The Tritton mineralisation is hosted within greenschist facies, deformed pelitic to psammitic sediments, and sparse zones of coarser sandstones. The Tritton sulphide mineralisation is classified as a stratiform “Besshi style” volcanogenic massive sulphide (VMS) deposit.

Mineralisation is dominated by banded to stringer pyrite chalcopyrite, with a relatively consistent massive pyrite - chalcopyrite unit along the hanging wall contact. Alteration assemblages adjacent to mineralisation are characterised by an ankerite/chlorite footwall and silica sericite hanging wall. After mineralisation emplacement the stratigraphic package has been variably folded producing regional scale and micro scale fold patterns.

Murrawombie is a sulphide copper gold deposit located on ML1280 in central New South Wales (NSW), Australia. The deposit geology is described as a Besshi style volcanic associated massive sulphide occurrence. It contains economic grades of copper with minor gold and silver.

Regionally mineralisation is hosted within early to mid-Ordovician turbidite sediments, forming part of the Girilambone Group. Mineralisation is hosted within greenschist facies, deformed pelitic to psammitic sediments, and sparse zones of coarser sandstones.

The Larsens sulphide mineralisation is stratiform and is classified as a “Besshi style” volcanogenic massive sulphide. Mineralisation is dominated by massive pyrite – chalcopyrite, with minor banded to stringer pyrite – chalcopyrite, and sparse locally important magnetite chalcopyrite.

Structurally the Larsens sulphide mineralisation is hosted within a corridor of moderate to intense shearing related to a thrust fault observed in the east wall of the Eastern Shear of the Murrawombie Pit (Murrawombie pit is located approximately 4 km SW of the Larsens mineralisation). The shear corridor has been traced by Sirotem (geophysical exploration tool) to the north west of the Murrawombie pit, with the Larsens mineralisation sitting Hanging Wall to the Eastern Shear, in relatively un-deformed sediments.

The North East and Larsens Mines are located 5 km north of Murrawombie.

Copper mineralisation at the North East Mine is hosted by weakly chlorite altered and silicified schist in a massive to banded pyrite – chalcopyrite lens that dips moderately to the east.

A higher grade core to the mineralisation is continuous across strike and plunge having a strike approximately 100 m and a width of 10 m.

Economic mineralisation strike is in the order of 175 m with a horizontal width averaging 30 m. The deposit is open at depth and resources, limited only by drilling.

Copper sulphide mineralisation, primarily chalcocite, at the adjacent Larsens Mine is hosted by weakly chlorite altered schist in three discrete, massive to banded pyrite – chalcopyrite lenses that dip steeply to the east and plunge moderately to the south – east. The central lens is the largest defined to date and comprises two sub parallel lenses each several metres thick with strike lengths of 40m.

The mining method assumed in the Ore Reserve estimate varies with the deposit. At the Tritton deposit, the method is sub-level open stoping with cemented paste fill. At the Murrawombie deposit, the ore is extracted using underground bench stopes and small open stopes with cemented rockfill. Future mining of the shallow remnant portion of the Murrawombie deposit will be by open pit, as the final extraction stage. The yet-to-be developed Avoca Tank deposit project is planned to use up-hole benching with dry rock fill.

Tritton Underground
Stope design and orientation of the extraction sequence was changed in late 2017 through to 2018, to accommodate the evolving orebody geometry and increasing ground stress, with the revised stoping design delivering stable stope production in 2019. The rock stress issues which emerged in the previous stope design have been eliminated. Reliable stope performance has assisted the mine in building and holding sufficient stocks of drilled and broken ore.

A truck loading loop and loading points, elevated to just above the truck tray were constructed on the 4110 RL sub-level, currently the lowest production level in the mine. This has been significant in reducing the truck loading time and hence improving truck haulage productivity. Compared with more traditional plans, the new stope design has significantly increased the total ore tonnes loaded from this one level and as a result, an investment has been made into the loading loop and short ore passes, which were uneconomic in the higher levels of the mine.

