Orebody OB32E: Preliminary Acid and Metalliferous Drainage ... J - OB32E... · This report documents the outcomes of a preliminary acid and metalliferous drainage (AMD) risk assessment

Orebody OB32E: Preliminary Acid and Metalliferous Drainage Risk Assessment (Above Water Table Mining)

Report Prepared for

BHP Billiton Iron Ore

Report Prepared by

SRK Consulting (Australasia) Pty Ltd

BHP150/1

May 2015

SRK Consulting Page i

HEND/LINK/cass BHP150_OB32E_AMD_Risk Assessment Report_AWT_Rev2 27 May 2015

Orebody 32E: Preliminary Acid and Metalliferous Drainage Risk Assessment (Above Water Table Mining)

BHP Billiton Iron Ore 125 St Georges Terrace, PERTH WA 6000

SRK Consulting (Australasia) Pty Ltd Level 1, 10 Richardson Street, WEST PERTH WA 6005

e-mail: [email protected] website: srk.com.au

Tel: +61 (08) 9288 2000 Fax: +61 (08) 9288 2001

SRK Project Number BHP150/1

May 2015

Compiled by Peer Reviewed by

Alison Hendry Senior Consultant (Geochemistry)

Claire Linklater Principal Geochemist (Geochemistry)

Email: [email protected]

Author:

Alison Hendry

SRK Consulting Page ii


Executive Summary Orebody 32E (OB32E) is located approximately 6 km northeast of Newman.

This report documents the outcomes of a preliminary acid and metalliferous drainage (AMD) risk assessment for OB32E, based on mining above the water table (AWT). The assessment relied mainly on assay data contained within the relevant drill hole databases. Other information sources were geological and mine planning information, Eastern Ridge surface and groundwater investigations and ecological studies.

Material was classed as potentially acid forming (PAF) using a sulfur threshold of 0.2% sulfur (in line with the current BHP Billiton Iron Ore (BHPBIO) practice for PAF classification) and a more conservative value of 0.1% (in recognition of the limited nature of geochemical data currently available, in particular with respect to the availability and reactivity of neutralisation potential).

The majority of material to be encountered at OB32E during mining above the water table has a low to negligible potential to generate acidity. The available assay database did not indicate the presence of sulfur exposures on the pit wall that exceeded a 0.1% threshold. The assessed assay dataset for OB32E is relatively small, having been obtained from a drillhole grid spacing of 100 x 200 m. Additional geochemical sampling at OB32E to improve spatial coverage of the assessment would improve the confidence associated with the assessment.

Based on the preliminary assessment, there is a low potential for AMD in seepage or runoff from overburden storage areas (OSA) or ore stockpiles, and a low potential for AMD in pit wall runoff. Further, more detailed geochemical data would be necessary to determine whether there is potential for any contaminants to leach at elevated concentrations in circum-neutral drainage. Thus, although the potential for AMD may be low, other potential impacts to surface water bodies and groundwater, such as neutral mine drainage, should be assessed.

In the event that PAF is encountered, it is anticipated that standard BHPBIO rehabilitation and closure protocols used in construction of landform structures would minimise contact between water and PAF material stored in OSAs, and therefore reduce risks to environmental receptors (i.e. Homestead Creek and Fortescue River). Further, BHPBIO has developed strategies to manage AMD risk in relation to public water supply bores, through the Eastern Pilbara Water Resource Management Plan (BHPBIO, 2014a) and the Newman Potable Source Protection Plan (P1) (BHPBIO, 2015). Therefore, whilst it is not possible to more precisely define the overall risks at the current time, it is considered that mitigation measures can be put into place to control potential risks to within acceptable levels.

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Table of Contents Executive Summary ..................................................................................................................................... ii

Disclaimer ..................................................................................................................................................... v

List of Abbreviations .................................................................................................................................... vi

1 Introduction .................................................................................................................. 1

1.1 Project Background ............................................................................................................................. 1

1.2 Scope of Work ..................................................................................................................................... 1 1.3 Report Structure .................................................................................................................................. 2

2 Background .................................................................................................................. 3

2.1 Climate ................................................................................................................................................ 3

2.2 Geological Setting ............................................................................................................................... 3

2.2.1 Regional Geology .................................................................................................................... 3

2.2.2 Local Geology ......................................................................................................................... 3

2.2.3 Potentially Reactive Shale Units ............................................................................................. 4 2.2.4 Potentially Acid Neutralising Units .......................................................................................... 4

2.3 Hydrogeological Setting ...................................................................................................................... 4

2.3.1 Introduction .............................................................................................................................. 4

2.3.2 Groundwater Quality ............................................................................................................... 5

2.4 Hydrology and Surface Water Management ....................................................................................... 5

2.5 Environmental and Social Receptors .................................................................................................. 6 2.5.1 Key Environmental Receptors ................................................................................................. 6

2.5.2 Flora and Fauna ...................................................................................................................... 7

2.5.3 Water Supply and Drinking Water Source Protection ............................................................. 7

2.6 Closure Planning ................................................................................................................................. 8

3 Assessment of Acid / Metalliferous Drainage Potential ............................................ 9

3.1 Background and Methodology ............................................................................................................ 9 3.1.1 Acid Drainage Potential ......................................................................................................... 11

3.1.2 Metal Leaching Potential ....................................................................................................... 12

3.2 Preliminary Geochemical Assessment ............................................................................................. 13

3.2.1 Available Geochemical Information ....................................................................................... 13

3.2.2 Mined Volumes ...................................................................................................................... 13

3.2.3 Pit Wall Composition ............................................................................................................. 14 3.2.4 Geochemical Characteristics of Mined Lithologies ............................................................... 15

3.2.5 Potential for Acid / Metalliferous Drainage ............................................................................ 17

4 Preliminary Risk Evaluation ...................................................................................... 19

4.1 Source-Pathway-Receptor Analysis ................................................................................................. 19

4.1.1 Sources ................................................................................................................................. 19

4.1.2 Pathways ............................................................................................................................... 19

4.1.3 Receptors .............................................................................................................................. 20

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4.2 Risk Analysis ..................................................................................................................................... 20

5 Conclusions ................................................................................................................ 21

6 References .................................................................................................................. 23

List of Tables Table 1: Average Monthly Precipitation and Evaporation .......................................................................... 3

Table 2: Aquifer parameter summary ........................................................................................................ 5

Table 3: Data files used for OB32E (AWT) geological modelling .............................................................. 9 Table 4: Summary of lithological categories addressed in the assessment ............................................ 10

Table 5: Summary of ore and overburden categories[1] addressed in the assessment ........................... 11

Table 6: Numbers of analytical values available within the OB32E pit shell ........................................... 11

Table 7: Volumetric quantities of overburden to be mined, by lithology .................................................. 14

Table 8: Volumetric quantities of ore to be mined, by lithology ............................................................... 14

Table 9: Areas exposed on pit walls, by lithology .................................................................................... 15 Table 10: Summary statistics for OB32E materials: Acid-base accounting surrogates and selected

metals (Fe, Mn) .......................................................................................................................... 16

Table 10: Estimation of the proportion of mined PAF-classed material within material to be mined ......... 17

List of Figures Figure 1: OB32E Location Plan ................................................................................................................. 26

Figure 2: Schematic of geological units associated with the OB32E mine (BHPBIO, RFP) ..................... 27

Figure 3: OB32E Regional Setting and Environmental Receptors ........................................................... 28

Figure 4: Image of OB32E pit shell showing spatial distribution of drill holes with sulfur data ................. 29 Figure 5: Image of OB32E pit shell showing exposed lithologies ............................................................. 30

Figure 6: Box and whisker plots showing sulfur statistics, by lithology (overburden) ............................... 31

Figure 7: Box and whisker plots showing sulfur statistics, by lithology (ore materials) ............................. 32

Figure 8: Image of OB32E pit shell showing the distribution of sulfur....................................................... 33

List of Appendices Appendix A: Eastern Ridge Water Quality

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Disclaimer The opinions expressed in this Report have been based on the information supplied to SRK Consulting (Australasia) Pty Ltd (SRK) by BHP Billiton Iron Ore (BHPBIO). The opinions in this Report are provided in response to a specific request from BHPBIO to do so. SRK has exercised all due care in reviewing the supplied information. Whilst SRK has compared key supplied data with expected values, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the supplied data. SRK does not accept responsibility for any errors or omissions in the supplied information and does not accept any consequential liability arising from commercial decisions or actions resulting from them. Opinions presented in this Report apply to the site conditions and features as they existed at the time of SRK’s investigations, and those reasonably foreseeable. These opinions do not necessarily apply to conditions and features that may arise after the date of this Report, about which SRK had no prior knowledge nor had the opportunity to evaluate.

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List of Abbreviations Abbreviation Meaning

3D 3 dimensional

ABCC Acid-Base Characteristic Curve

Acid-base account (ABA)

An Acid Base Account (ABA) calculates the balance between acid generation processes (oxidation of sulfide minerals) and acid neutralising processes. It involves determination of the maximum potential acidity (MPA) and the inherent acid neutralising capacity (ANC), both defined below.

Acid drainage A form of Acid and Metalliferous Drainage (AMD), characterised by low pH, elevated toxic metal concentrations, high sulfate concentrations and high salinity.

Acidity A measure of hydrogen ion (H+) concentration and mineral (latent) A measure of hydrogen ion (H+) concentration and mineral (latent) acidity; generally expressed as mg/L CaCO3 equivalent. Measured by titration in a laboratory or estimated from pH and water quality data.

ADWG Australian Drinking Water Guidelines

AER Annual Environmental Report

AHD Australian Height Datum

Alkalinity A measure of the capacity of a solution to neutralise an acid.

