投稿时间：2011-12-18
修订日期：2012-09-16
中文摘要:后万岭铅锌矿床是近年来海南省找矿的一项重要进展,探明的铅锌金属量大于29万吨(Pb 4.4万吨,Zn 24.6万吨),平均品位为锌2.23%、铅0.95%。该矿床产于千家超单元岩体内,后者是中-晚侏罗世在后造山期地壳大面积伸展减薄的构造背景下,由壳-幔混源岩浆间歇性多期侵入的产物。千家岩体各单元花岗岩属于壳-幔混合型的高钾钙碱性岩石或钾玄岩,具有明显的成分及结构演化的连续性。其稀土元素总量较高,但变化范围较大〔ΣREE=(122.61～410.58)×10-6〕,具有显著至中等的负铕异常(δEu=0.13～0.69),其稀土元素配分曲线呈右倾型(LREE/HREE=6.74～16.32),并强烈亏损Ba、Nb、Ta、Sr、P、Ti,相对富集Rb、K、Pb等。千家岩体花岗质岩浆演化过程中存在大量的热液流体,同时,其造岩矿物中Pb、Zn的含量远高于地壳丰度值,深部热能及浅部放射性生热元素的高含量促使浅部热液对流循环,在较长时间内不断萃取成矿物质,有利于在断裂带内富集成矿。后万岭铅锌矿床严格受到千家岩体及发育于其内的NNW向-近SN向扭张性断裂的控制,矿体以充填、交代的方式就位于NNW向-近SN向扭张性断裂带内及附近。矿相学分析和矿区地质资料揭示出该矿床至少经历了4期热液成矿作用:① 成矿早期,为粗粒黄铁矿形成阶段;② 成矿中期,是闪锌矿主要成矿阶段;③ 成矿中-后期,是黄铜矿主要形成阶段;④ 成矿后期,是方铅矿主要成矿阶段,其成矿热液可能受到斑岩岩浆的控制。矿区内的NNW向-近SN向断裂活动过程对应了后万岭铅锌矿的成矿过程,成矿早期与成矿中期归入左旋张扭性断裂活动阶段,成矿中-后期和成矿后期归入右旋压扭性断裂活动阶段。据此笔者认为,后万岭铅锌矿属于燕山晚期后造山环境下严格受NNW向-近SN向扭张性断裂约束的热液脉型矿床,就位于千家岩体斑岩成矿系统的顶端或远端,最终归纳总结出了后万岭铅锌矿床成矿模式图。
Abstract:The discovery of the Houwanling Pb-Zn deposit in Ledong County of Hainan Province has been a very important achievement in ore exploration of Hainan Province in recent years. The Houwanling deposit contains proved Pb+Zn metal reserves of 290 thousand tons with average grades of Zn 2.23% and Pb 0.95%. The deposit is hosted by the Cretaceous Qianjia pluton which had a crust mantle mixed origin due to intermittent magmatic intrusion and was produced in a post-collisional extensional environment in middle-late Jurassic period. This calc-alkaline-dominated pluton, which is extremely depleted in Ba, Nb, Ta, Sr, P and Ti and relatively enriched in Rb, K and Pb, shows a shift from high-K to shoshonite association and is characterized by obvious succession in composition and structure. The Qianjia pluton comprises the monzogranite-granodiorite-syenogranite association and is geochemically characterized by high REE content (ranging from 122×10-6 to 411×10-6), moderate to high negative Eu anomalies (δEu=0.13～0.69) and relatively high LREE/HREE ratios (6.74～16.32). There existed lots of hydrothermal fluids during the evolution of granitic magmas. Furthermore,the abundances of Pb and Zn in rock-forming minerals of the Qianjia pluton's granites are much higher than those in the earth's crust. Deep heat and high content of radioactive heat-producing elements (such as K, Rb) in the shallow part caused convective circulation of hydrothermal fluids in the shallow part, which continuously extracted metallogenic material in a fairly long time. At last, sphalerite and galena were deposited. The deposit is strictly controlled by both the Qianjia pluton and the NNW-nearly SN trending transtensional faults, whereas the ore bodies are largely hosted in the NNW-nearly SN transtensional fault zones or distributed adjacent to the fault zones. Based on thin section observation, the authors obtained abundant important information: course-grained pyrite and fractured pyrite were filled with chalcopyrite, indicating that some of the course-grained pyrite underwent faulting activities, and course-grained pyrite was generated earlier than chalcopyrite with mesh texture at a temperature of 300～400℃; skeletal texture resulted from replacement of course-grained pyrite by sphalerite, indicating that sphalerite was generated after course-grained pyrite; corona texture resulted from replacement of chalcopyrite by covellite, indicating that covellite was generated in the shallow part at a low temperature below 300℃; emulsion texture and grating texture resulted from the separation of chalcopyrite from sphalerite, indicating that chalcopyrite-sphalerite solid solution had a initial temperature of about 550℃. Geological data reveal that the Houwanling Pb-Zn ore deposit probably underwent multistage mineralization and experienced at least more than four main stages of hydrothermal mineralization: ① the generation of course-grained pyrite at early stage of mineralization; ② the deposition of sphalerite mainly at the middle stage of mineralization; ③ the formation of chalcopyrite mainly at the middle or late stage of mineralization; ④ the generation of galena mainly at the late stage of mineralization. The ore-forming fluid might have been released from fractiona- ting porphyry magma. The authors thus consider that the Houwanling Pb-Zn deposit is a hydrothermal vein-type deposit in peripheral or supergene location of the porphyry system, strictly controlled by NNW-nearly SN transtensional faults and formed in an extensional environment of post-collision in late Cretaceous. On such a basis, a metallogenic model to explain ore genesis of the Houwanling Pb-Zn ore deposit is put forward in this paper.
keywords:geology geochemistry ore-controlling factor hydrothermal vein-type deposit Houwanling Pb-Zn deposit Qianjia pluton Hainan Province
文章编号：
中图分类号：P618.42;P618.43
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基金项目:本文得到海南省资源潜力评价项目(编号: 1212010881625)资助
引用文本：
付王伟,许德如,傅杨荣,杨昌松,周迎春,杨东生,吴传军,王智琳.2012.海南省后万岭铅锌矿床控矿因素、矿床成因及成矿模式探讨[J].矿床地质,31(6):1211~1226FU WangWei,XU DeRu,FU YangRong,YANG ChangSong,ZHOU YingChun,YANG DongSheng,WU ChuanJun,WANG ZhiLin.2012.A tentative discussion on ore-controlling factors, ore genesis and metallogenic model of Houwanling Pb-Zn deposit in Hainan Province[J].Mineral Deposits31(6):1211~1226
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