滇西兰坪盆地富隆厂一带铅锌多金属矿床中闪锌矿的微量元素、S-Pb同位素特征及意义
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国家基础研究计划973项目(2009CB421000); 国家自然科学联合基金(U09336051); 国家自然科学杰出青年基金(40772067); 国家科技支撑计划项目(2006BA01A08); 国土资源大调查项目(1212010818096)


Characteristics of trace elements and S-Pb isotopes in sphalerites from lead-zinc polymetallic deposits in Fulongchang area, Lanping Basin, western Yunnan Province, and their implications
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    摘要:

    在野外地质观测基础上,对滇西兰坪盆地富隆厂一带的铅锌多金属矿床中广泛发育的闪锌矿进行了微量元素、S-Pb同位素组成的综合对比分析研究。结果表明,3个矿床的闪锌矿均表现出富Cd,贫Ge和Ga,Fe-Cd呈反相关关系,Zn/Cd平均比值较低,δ34S值基本一致,其变化范围较窄,峰值在5‰~6‰之间;不同矿床闪锌矿的铅同位素基本重合,在207Pb/204Pb-206Pb/204Pb和208Pb/204Pb-206Pb/204Pb投影图解中,主体均位于上地壳线和造山带线之间,在Δβ-Δγ图解中,总体上落入上地壳-地幔混合的俯冲带铅范围和上地壳铅范围内,与盆地内不同物质来源端员对比发现矿物中的Pb同位素基本在中新生代沉积岩系范围内。因此认为富隆厂一带铅锌多金属矿床是同一成矿流体活动的产物,只是产出空间位置不同,实为同一矿床。同时,其成矿温度为中低温,硫可能来自盆地中膏盐的有机质热化学还原或含硫有机物的分解,金属可能源自区域沉积地层。

    Abstract:

    There are many lead-zinc polymetallic deposits related to continental collision in Lanping Basin, western Yunnan Province. These deposits were formed in a continental collision environment, developed in a strong deformation sedimentary basin, controlled by thrust structure, had no obvious affinity to igneous activities and belong genetically to epigenetic mineralization. Thus they are significantly different from Sedex-type Zn-Pb deposits produced in the passive continental margin and also different from marine sandstone-type Pb deposits (SST) and sandstone-type Cu deposits (SSC). Although they are similar to the MVT lead-zinc deposits, they are not the typical characteristics of MVT lead-zinc deposits in such aspects as basin environment, structural location, source material, metals and ore combination. Therefore, due to their unique characteristics, they are an important research object for the comprehensive understanding of the sediments-hosted base metal mineralization. In the past, less researches have been devoted to the lead-zinc polymetallic deposits in Fulongchang area, and hence the relationship between the different deposits is not clear. On the basis of geological field observations, the authors selected sphalerite which exist in all these deposits as the object to study its trace elements and S-Pb isotopic composition so as to make a comparative analysis. On the whole, these deposits are developed in the thrust nappe structure system and the secondary faults caused by thrust, have no obvious wall rock affinity, and show injection filling epigenetic mineralization in the fault system. The ore minerals include not only sphalerite, galena, pyrite, gratonite and tetrahedrite but also cinnabar, realgar and orpiment, with the main gangue minerals being calcite, assuming a low temperature hydrothermal mineral assemblage. Ore structures mainly include brecciated, veinlike, massive, disseminated, spotted and banded structures. The mineral textures are mainly euhedral granular, hypidiomorphic granular, xenomorphic granular and saccharoidal textures. Besides Zn-Pb, these ore deposits also have Cu and Ag, showing features of Pb-Zn-Cu-Ag polymetallic assemblage. Wall rock alteration is mainly carbonation. The three deposits have rich Cd, poor Ge and Ga, inversely related Fe-Cd, low average ratios of Zn/Cd in sphalerite. δ34S values of sphalerite in the three deposits are basically consistent, have a narrow range, and show peaks at 5‰~6‰. Lead isotope values of sphalerite from different ore deposits are basically in coincidence. In the diagrams of 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb, the main data are located between the upper crust line and the orogenic belt line. In the Δβ-Δγ diagram, the whole values fall into the upper crust lead zone and the mixed range of the upper crust lead and the mantle subduction zone lead. Compared with the values of different metal source end-members in Lanping basin, the value of Pb isotope in sphalerite is consistent with the values of the Mesozoic and Cenozoic sedimentary rocks. Therefore, the lead-zinc polymetallic deposits in Fulongchang area must have been formed at the same ore-forming fluid activity in different spatial locations, being of the same origin. Meanwhile, the ore-forming temperature was of middle-low temperature, and sulfur was probably derived from the thermochemical sulfate reduction of organic matter in the basin or the decomposition of sulfur-bearing organic matter. The metals for mineralization might have come from regional sedimentary strata.

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王晓虎,宋玉财,侯增谦,张洪瑞,刘英超,杨竹森,杨天南,潘小菲,王淑贤,薛传东,2011,滇西兰坪盆地富隆厂一带铅锌多金属矿床中闪锌矿的微量元素、S-Pb同位素特征及意义[J].岩石矿物学杂志,30(1):45~59. WANG Xiao_hu, SONG Yu_cai, HOU Zeng_qian, ZHANG Hong_rui, LIU Ying_chao, YANG Zhu_sen, YANG Tian_nan, PAN Xiao_fei, WANG Shu_xian, XUE Chuan_dong,2011,Characteristics of trace elements and S-Pb isotopes in sphalerites from lead-zinc polymetallic deposits in Fulongchang area, Lanping Basin, western Yunnan Province, and their implications[J]. Acta Petrologica et Mineralogica,30(1):45~59.

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