paulsens geology and mineralisation. - aig.org.au · pdf filepage 5 paulsens mining background...

• AIG - MEGWA Presentation Sep 19

Paulsens – Geology

and mineralisation.

can little old Paulsens really contain 1Moz

Introduction

• Quick mention of Northern Star Resources

• Paulsens History (as known to me) and Mining

background

• Regional location

• Grids (MGA and local – rotated 41.50)

• Local Geology. Plan, section, stratigraphic column

• Mineralisation

• Structure and evolving ideas

• Morphology

• 50m spaced sections

• Genesis

• Gabbro offset

• Voy1 exploration story

• What’s next

Northern Star Resources

• Formed in 2003 to explore the Kimberlies

• Bought Paulsens in 2010

• Invested heavily in drilling and development

• Requires intensive drilling, 200+m drill drives (4 to

date)

• Each year adds 100 to 150 vertical metres

• Currently producing at 80,000oz pa ~650m below

surface, 60 to 70m vertical development annually

• 400,000 ounces in resource, 500,000 produced

• Nearby Ashburton project

•12,000g/t

Paulsens History

• Discovered 1930’s ~900 ounces produced from

Melrose mine (2,200t @ 12g/t)

• Asarco – 1982 to 1987

• CRAE -1987 to 1989

• Hallmark – 1991 to 1993

• Taipan – 1993 to 2002

• Feasibility, small pit plus UG

• St Barbara- 2002 to 2004

• Potential for large pit

• Nustar – 2004 to 2006

• Commenced UG mining, no pit

• Intrepid Mark I -2006 to 2008

• 895 Drill Drive, Voyager 1

• Intrepid Mark II – 2008 to 2010

• Northern Star

• Voy1 high grade extention, Voy2

•acknowledgements

•Stuart Owen

•Roger Majoribanks

•Bill Rose

•Russell Mason

•Brett Davies

•David Gray

Paulsens Mining Background

• Underground mining commenced 2004,

predominantly mechanised, minor airleg production

• Longhole retreat stoping method

• 2011 move to semi – owner operator

• Recent increase to two development jumbos

• >500m advance p/mnth

• One longhole drill

• Three MT6020 trucks

• 40,000 ore tonnes p/mnth

• Three LM90 diamond drill rigs

• ~8,000m core p/mnth

• Two are mobile carrier rigs

• Mined grade ~7g/t Mining cutoff ~2.5g/t

• Standard CIL plant

• ~380,000t p/a

Regional deformation associated with the Palaeoproterozoic Capricorn Orogeny

Wyloo Dome is a product of fold and thrust related uplift

Wyloo Dome Structural Setting (MGA grid)

•Paulsens Mine

•60km by

25km

Wyloo Dome (MGA grid)

•Local geology

Wyloo Dome Geology (MGA grid)

Paulsens – Local Stratigraphy

Appears as a distinctive vesicular basalt. Also seen as very thick flows that can

be quite coarse grained. Occasionally showing very large feldspars ‘cat rock’

•Distinctive unit of angular fragments.

•Upper Melrose Argillite. Increasing number of coarse grained beds

including ‘fish eye’ sandstone

•Lower Melrose Argillite. Graphitic siltstone with

sandy interbeds. Structures indicate sequence is

right way up.

•Clean quartz rich sandstone

• Gabbro and ‘cat rock’ same gamma signature?

•Gamma logging

proved to be a useful

tool to discriminate

between the many

coarse grained mafic

rocks.

???

Paulsens Local Setting – Plan view (mine grid)

• NW plunging folds in NW-dipping

Archean Fortescue Group stratigraphy

•Hinge zone of Wyloo anticline

•Bedding-parallel Melrose fault?

•Paulsens vein along the Melrose fault

•NW trending faults that offset the

gabbro, Vein and the host stratigraphy

Local

North

•From R Marjoribanks

Northern Star Resources Local Setting – Section (looking down plunge)

• Gabbro

• Quartz – 2 stages

• Mineralisation

• UZ

• LZ

• Apollo

• Faults (not shown)

• Dykes

?

?

UZ

LZ

Mineralisation – UZ and LZ (and UZ2)

• UZ

• Located in hanging wall of quartz

• Generally more massive sulphide

• ~7g/t in upper Paulsens, 5 to 10m thick

• ~15-20g/t in Voyager, 2 to 3m thick

• LZ

• Located on footwall of quartz

• More laminated in appearance, stylolitic

• 15g/t in upper Paulsens and Voyager, 0.2 to 3m thick

• UZ2 and “veins in gabbro”

• Gold if very fine, often intimately associated with pyrite but not refractory.

Also found as pinheads along stylolites and as rare coarse flakes

• Sulphide not always mineralised, gold after barren sulphide stage?

•Upper zone

•Lower zone


•~1m

Grade is associated with

- complex brittle failure (brecciation) in Stage 1 veins, especially in fold hinges

- cyclic opening events on limb positions

•Upper Zone •Lower Zone


•Upper Zone •Lower Zone

•Pyrite is the dominant sulphide but chalcopyrite and pyrrhotite also feature, at times quite concentrated.

‘Typical’ ASX announcement

Requirements for Paulsens Mineralisation

• Correct stratigraphy

Coarser more brittle unit over more ductile fine grained unit

Graphitic to facilitate slip

• Folding event

• Rigid body, oblique to fold axis

• Initial barren silica flooding

• Gold bearing fluids

• Graphite to facilitate gold dropping out of solution

• Position on Dome?