AMD Acid Mine Drainage or Acid and Metalliferous Drainage also known as Acid Rock Drainage (ARD) or Acid Mine Drainage.

ANC Acid Neutralisation Capacity

ANFO Ammonium Nitrate Fuel Oil

ANZECC Australian and New Zealand Environment Conservation Council

ASLP Australian Standards Leaching Procedure

Ave average

AWT above water table

BHPBIO BHP Billiton Iron Ore

BOM Bureau of Meteorology

BWT below water table

DEC Department of Environment and Conservation

Detritals Tertiary Detritals

DG Dales Gorge

DITR Department of Industry Tourism and Resources

DO discharge outlet

E east

EC electrical conductivity

EPBC Act Environmental Protection and Biodiversity Conservation Act (1999)

GARD Global and Metalliferous Drainage (Guide)

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Abbreviation Meaning

GDV Groundwater Dependent Vegetation

ha hectare

INAP International Network of Acid Prevention

kg kilogram(s)

kg H2SO4/t kilogram(s) of sulfuric acid per ton

km kilometre(s)

Km2 kilometre(s) squared

L litre(s)

m metre(s)

Mm millimetre(s)

m2 metre(s) squared (area)

m3 metre(s) cubed (volume)

m/day metre(s) per day

m2/d Metre(s) squared per day

Max maximum

MEND Mine Environmental Neutral Drainage (Programme)

meq/L Milli-equivalents per litre

Metalliferous drainage

Mine drainage with elevated heavy metal concentrations, high sulfate salinity

mg milligram(s)

mg/L milligram(s) per litre

Min minimum

MPA Maximum potential acidity

mRL metres above reference level

Mt (text) Mount

Mt (units) million tonnes

n number of samples

N Nitrogen

NAF Non-acid forming waste is unlikely to generate acid. NAF waste is designated as having an NPR >3.

NJV Newman Joint Venture

NWS Newman Water Supply

NPR Neutralisation Potential Ratio (ANC/MPC)

OB Orebody

OSA Overburden Storage Area

PAF Potentially acid forming waste is likely to generate acid. PAF waste is usually designated as having an NPR <1.

QA Quality Assurance

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Abbreviation Meaning

QC Quality Control

RL Reference Level

S Sulfur

S-P-R Source-Pathway-Receptor

SRK SRK Consulting (Australasia) Pty Ltd.

TDS Total Dissolved Solids

TEC Threatened Ecological Community

TPH Total Petroleum Hydrocarbons

TS Total Sulfur

TSS Total Suspended Solids

UC Uncertain acid forming potential

µm micrometre(s)

µS microsiemen(s)

µS/cm microsiemen(s) per centimetre

WA Western Australia

WC Act Wildlife Conservation Act (1950)

WT Water table

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1 Introduction 1.1 Project Background

Orebody 32E (OB32E) is located approximately 6 km northeast of Newman (Figure 1).

Ore from the existing Eastern Ridge operations (Orebodies 23/24/25) supplements high-grade ore recovered from the Mt Whaleback mine to produce the Newman Joint Venture (NJV) blend. Mining is by conventional open cut methods.

Environmental approval is required for mining of the OB32E deposit (north west of OB25), which is initially proposed to be progressed as an above water table (AWT) operation. This preliminary AMD risk assessment was undertaken to support the preparation of environmental approval documentation.

The mineralisation of OB32E occurs within the Hamersley Group, which is underlain by the Fortescue Group and older Archean granitic rocks. Tertiary detrital units lie unconformably over the bedrock.

The OB32E deposit is hosted within the Marra Mamba Iron Formation of the Hamersley Group, located in the Homestead Region (Figure 2). The geology of OB32E is complex, and incorporates stratigraphy from the Woongarra, Weeli Woolli, Wittenoom, Marra Mamba Formations of the Hamersley Group and the Jeerinah Formation of the Fortescue Group.

For reference, the location of OB23 is shown in Figure 3. Mine waste management will be integrated across the Eastern Ridge operations of OB25/24/32 to harness operational synergies and optimise closure outcomes.

Waste from OB32E will be managed locally through ex-pit Overburden Storage Areas (OSAs), with possible transport of some waste to OB24 and integration with the OB24 OSAs.

1.2 Scope of Work BHP Billiton Iron Ore (BHPBIO) commissioned SRK Consulting (SRK) to prepare a preliminary acid and metalliferous drainage (AMD) risk assessment for OB32E (AWT) based on the materials that are proposed to be mined. The AMD risk assessment was requested to comply with relevant Australian and International guidelines, including:

• Managing Acid and Metalliferous Drainage, February 2007, developed by the Australian Government, Department of Industry Tourism and Resource;

• The Global Acid and Metalliferous Drainage (GARD) Guide, May 2012, developed by the International Network of Acid Prevention (INAP); and

• The Australian and New Zealand Environment Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand 2000, Australian Water Guidelines for Fresh and Marine Waters and its updates.

The key objectives of this preliminary AMD risk assessment are to:

• Review available information to determine the risk of AMD generation by the materials that are to be mined;

• Provide a desktop assessment based on a source-pathway-receptor model; and

• Identify potential risk associated with mining activities, mine waste and pit void management and impacts on potential environmental receptors.



This AMD risk assessment is intended to provide information in support of the preparation of environmental approval documentation for AWT operations.

1.3 Report Structure The report comprises an introductory section (Section 1), which outlines the OB32E project background and the scope of work for this preliminary AMD risk assessment. A summary of the environmental setting is provided in Section 2, which incorporates a review of existing information and collates data relevant to a Source-Pathway-Receptor (S-P-R) analysis. The assessment of acid and metalliferous drainage potential from materials to be mined is presented in Section 3, with Section 4 presenting preliminary risk evaluation (incorporating an S-P-R analysis). Conclusions are presented in Section 5.



2 Background 2.1 Climate

The East Pilbara region has an arid climate characterised by hot summers with periodic heavy rain and mild winters with occasional rain. The region experiences highly variable rainfall, with tropical cyclones predominantly occurring between January and March.

The annual average rainfall recorded between the years 1965 and 2003 at the Newman weather station is 310 mm (BOM, 2013). Over this period, the annual rainfall ranged from a maximum of 537.8 mm (1997), to a minimum of 135.2 mm (1976).

The average monthly rainfall and evaporation rates for the Newman Airport weather station are shown in Table 1.

Table 1: Average Monthly Precipitation and Evaporation

Average Rainfall /

Evaporation (mm)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rainfall 57.3 78.8 40.3 19.9 18.1 14.2 14.9 8.0 4.6 4.9 10.3 37.6

Evaporation 461 369 343 290 174 173 199 193 264 377 424 466

Notes: Averages measured at Newman Airport weather station as cited as (BOM, 2011) - RPS Aquaterra, Orebody 35: Surface Water Impact Assessment, 2011, (page 2, Table 2.1)

2.2 Geological Setting

2.2.1 Regional Geology The OB32E deposit is hosted within the Marra Mamba Iron Formation within the Homestead Region to the west of the Eastern Ridge deposits. The Marra Mamba Iron Formation is within the Archean Hamersley Group, stratigraphically at the base of the Hamersley Group, underlying the Wittenoom Formation (Figure 2).

Tertiary detrital units lie unconformably over the bedrock. The Tertiary detrital units reflect periods of intermittent fluvial and lacustrine sedimentary deposition. Extensive calcrete horizons have developed within the more recent shallow fluvial sediments.

2.2.2 Local Geology The OB32E deposit is hosted within the Marra Mamba Iron Formation in the Homestead Region. The geology of OB32E is complex; affected by five deformation events, the deposit is bound by numerous large scale faults and exhibits fold regimes of varying intensity. The stratigraphy of OB32E incorporates Marra Mamba Iron Formation members including, Nammuldi Member (MU), MacLeod Member (MM), Mount Newman Member (N1 to N3 units), along with the West Angela Member (WA1 and WA2 units) and Paraburdoo Member (OB) of the Wittenoom Formation. Tertiary Detritals (TD1 to TD3 units) are also intercepted by the proposed OB32E pit shell. The stratigraphy of the OB32E area is most affected by Ali’s Fault which variably offsets the stratigraphy of the Jeerinah (stratigraphically below the Marra Mamba), Marra Mamba and Wittenoom Formations, and the Whaleback Fault which juxtaposes the stratigraphy of the Marra Mamba Iron Formations and the Wittenoom Formations against the Weeli Wooli and Woongarra Formations.



2.2.3 Potentially Reactive Shale Units Within the Pilbara stratigraphy, un-oxidised shale units can contain sulfide minerals (pyrite) and black shale units such as the Mt McRae Shale, also contain relatively elevated carbonaceous content. This combination can result in spontaneous combustion or generate sufficient heat to result in self-detonation of ammonium nitrate fuel oil (ANFO) explosives used in drilling and blasting operations.

The Jeerinah Formation, encountered below the Marra Mamba Formation, is known to host sulfide mineralisation and could be encountered during mining at OB32E.

2.2.4 Potentially Acid Neutralising Units Some carbonate-rich units are encountered within the Pilbara stratigraphy, and these, on occasion, can offer excess neutralising capacity to mitigate risks of acid generation. Such units include calcrete units within the detrital sequences, and dolomitic units of the Paraburdoo Member of the Wittenoom Formation, which have been intersected at OB32E.

2.3 Hydrogeological Setting

2.3.1 Introduction OB32E is located within the Hamersley (Fractured Rock) Aquifer, within the Precambrian rocks of the Hamersley Basin, principally comprising volcanics, shales and iron formation (Forrest and Coleman, 1996). The deposit is located within structurally complex geology with faulting, tight folding and overturning commonly observed. The influence of the faulting on groundwater flow within and surrounding the deposit is currently not well understood.

