云南金满、水泄铜多金属矿床的Ar-Ar同位素年代学及其地质意义

Ar-Ar Isotopic Ages of Jinman and Shuixie Copper Polymetallic Deposits in Yunnan Province,and Their Geological Implications

滇西北兰坪中新生代盆地西缘铜多金属成矿带受澜沧江断裂带控制 ,赋矿围岩为二叠系至第三系 ,主要由下二叠统经上三叠统到上侏罗统砂岩、粉砂岩和页岩组成的碎屑岩建造、火山岩建造及含盐红色碎屑岩建造 ,矿体主要以脉状或透镜状产出。对该成矿带上的金满铜矿床和水泄铜 (钴 )矿床主成矿阶段的石英进行了4 0 Ar- 39Ar快中子活化法同位素地质年龄测定 ,获得坪年龄分别为 5 6 .7± 1.0Ma和 5 9.2± 0 .8Ma ,且各自与对应的等时年龄在误差范围内完全一致 ,都可以代表矿石的形成年龄。综合已发表的有关兰坪盆地西缘及盆地内部铜、多金属矿床成岩成矿同位素年代学研究结果 ,表明两矿床与区域矿床具有一致的成矿时代 ,反映区域铜、多金属矿床均形成于喜马拉雅造山运动早期统一的地球动力学背景之下。

Lanping basin of the northwestern Yunnan province is an important Cu,Ag,polymetallic mineralization-concentrated area in the western China. There are many large,middle and small scale Cu-polymetallic deposits located in three metallogenic belts of the basin. The metallogenic belt of the western border of the basin is characterized by enrichment in copper and controlled by Lancangjiang fault belt. The host strata of the deposits in the metallogenic belt are Perimian system to Tertiary system which are mainly composed of clastic rock formation,volcanic rock formation and red,salty clastic rock formation. The occurrences of the ore bodies are mainly veins,networks and lens-shaped. In order to know the regional metallogenetic epoch and regularities,quartz from the major ore-forming stage of Jinman copper deposit and Shuixie copper (cobalt) deposit was analyzed by the 40 Ar- 39 Ar fast-neutron activation dating technique,which gives well-defined plateau ages of 56.7±1.0Ma and 59.2±0.8Ma,respectively. Each isochron age is corresponding to the plateau age respectively within the range of error. The Ar-Ar ages represent the forming ages of quartz,i.e.,the forming ages of the ores of Jinman and Shuixie deposits. Based on the research results of the isotopic geochronology on the mineralization and the magmatism of the Cu,Ag,polymetallic deposits in the western border and other parts of the Lanping basin,it is concluded that the isotopic ages of these two deposits are consistent with those of other deposits in the region,and the mineralization epoch is basically synchronous in regional mineralization of the basin. The copper,polymetallic deposits were formed in a unitary geodynamic background. The mineralization epoch of the deposits is the earlier stage of Himalayan orogeny. The formation of the deposits in the basin is constrained by the evolutionary geological events of the structure and thermal regime in the same time.