Overview

Mine Type	Underground
Status	Archived Information
Commodities	Gold Copper Silver Molybdenum
Mining Method	Block caving
Mine Life	...
Snapshot	Cadia PC2-3 delivered first ore to the mill in Q1 CY23 with activity now focused on mine development.

Deposit type

• Vein / narrow vein
• Porphyry
• Breccia pipe / Stockwork

Summary:

Mineralisation in the porphyry deposits occurs as sheeted and stockwork quartz–sulphide veins, and locally as broadly stratabound disseminated mineralisation (Cadia East) and skarn (Big Cadia and Little Cadia).

The Cadia district porphyry deposits have recorded a sequence of alteration and mineralisation events that evolved from early-stage magnetite-stable sodic, potassic and calc-potassic alteration with locally significant gold–copper mineralisation, through a period of transitional stage potassic alteration that introduced most of the gold–copper mineralisation. Propylitic and calc- silicate alteration were developed in the deposit peripheries at this time and a late stage of feldspathic alteration developed irregularly around the deposit margins and locally destroyed mineralisation.

The Cadia East–Far East deposit occupies a mineralised zone 2.5 km in strike length, 600 m in width and over 1,900 m in vertical extent. It is located below and to the east of the Cadia Hill deposit.

Mineralisation is developed in the Forest Reef Volcanics (FRV), and in a series of subvertical to steeply northdipping monzodioritic to quartz monzonitic dykes, that are termed the Cadia Far East intrusive complex (CFEIC). The syn-mineral nature of at least some of the intrusions is indicated by the presence of mineralised xenoliths within monzonite porphyry dykes that also host porphyry- style veining and alteration.

The Weemalla Formation has been intersected at depth, and consists of finely-bedded siltstone interbedded with basaltic volcanic rocks. Overlying this unit are five lithofacies of the FRV:
• Upper bedded unit: about 80 m thickness of finely planar-laminated feldspathic siltstone;
• Volcaniclastic unit: approximately 200 m thickness of sandy matrix polymictic conglomerate and volcaniclastic sandstones and locally volcanic breccia;
• Lower bedded unit: around 60 m thickness of bedded calcareous sandstone typically altered to skarn mineral assemblages;
• Massive volcanic rocks: about 150 m thickness of massive pyroxene phyric basalt to andesite lavas;
• Lower sequence: at least 1,100 m thickness of polymictic conglomerates and volcaniclastic sandstones.

Intrusive porphyry dykes and sills are interpreted to be co-eval with the FRV volcanic units. In the Cadia East area, the 5–30 m thick porphyry dykes appear to be stratigraphically controlled by the bedded units, and acted as feeders to overlying sills. The largest dyke has been traced for 1,500 m along strike, are coincident with a change in shape of the orebody on section 15570E, and are cross-cut by mineralised veins. Two large porphyry sills located above the lower bedded unit can be traced along the upper portion of Cadia East. Numerous smaller sills and dykes also exist in this area. The uppermost of the units termed the capping porphyry and is thickest (~70 m) in the middle of the deposit.

Mineralisation at Cadia East is divided into two broad overlapping zones: an upper, copper-rich disseminated zone and a deeper gold-rich zone associated with sheeted veins. The upper zone forms a relatively small cap to the overall mineralised envelope and has a core of disseminated chalcopyrite (and rare bornite), capped by chalcopyrite–pyrite mineralisation (Fox et al., 2009).

The deeper zone is localised around a core of steeply-dipping, sheeted, quartz–calcite–bornite– chalcopyrite–molybdenite veins, with the highest gold grades associated with the bornite-bearing veins. Copper and molybdenite form a mineralised blanket above and to the east of the higher- grade gold envelope.

Au:Cu values are vertically zoned. The upper, disseminated zone of volcanic-hosted mineralisation typically has low Au:Cu values (<1), whereas the envelopes of sheeted quartz-calcite-sulphide veins have higher Au:Cu values (typically >2).

Mining Methods

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Comminution

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Processing

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Production

Personnel

Job Title	Name	Profile	Ref. Date
.......................	.......................		Dec 2, 2022
.......................	.......................		Dec 2, 2022