Quiz 1 2021 Flashcards
Among the surface mining techniques, which ones are the most dominant with regards to (a) the number of operations, (b) economic value, (c) amount of raw material produced, (d) environmental impact.
a. Quarries. Low-value material therefore transport cost are a signifiant factor. To minimize transport cost quarries are open nearby where the material is needed. A lot of places need this material.
b. Open-pit: Mining high-value minerals yields most economic value per volume of material extracted
c. Strip Mining: Low-value material but huge available tonnages, leverages economy of scale to be most profitable which leads to huge tonnages being extracted
d. Mountain Top: mined area cannot be reclaimed in an easy way, Clearing before blasting leads to removal of trees and vegetations, biodiversity loss and adverse effect on water quality
Briefly discuss the relationship between semi-variogram and kriging (e.g what is the role of semi-variogram for the estimation process?)
The experimental semi-variogram provides information to derive semi-variogram model’s parameters such as the nugget effect, sill, range and anisotropies (through multiple variograms in different directions). The semi-variogram model is referred to during the kriging process to calculate the kriging weights then point grade estimation and also kriging variance.
As seen below, there are two proposals to operate a deposit through surface mining. Capare these options from economic and safety point of view. Also, to calculate the NPV of the project what additionnal stages and parameters are needed?
The 60’ pit is a superior option from an economic point of view and an inferior option from a safety point of view because slope grade is higher less waste material is needed to be removed but introduces more potential geotechnical issues.
To calculate the NPV we would need a complete mine plan which would take into account all the bloc’s economical value, all operational costs and extraction schedule.
Could you discuss the logic behind using (a) a cut-off grade in open-pit mines and (b) stripping ratio used in strip mines? In other words, why is not a stripping ratio used in open-pit mining of metallic deposit in general? Or why is not a cut-off grade used in strip mines of stratigraphic mineral deposits in general?
The stripping ratio is used in strip mining because this method is applied to very uniform and continuous deposits with neglected quality variability of the material (meaning the grade is considered fixed). Therefore, the main driver of performance is how many tonnes of waste material needs to be removed to extract the same amount of ore tonnage.
The cut-off grade is used in open-pit because this method is applied to vein type, disseminated metallic ores (hard rocks), or erratic stratigraphic units which have much higher quality variability of material (meaning that only selected blocks should extracted). The extraction selection criteria is determined by the cut-off grade.
Why are different equipment oftentimes used in large strip mining operations? For exemple, the dragline is used for overburden removal, and the electric power shovel is used for coal production. Briefly explain in the context of the case defined above. What are the parameters?
The goal is that the excavation and loading can be conducted in a continuous manner. Therefore, the equipment should be sized according to how much material needs to be moved. Since there is usually more overburden material to be removed than ore material its make sense to have a larger equipement removing the overburden (dragline) and a smaller equipment loading the ore (shovel).
As discussed, long-term open-pit mine planning has three sub-problems: determination of production rates or capacities, cut-off grades, and block sequencing. These three sub-problems are solved in a circular fashion. Why do we not determine the cut-off grade if capacities are not known previously? Why do we not determine the capacities if cut-off grades are not know previously?
If capacities are not known, setting a cut-off grade is difficult because capacities influence the operation costs related to economy of scale and therefore the amount of ore and waste processed, which affects the plant’s required capacity.
Conversely, without a known cut-off grade, setting capacities is challenging since the amounts of ore and waste material to be processed are unknown.
A mineral processing plant was designed according to an input grade range between 1.5 – 2.5 Cu%. Daily grades in the last 10 days fed into the processing plant are given as 1.4%, 4.1%, 2.7%, 0.7%, 3.3%, 2.4%, 0.9%, 1.3%, 1.6% and 2.6%. Do you observe problems in these deliveries to the processing? What are possible consequences of these problems? What solutions do you propose?
Yes there is a problem the grade being inputted are not from constant (stable). Grade sometimes higher than range sometimes lower than range.
The consquences of this problem are sub-optimal recovery and plant efficiency.
The solution is to use diffrent grade stockpiles to store the material and to blend the material for a constant (stable) input grade at the plant.
