Classical Methods for Estimating Ore Reserves
The classical methods of estimating ore reserves are:
Arithmetic Average Method
The contours are plotted on the plans or vertical projection. The area defined is determined by a planimeter or other method. The average thickness is estimated by the simple or weighted arithmetic mean. The average content and the density are determined in the same way. The body part between the inner and outer contour is generally calculated independently because the resources of this area are reported in a lower category.
Method of Geological Blocks
The ore body is divided into homogeneous blocks, essentially according to geological considerations. In this way, the ore body morphology (http://www.monografias.com/trabajos12/proce/proce.shtml) complex is replaced by a system of polyhedral prisms of height that corresponds to the average power within each block (Fig. 2.4). The contouring is done in any projection of the body. It is also necessary to assess the limits of the independent geological blocks.
Method of Exploration Blocks
Specific to underground mining, reserves of the deposit are calculated by the accumulation of reserves obtained from partial individual exploration blocks. Calculation blocks are bounded by portions of the reservoir on 2, 3, and 4 sides by digging, mining exploration, and development (counter-wells, short grain, galleries, trenches, etc.). The actual shape of the body within the block is replaced with a parallelepiped whose height is equal to the average power of the ore body in the block.
Method of Polygons
Used for the calculation of reserves in horizontal or sub-horizontal layers in regular bodies. If you calculate the reserves of a deposit under this method, the complex morphology of the reservoir is replaced by a system of polyhedral prisms, whose bases are the sites or areas of influence and its height is equal to the thickness of the body revealed in the well located in the center of the polygon. The method reduces to the separation of zones of influence of each well or tillage that intercepts the ore body. The establishment of zones of influence requires the following constructions:
Method of Contour Lines
The shape of the body is replaced by a volume equal to the natural body but bounded at its base by a straight plane (Fig. 2.6). This method begins with the drawing of maps of isolines (http://www.monografias.com/trabajos11/cartuno/cartuno.shtml) of the variables of interest (density, law, and linear density or booking). The isolines between the workings of exploration are built using the triangulation method with linear interpolation.
Method of Profiles
Can be used if the site was explored in a regular network that enables the construction of geological sections. The geological section of a site, depending on its orientation, can be horizontal, vertical, or non-parallel profiles. The distance from the special courts is not constant and corresponds to the distance between the scan lines in the case of vertical profiles or the height between levels of a mine in the case of horizontal cuts.
Airspace Reservations
- Tonnage (or volume) of exploitable material
- Average grade
- Cut-off grade
- The total economic value of these reserves
- Tonnage curves vs. grade
Extractable Reserves Selection
- Maximizing reservoir recovery (marginal)
- Maximization of stay in the mining business (cost-cutting)
- Maximizing the net present value (opportunity cost)
Marginal Criterion
Material is all treatment whose marginal cost is less than or equal to its marginal revenue. This definition allows to define a cut-off grade set at:
Formula: lcm = M / [(P – Cf) * Rc * RF]