Elem

enta

l con

cent

ratio

n (p

pm)

Elem

enta

l con

cent

ratio

n (p

pm)

Elem

enta

l con

cent

ratio

n (p

pm)

Dis

tanc

e to

pre

dict

edhy

drot

herm

al c

entr

e (k

m)

0.1

10

1

100

3

2

1

0Cu Zn As Sn Sb Pb Sr Ti/Ni Ti/Sr Ti/Li Ti/CoMg/Sr Mg/Ca

M

H

M

M

H H

KEY:

maximum

minimum

upper quartile

lower quartilemean

VST1/519.0VST2A/281.0VST5/285.0VST5/385/0

It’s not easy being green – detecting arc-related mineral system fingerprints usingmineral chemistry in ‘propylitic alteration’ in a Cambrian arc terrane, Victoria, AustraliaRob Duncan*, David TaylorThe Geological Survey of Victoria, Melbourne, Victoria Australia

Sebastien Meffre, Ivan Belousov, Leonid Danyushevsky, David CookeCentre for Ore Deposit and Earth Sciences, University of Tasmania, Hobart, Australia

* corresponding author - rob.duncan@ecodev.vic.gov.au

MELBOURNE

GZ OZ

TZDZ

KZ MaZ

BZ

SZ

MZ

Bendigo

Ballarat

V I C T O R I A

200 km

DelamerianOrogenLachlan Oro gen

Lachlan Oro gen

38oS

144o E

148o E

AUSTRALIA

Tectono-stratigraphy zones - GZ = Glenelg, GSZ = Grampians-Stavely, SZ = Stawell, BZ = Bendigo, MZ = Melbourne, TZ = Tabberabbera, OZ = Omeo, DZ = Deddick, KZ = Kuark,

MaZ = Mallacoota, BaZ = Bass

BaZ

Paleo-continentalboundary

StavelyProject

Area

Tectono-stratraphicboundary

Figure 1. Location of Stavely Project Area which forms part of theDelamerian Orogen and is distinct from the younger Lachlan Orogen.

GSZ

DD10BR001 170.7 m

GG01 321.9 m

Cambrian rocks of the Stavely Arc (Fig. 1) have demonstrated potential for a range of arc-related mineral systems. Mineral chemistry data from ‘green rock’ mineral assemblages were collected with the aim of identifying fertility and prospectivity indicators that have been developed for mineralised systems elsewhere (e.g., Wilkinson et al. 2015; Cooke et al. 2017). This project was completed as part of a wider collaborative program between The Geological Survey of Victoria and Geoscience Australia to de-risk mineral exploration programs in a largely covered terrane. More details on the program can be found at https://earthresources.vic.gov.au/projects/stavely/geological-data-and-information.

Stavely Arc rocks are contained within a series of volcanic belts that formed above thinned continental crust in response to west-dipping subduction from 525 and 500 Ma - some arc-related rocks may be as old as 540 Ma. The volcanic belts are 3 to 8 km wide and fault bound (Fig. 2a). The volcanic belts are separated by Cambrian marine sedimentary rocks and transition to a largely intact volcanic rock in the mid-crust.

The effects of post-arc magmatism deformation resulting from the ~400 Ma Bindian Orogeny (and so also post-the timing of arc-related mineral systems) can be removed and the volcanic belts restore to three major sub-parallel belts that have a cumulative strike length of over 1,100 km (Fig. 2b,c). Preservation potential for arc-related mineral systems in relatively high because the arc has undergone little tectonic uplift since 380 Ma.

