# Faulting and mineralisation of western Tasmania. AMIRA/ARC Project P.291A. Report No. 1, May 1994

Bull, SW, Kitto, PA, Berry, RF and Davidson, GJ 1994 , Faulting and mineralisation of western Tasmania. AMIRA/ARC Project P.291A. Report No. 1, May 1994.

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## Abstract

Project P291 on faulting and mineralisation in Western Tasmania applied the regional structure of the Dundas Trough to improve ore deposit and exploration models in the area. Two aspects arising out of this project required further study. A major aim of P291A is to use structure, geochemistry and sedimentology to test the model for Cambrian extensional faulting proposed in P291. A econdary aim was to tackle inconsistencies in the Devonian structure remaining from previous studies, and to further test the regional sections with gravity and magnetics.

AMIRA project P291A started with a meeting on 18 October 1993. Commonwealth ARC funding for the cooperative research grant began on 1 January 1994. The agreed program for 1994 included four items from the planned list of nine.

2. Examine the structural and stratigraphic evidence for the Cambrian extensional faults along the western boundary of the Dundas Group from Zeehan to Que River. The initial work on the Stitt Quartzite supported previous interpretation of a turbidite origin but suggested these lithologies formed above storm wave base. No evidence of a close western source was found on this limb of the syncline. Access difficulties have slowed the progress in studies closer to the basin bounding fault. Field work will continue into the next field season.

6. Investigate lithostratigraphic correlations within the Dundas Group and between the Dundas and Central Volcanic Complex. The Mount Read Volcanics have been subdivided into three depositional cycles, based on a literature review, each with a distinct basin geometry and history. Samples of sandstones have been collected from each of these cycles. Detailed petrography on these rocks has been started with a view to finding distinguishing characteristics for each cycle and variations in provenance within the belt.

8. The spatial and temporal relationship between cleavage formation, folding and faulting along the Rosebery Fault from Rosebery Lodes to the Pieman River. There is a close spatial relationship between the Rosebery Fault and a late N-striking cleavage (S$$_2$$).This cleavage occurs in the hangingwall at Rosebery but in the footwall in the Pieman River. The style of the cleavage reflects the thermal conditions during Devonian granitoid emplacement. An earlier cleavage was recognised at all localities. This cleavage was not visible in the most intense zones of S$$_2$$ cleavage development but overprinting was found on the edge of the zone of S$$_2$$ development. The earlier cleavage has a composite origin including both a NNW-striking Devonian cleavage and a N-striking cleavage of Devonian or Cambrian age.

9. The isotopic signature of veins related to discrete structural events in a transect from the Pieman River to the Murchison Dam. A preliminary study of both quartz and carbonate has been undertaken. The Devonian quartz bearing veins have oxygen isotopic values related to their distance from the granite. Cambrian and Devonian hydrothermal carbonates have distinctly different carbon and oxygen isotope values. Devonian veins in faults show inherited Cambrian isotopic values where there is no granite contribution.

Sampling has been carried out for an initial study on the application of laser ablation sulfur isotope methods to the detection/characterisation of Cambrian structures. Evidence from seafloor and ancient settings indicates that areas of shallow seawater convection are likely to be the isotopically detectable.

All the proposed sections have been started but only the cleavage study along the Rosebery Fault has reached an advanced stage. The results of further work on item 2 have pointed out future difficulties in accessing well exposed rocks. The isotopic work has supported the need to use an approach based on a range of techniques.

Item Type: Report (Technical Report) Bull, SW and Kitto, PA and Berry, RF and Davidson, GJ AMIRA/CODES View statistics for this item