Jabiluka Mill Alternative
2.0 The Proposal
2.1 Objectives of the Project
The objective of the project is establish an on-site mill at Jabiluka to recover and sell approximately 90,400 t of uranium oxide (U3O8) over a 29 year mine life, under operating and environmental conditions as stipulated by relevant supervising authorities and utilising "Best Practice" Technology.
2.2 The Need for the Project
Guidelines for the preparation of the PER specifically required the need for the proposed development to be fully examined.
ERA has identified a shortfall between production and demand for nuclear power generation material which will open significant market opportunities for high grade material. This increased production has been estimated to provide a national economic benefit of some $3.8 billion (equating to around $6.2 billion in real gross domestic product) over the mine’s life.
With updated information on expected production and value of production from the project as now proposed, the anticipated economic impacts are similar to those presented in the final EIS.
2.3 The Mine and Associated Infrastructure
A detailed description of the Jabiluka Mill Alternative is presented in Section 4 "Detailed Project Description" in the PER.
The project will comprise three distinct phases: a construction phase, lasting approximately 2 years; stage 1 of operations from years 1 to 10; and stage 2 of operations from years 11 to 29. At the completion of stage 1, mining and milling operations will cease at Ranger. Stage 2 involves a subsequent increase in mining and production rates at Jabiluka, expansion of the mill and installation of an acid plant at Jabiluka.
The Jabiluka Number 2 deposit is estimated by ERA to contain 90,400 t of U3O8 within 19.5 Mt of ore at a cut-off grade of 0.2% U3O8. Additional ore may be identified through continuing development and exploration.
The Jabiluka Number 1 deposit, located 400m to the west, is not proposed to be mined. The Number 1 orebody, and possible extensions to the identified resources of Number 2 orebody, have not been included in this assessment. The proponent has made a commitment not to mine orebody Number 1 as part of this project.
Under the JMA proposal, both the mining and milling operations will be located within the Jabiluka Mineral Lease, which has a total area of 7,275 ha. The JMA project area covers approximately 159 ha (including the Ranger-Jabiluka access road).
Figure 2 shows the site layout for the JMA (amended) proposal. And Figure 3 shows the mill layout for the JMA (amended).
The JMA (amended) site layout differs from the RMA (final EIS) in that:
- surface facilities would increase in size to cater for the process infrastructure;
- milling facilities would be required to process the ore;
- liquor storage facilities would be required for the process plant;
- tailings pits (in place of tailings dams as per the original JMA proposal) would be constructed;
- two substantial waste rock (inert) dumps would be constructed; and
- the ore stockpile would become the live feed stockpile for the mill.
During and immediately following construction, 21.5 ha will be rehabilitated, thereby leaving 137.5 ha as the operational area for the project life. The 21.5 ha for rehabilitation includes borrow pits, temporary access and other areas disturbed during the construction. Details are presented on page 4-1 of the PER.
2.3.1 Construction Activities
Construction of the project facilities is proposed to commence as soon as feasible after receiving approval to proceed from the relevant government agencies, taking into account the wet and dry seasons. Figure 4.3 in the PER indicates construction timing for the JMA. The program shows the development of mine decline, underground development, and construction of the processing plant (mill) and associated infrastructure over a two year period.
General arrangements would be similar to that proposed for the RMA (refer section 4.3 in the Draft EIS) but with additional allowance for the development of the mill and associated processing facilities and tailings repositories. Due to the more extensive area of disturbance, the time required for clearing and general earthworks would take longer in some cases although general site activity would be more intense and involve a larger construction workforce and more machinery. Due to the nature of the mill development, it would be necessary to move the timing for the development of the permanent access road forward.
An Authorization under UMEC was granted on 2 June 1998 allowing the commencement of construction of some elements of the project in common for both the JMA and RMA, that is, a portal, access decline and associated infrastructure at Jabiluka.
