Merlin Diamond Project
Environmental Assessment Report and Recommendations
Burnside Project Northern Gold NL
by
M.J.Nolen
Senior Environmental Officer
Environmental Assessment and Policy
Department of Mines and Energy
August 1997
| Contents | |||||
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| 1.0 | Introduction | ||||
| 2.0 | The Proposal | ||||
| 3.0 | Major Issues | ||||
| 4.0 | Environmental Assessment | ||||
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| 5.0 | Conclusion | ||||
| Appendices | |||||
| A | Synopsis of Advisory Bodies and Public Comments | ||||
1.0 Introduction
The Merlin Diamond Project, Public Environmental Report (PER) has been assessed in accordance with provisions of the Environmental Assessment Act and administrative arrangements between the Department of Lands, Planning and Environment and the Department of Mines and Energy.
This report assesses the possible environmental impacts of a proposal by Ashton Mining Limited to mine six kimberlite pipes (small open pits) and two bulk sample pits in the McArthur/Glyde region, 720km southeast of Darwin, Northern Territory.
Included in this report is a discussion of the main issues associated with the proposal, the potential impacts of the proposal on the environment and recommendations on how the identified impacts should be managed.
The assessment considered comments by the following advisory bodies:
- Aboriginal Areas Protection Authority
- Department of the Chief Minister
- Department of Mines and Energy
- Department of Lands, Planning and Environment
- Department of Primary Industries and Fisheries
- Department of Transport and Works
- Northern Territory Attorney-General's Department
- Parks and Wildlife Commission of the Northern Territory
- Power and Water Authority
- Museum and Art Gallery of the Northern Territory
- Territory Health Services
- Work Health Authority
Public Comments - One submission.
A synopsis of the comments is provided in Appendix A.
The contents of this report form the basis of advice to the Northern Territory Minister for Lands Planning and Environment in accordance with provisions of the Environmental Assessment Act and administrative arrangements between the Department of Lands Planning and Environment and the Department of Mines and Energy.
The proposed project is a relatively short term operation (2.5 years) mining 730,000 cubic metres of ore and is considered to have a limited potential to cause any significant long termed environmental impact, if appropriately monitored and managed.
Assessment of the PER has identified a number of aspects that require ongoing attention by Ashton Mining Limited. These issues are best addressed through reviewable Mine and Environmental Management Plans that require formal approval by the Department of Mines and Energy.
It is recommended that no further assessment of this proposal is required under the Environmental Assessment Act.
Recommendation 1
Ashton Mining Limited shall ensure that the proposal is implemented in accordance with the environmental commitments and safeguards identified in the Merlin Diamond Project, Public Environmental Report, or as modified in this assessment report, or an approved Environmental Management Plan.
2.0 The Proposal
Ashton Mining Limited have applied for MLN1154, covering their existing exploration leases ERL141, ERL142 and SEL8630, to develop the Merlin Diamond Project, located approximately 75 kilometres SSE by road from the McArthur River Mine, Northern Territory.
Ashton Mining Limited proposes to develop six open pits and two bulk sample pits over a period of 2.5 years. Ashton Mining Limited will mine 730,000 cubic metres of ore by open cut method from the eight pits for processing on site. The tailings produced in processing will be discharged to two tailings dams (fine and coarse tailings).
It is estimated that approximately 4.8 million cubic metres of waste rock will be produced from the eight pits and this will be placed into four above ground dumps located adjacent to the pits.
All of the kimberlite pipes to be mined in this first stage have the potential for future expansion and may lead to the eventual expansion of the open pits and/or underground mining at a future stage. The surrounding area also has significant exploration potential and additional kimberlite pipes may be discovered in the area.
3.0 Major Issues
The major issues associated with the Merlin Diamond Project are:
- Water management
- Weed and feral animal management
- Tailings management and rehabilitation
- Rehabilitation
- Heritage site management
This proposal differs from the majority of other mining projects in that the ore, surrounding waste rock and processing methods are relatively benign.
The diamond bearing material is composed of kimberlite (ultrabasic alkaline olivine/serpentine mineralogy). Waste rock is composed of sandstones, with minor inter-bedded siltstones and mudstones overlayed with a capping of laterites and skeletal sandy soils.
The processing methods are mainly mechanical with minimal use of chemicals in the processing. Processing of the diamond bearing material will center on a gravity separation process with the addition of ferrosilicon (non-hazardous) to aid processing.
Tailings will be comprised of finely ground waste rock, flocculants and water and will be placed in two tailings dams (coarse and fine). The tailings will be predominantly alumina-silicates in clay form and are expected to maintain a near neutral pH throughout.
4.0 Environmental Assessment
4.1 Water Management
Additional information was requested from Ashton Mining Limited in regard to their proposed water management plan and this was provided and assessed within the PER assessment period.
Key issues associated with the surface water runoff are erosion and sediment control, particularly during the initial pre-stripping and clearing for the dumps and pits and during dewatering of the mine pits. Sediment dams and erosion control structures will be constructed downslope of all waste dumps and mining pits to manage these issues.
Concerns relating to the mine water management system focus on containment of water from the mining and waste dump runoff and the potential effects on surface water.
Designs, schedules and monitoring proposals for the proposed water management systems will be required prior to the commencement of the project.
Recommendation 2
Ashton Mining Limited should prepare a water management plan which includes:
- site water balance;
- water storage design criteria;
- characterisation of discharge waters;
- a groundwater monitoring strategy; and
- monitoring of water quality/quantity prior to release/disposal.
This water management plan should be incorporated into the Environmental Management Plan and reviewed on a routine basis by the Department of Mines and Energy.
