New Insights From Old Data:

Examples from Historically Significant Tasmanian Ore Deposits

Tony WebsterMining Geoscience

December 2016

WHAT CAN A HOLE TELL US ABOUT ORE DEPOSIT GEOLOGY?

INTRODUCTION - PHILOSOPHY

The best way to understand orebodies is to understand their litho-structural architecture.

– Better-understand the ones we know about

There are new things to be understood about the great (or maybe not-so-great) deposits and mining fields.

– They have often been misunderstood by earlier workers, and poor theories have been perpetuated by a lack of geological context – understanding of the deposit architecture - for more detailed research.

Original source: Lionore P/L

2D and 3D models of mined deposits can utilise the rich geoscientific data collected as they were extracted & can help to solve this problem

AIM OF PROJECT - HISTORIC MINE GEOLOGICAL MODEL LIBRARY

Build accurate litho-structural models of historically and economically significant ore deposits

- Ore/grade controls, - structural evolution and deformation

history

Develop greater understanding of the geology of key type examples

- e.g Broken Hill

Compile and interpret the mine - and near-mine geological data

- Identify the controls on economic mineralisation & provide a context for efficient near mine exploration and mine design

Information dates from the mid- 19thC to the present.

Henderson Molybdenum Mine Block Cave Glory Hole. Colorado USAhttp://en.wikipedia.org/wiki/Henderson_molybdenum_mine

A firm context for research into the structural evolution of a deposit and its

genesis.

Cost-effective and accurate brownfields exploration

AIM OF PROJECT – BEYOND ECONOMIC GEOLOGY

Developing a ‘library’ of deposit models from across Australia.

Will eventually be released online.

History: Increase understanding of the historical & technological development of the Australian mining industry

- regional mining towns that are such a significant part of the nations history

Historical archaeology: how these historically important mines were developed- in earliest phases.

- Document the locations of underground workings, & the archaeological evidence that is likely to remain

EXAMPLES DISCUSSED

1. Mt Farrell Ag-Pb-Zn

2. Iron Blow/North Lyell Cu-Au

3. New Golden Gate – Au

Some of the most historic Tasmanian deposits (mines)

Mt Farrell Field:New North Mt Farrell Mine

Mt Farrell Mine

http://blog.mailasail.com/beezneez/3112

• Ag-Pb deposit (also Cu and barite in

some mines)

• Focus on the two main producing

mines – a single system

– North Mt Farrell (1899-1933) and

– New North Mt Farrell (1934-1973).

• Hosted in Cambrian laminated

shale, volcaniclastic sandstone

(“tuffs”), greywackes and minor

lava (the "Farrell Slate") which

strike NNE and dip steeply W.

ABOUT THE MT FARRELL (TULLAH) FIELD

Solomon, (1965); McNeill and Corbett, (1989)

Genesis: Current – Devonian vein mineralisation

Originally suggested to be related to intrusion of Devonian granitoids (Solomon, 1965)

Isotopic data indicated a Cambrian seawater source, with possible minor magmatic input for sulphur (Polya, 1981; Solomon et al., 1969)

+ lack of an obvious granitic source,

+ common deformation of galena, and lack of wall rock alteration, led Collins et al. (1981) to suggest that the mineralisation is probably remobilised volcanogenic massive sulfide.

Mineralogy is similar to Pb-Zn deposits associated with Devonian granites (Polya, et al., 1986), and the lead isotope data of Gulson and Porritt (1987) indicate that the lead is post-Cambrian

The Murchison Lode sulphur isotopes indicate significant Devonian sulphur content (Polya, et al., 1986) - with Post-Cambrian lead isotope ratios (Gulson and Porritt, 1987), suggest formation as Devonian vein style mineralisation.

CURRENT THINKING - GENETIC MODEL

From McNeill and Corbett, (1989)

RAW INFORMATION

NEW NORTH MT FARRELL

Workings

NEW NORTH MT FARRELL

Mapped Faults

NEW NORTH MT FARRELL

Mapped Lodes

NEW NORTH MT FARRELL

Lodes – Long Sections (stoped)

NEW NORTH MT FARRELL

Volcaniclastics

NEW NORTH MT FARRELL

Mapped bedding and foliation trends

NEW NORTH MT FARRELL - STRUCTURE Level Plan – 2 Level

NEW NORTH MT FARRELL - STRUCTURE Level Plan – 2 Level

NORTH MT FARRELL

North Mt Farrell Workings

• Spatial and geometric association of ore shoots with strongly folded and transposed ‘volcaniclastic’ units.

• Plunge sub-parallel to the plunge of the folded volcanoclastic unit

• Lodes hosted within the transposed limbs of isoclinal folds in the Farrell Slate – lodes are structurally hosted (but rarely faults).

