Geochemical characteristics of trace and rare earth elements in the late Permian coals from the Lutang Mine,Chongqing

In recent years,owing to the increasing demand for rare metals and the depletion of traditional deposits,coal and coal bearing strata are considered as the potential sources for extracting rare metals,which has attracted much attention. To understand the metallogenic potential of Li,Ga,Nb,Ta,Zr,Hf,and rare earth elements plus yttrium (REY) in the late Permian coals from the Lutang Mine of Chongqing,the concentrations of trace and rare earth elements and mineralogical compositions in coals were determined using inductively coupled plasma spectrometry (ICP-MS),X-ray fluorescence (XRF),and X-ray diffraction (XRD). The results indicate that the Lutang coals are classified as high sulfur,low medium ash anthracite. The high sulfur (5.06%) in the Lutang coals is associated with the marine sedimentary environment. The minerals of the Lutang coals are mainly composed of illite,mixed layer illite/smectite,kaolinite,and pyrite,followed by K feldspar,calcite,ankerite,quartz,jarosite,and anhydrite. Compared with world hard coals,Li,Be,B,F,V,Cr,Zn,Ga,Ge,Se,Zr,Nb,Mo,Ag,Cd,Hf,Ta,Hg,Th,U,and REY are enriched in the Lutang coals,where the concentration coefficients of Li,Ga,Nb,Ta,Zr,Hf,and REY are 7.81,2.19～7.99,6.58,8.39,5.82,and 2.85,respectively. From top to bottom,the concentrations of Li,Ga,Nb,Ta,Zr,Hf,Ga,and REY increase gradually along the coal seam profile. Li,Ga,Nb,Ta,Zr,Hf,and REY mainly occur in minerals due to their significant positive correlations with ash yield. Medium rare earth elements are enriched. The δCe and δEu indicates that the sediment source region is not mafic basalt of the Kangdian upland. Enrichment of Li,Ga,Nb,Ta,Zr,Hf,and REY is mainly attributed to the leaching of the tuff layer,immediately underlying the K1 coal. The Lutang coal ash is a possible material for extracting REY,Li,Ga,Nb(Ta),and Zr(Hf).