Evidence for pulsed brine exhalation in the formation of giant proterozoic stratiform sediument hosted Zn-Pb-Ag deposits of northern Australia

摘要

Studies of textures and sulfide-sediment relationships in the giant stratiform Zn-Pb-Ag ores at HYC, McArthur Basin, indicate that the deposit formed during sedimentation on the marine basin floor by the interplay of three processes: (1) continuous organic-rich pelagic sedimentation. (2) episodic oxic turbidite deposition, (3) episodic high density metalliferous brine expulsion. Each ore lens resulted from up to 10,000 pulses of hydrothermal fluid entering the basin to become interleaved with anoxic pelatic muds and oxic carbonate-bearing turbidites. The fluids were sourced from deep in the basin, associated with density driven convection of marine waters (Garven and Bull, this volume). Fluid discharge was along the Emu fault system that acted as a tapping structure to the brine reservoir in the upper Tawallah Group sandstone aquifer. Pulsing of the ore fluid may have resulted from episodic sealing and cracking of the Emu fault associated with mineral precipitation and fluid pressure fluctuations. Similar laminated sulfide-sediment textures in other stratiform Zn-Pb-Ag deposits in the North Australian zinc belt, such as Mt Isa, Hilton and Century suggests they may have formed by similar processes on the basin floor, rather than by the currently preferred models of syntectonic replacement.