桂东大瑶山成矿带新坪矿区花岗斑岩与金多金属成矿作用关系

摘要

The Xinping granite-porphyry occurring in the Xinping gold mining area is located in the middle part of the Dayaoshan Au metallogenic belt,eastern Guangxi Province.During our recent field geological survey,a gold deposit was found in contact zone between the porphyry and its wall rocks,whereas quartz-vein-typed molybdenum orebody and mineralized spot were also firstly recognized inside of the intrusion.These suggest that the Au-Mo-polymetallic mineralization is closely related to the granitic igneous activity.Zircons of the granitic porphyry are analyzed using LA-ICP-MS U-Pb isotopic method,which gives a weighted mean 206pb/238U age of (462.9-6.4) Ma.It reveals a mid-Ordovican magmatic timing,providing a lower constraint for the mineralization age.The Xinping porphyry samples show REE characteristics akin to those of the granite-porphyries occurring in nearby Gupao,Yuanzhuding and Dali minging areas,indicative of similar nature of source rocks and petrogenesis.Thus,a further potential is predicted by this study in exploring porphyry-related gold and molybdenum deposits in the Xinping gold field.%新坪花岗斑岩位于桂东大瑶山成矿带中部新坪金矿区内.在野外地质观察的基础上,报道了在该新坪斑岩体接触带附近发现金矿体并首次在岩体内部发现石英脉型辉钼矿(化)体,认为新坪花岗斑岩体与金多金属矿化关系密切.新坪花岗斑岩LA-ICP-MS锆石U-Pb同位素定年结果表明,该斑岩体形成于早古生代奥陶纪(462.9 ±6.4) Ma,属加里东期花岗岩类,因此与岩体有关的金矿化、铜钼矿化时间不会早于奥陶纪.岩体稀土元素分析结果显示,新坪花岗斑岩与邻近的古袍、圆珠顶、大黎矿区花岗斑岩体具有相似的稀土元素分布特征,可能为同源岩浆不同阶段的演化产物,说明新坪花岗斑岩体具有一定的金、钼等多金属成矿潜力.通过以上综合研究分析,初步认为新坪矿区具有寻找斑岩型金矿以及钼矿床的找矿前景.