Two main aquifer types identified within the OB32E area are the unconfined to semi-confined fractured-basement rock aquifer, and the unconfined valley fill aquifer within Tertiary to Recent alluvial sediments. These aquifers are generally in direct contact and are considered to be hydraulically connected, although localised areas of low permeability result in poor connectivity (BHPBIO, 2013c).

Within the main orebodies, the basement aquifers typically have higher conductivities as a result of secondary permeability and porosity associated with mineralisation. The basement aquifers are recharged via direct infiltration and by leakage from the valley fill alluvium.

Homestead Creek occurs to the west and south of the OB32E deposit, underlain by an alluvial aquifer within the alluvium-filled palaeovalley. The valley fill aquifers are permanent regional, semi-confined to unconfined aquifers which have formed within the Tertiary detrital creek systems. The valley fill aquifers comprise a generally consistent detrital sequence of sandy gravel, calcrete, gravelly sand, clay and sand, overlying the basement rocks (BHPBIO, 2013a). The detritals have been derived from alluvial drainage, outwash fans and scree slopes (Water and Rivers Commission, 2001). Flow within the valley fill aquifers occurs via primary granular permeability and porosity in sands and gravels. Within the calcretes, groundwater flow occurs via karstic weathering features (secondary permeability). Recharge of the valley fill aquifers occurs through infiltration of catchment runoff.

Aquifer parameters for key aquifer units in the Eastern Ridge region were reviewed as part of a previous AMD assessment (SRK, 2015b), and are reproduced here as Table 2.



Table 2: Aquifer parameter summary

Lithological/Aquifer Unit Hydraulic Conductivity (m/day) Specific Yield

OB23 Orebody 0.2-4 0.05

OB25 Orebody 1-4 0.05

Mt McRae Shale 0.01 0.001

Mt Sylvia Formation 0.01 0.001

Sub-mineralised Dales Gorge/Joffre 0.01-0.1 0.01-0.025

Valley Fill 3-30 0.06-0.1

Source: Taken from BHPBIO, 2013d and Aquaterra, 2008

2.3.2 Groundwater Quality A water monitoring programme (including surface water quality, groundwater levels and quality) is undertaken at the Eastern Ridge operations to assess the impacts of the mining operation on the local water environment and inform management practices.

Limited groundwater quality data is currently available for the OB32E site. Appendix A reproduces groundwater quality data obtained as part of the OB23/25 Eastern Ridge operations monitoring programme which has been reviewed as part of other AMD assessments (SRK, 2015b). These data are expected to be representative of groundwater compositions that could be encountered at OB32E. Further review of data specific to OB32E would be necessary to determine if any significant local variation in groundwater chemistry exists.

The groundwater quality monitoring results provided in Appendix A were compared to water quality guidelines relating to the 95% protection level for freshwater aquatic life (ANZECC, 2000) and Australian Drinking Water Guidelines (ADWG, 2004), as referenced in the BHPBIO Triennial Aquifer Review (BHPBIO, 2013d).

The groundwater is generally freshwater, with circum-neutral pH (pH 7.5 – 8.2), and total dissolved solids (TDS) in the range of 580-765 mg/L. More brackish groundwater has been encountered with bores screening the Dales Gorge D2 unit (878-2070 mg/L TDS).

2.4 Hydrology and Surface Water Management The Pilbara region typically experiences localised thunderstorms and cyclonic rainfall events, occurring during the period of December to April. These storms can generate large runoff events. From May to November, rainfall is relatively low and runoff events are uncommon.

OB32E is located within the Homestead Creek catchment (Figure 3). Homestead Creek rises approximately 20 km west of Newman and drains to the east, passing to the west and south of OB32E and on to its confluence with the Fortescue River upstream of Ethel Gorge. The creek is ephemeral, and typically experiences one to three short-lived flow events per year.

The Ophthalmia Dam is adjacent to the OB25 site on the Fortescue River and was installed to capture surface water runoff for subsequent slow release to replenish downstream aquifers which support the Ophthalmia Borefield.

The OB32E deposit is located on a ridge, approximately 45 m high, located between Eastern Ridge and Ophthalmia Range. The pre-mining ground surface elevations within the footprint of the proposed OB32E pit vary between 545-590 m RL, and surface water runoff naturally drains radially from the ridge. The western end of the proposed OB32E pit lies within the Homestead Creek floodplain, while the northern end of the pit is within a 23 km2 catchment draining the hills from the



north. These potential surface water catchment impacts to the pit would be managed by the construction of surface water diversions.

Natural surface water quality in the Homestead Creek/ Eastern Ridge area and adjacent creek systems is described as fresh; the pH is generally circum-neutral, pH 6-8 and TDS are generally low, less than 500 mg/L (RPS Aquaterra, 2014).

2.5 Environmental and Social Receptors A clear understanding of the environmental receptors is required in order to support a Source-Pathway-Receptor assessment. This section therefore incorporates a review of existing information and collates data relevant to the description of the key environmental receptors.

2.5.1 Key Environmental Receptors The key environmental receptors identified by BHPBIO within the Eastern Ridge deposit area are subterranean fauna (stygofauna) and potentially groundwater dependent vegetation.

Subterranean Fauna A stygofauna Threatened Ecological Community (TEC) has been identified at Ethel Gorge which is located approximately 11 km to the east of OB32E (Figure 3).

The Ethel Gorge Aquifer Stygobiont Community has been classified as a TEC B (ii) community, which is based on community being of “limited distribution, with few occurrences, each of which is small and/or isolated and all or most occurrences are very vulnerable to known threatening processes” (DEC, 2010).

Ethel Gorge is a regional outflow zone for the upper reaches of the Fortescue River Catchment. The Homestead, Whaleback, Shovellanna and Warrawanda Creeks all converge with the Fortescue River upstream of Ethel Gorge. The TEC stygofauna community identified in the Ethel Gorge area has an expected habitat related to the saturated shallow calcretes and gravels of an extensive Tertiary overburden sequence.

BHPBIO has identified a number of threats to the Ethel Gorge stygobiont TEC (BHPBIO, 2014b), which include:

• Groundwater drawdown related to dewatering activities;

• Changes to groundwater quality, caused by discharge of mine water in Ophthalmia Dam; and

• Obstruction of surface water flows through Ethel Gorge.

The Eastern Pilbara Water Resource Management Plan (BHPBIO, 2014a) provides the basis for ensuring no significant impacts on the TEC are caused by BHPBIO activities. The key indicators employed for the preservation of ecological values in Ethel Gorge are water level baselines and water quality baselines.

BHPBIO is currently undertaking a study to identify and document the ecological character of the TEC and determine the hydrogeological and biological extent of the community. The aim of the study is to successfully redefine the TEC boundary and revise the buffer which is currently set as a default 14 km radius from Ethel Gorge.

Riparian Vegetation Assessment of the potentially groundwater dependent vegetation in the Eastern Ridge area has identified a number of key Riparian Vegetation including, Tussock Grassland (Cenchrus ciliaris and Cenchrus setiger), and Low Woodland of Eucalyptus victric, Acacia citrinoviridis and Atalaya hemiglauca on brown sandy loam on the major drainage line and adjacent flood plains (BHPBIO, 2014c).



In addition, a further vegetation association has been recorded on the calcrete plains flanking the Ethel Gorge major drainage line, defined by the presence of two priority flora (Acacia subtiliformis and Goodenia sp. East Pilbara) (BHPBIO, 2013a).

2.5.2 Flora and Fauna Assessments of the flora and fauna within the vicinity of OB32E (Onshore Environmental, 2012; Biologic Environmental Survey, 2014; BHP, 2014c) have identified:

• Seven vegetation associations along the Homestead Creek and surrounding floodplains, none of which are categorised as Threatened Ecological Communities (TECs) or Priority Ecological Communities (PECs).

• Priority flora of interest - Eremophila magnifica subsp (Priority 3 species) and Velutina, Aristida jerichoensis var. subspinulifera (Priority 1 species).

• Various conservation significant fauna including: Rainbow Bee-eater (Merops ornatus), Pilbara Olive Python (Liasis olivaceus barroni), and the Western Pebble-mound Mouse (Pseudomys chapmani).

2.5.3 Water Supply and Drinking Water Source Protection The Ophthalmia Borefield, located approximately 9 km to the south-east of the OB32E study area, provides potable quality water to Newman and the nearby mining operations (Figure 3). The borefield abstracts groundwater from the valley fill aquifers, which comprise alluvial and chemical sediments that have in-filled palaeovalleys associated with the Fortescue River and its tributaries. Some of the bores within the Ophthalmia Borefield also draw water from the Wittenoom Formation (Department of Water, 2009).

Groundwater recharge in the vicinity of Newman occurs mostly by leakage from stream beds during runoff and to a lesser extent by direct infiltration of rain over the surface. The potable water supply bores are drawing from a superficial aquifer system, and therefore the water quality and quantity is heavily influenced by the quality and quantity of surface water.

The Ophthalmia Dam is located on the Fortescue River and, as noted before, was installed to capture surface water runoff for subsequent slow release to replenish the downstream aquifers which support the Ophthalmia Borefield. An aquifer recharge system has been constructed below the dam, comprising four excavated recharge ponds, two river basins and an open-earth canal, which can be flooded as required from the dam. The aquifer recharge scheme can be activated if monitoring indicates that groundwater abstracted from the Ophthalmia Borefield is projected to exceed the sustainable yield of the aquifer (Department of Water, 2009).

The Newman Water Reserve, covering an area of 840 km2, was proclaimed in 1983 under the Country Areas Water Supply Act 1947 (WA) for public drinking water source protection.

