Kavanagh, C, Daczko, N & Eggers, MJ 2023, 'Shale geochemistry: a proxy for shear strength in the Pilbara?', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference
, Australian Centre for Geomechanics, Perth, pp. 435-448, https://doi.org/10.36487/ACG_repo/2335_27
Australian iron ore is mined across the Hamersley Province, Western Australia, from open pit mines composed of mineralised interlayered strong banded iron formations (BIFs) and weaker shales. Slope design and failures are commonly controlled by shale units with low shear strengths. However, the principal controls on shale shear strength are poorly constrained. The purpose of this study is to investigate the potential relationship between shale geochemistry and shear strength.
The metasomatism that enriched iron in the BIFs has variably strengthened or weakened the interbedded shales. This study finds alumina (Al2O3), silica (SiO2) and iron oxide (III) (Fe2O3)to be the dominant element oxides in the shales. Shales with an alumina content <10 wt% are likely to have high strength and those >16 wt% are likely to be classified as weak. The alumina content of the shales was found to better correlate with shear strength than the defect surface condition; the latter previously having been considered the controlling factor on strength. This research permits shale shear strength to be estimated in a field environment using a portable X-ray fluorescence analyser to determine the alumina content, assisting selection of shale samples for direct shear testing.
Keywords: shale, shear strength, geochemistry, Hamersley Province
Alibert, C & Mcculloch, MT 1992, ‘Rare earth element and neodymium isotopic compositions of the banded iron-formations and associated shales from Hamersley, Western Australia’, Geochimica et Cosmochimica Acta, vol. 57, pp. 187–204,
Anbar, AD, Duan, Y, Lyons, TW, Arnold, GL, Kendall, B, Creaser, RA, … & Buick, R 2007, ‘A whiff of oxygen before the great oxidation event?’, Science, vol. 317, pp. 1903–1906,
Blake, TS & Barley, ME 1992, ‘Tectonic evolution of the late Archean to early Proterozoic Mount Bruce Megasequence Set, Western Australia’, Tectonics, vol. 11, pp. 1415–1425,
Cameron, EM & Garrels, RM 1980, ‘Geochemical compositions of some Precambrian shales from the Canadian Shield’, Chemical Geology, vol. 28, pp. 181–197,
Ewers, WE & Morris, RC, 1981, ‘Studies of the Dales Gorge Member of the Brockman Iron Formation, Western Australia’, Economic Geology, vol. 76, pp. 1929–1953,
Haruna, M, Hanamuro, T, Uyeda, K, Fujimaki, H & Ohmoto, H 2003, ‘Chemical, isotopic, and fluid inclusion evidence for the hydrothermal alteration of the footwall rocks of the BIF-hosted iron ore deposits in the Hamersley District, Western Australia’, Resource Geology, vol. 53, pp. 75–88,
Hencher, SR 1995, ‘Interpretation of direct shear tests on rock joints’, Rock Mechanics, pp. 99–106.
Jacques, AL, Jaireth, S & Walshe, JL 2002, ‘Mineral systems of Australia: An overview of resources, settings and processes’, Australian Journal of Earth Sciences, vol. 49, pp. 623–660,
Kurzweil, F, Wille, M, Schoenberg, R, Taubald, H & Van Kranendonk, MJ 2015, ‘Continuously increasing δ 98 Mo values in Neoarchean black shales and iron formations from the Hamersley Basin’, Geochimica et Cosmochimica Acta, vol. 164, pp. 523–542,
Laperche, V & Lemière, B 2021, ‘Possible pitfalls in the analysis of minerals and loose materials by portable XRF, and how to overcome them’, Minerals, vol. 11, no. 4,
Maldonado, A, Dight, PM & Mercer, K 2020, 'The intact rock strength of anisotropic rocks in the Pilbara: the use of field estimations, practical limitations of calibrations and statistical bias', in PM Dight (ed.), Slope Stability 2020: Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 691–702,
Maldonado, A, Mercer, KG & Robert, A 2017, ‘The relationship between mineralogy and shear strength of Pilbara Hamersley Group Shales across the weathering spectrum’, Proceedings of Iron Ore 2017, Australasian Institute of Mining and Metallurgy, Melbourne.
Martin, DMCB 2020, ‘Geology of the Hardey Syncline—the key to understanding the northern margin of the Capricorn Orogen’, Geological Survey of Western Australia, report 203.
