Sukulu Phosphate Project Scoping Report Page i Table of Contents 6 Tailings Dams... 6-1 6.1 Introduction... 6-1 6.2 Tailings behaviour... 6-1 6.2.1 Magnetics tailings... 6-1 6.2.2 Flotation tailings... 6-4 6.2.3 Gypsum tailings... 6-6 6.3 Tailings storage requirements... 6-7 6.3.1 Magnetics tailings... 6-9 6.3.2 Flotation tailings... 6-11 6.3.3 Gypsum tailings... 6-14 6.4 TSF capital and operating cost estimates... 6-16 6.4.1 Capital Cost Estimates... 6-16 6.4.2 Operating Cost Estimates... 6-18 6.5 Recommendations for Phase 2 Feasibility Study... 6-18
Sukulu Phosphate Project Scoping Report List of Tables Page ii Table 6.1: Phase 1: From Year 1 to end of mine life... 6-1 Table 6.2: Phase 2: Year 4 to end of mine life... 6-1 Table 6.3: Estimate of magnetic tailings slurry properties... 6-3 Table 6.4: Volume of magnetics tailings... 6-4 Table 6.5: Estimate of flotation tailings slurry properties... 6-5 Table 6.6: Volume of flotation tailings... 6-6 Table 6.7: Volume of gypsum tailings... 6-7 Table 6.8: Rate of rise curve: magnetic tailings... 6-9 Table 6.9: Rate of rise curve: flotation tailings... 6-11 Table 6.10: Impoundment wall construction requirements... 6-13 Table 6.11: Rate of rise curve: gypsum tailings... 6-14 Table 6.12: Capital cost estimate... 6-16 Table 6.13: Capital cost estimate for alternative design option... 6-16 Table 6.14: Possible capex cash flow for Phase 2 alternative design option (US$million)... 6-17 Table 6.15: Capital Phasing for TSF for Phase 1 only and Phase 1&2 scenarios (US$million)... 6-18 List of Figures Figure 6.1: Tailings gradings... 6-2 Figure 6.2: Conceptual tailings storage facility layout... 6-8 Figure 6.3: Cross-section through magnetics tailings dam... 6-10 Figure 6.4: Cross-section through flotation tailings dam... 6-12 Figure 6.5: Cross-section through gypsum tailings dam... 6-15
Sukulu Phosphate Project Scoping Report Page 6-1 6 Tailings Dams 6.1 Introduction This section sets out a brief description of the tailings dam requirements for the Sukulu Phosphate Project. This aspect has not been addressed in previous studies by Nilefos. As outlined in section 5, there are four tailings streams, as shown in Tables 6.1 and 6.2. Table 6.1: Phase 1: From Year 1 to end of mine life Item Tonnage 80% Passing 50% Passing 20% Passing Passing 16µm (tpa) (µm) (µm) (µm) (%) Coarse Magnetics 82 392 382.0 113.0 49.0 4.5 Fine Magnetics 44 401 23.9 8.5 1.7 67.1 Flotation Tails 126 007 7.6 2.3 0.7 99.0 Gypsum 66 288 Table 6.2: Phase 2: Year 4 to end of mine life Item Tonnage 80% Passing 50% Passing 20% Passing Passing 16µm (tpa) (µm) (µm) (µm) (%) Coarse Magnetics 1 235 884 382.0 113.0 49.0 4.5 Fine Magnetics 666 012 23.9 8.5 1.7 67.1 Flotation Tails 1 890 104 7.6 2.3 0.7 99.0 Gypsum 0 The objective of this section is, at a conceptual level, to: Assess the likely tailings behaviour; Assess the tailings storage facility ( TSF ) requirements; Estimate the likely capital and operating costs; Detail the feasibility study requirements. 6.2 Tailings behaviour 6.2.1 Magnetics tailings The magnetic coarse and fine tailings are quite different in grading as shown in Figure 6.1. The magnetic tailings grading curves can be compared with other projects and the preliminary conclusions are: The option of consolidating these tailings in a filter belt or press is unlikely to be viable, as the fineness of the material would clog the filter cloth The fine magnetics tailings on their own are likely to remain unconsolidated and to lack sufficient material strength to be used in a wall building capacity. These tailings would therefore have to be stored in an impoundment.
