康滇地軸東緣典型鉛鋅礦床分散元素鎘鍺鎵的富集規(guī)律及富集機制

1、康滇地軸東緣典型鉛鋅礦床分散元素鎘鍺鎵的富集規(guī)律及富集機制        康滇地軸東緣位于環(huán)太平洋構(gòu)造域與特提斯構(gòu)造域的結(jié)合部位,是松潘甘孜印支褶皺帶中的一個重要單元,自晚太古代以來,本區(qū)經(jīng)歷了長期、復(fù)雜的地質(zhì)構(gòu)造演化歷史,形成了大量的金屬礦產(chǎn)資源,其中包括富含分散元素鎘、鍺、鎵的鉛鋅礦床。本文以康滇地軸東緣幾個大(特大)型典型鉛鋅礦床(如四川天寶山礦床、大梁子礦床和云南會澤礦床)為解剖對象,在系統(tǒng)野外工作的基礎(chǔ)上,詳細描述了天寶山、大梁子和會澤三個典型鉛鋅礦床的地質(zhì)、地球化學(xué)特征。室內(nèi)研究在常規(guī)光片、薄片觀測的基

2、礎(chǔ)上,綜合運用化學(xué)分析、等離子質(zhì)譜分析、電子探針等技術(shù)手段,對礦床的巖石(礦石)和硫化物單礦物的常量元素、微量元素及鉛、硫、碳等的同位素地球化學(xué)、分散元素鎘、鍺、鎵含量、分散元素鎘、鍺、鎵的賦存狀態(tài)和富集特征等方面進行了系統(tǒng)研究。結(jié)合區(qū)域地質(zhì)構(gòu)造演化,論文探討了康滇地軸東緣鉛鋅礦床形成的地質(zhì)構(gòu)造條件和成礦作用,揭示了分散元素鎘、鍺、鎵在鉛鋅礦床中的富集規(guī)律與富集機制。本論文取得如下新認識:1.康滇地軸東緣典型鉛鋅礦床賦礦圍巖均為碳酸鹽巖,其中天寶山和大梁子礦床為上震旦統(tǒng)燈影組白云巖,會澤礦床為下石炭統(tǒng)擺佐組白云巖(或灰質(zhì)白云巖),這些地層都富含成礦元素Zn和Pb以及分散元素Cd。未受蝕變的賦礦

3、圍巖中Zn含量顯著高于地殼同類巖石的豐度,一些巖石可高出地殼豐度12個數(shù)量級;Pb在各類巖石中也有一定程度的富集,但富集程度低于Zn;分散元素Cd在巖石中的含量普遍高于地殼同類巖石豐度一個數(shù)量級以上,而Ga和Ge的含量與地殼同類巖石的豐度相近。由此可見,Zn、Pb和Cd等元素在區(qū)域巖石中的高背景值,為本區(qū)鉛鋅成礦及分散元素富集提供了物質(zhì)基礎(chǔ)。2.等離子質(zhì)譜分析和電子探針分析表明,分散元素Cd、Ge、Ga主要以類質(zhì)同象形式賦存于原生硫化物閃鋅礦、方鉛礦和黃鐵礦中,少量可能以超顯微獨立礦物的形式存在。其中Cd主要賦存于閃鋅礦中,Ge、Ga主要賦存于方鉛礦中。3.根據(jù)礦體的產(chǎn)出特征,結(jié)合礦床的鉛同位

4、素模式年齡資料,認為康滇地軸東緣鉛鋅礦床的成礦時代晚于賦礦地層時代,屬典型的后生礦床,鉛同位素構(gòu)造演化表明康滇地軸東緣鉛鋅礦床的礦石鉛主要來自于上地殼,特別是造山帶。4.賦礦圍巖、礦石和閃鋅礦具有相似的稀土元素地球化學(xué)特征,總體表現(xiàn)為輕稀土相對富集,Eu和Ce呈弱負異常,稀土元素分布曲線向右傾斜。說明礦石中的稀土元素組成特征繼承了賦礦圍巖稀土元素組成的特征,反映出礦石的稀土元素主要來自賦礦地層。5.康滇地軸東緣典型鉛鋅礦床硫化物的硫同位素組成總體上與賦礦地層形成時期的海相硫酸鹽的硫同位素組成相近,說明礦床的硫主要來自賦礦地層。但天寶山礦床硫化物的(34)S值明顯低于震旦紀(jì)時期海相硫酸鹽的(34

5、)S值,可能為細菌還原所致,成礦處于相對還原的環(huán)境。6.首次總結(jié)了康滇地軸東緣鉛鋅礦床分散元素的賦存狀態(tài)和空間分布規(guī)律:分散元素Cd、Ge、Ga主要以類質(zhì)同象和機械混入物形式賦存與硫化物礦物中,特別是閃鋅礦和方鉛礦中,但富集程度相對較低。自西向東,即由天寶山大梁子會澤礦床,分散元素富集有明顯的空間分帶現(xiàn)象,表現(xiàn)為礦床有富鎘鎵富鎘富鍺之變化趨勢。7.Pb、Zn等金屬元素主要呈氯化物絡(luò)合物的形式活化遷移,Cd、Ge、Ga等分散元素也可能形成了部分氯化物絡(luò)合物或者被Pb、Zn的絡(luò)合物吸附而隨之一起搬運;含礦熱液帶來的熱能造成礦化圍巖中有機質(zhì)的熱降解作用產(chǎn)生甲烷,從而導(dǎo)致硫酸鹽的還原和金屬硫化物的沉淀

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