安徽宣城茶亭铜金矿床赋矿石英闪长玢岩锆石U-Pb年龄及岩石成因  

Zircon U-Pb Age and Genesis of the Ore-bearing Quartz-dioritic Porphyries in the Chating Cu-Au Ore Deposit,Xuancheng City,Anhui Province

作　　者：江峰[1] 徐晓春[1] 钱仕龙 王蒙[1] 杨前国 李凯[2] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]安徽省地质矿产勘查局322地质队,马鞍山243000

出　　处：《高校地质学报》2017年第4期591-605,共15页Geological Journal of China Universities

基　　金：国家自然科学基金(41472066);安徽省国土资源科技项目(2014K3)资助

摘　　要：安徽宣城茶亭Cu-Au矿床是长江中下游成矿带内新发现的一个斑岩型矿床。文章对该矿床赋矿石英闪长玢岩进行了锆石LA-ICP-MS U-Pb同位素年龄及岩石主量与微量元素、Sr-Nd同位素和锆石Lu-Hf同位素分析,旨在探讨其岩浆起源和岩石成因。锆石U-Pb同位素年龄测定结果显示,赋矿石英闪长玢岩形成年龄为137.8±1.3 Ma(MSWD=0.72),为早白垩世岩浆活动的产物。岩石主量元素显示其具富碱富钠特征,为亚碱性准铝质高钾钙碱性系列岩石。岩石微量元素显示其富集大离子亲石元素K、Rb、Sr、Ba和轻稀土元素,弱富集Zr和Hf,亏损高场强元素Nb、Ta、Ti等,稀土元素配分型式表现为无明显Eu异常。岩石(^(87)Sr/^(86)Sr)_i值介于0.706403~0.707903之间,ε_(Nd)(t)值介于-7.4^-13.3之间(t=137.8 Ma)。锆石ε_(Hf)(t)值为-4.25^-11.75(t=137.8 Ma)。主量元素、微量元素、Sr-Nd同位素和锆石Hf同位素地球化学特征均指示,赋矿石英闪长玢岩可能是富集岩石圈地幔与扬子下地壳物质部分熔融形成的岩浆混合后侵位的产物。对比长江中下游成矿带断隆区和断凹区侵入岩发现,宣城茶亭矿床赋矿石英闪长玢岩与长江中下游成矿带断凹区(宁芜、庐枞矿集区等)侵入岩,无论是岩石主量与微量元素地球化学特征还是同位素地球化学特征都存在一定差异,而与断隆区(铜陵矿集区)赋矿岩浆岩表现出一致性,暗示宣城茶亭矿床赋矿石英闪长玢岩与长江中下游成矿带断隆区岩浆岩有着基本一致的成岩物质来源和岩石成因机制,是富集岩石圈地幔熔融岩浆及其引起的下地壳物质部分熔融岩浆发生岩浆混合作用并伴随着一定程度的分离结晶作用进而浅成侵位形成。The Chating Cu-Au deposit in the Xuancheng City of Anhui Province is a newly discovered porphyry deposit in the Middleand Lower Yangtze River Valley Metallogenic Belt(MLYB)during recent years. In this paper,we conducted zircon LA-ICP-MSU-Pb dating,major elements,trace elements(including REEs),Sr-Nd isotopes and zircon Hf isotope study on the ore-bearingquartz-dioritic porphyritic intrusive rocks from the drilling holes of the ore deposit,in order to reveal its geological and geochemicalcharacteristics,and to discuss petrogenesis of the rocks. The zircon U-Pb age for the ore-bearing quartz-dioritic porphyry is 137.8±1.3 Ma(MSWD=0.72),suggesting that it was generated during Early Cretaceous. The ore-bearing quartz-dioritic porphyries have highcontents of alkalinity,especially with Na enrichment,and can be grouped into sub-alkaline and high-K calc-alkaline series. They areenriched in light rare earth elements and large ion lithophile elements(e. g.,K,Rb,Sr,Ba),depleted in high field strengthelements(e. g.,Nb,Ta,Ti),and show unconspicuous negative Eu anomalies. These rocks have(^(87) Sr/^(86) Sr)iratios ranging from0.706403 to 0.707903,show low ε_(Nd)(t)values ranging from-7.4 to-13.3,and with variable zircon ε_(Hf)(t)values of-4.25^-11.75(t=137.8 Ma). Compared with the igneous rocks in other districts along the MYLB,the geochemical features and the emplacement ages ofthe ore-bearing rocks from the Chating Cu-Au ore deposit are quite different from those in the fault depression zone(e. g.,the Ningwuand the Luzong basins). Rather,they are much similar to those in the fault uplift zone(e. g.,the Tongling ore concentrated area).According to the above geological and geochemical characteristics,it is concluded that the magma of the ore-bearing quartz-dioriticporphyries were generated by mixing of enriched lithospheric mantle-derived magma and lower crust-derived magma. They might haveexperienced the same petrogenetic process as those of the Tongling ore concentrated area in the fault uplift of MYLB,that is,themagmas we

关 键 词：岩石成因 U-Pb年龄 SR-ND-HF同位素 斑岩铜金矿床 安徽宣城茶亭 

分 类 号：P597.3[天文地球—地球化学] P618.51[天文地球—地质学]