Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

There are significant variations in the concentration of trace elements in magnetite and hematite depending on the metallogenic environment at the time of formation of the deposit. This makes iron oxides useful as indicator minerals for mineral exploration. Iron oxides are a major component of Iron Oxide Copper-Gold deposits (IOCG) and of Iron Oxide-Apatite deposits (IOA). Magnetite and hematite in IOCG (n= 84 samples) and IOA deposits (n= 6), representative of 8 major IOCG and IOA deposits, worldwide, representing a range of geological environments and ages of formation, were analyzed by electron microprobe analysis (EMPA). A subset of IOCG (n = 30 samples) and IOA (n= 6) was analysed by LA-ICP-MS. The IOCG deposits samples are divided based on the principal iron oxide present: (1) Hematite (n = 10), (2) Magnetite (n = 37) and (3) Hematite ± Magnetite (n =8). Similarly, IOA deposits are divided: (1) Magnetite (n = 3) and (2) Magnetite ± Hematite. In these types of deposits, iron oxides are in mineralization and in host rock alteration assemblages, and there are typically multiple generations of iron oxides. Iron oxides are studied according to their paragenetic stage: (1) ore stage and (2) hydrothermal alteration of host rocks. Hydrothermal alteration iron oxides are grouped according to the type of alteration: (1) Ca-Fe alteration (Am-Ap-Mag), (2) Na(Fe) alteration (Ab-Scp-Mag/Hem), (3) High temperature K-Fe alteration (BtKfs-Mag) and (4) Low temperature K-Fe (Ser-Kfs±Chl±Cb-Hem). Preliminary results show hematite in Hematite-group IOCG deposits is depleted in Zn, Ni, Mn, V and enriched in K, Ti, Al, Si compared to magnetite in Magnetite-group IOCG deposits. In Magnetite-IOA deposits, magnetite is enriched in V, Al and Mg compared to Magnetite-HematiteIOA deposits, which is enriched in Ca. Compared to primary magnetite in Ni-Cu-PGE deposits, ore-stage magnetite in IOCG deposits are depleted in Ni, Cu and Cr and enriched in Ti, Al and Si.