滇东南白牛厂多金属矿床铅同位素组成及铅来源新认识_李开文
- 格式：pdf
- 大小：2.98 MB
- 文档页数：15
第42卷 第2期Vol.42, No.2, 116~1302013年3月GEOCHIMICAMar., 2013收稿日期(Received): 2012-05-15; 改回日期(Revised): 2012-08-14; 接受日期(Accepted): 2012-10-16基金项目: 矿床地球化学国家重点实验室“十二五”项目群(SKLODG-ZY125-04); 国家自然科学基金(40872074); 国家重点基础研究发展计划(2007CB411408)作者简介: 李开文(1984–), 男, 博士研究生, 主要从事矿床学及矿床地球化学研究。
E-mail: likaiwen0502@ * 通讯作者(Corresponding author): ZHANG Qian, E-mail: zhangqian@, Tel: +86-851-5891702滇东南白牛厂多金属矿床铅同位素组成及铅来源新认识李开文1,2, 张 乾1*, 王大鹏1, 蔡 伊1,2, 张永斌1,2(1. 中国科学院 地球化学研究所 矿床地球化学国家重点实验室, 贵州 贵阳 550002; 2. 中国科学院大学, 北京 100049)摘 要: 白牛厂矿床位于滇东南锡多金属成矿带中部, 是一个Ag 、Pb 、Zn 、Sn 等共生的多金属矿床, 但成因争议较大。
前人引用早期矿床矿石矿物铅同位素数据得出矿石铅主要来源于基底岩石淋滤, 矿床经历了热水沉积+岩浆热液叠加两个成矿阶段的结论。
本文采用最新铅同位素数据系统研究了白牛厂矿床的铅同位素组成, 其中, 白牛厂矿床矿石矿物的铅同位素组成206Pb/204Pb 、207Pb/204Pb 和208Pb/204Pb 分别为17.264~18.537、14.843~15.862和38.481~39.424; 薄竹山花岗岩长石铅同位素组成206Pb/204Pb 、207Pb/204Pb和208Pb/204Pb 分别为18.301~18.387、15.611~15.670和38.677~38.904; 薄竹山岩体接触带型矿床(点)矿石矿物铅同位素组成206Pb/204Pb 、207Pb /204Pb 和208Pb/204Pb 分别为18.302~18.417、15.603~15.692和38.596~38.868;区域地层及矿区地层钻孔样品铅同位素组成206Pb/204Pb 、207Pb/204Pb 和208Pb/204Pb 分别为18.307~19.206、15.622~15.809和38.436~39.932。
对比四者铅同位素组成特征, 白牛厂矿床矿石矿物、薄竹山花岗岩长石、薄竹山岩体接触带型矿床(点)矿石矿物具有一致的铅同位素组成, 与地层铅同位素组成相差甚远, 表明白牛厂矿床铅主要来自岩浆作用, 在侵入的过程中可能受到了地层的轻度混染。
矿床地质特征及近期地球化学和年代学研究成果表明, 白牛厂矿床的形成主要受岩浆作用影响, 沉积成矿作用在白牛厂矿床很可能是不存在的。
关键词: 铅同位素组成; 铅来源; 白牛厂多金属矿床; 滇东南中图分类号: P597 文献标识码: A 文章编号: 0379-1726(2013)02-0116-15New understanding on lead isotopic compositions and lead source of the Bainiuchangpolymetallic deposit, southeast Yunnan, ChinaLI Kai-wen 1,2, ZHANG Qian 1*, WANG Da-peng 1, CAI Yi 1,2 and ZHANG Yong-bin 1,21. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China ;2. University of Chinese Academy of Sciences, Beijing 100049, ChinaAbstract: The Bainiuchang deposit, located at the central tin-polymetallic ore belt of southeast Yunnan, is associated with large scale Ag, Pb, Zn reserves. However, the genesis of the deposit is controversial. With early Pb isotopic data of ore minerals from the Bainiuchang deposit, former researchers concluded that lead was mainly derived from the leaching of basement rocks, and the deposit was formed through two mineralization stages, i.e., hydrothermal sedimentation stage and magmatic hydrothermal