All Crown land (with the exception of the land within the gazetted town site) in the Newman Water Reserve is classified as Priority 1 (P1), which are areas defined as having the fundamental water quality objective of risk avoidance (the most stringent of the P1-P3 risk-based classifications).

BHPBIO owns and operates the water supply headworks at the Ophthalmia Borefield, and treats dewatering supply which is provided to the Water Corporation, subsequently reticulating the water to the town of Newman.

The Homestead Borefield, comprising 12 bores, is a public water supply to Newman, and is located approximately 0.5 km to the north west of OB32E within the Homestead Creek catchment.



2.6 Closure Planning BHPBIO will utilise this Preliminary AMD Risk Assessment to inform the development of a conceptual Closure Strategy for OB32E. Business as usual (BAU) AMD controls across BHPBIO operations include:

• Flagging PAF material in resource and mining models;

• Development of OSA designs addressing PAF encapsulation;

• The use of blast hole drilling to confirm the presence or absence of PAF; and

• Short-term mine planning scheduling PAF material to the designated encapsulation OSAs.



3 Assessment of Acid / Metalliferous Drainage Potential

3.1 Background and Methodology The propensity for mined materials to generate acid is a balance between the abundance of acid forming minerals (i.e. sulfides) and acid neutralising minerals (e.g. carbonates). This balance can be determined quantitatively using acid base accounting (ABA) methods. Acid and metalliferous drainage (AMD) is the term used collectively to drainage that may display one or more of the following chemical characteristics (DITR, 2007):

• Low pH (typically below pH 4.5);

• High soluble metal concentrations (e.g. iron, aluminium, manganese, cadmium, copper, lead, zinc, arsenic and mercury);

• Elevated acidity values;

• High sulfate salinity (typically 500 – 10,000 mg/L);

• Low concentrations of dissolved oxygen (< 6 mg/L); and

• Low turbidity or suspended solids (combined with one or more of the above characteristics).

No ABA or leaching test results are currently available for OB32E. Geochemical assessment that have been undertaken for equivalent materials in the nearby Orebodies 23, 24 and 25 (GHD, 2013; SRK, 2013; SRK, 2015a) have been reviewed to provide insights into the AMD potential of the overburden material for the current assessment.

The OB32E assessment, however, was principally reliant on chemical assay information contained within the BHPBIO drill hole database. The drill hole database contained results for the following parameters: Al2O3, CaO, Fe, K2O, MgO, Mn, P, S, SiO2, TiO2. These results are understood to be based on XRF analyses.

Geological and mine modelling software and current resource models were used to process the drill hole database. The source data files used are detailed in Table 3.

Table 3: Data files used for OB32E (AWT) geological modelling

3D Modelling Resource File Name

Resource Model EPH_20140814_OB32E_LPT_V2

Pit shells ob32_pit_surface.dxf

Overburden Storage Areas ob32osa.dxf

Material Designations EPH_20140820_OB32_mm_description_4m.xlsx

In order to calculate lithological volumes within the OB32E pit shell, the resource block models provided by BHPBIO were extracted into the pit shell using Vulcan (mine) modelling software. The pre-defined block volumes, along with their lithological and material designation descriptors, were used to calculate total volumes of each lithology by material designation, as they occur within the pit shell.

To assess the characteristics of the pit walls, GOCAD geological modelling software has been used to generate ‘maps’ of the pit wall lithological distribution. Surface areas of each lithology exposed on the pit shell surface were calculated by importing the geological wireframes (extracted from the resource model) and cutting the pit shell surface into smaller lithologically defined component surface areas. GOCAD was then used to calculate the sum total surface area of each lithology.



Leapfrog 3D modelling software was used to obtain a sub-set of the available drill hole database information pertaining to the materials located within the pit shell. Geological and assay data were merged to allow separation of the assay data into categories based on lithology. The lithologies considered in the current assessment are presented in Table 4. The assay data was then also separated into overburden and ore categories, based on the material designations detailed in Table 5. As summarised in Table 5, three categories of ore and one category of overburden material are recognised. Table 6 presents a summary of the number of assay values in the ore and overburden categories the OB32E pit shell. Additionally, a preliminary 3D sulfur model was constructed using Leapfrog to evaluate the distribution of sulfur concentrations on the pit walls.

At the current time, limited scheduling information is available for future material movements. For the purposes of the current assessment, it is assumed that different mined lithologies will be randomly mixed in the relevant OSAs and stockpiles.

Table 4: Summary of lithological categories addressed in the assessment

Lithological Category Abbreviation Comment/Description OB32E

Tertiary Detritals 1 TD1[1] Y

Tertiary Detritals 2 TD2 Y

Tertiary Detritals 3 TD3 Y

Wittenoom Formation, Paraburdoo Member (Ahdp) – OB Undifferentiated OB[1]

The carbonates within this unit may offer neutralising potential

Y

Wittenoom Formation, West Angela Member – WA2 (Shale Waste) WA2

These units are mineralised and form important ore hosts

Y

Wittenoom Formation, West Angela Member – WA1 WA1 Y

Marra Mamba Formation, Mount Newman Member – N3 N3 Y

Marra Mamba Formation, Mount Newman Member – N2 –shaly N2 Y

Marra Mamba Formation, Mount Newman Member – N1 N1 Y

Marra Mamba Formation, MacLeod Member (Ahmn) undifferentiated - MM MM Y

Marra Mamba Formation, Nammuldi Member (Ahmu) - MU MU Y

Notes: [1] OB and TD1 units are intercepted within the OB32E pit in small volumes, but to-date, no samples within the pit-shell have been assayed.



Table 5: Summary of ore and overburden categories[1] addressed in the assessment

Category Database Flag Comment/Description

High Grade 14 Material Fe content >= 57%; surface scree (SZ), Tertiary Detritals (TD1, TD2 and TD3) and Tertiary sediments (T) excluded

Detritals 8 Material Fe content >= 57%; surface scree (SZ), Tertiary Detritals (TD1, TD2 and TD3) and Tertiary sediments (T) lithologies only.

Low Grade 6 Fe contents between 54 and 57%; applicable to all lithologies

Overburden/Waste 1 Material with Fe content < 54%

Note: [1] Material designation categories sourced from EPH_20140820_OB32_mm_description_4m.xlsx

Table 6: Numbers of analytical values available within the OB32E pit shell

Number of assay samples

Overburden/ Waste Ore (High grade, detritals and low grade)

192 364

3.1.1 Acid Drainage Potential The total sulfur (S) analyses were used to infer maximum acid potential (MPA) based on the assumption that all sulfur present is in the form of reactive sulfide (AMIRA, 2002). This is a conservative approach, as some proportion of the sulfur may be present as sulfate in the form of gypsum or other non-acid forming minerals. Sulfur speciation results from the OB23/25/25W dataset (SRK, 2015a) suggested that sulfide-sulfur is the dominant form of sulfur in samples with greater than 0.1% total sulfur. The proportion of acid-soluble sulfur (i.e. sulfate-sulfur) was found to be greater (typically up to 40%) in samples with less than 0.1% total sulfur.

The acid neutralising capacity (ANC; AMIRA, 2002) of samples from the OB23/25 dataset was generally low. The majority of samples (193 of 219 samples) gave ANC values below 10 kgH2SO4/t, with 82 samples (37%) containing negligible ANC (i.e. less than or equal to 0.5 kgH2SO4/t). Six lithologies were represented within the samples that had ANC greater than 10 kgH2SO4/t (10.8-759 kgH2SO4/t): Surface Scree (SZ), Tertiary Sediments (T/TD2/TD3), Mt McRae Shale (R/RL/RN) Mt Sylvia (S) Wittenoom (OB) and Marra Mamba (N3). Of these lithologies, TD1, TD2, TD3, OB and N3 have been intersected at OB32E in drilling to-date.

In most rocks, the most effective neutralising potential is contributed by carbonate-based minerals, e.g. calcite (CaCO3) and dolomite (Ca0.5Mg0.5CO3). Such minerals are expected to be associated with the Wittenoom Formation and Tertiary Sediments – which are known to contain dolomitic and calcrete units.

Some examination of neutralising capacity was conducted as part of the AMD investigations for OB24 (GHD, 2013); acid-base characteristic curve (ABCC) testing on Mt McRae Shale and Dales Gorge samples indicated that carbonate-based minerals formed a low proportion of the measured neutralising capacity (typically less than 50%). This finding is consistent with experience elsewhere in the Pilbara, with only a small proportion of neutralisation potential being readily available. Based on these results, it would appear that reactive silicates present within the samples contribute to the laboratory ANC measurement. Using CaO and MgO assay results within the OB24 dataset, SRK calculated some illustrative surrogate ANC values and found there to be poor agreement between the surrogates and ANC measurements (generally the surrogate ANC over-estimated the measurement ANC).



For illustrative purposes, surrogate ANC values have been calculated in the current assessment. Comparison of MPA and ANC based on surrogates allows an initial assessment of the acid-base account and calculation of a neutralisation potential ratio (NPR) – or the ratio ANC/MPA. Using the NPR, waste rock or overburden materials can be classified as follows (AMIRA, 2002; MEND, 2009):

• ANC/MPA < 1 - Potentially acid forming, PAF;

• 1 < ANC/MPA < 3 – Uncertain potential to generate acid, UC; and

• ANC/MPA > 3 – Non-acid forming, NAF.

Note that because there is a low degree of confidence in the estimated ANC values, low confidence can be assigned to the material classifications using this method.

