In our last article we introduced what makes block caving an interesting option to address today's challenges. In this post, we'll examine the parameters to take into account when considering block caving for your mine site.
The first step merely determines whether block caving is a viable option. Mineral resource, geomechanical, and economic considerations can help answer the first question: can we mine this deposit using block caving?
For block caving to be productive, it’s all about cavability, proper development, reliable mine design, and optimum production schedule. We will explore mine design and production scheduling in more detail later in this series. However, the essential first step must be to locate a subsurface commodity or commodities to determine the basics: what’s there, how much is there, what’s the potential value, what does it look like underground, and can it be block caved?
Exploration requires geological studies, site evaluation, sampling, drilling, and mineral resource estimation (*see Note). Geotechnical conditions such as orebody dimensions, inclination, mine site location, stresses, and strengths affecting cavability and fragmentation must be right for block caving to be feasible. Other important non-technical factors include the availability of labor and whether local communities and government authorities will permit the mining operation.
The goal is to end up with a 3D block model containing all the characteristics and attributes of an orebody and associated waste located in a potential mine area. This model becomes 4D when time comes in during the production schedule stage.
Mineral Resource and Geotechnical Conditions
Block caving is considered low-cost because gravity fractures the rock and cave propagation occurs without much spending on drilling and blasting. However, the underground orebody needs a certain geometry for block caving (a massive vertical column that can be undercut and blasted from below to fall into draw points). Geotechnical parameters should be known with such certainty to ensure that the ore will fragment and flow naturally using only gravity force or minimum drilling and blasting once the undercut is blasted and extracted. The mineral reserve must be large enough to feed an ore processing plant over time at an economically viable rate.
It must be stressed that, for the long-term success of the mine, cavability is crucial. If the rock doesn’t cave naturally, then more money must be spent later to drill and blast during operations.
Orebody dimensions, inclination, cavability, fragmentation, size of the caved material, and the mine site location will influence how engineers will configure draw patterns, draw point or draw zone spacing, layout design, undercutting sequence, and support system design.
There are some guidelines to start with, such as the SME Mining Engineering Handbook and Laubscher Manual on Block Caving. Lessons from successful caving projects and implementing knowledge of experienced caving engineers can provide measures to analyze the project.
Capital Costs
The development phase of a cave mine is more extensive than other mining methods and can take up to several years of advance work before any production, this includes establishing access to the orebody (shafts/inclined shafts), conveyor access, undercut level, extraction level, haulage level, ventilation level, development drilling, drawbell development, and drawpoint construction. It also includes installing extensive ground control technologies to stabilize development openings, using shotcrete, cable bolts, steel sets, arches, and so on.
The upfront studies, underground excavations, and undercut development operations represent relatively high initial capital costs compared with other mining methods.
Assuming the investment into mineral exploration leads to the discovery of suitable ore reserves, economics and cavability must be factored for the future success of a block cave mine. An optimized mine plan for a block caving design process will be economically viable over the long term.
In our next post, we survey the footprint and best height of draw (BHOD) of a block cave operation, including mine design, optimum level (levels) for extraction, BHOD, and the best tools that can facilitate the process of making these critical decisions
*Note: See our series on the use of Artificial Intelligence (AI) and Machine Learning (ML) for resource estimation.
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
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