Weighted mean grade = 0.3069gm/yd³ (0.0098 oz/yd³)
(b) Geometric mean grade:
0.0098 x 0.12 = 0.0329 oz/yd³
However in the computation that follows with respect to
the estimated gold content in the gravels flanking the Pampana
Channel the geometric mean grade is used.
3. Estimate of volume of auriferous gravels:
The overlap between Rosint Development Company’s
ExPL7/94 and NDMC’s SEPL 2136 is approximately 40%.
Some of the deposits for which gravel volumes are quoted
by NDMC are outside the boundaries of ExPL7/94.
In determining the possible volume of auriferous gravels
within ExPL7/94, gravels within the present Pampana channel
are discussed separately from those developed in the flats
and terraces flanking the Pampana Right Bank.
Right Bank Deposits:
A study of the contours on Topographic Sheets 44 and 55
and the assumption that the gravels laid by the Pampana
would not spread more than 1,500 metres from edge of the
present river channel, have allowed possible gravel retention
sites to be outlined and measured. The area of these retention
sites total 11.7888km² (11,788,800sq.metres). The thickness
of the gravel is taken as the average of the gravel thicknesses
as in all areas tested by NDMC (SL) Ltd., in its A²
and A³ development sampling programme. This approximated
to 2.0 metres. The volume is therefore 23.577.600cu.metre
Pampana Channel Deposit:
Total length of river in ExPL7/94 approximates 24 kilometers,
with a mean width of the about 100 metres.
The following assumptions are made in computing a possible
volume of gravels in the channel
(i) only about 30% of the river is dredgeable.
(ii) Gravel thickness in the channel is 1.5 metres.
Possible gravel volume in channel:
8000 x 100 x 15 = 1,200,000cu.metres (1,569,540cu.yds.)
4. Gold content in ExPL7/94
(a) In the Pampana Channel:
(i) Assume the grade of 0.811gm/m³ recovered by 1950
Dredge for a section of the Pampana, south of ExPL7/94 holds
good for dredgeable sections in ExPL7/94, then the gold
content is 973 200 gms or 31.293ozs.
(ii) Assume that depletion due to illicit mining over the
years is set at 30% then the gold content is reduced to
(iii) At US$500/oz. The estimated gold value is US$10,952,000.
(b) In the Flanking Flats and Terraces:
Geometric Mean Grade = 0.0329oz/yd³
Gravel Volume = 47,155,200yd³
Assume 70% of gravel would be economic, volume is reduced
to = 33,008,640 yd³
Gold content = 1,085,984ozs.
Depletion of 15% Gold due to previous mining – lawful
and illicit: gold content is reduced to = 923,087ozs.
At gold price of US$500, the estimated gold value is US$461,543,500.
(c) The estimated gold value contained in ExPL7/94 is US$472,495,000.
The estimated gold value in excess of US$472,000,000 in
ExPL7/94 makes the property an attractive proposition.