Factor analysis of geogas data for concealed lithium deposits detection and false anomalies identification in Jiajika area

The Jiajika hardrock-type rare metal deposit in western Sichuan, China, is considered the largest spodumene deposit in Asia. The quaternary overburden of this area leads to ineffectiveness for ore prospecting using geochemical soil and geochemical stream sediment surveys. Although geogas prospecting has been proven to be effective in exploring buried orebodies, it is seldom deployed to explore concealed lithium deposits. In this work, the geogas samples were collected using the dynamic collection technique along the traverses over three concealed lithium deposits, namely, V-804, V-X03 (Line 7 and Line 35 were selected for sampling, denoted as V-X03–7 and V-X03–35, respectively), and V-STG. The samples were also collected from a Li-poor pegmatite (V-CLZ). The concentrations of Li, Be, Rb, Cs, Nb, Ta, Sn, B, Sr, Ba, and W in the nitric acid collector were measured by performing inductively coupled plasma-mass spectrometry (ICP-MS) measurements. The nanoparticles in geogas were analysed by using a transmission electron microscope coupled with performing energy dispersive spectroscopy (TEM-EDS) measurements. Apparent anomalies of Li, Be, Rb, Cs, B, and Sr were observed on all the traverses. These elements are regarded as pathfinders for the detection of concealed lithium deposits. Clear anomalies of Li, Be, Rb, Sn, B, and Sr were also found over V-CLZ. The concentrations of these elements in the nitric acid solutions were close to those over V-X03–35 and V-STG. The pathfinders are thus not effective in accurately recognizing the false anomalies over Li-poor pegmatite. The TEM-EDS measurements are not suitable for the characterization of nanoparticles in the Jiajika area because the particles from Li-rich and Li-poor pegmatites exhibited similarities in their morphologies. In addition, Li and Be cannot be detected by studying the EDS spectra, and the disturbance from the high background was non-negligible. To effectively address these issues, factor analysis (FA) was conducted on the concentrations of Li, Be, Rb, Cs, Nb, Ta, and Sn in geogas. The synthesis score (SSC) was computed based on three factors extracted by FA. At some sampling sites over V-804, V-X03, and V-STG, the SSC values were larger than 0.25, whereas the maximum SSC over V-CLZ was 0.15. Therefore, FA of geogas data is arising as a feasible method to detect concealed lithium deposits and identify false anomalies in the Jiajika area. The elemental concentrations in the samples from V-X03–7 were much higher than those from the other veins. This effect was attributed to the migration of the elements from buried orebodies to the ground surface, which was possibly promoted by the tourmalinized hornfels.