藏东芒康县巴达铜金矿床地质特征及找矿方向研究

Geological characteristics and prospecting of the Bada Cu-Au deposit in Mangkang County,East Tibet

巴达铜金矿位于藏东富碱斑岩带南段,是藏东地区近年来新发现的大型铜金矿。虽然对巴达铜金矿开展了大量勘查工作,但对该矿床的成因尚未取得共识。本文基于详细的野外调研、岩心与坑道编录及系统的镜下鉴定,对巴达铜金矿床地质特征进行研究。巴达矿床主要产于石英二长斑岩中,局部产于斑岩和砂岩地层的接触带内。矿床发育的围岩蚀变主要为青磐岩化、钾化、绢英岩化,高岭土化、蛋白石化、蒙脱石化次之,蚀变分带从内向外依次为钾硅酸盐化带、绢英岩化带、青磐岩化带、高岭土化带,铜金矿体主要赋存于钾硅酸盐化和绢英岩化带内,铜矿化主要以黄铜矿形式产出,金矿化主要以银金矿形式产于白云石±石英+细粒黄铁矿±黄铜矿脉中,铜矿化与金矿化呈正相关,矿体的产出受北西向逆冲断层的控制。与典型斑岩和浅成低温热液矿床不同,巴达铜金矿化主要产于白云石±石英+黄铁矿脉中;矿床内既发育碳酸盐、伊利石、绢云母和黄铁矿、黄铜矿、方铅矿、黝铜矿、低FeS闪锌矿等一套中硫型浅成低温热液矿床的蚀变矿物组合,又发育符合碱性斑岩系统的特征矿物赤铁矿。基于以上特征判断,巴达铜金矿矿床成因类型应为与富碱斑岩有关的浅成低温热液矿床,巴达铜金矿矿床成因的厘定,为下一步找矿提供了理论指导。

The Bada Cu-Au deposit,a newly discovered large Cu-Au deposit,is located in the southern part of the alkali-rich porphyry belt in East Tibet.The metallogenic features of the Bata Cu-Au deposit are not yet clear.Based on detailed field observation,geological logging and systematic microscopic examination,we studied the geological characteristics of the Bada Cu-Au deposit.The deposit developed within the quartz monzonite porphyry intrusion while the surrounding sandstones are controlled by a NW-striking thrust fault.We identified the alteration types,including potassic,phyllic and propylitic alterations,and delineated the alteration zones.We also found small quantity of localized secondary minerals such as kaolinite,opal and montmorillonite.The Cu-Au orebody mainly occurs in the potassic and phyllic alteration zone,showing positive correlation between Cu and Au mineralization.Copper mineralization mainly produces chalcopyrite,while gold occurs primarily as fine Ag-Au grains in dolomite±quartz+pyrite±chalcopyrite vein.Both alteration and mineralization are centralized along the NW-striking thrust fault.Unlike typical porphyry and epithermal deposit,mineralization in the Bada Cu-Au deposit mainly occurs in dolomite±quartz+pyrite vein,resembling the low temperature alteration assemblage.The alteration and mineralization associated minerals,such as carbonate,illite,sericite,galena,pyrite,chalcopyrite and tetrahedrite,are found in the ore district,consistent with intermediate sulfidation epithermal deposits.Moreover,hematite is ubiquitous,indicating an alkaline porphyry system.Thus,we conclude that the Bada Cu-Au deposit belongs to alkali-rich porphyry related epithermal deposit.Its metallogenic mechanism can be used to guide the next prospecting exploration.