Prediction of Hidden Ore Bodies using Integrated Geology, Source of Fluids and Stratagem EH4 Geophysical Survey in Kuoerzhenkuola Gold Deposit in Xinjiang, China

The Kuoerzhenkuola gold deposit is located in the Sawur gold belt in Xinjiang, China. An integrated geological, geochemical and geophysical investigation was carried out in the Kuoerzhenkuola gold deposit, to determine the extension of the principal mineralized system, in the search for new resources. Re‐examination of the rocks and structures in the Kuoerzhenkuola area showed that the study area features an elliptical caldera where the gold deposit lies. A re‐investigation of the mine geology found that the mineralization at the Kuoerzhenkuola gold deposit is not controlled by the EW‐striking regional fault as previously assumed, but by a caldera fracture system locally superimposed by regional faults; the host rocks are andesites and dacites of the Carboniferous Heishantou Group rather than the crypto‐explosive breccia of the Devonian Sawurshan Group. Gas components of fluid inclusions from quartz, trace element chemistry of pyrite and fluid inclusions in pyrite, Pb isotopes of pyrite, and whole‐rock geochemistry and Pb isotopes of the country rocks are used to study the source of fluids at Kuoerzhenkuola gold deposit. The ore‐forming fluids are characterized by low–moderate temperatures and low salinities estimated from fluid inclusion microthermometry. Quadrupole mass spectrometry indicated a CO₂‐bearing fluid. Inductively coupled plasma–mass spectrometry of the fluid inclusions indicated high Cu (average 70 ppm) for the Au mineralization, whereas the host rocks have low Cu (average 33 ppm), indicating that Cu of the ore‐forming fluids originated from magmatic fluid rather than the volcanic rocks. Pb isotopes of ores and host volcanic rocks indicate a similar, mixed source and some Pb could be sourced from the volcanism. This implied that magmatic fluids could play an important role in the Au mineralization process. These new geological findings and the fluids derived mainly from the magmatic fluids suggest that the ore‐forming fluids originate at depth, and are transported and precipitated within the caldera fracture system. Thus, we proposed a conceptual target area at depth. A detailed Stratagem EH4 measurement was carried out to test the validity of the conceptual target. Stratagem EH4 soundings over six parallel traverses perpendicular to the mineralized trend showed that the caldera fracture system could extend for approximately 900 m in the dip direction at the center of the caldera, an indication of the presence of potential deep mineralization under the surveyed area. Detailed modeling of the Stratagem EH4 sounding images provided well‐defined targets for test drilling. Subsequent test drilling on one of these targets, which extends down 850 m at an angle of 87°, returned encouraging results because four core‐intercepts of gold ore bodies at down‐hole depths of 40.5–42.0 m, 70.5–73.5 m, 357.0–358.5 m, and 384.5–385.5 m and a long interval gold mineralized body (0–720 m) were encountered.