Modeling of a uranium resource is the first and most important step in selecting a mining method that will optimize exploitation of a mineralized deposit. The term resource as used in this discussion is defined as any anomalous higher concentration of uranium. Mining methods considered are underground, open pit and in situ leaching (ISL).
The parameters used in modeling the resource will provide the physical data pertaining to the uranium occurrence and host rocks necessary to select a mining method as well as associated costs.
Whether or not the resource can be exploited for a profit will not be determined in this phase of evaluation. It should be noted which ever mining method is selected, it must always provide for the health and safety of workers under the ALARA (as low as reasonably achievable) principle.
The following list includes parameters that must be considered when modeling a resource:
The physical location and the land status or ownership of the resource is of primary importance in selecting a mining method. The physiography of the land, populated areas and regulatory constraints may dictate how the resource must be exploited even though all three mining methods could be utilized.
Resources discovered beneath bodies of surface water (lakes or rivers) or in aquifers may only be mined by underground methods or in situ leaching eliminating the open pit method, except in special cases.
This may also be true in populated areas where access to the resource is only possible by in situ leaching or possibly underground methods. Environmental, governmental and mining regulations and moratoriums may have the most influence on determining the method used to mine a resource. For example, regulations may prohibit major surface disturbance or surface stockpiling which would eliminate underground or open pit mining methods to exploit the resource leaving in situ leaching as the only viable mining method. For the above reasons, it is extremely important to know and understand the physiography of the land and the regulations pertaining to the area under which the resource has been located.
4.2. SHAPE
The shape of the resource is determined by various geological and or geophysical techniques including surface sampling, surface drill hole data (core, cuttings, electric and gamma logs) and radiometric surveys will certainly aid in determining the optimum mining method. The shape of the resource varies from long, narrow, continuous or discontinuous sinuous trends, to layer types of occurrences, to thick (ranging in excess of 30 metres) massive deposits. By itself, the shape of the resource may be exploited by all three mining methods. However, the optimum method can only be determined upon completion of the model.
4.3. SIZE
The quantity and quality of the resource must be determined to be able to select the most efficient and economic mining method. Sufficient geologic data must be gathered to permit accurate calculations of the volume, tonnage and grade of the resource. The data required to make these calculations will come from surface drilling (core and down hole electric and gamma logs) for deeper mineral occurrences; and radiometric surveys and pit sampling for near surface anomalies.
4.4. DEPTH
The depth of the resource will generally be determined from surface drill hole data (core and down hole electric logs). This information is usually the deciding factor in choosing the conventional mining method to be used either open pit or underground. Occasionally both methods should be employed based on the configuration and continuity of the resource extending from the surface to depths
beyond open pit limits. For underground mining methods, the depth of the resource is used to determine shaft depths or decline length and subsequent construction costs, and the number of mining levels required to efficiently and economically expedite exploitation of the deposit.
4.5. ORIENTATION
The orientation or attitude of the resource can range from horizontal to vertical and will generally be determined from surface drill hole data. This is a dimensional feature that must be considered when selecting a mining method. For example, uranium mineralization occurring in sedimentary rocks generally follows the bedding which can be flat lying or follow the dip of a particular stratigraphic unit as opposed to breccia pipes which stand nearly vertical.
4.6. GEOTECTONICS
Geotectonic data is the basic information obtained from surface mapping and surface drill holes that defines structural features and host rock types associated with the resource. Based on this information a mining method can be chosen as well as making the initial selection of equipment that will support the mining method. Both production rates and manpower requirements can be established allowing for labor and equipment costs to be determined. In addition, the competency of the host rock can be determined thus allowing for selection of ground support materials and associated costs. This is a major step in the preparation of a mine feasibility study. The information gained from this parameter is important for evaluating in situ leaching (ISL) projects as well as selection of an optimum conventional mining method.
4.7. MINERALOGY
The mineralogy of the resource is very important, as it will determine to a large extent the method of extraction and recovery. Some minerals will be difficult to extract and recoveries will be poor.
In some cases, minerals that are not amenable or cannot be mobilized by in situ leaching (ISL) techniques would eliminate this method of mining.
4.8. HYDROLOGY
The hydrologic conditions associated with the mineralization is one of the most important parameters to be established when modeling a resource. Dry conditions would certainly eliminate in situ leaching as mining method. In a wet environment, particularly in an aquifer, the determination of the host rock permeability and porosity is paramount. This data is used to determine production pumping rates (gpm or m3/h) for in situ leaching as well as draw down information of underground and open pit mining. The number of de-watering wells, the number of pumps and sizing can be made with their respective costs. In some cases freezing techniques must be employed when other methods to control water are unmerited. Again the cost of this technique can be determined.
4.9. BOUNDARY CONDITIONS
Knowledge of the boundary conditions of the resource for underground mining is essential for detailed mine planning and ore reserve estimation. The geology of the resource (rock types and structure) is determined from detailed analysis of core and cuttings produced from surface drilling.
Knowledge of the hanging and footwalls will aid in selecting the method of underground mining to be used, the mining equipment, and the type of ground support required to exploit the resource.
Usually the above parameters to model a resource will provide the necessary information to accurately select a method of exploitation and to establish estimated costs of the mining operation.
Detailed evaluation and analysis of these parameters will also provide data for feasibility.