Name of the Project
Woodlawn zinc/copper project.

Location
New South Wales, Australia.

Project Owner/s
Heron Resources.

Project Description
A feasibility study on the Woodlawn project supports the viability of a starter case to deliver zinc, copper and lead concentrates to the market over a significant reserves-based mine life.

The project has total underground mineral reserves of 2.8-million tonnes grading 14% zinc equivalent, 5.5% zinc, 1.6% copper, 1.9% lead, 0.45 g/t gold and 42 g/t silver. Reclaimed tailings mineral reserves are estimated at 9.5-million tonnes grading 6% zinc equivalent, 2.2% zinc, 0.5% copper, 1.3% lead, 0.31 g/t gold and 31 g/t silver.

An initial 9.3-year mine life, based on processing the combined underground and tailings mineral reserves, is expected. Inferred mineral resources defined in the underground and tailings projects demonstrate excellent potential to extend the mine life to more than 11.5 years.

The underground mine plan focuses on the shallower areas of the deposit, reflecting the success of the preliminary economic assessment completed in 2015 and the feasibility study drilling programmes.

The underground deposit will be accessed through a boxcut located to the west of the existing openpit, allowing for the early development of shallow underground material. Stoping areas will be accessed predominantly through a new decline and new access drives; however, in some areas, the existing workings are planned to be rehabilitated and used.

The reclaimed tailings will be mined using automated monitor-based hydraulic mining, which uses a high-pressure water cannon to agitate the ore into a slurry. In consultation with hydraulic mining consultants, the mining approach has been revised from a top-down to a bottom-up method, which is considered safer, with lower environmental impacts, easier control and more cost-effective outcomes.

The study envisages a processing rate of up to one-million tonnes a year from underground mining and up to 1.5-million tonnes a year from reclaimed tailings processed through a standard single-sulphide flotation facility.

For underground ore, a two-stage crushing circuit has been incorporated into the plant design, together with a primary ball mill.

For reclaimed tailings ore, a fine-grind mill will be installed to reduce the particle size to 30 μm, a size that previous and current testwork has confirmed maximises recovery performance from the flotation circuit.

For the underground ore, the initial float (copper concentrate) is undertaken at 75 μm, with a regrind of copper tails to 30 μm to maximise the subsequent recoveries from the lead and zinc flotation stages.

The flotation circuit comprises a gangue-prefloat, copper, lead and zinc differential flotation sequence.

Cleaner concentrate recovered from the prefloat flotation cleaner cell will be discarded to final tails to remove the silicate gangue before it reaches the differential base metal flotation circuit. A differential flotation circuit for copper, lead and zinc will be used, with concentrate regrind stages in the copper, lead and zinc circuits to produce cleaner concentrates. The copper circuit will also use a rougher and scavenger tailings regrind circuit prior to the lead flotation stage.

Concentrates from the copper, lead and zinc flotation circuits will be thickened and subsequently filtered for road transport.

The project is expected to produce 40 000 t/y of zinc, 10 000 t/y of copper and 12 000 t/y of lead at steady state, contained in zinc, copper and lead concentrates.

Potential Job Creation
Not stated.

Net Present Value/Internal Rate of Return
The project has a post-tax net present value, at an 8% discount rate, of A$207-million and an internal rate of return of 32%, with a payback of 2.3 years.

Capital Expenditure
Initial capital costs of A$144.2-million have been estimated.

Planned Start/End Date
Underground ore is expected to be delivered to the underground processing plant in 2019.

Latest Developments
Heron Resources has processed its first high-grade underground ore from its Woodlawn project.

Ore from the high-grade G2 lens has been mined to 135 m below surface.

“The first ore mined and now processed from the G2 lens is a significant achievement for the operations at Woodlawn. The high-grade G2 lens was planned to be the first underground ore through the plant and will generate early revenues in these first stages of underground mining,” Heron chairperson Stephen Dennis has said.

Ore processing at the Woodlawn project started in May this year. At steady state, the project is expected to produce 70 000 t/y of zinc concentrates, 30 000 t/y of copper concentrates and 25 000 t/y of lead concentrates.

The first stages of commissioning were completed using tailings reclaim feed material, with some preliminary commissioning of the crushing and ball mill plant during August and September.

The plant is now receiving run-of-mine underground ore, and will complete a campaign solely on this feed source, facilitating the next phase of commissioning for the crusher and ball mill, marking the start of the ramp-up phase for this part of the circuit.

At steady state, the plant will alternate between campaigns of tailings reclaim feed and underground ore.

Key Contracts and Suppliers
Ertech (earthworks contract) and Pybar Mining (underground mining contract).

On Budget and on Time?
The project has faced a seven-month delay in project construction completion that necessitated additional capital requirements.

Contact Details for Project Information
Heron Resources, tel +61 2 9119 8111 or email heron@heronresources.com.au.