Sukulu Phosphate Project Scoping Report Page 6-2 Indications are, however, that a combined fine and coarse tailings stream could be stored in a conventional tailings dam where the tailings itself can be used for wall building. This implies that the two magnetic tailings streams should be combined in the plant and pumped to one magnetics TSF. 100 90 80 70 60 Per cent passing 50 40 30 20 10 0 0.0001 0.001 0.01 0.1 1 Particle size (mm) Coarse Magnetics Fine Magnetics Flotation tailings Magnetics combination Mag&flot combination Figure 6.1: Tailings gradings The estimate of the slurry properties of the combined magnetics tailings is shown in Table 6.3. These properties would have to be confirmed by testwork during Phase 2 of the feasibility study.
Sukulu Phosphate Project Scoping Report Page 6-3 Table 6.3: Estimate of magnetic tailings slurry properties SG of water 1 1 1 1 1 1 1 1 Slurry density 1.677 1.94 2.909 3.1 3.21 3.24 3.333 3.625 SG of solids 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 %Solids 50.0 60.0 81 84 85 86 87 90 Volumetric water content Vw/Vt 16 22 45 50 53 53 56 63 Unit volume of solids 1 1 1 1 1 1 1 1 Unit volume of water 5.20 3.47 1.20 1.00 0.90 0.88 0.80 0.60 Unit total volume 6.20 4.47 2.20 2.00 1.90 1.88 1.80 1.60 Mass of solids for unit volume of 5.20 5.20 5.20 5.20 5.20 5.20 5.20 5.20 solids Mass of water 5.20 3.47 1.20 1.00 0.90 0.88 0.80 0.60 Total mass of slurry 10.40 8.67 6.40 6.20 6.10 6.08 6.00 5.80 Mass of solids/ton of solids 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Total mass of slurry /ton of solids 2.00 1.67 1.23 1.19 1.17 1.17 1.15 1.12 mass of water /ton of solids 1.00 0.67 0.23 0.19 0.17 0.17 0.15 0.12 Mass of dry tailings pumped into tailings dam (tons) per 1 901 896 1 901 896 1 901 896 1 901 896 1 901 896 1 901 896 1 901 896 1 901 896 annum Mass of water pumped (tons) per 1 903 301 1 268 449 438 937 365 749 329 340 320 031 292 693 219 450 annum Total mass of slurry (tons/a) 3 805 197 3 170 345 2 340 833 2 267 645 2 231 236 2 221 927 2 194 589 2 121 346 Volume of solids 365 749 365 749 365 749 365 749 365 749 365 749 365 749 365 749 Volume of water 1 903 301 1 268 449 438 937 365 749 329 340 320 031 292 693 219 450 Volume of slurry 2 269 050 1 634 199 804 687 731 498 695 089 685 780 658 443 585 199 dry density 0.84 1.16 2.36 2.60 2.74 2.77 2.89 3.25 void ratio 5.204 3.468 1.200 1.000 0.900 0.875 0.800 0.600 Slurry water content 100.07 66.69 23.08 19.23 17.32 16.83 15.39 11.54 It is therefore conceptually planned to pump the combined magnetic tailings to the tailings dams at a solids concentration of 60%. The estimated dry density in the tailings dam is 2.77t/m 3, which is based on a likely void ratio of 0.875.
Sukulu Phosphate Project Scoping Report Page 6-4 The volume of combined magnetic tailings to be stored, is estimated as follows (Table 6.4). Table 6.4: Volume of magnetics tailings Phase 1 Tonnage (tpa) Phase 2 Tonnage (tpa) Total Tonnage (tpa) Cum. Tonnage (t) Dry density Volume Year (t/m 3 ) 1 126 799 126 799 126 799 2.77 45 776 2 126 799 126 799 253 598 2.77 91 552 3 126 799 126 799 380 397 2.77 137 327 4 126 799 1 901 896 2 028 695 2 409 092 2.77 869 708 5 126 799 1 901 896 2 028 695 4 437 787 2.77 1 602 089 6 126 799 1 901 896 2 028 695 6 466 482 2.77 2 334 470 7 126 799 1 901 896 2 028 695 8 495 177 2.77 3 066 851 8 126 799 1 901 896 2 028 695 10 523 872 2.77 3 799 232 9 126 799 1 901 896 2 028 695 12 552 567 2.77 4 531 613 10 126 799 1 901 896 2 028 695 14 581 262 2.77 5 263 994 11 126 799 1 901 896 2 028 695 16 609 957 2.77 5 996 374 12 126 799 1 901 896 2 028 695 18 638 652 2.77 6 728 755 13 126 799 1 901 896 2 028 695 20 667 347 2.77 7 461 136 14 126 799 1 901 896 2 028 695 22 696 042 2.77 8 193 517 15 126 799 1 901 896 2 028 695 24 724 737 2.77 8 925 898 16 126 799 1 901 896 2 028 695 26 753 432 2.77 9 658 279 17 126 799 1 901 896 2 028 695 28 782 127 2.77 10 390 660 18 126 799 1 901 896 2 028 695 30 810 822 2.77 11 123 040 19 126 799 1 901 896 2 028 695 32 839 517 2.77 11 855 421 20 126 799 1 901 896 2 028 695 34 868 212 2.77 12 587 802 Totals 2 535 980 32 332 232 34 868 212 Chemically, indications are that the magnetics tailings can be expected to be relatively inert and will not require a lined tailings disposal facility. This will need to be confirmed by future testwork however. 6.2.2 Flotation tailings The grading of the flotation tailings is shown in Figure 6.1. This grading shows that the tailings are expected to be exceptionally fine with about 48% passing 2 microns particle sieve size. The flotation tailings is so fine that it will also require to be impounded. The volume of the flotation tailings is such that it cannot be successfully combined with another tailings stream to then be used to construct a tailings dam that will not require impoundment walls. Also, consolidation of these tailings by means of filters will again be unsuccessful. The estimate of the slurry properties of the flotation tailings is shown in Table 6.5. These properties would have to be confirmed by testwork during Phase 2 of the feasibility study.
