Study On The Relationship Between Gold And Copper Mineralizations Of The Katabasu Au-Cu Deposit Western Tianshan

The Katebaasu deposit is a newly discovered large-scale gold(copper)deposit in Xinjiang,China,in the "Asian Gold Belt" of the Western Tianshan Mountains.The proven gold reserves are 89 tons(average grade is 4.84 g/t)and copper reserves are 80,000 tons(grade is 0.65%),however,the relationship between gold and copper mineralization is doubtful and has attracted much attention.Based on field and indoor microscopic observations,this paper studies the relationship between gold and copper mineralization from the space-time-matter system by using Re-Os isotope dating and Cu-S-Os isotope tracing techniques,and the main results and understandings are as follows:(1)Spatially,prospecting line profiles at different locations in the eastern and Western sections show that gold(copper)orebodies mainly occur in the eastern of the mining area,and independent copper orebodies appear in the central and western of the mining area.The ore samples collected from the eastern and Western sections show that copper ores are mostly skarn ores,skarn occurs in the contact position between granite and limestone strata,and gold ores are dominated by pyritized ores hosted in cataclastic monzonitic granite.Microscopically,copper is mainly accreting with skarn minerals such as garnet,chlorite and epidote as chalcopyrite.There is a small amount of gold in the ores,which is unevenly distributed and may be a late mechanical mixing.Gold occurs mainly in the pyrite and between gangue mineral grains such as quartz,calcite and plagioclase in form of inclusions and gold in fissure.The superimposed ore sections in the central part show the characteristics of coexistence of gold-copper orebodies,and the trend changes from west to east as copper-copper-gold-gold-gold-copper-gold.(2)In terms of time,the Katebasu deposit can be roughly divided into two periods.The characteristics of early copper mineralization are obviously skarn mineralization,and characteristics of the late gold mineralization accompanied by tectonic movement are hydrothermal alteration mineralization.The Re-Os dating of chalcopyrite in the skarn of the western section yields an isochron age of 355±10 Ma(MSWD=5.3,n=5)and a weighted average age of 355.3±4.0 Ma.Compared with the golden metallogenic age of 310-322 Ma obtained by previous studies,it is obviously not of the same period and accords with the characteristics of two metallogenic periods.At the same time,the time of copper mineralization coincides with that of granite intrusion.(3)Materially,the copper isotope of chalcopyrite in western sections varies from 0.25‰ to 0.49‰,which is similer with I type granite.In terms of they are similer in space and time,their material might be provided by monzogranite.The copper isotope in eastern section varies from-0.12‰ to 0.08‰ and the pyrite,the main gold-bearing mineral,contains 187Os(187Os/188Os)of high radiogenic origin.Its weighted average is 1.449(+0.052),which indicates that the metallogenic metals may come from the crust of the Middle Tianshan Mountains.The results of sulfur isotope in western section is 9.1~11.2‰ and 6.8~8.8‰ for east.Its sulfur might come from the layers and are taken by magma and hydrothermal fluid.(4)Based on the above analysis,the early copper mineralization in Katebasu occurs with magma intrusion.Copper ore body formed in the western skarn with copper in magma and sulfur in layers.Tectonic hydrothermal fluid produced by late tectonic activity extracted mineralizing materials from strata and enriched them in the eastern part of the deposit.Katebasu experienced copper mineralization related to early Carboniferous monzonitic granite intrusion and related skarn mineralization,and gold(copper)mineralization related to tectonic-alteration in late Carboniferous.Katebasu deposit belongs to skarn-tectonic altered rock type copper-gold deposit.