康滇地轴东缘典型铅锌矿床分散元素镉锗镓的富集规律及富集机制

1、康滇地轴东缘典型铅锌矿床分散元素镉锗镓的富集规律及富集机制        康滇地轴东缘位于环太平洋构造域与特提斯构造域的结合部位,是松潘甘孜印支褶皱带中的一个重要单元,自晚太古代以来,本区经历了长期、复杂的地质构造演化历史,形成了大量的金属矿产资源,其中包括富含分散元素镉、锗、镓的铅锌矿床。本文以康滇地轴东缘几个大(特大)型典型铅锌矿床(如四川天宝山矿床、大梁子矿床和云南会泽矿床)为解剖对象,在系统野外工作的基础上,详细描述了天宝山、大梁子和会泽三个典型铅锌矿床的地质、地球化学特征。室内研究在常规光片、薄片观测的基

2、础上,综合运用化学分析、等离子质谱分析、电子探针等技术手段,对矿床的岩石(矿石)和硫化物单矿物的常量元素、微量元素及铅、硫、碳等的同位素地球化学、分散元素镉、锗、镓含量、分散元素镉、锗、镓的赋存状态和富集特征等方面进行了系统研究。结合区域地质构造演化,论文探讨了康滇地轴东缘铅锌矿床形成的地质构造条件和成矿作用,揭示了分散元素镉、锗、镓在铅锌矿床中的富集规律与富集机制。本论文取得如下新认识:1.康滇地轴东缘典型铅锌矿床赋矿围岩均为碳酸盐岩,其中天宝山和大梁子矿床为上震旦统灯影组白云岩,会泽矿床为下石炭统摆佐组白云岩(或灰质白云岩),这些地层都富含成矿元素Zn和Pb以及分散元素Cd。未受蚀变的赋矿

3、围岩中Zn含量显著高于地壳同类岩石的丰度,一些岩石可高出地壳丰度12个数量级;Pb在各类岩石中也有一定程度的富集,但富集程度低于Zn;分散元素Cd在岩石中的含量普遍高于地壳同类岩石丰度一个数量级以上,而Ga和Ge的含量与地壳同类岩石的丰度相近。由此可见,Zn、Pb和Cd等元素在区域岩石中的高背景值,为本区铅锌成矿及分散元素富集提供了物质基础。2.等离子质谱分析和电子探针分析表明,分散元素Cd、Ge、Ga主要以类质同象形式赋存于原生硫化物闪锌矿、方铅矿和黄铁矿中,少量可能以超显微独立矿物的形式存在。其中Cd主要赋存于闪锌矿中,Ge、Ga主要赋存于方铅矿中。3.根据矿体的产出特征,结合矿床的铅同位

4、素模式年龄资料,认为康滇地轴东缘铅锌矿床的成矿时代晚于赋矿地层时代,属典型的后生矿床,铅同位素构造演化表明康滇地轴东缘铅锌矿床的矿石铅主要来自于上地壳,特别是造山带。4.赋矿围岩、矿石和闪锌矿具有相似的稀土元素地球化学特征,总体表现为轻稀土相对富集,Eu和Ce呈弱负异常,稀土元素分布曲线向右倾斜。说明矿石中的稀土元素组成特征继承了赋矿围岩稀土元素组成的特征,反映出矿石的稀土元素主要来自赋矿地层。5.康滇地轴东缘典型铅锌矿床硫化物的硫同位素组成总体上与赋矿地层形成时期的海相硫酸盐的硫同位素组成相近,说明矿床的硫主要来自赋矿地层。但天宝山矿床硫化物的(34)S值明显低于震旦纪时期海相硫酸盐的(34

5、)S值,可能为细菌还原所致,成矿处于相对还原的环境。6.首次总结了康滇地轴东缘铅锌矿床分散元素的赋存状态和空间分布规律:分散元素Cd、Ge、Ga主要以类质同象和机械混入物形式赋存与硫化物矿物中,特别是闪锌矿和方铅矿中,但富集程度相对较低。自西向东,即由天宝山大梁子会泽矿床,分散元素富集有明显的空间分带现象,表现为矿床有富镉镓富镉富锗之变化趋势。7.Pb、Zn等金属元素主要呈氯化物络合物的形式活化迁移,Cd、Ge、Ga等分散元素也可能形成了部分氯化物络合物或者被Pb、Zn的络合物吸附而随之一起搬运;含矿热液带来的热能造成矿化围岩中有机质的热降解作用产生甲烷,从而导致硫酸盐的还原和金属硫化物的沉淀

6、The Eastern edge of Kangdian axis, is located in the combined zone of circum-Pacific tectonic and Tethys tectonic domains. It is a important tectonic cell of the SongpanGanzhi in India-China folded zone. The area has gone through a long and complex geologic-tectonic evolutionary history since late A

