Importance of Geology in Cave Mining

Abstract

Editor’s note: The Geology and Mining series, edited by Dan Wood and Jeffrey Hedenquist, is designed to introduce early-career professionals and students to a variety of topics in mineral exploration, development, and mining, in order to provide insight into the many ways in which geoscientists contribute to the mineral industry. Abstract Cave mining methods (generically referred to as block caving) are becoming the preferred mass underground mining options for large, regularly shaped mineral deposits that are too deep to mine by open pit. The depth at which caving is initiated has increased over the past few decades, and operational difficulties experienced in these new mines have indicated the need for a much improved geologic and geotechnical understanding of the rock mass, if the low-cost and high-productivity objectives of the method are to be maintained and the mines operated safely. Undercuts (the caving initiation level immediately above the ore extraction level) are now being developed at depths of >1,000 m below surface, with the objective of progressively deepening to 2,000 and, eventually, 3,000 m. Many of the deeper deposits now being mined by caving have lower average metal grades than previously caved at shallower depths and comprise harder and more heterogeneous rock masses, and some are located in higher-stress and higher-temperature environments. As a result, larger caving block heights are required for engineering reasons; mining costs (capital and operating) are also escalating. In these deeper cave mining environments, numerous hazards must be mitigated if safety, productivity, and profitability are not to be adversely affected. Fortunately, potential hazards can be indicated and evaluated during exploration, discovery, and deposit assessment, prior to mine design and planning. Major hazards include rock bursts, air blasts, discontinuous surface subsidence, and inrushes of fines. These hazards are present during all stages of the caving process, from cave establishment (tunnel and underground infrastructure development, drawbell opening, and undercutting) through cave propagation and cave breakthrough to surface, up to and including steady-state production. Improved geologic input into mine design and planning will facilitate recognition and management of these risks, mitigating their consequences.