7.   TAILINGS MANAGEMENT

7.2.1  

Sishen Mine

Sishen Mine currently has four tailings (slimes) dams and one plant waste rock dump. The tailings dams and waste rock dump are situated on near-horizontal ground. The dams contain iron ore washings. All of the dams are operational, and are used on a rotational basis. The waste rock dump is also operational, receiving coarse reject material from the plant.

Currently, each tailings dam has a top operating surface of approximately 700m by 700m, with the total surface area being 195.6Ha. The dams are about 10m high on average. The average monthly tonnage being deposited on to the operating tailings dam is 150ktpm (dry tonnes), which equates to 1.8Mtpa. The waste rock dump is about 60m high and currently covers an area of about 1km by 0.7km. Coarse waste is fed from the plant on to the dump via a conveyor at a current rate of approximately 360tph, which equates to 3.1Mtpa.

Current Conditions:

• Tailings Dams: The site inspection revealed that the tailings dams appear to be in good condition. No toe-line seepage was noted. The existing freeboard on the dams is good with the minimum freeboard being about 2.5m above current pool levels. Much of the slurry washings consist of clay, noted at about 26% by mass. The clay has exceptional impermeability qualities, which appears to be the main reason why the designed underdrain outlets and toe-line remain dry. Each dam has its own dedicated ringfeed discharge pipeline. This is a 200NB steel line with spigot holes at 1.0m centres. The holes are plugged using timber wedges. The slurry product has a sand fraction of about 17% by mass, which settles out quickly. This sand fraction forms the perimeter section of the beach and is about 50m wide. It is this sand fraction which provides much of the stability to the ring-dyke system of each dam. The balance of the fines consists of silt, equating to about 57% by mass. The dams do have standpipe piezometers installed in-situ.
• Plant Waste Rock Dump: The Sishen waste rock dump is located about 600m N/E of the tailings dam complex and is approximately 60m high. The sides of the dump have a slope angle of about 37°, which is the natural angle of repose of the loose waste rock. Waste rock is delivered to the dump on a conveyor belt system and is end-tipped off the conveyor using a rotatable conveyor section. Visually, the rock varies from about 150mm down to 25mm, although there are areas where a significant amount of fines – down to dust, were noted, hence the reason for erosion seen at the end of the N/W advance. The rock is delivered at about 8.485tpd, which equates to 3.1mtpa. It is estimated that the placed waste rock has an in-situ dry density of about 1,9tpm3. The dump was inspected for signs of cracking, sliding and toe-line heave. No abnormal signs were observed in this regard. It is concluded that the waste rock dump is in good condition and stable. However, the following is noted: The base of “inner” depositional area is covered with domestic refuse trucked in from Kathu; felled trees have also been placed in the vee area of the dump’s footprint; and some erosion was noted along the slope of the western flank and at the end of the N/W advance of the dump. While no signs of instability are currently apparent, it should be noted that the domestic refuse and cut vegetation could cause a rock slide should the thickness of domestic waste become excessive and or become saturated. The top (flat) surface of the dump should be inspected on a weekly basis for any signs of slumping/cracking in the placed waste rock, insofar that the conveyor tipping system is threatened. (Conveyor systems forming waste stockpiles have been known to collapse under sudden differential settlements initiated by sliding.)

Tailings Capacity:

• Tailings Dams: Only one dam at a time is used for slurry deposition. Each dam is continuously used for a period of between 12 and 16 months before switching over to the next dam. Approximately 150 ktpm is presently being deposited on the slimes dams on a rotational basis. The current rate of rise (“RoR”) of the operating dam is approximately 1,75m/yr during operations. However, the overall rate of rise of the 4-dam complex is currently 0,44m/yr. No problems are envisaged under the current dispensation. It appears that the average in-situ dry density of the settled tailings is about 2.31tpm³. (Six near surface density samples were taken for laboratory testing. The results have been meaned, slightly adjusted and incorporated in the model.) The dams do have standpipe piezometers installed in-situ.

