内蒙古常福龙沟金矿床地质特征和硫、铅同位素地球化学

Geological Characteristics and Sulfur and Lead Isotopic Geochemistry of the Changfulonggou Gold Deposit in Inner Mongolia

常福龙沟金矿位于华北陆块北缘隆起带,是中元古界渣尔泰群阿古鲁沟组在内蒙古中部金矿找矿的新突破。常福龙沟金矿体呈中脉状-薄脉状产出于渣尔泰山群阿古鲁沟组浅变质碎屑岩中,矿石矿物为黄铁矿及少量方铅矿、黄铜矿、自然金和银金矿;脉石矿物有石英、方解石、绢云母等。发育自形-半自形粒状结构、它形粒状结构、包含结构、交代残余结构、显微鳞片粒状变晶结构和压碎结构等,以及稀疏或稠密浸染状、网脉状、碎裂状、角砾状等构造。围岩蚀变主要为硅化、黄铁绢英岩化、碳酸岩化,其中硅化强度与金矿化呈正相关关系。载金矿物黄铁矿硫同位素组成介于-0.6‰~2.9‰之间,极差较小,暗示硫源比较单一且成矿环境和物理化学条件较为稳定,硫可能来自于岩浆。黄铁矿铅同位素206Pb/204Pb=16.849~17.035,207Pb/204Pb=15.343~15.411,208Pb/204Pb=37.310~37.547,与渣尔泰山群全岩铅同位素范围相近,结合铅同位素模式年龄,推测中元古界渣尔泰山群可能是成矿物质的提供者。

The Changfulonggou gold deposit,located in the uplift belt of the northern margin of the North China block,is a new prospecting breakthrough in the Agulugou Formation of the Zhaertaishan Group in central Inner Mongolia. The vein gold orebodies are hosted in the low-grade metamorphic clastic rocks of the Agulugou Formation. The main metallic minerals are pyrite and minor galena,chalcopyrite,native gold and electrum,and gangue minerals are mainly quartz and calcite. The ores have textures of euhedral-subhedral granular,anhedral granular,poikilitic,metasomatic relict,lepidoblast and crush,and structures of dissemination,net vein,cataclastic and brecciate. Wall-rock alteration contains silication,pyrite-sericitization and carbonation,of which the silication is closely related with gold mineralization. The pyrite δ34SV- CDTvalues vary from- 27. 9‰ to 2. 9‰,indicating that the sulfur was sourced from magma. The206 Pb /204 Pb,207Pb /204 Pb and208Pb /204 Pb ratios for pyrite have homogenous compositions,varying in 16. 849 ~17. 035,15. 343 ~ 15. 411 and 37. 310 ~ 37. 547,respectively. The Pb-isotopic compositions of pyrite are very close to the field of the Zhaertaishan Group and the model ages are Late Mesoproterozoic to Early Neoproterozoic time. The Pb-isotopic compositions indicate that the ore-forming materials likely emanated from the Mesoproterozoic Zhaertaishan Group.