Fluid inclusion studies on Archean lode gold deposits, Abitibi, Canada

摘要

Greenstone-hosted orogenic deposits are the most important gold deposits and the best represented type among the >10 Moz deposits, including Hollinger-McIntyre, Dome, Sigma- Lamaque, Victory-Defiance, Norseman, and Mt Charlotte. The quartz-carbonate veins in these deposits typically combine laminated veins in moderately to steeply dipping reverse shear zones with arrays of shallow-dipping extensional veins in adjacent competent and lower strain rocks. The reverse character of the shear-zone-hosted veins and shallow- dips of extensional veins attest to their formation during crustal shortening. In greenstone belts, the significant vein deposits are typically distributed along specific regional compressional to transpressional structures (Goldfarb et al. 2005; Robert et al., 2005). The larger camps and deposits are commonly spatially associated with late conglomeratic sequences as exemplified by the Timiskaming polymict conglomerates in the Abitibi greenstone belt. The deposits occur in any type of supracrustal rocks within a greenstone belt and, covering stratigraphic positions from lower mafic-ultramafic volcanic to upper clastic sedimentary stratigraphic levels (Robert et al., 2005). At the local scale, favorable settings for these deposits represent a combination of structural and lithologic factors (Groves et al., 1990). Shear zones and faults, universally present in these deposits, are developed along lithologic contacts between units of contrasting competencies and along thin incompetent lithologic units. Common lithologic associations include Fe-rich rocks such as tholeiitic basalts, differentiated dolerite sills and BIFs, and with competent porphyry stocks of intermediate to felsic composition, whether they intrude mafic-ultramafic volcanic or clastic sedimentary rocks.