Mt Boppy gold project
History - Gold production from underground mining operations at Mt Boppy commenced in 1901 and continued to 1923. In its day the mine was one of the largest gold producers in Australia. The orebody delivered some 417 000 ounces of gold from ore with a notional grade of 15g/t gold (12.2g/t gold recovered). Sporadic operation up to 2002 added a further 7 000 ounces of gold production. This included gold recovered from the first Carbon-In-Pulp (CIP) plant built in Australia in 1975 at Mount Boppy to re-treat the historic tailings.
Current - Manuka Resources Limited (MKR) is developing the Mt Boppy gold mine 43 km east of Cobar, in the Central West region of New South Wales. The Mt Boppy mine (which is held by Mt Boppy Resources Pty Ltd) is a wholly owned subsidiary of Manuka Resources Limited. The current Mt Boppy resource is some 368,000 tonnes of gold ore contained in a mix of oxidised, transitional/fresh ores and historic stoping sands. Approximately 60,000 tonnes of gold ore stockpiles are also present on surface at the Mt Boppy ROM.
Development - The Mt Boppy ore will be hauled on side tipping road trains to the Wonawinta processing plant, a distance of approximately 150km of which 122km are on sealed local highways. MKR will utilise and supervise contract mining and haulage operations at Mt Boppy, and process the ore at the Wonawinta plant with company employees. Post near term mining the Mt Boppy site will be progressed as an advanced exploration project for underground resources on the mining leases together with extensive field work on the surrounding exploration lease.
Mount Boppy is hosted within Devonian-age sedimentary and volcanic rocks of the Canbelego-Mineral Hill Rift Zone. Mineralisation occurs largely in brecciated and silicified fine-grained sediments of the Baledmund Formation, within and adjacent to a faulted contact with older Girilambone Group sedimentary rocks. Lodes strike approximately north-south and dip steeply west, although the widest zone of mineralisation is related to slightly shallower dips. Gold mineralisation is fine-grained and commonly associated with coarse grained iron rich sphalerite.
Figure 1 Existing open cut to 205RL - new design down to 165RL
Wonawinta silver and base metals project
History - The Wonawinta mine was originally developed by Cobar Consolidated Resources Ltd in 2011/12 as a shallow silver oxide project. Between 2012 and 2014 two of the four approved pits were commenced and their associated waste dumps constructed. A Processing Plant and associated Run-of-Mine (ROM) Pad, stockpile areas, offices, workshops and water management structures were constructed along with the initial lifts of the Tailing Storage facility. During this period the plant was modified with a log washer removed and a 400kw ball mill introduced to the flow sheet. A larger 1800kw drive ball mill was installed in early 2015 by Black Oak Minerals specifically to grind the Mt Boppy gold ores which are considerably harder than the local Manuka ores.
Current - Manuka Resources Limited acquired the project in late 2016 and initiated a thorough review of operational history and identified various improvements which could be introduced at the site leading to a proposed restart of operations in early 2020. During the non-operational review period the company completed engineering reviews to allow for certification of the last tailings wall lift completed in 2013 by Cobar Consolidated and conducted a number of site audits for the EPA and Resources Regulator. A comprehensive plant refurbishment plan was scoped and executed in late 2019 at a cost of some $5m. This included stripping and inspecting all rotating machinery, repairs to mill gearbox and installation of a fully reburbished mill motor (ABB) and numerous overdue maintenance projects. A lift of the tailing storage facility was commenced in December 2019.
Development - The company will infill drill the current oxide resources on the mining lease to produce mineable reserves whilst testing the deeper mineralised sulphide ores (Ag, Pb, Zn) on the lease. This will occur whilst toll processing of the Mt Boppy gold ore is carried out. Scoping studies have been completed to determine approximate capital estimate to add flotation capability to the existing flowsheet. This would allow the plant to process its own sulphides or toll process third party sulphides in the region, taking advantage of the strategic positioning of the Wonawinta plant in the southern extent of the Cobar basin.
Figure 2 Wonawinta plant flowsheet for initial Mt Boppy processing
Figure 3 Looking south at the Wonawinta plant