4.2 Weed and Feral Animal Management
The noxious weed Xanthium occidentale (Noogoora burr) occurs in the vicinity if the access road, particularly along watercourses. Appropriate management will be required to ensure that weed seeds are not transported during road construction and maintenance.
The project area itself has been relatively isolated due to its location and lack of access and as such safeguards need to be implemented to prevent the incursion of introduced and problem floral species into the area.
One of the prime ways of weeds entering a relatively weed-free area is on earth moving equipment, or in soil, fill, sand, gravel or other building materials. The disturbance occasioned by these activities also enable weed establishment and spread.
The cane toad, Chaunus marinus is found in numbers in the McArthur/Glyde Rivers region. Although the cane toad has become abundant in a range of habitats in the region appropriate management will be required to prevent the transportation of the toad to areas currently free from infestation.
Recommendation 3
In line with the Northern Territory Weed Management Strategy, 1996 - 2005, Ashton Mining Limited should design a weed management plan covering the mine site and access corridor to prevent the introduction and spread of weeds.
Ashton Mining Limited should implement a strict inspection program to prevent the transportation of cane toads from the area.
This information should be incorporated into the Environmental Management Plan and reviewed on a routine basis by the Department of Mines and Energy.
4.3 Rehabilitation
The PER identifies the construction and utilisation of two tailings dams for coarse and fine tailings respectively. There is the possibility that if the fine tailings are very fine, as is likely, these may be difficult to rehabilitate, and Ashton should investigate the possible need for discharge of thickened tailings. Additional information will be required prior to approvals being given for construction.
Recommendation 4
Ashton Mining Limited should prepare detailed tailings dam designs and tailings characterisation.
This information should be incorporated into the Environmental Management Plan and reviewed on a routine basis by the Department of Mines and Energy.
The rehabilitation strategy proposed in the PER is considered adequate at this time. During the development and operation of the mine, a detailed rehabilitation plan will be developed through rehabilitation trials and on-site experience.
Recommendation 5
Rehabilitation trials should be undertaken to develop a final rehabilitation strategy.
This information should be incorporated into the Environmental Management Plan and reviewed on a routine basis by the Department of Mines and Energy.
4.4 Heritage
A number of archaeological sites were identified near the proposed mine site and along the access road. The proposed development has the potential to impact on at least two of these, Catfish Hole 1 and Catfish Hole 2.
With respect to Catfish Hole 1 the preferred option is to realign the track and to construct a temporary fence to avoid damage by machinery operating in the area.
In regard to Catfish Hole 2 the PER identifies two protective strategies, these recommendations are supported and the proponent is strongly urged to adopt these measures.
Heavy machinery should be strictly prohibited from operating within the vicinity of archaeological sites.
Some form of fencing may be required to ensure that these sites are not inadvertently disturbed.
Recommendation 6
Ashton Mining Limited should, with respect to Catfish Hole 1, realign the access road and construct a temporary fence.
With respect to Catfish Hole 2, Ashton Mining Limited should fence the northern margin of the site and erect warning signs to prevent disturbance and damage.
This information should be incorporated into the Environmental Management Plan.
4.5 Environmental Monitoring
Ashton Mining Limited has outlined in the PER a proposed sampling and monitoring program. All components of the monitoring program will be implemented at the commencement of operations, including access road construction. Baseline surface water quality and groundwater level monitoring will be completed before the commencement of mining operations.
Recommendation 7
Ashton Mining Limited should complete and submit a baseline and operational monitoring programme, including identified parameters and thresholds, in an Environmental Management Plan.
Ashton Mining Limited should operate in accordance with the approved plans, with these plans being reviewed by the Department on a regular basis.
4.6 Other Issues
Social
The possibility of social impact on the township of Borroloola and surrounding area, by the construction and operational workforce, will be minimal. Given the isolation of the site, 130km by road, the fly in fly out staffing strategy and the accommodation of all construction and operational staff on-site (all employees and contractors will remain on site during their 14 day roster period).
Flora and Fauna
Several species of conservation significance were identified in both the project area and proposed access road corridor. The areal extent of the project, however, is small compared with the surrounding habitat, and if the proposed conservation measures are adhered to, there should not be a significant lasting effect on the local flora and fauna.
The Environmental Management Plan needs to consider measurers to manage flora and fauna of conservation significance. Additional surveys may be required to determine the relevant management strategies.
5.0 Conclusion
Assessment of the PER has identified some issues which will require attention/clarification by Ashton Mining Limited. These issues can be adequately addressed through existing regulatory and administrative processes such as the reviewable Environmental Management Plan.
As a result of this assessment the Department of Mines and Energy will require Ashton Mining Limited to prepare an Environmental Management Plan (EMP) for the approval of the Secretary. The EMP will address the 'Commitments' made by Ashton Mining Limited in the PER and all environmental issues identified as relevant in this report and Attachment A.
These issues include:
- Water management;
- Rehabilitation;
- Heritage sites management; and
- Environmental monitoring programs.
Through the assessment of monitoring results the EMP, or parts thereof, will be reviewed on a regular basis to assess the performance of management practices. Adverse trends can be detected before developing into environmental problems and can be dealt with through appropriate modification to management practices. The EMP becomes a practical management tool that can be utilised for environmental audit purposes.
Recommendation 8
Ashton Mining Limited should prepare and submit Mine and Environmental Management Plans to the Department of Mines and Energy for approval.
Ashton Mining Limited should operate in accordance with the approved plans, with these plans being reviewed by the Department on a regular basis.
Prior to commencement of any changes to the Mine Plans or Environmental Management Plan, Ashton Mining Limited will submit revised plans for approval.
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