SAMPLING , ANALYSIS AND LAB ASSAY
Maximising mineral potential
Intertek Group ’ s new Minerals Global Centre of Excellence , in Perth , Western Australia , features two Chrysos PhotonAssay units
The industry has a whole host of tools on hand to ensure it can make the most of its mineral potential . It now needs to leverage them for optimal results , Dan Gleeson reports
The data influx the mining industry has experienced in the last decade has brought new-found transparency to a sector that has been used to working with ‘ averages ’ and estimates .
What starts at the drill intercept and resource calculation level with ‘ average ’ grades is often carried through to the plant , with inherent orebody heterogeneity disregarded to employ a ‘ factory ’ mindset where the inputs and outputs are treated as uniform and consistent .
Yet , the convergence of analytical hardware and software are proving that orebodies are nowhere near as homogeneous as the numbers suggest .
Now , for companies to leverage value from these solutions , they need to sample and analyse minerals and metals on a regular basis , adapting their processes as they go .
IM looks at some of the leading solutions in this field and how miners can amend their workflows to make the most of them .
The fine print
As Trevor Bruce , Product Line Manager at FLSmidth , says , the argument from the sampling community around how better sampling , preparation and analysis ( SPA ) improves the possible precision of results for ore grades is completely valid , but backing this up with numbers is a trickier task .
“ One way to do this is by applying the SPA precision of your results to the selling price of the resource ,” Bruce said in a paper titled ‘ Effect of precision on resource pricing ’.
In this paper , he has come up with an example related to iron ore pricing , but he acknowledges the principle can be applied to any commodity .
He explained : “ Pricing guides are readily
available online for the various grades of different commodities . Specific grades , with upper specification limits on deleterious elements , are defined for each commodity , but after product loading , for final sale , the actual chemical and physical characteristics of the lot can be used to modify the price accordingly .”
A method of calculating this for iron ore is to consider the value in use index .
The Metal Bulletin ( now Fastmarkets ) publication of August 2018 , entitled ‘ Iron Ore Indices , Pricing Guide : Methodology specification and use ’, employs an index called “ Value-In-Use ” ( VIU ) to correct the price of specific ore grade / types using the final analyses of samples collected during the loading of iron ore .
The VIU index is released on the first working day of each month and could be applied as follows :
n P ac = IOI α + ( Δα x Fe VIU ); n P ac = the selling price of iron ore ( per dry tonne ) with an Fe concentration calculated during loading ; n IOI α = the index price for iron ore with α % Fe , using the Metal Bulletin Iron Ore Indices ( MBIOI ); n α = the required grade of Fe in the commodity , ( eg α = 62 % Fe fines Index ); n Fe VIU = the VIU index value ; n Δα = the difference of the actual measured grade for Fe to the required grade ( Fe reported - α ); and n Fe reported = the measured result ± the measured result multiplied by the precision . There is typically a large penalty payable by producers if they overstate the iron ( Fe ) content and it is , therefore , common for producers to understate measured Fe content by the level of confidence or precision they have in their SPA results , according to Bruce .
“ This results in a larger negative value for Δα , which directly impacts the price of the ore ( all other factors being equal ),” he said . “ The further away from the actual value that the reported value is , the more the producer will lose if the Fe content is understated .”
In manually operated sampling , preparation and analytical labs for port facilities an SPA precision of greater than 1 % has been achieved on occasion . In the iron ore port facilities that FLSmidth has designed and installed in Australia and South Africa – which are automated – the SPA precision consistently achieved has been less than 0.16 %, according to Bruce .
“ If we consider this variation on a grade / type 62 % Fe fines , having a daily index price of $ 132.19 / dry tonne with a monthly VIU index of $ 2.55 – and assuming a measured result of 62 %
In the automated iron ore port facilities that FLSmidth has designed and installed in Australia and South Africa , the sampling , preparation and analysis precision consistently achieved has been less than 0.16 %, according to Trevor Bruce
76 International Mining | FEBRUARY 2022