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Arkaroola Geology


 

The area around Arkaroola (South Australia) consist of two (?Palaeo-)Mesoproterozoic inliers, the Mount Painter and Mount Babbage Inlier, overlain by Neoproterozoic sediments. The area was affected by the Delamerian (=Pan-African, appr. 500 Ma) orogeny, and by a later magmatic-hydrothermal event around 440 Ma.


  Map Arkaroola
Map of the geology in the area around Arkaroola Village (AV). The undifferentiated meta-igneous rocks are mainly Mesoproterozoic granites, and their deformed equivalents. Numbers refer to pictures below.

 

Diopiside-titanite veins

Veins of diopside and titanite, overgrown by quartz, within the Mount Painter Inlier (location 2). The U-Pb age of the titanite is 442 ± 4 Ma.

 
 

Mt Gee Breccia

Breccia around Mt Gee (near location 1). Clasts consist of the local Mesoproterozoic granite.



MtGee-like overgrowth on Di-Ti veins

The diopside-titanite veins are affected by the same kind of quartz-hematite overgrowths that are found in Mt Gee, constraining this event to be later than 442 Ma.




Work is continuing on elucidating the timing of metamorphic and magmatic events in the area, and the heat source that drives them. Collaborators on this project are Paul Bons (Tübingen University) and Ronald Bakker (University of Leoben). We now think that the 440 Ma-event was followed by a later stage of lower-temperature fluid flow, which gave rise to the Mt Gee quartz-hematite mineralisation. The timing of large-scale pegmatite intrusions (informally named the "Pink Pegmatitic Granite") is not clear yet, but is provisionally assigned to the 440 Ma-event; this may also have caused the local uranium mineralisation, which was probably remobilised by the later Mt Gee-type veining.
 



  To pictures of the 2005 field season

To pictures of the 2007 field season









Fibrous calcite veins
Another ongoing area of study is the petrogenesis of fibrous calcite veins, which are found in the Neoproterozoic Tapley Hill Formation (Tindelpina Shale member).

FibrousCalciteVein

Previous work involved the analysis of the veins' Sr isotopic composition, which showed that some veins were in isotopic equilibrium with the calcite in the host rock, but some were not. Research by collaborators Paul Bons (Universität Tübingen) and Michael Montenari (Keele University) focuses on the possibility that the veins are the product of microbial activity. Trace element characteristics, in particular high Sr contents, of the veins may indicate that the present-day calcite is a pseudomorph of aragonite. The rare earth element geochemistry of these veins, and other, similar-looking ones from other localities (Italy, France, Switzerland) is now being investigated by PhD student Marc Bankuti. 


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