The foregoing capacities are based on the tailings dams having step-ins (benches) formed at 7m vertical intervals and being 10m wide. This applies to all flanks of the four tailings dams, giving an overall side slope angle of about 18°. Scenarios relating to 50m heights have not been reviewed in depth, as Scenarios 2 and 6 indicate that the respective tonnages can be placed for 67 and 45 years, beyond July 2005. The current LoM ends in December 2028, some 22.5 years earlier. However, based on the above side slope considerations the capacities to 50m in height are as follows: 4 dams only (56Mm3 ~ 117.6Mt) and 4 dams and cross (88.5Mm³ ~ 185.8Mt). It is likely that if the tailings dam complex rises beyond 35m in height, two dams and the cross may have to be operated simultaneously and that more stringent monitoring will also be necessary.

• Plant Waste Rock Dump: SRK has undertaken an evaluation of the remaining capacity of the plant waste rock dump based on the currently defined footprint area, which is almost square in the direction of current advance. The remaining base area is about 500m by 500m. The dump is currently about 60m high. Based on current geometry the dump has a remaining capacity of about 12.0Mm³. At an assumed in-situ density of 1.9tpm³, the remaining mass volume is 22.8 Mt. At a current delivery rate of about 360tph arising from the plant, it will take 7.25 years to complete. However, with the SEP plant earmarked to come on stream from July 2007, and ramping up to full production by June 2008, the life of the current plant waste rock dump will be less. Taking ramp-up figures into consideration, the existing dump will run out by the end of December 2009. This date assumes that the dump will receive both current and SEP waste; that only the current footprint is used and that the in-situ density is 1.9t/m³. In order to further accommodate both current and SEP waste streams till the end of 2028, an additional site will need to be secured. A base area of approximately 267ha will be needed for the new footprint. This equates to a square base having 1.2km long sides. The dump would have side slopes of 1V to 1.5H and be 60m high. The mass volume of this dump will be about 150Mt ~ 80Mm³. However, the Mine needs to confirm the actual in-situ density of the waste rock. This should be done on a quarterly basis to monitor trends and to obtain a reliable mean, which can be used to size future disposal zones.

Tailings Cost Review:

• Tailings Dams: With regard to operating cost requirements, an additional ZAR0.45mpa should be budgeted from 2006 onwards. This amount will be necessary to cover step-in formation, the cleaning out of existing drainage trenches in the event that bench penstocks are necessary, as well as installing bench penstocks. General operating costs relating to slimes handling at the plant are already included in the plant budget, in the LoM Plan.

In terms of the capital cost requirements the following is noted:

• If the slimes dams continue along the current sliming philosophy, and the product remains unchanged, new elevated penstocks will be required when the dams reach a height of about 25m. Replacement costs at today’s prices are estimated at ZAR2m per penstock. The penstock decant system should incorporate a “2-tower arrangement”, as this will provide some flexibility if a tower should fail. The base pipeline to the pump-house is also likely to need replacing. It is estimated that the replacement of the base pipeline and valves will be about ZAR2,5m – an amount of ZAR10,5m should be allowed for capital expenditure in 2032;
• An amount of ZAR0.75m should be budgeted to cover design review costs prior to handling of the SEP (and any other washings) that may arise. The study must focus on the impact of the SEP tailings on the current tailings dam complex, the best means to maintain an ongoing level of stability, as well as maintaining acceptable risk levels against failure linked to Zones of Influence.
• If the design review indicates that the preferred way forward is to incorporate the cross into future sliming operations (current plus SEP), then the Capital expenditure amount indicated by Sishen management should be sufficient to cover the incorporation, this amount being ZAR36m.
• Plant Waste Rock Dump: In assessing operating costs for the maintenance of the Plant Waste Rock Dump some additional cost is envisaged over and above that allowed in the plant expenditure. This will be necessary for slope configuration using a bulldozer part-time. It is believed that an additional ZAR0.45mpa should be budgeted from 2010 onwards to achieve such aims. Concerning capital cost requirements for the plant waste rock dump, no immediate capital is necessary. However, for the future expansion of the dump, it is recommended that an amount of ZAR0.05mpHa be set aside for the preparation of the dump base. SRK believes that an area equating to 154Ha should be secured for this purpose. SRK also notes that the proposed waste rock dump as indicated on drawing ALL-PPTT-SSS-D-XX Rev RR has a base area of 202Ha. SRK calculations show that according to information supplied (i.e. future production of 173Mt till December 2028), a base area of about 154Ha should suffice. The side-slope geometry indicated on the above-stated drawing is good. Therefore, a Capital expenditure amount of ZAR7.7m (say ZAR8m) should be allowed for base preparation. This amount can be phased in equal amounts to years 2008, 13, 18 and 23 – in ZAR2m modules.

