地学前缘 ›› 2023, Vol. 30 ›› Issue (2): 347-369.DOI: 10.13745/j.esf.sf.2022.2.76

• 成藏-成矿作用与评价 • 上一篇    下一篇

东昆仑夏日哈木矿区热液型铅锌矿体成因及地质意义

陈欣1(), 王辉1,*(), 毛景文1,2, 于淼3, 乔建峰4, 王治安4   

  1. 1.长安大学 地球科学与资源学院, 陕西 西安 710061
    2.中国地质科学院 矿产资源研究所 自然资源部成矿作用与资源评价重点实验室, 北京100037
    3.中南大学 地球科学与信息物理学院, 湖南 长沙 410083
    4.青海省第五地质矿产勘查院, 青海 西宁 810003
  • 收稿日期:2022-03-02 修回日期:2022-04-28 出版日期:2023-03-25 发布日期:2023-01-05
  • 通讯作者: 王辉
  • 作者简介:陈欣(2000—),男,硕士研究生,从事矿床学研究工作。E-mail: chenxin21s@163.com
  • 基金资助:
    国家自然科学基金项目(41902074);长安大学中央高校基本科研业务费专项资金项目(300102271202)

Genesis and geological significance of hydrothermal Pb-Zn orebodies in the Xiarihamu mining area, East Kunlun Mountains, China

CHEN Xin1(), WANG Hui1,*(), MAO Jingwen1,2, YU Miao3, QIAO Jianfeng4, WANG Zhian4   

  1. 1. School of Earth Sciences and Resources, Chang’an University, Xi’an 710061, China
    2. Ministry of Natural Resources Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
    3. School of Geosciences and Info-Physics, Central South University, Changsha 410083, China
    4. Qinghai No.5 Geological Mineral Exploration Institute, Xining 810003, China
  • Received:2022-03-02 Revised:2022-04-28 Online:2023-03-25 Published:2023-01-05
  • Contact: WANG Hui

摘要:

夏日哈木是近年来在东昆仑成矿带探明的一个超大型岩浆型Ni-Co硫化物矿床,然而,随着矿区深部和外围找矿工作的不断深入,矿区内相继发现与岩浆硫化物型矿体特征明显不同的热液型Pb-Zn±Cu±Ag矿体,已探明的金属量达10万吨。为进一步揭示热液型矿体的成因及其产出背景,本文系统地开展了矿化蚀变特征和成矿年代学研究工作。新发现的热液型矿体主要呈似层状产于古元古代金水口群白沙河岩组的大理岩与片麻岩的层间构造带内,矿石矿物主要为方铅矿、闪锌矿和黄铜矿,脉石矿物为辉石、石榴子石、绿帘石、绿泥石、榍石、磷灰石、石英及方解石等。电子探针分析结果显示,辉石属于透辉石-钙铁辉石系列,矿物端员组分为Di65.44~79.01Hd18.55~30.78Jo1.63~0.51;石榴子石属于钙铝榴石-锰铝榴石系列,矿物端员组分为Gro24.93~92.17And3.29~9.95(Spe+Alm)1.68~67.29;绿帘石和绿泥石均有高Mn特征。综合以上矿物学研究工作,认为其属于夕卡岩型矿体。LA-ICP-MS微量元素分析显示,榍石稀土元素总量较低,稀土配分模式为右倾的轻稀土富集型,Th/U为0.23~1.97,平均值为0.94,与典型的热液榍石稀土元素组成相近。LA-ICP-MS微区原位U-Pb定年获得的热液榍石207Pb校正后的206Pb/238U加权平均年龄为(413.3±3.6) Ma(n=23, MSWD=0.96);热液磷灰石207Pb校正后的206Pb/238U加权平均年龄为(414±13) Ma(n=17, MSWD=1.03),代表夕卡岩型矿体成矿作用发生于早泥盆世,与岩浆型镍钴硫化物矿体的成矿时代在误差范围内基本一致。结合成矿地质条件,本文认为夏日哈木矿区发育具有时空联系的岩浆型与热液型两套成矿系统,区域伸展背景下幔源岩浆上涌导致地壳岩石发生部分熔融,形成浅部酸性岩浆房,熔体沿着伸展作用形成的构造薄弱带上升,分异产生岩浆流体,与古元古代金水口群大理岩发生接触交代作用,形成夕卡岩型Pb-Zn±Cu±Ag矿体。此外,本文为东昆仑成矿带泥盆纪夕卡岩型铅锌成矿作用的存在提供了直接的成矿年代学佐证,关注岩浆型与热液型两套成矿系统的共存,对开展综合找矿评价具有重要的理论和实际意义。

