Identification of acid rock drainage sources through mesotextural classification at abandoned mines of Croydon, Australia: Implications for the rehabilitation of waste rock repositories

Journal of Geochemical Exploration xxx (2013) xxx–xxx

GEXPLO-05247; No of Pages 18

Contents lists available at ScienceDirect

Journal of Geochemical Exploration

j ourna l homepage: www.e lsev ie r .com/ locate / jgeoexp

Identification of acid rock drainage sources through mesotextural classification atabandoned mines of Croydon, Australia: Implications for the rehabilitation ofwaste rock repositories

Anita K. Parbhakar-Fox a,⁎, Mansour Edraki b, Kathleen Hardie c, Oskar Kadletz d, Tania Hall d

a Co-operative Research Centre for Optimising Resource Extraction (CRC ORE) Ltd, School of Earth Sciences, University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australiab Centre for Mined Land Rehabilitation (CMLR), Sustainable Minerals Institute, The University of Queensland, St. Lucia, QLD 4072, Australiac Xstrata Coal, Queensland, Level 26 111 Eagle St., Brisbane, QLD 4000, Australiad Department of Natural Resources and Mines, Level 16, 61 Mary Street PO Box 15216, City East, QLD 4001, Australia

⁎ Corresponding author.E-mail address: [email protected] (A.K. Parbhakar-

0375-6742/$ – see front matter. Crown Copyright © 2013http://dx.doi.org/10.1016/j.gexplo.2013.10.017

Please cite this article as: Parbhakar-Fox, A.Kmines of Croydon, Australia: Implica..., J. Geo

a b s t r a c t
a r t i c l e i n f o
Article history:Received 16 January 2013Accepted 31 October 2013Available online xxxx

Keywords:Acid drainageStatic testsMineralogyTextureSulphide oxidation

Developing effective strategies to manage acid rock drainage (ARD) from historic and abandoned mine sites is asignificant rehabilitation challenge. In Australia, there are more than 50,000 recorded abandoned mine sites,many of which have associated ARD and water quality issues. Traditional rehabilitation strategies focus onutilising a blanket approach to management. However, if sources of ARD were instead thoroughly characterised,cost-effectivemanagement strategies based onmineralogy could be formulated, potentially enhancing site reha-bilitation and ensuring longer-term success.Amesotexturalmethodwas developed to domainwaste rocks into groups based on theirmineralogical, texturaland chemical similarities, using routine geological tools and field-based analytical instrumentation. This wastested at the abandoned mining operations at Croydon, North Queensland, from which uncapped sulphidicwaste rock piles were sampled. Surface water and sediment samples collected from creeks up to 10 km down-stream of the site showed elevated concentrations of As, Cd, Cu, Ni, Pb, S and Zn relative to local backgroundlevels, indicating the necessity for effective rehabilitation strategies to be implemented at these sites. Tenmesotextural waste rock groups (A to J) were identified in the piles across both mine sites and comprise ofhydrothermally altered rhyolites, and massive sulphides. Three major sulphide-bearing groups were identified(G, H and J). Mineralogical and geochemical data indicated that group J (quartz–pyrite) was acid forming, withpyrite containing significant concentrations of As, Pb, Zn and Cu. Pyrite was in early weathering stages withsome hydrous ferric oxides observed on grain rims and fractures. Group H (arsenopyrite–quartz–pyrite) wasalso acid forming; with scorodite extensively precipitated in fractures and rims, likely retarding arsenopyrite ox-idation. Significant quantities of Zn and Cd were leached from Group G (quartz–sphalerite–galena) in first flushexperiments, andwere alsomeasured downstreamof theGlencoe site (atwhich themajority of groupGmaterialwas identified).Microtextural analyses showed galenahad partial weathering to anglesite, suggesting a potentialPb source. High concentrations of Fe and Cd (8.5 wt.% and 0.19 wt.% respectively) were measured in sphalerite,which likely encouraged oxidation, and subsequent release of Zn. Considering the diversity of the sulphidemineralogy and the associatedweathering pathways, a rehabilitation strategy which focuses on segregatingwaste on the basis of mesotextural classification should be considered.

Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.

1. Introduction

Effective management of acid rock drainage (ARD) is a significantrehabilitation challenge for abandoned mine sites. At these sites, theexposure of sulphides to water, air and microorganisms, leads to oxida-tion and ARD generation (Egiebor and Oni, 2007; Evangelou and Zhang,1995). Under these acidic conditions, liberation of dissolved compo-nents including heavy metals (e.g., Cd, Co, Cu, Hg, Ni, Pb and Zn) andmetalloids (e.g., As, Sb) is promoted (Ashley et al., 2004; Plumlee,

Fox).

Published by Elsevier B.V. All rights

., et al., Identification of acid rochem. Explor. (2013), http://

1999). Once metals enter streams, complex pH and redox dependantprocesses (including transformation, speciation and complexation) in-fluence the transport and fate of metals and determine their concentra-tions in both surface and subsurface environments (Caruso and Bishop,2009). Subsequently, aquatic and terrestrial ecosystems downstream ofmineworks are at risk of significant environmental degradation (David,2003; Gray, 1997; Hudson-Edwards and Edwards, 2005; Luís et al.,2009).

In Australia, there are over 50,000 registered abandoned mineswhich range from isolated minor surface works, to large and complexsites (Franco et al., 2010; Unger et al., 2012). Features of these sitescan include waste rock piles, tailings storage facilities, mineral

reserved.

ck drainage sources throughmesotextural classification at abandoneddx.doi.org/10.1016/j.gexplo.2013.10.017

http://dx.doi.org/10.1016/j.gexplo.2013.10.017

mailto:[email protected]


http://www.sciencedirect.com/science/journal/03756742


142”15’

18’10

13

Recent Sediments

Rivers/Creeks

Roads

Mount Isa

QUEENSLAND

Esmerelda Granite

Croydon Volcanic Group

0 15km

Croydon Townsville

Cairns

Coral Sea

Gul

f of

Car

pent

aria

2

Carron River

Tabletop Creek

Deadhorse C

reek

Mine Locations

1. Federation2. La Perouse

3. Glencoe

CROYDON

Fig. 1. Simplified geology of the Croydon area showing locations of abandoned gold minesites (after Bain et al., 1998).

2 A.K. Parbhakar-Fox et al. / Journal of Geochemical Exploration xxx (2013) xxx–xxx

processing wastes, and remains of mining infrastructure. Abandonedwaste rock piles are significant sources of ARD (cf. Ashley et al., 2004;Aykol et al., 2003; Harris et al., 2003; Lottermoser et al., 2005;Marescotti et al., 2007; Mudd, 2005; Smuda et al., 2007; Tarras-Wahlberg and Nguyen, 2008). Current mining practices dictate thatwaste rock piles are engineered based on geochemical classifications,with waste rock classes or types defined by acid forming/neutralisingcharacteristics (e.g., Andrina et al., 2006; Brown et al., 2009; Hutchisonand Brett, 2006; Smith et al., 2009, Tran et al., 2003). However, at aban-doned mine sites, waste rock piles were not constructed in this manner(Ashley et al., 2004; Harris et al., 2003; Hudson-Edwards and Edwards,2005; Lottermoser et al., 1999), with costs of remediating associatedARD estimated at AUD$100,000 or more per hectare (Harries, 1997).Current rehabilitation strategies are responsive in their nature (i.e., onlyimplemented if acid rock drainage occurs). Consequently, a ‘blanketapproach’ to management is adopted whereby techniques such as limedosing andwaste rock capping are implemented, but havemixed success(e.g., Edraki et al., 2009, 2012; Gasparon et al., 2007; Gore et al., 2007;Mudd and Patterson, 2010). Alternatively, undertaking detailed and effec-tive predictive characterisation on an individual site basis may allow forthe breakage of source–pathway–receptor chains (Vik et al., 2001), andimprove rehabilitation long-term.

The objective of this study was to develop a systematic approach tocharacterising waste rock pile materials and identifying ARD sources atabandoned mine sites. Therefore, a mesotextural classification methodbased on mineralogical and textural differences observed in hand-specimen samples to define waste rock groups is proposed. The methodwas tested at the abandoned Croydon gold mines, north Queensland,Australia, from which ARD (pH b 4) is emanating as measured througha local geochemical study of sediments and surface waters. Followingmesotextural grouping, samples were subjected to ARD predictive testsaccording to the geochemistry–mineralogy-texture (GMT) approachproposed in Parbhakar-Fox et al. (2011). This contribution demonstratesthat through adopting a systematic mesotextural classification scheme,ARD sources are readily identified and can be prioritised for remediationas part of an effective long-term rehabilitation plan.

2. Croydon mining area

2.1. Mining history

The Croydon gold mining district is located approximately 15 kmnortheast of the Croydon Township and 400 km northeast of Mt. Isa,north Queensland (Fig. 1). Small-scale historic mining of reef gold wasundertaken in the 1880 to 1890s, and modern open pit mines targeted2.84 Mt of ore (3.4 g/t Au) from 1981 to 1991 at two main sites:Federation/La Perouse and Glencoe (Van Eck and Child, 1990). Themine workings and waste rock piles have remained undisturbed since1991. Currently, the Department of Natural Resources and Mines arein management of this site, with estimated rehabilitation liabilities ofAUD $1.8 million for the waste rock piles alone (DME, 2008).

2.2. Physiography and climate

The region has a tropical savannah type climate with an averageannual rainfall of 750 mm, much of which falls between December toMarch. The average annual temperature is 33.8 °C, with maximum tem-peratures experienced during November to January (Fig. S1; Bureau ofMeteorology, 2013). Tabletop Creek and Deadhorse Creek drain theFederation/La Perouse and Glencoe sites respectively (Fig. 1). DeadhorseCreek is a tributary of Tabletop Creek, with the confluence approximately10 km from themining operations. Tabletop Creek is in turn a tributary ofthe Carron River, which flows into the Gulf of Carpentaria. Much of theCroydon district is used for grazing, including the immediate mine area(DME, 2008).

Please cite this article as: Parbhakar-Fox, A.K., et al., Identification of acid romines of Croydon, Australia: Implica..., J. Geochem. Explor. (2013), http://

2.3. Geology and mineralisation

The geology of the Croydon district is dominated by theMesoproterozoic rhyolitic CroydonVolcanic Group (CVG) and EsmereldaSupersuite (Fig. 1). The Croydon lode gold deposits are hosted by theCVG, which is overlain by the Gilbert River Formation. The lodes consistof major quartz, potassium feldspar, muscovite, plagioclase, minor illite,kaolinite, sulphides (pyrite, arsenopyrite, sphalerite, galena), and tracesof pyrrhotite and chalcopyrite (Van Eck and Child, 1990).