Sukulu Phosphate Project Scoping Report Page 6-5 Table 6.5: Estimate of flotation tailings slurry properties SG of water 1 1 1 1 1 1 1 1 1 Slurry density 1.35 1.4 1.3 1.5 1.6 1.909 2 2.111 2.25 SG of solids 3 3 3 3 3 3 3 3 3 %Solids 39 43 35 50 56 71 75 79 83.3 Volumetric water content Vw/Vt 18 20 15 25 30 45 50 56 63 Unit volume of solids 1 1 1 1 1 1 1 1 1 Unit volume of water 4.71 4.00 5.67 3.00 2.33 1.20 1.00 0.80 0.60 Unit total volume 5.71 5.00 6.67 4.00 3.33 2.20 2.00 1.80 1.60 Mass of solids for unit volume of 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 3.00 solids Mass of water 4.71 4.00 5.67 3.00 2.33 1.20 1.00 0.80 0.60 Total mass of slurry 7.71 7.00 8.67 6.00 5.33 4.20 4.00 3.80 3.60 Mass of solids/ton of solids 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Total mass of slurry /ton of 2.57 2.33 2.89 2.00 1.78 1.40 1.33 1.27 1.20 solids mass of water /ton of solids 1.57 1.33 1.89 1.00 0.78 0.40 0.33 0.27 0.20 Mass of dry tailings pumped into tailings dam 1 890 104 1 890 104 1 890 104 1 890 104 1 890 104 1 890 104 1 890 104 1 890 104 1 890 104 (tons) per annum Mass of water pumped (tons) 2 970 163 2 520 139 3 570 196 1 890 104 1 470 081 756 180 630 035 504 141 378 021 per annum Total mass of slurry (tons/a) 4 860 267 4 410 243 5 460 300 3 780 208 3 360 185 2 646 284 2 520 139 2 394 245 2 268 125 Volume of solids 630 035 630 035 630 035 630 035 630 035 630 035 630 035 630 035 630 035 Volume of water 2 970 163 2 520 139 3 570 196 1 890 104 1 470 081 756 180 630 035 504 141 378 021 Volume of slurry 3 600 198 3 150 173 4 200 231 2 520 139 2 100 116 1 386 215 1 260 069 1 134 176 1 008 055 dry density 0.53 0.60 0.45 0.75 0.90 1.36 1.50 1.67 1.88 void ratio 4.714 4.000 5.667 3.000 2.333 1.200 1.000 0.800 0.600 Slurry water content 157.14 133.33 188.89 100.00 77.78 40.01 33.33 26.67 20.00 High rate thickeners will most likely be required to prepare the flotation tailings to a percent solids of 30% to 35% to be pumped to the tailings dam site using positive displacement pumps. It is also likely that the final target dry density will be about 0.75t/m 3 to 0.9t/m 3 depending on the actual consolidation behaviour and the evaporative drying that can be considered. The volume of flotation tailings to be stored, is estimated as follows (Table 6.6).
