Transactions of Nonferrous Metals Society of China The Chinese Journal of Nonferrous Metals

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中国有色金属学报

ZHONGGUO YOUSEJINSHU XUEBAO

第27卷    第4期    总第217期    2017年4月

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文章编号:1004-0609(2017)-04-0795-16
厄立特里亚阿斯马拉VMS矿床S、Pb同位素对成矿物质来源的约束
成曦晖1, 2,徐九华1, 2,王建雄3,禇海霞4,肖 星1, 2,张 辉1, 2

(1. 北京科技大学 土木与资源工程学院,北京 100083;
2. 北京科技大学 金属矿山高效开采与安全教育部重点实验室,北京 100083)
3. 中国地质调查局武汉地质调查中心,武汉 430205;
4. 中国地质大学(北京),北京 100083
)

摘 要: 阿斯马拉(Asmara)地区位于非洲东北部的厄立特里亚,是重要的VMS型矿床成矿带。对其矿石结构特征和成矿物质来源的分析研究有利于区域成矿规律的总结。在分析矿床成矿地质条件的基础上,研究Emba Derho和Debarwa VMS型矿床的矿石结构特征、矿石硫、铅同位素组成及闪锌矿中的流体包裹体特征。结果表明:Debarwa和Emba Derho矿床成矿作用在经过VMS过程之后,其后期的变形变质过程对成矿的改造和叠加作用有限。闪锌矿中的流体包裹体研究显示其成矿流体具有低盐度、中-高温的特征。Debarwa和Emba Derho矿床中黄铁矿、闪锌矿和黄铜矿等原生硫化物矿物的δ34SCDT值变化范围较窄,数据集中在0.01%~0.48%之间,重晶石S同位素为高正值(δ34S=1.66%~1.73%),具有地幔硫和海水硫的混合来源特征。Debarwa 和Emba Derho矿床矿石铅同位素组成稳定,显示正常铅的特征。对矿石铅同位素进行特征参数示踪、铅构造模式示踪和Δβ-Δγ图解示踪的结果表明:Debarwa和Emba Derho矿床中矿石铅主要为地壳与地幔混合的俯冲铅。

 

关键字: 硫同位素;铅同位素;流体包裹体;VMS型矿床;厄立特里亚

Sulfur and lead isotope constrains on source of ore-forming materials in Asmara VMS-type deposits, Eritrea
CHENG Xi-hui1, 2, XU Jiu-hua1, 2, WANG Jian-xiong3, CHU Hai-xia4, XIAO Xing1, 2, ZHANG Hui1, 2

1. School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China;
2. Key Laboratory of High-Efficient Mining and Safety of Metal, Ministry of Education, University of Science and Technology Beijing, Beijing 100083, China;
3. Wuhan Center of China Geological Survey, Wuhan 430205, China;
4. China University of Geosciences, Beijing 100083, China

Abstract:Volcanogenic massive sulfide (VMS) deposit is an important type of nonferrous deposit. In Eritrea, Neoproterozoic volcanogenic massive sulphide deposits and occurrences, to a large extent, distribute in Asmara-Nakfa Belt (ANB). The most important mineral deposits and occurrences known in Asmara-Nakfa Belt are those of the Emba Derho and Debarwa VMS deposits. Based on the research related to the Debarwa and Emba Derho deposit’s oreforming geological conditions, the compositions of S, Pb isotopes as well as the characteristics about fluid inclusions in sphalerite and ore textures were studied, and the origin of oreforming materials was discussed. The results show that the transformation and superposition of regional metamorphism for deposits are limited. Ore-bearing fluids are characterized by medium-high temperature, low salinity. The δ34SCDT values of primary sulfide ore minerals distribute narrowly (0.01%-0.48%) in Debarwa and Emba Derho deposits, δ34SCDT value of barite in Debarwa deposit is 1.66%-1.73%. The characteristics of sulfur isotopic composition show that the sulfur in these two deposits is derived from the mantle mixed seawater. Meanwhile, the Pb isotopic composition of ore sulfides is stable and the ore lead is ordinary common lead with little U and Th radiogenic lead. According to the tracer analysis regarding the characteristic parameters, lead composition model and Δβ-Δγ diagram, the conclusion is drawn that the ore lead is typically crustmantle mixed subduction lead.

 

Key words: sulfur isotope? lead isotope? fluid inclusions; VMS deposit; Eritrea

ISSN 1004-0609
CN 43-1238/TG
CODEN: ZYJXFK

ISSN 1003-6326
CN 43-1239/TG
CODEN: TNMCEW

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