The map based index includes outlines for some 8,000 opencast coal prospecting sites dating from the 1940s until the mid 1990s. The index leads to information on the records of some 1 million boreholes (additional to those shown in the Borehole Records layer) drilled during site exploration and also the accompanying plans and other data, all filed in 3,618 boxes. The sites include those that have been drilled and not worked and also those that have been exploited. The original data, hardcopy maps, were received from the Coal Authority in 2001.

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