Gutierrez, LAF, Viterbo, VC, McLemore, VT & Aimone-Martin, CT 2008, 'Geotechnical and Geomechanical Characterisation of the Goathill North Rock Pile at the Questa Molybdenum Mine, New Mexico, USA', in AB Fourie (ed.), Rock Dumps 2008: Proceedings of the First International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads
, Australian Centre for Geomechanics, Perth, pp. 19-32, https://doi.org/10.36487/ACG_repo/802_2
Physical changes due to weathering are of interest with respect to predicting long-term geotechnical slope
stability of rock piles at the Questa molybdenum mine, New Mexico, USA. Geotechnical and geomechanical
characterisation was conducted on matrix soil and rock fragments in the Goathill North (GHN) rock pile
and on non-weathered drill core samples of rock typical of GHN. Shear strength and rock durability was
estimated by performing direct shear, point load strength, and slake durability tests. Measurements for
Atterberg Limits, particle size, moisture content, and density were also performed.
Samples had high peak internal friction angles (φ) between 42º and 47º, which can in part be attributed to
the grain shape (subangular to very angular). Point load strength index (Is50) and slake durability index
(ID2) classified the samples as medium to very high strength and having high to extremely high durability,
respectively. Lowest values of φ, Is50, and ID2 were observed for samples from the outer margin of the pile.
ID2 results suggest that samples from the interior of the pile have been weathered little since deposition. In
general, GHN rock pile samples have high durability and strength even after having undergone
hydrothermal alteration and blasting prior to deposition and after potential exposure to weathering for
about 40 years. Collectively, these results suggest that future weathering will not substantially decrease the
friction angle of the rock piles with time.
ASTM (1998) Standard test method for direct shear test of soils under consolidated drained conditions: D3080,
American Society for Testing and Materials publication.
ASTM (2001a) Standard laboratory determination of water (moisture) content of soil, rock, and soil-aggregate
mixtures: D2216, American Society for Testing and Materials publication, 482 p.
ASTM (2001b) Standard test method for liquid limit, plastic limit, and plasticity index of soils: D4318, American
Society for Testing and Materials publication, 482 p.
ASTM (2001c) Standard Test Method for Slake Durability of Shales and Similar Weak Rocks: D464487 (Reapproved
1992), American Society for Testing Materials publication, 482 p.
ASTM (2002a) Standard test method for particle-size analysis of soils (D422), American Society for Testing and
ASTM (2002b) Standard test methods for specific gravity of soil solids by water pycnometer (D854), American Society
for Testing and Materials publication.
Birkeland, P.W. (1999) Soils and geomorphology, Oxford University Press publication, 430 p.
Bowles, J.E. (1979) Physical and geotechnical properties of soils, McGraw-Hill publication, 478 p.
Broch, E. and Franklin, J.A. (1972) The Point Load Strength Test, International Journal of Rock Mechanics, Min. Sci.,
Vol. 9, pp. 669-697.
Campbell, A.R. and Lueth, V.W. (in press) Isotopic and Textural Discrimination Between Hypogene, Ancient
Supergene, and Modern Sulfates at the Questa Mine, New Mexico: Applied Geochemistry.
Clark, M.J. and Samall, R.J. (1982) Slopes and weathering, Cambridge University Press publication, 112 p.
Das, B.M. (1983) Advanced soil mechanics, McGraw-Hill publication, 511 p.
Donahue, K., Dunbar, D. and McLemore, V.T. (2007) Origins of clay minerals in the Molycorp Goathill North rock
pile, Questa, NM, SME preprint, 2007 annual meeting, 19 p.
Filipowicz, P. and Borys, M., 2005, Geotechnical properties of mining wastes and their utilization in civil engineering;
in Proceedings of International Conference on Problematic Soils: May 25-27, 2005, Eastern Mediterranean
University, Famagusta, N. Cyprus, pp. 259-267.
Franklin, J.A., Chandra, A. (1972) The Slake Durability Test, International Journal of Rock Mechanics and Mining
Sciences, Vol. 9, pp. 325-341.