The CVG has been subjected to varying degrees of hydrothermal al-teration, with evidence of silicification, kaolinitisation and sericitisationobserved in wall rock adjacent to the quartz veins (Van Eck and Child,1990). In termsof acid formingpotential, the host rocks tomineralisationhave little potential for buffering acid produced from sulphide oxidation,as carbonates are notably absent. Effective silicate neutralising minerals(e.g., biotite, chlorite and serpentinite) as defined by Bowell et al.(2000) and Jambor et al. (2002) are also absent.

2.4. Site description

The Federation/La Perouse site consists of two pits (Federation:320 m × 160 m × 35 m; and La Perouse: 270 m × 180 m × 40 m),two waste rock piles (Federation/La Perouse pile: 1.5 million m3 and35,000 m3), one stockpile (25,000 m3), heap leach pads (55,000 m3), acatch dam (170 m × 65 m), a seepage collection pond (100 m × 30 m)and relict mining infrastructure including a crusher platform. The wasterock piles comprise materials ranging from boulder (N0.5 m diameter)through to coarse sand crushings (0.2–1 cm) and abundant fines(b0.2 cm). The entire waste rock piles comprise approximately 70%flow-banded rhyolite, 20% red-stained rhyolites and tuffs, and 10%quartz–sulphide veinmaterial (DME, 2008).Most of thismaterial displays



07

00

01

02

03

04

05

06

99

98

Glencoe

33

3435

36

38

37

39

2

1

3

Federation/ La Perouse

DeadhorseCreek

Tabletop Creek

27 28

2629

25

24

2322

21 31

30

32

45

6 78910

11

12

2km

N

4038373635

Fig. 2. Plan view of stream sediment and water sample locations (with numbers given)both upstream and downstream of the Federation/La Perouse and Glencoe mine opera-tions, Croydon.

3A.K. Parbhakar-Fox et al. / Journal of Geochemical Exploration xxx (2013) xxx–xxx

dark to medium brownish–red Fe-staining, with metallic bluish blackMn-stains also observed.

Federation pit captures runoff and seepage from themain Federation/La Perouse waste rock pile. A catch dam was constructed below Federa-tion pit for the purpose of containing seasonal overflow from the pitlake. A seepage pond was constructed below this to contain and pumpback seepage to the catch dam. However, during the wet season, wateroverflows from the catch dam and seepage pond into Tabletop Creek.Consequently, the catch dam is acidic with an average pH of 2.9 (DME,2008). There is also seepage from the waste rock pile directly intoFederation and Tabletop Creeks during the wet season. Operationswere smaller at Glencoe with one open pit (330 m × 60 m × 25 m)and a waste rock pile (483,000 m3). Seepage from this waste rock pileenters Deadhorse Creek. Field observations indicate that galena andsphalerite dominate the sulphide mineralogy of this pile.

Acid rock drainage has been established immediately downstream(b2 km) of the mine workings, with elevated concentrations of Cd(max. ~80 μg/L) and Zn (max. ~8000 μg/L) relative to the local baselinemeasuredwithin 10 kmof the operations. Remedialworkswere under-taken in November 2007 to improve thewater quality in Federation pit,through addition of 140,000 t of lime (CaO) to raise pH. Lime was alsosprayed on the pit walls and deposited on the surface of the Federa-tion/La Perouse waste rock pile. Whilst initially pH values rose (pH 11to 12), within two months pH values had declined to pH 3 to 4 (DME,2008). Further remediation works (2009 to 2011) were conducted toreduce the volume of contaminated seepage waters entering TabletopCreek, with the construction of the seepage pond described. Althoughthese works have reduced the volumes of seepage entering TabletopCreek, seepagewater quality has not improved. Therefore, additional re-habilitation efforts are required and should instead focus on the identi-fication and management of ARD sources rather than the treatment ofARD waters.

3. Materials and methods

3.1. Sampling and sample preparation

Field work was conducted in May 2008. Hand-specimen sized(c. 2 kg) waste rock samples (n = 53) were selected to provide a rangeof lithologies from four different locations across the waste rock piles.Samples were sawn, with one piece kept for textural studies, and theother jaw crushed to b5 cm (University of Tasmania (UTAS), Hobart,Australia). A split was taken, and the remaining material ground in aringmill to b125 μm formineralogical and geochemical characterisation.

Surface water samples (n = 29) were collected directly from Table-top andDeadhorse Creeks, and at their confluence (Fig. 2). These sampleswere collected around the district to allow for comparison of water qual-ity upstream and downstream of the mine operations. Only duplicatesamples were obtained due to the limited amount of surface water avail-able atmost locations. Additionally, sampleswere obtained from the sur-faces of Federation (35 m depth), La Perouse (40 m depth) and Glencoe(25 m depth) pit lakes. Water samples were collected for analysis ofmajor cations and anions (unfiltered), and trace metals and metalloids(0.45 μm filtered) with samples preserved using 10% HNO3 at pH b 1.Electrical conductivity (EC) and pH were measured in the field. Valuesof pH were measured using a TPS WP-81 meter, which was calibratedto pH 4 and 7 prior to each measurement. The EC was also measuredusing this instrument which was calibrated at the start of each samplingday using a 0.01 M KCl solution.

Stream sediment samples (n = 34) were also collected upstreamand downstream of the Federation/La Perouse site, and representedbackground and ‘mine-impacted’ materials. Samples were taken at,and downstreamof Glencoe only. Duplicate sediment sampleswere col-lected from the middle of streams at a depth of 0 to 10 cm. Sampleswere dry sieved (using a stainless steel sieve) to b63 μm, with boththe whole and the fine fraction (b63 μm) analysed for geochemical


comparison. For water and sediment analyses, sampling equipmentand HDPE sample bottles were cleaned prior to sampling by soakingthem in HNO3 (trace metal grade) and rinsing in deionised (DI) water.

3.2. Mesotextural classification

Previously, only three lithological groups were identified in thesewaste rock piles (flow-banded rhyolite, red-stained rhyolites and tuffs,and quartz–sulphides; DME, 2008). However, when considering thestyles of mineralisation and alteration, it is likely that additional groupsexist. Therefore, a mesotextural classification method was developed asa means of identifying the major waste rock lithologies, and measuringtheir acid forming characteristics. Polished slices were prepared fromeachwaste rock sample to facilitate the identification of primary and al-teration minerals and textures, which was performed using a handlensand a binocular microscope. Lithologies were described, with particularattention given to the texture (e.g., porphyritic, flow-banded), and esti-mating the modal mineralogy. As the groundmass of rhyolite sampleswas fine-grained, a portable short-wave infrared (SW-IR) mineralanalyser (Terraspec)wasused formineral identification. In this analysis,three 30 mm2 spots across each polished slab were analysed, with thespectra interpreted using The Spectral Geologist™ software. Pressedpowder pellets were also prepared from each sample and analysedusing a field-portable X-ray fluorescence instrument (InnovX X50).Based on the mineralogical and textural differences observed in hand-specimen, samples were categorised into mesotextural groups. Tenmesotextural groups were identified (A to J), with one representativesample from each group shown in Fig. 3.

One polished slice from each mesotextural group was evaluated bythe acid rock drainage index (ARDI), whereby textural parametersknown to influence acid formation were examined. As this is a site-



A

1 cm

subhedral qtzphenocrysts

Fe-ox staining qtz veins bearing disseminated py

msc

mm-scale qtz veins qtz

phenocrystsmsc

msc

graphite clots

fiamme

msc altered ksp phenocrysts

msc

msc

qtz phenocrysts

<1cm qtz veinsbearing mm-scaledisseminated py

C

msc

intensely weathered Fe-ox rind

D

msc

msc

qtz phenocrysts

qtz veinlets

msc altered kspphenocrysts

B

D

msc

ksp phenocrysts

msc altered ksp phenocrysts

qtz phenocrysts

F

msc

msc

ksp

weathered qtz vein

E F

qtz

lithic fragments

gl

spl

qtz

massive asp

lithicfragments

G H

weathered rindqtz

py

chl

msc

qtz phenocrysts

I J

msc

msc

msc

qtz phenocrysts

qtz phenocrysts

1 cm

1 cm

1 cm

msc

msc

msc

msc

msc

msc

msc

qtz phenocrysts

msc

msc

msc

msc

ksp

qtz

gl

spl

qtz

msc

chl

py

qtz

1 cm

1 cm

1 cm

1 cm

1 cm

1 cm

Fig. 3. Representative mesotextures (A to J) of the ten main lithologies observed at the Federation/La Perouse and Glencoe waste rock piles (scale bar = 1 cm). Stars indicate areasanalysed by short-wave infrared, with the identifiedmineral phase given in italic. NB.Mineralogical descriptions of mesotextural groups are given in Table 1. Abbreviations: asp, arsenopyrite;chl, chlorite; Fe-ox, iron-oxide; gl, galena; ksp, potassium feldspar; msc, muscovite; py, pyrite; qtz, quartz; spl, sphalerite.


Please cite this article as: Parbhakar-Fox, A.K., et al., Identification of acid rock drainage sources throughmesotextural classification at abandonedmines of Croydon, Australia: Implica..., J. Geochem. Explor. (2013), http://dx.doi.org/10.1016/j.gexplo.2013.10.017



specific index, samples were screened prior to evaluation to define theranking criteria. The ARDI evaluates sulphide content; sulphidealteration; sulphidemorphology; neutralisingmineral content; and sul-phide mineral associations following the methodology described inParbhakar-Fox et al. (2011). The first three parameters (A to C) areranked from 0 to 10; and the latter two (D and E) −5 to 10. Scoreswere averaged across each sample to calculate an overall ARDI value.To refine the ARDI value, evaluations were performed on a polishedthin section made from the slab using a petrographic microscope.Values obtained from both hand-specimen and thin section analyseswere averaged to obtain a final score. Samples scoring from 41 to 50were classified as extremely acid forming (EAF); 31 to 40 as acidforming (AF); 21 to 30 as potentially acid forming (PAF); 11 to 20 arenon-acid forming (NAF); 1–10 are NAF or have a potential neutralisingcapacity (PNC); and−10 to 0 have an acid neutralising capacity (ANC).These values are recommended for use alongside static geochemicaldata to enhance waste classification (Parbhakar-Fox et al., 2011).

