EXPLORATION (Oveview)

Before any preparation for mining operations commence, it is necessary to know at least something of the resource to be exploited to be sure it will be an economic exercise. The gaining of information for this purpose is a process known as exploration. The process should include more than just geological factors and should include environmental and social factors as well.
How much exploration is required is a very difficult judgment to make. While there are certain legal requirements for Companies listed on the stock exchange with regard to the spacing of boreholes over a lease area in order to classify a resource (the JORC Code, the Australian Code for Reporting of Identified Mineral Resources and Ore Reserves), much more is required for mine planning and operational purposes. Ultimately it is an exercise in risk management – the greater the level of information obtained with regard to the planning and operation of a potential mine site, the lower the risk in relation to unforeseen factors which can greatly affect the mine's future profitability
Almost any form of exploration is expensive so as a general rule one should obtain as much information as possible from each individual operation. For example it may be desirable to drill a borehole at a location primarily to obtain coal quality information. However, having drilled to the seam it would be sensible to collect as much information as possible from that hole (e.g. gas content, immediate roof and floor materials, seam depth, etc) as the extra information would only necessitate incremental extra costs.
With most lease areas, something is likely to be known of the resource at the commencement of the project evaluation due to the conduct of earlier exploratory drilling by relevant government authorities. However, this information is frequently limited in nature and may only indicate that there is a resource of some sort present.
There is a wide range of exploration techniques available from very basic visual examination through to sophisticated geological processes, and a mixture of these is normally used.
A program could well follow a process as listed below, though the sequence may be a little different depending on time and resources available. There should be frequent reviews throughout, certainly after each phase, to see if information gained requires changes to the future work plan or if in fact it indicates that work should be postponed or even abandoned altogether.

1. The starting point of any exploration program would be a search of any publically available information related to the permit or lease area. This would particularly relate to drilling records or geological surveys (often provided as part of the Invitation to Tender documents) but should also include such items as climate records, land use and zoning, cultural or heritage reports. Historical records for the area may even be of use. Bore cores from old drilling programs may also be available for inspection.
   
2. Probably in conjunction with phase 1, enquiries should be made regarding availability of private information which may be obtained (possibly purchased). Such information may be obtainable from sources such as local water bore drillers, farmers on outcrop areas, planning and statutory authorities and similar sources and may also be available from other mining or oil interests (who may have had aerial surveys of some type carried out). In particular, information should be sought from any neighbouring or nearby mines as this latter source of information, if available, is of great value as seam conditions generally only change gradually over distance.
   
   
3. Also possibly in conjunction with phases 1 and 2, a visual inspection of the surface topography should be carried out. This can be done from the air to some extent but at least a large portion should be on the ground and probably on foot. Geological expertise is required on such exploration. Heritage/cultural expertise and botanical/zoological assessment will also be required at some stage, but unless access is particularly difficult these can be included at a later stage in order to defer costs which may not be required if the project does not proceed. These latter assessments will probably be required at an early stage if drilling is to be carried out.
   
   
4. A review of the above phases will often result in parts of the permit or lease being removed from any future exploration because that part of the resource will not be economic or be subject to surface constraints (water courses, dams, heritage buildings, archaeological sites, bridges, national parks, etc). It may also identify where drilling or other types of surface based exploration may be restricted for similar reasons.
   
   
5. At this point a decision has to be taken as to whether or not to carry out additional surface (possibly aerial) surveys such as magnetometer surveys (comprising detection of changes in the Earth's magnetic field at a localized level which indicate changes in mineralogy or the presence of geological features) seismic surveys (comprising the detection of surface initiated sound vibrations as reflected by underground strata and structures). This may be beneficial to assist in designing the best drilling programme or it may be preferable to carry out drilling first to decide if such surveys are worthwhile.
   
   
6. At some stage, a drilling exploration program will almost certainly be required. This will most likely involve cross measure drilling from surface to seam. At least some, if not all of these holes will involve coring of a substantial length of the strata and certainly of the seam itself. A proportion of the holes should also involve drilling below the seam(s) likely to be worked at least to the lowest seam in the sequence or at least to a depth which may be affected by any goaf above. Apart from standard geological information regarding strata sequences and thicknesses and possible indications of structures, any borehole can be tested for:
   
   • Coal quality and washability
   • Coal or rock strength and other properties
   • Stress magnitude and direction
   • Ground water information
   • Seam and surrounding strata gas content and composition
   It is not worth paying for information which will be filed and never used, but having to drill another hole later to collect information not obtained initially is very expensive. It is therefore usually worthwhile to maximize the information collected. Note that more than one core can be obtained from a single borehole, if required.
   

Usually, a drilling program will complete the exploration of a lease area, but it should be noted that not all the drilling may be done at the one time. It is only necessary initially to fully explore enough of the lease to ensure it is economic. Further exploration can be, and normally is, carried out after the mine has started, provided it is done in advance of the areas to be worked.
Some exploration may be carried out from underground once work sites are available, using in seam boreholes rather than drilling from surface. This has the advantages of reducing potential effects on surface areas and covering extensive distances in- seam and utilizing holes which have to be drilled for other purposes. However, it is more difficult to drill "cross measure holes" (holes which cut across layers of strata rather than follow them) ahead of the workings from underground if cross measure drilling is required.
Because of the expense involved with boreholes the possible use of exploration holes for other purposes or vice versa should also be considered. Coal bed methane production is becoming more common, whether primarily for gas production or to remove gas prior to mining. If these holes can be used for exploration without compromising their use for gas drainage then savings can be obtained.
There is a tendency in recent times to run mine services (air, water, power cables, etc) in boreholes rather than in drifts or shafts - exploration holes could be used for this purpose if the required location can be decided before the exploration is carried out. It is unlikely that exploration boreholes will be able to be used for such purposes unless a decision is taken prior to completing the holes and the holes are lined rather than being filled with cement or similar to prevent them becoming a potential water inrush hazard if intersected by mine workings.