Open cut or surface mining in coal is a suitable choice when coal seams are closer to the natural surface. It is an effective method of retrieving a higher proportion of coal when compared to underground mining.
The basic process involves:
2) Geological Modelling
3) Mine Design
4) Top Soil Stripping
5) Drilling & Blasting
6) Pre-strip Operations
7) Dragline Operations
8) Coal Mining
Basic graphical overview:
(Source: World Coal Institute - http://www.worldcoal.org/coal/coal-mining)
In any mine, regardless of the mineral - exploration has to be completed to determine where minerals exist, how deep they are, the amount of resources available and to determine the quality of the mineral. This is done using exploration drills. Surveying involvement at this stage is generally through recording the positions drilled as well as seismic surveys to help determine what is in the ground.
Geological modelling involves reviewing and modelling the data from exploration to determine what inconsistencies exist and to establish a general plan for mining which will make best use of resources and equipment.
Engineers design plans for safe and cost effective mining of the mineral. These plans are what Surveyors are required to set out in order for machinery to begin work.
Top Soil Stripping
Top soil is easy to dig as it is usually soft. The machinery will remove this material and usually store it in a stock pile for later rehabilitation use. At all stages of material movement in mining, surveyors record the amount of material moved. They will also keep records of top soil stockpiles for later use.
Drilling & Blasting
Once top soil has been stripped, hard rock or earth material will be discovered. As this material is too hard to dig, it has to be exploded first. Overburden drills are used to drill a 'pattern' as designed by engineers and are then packed with explosives and are subsequently detonated. Surveyors can be used to set out pegs for each hole or line of holes to guide the drills, however in some cases the drills can be fitted with GPS and are able to drill a pattern without pegs. In the event of a misfire (e.g. explosives doesn't detonate), surveyors will locate the suspected misfire and place pegs in the area for machines to remove any remaining explosives carefully prior to normal excavation procedures. When an explosive device such as a booster is located in shot ground, surveys will take a record of the position it was found and keep a permanent record of this.
Once blasted, overburden can be dug using excavators, shovels and use rear dump trucks to move the material. Depending on how many seams of coal are being mined, excavators and shovels are generally used to uncover the more shallow seams and to dig a strip deep enough in preparation for a dragline. In smaller mines and pits, the entire operation can be completed without a dragline. Surveyors place pegs at protected batters for these machines to follow and to dig to the appropriate position at the design level (design level may be at a desired level or on top of coal). Surveyors also 'locate' or 'pickup' a 3D area of materials moved to calculate volumes. If an excavator is being used to uncover coal, surveyors will be involved in doing a pickup of the coal 'roof' (top of coal).
Draglines are large machines that can move a lot more materiel quicker than a truck and shovel or excavator combination. They are effective in moving overburden from above the coal to a 'spoil' pile within the length of the boom of the dragline. Therefore; trucks are great to move material to an extended distance from the pit, but draglines are great to move material quickly but to a limit distance. Surveyors place pegs to allow a dragline to be in the optimum position at all times. The dragline will generally take a few passes, as it is limited by the length of it's boom while the width of the pit is usually longer than this. While uncovering coal, draglines are also used to dig a ramp down to the coal which trucks can haul on. Surveyors will also set out the appropriate dig limits for the ramp design as well as complete pickups on the material moved by the dragline and the 'roof' of the coal as it is uncovered.
Once coal has been uncovered by either an excavator or dragline, an excavator and truck combination are used to mine the coal. To ensure coal is mined optimally as well as accurate reconciliations, surveyors complete a pickup of both the top of the coal (roof) and once removed, the bottom of the coal (floor). Therefore it is usually a good practice to remove the overburden from above the coal prior to digging the coal. In some mines with large coal seams, a bucket wheel excavator can be used to mine the coal. Surveyors have daily involvement in the coal mining process to ensure that they do not miss any important pickups before it is no longer available. Surveyors will also keep ongoing plans of coal mined to ensure accurate records of what material remains and that none is left behind. Any coal stored in stockpiles will also need to be surveyed monthly, this can be by conventional methods of aerial flyover data.
Rehabilitation is an important part of the mining process, especially in opencut mining. As the land being mind is massively disturbed, the intention of rehabilitation is to try and reproduce a 'natural' landscape once the mining process is over. Mines will generally have yearly targets of land area which they are required to rehabilitate. The rehabilitation process usually involves flattening land to a safe and natural looking grade, covering it with top soil and spreading seeds to encourage the growth of plants. Surveyors are involved in setting out the areas to be rehabilitated, maintaining records of areas rehabilitated as well as monitoring the use of top soil from stockpiles used in the rehabilitation process.
Once coal has been mined, it can't just be loaded onto trains. It has to go through a preparation process to remove waste materials and to ensure the best quality. This is where a coal preparation plant comes into play. In most mines, the coal will be transported from dump stations to a preparation plant using conveyor belts. It is washed and stacked at the wash plant until it is ready to be loaded onto trains.
Transporting coal from a mine to an export facility can account for a large proportion of the expenses in mining. Mines must establish contracts with the train company (e.g. Queensland Rail) which will outline how much coal they can transport in any year (and therefore the transport availability guarantee for this purpose). Coal stored at a wash plant is loaded onto coal trains through large hoppers, however in smaller mines machines such as front end loaders can be used to load the coal. Some smaller mines may also determine it is more feasible to transport coal by trucks to the closest railway loading facility as opposed to funding an expansion directly to the mine.
Once loaded onto trains, the coal is transported to an export facility. Major coal export ports in Australia are located in New Castle, Hay Point, Gladstone, Abbot Point, Port Kembla and Brisbane. These ports have equipment for taking the coal off the trains and loading onto bulk carriers.