An alternative approach to classify materials is to identify a sulfur cut-off threshold. Materials with a sulfur content below the threshold are considered to represent a low risk of acid generation. At BHPBIO, as general practice a 0.2% sulfur cut-off value is often utilised to differentiate PAF overburden material. The 0.2% sulfur cut-off is only applied in the case of materials that lie below the base of complete oxidation (BOCO). Materials located above the BOCO are categorised as NAF, irrespective of the sulfur content. In addition, all Mt McRae Shale and Mt Sylvia Formation waste rock from below the BOCO is categorised as PAF regardless of the sulfur content, as these units are considered high risk for acid generation.

Identification of a defendable sulfur cut-off should be supported by site-specific assessment of the availability in ANC in the materials of concern. Given the lack of site-specific ANC data for OB32E, the most conservative approach would be to assume no ANC. For materials that contain little or no ANC, then a lower sulfur cut-off value of 0.1% is often used (e.g. Green and Borden, 2011). In the assessment that follows, the lower, more conservative, cut-off value has been adopted for most discussions. However, where appropriate, discussion has been extended to include a higher sulfur cut-off value.

Of the two approaches to material classification described above, the sulfur cut-off approach is considered to be most conservative as this approach allows no credit for neutralising potential that may be present within the materials.

3.1.2 Metal Leaching Potential Analytical results for metals and other potential contaminants within the drill hole assay database are limited to a few analytes (Al2O3, Fe, K2O, Mn, P, SiO2, TiO2). No extended assays or leach testing have been conducted for OB32E materials.

The OB23/25/25W assessment (SRK, 2015a) included samples from the Marra Mamba Formation, Wittenoom Formation and Tertiary Detritals - lithologies which are present at OB32E. Data assessed included assay (22 samples) and leach test (9) results for some additional parameters including: Ca, Mg, Na, K, Cl, P, Si NO2, NO3, SO4, Al, Ag, As, B, Be, Bi, Cd, Ce, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, Tl, V, W, Zn.

The leach testing (SRK, 2015a) included samples from the Mount Newman Member (9), MacLeod Member (4), West Angela Member (2), Paraburdoo Member (2) and Tertiary Detritals (5). The samples all gave leachates with circum-neutral pH values (pH 7.1-8.5).

Major elements Ca, Mg, Na, K, Cl, Si and SO4, were generally detectable in leachates from all the samples. The samples all contained low sulfur (<0.01-0.07%S), and the majority of trace elements leached at concentrations that were close to or below the detection limits of the analytical methods. Trace/minor elements that were readily detectable in some leachates were Al, B, Ba, Fe, Mn, Mo, Ni and Sr.



The assessment that follows is based on the assay results contained within the main drill hole database. The approach adopted as a ‘first pass’ assessment of the potential for metalliferous leaching was as follows:

• The distribution of S was used to infer the potential for AMD. The PAF materials are considered to be linked to the potential for metalliferous leaching on the basis that many elements are more soluble and leachable under acidic conditions. Also, the distribution of many trace elements is likely to be coincident with the distribution of sulfides minerals and sulfide weathering products.

• Available Fe results provide an understanding of the distribution of iron oxides in the overburden materials. In many samples, iron is a major component and a high proportion of iron is probably in the form of iron oxides such as magnetite (Fe3O4), hematite (Fe2O3) and goethite (FeOOH). Many minor and trace components could be present as impurities within these iron oxides (e.g. positive correlations between arsenic and iron have been noted elsewhere in the Pilbara, and have been attributed to incorporation in iron oxides). Iron oxides and oxy-hydroxides are also known to be strong adsorbents, and could be coincident with high adsorbed trace element loads.

• The distribution of Mn was examined as a possible indicator of the distribution of transition metals in the mined materials.

The other analytes contained within the database are considered of limited value with respect to assessing the potential for acid or metalliferous drainage. SiO2, Al2O3 and K2O are major components of silicates – a mineral group that is considered unlikely to be reactive under the geochemical conditions expected within most overburden storage areas or stockpiles (unless strongly acidic conditions are encountered). TiO2 is most likely hosted by similarly unreactive minerals such as ilmenite (FeTiO3) or rutile (TiO2). Phosphorus (P) is likely to be present either as an impurity in the iron oxides or the silicates, or possibly in the form of minor phosphates (also likely to be relatively unreactive).

3.2 Preliminary Geochemical Assessment

3.2.1 Available Geochemical Information The number of analytical values from OB32E (AWT) is presented in Table 7. Figure 4 presents the spatial distribution of drill holes containing sulfur assays, which have been sampled from drillholes at approximately based on a 100 x 200 m grid spacing.

3.2.2 Mined Volumes Estimates of the volumes of material to be mined from the OB32E pit are presented in Table 7 (overburden) and Table 8 (ore). The pit will produce around 3.6 million cubic metres of overburden and 8.3 million cubic metres (Mm3) of ore.

Overburden is distributed evenly across the Tertiary Detrital units (TD2-3), the West Angela units (WA1-2), the Mt Newman unit (N1-3) and the McLeod Member (MM), with lesser contributions from TD1, Wittenoom (OB) and Nammuldi Member (MU).

Ore material comprises fairly similar volumes of low grade and high grade ore, predominantly from units N1-N3 (Mount Newman Member) and MM (McLeod Member).



Table 7: Volumetric quantities of overburden to be mined, by lithology

Lithological Unit Total (m3) % of volume

TD3 397,025 10.9%

TD2 804,275 22.2%

TD1 1,775 0.05%

OB 54,875 1.5%

WA2 333,175 9.2%

WA1 381,300 10.5%

N3 360,950 10.0%

N2 554,325 15.3%

N1 346,400 9.6%

MM 380,475 10.5%

MU 11,450 0.3%

Total 3,626,025 100.0%

Table 8: Volumetric quantities of ore to be mined, by lithology

Lithological Unit Low Grade High Grade Total (m3) % of volume

TD3 47,175 47,175 0.3%

TD2 29,100 29,100 0.2%

OB 5,375 7,200 12,575 0.1%

WA1 15,850 274,350 290,200 1.8%

WA2 5,375 7,200 12,575 0.1

N3 1,231,275 1,255,025 2,486,300 15.6%

N2 2,735,325 2,441,775 5,177,100 32.4%

N1 2,647,600 3,021,850 5,669,450 35.5%

MM 1,564,350 624,600 2,188,950 13.7%

MU 33,725 17,100 50,825 0.3%

Total 8,315,150 7,629,100 15,964,250 100% Notes: [1] Five detritals ore samples were included within the OB32E assay dataset (TD2, n=1; TD3, n=4); however these materials contribute a small volume within the total OB32E ore volume to be mined and volumes have not been quantified at this time.

3.2.3 Pit Wall Composition The estimated lithological composition of the exposed final pit walls is summarised in Table 9, and illustrated in Figure 5.

Units N1-N3 (Marra Mamba Formation, Mount Newman Member) would form a significant proportion (70%) of the exposed pit walls, along with unit MM (14%; Marra Mamba Formation, McLeod Member).



Table 9: Areas exposed on pit walls, by lithology

Lithological Unit Total (m2) % of exposed surface

OB 6,231 1%

WA2 45,348 6%

WA1 61,001 8%

N3 180,564 25%

N2 177,903 24%

N1 154,089 21%

MM 100,934 14%

MU 2,072 0.3%

Total 330,434 100%

3.2.4 Geochemical Characteristics of Mined Lithologies The distribution of the sulfur analyses for materials from OB32E are shown in Figure 6 (overburden) and Figure 7 (ore). Pink highlighting indicates regions where the total sulfur content is above a 0.1% sulfur cut-off (i.e. could be considered as PAF). The figures include the sulfur assay numbers (n counts) for each lithology. Some of the n counts are low, less than 10 assays, and not sufficient to support a robust statistical analysis. However, low n counts generally coincide with volumetrically insignificant units. The only notable exception is the WA2 unit within waste, which only has 8 assay samples but accounts for 9.2% of the overburden volume.

The results can be summarised as follows:

• All materials (overburden and ore) show similarly low ranges of sulfur content. Median sulfur values lie below 0.1% for all materials, suggesting a low potential for acid generation.

• A single TD3 sample within the waste category (192 samples) contained sulfur at levels marginally above 0.1% threshold (0.102%).

• Within the ore grade categories, maximum sulfur values are low, invariably below the 0.1% threshold.

Summary statistics for MPA, inferred ANC, and Fe and Mn content are shown in Table 10.



