CHAPTER 3 – Project description...Chapter 3 - Project description Twin Bonanza 1 Gold Mine 3.1...

ABM RESOURCES NL DRAFT Environmental Impact Statement

Page 56 of 108 Chapter 3 - Project description Twin Bonanza 1 Gold Mine

CHAPTER 3 – Project description

3.1 Project background & history ............................................................................................ 58

3.1.2 Project area geology .............................................................................................. 58

3.1.2.1 Regional geology................................................................................................. 58

3.1.2.2 Resource drilling and surface work .................................................................... 59

3.1.2.3 Resource estimation ........................................................................................... 61

3.2 Proposed project ................................................................................................................ 61

3.2.1 Staged approach to development designed to minimise risk and maximise return ............................................................................................................................... 62

3.2.2 Staged approach versus feasibility studies ................................................................ 62

3.2.2.1 Stage one – trial mining and processing ........................................................ 64

3.2.2.2 Stage two – open pit mining to approximately 35 metres depth .................. 64

3.2.2.3 Stage three – open pit mining ........................................................................ 65

3.2.2.4 Beyond stage three............................................................................................. 65

3.3. Proposed mining project ................................................................................................... 66

3.4 Mining ................................................................................................................................ 74

3.4.1 Overview .................................................................................................................... 74

3.4.2 Mining techniques – open pit excavation and mine sequencing .............................. 74

3.4.3 Open pit stability ........................................................................................................ 77

3.4.4 Slope design ............................................................................................................... 77

3.4.5 Haul ramp design ....................................................................................................... 78

3.4.6 Mining activities ......................................................................................................... 78

3.4.7 Mining offices, workshops and associated infrastructure ......................................... 79

3.4.8 Drilling and blasting .................................................................................................... 79

3.4.9 Mining and ancillary fleet ........................................................................................... 80

3.4.10 Mine water management ........................................................................................ 81

3.4.11 ROM pad / ore haulage ............................................................................................ 85

3.4.12 Handling and stockpiling of waste rock and waste rock design .............................. 85

3.4.12.1 Physical characterisation of waste ................................................................... 88



3.4.12.2 Chemical characterisation of waste ................................................................. 88

3.5 Processing .......................................................................................................................... 89

3.5.1 Processing facilities .................................................................................................... 89

3.5.2 Concentrate upgrade ................................................................................................. 92

3.5.3 Tailings ........................................................................................................................ 92

3.5.3.1 Characterisation of tailings ................................................................................. 94

3.5.4 Tailings dam ................................................................................................................ 94

3.5.4.1 Tailings dam design ............................................................................................ 95

3.5.5 Clay source for tailings dam construction .................................................................. 96

3.5.6 Process water ............................................................................................................. 96

3.5.7 Project process inputs and outputs ........................................................................... 97

3.6 Concentrate storage, pouring / shipping ........................................................................... 97

3.7 Infrastructure ..................................................................................................................... 97

3.7.1 Potable water supply ................................................................................................. 97

3.7.2 Power ......................................................................................................................... 98

3.7.2.1 Power generation and power requirements ...................................................... 98

3.7.2.2 Thermal solar energy .......................................................................................... 99

3.7.3 Fuel (diesel) supply .............................................................................................. 100

3.7.4 Fuel storage ......................................................................................................... 100

3.7.5 Explosives storage .................................................................................................... 101

3.7.6 Sewage ..................................................................................................................... 101

3.7.7 Accommodation village ............................................................................................ 101

3.7.7.1 Telecommunications ........................................................................................ 103

3.7.8 Airport ...................................................................................................................... 103

3.8 Construction activities ..................................................................................................... 104

3.8.1. Pre-construction phase ........................................................................................... 105

3.8.2 On-site civil construction.......................................................................................... 105

3.8.3 Construction workforce ........................................................................................... 105

3.9 Operational activities ....................................................................................................... 106

3.9.1 Operational workforce ............................................................................................. 106

3.9.2 Emissions .................................................................................................................. 107

3.10 Rehabilitation and closure ............................................................................................. 108



3.1 Project background & history The Twin Bonanza gold project is a leading asset of ABM and is one of the last known out-cropping high-grade gold deposits in Australia that has not been previously mined. ABM has spent in excess of $20 million on this ground since acquiring the Twin Bonanza tenement from Newmont Asia Pacific (Newmont) in March 2010. Prior to ABM’s involvement in the project, previous owners had carried out exploration work in the area.

Since acquisition ABM has completed a number of close spaced drilling programs along with extensive surface sampling which has led to a maiden resource at Old Pirate in April 2012. The April 2012 JORC Compliant Resource estimation for Old Pirate was subsequently updated in the first quarter of 2013.

At the time of acquisition of the Twin Bonanza Project Newmont had completed 315.8m core drilling, 4,400m reverse circulation (RC) drilling, 514.5m core tails to RC drill holes and 10,877m of other forms of drilling (totalling 16,107m) at Old Pirate. ABM has drilled an additional 44,416m within the proposed mineral lease area, closing up the drill spacing to a nominal 25m x 25m in key parts of the deposit.

The total operational workforce for production (mining and processing operations) is estimated to be approximately 68 personnel. The majority of the operational employees will work a 2 weeks on/1 week off roster (mill – day and night shift), or 2 weeks on/1 weeks off roster (mine – day shift only). Site based management, technical and support staff will work either a 2 weeks on/1 week off roster or other rosters as such as required commensurate with their roles.

3.1.2 Project area geology

3.1.2.1 Regional geology

The regional geology of the project is almost exclusively on Proterozoic age marine turbidite sediments, of the Dead Bullock Group and Killi Killi formations (Boucher, 2011), and intruded by the Buccaneer Monzogranite in the northwest of the project area. To the east the Killi Killi formation transitions to the Dead Bullock Group. Air-photo interpretations and field mapping show low-levels of outcrop outside of the main Old Pirate trend. The rocks are all Proterozoic age with deposition 1900 to 1800Ma and intrusions / mineralisation 1800Ma to 1790Ma.

Local geology

In the vicinity of the Old Pirate deposit, outcrop and drill core reveal very coarse to fine grained sands inter-bedded with 2 to 8m wide shale. Occasional amalgamated coarse sands and thicker-shales occur, with the latter hosting the gold-bearing quartz veins. A solitary chert bed has been found at Old Pirate and acts as a key marker horizon in geological



mapping. The Old Pirate anticline can be traced 2.5km south and 5 km north of the main deposit area.

Mineralisation

The Old Pirate high-grade gold deposit sits within a 4 kilometre long anomaly of gold in soil samples. Old Pirate consists of outcropping gold bearing quartz veins hosted by folded shale and sandstone, with the quartz veins preferentially developed in the thicker shale units. Multiple veins have been mapped covering an overall area of 1800 metres by 300 metres and range from a few centimetres to several metres in width. Drill results indicate gold extends from surface to a depth of at least 200 metres. Gold is very coarse and can be extremely high grade in the veins, however, is unevenly distributed resulting in a statistical nugget effect. ABM’s application of detailed structural mapping combined with systematic sampling has, in part, enabled the company to understand the statistical parameters enabling a resource estimate to be completed. ABM has released surface trenching results and drilling from three field seasons, along with its JORC compliant resource estimates, scoping study results and subsequent discoveries of new clusters of veins.

3.1.2.2 Resource drilling and surface work

Field mapping by ABM in 2010 and 2011 provided the basic framework for the surface geology. Prior to the acquisition in March 2010 previous explorers drilled numerous reverse circulation, vacuum and core holes, totalling 16,107m in the Old Pirate area. ABM has drilled an additional 44,416m at Old Pirate, with the drill spacing being a nominal 25m x 25m in key parts of the deposit (Figure 3-1).

ABM conducted a series of surface sample programs, following the veins along strike to a maximum depth of 60cm and excavating short costeans across the veins.



Figure 3-1. Drilling and surface work at Old Pirate, as of July 2013.


1 of 108 Chapter 3 - Project description Twin Bonanza 1 Gold Mine

3.1.2.3 Resource estimation

In April, 2012 ABM completed its first resource modelling and estimation of the Old Pirate deposit. An updated resource estimation was completed in February 2013.

The Old Pirate trend consists of a series of a series of gold bearing quartz veins over a 1.8 km strike length consisting of 3 distinct vein clusters of mineralisation named Old Pirate, Old Glory and Golden Hind Deposits (Figure 3-1). Gold mineralisation is hosted primarily within narrow quartz veins of between a few centimetres and 6m in width. Mineralised zones are up to 40m in width and consist of multiple veins hosted primarily within sedimentary shale horizons. Structurally the sequence has been folded into a faulted anticline. The resource modelling is based on a total of 56,652m of drilling; in addition a further 3,355 surface longitudinal trench samples were used to aid with the definition of the near surface geology and grade distribution.

The resource modelling consisted of both manually constructed 3D grade shells and automated grade shells generated from LeapFrog Modelling software. All mineralised grade shells were constrained by a geological model constructed by ABM. The Old Pirate gold deposit has a total uncut mineral resource estimate of 1.88Mt averaging 11.96g/t gold for 723,800 ounces (Table 3-1).