3.3. Chemical and mineralogical analyses

The bulk elemental composition (major: Al2O3, CaO, Fe2O3, K2O,MgO,MnO, Na2O, P2O5, PbO, SiO2, TiO2; trace: Ag, As, Bi, Cd, Cu, Ni, Pb, S, Sb, Zn,Zr) of all waste rock samples was assessed by X-ray fluorescence (XRF;Philips PW1480 X-ray Spectrometer, UTAS, Australia). In-house stan-dards (TASGRAN, TASBAS, TASMONZ, TASDIOR, and a blank) wereanalysed during this run, in addition to standard reference materials(i.e., BCR-2, BHVO-2, RGM-1,W-2,WS-E, AC-E, GSP-2). These standardswere run at the start of the analysis, and at the end with the relativestandard deviation calculated as b1.5%. One sample from eachmesotextural group was analysed for their mineralogical compositionby quantitative XRD (SiemensD501 diffractometer, University of Ballarat,Australia).

One inch polished laser mounts (n = 15) were prepared frommajor sulphide bearing mesotextural groups (G, H and J), and electronprobe microanalysis (EPMA) performed (Cameca SX100 electron mi-croprobe; Central Science Laboratory (CSL), UTAS, Australia). Naturaland synthetic materials were used as standards and includedsphalerite-ast modified (S, Zn), marcasite (Fe), Cd–metal-UTAS4 (Cd),cuprite–ast modified (Cu) and astimex. Spot analyses were performedoperating with a 20 keV accelerating voltage, 15 nA beam currentand a 2 μm beam diameter to measure concentrations of minor ele-ments (e.g., As, Cd, Co, Ni) for comparison with Laser-Ablation ICP-MS (LA-ICPMS) data. In the case of sphalerite, Zn measurementswere used as an internal standard. Both spot and mapping analyseswere performed on these samples using LA-ICPMS (Agilent HP4500Quadripole ICPMS; UTAS, Australia). Calibration was performedusing an in-house standard (STDGL2b-2) comprising powderedsulphides dopedwith certified element solutions and fused to a lithiumborate glass disc (Danyushevsky et al., 2011). These analyses were per-formed to quantify trace elements in sulphides and observe their spatialdistribution.

Static acid base accounting (ABA) tests were performed on all wasterock samples (at both UTAS and University of Queensland (UQ), Bris-bane, Australia), and included paste pH, Sobek, modified Sobek and arange of standard andadvanced net acid generation (NAG) tests, follow-ingprocedures given inWhite et al. (1999) and theAMIRAP387AHand-book (Smart et al., 2002). During paste pH testing, solutions weremeasured in triplicate (per sample) using a Eutech Instruments 510pH meter. The pH probe was calibrated to pH 4 and 7 using standardbuffer solutions (Merck Ltd.) after each sample measurement. Sampleblanks (deionised water) were tested before and at the end of eachsample batch. The EC was measured using a TPS WP-81 meter, withthe probe calibrated prior to use with a 0.01 M KCl solution. DuringSobek and modified Sobek testing, KZL-1 (sericitic schist) andNBM-1 (altered feldspar porphyry) standards (obtained from CANMET,Natural Resources, Ottawa, Canada) were used, with one sample of


each tested for every five samples. Both reference materials are com-monly used in ARD studies (e.g., Goodall, 2008; Paktunc, 2001). Therelative standard deviation calculated between the standard measure-ments was b5%.

First flush experiments were performed on 2 kg samples (b10 mmand b4 mm) from mesotextural groups E (flow-banded rhyolite con-taining disseminated sulphide), G (quartz−sphalerite−galena), H(arsenopyrite−quartz−pyrite) and J (quartz−pyrite). Samples wereloaded into a Buchner funnel with water added until the surface of thematerial was saturated. The pH and EC of leachates were measuredafter 24 h (using the same instruments aswith paste pH testing, and fol-lowing the same calibrationmethods). Selected trace elements (e.g., Ag,Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Se, Zn) were determinedusing ICP-MS techniques (Agilent 4500 ICP-MS; UTAS, Australia).During ICP-MS analysis, three internal standards and a multi-elementcalibration standard (MISA29; Choice Analytical) were used before,and at the end of each sample run, in addition to two blank samples.The relative standard deviation for these data was b5%.

3.4. Textural analyses

Samples from mesotextural groups C, E, G, H and J were selectedfor microtextural analysis (FEI Quanta 600 environmental scanningelectron microscope (ESEM); Central Science Laboratory (CSL),UTAS, Australia). Relationships between primary sulphides and sec-ondary minerals (e.g., scorodite, anglesite, rhomboclase which wereidentified by XRD; Table 1), were examined in this analysis. Addi-tionally, inhomogeneties, which may influence trace element distri-bution (e.g. compositional zoning or mineral inclusions), wereobserved. Additionally, one sample from each of these groups (i.e., C,E, G, H and J) were subjected to textural mapping to examine sulphidemineral associations (FEI Quanta 600 mineral liberation analyser scan-ning electron microscope (MLA-SEM), CSL, UTAS, Australia). One inchpolished tiles (3 cm × 3 cm)were prepared and analysed using the ex-tended back scattered electron (XBSE) technique as described byFandrich et al. (2007). Data were processed in MLA Image Viewer andin-house Texture Viewer software to produce classified images foreach sample based on a site-specific mineral library.

3.5. Sediment analyses

Selected sediments were analysed for their mineral composition byXRD powder diffraction (Bruker D8 Advance X-Ray diffractometer;UQ, Brisbane, Australia). Both the whole sediment and the fine-grained (b63 μm) sediment fraction were partially digested in hotaqua regia. The resulting extractants and the water samples collectedfrom around the Croydon district were analysed for selected trace ele-ments (e.g., Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Se, Zn)using ICP-MS techniques (UQ, Brisbane, Australia). During ICP-MS anal-ysis, two reference standards were used, a multi-element calibrationstandard-2A (Agilent Technologies) and an arsenic reference standard(Eawag aquatic research, Swiss Federal Institute of Aquatic Scienceand Technology). Both were analysed before and at the end of eachsample run in addition to two blank samples. The relative standard de-viation for these data was less than 10%.

Determination of the solid speciation of selected metals, was per-formed through a six-step sequential extraction analysis (Centre forMined Land Rehabilitation (CMLR), UQ, Australia) on Fe-rich streamsediments (n = 6) collected at the Federation/La Perouse site only.The analytical procedure of Dold (2003)was followed,which differenti-ated between water soluble, ion exchangeable, Fe3+ oxyhydroxide,Fe3+ oxide, organic/sulphide and residual fractions. An additional stepwas added to include Mn oxides (20 mL 0.1 M NH2OH−HCl; pH 2;shake 2 h).



Table 1Mineralogy and Croydon waste rock samples as measured by quantitative X-ray diffrac-tometry (QXRD). One sample is shown per mesotextural group (A to J).

Mesotexturalgroup

Lithologicaldescription

Gangueminerals

Primarysulphides

Secondarysulphates and(hydro)oxides

A Porphyritic pale-mid grey rhyolitewith sub-cm mus-covite pheno-crysts with mm-scale quartz vein-lets.

MajorQuartz

MuscoviteKaoliniteMinorFluorite

MinorPyrite

ChalcopyriteGalena

MinorSzmolnokiteAnglesiteScorodite

B Flow-banded blue-grey rhyolite withsub-roundedquartz phenocrystswith graphite clotspresent.

MajorQuartz

MuscoviteKaolinite

MinorArsenopyrite

PyriteGalena

MajorGoethiteMinorAnglesite

SzmolnokiteGypsum

RhomboclaseScorodite

C Porphyritic light-mid grey rhyolite-tuff with quartzphenocrysts. Subcm-scale quartzveinlets containingmm-scale pyrite.

MajorK-feldsparQuartz

MuscoviteMinorFluorite

MajorPyrite

MinorArsenopyriteChalcopyrite

Galena

MinorAnglesiteGypsum

SzmolnokiteRhomboclase

D Flow-banded darkgrey rhyolite withmm-scale quartzveins & mm-scalegraphite clots.

MajorQuartz

K-feldsparMuscoviteKaoliniteMinorFluoriteChlorite

MinorPyriteGalena

MinorSzmolnokiteAnglesite

Rhomboclase

E Flow-bandedbeige-grey rhyo-lite containingmm-disseminatedpyrite.

MajorQuartz

K-feldsparMuscoviteMinorFluoriteChlorite

MinorPyrite

ChalcopyriteGalena

MinorAnglesite

SzmolnokiteScorodite

Rhomboclase

F Porphyritic mid-grey-pinkrhyolite-tuff withmm-quartz phe-nocrysts and cm-scale quartz vein-ing.

MajorQuartz

K-feldsparMuscoviteMinorFluoriteChlorite

MinorGalenaPyrite


Rhomboclase

G Massive quartzwith sub cm-scalesphalerite andgalena inter-growths andMinor mm-scalepyrite.

MajorQuartz

MuscoviteMinorAlbite

K-feldsparKaolinite

MajorSphaleriteGalenaMinor

Chalcopyrite

MajorSzmolnokiteAnglesiteMinorGypsumScorodite

RhomboclaseH Massive quartz

with cm-scalearsenopyrite-pyrite inter-growths and mm-scale disseminatedgalena.

MajorQuartzApatite

MajorArsenopyrite

Pyrite

MinorScorodite

SzmolnokiteHematiteAnglesite

Rhomboclase

I Porphyritic blue–grey rhyolite,silicified.

MajorQuartz

MicroclineAlbite

MuscoviteChloriteMinorFluoriteKaolinite

MinorPyriteGalena

Chalcopyrite


Rhomboclase

J Massive quartzcontaining cm-scale pyrite withcm-scale Fe-oxideweathering rind.

MajorQuartzMinorFluorite

MuscoviteMagnetite

MajorPyrite

MinorGalena

MajorRhomboclaseSzmolnokiteAnglesiteMinorGypsum



4. Results

4.1. Mineralogy and textural groups

Themineralogy of eachmesotextural group is summarised in Table 1.From the ten mesotextural groups, four were porphyritic rhyolites(groups A, C, F and I), three were flow-banded rhyolites (groups B, Dand E) and the remainder quartz–sulphides (groups G, H and J;Table 1). Theporphyritic rhyolite groups differed in their componentmin-eral proportions, presence/absence of quartz veinlets, phenocryst and al-teration type. For example, in group C textural evaluations identified tracesulphides (b1 wt.%) in both the groundmass and quartz veinlets. Thisconsisted of euhedral–subhedral quartz-associated disseminated(b1 mm) pyrite and arsenopyrite, but similar sulphides were notobserved in other porphyritic rhyolite groups. Additionally, whilstflow-banded rhyolite groups B and D are similar in appearance; groupB had been more silicified, and group D weathered, so were classifieddifferently.