Sukulu Phosphate Project Scoping Report Page 6-6 Table 6.6: Volume of flotation tailings Phase 1 Tonnage (tpa) Phase 2 Tonnage (tpa) Total Tonnage (tpa) Cum Tonnage (t) Dry density Volume Year (t/m 3 ) 1 126 007 126 007 126 007 0.75 168 009 2 126 007 126 007 252 014 0.75 336 019 3 126 007 126 007 378 021 0.75 504 028 4 126 007 1 890 104 2 016 111 2 394 132 0.75 3 192 176 5 126 007 1 890 104 2 016 111 4 410 243 0.75 5 880 324 6 126 007 1 890 104 2 016 111 6 426 354 0.75 8 568 472 7 126 007 1 890 104 2 016 111 8 442 465 0.75 11 256 620 8 126 007 1 890 104 2 016 111 10 458 576 0.75 13 944 768 9 126 007 1 890 104 2 016 111 12 474 687 0.75 16 632 916 10 126 007 1 890 104 2 016 111 14 490 798 0.75 19 321 064 11 126 007 1 890 104 2 016 111 16 506 909 0.75 22 009 212 12 126 007 1 890 104 2 016 111 18 523 020 0.75 24 697 360 13 126 007 1 890 104 2 016 111 20 539 131 0.75 27 385 508 14 126 007 1 890 104 2 016 111 22 555 242 0.75 30 073 656 15 126 007 1 890 104 2 016 111 24 571 353 0.75 32 761 804 16 126 007 1 890 104 2 016 111 26 587 464 0.75 35 449 952 17 126 007 1 890 104 2 016 111 28 603 575 0.75 38 138 100 18 126 007 1 890 104 2 016 111 30 619 686 0.75 40 826 248 19 126 007 1 890 104 2 016 111 32 635 797 0.75 43 514 396 20 126 007 1 890 104 2 016 111 34 651 908 0.75 46 202 544 Totals 2 520 140 32 131 768 34 651 908 Chemically, indications are that the flotation tailings is expected to be relatively inert and will not require a lined tailings disposal facility. This will need to be confirmed by future testwork however. The flotation tailings will however remain in a relatively unconsolidated state and will require fencing or other security of access into the future. 6.2.3 Gypsum tailings The gypsum tailings are generally of very poor quality and very acidic. They will have to be stored in a lined facility. The target dry density is estimated as 0.8t/m 3. The volume to be stored can be assessed as shown below (Table 6.7).
Sukulu Phosphate Project Scoping Report Page 6-7 Table 6.7: Volume of gypsum tailings Phase 1 Tonnage (tpa) Phase 2 Tonnage (tpa) Cum tonnage Dry density Volume Year (t) (t/m 3 ) 1 66 288 0 66 288 0.8 82 860 2 66 288 0 132 576 0.8 165 720 3 66 288 0 198 864 0.8 248 580 4 66 288 0 265 152 0.8 331 440 5 66 288 0 331 440 0.8 414 300 6 66 288 0 397 728 0.8 497 160 7 66 288 0 464 016 0.8 580 020 8 66 288 0 530 304 0.8 662 880 9 66 288 0 596 592 0.8 745 740 10 66 288 0 662 880 0.8 828 600 11 66 288 0 729 168 0.8 911 460 12 66 288 0 795 456 0.8 994 320 13 66 288 0 861 744 0.8 1 077 180 14 66 288 0 928 032 0.8 1 160 040 15 66 288 0 994 320 0.8 1 242 900 16 66 288 0 1 060 608 0.8 1 325 760 17 66 288 0 1 126 896 0.8 1 408 620 18 66 288 0 1 193 184 0.8 1 491 480 19 66 288 0 1 259 472 0.8 1 574 340 20 66 288 0 1 325 760 0.8 1 657 200 Totals 1 325 760 0 6.3 Tailings storage requirements The most obvious place to store the bulk of the tailings material would be back into the mined-out areas in the carbonatite pipe. However this option cannot be seriously considered until it is established by deeper drilling within the orebody, that no further minerals of economic interest occur beneath the known phosphate deposits. This drilling is planned for phase 2 of this feasibility study. For this phase of the study, it is necessary to assume that all tailings material will be stored in facilities that are outside of the orebody area, as is further described below. The tailings storage requirements can therefore be summarized as follows: The gypsum tailings will be stored in a specific lined tailings dam and the gypsum return water facility will also have to be lined. The flotation tailings has to be stored in a impoundment. The magnetics tailings can be stored in a conventional tailings dam. It may later be decided to provide an outer laterite or earth wall layer to assist in the ongoing rehabilitation of the facility. A return water dam ( RWD ) facility will be required for both the magnetic tailings and for the flotation tailings. This could either be separate RWD facilities or combined facilities. These principles for the conceptual TSF layout are shown in Figure 6.2. For the calculations in the following sections it is assumed that the slope of the various tailings dams sites will be about 1(v) in 33 (h). The 100 foot contours were used in this assessment.