Materials were collected from two prospects in exposed portions of volcanic belts. At Thursday’s Gossan (Stavely Belt) calc-alkaline andesitic to rhyolitic volcanic, volcaniclastic and sedimentary rocks have been intruded by dacitic to tonalitic sub-volcanic porphyry stocks. An ~8 km2 propylitic alteration zone (Fig. 3) is roughly coincident with a small supergene resource (inferred 28.1 Mt at 0.4 % Cu at 0.2 % cut-off grade). Hypogene mineralisation associated with porphyry-like veins (Fig. 3) (and phyllic and potassic hydrothermal alteration assemblages) have returned encouraging exploration intercepts (e.g., 952 m at 0.23% Cu from 11 m) (Stavely Minerals, 2019).At Eclipse (Black Range Belt) calc-alkaline dacitic to rhyolitic volcanic and volcaniclastic rocks host massive Cu-Zn mineralisation that appears to be of VHMS affinity. Phyllic hydrothermal alteration is associated with a quartz-carbonate-sulphide mineralisation transitions to a propylitic assemblage (Fig. 4). No resource has been estimated. Significant intercepts include 267.1 m at 0.3 % Zn, 2 g/t Ag and 0.1 g/t Au from 1.3 m (Navarre Minerals, 2014). Eight polished samples mounts were prepared and imaged using scanning electron microscopy. Epidote and chlorite were analysed for major, minor and trace elements using the laser ablation ICP-MS facility at CODES, University of Tasmania. Fig. 5 shows selected results.

Overview Geodynamic Context

NN

Tyar Belt

Tyar Belt

Tyar Belt

Black Rang

e

Black Rang

e

Stavely Belt

Stavely Belt

Elliott Belt

Elliott Belt

Bo

on

awah

Belt

Bo

on

awah

Belt

Bunnigal BeltBunnigal Belt

Dryden Belt

Dryden Belt

Dryden Belt

Dryden Belt

Dim

boola Belt

Dim

boola BeltSTAVELY16

GG-01

Yarramylijup Fault

Yarramylijup Fault

Yarramylijup Fault

Dryden Belt

Dryden Belt

Bunnigal Belt

Dim

boola Belt

Bo

on

awah

Belt

Elliott Belt

Stavely Belt

Black Rang

e

heavy mineral sands

intrusion-related base metalintrusion-related gold

orogenic gold

copper-zinc(-gold) VHMScopper(-gold-silver-molybdenum) porphyrygold(-silver) epithermal

Mineral Occurences

Cambrian-aged

Siluro-Ordovician

Devonian

6000000

5980000

5960000

5940000

5920000

5900000

540000 560000 580000

600000 620000 640000 660000

Cambrianvolcanic belt

selecteddrillhole

extent ofCambrian bedrockexposure

STAVELY16 Eclipse

20 km

Thursday’sGossan

Moyston Fault

STAWELL ZO

NE

STAWELL ZO

NE

STAWELL ZONE

STAWELL ZONE

STAWELL ZONE

STAWELL ZO

NE

Stavely Belt

Stavely Belt

Stavely Belt

Moyston Fault

Moyston Fault

Moyston Fault

Bunnigal Belt

Bunnigal Belt

Bunnigal Belt

Dryden Belt

Dryden Belt

Dryden Belt

Elliott Belt

Elliott Belt

Elliott Belt

STAWELL ZONE

GLENELG ZONE

Boonawah Belt

Dimboola-Black Range-Elliott-Stavely-Bunnigul Belt

Dryden Belt

Yarramyljup Fault

Dryden Belt

B inset

Moyston Fault

Moyston Fault

Moyston Fault

N

N

~50 km

~50 km

b

a

c

Moyston Fault

DD10BR001 267.5 m DD11BR005 105.0 m DD11BR006 231.0 mDD10BR001 171.3 m

SMD003 340.6 m

Case study areas

Cu (ppm)

Mo (ppm)

Sn (ppm)Pb (ppm)

Zn (ppm)

103

100

10

1

As (ppm)0.1

1

1

10

10

1000.1 0.1

11

10

10

100100

Sb (p

pm)

Sb (p

pm)

As

(ppm

)

