Identification of metal sources in Geogas from the Wangjiazhuang copper deposit, Shandong, China: Evidence from lead isotopes

The Geogas survey has been confirmed to be a useful geochemical pathfinder in prospecting for mineral deposits concealed beneath various types and thicknesses of overburden. To understand the sources of metals in Geogas, the lead isotopes were chosen as tracers. The Pb isotope ratios in soil, host rocks and ores were determined following separation and purification by Nu Plasma HR Ionization Mass Spectrometer and those in Geogas samples were analyzed by HR-ICP-MS (High Resolution Inductively Coupled Plasma-Mass Spectronmetry) (Element 2) and iCAP Q-ICP-MS (Quadrupole Inductively Coupled Plasma-Mass Spectronmetry) with optimized operating parameters. The utilization of HR-ICP-MS and iCAP Q-ICP-MS can be effective in determining extremely low levels of Pb isotopes and make great progress in analytical precision and sensitivity to render the test data and experimental results more convincing. The results of this study of different samples collected at the Wangjiazhuang Cu deposit show that Pb isotope ratios of Geogas background samples are apparently different from those of various media (soil, host rocks and ores) in the vicinity of the ore bodies. The Pb isotope ratios in Geogas anomalous samples are quite distinct from those in Geogas background samples. The Pb isotope ratios of Geogas anomalous samples scatter close to ores. It is assumed that the anomalous Pb in Geogas samples came mainly from deeply concealed mineral deposits, this research provides much more reliable evidence for the explanation of Geogas anomalies and further demonstrates that the Geogas technique is a viable tool to identify deeply buried mineralization under exotic overburden.