东川铜矿硅质角砾^(40)Ar-^(39)Ar定年探讨  

^(40)Ar-^(39)Ar dating techniques for a hydrothermal siliceous breccia sample from the Luoxue Mine, Dongchuan Copper Deposits, Yunnan,by crushing in vacuum and then by stepped heating on its powders

作　　者：邱华宁[1] 朱炳泉[1] 孙大中[1] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球化学》2000年第1期21-27,共7页Geochimica

基　　金："九五"国家攀登预选资助!95-预-25;中国科学院大型仪器功能开发项目!9804A-077-26;中国科学院广州分院测试基金

摘　　要：为了探索热液成因含微量钾矿物40Ar－39Ar定年的最佳实验方案，从而获得可信的成矿年龄，本文进行了东川落雪铜矿稀矿山矿段落雪组角砾状矿石硅质角砾流体包裹体及其固体粉末的40Ar-39Ar对比实验：先采用真空击碎技术提取硅质角砾（DC-5-2）的流体包裹体进行40Ar－39Ar分析，接着对击碎后的固体粉末样品进行常规的40Ar－39Ar阶段加热分析（170～800℃）。与以往样品的流体包裹体之逐渐下降的年龄谐相反，此样品真空击碎分析形成了逐渐上升的阶梯形年龄谱，数据点在40Ar／36Ar－39Ar／36Ar图解上明显的线性关系被认为是两个气体端员混合的结果。此样品粉末阶段加热分析得出了有意义的成矿年龄数据：第10～16阶段（600～800℃）形成年龄坪（对应释出的39Ar占71％），坪年龄为（691±7）Ma，其对应的40Ar－39Ar反等时线年龄为（696±57）Ma，代表了硅质角砾中原生的碱性长石和软钾镁矾（？）微晶的结晶年龄。此等时年龄与汤丹铜矿落雪组之脉状铜矿石英DC－51-1Q流体包裹体40Ar-39Ar等时年龄（712±33）Ma一致，再次证实东种铜矿的主成矿期为晋宁晚期—澄江早期。本文工作表明，对硅质角砾粉末样品进行40Ar-39Ar阶段加热分析是另一种可能获得有意义成矿年龄的有效途径。To investigate the difference of 40Ar-39Ar dating results between the fluid inclusions by crushing and its powder by heating, a hydrothermal siliceous breccia sample from the Luoxue Mine, Dongchuan Copper Deposits, Yunnan, was analyzed with 40Ar-39Ar method hy crushing in vacuum and then by stepped heating on its powder through directly heating outside the stainless steel tube which contained the sample during crushing (controlling the temperature below 800℃ because of the steel tube heater).The crushing experiment yields a rising-up age spectrum consisting of about three plateaus: 40 ~ 140 Ma,650 ~ 850 Ma and 1000 ~ 1170 Ma (Fig. 2), which is different from those of other quartz samples by crushing experiments with the shapes of falling-down or flat spectra. This kind of age spectrum may be formed by two or three periods of fluid inclusions. The apparent age of 39 Ma of the second stage strongly shows the Himalayan fluid interruption, which corresponds to the fact of the late calcite vein observed under microscope. The correlative diagram of 40Ar-39Ar vs. 39Ar/36Ar based on the argon isotope data by crushing yields a line (Fig. 3), which indicates the argon isotopes were mixed by two endmembers, the Jinning-Chengiiang fluid inclusions and the Himalayan fluid inclusions. The mixed line, corresponding to a non-significant 'isochron' age of 1193 Ma, is mainly controlled by the end of Jinning - Chengjiang fluid inclusions.In order to correctly interpret the age spectrum of the heating experiment for the powder sample, the sample was analyzed by EPMA and XRD. The EPMA K-Kα image (Fig. 1) shows microcrystals of K-rich minerals distributing among the micro-quartz grains. The XRD analysis indicates the K-rich minerals are the original minerals of alkali feldspar, picromerite (?) and the altered minerals of illite and montmorillonite. A significant mineralization age is obtained from the stepped heating experiment for the powder after extracted the fluid inclusions. The age spectrum for the first 9 stages shows U-shap

关 键 词：硅质岩 流体包裹体 铜矿 云南 氩40-氩39定年 

分 类 号：P618.410.2[天文地球—矿床学] P597[天文地球—地质学]