The Rosh Pinah mine is an underground zinc-lead mine located in south-western Namibia. Operational since 1969, the mine is jointly owned by operator Trevali (90%) and by Namibian Broad-Based Empowerment Groupings and an Employee Empowerment Participation Scheme (EEPS).
The Rosh Pinah mine produces zinc and lead sulphide concentrates containing minor amounts of copper, silver, and gold.
A positive pre-feasibility study for the expansion of the mine was released in August 2020. With an estimated investment of approximately £70m ($93m), the expansion project is expected to increase the production capacity by 86% by raising the nominal throughput from 0.7 million tonnes per annum (Mtpa) to 1.3Mtpa.
The construction activities for the mine expansion are expected to be started in the first quarter of 2022 with the start of commercial production expected the first half of 2023.
The Rosh Pinah mine expansion
The Rosh Pinah zinc-lead mine has processed approximately 30 million tonnes (Mt) of ore over its 50-year operating life, while the remaining recoverable resources are estimated to be approximately 16Mt.
The expansion project, which targets the WF3 deposit at the existing mine site, is expected to extend the mine life by an additional 11 years while increasing the production capacity and reducing the overall operating cost.
The Rosh Pinah mine expansion will involve the modification of the processing plant, a new paste fill plant and a dedicated portal and ramp to the WF3 deposit.
Location and geology
The Rosh Pinah mine is located at the edge of the Namib Desert near the town of Rosh Pinah in south-western Namibia. The property is situated approximately 800km south-west of the capital city of Windhoek and 20km north of the Orange River.
The Rosh Pinah deposit is hosted by the Rosh Pinah Formation of the Hilda Subgroup of the Port Nolloth Group which forms part of the Neoproterozoic to Early Cambrian Gariep Belt.
The Gariep orogenic belt stretches from south-western Namibia to the west coast of South Africa.
Mineralisation and reserves
The base metal sulphides (BMS) mineralisation at Rosh Pinah is found hosted in the 30m-thick mineralised horizon. Mineralisation occurs as a thick package of turbidites comprising hinterland and contemporaneous volcanic clastics deposited in a Neo-Proterozoic rift basin.
The recoverable mineral reserves at Rosh Pinah were estimated to be 11.23Mt grading 6.3% zinc, 1.3% lead, and 19 g/t silver as of June 2020.
Post expansion, the Rosh Pinah mine is expected to produce 132 million pounds (Mlbs) of zinc, 21.8Mlbs of lead and 286,000 ounces (oz) of silver a year.
Mining methods at Rosh Pinah
The Rosh Pinah Mine currently uses long hole open stoping (LHOS) underground mining methods without backfill to mine the primary, secondary, and tertiary stopes in a top-down extraction sequence.
Ore is currently being extracted from steeply-dipping mineralized zones of the Eastern Orefield (EOF) as well as the SF3, SOF, and BME deposits of the Southern and the Central Orefield. The expansion project focuses on the extraction from the WF3 deposit of the Western Orefield.
The recently proposed expansion will introduce the paste fill method as the long hole stoping without backfill over the years has resulted in significant voids within the historical and currently mined areas.
The proposed extraction sequence with the expansion will see mining operations starting from the centre of the mineralised zones to the strike extents of each level in an overhand (bottom-up) method.
The current Rosh Pinah concentrator utilises a conventional three-stage crushing circuit, a semi-autogenous (SAG) milling circuit, ball milling circuit, and flotation circuits. The current processing capacity of the facility is estimated to be up to 0.71Mtpa of run-of-the-mine (ROM) capable of producing up to 60,000t of zinc flotation concentrate and 7, 500t of lead flotation concentrate a year.
Primary crushed ore is conveyed to the SAG milling circuit at a maximum rate of 164 (dry) tph and mixed with water to form a dense slurry. The screen undersize is transferred to a cyclone cluster to produce an overflow product and the cyclone underflow is returned to the SAG mill feed.
The screen undersize is fed to separate rougher and scavenger flotation circuits for the production of zinc and lead concentrates. The lead and zinc rougher scavenger concentrates are recovered through froth floatation and collected in separate transfer tanks to be treated in separate concentrate regrind and cleaner flotation circuits.
The zinc and lead cleaner flotation concentrates are treated in a re-cleaner micro cell column to produce the second final concentrate. The concentrates are dewatered, thickened and stored before shipment.
The property is accessible via sealed roads from the South African border to the south and from Windhoek which lies approximately 800 km to the north. Railhead access is located at Aus on the Lüderitz - Keetmanshoop line, which is accessible via a 165km sealed road.
The power required for Rosh Pinah operations is directly supplied by the National Power Utility Company of Namibia (NamPower) from its grid system.
Water is supplied from the Orange River via a 250mm pipeline that runs for approximately 20km. The water received is converted to potable water by chlorination and stored in a 600m3 potable water reservoir.
The majority of the workforce lives in the town of Rosh Pinah, while guest house and hostel-style lodging facilities are available at the project site for short-term accommodation.
Australia-based consultancy firm AMC Consultants prepared the pre-feasibility study report for the Rosh Pinah mine expansion that was released in August 2020.