辽宁小佟家堡子金矿床成矿时代探讨  

Study on Ore-forming Epoch of Xiaotongjapuzi Gold Deposit, Liaoning Province

作　　者：刘国平[1] 艾永富[2] 

机构地区：[1]北京矿产地质研究所,北京100012 [2]北京大学地质学系,北京100871

出　　处：《矿床地质》2002年第1期53-57,共5页Mineral Deposits

基　　金：有色地质总局重点科研项目 (编号 :96D_9)资助

摘　　要：小佟家堡子金矿床位于辽东金矿集中区 ,为产于古元古代变质岩系中的微细粒浸染型金矿 ,矿床类型独特。文章采用了绢云母4 0 Ar/ 3 9Ar法对样品从 45 0℃到 140 0℃进行了 8个阶段的加热分析。从绢云母石英交代岩型金矿石中挑选出与金矿化密切共生的绢云母单矿物 ,通过4 0 Ar/ 3 9Ar快中子活化阶段加热法获得坪年龄为 16 7Ma。绢云母4 0 Ar/ 3 9Ar法测年结果与矿床的控矿构造特征、区域岩浆活动的演化规律相吻合 ,进一步证明了该金矿床为燕山期成矿。同时 ,绢云母4 0 Ar/ 3 9Ar的马鞍形年龄谱还表明 ,在绢云母石英交代岩形成过程中 ,可捕获部分“过剩氩” ,这可能是造成K_Ar法年龄值高。Located in gold concentration area of eastern Liaoning Province, the Xiaotongjapuzi gold deposit is hosted by fine-grained leptite and marble of Paleoproterozoic metamorphosed sequence. The wall rock alterations associated with gold mineralization include silicification, hydro-sericitization and sericitization, pyritization, and ankeritization, which represent a low-temperature mineral assemblage. The mineralization style is unique, considered to be of the submicron-sized dissemination type. There exists controversy on the genesis and ore-forming epoch of the deposits. K-Ar dating of rocks and 40Ar/ 39Ar technique were used to study the ore-forming epoch. The K-Ar ages of lamprophyre can be divided into two groups, i.e., 130～149 Ma and 183～211 Ma, corresponding to Yanshanian and Indosinian periods respectively. The K-Ar ages of Au-bearing alteration rock range form 182 to 272 Ma. In 40Ar/ 39Ar sericite determination, Ar extraction for incremental heating analysis was performed at 8 points (steps) from 450℃ to 1?400℃. A plateau age of 167 Ma was obtained for the fractions released by four steps from the sericite sample separated from gold-bearing sericite-quartz alteration rock in the Xiaotongjapuzi gold deposit, which is consistent with the isochron age. The fractions comprised 90% of the total Ar cumulative release. The structural control of the deposit and the regional magmatic activity support the result of 40Ar/ 39Ar spectral method, so the ore-forming process must have taken place in Yanshanian period. The determination of the ore-forming age provides sound evidence for the genesis of the deposits. Meanwhile, the result of 40Ar/ 39Ar dating suggests that some 'excess argon' was captured by sericite-quartz alteration rock during its formation. The 'excess argon' could be one of the causes responsible for the fact that the K-Ar ages are relatively old and are distributed in a wide range.

关 键 词：金矿床 成矿时代 燕山期 氩同位素 岩浆岩 绢云母 

分 类 号：P618.51[天文地球—矿床学]