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Faulting and mineralisation in western Tasmania AMIRA/CODES Project P.291A Report No. 4, October 1995


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Berry, RF, Selley, D, White, M, Davidson, GJ and Kitto, PA 1995 , Faulting and mineralisation in western Tasmania AMIRA/CODES Project P.291A Report No. 4, October 1995 .

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RF Berry, D Selley and MJ White

The whole rock chemistry of the sedimentary rocks of the Mt Read Volcanics were compared to see if they were useful in distinguishing sedimentary sources sufficiently well to support a basin analysis. The chemical data was also investigated to demonstrate whether it could be used to solve some difficult lithostratographic correlation problems.

The trace element chemistry indicates that at least four sources can be readily discerned. These are a low Ti basalt (MUC and Hellyer basalt), an intermediate Ti basalt (from normal Crimson Creek Formation and a very high Ti basaltic suite (unknown source for Tyndall Group), and a felsic source. The separation of the felsic source into several groups may be possible with more Th data. The Precambrian basement source signature lies in the middle of these four types and cannot be detected unless it is a dominant component such as in the Stitt Quartzite. It is best detected by the presence of rounded zircon and tourmaline (and detrital mica).

The preliminary investigation indicated whole rock chemistry may be very useful in distringuishing a range of different rock types. The Animal Creek greywacke and Farrell Slate are clearly distinct from Dundas Group. The EQPS has a lower Ti/V than CVC volcaniclastics. The Tyndall Group was separated by high Ti/Th. These relationships need more data for a proper assessment but they are very encouraging.

Sedimentological evidence for Cambrian growth faults on the eastern side of the Dundas Trough, western Tasmania - Matt White

Geological evidence in the Anthony River area suggests that Cambrian movement was apparent on what is referred to as the Selina fault, during upper Tyndall Group (Middle to Late Cambrian) time. This is consistent with observations of Keele (1991) and Berry & Keele (1993), who interpreted a normal fault on the contact of the Tyndall Group and the Eastern Quartz-phyric sequence in this area. A southern bounding possible transfer fault may have constrained Tyndall Group deposition into a small fault-bounded basin. Reverse movement on the fault involving east-block upward movement is another possibility.

Progress Report 4: Detecting Cambrian structures in
the Mount Read Volcanic Belt using sulfur isotopes
- sulfur isotopes of growth faults
- Garry J. Davidson and Paul Kitto

Sulfur isotope results from Cambrian growth faults can be tentatively divided according to fault style and fluid history. Those containing base-metal sulfides have values similar to known base-metal deposits in the Mount Read Volcanics (Carters Prospect). These consistently vary from north (d34S = 5-9 permil) to south (d34S = 7-15 permil) in the belt (Solomon et al., 1988). Those faults with small displacements, likely original Normal fault geometries, and pyrite rather than base-metal sulfides in the alteration assemblage, contain heavy sulfur (e.g. Comstock - Zig Zag Hill, d34S > approx 20 permil). Some of these have tentatively been identified at the margins of large base metal deposits, such as Rosebery. Thirdly, faults that lie sub-parallel to stratigraphy, are extensively sericite-chlorite altered, and are defined by wide shear zones (e.g. Moxons Saddle), have d34S = 0 ± 5 permil, and may represent deep rock-buffered fluid circulation, although this conclusion requires confirmation of a Cambrian origin, because these values overlap those expected from Devonian magmatism. These conclusions are very preliminary, and will require detailed work on each scenario in the coming field season.

Fluid inclusion microthermometry of Cambrian and
Devonian fault structures
- Paul A. Kitto

Geochemical and isotopic signatures associated with
Cambrian and Devonian fault structures
- Paul A. Kitto

Item Type: Report (Technical Report)
Authors/Creators:Berry, RF and Selley, D and White, M and Davidson, GJ and Kitto, PA
Publisher: CODES/AMIRA
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