AngloGold Ashanti (100%)
Archaean mesothermal orebody
Multiple open-pit and underground operation
The Geita open-pit gold mine is located 80km south-west of Mwanza, north-western Tanzania, and is 100% owned by AngloGold Ashanti.
It is the biggest of the group’s eight open-pit mines in Africa and is its only operation in Tanzania.
Prior to April 2004, the gold mine was managed under the joint venture between Ashanti and AngloGold. Since the merger of these businesses, Geita Gold Mining is now a wholly owned subsidiary of AngloGold Ashanti.
Operations at Geita are slowly improving year-on-year, following the more than 50% drop in production for 2006 to 308,000oz. Production for 2007 experienced a 6% increase at 327,000oz while the average grade of ore processed increased from 1.68g/t in 2006 to 2.01g/t in 2007.
Open-pit operations commenced in 2000 while multiple open-pit and underground mining operation commenced from 2016 and is set to continue until the entire economic open-pit mineral resource is exhausted.
The Geita mine is powered by a 40MW power plant that was commissioned in August 2018. The plant comprises four diesel generators and provides a reliable power supply for mining operations.
Tanzania Electricity Supply Company (TANESCO), however, unveiled plans to supply electricity to the mine from the national grid in 2020. The plan is currently being implemented to connect the mine having 33/11kV 60MVA mine substation to 220/33kV at Mpomvu village, 6km from the mine.
Geology and reserves at the Geita gold deposit
The Geita gold deposit is an Archaean mesothermal orebody, largely hosted in a banded ironstone formation (BIF). Mineralisation is found where auriferous fluids, which are interpreted to have moved along shears often on BIF-diorite contacts, reacted with the BIF. Some lower-grade mineralisation can also occur in the diorite (usually in association with BIF-hosted mineralisation). Approximately 20% of the gold is hosted in the diorite.
The mineral resource at the Geita gold mine was estimated at 7.92Moz, as of December 2020.
Mining and processing
Geita is a multiple open-pit and underground gold mining operation, which is currently serviced by a 5.1Mtpa carbon-in-leach (CIL) processing plant. Standard open-pit mining methods are employed, hard overburden is drilled and blasted, hydraulic excavators are used to loading waste material into a fleet of 100t dump trucks to expose the gold-bearing ore material, which is directed to the processing plant.
In 2019, approximately 4,568m of development was completed at Star & Comet and Nyankanga, to access new areas for stope mining and further exploration with open-pit mining at Nyankanga. The surface exploration continued at Selous, a satellite pit 2.4km from Star & Comet deposit to supplement the underground operation.
The mining operation is successfully transitioning to predominantly underground operations with the development of the Nyankanga Block 1 Portal that began in December 2019.
Approximately 1,555m of development at the Star & Comet, Nyankanga and Geita hill underground sections to access new areas for stope mining and further exploration were completed in 2021. Open-pit mining at Nyankanga was completed in September 2020 and is currently being conducted at Geita hill that is approaching the end of its economically viable life.
Production at Geita
Production and grades have started to improve at Geita after a disappointing 2006. AngloGold Ashanti projected that gold production at the mine would increase to between 330,000oz and 340,000oz at a cost ranging from $605/oz to $615/oz.
The production problems were made worse by the collapse of part of the Nyankanga pit sidewall during the first quarter of 2007, which covered a portion of the higher-grade orebody.
The collapse of the Nyankanga pit in the first quarter delayed access to the higher-grade exposed ore in this area and resulted in the mining plan for the year being revised.
Production, and tonnage throughput, in particular, were further hindered by wet ore, mill lubrication problems and a full-scale shutdown of the primary crusher for planned maintenance, as well as damage to the ball mill discharge, which led to reduced processing plant availability.
The resumption of ore mining from Nyankanga in the third quarter of 2007 led to a marked improvement in production over that period. However, harder material and poor grades saw a reduction in plant throughout that flowed through to reduce gold throughout during Q4.
AngloGold Ashanti reported a 9% reduction in cash costs to $452/oz with the increased level of production. Reduced expenditure on equipment re-builds and contractor services also contributed to the containment of costs. Capital expenditure for 2007 was $27m (2006: $67m), which was spent largely on the replacement of heavy earthmoving equipment.
The mine produced 604,000oz of gold in 2019 compared with 564,000oz in 2018.
The future of the Geita mine
AngloGold Ashanti has undertaken numerous studies of the Geita site and surrounding areas.
At the end of 2007, advanced grade control drilling had begun at the Star & Comet project in preparation for the start of mining in the second quarter of 2008. Exploration activities during 2007 focused on strike additions at Area 3 and the detection of regolith gold anomalies below laterite cover through air core drilling.
In April 2021, Geita Gold Mining began open-pit mining activities at Nyamulilima, located 2.4km from Star & Comet to produce an estimated one million ounces in the next six years, following the receipt of approval of the 2021 Mining Plan for underground and open-pit operations by the Chief Inspector of Mines in the same month.
In April 2021, AngloGold Ashanti facilitated the establishment of the BG Umoja joint venture between Africa Underground Mining Services (AUMS) Tanzania, a subsidiary of Australia’s Perenti Group; and Geofields Tanzania, local drilling services and mining supply company. The JV was awarded a $186m two-year mining contract for the Nyankanga and Geita Hill underground mining projects.
Another approximately $10.8m a year contract has been awarded to two local contractors for fuel transportation for two years.
Aurecon Group served as AngloGold Ashanti’s engineer for the Geita Gold Mine Power project while Wartsila provided a turnkey engineering, procurement and construction (EPC) solution and will perform the operation and maintenance works for the 40MW power plant under a ten-year agreement.