The gold at Old Pirate can be very coarse with gold grains commonly observed up to 3mm and unevenly distributed throughout the veins. Drill sampling of individual veins and even duplicate assaying of individual samples show a high-level of variability. This sampling effect, also referred to as “nugget effect”, adds uncertainty to the overall magnitude of the system. The defined indicated resource, with a moderate level of confidence, is based on zones where there is extensive surface sampling along with 25m drill spacing to a depth of 50 to 100m and where drilling is consistent with the known geological model. The inferred resource, with a lower level of confidence, refers to zones with wider drill spacing or no areas of surface sampling or areas where the geological model is less well understood.

The total latest JORC compliant mineral resource reported by the company to the ASX on 4th February, 2013 is as follows in table 3-1 below;

Table 3-1. Old Pirate resource estimations.

Category Tonnes Gold grade (g/t) (300g/t top-cut)

Gold grade (g/t) (un-cut)

Ounces gold (300g/t top-cut)

Ounces gold (uncut)

Indicated 889 000 8.19 8.93 234 100 255 300

Inferred 993 000 11.80 14.67 396 900 468 500

TOTAL 1 882 000 10.10 11.96 611 000 723 800

3.2 Proposed project



ABM proposes to conduct mining and processing at the Old Pirate deposit and surrounding prospects, including Golden Hind and Old Glory (collectively called the “Twin Bonanza - 1” project). It is hoped that further exploration and mining activity will identify other mineralised zones to expand the mining inventory in the future.

Based on the currently defined resources this proposal seeks approval up to and including the beginning of stage three of the staged mine development as detailed in sections 3.3.1 and 3.3.2. ABM plans open pit mining from three deposit areas, with onsite processing as well as associated tailings dams, waste rock dumps and required infrastructure including power station, accommodation, workshops and offices. It needs to be noted that underground mining is not included in stage three and as such no approval is being sought for this activity. The basis of the decision to proceed with the project is discussed in Chapter 4: Project rationale and alternatives.

3.2.1 Staged approach to development designed to minimise risk and maximise return

The Old Pirate high grade deposit (Old Pirate) is typical of gold deposits in the region and has similar geological characteristics to the Coyote Gold Mine (45 kilometres NW) and the Callie Gold Mine (100 kilometres to east-southeast). The deposit contains sporadically distributed fine gold (<0.5mm) and coarse gold (>0.5mm) hosted in quartz veins ranging from a few centimetres to >6 metres in width. More than 15 individual gold bearing veins have been identified to date at surface and cover a combined strike length of ~2 kilometres within a zone 1.8 km long. In order to understand the mining economics and the risks one must understand the process under which ABM is undertaking work.

ABM is instigating a risk managed staged approach to development where the scale of the project is grown incrementally based on the knowledge derived during trial and mining phases. ABM believes that this is a better approach to standard feasibility studies as the level of disturbance and amount of capital is applied incrementally rather than upfront.

3.2.2 Staged approach versus feasibility studies

In modern day mining and exploration it is typical that a company conducts a detailed assessment of the technical merits and the risks involved along with the scope of works and value of the project. This is what is referred to as a “feasibility study” and is noted in the JORC Code 2012.

A feasibility study is not a guarantee of success and in the modern era of mining approximately 70% of projects with detailed and positive feasibility studies generally fail to achieve the target valuation. This failure of projects to achieve the value noted in typical feasibility studies is well documented (e.g. McCarthy, 2013). The reasons for failure of a project to achieve the outcome predicted in the feasibility study are numerable but include



misestimations of resource, mining dilution factors, overall costs and future value of the product.

As with other gold systems, the Old Pirate project has a number of technical risk factors associated with the scale and the value of the project. These are noted in Table 3-2 below.

Table 3-2.Technical risk factors for Old Pirate project.

Risk factor Generic comment Applied to Old Pirate

Resource estimation

Resource estimation contains application of geological understanding and low-relative sampling compared to the overall size of the resource reserve. There are at least 5 factors for uncertainty including sampling representation, variance (spatial variability), arbitrary use of top cutting of samples and errors in estimating width of mineralised zones and the overall volume of the ore-system.

Coarse gold system means that samples have a high degree of variability. i.e. two samples from the same place (e.g. two halves of drill core) can be very different. Old Pirate sampling has a high-degree of variability.

Geological model 3D geological interpretation is subject to error due to paucity of information.

There is approximately 80% surface exposure currently at Old Pirate reducing overall risk to geological interpretation. However the geology may differ at depth compared to the surface.

Geotechnical risks Ground conditions and strength of the rock may have high variability.

Typical knowledge base established from geotechnical reports.

Mining parameters e.g. minimum mining width, mining dilution assumptions and ore loss.

Dilution will result in a net reduction of grade

Quartz veins change in thickness over relatively short strike lengths.

Metallurgical recovery Modelled recovery may differ from actual recovery.

Old Pirate has a high gravity gold recovery rate. However, the metallurgical recovery parameters may vary from those estimated in laboratory tests.

Future metal price assumptions Metal prices are subject to the vagaries of global economic conditions.

As a result of the above factors, ABM considers the “staged approach” to development (as alternative to typical feasibility study) as being the best way to manage risk. This ensures that the overall feasibility of the project is not based on the pre-development knowledge-base and estimations of the project, but is alternatively presented as individual stages. The economics of each stage inform the subsequent stages.



The resource estimation model is defined as compliant with JORC 2012 reporting. As defined in JORC 2012, inferred resource estimations are not to be used in assessing economic parameters and in feasibility studies. However, as ABM progresses the staged approach it anticipates converting aspects of the inferred resource into the indicated resource category and subsequently reserves.

3.2.2.1 Stage one – trial mining and processing

Stage one, trial mining up to 10 000 tonnes, including on site processing, is approved and being completed at the Old Pirate project. Stage one is being conducted under an exploration licence with permission from the Central Land Council (CLC) and the Department of Mines and Energy (DME). This process involves open pit mining the top 5 metres of the project and processing the material using a small scale portable gravity gold plant.

The high-grade gold at surface of Old Pirate makes it an unusual scenario in modern day Australian mining industry as most high grade outcropping deposits were mined during the gold-rush eras from the 1860s to 1930s. The trial mining stage is expected to increase understanding of the geology, including grade, grade distribution, thickness, orientation and mineralisation controls as well as the overall amenability to gravity gold recovery methods. It may also expose additional veins and further increase the resource base.

3.2.2.2 Stage two – open pit mining to approximately 35 metres depth

Utilising the same processing plant (with minor upgrades) that is used in stage one, ABM has developed a mine plan to optimally extract ores from surface to a depth of approximately 35 metres. The project economics for stage two have been modelled by ABM in conjunction with Entech Mining Pty Ltd and a summary is presented Table 3-3. The model involves the extraction of 276,403 tonnes of ore with a grade of 12.3g/t gold for a total of 109,000 ounces of gold. This model only uses indicated resource blocks, and any inferred resource blocks in the top 35 metres have not been taken into account but provide further upside to this model. It is important to note that the stage two model has not yet been updated from findings from stage one and the overall outcome may differ from those presented.

Table 3-3. Cost summary / structure of stage two as modelled by Entech Mining Pty Ltd assuming A$1600 gold price. Inferred Resourcenot included but adds upside to the existing model.

Total rock tonnes 4059722 tonnes

Strip ratio 13.7 to 1 (waste to ore)

Ore tonnes (inferred resource not included) 276403 tonnes

Recovered grade (95% recovery) 12.3g/t gold

Recovered gold (inferred resource not included) 109398 ounces

Mine life ~2 years



3.2.2.3 Stage three – open pit mining

Stage three economics cannot be accurately estimated until mining history is established during stage two. However, given the high grade nature of the Old Pirate system and compared to other similar projects around the world it is anticipated that the stage three project will be economically feasible at an undetermined scale. Stage three will include deepening of the open cut pits to continue high grade quartz vein mining at depth. For the purposes of this document ABM is not able to present economics for stage three. However, on the assumption that mining is economic and noting the disclaimer above, an approximate 70% conversion of resource to ultimate mining inventory is presented as a possible outcome. This will produce a further 1 million tonnes of material at an average grade of 10g/t gold for 340,000 ounces. Stage three is likely to include an expansion of the stage one / two plant to processing a nominal 240,000 tonnes per annum and thus providing a further 4 year mine life. A comparison of development stages how they will be upgraded overtime is presented in Table 3-4

3.2.2.4 Beyond stage three

The Buccaneer Porphyry gold project is located 5 kilometres north west of the Old Pirate deposit. Whilst Buccaneer is included in the mineral lease area, mining gold bearing material at Buccaneer is not part of the mining development plan and is not addressed in this EIS process. As the stages two and three progress, ABM will look at the economic viability of processing Buccaneer mineralised material using some of the infrastructure of the Twin Bonanza gold project.

ABM seeks to continue mining and processing activity after the stage one trial is completed and is seeking a mineral lease and all relevant approvals for that purpose, with the aim to minimise delay between stage one and stage two.

The project will be developed in stages, from the trial mining (2013) through to the full scale mining as proposed in this EIS report. The current EIS is seeking approval up to and including the early parts of stage three. Further developments beyond this point including the potential underground and mining of Buccaneer requires additional evaluation. Once further developments are proven feasible, the company will consult with relevant regulatory authorities on the requirements for additional approvals.



Table 3-4. Existing trial bulk sample operation compared to the project

Component Stage one (underway 2013) Stage two (modelled and will be updated following

stage one)

Stage three (will be updated during stage one)

Resource 10 000 tonnes @ 10g/t gold 276 000 tonnes @ 12.3g/t 1Mt @ 10g/t

Mining rate 60 to 200 tonnes per day depending on shifts and maintenance.

