SAMPLING , ANALYSIS AND LAB ASSAY
Operated from the drill cabin or a remote control unit , IMA ’ s Autosampler automates the sampling , sample splitting and sample bag change process . Pictured is an installation at an Arctic gold mine
The impact of the Autosampler is also being felt underground with Auranen confirming that IMA has developed a solution to deal with wet drill cuttings from operations below surface .
He explained : “ There are very few underground drill cutting samplers on the market – actually , I don ’ t know of any – with most underground mines using grab samples . The challenge with grab sampling is there is a human taking a sample , so , inherently , the ‘ sample ’ obtained is a rock , despite most of the underground material being very fine . This rock is sent to the lab to be analysed , with the results often coming back too late to affect changes in the blasting process .”
IMA has delivered an underground Autosampler to a gold mine in Northern Europe , in addition to an operation in Mexico , to help improve the sampling and analysis accuracy and affect such change , Auranen confirmed .
When it comes to conveyor-based analysis , IMA also has an offering for the market , with its IMA FCA ( Fast Conveyor Analyzer ) used for bulk ore sorting applications , as well as analysing mill and concentrator feed .
In addition to providing accurate and fast analysis of the ore grade , these analysers are easy to install on top of any existing conveyor , according to IMA . Further , they can be calibrated with ease – even remotely . This has allowed IMA to offer the FCAs for short-term trials on a rental basis , providing immediate returns on investment , according to Auranen .
The company recently registered two orders for the analysers from Chile-based iron ore mining company Compañía Minera del Pacífico .
Moving further down the mining value chain , IMA has also installed its IMACON 100 systems at several process plants across the globe in the last year , in the face of COVID-19-related travel restrictions .
Comprised of samplers , multiplexers and the online analyser , IMACON systems are used to analyse oxide or elemental compositions in finely ground dry powders , or in wet slurries at the plant . The rapid and automatic analysis that it offers allows producers to promptly detect changes in incoming material and products , enabling them to take appropriate action in the process streams .
“ The whole system needs to be understood for this process to work well ,” Auranen said . “ You have to have reliable samplers , you need to install the piping that leads to the analyser and then you need to have a properly calibrated slurry analyser that can measure and analyse many different products from different parts of the concentration process .”
IMA helps design a representative sampling process by advising on the shortest possible sampling lines and ensuring the analysers are cleaned between flows to avoid contamination .
“ As with all processes , the sample is only as good as the process to obtain it ,” Auranen said . “ By advising on all aspects of the process and offering 24-7 support , we ensure customers achieve the best possible results .”
And , as with all IMA products , the company relies on lab machines to ensure its IMACON analysers are accurately configured .
“ Traditional lab analysis is still needed now , and it will be needed in the future ; a future where we see online methods for sampling and analysis , and traditional lab-based analysis for quality assurance and control ,” Auranen said .
Conveying the measurements
Scantech International Pty Ltd has been pushing for increased use of online analysers over traditional sampling methodologies in process control applications arguing that , when applied to material flows on a conveyor , the results enable operators to select material and remove it from the plant feed through bulk ore sorting , particle sorting , screening or other upgrading processes .
Instead of having to take numerous large samples to represent a period of conveyed flow , technology such as Prompt Gamma Neutron Activation Analysis ( PGNAA ) and microwave transmission can provide real-time feedback on ore quality and moisture content to maximise opportunities to manage the process . In this context , full flow analysis is preferable to
analysing sampled flows due to potential sampling errors , the company argues .
PGNAA is a preferred method for on-belt multielemental analysis as it is penetrative through more than 500 mm of rock thickness and is unaffected by particle size , belt speed , mineralogy , vertical or lateral segregation and moisture content , according to Henry Kurth , Chief Marketing Officer and Minerals Consultant at Scantech .
“ Neutrons generated by a source ( radioactive source or generator typically located under the conveyor belt ) are emitted so that the conveyed flow passes through an activation zone ,” he explained . “ Elemental nuclei capture neutrons and emit gamma radiation energies unique to each element . A detector array ideally above the conveyed flow senses the gamma emissions and generates spectral curves representing the emitted energies in the proportion of the elements present .”
The relative amount of each element is determined from the spectral data over a measurement increment and results are tonnageweighted by mass flows during that measurement time , which , themselves , are adjusted based on a separate measurement of moisture content , according to the company .
These measurements are then reported to the plant control system , with high specification PGNAA systems , such as GEOSCAN-M , able to measure elements to precisions suitable for process control and ore reconciliation .
“ Measurement precisions of 0.02 % copper over a 0.2-1.6 % copper range in copper-gold ore have been achieved as well as 0.5 parts per million ( ppm ) mercury precision over a 1-20 ppm mercury range in iron ore ,” Kurth said .
“ Not all elements can be measured . Elements such as carbon , nitrogen and sodium upwards in
PGNAA is a preferred method for on-belt multielemental analysis as it is penetrative through more than 500 mm of rock thickness and is unaffected by particle size , belt speed , mineralogy , vertical or lateral segregation and moisture content , according to Henry Kurth . Pictured is the company ’ s high specification PGNAA system , GEOSCAN-M
78 International Mining | FEBRUARY 2022