Character Of Geological And Geochemical Of Xiajiadian Carlin-type Deposit In Shanyang County, Shaanxi Province

Tectonic location of the studying area was a passive continental margin of the Yangtze plate in early Paleozoic era. Strata of studying area belongs to Feng-Xunyang' district,outcrop is from Sinian to Devonian, upper Sinian Doushantuo formation parallel unconformity from new proterozic Yaolinghe groups and lower Cambrian Shuigoukou formation parallel unconformity from the underlying Sinian and Devonian parallel unconformity from pre-devonian. The overturned fold is composed of basement' tectono-stratigraphy of precambrian and cover'tectono-stratigraphy of lower Paleozoic, multi-syncline is composed of upper palaeozoic tectono-stratigraphy. Xiajiadian deposit situated in the special place where is south of Douling ancient uplift and the territorial deep-great faults of Shanyang-Fengzhen and Zhenan-Banyanzhen is intercross and tectonic deformation is intricate and intense. Deposit located directly in the NW-trending and EW-trending brittle-ductile shear zone of the south of Yanjiagou-Yaolinghe overturned anticline where ore-bearing rock series of lower Cambrian Shuigoukou formation is widely and is superposed by the sub-class' brittle-ductile shear zone which is active multi-stage.Ore-bearing rock series of Xiajiadian gold deposit belongs to black rock series which is composed of No.1 and No.2 segment of lower Cambrian Shuigoukou formation, which contains thin-interbed barite-carbonaceous-slimy-silicic slate and slimy slate and quartzite. This rock series was formed from hydrothermal exhalative sediment in extend rift valley of margin of shelf in early Cambrian where the depth of sea is deep to sub-deep and current is stagnant and oxygen is scarce.There are seven metallogenetic belts been surveyed in this area, of which No.1 metallogenetic belt is maximal in scale and industrial bodies occur in it. No.1 metallogenetic belt been controlled by NW-trending fault F4 that is possess the property ofbrittle-ductile,tensive breccias and fracture deformation. That is the most complex and best fault-controlled. Fault F4 come through this process that from normal fold to overturned fold to brittle-ductile slip-nappe along with unconformity region of strata to NE-trending brittle fault been superposed along with raising part of subsyncline.Metallic minerals of ore consists of diverse stage hydrothermal pyrite which possess hyperplasic zone, marcasite,remnants of sedimentary pyrite and little quantity arsenopyrite and so on.According to structure-controlled,minerals and structure of ore, pre-exist ore can be divided into ore-poor types that are comprise from sheeten barite-carbonaceous-slimy-silicic slate, veining barite-quartz and veining barite-calcite, ore-rich types are mostly breccias that gravel is comprise from barite-carbonaceous-slimy-silicic slate, veining quartz, dolomite, barite-carbonaceous- slimy-silicic slate breccias and quartz breccias. Ore structures are mainly brecciaed ,microveinlet-disseminated, veinlet, berry and so on.Ore textures are mainly euhedral-subeuhedral granular.zonal, metasomatic relict and false appearance.Gold in pre-exist ore occurrence in arsenic pyrite,marcasite,arsenopyrite in invisible, metallogenetic elements possess Au-As-Sb-Hg-Ba assembled feature.Wall-rocks altered are not developed, including silicification,baritization, pyritization, calcification and limonitization.According to structure-controlled and assembled of altered minerals, mineralizing process of this deposit can be divided into preliminary accumulating epoch of mineralizing materials in rock-forming, hydrothermal reworking epoch in superimposing of structural deformation, secondary enrichment epoch in supergene 3 epochs. That can be further divided into 6 stages that are rock-forming stage, early stage, middle stage, late stage of structure superimposing,supergene stage and secondary enrichment stage. Structure that controlling formation and emplacement of ore bodies possess the complex features of brittle-ductile and brittle deformation and the activity of structure possess the character of multi-epoch and multi-stage.Fluid inclusions isotopic composition of fluid inclusions trapped (oxygen and hydrogen ) of mineralizing altered-rocks indicates mineralizing water come from precipitation which be reworked strongly. Lead isotope possesses the feature of orogenic lead, this indicates lead come from orogenic settings and mineralizing dynamics comefrom the intracontinental orogenic action. Trace element and REE indicates matter of ore-bearing come from wall-rocks of ore-bearing. Fluid inclusions in quartz have homogenization temperature from 240 to 280 "C and 180 to 220°C,pressure range from 370 to 820xl05Pa.In mineralizing processes, homogenization temperature of fluid inclusions was descending gradually, pH values was increasing gradually(range from 5.84 to 0.62), salinity was increasing gradually(range from 3.27 to 5.25 Nacl equivalent wt percent),/02 was increasing , the dense of Na\ Cl* and Ca2+ was ascending, the dense of K+ and SO42" was descending, F7C1" ((1, ore-forming fluid is basically from the H2O-CO2-KCI system to H2O-CO2-NaCl system, which indicates this deposit possess the feature that mineralizing depth is middle-low, mineralizing temperature is middle-lower and mineralizing process is multi-stage.According to the character of geological and geochemical that been show above, this paper ascertain this deposit carlin-type related to black rock series.The forming of this deposit is dominated by ore-bearing rock series which are comprise from thin-interbed barite-carbonaceous-slimy-silicic slate and slimy slate and quartzite of lower Cambrian Shuigoukou formation and by brittle-ductile deformation which is engendered from trust-napped in Intracontinental orogenic process.This paper summarize 4 geological marks of exploring that are black rock series of lower Cambrian Shuigoukou formation(strata), brittle-ductile deformation strongly and intersection of EW-trending and NE-trending structure and appearance of overturned subanticline(structure),development of silicification,calcitization and baritization(wall-rock altered), high Au-As-Ag abnormity of geochemistry(geochemical abnormity). This paper analysis No.7 geochemical abnormity, points out the appearance of this abnormity is related with lower Cambrian Shuigoukou formation unconformity from its downlying strata, outcrop of lower Cambrian Shuigoukou formation is integrate and brittle-ductile deformation strongly in this area. Directed by this apprehension, explorer detected thick bodies in No.2 metallogenetic belt(the head of No.7 geochemical abnormity).