WORLD PROSPECTS
AngloGold outlines Colombia caving plans
The virtual Massmin 2020 conference crowd in
December 2020 got a glimpse of just what will be required to build Colombia ’ s first underground caving mine during a presentation from AngloGold Ashanti ’ s Lammie Nienaber . The Nuevo Chaquiro deposit is part of the Minera de Cobre Quebradona ( MCQ ) project , which is in the southwest of Antioquia , Colombia , around 104 km southwest of Medellin .
A feasibility study on MCQ was expected by end- 2020 , but the 2019 prefeasibility study outlined a circa- $ 1 billion sublevel caving ( SLC ) project able to generate an internal rate of return of 15 %. Using the SLC mining method , a production rate of 6.2 Mt / y was estimated , with a forecast life of mine of 23 years . The MCQ deposit is a large , blind copper-gold-silver porphyry-style deposit with a ground surface elevation of 2,200 metres above sea level ( masl , on mountain ) and around 400 m of caprock above the economic mineralisation .
Due to the caving constraints of the deposit , the first production level to initiate caving ( undercut ) is expected to be located around 100 m below the top of the mineralisation at 1,675 masl ( circa-525 m below the top of the mountain ), with the mining block extended around 550 m in depth ( 20 production levels at 27.5 m interlevel spacings ).
The main ore transfer horizon is located 75 m higher in elevation than the mine access portals at 1,080 masl and the proposed valley infrastructure . The initial mining block will be accessed by twin tunnels developed in parallel for 2 km at which point a single access ramp will branch up towards the undercut ; the twin tunnels will continue another 3.7 km to the base of the SLC where the crushing and conveying facilities will be located .
The MassMin 2020 conference also included
an in-depth paper from PT Freeport Indonesia that covers the extensive learnings from the Deep Ore Zone ( DOZ ) mine on dealing with wet ore , or so-called wet muck mining , including how it influenced the development of PTFI ’ s remote control mining fleet and ultimately how the company is now applying this experience in planning for a more comprehensive autonomous underground mining approach using the latest technology at its new Grasberg Block Cave ( GBC ) and Deep Mill Level Zone ( DMLZ ) mines .
Over the years , the Deep Ore Zone ( DOZ ) panel cave mine has experienced a steady increase in the prevalence of wet ore or “ wet muck ” within the mine and due to the risk factors the mine has converted 100 % of its LHD operations to remote ( using the MineStar Command for underground system from Caterpillar ). The mine is also largely complete in converting its water cannons to remote operation ( using Getman water cannons equipped with a remote operating system from Remote Control Technologies - RCT ) and is in the process of finalising a work plan to convert the mobile rock
The company is currently weighing up whether to use tunnel boring machines or drill and blast to establish these tunnels . Nienaber confirmed the 20 level SLC panel cave layout would involve 161 km of lateral development and 14 km of vertical development . There would be six ore pass connections on each level , four of these being ‘ primary ’ and two acting as backups . The crusher would be located on the 1155 bottom production level .
Due to the ventilation requirements in Colombia the mining fleet selected for Quebradona is predominantly electric , Nienaber said , adding that the units will initially be electric cable loaders powered by 1,000 v infrastructure . Fourteen tonne LHDs were selected for the production levels based on their speed , bucket size ( enables side-to-side loading in the crosscut and identification of oversize material ) and cable length , the authors said . On the transfer level , 25 t loaders were specified to accommodate the shorter tramming lengths and limited operating areas ( there are a maximum of two loaders per side of the crusher due to the layout ).
As battery technology improves in the coming years , the selection of loader sizes may change as additional options become available , according to the authors . This decision also accounted for the use of automation for the majority of production activities , with the use of a common platform seen as the most
Freeport ’ s ROR for new block caves
breakers and other support equipment to remote operation . All remote operations will be housed in a single location on the surface . Although driven by the safety requirements of managing wet muck , this change points to the future of mining as a continuous and remote operation .
As a result of these changes , the mine has evolved as a prototype for an underground autonomous caving operation . This prototype has allowed PTFI to map a development plan that will see the Grasberg Block Cave ( GBC ) and Deep Mill Level Zone ( DMLZ ) mines operating autonomous , remote and manual operations seamlessly within the same Autonomous Mining Area ( AMA ), managed from a single Remote Operating Room ( ROR ) on the surface . All entities within the AMA will be equipped with SafeDetect ( a Minetec product ) and will be pragmatic option at this stage . It has also been proposed that the maintenance of the machines be carried out by Sandvik under a maintenance and repair style contract since there is a heavy reliance on the OEM ’ s equipment and systems .
The process plant will include high pressure grinding rolls as the main crushing unit on the surface , supported by a secondary crusher to deal with oversize material . The ore then feeds to a ball mill before being discharged to the flotation circuit .
The gold-enriched copper concentrate will be piped to the filter plant for drying and the removal of water down to a moisture content of 10 %, while the tailings will be segregated to pyrite and non-pyrite streams before being distributed to one of two filter presses . Dry stacking of the tailings will be used , with the pyrite-bearing tailings being encapsulated within the larger inert tailings footprint . www . anglogoldashanti . com
managed by the Area Isolation Management System ( AIMS ). AIMS was being developed in partnership with Caterpillar for trial in late 2020 and allows both dynamic and remote changes in the allocation of sections of the mine to manual , remote or autonomous use . The boundaries of the AMA will be the only locations deploying physical barricades and those barricades demarcate the point beyond which entities must have the appropriate systems on-board and in which all persons entering or operating require competence in AIMS and AMA procedures . www . ptfi . co . id ; www . cat . com ; www . minetec . com . au
4 International Mining | JANUARY 2021