Fookes, P.G., Dearman, W.R. and Franklin, J.A. (1972) Some Engineering Aspects of Rock Weathering with Field
Examples from Dartmoor and elsewhere, Q. J. Eng. Geol., Vol. 4, pp. 139-185.
Gerrard, A.J. (1988) Rocks and landforms, Academic Division of Unwin Hyman publication, 319 p.
Gutierrez, L.A.F. (2006) The influence of mineralogy, chemistry and physical engineering properties on shear strength
parameters of the Goathill North rock pile material, Questa Molybdenum mine, New Mexico: M. S. thesis,
New Mexico Institute of Mining and Technology, Socorro, 201 p.,
, accessed December 06, 2007.
Hawley, P.M. (2001) Site selection, characterization, and assessment. in: W.A. Hustrulid. Slope Stability in Surface
Mining. M.K. McCarter and D.J.A. Van Zyl (Ed), Society for Mining, Metallurgy, and Exploration,Inc.,
Littleton, pp. 267-274.
Holtz, R.D. and Kovacs, W.D. (2003) An introduction to geotechnical engineering, Pearson Education Taiwan
publication, 733 p.
Irfan, T.Y. (1996) Mineralogy, Fabric Properties and Classification of Weathered Granites in Hong Kong, Quaternary
Journal of Engineering Geology, Vol. 29, pp. 5-35.
Irfan, T.Y. (1999) Characterization of Weathered Volcanic Rocks in Hong Kong, Quaternary Journal of Engineering
Geology, Vol. 32, pp. 317-348.
International Society for Rock Mechanics-ISRM (1979) Suggested methods for determination of the slake durability
index, Int. J. Rock Mech. Min. Sci. Geomech.,Vol. 16, pp. 154-156.
Koncagül, E.C. and Santi, P.M. (1999) Predicting the Unconfined Compressive Strength of the Breathitt Shale Using
Slake Durability, Shore Hardness and Rock Structural Properties, Int. J. Rock Mech. Min. Sci., Vol. 36, pp.
Luddington, S., Plumlee, G., Caine, J., Bove, D., Holloway, J., and Livo, E. (2005) Questa baseline and pre-mining
ground-water quality Investigation, 10. Geologic influences on ground and surface waters in the lower Red
River watershed, New Mexico: U.S. Geological Survey, Scientific Investigations Report 2004-5245, 46 p.
McLemore, V.T., Lueth, V. and Walker, B.M. (2004) Alteration Scars in the Red River Vallley, Taos County, New
Mexico. New Mexico Geological Society Guidebook, Vol. 55, pp. 19-24.
McLemore, V.T., Walsh, P., Donahue, K., Gutierrez, L., Tachie-Menson, S., Shannon, H.R. and Wilson, G.W. (2005)
Preliminary status report on Molycorp Goathill North trenches, Questa, New Mexico, 2005 National Meeting
of the American Society of Mining and Reclamation. American Society of Mining and Reclamation,
Breckenridge, 26 p.,
, accessed December 06,
Geotechnical Issues – Strength, Stability and Seepage
Rock Dumps 2008, Perth, Australia 31
McLemore, V.T., Donahue, K.M., Phillips, E., Dunbar, N., Walsh, P., Gutierrez, L.A.F., Tachie-Menson, S., Shannon,
H.R., Luth, V.W., Campbell, A.R., Wilson, G.W. and Walker, B.M. (2006a) Characterization of Goathill
North mine rock pile, Questa molybdenum mine, Questa, New Mexico. 7th International Conference of Acid
Rock Drainage, American Society of Mining and Reclamation, Lexington, pp. 1219-1249.
McLemore, V.T., Donahue, K., Phillips, E., Dunbar, N., Smith, M., Tachie-Menson, S., Viterbo, V., Lueth, V.W.,
Campbell, A.R. and Walker, B.M. (2006b) Petrographic, mineralogical and chemical characterization of
Goathill North mine rock Pile, Questa Molybdenum mine, Questa, New Mexico, 2006 Billings Land
Reclamation Symposium, American Society of Mining and Reclamation, Lexington, CD-ROM,
, accessed December 06, 2007.
