MT MORGAN OPEN CUT PIT WATER QUALITY MODELLING stage 2 ● 5
Scenario 2 in Table 4-1, and reproduced below, corresponds to Heritage Minerals’ proposed operating conditions: a new tailings pH of 9.6, EC of (up to) 4,000 µS/cm and sulfate (up to) 2,000 mg/L at a volume ratio of 0.61:1 (tailings to OCP water). This equates to approximately 2 MT of tailings processed per annum. Modelling predicts an overall improvement in OCP water quality, with minimal changes to concentrations of key anions and cations. The model suggests that the OCP water pH remains relatively stable up to tailings pH 10, with a marked increase in pH occurring only when tailings pH exceeds 11. Additionally, a gradual pH rise is predicted with increasing tailings-to-water ratios. It should be noted that results are based on the best available data and several assumptions. Accuracy of predicted metal concentrations (e.g. iron and zinc) would improve with the inclusion of measured dissolved-phase concentrations from the new tailings slurry.
GWB modelled OCP water quality
New Tailings (solution)
Scenario 1 (0.3)
Scenario 2 (0.61)
Scenario 3 (1)
Scenario 4 (2)
Analyte
Unit
OCP Water
pH
pH
3.77
9.57
3.86
3.93
4.01
4.17
EC
µS/cm
15962
4000
10237
8954
7850
6235
TDS
mg/l
11,166
30
8596
6947
5598
3742
Mg
mg/l
2,553
100
1972
1612
1317
911
Na
mg/l
554
70
439
368
310
230
Sulfate
mg/l
16973
2000
13418
11219
9421
6946
Cl
mg/l
224
20
176
146
121
87
Hardness as CaCO 3
mg/l
11,437
514
8988
7347
6001
4142
Fe
mg/l
362.8
59
291
246
210
159
Mn
mg/l
162.7
10
127
104
86
60
Zn
mg/l
46.17
9.57
37
32
28
22
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