Earthworks proposed for the first year involve:
- temporary site access road;
- portal and decline development;
- pad for mill, buildings and infrastructure facilities;
- commencement of tailings pit #1 and unmineralised waste rock stockpile #1;
- water management system;
- permanent site access road; and
- power and water supply.
A key factor during the construction phase is the installation of appropriate drainage and erosion control works. Construction involves maximum physical disturbance to the site, which results in a high erosion potential. Site stabilisation and erosion control works will be conducted on a progressive basis wherever possible.
The first of the tailings pits will be excavated immediately on project commencement to contain Total Containment Zone (TCZ) water and tailings upon commissioning of the plant. The second pit will be excavated between years 8 and 9 as the first pit approaches its maximum fill level.
With the development of the JMA amended layout, there will be a considerable reduction in the amount of material needed to be sourced from outside of the project. The excavation of pit #1 will produce approximately 2.7Mm3 (in situ) of benign material. With a swell factor of 1.5, this will produce approximately 4Mm3 of material for site construction works and Stockpile #1. The pit material in excess of construction requirements will be stored in Stockpile #1. Excavation of Pit #2 (around year 8) will produce a further 7.6Mm3 (in situ) of benign material. Some of the waste rock will ultimately be reclaimed from the stockpile to cap the tailings pits.
Equipment required for the construction of the process plant and mine surface facilities, including the access road, would essentially be the same as indicated in the Draft EIS. Construction access for the majority of the process plant construction would need to be of a higher standard than the access available via the Oenpelli Road. Construction of the Ranger-Jabiluka access road would therefore be brought forward to provide this access early in the process plant construction phase.
Ja Ja camp will no longer be required to accommodate construction personnel as accommodation will be provided in Jabiru. Facilities will be provided for a single person caretaker as well as a temporary fuel storage and hardstand laydown area.
2.3.2 Mining
The Jabiluka resource is described in detail in the Draft EIS. The resource extent to be mined under the JMA is the same as for the RMA.
The PER proposes an initial ore production rate of 200,000 t/a in the first year and then 450,000 t/a for the next nine years of operation. When Ranger production ceases, the production rate at Jabiluka would increase to 900,000 t/a, a similar rate to that proposed for the RMA. It is also proposed to maintain a head grade as high as possible in the first 10 years, specifically targeting greater than 0.6% U3O8 for the first 5 years and then greater than 0.4% for the next 5 years.
The methods of mining and the underground mine configuration for the JMA would not vary from that described for the RMA in the Draft EIS (sections 4.6.3 to 4.6.5). Due to modifications to the mining rate in order to access the higher grade ore areas, the internal declines to the eastern and western stoping areas would be developed more rapidly.
Uranium bearing ore will be mined by underground techniques using non-caving mining methods adapted to the different sizes, attitudes and grades of the orebody. The mining method uses drilling and blasting to break up a large cavity of ore, which is then extracted from a tunnel at the base. Empty stopes will be back-filled with cemented tailings paste from the Jabiluka mill.
The ventilation system has been designed to manage and control ventilation in a way that will maintain employee radiation exposure levels below the 20 mSv/a average dose limit proposed by the International Commission on Radiological Protection (ICRP).
Mine access ways and working places will be positioned in barren or low grade material, with high grade ore mined by methods designed to reduce radiation exposure of the workers.
Section 4.6.9 in the Draft EIS identifies the general strategies for health, safety and radiation management at the mine. Such strategies also apply for the JMA and are discussed in further detail in Chapter 9 of the PER.
These mining methods proposed are standard for other underground mines.
A run-of-mine (ROM) ore stockpile will be developed on an impervious pad immediately to the south of the decline portal. The ROM pad would be 90 m x 90 m in size and underlain by double-layer of 1.5 mm HDPE. Ore will be transported from underground by means of haul trucks which could dump either onto the ROM stockpile or directly into the primary crusher dump pocket. The ROM storage would hold a maximum of 50,000 t on which would be reclaimed by front end loader and fed into the crushing and milling circuit of the process plant.
