Metallogenetic Geochemical Characteristics Of The Auriferous Granitic Intrusions In The Bumo Deposit,Hainan Province Of South China:Implication For Mineralizing Potential

With the increasing demand for gold in the international market,countries in the world are also stepping up the mining and exploration of all kinds of gold deposits.The easy gold deposits have gradually decreased due to the exploitation in the last ten years.Miners are look forward to find a new way to discover a deep deposit.However,the discovery of economically gold deposits is expensive.At present,researchers have summarized a series of geochemical indicator of ore bearing rock mass by studying the world’s large gold deposits.The application of these geochemical indicators can help us identify and evaluate the metallogenic potential of intrusions.The gold deposit related to intrusions is one of the important exploration types of gold source.a significant number of gold deposits show close spatial,temporal,and genetic relationships with the associated intrusions and contain fluids that have a direct connection to them,such as porphyry copper gold deposit,Carlin gold deposit and so on.Most studies show that the magmatic rocks associated with mineralization usually have the characteristics of high oxygen fugacity and high-water contentHainan Island is one of the gold metallogenic areas in the South China Plate,and more than 50 gold deposits and gold mineralization spots have been discovered.The Gezhen shear zone is an important orogenic gold metallogenic belt in the west of Hainan Island,where a series of gold deposits such as Tuwaishan,Erjia and Bumo deposits are developed.The Bumo gold deposit is located in the southern margin of the Gezhen shear zone,and the gold mineralization types are quartz vein type and altered rock type.Recently,mine geologists discovered a new gold-bearing granitic intrusive rock in the deep part of the Bumo ore area.And the gold-bearing granitic intrusive rocks show strong pyritization.However,there are unknow of the emplacement age of the gold-bearing granitic intrusion,the source of gold mineralization,the mineralization potential and its genetic connection with the Bumo gold deposit.In this paper,we will be carried out to resolve the above issues by methods of zircon LA-ICP-MS U-Pb dating,zircon geochemical characteristics,in-situ S isotopes and pyrite trace elements.The research obtained in this paper are as follows:1.The gold-bearing intrusion occurred at the depth of–30 m level in the Bumo deposit.According to its exposure of the middle section and microscopic observation,the gold-bearing intrusion is composed of diorite porphyry,quartz monzodiorite and monzodiorite.Zircon LA-ICP-MS U-Pb dating shows that the emplacement ages of diorite porphyry,quartz monzodiorite and monzodiorite are 104±1 Ma,114±1 Ma and 114±1 Ma,respectively,which are younger than the metallogenic age of 244±12Ma for the Bumo deposit.2.The gold concentrations in pyrite of the diorite porphyry,quartz monzodiorite and monzodiorite by LA-ICP-MS are 0.1～5.0 ppm,0.1～0.2 ppm and 0.0～1.1 ppm,respectively.Theδ³⁴S values of the pyrite in the gold-bearing intrusions is 0.2—4.4‰,lower than those of the sulfides in the Hercynian to Indosinian（378—219 Ma）orogenic gold deposits of the Gezhen shear zone(δ³⁴S=1.9—9.8‰).The source of S and Au in the gold-bearing intrusion might be a magma source(δ³⁴S=0‰).3.Gold-bearing intrusions show zircon geochemical characteristics similar to the porphyry copper gold deposits,such as Eu/^*values greater than 0.4,high Hf concentrations of more than 8000 ppm,（Ce/Nd）/Y ratios of more than 0.01,10,000*（Eu/Eu*）/Y ratios of more than 1,and Dy/Yb ratios of more than 0.3.These geochemical characteristics indicate that the gold-bearing intrusion is characteristic of high-water content and high oxygen fugacity.4.During the late Yanshanian of late Mesozoic,South China including Hainan Island was affected by the breakoff and tearing of the paleo-Pacific subducted slab.This event might lead to an extensional tectonic environment that is conducive to the emplacement of the gold-bearing granitic magma in the Bumo mining district.The discovery of the early-middle Cretaceous gold-bearing intrusion indicates that the late Yanshanian magmatic rocks in Gezhen shear zone can be regarded as a key exploration target in the future.