Mesotextural groups G, H and J differed significantly in terms of theirsulphide mineralogy and texture (Fig. 4). Group G was dominated bysphalerite and galena (Fig. 4A), withminor pyrite also identified. In gen-eral, larger (N500 μm) sphalerite grains appearedmoreweathered thansmaller grains, with secondary minerals pervasively developed withingrains. Galena alteration was observed, with fine-grained anglesiteidentified as the alteration product (Fig. 4B). Sphalerite containing galenainclusions appeared strongly weathered (Fig. 4C). This is likely the resultof galvanic interactions between these sulphides, with sphalerite prefer-entially weathering due to its lower rest potential (−0.24 V) relative togalena (0.28 V; Kwong et al., 2003; Lottermoser, 2010).

Mesotextural group H displayed a massive arsenopyrite–quartz–pyrite texture with scorodite extensively precipitated at the inter-face of these minerals, andwithin fractures (Fig. 4D). Euhedral pyritegrains appeared relatively unweathered when encapsulated in scorodite.However, when intergrownwith arsenopyrite, pyrite hadweathered to agreater degree. Galena micro-inclusions were a common feature withinpyrite (Fig. 4E). Smaller (b200 μm)quartz-associated arsenopyrite grainsappear unfractured and unweathered. Scorodite layers within massivearsenopyrite had a relatively uniform thickness (c. 20 μm), but was occa-sionally observed as spherules (Fig. 4F).Weathering of scorodite to amor-phous ferric arsenate phases rich in As, Cu, Fe and Pbwas also recognised(cf. Murciego et al., 2011).

Pyrite was observed as both grains and very fine (b100 μm) veinletsin group J (Fig. 4G). Smaller, euhedral grains containing galena micro-inclusions (Fig. 4H) were less weathered than larger euhedral–subhedral pyrite grainswhichwere highly fractured (Fig. 4I). Secondaryproducts of pyrite oxidation (i.e., coatings) were not frequentlyobserved.

4.2. Waste rock chemistry

4.2.1. Major and trace elements per groupAll groups were dominated by SiO2 (55 to 87 wt.%) except in group

H,where Fe2O3 dominated (36 wt.%)with valuesmeasured by XRF. Thefeldspar–biotite model ((2Ca + Na + K) / Zr vs. Al / Zr) of Downingand Madeisky (1997) was constructed to assess, based on whole rockchemistry, the buffering potential of each group (Fig. S2). This model al-lows for an assessment of alteration based on the stoichiometrically de-fined co-variation of the sum of the alkalis with Al in anorthite(CaAl2Si2O8), albite (NaAlSi3O8), orthoclase (KAlSi3O8) and biotite[K(Fe,Mg)3AlSiO10(OH)2] used. Unaltered rocks plot on the model lineof slope 1, and altered rocks plot either above or below the model line,depending on whether they gained or lost alkalis during alteration pro-cesses (Downing and Madeisky, 1997). Group I was the least altered,plotting above the unaltered feldspar line. All other groupswere altered,plotting below themodel line indicating no significant buffering poten-tial. Themodel suggests that groups G, H and J have undergone extreme



50mm

A

qtz

gl

sp

A

50mm

B

Fig.6g

qtz

py

asp

arsenopyrite

invalidmuscovite

galenapyrite

quartz

scorodite

unknown

D

50 mm

qtz

py

msc

G

sphalerite

unknownmuscovite

galenapyrite

quartz

anglesite

kaolinite pyrite quartz

muscovitegalena potassium feldspar

secondary sulphate

gl

ang

qtz

spl

qtz

gl

gl

50 µm20 µm

C

asp

py

gl

CE

py

scribbons

sphericule sc qtz

glBF

qtz

A B

pyqtz

pygl

gl

H I

D G

B C E F H I

50 µm 100 µm 100 µm 500 µm

50 mm 50 mm

sc

Fig. 4. Classifiedmineral map of MLA tile (3 cm × 3 cm) and BSE images frommesotextural groups G, H and J: (A) Classified XBSE mineral map image of mesotextural group Gmaterial;(B) BSE image of altered reaction interface between galena and anglesite; (C) oxidised sphalerite grains (skeletal grain outlined) intergrownwith galena; (D) classified XBSEmineral mapimage ofmesotextural groupHmaterial; (E)massive arsenopyrite and pyrite; (F) scoroditemicrotextures (ribbons, spherules andmasses) identified in pyrite; (G) classifiedXBSEmineralmap image ofmesotextural group Jmaterial; (H) unweathered pyritewith galenamicro-inclusions; (I) highly fractured pyritewith galenamicro-inclusions. Abbreviations: ang, anglesite;asp, arsenopyrite; gl, galena, msc, muscovite; py, pyrite; qtz, quartz, sc, scorodite; spl, sphalerite.

0 2 4 6 8 10 12 14 16 181

10

100

1000

0 2 4 6 8 10 12 14 16 18

S (wt. %)S (wt. %)

S (wt. %)

1

10

100

1000

0 2 4 6 8 10 12 14 16 18

S (wt. %)0 2 4 6 8 10 12 14 16 18

S (wt. %)0 2 4 6 8 10 12 14 16 18

As

(pp

m)

Cd

(p

pm

)

Cu

(p

pm

)

Pb

(p

pm

)

Zn

(p

pm

)

A B C D E

F G H I J

1

10

100

1000

10,000

100,000

1

10

100

1000

10,000

100,000

1

10

100

1000

10,000

100,000

1,000,000A B

C D

E

Fig. 5. Concentrations (ppm; measured by XRF) of As, Cu, Cd, Pb and Zn shown against S (wt.%) for Croydon waste rock materials grouped by mesotextural characteristics (A to J).


Please cite this article as: Parbhakar-Fox, A.K., et al., Identification of acid rock drainage sources throughmesotextural classification at abandonedmines of Croydon, Australia: Implica..., J. Geochem. Explor. (2013), http://dx.doi.org/10.1016/j.gexplo.2013.10.017



acid leaching as several samples plotted along the X-axis (cf. Downingand Madeisky, 1997). Field evidence for this manifested as vuggyquartz–sulphide textures observed in waste rock materials belongingto these particular sulphide-dominated groups.

Concentrations of As, Cd, Cu, Pb and Zn (measured by XRF and givenin ppm) were plotted against sulphur (wt.%) per mesotextural group(Fig. 5A–E) to demonstrate their concentration ranges within thesegroups. Average concentrations of Bi, Ni and Sb were b100 ppm for allgroups and are therefore not shown. Mesotextural groups A to F and Icontained low concentrations of As, Cd, Cu, Pb, S and Zn. In relativeterms, Cd, Pb and Zn measured high in group G (Fig. 5B, D and E), Asin groups H and J (Fig. 5A), and Cu in groups G, H and J (Fig. 5C). Onegroup J sample contained high Pb (~35,000 ppm), but relatively low S(Fig. 5D) for the group, suggesting that the Pb is possibly hosted by asecondary hydrous ferric oxide (HFO) phase in this group. Zinc concen-trations were relatively low in groups H and J (Fig. 5E). The greatestquantities of S were measured in groups G, H and J, confirming thepresence of sulphides as they are the major sulphur bearing mineralgroup identified by XRD (Table 1). Based on this, the abundance ofseveral environmentally significant elements (including As, Cd, Cu, Pband Zn) was investigated further in sulphides frommesotextural groupsG, H and J. Thiswas performed to allow for accurate determination of theelement contents and distribution in sulphides in order to identify con-trols on sulphide oxidation.

4.2.2. Sulphide mineral chemistrySphalerite in groupG is iron rich, with EPMA spot analyses (n = 58)

measuring average contents of 8.4 wt.% Fe (sd: 1.28 wt.%) and0.19 wt.% Cd (sd: 0.05 wt.%). The bulk chemical compositionwas calcu-lated as (Zn0.85, Fe0.15)S. These grains are likely to be relatively suscepti-ble to weathering (compared to trace element poor sphalerite; cf.Weisener et al., 2004; Stanton et al., 2006). Distributions of Cd and Fewere homogeneous, with both pervasively distributed across the grainas shown by LA-ICPMS mapping, with an example shown in Fig. 6.This implies that Fe and Cd are in solid solution, as is typical for these el-ements (Cook et al., 2009). Sub-5 μm blebs of chalcopyrite (Fig. 6C)characteristic of chalcopyrite disease were recognised (cf. Barton and

Cd

Pb S

B

C

E F

cps

1000 µm

cps

1e2

1e3

1

10

1e4

1e5

1e2

1e3

1

10

1e41e51e61e71e8

1e9

qtzspl

gl

A

Fig. 6. Relative element distribution (cps; analysed by LA-ICPMS) in a sphalerite grain (with gelectron image of the original grain; (B) Cd; (C) Cu; (D) Fe; (E) Pb; (F) S; (G) Zn. Abbreviation


Bethke, 1987; Cook et al., 2009). Lead was present in veins (Fig. 6E) asgalena intergrowths. A slight decrease in Zn concentration at the grainboundary was observed (Fig. 6G), implying the dissolution of sphaleriteto form a Zn-deficient layer (Cook et al., 2009; Weisener et al., 2004).Galena present in group G (subjected to LA-ICPMS spot analysis;n = 61; data not shown) was identified as relatively enriched in Bi(maximum: 1508 ppm; average: 454 ppm; sd: 225 ppm) and Sb (max-imum: 1026 ppm; average: 867 ppm; sd: 185 ppm), with similar ele-ment signatures reported in Diehl et al. (2008). Element mappingindicated no trace element zonation, and is therefore consistent withobservations made by Bethke and Barton (1971) for lead sulphides as-sociated with igneous activity, or heated after formation (i.e., orogenicareas).

Electronmicroprobe spot analyses of both larger arsenopyrite grainsin mesotextural group H (n = 29) reported concentrations of Cd, Cu,Co, Ni, Pb, Sb and Zn below detection limit. However, LA-ICPMS anal-yses (spot: n = 11, mapping: n = 3) showed that in these grains Sb(maximum: 200 ppm; average: 140 ppm; sd: 31 ppm) is pervasivelydistributed, with minor Co (maximum: 27 ppm; average 10 ppm; sd:5 ppm) and Ni (maximum: 5 ppm; average 1 ppm; sd 2 ppm) demon-strating a banded distribution (Fig. 7). Concentrations of Cd, Pb and Znare relatively high in grain fractures and rims compared to arsenopyriteand quartz, potentially indicating adsorption of these elements to sec-ondary scorodite (Fig. 7).

