Kanmantoo group

Sedimentary rock of the Kanmantoo Group, showing how it was folded under pressure.(Kangaroo Island)

The Kanmantoo group are a group of rocks found in South Australia, mainly along the eastern side of the southern Mount Lofty Ranges, including Fleurieu Peninsula and Kangaroo Island. They are grey metamorphic rocks which can be seen on natural outcrops, road cuttings and along the coast of southern Fleurieu Peninsula and Kangaroo Island.

The Kanmantoo Group is made up of many layers of different types of rocks that have been changed a lot by heat and pressure (metamorphism). When rocks are buried deep inside the Earth, they can be heated and squeezed, which changes their minerals and texture. This happens at medium to high temperatures (about 500 to 750 degrees Celsius) and moderate to high pressure. The Tapanappa Formation, part of the Kanmantoo Group, contains deposits of copper and gold, lead, zinc, silver, iron and sulfur, and small amounts of arsenic, bismuth, and tungsten.

Scientists agree that the iron and sulfur deposits formed at the same time as the sediment was laid down. But there is debate about how the copper and gold deposits formed. Some scientists think the lead, zinc, silver, copper, and gold formed with the sediment too, while others think they formed later because of movements in the rocks.

There are three main ideas about how the Kanmantoo copper and gold deposits formed:

  1. The first idea is that the minerals formed at or just below the sea floor by hot water processes when the sediment was being laid down. Later, the rocks were changed by heat and pressure, which moved the minerals around.
  2. The second idea is that the minerals formed during the time when the rocks were being changed by heat and pressure
  3. The third idea is that the minerals came from hot fluids from granite rocks after the main period of metamorphism, during the late Cambrian to early Ordovician periods, roughly between 514 million and 490 million years ago, which was a mountain-building event.

Scientists have studied these ideas and still discuss which one is correct.

Kanmantoo is a small town in the Adelaide Hills of South Australia, where copper was found in the 1840s. The name comes from Kunga Tuko a word from the Peramangk, a local Indigenous Australian people, and means, "different speech".

References

  1. ↑ Jago, J. B., Gum, J. C., Burtt, A. C., & Haines, P. W. (2003). Stratigraphy of the Kanmantoo Group: A critical element of the Adelaide Fold Belt and the Palaeo‐Pacific plate margin, Eastern Gondwana. Australian Journal of Earth Sciences, 50(3), 343–363. https://doi.org/10.1046/j.1440-0952.2003.00997.x
  2. ↑ Noel Hiern. "Victor Harbor Geological Trail" (PDF). Geological Society of Australia. Archived from the original (PDF) on 27 February 2015. Retrieved 28 February 2015.
  3. 1 2 3 Pollock, Meaghan V. (2018). "The origin of the sediment-hosted Kanmantoo Cu-Au deposit, South Australia: Mineralogical considerations". Ore Geology Reviews. 95: 94. Bibcode:2018OGRv...95...94P. doi:10.1016/j.oregeorev.2018.02.017. Retrieved 11 May 2026.
  4. ↑ "2905.0 - Statistical Geography: Volume 2 -- Census Geographic Areas, Australia, 2006". Australian Bureau of Statistics. 17 July 2007. Retrieved 8 December 2009.