Sukulu Phosphate Project Scoping Report Page 6-8 Figure 6.2: Conceptual tailings storage facility layout
Sukulu Phosphate Project Scoping Report Page 6-9 6.3.1 Magnetics tailings A preliminary rate of rise curve was developed for the magnetics tailings as shown below in Table 6.8. Table 6.8: Rate of rise curve: magnetic tailings Elevation L (m) B (m) Area (m 2 ) Volume Cum Volume Rate of rise (m/yr) Time (yrs) 0 880 0 0 1 872 29 25 288 12 644 12 644 3.62 0.3 2 864 62 53 568 39 428 52 072 1.16 1.1 3 856 95 81 320 67 444 119 516 0.68 2.6 4 848 128 108 544 94 932 214 448 0.48 3.1 5 840 161 135 240 121 892 336 340 0.38 3.3 6 832 194 161 408 148 324 484 664 0.31 3.5 7 824 227 187 048 174 228 658 892 0.26 3.7 8 816 260 212 160 199 604 858 496 0.23 4.0 9 808 293 236 744 224 452 1 082 948 3.26 4.3 10 800 326 260 800 248 772 1 331 720 2.94 4.6 11 792 359 284 328 272 564 1 604 284 2.69 5.0 12 784 392 307 328 295 828 1 900 112 2.48 5.4 13 776 425 329 800 318 564 2 218 676 2.30 5.8 14 768 458 351 744 340 772 2 559 448 2.15 6.3 15 760 491 373 160 362 452 2 921 900 2.02 6.8 16 752 524 394 048 383 604 3 305 504 1.91 7.3 17 744 557 414 408 404 228 3 709 732 1.81 7.9 18 736 590 434 240 424 324 4 134 056 1.73 8.5 19 728 623 453 544 443 892 4 577 948 1.65 9.1 20 720 656 472 320 462 932 5 040 880 1.58 9.7 21 712 689 490 568 481 444 5 522 324 1.52 10.4 22 704 681 479 424 484 996 6 007 320 1.51 11.0 23 696 673 468 408 473 916 6 481 236 1.55 11.7 24 688 665 457 520 462 964 6 944 200 1.58 12.3 25 680 657 446 760 452 140 7 396 340 1.62 12.9 26 672 649 436 128 441 444 7 837 784 1.66 13.5 27 664 641 425 624 430 876 8 268 660 1.70 14.1 28 656 633 415 248 420 436 8 689 096 1.74 14.7 29 648 625 405 000 410 124 9 099 220 1.79 15.2 30 640 617 394 880 399 940 9 499 160 1.83 15.8 31 632 609 384 888 389 884 9 889 044 1.88 16.3 32 624 601 375 024 379 956 10 269 000 1.93 16.8 33 616 593 365 288 370 156 10 639 156 1.98 17.3 34 608 585 355 680 360 484 10 999 640 2.03 17.8 35 600 577 346 200 350 940 11 350 580 2.09 18.3 36 592 569 336 848 341 524 11 692 104 2.14 18.8 37 584 561 327 624 332 236 12 024 340 2.20 19.2 38 576 553 318 528 323 076 12 347 416 2.27 19.7 39 568 545 309 560 314 044 12 661 460 2.33 20.1 A schematic cross-section through the proposed tailings dam is shown in Figure 6.3. The main assumption is that the outer wall of the magnetic tailings dam will be constructed at a slope of 1(v) in 4 (h).
