西藏班公湖-怒江缝合带中段雄梅斑岩铜矿的发现及意义

摘要

通过遥感蚀变信息提取和遥感异常的实地检查,笔者在班公湖-怒江缝合带中段申扎县雄梅乡首次发现了一处斑岩铜矿.矿区铜矿化由孔雀石化花岗闪长斑岩和脱玻化英安岩组成.岩石地球化学分析表明,含矿斑岩富集大离子不相容元素Rb、Th、U、K、Pb,亏损高场强元素Nb、Ta、Ti；同时,轻稀土元素显著富集,岩体显示出埃达克岩的亲和性.锆石U-Pb LA-ICP-MS定年得出岩体的206Pb/238U加权平均年龄为(106.07±0.48) Ma,MSWD=0.92,表明矿床形成于碰撞后地壳伸展环境.雄梅斑岩铜矿距离班-怒缝合带西段的多不杂超大型斑岩铜金矿床有500km之遥,但两者的含矿斑岩却具有完全一致的岩石地球化学特征,都具有埃达克岩的亲和性,且成矿年龄相近,暗示着它们属于同一成矿系统.该矿床的发现表明,沿着班公湖-怒江缝合带确实发育有一条斑岩铜矿带,其找矿意义在于人们有可能在辽阔的藏北高原上找到更多的斑岩铜矿床.%Based on extraction of alteration information from remote sensing data and field anomaly examination, the authors found for the first time a porphyry copper deposit at Xiongmei Township of Xainza County in the middle segment of Bangonghu-Nujiang suture zone. The copper mineralization is composed of malachitized granodioritic porphyry and devitrified dacite. Petrogeochemical analysis indicates that the ore-bearing porphyry is enriched in large ion lithophile elements (LILE) Rb, Th, U, K, Pb and depleted in high field strength elements (HFSE) Nb, Ta, Ti, and also has a notable enrichment of light rare earth elements relative to middle-heavy rare earth elements. The rock bodies show an affinity to adakite. Zircon U-Pb LAICPMS dating yields a weighted 206Pb/ 238U mean age of (106.07 + 0.48) Ma.with MSWD being 0.92, indicating that the porphyry was formed in a post-collisional crust-extensional environment. Although the newly-discovered Xiongmei porphyry copper deposit is more than 500 km from the Duobuza porphry copper-gold deposit in the west segment of Bangonghu-Nujiang suture zone, the ore-bearing porphyries in the two ore deposits have consistent petrogeochemical characteristics. They both have adakite affinity and their mineralization ages are close to each other, thus belonging to the same one ore-forming system. The discovery of the Xiongmei porphyry copper deposit suggests that a porphyry copper belt does exist along Bangonghu-Nujiang suture zone. With this discovery, people have reasons to expect the discovery of more porphyry copper deposits in northern Tibetan plateau.