HIGH PROFILE
SRK ’ s stepwise approach to pre-concentration analysis
Having outlined a new vendor-agnostic , lab-based “ preconcentration screening test ” for mining in part one of this three-part series , SRK is back for part two , discussing the wider pre-concentration evaluation process that this testing fits into
SRK ’ s five-step approach is deliberately designed to allow companies to pause at the end of each phase to re-evaluate if there is a strong enough case to continue investing the time and finances required
“ With any pre-concentration analysis , we need to , first , understand the heterogeneity of the deposit ; simply put , if you don ’ t have heterogeneity , you don ’ t have the ability to separate the good stuff from the bad stuff and carry out preconcentration ,” Bob McCarthy , Principal Consultant , SRK Consulting ( Canada ) Inc , says .
With this baseline in mind , SRK Consulting has devised a pathway for companies with drill core at their disposal to analyse whether preconcentration is a viable option for their flowsheet .
Made up of five steps , this staged approach is deliberately designed to allow companies to pause at the end of each phase to re-evaluate if there is a strong enough case to continue investing the time and finances required .
The heterogeneity analysis is first up , which , under SRK ’ s evaluation , includes two different approaches based off drill hole analysis : Heterogeneity and Scale and Composite-Sample Relationship Analysis .
“ Heterogeneity and Scale involves a process of looking up and down the bore hole at different aggregation distances from every sample and interrogating the sample grade – or net smelter return – against the aggregations above and below that individual sample ,” he explains . “ We then increase the size of the aggregation to see how that relationship changes .”
Such analysis enables SRK experts to derive the heterogeneity measures typically dubbed ‘ waste in ore ’ ( mineralisation below the cutoff grade within an above cutoff grade zone ) or ‘ ore in waste ’ ( mineralisation above the cutoff grade within a waste or marginally below cutoff grade zone ). Using a cutoff grade derived from industry benchmarking , the consultants assess the aggregation distance , as resolved in the vertical direction , with the “ selective mining unit ” ( SMU ), which typically relates to equipment sizing for mining .
“ The pitfall some companies go down is picking your SMU to match an equipment size and production rate typically aligned to a corporate or strategic objective ,” McCarthy says . “ This could mean generating a 12-14-year mine life for a gold operation , or some other investor-led metric that doesn ’ t necessarily respect the deposit ’ s heterogeneity .”
The second approach – Composite-Sample Relationship Analysis – allows consultants to further quantitatively assess those waste in ore / ore in waste heterogeneity measures .
“ Those parameters have multiple uses after being determined ,” McCarthy says . “ For example , they help guide in the sample selection – you can even visualise them in 3D with something like Leapfrog . You can also see contiguous lengths of above or below cutoff grade material in ore zones or marginal waste zones , representing what an ore sorter may see . These would be targeted for testing .”
Responding to industry calls , SRK now offers a step between this fundamental heterogeneity analysis and the test work it can conduct at Base Metallurgical Labs ’ Kamloops facility in British Columbia , with what McCarthy calls “ size the prize ” economics . It provides insight into possible pre-concentration strategy outcomes and , just as important , justification to continue to the next step of lab test work .
This process – carried out by SRK on several projects in the past – is designed to allow the mining company and consultant to test preconcentration strategies from an economic perspective , assessing if an operation should be
removing waste from ore or looking to recover above cut-off grade material from “ marginal waste ”.
McCarthy added : “ It is about answering these questions : is it best to remove waste from mill feed , and to what maximum grade of feed , or to extract mineralised material from marginal , below cut-off grade material that increases the mineral reserve ? And , of course , do the expected results of this process look promising ?”
Gold is a good example here as the economic case study for pre-concentration often only stacks up when a “ cap ” is applied to the grade of ore subjected to pre-concentration . In other words , the highest-grade material should not be targeted . Even high-efficiency pre-concentration methods incur some metal loss , and any amount of “ loss ” that occurs in a gold project is difficult to make-up within a conventional flowsheet .
The third step in this five-step process is the lab test work McCarthy ’ s colleague , Adrian Dance ( Principal Metallurgist at SRK Consulting ), previously outlined in detail in the first article in this three-part series .
The “ pre-concentration screening test ” leveraging X-ray Transmission based sensor technology can not only indicate preconcentration amenability , but also provide key inputs into the pre-concentration strategy selection and evaluation , Dance says . He says the testing offers an assessment of pre-concentration potential , as well as an estimate of material bypass and metal upgrade from samples as small as half cores .
Used in conjunction with crushing and screening , this testing rapidly – and cost effectively – assesses the potential for preconcentration , which can then be applied to scoping or pre-feasibility studies , according to SRK and Base Metallurgical Labs .
Which is where steps four and five of the SRK evaluation – mine planning and mine economics – come in .
“ With the heterogeneity measures assigning
“ Heterogeneity and Scale involves a process of looking up and down the bore hole at different aggregation distances from every sample and interrogating the sample grade – or net smelter return – against the aggregations above and below that individual sample ,” Bob McCarthy says
64 International Mining | FEBRUARY 2024