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 gone into voluntary administration after failing to secure funding for the Woodlawn zinc/copper project.

The company launched a strategic process in August last year to explore various options for the mine, including refinancing, a joint venture and either a partial or complete divestment, after operations at the mine had been suspended in March 2020 with the emergence of the Covid-19 pandemic.

Heron said on July 16 that the company had been unable to secure a suitable transaction through the strategic process, despite having conducted a comprehensive and wide-ranging process, engaging with more than 90 organisations to secure a suitable outcome for its stakeholders and establish a pathway to restart Woodlawn.

The company further noted that, with creditor forbearance coming to an end in August and none of the alternatives investigated during the strategic process  suitable for implementation before then, in addition to the current capital structure of the company, the administration appointment was made to restructure and recapitalise the company.

FTI Consulting administrator Chris Hill has said that the care and maintenance regime at Woodlawn will continue while the process to restructure and refinance the business is undertaken to bring it out of administration as soon as possible. 

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

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