CENTRE FOR ORE DEPOSIT AND EXPLORATION STUDIES

STRUCTURE AND MINERALISATION OFWESTERN TASMANIA

AMIRA PROJECT P.291Report No. 4August 1992

University of Tasmania

CONTENTS

page

Progress review P291 - Structure and Mineralisation of Western Tasmania 1

The King River regional cross-section: a transect through the Dundas Trough 11

Strahan to Queenstown structural section 31

A structural cross section through the Boco Road area 39

Geochemical evidence for the structure of the Rosebery deposit 51

Mount Lyellleases: summary 67

Quartz veins and cleavages: a note on the mesoscopic structures at Mt Lyell 77

An overview of the Southern Arthur Lineament 87

CODES: AMIRA Project P291 - Structpre and ~Mineralisation of Westem Tasmania. August 1992~

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1

Progress Review - P291Structure and Mineralisation of Western Tasmania

R.F. BerryCentre for Ore Deposit and Exploration Studies

ABSlRACf

The project aims were to understand the regionalstructure of the Dundas Trough and to apply thisunderstanding to ore deposit and exploration models.So far the Devonian structural history has been welldetermined for 4 regional sections and at Roseberyand Mt Lyell. The Cambrian structurehas beenpartlydetermined with a clearMiddle Cambrian extensionalphase followed by a compressional or wrench phasein the Late Cambrian. The significance of theseCambrian events must be considered in the light ofthe synchronous compressional tectonics in SouthAustralia and Northern Victoria Land. Tasmania wasin an active tectonic zone in the Late Cambrian.

INlRODUCTION

The AMIRA project started with a number of aims.Primarily these were to understand the regionalstructure of the Dundas Trough and to apply thisunderstanding to ore deposit and exploration models.

The regional component of the study is to consider5 regional transects and the South HentyFault system.The major aims were to define the Devonian faulthistory on these sections and to use the existinglithological database to produce restorable sections.The expectation was that this process would identifyany Cambrian structures as anomalous areas in termsof the reconstructions.

The identified mine geology component was theLyell and Rosebery mines. An assessment of the MtFarrell deposit was included at the November 1991meeting. TheLyell projectconcentrated on the controlson North Lyell style mineralisation and the overall

structure of the mine leasebased on surface exposures.The Rosebery study was a mine scale structuralassessment largely based on core and level plans. TheMt Farrell deposit study is to be largely a considerationof existing data.

PROGRESS

The regional structural program is running nearly toschedule. As of this meeting a major report has beengiven on three regional sections and work is wellunderway on two more. The first section acrossHellyer has been the subject of further considerationas part of Mr. D. Selleys Ph.D. program and resultingfrom a geophysical assessment. An updated versionof this section is included in this volume and weexpect further improvements. The Victoria Pass toStrahan section is completed with the western sectionin this volume. The King River section is reportedhere. The South Henty Fault system was consideredin Keele (1991) but a more formal assessment will beprovided in the final report. The section near Roseberyhas been started. The no~thern section across the DialTrough remains to be done.

The Rosebery Mine structural assessment iscompleted with the geochemical test case reported inthis volume. The Lyell leases have been discussedover all three earlier reports. Some further geo­chemistry modelling is being carried out at NorthLyell and a final overview will be given in the reportat the end of the project but the major results areunlikely to change from the summary included inthis volume. The Mt FarrelJ study is yet to be carriedout.

CODES: AMIRA Project P291 - Structure and ~Mineralisation of WesterniTasmania. August 1992~

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