关键词: 铅锌矿, 夕卡岩, 矿床成因, 夏日哈木, 东昆仑

Abstract:

The Xiarihamu deposit is a giant magmatic Ni-Co sulfide deposit discovered recently in the East Kunlun metallogenic belt. With the advancement of deep, peripheral ore prospecting, however, some distinct hydrothermal Pb-Zn-(Cu, Ag) orebodies—which are obviously different from the magmatic sulfide deposit—have been found at the Xiarihamu mining area, with nearly 100,000 tons of proven reserves. In order to further reveal their genesis and production background, a systematic study of the mineral alteration characteristics and metallogenic chronology of the newly discovered hydrothermal orebodies is carried out. The hydrothermal orebodies are mainly stratified in the marble/gneiss interlayer structural belt of the Paleoproterozoic Baishahe Formation of the Jinshuikou Group. The main metallic minerals are galena and sphalerite, followed by chalcopyrite, and the gangue minerals are pyroxene, garnet, epidote, chlorite, titanite, apatite, quartz, calcite, etc. According to EPMA analysis, the pyroxene is mainly composed of the diopside-hedenbergite series, with the end component mainly Di65.44-79.01Hd18.55-30.78Jo1.63-0.51; the garnet belongs to the andradite-spessartine series, with the end component mainly Gro24.93-92.17And3.29-9.95(Spe + Alm)1.68-67.29; and the epidote and chlorite in the skarn are both characterized by high Mn contents. Based on the above results it is considered that the hydrothermal orebodies are of skarn type. The trace element composition of the hydrothermal titanite from the skarn is similar to that of typical hydrothermal titanite according to LA-ICP-MS analysis. It has relatively low ΣREE, is enriched in LREE, with small LREE/HREE fractionation, and has a Th/U ratio of 0.23-1.97 (averaging 0.94). By LA-ICP-MS in-situ U-Pb dating the 206Pb/238U weighted mean age (after 207Pb correction) of the hydrothermal titanite is (413.3 ± 3.6) Ma (n = 23, MSWD = 0.96), and for the hydrothermal apatite it is (414 ± 13) Ma (n = 17, MSWD = 1.03). These results indicate that mineralization of the skarn orebodies occurred in the Early Devonian, which is consistent with the metallogenic age (within the error range) of the magmatic Ni-Co sulfide ore body. Combined with the regional metallogenic geological conditions, this paper considers that there are two temporospatially related metallogenic systems-magmatic and hydrothermal systems-developed in the Xiarihamu mining area. Briefly, under the extensional background the upwelling of the mantle-derived magma results in the partial melting of rocks in the middle-upper crust to form a felsic magmatism chamber; the melts then rise along the extensional structure zone and differentiate to produce the ore-forming fluids which then react with Paleoproterozoic marble or calcareous siltstone to form the Pb-Zn-(Cu, Ag) orebodies. This paper provides direct metallogenic and chronological evidences for the existence of Devonian Pb-Zn skarn deposits in the East Kunlun metallogenic belt. It is of theoretical and practical significance, therefore, to consider the coexistence of magmatic and hydrothermal ore-forming systems in the region and carry out a comprehensive prospecting evaluation accordingly.

Key words: Pb-Zn deposit, skarn, ore genesis, Xiarihamu, East Kunlun

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