滇东北毛坪和会泽超大型铅锌矿床粗—巨晶碳酸盐岩成因及其找矿指示意义
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本文为国家重点研发计划项目(编号:2018YFC0603900)、国家自然科学基金资助项目(编号:41102049)、云南省矿产资源预测评价工程实验室(2010)和云南省地质过程与矿产资源创新团队(2012)项目的成果


Genesis of coarse—giant carbonate rocks in Maoping and Huize super-large lead—zinc deposits in Northeast Yunnan and its prospecting significance
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    摘要:

    云南毛坪和会泽铅锌矿床是川滇黔碳酸盐岩型铅锌成矿域的重要组成部分,是滇东北铅锌矿集区内两个最具代表性的超大型矿床。靠近铅锌矿体常见透镜状、囊状产出的蚀变围岩,因呈麻点状而被俗称为“麻石”,空间上与断裂、矿化结伴出现,是重要找矿标志。本文以这种麻点状的蚀变围岩为主要研究对象,通过大比例尺坑道剖面精细测量、岩相分析、电子探针分析、X射线微区衍射分析、主量—微量元素分析,研究其物质组成、组构特征及形成过程。根据组构特征将蚀变围岩分为两类,Ⅰ类呈砂糖状,矿物颗粒主要为粗晶结构(0.5~1 mm)的白云石和方解石,被褐色伊利石等黏土矿物胶结;Ⅱ类呈斑点状,矿物颗粒主要为巨晶结构(1~3 mm)的方解石和白云石,重结晶现象明显,被黑色泥质和有机质胶结。通过手标本观察、镜下鉴定和综合分析,将Ⅰ类蚀变围岩定名为弱大理岩化粗晶泥质白云岩,Ⅱ类蚀变围岩定名为去白云石化巨晶灰岩。两类蚀变围岩的主量元素特征相比,Ⅰ类中SiO2、Al2O3、K2O含量较高。微量元素特征显示两类蚀变围岩中主要矿化元素(Zn、Pb)明显富集。稀土元素特征显示,Ⅰ类中稀土元素含量均高于Ⅱ类,其中Ⅱ类与矿化白云岩稀土元素特征相似。两类蚀变围岩是同一流体系统不同阶段的产物,构建其成岩作用模式:弱大理岩化粗晶泥质白云岩(Ⅰ类)的原岩为钙质泥岩,高盐度卤水下渗,在岩性界面处与泥岩和白云岩反应形成泥质白云岩,沉积稳定后受构造运动影响,热液流体沿断裂上升,在有利地段形成泥质白云岩大理岩化(结构上改变);去白云石化巨晶灰岩(Ⅱ类)比弱大理岩化粗晶泥质白云岩(Ⅰ类)蚀变更强烈,经历矿化、大理岩化作用和去白云石化(结构和成分上改变)而形成。综合分析认为两类蚀变围岩与铅锌矿体在时间、空间、成矿物质和成矿流体等方面都具有密切的成因联系,提出大理岩化、去白云石化作用对该类矿床成矿与找矿均具有重要的指示意义。

    Abstract:

    Objectives: Maoping and Huize Pb—Zn deposits in Yunnan Province are important parts of carbonate type Pb—Zn metallogenic domain in Sichuan, Yunnan and Guizhou, and are the two most representative super-large deposits in northeast Yunnan Pb—Zn concentration area. The lenticular and cystic alteration near the lead—zinc ore body is commonly known as “mottling rock” because of its mottling-like appearance, which is accompanied by faults and mineralization in space, and is an important prospecting sign. Methods: In this paper, mottling altered wall rock is taken as the main research object, the material composition, fabric characteristics and formation process were studied by fine measurement of large-scale tunnel section, petrographic analysis, electron probe analysis, X-ray micro-area diffraction analysis and principal and trace element analysis. Results: According to the fabric characteristics, altered wall rock can be divided into two categories. the type-Ⅰ altered wall rock is saccharoidal, and the mineral particles are mainly dolomite and calcite with coarse crystalline structure (0.5~1 mm), which are cemented by clay minerals such as brown illite; the type-Ⅱ altered wall rock is mottled, and the mineral particles are mainly calcite and dolomite with giant crystal texture (1~3 mm), which are obviously recrystallized and cemented by black argillaceous and organic matter. Through hand specimen observation, microscopic identification and comprehensive analysis, the type-Ⅰ altered wall rock is named as weakly marbled coarse-grained argillaceous dolostone, and the type-Ⅱ altered wall rock is named as dedolomitized giant crystalline limestone. Compared with the major element characteristics of the two types of altered wall rock, the content of SiO2, Al2O3 and K2O in type-Ⅰ is higher. The trace element characteristics show that the main mineralized elements (Zn, Pb) are enriched in the two kinds of altered wall rock. The REE characteristics show that the REE contents in weakly marbled coarse-grained argillaceous dolostone (type-Ⅰ) are higher than that of dedolomitized giant crystalline limestone (type-Ⅱ), and the REE characteristics of dedolomitized giant crystalline limestone (type-Ⅱ) are similar to those of mineralized dolomite. Conclusions: Two types of altered wall rock are products of different stages of the same fluid system, and their diagenesis models are constructed: the original rock of weakly marbled coarse-grained argillaceous dolomite (type-Ⅰ) is calcareous mudstone, and high-salinity brine seeps down, which reacts with mudstone and dolomite at the lithologic interface to form argillaceous dolomite. After the sedimentation is stable, due to the influence of tectonic movement, hydrothermal fluid rises along the fault, and argillaceous dolomite marmalization is formed in favorable sections (structural change). Dedolomitized giant crystalline limestone (type-Ⅱ) is more strongly altered than the weakly marbled coarse-grained argillaceous dolostone (type-Ⅰ), which has undergone mineralization, marbling and dedolomitization. The comprehensive analysis shows that there is a close genetic relationship between altered wall rock and lead—zinc ore bodies in terms of time, space, ore-forming materials and ore-forming fluids, etc. It is suggested that the marbling and dedolomitization have important indicative significance for the ore-forming and ore-prospecting of this type of deposit.

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谭茂,吴鹏,韩润生,张艳,黄智龙,姜龙燕,杨航.2021.滇东北毛坪和会泽超大型铅锌矿床粗—巨晶碳酸盐岩成因及其找矿指示意义[J].地质论评,67(6):67120012,[DOI].
TAN Mao, WU Peng, HAN Runsheng, ZHANG Yan, HUANG Zhilong, JIANG Longyan, YANG Hang.2021. Genesis of coarse—giant carbonate rocks in Maoping and Huize super-large lead—zinc deposits in Northeast Yunnan and its prospecting significance[J]. Geological Review,67(6):67120012.

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  • 收稿日期:2021-05-06
  • 最后修改日期:2021-11-23
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  • 在线发布日期: 2021-12-19
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