The 100% owned Boorara Gold Project is 10 kilometres east of Kalgoorlie’s Super Pit gold mine located on the eastern edge of the city of Kalgoorlie-Boulder, Western Australia. The Boorara Project contains over 1.5 kilometres of gold mineralisation striking north-west at 330 degrees. The project is divided into three project areas, namely Royal (Southern), Crown Jewel (Central) and Regal (Northern) deposits.
Gold mineralisation is hosted in a series of stacked quartz vein arrays that dip at 40-45° to the northwest. The true thickness of the arrays is up to 50 metres vertical and they are hosted within the quartz dolerite which dips at 73° to the northeast. The mineralised dolerite has a true width of up to 40 metres and within the mineralised Boorara dolerite high grade localised ore shoots consist of vein arrays up to 20 metres in width. The increased width of the mineralised dolerite indicates that this is potentially a larger mineralised system.
The Boorara deposit has a JORC 2012 Mineral Resource Estimate of:
11.03 Mt at 1.26 g/t gold for 448,240 oz of gold at a 0.5 g/t lower cut-off grade.
Grade Control (GC) drilling (closer spaced drilling) allows for the complexity of the Boorara deposit to be resolved. Following GC drilling in 2016, a trial pit was completed in the Royal deposit with ore treated at the FMR Greenfields treatment plant at Coolgardie. A total of 30,000 dry tonnes at a head grade of 1.73 g/t produced 1,525 oz of gold, which reconciled well with the GC model. The trial open pit was excavated to a final depth of 20 metres exposing the orebody allowing the quartz veining to be measured and understanding improved.
On the back of the success of the trial pit and GC drilling, in late 2019, Horizon conducted 18,000m of GC drilling to demonstrate an increase in metal with closer spaced drilling. A revised GC model was developed as a subset of the broader Boorara Resource to 50m depth which was used for open pit optimisation and design in February 2020. Mining commenced in April 2020 and was completed in August 2020 with total material movement of 513,000 BCM with total ore mined (high and low grade) of 267,000t at a mine claimed grade of 1.23g/t Au for 10,560 ounces mined. Treatment through the Lakewood processing facility comprised 138kt of the higher-grade material processed over four toll milling campaigns with a reconciled mill feed grade of 1.45g/t Au and a gold recovery of 94.7%. A 17kt parcel of lower grade was also milled to test grade allocation processes. Gold production from the trial totalled 6,568oz at 94.5% recovery generating A$16.8 million in revenue at an average sale price of $2,551/oz which generated A$3.6 million in free cash flow after all costs.
The trial and pit mapping were considered highly successful in providing a greater understanding of the deposits and highlighting a number of opportunities to optimise grade control practises, mining and processing. All geology, mining and processing trial information was incorporated into an updated independent open pit geological model for Boorara of 448koz as stated above.
The Company sees Boorara as a large baseload feed that could be supplemented by lower tonnage, higher grade feed to support a standalone milling facility. A feasibility study was advanced during 2020 and 2021, and was placed on hold in early 2022 due to significant short-term volatility in capital and operating costs due to labour shortages, materials cost inflation and supply shortages. In these volatile times, the company aims to develop smaller scale, higher grade underground projects through a toll milling facility as it has successfully undertaken in the past, and recommence the study when the economic volatility is more stable.