Optimising for success at the Grasberg Block Cave

Abstract

At PT Freeport Indonesia's Grasberg mining complex, the Grasberg open pit is scheduled to cease production in early 2019. Mining of the Grasberg deposit will then transition to the underlying Grasberg Block Cave (GBC) mine, with initial undercutting currently planned for late 2018. The GBC is projected to become the district's flagship underground mine for the next two decades. Early-stage production areas at the GBC are hosted within a heterogeneous rock mass. The footprint will be subjected to variable abutment and cave loading conditions. Mine design and sequencing adjustments, combined with customised ground support options, continually evolve to improve footprint reliability and permit a favourable transition between open pit and underground operations. This paper provides a snapshot of strategies employed to promote the successful caving operation at the GBC mine.

Early experiences from the Grasberg block cave: A rock mechanics perspective

“…Prior to undercutting, a number of mine-scale design changes were implemented based on an improved understanding of geological and stress conditions (Campbell et al 2018). Specific to the undercut and extraction levels, changes focused mainly on undercut and development sequencing, the prioritisation of various blocks within the footprint and the transition from pit operations.…”

“…The diorite is typically massive to semi-massive characterized by poorly developed jointing and moderate vein intensity. The mean intact strength of the diorite is approximately 110 MPa (Campbell et al 2018). Field and laboratory observations at the GBC have recently shown that veining plays a key role in rock mass strength reduction (Bewick et al 2019).…”

A case study for rebar-reinforced shotcrete arches and void filling at the Grasberg Block Cave mine, Indonesia

“…Geological condition is one of the key parameters of developing drifts in the GBC due to a wide range of complex lithological units dominated by tertiary dioritic-monzonitic intrusions of Grasberg Igneous Complex and sedimentary country rocks associated with strike-slip faulting (Campbell et al 2018). This complex lithology condition, combined with geological structures, results in poor and very poor ground conditions in several areas including the Drainage Drift 4 (DD4).…”

Development, reconciliation and visualisation of hang-up frequency and fines entry forecasts at PT Freeport Indonesia

“…Both mines have broken through into overlying mines with GBC into the GRS and DMLZ into the Deep Ore Zone (DOZ) panel cave mine. Although the GBC and DMLZ both face their own challenges due to nature of mass mining, style of deposits, interactions with overlying mines and location in mountainous terrain with high rainfall, both mines share a common challenge related to oversize and fines management (Campbell et al 2018;Nugraha et al 2020;Priatna et al 2020).…”