120 000 to 150 000tpa 240 000 to 300 000 tpa

Mine life 3 to 5 months 2 years 4 years

Mining method Open pit mining using rock-breaker.

Open pit mine using conventional drilling, blasting, loading and haulage methods.

Open pit mining expansion using conventional drilling, blasting, loading and haulage methods.

Tailings Tailings discharged to below natural surface tailings dam

New tailings dam construction – old tailings dam converted to a water storage dam

Tailings dam designs 2A and 2B, and concentrated residual dam (within EIS) represents staged designs for the management of tailings until the end of stage three

Pit dimensions Multiple small test pits up to 200m long 5 to 20m wide.

Separate pits for Old Pirate and Golden Hind. Maximum size 800m x 200m

Pit design in this EIS represents the early part of stage three. Pits cover an area of 22.5 hectares

Waste rock Stored on surface next to the excavation areas.

Stored on surface in waste rock dump

Two waste dumps as contained in this EIS with a nominal height of 20 metres and covering a total area of 60.5 hectares. Potential to expand in the future.

Processing Small scale gravity gold plant.

Small scale gravity gold plant with potential intensive cyanide leach if required.

Expanded scale gravity gold plant with possible intensive cyanide leach if required.

Power Diesel generators with 1 to 2MW Diesel generators 1 to 2MW

Diesel generators 2 to 3MW

Product 3 000 ounces of gold 109 000 ounces of gold 340 000 ounces of gold

Transport Air freight for gold product Air freight for gold product Air freight for gold product

Water management 2 bores 2 bores +

2 bores +

Workforce Approximately 30 Approximately 68 Approximately 68

3.3. Proposed mining project

The proposal will upgrade and expand the existing pilot processing plant and infrastructure (built for stage one). All components were specifically designed to allow modular upgrades.



It is intended that the tailings dam used for stage one will become the water storage dam for stage two. The tails will be progressively pumped out and potentially reprocessed through an improved gravity circuit, once reprocessed the tails will be placed into a larger tails dam.

The expanded mining process (stage two) will involve the construction and operation of the following components:

a. The mining of three open pits using drill, blast, load and haul techniques.

b. Converting the stage one tailings dam to a water storage dam.

c. The expansion and operation of gravity processing equipment for refining ore with the addition of an enclosed intensive leach reactor, such as an Acacia Reactor, for cyanide leaching of concentrates.

d. Installation of associated tailings dams, incorporating a dual cell tailings dam and a concentrate residual dam (CRD) for cyanide treated tailings.

e. Constructing two waste rock dumps.

f. Installing ancillary infrastructure, including: generators/power plants, staff accommodation, workshop and office areas.

g. Establishing a new sewage system and landfill area.

h. Upgrading and expanding a reverse osmosis plant for producing potable water.

i. Potentially upgrading and lengthening of the existing airstrip.

j. Upgrading existing roads, and constructing new roads and haul roads.

k. Sourcing of water initially from within and external to MLA 29822.

As illustrated in Figure 3-2 and documented in Table 3-5 the facilities associated with the project’s operations will include:

a. three Run of Mine (ROM) pads containing ore stockpiles associated with the open pits and processing plant

b. ore processing facilities

c. tailings dams cells 2A and 2B (for deposition of gravity treated tailings only)

d. CRD (for deposition of small volumes of cyanide treated tailings with cyanide removed prior to deposition)

e. two waste rock dumps (Northern Waste Rock Dump and Southern Waste Rock Dump)



f. borrow pit (for sourcing of clay material).

g. topsoil, sandstone, siltstone and pisolite/gravel stockpiles associated with rehabilitation activities

h. water management structures (water bores, pumps, monitoring bores pipelines, surface water diversion drains and sediment settlement ponds)

i. accommodation, offices, and ablutions

j. heavy vehicle hard-stands (parking areas) and light vehicle car parks

k. heavy equipment workshop with associated wash down bays and service areas

l. roads, haul roads and firebreaks

m. stores warehouses and lay down areas

n. explosives magazine

o. airstrip (upgrade existing airstrip)

The planned ROM pad, processing facility, offices, maintenance facilities and other infrastructure sit centrally to the known mineralised zones. Only areas actually required for use will be cleared and all topsoil will be stockpiled for future rehabilitation. The majority of the disturbance is associated with the pits, waste rock dumps, tailings dams, abandonment bund area and topsoil stockpiles (Table 3-5). The project will result in the clearing of 223.3 hectares during stages two and three, this is in addition to existing 32.5 hectares that has been disturbed during stage one.

The processing facility is planned to be an expanded version of the facility installed for stage one, which utilises a gravity gold recovery method. It is anticipated that gravity gold recovery can remain the primary method of gold recovery. A fully enclosed intensive leach circuit for the treatment of approximately 1 to 2 tonnes of concentrate per hour (using cyanide on a small scale) has the potential to become part of the processing plant in the future. The aim of the intensive leach circuit will be to extract gold from gravity concentrated product and will be dependent on recoveries from tabling processes.

It is planned that the processing plant can be upgraded to between 200 000t and 300 000t per annum by stage three should it be economically viable. The tailings will report to the two celled tailings dam with the intense leach material being deposited in a lined CRD once cyanide has been removed.

The tailings dam will be established in stages. Initially a five metre deep below ground starter pit will be established with the capacity of 250 000 tonnes. This will be expanded to hold an additional 600 000 tonnes via an above ground 5 metres high embankment



enclosed tailings dam. This process is to be completed again to produce a second tailings dam cell adjoining the first with the same configuration. Tailings dams will be designed, constructed, and operated in line with the Australia National Committee on Large Dams Guidelines on Tailings Dams 2012 (ANCOLD, 2012). External parties have been engaged to design the tailings dams.

Site roads will require upgrading and new roads will need to be established to allow safe transit around the operation. This will include haul roads that allow for traffic to operate without disruption in both directions. Haul roads between the mine and processing facility will be designed and updated as operations are progressed.

The current accommodation facility is proposed to be expanded during stage two or three. The facility will be expanded to the west of the current camp, along the western side of the planned mineral lease. The upgraded accommodation facility is expected to largely consist of portable buildings. The existing disturbance will be retained for use as a recycling and laydown area and equipment storage area.

The proposed mineral lease extends to the Buccaneer deposit, to the north-west of Old Pirate (Figure 3-2). The extension of the mineral lease to include Buccaneer allows for the extraction of clay that may be required in the construction of the tailings dam and CRD.

Water will be sourced from bores on the lease and bore fields to the west of the mineral lease, under a section 19 agreement with the CLC. Refer to Chapter 6: Water management.

Upgrading of the main access road will only require gravel sheeting to maintain the surface as the only large vehicles using the road will only be transporting mining infrastructure and logistical supplies. Material to maintain the road is to be sourced from mine pits. No bulk haulage is required for the product as the produced gold volumes can be easily transported by other means to the Perth Mint.



Table 3-5. Summary of Twin Bonanza project components and disturbance areas.

Component Proposed

area (Hectares)

Existing area (Hectares)

Total area (Hectares) including existing

areas

Description EIS section

Pit 1 (Old Pirate) 8.9 7.1 16

Bulk sample trenches engulfed by open pits.

Chapter 3

Pit 2 (Old Glory) 3.6 0.7 4.3 Bulk sample trenches engulfed by open pits.

Chapter 3

Pit 3 (Golden Hind) 1.3 1 2.3

Bulk sample trenches engulfed by open pits.

Chapter 3

North waste rock dump 41.8 0 41.8

Nominal height of 20 metres. Constructed of two 10 lifts.

Chapter 10

South waste rock dump 18.8 0 18.8

Nominal height 16.5 metres constructed of one 10 metre lift and one 6.5 metre lift.

Chapter 10

Tailings dam 26.7 0 26.7

Composed of two cells. Cell 2A and 2B. Embankment constructed to 5 metres high.

Chapter 10

CRD 3.7 0 3.7 Embankment constructed to 5 metres high.

Chapter 10

Water storage dam 0 1.3 1.3

Current tails storage converted to water storage dam.

Chapter 10

Siltstone stockpile 1.6 0 1.6

Material used to cap tailings dam and CRD at closure.

Chapter 10

Sandstone stockpile 1.6 0 1.6


Chapter 10

Gravel/pisolite stockpile 4.2 0 4.2


Chapter 10

Camp 4 4.8 8.8

Expansion of camp. Existing disturbance used for laydown, storage and bioremediation area.

This Chapter

Landfill/burn area 1 0 1 Burn area with

fenced landfill area. Chapter 9

Sewage pond – wastewater area

1 0 1 Earthen dam for leaching and evaporation.

Chapter 9



Component Proposed

area (Hectares)



areas


Processing area 1.6 0.6 2.2

Expansion of existing area. May or may not be raised.

Chapter 3

Processing ROM pad 1.3 0.2 1.5

Storage and management of ore stockpiles. May or may not be raised.

Chapter 3

ROM pad pit 1 2.3 0 2.3

Storage and management of ore stockpiles from Old Pirate. May or may not be raised.

Chapter 3

ROM pad pit 2 and 3 2.3 0 2.3

Storage and management of ore stockpiles from Old Glory and Golden Hind. May or may not be raised.

