“…The common spectral MEIs include sericite Al-OH absorption peak (Pos2200) shift and illite crystallization (IC) [1,2,[29][30][31][32][33][34][35][36], chlorite Fe-OH absorption peak (Pos2250) shift [1,4,33,[37][38][39][40], alunite 1480 nm absorption peak (Pos1480) shift [3,41] and REE-bearing mineral absorption features at the bands of 640-870 nm [5][6][7][8]42]. The common chemical MEIs include contents of Ti, Sr, Mn, Pb, and their ratio values in chlorite [4,[43][44][45][46][47], contents of Si, Al, Mn, Zn, and their ratio values in sericite [30,48], contents of As and Sb, and their ratio values in epidote [45,46,49] and contents of K, Na, La, Sr, Pb, and their ratio values in alunite [3,41].…”