Signatures of Cu (-Au) mineralisation reflected in inorganic and heavy mineral stream sediments at Vähäkurkkio, north-western Finland

Exploration Potential of Fine-Fraction Heavy Mineral Concentrates from Till Using Automated Mineralogy: A Case Study from the Izok Lake Cu–Zn–Pb–Ag VMS Deposit, Nunavut, Canada

“…When using the MLA software, a section to be scanned in a sample run can be copied and re-applied to the exact same section, ensuring that all frames are analyzed in the same location, with the same operating parameters. This overcomes the potential for nugget effects skewing results as described in Hulkki et al [47]. Their estimation of error had the caveat that their repeat scan could not be performed on precisely the same area, leaving the possibility that grains present along the edges of the scanned area could be missed between consecutive scans.…”

“…When using grain counts it is important to normalize values to allow for comparison between samples containing varying numbers of grains. Hulkki et al [47] used two methods for normalizing grain count data, with their disaggregated bedrock samples being normalized using the equation: This ratio accommodates the varying number of grains analyzed between subsamples. The stream sediment grain counts of Hulkki et al [47] were normalized to a 1 kg processed sample weight, although the authors noted that given the extremely low abundance of the Cu minerals of interest, the normalized values were very close to the numbers of observed mineral grains.…”

“…The option to gather information only for grains above a specific brightness threshold is available in MLA. This option was successfully utilized by Hulkki et al [47], using the grey level of hematite as a lower limit, to increase the detection of Cu-bearing mineral phases in stream sediment HMC samples. These techniques have the added benefit of decreasing the number of EDS analysis necessary during scanning routines, which decreases the overall analysis time for each sample.…”

“…Chalcopyrite and pyrite are commonly present in small amounts in mineralized and barren metamorphosed mafic rocks, and thus the presence of chalcopyrite or pyrite inclusions in other minerals alone, although most likely related to mineralization at this specific site, can be an unreliable indication of mineralization in a regional exploration context [47]. The preservation of chalcopyrite and pyrite as inclusions in more robust grains, combined with the common occurrence of both minerals in mineralized and unmineralized bedrock, means that establishing accurate background values for both minerals is important when using automated mineralogical methods.…”