most important aspect in the backup calculation is the assessment method, there are various methods of estimation that can be done namely the classic method consisting of NNP (Neighborhood Nearest Point) and IDW (Inverse Distance Weighting) as well as non-classical methods that are estimation using Kriging. Kriging method is the best in terms of the accuracy of its assessment (interpolation), this method already includes the spatial aspect (position) of the reference point that will be used to estimate a certain point. d. Polygon method (area of influence) This polygon method is a conventional method of calculation. This method is commonly applied to deposits that are relatively homogeneous and have simple geometry. The rate of an area inside a polygon is estimated by the conto value that is in the middle of the polygon so that this method is often referred to as the polygon method of the area of influence. The area of influence is created by dividing the two distances between the two conto points with a single axis of Coal Reserves is 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 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 measurement evidence for the thickness and presence of coal is 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 as identified resources. 2. Inferred 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 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 Designated 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 preliminary exploration 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 Measured coal resources are the amount of coal in the exploration area or part of the investigation area, which is calculated based on the eligible data set out for the detailed exploration 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). Coal Resource Counting Rules by Circular Method (USGS) (Wood et al., 1983) Calculation of coal resources by USGS can be calculated by the formula Tonnase coal = A x B x C, where A = average thickness weight of coal in inches, feet, cm or meters B = coal weight per stuan corresponding volume or metric ton. C = coal area in acre or hectare The slope of the coal seam also exerts 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. Slope > 300 For slope > 300, coal tonase is multiplied by the cosinus value of the coal seam slope.
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