Ore Liberation and Characterization Using Electric Pulse Disaggregation and Other Novel Techniques

Abstract

Preliminary tests were performed to determine the efficiency of electric pulse disaggregation (EPD) technology on ore mineral liberation, from the surrounding gangue material on a wide range of ore deposits types. In addition to processing using EPD technology, samples were scanned using X-ray computed tomography (XRCT). All the collected data were then used to characterize the ore particles in novel ways. The samples in this investigation came from the following deposit types; a liquid-magmatic deposit that represents Si-differentiation, liquid-magmatic deposits that represent immiscible sulfide melts, porphyry deposits, VHMS deposits, an MVT deposit, and an SSC deposit. Ten samples from different ore deposits were processed in a SELFRAG EPD machine. The samples were then fractionated by sieving where a grain size of -250 µm to +150 µm was chosen for constructing grain mounts. The grain mounts were scanned in an SEM using mineral liberation software where the percentage of ore that had achieved liberation was used to evaluate the efficiency of the EPD process. Solid portions of all the samples that were not disaggregated were scanned in an XRCT. Data from these scans were then processed as raw numerical information or processed using 3D visualization software. The results from EPD efficiency display a wide range of possibilities, anywhere from no liberation to values as high as 97%, with most samples displaying good liberation percentages in the high 60% if the null liberation values are ignored. Null liberation values were ignored because it was discovered, through analysis of ore grain size data exported from XRCT scans, that the in-situ ore grain size was greater than that of the material selected for the grain mounts. This realization informed the decision to ignore these null values when calculating the average liberation of all samples. By using data acquired from XRCT scans, three useful techniques were employed that have the potential to aid in future studies of ore bodies. 3D reconstructions of scanned cores allowed for the identification of micro-structures such as; planar mineralization pathways that were sub-100 µm thick, possible shear surfaces expressed as abrupt planar terminations of ore occurrences, and interruptions in stratigraphically controlled ore that may have been important fluid migration pathways for the movement of ore-bearing fluids. Shape analysis graphs were constructed comparing the long and short axis information exported from XRCT scans. The results of these graphs revealed that most samples contained roughly equal proportions of spherical and elongate ore grains, but a sample from a liquid-magmatic Si-differentiation deposit was much more spherical in its ore morphology while a sample from an SSC deposit was the most elongate in morphology. Finally, vector graphs were constructed that illustrate the long axis orientation of ore grains in-situ within scanned samples. A number of these samples display apparent preferred orientation directions. For samples that originated in deposits where fluid flow is a key factor in ore emplacement, these vector graphs have the potential to inform the investigator as to the direction of ore propagation. The results that were arrived at in this study, while promising, are preliminary and further work is required verify the utility of the techniques.