GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS AND THE ORE-FORMING MECHANISM OF HAIGOU GOLD DEPOSIT

Haigou gold deposit, occurring in Haigou granite body, is a large low-sulfide quartz-vein type of deposit, controlled by NE-to NNE-trending faults. Analysis on trace element geochemical characteristics of ores, altered rock and wall rocks shows that infilling mineralization is dominant in the ore-forming process. The main indicator elements are Au,Hg, Pb, Bi and Mo. The axial zonal sequence of the deposit, from upper to lower, is presentedAg, as Ba-Hg-Ag-Bi-Au-As-Sb-Pb-Mo. The data of isotope and fluid geochemistry show that the ore-forming elements are derived from the metamorphic rocks of Seluohe group and Haigou granite. The ore-forming fluid is composed of magmatic water and paleo-meteoric water, which belongs to CO₂-NaCl-Na₂SO₄-H₂0 type. Under the background of regional geological evolution, the movement of lithospheric faults causes the anatexis of the metamorphic rocks of Seluohe group in the deep,forming Haigou granite and magmatic fluid rich in ore-forming elements and mineralizers, as well as the ore-forming fluid dominated by paleo-meteoric water. With the conversion of the stress field in the studied area to tension, and the forming of many secondary NE-to NNE-trending faults in Haigou granite body and its periphery at about 143 Ma, the equilibrium between magmatic fluid and paleo-meteoric water is disturbed, leading the migration of the two kinds of fluids to the dilation zones of the fault system. The mixture and ebullition of fluid and the change of physicochemical conditions result the deposition of gold from fluids, and form the Haigou gold deposit.