Study On Multiple-stage Mineralization Of The Zhulazaga Gold Deposit In Inner Mongolia

The Zhulazaga gold deposit that is located in Inner Mongolia and was discovered in 1990s is a super-large gold deposit with total reserves over 70t.It is in the Mesoproterozoic metasedimentary rocks in the northern margin of the North China Craton.The Agulugou Formation where the gold deposit is located and the Bilute Formation where the Haoyaoerhuodong super-large gold deposit(with reserves of up to 200t)in Inner Mongolia belong to the Mesoproterozoic,and they are connected.Therefore,the study of the Zhulazaga gold deposit play an important role in the resource exploration in the northern margin of the North China Craton.In addition,the Zhulazaga gold deposit has obvious multistage mineralization and this characteristic is similar to world-class gold deposits such as Muruntau gold deposit and Sukhoi Log gold deposit.Therefore,the study of multiple epochs of gold mineralization of the Zhulazaga gold deposit is of great significance for understanding the similar type of deposit.In this paper,the research object is Zhulazaga gold deposit.Based on the previous work,a detailed field geological survey,petrographic study under Light microscope and Electron microscope,LA-ICP-MS analyses of different genetic metallic minerals and zircons,the main conclusions are as follows:(1)The gold mineralization could be divided into sedimentary-diagenetic stage,metamorphic-deformation stage,magmatic hydrothermal stage and oxidation stage.The sedimentary-diagenetic stage mainly have the effect of gold preconcentration.The metamorphic-deformation stage is the main mineralization epoch.And the altered ores which are major ores were formed during this stage.The magmatic hydrothermal stage superimposed the deposit.And the quartz vien type ores were formed during this stage.(2)It was determined that Au in the Zhulazaga gold mine occurred in two states:natural gold and lattice gold.The former is the main occurrence form of Au,while the latter only occurs in the arsenopyrite of magmatic hydrothermal period.(3)The U-Pb age of zircons from the diorite porphyrite closely related to mineralization is 269±12Ma,which demonstrate the magmatic hydrothermal stage took place in the Hercynian Period.The ages of detrital zircons collected from the Agulugou Formation imply that the deposit limit of the Agulugou Formation may be 1589±50Ma.(4)The mineralization process of the Zhulazhaga gold deposit is as follows:In Mesoproterozoic,during the sedimentation of the Agulugou Formation,Au in seawater which may have been brought up by volcanic rocks from the lower crust or deeper positions was sealed into sediments.And this process was similar to that of SEDEX deposits.Organic matter also played a role in Au enrichment from seawater to sediments.At the same time,the sedimentary pyrite and other metal minerals were formed.In metamorphic-deformation stage,the transformation of pyrite to pyrrhotite in the Agulugou Formation forms HS~-rich fluid.Au extracted from the sediments of the Agulugou Formation accumulates,migrates and precipitates at favorable locations.The Hercynian magmatism played a further superposition on the formation of gold deposits and further improved the reserves and grade of gold deposits.(5)The Zhulazaga gold deposit is defined as a stratabound sedimentary-metamorphic gold deposit superimposed by magmatic hydrothermal fluids.