西藏雄村斑岩型铜金矿集区I号矿体的硫、铅同位(2)

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地 球 学 报 第三十三卷

Gangdise orogenic belt, and its south margin is Shigatse forearc basin. The latest exploration data indicate that there are several potential mineralization-alteration areas and three large-size copper-gold ore bodies (No. I, II and III) in the Xiongcun porphyry copper-gold ore concentration area. In this paper, Xiongcun No. I ore body was chosen as the research object. According to sulfur and lead isotope composition of ore-baring porphyry, tuff and main sulfides of the ore, the authors have reached the following two conclusions: 1) Sulfur isotopic compositions vary in a narrow range of δ34S values from 3.5‰ to +2.7‰ ( 1.07‰ on average) and are close to zero, indicating a mantle sulfur signature. 2) They have uniform Pb isotope compositions with low content of radiogenic Pb. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios vary in the ranges of 18.104-18.432, 15.473-15.533 and 37.918-38.3072, respectively. They are located in the transition zone of mantle Pb and orogen Pb but are closer to the former, reflecting a mixing between the mantle material and minor crust material. Through a comparative study of sulfur and lead isotopes of porphyry copper deposits of the island arc environment (e.g., Xiongcun No. I ore body) and those of the collisional orogenic environment in the Gangdise porphyry copper belt, the authors found that they have similar metal sources, but porphyry copper deposits of the island arc environment have experienced weak contamination of crust materials, whereas porphyry copper deposits of the collisional orogenic environment have experienced strong contamination of crust materials.

Key words: sulfur isotope; lead isotope; Xiongcun; porphyry copper-gold deposit; Gangdise belt in Tibet

西藏冈底斯斑岩铜矿带产于冈底斯火山-岩浆弧内, 近年来该带的资源评价工作取得了重要进展, 已发现的矿床(点)主要位于东起工布江达县、西到昂

仁县的区域, 大致分布于雅鲁藏布江北岸20~60 km 甲玛、沙让、冲江、厅宫、白容、朱诺、程巴、冲

范围内(以25~35 km 最为集中), 发现有雄村、驱龙、木达、拉抗俄、达布、吹败子、吉如等斑岩型矿床,

C

总体具有东西成带、北东成群分布特征(芮宗瑶等, 2003a, b; 李光明等, 2005, 2006; 曲晓明等, 2001; 王全海等, 2002; 侯增谦等, 2003; 郑有业等, 2007; 2009b, 2010a, b, 2012; 胡正华, 2011; 郎兴海等2010c, 2012a)。

雄村斑岩型铜金矿集区位于西藏冈底斯斑岩铜矿带西段, 是近年来西藏冈底斯斑岩铜矿带上发现的以铜为主伴生金、银的超大型铜金矿集区, 属西藏日喀则地区谢通门县荣玛乡管辖。雄村斑岩型铜金矿集区大地构造位置属冈底斯火山-岩浆弧的中段南缘, 其南侧紧邻日喀则弧前盆地(郎兴海等, 2010c), 研究表明其形成于与新特提斯洋向北的洋内俯冲作用有关的岛弧环境, 成矿时代为中侏罗世(唐菊兴等, 2009b; 郎兴海等, 2010c)。在雄村斑岩型铜金矿集区, 目前探明I(原命名为雄村铜矿床)、II、III号铜金矿体规模达大型-超大型, 同时还存在多个矿化异常带。三个主矿体呈北西-南东向展布, II

黄志英等, 2004; 张洪涛等, 2004; 唐菊兴等, (2007b)、黄勇等(2011a)对I号矿体的成矿物质来源

有过研究, 但由于测试数据较少且不够全面和系统, 缺乏对成矿物质来源的深入探讨, 因此, 本文将在前人研究基础之上, 通过系统研究雄村I号矿体的含矿斑岩、赋矿凝灰岩和主要硫化物的硫、铅同位素组成, 分析其成矿物质来源, 并与区域上的斑岩型铜矿床进行对比, 初步探讨新特提斯洋俯冲阶段岛弧环境与印度-亚洲大陆碰撞造山环境形成的斑岩铜矿床成矿物质来源的异同, 为深入研究雄村斑岩型铜金矿集区的成矿作用乃至整个冈底斯成矿带构造-岩浆演化与成矿作用奠定基础。

AG

S

号矿体位于I号矿体(原雄村铜矿床)北西向约3.4 km

处, III号矿体位于II号矿体北西向约2.1 km处(图1)。雄村斑岩型铜金矿集区的地质研究工作起步较晚, 其中以雄村I号矿体(原命名为雄村铜矿床)研究丁枫等, 2006; 张丽, 2007; 唐菊兴, 2007, 2009a, c, 2010; 曲晓明等, 2007a, b; 郎兴海等, 2010a, b, c, 2011, 2012b; 黄勇等, 2011a, b; 黄勇, 2012; 丁枫, 2012), 但其成矿物质来源尚未得到明确的认识。尽管丁枫等(2006)、徐文艺等(2006b)、曲晓明等

最为详尽(Qin et al., 2005; 徐文艺等, 2005, 2006a, b;

1 雄村I号矿区地质概况

雄村I号矿区出露地层(图1)主要为中-下侏罗统雄村组(J1-2x)和全新统崩积物-冲积物(唐菊兴等,