Laser ablation ICPMS study of trace element chemistry in molybdenite coupled with scanning electron microscopy (SEM) - An important tool for identification of different types of mineralization
Abstrakt
Using the example of four different types of associations from the Bohemian Massif (greisen-, gold-, base metal-, and "barren granite"-related) and of one porphyry-Cu-Mo(Au) deposit from Uzbekistan, it is shown that molybdenite from a specific type of mineralization possesses a distinct trace-element geochemical composition, which is locally influenced by the presence of relevant mineral phases occurring in the form of sub-nano-, nano-to micron-scale impurities/inclusions. It is documented that, besides typically lattice-bound elements (Re, and W) and isostructural concentrations of Se and Te (substituting for S), molybdenite can concentrate other metals (e.g., Ag, As, Au, Bi, Cu, Nb, Pb, Zn, Zr) which mostly form inclusions or impurities.
Typical lattice-bound elements (W, Se, Te) can locally occur as impurities or micro-inclusions. The distribution of Re in molybdenite indicates crustal sources for the group of greisen-, base-metal-, and a few of the granite-related deposits, compared to a mixed mantle/crustal source for the Au-related and majority of granite-related deposits.
Greisen-related molyb-denites show the highest mean values of As (40 ppm), Cu (58 ppm), and Zn (45 ppm), but the lowest mean Re value (0.4 ppm). They contain abundant inclusions of native bismuth, which are accompanied, depending on the individual deposit, by variable quantities of Bi(Se)-, Bi(Pb)-, Pb(Bi)- and Pb-Bi-Cu-bearing phases and also bismuthinite (Bi2S3), wolframite and scheelite.
Gold-related molybdenite typically has the highest mean values of Ag (464 ppm), Au (24 ppm), Bi (1188 ppm), Sb (39 ppm), and Te (112 ppm) and also the highest median values of these elements. Gold mostly occurs as inclusions of native Au or in association with Bi (maldonite) and/or as Bi-Au-Te phases whereas silver is commonly present in the form of Au(Ag), and less commonly as Bi-Te-Ag, Ag-Se and Ag-Te phases.