Structural controls on the emplacement of the vein-type tungsten-tin ore at Mount Carbine, Queensland, Australia

Abstract

Formation of the vein-type tungsten-tin deposits at Mount Carbine, Queensland, is explained in terms of mineralization in favorable structural sites, created by three major deformations in the host succession of Devonian clastics. Upright folds with a vertical axial plane cleavage (S 1 ) formed during the first deformation (D 1 ), which was followed by conjugate kinking (D 2 ) of S 1 , where this cleavage is strongly developed, and by granitic intrusion. Contact metamorphic assemblages in the granite aureole were established before local recumbent folding (D 3 ) of S 1 . At late stages of this latter event, vein mineralization developed along D 2 kink planes in sites of high D 1 strain, where capped by domains of D 3 folding.Evolution of this mineralization can be recognized at the Mount Carbine mine. Early stages of fracture dilation are marked by tourmaline infill and associated wall-rock alteration, with fibrous crack-seal microstructures indicating repetitive tensile failure and tourmaline deposition. Subsequent major dilations are marked by veins of nonfibrous quartz and feldspar, and ore-grade wolframite. In similar mineralizations in nearby prospects, these veins merge with greisen veins and granite dikelets, supporting a granite hydrothermal model for the origin of the tin and tungsten in the area.The late D 3 vein mineralization was, however, preceded by the local formation of a differentiated layering (S 3 ), and of sets of barren veins along S 3 and the D 2 kink planes. Both the layering and barren veins postdate the growth of the contact metamorphic assemblage around the undeformed granite.