滇西马厂箐斑岩型铜钼(金)矿床成岩成矿时代研究

Geochronological study of magmatic intrusions and mineralization of Machangqing porphyry Cu-Mo-Au deposit,Western Yunnan Province

滇西马厂箐铜钼(金)矿床是金沙江—哀牢山构造带与喜马拉雅期富碱斑岩有关的典型斑岩型矿床之一。富碱斑岩侵入体为多期、多阶段岩浆活动形成的复式岩体,已有的研究资料表明岩浆活动时限在64～29Ma。文中提供的锆石LA-ICP-MS U-Pb和辉钼矿Re-Os同位素年代学研究资料显示,马厂箐含矿岩体锆石U-Pb年龄(封闭温度约800℃时)为(37.93±0.82)Ma,代表了富碱斑岩的成岩年龄;辉钼矿的Re-Os年龄(封闭温度约500℃)为(34.72±0.5)Ma,代表成矿时代。该研究结果与前人确定的晚期富碱斑岩岩浆活动的时间(32 Ma)相近,也与前人获得的蚀变黑云母K-Ar定年(封闭温度300℃)结果(35.1±0.8)Ma相近,因此可以认为成矿作用与岩体快速冷却过程中发生成矿流体大量分离和出溶有关。成岩作用与成矿作用的时间跨度大约为2 Ma。因此,金沙江—哀牢山多金属成矿带的斑岩型铜钼矿床是与富碱斑岩成岩作用近同期成矿作用的产物,成矿作用时限集中在40～35 Ma左右。

The Machangqing porphyry Cu-Mo-Au deposit is one of the typical deposits associated with the alkaline-rich porphyry in the Jinshajiang-Ailaoshan tectonic belt of the Himalayan epoch.Alkalite intrusive rock is a superimposed intrusive complex formed by multiperiodic and multistage magmatic activities.The time limit of magmatic activity is 64-29 Ma.In situ zircon LA-ICP-MS U-Pb ages and molybdenite Re-Os ages indicate that the age of ore-bearing granite prophyry is 37.93±0.82 Ma,whereas the mineralization age is 34.72±0.5 Ma,which shows that the mineralization mainly related to the later magmatic activity.The closeness among zircon U-Pb,molybdenite Re-Os,and K-Ar ages in the Machangqing porphyry indicates that the ore-forming system cooled from about 800 ℃（zircon crystallization temperature） through 500 ℃（closure temperature for Re-Os in molybdenite） to below 300 ℃（closure temperature for Ar in biotite） in a very short period.The duration of the Machangqing giant ore-forming system is less than 2 Ma.The porphyry copper and molybdenum deposit of Jinshajiang-Ailaoshan mineralization belt was the product of the syn-mineralization,and the mineralization time limit focused on 40-35 Ma.