Table 10: Summary statistics for OB32E materials: Acid-base accounting surrogates and selected metals (Fe, Mn)

Lithology Acid-Base Accounting Surrogates Distribution of Selected Contaminants

MPA, kgH2SO4/t[1] ANC, kgH2SO4/t[2] ANC/MPA[3]

Fe, % Mn, % n Min Ave Max n Min Ave Max n Min Ave Max n Min Ave Max

High Grade MU 5 0.5 0.9 1.4 5 0.3 0.6 1.1 0.7 5 58.9 60.5 61.6 5 0.023 0.034 0.047 MM 16 0.1 0.6 1.2 16 0.2 1.0 4.4 1.7 16 57.1 59.0 63.1 16 0.026 0.495 3.102 N1 74 0.1 0.6 1.2 74 0.1 0.7 3.7 1.2 74 57.1 61.0 65.5 74 0.016 0.199 1.560 N2 114 0.1 0.4 1.4 114 0.2 0.7 8.4 1.8 114 57.0 61.5 65.4 114 0.019 0.299 2.749 N3 79 0.1 0.4 1.5 79 0.1 0.8 5.4 1.9 79 57.0 61.8 66.0 79 0.017 0.280 2.985

WA1 9 0.1 0.3 0.6 9 0.4 1.2 3.9 4.0 9 57.1 59.4 62.5 9 0.226 0.621 1.018 WA2 4 0.2 0.6 0.9 4 0.5 1.2 1.8 2.0 4 57.0 59.7 61.1 4 0.060 0.134 0.307

Detritals TD2 1 1.84 1.8 1.8 1 1.6 1.6 1.6 0.9 1 43.5 43.5 43.5 1 0.119 0.119 0.119 TD3 4 0.58 0.8 1.2 4 1.5 3.1 4.5 3.9 4 56.6 60.2 63.0 4 0.093 0.154 0.267

Low Grade MM 13 0.3 0.7 1.6 13.0 0.3 1.0 3.7 1.5 13 54.4 56.0 57.0 13 0.007 0.093 0.262 N1 14 0.1 0.6 1.2 14.0 0.2 0.8 1.9 1.4 14 54.2 55.7 56.7 14 0.019 0.576 5.600 N2 13 0.2 0.6 1.2 13.0 0.4 1.9 12.5 3.1 13 54.1 55.8 57.0 13 0.046 1.085 3.985 N3 13 0.2 0.6 1.6 13.0 0.2 3.3 13.9 5.4 13 54.6 56.0 57.0 13 0.050 0.378 1.739

WA1 5 0.2 0.4 0.9 5.0 0.4 2.8 6.5 7.0 5 54.0 55.3 56.6 5 0.128 1.196 3.115 Waste

MU 8 0.03 0.1 0.2 8 0.2 0.2 0.3 2.2 8 22.4 26.4 31.8 8 0.004 0.012 0.037 MM 23 0.09 0.6 2.4 23 0.2 1.5 10.6 2.5 23 32.4 46.7 53.9 23 0.007 0.290 2.882 N1 31 0.03 0.8 1.8 31 0.1 0.8 3.2 0.9 31 14.0 43.5 53.8 31 0.008 0.428 6.583 N2 36 0.15 0.8 1.9 36 0.3 2.7 21.1 3.4 36 26.0 47.7 53.7 36 0.021 0.618 3.606 N3 19 0.24 0.8 1.7 19 0.6 6.0 19.9 7.4 19 44.7 50.8 53.9 19 0.055 0.466 3.391

WA1 16 0.12 0.6 1.3 16 0.8 3.0 7.2 5.1 16 42.5 49.9 53.6 16 0.166 2.215 7.245 WA2 8 0.18 0.3 0.4 8 2.8 4.1 4.9 13.7 8 17.8 34.7 49.6 8 0.451 3.211 5.570 TD2 27 0.24 0.8 2.0 27 0.2 2.7 2.7 3.4 27 1.6 45.8 58.7 27 0.009 0.111 0.496 TD3 24 0.31 1.3 3.1 24 0.2 3.0 22.6 2.3 27 19.1 39.6 55.3 24 0.020 0.204 0.728

Notes:[1] Total S has been used to calculate MPA - total S (%) multiplied by 30.6 gives units of kgH2SO4/t

[2] ANC is inferred on the basis of the sum of the CaO and MgO content, following a conversion to units of kgH2SO4/t as follows – CaO (%) multiplied by 17.5 and MgO multiplied by 24.5. A further reduction factor, 0.1, was applied to account for the fact that (i) some proportion of Ca and Mg will be present in non-neutralising minerals, and (ii) based on experience elsewhere in the Pilbara, only a small proportion of neutralisation potential is readily available

[3] Neutralisation potential ratio (ANC/MPA) is inferred from the average MPA and inferred ANC values



In Table 10, the MPA has been calculated based on the conservative assumption that all sulfur is present is sulfide sulfur. As noted before, some portion of the sulfur present may comprise sulfates or hydroxy-sulfates rather than sulfides, particularly in the case of near-surface units (e.g. TD2, TD3).

The total sulfur (and therefore MPA) values are consistently low, with the maximum MPA value being 4 kgH2SO4/t calculated for the TD3 sample with a sulfur content of 0.102%. Average MPA values are generally less than 1 kgH2SO4/t.

Average ANC is generally low, ranging between 0.2 and 6 kgH2SO4/t. The highest ANC value calculated was for TD3 (waste) 23 kgH2SO4/t.

Average MPA and ANC were used to calculate neutralisation potential ratios (NPRs, the ratio of ANC/MPA). The majority of the waste and ore lithologies give NPR values either between 1 and 3 (of uncertain potential to generate acidity) or greater than 3 (non acid forming, NAF). There are three instances where NPR values less than 1 are calculated – high grade ore, MU; detrital ore, TD2; and waste, N1. In all cases, based on low total sulfur contents, the materials would be classed as NAF using sulfur cut-off thresholds.

The average and maximum Fe content of the materials is uniformly high – as would be expected for the geological setting. The range of Fe contents extend to lower minima in the shallow TD2 unit (1.6% Fe). It is expected that Fe is hosted by iron oxides such as hematite, magnetite and goethite and therefore is unlikely to be readily leachable. The widespread distribution of Fe as iron oxides could be beneficial in that these minerals represent strong adsorbents. Sorption can reduce dissolved contaminant levels in contacting waters, and attenuate contaminant transport. The lower minimum Fe contents observed for some units may be of significance if this is coincident with a lower sorptive capacity.

Mn content is generally quite low, with average contents mostly less than 1%. Higher average Mn contents are noted in the waste WA1 and WA2 units (2.2-3.2%). Maximum Mn contents range from 0.05% (MU, high-grade) to 7.25% (WA1, waste).

The Mn contents appear to correlate with the inferred ANC values. Similar observations were made in previous assessment (of data for the OB29, 30 and 35 orebodies, SRK 2013; and OB25 Pit 3, SRK, 2015b). The correlation, though not strong, is interpreted as possible evidence of incorporation of Mn in carbonates. Note that Mn (and by analogy other transition metals) present within carbonates could be readily leachable if exposed to acidic conditions.

3.2.5 Potential for Acid / Metalliferous Drainage Within the dataset available so far, one sample only (waste from the TD3 lithology) has been associated with a sulfur content very marginally above the 0.1% sulfur threshold. This corresponds to a proportion of 0.1% PAF material within the overburden volume, and 0.02% of the total volume of material to be mined.

Table 11: Estimation of the proportion of mined PAF-classed material within material to be mined

Material Total Volume (m3)

0.1% sulfur cut-off 0.2% sulfur cut-off

Volume of PAF material

% of PAF material

Volume of PAF material

% of PAF material

Waste 3,626,025 3,970 0.1% - -

High Grade 7,629,100 - - - -

Low Grade 8,315,150 - - - -

Total 19,577,700 3,970 0.02% - -

Note: The volume of PAF waste has been calculated based on a proportion of 1% PAF being present within the volume of TD3 material to be mined (397,025 m3), which corresponds to 0.1% of the total waste volume to be mined



BHPBIO modelling did not identify any PAF material within the OB32E pit. Although the current assessment did identify PAF materials, the volumes were very low and the two approaches are considered to be broadly consistent. The slight differences are attributed to the fact the BHPBIO approach does not consider materials above the BOCO as having the potential to generate acid.

On this basis, there is a low to negligible potential for the generation of acid and metalliferous drainage from either ore stockpiles or OSAs.

Note however that these conclusions are based on a relatively small dataset, and should be revisited when more data become available. Additionally, more detailed geochemical data, in particular static and kinetic leach data to describe contaminant leachability and key reaction rates, would increase confidence in the assessment of overall potential for AMD.

The sulfur content of the exposed OB32 pit shell walls is shown in Figure 8. Based on assessment of the available assay dataset there are no instances where sulfur would exceed the 0.1% threshold in the rock exposed on the pit wall. However, again, note earlier comments with respect to sampling density and spatial coverage.



4 Preliminary Risk Evaluation 4.1 Source-Pathway-Receptor Analysis

4.1.1 Sources The potential sources of AMD considered include:

• OSAs;

• Stockpile areas; and

• Exposed pit walls.

The potential for these sources to contribute AMD has been described in the preceding section. In summary, OSAs and ore stockpiles would represent a low to negligible source of AMD due to the presence of limited volumes of PAF-classed materials.

As the proposed pit will be above the pre-mining water table, the formation and potential resulting environmental impacts/ risks of the formation of a pit lake within the mined out void have not been considered.

The closure options for the pit are still being evaluated by BHPBIO; however, two possible scenarios have been considered within this assessment in relation to the final pit void:

• Backfilled Void; and

• Open Void (i.e. Uncontrolled).

In the case of the backfilled void, backfill materials could represent an AMD source. It could be expected that the backfill comprise overburden materials from local OSAs, or perhaps be sourced from overburden generated by a nearby operation. As already discussed, OB32E overburden does not contain significant PAF-classed material, and therefore – if used as a backfill material – would not be expected to be a significant source of AMD. It should be noted that even if not a source of AMD, there is a possibility that the backfill could represent a transient source of salinity – depending on the readily soluble solute content at the time of backfilling.

4.1.2 Pathways The following pathways for AMD release have been identified:

• Seepage from the OSAs/stockpiles to surface water or percolate to groundwater; and

• Transport of solutes from the backfilled materials to groundwater (or surface water for the completely backfilled scenario).

The main potential surface water transport pathways are:

• Homestead Creek – the most proximal creek to which OB32E drains; and

• Fortescue River – to the east of OB23 and OB25, to which Homestead Creek is a tributary.

It is assumed that surface water will be appropriately managed, in line with current BHPBIO management practice, to prevent significant surface water inflow to the pit, and limit the interaction with runoff from stockpiles and OSAs.

Regional groundwater flows may be toward the east or northeast, influenced by dewatering activities taking place for OB23 and OB25. However, as already mentioned (Section 2.3), the OB32E deposit is structurally complex, and regional groundwater flow within and around the deposit is not well understood.



