内蒙古霍各乞Cu-Pb-Zn矿床^(39)Ar/^(40)Ar年代学研究:元古代预富集叠加印支期变质热液矿化实例  

^(39)Ar/^(40)Ar geochronological study on the Huogeqi Cu-Pb-Zn deposit in Inner Mongolia: A case of Proterozoic pre-enrichment followed by Indosinian metamorphogenic mineralization

作　　者：钟日晨[1,2] 李文博[2] 霍红亮[3] 

机构地区：[1]北京科技大学土木与环境工程学院,北京100083 [2]北京大学造山带与地壳演化教育部重点实验室,北京100871 [3]巴彦淖尔西部铜业有限公司,巴彦淖尔015500

出　　处：《岩石学报》2015年第6期1735-1748,共14页Acta Petrologica Sinica

基　　金：国家973项目(2012CB416602;2013CB429801;2006CB403500);国家自然科学基金项目(40972057)联合资助

摘　　要：霍各乞大型Cu-Pb-Zn矿床地处华北陆块北缘的狼山-渣尔泰山成矿带。该矿赋存于元古代带裂谷沉积岩系,矿区内围岩发生角闪岩相变质作用,并遭受剪切变形。赋矿围岩主要包括石英岩、云母片岩、碳质千枚岩、大理岩。此外,在赋矿围岩中存在铁建造层位,主要由磁铁矿及富铁角闪石构成。该矿的Cu-Pb-Zn矿化受剪切带控制,且发生于围岩剪切变形的晚期,退变质抬升阶段。成矿流体为变质流体。尽管霍各乞矿床Cu-Pb-Zn均显示后生热液矿化特征,矿床中硫化物却普遍具有元古代两阶段铅模式年龄(约1000Ma),表明成矿元素最初起源于元古代海底喷流沉积过程。此外,硫化物普遍富集重硫同位素,亦表明其最初来源于海水中硫酸盐的还原。为揭示Cu-Pb-Zn矿化及围岩变质时代,我们对围岩铁建造中的变质角闪石及成矿期的热液黑云母进行39Ar/40Ar年代学测试。围岩铁建造中的变质角闪石坪年龄为271.4±29.5Ma,代表峰期变质年龄。成矿期热液黑云母坪年龄为239.8±3.4Ma,代表Cu-Pb-Zn热液矿化时代。霍各乞热液矿化年龄略晚于围岩峰期变质年龄,这与该矿退变质期成矿的现象非常吻合。由于岩石在其退变质阶段无法产生变质流体,霍各乞Cu-Pb-Zn矿化的成矿流体来自深部岩石的进变质脱水。据此提出霍各乞矿床两阶段矿化模式:元古代期间,伴随海底热液活动发生同生沉积期Cu-PbZn预富集,形成富含成矿元素的裂谷火山-沉积岩。在印支期(二叠纪末-三叠纪初)的变质过程中,这些经历预富集的裂谷岩系变质脱水,其中的Cu、Pb、Zn再活化,含矿流体向浅部迁移,形成受剪切带控制的变质热液Cu-Pb-Zn矿床。从更宏观的角度考察,霍各乞印支期Cu-Pb-Zn矿化事件并不是孤立发生的,而是中国印支期大规模矿化事件的一部分。霍各乞变质热液CuPb-Zn矿化实例反映了此次印支期事件的成矿类型多样性,进�The large Huogeqi Cu-Pb-Zn deposit is located in the Langshan-Zhaertai area in the northern margin of the North China Block. This deposit is hosted in Proterozoic rift-related rocks,which were metamorphosed to amphibolite facies and mostly deformed by shearing. The major lithological units include mica schist,quartzite,carbonaceous shale,and marble. Some intercalated iron formations are distributed within the host rock sequences,and mainly composed of magnetite and Fe-rich amphibole. Cu-Pb-Zn mineralization of the Huogeqi deposit was controlled by shear zones in the mining field,and took place during uplift and retrograde metamorphism of the host rocks. The mineralization took place at pressure-temperature conditions that similar with those of greenschist facies metamorphism. Given that the host rocks were amphibolite facies metamorphosed,the Cu-Pb-Zn mineralization occurred at the retrograde stage of host rock metamorphism. This conclusion is evidenced by the fact that the peak metamorphic minerals（ e. g.,almandine） in the host rocks were locally cutcross and replaced by Cu-Pb-Zn sulfides. The ore-fluid is CH4-rich and low-salinity,and of metamorphic origin. Although Cu-Pb-Zn orebodies show characteristics of epigenetic mineralization,sulfides of this deposit are poor in radiogenic lead and have Proterozoic two-stage model ages（ ~ 1000Ma）,indicating that the ore-forming elements were originally derived from a crustal source in a syngenetic process during the development of the ore-hosting rift sequences. Furthermore,sulfides of the Huogeqi deposit are enriched in heavy sulfur isotopes,which is a characteristic of reduction of sulfates in sea water. To reveal the ages of hydrothermal Cu-Pb-Zn mineralization and host rock metamorphism,a39 Ar /40 Ar geochronological study was carried out.Metamorphic Fe-rich amphibole is separated from iron formation of the host rock sequences,and it yields a39 Ar /40 Ar plateau age of271. 4 ± 29. 5Ma. Given that the enclosure temperature of amphibole（ ca. 500 ~ 600℃）

关 键 词：狼山-渣尔泰山 CU-PB-ZN 39Ar/40Ar年代学 内蒙古 

分 类 号：P597.3[天文地球—地球化学]