安徽铜陵新桥铜硫金矿床的成因:来自两类黄铁矿微形貌学、地球化学特征的证据  

LA-ICP-MS in situ trace elements and FE-SEM analysis of pyrite from the Xinqiao Cu-Au-S deposit in Tongling,Anhui and its constraints on the ore genesis

作　　者：肖鑫[1] 周涛发[1] 范裕[1] 谢杰[1] 张乐骏 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]Centre of Excellence in Ore Deposit,University of Tasmania

出　　处：《岩石学报》2016年第2期369-376,共8页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41320104003;41172086;41172084;40830426);中国地质调查局地质调查工作项目(1212011121115;1212011220243;12120114039701);国家深部专项(Sino Probe-03-02-05);安徽省公益性地质工作项目(2011-20)联合资助

摘　　要：新桥矿床是长江中下游成矿带铜陵矿集区内大型铜金硫矿床。本文以矿床中的黄铁矿为研究对象,在详细的野外观察和室内鉴定的基础上,将矿床中的黄铁矿分为胶状黄铁矿（Py I）和半自形-自形黄铁矿（Py II）两种类型。通过场发射扫描电镜（FE-SEM）和等离子激光质谱（LA ICP-MS）对两类黄铁矿的矿物相、形貌、微结构和微量元素成分进行研究。FE-SEM分析结果表明,Py I基本由极细粒黄铁矿组成,以自形-半自形立方体晶形为主,粒径大约100~500nm,而Py II主要为粒度为50~100μm,以八面体和五角十二面体晶形态为主,两类黄铁矿的形貌和微结构特征明显不同。LA-ICP-MS分析测试显示,Py I中相对富含As、Se、Te等元素,而Py II中成矿元素Cu、Pb、Zn、Au、Ag的含量则比Py I型黄铁矿明显偏高,分别为792.0×10-6、2125×10-6、1.67×10-6、0.29×10-6和190.7×10-6,且Bi、Co、Ni、V、Ti、Mg、Cr、Cd、Al、Mn等微量元素含量较Py I均明显偏高1~2个数量级。在综合分析黄铁矿的结构形态和微量元素组成特征的基础上,本文认为Py I可能形成于晚古生代海底热水沉积环境,Py II形成于中生代岩浆热液环境。新桥铜金硫多金属矿床的成矿作用包括了海西期同生沉积成矿作用和燕山期与岩浆活动有关的热液成矿作用。晚侏罗世-早白垩世广泛发育的强烈岩浆侵入及与之有关的热液活动,对矿床的最终形成起了主导作用,提供了Cu、Au等主要成矿物质。Xinqiao deposit is one of most typical stratiform and stratoid copper-gold-sulfide deposits in Tongling ore concentration area of the Middle and Lower Reaches of Changjiang River metallogenic belt. Two types of pyrite were recognized through detailed field work and paragenetic studies. Textures and trace element composition of two types of pyrite has been studied by scanning electron microscope and laser ablation-inductively coupled plasma-mass spectrometry. FE-SEM analyses of two types of pyrite indicate that the Py I is consisted of tiny cube pyrite with garin size of 100 ~ 500 nm,Py II is consisted of medium-coarse octahedral and pentagonal crystal pyrite with garin size of 50 ~ 100μm. LA-ICP-MS analyses of two types of pyrite indicate that the Py I contains the highest values of As,Se,Te. Py II pyrite enrich Cu,Pb,Zn,Au and Ag with variable content of ore-forming elements such as Bi、Co,Ni,V,Ti,Mg,Cr,Cd,Al,Mn. Textures,paragenesis and trace element geochemistry of pyrite indicate that Py I was formed in the process of the Late Paleozoic submarine sedimentation,whereas Py II pyrite may occur during the Mesozoic hydrothermal superimposition. Therefore,the formation of Xinqiao Cu-Au-S deposit may have recorded both the Late Paleozoic submarine or exhalation sedimentation and hydrothermal overprint in Mesozoic. Colloform pyrite without Cu and Au mineralization deposited during sedimentation,while most of economic metals,e. g.,Cu,Pb,Zn,Au and Ag,were introduced through hydrothermal fluids during emplacement of the Yanshanian dioritic intrusions.

关 键 词：黄铁矿 形貌学特征 微量元素 新桥矿床 铜陵 

分 类 号：P578.292[天文地球—矿物学]