Archean polyphase deformation in the Lake Johnston Greenstone Belt area: Implications for the understanding of ore systems of the Yilgarn Craton

The new D2LJ deformation age is younger than previously constrained ages for major deformation in the 2900 Ma greenstone belts. Deformation within the LJGB was broadly coeval with the waning stage of formation of gold deposits in adjacent greenstone belts. Most peak magmatic and metamorphic events preserved in the greenstone belts have been constrained to ca. 2640-2650 Ma. The presence of such a high temperature deformation event recorded at ca. 2630 Ma in the LJGB belt has implications for the thermal history, fluid formation, and geodynamic context of the development of these gold systems. The 2630 Ma age correlates with late-stage and post-gold emplacement of pegmatite dykes in surrounding terranes. The LJGB is interpreted to have been a mobile belt associated with high grade metamorphism that was inboard (west) of, and active, during the formation of major world class gold systems in the Eastern Goldfields Terranes. The D1LJ to D2LJ changes in the kinematics of the system (i.e. D1LJ to D2LJ), may correlate with a stress switch linked to the influxes of gold-bearing fluids in adjacent greenstone belts.