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引用本文:向安平,陈毓川,佘宏全,李光明,李应栩. 内蒙古苇莲河石英脉型黑钨矿赋矿花岗岩成岩时代、地球化学特征及其地质意义[J]. 中国地质, 2018, 45(5): 963-976.
XIANG Anping,CHEN Yuchuan,SHE Hongquan,LI Guangming,LI Yingxu. Chronology and geochemical characteristics of granite in Weilianhe of Inner Mongolia and its geological significance[J]. Geology in China, 2018, 45(5): 963-976(in Chinese with English abstract).
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内蒙古苇莲河石英脉型黑钨矿赋矿花岗岩成岩时代、地球化学特征及其地质意义
向安平1,2, 陈毓川2, 佘宏全2, 李光明1, 李应栩1
1.中国地质调查局成都地质调查中心, 四川 成都 610081;2.中国地质科学院矿产资源研究所, 北京 100037
摘要:
内蒙古苇莲河地区是近年来进行黑钨矿找矿勘查的区域,位于兴蒙造山带中东部,大兴安岭主脊中部。矿床类型可能为典型的石英脉型黑钨矿。黑钨矿石英脉以近于直立(75°)的平直脉体产于花岗岩内或岩体与地层的外接触带,脉体向下尖灭于岩体内部,主要的矿化蚀变类型有钾长石化、绿帘石化、绢云母化、硅化等。本文在初步研究矿床地质特征的基础上,对成矿岩体——花岗岩进行高精度LA-ICP-MS锆石U-Pb测年及地球化学分析。UPb测年结果显示,206Pb/238U谐和年龄为(145±1)Ma,加权平均年龄为(143±1)Ma。地球化学特征显示,岩体具有典型的富硅、富碱特征,SiO2平均74.13%,(Na2O+K2O)平均9.44%,Na2O/K2O平均0.95,属高钾钙碱性系列岩石;Al2O3平均为12.91%,铝饱和指数A/CNK全部靠近1.0,为准铝质到弱过铝质花岗岩类,相对贫Mg;稀土总量较低,∑REE变化于122.02×10-6~235.79×10-6,表现为右倾稀土元素配分模式,弱富集轻稀土,并具有强烈的负铕异常,高场强元素Th、U、Nd、Hf明显富集,而Ba、Sr、P、Ti、Nb显著亏损;低Sr,高Yb,Nb/Ta比值变化于12.12~13.78,强不相容元素Rb高度富集,Rb/Sr比值1.25~14.58,Ti/Y比值42.49~114.48,Ti/Zr比值5.20~8.45;总体为壳源岩浆的特征。苇莲河花岗岩侵位时代为早白垩世,属燕山期构造岩浆活动的产物,其可能的形成构造背景为古太平洋板块斜向俯冲后,后退过程中的伸展滑塌背景。
关键词:  内蒙古  苇莲河  石英脉型  黑钨矿  锆石LA-ICP-MS年代学  地球化学
DOI:10.12029/gc20180506
分类号:P597;P588.12+1
基金项目:国家基础科研项目(2013CB429800)、中国地质调查局综合地质调查项目(121201010000150014)联合资助。
Chronology and geochemical characteristics of granite in Weilianhe of Inner Mongolia and its geological significance
XIANG Anping1,2, CHEN Yuchuan2, SHE Hongquan2, LI Guangming1, LI Yingxu1
1.Chengdu Center of China Geological Survey, Chengdu 610081, Sichuan, China;2.Institute of Mineral Resources, Chinese Academy of Geology Sciences, Beijing 100037, China
Abstract:
The Weilianhe W deposit in eastern Ujumchin of Inner Mongolia is a quartz-vein type deposit in the mid-eastern part of the Central Asian Orogen. Based on spatial relationships, the authors revealed that granite is closely associated with mineralization. The authors conducted precise laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) U-Pb zircon dating and geochemical analysis of the granite. The U-Pb dating shows that the granite is (145 ±1)Ma, and the weighted average age is (143±1)Ma. Major and trace element geochemistry shows that the granite is characterized by high SiO2 and K2O content, a "rightinclined" shape of the chondrite normalized REE patterns, enrichment of large ion lithophile elements (LILEs), and depletion of high field strength elements (HFSEs) such as Nb, P, Ba. The granite is high-K calc-alkaline, has a strong negative Eu anomaly (Eu/Eu*=0.22-0.42), low P2O5 content, A/CNK near the value of 1, enriched in large-ion lithophile elements (LILEs such as Th, U, Nd, and Hf), and notably depleted in Ba, Sr, P, Ti, and Nb. These characteristics define the Weilianhe granite as a highly fractionated peraluminous granite. According to the granite age and the characteristics of granite, the authors hold that the Weilianhe deposit is related to a major Early Cretaceous mineralizing event in China known as the Yanshanian movement. The tectonic setting for the ore deposit was the post-tectonic stretching setting after the oblique subduction of the Pacific plate.
Key words:  Inner Mongolia  wolframite  geochronology  quartz vein  granite  LA-ICP-MS  geochemistry  Weilianhe