Constraints From CSAMT Data On The Metallogenic Mechanism Of The Zhaishang Gold Deposit,Western Qinling,China

The Western Qinling Mountains is the world's second largest metallogenic province of Carlin and Carlin-like gold deposits in the world.There were many periods of intense magmatism in this region,and the Indosinian-Yanshanian magmatism was considered to be closely related to the Carlin and Carlin-like gold deposits mineralization in this region.The Zhaishang gold deposits,which was formed in the late yanshanian period(130 Ma),has been a research hotspot in recent years for its late discovery,rapid growth and huge reserves.Magmatic rocks are not exposed in Zhaishang gold deposits area(Diorite porphyrite vein of concealed carbonatization is found in some boreholes and tunnels)and the ore-forming fluids have both chemical characteristics of atmospheric precipitation,metamorphic water and deep source fluids.There are two major controversies in the metallogenic model: The first issue is whether there is a connection between the gold depositing and the Mesozoic medium-acid granite intrusive rocks.The second issue is about the sources of ore-forming fluids and their migration pathways.In this research,we use 8 CSAMT profiles,obtaining the underground electrical resistivity structure of this gold deposit through high-resolution 2-D inversion.A ~1 km wide high-resistivity(>3000 ??m)body occurs at the depths of ~600m on the bottom of the resistivity model.Besides,two nearly upright,slightly NE-dipping high-conductivity channels distribute on the both sides of the high-resistivity body and approximately connect it with the proven gold-bearing quartz veins on the ground.Combined with other geological and geophysical information,we suggest that this high-resistivity body could be the Mesozoic granitic intrusive rock.These two high-conductivity channels are interpreted to be the wings of an NE-dipping anticline being formed under the regional compression stress field during the Caledonian orogeny and reactivated under the violent tectonic movements during Indosinian and Yanshanian periods,which could play a role as the pathways for the deep-derived ore-forming fluids(most likely the magmatic water)going upward and near-surface groundwater and meteoric water infiltrating downward,as well as providing the space for their mixture.Accordingly,we propose an integral metallogenic model as “Formation of regional fault—Intermediate-acid magma intrusion—Mixture of deepand shallow-derived ore-forming fluids—Differentiation—Mineralization” to constrain the metallogenic mechanism of the Zhaishang gold deposit.The discovery of concealed magmatic rock intrusion and fluid channel in the lower part of the mining area strongly proves that the formation of the deposit is closely related to the regional magmatism,and provides a certain geophysical constraint for solving the dispute over the metallogenic model of the Zhaishang gold deposit.In addition,the electrical characteristics of "high resistance+high conductivity channel" in the resistivity model belong to the structural fracture zone composed of secondary faults and the small-scale rock mass combination of post-emplacement,which can support the theory of the large deposit formed by smaller intrusion to some extent.