7.2.2  

Sishen South Project

It is noted from documentation provided that it is intended to operate the Sishen South Project on a direct shipping ore basis and for this reason no tailings dams will be required at the Sishen South Project. It is noted that provision has only been made for waste rock stockpiles strategically placed on the site. An initial capital amount of ZAR1m should be budgeted for footprint preparation and thereafter an operating cost amount of ZAR0.25mpa for shaping of the waste rock dumps.

7.2.3  

Thabazimbi Mine

Thabazimbi Mine currently has four tailings (slimes) dams. These are hillside tailings dams accommodating iron ore washings. Three of the dams are currently operational and one is dormant. The following indicates current conditions:

Tailings Capacity: SRK has reviewed what is perceived to be the remaining current capacity on the tailings dams, based on our site inspection and documentation at hand. During the site visit, a number of near surface in-situ “undisturbed” samples of tailings were taken for laboratory testing. The samples were taken from the beach adjacent to the catwalk on dam 1. Returned results indicate that the finer material in the dam has a near surface in-situ dry density of 1.75t/m³. This value has been used in the SRK model to determine the RoR and remaining life of the dams. While it is understood that the average tonnage for the past 18 months has been about 23ktpm, the highest monthly value was 42.5ktpm. As the variation spread is large, SRK has elected to use 40ktpm as the baseline value. With the above-stated in mind, the remaining life of the dams is as follows:

• 40ktpm scenario distributed pro rata on surface areas – with dam 2 dormant – 5.96 years. Say 6 years (2.86Mt ~ 1.63Mm³); and
• 40ktpm scenario distributed pro rata on surface areas – with dam 2 recommissioned – 6.6 years (3.17Mt ~ 1.81Mm³).

SRK has selected the preferred rate of rise based on the assumption that no materials characterisation records are available, neither slope stability analyses. From the tables set out below, it can be seen that the recommissioning of dam 2 will provide some respite to the current RoRs and will also help to lower risk.

Tailings Cost Review: With regard to operating cost requirements, an additional handling cost of ZAR1.75/t of dry solids deposited as presented by Fraser Alexander Tailings is considered a reasonable rate (excludes VAT). This rate includes plant for raising the perimeter paddock walls which is also required. In terms of the capital cost requirements the following is noted:

• Undertake a detailed stability review (piezocone tests as applicable) and report compilation. (Continuation report) on all 4 dams and return water dam. Estimated cost of ZAR0.3m;
• Upgrade the operating manual, including appropriate topographical survey for the existing complex. Estimated cost of ZAR0.275m;
• Upgrade Code of Practice for the existing complex. Estimated cost of ZAR0.075m; and
• Install piezometers, including supervision and survey on all 4 dams. Estimated cost of ZAR0.08m.

A total additional capital cost of ZAR1.1m is estimated.

1 SRK’s preferred RoR is 1.00m/yr and is based on the following:
	No designed under-drains under the current tailings dams;
	Fine (predominantly clay) material seen in the perimeter wall make-up. Operating techniques can be improved; and
	No stability analysis seen at the time.

Until such time as it can be proved through adequate engineering analyses that a higher RoR is not detrimental to the stability of the existing tailings dams, SRK does not advocate a higher RoR. Even our RoR limitations should be reviewed, but for the interim it does set a conservative limit, which will help in lowering the current risk of failure. SRK’s RoR recommendation will also bring on stream a new tailings dam which, as we see it, is necessary in lowering risk on the existing tailings dams.