Calibrated X-ray micro-tomography for mineral ore quantification

Abstract

Scanning Electron Microscopy (SEM) based assessments are the most widely used and trusted imaging technique for mineral ore quantification. X-ray micro tomography (XMT) is a more recent to the mineralogy toolbox, but with the potential to extend the measurement capabilities into the three dimensional (3D) assessment of properties such as mineral liberation, grain size and textural characteristics. In addition, unlike SEM based assessments which require the samples to be sectioned, XMT is non-invasive and non-destructive manner. The disadvantage of XMT, though is that the mineralogy must be inferred from the X-Ray attenuation measurements, which can make it hard to distinguish from one another, whereas SEM when coupled with Energy-Dispersive X-ray Spectroscopy (EDX) provides elemental compositions and thus a more direct method for distinguishing different minerals. A new methodology that combines both methods at the mineral grain level is presented. The rock particles used to test the method were initially imaged in 3D using XMT followed by sectioning and the 2D imaging of the slices using SEM-EDX. An algorithm was developed that allowed the mineral grains in the 2D slice to be matched with their 3D equivalents in the XMT based images. As the mineralogy of the grains from the SEM images can be matched to a range of X-Ray attenuations, this allows minerals which have similar attenuations to one another to be distinguished, with the level of uncertainty in the classification quantified. In addition, the methodology allowed for the estimation of the level of uncertainty in the quantification of grain size by XMT, the assessment of stereological effects in SEM 2D images and ultimately to obtain a simplified 3D mineral map from low energy XMT images. Copper sulphide ore fragments, with chalcopyrite and pyrite as the main sulphide minerals, were used to demonstrate the effectiveness of this procedure.

Visualization and quantification of capillary drainage in the pore space of laminated sandstone by a porous plate method using differential imaging X‐ray microtomography

“…In recent years, micro‐CT has been widely used in geologically related studies [ Ketcham and Carlson , ; Cnudde and Boone , ; Lin et al ., ; Al‐Khulaifi et al ., ; Reyes et al ., ; Saif et al ., ], especially for visualizing multiphase flow, measuring contact angle, and obtaining capillary pressure from curvature measurements in the pore space [ Arns et al ., ; Armstrong et al ., ; Iglauer et al ., ; Blunt et al ., ; Andrew et al ., ; Schlüter et al ., ]. To visualize and understand flow properties as a function of rock geometry and topology, accurate imaging methods are essential.…”

Imaging and Measurement of Pore‐Scale Interfacial Curvature to Determine Capillary Pressure Simultaneously With Relative Permeability

“…In recent years, pore-scale X-ray microtomography (micro-CT) imaging has been widely used in geologically related studies (Al-Khulaifi et al, 2018;Al-Menhali et al, 2016;Andrew et al, 2014a;Berg et al, 2013;Blunt et al, 2013;Cnudde & Boone, 2013;Ketcham & Carlson, 2001;Lai et al, 2015;Lin et al, 2018;Lin, Al-Khulaifi, et al, 2016;Lin, Neethling, et al, 2016;Qajar & Arns, 2016;Reyes et al, 2017;Reynolds et al, 2017;Saif et al, 2017;Schlüter et al, 2016). In particular, imaging of multiphase flow in porous rock has been performed, covering a wide range of topics, including wettability characterization based on contact angle measurement, relative permeability, and curvature analysis in the pore space to estimate capillary pressure (Akbarabadi & Piri, 2013;Alhammadi et al, 2017;AlRatrout et al, 2017;Andrew et al, 2014b;Armstrong, Pentland, et al, 2012;Arns et al, 2003;Berg et al, 2016;Gao et al, 2017;Garing et al, 2017;Herring et al, 2017;Krevor et al, 2012;Lin et al, 2017;Lv et al, 2017;Norouzi Apourvari & Arns, 2016).…”

Accurate Measurement of Small Features in X‐Ray CT Data Volumes, Demonstrated Using Gold Grains

“…Fewer have approached the problem of measuring the size and shape of discrete particles or pores that are small in two or three dimensions. In most cases, a simple threshold is used to segment small features (e.g., Bagheri et al, ; Garboczi et al, ; Reyes et al, ; Schmitt et al, ; Zhou et al, ), often with an acknowledgment that resolution limitations will influence some results but without any attempt to quantify that effect. The industrial CT community, which strongly emphasizes accuracy in metrology, also tends to utilize thresholding approaches (Kruth et al, ); although more sophisticated methods and corrections likely exist, they are proprietary and thus less documented (Carmignato, ; Kruth et al, ).…”

“…CT has been demonstrated as an excellent tool for investigating gold deposits and their genesis (Kyle & Ketcham, ), and indeed any deposits that host economic trace phases (Godel, ), as concentrations in the parts‐per‐million range can be economic to mine but difficult to study using traditional petrography. Attributes of interest include net concentrations (i.e., assay), size and shape distributions, petrologic associations, and orientations and structural context (e.g., Furat et al, ; Godel et al, ; Mote et al, ; Reyes et al, ).…”