Authors: Becerra Abregu, GA; Valencia Jeri, E; Garcia, E; Yuan, P; Byers, T

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Becerra Abregu, GA, Valencia Jeri, E, Garcia, E, Yuan, P & Byers, T 2013, 'Case history: deep-seated slope failure in weak rocks, El Tapado pit north wall, Yanacocha operation', in PM Dight (ed.), Slope Stability 2013: Proceedings of the 2013 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 409-423,

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The Yanacocha Operation is an open pit gold mining operation in the Andes Mountains of Northern Peru. Since 1993, mining at Yanacocha has occurred in eight large pits, and several smaller pits. Mineralisation typically occurs in hydrothermally-altered volcanic rocks. Weak rocks at Yanacocha include argillically- and propylitically-altered volcanic rock masses, which are often in sharp contact with higher-strength rock masses with silica and silica-alunite alteration. Although mineralisation generally occurs in the silica-altered rock masses, pit slopes are developed in part in the weaker rocks. In October–November 2010, a deep-seated instability was identified in the north and northeast walls of the El Tapado (ET) Pit. The implications of the instability were substantial, in that it put up to 400,000 ounces of gold at risk in the ET Pit; and affected the planned production schedule for the adjacent El Tapado Oeste (ETO) Pit, as much of the waste from ETO was to be placed as backfill in the ET Pit. This instability also possessed the potential to propagate beyond the pit crest, and impact the stability of a large waste dump and a main haul road located just outside the pit limit. Mining in the area of the north wall was discontinued between December 2010 and July 2011 to allow for: Mining resumed in July 2011, subject to slope displacement monitoring, and a process of continuous input and review from the site Geotechnical, Hydrogeological, Planning, and Mine Operations groups; and a group of external geotechnical and hydrogeological professionals. The ET Pit was completed successfully in July 2012. This case history summarises the conditions that contributed to the instability in the ET North wall; characterisation and mitigation work that contributed to a decision to proceed with mining; and results of subsequent pit development.

MYSRL Operation and Planning Departments (2010–2011) Internal documents of strategic planning and mining to stabilize El Tapado north wall.
MYSRL Hydrogeological Department (2010–2011) Internal documents for depressurization of El Tapado north wall.
Perez, V., Robles, H., Soto, F., Beale, G. and McGlone, M. (2011) The role of depressurization in stabilizing a large pit slope in Northern Peru, in Proceedings International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering (Slope Stability 2011), E. Eberhardt and D. Stead (eds), 18–21 September 2011, Vancouver, Canada, Canadian Rock Mechanics Association, Canada, CD-rom only.

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