Relationship between Jiaodong Gold Deposit and Mesozoic Regional Granite Metallogenic Predication and Prospecting Direction
Jiaodong area is a world-renowned gold resource base.By the end of June 2023,a cumulative proven gold resource is over 5757t.The Mesozoic granites which are closely related to gold mineralization are widely distributed and have diverse rock types.It is the most developed and typical area in Shandong province.The relationship between gold deposits in Jiaodong area and the spatial distribution,formation era,and formation environment of regional granite in Mesozoic era has been analyzed and studied.The widely distributed Mesozoic granites in this area are classified as late Jurassic Linglong period(166～146Ma),early Cretaceous Guojialing period(135～123Ma),late early Cretaceous Weideshan period(123～110 Ma),and Laoshan period(118～108 Ma).It is regarded that regional magmatic events generally last for about 10Ma,while remelting granites generally last for 20Ma.It reflects two stages from the melt-ing of the basement rock to the intrusion crystallization.It has a process of melting from the basement sol-id rock,which also requires approximately 10Ma.The melting of the solid rock is about 10Ma and the in-trusion crystallization of the magma activity is about 10Ma.The Linglong period remelting granite is a post collision product of the Yangtze and North China plates.Guojialing period magmatic event represents the beginning of the Mesozoic tectonic system transformation in eastern China,Weideshan period magmat-ic event represents the peak period of tectonic system transformation,and Laoshan period magmatic event represents the end period of tectonic system transformation.86.8％of gold deposits are hosted in the granites of Linglong period,and 6.9％of gold deposits are hosted in the granites of Guojialing period.The background of Au element in the granites of Linglong period and Guojialing period is significantly higher than that in Weideshan period and Laoshan period.The range of ore sulfur is similar to granites in Lin-glong period and Guojialing period,especially with a large overlap with granites in Linglong period.It has the characteristics of small changes in sulfur isotopes in magmatic hydrothermal fluids.It is indicated that main source of ore sulfur is granites in Linglong period and Guojialing period.The ore lead mainly consists of reactivated lower crustal lead,namely pre-Cambrian crystalline basement lead,with mantle derived lead added.The mineralization age of gold deposits ranges from 162～146Ma,133～120Ma,120～115Ma and 112～105Ma,corresponding to the formation time of four regional granites in Jiaodong area.The min-eralization age is generally later than the diagenetic age of 3～5Ma.According to the correspondence be-tween Jiaodong gold deposits and polymetallic deposits and magmatic hydrothermal events,it can be divid-ed into Linglong gold mineralization period,Guojialing gold mineralization period,Weideshan gold and polymetallic mineralization period,and Laoshan polymetallic mineralization period.The gold deposits in Jiaodong area are mainly formed by the activation,migration,and enrichment of gold elements through remelting in metamorphic strata of Neoarchean and the bottom schist layers of Pal-eoproterozoic,as well as magmatic activity during Guojialing period.Based on the understanding of ore-forming processes mentioned above and based on the theory of geochemical blocks,the potential of Jia-odong gold deposits has been estimated.The potential of shallow gold deposits in Jiaodong area is about 18000t,and a systematic predication has been made for deep gold deposits in the northwest of Jiaodong ar-ea.It is predicated that shallow gold resources in the 3000m area will be 3997t,and the shallow gold re-sources in the 5000m area will be 7497t.Through comprehensive geological research,it has been found that there are hidden granites in Lin-glong period in the lower part of Neoarchean metamorphic rocks in Qixia area.Based on spatial distribu-tion of gold deposits mainly occurring in the granites in Linglong period,isotopes as S and Pb,and gran-ites in Linglong period are the recognition of direct surrounding rocks or parent rocks for gold mineraliza-tion.There are numerous quartz vein type small and medium sized gold deposits and mineralization points developed in the metamorphic rocks in the area,which may be manifestations of shallow or top ore bodies.It is believed that this area has a good mineralization background and potential.It is an important area for future gold exploration in Jiaodong area.It is recommended to deploy seismic and high-power induced po-larization profiles and geological research drilling to identify a series of faults with the trend of NE and geo-logical structures,providie a scientific basis for gold exploration.
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