Chapter 3

Power generation area 0.2 0 0.2 Positioned in

process area. Chapter 3

Haul roads 3.2 0 3.2 Haul roads designed to be water shedding.

Chapter 12

Fire breaks 1.3 0.3 1.6 Fire breaks maximum clearing width 6 metres.

Fire Management Plan – Appendix Z

Other roads 0.7 3.5 4.2

Existing roads incorporates both pre bulk sample and bulk sample roads.

Chapter 12

Abandonment bund and internal area pit 1

29.9 0 29.9 Area encompassing abandonment bund and area within.

Chapter 3

Abandonment bund and internal area pit 2 and 3

18.8 0 18.8 Area encompassing abandonment bund and area within.

Chapter 3

Mining support area including workshops and camp

2.3 0 2.3 Included wash down and support infrastructure.

Chapter 3

Main topsoil stockpile 23.1 0 23.1

Stockpiles paddock dumped to have high surface to volume ratio.

Chapter 11, Conceptual Mine

Closure Plan – Appendix O



Component Proposed

area (Hectares)



areas


Camp topsoil stockpile 1 0 1

Stockpiles paddock dumped to have high surface to volume ratio.

Chapter 11, Conceptual Mine

Closure Plan – Appendix O

Borrow pit 2 0 2 Required for potential clay lining. Chapter 3

Water bores 0.2 0.2 0.4 Each Water Bore 30 metre x 30 metre area.

Chapter 7, Water Management

Plan – Appendix F

Monitoring bores 1.5 0 1.5

Each Monitoring Bore 30 metre x 30 metre area.

Chapter 7, Water Management

Plan – Appendix F

Access tracks and pipelines to bores

0.6 0 0.6

3 metre wide tracks for access and pipelines. A number of existing tracks are to be used in conjunction with the proposed disturbance.

Chapter 3

Main diversion structures 3.4 0 3.4

Designed to 1:1 000 year peak flow event.

Chapter 7, Erosion and

Sediment Control Plan – Appendix E

Internal diversion structures

1.4 0 1.4 Designed for 1:100 year peak flow event.



Settlement ponds 0.5 0 0.5

Designed for 1:20 year peak flow event.



Explosive magazine 1.5 0 1.5

Incorporates access track from haul road.

Chapter 3

Airstrip 6 12.8 18.8

Airstrip to be lengthened and widened. Based on airstrip 2000 m long and 90 m wide with parking apron.

Chapter 12

Total 223.3 32.5 255.8



Figure 3-2 Mineral lease infrastructure layout.



3.4 Mining

3.4.1 Overview

The ore will be trucked from the open pits to one of three ROM pads for storage prior to crushing and processing.

Mine waste rock will be placed into one of two waste rock dumps (Figure 3-3). The southern waste rock dump will receive mined waste rock from the southern Old Glory and Golden Hind pits. While the northern waste rock dump is to receive waste rock mined from the northern Old Pirate pits. Indicative waste dump volumes are provided in Appendix M: ABM Waste Memo which may vary slightly if final open pit mining designs are varied. Final waste dump external batters will be at a gradient of 15 degrees to ensure effective rehabilitation and to blend sympathetically with existing natural topography of the area.

In addition, selective siltstone and sandstone waste rock units and the top 800mm to 1000mm pisolites/gravel horizon covering the pits will be selectively handled and stockpiled for the capping and rehabilitation of the tailings dam and CRD (Figure 3-7).

All waste dumps will be rehabilitated with topsoil (which will be removed and stockpiled prior to establishment) and revegetated. For on-going expansion, it is expected that some open pits will be able to be partially backfilled to reduce waste dump expansion. Backfilling opportunities may be assessed as an ongoing part of mine planning and undertaken where sterilisation of the ore bodies are likely to occur.

3.4.2 Mining techniques – open pit excavation and mine sequencing

Mining operations are proposed to be undertaken using conventional open pit mining methods (drill, blast, load and haul), with a particular focus on selective mining / minimising dilution of high-grade zones in the deposit.

Mining will involve mining a series of open pits, including cut backs. The staged approach will allow continued assessment of the ore system as more information becomes available from both mining and resource extensional work.

Open pit mining will include the pegging out of the pit outline, clearing of top soil, the establishment of safety and abandonment bunds and required roads.

The project’s open pit mining process will involve excavating overlying waste rock in horizontal benches to expose the near vertical target quartz veins that host the gold, which will then be removed for processing. The excavation will be undertaken in stages, commencing at the shallowest depths of the ore-body. Based on the current resources the indicative mining schedule is summarised in Table 3-6 and illustrates how mining will be ramped up during staged development.



Table 3-6. Indicative mining schedule stage two and stage three.

Year Ore Waste rock Comments

2014 140 000 1 890 000 Based on stage two designs

2015 140 000 1 890 000 Based on stage two designs

2016 240 000 3 500 000 Based on Stage three designs

2017 240 000 3 500 000 Based on Stage three designs

Total 760 000 10 780 000

Figure 3-3 details the larger items contained in the proposed footprint of the development of the Twin Bonanza project and focus of the EIS.



Figure 3-3. Stage three with indicative waste dumps and tailings dams.



3.4.3 Open pit stability

Geotechnical drilling and shear strength testing was conducted in late 2012 to enable the geotechnical engineering of pits 1, 2 and 3. The main aspects of open pit mining requiring geotechnical design include:

i. pit wall slopes, on an overall scale and on a bench scale

ii. batter angles and berm widths and intervals

iii. ground support requirements.

The geotechnical assessment included:

• assessment of ground conditions influencing wall stability

• potential mechanisms of wall stability

• stability analysis.

Further geotechnical assessment will be undertaken with the exposure from the stage one trial mining pits and with reference to final open pit designs.

3.4.4 Slope design

To determine pit wall stability numerous parameters including rock properties, geometry of the open pit wall in relation to rock structure, stresses, weathering, life of the slope and possible failure mechanisms are assessed to give a factor of safety (FoS). This quantifies the risk of slope failure. Setting a minimum acceptable FoS level at 1.2 under static conditions and 1.0 for transient seismic events, the analysis found that geotechnical parameters shown below in table 3-7 produced acceptable FoS.

Table 3-7. Old Pirate geotechnical parameters

Pit Name Wall Rock Type Batter H i ht

Batter A l

Berm Width

Old Pirate All

Oxide 10m 50o 5m

Transitional 20m 55o 5m

Fresh 20m 60o 5m

With consideration given to the in-pit haul ramp, the overall wall angles that are generated are presented below in Table 3-8. These angles were used for the pit design and will have a maximum slope angle between haul ramp segments.



Table 3-8. Old Pirate optimisation overall wall angles

Material type Overall slope angle

Oxide 38o

Transitional 42o

Fresh 45o

Stage three pits are envisaged to a depth of between 35m and 150m below surface, however ore body grade remains critical in determining the total optimal depth. For the purposes of this EIS, a potential open pit boundary is based on an 80m deep excavation, consistent with submissions related to the mineral lease.

An abandonment bund will be constructed around each of the open cut pits using the most competent rock available. The bund dimensions are to be approximately 2 metres high with a base of 5 metres and positioned at least 10 metres outside of the area designated as the zone of instability. Approval is being sought to allow the clearing of the vegetation within the bund boundaries in order to provide flexibility with the placement of infrastructure, however, in practice this may not occur.

3.4.5 Haul ramp design

The ramps will be designed to allow the safe transit of either, two-way or one-way passage of the largest trucks on site. Haul ramps will be designated either single lane or dual lane and will encompass an allowance for drains and safety bunds. For a dual access ramp, utilising Hitachi B50D trucks, a minimum road width of approximately 21m is required. For single lane ramps utilising Hitachi B50D trucks, a minimum road width of approximately 13m is required.

3.4.6 Mining activities

The mining processes for the extraction of overburden and ore are similar to the practice used in stage one; with the exception of the use of explosives. The mining technique is conventionally known as the drill, blast, load and haul method.

Key to maximising recovered grade for the operation will be the selective extraction of the ore from waste rock. Grade control for the operation will carried out using a combination of methods, including in-pit drilling, blast hole sampling, mapping and sampling of pit floors. It is expected that extensive visual control, backed by sampling data, will be used to guide ore extraction.

The various stages of the mining process are described below.



3.4.7 Mining offices, workshops and associated infrastructure

Site facilities that will be required as part of the mining offices, workshops and associated infrastructure are detailed below:

1. fuel farm

2. oil farm

3. offices

4. crib (messing) rooms

5. workshops

6. ablutions

7. generators

8. potable water

9. non-potable water

10. heavy vehicle parking areas

11. light vehicle parking areas

3.4.8 Drilling and blasting

Some of the oxidised material can be extracted without blasting. Conventional drill and blast will be used for rock that is unable to be dug freely. Drill and blast equipment proposed for this is a ROC T30 top-hammer drill rig and one mobile explosives manufacturing truck.

Details of proposed blasting parameters for the project’s open pit are shown in Table 3-9. Blasts are expected to occur every two to three days with multiple shots fired at the same time.

Refer to section 3.7.5 for details of explosives storage.

Table 3-9. Blasting parameters.

Material Bench height (m)

Hole depth (m)

Hole diameter (mm)

Holes drilled per day

Area of typical shot

(m2)

Shots per year

Ore zone 2.5m 2.8m 64mm 80 200m2 300

Waste rock 5m 5.5m 64mm 60 1b000m2 240



3.4.9 Mining and ancillary fleet

ABM proposes to use 1 Hitachi excavator (EX1200) for loading and 4 Hitachi dump trucks (B50D) or equivalent for haulage to and from the pit and ROM.