KEY:DD10BR001/267.0DD10BR003/160.0DD11BR005/105.0DD11BR006/231.0

regionalmetamorphic

proximal(or smaller )

distal (or larger)

porphyry-relatedpropylitic

hydrothermalalteration

proxim

al

hydrothermalhydrothermal

metamorphic

metamorphic

Chlorite proximitor1@Eclipse

@Thursday’s GossanChlorite results

H = hydrothermalM = metamorphic

0.1

10

100

103

1

Cu Zn As Sn Sb Pb Sr

Dis

tanc

e to

pre

dict

edhy

drot

herm

al c

entr

e (k

m)

3

2

1

0Ti/Ni Ti/Sr Ti/Co Mg/Sr Mg/Ca

Chlorite proximitor1

Ti/Li

KEY:

maximum

minimum

upper quartile

lower quartilemean

DD10BR001/267.0DD10BR003/160.0DD11BR005/105.0DD11BR006/231.0

‘consistent’ distance window

‘consistent’ distance window

Figure 5. Box and whisker plots for filtered chlorite data for selected elements. Threshold values for Zn, As and Sr distinguish between propylitic hydrothermalalteration and regional metamorphic compositions. 1calculated using equationsfrom Wilkinson et al. (2015).

Figure 2. (a) Reduced-to-pole total magnetic intensity pseudocolour image for Stavely Project Area withextent of Cambrian rock exposure, distribution of Cambrian volcanic belts and location of mineral occurrences. (b) Inset of restored Stavely and Elliott belts byremoval the effects of faulting and rotation associated with the Bindian Orogeny to show original distribution of volcanic belts. (c) Restoration of original volcanicbelts across the entire arc resolves to three sub-parallel belts.

a

ab

c

da

b

b

c

c d

d

e

VST006 223.4 m

VST001 519.0 m VST005 285.0 m

VSTD005 385.0 m

1 cm

1 cm

1 cm

1 cm

1 cm 1 cm 1 cm 1 cm

1 cm

Sample material

At Thursday Gossan Prospect elevated Sr and Zn in chlorite are indicative of hydrothermal alteration associated with pyropylitic hydrothermal alteration. Chlorite proximitors demonstrate a vertical temperature gradient to the hydrothermal system.

At Eclipse elevated As and Sb in epidote and elevated Zn, Cu, and Pb in chlorite are indicative of hydrothermal alteration associated with propylitic hydrothermal alteration. Systematic variations in chlorite Cu -Pb and As-Cu in epidote at Eclipse identify an untested area for follow-up mineral exploration.

This study demonstrates that even a small green rock mineral chemistry dataset may assist in mineral exploration programs. These data are consistent with whole rock geochemistry fertility data (e.g., Sr/Y and V/Sc) and geodynamic models that demonstrate prospectivity for arc-related mineral systems in the Stavely Arc. dist

al

proxim

al

distal

Key outcomesFigure 6. Box and whisker plots for filtered epidote data for selected elements.Threshold values for Sb and As distinguish between propylitic hydrothermalalteration and regional metamorphic compositions. Same key as Figure 5c.

REFERENCES: COOKE, DR et al. (2017) Porphyry indicator minerals (PIMS) and porphyry vectoring and fertility tools (PVFTS) – Indicators of mineralization styles and recorders of hypogene geochemical dispersion halos. Proceedings of Exploration 17: p. 457–470.NAVARRE MINERALS, 2014, Navarre extends copper zone at Eclipse prospect, western Victoria. ASX Release 6 August 2014.STAVELY MINERALS, 2018, Thursday’s Gossan Copper- Gold Porphyry – Diamond Drilling Update. ASX Release 20 April 2018. WILKINSON, JJ et al. (2015) The chlorite proximitor: A new tool for detecting porphyry ore deposits. Journal of Geochemical Exploration 152: 10–26.

Figure 4. Eclipse - samples of (a) sphalerite-chalcopyrite-pyrite mineralisa-tion, (b to d) chlorite- and epidote-bearing green rock assemblages analysed.

Figure 3. Thursday’s Gossan - sam-ples of (a) chalcopyrite-bornite-pyrite D vein, (b) quartz-chalcopyrite-pyrite B vein, (c to e) chlorite-bearing green rock assemblages analysed.

Epidote @Eclipse