Authors: Bewick, R; Brzovic, A; Rogers, S; Griffiths, C; Otto, SA

Open access courtesy of:


Cite As:
Bewick, R, Brzovic, A, Rogers, S, Griffiths, C & Otto, SA 2022, 'Benchmarking framework for porphyry copper-gold rock masses for caveability and fragmentation decision-making', in Y Potvin (ed.), Caving 2022: Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1303-1318,

Download citation as:   ris   bibtex   endnote   text   Zotero

Caveability and fragmentation are two important aspects in a caving project; being very high risks or fatal flaws if they are not properly assessed. There is evidence from historic and current caving mines that there has been significant failure of revenue recovery because the rock mass characterisation process did not properly determine the key elements that control rock mass behaviour. The main rock mass characteristics of porphyry copper-gold orebodies are the networks of vein systems where most of the ore is located which are super imposed by faults systems. At depths greater than about 500 m, in these massive, competent and multimineral orebodies, joints are typically sparsely occurring or almost nonexistent. The main structural features that control strength in these rock masses are faults and the subset of veins that are infilled with minerals of weak strength such as gypsum, calcite, chlorite, and, in some cases, chalcopyrite. Traditional caveability and fragmentation assessments use classification schemes and tools that are not designed for a rock mass without joints (except for the in situ rock mass rating system). Rock masses that match these structural characteristics have been shown to range in fragmentation and caving performance from good to not so good. This paper presents the benchmarking framework that focuses on the key porphyry rock mass characteristics of fault/open structure and weak vein system intensity. A matrix has been developed to allow for consistent benchmarking of rock masses in porphyry deposits so that caveability and fragmentation challenges may be better forecasted in the future and engineering design decision making improved.

Keywords: block cave, caveability, fragmentation, discrete fracture network, rock mass characterisation, rock mass strength

ASTM International 1991, Standard Test Method for Unconfined Compressive Strength of Intact Rock Core Specimens (ASTM D 293886), ASTM International, West Conshohocken.
Bewick, RP, Amann, F, Kaiser, PK & Martin, CD 2015, ‘Interpretation of UCS test results for engineering design’, Proceedings of the 13th International Congress on Rock Mechanics: ISRM Congress 2015 – Advances in Applied & Theoretical Rock Mechanics, International Society for Rock Mechanics and Rock Engineering, Lisbon, paper 521.
Bewick, RP, Kaiser, PK & Amann, F 2019a, ‘Strength of massive to moderately jointed rock masses’, Journal of Rock Mechanics and Geotechnical Engineering, vol. 11, no. 3.
Bewick, RP, Campbell, R, Brzovic, A, Schwarz, A & Pierce, M 2019b, ‘Incorporating veined rock mass characteristics into engineering design and caving’, Proceedings of the 53rd US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association, Alexandria, paper 304.
Bewick, RP 2021, The Strength of Massive to Moderately Jointed Rock and its Application to Cave Mining,
Brzovic, A & Villaescusa E, 2007, ‘Rock mass characterization and assessment of block-forming geological discontinuities during caving of the primary copper ore at the El Teniente Mine, Chile’, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 44, pp. 565–583.
Brzovic, A, Schachter, P, de los Santos, C, Vallejos, JA & Mas Ivars, D 2014, ‘Characterization and synthetic simulations to determine rock mass behaviour at the El Teniente Mine, Chile. Part 1’, in R Castro (ed), Caving 2014: Proceedings of the Third International Symposium on Block and Sublevel Caving, University of Chile, Santiago.
Brzovic, A & Leon, I 2017, ‘Integrated photogrammetry and discrete fracture network modelling to determine rock structure around excavations at the El Teniente Mine’, in JA Vallejos (ed), RaSiM9: Proceedings of the 9th International Symposium on Rockburst and Seismicity in Mines, University of Chile, Santiago, pp. 196–203.
Chilès, JP, Wackernagel, H, Beucher, H, Lantuéjoul, C & Elion, P 2008, ‘Estimating fracture density from a linear or areal survey’, in JM Ortiz & X Emery (eds), Proceedings of the Eighth International Geostatistics Congress, Gecamin Ltda, Santiago, pp. 535–544.
Contreras, LF, Brown, ET, Ruest, M 2018, ‘Bayesian data analysis to quantify the uncertainty of intact rock strength’, Journal of Rock Mechanics and Geotechnical Engineering, vol. 10, pp. 11–31.
Day, JJ, Diederichs, MS & Hutchinson, DJ 2019, ‘Composite geological strength index approach with application to hydrothermal vein networks and other intrablock structures in complex rockmasses’, Geotechnical and Geological Engineering, vol. 35,
pp. 5285–5314,
Dershowitz, WS & Herda, HH 1992, ‘Interpretation of fracture spacing and intensity’, Proceedings of the 33rd US Rock Mechanics/Geomechanics Symposium.
Goodman, R 1989, Introduction to Rock Mechanics, 2nd edn, John Wiley & Sons, New York.
Hoek, E & Brown, ET 1980, Underground Excavations in Rock, The Institution of Mining and Metallurgy, London.
Laubscher, DH 1975, ‘Class distinction in rock masses’, Coal, Gold, Base Minerals South Africa, vol. 23.
Laubscher, DH & Jakubec, J 2000, ‘The MRMR rock mass classification for jointed rock masses’, Underground Mining Methods: Engineering Fundamentals and International Case Studies, Society of Mining Metallurgy and Exploration, Englewood,
pp. 475–481.
Perras, MA & Diederichs, MS 2014, ‘A review of the tensile strength of rock: concepts and testing’, Geotechnical and Geological Engineering, vol. 32, no. 2, pp. 525–546.
Rogers, S, Elmo, D, Webb, G & Catalan, A 2010, ‘A discrete fracture network based approach to defining in situ, primary and secondary fragmentation distributions for the Cadia East panel cave project’, in Y Potvin (ed.), Caving 2010: Proceedings of the Second International Symposium on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth,
pp. 425–439,
Rogers, S, Elmo, D, Webb, G & Catalan, A 2014, ‘Volumetric fracture intensity measurement for improved rock mass characterization and fragmentation assessment in block caving operations’, Rock Mechanics and Rock Engineering,
Russo, A, Vela, I & Hormazabal, E 2020, ‘Quantification of the intact geological strength index for rock masses in hypogene environment’, in R Castro, F Báez & K Suzuki (eds) MassMin 202: Proceedings of the 8th International Conference and Exhibition on Mass Mining, University of Chile, Santiago, pp. 1188–1201.
Sillitoe, R 2010, ‘Porphyry copper systems’, Economic Geology, vol. 105, pp. 3–41.

© Copyright 2022, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries or error reports to