classification of gold ore on the basis of industrial use
does not arise. However based on the association of gold with
sulfate minerals like arsenopyrite, the ore can be grouped
as under: -
Free Milling ore:
gold is generally medium coarse grained and can be recovered
by crushing, milling and gravity separation on blankets. The
tailing loses are generally as low as 0.3 to 0.4 g/t.
gold is associate with minerals such as arsine pyrite, pyrite,
etc. and is usually fine Grande. The gold recovery needs in
addition to crushing, milling and gravity separation, flotation,
roasting, etc., for good recovery. Also, the ore needs more
grinding. The tailing losses after gravity separation and
cyanidation of table tails, is generally high (o.8 to 1.0
Semi – Refractory Ores:
the Mineral Inventory as on 01.01.85 the cut off grade for
classifying "reserve" has been considered as +3g/t considering
experience in the existing mines. Reserve below his cut off
(-) 3 g/t has been classified as "conditional resources".
representative of BGML has observed that it is necessary to
have "planning cut off’ at exploration stages and "operational
cut off" while mining. While delineating ore bodies with a
given cut of grade. It is necessary to have an appropriate
cost of operation and what should be the minimum cut off grade
to start with. Delineation of ore bodies with operational
cut off grades should be carried out bodies with operational
cut off grade should be carried out keeping in view the mining
various operational cut-off options should be examined in
relation to the safety in the mining methods. Mining costs,
milling cost and overheads in an operating mine. In K. G.
F. mines different mining method are employed. Stop drive
– a costly one, is practiced in ultra deep champion reef mine
and cut and fill method in Nandydurg mine at moderate depths.
The costs of these methods vary considerably. Secondly, mining
cannot be limited to the zones delineated with a given cut
off grade since the low-grade reserve blocks in the mining
sequence have also be mined for safety purpose.
cut off concept has been generalized by the BGML representative
0.1, 0.2 and 0.5 Au g/t cut off grades for placer deposits
where the area covered is large, the volume of mining by mechanization
is also large and the treatment cost is very low to recover
A 3-g/t cut off grade could be used in vein types of deposits
in shallow to moderate depth where cost is moderate. A high
cut off grade is necessary for deeper operations, where the
mining costs are higher.
K. G. mines where the high-grade zones are already mined out
the residual ore reserves have been re-estimated using the
geometric mean grade with 4 g/t and 6 g/t cut off grade and
minimum stopping width of 122 cm in case of champion load
and 137 cm in case of the oriental load. The Hutti Gold mines
practiced a cut off grade of 2 g/t and 1.5 M minimum stopping
width mainly because of grade of individual sample data are
higher and the ore body is wider. Therefore, even at 2-g/t
cut off grade, the average grade of total reserve is 6 g/t.
Au (+) 0.5g/ m3
Au 3 g/t m3
Au (-) 0.5 g/ m3
Au (-) 3 g/t (free milling)