For a closure scenario where the pit void is backfilled, there is a possibility that there be preferential recharge through the unconsolidated backfill. Such recharge could form a pathway for transport of solutes from the backfill to the groundwater. There may also be the potential for groundwater mounding below the void, which could lead to the development of local hydraulic gradients that differ from the main regional gradients.

4.1.3 Receptors The potential receptor areas, as described in Section 2.5, include:

• Fortescue River (incorporating Ophthalmia Dam and Ethel Gorge);

• Homestead Creek;

• Ophthalmia Dam (amenity and human health);

• Newman Water Reserve public drinking water source protection zones (Priority 1 and Priority 3) (human health); and

• Homestead Borefield.

In terms of flora and fauna, the closest Threatened Ecological Community (TEC) is the Ethel Gorge Aquifer Stygobiont Community, located on the Fortescue River, and two vegetation associations have been recorded along the Ethel Gorge drainage line (considered to be a specialised habitat of local significance).

The following section outlines a preliminary assessment of the risk posed to these receptors, including flora and fauna, by potential generation of AMD at OB32E.

4.2 Risk Analysis Surface water accounts for a large contribution to groundwater recharge, and therefore, any potential risks posed by AMD from mining activities to surface water quality should be considered in relation to being protective of both surface water ecology and groundwater quality.

As detailed in Section 3.2, very small volumes of PAF-classed materials have been identified within the overburden materials, and therefore there is limited overall potential for AMD generation from the mining area.

No extended chemical assays from OB32E were available for review, and the distribution of environmentally significant elements of concern within the mined materials (e.g. Cu, Cd, Zn, As and Se) could not be determined. Similarly, leach testing data is limited to equivalent lithologies collected from other Eastern Ridge deposits. The available leach test results suggest circum-neutral leachates and limited leaching of elements of concern. Based on the premise that contact waters remain circum-neutral, many potential metal concentrations and loadings in runoff (from OSAs, pitwalls and backfill materials) would be low. Further data would build confidence in this premise. Potential impacts from site drainage to surface water bodies and groundwater cannot be ruled out.

Where PAF overburden material is encountered and is to be placed in OSAs, management measures including OSA construction designs (e.g. encapsulation) and cover designs (e.g. cover designs to minimise infiltration and reduce erosion) can be utilised to reduce AMD risks.

In the event that PAF is encountered, it is anticipated that standard BHPBIO rehabilitation and closure protocols used in construction of landform structures would minimise contact between water and PAF material stored in OSAs, and therefore reduce risks to environmental receptors (i.e. Homestead Creek and Fortescue River). Further, BHPBIO has developed appropriate strategies to manage any AMD risk in relation to public water supply bores (BHPBIO, 2014a; 2015). Therefore, whilst it is not possible to more precisely define the overall risks, it is considered that mitigation measures can be put into place to control potential risks to within acceptable levels.



5 Conclusions The AMD assessment has evaluated the potential for lithologies at OB32E to generate acid or metalliferous drainage. The assessment relied mainly on assay data contained within the relevant drill hole databases.

Material was classed as PAF based on a sulfur threshold. A threshold of 0.2% sulfur was applied in line with the current BHPBIO practice for PAF classification, and also a more conservative threshold of 0.1% (in recognition of the limited nature of geochemical data currently available, in particular with respect to the availability and reactivity of ANC).

The majority of material to be encountered during mining above the water table has a low to negligible potential to generate acidity. In detail:

• PAF overburden would represent less than 0.1% of the overburden mined from the OB32E AWT pit, whether using a 0.1% or a 0.2% sulfur cut-off threshold.

• None of the ore to be mined is expected to contain PAF material.

• Pit walls are not anticipated to have any significant exposure of PAF material (no PAF material was identified in any of the lithologies that are mapped on the walls).

Based on these conclusions, there is a low potential for AMD in seepage or runoff from OSAs or ore stockpiles, and a low potential for AMD in pit wall runoff. Further more detailed geochemical data would be necessary to determine whether there is potential for any contaminants to leach at elevated concentrations in circum-neutral drainage. Potential impacts from site drainage to surface water bodies and groundwater cannot be ruled out.

It is noted that the assay dataset available at OB32E is limited, having been obtained from a 100 x 200 m drillhole grid; additional sampling to increase the sample density and spatial coverage would improve the confidence of the AMD assessment conclusions.

In the event that PAF is encountered, it is anticipated that standard BHPBIO rehabilitation and closure protocols used in construction of landform structures would minimise contact between water and PAF material stored in OSAs, and therefore reduce risks to environmental receptors (i.e. Homestead Creek and Fortescue River). Further, BHPBIO has developed appropriate strategies to manage any AMD risk in relation to public water supply bores (BHPBIO, 2014a; 2015). Whilst it is not possible to more precisely define the overall risks at the current time, it is considered that mitigation measures can be put into place to control potential risks to within acceptable levels.



Project Code: BHP150 Report Title: Orebody OB32E: Preliminary Acid and Metalliferous

Drainage Risk Assessment (Above Water Table Mining)

Compiled by

Alison Hendry

Senior Consultant (Geochemistry)

Peer Reviewed by

Claire Linklater

Principal Consultant (Geochemistry)



6 References ADWG, (2004). Australian Government, National Health and Medical Research Council (NHMRC),

2004. Australian Drinking Water Guidelines (ADWG) (6) (National Water Quality Management Strategy) (2004).

Australian Government, Department of Industry Tourism and Resources (DITR) (2007). Managing Acid and Metalliferous Drainage, Leading Practice Sustainable Development Program for The Mining Industry. February 2007.

ANZECC (2000). Australian and New Zealand Guidelines for Fresh and Marine Water Quality (2000). Volume 1 – The Guidelines, (National Water Quality Management Strategy), 2000.

BHP Billiton Iron Ore (2010). Orebody 23/25 Waste Rock Management Plan, 2010.

BHP Billiton Iron Ore (2012). Annual Environmental Report, Orebody 23/25, July 2011-June 2012, 2012.

BHP Billiton Iron Ore (2013a). Closure Stakeholder Requirements Specifications, OB25 Closure Planning Study, Draft C, July 2013.

BHP Billiton Iron Ore (2013b). Eastern Ridge, Eco-hydrological model (in progress). (Presentation, presented 4th October 2013).

BHP Billiton Iron Ore (2013c). BHP Billiton Iron Ore FY13 Triennial Aquifer Review – Eastern Ridge Borefields (September, 2013).

BHP Billiton Iron Ore (2014a). Eastern Pilbara Water Resource Management Plan, 2014.

BHP Billiton Iron Ore (2014b). BHP Billiton Iron Ore Factsheet: Ethel Gorge TEC (2014).

BHP Billiton Iron Ore (2014c). Powerpoint presentation, 13th November 2014.

BHP Billiton Iron Ore (2015). Potable Source Protection Plan - WAIO Newman, 2015.

Biologic (2014) Orebody 25 Targeted Vertebrate Fauna Survey.

Bureau of Meteorology (2011). Monthly Climatic Statistics for Newman (007151).

Department of Environment and Conservation (DEC) (2010). Definitions, Categories and Criteria for Threatened and Priority Ecological Communities, 2010.Department of Water (Government of Western Australia) (2009). Newman Water Reserve drinking water source protection plan – Newman town water supply. Water resource protection series. Report No. 97, 2009.

Department of Water (2009). Newman Water Reserve drinking water source protection plan – Newman town water supply. Water resource protection series, Report No. 97 (2009).

Forrest and Coleman, (1996). Pilbara Region Water Resource Review and Development Plan. Volumes 1 & 2. WRC Water Resource Allocation and Planning Series Report, WRAP 04, Perth.

Green, R and Borden, RK (2011). Geochemical risk assessment process for Rio Tinto’s Pilbara iron ore mines, Integrated Waste Management – Volume I (Ed. Sunil Kumar), 365-390. ISBN 978-953-307-469-6.

International Network for Acid Prevention (INAP) (2012). Global Acid Rock Drainage Guide (GARD Guide).

MEND, MEND Report 1.20.1, (2009) Prediction Manual for Drainage Chemistry from Sulphidic Geologic Materials.



Onshore Environmental (2012) Targeted Significant Flora Survey Vegetation Mapping of Homestead Creek.

RPS (2013). Eastern Ridge Strategic Environmental Assessment (RevB), 2013.

RPS Aquaterra (2011), Orebody 35: Surface Water Impact Assessment, 2011.

RPS Aquaterra (2013). Hydrogeological Assessment of Orebodies 29, 30 & 35 for Mining Below Water Table Approvals (RevA), March, 2013.

SRK (2013). Preliminary Acid and Metalliferous Drainage Risk Assessment (OB23 and OB25), November 2013. SRK project report, BHP117.

SRK (2015a). Eastern Ridge Geochemical Characterisation Programme, January 2015. SRK project report, BHP137.

SRK (2015b). Preliminary Acid and Metalliferous Drainage Risk Assessment (OB23 and OB25), March 2015. SRK project report, BHP117 (Rev1).

Water and Rivers Commission (2001). Central Pilbara Groundwater Study. (S.L. Johnson and A.H. Wright), Waters and Rivers Commission, Hydrogeological Record Series, Report HG 8, 2001.



Figures



Figure 1: OB32E Location Plan



Figure 2: Schematic of geological units associated with the OB32E mine (BHPBIO, RFP) Note: The bold text and shaded table cells indicate the lithological units that were intersected during the drilling of OB32E.