Sukulu Phosphate Project Scoping Report Page 6-10 Figure 6.3: Cross-section through magnetics tailings dam
Sukulu Phosphate Project Scoping Report Page 6-11 6.3.2 Flotation tailings A preliminary rate of rise curve was developed for the flotation tailings as shown below in Table 6.9. Table 6.9: Rate of rise curve: flotation tailings Elevation L (m) B (m) Area (m 2 ) Volume Cum Volume Rate of rise (m/yr) Time (years) 0 2 300 0 0 0 1 2 300 33 75 900 37 950 37 950 4.43 0.2 2 2 300 66 151 800 113 850 151 800 1.48 0.9 3 2 300 99 227 700 189 750 341 550 0.89 2.0 4 2 300 132 303 600 265 650 607 200 0.63 3.6 5 2 300 165 379 500 341 550 948 750 7.87 3.7 6 2 300 198 455 400 417 450 1 366 200 6.44 3.9 7 2 300 231 531 300 493 350 1 859 550 5.45 4.1 8 2 300 264 607 200 569 250 2 428 800 4.72 4.3 9 2 300 297 683 100 645 150 3 073 950 4.17 4.5 10 2 300 330 759 000 721 050 3 795 000 3.73 4.8 11 2 300 363 834 900 796 950 4 591 950 3.37 5.1 12 2 300 396 910 800 872 850 5 464 800 3.08 5.4 13 2 300 429 986 700 948 750 6 413 550 2.83 5.8 14 2 300 462 1 062 600 1 024 650 7 438 200 2.62 6.2 15 2 300 495 1 138 500 1 100 550 8 538 750 2.44 6.6 16 2 300 528 1 214 400 1 176 450 9 715 200 2.28 7.0 17 2 300 561 1 290 300 1 252 350 10 967 550 2.15 7.5 18 2 300 594 1 366 200 1 328 250 12 295 800 2.02 8.0 19 2 300 627 1 442 100 1 404 150 13 699 950 1.91 8.5 20 2 300 660 1 518 000 1 480 050 15 180 000 1.82 9.0 21 2 300 693 1 593 900 1 555 950 16 735 950 1.73 9.6 22 2 300 726 1 669 800 1 631 850 18 367 800 1.65 10.2 23 2 300 759 1 745 700 1 707 750 20 075 550 1.57 10.9 24 2 300 792 1 821 600 1 783 650 21 859 200 1.51 11.5 25 2 300 825 1 897 500 1 859 550 23 718 750 1.45 12.2 26 2 300 858 1 973 400 1 935 450 25 654 200 1.39 12.9 27 2 300 891 2 049 300 2 011 350 27 665 550 1.34 13.7 28 2 300 924 2 125 200 2 087 250 29 752 800 1.29 14.5 29 2 300 957 2 201 100 2 163 150 31 915 950 1.24 15.3 30 2 300 990 2 277 000 2 239 050 34 155 000 1.20 16.1 31 2 300 1 023 2 352 900 2 314 950 36 469 950 1.16 17.0 32 2 300 1 056 2 428 800 2 390 850 38 860 800 1.12 17.8 33 2 300 1 089 2 504 700 2 466 750 41 327 550 1.09 18.8 34 2 300 1 122 2 580 600 2 542 650 43 870 200 1.06 19.7 35 2 300 1 155 2 656 500 2 618 550 46 488 750 1.03 20.7 A schematic cross-section through the proposed tailings dam is shown in Figure 6.4.
Sukulu Phosphate Project Scoping Report Page 6-12 Figure 6.4: Cross-section through flotation tailings dam
Sukulu Phosphate Project Scoping Report Page 6-13 The assumption is made that the outer containment wall will be constructed at an outside slope of 1(v) in 4 (h), and that the interface between the containment or impoundment wall and the flotation tailings will be near vertical. This means that the costs of the containment wall will be expended to keep to the rate of rise of the tailings material deposition and consolidation. A significant source of earthfill material will be required to construct the impoundment wall of between 10 million and 13 million m 3 as shown in Table 6.10. Table 6.10: Impoundment wall construction requirements Lift Percentage of impoundment wall required 1 1.74 2 10.48 3 9.29 4 54.97 5 4.31 6 3.97 7 3.61 8 3.22 9 2.80 10 2.35 11 1.88 12 1.38 It must be appreciated that the capital costs involved in constructing an earthfill impoundment of this size are enormous and are unlikely to be able to be carried by the project. For this reason, an alternative scheme has been proposed, where it may be possible to use the magnetics tailings as the construction material for the flotation tailings impoundment wall. This implies that the magnetics tailings could then not be remined in the future; unless the outer slopes of the magnetic tailings and the flotation tailings are kept the same, i.e. the width of the magnetics tailings containment wall be kept constant, at about 80m to 100m. This trade-off study needs to be addressed in detail during the second phase of the feasibility study.
