藏东类乌齐-左贡成矿带地果大型石墨矿床含矿岩体时代与矿床成因

Ore-Bearing Granite Age and Genesis of Diguo Large-Scale Graphite Deposit in Leiwuqi-Zuogong Metallogenic Belt,Eastern Tibet

藏东类乌齐-左贡成矿带石墨矿近年来取得重大找矿进展,新发现以地果为代表的3处大型石墨矿床,然而地果石墨矿床的成矿地质背景、矿床成因及成矿机制尚不清楚,制约了该成矿带内石墨矿找矿潜力的评价.对地果石墨矿床开展了详细的野外调查、锆石U-Pb测年、碳同位素分析和扫描电镜等研究.锆石U-Pb测年结果显示,含矿二长花岗岩成岩年龄为239.1±1.8 Ma,其捕获锆石的年龄集中于早石炭世(347~326 Ma);碳同位素δ^13C值揭示石墨中的碳为有机成因.地果石墨矿床主要受控于含碳地层与中三叠世岩浆的侵入活动,矿床成因属于岩浆混染型和接触变质型共生的复合类型;含矿二长花岗岩侵位时限近似代表了石墨矿成矿时代,为中三叠世.区域成矿地质条件表明,类乌齐-左贡成矿带具有较好的石墨矿找矿潜力,中三叠世侵入岩与卡贡组含碳地层的交接部位是取得石墨矿找矿突破的关键地段.

In recent years,great progress has been made in the exploration of graphite deposits from Leiwuqi-Zuogong metallogenic belt,Tibet.The Diguo graphite deposit is one of the three large-scale graphite deposits which have been discovered recently.However,the geological background,genetic type and mineralization mechanism are still not clear,which has restricted the resources potential assessment of the metallogenic belt.Field geological survey,zircon U-Pb,carbon isotope analysis,and scanning electron microscopy(SEM)have been done for the Diguo deposit.Zircon U-Pb dating results show that the age of the orebearing monzogranite is 239.1±1.8 Ma,and the ages of the inherit zircon are concentrated in the Early Carboniferous(347-326 Ma).The carbon δ^13 C isotopic values reveal the organic origin of the carbon in the ore.This study shows that Diguo graphite deposit was constrained by both carbonous strata and the Middle Triassic intrusions,and belongs to the complex type which is the mix of magmatic type and contact metamorphic type.The emplacement time of the ore-bearing monzogranite represents the mineralization age of the graphite deposit approximately,which is the Middle Triassic.The regional metallogenic conditions show that the Leiwuqi-Zuogong metallogenic belt has a good exploration potential for the graphite deposits,the connection zone between the Middle Triassic intrusion and the carbonous Kagong stratum might be the key areas of the prospecting breakthrough.