Study On The Genesis Of The Tassiak Copper Deposit

Sareke copper deposit is located in the west tarim basin.Considered with geotectonic view,it's the combinative region of Southwestern Tianshan and West Kunlun which is the typical sandstone-type copper deposits in the region.In this paper,we study on the geological characteristcs,mineragraphy,mineralogy,ore-forming fluid evolution and source of ore-forming materials.Based on summarizing the character of mineral geology,this article discuss the mineralization as well as combined with regional tectonic evolution history,attempting to establish the metallogenic model of Sareke copper deposit.In order to provide a useful reference for metallogenic regularity and metallogenic prediction of sandstone copper deposits in the zone.Ore deposit geological characteristics reveal that Sareke copper deposit is a typical low temperature hydrothermal deposit related to the basin brine,mineral assemblage are chalcocite +bornite + calcite,chalcopyrite + quartz + pyrite and chalcocite + chalcopyrite + calcite,wall rock alteration are mainly purple sandstone fade,focally,calcite and chloritization is present,these show low temperature hydrothermal activities characteristics.Mineralography features show that ore has close associate with structure.In the constructing development zone,the ore structure is thick vein and dense disseminated and metal sulfides have good crystal shape.In the weak tectonic zone,the ore structure are mainly fine vein,sparse disseminated and metal sulfides have bed crystal shape.Mineralogy characteristics show that mineral have geochemical petrography zoning characteristics:Silver chalcocite(strong reducing phase)?Chalcocite(reduction)?Iron chalcocite(oxidation-reduction phase)?Copper hematite(oxide),the convert of oxidation-deoxidation environment created ideal conditions for the formation of a large number of metal sulfides.The research results about the metallogenic fluid can reavel that there are rich liquid(WL type),polyphase daughter mineral fluid inclusion(S1 type),three-phase inclusions contai ning CO2(C type)and organic fluid inclusion(O type)in quartz,Micro-thermometry show that ore-forming fluid had a higher temperature and higher salinity at this stage,and the p aragenesis phenomenon of WL type,S1 type,C type and O type show that ore-forming flu-id is mixtured by multiphase fluid.There are rich liquid(WL type)and organic fluid inclu-sion(O type)in calcite.Micro-thermometry show that ore-forming fluid temperature droped at this stage.C isotope test show that C in fluid is mainly from marine carbonate,a smal 1 amount is from the sedimentary organic carbon.H-O isotope test show that ore-forming flu id is mainly from formation water in basin and a little meteoric waters.In general,the ore-forming fluid is mixtured by rich hydrocarbon reducing fluid from deep and basin oxidi-zin g fluid.With the decrease of temperature and pressure,fluid has experienced from medium-high temperature,and high salt saturated fluid to medium-low temperature unsaturated fluid.834S of molybdenite and pyrite in the Sareke copper is in the range of-15‰?-28.3‰,indicating that the sulfur are mainly derived from biological reducation of the regional strat a.Lead isotope characteristics of molybdenite illustrate that the ore-forming matters are mai nly from basin and orogenic belts.In ore-forming age respect,the phenomenon of that diabase is surrounded by contain mineral calcite vein and quartz vein explains that diabase emplacement age is the floor of mineralization age,ang diabase intrude into Cretaceous strata,so the mineralization age sho uld be later than Early Cretaceous;At the same time,calcite vein + asphalt cause fade alt eration of wall rock,The surface of asphalt shows a lot of thin film of metal sulfide.Asph alt have closely associated with mineralization andpossible migration along faults,and Metal logenic epoch is the same or slightly later than asphalt(oil and gas)in place,asphalt Re-O chronology aged is 50?57 Ma,Reflecting that the mineralization age is later then Eocene.Combined with regional tectonic evolution,Sareke copper deposit is sandstone type stratabound copper deposits that is related to the basin brine.Early Jurassic-cretaceous,basinaccept high background values the Great Wall clastic on both sides,forming a set of redconglomerate.Late cretaceous-paleogene,external fluid dissolve evaporite in the basin and formation high salinity brine in the basin,at the same time,the basin brine extract metalion in wall rock in cecycle,forming the high metal content of the basin brine;In the Paleogene,due to regional orogeny,deep basin reducing fluid mixed with high salinity brine,oxidation basin brine in boulder bed,then form layered,stratified,lenticular orebody which have the same occurrence with wall rock.