Print4.1.2: Natural and Geologic Factors
The technical characteristics of the orebody, the geologic setting in which the orebody is found, and the surface features of the land over the orebody will influence significantly your choice of a mining method and the way that you will lay out the mine and supporting infrastructure. The most important natural and geologic factors that will be assessed include:
Topography
The location of your surface facilities, e.g., shops, warehouses, and roads, will be influenced by the topography. Mountainous terrain creates more challenges than a gently rolling countryside.
Spatial Characteristics of the Orebody
The depth, size, shape, and attitude will have a major impact on the type of mine and mining operation that you can have. A shallow orebody allows consideration of a surface rather than underground mine. A large orebody allows for larger-scale and potentially cheaper bulk methods, and a long life means more time to recover certain costs. The orebody may be tabular in shape, which lends itself to certain types of mining, or it may be a big amorphous blob, or perhaps the ore is contained in sinuous veins. These shapes, in conjunction with other characteristics, will suggest certain mining methods. And finally, there is attitude. The attitude of the orebody is important. After all, who wants to develop a mine in an orebody that has a bad attitude! Just kidding... attitude is a term for the angular orientation of the orebody, and, in particular, we are interested in the vertical angle of the orebody. If the deposit is flat lying, the vertical angle or dip is zero degrees. As we begin to tilt one end of the orebody downward, the dip angle is measured with respect to the horizon. Steeply pitching ore bodies with dip angles of 70 degrees or more are not uncommon. As it turns out, some mining methods require steeply pitching deposits, while others work best with dip angles approaching zero degrees.
Geomechanical Properties of the Orebody and the Surrounding Rock
Undoubtedly, we will want to create openings in the orebody or the surrounding rock as part of the mining process. How difficult will it be, and how much energy will it take to break the ore and the surrounding rock? Will explosives be required? Once we remove a section of ore, will the opening be stable, or will the surrounding ore rush in to fill the void? When the ore is removed will the surrounding rock remain stable, or will it fracture and cave-in? The answers to these questions depend largely on the mechanical properties of the materials. Compressive strength, modulus of elasticity, hardness, and abrasiveness are some of the important properties that will determine how challenging it will be to safely and productively operate the mine. We can take core samples and conduct laboratory tests to quantify the characteristics, and we can avail ourselves of any data that others have compiled on similar deposits.
Geology
Structures such as cleavage patterns, joint sets, and faults can significantly affect the mineability as well as the stability of the materials, regardless of certain mechanical properties such as strength. The stratigraphy, or layers of rock formations, is important in the design of many mine types. The mineralogy of the deposit and the genesis of the orebody will give us an indication of both mining and subsequent mineral processing challenges. The presence of thermal gradients will likely require expensive cooling of the ventilating air. Water-bearing strata or aquifers will increase the complexity of the mining as we work to protect them as well as to deal with groundwater inflows to the mine. There are other examples that will be considered early in the evaluation process, and this once again illustrates the importance of including geologists on the team.
Ore Beneficiation
The ore has physical and chemical properties that will affect the way in which we extract the valuable components from the mined ore. Some copper ores are easier to process than others based on the mineralization, orebody genesis, and so on. These factors will affect the cost of the mineral processing and will be examined before a decision to move forward with the project is made.