Review of the spatial interpolation techniques used for estimating economic coal properties
Kane Maxwell
School of Earth and Environmental Sciences,
University of Queensland, QLD
4072, Australia.
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Abstract
Coal resource estimation relies on the spatial interpolation of coal quality properties, such as ash content and density. There are many available spatial interpolation techniques, and over the past decade geostatistical methods such as kriging have been recommended over simpler, historically popular techniques such as inverse distance. Despite this recommendation, it is shown in this study that inverse distance remains the most popular method for interpolating coal quality properties. This study analyses publicly available resource estimation reports from companies which are listed on the Australian Stock Exchange (ASX) from a period spanning 2013 through to 2019. A semi-automated approach to compiling resource estimation reports is undertaken and 53 documents from 30 of the largest companies (by market capitalisation) are compiled. From the analysis of these documents it is shown that inverse distance is used for interpolating coal quality properties in all but one document. The only other reported method was an alternative non-geostatistical method. Further, despite clear ASX rules mandating the report of quantitative reasons for the usage of an interpolation technique, reasons were totally absent or qualitative in all but one resource estimation report.
Keywords: Spatial interpolation, inverse distance weighting, geostatistics, coal resource, JORC
VICTORIA HILL MINING RESERVE – Geological & Heritage Guide
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Introduction
History
Alluvial gold was discovered in Bendigo Creek in 1851. Victoria Hill was used as a hideout for bushrangers until reef gold mining took leases along the hill in 1854. Small open cut & shallow shaft leases were amalgamated into large, deep operations. The last was overcome by water in 1910 while attempting to sink beyond 5,000’ (1,500 m). Approximately 500,000 oz of gold was won from Victoria Hill, valued at over $1,000,000,000 today.
Geology
The rocks at Victoria Hill are the same as those that make up the majority of central Victoria. These rocks were deposited at the bottom of the ocean (turbidites) approximately 475 million years ago during the Ordovician Period. Rocks of this age around the world from the Early Ordovician were known as Bendigonian until recently.