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Sediment-hosted base metal deposits. CODES/AMIRA Project P.384A. Report No. 3, April 1997.

Winefield, PR, Bull, SW, Cooke, DR, Selley, D, Wallace, MW, McGoldrick, PJ, Dunster, J, Boden, SB and Leaman, DE 1997 , Sediment-hosted base metal deposits. CODES/AMIRA Project P.384A. Report No. 3, April 1997..

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This is the third progress report for AMIRA Project P384A and covers work during the six months November 1996 to April 1997.

The work reported here covers several aspects of middle McArthur group sedimentology and diagenesis, and possible links to tectonic processes operating during middle McArthur times. The report by Winefield re-examines enigmatic 'Coxco needles'from the Teena Dolomite and concludes they are pseudomorphs after chemically precipitated aragonite. Elevated HC03- in the basin waters (needed to stabilise primary aragonite) may be yet another manifestation of regional tectonism preceding the main HYC ore-forming event.

A description of a condensed Teena Dolomite Barney Creek Formation - Reward Dolomite section from the Berjaya area to the west of HYC is presented in the report by Bull, Cooke and Winefield. Their observations, including algal features suggestive of photic zone deposition, are consistent with a halfgraben model for the area with the Berjaya section accumulating on the uplifted footwall block.

The report by Winefield et al. describes sediment and fibrous cement-infilled fractures (Neptunian dykes) in the Teena and Emmerugga Dolomites from the southern McArthur Basin. The fibrous dolomite cements are similar to marine calcite cements from Phanerozoic sequences, and there is no evidence for emergence prior to Barney Creek Formation times. Furthermore, the consistent orientation of the dykes and sills suggest slumping of lithified sediments during tilt block formation and/or deformation directly linked to syn-sedimentary faulting. In the area of the Gorge Prospect this tilting pre-dates deposition of the Barney Creek Formation.

Reports by Cooke and co-workers continue the systematic geochemical modelling of important constituents of sedimentary Zn-Pb deposit, and extends the base metal modelling to very high salinities (25wt% NaCl equivalent).

The final report is a preliminary geological interpretation of gravity and magnetic data from parts of the Camooweal and Dobbyn 1:250,OOO map areas. Much of the data from Camooweal are consistent with interpretations from previous reports for map areas to the west and north. To the east the rocks display evidence for east facing overthrusting, and there may be (younger) west facing thrusts where the western and eastern domains abut.

Also to be presented at the meeting, but not reported here, are descriptions of the Grevillea prospect mineralisation and associated primary geochemical dispersion halos. A written report will be presented to sponsors at a subsequent meeting. John Dunster will present an overview of his PhD work on the Lady Loretta Formation. Logs from a 'distal' hole at Lady Loretta (DDH LA64) will be on display comparing lithological, geochemical and radiometric ('gamma-log') data for this hole. A short review paper describing an exploration model for sediment-hosted base metal deposits is included as an appendix to the report.
Peter McGoldrick
Project Manager

Item Type: Report (Technical Report)
Authors/Creators:Winefield, PR and Bull, SW and Cooke, DR and Selley, D and Wallace, MW and McGoldrick, PJ and Dunster, J and Boden, SB and Leaman, DE
Publisher: CODES/AMIRA
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