Element distributionmaps and spot analyses (n = 7 and n = 57 re-spectively; analysed by LA-ICPMS) were performed on pyrite grains inmesotextural group J, with a representative example shown in Fig. 8.The BSE images (Fig. 8A and B) and Fe-distribution map (Fig. 8F) showthe grain outline, and the absence of fractures. Arsenic was relativelyenriched in areas of the grain (Fig. 8C; maximum: 19,080 ppm; average:3800 ppm; sd: 5770 ppm), and showed an antithetic distribution to themetals. Pyrite (particularly towards the core)was rich inCu (Fig. 8E;max-imum: 8290 ppm; average: 430 ppm; sd: 1139 ppm), Pb (Fig. 8G; maxi-mum: 3164 ppm; average: 150 ppm; sd: 446 ppm) and Zn (Fig. 8H;maximum: 4720 ppm; average: 820 ppm; sd: 1499 ppm). Galenamicro-inclusions as shown in BSE images (Fig. 4H), were again observedwith localised highs, and coincident distribution of Ag and Bi

Zn

Feu

C D

G

cps cps

cps cps

1e2

1e3

1

10

1e4

1e5

1e6

1e3

1e4

1e5

1e6

1e4

1e5

1e2

1e3

1e4

1e5

1e6

1e7

alena intergrowths) from Croydon waste rock mesotextural group G: (A) Back scattereds: gl, galena; qtz, quartz; spl, sphalerite.



Cu

Co

Ni

Sb

Zn

1000

100

10

1

1e5

1e4

1e3

100

1e5

1e4

1e3

1e2

10

1

1e5

1e4

1e5

1e41e3

1e2

1e6

1e5

1e4

1e3

1e71e6

1e5

1e4

1e31e2

1e5

1e4

103

1e5

1e4

1e3

1e2

10

1e5

1e4

1e3

1e2101

1e5

1e4

1e3

1e2

10

1

1000

100

10

1

1e5

1e6

1e4

1e3

1e2

1e3

1e4

1e2

10

1

1e5

1e4

1e3

A B C

cps

cps

cps

cps

cps

1e210

1e3

1e2

cps

cps

cps

cps

cps

cps

cps

cps

cps

cps

50 µm 200 µm

asp asp

aspqtz qtz

qtz1.5 cm

Fig. 7. Back scattered electron image (A), reflected light image (B) and photograph (C) of three arsenopyrite grains from Croydonwaste rockmesotextural group H, with relative elementdistribution maps for Cu, Co, Ni, Sb and Zn shown (cps; analysed by LA-ICPMS). Abbreviations: asp; arsenopyrite; qtz, quartz.


(b10 ppm). These Zn–Pb–Cu zones were rimmed by a fine band ofCo (~10 ppm).

4.2.3. Static geochemical testsA summary of static geochemical results are shown in Table 2. Aver-

age paste pH values were NpH 5.5 for all groups except G (pH 4.5); H(pH 5.09) and J (pH 3.76), classifying these as potentially acid forming


(PAF). These three groups also returned relatively high average valuesfor total-sulphur (STotal) of 1.21 wt.%, 14.10 wt.% and 10.5 wt.% respec-tively. The remainder of groups returned STotal values below b0.25 wt.%.Accordingly, groups G, H and J returned relatively high MPA values(approximate range 37 to 431 kg H2SO4/t; Table 2). Sobek ANCvalues were low for all groups (approximately −4 to 5 kg H2SO4/t;Table 2), reflecting the absence of carbonates. Additionally, silicate



As

Cu Fe

Zn

C

E

1e5

1e4

D1e51e41e3100101

cps cps

Co

1e51e41e3100

1e6

cps

F 1e51e41e3100

1e6

cps

G

cps

11e21e41e6

Pb

H

cps1e5

1e4

1e3

100

2000 µmQtz

QtzPy

LA-ICPMS pits

PyA B

Fig. 8. Relative element distribution (cps; analysed by LA-ICPMS) in a pyrite grain from Croydon waste rock mesotextural group J: (A) Back scattered electron image of grain; (B) backscattered electron image of mapped area; (C) As; (D) Co; (E) Cu; (F) Fe; (G) Pb; (H) Zn.


minerals which may contribute to ANC (e.g., serpentinite, chlorite,olivine; Jambor et al., 2002, 2007) were not identified in these samples.Average NAPP values N20 kg H2SO4/t were calculated for groups G, Hand J only, identifying these as PAF (Skousen et al., 2002), as confirmedin the NAPP against NAG plot shown in Fig. S3. Several samples fromgroup C were identified as PAF (Fig. S3). However, ARDI assessmentsconsidered this group overall as NAF (Table 2). Several samples fromgroup E plotted in the PAF field (Fig. S3), with the ARDI value for thisgroup supporting this classification.

Table 2Static test geochemical data formaterials representative of Croydonwaste rockmesotextural groupeach group. (* = kg H2SO4/t). Abbreviations: ANC, acid neutralising capacity; (M)NAG, (multi-ad

Group Paste pH Total-S (%) Maximum potential acidity* Sobek ANC* Net acid

A avg: 6.91sd: 0.07

avg: 0.14sd:0.19

avg: 4.14sd:5.85

avg: 4.81sd:0.64

avg: −0sd:6.49

B avg: 7.51sd: 0.86

avg: 0.02sd: 0.02

avg: 0.74sd: 0.85

avg: 1.17sd: 2.73

avg: 12.sd:27.51

C avg: 6.12sd: 0.82

avg: 0.25sd: 0.23

avg: 7.55sd: 6.89

avg: 0.49sd: 3.2

avg:7.06sd: 8.44

D avg:7.65sd: 0.18

avg: 0sd: 0

avg: 0sd: 0

avg: 4.01sd: 2.19

avg: −4sd: 2.19

E avg: 6.37sd: 1.70

avg: 0.13sd: 0.17

avg: 3.84sd: 5.26

avg: 2.01sd: 3.48

avg: 1.8sd: 8.52

F avg: 7.38sd: 0.70

avg: 0.02sd: 0.05

avg: 0.76sd: 1.52

avg: 3.63sd: 1.54

avg:-2.8sd:1.91

G avg: 4.5sd: 1.12

avg:1.21sd: 0.96

avg: 36.88sd: 29.32

avg:−0.44sd: 2.46

avg: 37.sd: 29.8

H avg: 5.09sd:0.06

avg: 14.1sd: 0.28

avg: 431.47sd: 8.67

avg: 1.84sd: 2.60

avg: 429sd: 5.60

I avg: 7.39sd: 0.82

avg: 0.01sd: 0.01

avg: 0.36sd: 0.50

avg: 4.43sd: 0.01

avg: −4sd: 0.50

J avg: 3.63sd: 1.05

avg: 10.5sd: 4.58

avg: 321.47sd: 140.20

avg:−3.76sd: 4.42

avg: 261sd: 158.


4.2.4. First-flush chemistryUsing the same cut-off criterion for paste pH (whereby leachates

measuring NpH 5.5 are considered PAF) all samples from groups E, G,H and J were classified as PAF (Fig. 9A; range: pH 3.0 (group J,b4 mm) to 4.7 (group E, b10 mm fraction)). This indicates the potencyof pyrite to generate acid in the absence of neutralisingminerals for thistype of mine waste even when pyrite is present in very low concentra-tions i.e., group E where b0.5 wt.% was measured by QXRD. No signifi-cant differences between pH values from the finer (b4 mm) and

sA to J,with average (avg) and standarddeviation (sd) values shown(where appropriate) fordition) net acid generation; ARD, acid rock drainage.

producing potential* (M)NAG* NAG pH ARD index (/50) No. of samples

.67 0 avg: 5.20sd:0.19

8 2

57 0 avg:5.32sd:0.25

8 4

avg: 3.44sd: 0.49

avg: 3.54sd: 0.96

16 10

.01 0 avg: 4.89sd: 0.10

8 2

4 avg: 1.33sd: 0.26

avg: 4.53sd: 1.39

21 5

7 avg: 0.07sd:0.22

avg: 5.24sd: 0.59

8 13

315

avg: 13.79sd: 8.49

avg: 2.69sd: 0.67

22 3

.97 avg: 487.8sd: 3.21

avg: 1.46sd: 0.21

41 2

.07 avg: 6.55sd: 0.92

avg: 5.73sd: 1.03

9 2

.6602

avg: 144.54sd: 75.61

avg: 1.73sd: 0.09

43 10



05,000

10,00015,00020,00025,00030,000

E G H J1 J2 J3

H

020,00040,00060,00080,000

100,000120,000

E G H J1 J2 J3

0

2,000

4,000

6,000

8,000

E G H J1 J2 J3

Fe

PbG

mg

/L

mg

/L

F

Sample

Zn

mg

/L

Sample

0

500

1,000

1,500

E G H J1 J2 J3

020406080

100120140

E G H J1 J2 J3

Cd

Cu

mg

/L

mg

/L

< 4 mm < 10 mmSize fraction

0

1,000

2,000

3,000

4,000

E G H J1 J2 J3

AlB

0

5,000

10,000

15,000

E G H J1 J2 J3

As

mg

/L

C D

E

0

1

2

3

4

5

E G H J1 J2 J3

pHA

pH

mg

/L

Fig. 9. First flush chemistry (mg/L;measured by ICP-MS) of leachates derived frommaterial representative of Croydonwaste-rockmesotextural groups E, G, H and J: (A) pH; (B) Al; (C) As;(D) Cd; (E) Cu; (F) Fe; (G) Pb and (H) Zn. Values for both the b10 mm and b4 mm size fractions are shown.


coarser (b10 mm) fractionsweremeasured (Fig. 9A). However, a greaterreactivitywas expected from the coarser (b10 mm) fraction as a functionof surface area (cf. Stomberg and Banwart, 1999), and this was observedin kinetic column leach experiments performed on these materials(Parbhakar-Fox et al., 2013). The lowest elemental concentrations (mea-sured by ICP-MS)were fromGroup E, with the lowest quantities of Al, As,Cd, Cu, Fe, Pb and Zn measured (Fig. 9). Such a first-flush leachate signa-turewas anticipated for this groupwhen considering the lowpyrite abun-dance, and its textural form (i.e., euhedral pyrite encapsulated in aquartz–muscovite groundmass). The highest values for Al and Zn weremeasured from the b4 mm fraction of group G (Fig. 9B; 3626 mg/L and9 g; 26, 260 mg/L respectively). High concentrations of Zn in first-flushleachate was anticipated when considering the presence of sphalerite inthis material (Table 1). In group H the highest As concentrations weremeasured (~14,000 mg/L; Fig. 9C) corresponding to the high arsenopy-rite and scorodite contents (Table 1). Generally, relatively similar elementconcentrations were measured between the two size fractions, howeverslightly higher As, Cd, Pb and Znweremeasured from the b4 mm fraction(Fig. 9). High concentrations of Pb were measured from both size frac-tions, and were likely sourced from Pb micro-inclusions identified inpyrite intergrown with arsenopyrite (Fig. 4D).


