Stress analysis, post-orogenic extension and 3.01Ga gold mineralisation in the Barberton Greenstone Belt, South Africa

Geochemical identification of episodes of gold mineralisation in the Barberton Greenstone Belt, South Africa

“…This has been alternatively attributed to different ore-forming processes or a zonation outwards from the epicentres of the mineralising fluids at Agnes and New Consort and Sheba (Gribnitz, 1961;Gay, 1964), which correlates well with the structural controls described by Dirks et al (2013). Tomkinson & Lombard (1990) suggested a formation temperature of gold in pyrite and arsenopyrite above 500⁰C, which results in gold that appears to be of primary origin, as indicated by the gold grain morphology.…”

“…The third event is dynamic metamorphism associated with shearing, which caused brecciation and fracturing . This resulted in structural porosity for the syn-to late genetic mineralized fluids (Dirks et al, 2013). All these metamorphic episodes resulted in changes to the mineralogy and morphology of the rocks of the Sheba Mine.…”

“…However, gold is found in variable amounts in all of the BGB rock types (Dirks et al, 2013), which is indicative of pervasive fluid flow and extensive fluid-wall rock interaction over long periods of time (Bierlein & Maher, 2001). The majority of the gold is associated with quartz-carbonate veins (Stage 3) with mineralized fractures spatially proximal to large-scale compressional and/or shear zones (structural porosity) (Dziggel et al, , 2010Dirks et al, 2013).…”

“…The majority of the gold is associated with quartz-carbonate veins (Stage 3) with mineralized fractures spatially proximal to large-scale compressional and/or shear zones (structural porosity) (Dziggel et al, , 2010Dirks et al, 2013). Most of the gold deposits are located in the second and third order structures (Dirks et al, 2013), or in the fault intersections, corresponding to places of low stress, which increases fluid passage. The structural patterns of gold mineralization in the studied mines are similar to that of Pilbara in Western Australia (Thèbaud et al, 2008).…”

“…The regional geology and structural evolution of the BGB is complex, as reflected in the extensive literature, which makes unravelling the sequence of events leading to the timing and mode of emplacement of the gold mineralisation complicated. The gold distribution in the BGB is structurally controlled (Dirks et al, 2009), and recent work has shown that the main phase of gold mineralisation in the BGB was controlled by pre-existing faults and fractures, and postdates the main structural and metamorphic episodes (Dziggel et al 2010;Munyai et al 2011;Dirks et al 2013). Dirks et al (2013) proposed that the principal stage of gold enrichment in the BGB occurred after tectonic and thermal stabilisation of the Kaapvaal Craton, suggesting that brittle-ductile shear zones allowed mineralising fluids to exist during cratonic extension.…”