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Adelaide Geosyncline / Stuart Shelf

Age

Sedimentation — Neoproterozoic to Middle Cambrian

Deformation — Delamerian Orogeny, Middle Cambrian to Early Ordovician (514–485 Ma)

Prospective commodities

Cu, Au, Pb, Zn, diamonds, barite, magnesite, talc, kaolin, carbonate for industrial use, phosphate, dimension stone and construction materials.

 

Major exploration models

  • Sediment-hosted copper (ącobalt)
  • ‘Oxide’ copper (leachable)
  • Mississippi Valley type (MVT) Pb–Zn
  • ‘Non-sulphide’ zinc (willemite, smithsonite)
  • Reduced-shale-hosted Pb–Zn
  • Vein gold (various styles including Telfer)
  • Porphyry related Cu, Mo and Au
  • Diamonds

 

Geology

Deeply subsident sedimentary basin with at least four main phases of rifting in the Adelaidean (Neoproterozoic) and one in the Early Cambrian; 12 major transgressive–regressive cycles (sequence sets) in the Adelaidean, three in the Early to Middle Cambrian.

Dominant lithologies are, in order of decreasing abundance, siltstone, sandstone (both mature and feldspathic), dolomite, limestone, diamictite, magnesite and conglomerate. Mafic lavas occur in the early Adelaidean and Early Cambrian. Relatively immature sandstone characterises the Cambrian Kanmantoo Group.

Deformation occurred at ~500 Ma in the Delamerian Orogeny, and was strongest in the Fleurieu Arc, with granitoid intrusions in the eastern Nackara and Fleurieu Arcs, and in basement inliers of the northern Flinders Ranges. Metamorphic grade varies from sub-greenschist to mid-amphibolite facies.

Kanmantoo Trough

The Kanmantoo Trough forms the southeastern extent of the Adelaide Geosyncline.

The Kanmantoo Trough formed as a rapidly subsiding, fault-controlled rift basin during the last of several phases of major crustal extension that occurred along the Early to Middle Cambrian palaeo-Pacific margin of Gondwana. The dominantly siliciclastic sediments deposited in the Kanmantoo Trough crop out along the eastern Mount Lofty Ranges, through Fleurieu Peninsula and on Kangaroo Island.

Geochronology, drillhole information and geochemical analysis of the volcanics tenuously link the Kanmantoo Trough with the Nackara Arc and Koonenberry Belt, New South Wales. Based on structural pattern and sequences that have undergone similar tectono-thermal histories, it has alos been proposed that there is a continuity between the Kanmantoo Trough (Delamerian Orogen) and Wilson Terrane, Antarctica.

More information on the Kanmantoo Trough.