UBC Theses and Dissertations
Trace element analysis of native gold by laser ablation ICP-MS : a case study in greenstone-hosted quartz-carbonate vein ore deposits, Timmins, Ontario Velasquez, Alejandro
Native gold contains trace amounts of other elements and from the relative abundance of these a geochemical signature can be obtained. The trace element composition provides a “fingerprint” that is unique to the gold deposit it comes from. This fingerprint can be used to distinguish gold sources and potentially provide insight into the geochemical processes operating in the formation of Au deposits. Native gold grains were acquired from 3 gold ore deposits; Hollinger, McIntyre, and Aunor. These ore deposits are located near Timmins, Ontario, in the western end of the Porcupine gold camp, the south-western part of the Abitibi greenstone belt. Respectively, Scanning Electron Microscope analysis/Energy Dispersive Spectrometry (SEM/EDS) was used to determine major elements in gold grains. Ag concentrations from the SEM/EDS analyses were used as the internal standard for the laser ablation inductively coupled plasma mass spectrometry technique (LA-ICP-MS) that yielded trace element concentrations. A new reference material (AuRM2) served as the external standard for 22 elemental analytes for the LA-ICP-MS analyses. Trace elements in native Au associate according to Goldschmidt’s classification of elements demonstrating that element behavior in native Au is not random. Such element behavior suggests that samples from each deposit formed under similar geological conditions. Chalcophile and siderophile elements provide the most compelling fingerprints of the three ore deposits and they appear to be in solid solution in Au whereas lithophile elements are not very advantageous for distinguishing deposits and element concentrations appear to be controlled by micro inclusions such as tourmaline. The deposits show low Ag contents, which is consistent with mesothermal Au. Hollinger and McIntyre deposits have similar trace element abundances with high Ag, Pb, Bi, Sb and Pd and low Cu; however Cu concentrations in McIntyre are higher than in Hollinger. In contrast, Aunor has high Cu abundances and low Ag, Bi, Sb, Pb and Pd. Gold grain signatures reflect the chemical characteristics of the host rock superimposed on the chemical signature of the mineralizing fluid. The association of Pb-Bi-Cu bearing phases such as galena and chalcopyrite with gold supports hydrothermal fluids with high concentrations of these elements.
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