It is anticipated that 17 ancillary vehicles will be required as support vehicles for safe and effective functioning of the mine. Table 3-10 outlines the nature of these tasks and the equipment required.

Table 3-10.Mining fleet.

Make Model (or equivalent) Quantity Tasks

Excavators Hitachi (EX1200) 2

Miscellaneous loading, crusher loading Rock breaking, pit wall scaling, pump moving

Haul trucks Hitachi B50D 4 Haulage of ore and waste

Dozer Caterpillar D9T dozer 1

Clean-up at loading areas, clearing of new mine areas, road building, pushing and rehabilitation on the overburden emplacement facilities

Grader Caterpillar 14H grader 1

Formation and maintenance of haul roads and work areas, clearing of new mine areas, formation of drainage furrows and swales

Water cart Converted Hitachi B50D 1 Dust suppression on roads, drills, rock piles and blasted ground

Drill rig PowerROC T30: Tophammer drill rig 1 Grade control and blast hole

drilling Mobile manufacturing truck (explosives truck) TBA 1 Mixing and transport of

explosives

Service truck Toyota service truck 1 Service vehicle

Light vehicles Toyota Landcruiser 8 Staff transport

Front end loaders Caterpillar 990 Series II 1 Loading from ROM to processing plant

Loader Caterpillar 938H 1 Use for moving material and consumables

Bus Toyota coaster bus (21 seats) 1 Staff transport

Lighting plant Allight 5 Illumination of working areas



3.4.10 Mine water management

Mine water requirements include, but are not limited to, ore processing, dust suppression, laundering, camp and a wash-down bay. Stage one and stage two, water requirements are on the order of 4.1 L/s. Water requirements will be in the order of 11.1 L/s for stage three; including loss to tails, loss at the processing plant, camp use and mining.

To accommodate stage two water needs, ABM will utilise at least one bore within the mineral lease and also water resources adjacent. The adjacent water resources will be located within a palaeochannel to the south west of the mineral lease where a borefield and connecting pipeline are required (Figure 3-4). These areas are secured by the grant of an interest in the land pursuant to s.19 of the Aboriginal Land Rights Act by the relevant land trust. Two large paleochannels encircle the project area; these have been identified as the most likely place to find further water if required during stage three.



Figure 3-4. Existing and proposed water and monitoring bores.



There is no proposal to take, or use surface water. ABM will not take, direct or use surface water without first notifying all relevant stakeholders and seeking approvals. The overall objectives of ABM’s surface water management will be in accordance to the Water Management Plan (Appendix F) and Erosion and Sediment Control Plan (Appendix E). ABM will divert the majority of the surrounding surface run-off around disturbed areas with the use of surface diversion structures. As the project is positioned on high-ground in the landscape and on diverging catchments no large catchment areas or rivers will be diverted as part of the project (Figure 3-5).



Figure 3-5. Proposed surface water diversion structures.



Within the project area the water table is typically situated approximately 100m below surface, therefore dewatering is highly unlikely to be required. For any small volumes of perched water (above the water table) the use of temporary in pit sumps for water capture may be required in order to secure dry open pit working conditions. Subsequent water captured will be available for use for dust suppression. This process would be sufficient for all normal groundwater conditions.

During the wet season, it is likely that water will need to be removed from open pits. This water will be directed to water storage facilities for future use whenever practicable. If it is not practicable to dewater open pits to water storage facilities, such as when freeboard is limited or tailings deposition may be compromised, water may be pumped to an alternate open pit if available or discharged to the environment via a discharge method to prevent erosion, such as rock discharge.

Water runoff from operational areas will be directed to 1:20 year peak flow, sized sedimentation traps. All traps will be designed to appropriate standards and sized in accordance with calculations from the site surface water modelling (Figure 3-4).

ABM is committed to the efficient use and responsible management of water resources in its activities. By implementing water efficient work practices and recycling, the consumption of raw water will be minimised. ABM will specifically achieve this through maximising the recirculation of process water and tailings supernatant water for use within processing facilities.

Further detail on mine water management is provided in Chapter 7: Water management, and Appendices F: Water Management Plan, G: Surface Water Assessment Memo and H: Groundwater Monitoring Standard Procedures.

3.4.11 ROM pad / ore haulage

Ore from the open pits will be hauled to one of the three designated ROM pads in preparation for processing. Two ROM pads are located close to the pits for proximal ore storage, and one located at the processing plant to enable blending and management of ore feed to the plant.

To manage surface water flow and sediment, the ROM pads may be raised with any liberated sediment to be captured by settlement ponds. If the pads are not raised diversion drains will be used to divert surface water and sediment to the settlement ponds.

3.4.12 Handling and stockpiling of waste rock and waste rock design

A total of 10.9 million tonnes of waste rock will be produced during the project (stage two to three). The following swell factors were used for each material type to estimate the surface volumes, and are presented below in



Table 3-11 Rock swell factors

Material type Swell factor

Topsoil 130%

Transported Material cover 130%

Oxide and transition 130%

Fresh 125%

Two waste rock dumps known as the north and south waste rock dumps have been located as close to the pits as possible and take into account the local constraints of potential future deposits, zone of instability and any archaeological sites (Figure 3-3).

Waste rock dump design has incorporated the findings of both physical and chemical characterisation. This has led to the more erosive and potentially less geochemically stable units being encapsulated in the waste rock dump by more competent and inert materials. This is illustrated in Figure 3-5. Further detail is provided in Chapter 10: Tailings and waste rock management.



Figure 3-6. Cross section through the northern waste rock dump detailing the positioning of waste rock.



3.4.12.1 Physical characterisation of waste

The final design of the waste rock dumps was a two staged geotechnical process to ensure the landforms will be stable.

The first stage was the identification of the most resistant unit to erosion and potential weathering with sufficient volumes to cover the waste rock dump. A 300kg sample of oxidised sandstone was collected during the bulk sampling program and sent for laboratory-scale erosion testing. A laboratory-scale rainfall simulator was used to measure the potential erosion rates at varying slope angles.

It is predicted the average erosion rate for near-flat surfaces (i.e. pads, roads, etc.) was negligible, at < 0.2 t/ha/yr, with approximately 90% of the predicted erosion expected in the months of December, January, and February. In the case of waste dump batters with a vertical height of 10 metres the erosion rate ranged between 5.1 t/ha/yr for a slope of 150 to 5.4 t/ha/yr for a slope of 210. Erosion rate increased as the vertical batter height increased. Further details on the erosion testing can be sourced from Chapter 10: Tailings and waste rock management.

A 150 batter angle was selected for the slope design with two 10 metre vertical lifts divide by a 10 metre wide berm. This slope configuration then underwent landscape evolution modelling via the Siberia Model over a period of 1000 years; further details of the erosion modelling is Appendix AB: Topsoil Characterisation and Erosion Analysis. This highlighted that the waste rock dumps were likely to have erosion levels that stabilise over time with sediment contained inside the footprint of waste rock dump over the first 100 years. The design parameters for the site waste dumps are outlined in table 3-12.

Table 3-12 Waste dump design parameters.

Waste rock dump design parameters

Nominal height 20m above topography

Individual slope angle 15°

Vertical slope height 10m

Overall slope angle 13°

Inter-berm face angle 5°

Berm width 10m

3.4.12.2 Chemical characterisation of waste

A geochemical review was undertaken on a selection of waste rock samples across the deposit. Characterisation of the materials was carried out as defined by AMIRA1 as well as an Acid Potential Ratio (APR) approach. In addition x-ray diffraction and x-ray fluorescence



were carried out with XRF to determine the Geochemical Abundance Index (GAI) of the materials. Leaching potential of the materials was determined by applying the Australian Standard Leaching Procedure (ASLP) with pH, EC, major cations and anions as well as trace elements determined on the leachates.

The geochemical review found that the bulk of the waste was classified as non-acid forming (NAF (using the ABA/NAG approach)), with trace sulphides present in vein systems. The samples were therefore deemed to have limited potential for Acid Mine Drainage (AMD). The presence of arsenopyrite, pyrite and galena minerals in some of the samples indicated that there is limited potential for leaching of As and Pb from the trace sulphides.

Management of the materials will primarily focus on isolating the material with the potential to liberate elements thereby limiting the potential for leaching of elements in the environment. ABM’s proposed waste rock dump design will involve isolating the material with potentially arsenopyrite, pyrite and galena, in the centre of the waste dump, with the benign and stable waste (NAF) used as the outer embankment walls.

For further details refer to Chapter 10: Tailings and waste rock management, and Appendices L: ABM Tailings Memo and N: Geotechnical characterisation Memo.

3.5 Processing

3.5.1 Processing facilities

The layout of the processing plant is shown in Figure 3-2, and in more detail in Figure 3-7. Upgrading of the stage one plant will produce a staged output of initially 140 000 tonnes per annum ramping up production to 240 000 tonnes per annum (stage three). All items of the plant are designed to be as mobile and modular as practicable. Additional, components including conveyors, cyclones, hoppers, pumps, concrete and pipe work for the expansion are to be transported to the site via the Tanami Road for assembly.

