GEOLOGICAL SETTING
The CSA deposit is one of several base metal- and Au-bearing deposits of the Cobar Mineral Field. It occurs on the E margin of the early Devonian Cobar Basin (Central Lachlan Orogen) and is hosted by the CSA Siltstone (turbiditic siltstones and sandstones). The CSA Siltstone (Glen, 1991) is part of the Cobar Supergroup, consisting of. lower syn-rift sediments (Nurri Group) and upper post-rift sag phase sediments (Amphitheatre Group). These rocks have undergone lowergreenschist metamorphism.

The CSA deposit lies near the stratigraphic top of the CSA Siltstone (Glen, 1994). It is bound to the W by the Footwall Fault (Kappelle, 1970) and located immediately N of the WNW-trending Plug Tank Fault and W of a NNE-trending right lateral fault (Glen, 1988). Between these structures, ore zones occur as a series of N-trending, steeply E-dipping lenses within the W- dipping host sequence. The lenses are parallel to the regional, steeply E-dipping cleavage. Rocks enclosing the mineralization show extensive alteration. Green Fe-rich chlorite and silica are prominent alterations.

Minor gossans occur close to the CSA mineralization. Weathering commonly reaches 20-100 m. Strong oxidation reaches 60 m and moderate to weak oxidation penetrates to 100 m. Secondary hematite and goethite mottling extends from surface to 75 m. Deeper oxidation commonly extends to >100 m along faults and shears and to >160 m over the CSA deposit itself.

MINERALIZATION
Mineralization is as structurally controlled, epigenetic vein-complexes containing semi- massive to massive sulphide bodies. There are four main ore systems striking approximately N and dipping steeply E, subparallel to the cleavage. Each system contains many sub-parallel ore lenses that extend along strike for up to 120 m and range to 20 m in thickness. They plunge steeply N for several hundreds of m. In addition to the four main ore zones, a large number of smaller zones of variable size and similar composition occur (Kappelle, 1970). The ore lenses are predominantly chalcopyrite, cubanite (CuFe2 S3 ), pyrrhotite, pyrite and sphalerite with minor galena. Minor and trace ore minerals include arsenopyrite, bisthmuthinite (Bi2 S3 ), bornite, galenobismutite (PbBi2 S4 ), guanajuatite (Bi2 Se3 ), native Bi, native Ag, stannite (Cu2 FeSnS4 ) and tetrahedrite ([Cu,Fe]12Sb4 S13) (McDermott et al., 1996). The ore zones also contain a large number of quartz-sulphide veins subparallel to the crenulation foliation. The sulphides and quartz are hosted in intensely cleaved chloritic siltstones. There are also numerous flat, W-dipping, strike slip faults. Fault zones are generally unmineralized.

Alteration associated with the mineralization includes a broad halo of green, Fe-rich chlorite that surrounds the ore zones and extends outwards for up to 50 m (Scott and Phillips, 1990). Pervasive silicification occurrs as a broad zone surrounding the entire mineralized area. Extensive but cryptic Li-depletion haloes (up to 500 m across strike) and less extensive depletions of Na, K, Sr and Ba (up to 100 m) have been documented around the CSA ore zones (Robertson and Taylor, 1987). These are coincident with reduced feldspar and sericite in the rocks. Small areas of intensely siliceous rock known as ‘elvan’ (Scott and Phillips, 1990) were encountered around the Western System. Black chlorite is developed along late-stage shear zones. Large bodies of talc, commonly containing euhedral pyrite, are associated with most black chloritic shear zones (Scott and Phillips, 1990).

