辽宁小佟家堡子金矿床成矿时代探讨

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^40Ar/^39Ar法对样品从450℃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^40Ar/^39Ar快中子活化阶段加热法获得坪年龄为167Ma。绢云母^40Ar/^39Ar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^40Ar/^39Ar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“过剩剩氩”,这可能是造成K－Ar法年龄值高、范围较大的原因之一。

Study on Oreforming Epoch of Xaotongjapuli Gold Deposit , Liaoning Province Liu Guoping

Located in gold concentration area of eastern Liaoning Province , the Xiaotongjapuzi gold deposit is hosted by fine-grained leptite and marble of Paleoproterozoic meta morphosed sequence. The wall rock alterations associated with gold mineralization include silicification, hydro-sericitization and sericitization, pyritization, and ankeritization, which represent a low- te mperature mineral asse mblage. The mineralization style is unique , considered to be of the sub micron-sized disse mination type. There exists controversy on the genesis and ore-forming epoch of the deposits. K-Ar dating of rocks and ⁴⁰ Ar/³⁹ Ar technique were used to study the ore-forming epoch . The K- Ar ages oflamprophyre can be divided into two groups , i.e ', 130 ~ 1 49 Ma and 183 ~ 211 Ma , corresponding to Yanshanian and Indosinian periods respectively. The K- Ar ages of Au-bearing alteration rock range form 182 t0 272 Ma. In ⁴⁰Ar/¹⁹Ar sericite determination, Ar extraction for incremental heating analysis was performed at 8 points ( steps) from 450 'C tol 400 'C. A plateau age of 167 Ma was obtained for the fractions released by four ste ps from the se ricite sa mple se parated from gold bearing se ricite- quartz alte ration rock in the Xiaotongjapuzi gold deposit , which is consistent with the isochron age . The fractions comprised 90 % of the total Ar cu mulative release . The structural control of the deposit and the regional mag matic activity support the result of ⁴⁰ Ar/³⁹ Ar 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/³⁹ Ar dating suggests that some "excess argorf' was captured by sericite-quartz alteration rock during its formation. The "excess argorf' 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 .