Sukulu Phosphate Project Scoping Report Page 6-14 6.3.3 Gypsum tailings A preliminary rate of rise curve was developed for the gypsum tailings as shown below in Table 6.11. Table 6.11: Base Elevation Rate of rise curve: gypsum tailings L (m) B (m) Area (m 2 ) Volume Cum Volume Rate of rise (m/yr) Time (years) 0 460 0 0 0 1 450 28 12 600 6 300 6 300 13.15 0.1 2 440 61 26 840 19 720 26 020 4.20 0.3 3 430 94 40 420 33 630 59 650 2.46 0.7 4 420 127 53 340 46 880 106 530 1.77 1.3 5 410 160 65 600 59 470 166 000 1.39 2.0 6 400 193 77 200 71 400 237 400 1.16 2.9 7 390 226 88 140 82 670 320 070 1.00 3.9 8 380 259 98 420 93 280 413 350 0.89 5.0 9 370 292 108 040 103 230 516 580 0.80 6.2 10 360 325 117 000 112 520 629 100 0.74 7.6 11 350 315 110 250 113 625 742 725 0.73 9.0 12 340 305 103 700 106 975 849 700 0.77 10.3 13 330 295 97 350 100 525 950 225 0.82 11.5 14 320 285 91 200 94 275 1 044 500 0.88 12.6 15 310 275 85 250 88 225 1 132 725 0.94 13.7 16 300 265 90 000 87 625 1 220 350 0.95 14.7 17 290 255 84 100 87 050 1 307 400 0.95 15.8 18 280 245 78 400 81 250 1 388 650 1.02 16.8 19 270 235 72 900 75 650 1 464 300 1.10 17.7 20 260 225 67 600 70 250 1 534 550 1.18 18.5 21 250 215 62 500 65 050 1 599 600 1.27 19.3 22 240 205 57 600 60 050 1 659 650 1.38 20.0 A schematic cross-section through the proposed gypsum tailings dam is shown in Figure 6.5. The gypsum tailings dam, solution trenches and its return water dam have to be lined (most likely liner material will have to be HDPE liners) to cater for the low ph water that will develop, which could seep through the tailings dam. For this conceptual design, the outer slopes have been flattened rather than to provide for impoundment walls. This trade-off study will also have to be addressed as part of the phase 2 feasibility study.
Sukulu Phosphate Project Scoping Report Page 6-15 Figure 6.5: Cross-section through gypsum tailings dam
Sukulu Phosphate Project Scoping Report Page 6-16 6.4 TSF Capital and Operating Cost Estimates 6.4.1 Capital Cost Estimates The tailings dam and return water dam capital costs were estimated comparing the size of the required facilities with a tailings dam and return water dam which were costed by three contractors in Ghana in September 2008. It may be that better prices for the construction of these major earthworks structures will be forthcoming from local Ugandan contractors. This possibility will be tested during the detailed feasibility study (phase 2). A lower-bound estimate has been given for these capital costs, for the purposes of economic sensitivity assessment only. The capital cost estimates are summarised in Table 6.12. Table 6.12: Capital cost estimate Item Base Estimate Lower-bound Estimate Total cost (US$million) Total cost (US$million) Magnetics TSF 10.20 7.6 Flotation TSF 38.50 28.8 Flotation impoundment wall 83.60 62.7 Gypsum TSF including liner 6.62 4.9 Magnetics and Flotation RWD 5.00 3.7 Gypsum RWD including liner 0.70 0.5 Totals 144.62 108.2 If the trade-off study indicates that it will be possible to use the magnetics tailings material as an equivalent impoundment wall for the flotation tailings, then the following alternative cost estimate would be relevant (Table 6.13). The study evaluation has been based on the assumption that this design option and hence capital cost will be possible. Table 6.13: Capital cost estimate for alternative design option Item Base Estimate Lower-bound Estimate Total cost (US$million) Total cost (US$million) Flotation and Magnetics TSF 50.50 37.8 Flotation impoundment wall - - Gypsum TSF including liner 6.62 4.9 Magnetics and Flotation RWD 5.00 3.7 Gypsum RWD including liner 0.70 0.5 Totals 62.82 46.9 The cost estimates include allowances for: Liners where required; Starter walls; Drains; Penstocks; Access roads; Upstream stormwater cut-off trenches and berms; Solution trenches where required;
Sukulu Phosphate Project Scoping Report Page 6-17 Catchment paddocks where required; Tailings delivery and distribution piping. Closure and rehabilitation costs are excluded from the costs shown in Tables 6.12 and 6.13 above. The phased capex cash flow for the alternative tailings design option could be as shown in Table 6.14. Table 6.14: Possible capex cash flow for Phase 2 alternative design option (US$million) Gypsum TSF including Magnetics and Flotation Gypsum RWD including Phase Years Magnetics TSF Flotation TSF Flotation impoundment wall liner RWD liner Total Cost 1&2 Total 10.20 40.30-6.62 5.00 0.70 62.82 0 4.15 11.55 4.81 5.00 0.70 26.21 1 0.00 1 2 0.00 3 0.00 2 4-20 6.05 28.75 1.81 36.61 It should be noted that the capital estimates in Tables 6.12 to 6.14 are based on the Phase 2 annual production rate. If the Sukulu Project was restricted to the Phase 1 tonnages only, i.e. 320ktpa RoM, the tonnage of about 250ktpa to be disposed each year is about 7.5% of the total annual Phase 2 arisings designed for. In this situation, the initial size of the facilities can be reduced, and then expanded progressively through the life of the project. The final size of the facilities at the end of the LoM will still be the same as shown. While the total construction cost for the facilities using a phased approach will be higher, this would be offset by the time-value of money benefits to be derived from delaying this expenditure over time. Given this possibility, which was not part of the original scope, SRK did not redo the capital estimates but rather factorised the capital costs based on experience with other projects. Based on the Phase 1 tonnages to be disposed being about 7.5% of the total (i.e. Phase 2 tonnages), the Phase 1 capital cost should then most likely lie within the range of 7.5% to 15% of the total of US$62.8million, i.e. between US$4.7million and US$9.4million. It is important to note that this is a ratio calculation and is not based on a re-assessment of the likely site conditions. The FM considers project cash flows for Phase 1 which are based on a 50-year period processing some 16Mt of RoM material. This represents approximately 18% of the total Phase 2 production schedule, for which the initial Phase 1 TSF above would not have sufficient space. Based on the above factorisation, the cost for a TSF for this larger tonnage should lie within the range of 18% to 25% of the total cost, i.e. from US$11.3million to US$15.7million. For evaluation purposes, SRK has set the initial capital cost for the Phase 1 tailings facilities at US$7.1million (the average of US$4.7million and US$9.4million) and then added US$6.4million in year 14 to get to US$13.5million (the average of US$11.3million to US$15.7million) (see Table 6.14).
