Research On Isotope Identification For Anomalous Sources Of Deep-Penetration Geochemistry

Deep-penetration geochemistry, which is mainly used to prospect concealed deposits and blind ore bodies, is an emerging branch of geochemistry. In this paper, through research on lead and sulfur isotopic characteristics of different media （earthgas, fine-grained soil, surrounding rock, ore） in two known concealed deposits （the Jinwozi gold deposit in Xinjiang, Bairendaba-Weilasituo polymetallic deposit in Inner Mongolia）, two scientific issues have been discussed: contrast different capture fluids （aqua regia, nitric acid） when trapping earthgas; trace the source of abnormal substances by lead, sulfur isotop in earthgas and soil. The following conclusions are drawn.1) Aqua regia and nitric acid trapping earthgas, the lead isotopic compositions made a difference. But the analysis of variance revealed that this difference was the result of random factors. That is to say, when gathering the earthgas, no matter with aqua regia or nitric acid, the effect is the same.2) In these two deposits, lead isotopic ratios (²⁰⁸Pb/²04Pb、²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb) generally increased from the earthgas, ores, surrounding rocks to the soil. Theδ34S‰of anomaly zones was high compared with those of soil background areas.Through test of variance analysis on the lead isotopic compositions of earthgas in background and abnormal areas, the lead and sulfur isotopic characteristics of soil in background and abnormal areas, there was no significant differences between them, which preliminarily proved that it is inappropriate to trace the source of abnormal substances by lead, sulfur isotop in earthgas and soil.l3) The Pb isotopic compositions of ores and surrounding rocks in these two deposits were significantly different. That is, the surrounding rocks of the two deposits obviously have accumulation of radiogenic lead. However, this difference was not significantly reflected in the earthgas of background and abnormal areas. The reasons need to be further studied. This paper discussed this phenomenon only from the perspective of the capture fluids.4) In this paper, the soil total lead, sulfur isotopic compositions were analyzed to trace the source of abnormal substances, which was not successful. Further research will adopt partial extraction method to measure lead, sulfur isotopic compositions in active phase.5) In terms of the method of the isotope tracing on the deep-penetration anomaly sources, the problems of three aspects, which should be paid attention to, have been summed up in this paper, including the selection and preparation of capture fluid, collection of samples and laboratory analysis.