Prior to the expansion the area will be cleared and topsoil will be recovered. The upgraded processing operation consists of the following components:

1. ROM pad

2. crushing circuit

3. coarse gold gravity recovery

4. milling

5. fine gold gravity recovery

6. concentrate upgrade



Figure 3-7. Layout of proposed processing area.



The general layout of the processing area is shown in Figure 3-7 and a preliminary design of the processing circuit, as established for the bulk sample, is provided in Figure 3-8.

Figure 3-8. Processing circuit flowchart (Note: subject to change).

Crushing

ABM plans to use a multi stage crushing circuit, consisting of jaw, cone and impact crushers to produce a product size in the order of 6mm from a maximum feed size of around 500mm feed size is expected to be 250mm and target output is <6mm.

A scrubber is planned to sort oversize and produce slurry. Oversize will be re-fed to the crushing circuit by a small front end loader.

Coarse gold gravity recovery

Coarse gold recovery is planned using a jig with table upgrade. Currently planned are a Russell Jig and Wilfley Table. Concentrates will be pumped for further upgrading and tails will be forwarded to the mill for grinding.

Milling

All ore, other than material already captured for coarse gold recovery, will be milled to liberate finer gold particles. The mill will be fed directly from the jig tails but will also receive recirculating lode from throughout the circuit. The mill will be sized to handle the



recirculating lode and the 10t to 35t per hour (depending on stage) minimum net circuit throughput.

Target final grind size before going to tails is expected to be less than 106 micron. Determination of optimal final grind size will be an important outcome of the stage one work.

Fine gold gravity recovery

It is planned that all material from the mill, subject to screening of oversize, will go through a centrifugal gravity concentrator. Currently, this is planned to be a Knelson concentrator. The centrifugal concentrator will recover fine gold above the 20 micron size and is expected to result in a high overall gold recovery.

Tailings from the centrifugal gravity concentrator will be passed through a cyclone and subsequent underflow (being the larger and heavier particles) will be returned to the mill for further grinding. Cyclone overflow (being the finer and lighter particles) will be sent to the tailings dam.

Final gold gravity recovery

As an outcome of the stage one trial processing, currently still in progress, ABM are expecting to review further options for fine gold recovery from the tailings stream. This may result in the installation of additional centrifugal gravity concentrator(s) combined with intensive leach reactors.

3.5.2 Concentrate upgrade

Upgraded concentrates will be converted to gold dore by a small smelter located in a ventilated gold-room. The smelter is expected to be diesel powered. Gold dore will be securely stored onsite before being transported for sale.

Depending on overall recoveries and results of stage one, an intensive cyanide leaching and elution circuit may be required. Intensive cyanidation involves a small scale pressure reactor (such as an Acacia Reactor) and is applied to concentrates only. Intensive cyanidation uses considerably less cyanide than conventional CIL or CIP processing.

3.5.3 Tailings

Gravity circuit tailings

It is proposed that gravity recovery for gold will be used and reagents, including cyanide, will not be used in the gravity circuit. Tailings will be the crushed and ground material that has been extracted from the local mineralised resource only.



Bulk density test work has been conducted on tailings samples from laboratory gravity recovery test work. The density has been calculated as 1.2t/m3 by testing the weight of prepared samples in water and out of water to determine the both weight and displaced volume of the tails sample.

The final tailings stream from the gravity circuit will be pumped to the tailings dam. Further details of the existing and proposed tailings management operations are provided in Chapter 10: Tailings and waste rock management, and Appendix I: Tailings Storage Facility Conceptual Design report.

Tailings concentrate leach

In the event that cyanide leaching is used, the small proportion of the ore (after concentrating) will be selectivity leached as a concentrate within a closed circuit intensive leach reactor (Figure 3-9). This is estimated a total 60 000 tonnes for the life of mine.

Within the intensive leach reactor process, a recycling and detoxification module using sodium hypochlorite breaks down the cyanide. Once detoxified, the cyanide free waste solution is to report to a purpose built CRD.

For further details refer to Chapter 10: Tailings and waste rock managment, and Appendix I: Tailings Storage Facility Conceptual Design report.

Figure 3-9. Simplified process flow diagram for a Concep Acacia refinery system, as an example of an intensive leach reactor.



3.5.3.1 Characterisation of tailings

A geochemical review was undertaken on a selection of ore samples across the deposit. Characterisation of the materials was carried as defined by AMIRA1 as well as by Acid Potential Ratio (APR) approach. In addition, x-ray diffraction and x-ray fluorescence analyses were carried out to determine the Geochemical Abundance Index (GAI) of the samples. Leaching potential of the samples was determined by applying the Australian Standard Leaching Procedure (ASLP) with pH, EC, major cations and anions as well as trace elements determined on the leachates.

The geochemical review found that the bulk of the tailings were classified as NAF (non- acid forming (ABA/NAG)) with minimal potential for acid mine drainage (AMD). The tailings contain trace pyrite arsenopyrite and galena. The review highlighted that oxide tailings has the limited potential to liberate arsenic into the environment.

Management of the tailings will involve:

• locating the tailings dam on existing areas within known arsenic anomalism so as to reduce the adverse effects on the environment

• installing a permeability barrier of 1x10-8 to limit seepage

• recycling process water to reduce the potential for water to enter the natural water-cycle

• installing monitoring boreholes around the tailings dam to monitor any seepage into the environment.

Further details of the tailings management are provided in Chapter 10: Tailings and waste rock management.

3.5.4 Tailings dam

ABM is committed to minimising the lasting impacts from mining and processing of the Twin Bonanza project. The conceptual geotechnical design for the Twin Bonanza tailings dam has been carried out in accordance with the ANCOLD Guidelines on Tailings Dams (ANCOLD, 2012).

The tailings physical characteristics are as follows:

• tailing slurry will be in the order of 30% solids

• particle size distribution (PSD) of tailings ranges from sub 50 micron to 250 microns (μm), with 80% expected to be below 106 micron

• specific gravity (SG) of the tailings is 1.23 t/m3 (1.2 t/m3 used for all calculations)



• around 5% of tailings delivery will consist of leach concentrate, deposited into a separate dam.

3.5.4.1 Tailings dam design

The proposed management of the tailings during mining operations involves a multi-staged approach, comprising both below (in pit) and above ground tailings dam structures.

Based on the tailings characteristics above, the following storage requirements were used for the conceptual design:

• Tailings dams (2A/2B)

• Pit 1A and 1B each required to store 208 334m3 of tailings (250 000t) in pit

• Cell 2A and 2B each required to store 500 000m3 of tailings (600 000t) above ground but over the initial pits.

• Lined CRD required to store 50 000m3 of leach material (60 000t).

The 1A/2A tailings dam configuration has been designed to store the tailings below and above ground for the initial 850 000t of material. A similar 1B/2B tailings dam impoundment cell will also hold an estimated 850 000t of material below and above ground. The option of two dams with an interconnected wall far exceeds the projected volumes for this proposal but provides contingency should further mining occur. Additionally, the staged design can be either rehabilitated as below ground pits creating low rises or capped as stable landforms, if the mining ceases prior to above ground use.

The CRD is designed to store tailings leached with cyanide through the intensive leach reactor, and has a separate design and management. Tailings that have been subjected to cyanidation will undergo total cyanide destruction prior to deposition in the CRD, however ABM is using a conservative approach and separating all of the cyanide treated tailings from the gravity only separated tailings stream.

The excavated spoil from the construction and excavation of 1A and 1B pits will provide the necessary material required constructing both the tailings dams and the CRD embankments; however additional material can be sourced from selected mine waste (Refer to section 3.4.14).

Investigations are still required to establish the natural soil permeability to assist with the engineering of any required liner or construction works to achieve sufficiently low floor permeability. This will be undertaken prior to the submission of the mining management plan under the Mining Management Act.



Limited information of the permeability and exact nature of the subsurface conditions is available across the tailings dam footprint. Therefore, the use of clay or synthetic liners may not be required to prevent downward migration of tailings water/leach, and could possibly be substituted with effective earthworks/ground treatment to achieve a sufficiently low permeability subgrade (1 x 10-8 m/s). The need for a liner will be evaluated during detailed geotechnical investigation (refer to Appendix I: Tailing storage facility geotechnical conceptual design).

The tailings will be transported from the mill to the tailings dams via a pipeline, and discharged sub-aerially via a spigotted system. The system will be spaced equidistantly at ~50m intervals around the embankment perimeter. The spigots will operate either individually, or in groups of adjoining outlets, in sequence around the tailings dam to develop a beach of deposited tailings and force the supernatant water to flow to the centre of the pond where it can be recovered by the decant pump for re-use in the plant.

Supernatant water from the tailings will be managed using a decant system. The recovered water is transport via an HDPE pipeline to a water storage dam or the processing plant for re-use. A spillway has been incorporated into the conceptual design of the tailings dam, with the spillway invert located 500mm below the crest level and the supernatant pond to be maintained at least 1.0m below the spillway invert. This spillway has been added as a contingency in case a probable maximum precipitation event occurs during operations.

For further details and conceptual designs refer to Appendix I.

3.5.5 Clay source for tailings dam construction

If the in-situ materials at the proposed tailings dam location cannot be conditioned to produce permeability to 1x10-8, ABM intends to locally source clay from the Buccaneer borrow pit. This is included within the boundaries of the intended mineral lease and will be extracted as allowed by the conditions of the mineral lease (Figure 3-2 Site infrastructure). The primary purpose of the clay is for tailings dam construction.