7、rchean. A great quantity of metal mineral resources had been formed in this area. There into, they include lead-zinc deposits of enrichment dispersed elements such as cadmium (Cd), germanium (Ge) and gallium (Ga). Several giant (supergiant) typical lead-zinc deposits (such as Tianbaoshan deposit in

8、Sichuan, Daliangzi deposit in Sichuan and Huize deposit in Yunnan) were studied in this article. Based on systematic field investigations, the article described in detail the geologic and geochemical characteristics of three typical Pb-Zn deposits from Tianbaoshan, Daliangzi and Huize. Study in door

9、, based on common observation of polished sections and thin sections, the author synthesize to use chemical analysis, ICP-MS analysis and electronic microprobe (EMP) analysis to technical means. The thesis has finished systematic research in many aspects such as the major elements, trace elements an

10、d lead, sulfur, carbon isotope geochemistry of rocks (ores) and minerals in deposits, the content of dispersed elements cadmium (Cd) and germanium(Ge) and gallium(Ga), the occurrence and characteristics of enrichment of dispersed elements cadmium(Cd) and germanium(Ge) and gallium(Ga). Combined with

11、the evolution of the regional geology and structure, the article has researched the geological and structure conditions and the mineralization of lead-zinc deposits in the eastern edge Kangdian axis, revealed the enrichment occurrence and enrichment mechanism of dispersed elements cadmium (Cd), germ

12、anium(Ge) and gallium(Ga) in the lead-zinc deposits, and summed up the enrichment regularity of dispersed elements cadmium(Cd), germanium(Ge) and gallium(Ga). In this paper, to obtain new understanding as following:1. The host rock of occurrence ore are all carbonate rock in typical lead-zinc deposi

13、ts in the eastern edge of Kangdian axis. There into, deposits of Tianbaoshan and Daliangzi are dolomite of the upper Sinian Dengying group, Huize deposit is dolomite (or gray dolomite) of under Carboniferous Baizuo group. These layers are all rich ore-forming elements Zn and Pb, as well as dispersed

14、 elements cadmium (Cd) et al. The contents of Zn in no-alteration host rocks of occurrence ore were obviously higher than Clarke number of similar rocks in the earth's crust. Some of rocks may be higher to over several-ten times of Clarke number. Lead also has a degree of enrichment in various t

15、ypes of rock, but degree of enrichment is below than Zn. The contents of dispersed element cadmium(Cd) is commonly higher upper ten times of Clarke number of similar rocks in the earth's crust. But the contents of dispersed element germanium and gallium are similar to Clarke number of same rocks

16、 in the earth's crust. From this we can see, the high based value of zinc,lead and cadmium et al elements in region rocks, supply the matter foundation for the Pb-Zn mineralization and the enrichment of dispersed elements.2. ICP-MS analysis and electronic microprobe (EMP) analysis showed that di

17、sposed elements cadmium(Cd), germanium(Ge)and gallium(Ga) are mainly as the form of isomorphism occurrence in the primary sulfide such as sphalerite, galena and pyrite. A small amount of them may be occurrence as ultra-micro independence minerals. Cadmium(Cd) is major occurrence in sphalerite , germ

18、anium(Ge) and gallium(Ga) are major occurrence in galena.3. .According to the characteristics of the ore bodies occurrence, combined with the data of lead isotope model age of deposits, the author thought that the forming ore times are later than layers of occurrence ore in the eastern edge of Kangd

19、ian axis. They are typical epigenetic deposits. The lead isotope tectonic evolution showed that ore leads of lead- zinc deposits in the eastern edge of Kangdian axis come mainly from the upper crust, especially the orogenic belt.4. The host rocks of occurrence ore, ores and sphalerite have similar g

20、eochemistry characteristics of rare earth elements. They showed in total relatively enrichment light rare earth, europium(Eu) and cerium(Ce) were weak negative anomaly, the distribution curve of rare earth elements trended to right. It illustrated that the rare earth elements composition characteris

21、tics of ores inherited the characteristics of rare earth elements composition of the host rock of occurrence ore. They reflected that the rare earth elements of ore come from the layers of occurrence ore.5. The sulfur isotope composition of sulfide from typical lead-zinc deposits in the eastern edge

22、 of Kangdian axis are totally similar to the sulfur isotope composition of marine sulphate which the layers of occurrence ore form times. They illustrated that sulfur of deposits mainly come from the layers of occurrence ore. But(34)S value of sulphide from the Tianbaoshan deposit is obviously lower

23、 than(34)S value of sulphide from marine sulphate of Sinian period. It may be caused by bacterial reduction, mineralization was in the environment of relatively reduction.6. For the first time, this article summed up the state of occurrence and distribution laws in space of dispersed elements from t

24、he typical lead-zinc deposits in the eastern edge of Kang-Dian axis. Dispersed elements cadmium(Cd), germanium(Ge) and gallium(Ga) are mainly as omorphism and mechanical mixed matters in single minerals of sulfides, especially in sphalerite and galena, but the degrees of enrichment are relatively lower. From west to east, in other words, from Tianbaoshan deposit