Archives: Knowledge Base

Mining often requires penetrating the local and regional water table. This creates inflows, which if the area is wet and the country rock highly permeable, becomes at best a nuisance to operations and at worst an extreme hazard. Effective dewatering creates dry working conditions which are preferable as they reduce risk, reduce wear and tear on machinery, reduce earth moving costs, improve slope stability for open pits and therefore improve safety. Dewatering success is directly linked to a detailed understanding of the
groundwater regime enabling application of the best strategy to intercept groundwater inflows. Options available are both passive and active methods including detailed stormwater design, drainage trenches, drain-holes, pit-perimeter pumping boreholes (wells), in-pit boreholes, sumps, dewatering galleries, or a combination of methods. A phased approach assists with logically managing the data, information and knowledge for use in dewatering design and implementation.
The potential effects of groundwater inflows should be assessed at the pre-feasibility stage but can be done at any stage of the mine life. A hydrogeological investigation is best tackled in three phases. The first phase is a desktop study to identify the problem, collect site data, create a detailed initial conceptual hydrogeological model then use the information to identify the most practical options for water control.
Phase 2 comprises numerical modelling of the conceptualisation, supported with accurate and interpreted monitoring data. The objective is to use predictive simulations of dewatering options to determine the best strategy for water control. Phase 3 sets dewatering targets to support the mine design, creates an initial dewatering design then implements a prototype to test the concept. Success is evaluated, and the design improved to increase efficiencies and enable full implementation. The phased approach is iterative as the conceptual and numerical models are regularly updated, recalibrated with the latest monitoring information, and used to review and implement the dewatering strategy. The monitoring network is continually improved, and the phased approach repeated annually to ensure water control objectives are met for each stage of mining. This paper is an update of the IMWA paper Morton et al. (1993) which is still widely read.

K.L. Morton and W.L. van HeerdenKLM Consulting Services Pty Ltd, South Africa AbstractThe monitoring of movement of a tailings storage facility (TSF) is often too […]

Alastair B Bovim, Kym L Morton²Insight Terra UK Limited, 112 Jermyn Street, St James, London,²KLM Consulting Services Pty Ltd, 22 Central Road, Sunrella AH, South, […]

Kym L Morton, Barry D Millsteed, Wayne van Heerden, Moses Msitsini AbstractAfrican mines are predominately located in hard rock. Inflows to the underground or surface […]

Valuable groundwater information becomes available as soon as drilling starts, particularly during early mineral exploration campaigns. Often the information is not collected as the value does not become evident until the exploration sites become a mine. This paper describes what information can be collected very inexpensively during exploration drilling and how drill holes can be used to create an early monitoring network for the collection of water levels across the site. Examples of logging sheets, daily drill records and construction designs for monitoring boreholes are provided.
During drilling and logging of exploration coreholes the emphasis is all on characterising the orebody. Drilling methods include rotary, air percussion and core drilling. All encounter water and, with very little effort, the information on water intersections, drilling fluid circulation losses, basic water chemistry and rest water levels can be collected by the drilling contractor and the site geologist, under direction from the project managers.
If the basic information is captured, then this significantly reduces the cost of the initial hydrogeological study for the pre-feasibility reports. Some of the holes can be equipped for use as water level monitoring boreholes or preserved for use at a later stage. Old core holes that are not sealed can create conduits for underground inflows when the mine is developed.
Decision criteria are provided for the use of the hole after drilling to optimise information from all drillholes and reduce risk when mining commences.