Other materials such as aggregates may be sourced for further works, such as road upgrades or the air strip upgrade. Depending on location, quality of materials and onsite sourcing, material may be brought in from other locations and will be the subject of negotiation with the CLC and approval under relevant legislation. Where applicable mine waste rock will be utilised for road base.

3.5.6 Process water

All water flows (including to and from the tailings dam, CRD and water storage dams) will be monitored and recorded on a daily basis.



Daily water level monitoring will be undertaken at the tailings dam, CRD and process water plant. Monthly sampling of the tailings/process dam water will be undertaken, including a full suite of metals, major ions and general parameters to monitor metal levels in the water.

The consumption of raw water is kept to a minimum by the implementation of water recycling where possible. Decanted water from the tailings dam is re-used in the processing plant to reduce water consumption and assist in the consolidation of tailings.

For further details refer to Chapter 7: Water management and Appendix F: Water Management Plan.

3.5.7 Project process inputs and outputs

Table 3-13 describes the input material required for the project ore processing operation.

Table 3-13. Project mining operation annual average use of consumables

PROCESS STAGE INPUT QUANTITY (t/annum)

Comminution

ROM ore (average) 140 000 to 300 000 (t/annum) Crushing consumables including for impact crusher(s). Approx. 1kg per tonne processed.

Milling consumables Approx. 2kg per tonne processed.

New processing water Bore water to be used and recycled. Approx. 1t to 1.5t per tonne processed.

Smelting Flux Approx. 10t per annum.

Acacia Reactor

Sodium Cyanide Approx. 10.95t per annum

Sodium Hydroxide Approx. 1.95t per annum

Sodium Hypochlorite Approx. 45.6 per annum

3.6 Concentrate storage, pouring / shipping

Upgraded gold bearing concentrates (estimated 10 to 50% gold) will be smelted using a small furnace and a gold dore product will be generated on site. The company will arrange shipping of gold dore to the Perth Mint.

3.7 Infrastructure

3.7.1 Potable water supply

All water for human consumption will be extracted from one of the designated bores or bore fields (refer to Chapter 7: Water Management) and processed through a Reverse Osmosis (RO) plant. The RO plant will desalinate the water extracted from the bore fields and make it suitable for human consumption. Additionally the RO water will be passed through a UV sterilisation system in order to kill any bacteria in the water and system.



The current plant, installed for exploration, has a nominal capacity of 15 000 litres per day and will be upgraded if required with staged expansion of the operation. RO water will also be used where applicable for certain machinery and operations on site.

ABM will actively monitor the quality of the water from the RO plant and the processing plant. Currently rejected RO water is combined with the process water in the existing water storage dam.

Permanent raw and potable water tanks will be installed to hold water prior to and after RO treatment, tanks will have the capacity to hold approximately 100kL which will equate to approximately 2 days water storage each.

Refer to Chapter 7: Water management and Chapter 9: Waste management for further details.

3.7.2 Power

The proposed operation will include the development of additional infrastructure for power generation and fuel storage. Power generation will be from diesel generator sets. Power will be used for construction processes, operation of the processing plant, accommodation, workshops and office infrastructure.

Power for the stage one trial mining and processing has been provided by diesel generators, which have powered the camp and infrastructure including the processing plant. Currently power generation occurs at each location and is separate for accommodation, kitchen and ablutions, and processing.

Power lines or underground cables will be progressively installed, as staged expansion of the operation progresses, to centralise power generation adjacent to the processing facility. Bore fields are expected to remain as isolated power generation facilities, with a single small generator set for each bore.

3.7.2.1 Power generation and power requirements

Presently a single diesel generator (genset) that has 1250kVA total power capacity powers the processing plant for the bulk sample. For the bulk sample, power draw is in the order of 250kW at a processing rate of 10t per hour, or 25kWh per tonne. Additional, but smaller power requirements are needed for accommodation and camp facilities as well as bores.

From the bulk sample, as total power draw of up to 35kWh per tonne processed is considered reasonable for estimating total power requirements for ongoing operations, without consideration of any potential future underground operations. Additional capacity is required start-up of plant, such as the mill.



For a processing rate of 300 000t per annum (40t per hour allowing for downtime) an operating power capacity of 1 400kW is required, with an available power capacity of 3MVA available for start-ups and variations in power draw. A range of options are under consideration and power capacity will be progressively installed as staged expansion occurs.

Preliminary assessments indicate that the most feasible option will be to upgrade to utilise four 1 MVA genset units on site. The aim will be to have two operating at any given time, with one on standby for start-ups and one spare to allow servicing.

The final power configuration is yet to be finalised and ABM is exploring the feasibility of using thermal solar energy to supplement the power generation (refer to thermal solar energy and Chapter 16: Environmental Offsets.

Diesel consumption is expected to be in the order of 0.3 litres per kilowatt, or up to 3.2 million litres per annum.

The generator sets will be located centrally to infrastructure, on the south side of the main east – west access road between camp and mining operations and north of the processing facility (Figure 3-7).

3.7.2.2 Thermal solar energy

The final power configuration is yet to be finalised and ABM exploring the feasibility of using thermal solar energy to supplement the power generation. Current proposals involve a 3MWe CSP (Concentrating Solar Power) solar thermal plant with an option of 6 hours storage (using molten salt as a heat reservoir). ABM will still require diesel generators for hours of low solar output and high energy requirements. The current proposal that ABM is considering will utilise solar-diesel hybridisation where the exhaust gases from the diesel generating sets could be directed through a heat exchanger (that incorporates the solar thermal oil pipework). In the standard genset system, that ABM currently employs, the exhaust gasses will be around 390°c which results in around 305% of the fuel input being lost to the atmosphere. Utilising the heat exchanger is estimated to recover 50% of the emissions generating 0.45 MW (15%) further reducing the diesel fuel usage.

The advantages of CSP over standard PV (Photovoltaic) for ABM include:

1. Twin Bonanza is an ideal location of solar thermal power with minimal de-rating ( loss of efficiency) for high ambient temperatures.

2. Use of thermal energy allows lower cost thermal storage which is easily integrated.

3. Extra thermal energy can be utilised from the diesel genset further reducing costs – which is not feasible for PV circuits.



Please note that thermal solar energy is only in a preliminary investigative stage that requires further development. Until the technology viability has been confirmed and evaluated, the operation will run on diesel power generation.

3.7.3 Fuel (diesel) supply

Details of the mine fleet, fuel consumption and emissions can be found in Chapter 9: Air quality and greenhouse gases. Fuel consumption is estimated at 3823.4 KL/year for production rate of 240 000 tpa.

3.7.4 Fuel storage

Fuel storage areas are currently located at the processing plant (220Kl), which has been constructed and bunded in accordance with the relevant specifications of AS1940:1993 The Storage and Handling of Flammable and Combustible Liquids and regulatory requirements and Dangerous Goods Act 2012 (NT). Additional sources of fuel include AvGas for the fuelling of aircraft, and smaller bunded fuel containers at the water bores and mine camp.

All fuel drums / chemical products shall be stored within either self bunded tanks, bunded lined areas or within portable self bunded pallets. Permanent bunded storage areas are to be located away from the accommodation site and drainage lines. Regular checks of the fuel and chemical storage areas will be undertaken to check for the presence of leaking drums. When leaking drums are identified the drum will be isolated and the liquids transferred into a suitable container for ongoing storage.

It is not currently anticipated that an upgrade of the fuel storage capacity will be required in the short term for stage two, however upgrades will be required for stage three to allow enough storage capacity for operation through the wet season. With the upgrade all relevant regulations and standards will be adhered to and appropriate regulatory authorities notified.

The approved aviation fuel storage facilities at the project comprise solely AvGas for piston-engine aircraft, stored appropriately in 205L steel drums on bunded pallets; storage is aligned with AS1940-2004 Australian Standards (The storage and handling of flammable and combustible liquids) and CASA Regulations. These facilities may require expansion if the capacity of the airstrip and frequency of flights increase. Any expansion of the facilities will be conducted in accordance with AS1940-2004 Australian Standards and CASA Regulations.

There will be no offsite fuel storage. Fuel will be provided by certified and authorised contractors, and during transport will be the responsibility of the contractors.

Refer to Chapter 12: Road transport and Chapter 9: Waste management for further details.



3.7.5 Explosives storage

The raw materials (blasting agents) which are not classed as explosives will be stored in purpose built facilities. Diesel will be stored in bulk fuel tanks while ammonium nitrate with be stored in an enclosed area (Figure 3-2). These materials will be loaded into purpose built mobile manufacturing trucks for transport to the blasting area. The blasting agents will not become explosives until they are mixed as the product is loaded into the blast holes.

Detonators and boosters, which are classed as explosives, will be kept secure in licensed magazines in accordance with the relevant Northern Territory legislation and Australian Standards (Figure 3-2). Explosives magazines will be located to the south of mining operations and removed from any direct access from the Tanami Road.

3.7.6 Sewage

Ablutions will be established with the camp to service the work force. Septic tanks with associated leach/evaporation systems will be installed in line with the Public Health (General Sanitation, Mosquito Prevention, Rat Exclusion and Prevention) Regulations – Regulation 28. As part of this process the Department of Health will receive, via the prescribed form, notice of our intent to expand our waste management system.

Refer to Chapter 9: Waste management for further details.

