Coal Resources is part of the coal deposits that are expected to be utilized. These coal resources are divided into classes of resources based on geological confidence levels determined qualitatively by geological conditions/levels of complexity and quantitatively by information point distance. These resources can be increased into reserves if after a feasibility study is declared feasible.
Coal Reserves are part of a known coal resource of dimensions, quantity distribution, and quality, which at the time of feasibility assessment was declared feasible for mining.
Classification of coal resources and reserves is based on geological confidence levels and feasibility studies. The grouping contains two aspects, namely the geological aspect and the economic aspect.
Resource Class
1. Hypothetical Coal Resource
Hypothetical coal resources are coal in the investigation area or part of the investigation area, which is calculated based on data that meets the requirements set for the survey review investigation stage.
A number of uns not-yet-found classes of resources are the same as coal reserves that are expected to exist in the same coal regions or regions under geological conditions or the expansion of renewable coal resources. In general, resources are located in areas where sampling points and fiber measurements of evidence for the thickness and presence of coal are taken from distant outcrops,mines, quarry holes, and wells. If the exploration states that the truth of the resource hypothesis and reveals sufficient information about its quality, quantity and rank, then they will be reclassified asidentified resources.
2. Inferred Coal Resource
A tereka coal resource is the amount of coal in the investigation area or part of the investigation area, which is calculated based on data that meets the conditions set for the prospecting investigation stage.
The observation point has a considerable distance so the assessment of the resource is unreliable. This area of resources is determined by the projection of thickness and soil cover, rank, and data quality of the measurement and sampling points based on geological evidence in an area between 1.2 km – 4.8 km. including anthracrate and bituminus with a thickness of 35 cm or more, sub bituminus with a thickness of 75 cm or more, lignite with a thickness of 150 cm or more.
3. Indicated Coal Resource
The designated coal resource is the amount of coal in the investigation area or part of the investigation area, which is calculated based on data that meets the requirements set for the preliminaryexploration stage.
The density and quality of the observation point is sufficient to interpret relistically of the thickness, quality, depth, and number of coal insitu and on the grounds that the resources interpreted will not have a large enough variation if more detailed exploration is carried out. This area of resources is determined by the projection of the thickness and soil cover, rank, and data quality of the measurement and sampling points based on gteological evidence in an area between 0.4 km – 1.2 km. including anthracist and bituminus with a thickness of 35 cm or more, sib bituminus with a thickness of 75 cm or more, lignite with a thickness of 150 cm.
4. Measured Coal Resourced
Measurable coal resources are the amount of coal in the investigation area or part of the investigation area, which is calculated based on data that meets the requirements set for the detailedexploration stage.
The density and quality of the observation point is sufficient to be relied upon to interpret the thickness of coal, quality, depth, and amount of coal insitu. This area of resources is determined by the projection of the thickness and soil cover, rank, and data quality of the measurement and sampling points based on geological evidence within a radius of 0.4 km. Includes anthracrate and bituminus with a thickness of 35 cm or more, sub bituminus with a thickness of 75 cm or more, lignite with a thickness of 150 cm.
Resource Calculation
There are several methods that can be used to calculate coal resources in research areas. The use of methods is adjusted to the quality of the data, the type of data obtained, and the conditions of the field and mining methods (e.g. mining angles). Because the data used in the calculation is only outc view data, the method used for calculating research area resources is circular method (USGS) (Image).
Rules for Calculating Coal Resources by Circular Method (USGS) (Wood et al., 1983)
The calculation of coal resources according to the USGS can be calculated by formula
Coal tonnase = A x B x C, where
A = average thickness weight of coal in inches, feet, cm or meters
B = weight of coal per stuan corresponding volume or metric ton.
C = coal area in acre or hectare
The tilt of the coal seam also exerts an influence in the calculation of coal resources. If the coal seam has different slopes, then the calculation is done separately.
1. Slope 00 – 100
Tonnage calculation is done directly using the formula Tonnase = thickness of coal x coal type weight x coal area
2. Slope 100 – 300
For slopes 100 – 300, the coal tonase should be divided by the cosinus value of the coal seam slope.
3. Tilt > 300
For tilt > 300, coal tonase is multiplied by the value of cosinus slope of the coal layer.
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