| Summary: | The Stirling Group consists of ca. 680 Ma volcanic and volcaniclastic rocks, interpreted to have been deposited in and around a trough flanked by felsic volcanic centres. The volcaniclastic rocks are dominated by lapilli tuff and tuffaceous litharenite sequences. The lapilli tuffs show some evidence of subaqueous reworking but most may have originated as air-fall deposits. Sedimentary structures in the litharenites suggest subaqueous mass transport into the trough and deposition below wave base. Pyritic siltstone-chert-carbonate laminites, which are locally associated with the litharenites along the southeastern side of the trough adjacent to felsic volcanic centres, probably represent a mixture of fine-grained distal turbidites and chemical precipitates from subaqueous volcanic exhalations. The volcanic rocks of the Stirling Group do not show convincing evidence for subaqueous deposition: the felsic rocks appear to form subvolcanic intrusions and domes flanked by felsic crystal-rich lapilli tuff and rare welded(?) tuff; the mafic volcanic rocks are not pillowed but are closely associated with breccias which may have formed partly by quench fragmentation. The overall facies assemblage and its association with VMS Zn-Pb-Cu-Ag-Au mineralization are compatible with generation in an intra-arc basin. As the Stirling Group is significantly older than the volcanic belts which flank it, it may represent a tectonically displaced remnant of a pre-existing arc. RÉSUMÉ Le Groupe de Stirling consiste en roches volcaniques et volcanoclastiques d'environ 680 Ma, interprétées comme ayant été déposées à l'intérieur et autour d'une fosse bordée de centres volcaniques felsiques. Les roches volcanoclastiques sont dominées par des séequences de tufs à lapilli et de litharénites tuffacées. Les tufs à lapilli montrent quelques évidences de remaniement subaqueux mais la ...
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