Paste backfill performance was stable for the year. New boreholes and pipelines within the mid levels of the mine have been established to remove several dog-leg bends, which reduced the pressure losses. Paste fill recipe optimisation continued to balance cement consumption and the paste flow characteristics.

Murrawombie Underground Mine
Murrawombie is the secondary production source for the Tritton Copper Operations. Production at commercial rates was achieved in 2018 and was increased in 2019 to 470,000 tonnes.

The mining methods employed at Murrawombie are either small open stopes, or bench stopes, with a combination of cemented and dry rock backfill. Stopes are sequenced in panels for mining from the bottom upwards towards small crown pillars separating the panels. Stope stability and ore extraction have met planned expectations and performance is improving with growing experience in the behaviour of the ore body. Small stopes are being mined so that mining extraction is flexible in consideration of the often-complex detailed geology, with the mining design selected to achieve the optimum balance of grade and resource extraction.

There are three significant mineralised lodes included in the underground mining plan – 102, 105 and 108 lodes – with current production focused on the 102 and 108 lodes that are a higher grade and close together.

Murrawombie uses a backfill of cemented rock where mining of adjacent stopes is required. Cemented rockfill preparation and placement is new for the Tritton Copper Operations, with rockfill placement rates achieved exceeding expectations and facilitating more selective mining operations. Exploration drilling undertaken towards the end of the year indicates that the higher-grade zones of the deposit are shifting towards the north. Deposit strike length and lode width are consistent with the current resource models and there is no indication that the deposit is diminishing as it is mined deeper down plunge.

The crushing circuit comprises an ore bin with a fixed 800 mm aperture grizzly, feeding ore via a vibratory feeder to a Kemco S7N single toggle jaw crusher with a feed opening of 1.22 x 1.02 m.

Crushed ore of P80 100mm is conveyed to a 6,000 tonne stockpile where it is reclaimed via three vibrating feeders.

Grinding comprises an ANI Ruwolt fixed speed high aspect 6.7m dia X 2.13, 1500 kW SAG Mill, discharging via a trommel screen to the secondary grinding circuit. Lime is added at the SAG to target pH 10.5 for pyrite suppression.

Secondary grinding comprises a Marcy 3.81 m dia x 5.18 m 1250 kW ball mill operating in closed circuit with 500 mm dia Linatex hydrocyclones. Cyclone overflow discharges to two parallel Metso Vertimills (VTM800STD) installed as part of the TEP and shown in the foreground of the lower photo.

Maintenance completed four planned major shutdowns during the year for re-lining of the grinding mills, (SAG mill, Ball mill, Vertical mill), and repairs. Availability between planned shutdowns was excellent.

The primary crusher, which had been operational from more than 40 years ago, was showing signs of damage and was replaced during the year with a new jaw crusher of the same size. The new crusher is now wellestablished and is performing as expected.

The Tritton processing plant treated 1.67 million tonnes of ore, producing 119,000 tonnes of copper concentrate at 23% copper grade in FY2019. Plant throughput was a 5% improvement on the previous year, reflecting better ore delivery from the mines. Actual plant capacity is 1.7 to 1.8 million tonnes per annum, depending on ore hardness and variations in ore supply and quality.

Replacement of the cleaner and scavenger flotation cell banks with new tank bodies was completed during the year with mechanisms refurbished and transferred to the new bodies. Refurbishment of the insides of the primary rougher flotation cells will occur in FY2020.

The grinding circuit produces a cyclone overflow product of P80 75 µm at 30 to 35% w/w solids.

The tertiary cyclone overflow feeds two 50 m³ Wemco tank cells (installed as part of the TEP) in series for primary rougher flotation.

Regrind is achieved by a 2.0 m dia x 3.4 m 150 kW ball mill in closed circuit wi ........