iderite- 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.rn 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 overlyingsediments. Secondly, hydrothermal synsedimentary subfacies is made up of albite rock, sideritite, baritite. Theserocks 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 precipi-tation in the subbasin on the sea bed while sideriteolites were produced by Fe - rich carbonate hydrothermal fluid inthe same way at the same subbasin. These rock layers are characterized by bedded, laminated, layer - massive struc-tures which change regularly in the subbasin. Thirdly, the hydrothermal synsedimentary replacement subfacies in-clude siliceous ferrodolomitite, ferrodolomite, dolomitic limeston and, siderite ferrodolomile. These hydrothermalrocks occur in the footwall rocks of the orebody or in the pinning - out layer of hydrothermal rocks. They mighthave been produced by the synsedimentation of the hydrothermal. At the same time, synmetasomatism between thehydrothermal fluids and soft sediments on the bed or the slope of the subbasin could take place because replacementstructures are easily recognized in the field and lab study. Results of research on minerology, structures and texturesof the rock and petrochemistry have suggested that SiO2, A12O3 and FeO from the hydrothermal in the subbasin hasbeen 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 byK, Na and Cl - rich hot - brines during their diagenetic processes in the extensively geothermal environment but itis difficult for them to be formed by the processes related to magmatic activities during superimposed stage with theexception of the hornstone enclosing magrnatic intrusions. Finally, the subfacies of mixing of different chemicalcomponents and physical- chemical states of the hydrothermal fluids, one of the most important subfacies, includesulfide rocks and albite chert with ore formation. These rock layers or ore layers are characterized by bedded, lami-nated, layer - massive, graded bedding and graded rhythmite. and chemical bedding, The most important charac-teristic exists in these rock layers or ore layers. The chemica lbedding is asfollows: 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. Most silver polymetallic ore layers were accumulated bythe mixing of different components and states of the hydrothermal ore - forming fluids in a way of extensive accu-mulations in the subbasin on the sea bed, for ore- forming materials were enriched by extensive chemical reactionsbetween the different components and states of ore - forming hydrotheral water layers in the unequilibrium sys-tems.rn Zhashan Devonian sedimentary basin were formed in the extensional ervironment in the upper crust duringslow subduction of the Qinling subplate. The basin is an extensional basin on the passive continental north marginof the QinLing subplate. Daxigou to Yingdongzi hydrothermal ore- forming subbasin, an extensional - downfault-ed basin, were formed by the same downfalling roof of two synfaults where were the passways for the hydrothermalwater derived from the pre- Deonian underlying strata for the basin. The subbasin what is called is an extensivelychemical recaction dimension is a space for the ore - forming hydrothermal water forming ore layer or hydrothermalrock facies, which were closed by overlying argillite.%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。
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