Continuous Hydrogeological Characterisation in Iron Ore Deposits Using Borehole Magnetic Resonance

Abstract

SUMMARYIn situ dewatering of iron ore deposits is essential for safe and efficient mining operations, as well as reducing requirements for subsequent moisture removal for processing and transportation. Evaluating porosity, residual moisture content, and hydraulic conductivity is key to designing effective dewatering schemes.Modern borehole magnetic resonance has been used in the oil and gas industry for over twenty years to provide continuous evaluation of porosity, bound and free fluid volumes, and permeability. As such, it is uniquely suited to provide subsurface characterisation data for dewatering scheme design. However, applying these methods in iron ore settings introduces complications that are not observed in typical oil and gas environments due to the high concentrations of paramagnetic and ferromagnetic iron-containing compounds making up the ores. This requires explicitly accounting for the impact of these compounds on surface and diffusional relaxation when estimating fluid volumes and permeability from magnetic resonance measurements.Development of robust methods for accommodating these effects would allow for practical application of borehole magnetic resonance measurements in iron ore settings, providing continuous and cost effective hydrogeological characterisation.

Hydrogeological Characterization of Crystalline Bedrock Using Borehole Magnetic Resonance

“…Especially at the Olkiluoto Island, there have been reported paramagnetic minerals associated to mafic rocks (e.g., Paananen 2004). The presence of ferromagnesian minerals, on the other hand, tend to delay the T2 relaxation times: the high concentrations of these compounds enhance both surface and diffusional relaxation effects, and thus also present additional challenge for the BMR readings (Trofimczyk et al 2018 (Kozeny 1927;Carman 1956). The T-C model takes into account the relationship between the movable, free water, and the bound water once the cutoff 2 value has been estimated, while the SDR (or mean T2) model utilizes the logarithmic mean of the T2 distribution.…”

“…Especially at the Olkiluoto Island, there have been reported paramagnetic minerals associated to mafic rocks (e.g., Paananen 2004). The presence of ferromagnesian minerals, on the other hand, tend to delay the T2 relaxation times: the high concentrations of these compounds enhance both surface and diffusional relaxation effects, and thus also present additional challenge for the BMR readings (Trofimczyk et al 2018).…”

“…The cutoff criteria were applied within these more magnetic levels which locally reached anomalously slow T2 relaxation times. However, as stated by Trofimczyk et al (2018), laboratory studies are required to quantify the magnitude of surface and diffusional relaxation effects and better understand how these properties relate to magnetic susceptibility. It is challenging to recognize these effects reliably especially in the cases where lower-level noise or magnetic anomalies were significant, requiring more advanced processing techniques and experience.…”

“…These new NMR tools are suitable for crystalline bedrock where the borehole diameters are typically small, yet applications in crystalline bedrock are still lacking. Very few studies have been published (Dlubac et al 2013;Trofimczyk et al 2018;Flinchum et al 2019;Ren et al 2019;Karjalainen 2020), even though the BMR method could be promising for estimating porosity, permeability, and hydraulic conductivity in crystalline bedrock, as well. Krejci et al (2018) compared the BMR method with core measurements and packer tests investigating the groundwater flow properties in coal mining operations in the southern Sydney Basin, Australia.…”