The Relationship Between Intermediate-felsic Dikes And Gold Mineralization Of The Ge'erke Gold Deposit,West Qinling Belt

The relationship between dikes and gold mineralization and the contribution of dikes in the process of gold mineralization have been hot topics of geologists.The Ge'erke large gold deposit(> 90t)is located in the Dashui-Zhongqu District of the West Qinling Belt.It has developed a large number of intermediate-felsic dikes and is an ideal selection area for studying the relationship between the intermediate-felsic dikes and gold mineralization.Based on previous studies,this paper systematically studied the geological and geochemical characteristics of the deposit,identified the contact metasomatism,and redefined the origin of the hematite.By discussing the contribution of contact metasomatism to gold mineralization,it is concluded that there is a close spatial relationship between the dikes and gold mineralization in the Ge'erke gold deposit,but it does not have a temporal and genetic relationship.The deposit is mainly composed of natural gold,and the purity of natural gold is very high(> 99%),indicating that it is secondary gold.The natural gold is symbiotic with hematite.The uniform oxygen isotope(-4.71?0.39)characteristics of hematite and the geological phenomenon of remnants of pyrite in some hematite deposits suggest that hematite in the deposit is formed by the oxidation of pyrite.The zircon U-Pb ages of the diorite dikes before and after mineralization were 211.2 ± 3.2 Ma and 183.0 ± 5.8 Ma,respectively,combined with the fact that some ore bodies developed in the Early Jurassic(174 ? 201 Ma)formation,indicating that the gold metallogenic age of this deposit is between 183 Ma and 201 Ma.The gold metallogenic age is similar to the diagenesis age of granodiorite porphyry dikes(?214 Ma),indicating that the dikes and gold ore-body in the Ge'erke gold deposit haven't close time relationship.The magnetite developed in the magnetite-calcite veins on the east side of the Ge'erkuohe porphyry is of hydrothermal origin.Granodiorite porphyry vein develops minerals formed by contact metasomatism such as garnet and diopside.Therefore,the mining area has experienced a stage of contact metasomatism,but it is only developed in the northeast of the mining area,and its scale is small.The major metallic minerals formed by contact metasomatism were magnetite and a small amount of pyrite.However,the magmatic type and hydrothermal type magnetite and pyrite do not contain gold(the average value of gold is close to 0),indicating that contact metasomatism didn't provide metallogenic material for gold mineralization.There is no obvious altered mineralization zoning centered on the granodiorite porphyry dikes.At the same time,the breccia-type ore-rock of the ore-body in the granodiorite porphyry dikes is not mineralized in the breccia,but the cement is mineralized,which further shows that there is no obvious genetic relationship between the dikes and the gold mineralization in the Ge'erke gold deposit.The Ge'erke gold deposit is obviously controlled by structure and the metallogenesis has no selectivity to strata.The spatial relationship between dyke and gold orebody is close because: The rock mass as a pressure shadow,forming a tensile space,which is conducive to gold precipitation.The contact site of dyke and fault is the site of stress mutation,and also the common site of metallogenic fluid and gold precipitation.Therefore,the contact site is the site of mineralization.