Golden Star Bogoso Prestea (GSBPL) plans to restart the Prestea gold mine, which has been under care and maintenance since 2002, in western Ghana. The gold mine is located approximately 15km south of the Bogoso mine and adjacent to the town of Prestea.
GSBPL, a subsidiary of Golden Star Resources (GSR), holds 90 % interest in the gold mine and the government of Ghana holds the remaining interest.
Mining at the deposit started in 1870s and continued until 2002, during which it produced approximately nine million ounce (Moz) of gold, making it the second biggest mine by production in Ghana.
The current focus is on the development of a new zone known as the West Reef within the underground mine, and other adjacent undeveloped surface deposits into open-pits.
An environmental permit for the open-pit development was granted by the Ghanaian environmental protection agency in June 2015 and production is expected to begin by the end of 2015.
Development and rehabilitation plan for the Prestea mine
Golden Star (Wassa) (GSWL), a subsidiary of Golden Star, owns and operates the Wassa gold mine located in south-west Ghana.
The West Reef zone consists of an underground mine with a production life of five years. The mine rehabilitation plan includes a pre-production period of 24 months between January 2015 and December 2016. It is expected to operate at full production level between January 2017 and December 2020, over a four-year period, upon completion of the rehabilitation.
Prestea gold mine geology and mineralisation
The Prestea-Bogoso mineralisation occurs at the southern end of the Ashanti Belt, and is localised principally along up to three steep-to-sub vertical major crustal structures. Rock assemblages are believed to have formed between 2,080 and 2,240 million years ago, with the Sefwi Group being the oldest rocks and the Tarkwa sediments being the youngest.
The principal structure at Prestea is the mineralised quartz vein, the Main Reef, which is relatively continuous and extends over a strike length of approximately 6km.
The West Reef mineral resource occurs as a steeply-dipping, narrow vein structure.
Prestea gold mine reserves
As of 31 December 2014, the indicated gold resources at Prestea underground mine were estimated to be 1.32 million tonnes (Mt) grading 14.82g/t Au, and containing 630,000oz of gold.
The Prestea surface deposits are estimated to contain proven and probable mineral reserves of 1.69Mt of ore at an average grade of 2.24g/t. The contained gold is estimated to be 122,000oz.
Mining and processing of ore from Prestea underground mine
Traditional shrinkage mining method, using modern rock bolts and wood stulls / props, is proposed for the underground mine. The shrinkage stopes are proposed to have a 60m strike length and a height of 40m for the upper levels or a height of 35m for the lower levels.
The mine will be accessed via two surface shafts, one near the town of Prestea (Central Shaft) and the other at approximately 4km to the south-west at Bondaye. The run-of-mine ore will be transported by road approximately 15km to GSR’s operating Bogoso processing plant and processed at a rate of 500 tonnes a day (t/d).
It is expected that the Prestea West Reef material will have a metallurgical recovery of more than 90% and is proposed to be processed using carbon-in-leach (CIL) technology.
The ore from the underground mine will be crushed in a conventional two-stage crushing circuit and grinded in a ball mill before passing through elution and electro-winning circuits for gold extraction.
Golden Star secured $150m financing from Royal Gold (RGI) to develop the Wassa and Prestea gold mines in May 2015. The financing comprises a $20m term loan from RGI, and $130m stream transaction with RGI’s subsidiary RGLD Gold.
Infrastructure facilities at the Prestea gold mine
Power for the Prestea mine is proposed to be supplied from the Prestea Slimes substation, which is owned by the local utility, ECG (Electrical Company of Ghana).
Tailings generated from the processing of Prestea ore will be delivered to the existing tailings storage facility (TSF) at the Bogoso plant.
MDM Engineering was awarded the contract to design the process flow for the West Reef material in the existing Bogoso Plant. SRK Consulting was engaged for preparing the technical report for the Prestea West Reef development.