Abstract:The Wushenjiagayiti gold deposit is by far the largest gold deposit in the Xiemisitai—Shaerburti metallogenic belt, with a gold resource of 2t at grade of 8×10-6. The geological features, rockforming age and geochemical features of the felsophyre dyke are of great significance to the mineral search work in the area. The gold ore body is produced in the contact shear zone between the medium acidic rock body and the stratum, and is closely syngenetic with the felsophyre dyke, mainly developing two ore types of sulphide quartz vein type and alteration rock type, and the industrial type is quartz vein alteration rock type gold deposit. In this paper, we measured 429.1±1.6 Ma for the nonmineralised felsophyre dyke and 426.5±1.7 Ma and 426.0±1.6 Ma for the two mineralised felsophyre dyke, suggesting that the deposits were formed during the Middle to Late Silurian. The andesite, monzonite, felsophyre dyke and both types of gold ores have similar trends of rare earth element distribution and trace element evolution, with a progressive evolutionary relationship from front to back. All rocks show enrichment of light rare earth elements and loss of heavy rare earth elements, with a clear differentiation between light and heavy rare earth elements, an obvious enrichment of large ionophile elements Rb, Ba and Th, a relative loss of high field strength elements Ti and Nb, and no Eu and Ce anomalies, showing the characteristics of subduction zone island arc magmas. The εHf(t) isotopes (+8.86~+15.41) of the felsophyre dyke are highly overlapping with the regional rocks (+5~15.4), corresponding to diagenetic ages of 429~844 Ma, slightly older than the zircon ages, indicating that the magmatic hydrothermal fluids that formed the mineralisation originated from the age crust added by the lossy mantle, and that the source area survived in the crust for a relatively short period of time. The felsophyre dyke，monzonite and region I granite fall into the same area on the petrogenetic and tectonic discrimination diagrams, and the genetic type is a high potassium—calciumalkaline quasialuminiumvalued Itype granite. The geological, chronological and geochemical characteristics of the deposit suggest that the genetic type is a magmatic—hydrothermal gold deposit, a product of the evolutionary divergence of homogenous magmatic activity with intrusive rocks in a southward subduction context of the late silurian PalaeoAsian Ocean, and predict that there are multiple types of Au—Cu deposits associated with Itype granites in the region.