For group J, the b4 mm fraction consistently measured highestvalues for each element, with the exception of Pb in sample 3(Fig. 9G). Of the group J samples, J1 contained the highest As (b4 mm:~210 mg/L; Fig. 9C), followed by group J3 (b4 mm: ~130 mg/L;Fig. 9C) and sample J2 the lowest (b10 mm: ~2 mg/L; Fig. 9C). Thesevalues increase with pyrite content, inferring As release during oxida-tion, and its consequent redistribution to soluble secondary minerals.The presence of significant sulphide sources of Cd (i.e., sphalerite) inthis group was not inferred by this data (as confirmed by QXRD;Table 1). However, Cd concentrations ~120 mg/L were measured fromthe b4 mm fraction of sample J3 (Fig. 9D). This suggests that secondaryminerals present in this group are Cd-bearing. Irwin et al. (1997) andTauson et al. (2004) reported of Cd-bearing anglesite, therefore this isconsidered here a potential Cd source in material from this group.High concentrations of Cu were measured in leachate from samples J1(b4 mm: ~2900 mg/L; Fig. 9E) and J3 (b4 mm: ~1500 mg/L; Fig. 9E),and likely relate to the presence of Cu in pyrite (Fig. 8E), furthermore,minor quantities of chalcopyrite were identified in SEM and MLA stud-ies. The highest concentrations of Fe (range: ~133,780 to 997,800 mg/L;Fig. 9F) were measured in this group, specifically from the b4 mmfraction, and likely represents the dissolution of soluble secondary




Fe-sulphates, which were identified by QXRD (Table 1). Measurementsof Pb are linked to weathering of galena to anglesite with both mea-sured the highest in sample J3 (Fig. 9G). Zinc is most likely sourcedfrom pyrite and its alteration products rhomboclase and anglesitewhich were detected in minor quantities (Fig. 9H; Table 1; cf. Buckbyet al., 2003; Giere et al., 2003; Nordstrom, 2004).

4.3. Stream sediments

Element contents of stream sediment samples (measured by ICP-MS)collected in the Croydon area were compared against Australian andNew Zealand interim sediment quality guidelines (ISQGs). These em-pirical guidelines are derived from the North American effects database(ANZECC/ARMCANZ, 2000a; in Simpson et al., 2005). The guidelinescontain two concentrations, the ISQG-Low concentration (or trigger

Tabletop Creek FederationLa Perouse

Deadhorse Creek

Gle

nco

e

Co

nfl

uen

ce

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number

Distance upstream (km)

-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1

Distance downstream (km)

3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0 8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.7


Deadhorse Creek

Gle

nco

e

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number


-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1


3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0 8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.7

Co

nfl

uen

ce

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

Co

nce

ntr

atio

n (

mg

/kg

)


A

ISQG-High

Deadhorse Creek

Gle

nco

e

Co

nfl

uen

ce

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number


-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1 ISQG-Low


3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0 8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.7

0

50

100

150

200

250

0

5

10

15

20

25

ISQG-High

ISQG-Low

ISQG-High

ISQG-Low

Co

nce

ntr

atio

n (

mg

/kg

)C

on

cen

trat

ion

(m

g/k

g)

As

C Cu

E Sb

Total fraction < 63 µm fraction

Fig. 10. Trace element content (mg/kg; measured by ICP-MS) in stream sediments (total aand ISQG-Low values are shown for comparison: (A) As; (B) Cd; (C) Cu; (D) Pb; (E) Sb; (F) Zn. Nshown on Fig. 2.


value) and the ISQG-High concentration. The trigger value is a thresholdconcentration, and below this the frequency of biological effects is ex-pected to be very low (Simpson et al., 2005). The ISQG-High concentra-tion is intended to represent a concentration, above which adversebiological effects are expected to occur more frequently (Simpson et al.,2005).

The upstream (local baseline), on site, and downstream concentra-tions of selected metals and metalloids in both the total and fine(b63 μm) fractions are shown (for bothmine sites) in Fig. 10 (measuredby ICP-MS). Generally, background (upstreamofmine operations) sam-ples contain low concentrations of As (b20 mg/kg), Cd (b1.5 mg/kg),Cu (b65 mg/kg), Pb (b50 mg/kg) and Zn (b200 mg/kg). These valuesare within the ANZECC (2000) ISQG-High values. Several backgroundsamples with elevated As, Pb and Sb relative to ISQG-Low values(Fig. 10A, D and E) were measured and likely indicate the presence of


Deadhorse Creek

Gle

nco

e

Co

nfl

uen

ce

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number


-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1


3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0 8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.70

2

4

6

8

10

12


Deadhorse Creek

Gle

nco

e

Co

nfl

uen

ce

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number


-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1


3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0 8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.7


Deadhorse Creek

Gle

nco

e

Co

nfl

uen

ce

2 3 1 4 5 67 8 910 12 31 21 22 23 24 25 2714 16 17 19 2018 28 29 30 32 34 33 39 36 35 37

Location number


-4.4

-3.7

-3.6

-2.8

-2.6

-1.8

-1.7

-1.6

-1.3

-1.2

-1.1


3.3

3.4

3.6

3.9

4.3

7.8

10.1

10.0

8.3

4.3

2.8

1.9

1.7

1.3

1.1

0.9

0.7

0

500

1,000

1,500

2,000

0

100

200

300

400

500

600

700

ISQG-Low

ISQG-High

ISQG-HighISQG-Low

ISQG-High

ISQG-Low

B

Co

nce

ntr

atio

n (

mg

/kg

)C

on

cen

trat

ion

(m

g/k

g)

Cd

D Pb

Co

nce

ntr

atio

n (

mg

/kg

)

F Zn

ISQG -High ISQG -Low

nd b63 μm fractions shown) around the Croydon district. ANZECC (2000) ISQG-HighB. Sample location numbers are shown at the top of each graph, and correlate to locations




sulphide bearing lodes andmineralised rocks, causing localised elementenrichment.

At the Federation/La Perouse site, elevated concentrations of As(total and 63 μm fractions), Cu (b63 μm), Cd (b63 μm), Pb (b63 μm)and Sb (b 63 μm) relative to ISQG-Low values were measured. Only Aswas elevated relative to the ISQG-High value at the Glencoe site. Thespatial distribution of sediment-associated metals downstream of bothsites did not display a simple distance–metal concentration decay pat-tern. Downstream of Federation/La Perouse in Tabletop Creek, relativeto the ISQG-High value, As remained generally in the b63 μm fractionto approximately 8 km (location 25; Fig. 10A). Cadmium was generallybelow the ISQG-Low value from approximately 3 km downstream ofthe Federation/La Perouse site (Fig. 10B) until the confluence (at ap-proximately 10 km; location 27). Maximum concentrations of Cd(b63 μm) and Zn (b63 μm) exceeding ISQG-High values were mea-sured in Deadhorse Creek approximately 0.9 km downstream of theGlencoe site (location 35; Fig. 10B and F). These concentrationsfluctuatedto the confluence,withoccasional highs (e.g., location30) againpotential-ly indicating the presence of a mineralised sulphide body in proximity tothe sampled location. Copper concentrations fluctuated downstream ofthe Glencoe site to the confluence (Fig. 10C). Lead concentrations alsofluctuated for approximately 8 km downstream of the Glencoe site,after which it was measured below the ISQG-High value (Fig. 10D). Atthe confluence of Tabletop and Deadhorse Creek concentrations for As,Cu, Cd, Pb and Zn were measured below ISQG-High values. Monitoring(since 1998) of Tabletop Creek below the confluence (c. 17 and 30 kmdownstream of the Federation/La Perouse site) reported concentrationsbelow ISQG-Low values for As, Cu, Cd, Pb and Zn (DME, 2008).

Sequential extraction results for six samples collected at theFederation/La Perouse site are presented in Fig. 11 as cumulative per-centages (element concentrations measured by ICP-MS). Arsenic ismainly the immobile residual fraction (45%) and the less mobile Fe(III) oxide fraction (42%), with values below detection limit measuredfor the water soluble and exchangeable fractions. Cadmium belongsmainly to the water soluble (43%) and exchangeable (32%) fractions.Copper is dominantly associated with the Fe (III) oxyhydroxide (36%)and Fe (III) oxide (32%) fractions. Maximum concentrations of Ni, Pband Sb were measured from the residual fractions (83, 66 and 100%respectively). Zinc showed a diverse behaviour and was divided intothe following fractions: 22% water soluble, 20% Fe (III) oxide, 14% ex-changeable, 11% Mn oxide, and 11% Fe (III) hydroxide. In generalterms, a higher proportion of Cd, Zn and Cu are associated with thereadily mobile fractions of sediments with the following general orderof mobility: observed Cd N Zn N Cu N As N Pb N Ni N Sb. Similar trendsof elementmobility inmining affected areaswere reported by Bird et al.(2003) and Teixeira et al. (2003).

0

20

40

60

80

100As Cd Cu Ni Pb Sb Zn

Water soluble Exchangeable Mn oxideFe (III) hydroxide

Fe (III) oxide Organic/secondary sulphideResidual

cum

ula

tive

per

cen

tag

e (%

)

Fig. 11. Cumulative percentage of As, Cd, Cu, Ni, Pb, Sb and Zn (mg/kg;measured by ICP-MS)in different steps of sequential extraction performed on sediment samples collected at theFederation/La Perouse mine site, Croydon.