metallogenetics stage. Lead isotopic composition of the Bainiuchang deposit was systematically studied with the latest lead isotopic data in this study. The Pb isotope ratios of ore minerals from the Bainiuchang deposit are 206Pb/204Pb = 17.264–18.537, 207Pb/204Pb = 14.843–15.862,208Pb/204Pb = 38.481–39.424. As for the Pb isotopic composition of feldspar of monzogranite from the Bozhushan第2期李开文等: 滇东南白牛厂多金属矿床铅同位素组成及铅来源新认识 117granite rocks, the ratios are 206Pb/204Pb = 18.301–18.387, 207Pb/204Pb = 15.611–15.67, 208Pb/204Pb = 38.677–38.904, while those of ore minerals from contact zone type deposits (ore spots) of the Bozhushan granite rocks are 206Pb/204Pb = 18.302–18.417, 207Pb/204Pb = 15.603–15.692, 208Pb/204Pb = 38.596–38.868. The Pb isotope ratios of the samples from regional strata and drilling of mining strata are 206Pb/204Pb = 18.307–19.206, 207Pb/204Pb = 15.622–15.809, 208Pb/204Pb = 38.436–39.932. The orebodies have lead isotopic compositions similar to those of feldspar in granites, but are different from those of strata samples. Therefore, lead in the Bainiuchang deposit was mainly derived from magmatism, but may be contaminated slightly by strata in the process of magma intrusion. Based on geological characteristics and recently geochemistry and chronology data, sedimentary mineralization is not the main process in the Bainiuchang deposit, and magmatism is the key factor for mineralization.Key words: lead isotopic composition; lead source; the Bainiuchang polymetallic deposit; southeast Yunnan0 引言白牛厂多金属矿床位于滇东南锡多金属成矿带的中部, 其中Pb、Zn、Sn达到大型规模, Ag达到超大型规模, 同时还伴生大量的分散元素(In、Cd、Ge、Ga等)。
关于矿床成因, 先后提出了岩浆热液成因[1–2]、岩浆热液+后期改造成因[3]、热水喷流沉积成因[4]、热水喷流沉积+岩浆热液叠加改造成因[5–9]等多种不同的观点。
成矿物质来源的确定是解决矿床成因争议的关键。
Zhu et al.[10]对该矿床的铅同位素组成研究也得出了热水喷流沉积+岩浆热液叠加改造成因的认识。
近年来我们对白牛厂矿床的铅同位素组成进行了重新研究, 发现了铅来源的新线索, 得出了铅来自岩浆作用的新认识, 本文报道这一最新的研究成果。
1 地质1.1区域地质背景滇东南地处扬子地块、华南褶皱系和三江褶皱系的交汇处, 区内构造线主体方向为NE向, 其次为NW向, 由一系列背斜、向斜及压性断层组成(图1)。
该区自新元古代开始, 地壳活动经历了沉积(加里东期)到抬升(海西期)再到沉积(印支期)的复杂演化过程。
震旦纪为沉积阶段, 发育类复理石建造; 早古生代表现仍较活动, 连续沉积了较厚的砂泥质建造和碳酸盐建造。
中奥陶世本地区可能隆升成陆, 缺失上奥陶统和志留系。
晚古生代其基本地质构造特征与扬子地台一致, 地壳运动以升降运动为主, 因而泥盆纪至早二叠世时期, 由陆相环境迅速转变为稳定的浅海相环境, 广泛沉积了碳酸盐建造和部分陆屑建造; 到晚二叠世-晚三叠世早、中期, 部分地区再度转化为地壳下降, 沉积了巨厚的复理石建造、基性火山岩建造和火山碎屑岩建造; 晚三叠世末印支运动使全区褶皱回返而形成褶皱带, 未接受侏罗纪及白垩纪的沉积[12]。
