Tectonic and metallogenic framework of the Cambrian Stansbury Basin - Kanmantoo Trough, South Australia

The Early to Middle Cambrian Stansbury Basin preserves a palaeogeographic zonation, from shallow shelf carbonates in the west (Spencer and Ardrossan Shelves) through extensional siliciclastic rift facies (Kanmantoo Trough) and volcanogenically influenced back-arc basin environments (Murray Basin basement). Sedimentation occurred from about 540 Ma to at least 510 Ma, with a distinctive phase of thick rift sedimentation in the Kanmantoo Trough from 526 Ma. Sedimentation continued beyond the 510 Ma onset of compressional orogenesis, in back-arc basin environments east of the Padthaway Ridge and, possibly, in a foreland setting now occupied by Gulf St Vincent.  Granitoid emplacement accompanied both the main compressive deformation (syntectonic 1- and S-type c.51 0- 500 Ma) and subsequent relaxation and extension (post-tectonic A-type granitoids and mantle-derived mafics c.480-490 Ma). Variably deformed, syn- to post-orogenic acid volcanics occur along the Padthaway Ridge. Listric faults associated with extensional rift development along the southeastern margin of the Gawler Craton were inverted during the Delamerian Orogeny as preferential zones of shearing and thrusting. The change from rift basin to platform sequence is now marked by a discrete shear zone on Kangaroo Island and a broader zone of imbricate thrusting on western Fleurieu Peninsula. There was little detachment between basement and cover, with most thrusts rooted in southeast-dipping shear zones within the basement.  Cambrian carbonates of the Ardrossan and Spencer Shelves have potential for epigenetic, structurally modified Mississippi Valley-type (MVT) mineralisation associated with basin dewatering along major structures. Key areas for mineralisation are unconformities, karst and porous carbonates around the margins of the basin and near reactivated thrusts and fractures that acted as conduits for fluid movement. There is also potential for stratabound Cu mineralisation at redbed-to-marine stratigraphic transitions on the shelf. Many base-metal deposits with stratiform or structurally modified genetic characteristics have been discovered in outcrop in the Kanmantoo Trough. A syngenetic association with flooding surfaces (sequence boundaries) and manganiferous sea-floor exhalites has been recognised. Varying degrees of structural control or structural modification of originally stratiform and sedimentary exhalative mineralisation are evident. Recent sub-economic discoveries at the Angas and Mt Torrens prospects are significant and encouraging for undiscovered economic syn-sedimentary lead- zinc- silver- gold deposits.  Beneath the Murray Basin, there is potential for volcanogenic massive sulphide mineralisation analogous to the Mt Read Volcanics. Recent drilling on the northern flank of the Padthaway Ridge encountered a number of anomalous Zn, Pb, Cu and Au intervals associated with post-collisional lavas, intrusives and pyroclastics. Extensive syn- and post-tectonic granitoids near the southern and eastern limits of Kanmantoo Group exposure are potential sources for porphyry Cu-Mo, epithermal Cu-Au and skarn deposits. Platinum-group element mineralisation is also evident in post-orogenic, mantle-derived mafic intrusives.

Tags: Earth Sciences, GA Publication, Journal, Published_External, SA
Organization: Geoscience Australia Data