Investigating the Amount Gold in Old Leached Dump

8/10/2019 Investigating the Amount Gold in Old Leached Dump

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TO DETERMINE THE AVERAGE GOLD CONTENT OF THE LEACHED DUMP

REPORT PREPARED

BY

TENDAI CHIGODO

FEB 2012



TERMS OF REFERENCE

The main object of the exercise was to determine the average grade of gold that can be reclaimed from

the old leached dump. This will help us to classify the leached residue to ore, low grade ore or waste.

WORKDONE

A trench with length of 222 metres and an average depth of 3metres was dug using an excavator. Both

sides (north and south) of the trench were sampled, of which symbol TN denotes vertical channels cut

on the northern side of the trench and TS denotes vertical channels cut on the southern side of the

trench. The channels were marked at an interval of 10 metres on both sides in a staggered pattern, and

the sample interval on all channels was 1 metre. From this exercise, 123 samples were collected and

sent to the Freda Rebecca laboratory for assaying.

The dump was surveyed and is believed to be sitting on 2.8 million tons.



RESULTS

Below is a table showing assay results, average grade versus the channel id.

Sample number Assay results Av Grade Channel id

S9401 0.21

S9402 0.56 0.60 TN1

S9403 0.85

S9404 0.77

S9405 0.10

S9406 0.79 0.57 TS1

S9407 0.32

S9408 1.07

S9409 0.30

S9410 0.79 0.56 TN2

S9411 0.34

S9412 0.82

S9413 0.28

S9414 0.11 0.15 TS2

S9415 0.06

S9416 0.18S9417 0.18 0.39 TN3

S9418 0.81

S9419 0.56

S9420 1.96 1.24 TS3

S9421 1.20

S9422 0.70

S9423 0.06 0.77 TN4

S9424 1.56

S9425 0.93

S9426 0.65 0.68 TS4

S9427 0.63

S9428 0.49

S9429 0.57

S9430 0.32 0.55 TN5

S9431 0.76

S9432 0.36



S9433 0.85 0.66 TS5

S9434 0.76

S9435 1.08

S9436 0.59 0.87 TN6

S9437 0.95

S9438 0.17

S9439 0.33 0.51 TS6

S9440 1.03

S9441 0.24

S9442 0.30 0.47 TN7

S9443 0.88

S9444 0.95 1

S9445 1.90 TS7

S9446 0.70

S9447 0.70 0.52

S9448 0.17 TN8

S9449 0.12

S9450 0.16 0.36

S9451 0.65 TS8

S9452 0.49

S9453 0.12

S9454 0.36 0.34 TN9

S9455 0.20

S9456 0.66

S9457 0.14

S9458 0.59 1.27

S9459 3.66 TS9

S9460 0.67

S9461 0.43

S9462 1.69 0.91

S9463 0.91 TN10

S9464 0.62

S9465 0.81

S9466 0.36 0.76

S9467 0.58 TS10

S9468 1.29

S9469 0.77

S9470 1.29 0.79 TN11

S9471 0.32

S9472 0.79

S9473 1.32



S9474 0.72 1.05

S9475 0.97 TS11

S9476 1.18

S9477 2.24

S9478 2.89

S9479 3.74 2.59 TN12

S9480 1.50

S9481 1.00

S9482 1.34 1.61 TS12

S9483 2.50

S9484 0.40

S9485 1.73 0.97 TS13

S9486 0.77

S9487 0.16

S9488 0.40 0.98 TS14

S9489 2.37

S9490 0.19

S9491 0.27 0.54 TN13

S9492 0.96

S9493 0.73

S9494 0.33

S9495 0.61 0.58 TS15

S9496 0.80

S9497 0.39

S9498 0.67 0.58 TN14S9499 0.68

S9500 0.75 0.52

N8901 0.28 TS16

N8902 0.67

N8903 0.76 0.72 TS17

N8904 0.29

N8905 0.85 0.57 TS18

N8906 0.31

N8907 0.22 0.40 TN15

N8908 0.67

N8909 0.35

N8910 1.17 0.76 TS19

N8911 0.13

N8912 0.74 0.44 TN16

N8913 0.26

N8914 0.20 0.23 TS20



N8915 0.16

N8916 0.14 0.15 TN17

N8917 0.08

N8918 0.23 0.16 TS21

N8919 0.06

N8920 0.24 0.15 TN18

N8921 0.15

N8922 0.62 0.31 TS22

N8923 0.16

Two sections were produced (TN and TS) showing the distribution of grades and two lithologies.

The heap leach dump is overlaid by a thick layer which is composed of slimes, mineralized rocks and

barren rocks. The average thickness of this layer is approximately one metre. This top layer (Slimes)

which was being classified as waste posted the average that was not anticipated. The highest value is

2.50g/t and the lowest is 0.34g /t. To calculate the gold content in slimes;

Volume of Slimes 103 908m2 X 1m =103 908m

3

Total tonnage 103 908m3 x 2.5=259 770 t

Gold content (g) 259 770 t x 0.90g = 233 733g

Gold content(kg) 233 733g / 1000g = 233.79kgs

Figures above show us that, the amount of gold in the slimes layer is 233.794kgs

The bottom layer is composed mainly of oxidized materials and the grades are not evenly distributed.

Mineralization is not so strong in this layer due to the fact that, some of the minerals were leached. The

grades of the heap leach residue are not evenly distributed as illustrated on section TN and TN. T

calculate the gold content of bottom layer;

Volume of Oxides, 103 908m2 x 3m = 311724m3

Total tonnage, 311724m3

x 2.5 = 779 310 t

Gold content (g) 779 310 t x 0.66 = 514 344.60g

Gold content (kg) 514 344.60 / 1000 = 514.34kgs

The average grade of both layers is calculated as follows;

(259770 x 0.90 + 779310 x 0.66)/ (259770 + 779310) = 0.72g/t



The total gold content;

233.79kgs + 514.34kgs =748.13kgs

RECOMMENDATION

The findings of the exercise cannot represent the whole leached dump, so to increase the level

confidence; more pits can be dug at an equidistance covering the whole dump. This will help to



ascertain the true representative grade of the dump. And also it will be easier to point out areas

with high values during mining operations.

I strongly recommend blending the heap leach residues with material from underground since

the material is of low grade.

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Investigating the Amount Gold in Old Leached Dump