Sukulu Phosphate Project Scoping Report Page 6-18 Using the same philosophy, the construction of the Phase 2 tailings facilities has been phased for evaluation purposes as shown in Table 6.14, bearing in mind the construction costs assumed for Phase 1 above and the shorter mine life when operating at the Phase 2 production rate. To allow for the higher construction cost for the facilities using a phased approach, the US$36.6million for years 4-20 shown in Table 6.14 was increased by 10% and then expended in three tranches in years 7, 10 and 14 (see Table 6.15). Table 6.15: Capital Phasing for TSF for Phase 1 only and Phase 1&2 scenarios (US$million) Year Phase 1 TSF Phase 1 & 2 TSF (50-year LoM only) (21-year LoM) 0 7.1 7.1 1 2 3 19.1 7 13.4 10 13.4 14 6.4 13.4 Total (for modelled LoM) 13.5 66.5 6.4.2 Operating Cost Estimates It is difficult to estimate the likely tailings dam operating costs with any accuracy until the phase 2 study testwork has been done. The following costs are proposed, based on previous experience: Operating costs per ton of magnetics tailings: US$0.25/t. Operating costs per ton of flotation tailings: US$0.50/t. Operating costs per ton of gypsum tailings: US$0.40/t. 6.5 Recommendations for Phase 2 Feasibility Study The conceptual design proposal needs to be developed into a feasibility study design. The following main activities are proposed: An overall block plan will have to be developed considering the preliminary sizes of the various facilities. This will define an area to be surveyed in detail for feasibility study levels: this will also include additional areas for alternative layouts etc. such as different plant locations, TSF and RWD locations and routes of infrastructure such as roads and other utilities. A site selection study then has to be undertaken for the tailings dams and return water dams. The site selection study will identify the options and sites to be taken into account and will select the most suitable options for the feasibility design. This study will include the options of in-pit disposal of tailings as well as utilisation of the magnetics tailings material for impoundment walls. Geotechnical investigation of the magnetics, flotation and gypsum TSFs and the two return water dams.
Sukulu Phosphate Project Scoping Report Page 6-19 Geotechnical investigation to source the volume of earthfill required to impound the flotation tailings. Geotechnical investigation of construction materials including sources for aggregates, drain and filter materials. Geotechnical testing of representative samples of tailings of the fine and coarse magnetics, combined coarse and fine magnetics, flotation tailings and gypsum tailings. The required testing will include: specific gravity, gradings down to 2 microns, Atterberg limits, tropical soil testing, beaching trials, settling trials, evapo-transpiration tests, consolidation testing, compaction testing, tri-axial strength testing. On the metallurgical testing related to tailings management the testing will include rheology testing, thickening testing, and transportation testing by pumping. Furthermore the long term behaviour of the tailings materials have to be determined also in terms of potential acid mine drainage behaviour. The salt content of the tailings has to be determined and other possible environmental impacts. The impacts of ph variations on the behaviour of the tailings also has to be determined. Feasibility tailings dam and return water dam designs have to be undertaken. There will be a requirement for various trade-off studies to assess how the costs can be reduced from a capital and operating cost. The impact on the capital costs if construction is phased will need to be carefully assessed. All designs will have to be done taking into account that the project falls within an area that is classified as a Seismic Zone 1, with an expected maximum event of magnitude 4.6.