Slope Optimization For The Hypogene Project (Esteban Hormazábal, Mauricio Tapia, René Fuenzalida & Gabriel Zúñiga, 2011)

Proceedings, Slope Stability 2011: International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Vancouver, Canada (September 18-21, 2011)

Slope Optimization for the Hypogene Project at Carmen de Andacollo Pit, Chile
E. Hormazabal Principal Geotechnical Engineer, SRK Consulting, Chile M. Tapia Senior Geotechnical Engineer, TECK Carmen de Andacollo, Chile R.Fuenzalida Senior Geotechnical Geologist, TECK Carmen de Andacollo, Chile G. Zúñiga Senior Geotechnical Geologist, SRK Consulting, Chile

Abstract
Teck Carmen de Andacollo is currently developing the first benches of the hypogene project below the current supergene open pit operations at the Carmen de Andacollo pit.The Carmen de Andacollo pit is located in central Chile, adjacent to the town ofAndacollo, approximately 55 kilometres southeast of La Serena and 350 km north of Santiago. The mine is located near the southern limit of the Atacama Desert at an elevation of 1,000 m. This project involves the use of steeper slopes below the current supergene benches. A geomechanical assessment is being carried out to evaluate the stability of the walls of the final open pit and several mining phases,particularly in sectors where the rock mass is of poor geotechnical quality. To evaluate the mechanical stability of the open pit, a series of geomechanical studies have been performed. These studies have allowed the definition of structural domains, and geotechnical units as well as the creation of a 3D geotechnical model and slope stability analyses based on limit equilibrium methods and finitedifference numerical models. This paper describes the methodology used, slope stability analyses carried out and the slope design proposed for slope optimization, considering the influence of major faults.

1

Introduction

The Carmen de Andacollo (CDA) pit is located in central Chile, adjacent to the town of Andacollo, approximately 55 kilometres southeast of La Serena and 350 km north ofSantiago (Figure 1). The mine is located near the southern limit of the Atacama Desert at an elevation of 1,000 m. Carmen de Andacollo is an open pit mine which produces copper in concentrates from the hypogene portion of the orebody. Copper cathode production from the supergene portion of the orebody is currently approaching completion. The mine’s life was recently extended by approximately 20years with the achievement of commercial production at its new copper concentrator.

2

Engineering geology

The main rock types in the Carmen de Andacollo area are the Lower Volcanic Unit, Upper Volcanic Unit, Intrusive Rock Unit, Breccia Unit, Undifferentiated Rocks, and Gravels. Lower Volcanic Unit: This corresponds to a volcanic sequence mainly formed by andesitic flows and autobrecciaswith smaller interspersed tuffs and volcanoclastic rocks. Lithologies included in this unit are Coarse Porphyritic Andesite (APG), Microporphyritic Andesite (AMIC), Medium Porphyritic Andesite (APM), Amygdaloidal Andesite (AAMI), Fine Porphyritic Andesite (APF), Andesitic Breccia (BXA) and Aphanitic Andesite (AAF).

Figure 1.

‘Carmen de Andacollo’ mine location.

Upper Volcanic Unit: Thismostly corresponds to pyroclastic rocks that are distributed on the Lower Volcanic Unit. From an economic point of view, the current work acknowledges the permeability of its texture, which greatly favoured the invasion of hypogene mineralizing solutions, as a fundamental characteristic of this Unit. Lithologies defined in this Unit are Crystalline Tuff (TBC), Vitreous Tuff (TBV), Trachytic Lava(LTR), Lithic Tuff (TBL) and Volcanoclastic Rock (VCL). Intrusive Rocks Unit: They cut all previous stratified units. They correspond to stock and dikes of rhyolitic, granodioritic, dacitic and andesitic composition. The first group of these lithologies, predominant orientation NW, is directly related to alteration-mineralization events which gave rise to the ore: Granodioritic Porphyry (PFE):...