In situ geochemistry of dyke−marble interfaces obtained by portable X-ray fluorescence (pXRF) spectroscopy: Implications for sources of ore-forming materials in the Baiyinnuo’er Zn−Pb deposit, Inner Mongolia, China

Abstract In situ analysis performed by portable X-ray fluorescence (pXRF) spectroscopy was used to measure two different contact interfaces of dyke and marble in the Baiyinnuo’er Zn−Pb deposit located in Inner Mongolia, China. The limit of detection (LOD) standardisation method was used to assess pXRF readings through dividing readings into low, medium and high concentrations, and readings were screened according to the concentration range distribution. Spatial trend analysis and enrichment factor calculation were used for data processing. In both profiles of quartz porphyry−marble (Q−M) and granodiorite−marble (G−M), high values of Ca and Mg, and Si, Al and K, respectively, could be used to distinguish the distribution of marble and dykes. However, there were significant differences in the distributions of ore-forming elements between the two profiles. No ore-forming elements were enriched near the contact interface of the Q−M profile, but all ore-forming elements, such as Zn, Pb, Cu and Fe, were significantly enriched in the skarns located between granodiorite and marble. Therefore, the intrusion of granodiorite resulted in the enrichment of ore-forming elements, and provided metals for mineralization. Based on the results of the calculated enrichment factor for the G−M profile, the enrichment degree of selected elements in descending order was Pb, Zn > Ca > Fe > Al, Si > K in skarns relative to granodiorite, and Pb, Fe > Si, Al > Zn > K > Ca in skarns relative to marble. Zn and Pb were enriched in skarns relative to granodiorite but partially depleted relative to marble, indicating the high background Zn and Pb in marble; therefore, marble could provide at least part of the Zn and Pb. As a consequence, the intrusion of granodiorite resulted in skarnisation and mineralisation, and introduced ore-forming elements including Zn, Pb, Cu and Fe, but marble also provided at least part of the Zn and Pb, and the deposit was considered to be a skarn Zn−Pb deposit. In situ geochemical analysis at the outcrop scale is a useful approach for research into geological processes including skarnisation and mineralisation, as well as determining the source of ore-forming materials.