Meyer, J.W. and Leonardson, R.W. (1990) Tectonic, Hydrothermal and Geomorphic Controls on Alteration Scar
Formation near Questa, New Mexico, New Mexico Geological Society Guidebook, Vol. 41, pp. 417-422.
Miura, K. (1973) Weathering in Plutonic Rocks (Part I)-Weathering During the Late-Pliocene of Gotsu Plutonic Rock,
Journal Society Engineering Geology Japan, Vol. 14, No. 3.
Norwest Corporation (2003) Goathill North mine rock pile evaluation and conceptual mitigation plan. Unpublished
Report to Molycorp Inc, 56 p.
Norwest Corporation (2004) Goathill North slide investigation, evaluation and mitigation report, Unpublished Report to
Molycorp Inc, 94 p.
Pasamehmetoglu, A.G., Karpuz, C. and Irfan, T.Y., 1981, The weathering characteristics of Ankara andesites from the
rock mechanics point of view; in Weak rock; soft, fractured and weathered rock: Proceedings of the
international symposium on weak rock; v. I,, A.A. Balkema, Rotterdam, Netherlands, p. 185-190 .
Pernichele, A.D. and Kahle, M.B. (1971) Stability of Waste Dumps at Kennecott's Bingham Canyon Mine. Tansactions,
Society of Mining Engineers, AIME, Vol. 250, pp. 363-367.
Reiche, P. (1943) Graphic Representation of Chemical Weathering, Journal Sedimentary Petrology, Vol. 13, Society for
Sedimentary Geology, pp. 58-68.
Seedsman, S.A. and Emerson, W.W. (1985) The Role of Clay-rich Rocks in Spoil Pile Failures at Goonyella Mine,
Queensland, Australia. International Journal of Rock Mechanicas and Mining Science, Vol. 22, pp. 113-118.
Snedecor, G.W. and Cochran, W.G. (1967) Statistical methods, The Iowa State University Press publication, Ames,
Iowa, 593 p.
Shaw, S.C., Wels, C., Roberston, A. and Lorinczi, G. (2002). Physical and geochemical characterization of mine rock
piles at the Questa mine, New Mexico: An overview. 9th International Conference on Tailings and Mine
Waste, Balkema, Rotterdam.
Tesarik, D.R. and McKibbin, R.W. (1999) Material properties affecting the stability of a 50-year-old rock dump in an
active mine. U.S. Department of Health and Human Services, Pittsburgh Research Laboratory (ed),
Pennsylvania, p. 2.
Uhle, R.J., Jr., 1986, A statistical analysis of rockfill data—Shear strength and deformation parameters with respect to
particle size: M.S. thesis, Colorado State University, Fort Collins.
URS Corporation (2000) Interim mine rock pile erosion and stability evaluations, Questa mine. Unpublished Report to
URS Corporation (2003) Mine rock pile erosion and stability evaluations, Questa mine, Unpublished Report to
Vallerga, B. A., Seed, H. B., Monismith, C. L., and Cooper, R. S. (1957) Effect of Shape Size and Surface Roughness
of Aggregate Particles on the Strength of Granular Materials, Special Technical Publication No. 212, ASTM.
Viterbo, V.C. (2007) Effects of pre-miming hydrothermal alteration processes and post-mining weathering on rock
engineering properties of Goathill North rock pile at Questa mine, Taos County, New Mexico: M. S. thesis,
New Mexico Institute of Mining and Technology, Socorro, 274 p.,
, accessed December 2007.
Viterbo, V.C., McLemore, V.T., Fakhimi A. and Sweeney, D. (in review) Effects of weathering on engineering
properties of the Goathill North rock pile at the Questa mine, New Mexico: Engineering Geology.
Wilson, G.W., Fredlund, M.D. and Fredlund, D. (2005) The influence of shear strength properties on the stability of
rock piles. Geological Society of America Abstract with programs, Vol. 37, No. 7, p. 395.
Geotechnical and Geomechanical Characterisation of the Goathill North Rock Pile
at the Questa Molybdenum Mine, New Mexico, USA L.A.F. Gutierrez, et al.
32 Rock Dumps 2008, Perth, Australia