Amid underground logistical constraints and the impact of the Covid-19 pandemic on contractor operations, gold producer Caledonia Mining restarted exploration on its flagship operation the Blanket mine, in Zimbabwe, in January.

Favourable results have been achieved to date from the ongoing underground drilling programme, with about 5 600 m of drilling completed from January to May. An additional 12 900 m are planned for the remainder of the year.

Following completion of the central shaft and other infrastructure, drilling is focused on the Eroica orebody, where a crosscut has been mined to allow for better access to drill the deeper zones of the steeply-dipping orebody.

The 1 200-m-deep shaft provides access for horizontal development in two directions on two levels below 750 m, thereby increasing production to 80 000 oz from 2022 and extending the life-of-mine (LoM).

Completing the central shaft has created underground flexibility for the company, as it can now move the waste arising from ore production and from excavating the exploration platforms, Caledonia CEO Mark Learmonth tells Mining Weekly.

“More flexibility has allowed us to restart exploration this year.”

At the Eroica zone, drilling from an exploration drive on the 750 m level of the mine has focused on converting inferred resources to indicated resources, in addition to drilling areas outside of inferred resources as the mineralisation extends to a depth of between 850 m and 1 150 m below surface.

Learmonth explains that Blanket mine’s infrastructure reaches up to 1 200 m below surface and, while Caledonia is focusing on exploiting existing resources above 1 200 m, the company aims to increase the overall ounces and tonnes of ore, and to revise its mine plan by the end of this year to extend the LoM using existing infrastructure.

“We are depreciating the capital cost of our existing infrastructure over more ounces, meaning that the cost an ounce should come down while the ore grades and widths remain larger. A wider orebody is typically cheaper to mine on a cost-per-tonne basis, and higher grades and widths tend to improve profitability,” he notes.

Learmonth describes the ore grades of 4.5 g/t as “encouraging, compared with previous mining grades from Eroica, noting that the central shaft and related infrastructure are vital to increase production and provide capacity to restart exploration to extend the life of the Blanket mine.

Additionally, the deepest hole drilled in the programme – hole ERC750EX2214 – returned strong intersections at depths of 120 m beneath the current inferred resource, which returned a high mineralised zone of 5.78 m grading at 8.18 g/t of gold, and another 8 m zone grading at 7.7 g/t of gold.

The zone also remains completely open below these intersections.

Caledonia has also started exploration on the southern side of the Blanket mine around the Blanket orebodies, with the results of this drilling programme, and further planned exploration, to be reflected in a revised mineral resource statement, which will be published later this year.

The company aims to keep Blanket mine operational for as long as possible with output of about 80 000 oz/y of gold ore to eventually generate enough capital to contribute to the capital costs of other gold projects in Zimbabwe.

“We have invested heavily in Blanket mine in the past seven years, including investment in 2023, which will be continued in 2024, in a new tailings facility with an anticipated life of 14 years, to create a mine infrastructure which can sustain production beyond the current production horizon.

"These results are encouraging and we look forward to receiving results from extension drilling at the Blanket orebodies and also from the next phase of drilling,” Learmonth concludes.