Orion to Redevelop Prieska Mine
Orion is an Australian company headquartered in Melbourne and listed on the Australian and Johannesburg stock exchanges. Capital cost of construction of the Prieska project is estimated at A$360 million to A$390 million, including a 20% contingency. The construction period to first mining underground is estimated at about 24 months. Underground mining costs including labor are estimated at approximately A$48/mt. All-in-sustaining costs are estimated at approximately A$100/mt.
A bankable feasibility study is due for completion in the second quarter of 2019. Orion Managing Director and CEO Errol Smart said, “The scoping study indicates solid operating margins ... and identifies important opportunities for further financial upside, both from extending the life of the mine and from optimizing the grade of extraction following further drilling to be conducted from underground. “The application of further modernization making optimized use of low-cost available renewable energy also provides an important cost saving opportunity being investigated in depth by the bankable feasibility study.”
The Prieska mine was owned and operated by Prieska Copper Mine Ltd., a subsidiary of Anglovaal, from 1971 to 1991. Some of the infrastructure that serviced those operations is still serviceable and can be used for the new project. This includes a 60-kilometer (km)-long bulk water supply pipeline, tarred roads, regional grid power and an airstrip. The main hoisting shaft, which is 1,024 meters (m) deep, and its associated headgear are intact and reuseable. Some 37 km of underground tunnels and mined-out stopes are currently flooded to a depth of 330 m below surface, and an 18-month pumping program would be required to de-water these workings.
Tunnels established during previous operations allow for early access to underground production areas. A combination of longhole stoping and drift-and-fill mining has been selected as the preferred mining method. Longhole open stoping was successfully employed during historical operations down to an approximate depth of 900 m below surface. Using paste fill and drift-and-fill methods would cater for mining at greater depths and would accommodate the changing dip of the deposit. Other improvements on historical mining practices would be the use of a more technologically- advanced mining fleet to provide faster tunnel development and more accurate production drilling.
Underground development and production operations are planned to be fully mechanized, with all development headings being advanced using twin-boom jumbos and supported using bolting rigs. Loadhaul- dump units would be used to load blasted development and production rock into ore passes in the upper levels and into a truck fleet, which would haul up 1-in. inclined roadways to the central crusher location, the excavations of which already exist. The main shaft would be equipped for rock-hoisting capacity of 2.4 million mt/y, utilizing two 14-mt skips. A Koepe winder would be used for rock hoisting and would have a power rating of approximately 1.8 megawatts (MW). A ground-mounted double- drum, 4.9-m-diameter winder would be used for the men-and-materials cage. The main processes within the proposed copper flowsheet are primary crushing, secondary crushing, and screening followed by milling, rougher flotation, regrind of the rougher concentrate, cleaner flotation, and re-cleaner flotation to produce a copper concentrate.
The zinc recovery section would start from the copper rougher tails and would include rougher flotation, rougher lowgrade concentrate re-grind, low-grade cleaning, low-grade re-cleaning to produce a zinc concentrate, and rougher high-grade concentrate cleaning, also to produce a zinc concentrate. The highgrade cleaner tails would be sent to the low-grade re-cleaner flotation stage. Process plant recoveries would range between 80% and 88% for both zinc and copper. Production would be approximately 145,000 mt/y of zinc concentrate grading 48% to 52% zinc and 94,000 mt/y of copper concentrate grading 22% to 26% copper.