Figure 3: OB32E Regional Setting and Environmental Receptors



Figure 4: Image of OB32E pit shell showing spatial distribution of drill holes with sulfur data

Joffre (AWT)



Figure 5: Image of OB32E pit shell showing exposed lithologies

ParaburdooAngela2Angela1Newman3Newman2Newman1McLeodNammuldi



Figure 6: Box and whisker plots showing sulfur statistics, by lithology (overburden) Note: The box and whisker plots show the minimum and maximum sulfur values (short horizontal dashes), median sulfur values (bold black dashes), and data falling within the 25th and 75th percentiles (green boxes). The number of samples, n, from each lithological unit is shown along the x-axis.



Figure 7: Box and whisker plots showing sulfur statistics, by lithology (ore materials) Note: The box and whisker plots show the minimum and maximum sulfur values (short horizontal dashes), median sulfur values (bold black dashes), and data falling within the 25th and 75th percentiles (green boxes). The number of samples, n, from each lithological unit is shown along the x-axis.

High Grade

Low Grade

Detritals



Figure 8: Image of OB32E pit shell showing the distribution of sulfur

SRK Consulting Appendices


Appendices

SRK Consulting Appendix A


Appendix A: Eastern Ridge Water Quality

SRK Consulting Appendix A-1


Table A-1: Groundwater chemistry from boreholes screening ore (Dales Gorge) and Mt McRae Shale (OB25 Pit 3) (2008-2013)

Screened Lithology OB23 (Dales Gorge - D2)a OB25 Pit 1 (Dales Gorge)b OB25 Pit 3 (Dales Gorge)c OB25 Pit 3 (Mt McRae Shale)d ANZECC Freshwater

Trigger Levels (95%)e

ADWG Healthe

ADWG Aesthetice Determinand Units n= Min. Ave. Max. n= Min. Ave. Max. n= Min. Ave. Max. n= Min. Ave. Max.

pH - 48 7.45 7.83 8.21 7 7.57 7.76 8.01 5 7.56 7.79 8.03 3 7.61 7.82 8.07 6.5-8.0f - 6.5-8.5

Bicarbonate Alkalinity mg/L 48 288 329 382 7 355 363 374 5 283 306 348 3 275 297 311 - - -

Carbonate Alkalinity mg/L 43 <1 <1 <1 7 <1 <1 <1 4 <1 <1 <1 3 <1 <1 <1 - - -

Hydroxide Alkalinity mg/L 41 <1 <1 <1 4 <1 <1 <1 3 <1 <1 <1 3 <1 <1 <1 - - -

Total Alkalinity mg/L 48 288 329 382 7 355 363 374 5 283 306 348 3 275 297 311 - - 200

Aluminium mg/L 40 <0.01 <0.01 <0.01 7 <0.01 <0.01 <0.01 5 <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 0.055 (pH>6.5) - 0.2

Arsenic mg/L 40 <0.001 <0.001 <0.001 7 <0.001 0.002 0.006 5 <0.001 0.002 0.003 3 0.004 0.004 0.005 0.013 (As V) 0.01 -

Barium mg/L 40 0.024 0.032 0.046 7 0.004 0.008 0.011 5 0.012 0.014 0.016 3 0.016 0.017 0.017 - 2 -

Boron mg/L 14 0.31 0.34 0.36 2 0.22 0.22 0.22 2 0.24 0.24 0.24 1 0.24 0.24 0.24 0.37 4 -

Cadmium mg/L 40 <0.0001 <0.0001 <0.0001 7 <0.0001 <0.0001 <0.0001 5 <0.0001 <0.0001 <0.0001 3 <0.0001 <0.0001 <0.0001 0.0002g 0.002 -

Calcium mg/L 48 47 91 120 7 50 62 72 5 63 69 78 3 58 61 64 - - -

Chloride mg/L 48 203 470 681 7 129 139 148 5 155 175 213 3 118 131 150 - - 250

Chromium mg/L 40 <0.001 <0.001 <0.001 7 <0.001 <0.001 <0.001 5 <0.001 <0.001 <0.001 3 <0.001 <0.001 <0.001 0.001 (CrVI) 0.05 (CrVI) -

Copper mg/L 40 <0.001 0.004 0.022 7 <0.001 0.001 0.003 5 <0.001 0.002 0.007 3 <0.001 0.001 0.002 0.013h 2 1

Fluoride mg/L 9 0.60 0.69 0.80 2 0.60 0.60 0.60 3 0.50 0.57 0.60 1 0.60 0.60 0.60 - 1.5 -

Iron Soluble mg/L 48 <0.05 0.07 0.38 7 <0.05 <0.05 <0.05 5 <0.05 <0.05 <0.05 3 <0.05 <0.05 <0.05 - - 0.3

Lead mg/L 40 <0.001 <0.001 <0.001 7 <0.001 <0.001 <0.001 5 <0.001 <0.001 <0.001 3 <0.001 <0.001 <0.001 0.0034f 0.01 -

Magnesium mg/L 48 73 100 124 7 67 71 76 5 67 74 81 3 61 62 64 - - -

Manganese mg/L 40 <0.001 0.001 0.003 7 <0.001 <0.001 0.001 5 <0.001 0.010 0.019 3 0.166 0.178 0.186 1.9 0.5 0.1

Molybdenum mg/L 40 <0.001 0.001 0.002 7 <0.001 0.001 0.002 4 <0.001 <0.001 0.001 3 <0.001 <0.001 <0.001 - 0.05 -

Nickel mg/L 40 <0.001 0.003 0.034 7 <0.001 <0.001 <0.001 5 <0.001 <0.001 <0.001 3 <0.001 <0.001 <0.001 0.011g 0.02 -

Nitrite as N mg/L 41 <0.01 <0.01 0.02 4 <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 - 0.9 -

Nitrate as N mg/L 48 0.42 1.07 4.69 7 0.12 0.45 1.12 5 0.32 1.03 1.93 3 0.01 0.02 0.03 0.16 11.3 -

Potassium mg/L 48 8.0 11.9 15.0 7 6.0 6.9 7.0 5 7.0 7.6 8.0 3 6.0 6.3 7.0 - - -

Selenium mg/L 34 <0.01 <0.01 <0.01 7 <0.01 <0.01 <0.01 5 <0.01 <0.01 <0.01 3 <0.01 <0.01 <0.01 0.005 0.01 -

Silica mg/L 35 24.8 31.7 41.6 2 15.8 16.1 16.4 1 16.4 16.4 16.4 2 13.9 14.0 14.0 - - -

Silicon mg/L 14 11.8 22.2 45.6 5 18.8 19.4 20.2 3 18.2 19.6 20.8 1 16.1 16.1 16.1 - - -

Sodium mg/L 48 108 267 426 7 72 81 90 5 79 85 99 3 71 74 79 - - 180

Sulfate mg/L 28 129 238 354 7 75 78 82 5 96 109 130 2 94 95 95 - 500 250

Zinc mg/L 40 <0.005 0.014 0.082 7 <0.005 0.008 0.024 4 0.007 0.019 0.044 3 <0.005 0.006 0.007 0.072h - 3

Total Dissolved Solids at 180°C mg/L 48 878 1486 2060 7 616 664 700 5 644 705 765 3 582 629 682 - - 500

Total Hardness as CaCO3 mg/L 48 463 639 793 7 434 449 464 5 433 476 528 3 396 408 423 - - 200

Notes: The groundwater data (“Eastern Ridge Hydrochem.xls”; 25/10/2013) has been screened in line with the groundwater screening presented in the BHPBIO Triennial Aquifer Review (BHPBIO, 2013f). Cells shaded in blue denote exceedances of ANZECC (2000) Freshwater Trigger 95% values, cells shaded green denote exceedances of NHMRC/NRMMC ADWG (2004) Aesthetic Guideline values. a OB23 bores screening Dales Gorge (D2): HEA002P, HEA0010P, HEA0012P, HEA0015P, HEA0016P, HEA0018P. b OB25 Pit 1 bores screening Dales Gorge: HEC0019P, HEC0020P, HEC0021P. c OB25 Pit 3 bores screening Dales Gorge: HEC0010P, HEC0023P. d OB25 Pit 3 bore screening Mt McRae Shale: HEC0017P. e Trigger Values taken from ANZECC/ARMCANZ (2000) Fresh Water Guidelines for slightly to moderately disturbed ecosystems, and NHMRC/NRMMC ADWG Guidelines (2004), as specified in BHPBIO (2013d). f This range is for upland and lowland rivers in SW Australia (ANZECC/ARMCANZ, 2000). g Guideline is based on a hardness (CaCO3) of 30 mg/l. h Adjusted guideline trigger value calculated for measured hardness (as CaCO3, mg/L), using Table 3.4.3 of ANZECC/ARMCANZ (2000), and an average a total hardness value of 400 mg/L (as CaCO3).

SRK Consulting Distribution Record


SRK Report Client Distribution Record

Project Number: BHP150/1 Report Title: Orebody 32E: Preliminary Acid and Metalliferous Drainage Risk

Assessment (Above Water Table Mining) Date Issued: 27 May 2015

Name/Title Company

Richard Marton, Principal GeoEnvironmental Advisor BHP Billiton Iron Ore (BHPBIO)

Rev No. Date Revised By Revision Details

0 23/12/2014 Alison Hendry Draft report

1 25/05/2015 Alison Hendry Final report

2 27/05/2015 Alison Hendry Final report

This Report is protected by copyright vested in SRK Consulting (Australasia) Pty Ltd. It may not be reproduced or transmitted in any form or by any means whatsoever to any person without the written permission of the copyright holder, SRK.

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Orebody OB32E: Preliminary Acid and Metalliferous Drainage ... J - OB32E... · This report documents the outcomes of a preliminary acid and metalliferous drainage (AMD) risk assessment