• Association with folds suggests remobilisation and lode formation during deformation (folding)

ADDITIONAL INFORMATION FROM THE MODELLING

Mt Lyell FieldIron Blow, South Lyell &

North Lyell

ABOUT

• Pyrite, copper, silver, gold deposits (plus Pb-Zn)

• Hosted in Mt Read Volcanics– the Lyell Schist

• Remobilisation of metals during intense deformation

• Though some suggest it is a hybrid porphyry system

CURRENT THINKING - GENETIC MODEL

• A Cambrian subsea floor replacement style VHMS deposit

• Hosted in Mt Read Volcanics –the Lyell Schist

– Suggested that it is a hybrid porphyry system

• Some remobilisation of metals during later deformation –focussed at structural contact with younger Owen Conglomerate – ‘bonanza’ shoots

Gregory, (1905)

RAW INFORMATION

Iron Blow & South Lyell

Corbett, 2001

IRON BLOWLong Section – Through Plane of No 4 Tunnel

Note: grid scale is in FEET

Iron Blow Outcrop

IRON BLOW MODELLong Section – Through Plane of No 4 Tunnel

View approximately to north

IRON BLOW MODELOriginal Topography and ‘Iron Blow’ Outcrop

View approximately to north

IRON BLOW MODELNo 4 Tunnel and Early Workings

View approximately to north

IRON BLOW MODELWorkings – to No 9 Level

View approximately to north

IRON BLOW MODELIron Blow Orebody – Pyrite-Cu-Au

View approximately to north

IRON BLOW MODELSouth Lyell Orebody – Pyrite-Cu-Au

View approximately to north

Inset: view to northeast

IRON BLOW MODELConglomerate Contact

View approximately to north

Inset view: approximately southwest

IRON BLOW MODELConglomerate Contact

View approximately to north

IRON BLOW MODELConglomerate Contact

View approximately to northFault offset of South Lyell Orebody from Iron Blow

Orebody?

IRON BLOW MODEL‘Bonanza’ Shoots

View approximately to north

On the eastern (footwall) of the pyrite orebody, at the boundary between the sulphide oreand the lower continuation of the haematite of the “Iron Blow”

850 tons of ore - copper glance (redruthite), bornite, “fahlore” and argentite (silver glance).

Haematite and barite, with rich ore between this and the wall and on the floor

Richest ore was chalcopyrite and argentite or stromeyerite. Bornitic ore often contained asmuch as 5% Ag and often had “arsenical fahlore” (tennantite).

Also abundant chalcopyrite containing from 200 - 400 oz Ag/ton.

Daly, (1901) and Gregory, (1905)

IRON BLOW MODEL‘Bonanza’ Shoots

View approximately to north

On the eastern (footwall) of the pyrite orebody, at the boundary between the sulphide oreand the lower continuation of the haematite of the “Iron Blow”

850 tons of ore - copper glance (redruthite), bornite, “fahlore” and argentite (silver glance).

Haematite and barite, with rich ore between this and the wall and on the floor

Richest ore was chalcopyrite and argentite or stromeyerite. Bornitic ore often contained asmuch as 5% Ag and often had “arsenical fahlore” (tennantite).

Also abundant chalcopyrite containing from 200 - 400 oz Ag/ton.

Daly, (1901) and Gregory, (1905)

The discovery of this shoot provided most of the capital to develop the mine.

IRON BLOW MODEL‘Bonanza’ Shoots

View approximately to north

Inset view: approximately southwest

North Lyell

Corbett, 2001

NORTH LYELL MODELBase Plan

NORTH LYELL MODELStoped Orebodies

NORTH LYELL MODELContacts – Lyell Schist and Conglomerate

NORTH LYELL MODEL

Transposed tight to isoclinal fold – looking down-dip

Orebody Geometry

ADDITIONAL INFORMATION FROM THE MODELLING

• The Mt Lyell mineralised system is structurally dislocated,

– was probably once a single continuous stratabound zone of alteration and mineralisation – put it back together

• Complexly folded (very tight to isoclinal) and transposed

– probably structurally differentiated by cleavage formation – particularly North Lyell

• Dislocated by NW-trending faults

• High grade Cu-Ag shoots located at structural contact with conglomerate – remobilised copper and silver (exploration target?)

ADDITIONAL INFORMATION FROM THE MODELLING

Some Exploration Questions

• Have all dislocated segments of the copper mineralisation been located between North Lyell and the Iron Blow (e.g. beyond the South Lyell)?

• Where is the lead-zinc? This part of the system is under-represented - seems largely to be missing – does it remain to be found in dislocated segments?

• The style of deformation – dislocation, folding and foliation/differentiation is very similar to that of the Hercules VHMS, near Rosebery

Explore as a single giant VHMS and sub-seafloor replacement system –

But first understand the whole system architecture – especially the structure

TAKE HOME MESSAGE

• Maintaining data from even mined out deposits is so important – you may never know when it is needed

• Why geological surveys are so important as data repositories

• Companies should maintain mine data – it is an asset

and

WHAT CAN A HOLE TELL US ABOUT ORE DEPOSIT GEOLOGY?

The data that came from that hole – the mined orebodies (and their wall rocks) – may be the key to any future brownfields

exploration, mining feasibility studies, and ore deposit research

NOTE

Models will be available to anyone that wants them

Some of the models built to date include:

Broken Hill Mining Field, NSW.Zeehan Mining Field, Tasmania.ABH Consols Mine (Broken Hill), NSWMt Morgan, Queensland.The New Golden Gate Mine - Mathinna, Tasmania.The Iron Blow and North Lyell Mines, Tasmania.The Mt Farrell Mining Field - Tullah, TasmaniaThe Botallack Mine, Cornwall, UK.Coal mines – saltwater riverThe Blackstone Hill coal mining area, Ipswich, Queensland.Various Tennant Creek and Cloncurry depositsHannans North Mine

The model library will eventually be released online.

It is made possible by the academic licence software support to CODES/UTAS by ARANZ Geo (Leapfrog Geo software) and by Maptek (Vulcan).

ACKNOWLEDGEMENTS

ARANZ Geo

Maptek

Research software

Mineral Resources Tasmania Digital archival data