Paulsens – Evolving ideas

• Basic frame work still valid.

• Gabbro oblique to Wyloo Dome

• Folds parallel to Wyloo Dome

Ripple analogy

• Effect of Apollo Faults (shears?)

• Paulsens overturned fold

• Voyager 1

• Voy 1 high grade hinge

• Flex and flattening in Gabbro unit

• Position on Wyloo Dome fold nose

Plan view – (mine grid)

Wyloo Dome Axis

Voyager 1 fold axis

Paulsens fold axis

Voyager 2 fold axis

Local

North

Oblique view (looking up plunge - SE)

Brett Davies – Renaissance Geology

50m cross section location looking North West

•High grade

Local

North

Apollo

Melrose Mine

Apollo

Lower Zone

Weak Upper

Zone

Upper Zone

Upper Paulsens

becoming

recumbant

Voyager 1

Voyager 1

high

grade

hinge

Zone Z

Remnant Upper

Paulsens

Voy 1, high grade hinge

Voy 1, weak UZ

•Voyager 2

End of Dyke

interps

Odd flat dyke

Pluto

High grade

Voyager 1 Ext

•Patchy but extreme

grade in Voy2

Gabbro disappearing?

Paulsens – Genesis (with minimal Melrose Fault movement)

• Deposition

Paulsens – Genesis

• Extensional event leading to

dyke emplacement. A non-

planar gabbro dyke intrudes

the succession.


• Onset of Regional

shortening related to the

Capricorn Orogeny. District

scale Wyloo Dome begins to

develop with folding

accompanied by rotation of

bedding and the gabbro

dyke.


• The Wyloo (Dome) fold

amplifies and tightens,

inducing greater rotation of

bedding and the dyke.

Failure begins to occur in

the ‘kink’ position, which is

probably accompanied by

vein formation.


• Further evolution of the Wyloo Dome

sees increased tightening on the north

limb and yet further rotation of the

gabbro dyke.

• Discrete zones of bedding plane parallel

shear become established.

• Brittle failure of Gabbro dyke begins


• Continued shortening

• Tightening of Wyloo dome

• Development of NNW

vergent asymmetry

• Steeper NNE dipping limbs

• Failure in kink zone of

Gabbro and initial

deposition of barren quartz


• Bedding plane shear well developed as folding

progresses

• Produces high permeabilities

• fluid flow and vein formation

• Gold mineralisation developing along bedding plane parallel veins

• Veins are laminated

• Continued pervasive, irregular failure in gabbro ‘rafts’


• Failure developing within the barren veins in gabbro kink domain

• Failure is driven by attempts to accommodate strain through buckling (folding)

• Failure located in apical positions with respect to fold hinge positions

• ‘Upper Zone’ mineralisation

• Apollo ore body now established on the moderate to steep dipping NNE limb


• Probable ‘out-of-sequence’ thrust elements develop

• Dominant reverse displacement

• North vergence

• The ‘Apollo Fault System’

• The current model sees the last significant event associated with the Capricorn contractional history manifest as the development of the Apollo Fault system


• The ‘Apollo Fault System’ controls folding of the barren and mineralised vein elements

• Observed in the Paulsens Structural Domain

• Probable affects the domain external to the trap site

• Offsets gabbro dykes?

• Displacement on AFS elements is minor: they tip-out close to the Voyager positions so far exposed

• It is likely that the vein deformation gave rise to local

structurally induced upgrading of gold contents in

some Voyager positions

Paulsens – Genesis - continued

• Post ore late stage dykes

• Post ore late stage faults

• Down plunge the gabbro orientation becomes flatter.

• Due to position on fold?

• Questions:

• Mineralisation timing

• Basement thrust feeder or Apollo Fault system feeder

Gabbro offset idea

Oblique view (looking up plunge)

Brett Davies – Renaissance Geology

Gabbro offset – oblique view (looking up plunge)

• Drill testing ongoing

• Technical success

• Sporadic high grade

• Prime position may be further

down plunge

• Effect of Gabbro flattening

Voyager 1 – Exploration story

• Taipan 1998 –first intercepted

• 17 intersections before 2008

• SBM,Nustar,Intrepid v1

• Re-Interp using UG ideas

• Apparent success then apparent

failure -200 holes in 2008/2009

• Spotted Dog and last chance

• 38,000m total drill metres

• Resource at Jun 2012 -200,000oz

•Pre 2008

•2008/2009

•200 holes

•Only 6 graded well

•All drilling to

2010

•Hinge test 2009

Further Potential

Regionally:

• 30 years and 9 companies, yet still under-

explored

• More geophysics to be trialled

• Close spaced aeromagnetic targets still to

be followed up

• Paulsens appears a unique set up so non-

Paulsens style trap sites need to be

identified under cover

• 8 years mine life so far

• 500,000 oz produced

• 400,000 oz in resource

• On track to produce 1 Moz?

Locally:

• Continue down plunge

• Feeder structure?

• Gabbro offsets – need time

• Voyager established after 38,000m

Thank You - Questions

Not Paulsens

Thank You - Questions

Steep limb Voyager1

High grade hinge

Barren Quartz

paulsens geology and mineralisation. - aig.org.au · pdf filepage 5 paulsens mining background...

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