Paul, Matthew1; Cook, Nigel J.

2; Ciobanu, Cristiana L.

2; Anderson, John

3; Murray, Jason

3

1School of Physical Sciences, University of Adelaide, Adelaide S.A. 5005, Australia School of Physical Sciences, University of Adelaide, Adelaide S.A. 5005, Australia

2School of Chemical Engineering, University of Adelaide, Adelaide S.A. 5005, Australia

3Investigator Resources, Norwood, S.A. 5067, Australia

Introduction Introduction

The Paris silver deposit, Northern Eyre Peninsula (Fig. 1), is hosted by rocks of the ~1,600 Ma Gawler Range

Volcanics (GRV) deposited upon the Katunga dolomitic marble of the Paleoproterozoic Hutchison Group (Fig.

2). Together with several other prospects, Paris occurs in the Uno Province, a region of Ag-base metal minerali-2). Together with several other prospects, Paris occurs in the Uno Province, a region of Ag-base metal minerali-

zation located along the Uno Fault, marking the southern boundary of the GRV. Mineralization is hosted within

intensely clay-altered polymict volcanic breccias and an upper, oxidised zone of the Katunga dolomite. Paris

contains an inferred resource of 8.8 million tonnes at 116 g/t Ag for a total of 33 Moz Ag (Inv Res 2015) . contains an inferred resource of 8.8 million tonnes at 116 g/t Ag for a total of 33 Moz Ag (Inv Res 2015) .

The dolomite is intruded by a series of narrow, NW-trending granitic dykes, which although yet to be dated, are

considered temporally related to the Kimban orogeny. Genetic relationships between mineralisation and these in-

trusions remains inadequately constrained. In addition, trusions remains inadequately constrained. In addition,

the dolomite is host to rare ginguro veins and narrow,

discontinuous, deformed magnetite- and sulphide-

bearing veins, which contain comparable assemblages to bearing veins, which contain comparable assemblages to

sulphide-rich clasts in the breccias. An oxidised interface

is present between the dolomite and the breccias, poten-is present between the dolomite and the breccias, poten-

tially representing the pre-eruption paleosurface. This

zone, in addition to the upper, altered dolomite form the

base of the ore zone at Paris. At depth, magnesian skarn base of the ore zone at Paris. At depth, magnesian skarn

assemblages, dominated by forsterite but also containing

spinel and retrograde assemblages of chlorite, pyrite and

secondary carbonates (calcite and kutnohorite), prevail across the footwall to the silver deposit.

Figure 2: Regional geology.

secondary carbonates (calcite and kutnohorite), prevail across the footwall to the silver deposit.

Ore assemblages in both dolomite and breccia clasts are characterized by galena, arsenopyrite, pyrite, sphalerite and chalcopyrite. Silver is pri-

marily present as acanthite and native silver; however, significant amounts of refractory silver have been measured in pyrite, galena, arsenopy-

rite and sphalerite. Pyrite demonstrates significant variation in trace element chemistry between different sulphide-rich zones, indicating that rite and sphalerite. Pyrite demonstrates significant variation in trace element chemistry between different sulphide-rich zones, indicating that

the sulphide-rich breccia clasts may not all be sourced from the magnetite/sulphide veins at depth, as previously suggested in early interpreta-

tions (Inv Res 2013). tions (Inv Res 2013). Figure 1: Loca�on map.

Sulphide trace elements a. b.

The sulphide minerals at Paris are host to elevated concentrations of several trace elements, with

Ag being of most economic interest. Table 1 indicates the highest average concentration of Ag can Ag being of most economic interest. Table 1 indicates the highest average concentration of Ag can

be found in pyrite and sphalerite in the breccia, and galena in the ginguro. be found in pyrite and sphalerite in the breccia, and galena in the ginguro.

Ag can be present both as discrete inclusions and in solid solution within the host mineral, which

can be distinguished by the LA-ICP-MS spectra. The pyrite from the breccia (Fig 3a), with rough can be distinguished by the LA-ICP-MS spectra. The pyrite from the breccia (Fig 3a), with rough

spectra with peaks and toughs indicates for Ag and Sb indicates the presence of discrete Ag-Sb in-spectra with peaks and toughs indicates for Ag and Sb indicates the presence of discrete Ag-Sb in-

clusions in the pyrite grain. Conversely, the smooth spectra for sphalerite and galena (Fig 3b,c,d)

indicate Ag is likely to be

c. d.

indicate Ag is likely to be

present in solid solution. It is Pyrite Arsenopyrite Galena Sphalerite

11492 79 163 1894 also possible for Ag to be

present in homogenously dis-

Breccia 11492 79 163 1894

Veins 115 16 340 44 present in homogenously dis-

tributed nano-inclusions. Veins 115 16 340 44

Ginguro N/A N/A 1071 59

Table 1: Average Ag (ppm) values for different sulphides by lithology.

Ginguro N/A N/A 1071 59

Figure 3: Time resolved counts per second LA-ICP-MS spectra for sulphides from both the breccia and ginguro.

Coupled substitution +↔

2+

a. b.

Ag is largely insoluble in galena via simple 2Ag+ ↔ Pb2+ substitution, as one of the Ag atoms

must be placed in a interstitial position in the galena lattice (George et al. 2015). Coupled substitu-

R2=.96

must be placed in a interstitial position in the galena lattice (George et al. 2015). Coupled substitu-

tion is necessary for galena accommodate large concentrations of Ag, most commonly Sb and Bi.

Figure 4 demonstrates the correlation between Ag and Sb for galena from the breccia (fig. 4a), R2=.96

R2=.84

Figure 4 demonstrates the correlation between Ag and Sb for galena from the breccia (fig. 4a),

and Ag and Bi for galena from the ginguro, and the proposed coupled substitution mechanism.

PbS → AgSbS2

Sb3+

+ Ag+ ↔ 2Pb

2+

PbS → AgBiS2

Bi3+

+ Ag+ ↔ 2Pb

2+ Sb

3+ + Ag

+ ↔ 2Pb

2+ Bi

3+ + Ag

+ ↔ 2Pb

2+

References Figure 4: Graphs for trace element concentra�on (ppm) for galena in a. breccia and b. ginguro. References

George LL, Cook NJ, Ciobanu CL, Wade BP (2015) Trace and minor elements in galena: A recon

naissance LA-ICP-MS study. American Mineralogist 100, 548-569. Conclusions

naissance LA-ICP-MS study. American Mineralogist 100, 548-569.

Investigator Resources Ltd (2013) Paris Interpretive Geology. Unpublished report. • The sulphides pyrite, sphalerite and galena host significant concentrations of Ag.

Ag is present both as inclusions and in solid solution within sulphides. Investigator Resources Ltd (2015) Assay results continue to develop copper gold and silver poten

tial around the Paris Silver Project. http:www.investres.com.au

• Ag is present both as inclusions and in solid solution within sulphides.

• Galena from different lithologies demonstrate different coupled substitution mechanisms for Ag. tial around the Paris Silver Project. http:www.investres.com.au