MGO is located in the Achaean Murchison Province, a granite-greenstone terrane in the northwest of the Yilgarn Craton. Greenstone belts trending north-northeast are separated by granite-gneiss domes, with smaller granite plutons also present within or on the margins of the belts.

The Paddy’s Flat area is located on the western limb of a regional fold, the Polelle Syncline, within a sequence of mafic to ultramafic volcanics with minor interflow sediments and banded iron-formation. The sequence has also been intruded by felsic porphyry dykes prior to mineralisation. Mineralisation is located along four sub-parallel trends at Paddy’s Flat which can be summarized as containing three dominant mineralisation styles:
• Sulphide replacement BIF hosted gold. Quartz vein hosted shear-related gold.
• Quartz-carbonate-sulphide stockwork vein and alteration related gold.

The Yaloginda area is a gold-bearing Archaean greenstone belt situated ~15km south of Meekatharra. The deposits in the area are hosted in a strained and metamorphosed volcanic sequence that consists primarily of ultramafic and high-magnesium basalt with minor komatiite, peridotite, gabbro, tholeiitic basalt and interflow sediments. The sequence was intruded by a variety of felsic porphyry and intermediate sills and dykes.

The Reedy’s mining district is located approximately 15 km to the south-east to Meekatharra and to the south of Lake Annean. The Reedy gold deposits occur with- in a north-south trending greenstone belt, two to five kilometres wide, composed of volcano-sedimentary sequences and separated multiphase syn- and post-tectonic granitoid complexes. Structurally controlled the gold occur.

The Paddy’s Flat Trend is mineralised a strike length of >3,900m, a lateral extent of up +230m and a depth of over 500m.

Bluebird is mineralised a strike length of >1,800m, a lateral extent of up +50m and a depth of over 500m.

Triton – South Emu is mineralised a strike length of >1,100m, a lateral extent of several meters and a depth of over 500m.

At the core of the MGO output is the Paddy’s Flat underground mine which the company has now been operating for four years. Two other underground mines operate at MGO being the South EmuTriton underground mine at the Reedy’s gold mining centre and the Bluebird underground mine at Yaloginda just 1km south of the Bluebird Plant. South Emu is now in a steady state of production, the Triton underground lodes are just being developed and the Bluebird underground mine has just hit its first ore and continues to be in a development phase. These three underground mines will combine to deliver more than 105,000oz per annum to the Bluebird processing plant over the long term.

Underground ores are supplemented by a procession of smaller open pits, primarily cut-backs which have become economically viable as the gold price has risen. In the FY 2021 open pit mining will occur at the Five Mile Well, Maid Marion, Albury Heath and Aladdin open pits.

Westgold’s strategy at MGO is focussed on the higher grade underground ore sources.

MGO has an existing conventional CIL processing plant – which has been operational in various periods since the late 1980’s.

The plant has a nameplate capacity of 1.6Mtpa though this can be varied between 1.2- 1.8Mtpa pending rosters and material type.

Gold extraction is achieved using single stage crushing, SAG & ball milling with gravity concentration and Carbon in Leach.

A long history of processing through the existing facility demonstrates the appropriateness of the process to the styles of mineralisation considered.

The processing circuit is a simple CIL scenario and consists of:
• Delivery of ore to a Run-of-Mine (ROM) pad for direct tip to a primary crusher;
• Single stage jaw crushing of ROM ore;
• Two stage grinding via a primary SAG (semi autogenous grinding) mill and ball mill to P80 75 µm;
• Scrubbing and pre-leach thickening of historic tails;
• Carbon in Leach and Adsorption;
• Elution of Gold;