Adjacent to the ROM stockpile, a mineralised waste stockpile will be established for temporary storage of mineralised waste. The mineralised waste will be progressively placed back underground or into the tailings pits along with the tailings paste.
At the completion of operations the underground mine will be completely sealed, mine surface facilities removed and disturbed areas landscaped and revegetated to approved standards. The haul road may remain if requested by the Traditional Owners.
2.3.3 Ore Processing
The JMA proposal provides for an on-site mill and processing facilities. Section 4.5 of the PER provides a detailed description of the ore processing. Ore processing will essentially be the same as the process employed at the Ranger mine.
Initially an ore treatment plant will be constructed with a design capacity to process 450,000 t/a of high grade ore for a nominal production of 2,700 t/a of U3O8. The plant would then be expanded in about year 10 to coincide with the completion of milling operations at Ranger. The expanded plant would process 900,000 t/a of ore of a lower grade corresponding to an average output of around 4,000 t/a. Space has been included in the site layout for the plant expansion. The ore process would be almost identical to the current operations at the Ranger process plant. This is standard technology for uranium ore processing. The site layout for the plant area is shown in Fig 4.8 of the PER and process flowsheets are presented in Figs 4.9 and 4.10.
The process plant would include facilities for the following:
- crushing and storage of run of mine ore;
- semi-autogenous milling of ore followed by ball milling;
- thickening of mill discharge in a high rate thickener to 55% solids;
- leaching of ore with sulphuric acid in six mechanically agitated tanks;
- counter current decantation thickening of leach residue in seven thickeners;
- clarification of thickener overflow by reactor clarifier and polishing filters;
- recovery of soluble uranium by solvent extraction;
- stripping of uranium with ammonium sulphate solution;
- precipitation of ammonium diuranate followed by dewatering and calcination;
- packaging and storage of product;
- neutralisation of tailings with lime;
- disposal of tailings as cemented paste fill to underground backfill or tailings pits; and
- facilities to receive, store and mix reagents used in the process.
Acid will be produced at the acid plant at Ranger or trucked from Darwin during the first 10 years of operation. An acid plant will be installed at the Jabiluka mine site prior to completion of milling operations at Ranger.
2.3.4 Tailings
Tailings produced from the ore processing are pumped to a tailings neutralisation circuit. Here lime is added to raise the pH to 5.0 in a series of two agitated vessels with a total residence time of four hours. The resultant slurry is stored in a large agitated tank to hold 15 hours supply of neutralised tailings. The neutralised tailings slurry is then filtered on a single belt filter and the resultant filter cake is repulped with a cement additive prior to being pumped to the tailings disposal site. Approximately 80% of the tailings to be discharged underground would receive a 4% cement addition prior to being pumped to the primary stopes as paste backfill. The remainder of tailings would have a 1% or more cement addition and would be preferentially pumped to secondary stopes as the underground void became suitable for such disposal. Tailings that could not be pumped to underground due to space limitations and operational constraints would be pumped to surface tailings disposal repositories.
Due to the swell factor associated with the ore processing operation, approximately 50% of the tailings can be disposed as underground backfill and the remaining 50% disposed in surface repositories. The original JMA proposal has been significantly improved by the amended JMA proposal to replace the above ground tailings dams with two purpose built tailings disposal pits.
Pit #1 has a total containment volume of 2.6 Mm3 and Pit #2 has a total containment volume of 7.6Mm3. The total volume of tailings to be disposed of in the tailings pits is 5.4 Mm3. The excavation of the two tailings pits will create the need for the construction of two waste rock dumps adjacent to the pits. These waste dumps will comprise of inert Kombolgie sandstone and a small amount of surface soil identified as earthy sands.
Tailings disposal issues are discussed in detail in Section 4.6 of the PER.
2.3.5 Other Infrastructure
Ventilation
The ventilation system presented for the RMA (see Section 4.5.3 of the Draft EIS) would also apply to the JMA. However, due to the possible restrictions on access to the Boyweg site area (see Section 2.2.2 of the PER), ERA considered options to move the location of some of the fresh air vent shafts if required to protect the site. Relocation of some vent shafts would involve some additional underground shaft development.