Myers, JS 1993, ‘Precambrian history of the West Australian Craton and adjacent Orogens’, Annual Review of Earth and Planetary Sciences, vol. 21, pp. 453–485,
Nagendran, SK & Mohamad Ismail, MA 2021, ‘Probabilistic and sensitivity analysis of rock slope using anisotropic material models for planar failures’, Geotechnical and Geological Engineering, vol. 39, pp. 1979–1995,
Occhipinti, SA, Sheppard, S, Tyler, IM, Sircombe, KN, Reddy, S, Hollingsworth, D, … & Thorne, AM 2003, ‘Proterozoic geology of the Capricorn Orogen, Western Australia — a field guide’, Geological Survey of Western Australia, record 2003/16.
Pickard, AL 2002, ‘SHRIMP U–Pb zircon ages of tuffaceous mudrocks in the Brockman Iron Formation of the Hamersley Range, Western Australia’, Australian Journal of Earth Sciences, vol. 49, pp. 491–507,
Ray, E & Paul, D 2021, ‘Major and trace element characteristics of the average Indian post-Archean shale: implications for provenance, weathering, and depositional environment’, ACS Earth Space Chem, vol. 5, pp. 1114–1129,
Shibuya, T, Aoki, K, Komiya, T & Maruyama, S 2010, ‘Stratigraphy-related, low-pressure metamorphism in the Hardey Syncline, Hamersley Province, Western Australia’, Gondwana Research, vol. 18, pp. 213–221,
Simonson, BM, Mcdonald, I, Shukolyukov, A, Koeberl, C, Reimold, WU & Lugmair, GW 2009, ‘Geochemistry of 2.63–2.49Ga impact spherule layers and implications for stratigraphic correlations and impact processes’, Precambrian Research, vol. 175,
Taylor, D, Dalstra, HJ, Harding, AE, Broadbent, GC & Barley, ME 2001, ‘Genesis of high-grade hematite orebodies of the Hamersley Province, Western Australia’, Economic Geology, vol. 96, pp. 837–873,
Trendall, AF 1990, ‘Hamersley Basin: geology and mineral resources of Western Australia’, Geological Survey of Western Australia, memoir 3, pp. 163–191.
Trendall, AF, Compston, W, Nelson, DR, De Laeter, JR & Bennett, VC 2004, ‘SHRIMP zircon ages constraining the depositional chronology of the Hamersley Group, Western Australia’, Australian Journal of Earth Sciences, vol. 51, pp. 621–644,
Trendall, AF & Blockley, JG 1970, ‘The iron formations of the Precambrian Hamersley Group, Western Australia; with special reference to the associated crocidolite’, Geological Survey of Western Australia, bulletin 119, pp. 1–336.
Tyler, IM & Thorne, AM 1990, ‘The northern margin of the Capricorn Orogen, Western Australia - an example of an early Proterozoic collision zone’, Journal of Structural Geology, vol. 12, pp. 685–701,
Webb, AD, Dickens, GR & Oliver, NHS 2003, ‘From banded iron-formation to iron ore: geochemical and mineralogical constraints from across the Hamersley Province, Western Australia’, Chemical Geology, vol. 197, pp. 215–251,
Webb, AD, Dickens, GR & Oliver, NHS 2004, ‘Carbonate alteration of the Upper Mount McRae Shale beneath the martite-microplaty hematite ore deposit at Mount Whaleback, Western Australia’, Mineralium Deposita, vol. 39, pp. 632–645,
Webb, AD, Dickens, GR & Oliver, NHS 2006, ‘Carbonate alteration of the Upper Mount McRae Shale at Mount Whaleback, Western Australia – implications for iron ore genesis’, Applied Earth Science, vol. 115, pp. 161–166,
White, AJR, Legras, M, Smith, RE & Nadoll, P 2014, ‘Deformation-driven, regional-scale metasomatism in the Hamersley Basin, Western Australia’, Journal of Metamorphic Geology, vol. 32, pp. 417–433,
Young, KE, Evans, CA, Hodges, KV, Bleacher, JE & Graff, TG 2016, ‘A review of the handheld X-ray fluorescence spectrometer as a tool for field geologic investigations on Earth and in planetary surface exploration’, Applied Geochemistry, vol. 72, pp. 77–87,