Let’s talk block caving : Material flow

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In our previous article, we talked about mine layout and how long-term economic viability of a block caving operation is calculated based on how much minable reserves will flow down through multiple columns of ore over time. This flow represents one of the main differences between block caving and other mining methods in terms of its influence on production.

 

Material flow in block cave mining introduces uncertainties that can change production outputs. Production scheduling without consideration of material mixing can jeopardize the long-term goals of the project.

Fragmented rock in the caving zone doesn’t always move down to draw points below them. The material can flow between adjacent draw columns before being extracted due to varying particle sizes and velocities. Rocks can fracture in a number of ways, and the nature of block caving and material flow mixing introduces uncertainties in key parameters such as grade and tonnage.

Fragmentation in caving operations can be divided into three categories:

  • in-situ fragmentation, the natural fractures and discontinuities that exist within the rock mass.
  • primary fragmentation, which occurs when the particles detach from the cave back as the undercut is created and the caving begins.
  • secondary fragmentation occurs when the detached particles move within the draw columns in the caving zone.

This fragmentation and subsequent flow create uncertainties because parameters such as grade and tonnage are not fixed quantities. As a result, variability and randomness (stochastic) are injected into the process.

Fragmentation and caving stages

 

Material Mixing models

GEOVIA PCBC, the most used commercial software in block caving mines, is integrated into a general-purpose geological modeling and mine planning system so that it can be used for studies ranging from pre-feasibility to daily draw control. Various mixing tools include vertical and horizontal mixing, rilling, cone erosion, and toppling are modeled in PCBC. The mixing simulation in PCBC renders extraction from each active draw point period-by-period with modeling that captures uncertainties of material flow, optimizes the best height of draw, improves production scheduling, achieves production goals, satisfies project constraints, and maximizes NPV. The current main mixing tools in PCBC are Vertical Mixing, Template Mixing, Marker Mixing, and CA3D (Cellular Autonomous in 3D); depending on the purpose of the study and the specifications of the caving project, any (or combination) of the following models can be used:

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Firouz Khodayari

Firouz Khodayari​​​​​​​ is an industry consultant, author, and professional engineer with a PhD in mining engineering and more than a decade of international mine planning and optimization experience. He specializes in mathematical modelling and production schedule optimization for open pit and underground mining