Under Ground Mining options

This section has been included to show that
different mining methods require different
selection criteria. During the study, alternative
underground mining methods suitable for the
extraction of a medium-dipping, thick seam,
were examined. In-seam mining (a) and crossseam
(b) mining were considered.
As a computer database was being used, it was
possible to try sensitivity analyses on the various
selection criteria. These were used to assist
in the selection of the best mining methods
and in the calculation of the ROM tonnages
and qualities. The weighted average quality
of the in situ and mineable lignite was calculated
using tabulated data examples.

In-seam mining :-
        The mineable lignite was determined once
waste partings (material with >55% ash content
and/or <1800 kcal kg−1) greater than 1.5 m
thick were rejected. Occasionally thin lignite
beds within the thick waste partings were also
rejected. The top and bottom of the in situ and
mineable lignite are the same. It was assumed
that there would be a 100% recovery of the lignite
in the longwall slice, and 60% recovery of
lignite and 40% dilution by waste in the caved
zones above the longwall zones. The mineable
quality takes into account the lignite losses
and waste dilution which would occur during
caving. It was considered that selective mining
could be implemented above and below a waste
parting greater than 1.5 m thick.

Cross-seam mining :-
         The mineable lignite was determined once the
top and bottom waste material were excluded.
As this method is less selective, dilution of the
lignite is inevitable. This is accounted for by
expecting a 60% recovery of lignite and a 40%
dilution by waste.