Aeris Resources Ltd (ASX:AIS) has updated copper, gold and silver resources and reserves for the Tritton and Murrawombie deposits at the Tritton Copper Operations in central NSW.
Allowing for mining depletion and changes to the resource estimates, the underground mines have a combined reserve of 69,000 tonnes of copper, 80,000 ounces of gold and 742,000 ounces of silver.
The Murrawombie open pit reserve which is yet to be mined has a reserve of 14,000 tonnes of copper, 8,000 ounces of gold and 150,000 ounces of silver.
Mines perform ahead of plan
This comes after both underground mines performed ahead of plan during the 2019 financial year, producing 26,852 tonnes of copper at a C1 cash cost of A$2.78/pound, exceeding the original guidance of 24,500 tonnes.
At Tritton, the resource at June 30, 2019, was 5.8 million tonnes in the measured and indicated categories at 1.4% copper, 0.10 g/t gold and 4.4 g/t silver for 84,000 tonnes of copper, 18,000 ounces of gold and 826,000 ounces of silver.
Inferred resources total 3.4 million tonnes at 1.2% copper, 0.13 g/t gold and 3.9 g/t silver for 40,000 tonnes of copper, 14,000 ounces of gold and 430,000 ounces of silver.
This compares to the June 30, 2018, measured and indicated resources of 6.9 million tonnes at 1.6% copper, 0.1 g/t gold and 5.2 g/t silver for 110,000 tonnes of copper, 26,000 ounces of gold and 1.1 million ounces of silver.
Inferred resources at that date totalled 3.8 million tonnes at 1.3% copper, 0.1 g/t gold and 4 g/t silver for 50,000 tonnes of copper, 26,000 ounces of gold and 489,000 ounces of silver.
Tritton reserve
Tritton’s reserve was 3 million tonnes at 1.5% copper, 0.1 g/t gold and 5.1 g/t silver for 45,000 tonnes of copper, 65,000 ounces of gold and 480,000 ounces of silver.
This compares to the June 30, 2018, reserve of 3.7 million tonnes at 1.5% copper, 0.1 g/t gold and 5.2 g/t silver for 56,000 tonnes of copper, 47,000 ounces of gold and 610,000 ounces of silver.
Material changes to the Tritton resource include mine depletion, sterilisation of remnant mineralisation surrounding mined out areas and additional grade control drilling data resulting in spatial changes to the mineralised system.
Diamond drilling and geology modelling have resulted in portions of the mineral resource being upgraded from inferred to indicated or measured category, making this material available for conversion to ore reserve.
Processed as a blend
Mining of Tritton ore body began in 2004 with the development of an access decline and construction of a sulphide ore processing plant. Stope production started in March 2005.
In its first year of production, Tritton produced 23,088 tonnes of copper in concentrate with production rates are now around 18,000 tonnes per annum of copper in concentrate.
Tritton ore is processed as a blend with ore mined from other mines in the region.
The Tritton ore processing plant working with blended ore has produced up to 30,000 tonnes of copper in concentrate per annum. Total blended ore production is now around 25,000 tonnes.
Murrawombie underground mine is the other current source of ore for blending with Tritton mine production.
This ore has a relatively higher gold grade of 0.2 to 0.3 g/t and blending of this has the effect of assisting the Tritton ore to deliver payable gold grades in copper concentrate.
Annual ore production rates from Tritton mine have increased over time from 0.8 million tonnes to 1.2 million per year, despite mining getting progressively deeper.
Murrawombie estimate
At Murrawombie, the updated resource estimate is 4.6 million tonnes in the measured and indicated categories at 1.6% copper, 0.3 g/t gold and 5.3 g/t silver for 73,000 tonnes of copper, 46,000 ounces of gold and 780,000 ounces of silver.
There are also 800,000 tonnes in the inferred category at 1.3% copper, 0.3 g/t gold and 5.4 g/t silver for 10,000 tonnes of copper, 10,000 ounces of gold and 100,000 ounces of silver.
The estimate at June 30, 2018, was 4.6 million tonnes in the measured and indicated categories at 1.6% copper, 0.3 g/t gold and 6.0 g/t silver for 74,000 tonnes of copper, 43,000 ounces of gold and 896,000 ounces of silver.
Inferred resources are unchanged.
Reserve estimate
The reserve estimate for underground is 1.4 million tonnes at 1.8% copper, 0.3 g/t gold and 8.2 g/t silver for 24,000 tonnes of copper, 15,000 ounces of gold and 262,000 ounces of silver.
There has been a decrease in underground reserves from 2018 of 14,000 tonnes of copper, 8,000 ounces of gold and 238,000 ounces of silver while the open pit reserve in unchanged.
Changes to the reserves have occurred since the 2018 report from depletion due to mining; changes in the resource estimate; changes to the mining method; and changes in the cut-off grade.
Production in the year to June 30, 2019, was 470,000 tonnes at 1.7% copper for 8,000 tonnes of contained copper metal.
Murrawombie ore is transported from a surface stockpile at the underground mine to the Tritton processing plant by road train truck on sealed road, a distance of 24 kilometres.
Further deposits
Further resources at other deposits, including Budgerygar, are expected to add to the mine life.
Development of an exploration and access decline drive to Budgerygar, which is 600 metres northeast of the Tritton mine, began late in the financial year.
Aeris is targeting 24,500 tonnes of copper production in FY2020 at a C1 cash cost between A$2.80 and A$2.95 per pound.