小秦岭东桐峪金矿Q8501脉锆石U-Pb年龄及其地质意义  

Zircon U-Pb Ages and Their Geological Significance of the Dongtongyu Gold Deposit, Xiaoqinling Area, China

作　　者：张国瑞[1] 徐九华[1] 林龙华[1,2] 魏浩[1] 吴晓贵[1] 惠德锋 

机构地区：[1]北京科技大学资源工程系,北京100083 [2]中国五矿集团公司,北京100010 [3]潼关中金黄金矿业有限责任公司,陕西潼关714300

出　　处：《大地构造与成矿学》2015年第4期743-754,共12页Geotectonica et Metallogenia

基　　金：全国危机矿山接替资源找矿专项典型矿床及成矿规律总结研究项目(20109903);国家自然科学基金项目(40972066)联合资助

摘　　要：东桐峪金矿是小秦岭金矿田主要的石英脉型金矿之一,其主矿脉Q8501的脉石英及其脉旁蚀变片麻岩中含有丰富的变质锆石。岩相学、CL图像特征表明,这些锆石呈半自形–它形,无紧闭振荡环带构造,常见固体包裹体和次生的流体包裹体。锆石具有陡直的重稀土富集配分模型, LREE/HREE比值很低为0.02～0.14,具显著的Ce正异常（δCe=5.6～96.3）和Eu负异常（δEu=0.04~0.77）。大部分锆石的Th/U比值较低,特别是第1组（Th/U=0.14～0.56,平均0.30）；Nb/Ta比值很小（0.06～0.31）,普通铅含量也很低。推测变质锆石是在石英脉形成过程中从脉侧蚀变片麻岩中捕获的。LA-ICP-MS 锆石微区U-Pb定年分析表明, Q8501脉第1组锆石的207Pb/206Pb表观年龄为1776～1877 Ma,加权平均年龄为1810±17 Ma,可能代表了华北克拉通中部造山带与碰撞后伸展作用有关的热事件；第2组锆石207Pb/206Pb表观年龄为1899～1922 Ma,加权平均年龄为1910±11 Ma,记录了小秦岭地区相当于五台–中岳期的第二期区域变质事件。小秦岭含金石英脉的形成可能跨越了很长的地质年代,金（钼）矿化主要发生在中生代,而载体石英脉有些可能在古生代就形成了。The Dongtongyu gold deposit is one of the main lode gold deposits in the Xiaoqinling gold field. A great number of metamorphic zircon grains were retrieved from the vein Q8501. Petrography and CL images show that the zircon grains are subhedral, xenomorphic crystals, without compactly closed oscillation zonation. Solid inclusions and secondary fluid inclusions are common in these zircon grains. Zircon grains from the quartz vein Q8501 have rather low LREE/HREE （0.02-0.14） ratios showing and steep HREE patterns, significant positive Ce anomalies （5.6-96.3） and negative Eu anomalies （0.04-0.77）. The ratio of Th/U is relatively low, especially for the first group of zircon （0.14-0.56, average 0.30）. The zircon grains have Nb/Ta ratio of 0.06-0.31 and low common Pb contents. It can be inferred that the metamorphic zircon grains were captured from nearby wall rocks. LA-ICP-MS zircon U-Pb dating results show that 207Pb/206Pb ages of the first zircon group are 1776-1877 Ma with a weighted average age of 1810±17 Ma, which is consistent with the post-collisional extention in the central part of the North China Craton. 207Pb/206Pb apparent ages of the second zircon group are 1899-1922 Ma with a weighted average age of 1910±11 Ma, which may relate to another phase of regional metamorphic event in the Xiaoqinling area equivalent to Wutai-Zhongyue movement. The formation of auriferous quartz veins may have spanned a much longer geological ages： the gold （molybdenum） mineralization occurs mainly in the Mesozoic, whereas some carrier quartz veins may be formed in the Paleozoic era.

关 键 词：锆石U-PB定年 变质锆石 含金石英脉 小秦岭 

分 类 号：P597[天文地球—地球化学] P612[天文地球—地质学]