Century zinc mine is situated in Lawn hill in the Lower Gulf of Carpentaria, Australia. Considered as one of the world’s biggest zinc mines, the Century zinc mine was operated for 16 years from 1999 to 2015 by Rio Tinto before ceasing operations in 2016.
Rio Tinto sold the property to MMG in 2016, which, in turn, sold the mine to New Century Resources in 2017.
New Century launched a restart feasibility study (RFS) for the project to process the tailings from previous operations. The results from the RFS were released in November 2017, while an independent technical review of the RFS was announced in April 2018.
The restart operation commenced production in August 2018 and is expected to have a life of six years.
Century mine geology and mineralization
The mining license and exploration permits of the Century mine covers 783km² and contains significant number of high-grade deposits apart from three in-situ deposits named Silver King, South Block, and East Fault.
The Silver King deposit is located 1.5km south-west of the historical Century open-pit. It hosts a sequence of moderately to steeply dipping veins containing quartz, galena, sphalerite, and siderite mineralization.
The South Block deposit lies in southern part of the Century mine and is a continuation of the historical ore body. The East Fault Block is a small deposit that lies 35m below the run-of-mine (ROM) stockpile area.
The Century mine also contains the Phantom hills deposit, which hosts significant phosphate reserves. The reserves of the deposit are yet to be defined, although extensive drilling activities have been undertaken. Other minor deposits are also located north-east of the Century open-pit.
Century mine reserves
The Century open-pit encompasses substantial tailings deposits generated from 16 years of operation. The in-situ deposits, Silver King, South Block and East Fault, are also planned to be developed during the restart operation.
The proved reserves of the Century tailings deposit are estimated to be 77.3 million tonnes (Mt) graded at 3% zinc and 12% silver. The Silver King, South Block and East Fault deposits are estimated to contain 9.3Mt of indicated and inferred resources.
Mining and ore processing at Century zinc mine
The Century zinc mine is planned to be redeveloped in two phases using the hydraulic mining method. The first phase includes the processing of up to 8Mtpa of tailings, which will be ramped up to 15Mtpa in the second phase. The mining fleet includes six Komatsu 630E dump trucks, five Caterpillar D10/D11 dozers, and four Komatsu PC excavators.
The Century tailings deposit was reprocessed through three independent metallurgical studies, which proved that minor modifications to the existing plant would produce saleable zinc concentrate of 52% purity.
The existing century processing plant consists of one semi-autogenous grinding (SAG) mill, two ball mills, 15 ultrafine sand mills, and a froth flotation circuit consisting of 21 stirred mills and 79 flotation circuits. It was modified to handle the tailings processing.
The hydraulic mining method transfers the re-slurried tailings into sumps from where it is pumped to the processing plant. Tailings are then passed through feed preparation followed by primary grinding.
The ground ore then passes through a zinc rougher scavenger flotation circuit from where the tailings are disposed. The processed ore from the scavenger flotation circuit passes through the first stage of cleaner flotation, following which it passes through a concentrate regrind process and three stages of cleaner flotation.
The final concentrate produced is transported to a concentrate handling plant. The concentrate is transported through overland pipeline to the Karumba Dewatering center located 304km away, for shipment to customers.
The mine can be accessed through all-weather dual lane sealed roads, which were used in the previous operation.
An existing high-voltage (220kV) line connected to Queensland’s North West Power System (NWPS) grid supplies power to the mine. Water requirement is met through the evaporation pond dam, on-site borefields, and catchment ponds.
Sedgman prepared the RFS for the mine, while SRK Consulting carried out the technical review of the RFS.
Sedgman subcontracted MEC Mining and Boya Resources to prepare the mine development plan.
A joint venture of National Pump & Energy and Paragon Tailings has been contracted to provide mining equipment and services for Century zinc mine.