闽西南大排铁铅锌多金属矿床O、S、Pb同位素特征及其成因意义

发布时间：2018-02-26 05:36

  本文关键词： 氧、硫、铅同位素 成矿物质来源 矿床成因 大排铁铅锌矿床 福建闽西南　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：闽西南大排铁铅锌多金属矿床位于福建闽西南坳陷带南缘,大地构造位置上位于华南板块东部,该区经历了复杂的构造岩浆演化过程,尤其中生代以来,强烈的构造岩浆活动在该区表现的尤为突出,并伴随有大量的晚中生代花岗质侵入岩在该区分布。“马坑式”铁矿床在闽西南地区呈带状大面积分布,其成因备受地质同仁的关注,为探索该区“马坑式”铁多金属矿床的成因机制,有必要从同位素角度探讨成矿物质来源并进一步分析其对闽西南“马坑式”铁矿成因的指示意义。大排矿床是闽西南地区新发现的铁铅锌多金属矿床,同时也是“马坑式”代表性铁矿床之一,对其开展研究工作很有必要。大排矿床矿体主要赋存于该区碳酸盐岩层位中,一系列浅层次逆冲推覆构造及层间滑脱构造带为其主要的控矿构造,与成矿关系密切的岩浆岩主要为中细粒似斑状花岗闪长岩,其与围岩碳酸盐岩的接触带附近常伴随有矽卡岩化、碳酸盐化、硅化等蚀变。矿床的形成主要经历了早期矽卡岩阶段、磁铁矿阶段、石英-硫化物阶段及晚期碳酸盐阶段,其中磁铁矿阶段及石英硫化物阶段为大排铁铅锌多金属矿床主要的成矿阶段,矿床具典型矽卡岩矿床的成矿特征。本文在对闽西南大排铁铅锌多金属矿床地质特征调查的基础上,分别开展了矿石中主要矿物磁铁矿、石榴子石的氧同位素及黄铁矿、闪锌矿和方铅矿的硫、铅同位素测试。结果表明,石榴子石中δ18O值变化范围为3.4~6‰,与正常花岗岩的的氧同位素十分接近,暗示可能继承了该区花岗质侵入岩的的同位素组成;根据磁铁矿的氧同位素组成(2.2~4.3‰)所计算的磁铁矿阶段成矿流体的δ18O为9.23~11.34‰(500℃)或8.58~10.69‰(600℃),表明在成矿流体中有含较多δ18O的CO2加入。矿石硫化物δ34S组成变化范围较窄,变化范围为-2.6~1.5‰,多数集中在0值左右,具有岩浆硫(0±3‰)的特点。硫化物的铅同位素组成206Pb/204Pb、207Pb/204Pb、208Pb/204Pb的数值分别为18.486~18.537、15.665~15.712、38.823~38.979,铅同位素比值变化范围小,整体上具有壳幔混合且以壳源物质为主的特点。结合对闽西南“马坑式”铁多金属矿床及闽西南花岗岩年代学讨论,认为大排铁铅锌多金属矿床的形成主要与晚中生代(~130Ma)花岗质岩浆侵入作用有关。
[Abstract]:The Fe-Pb-Zn polymetallic deposit is located in the southern margin of southwestern Fujian depression, and the tectonic position is located in the eastern part of South China plate. The area has undergone complicated tectonic magma evolution process, especially since Mesozoic. The strong tectonic magma activity is especially prominent in this area, and accompanied by a large number of late Mesozoic granitic intrusive rocks in the area. In order to explore the genetic mechanism of the "Ma Hang type" iron polymetallic deposit in this area, It is necessary to probe into the source of ore-forming materials from the perspective of isotopes and to further analyze its indicative significance to the genesis of "maqing-type" iron ore deposits in southwestern Fujian, where the Dapai deposit is a newly discovered iron-lead-zinc polymetallic deposit. At the same time, it is also one of the representative iron ore deposits of "Ma-Peng" type, so it is necessary to carry out research work on them. The ore bodies of Dapai deposit mainly occur in the carbonate strata in this area. A series of shallow thrust-nappe structures and interlayer slip belts are the main ore-controlling structures, and the magmatic rocks closely related to mineralization are mainly meso-fine-grained porphyry granodiorite. The contact zone between the deposit and the surrounding rock carbonate rocks is often accompanied by skarnization, carbonization, silicification and other alteration. The formation of the deposit mainly experienced the early skarn stage, the magnetite stage, the quartz-sulfide stage and the late carbonate stage. The magnetite stage and quartz sulfide stage are the main metallogenic stages of the Da-Pai Fe-Pb-Zn polymetallic deposit. The ore deposit has the metallogenic characteristics of typical skarn deposits. Based on the investigation of the geological characteristics of the Dadai iron, lead and zinc polymetallic deposits in the west of Fujian, the oxygen isotopes and pyrite of the main minerals magnetite, pomegranate and pyrite in the ore have been developed respectively. The sulfur and lead isotopes of sphalerite and galena are tested. The results show that the 未 18O value of pomegranate varies from 3.4 to 6 鈥，

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