Geologic setting of the Teutonic Bore massive sulfide deposit, Archean Yilgarn Block, Western Australia

Abstract

The Teutonic Bore massive sulfide deposit occurs in a sequence of Archean mafic and felsic volcanic rocks in the northeastern Yilgarn Block, Western Australia. Felsic volcanic rocks form part of a regionally continuous linear belt consisting of locally emergent volcanic centers separated by interbedded aquagene tuffs and water-lain epiclastic sedimentary rocks. Mafic and felsic rocks in the area have been extensively intruded by gabbro and subsequently by high-level granitoids believed to be cogenetic with the rhyolitic rocks.Regionally the deposit lies in a linear zone of complex structure and lithology characterized by repeated periods of extensional tectonism. Rhyolite and cogenetic granitoids are related to earlier phases of extension, whereas subsequent activity led to the formation of a suite of saturated to undersaturated syenites and fault-bounded units of polymictic conglomerate derived largely from the rhyolite and high-level granitoids.The Teutonic Bore deposit consists of one relatively small, steeply dipping lens of predominantly banded massive sulfides (mainly pyrite, sphalerite, chalcopyrite, and galena) underlain by concordant and discordant stringer mineralization. The mineralization occurs within a sequence of pillowed basalt and tuffaceous sediment 0 to 150 m stratigraphically above rhyolitic volcanic and volcaniclastic rocks. Primary textures within the massive sulfides and underlying chert indicate depositional instability. Active growth faulting controlled the deposition of felsic epiclastic sedimentary rocks, subsequent basaltic rocks, and the development of the third-order basin which provided the site for deposition of massive sulfides. The faults probably provided the conduits for hydrothermal solutions; these fluids spread laterally and vertically prior to exhaling at the rock-seawater interface during a volcanic hiatus. Features within the local environment are compatible with regional extension. Regional extension resulted in bimodal magmatism, and the associated rifting formed basins suitable for the deposition of extensive epiclastic sedimentary rocks.The bimodal volcano-plutonic host at Teutonic is similar to many examples from the Archean of Canada, but the style of felsic volcanism, the carbonate-rich alteration, and the lead- and silver-enriched ore are most similar to deposits in the Sturgeon Lake area.