Walled, Minxian, Deposits Geological And Geochemical Characteristics And Genesis

Zhaishang area lie in the south of Li-Min forland basin in the West Qinling, which is make up of the turbidite with the different lithology and granularity in the environment of seabed slope fan. With the continual tectonical superimposition, the movement of orogeny subduction and the intracontinental thrust nappe structures from North-South continent, which gradually develop the environment of the good ore-forming tectonic and geological background.Ore field is located in Tieshanqun stratigraphic formation of upper Devonian series. The gold deposit exist in the below layer of sediment formation, and carbon -bearing, calcium-bearing flysch formation. Rocks have the character of high frequency fold, which are make up of carbonaceous slate, sandstone, marlite ore-bearing rock series. As a large number of diagenetic pyrite occur, there lead to Arsenic and gold excessive enrichment in ore-bearing and microclastic rocks.By studying ore area, we can conclude that Zhaishang gold deposit is controlled by the structure of ductile-brittle shear belt, along NWW-trenching, obliquity 30-50?and have the character of multiphases and polystages. Ductile-brittle shear belt is the main ore-forming and ore-controlling factors in Zhaishang gold deposit.Zhaishang gold deposit is controlled by the structure of ductile-brittle shear belt, which controlled ore structure superpose prospective ore-bearing rock formation, studying field can form mineralize abnormaly and industrial ore body. Without magma hydrothermal activity, ductile-brittle shear action is the main dynamic origin of ore-forming in studying field.Bying a lot of work study,we can divide structure-forming into three phases, that is, pre-enrichment stage of ore-forming sediment, shearing structure and hydrothermal alteration stages, surface evolvement stages. At the same time, we recognise a series of evidence of ductile structure under microscope, such as microshear structure, S-C, shear stress shadow,etc.Ore-bearing wall rock have the weak hydrothermal alteration, mainly present disseminated, stringer vein-disseminated arsenical pyritization, micro-stringer vein and stringer network vein siliconization,ankeritization, which are associate with Au; Copper mineralize include clinoedrite, blister copper ore, chalcocite and ankerite-siliconization stringer vein in middle stage; antimonitization, calcitization, baritizati-on. Ore structure have micro-disseminated, micro-stringer vein, conglomeration disseminated,strawberry,and ore frame have automorphic-hypautomorphic granular, allotriomorphic granular.etc in late stage. Furthermore, arsenic-bearing pyrite andarsenopyritization growth-bands can be found.At present, Main industrial ore body occur in the transition and alternation position of carbonaceous microclastic rocks and carbonaceou marlite, which are composed of three ore straps, southern,northern, middle straps respectively. Northern ore strap is main industrial ore body , which have pyrite, pyrite-arsenopyrite, Sb-Au type gold ore; the main ore body is Cu-Au type gold in the southen strap.which is still exploited. Industrial ore body mainly exist in the intensity structure position.According to the bulk analyses chemistry, trace element, fluid inclusion and REE analyses from rocks or ores of Zhaishang gold deposit, it shows that ore-forming fluid have metallogenic temperature of 160-300C, fluid salinity mainly of 4.9%-10.9% (NaCleq), pressure of 30-55MPa and depth of 1.5-4.5km.Ore-forming hydrothermal fluid have the character of Na+-Ca2+-Cl-, poor K+ and Mg2+, pH is 8.23, feeble alkaline,Eh is 0.42V. Ore-forming sulfur come from sea sulfide,partly have been associate with biogenic sulfur. Ore inherit the substance composition of wall rock, LREE/ HREE is1.14-2.21, and have the character of ligh REE enrichment, plain heavy REE. The pattern of wall rock and ores are identical.Above all,we can draw a conclusion from above study by analyses of tectonic background, lithofacies geography and geochemistry of deposit:1 .The paper find some clues that the source...