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Structure and mineralisation of western Tasmania. AMIRA Project P.291A. Report No. 3 March 1995

Berry, RF, Fulton, R, Selley, D, Bull, SW, Keele, RA, Davidson, GJ and Kitto, PA 1995 , Structure and mineralisation of western Tasmania. AMIRA Project P.291A. Report No. 3 March 1995.

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The work defining a western margin for the Dundas Trough has reached an advanced stage. Three types of work have been applied to this study. Detailed conventional provenance studies have indicated that the Crimson Creek Formation was being actively eroded as a source terrain throughout the Dundas Group deposition. The sedimentology supports a very close source. The need to erode Crimson Creek Formation throughout the depositional history of the Dundas Group means that it was not covered by Dundas Group at any time. No acid volcanic material is mixed with this source.

The provenance was also studied using heavy minerals. Several distinct source signatures were recognised. These are:
• The western source component has a distinctive high chromite/zircon ratio, high tourmaline, high apatite and low total Fe oxides. Most micaceous sandstones from Cycle 3 carry this signature.
• The eastern source signature (Tyennan region) was defined from the Sticht Range Formation. This signature (rounded zircon) has not been recognised in any of the other sandstones in this study.
• The CVC/Yolande signature is high euhedral zircon and TiO\(_2\)
• The Tyndall Group signature is very high FeTi oxides

The difference between source signatures of Cycle 1 and Cycle 3 sandstones suggests the western source is transformed from a low relief deeply weathered area in the Middle Cambrian to an actively eroding area with fresh rocks exposed in the Late Cambrian. Despite this transformation the western source has been recognised very widely as predicted by the more localised study on the western margin of the belt.

The sedimentological studies in the Stitt Quartzite have suggested the mature turbidite fades sandstones are transported along the graben axis while the pebbly sandstones are locally derived material eroding from horst blocks along the basin margin. Despite this difference both suites carry the western source signature. The Husskisson Group is consistent with a ramp facies. All three types of information are consistent with the structural interpretation which shows a discrete graben margin along the western side of the Dundas Trough.

The S isotope work has been largely committed to a baseline study at Rosebery and has demonstrated evidence for complex sea-water circulation patterns. This work is now being extended out to growth faults throughout the Mt Read belt to define a growth fault signature.

Initial work on the new structural section near the Firewood Siding Fault has demonstrated the complex nature of Cambrian deformation based on the field relationships at the base of the Owen Conglomerate and its correlates. Further work is refining the pattern of Cambrian deformation in this area and its relationship to the Henty Fault wedge.

The project is now providing strong additional evidence for the existence of Cambrian faults in the Mt Read Volcanics. The sedimentological tests are supporting the general geometry defining which blocks are subaerial during the Cambrian. The outstanding result so far is that the western block is a major source during the Mt Read depositional cycles. The Tyennan block does not figure substantially until late in the sedimentary history. The S isotope work has shown that a Cambrian seawater can produce a detectable signature in an area of cold infiltration. This work is now being used to set up a growth fault signature to aid detailed identification of Cambrian growth faults.

Item Type: Report (Technical Report)
Authors/Creators:Berry, RF and Fulton, R and Selley, D and Bull, SW and Keele, RA and Davidson, GJ and Kitto, PA
Publisher: CODES/AMIRA
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