Toweranna might be known as the initial intrusion-hosted gold deposit that led De Grey towards making its world-class 8.5Moz Hemi discovery, but recent drilling has clearly highlighted Toweranna still has much to contribute to the Mallina Gold Project.

Diamond drilling to improve resource definition at the deposit returned outstanding results which not only confirm the current mineralisation model but also indicate that the current Toweranna resource of 525,000oz is likely to get bigger.

It’s certainly not hard to see why with standout assay results such as 10m grading 13.2 grams per tonne (g/t) gold from 288m including 2m at 64.2g/t gold from 288m (MWDD0007) along with 6m at 11.3g/t gold from 216m and 5m at 12.8g/t gold from 234m (MWDD0006) while drilling outside the resource struck 41.5m at 4.7g/t gold from just 12m and 22m at 1.4g/t gold from 60m in hole MWDD003.

De Grey Mining (ASX:DEG) noted that the thickness of this steeply dipping high grade structure intersected by MWDD003 east of the existing resource likely reflects drilling down the dip of the structure.

And if that wasn’t enough, Toweranna mineralisation has been shown to be amenable to ore sorting, with recent testwork highlighting the potential to increase the grade – currently estimated at 2.1g/t for the open pit and 3.6g/t for the underground – whilst reducing the tonnage of run-of-mine ore.

This testing has returned 97% ore recovery with a mass rejection of 29%, which results in an average upgrade ratio of 1.37 though the company noted the potential for further optimisation, which will reduce haulage and processing costs while increasing production.

“The new resource definition and extensional drilling results at Toweranna demonstrate the high grade nature of mineralisation within the overall intrusion. These results also point to resource extensions. Exploration will now focus on delivering on that potential,” general manager exploration Phil Tornatora said.

“New drilling results and technical studies will be incorporated in an updated resource estimate and contribute towards development of a maiden reserve at Toweranna for the DFS currently in progress and scheduled for completion mid-2023.”

Toweranna drilling

Drilling at the Toweranna regional deposit, which has a resource of 6.8Mt at 2.1g/t gold for 460,000oz in open pit resources and 0.6Mt at 3.6g/t Au for 65,000oz in underground resources, was focused primarily on zones of Inferred resources within pit optimisation shells.

This was designed to increase the potential reserve for the Definitive Feasibility Study and provide increased confidence in the Mallina project’s projected cashflow from early production sources.

De Grey notes that mineralisation at Toweranna generally occurs as gently dipping, stacked quartz-sulphide lodes throughout the intrusion, which extend to some degree into surrounding metasedimentary country rocks.

Some of the quartz-sulphide veins carry very high local grades with visible gold while subvertical northeast trending structures that appear to have some control on mineralisation have also been identified.

Ore sorting

Metallurgical testing has also demonstrated that the quartz-sulphide associated gold mineralisation at Toweranna is free milling – making it suitable for standard CIL processing technology without requiring pressure oxidation – and amendable for upgrading through ore sorting.

The latter has been proved by testing to date though the use of XRT sorting on one sample that resulted in 93% gold recovery with a mass rejection of 75% – or a gold upgrade ratio of 3.7 – indicates that there is further potential for flowsheet optimisation using XRT sorting alone.

This has the potential to significantly reduce operating costs per ounce of gold produced from Toweranna by reducing ore haulage costs between Toweranna and Hemi, reduce processing costs at Hemi, and significantly increase the grade of ore processed from Toweranna at Hemi.

Ore sorting is not being considered at other deposits at Hemi.

Upcoming work

With DFS drilling now complete and the study due for release around the middle of the year, the company will now focus regional work on exploration aimed at increasing resources and discovering new mineralisation at Toweranna as well as the surrounding district.

Follow-up drilling will target interpreted structures extending from the intercept in MWDD0003 towards a smaller intrusion to the northeast, in addition to other intrusion and structural targets in the area.

Diamond drilling to follow up on previously reported mineralisation at Charity Well, located 4km to the north of Toweranna is also ongoing, with reverse circulation drilling expected to commence in the near future.

De Grey is also waiting on results from a recently completed aircore program to test easterly extensions of Charity Well.

Additionally, metallurgical testwork of mineralisation from Toweranna to optimise the process route, operating costs, production schedule and resource to reserve conversion is continuing.




This article was developed in collaboration with De Grey Mining, a Stockhead advertiser at the time of publishing.


This article does not constitute financial product advice. You should consider obtaining independent advice before making any financial decisions.