Open-Pit Mining Production
With the rise in prices of metallic commodities and minerals, previously overlooked low-grade mineral resources are now attracting the interest of mining companies. Additionally, establishing order while operating high-tonnage shallow ore deposits is crucial. The initial investment costs, revolutionary machinery technology, and the modernization of open-pit operations that enable faster ore production have become unavoidable. The habits of traditional miners often fall short in addressing the challenges faced when operating many low-grade resources today. Therefore, regardless of the commodity, mechanized mining using modern methods is emerging as a necessity, not a luxury.
In this article, we will examine step-by-step how systematic production is carried out in modern open-pit mining.
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In order for open-pit mining to be carried out smoothly, efficiently and sustainably, a complex process management is required. When the high production tonnage per unit time and the burden of downtime and loss caused by the problems to be experienced are considered, it makes the system established with experience important. This process starts with the analysis of orebody models obtained from exploration studies and continues with the creation of the final pit plan. Supported by operation design, production arrangement, grade control procedures and efficiency-enhancing measures, it aims to both reduce costs and increase resource production efficiency in open pit operations. Let’s consider the steps in order for personnel from different disciplines to come together in an open-pit and create a systematic ore production cycle.
1. Exploration – Modeling - Open-Pit Design
The final pit plan (Pit Shell) is made for the section to be taken with open pit based on the resource model created by exploration drillholes & field data. Stages are created within the final pit plan in order to ensure a regular ore production flow by considering the ore/waste ratio.
It is useful to examine the stages of creating an orebody model (wireframing) in a basic way.
2. Determining Open Pit Production Levels
In line with the standards determined by the meeting to be held at the beginning, firstly the floors (elevation/level/RL) are taken as basis, the slices/segments defined for each level are excavated one by one and the pit plan is executed. In open pit mining terminology, the production floor/elevation/level always represents the altitude value of the surface we step on, this altitude may not always be the height relative to sea level.
3. Production Plan Cycle Decision
Modeling, open pit planning, survey, production and grade control teams/departments meet to determine standards, determine the direction of pit work and slice directions, and reach an agreement for the “production cycle”. The basic motivations of the departments/teams are generally as follows, and are not limited to the ones given. However, mastering the type of mineralization and formation dynamics is of great importance for the decisions to be made.
- Modeling: Watches the orebody direction and dipping, the potential resource development and exploration direction. It also watches the model block sizes according to the bucket volumes of the excavators (excavators, loaders, draglines, etc.) in the machine park.
- Open Pit Planning: Watches the stage productions based on expectations about resource, optimization of the production excavation elevations/levels according to the machine park. And also sets up the cut-off grades.
- Production: Watches the floor heights, slice widths, slice working direction, the pit road route for support and logistics, and the expected slope. Excavations in each slice are generally started from the slope direction of the ore body (from the hanging wall to foowall). The direction of movement of the excavator bucket and the position of the ore body must be optimized to ensure the most efficient and cleanest excavation possible.
- Survey: Sets the type of projection to be used, and the line naming according to the model rotation if it is applied.
- Mine Geology: Watches the most appropriate method for grade control such as line/channel sampling or sampling from blast holes and the creation of the grid, the production slice height in order to optimize the number of representative samples per ton and the number of floors that the grade control will represent. Grade control work may not be performed on every floor, and there may not be a need for grade control in every region of the floor, those who perform the work follow-up can speed up production by paying attention to these with drillholes and resource models, and can include extras outside the model in production without missing.
4. Determining Production Slices (Segments) and Production Direction
The longest and shortest axes of the orebody are determined. Generally, slices parallel to the short axis are named with the last 3 or 4 digits of the latitude or longitude (UTM) value. Considering that the same lines represent slices, especially grade control lines, this slice naming, which will be the address for production, should be known by all personnel. This terminology regarding systematic operation, which seems difficult, will be adopted by all supervisors, workers and contractors spontaneously during the process and will show its benefits in a short time. Generally, the main road route is given from the downhill side of the long axis and slices are started to be excavated from this side. Generally, the slice excavation progress direction is determined to start from the orebody dipping direction (Hanging wall side) of the short axis and thus the production cycle is started.
5. Open Pit Grade Control and Mark Up
In the slices where the production excavation is completed, grade control work is carried out for the base. Afterwards, drilling and blasting is carried out in the area where the grade control process is completed. During this time, the lines that come with the grade control work results are evaluated and the production “mark up” map and slice information are created and given to the ore pointer/sampler (Spotter) and the survey department. Along with the document, the ore pointer (Spotter) and survey personnel make the top mark using rock pieces, spray paint, and tape in the area where the blasting has been completed.
It would be useful to review the open pit grade control program.
6. Ore Production Excavation
Production excavation is directed by the relevant ore spotter personnel by considering the mark up made on each floor and the slope of the ore. Production is continued by making the mark-ups again on the intermediate floors. The excavator deployed in the production area climbs up to the slice, unearths the material along the designated production direction, and loads it onto the trucks. Spotter standing at a suitable distance helps the operator to distinguish the ore type contacts. The spotter also directs the truck drivers, who are loaded by the excavator, on where to dump the ore in the stock area. The spotter guides the whole production excavation, ensures that the ore is stacked in a clean and orderly manner in the desired grade categories and keeps the necessary records for production.
7. Assigning Grade Value to Production (Valuation)
The grade is calculated based on the “grade control model” updated with the results obtained from the grade control program, and the grade is updated based on the part of the depleted volume, and the status of the relevant stocks is updated. As a result of the consumed slices, grade control is performed again on the lower floors in the area cleaned, and the cycle continues.
8. Conclusion
When a certain order is established in the pit operation, multiple excavators are operated simultaneously on different floors to ensure a fast and problem-free production cycle.
Open pit geologists who conduct grade control work should lead production. They should be familiar with mineralization and faulting, and should always be one step ahead to inform spootters and production engineers.
In the past, the production cycle was attempted to be carried out by self-taught miners without a specific order. Especially the fact that mechanized mining has increased tonnage and current commodity prices have made ore extraction efficiency important has made “grade control” work a necessity rather than a luxury.
In short, it is the duty of the “Mining Geology Department” to ensure that ore production in the open pit is carried out sustainably and problem-free, and to record the value of the excavated ore and stock it in the cleanest way.
Au, Ag, Pb, Zn, Fe, Cu, Ni, Cr… No matter what ore or commodity you are producing, grade control studies allow you to effectively control and manage all processes from production excavation to the final product.
Subjects discussed in this article may overlap with your mineral exploration, modeling, mining operation and business development issues and may provide solutions for those. However, remember that various factors specific to your business may bring about different challenges. Therefore, seek support from expert consultants to evaluate all data together in order to convert potential into profit most efficiently.
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