REGOLITH EXPRESION
Only the Western System Cu ore body and the adjacent pyrite-Pb-Zn lodes are exposed at surface (Kappelle, 1970). Here, surface gossans are surrounded by elongate haloes of silicification. The upper parts of the gossans are strongly leached of base metals with only traces of secondary Cu and Pb carbonates (Andrews, 1913). Malachite and azurite veining, native Cu (psudomorphing pyrite and infilling cavities), minor cerussite (PbCO3 ) and chlorargyrite (AgCl) occur from 85-115 m. In the original CSA workings, a large mass of supergene cerussite (up to 10 m thick) occurs at the base of oxidation, near the water table (Andrews, 1913). A supergene chalcocite zone also occurred in the northern shoots of the Western System between 140-146 m (Brooke, 1975). Some sulphides, particularly pyrite, occur in the oxidized zone, where they are protected by silica alteration. Iron and Mn oxide staining extends across the surface projection of the blind Eastern System. The other CSA ore bodies are well below the weathering zone and have no weathering expression, although a zone of hematite and goethite above the QTS North lenses occurs at a depth of 1.5 m and probably reflects the near-surface periphery of this system.

Saprolite
Ferruginous veins and mottles in the saprolite and saprock are an important sampling medium for CSA style mineralization with contents of Cu >140 ppm, Pb >450 ppm and Zn >600 ppm in near surface saprolite, up to 50 m from mineralization. Around the CSA deposit, mottled saprolite contains numerous well-defined multi-element geochemical anomalies. Copper and Cd anomalies clearly define the main mineralized zones with abundances of up to 265 ppm and 8 ppm respectively. Zinc has been more widely dispersed. These anomalies are short in strike and narrow in width, and are consistent with the N-trending ore structures. Arsenic has a limited distribution over the main mineralized zone, but it is particularly enriched around the Western System. Barium has a patchy distribution over the main ore systems. Lead is particularly enriched (up to 3000 ppm) in the Western System, with a limited distribution over the Eastern System. Bismuth, Sb, Hg and Zn generally show an even distribution over the QTS North mineralization and the surrounding area, with respective maximum concentrations of 1.9, 15, 0.29 and 336 ppm.

Soil
The regional, red-brown silty loam contains a significant transported component, including wind-blown dust. Important pathfinder elements for soil exploration here include Ag, Ba, Cd, Cu, Pb and Zn, with threshold values of 0.6 ppm, 255 ppm, 0.7 ppm, 75 ppm, 435 ppm and 360 ppm respectively.

Lag
Lag around the CSA deposit is a mixture of coarse (>2 mm), locally derived bedrock fragments, quartz clasts, gossan fragments and variably transported, highly ferruginous pisoliths. The lithic fragments show variable ferruginization and the ferruginous pisoliths commonly consist of cemented sand and silt, typically with a homogeneous internal structure. The pisoliths commonly have a smooth, varnished surface. A proportion of this ferruginous lag is magnetic (maghemite-bearing).

The lag from around the CSA deposit generally has elevated Pb, As, Sb and, in some, Ag in the more ferruginous fractions and Cu and Zn typically in the lithic materials relative to regional background. Contents of Pb, As, Sb and Ag are up to 3096 ppm, 509 ppm, 227 ppm and 5 ppm respectively and of Cu and Zn up to 690 ppm and 537 ppm respectively. There is a well- defined positive correlation between the abundance of Fe and hematite with the contents of Pb, As and Sb. This is related to a previously recognized weathering-controlled fractionation of these elements during surface maturation of the lag (McQueen and Munro, 2003). Copper and Zn show a strong negative correlation with Fe and hematite abundance, except in lag derived from gossanous outcrops. A lag sample collected near an outcropping Pb-Zn gossan associated with the Western System has distinctly anomalous concentrations of Pb (330-3100 ppm), As (61-510 ppm), Bi (7-77 ppm), Cu (100-690 ppm), Zn (150-540 ppm) and Ag (0.3-3.1 ppm) in the different lag fractions (lithic and ferruginous).

Mining Method
The mining method used at the CSA Mine for the majority of stoping remains as top down, continuous advance, long-hole open stoping. Most stopes to date are filled with Cemented Hydraulic Fill (CHF) and the balance is filled with development waste, either as clean waste co- disposal with CHF or as Cemented Rock Fill (CRF). CHF has generally been phased out to be replaced with Cemented Paste Backfill (CPB) commissioned July 2018 with full filter plant commissioning completed by November 2018.