Administration/Workshop
The administration and workshop facilities for the JMA will be similar to those proposed for the RMA with some increase in the size of those that cater for workforce personnel. The increase in the operational workforce (from a maximum of 110 personnel for the RMA to 170 for the JMA) will require increased ablution, mess and parking facilities. Workshop and administration facilities would be essentially the same assuming administration, store, workshop and laboratory facilities stay at Ranger.
Truck Wash Station
Truck wash stations were proposed for the RMA primarily to wash down the haul trucks carting ore between Jabiluka and Ranger. Demands on such a facility with the implementation of the JMA would be significantly reduced; however all construction and earthmoving machinery or other vehicles that may have come into contact with contaminated material would be washed down at this station prior to departure to Ranger. A similar arrangement will also apply for vehicles departing from Ranger to Jabiluka. All wash water from this facility will be regarded as contaminated and be contained within the Total Containment Zone.
Water Supply
Two alternative sites have been identified as potential locations for a borefield to supply potable water and plant water. The primary target is an area 0.8 km x 1.2 km approximately 1–2 km southeast of the mine portal. This area was identified on the basis of interpreted intersecting faults and fractures in the Kombolgie Sandstone. The second potential borefield location is in the Hades Flat area to the south of the Jabiluka Outlier and is approximately 6–8 km south of the mine. Drilling and testing of the borefield was completed in 1981 and the long-term yield was estimated to be 6,230 m3/d (AGC 1981).
Groundwater volumes required by the Mill Alternative are estimated to be an average of 3.7 L/s ranging up to 5.7 L/s as a worst case scenario. It is anticipated that this volume can be obtained from the Kombolgie Sandstone in the primary target area to the south east of the mine portal. Drilling and testing of this site is planned once access is available. The Hades Flat alternative may be investigated further if suitable supplies are not located close to the mine.
Sewage Treatment
The increased personnel requirement for the JMA (a maximum of 170 at Jabiluka with a possible peak at any one point in time of up to 220 personnel) would require an increased capacity (essentially on a personnel pro-rata basis) in the facilities; however the method of treatment (i.e. septic as opposed to a sewage treatment plant) is considered to be appropriate. Sludge from the tanks would be removed by an approved contractor and disposed of at the Jabiru sewage treatment facility. Investigations have indicated that this plant has adequate capacity to accommodate this material.
If, in the longer term, the balance of personnel (approximately 70 at Ranger) have to be relocated to Jabiluka, ERA would commit to designing and building a suitable sewage treatment plant.
Fuel Storage
Both diesel and petrol fuels would be stored in cylindrical tanks on a concrete pad and footings with the area surrounded by concrete bund walls. The void volume in the bund would be in accordance with AS 1940. Tankage would consist of two 110,000 L diesel tanks, one 4,000 L petrol tank and one 3,000 L lube tank. Tank capacities would be sufficient to provide the approximate consumption for operations over a one month period.
Explosives Storage and Handling
The provisions outlined for explosives storage and handling in the Draft EIS (Section 4.5.9) and the Supplement (Section 5.5.7) remain valid for the JMA.
Power Supply
Initially, on-site diesel generators will provide power. Power will then be delivered to the mine site by a 66 kV transmission line running alongside the access road from the Ranger power station. All lines will be aerial except at major creek crossings where they will be incorporated within bridge structures.
Fencing
The main purpose of the fencing is to delineate the boundaries of the Jabiluka Project Area and haul road corridor so that there is a clear demarcation to mine employees not to enter adjacent lands, particularly the Jabiluka outlier.
The location and configuration of fencing around the mine site and haul road will be the subject of discussion with the Aboriginal landowners. Fencing will be established along the Australian Heritage Commission area boundary as well as most of ‘Mine Valley’, the mine site and the haul road corridor down to the boundary with the Ranger Project.
