A Study On The Relationship Between Structural And Magmatic Acitivity And Micro·disseminated Gold Deposits Mineralization In Zhongchuan Area, West Qinling

Zhongchuan area is located in the southern margin of the Li-Min forland basin which is caused by yangtze plate's subducting to Huabei plate,and it situated in the region between Lixian-taoping deep fault and its subfault Lixian-luoba fault.This area is undergone 3 periods large tectonic deformation from Late Paleozoic Era to Canozoic era.Early Peroid (Late Caledonia-Early Hercynian),there are several structural replacements and a group of rigional s1 face;Middle period(Late Hercynian),the basic framework of zhongchuan area is formed by the regional folding and EW trend strike-slip shearing;Late period(Indiosinia-Yanshania ),thrusting,brittle shearing and post orogenitic extending form a series of EW trend brittle faults and closed folds.There are 4 perids and 6 times magmatic intrusions.The Indosinia-Yanshania S-type syn-collision granite which intruses along the Lixian-Taoping deep fault is the most scale.The analysis results of isotope elements(sulfure,oxygen,carbon and hydrogen), trace elements,REE and the fluid inclusions indicate that the ore-forming materials maily come from the Upper Paleozoic ore-bearing turbidite foration (Liba Group and Zhongchuan Group),and the mineralizing fluids water is mainly rainwater, less magmatic and metamorphic water take part in the mineralizing processes in the early time.Ore-bodies lie in EW-NWW trend brittle faults which are located in the corel of the IV folds or near to the core of them.The folds and the multiple grade faults-joints(fissures) nets compose of the mineralizing spaces where mineralizing elements are extracted, fluids are transported and Au elements are accumulated.The gold of the deposits in Zhongchuan area is individual mineral which is located among the fissures or grains of all kinds of minerals.Most of them are microscopic golds,less are sub-microscoptic golds.The paragentic associations of gold have two series.The one is middle-low temperature associations composed of low temperature arsenopyrite and antimony-bearing minerals, the other is middle-high temperature associations mainly composed of sulfide,multiple sulfide and sulfate minerals.The mineralizing processes of micro-dissemineted gold deposits in Zhongchuan area are divided into 2 stages: preliminary accumulation of mineralizing materials stage and structural superposition and hydrothermal mineralizing fluids re-formed stage. Due to the brittle deformation in early period, Au elements mobilize and transport between different lithfaces. Regional folding and strike-slip shearing couse a large areas gold abnormality in the middle period.Thrusting in the late period is the mineralizing fluids strongly reformed stage,and many industrial deposits are formed.Indosinia-Yanshania magmatic acitivity helps to mineralize by means of changing the environment of industrial deposits. High temperature is very benefical for improving the abundance of the ore-bearing formation. The structure caused by granite intrusion is very useful for mineralizing fluids extracting,transporting and precipitating.The micro-dissemineted gold deposits in Zhongchuan area are epithermal ore deposits. They are similar to American Carlin type gold deposits and micr-disseminated gold deposits in Guizhou,Yunlan and Guangxi. Being short of typical low temperature paragentic associations and closely related to magmatic acitivity,the gold deposits in this area belong to sensu cato carlin type gold deposits(quasi-carlin type gold deposits).