世吉维特期之上的热水岩相中,其微相可划分为热水同生沉积 -沸腾交代微相、热水同生交代微相、热水同生沉积微相、热卤水渗滤交代微相、热水混合沉积微相。热水沉积岩富Na、Si、Fe、Mg、Mn、Ba、Cu、Pb、Zn、As、Ag、B等。在热水沉积盆地中,由富Ba的硫酸质热水、富Fe碳酸质热水以快速化学沉淀方式发生同生沉积成矿作用形成重晶石、菱铁矿层。银多金属矿层是由不同成分、性状、富Na、B、Si的铝硅酸质、硼酸质热水与前两类热水相互混合而形成热水混合体系,这种非平衡体系发生了剧烈地化学反应而使矿质发生骤沉。
Abstract:
Siderite-silver-polymetallic deposits in Yindongzi and Daxigou,Shaanxi, Province, China, occur at the Middle Devonian hydrothermal sedimentary facies in the subbasin on the sea bed. There is a major economic orebody in Daxigou which is 2000 m long, from 10 m to more than 100 m thick, and there is the main economic orebody of silve-polymetals in Yingdongzi which is 1900 m long, from 1.0 m to 20.0 m thick. According to patterns of hydrothermal sedimentation,based on petrology,mineralogy, petrochemistry, geochemistry for the hydrothermal sedimentary facies,the hydrothermal sedimentary facies and their rocks can be classified into five subfacies, respectively,hydrothermal synsedimentary replacement-ebullitional subfacies,hydrothermal synsedimentary subfacies,hydrothermal synsedimentary-replacement subfacies,hot-brine vadose-replacement subfacies,and hydrothermal-mixing synsedimentary sub facies.First,the hydrothermal synsedimentary replacement-ebullitional subfacies consist of brecciated albite carbonate rock and ore-bearing brecciated albite siliceous rock.These brecciated rocks may have formed by the synsedimentary replacement and ebuilition of hydrothermal fluids along pouring passways (synfaults)in the subbasin on the sea bed,for hydrothermal fluids could explode and ebuilite along their passways covered by pre-existing hydrothermal sediments under the pressure of hydrothermal fluid overpassing total pressure of their overlying waterbody in the subbasin and their overlying sediments.Secondly,hydrothermal synsedimentary subfacies is made up of albite rock,sideritite, baritite. These rocks essentially stratiform with their elongation parallel to the bedding and with subfacies change and thinning-out. For examples,Bariteolites were formed by the Ba-richi sulfate hot-brine in a way of rapid chemical precipitation in the subbasin on the sea bed while sideriteolites were produced by Fe-rich carbonate hydrothermal fluid in the same way at the same subbasin.These rock layers are characterized by bedded,laminated,layer-massive structures which change regularly in the subbasin.Thirdly,the hydrothermal synsedimentary replacement subfacies include siliceous ferrodolomitite,ferrodolomite,dolomitic limeston and, siderite ferrodolomile.These hydrothermal rocks occur in the footwall rocks of the orebody or in the pinning-out layer of hydrothermal rocks.They might have been produced by the synsedimentation of the hydrothermal.At the same time, synmetasomatism between the hydrothermal fluids and soft sediments on the bed or the slope of the subbasin could take place because replacement structures are easily recognized in the field and lab study.Results of research on minerology,structures and textures of the rock and petrochemistry have suggested that SiO 2,Al 2O 3 and FeO from the hydrothermal in the subbasin has been extensively replaced in the underlying carbonate sediments on the sea bed. Fourthly,the hot-brine vadose-replacement subfacies is composed of scapolite biotite hornstone and scapolite slate. These rocks can be formed by K, Na and Cl-rich hot-brines during their diagenetic processes in the extensively geothermal environment but it is difficult for them to be formed by the processes related to magmatic activities during superimposed stage with the exception of the hornstone enclosing magmatic intrusions. Finally,the subfacies of mixing of different chemical components and physical-chemical states of the hydrothermal fluids,one of the most important subfacies,include sulfide rocks and albite chert with ore formation. These rock layers or ore layers are characterized by bedded,laminated,layer-massive, graded bedding and graded rhythmite.and chemical bedding, The most important characteristic exists in these rock layers or ore layers.The chemica lbedding is as follows: laminated albite layer→albite-sulfide layer→albite-carbonate mineral-sulfide layer→albite-barite laminated layer→lamineated barite layer→barite-albite-chert layer→ferrdolomite lamnated layer.
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