Trials for the implementation of Modified Avoca mining method was successfully concluded which will add a lower cost mining method with UG waste disposal advantages – this is envisaged to be implemented in Western and QTSC mining areas with stoping due to commence here at the end of 2019.

During the reporting period, underground horizontal development advancement totalled 4,534m. The primary focus was advancing the decline towards the 8500 level; the main decline position was 19m ahead of original budget position. This was completed along with completing the 8540 and 8580 levels, establishing the 8540 level, production-related development in QTS North, and access development to establish mining in QTS Central.

Mining is almost complete above the 8700 level in the QTS North, except for some already developed remnant material between 8850 and 8950. QTS South mining is complete above the 9015 level.

The economic bottom of the QTS South ore body is currently 9015. During the reporting period, development will continue for access to the Central System and access to the Western System. Development below the 8500 level in QTS North will continue.

Backfilling and Tailings
The long-hole open stoping mining method used requires cemented backfill as the main control for stope ground conditions. The behaviour of the filled mass has a significant impact on ore body dilution and recoveries from processing. Cemented hydraulic fill (CHF) has been used extensively in the past at CSA since 2005. The 2017 year has seen the introduction of Cemented Paste Backfill (CPB) as the primary method for filling voids at CSA. CPB is produced by vacuum filtering the mill tailings production of the floatation circuit. The placed backfill is exposed both horizontally and vertically. Strength requirements and cement additions for CPB are 1.4mPa for horizontal exposures achieved with 11.0% cement addition by mass and 0.45mPa for vertical exposures achieved with 4.0% cement addition. As confidence in the strength- binder relationship grows to dosage rates will be reviewed and further optimised, alongside work to reduce cement addition via the use of a cement slag blend and/or water reducers.

Paste fill is obtained by removal of water from full stream tailings through vacuum filters to produce filter cake. This filter cake will be stockpiled during periods where paste is not required. The installed plant also has the flexibility to utilise reclaimed tailings to further decouple paste production from milling production.

Stopes that do not require future horizontal or vertical exposure are filled with un-cemented bulk fill only, using development waste / backfill dig out (backfill contaminated) waste. Where cemented fill is required for vertical exposures and paste fill is not practically available, Cemented Rock Fill (CRF) is used. CRF is a blend of development waste rock, cement and water which is mixed in a dedicated mixing bay mined on each level where required. The CRF is placed into the stope before filling with uncemented rock fill.

With the introduction of paste fill, the cemented hydraulic fill (CHF) plant will remain idle and maintained in a ready to operate state, to provide redundancy throughout the commissioning stage of paste fill and beyond, until such time as the paste backfill system operates optimally.

The milling circuit consists of two primary Semi-Autogenous (SAG) mills in either open or closed circuit as required, with hydrocyclones. A third mill of the same size is used as a ball mill when further grinding is required.

Metallurgy
After grinding, ore slurry is pumped to the flotation circuit comprising of rougher, scavenger, cleaner and re-cleaner stages that use mechanically agitated flotation cells. One bank of Wemco rougher cells, one bank of FLSmidth rougher cells and one bank of Outotec scavenger tank cells float the sulphides until generating a final tail that is sent to the tailings thickener. Two Jameson Cells perform the final cleaning of concentrate. Recovery of Cu minerals, mainly chalcopyrite, is excellent with typically 96% to 98.5% of the Cu and around 80% of the silver reporting to the concentrate. The concentrate grade generally ranges between 25 - 29% Cu and 72 - 88g/t silver (Ag) depending on the mineralogy of the ore.

Flotation concentrate is pumped to a conventional thickener where it is dewatered. Thickener underflow is pumped to a Filter Feed Tank. This slurry is pumped to two pressure Filters where water is removed. The filtered concentrate is discharged and tram ........