Sulphur isotopes across the GawlerCraton: new data on ore sourcesLaura Morrissey, Crystal LaFlamme, Justin Payne, Tom Raimondo

ARC Linkage Project: Source to Spectrum

UPDATE

Hiltaba – GRV associated mineralisation

Hiltaba – GRV associated with diverse series of deposits and prospects

• IOGC (Olympic Dam, Prominent Hill, Carapateena)

• Au (Tarcoola, Tunkillia, Barns)

• Skarn Fe–Au ± Cu (Weednanna, Punt Hill, Hillside)

• Pb–Zn (Menninnie Dam, Telephone Dam)

• Ag (Paris)

ARC Linkage project: Source to spectrum

Our 3 year aim is to produce an over-arching genetic scheme for the spectrum of deposits on the Gawler Craton and convert that into tangible results that assist exploration

What are the key ingredients for IOCG, Au, Pb-Zn and Ag deposits in the Gawler Craton?

1. The right place and time

2. Metal sources

3. Fluid sources and pathways

4. Crustal prospectivity

Source to spectrum: 2017 outputs

(1) The right place and time and (4) crustal prospectivity• New geochronology from the southern Gawler Craton (Paris, Barns)• New geochronology from the Mt Woods Inlier

(2) Metal sources• Geochemistry of mafic Hiltaba Suite magmatism (PhD chapter- Claire Wade)

(3) Fluid sources and pathways• Saline fluids: evaporites?• Trace element compositions of garnet and whole rock stable isotope

compositions as a vector for mineralisation (2 honours theses- UofA)• Sulphur isotopes

Local geology control on deposit types?

Local geology- key ingredients?

A multiple sulphur isotope pilot study across the Gawler Craton

- 7 prospects, different regions and deposit types

- Au: Tarcoola, Barns

- Pb-Zn-Ag: Paris, Menninnie Dam, Telephone Dam

- Skarn Au-Fe: Weednanna, Punt Hill

What do sulphur isotopes tell us?

Sulphur is a ligand that complexes with many metals in ore-forming fluids

Sulphur sources include:• Magmatic fluids• Metamorphic fluids• Remobilisation from magmatic rocks• Remobilisation from sediments or older

hydrothermal alteration• … Or a combination

Each of these sources will require a different set of ingredients and local geology

Cook et al. 2016

Measuring multiple sulphur isotopes

After Ünal İmer et al. 2013

Mass Independent Fractionation

MIF is a feature of the Archean (>2.3 Ga) supracrustal record

This signature is diluted by later geological processes but not destroyed.

So can be used to determine if S is being sourced from Archean sediments (Sleaford/MulgathingComplex)

Does the Archean crust in the Gawler Craton play a role in deposit type?

Maynard et al. 2013, Farquhar et al. 2010

Archean contributions?

Johnson 2011

New sulphur isotope data: central Gawler Au deposits

Shear-hosted Au, mineralisation associated with sericite alteration, mineralisation dominantly in quartz-pyrite veins

• Tarcoola: • Tarcoola Formation (c. 1650 Ma) and

monzogranite (Paxton Granites, c. 1715 Ma)

• Tunkillia: • Granodiorite (Tunkillia Suite, 1680 Ma)

• Barns:• Granodiorite (Tunkillia Suite, 1693 Ma)

Budd and Skirrow 2007

Sulphur isotope data: central Gawler Au deposits

Similarities?

Dolerites coeval with mineralisation

Mineralising style: qz-py veining and sericite alteration

Differences?

Host rock: Tarcoola Formation vs Tunkillia Suite and metamorphosed Kimban metasediments

Prospects across the southern GRV

Menninnie Dam, Telephone Dam: volcanogenic Pb-Zn

Paris:epithermal Ag

Weednanna: skarn Fe-Au

Paris Ag

New LA-ICP-MS geochronology confirms GRV-aged magmatism, high precision TIMS age coming tomorrow

Data comes from sulphide-rich interval, pyrite + galena

Mean δ34S = +0.67 ‰, likely mantle source of sulphur.

Mineralisation mostly hosted in brecciated GRV

Picture

Ore genesis modelGeochron plot

Investigator Resources 2017

Southwest Northeast

Skarn systems (southern GRV): Weednanna Au

• Magnetite skarn with Au mineralisation

• Hutchison Group sediments

• Hiltaba Granite adjacent/at depth

Schlegel et al., 2017

Archean contributions?

Traditional limit of mass independent fractionation:Δ33S = 0 ± 0.2 ‰

Weednanna Au

Archean contributions and follow up work

• MIF (expressed as Δ33S ≠ 0) indicates a source of Archean supracrustalsulphur

• A constant Δ33S within a deposit is a powerful tool because it allows us to link changing δ34S to changing fluid conditions rather than variations in S source

• Ensuing detailed study on Weednanna will be the first use of this methodology in South Australia

Conclusions

• Fluid sources in the Gawler Craton are complex!

• Similar deposit types may have very different δ34S isotope characters• More work needed to link δ34S values of

sulphides to fluid character

• Thanks to John Anderson, Anthony Reid, Rian Dutch, Adrian Fabris and the GSSA staff at the core library for help and discussions