Summary:
Mineral Resource inventory of approximately 470,000 ounces of gold, 16.2 million ounces of silver and 177,000 tonnes of zinc from ore located at Fountain Head, Glencoe and the Hayes Creek VMS deposits (Mt Bonnie and Iron Blow).
Fountain Head
Mineralisation occurs in veins as either conformable anticlinal lodes (with flanking mineralisation) or subvertical structurally hosted (“ladder vein style”) mineralisation associated with faults and shears sub-parallel to the fold axis, and is found within interbedded mudstones, greywackes and phyllite units. Sheeted quartz vein stock-works occur mainly in the axial zone (hinge zone) with veins predominantly dipping northeast, and some saddle reefs occur in the axial zone. Increased grades encountered at Fountain Head are thought to result from secondary deformation of the Fountain Head anticline. Gold is associated with quartz veining containing a pyrite-arsenopyrite sulphide assemblage and coarse gold is not uncommon.
The following key structural settings appear to control gold mineralisation at Fountain Head:
- The structurally controlled system of mineralised quartz veins appears largely restricted to the southwestern limb and hinge zone of the Fountain Head Anticline. Mineralisation is preferentially hosted in greywacke and sandstone units;
- Subvertical faults or shears subparallel to fold axial planes;
- Vein infill in dilatant zones in the apex of small-scale anticlinal folds associated with the Fountain Head Anticline;
- Conformable veins dipping away on the limbs of the fold, and conformable saddle reefs within the hinge zone of the fold.
Glencoe
Gold mineralisation at Glencoe is hosted by greywacke, sandstone, siltstone and mudstone of the Paleoproterozoic Mount Bonnie Formation, and is contained within complex quartz veins and shears spatially associated with the axial regions of shallow plunging anticlines. The majority of the gold-bearing quartz veins occur within sub-vertical to steeply dipping fracture and shear zones. Other gold-bearing quartz veins are interpreted to have conformable or ‘saddle reef’ geometries, and occur as stratabound bodies extending outwards from the discordant fracture-filled zones.
Late-stage chlorite alteration, shearing and brecciation overprint the gold-bearing veins, including country rock breccias with a chlorite matrix. There is a strong association of gold with sulphides, predominantly pyrite and arsenopyrite, and a close association between chlorite alteration and sulphide/gold/quartz vein development. Mineralisation has typically favoured the more ductile carbonaceous mudstone horizons. There appears to have been some gold redistribution by near-surface supergene processes.
Mt Bonnie
A tabular north-west dipping zone of high-grade massive sulphides surrounded by a larger halo of lower grade brecciated and carbonate altered rocks has been defined, with a flat-lying silver-rich supergene zone identified near-surface to the north of the historical open-pit. These three mineralised zones have been modelled and reported separately as zinc, gold and silver domains.
Excellent geological continuity and consistency of mineralisation is evident in the resource modelling, resulting in greater than 90% of the MRE being classified in the higher confidence Indicated category. The majority of the MRE is comprised of sulphide ore and occurs from approximately 25m to 170m below surface directly beneath the historical oxide pit.
Previous drilling by PNX intersected new mineralisation to the south of the historic pit and shows that mineralisation continues further south than previously anticipated and beyond the limit of current drilling. Potential also exists for a high-grade shoot(s) to extend underneath the current extent of drilling and the pit shell design.
The highest base metal and gold grades in the deposit are contained within the massive sulphide unit, which is up to 15m thick below the pit and appears to narrow with depth. The brecciated, carbonate altered unit below the massive sulphides contains lower grade disseminated mineralisation, often with a coarse blebby appearance.
In the oxide zone (Stage 1 CIL), the lead and gold are enriched and the zinc depleted. Within the primary massive sulphide mineralisation (Stage 2 flotation) no notable metal zonation has been observed, and metal grades appear to be remarkably uniform. Towards the south of the deposit, the massive sulphides appear to break into two separate units, likely to be fold or fault repetition, and remain open to the south and at depth. Gold mineralisation also occurs in a separate association outside of the massive sulphide zones, mostly in the Footwall Series.
Iron Blow
Drilling delineated two main massive sulphide lodes; an eastern hanging-wall lode defined by its significant zincgold-silver-lead mineralisation, and underneath, a broader predominantly zinc-gold rich western footwall lode. Four additional subsidiary lodes were also geologically modelled and reported separately; two gold rich zones located in the hanging-wall to the East Lode and footwall to the West Lode, and two gold and base metal zones delineated between the East and West Lodes (the “interlode” domain).
The majority of the MRE is comprised of sulphide ore and occurs within 270 metres of surface directly beneath and to the south of the historical oxide pit. The highest base metal and gold grades in the deposit are contained within the two massive sulphide lodes, which have been defined continuously over a strike length of about 250 metres, with true widths between 1 and 30 metres and plunging moderately to the south.