4.4. Surface waters

The pH values measured across the Croydon district were comparedagainst concentrations of As, Cd, Cu, Pb and Zn (Fig. 12). In TabletopCreek upstream of the Federation/La Perouse site the pH range was 6.4to 8.6, with low concentrations of Al (b67 μg/L), As (b6.1 μg/L), Cd(b2 μg/L), Cu (b3 μg/L), Pb (b1.1 μg/L), S (0.42 mg/L) and Zn (b9 μg/L)measured. Concentrations of Fe were elevated upstream of the mine op-erations (Fig. 12E). At the Federation/La Perouse site, pH values decreasedto 3.7, with elevated concentrations of Al, As, Cd, Cu, Ni, Pb, S and Zn rel-ative to local background/upstream value measured (Fig. 12). Down-stream, pH values generally increased with a maximum of pH 7.6recorded. Generally, concentrations of Cd, Cu, Pb and Zn decreaseddownstream.

At Glencoe, pH values were between 4.3 and 6.3 (Fig. 12), and ele-vated concentrations of As (20.4 μg/L), Cd (53 μg/L), Pb (14 μg/L) andZn (7715 μg/L) relative to ANZECC (2000) drinking water guidelines(DWG) values were measured. In Deadhorse Creek adjacent to the site(location 36; Fig. 2), pH 3.95 was measured. However, by c. 1.7 km(location 33; Fig. 2), pH ~11 was measured. High dissolved Fe(2125 μg/L) was also measured at this location. At the confluence of Ta-bletop and Deadhorse Creeks, a near-neutral pH 6.7 was measured,with only Cu (13 μg/L), Ni (12 μg/L), S (18 mg/L) and Zn (137 μg/L) el-evated relative to background/upstream concentrations (Fig. 12), butare not elevated in comparison to ANZECC (2000) DWG values.

Element concentrations and pH values for Federation, La Perouseand Glencoe pit lakes are given in Table 3. Federation pit was the mostacidic (pH 3.9) whilst La Perouse and Glencoe were only mildly acidicwith measured values of pH 6.1 and 6.3, respectively. These values aresimilar to previous monitoring data collected by the DEEDI since 1998(DME, 2008). The Federation Pit lake contained the highest concentra-tions of Cd (83.6 μg/L), Cu (989.6 μg/L), Ni (65.6 μg/L), Pb (71.3 μg/L)and Zn (1918 μg/L), and the highest As concentration was measuredat Glencoe (20.4 μg/L). Elevated concentrations relative to ANZECC(2000) DWG values were detected for As (Glencoe) and Pb (Federa-tion). Overall, La Perouse and Glencoe pit lakes have better water qual-ity than Federation. Since the construction of the catch dam, waterquality in Federation pit has deteriorated as in the dry season, waterquality in the catch damworsens due to evapo-concentration of solutes,and in the wet season the water bodies become linked.

5. Discussion

5.1. Acid forming groups and metal/metalloid sources

Detailed microtextural and chemical studies of the main sulphide-bearing groups revealed diversity of minerals and, in conjunction withgeochemical data helped to identify the current ARD and metal/metal-loid sources.

Paste pH experiments indicate that material representative of groupG (quartz–sphalerite–galena) is weakly acid forming, with the ARDIclassifying them as PAF (Table 2). This group is a significant source ofCd, as indicated by first-flush experiments (Fig. 9). Specifically Cd issourced from finer-grained sphalerite (b200 μm), which is undergoingoxidation at a greater rate than coarser-grained sphalerite (N200 μm)asa function of surface area, higher Fe-content and the presence of galenainclusions (cf. Lottermoser, 2010; Moncur et al., 2009; Stanton, 2005;Weisener et al., 2004). Zinc is also primarily sourced from sphalerite.Neither Zn nor Cd is retained surficially on sphalerite, indicating thaton oxidation, metal deficient surface layers have formed (cf. Buckleyet al., 1989). Chalcopyrite was not detected as a major sulphidemineralin any mesotextural group. However, it was observed in sphalerite asmicro-inclusions. The presence of these micro-inclusions causes sphaler-ite lattice destabilisation, and enhancing oxidation (cf. Lottermoser, 2010,Urbano et al., 2007).



0

5000

10,000

15,000

20,000

25,000

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Al

0

5

10

15

20

25

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0102030405060708090

1 2 3 4 5 6 7 8 9 10 11 12 13 140

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0

500

1000

1500

2000

2500

3000

1 2 3 4 5 6 7 8 9 10 11 12 13 140

102030405060708090

1 2 3 4 5 6 7 8 9 10 11 12 13 14

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13 140

20

40

60

80

100

120

140

1 2 3 4 5 6 7 8 9 10 11 12 13 14

01,0002,0003,0004,0005,0006,0007,0008,0009,000

1 2 3 4 5 6 7 8 9 10 1112 13 14pH

pH

pH

pH

pH

pH

pH

pH

pH

mg

/Lµ

g/L

µg

/Lµ

g/L

µg

/Lµ

g/L

µg

/Lµ

g/L

µg

/L

Tabletop Creek (Upstream)

Tabletop Creek (Downstream)

Confluence

Glencoe

Deadhorse Creek (Downstream)

A AsB

CdC CuD

FeE NiF

PbG SH

ZnIFederation/La Perouse

Fig. 12. Trace element concentration (μg/L; measured by ICP-MS) versus pH in surfacewater samples collected from around the Croydon district: (A) Al; (B) As; (C) Cd; (D) Cu; (E) Fe; (F)Ni; (G) Pb; (H) S; (I) Zn.


Galena in group G is rich in Ag, Bi and Sb increasing its potential forweathering and Pb release, with anglesite developed as a secondaryproduct (cf. Diehl et al., 2003; Diehl et al., 2007; Savage et al., 2000).Finer-grained (b200 μm) galena appeared more weathered thancoarser-grains, indicating that grain size poses a significant control on


oxidation in accordance with Liu et al. (2008). Diehl et al. (2008) statedthat anglesite does not function as a protective barrier againstfluid infil-tration because it is porous and fine-grained. However, Moncur et al.(2009) stated that anglesite rims slow oxidation progress. Observationsfrom this study support Diehl et al. (2008).



Table 3Element concentrations (μg/L; analysed by ICP-MS) and pH values measured in Federa-tion, La Perouse and Glencoe pit water samples (obtained from the surface). Drinkingwater guidelines (DWG) published by ANZECC (2000) are shown for comparison.

Federation La Perouse Glencoe DWG

pH 3.9 6.1 6.3 6.5 to 8.5Al 17,680 25 11 –

Ag 1 1 1 100As 4 2 20 7Cd 84 BDL 1 2Co 2 BDL BDL –

Cr 4 6 6 50Cu 990 2 1 2000Fe 44 105 56 –

Mn 609 53 77 –

Ni 66 3 4 –

Pb 71 BDL BDL 20Rb 14 7 10 –

Se 11 BDL 1 10Sr 44 6 3 –

Ti 743 10 20 –

Tl BDL BDL BDL –

U 39 BDL BDL 10V 2 3 3 –

Zn 1918 17 43 3000


Material representative of mesotextural group H (arsenopyrite–quartz–pyrite) was classified as extremely acid forming by geochemicaltests and theARDI. Highly fracturedmassive arsenopyrite dominated, andis in early stages of weathering, with scorodite dominating the secondarymineralogy. Scorodite behaves as a protective weathering barrier underacidic conditions as its dissolution is slow (10−9 to 10−10 mol m2 s−1;Harvey et al., 2006). Scorodite precipitates within arsenopyrite fracturesand on grain boundaries as confined laminated layers of uniform thick-ness parallel to grain boundaries. Where scorodite growth is unconfined(e.g., in proximity to pyrite), a greater diversity of microtextures is ob-served, including spherules (DeSisto et al., 2011; Murciego et al., 2011)and ‘ribbons’. Paste pH results indicate that to an extent, scorodite isretarding acid formation, as Craw et al. (2003) summarised that evenat submicron-scale, this mineral offers protection.

Mesotextural group J samples (quartz–pyrite) were consistentlyclassified the most acid forming group at Croydon by all geochemicalmethods and the ARDI. In general, larger pyrite grains were moreoxidised as a result of extensive fracturing. Group J samples had thehighest total concentration of metals (Cd, Cu, Ni, Pb and Zn). Arsenicin pyrite decreases resistance to oxidation (cf. Blanchard et al., 2007;Plumlee, 1999), here this has caused accelerated weathering of thesecores, with weathering further enhanced by the presence of galenamicro-inclusions (b10 μm diameter) straining the lattice (cf. Jambor,1994; Kwong, 1995; Lottermoser, 2010; Plumlee, 1999). HFO have pre-cipitated in pyrite fractures, and have adsorbed elements released onpyrite oxidation, particularly As (cf. Foster et al., 1998). In addition,szomolnokite and rhomboclase have precipitated and also represent atransient store of trace elements (Buckby et al., 2003; Lottermoser,2010). These minerals are highly soluble under the pH range (3.0 to4.7) measured in paste pH tests (cf. Harris et al., 2003), and therefore,a likely source of As, Cd, Cu, Pb and Zn.

Observations made in minor sulphide bearing groups i.e., A(muscovite-altered porphyritic rhyolite with minor disseminated pyritein quartz veins), C (muscovite-altered porphyritic rhyolite with dissemi-nated pyrite in quartz veinlets) and E (muscovite-altered porphyriticrhyolite with disseminated pyrite in the groundmass) show thatgroundmass-associated sulphides are more susceptible to weatheringthan quartz-associated sulphides. Smuda et al. (2007) made similar ob-servations at the Excelsiorwaste rock dump, Cerro de Pasco, Peru. Theseauthors concluded that fine-grained disseminated pyrite in a volcanicgroundmass oxidised much faster than massive pyrite from the orebody due to the high porosity. Considering the small total sulphide


contents (i.e., b1 wt.%), only a small contribution to net-ARD is likelyfrom material representative of these groups.

5.2. Metal and arsenic dispersion at Croydon

At Croydon, surface water downstream of bothmine sites is classifiedas acid-low metal to neutral-low metal by the general Ficklin diagramgiven in Plumlee (1999). As pH values increased above 4.5 downstreamof both the Federation/La Perouse and Glencoe sites, concentrations ofAl, As, Co, Cd, Ni, Pb, S and Zn declined. However, concentrations of Fewere measured higher in background and downstream samples. AroundpH 4.5 to 5 As and Pb have likely sorbed onto Fe-bearing precipitates,with sequential extraction results indicating concentration of theseelements to this fraction (cf. Ashley et al., 2004; Hudson-Edwardsand Edwards, 2005; Lottermoser, 2010). Sediment loads of Cu, Cdand Zn declined downstream, with Cu sorbed onto Fe-bearing precipi-tates around neutral pH (Hudson-Edwards and Edwards, 2005).Cadmium and Zn concentrations correlate with Mn indicating co-precipitation of these elements with manganese oxides. At the conflu-ence approximately 10 km downstream of both sites, neutral pH wasmeasured, with metal (Al, Cd, Cu, Pb and Zn) concentrations similar toupstream values and below guideline values recommended by govern-ment authorities (e.g., ANZECC, 2000), indicating effective attenuation.However, at Croydon seasonal fluxes of metals may occur as a functionof lowflowconditions (lowpH)or heavy rainfall events (high pH) caus-ing desorption of elements (cf. Ashley et al., 2004; Harris et al., 2003;Nordstrom, 2009).