3.7.7 Accommodation village

The current camp, Wilsons Camp, will be expanded to encompass the increased staff numbers and subsequent waste as required with staged expansion. Figure 3-10 below outlines the existing camp infrastructure and the proposed expansion footprint and generalised layout, including sewage pond, incineration area and landfill. Preparation and storage of food will be in accordance to the requirements of the Department of Health. The upgraded camp is located approximately 1.5 kilometres to the west of the processing plant. ABM intends to have a walking track to the plant allowing individuals to walk to work if they would prefer. The site is located on Aboriginal Freehold Land the agreement ABM has with the Traditional Owners prohibits the storage or use of alcohol on site, as such there is no requirement for a licenced premise.



Figure 3-10. Expansion footprint of existing accommodation village and associated infrastructure.



3.7.7.1 Telecommunications

The existing communications system on site comprises of an Orion Satellite System, which is a re-deployable system that includes the following:

1. 98cm Anntenna

2. 2 Watt Radio

3. HN7740 VSAT Modem

ABM currently has two phone lines on site as well as WIFI internet access. Additional communications are in the form of UHF for truck and vehicle movements. Satellite phones are also available in every vehicle.

A VHF Air radio (licensed) is also in use for communications with aircraft coming to site.

An expansion of the camp as proposed in section 3.7.7 will require an upgraded communications system. There are several options available based on a 100 man camp (allows additional resources larger than current calculated camp numbers). The following equipment and hardware are presently being reviewed for on-site use:

1. 1.8 HX Satellite system, comprising

a. HX200 VSAT Modem

b. 6watt Radio

c. LNB

d. 1.8M Antenna

e. Non Penetrating Ground Mount

f. Cisco UC320 (10 Handsets with 6 Lines)

The system will have the capacity to support 10 handsets with 6 phone lines and allow a substantial amount more data capacity. Additional communications are in the form of UHF radios for truck and vehicle movements. Satellite phones are also available in all vehicles. Trucks, and most contractors coming to site will have the UHF radios and these would normally be used around site.

3.7.8 Airport

The Wilson Camp Aerodrome is a refurbished older Aeroplane Landing Area from the 1980s. It has recently been regraded and re-established. The airstrip was recommissioned, by ABM after an assessment by Aerodrome Management Services Pty Ltd (AMS) in 2012. The airstrip



meets design guidelines provided by CASA as an Aeroplane Landing Area and is constructed of compacted good quality lateritic gravel, with the capacity to fly in aircrafts that have less than 9 seats.

It is likely that the airstrip will require upgrading for a larger operation. It is expected that the upgrade will consist of lengthening the air strip to allow larger aircraft to land. Refer to Chapter 12: Road transport and traffic management for further details.

3.8 Construction activities

The staged approach of the Twin Bonanza mine requires the incremental construction of infrastructure as the project develops. As previously discussed the existing infrastructure from the bulk sample has been specifically designed to require only modular upgrades, and thereby reducing the amount of pre-mining construction required.

Mine site infrastructure that will require progressive upgrades includes, but is not limited to;

1. camp / accommodation including sewage management systems and water supply

2. water bores supplying water for increased demand from both processing and camp areas

3. processing plant

4. haul roads

5. pits

6. airstrip

New infrastructure to be constructed includes, but is not limited to:

1. tailings dam

2. CRD

3. waste rock dumps

4. additional ROM pads

5. rehabilitation stockpiles

6. borrow pits

7. explosive magazine

8. surface water diversion structures.



Wherever practicable the labour and equipment will be sourced locally. However due to the specialised skills, equipment and components required, a variety of supplies and services will be sourced from regional centres. Personnel and mobile equipment will be transported through existing transport infrastructure with additional vehicles, trucks and planes put on during peak times.

3.8.1. Pre-construction phase

Prior to construction the design of the facilities, procurement and tendering for the work will be finalised.

3.8.2 On-site civil construction

To undertake the construction vehicles additional to that already on the mine site will be required. Where practicable equipment will have multiple applications to reduce mobilisation and increase flexibility; for example the same excavator used for mining may also be utilised for construction of the tailings dam. Additional equipment includes, but is not limited to, the following:

1. dozer - Caterpillar D9T Dozer x1

2. excavator – Hitachi EX1200

3. water cart - Converted Hitachi B50D

4. two light vehicles - Toyota Land cruiser

5. compaction roller

6. haul truck - Hitachi B50D

7. front end loader

8. crane

9. cherry picker/ elevated platform.

Prior to construction each area will be progressively cleared, contoured and conditioned depending on the locational requirements. Once completed, the staged earthworks and positioning of infrastructure will occur. To minimise disturbance existing laydowns will be used and areas of proposed infrastructure may be used as temporary laydowns. During construction the Sediment and Erosion Control Plan (Appendix E) will be implemented with this plan transitioning into an operational plan.

3.8.3 Construction workforce

The construction workforce is expected to include contractors, consultants and ABM employees. The construction workforce is estimated to comprise of mobile machinery



operators, boilermakers, construction workers (including general labourers, fabrication and builders), tailings dam specialists and process engineers. With the staged approach, construction of the project components will be expanded in increments and the construction workforce could vary from 10 to 20 depending on the nature of the activity and may occur at times concurrently with operations.

3.9 Operational activities

3.9.1 Operational workforce

The total operational workforce for mining is estimated to be approximately 68 personnel. The majority of the operational employees work a 2 weeks on/1 weeks off roster (mill – day and night shift), or 2 weeks on/1 weeks off roster (mine – day shift only). Management and support staff at head office will work 5 days a week in accordance with standard business hours. Table 3-14 outlines specific roles to be filled and relevant skills base required for these roles. These represent the minimum requirements for qualifications and experience. From time to time, depending on the activities, additional personnel may be required above the anticipated workforce

Generally staff and contractors, except for local Traditional Owners, will fly in fly out offsite. On occasions staff might be required to drive in via the Tanami Road and access road.

ABM has had a policy to hire Indigenous Australians from the local community as per ABM’s agreements with the CLC. Refer to Chapter 13: Social, economic, cultural and heritage risks for further details. The environmental management of the site is the task of an environmental manager supported by an environmental officer; in addition it will also be the responsibility of the respective managers and staff to support the implementation of the environmental commitments and conditions.



Table 3-14.Specific roles required for operational workforce for mining. Minimum requirements for qualifications and experience.

ROLE MINIMUM REQUIREMENTS FOR QUALIFICATIONS AND EXPERIENCE

Site general manager, directly responsible for all on site activities.

Technical qualification. Extensive management experience on multidisciplinary mining projects

Site processing manager Metallurgist with extensive processing experience

Site mining manager Experienced mining engineer

Site near mine exploration manager

Extensive exploration geology and management (exploration and resource development)

Site camp manager Experienced with camp operations and general management

Site stores and logistics manager Experienced logistics manager, with supply chain background

Site environmental manager Environmental qualifications, and on-ground experience

Site safety manager Experienced safety manager with high safety performance across multiple surface mining operations.

Staff under site processing manager

Includes the following staff: metallurgists, electricians, fitters, boiler makers diesel mechanics, haulage, machinery operators, processing personnel and construction contractors.

Staff under site mining manager

Includes the following staff: mine operators, blast crew, technical services (engineers, surveyors and geologists).

Staff under site near mine exploration manager

Includes the following staff: near mine exploration geologists and field assistants

Staff under site camp manager Includes the following staff: cooks, cleaners, and camp maintenance crew.

Staff under site stores and logistics manager Includes the following staff: storemen and freight delivery drivers.

Staff under site environmental manager

Includes the following staff: environmental officers, environmental technicians.

Staff under site safety manager. Includes health and safety advisors and medics

3.9.2 Emissions

Total emissions for the project were calculated and presented in Chapter 8: Air quality and greenhouse gas emmissions.

The total emissions estimated (greenhouse gases – CO2, CH4, N2O, including emissions from land clearing), fall well below the 50 kilotonnes annual reporting threshold for the National Greenhouse Gas Account (NGA), stipulated by the National Greenhouse and Energy Reporting Act (2007) (Cth). Chapter 8 and Appendix K: Air Quality Management Plan outlines the management and mitigation strategies for the project.



3.10 Rehabilitation and closure

The overall objective of closure is to rehabilitate the disturbed lands to create stable, non-polluting and self-sustaining landscapes capable of being incorporated into post mining land use. To achieve this rehabilitation aim, resources including topsoil, pisolite/gravel, siltstone and sandstone will be recovered and strategically stored during construction for use in rehabilitation. During mining operations ore and waste rock will be selectively handled and disposed in geotechnical stable structures that are managed to minimise erosion and the liberation of pollutants.

At closure the infrastructure not used for the purposes of the post-mining land use will be removed, tailings dams and CRD capped and waste rock dumps contoured for the re-establishment of native vegetation. During operations, continuing stakeholder engagement will further refine the proposed post mining land use to ensure the closure outcomes are acceptable to the community, minimise liability and integrate into the surrounding land management practices.

Further details on rehabilitation and closure can be accessed in Chapter 10: Tailings and waste rock management, Chapter 11: Closure and rehabilitation and Appendix O: Conceptual Mine Closure Plan and Appendix P: Conceptual Care and Maintenance Plan.

CHAPTER 3 – Project description...Chapter 3 - Project description Twin Bonanza 1 Gold Mine 3.1...

Documents

Transcript of CHAPTER 3 – Project description...Chapter 3 - Project description Twin Bonanza 1 Gold Mine 3.1...