Géochimie de la minéralisation aurifère à la mine Eldrich, region de Rouyn-Noranda, Québec, Canada

Abstract

Abstract The Eldrich mine gold deposit is located in the Abitibi volcanic belt, a subprovince of the Canadian Shield. The mineralization lies in a sheared and hydrothermally altered zone within the Flavrian batholith, an intrusion consisting mainly of felsic rocks. The intrusion and the enclosing volcanic rocks are of Archean age and have been subjected to regional greenschist facies metamorphism. The mineralized zone comprises gabbros, tonalites and trondhjemites, all enriched in S, CO2 and Na2O, and depleted in SiO2 and K2O. These compositional changes were caused by pyritization, carbonatization and albitization of the mineralized rocks. The ore zone is characterized by a strong enrichment in Au, but shows only minor or no enrichment in As, Sb, W, Cu, Pb and Zn, elements which are commonly concentrated in the gold deposits of the Abitibi belt. In the mineralized zone, 33 trace elements analyzed did not show any significant enrichment. A geochemical soil survey (humus) also detected an Au anomaly above the orebody, but failed to outline any enrichment in Ag, As, Cu, Ni, Sb and Zn. The Na2O enrichment in rocks is associated with the shear zone containing the orebody, and thus represents a regional indicator of mineralization. The S, CO2 and Au anomalies are restricted to the mineralized zone itself and constitute local indicators. Humus analysis offers a significant potential, although the anomalies are restricted, which favors the use of this method on a local rather than a regional scale.