Generally water quality is similar in both creeks. Elevated Cd and Znconcentrationsmeasured in Deadhorse Creek provide an indication thatmaterial representative of mesotextural group G dominates in theGlencoe waste rock pile. Consequently, there is a potential risk to cattlefrom ARD seepage at the site. However, these results suggest that Cdconcentrations are relatively low from 1 km downstream of Glencoe.Instead, as the Croydon mine sites are currently designated grazingland, attention should be given to the presence of plant Calotrope(Calotropis procera) observed around the Croydon mines, as it is toxicif consumed (cf. Lottermoser, 2011).

5.3. Implications for site rehabilitation

Historic and abandoned sulphidic mine sites require rehabilitation.However, extensive ARD processes, limited capital and excessive costsassociatedwith planning and remediationworksmean that comprehen-sive site rehabilitation is rarely achievable. At these sites, rehabilitation isdriven primarily by impacts on receiving environments i.e. soil andwater quality (e.g., Alvarez and Ridolfi, 1999; Mudd and Patterson,2010).

If water quality data alone is used to assess the requirement for reha-bilitation at Croydon, the sitewouldnot beprioritised underQueensland'sAbandoned Mine Lands Program (AMLP). Our observations indicate thatsulphidic mine wastes are in early weathering stages by the generalmine waste paragenesis proposed by Moncur et al. (2009). However,first-flush data indicated that there would be significant discharge ofmetals and As after a heavy rainfall event. Thus, both Croydon sites stud-ied are considered as long-term contamination sources posing significantenvironmental risk to the downstream environment.

Previous rehabilitation strategies at the site focused on raising pH inpit lakes and managing ARD seepage downstream. However, as shownin this study, this strategy can only have a temporary effect and amore sustainable long-term strategy should focus on the relocation ofARD sources into newly constructed impoundments, containing wasterock pile material domained into the ten mesotextural groups identi-fied. Whilst upfront financial costs of adopting such a scheme may beconsidered high, a long-term cost saving is anticipated when consider-ing that global liability costs associated with current and future ARD re-mediation is estimated atUS $100 billion (Tremblay andHogan, 2001 in




Hudson-Edwards et al., 2011), indicating that a proactive rather than re-sponsive approach to ARD management is required.

Material representative of mesotextural group H is the dominantsource of As, with its concentration in dissolved waters controlled in-part by scorodite formed in waste rock material. However, evidence ofscorodite weathering was observed, indicating a likely temporal in-crease in dissolved As in waste pile leachates. Material representativeof mesotextural group G contains significant quantities of Cd (and Zn)which is homogenously distributed in sphalerite grains and thereforeidentified as a long-term source of these elements. Whilst relativelylow metal and As concentrations were measured from mesotexturalgroup J in kinetic trials (Parbhakar-Fox et al., 2013), it is identified as asignificant contamination source due to its high pyrite contents (i.e.,generating low pH conditions). Considering these diverse chemical andmineralogical characteristics, consideration should be given to handlingand managing mesotextural group G, H and J materials separately. Co-disposal of these materials has potential to increase the environmentalrisk posed, through geochemical interactions. Such waste segregationpractices are described in theGARDguide (2010). For example, sphaleriteleaching is enhanced at low pH (2 to 4; Stanton et al., 2008), and first-flush pH measurements from group H were below 4. Therefore, co-disposal may enhance sphalerite oxidation, releasing increased amountsof dissolved Cd and Zn.

As an alternative to impermeable covers, neutralisation strategiescould be implemented in the impoundments containingmaterial repre-sentative of mesotextural group G and J (and E, which can be co-disposed with J) waste in order to raise pH and reduce heavy metaland metalloid mobility (cf. Ashley et al., 2004). Alternatives to limeshould be sought as neutralising materials given the limited successpreviously experienced (DME, 2008). As scorodite has extensively pre-cipitated inmesotextural groupH, the pH in the repository containing itshould bemaintained in a range where it is relatively insoluble. Bluteauand Demopoulos (2007) reported low solubility rates (0.35 mg/L−1) ofAs at pH 5, with its dissolution from pH 5 to 9 similarly low. However,Krause and Ettel (1988) reported that ~90 mg/L−1 As was leachedfrom scorodite at pH 5. Drahota and Filippi (2009) proposed that rea-sons for these differences may be linked to the degree of scoroditecrystallinity used, with two types of scorodite texture observed inhere (spherules, and acicular grains). Therefore, prior to recommendingthe geochemical conditions at which this material representative of thismesotextural group should bemaintained at, furtherwork is required toelucidate the crystallinity and stability of scorodite in this mesotexturalgroup.

The mesotextural classification method developed in this study issimple and cost-effective to perform at abandoned mine operations be-cause it allows for the rapid assessment of large quantities of wastema-terials. Such a site-specific methodology should be designed primarilyby geologists (in conjunction with site managers), as an understandingof the waste rock mineralogy is fundamental for scheme to be effective.Based on the collection of real data (i.e., pXRF, SW-IR) and improvedmineralogical and textural assessments ofwastematerials, the selectionof the most appropriate samples for standard geochemical tests and in-depth mineralogical evaluations is permitted. This allows for full ARDcharacterisation i.e., identifying sulphide oxidation controls and under-standing of ARD evolution on a mesotextural group basis. This method-ology has been adapted for use at several operational Australian minesites, where such mesotextural evaluations were performed to supportdeposit-wide domaining of ARD characteristics, and has allowed for thedevelopment of improved waste management schemes.

6. Conclusions

Rehabilitation strategies at historic and abandoned metalliferousmine sites are only undertaken when ARD is generated. Consequently,a ‘blanket approach’ to rehabilitation is typically adoptedwhereby tech-niques such as lime dosing and waste rock capping are performed.


Additionally, waste rock piles are treated as mineralogically homoge-nous entities. Consequently, rehabilitation schemes can have limitedsuccess, with significant associated financial costs. This study demon-strated that through improving the mineralogical and geochemical un-derstanding of ARD sources in waste rock piles, better managementschemes can be developed, rather than utilising reactive strategies.

Materials collected fromwaste rock piles at the abandoned Croydonmine operations (north Queensland, Australia), were used to developand test a mesotextural groupingmethodology. This method accuratelydomains material based on chemical, mineralogical and texturalsimilarities by using geological logging techniques, pXRF and SW-IRanalyses. Mineralogical variability is better accounted for than if usinglithology or alteration classes, with samples domained based on ARDforming characteristics prior to ARD testing. Mesotextural groupingof Croydon waste materials identified ten major groups (A to J),which comprised of hydrothermally altered rhyolites and massive/semi-massive sulphides.

Three major acid forming mesotextural groups were identi-fied: J (quartz–pyrite), H (arsenopyrite–quartz–pyrite), and G(quartz–sphalerite–galena). Group J contained moderate-high concen-trations of As, Pb and Zn sourced from pyrite, and was consistently themost acid forming. Some secondary HFO had developed. However,high concentrations of elements Pb, Zn and Cu were measured infirst flush experiments, suggesting dissolution of secondary sul-phates (e.g., rhomboclase, szomolnokite). Group H contained majorarsenopyrite; however scorodite had extensively precipitated in frac-tures and rims, thus oxidation is controlled by its solubility. Group Gcontains high amounts of Zn, Cd and Pb sourced from sphalerite and ga-lena. Galena had undergone partial weathering to anglesite with Pb lib-erated, as observed in first flush experiments. Elevated Zn and Cd alsomeasured in these experiments was a consequence of the absence ofarmouring secondary minerals on sphalerite, and as sphalerite wasFe-rich with abundant micro-inclusions, continued oxidation isexpected.

Elevated Cd, Pb and Zn relative to ANZECC (2000) ISQG weremeasured within 10 km downstream of the site operations, indicatingthat these sources of contaminants are impacting the local environ-ment. This study indicates that a rehabilitation strategy involving thesegregation of sulphidic material into repositories designated for eachmesotextural groups (i.e., G, H and J) should be considered as an optionfor future waste management at this site. Such a strategy will limit in-teractions between these materials, thus limiting liberation of environ-mentally significant elements. Furthermore, different pH conditions canbe maintained in each pile to encourage formation of secondary min-erals and ensure their stability.

Further studies should focus on a better understanding of thelong-term geochemical behaviour of waste rock, identifying the loca-tion and flow rates of seepage points, measuring volumes of water insub-catchments and understanding the characteristics of shallowgroundwater.

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.gexplo.2013.10.017.

Acknowledgements

The authors acknowledge the Queensland Department of NaturalResources andMines for allowing access to the Croydon sites for samplecollection. Thanks are extended to Dr. Karsten Goemann (CSL, UTAS),Katie McGoldrick (CODES, UTAS), Dr. Nathan Fox (CODES, UTAS),Sarah Gilbert (CODES, UTAS) and Ian Little (CODES, UTAS) for analyticalassistance. Additional thanks are extended to Professors BerndLottermoser, Dee Bradshaw, Dave Craw and Bernard Dold for reviewingthe Ph.D thesis from which this manuscript is synthesised, and twoanonymous reviewers, whose comments have greatly improved thequality of this manuscript.






References

Alvarez, S.M., Ridolfi, B.A., 1999. Moon Creek reclamation project creative solution for anhistoric mine site. SME Annual Meeting March 1999, Denver Colorado, pp. 1–7.

Andrina, J., Wilson, G.W., Miller, S., Neale, A., 2006. Performance of the acid rock drainagemitigation waste rock trial dump at Grasberg mine. 7th International Conference onAcid Rock Drainage (ICARD), pp. 30–44.

ANZECC, 2000. Australian guidelines for water quality monitoring and reporting. NationalWater Quality Management Strategy Paper No 7, Australian and New Zealand Envi-ronment and Conservation Council & Agriculture and Resource Management Councilof Australia and New Zealand, Canberra.

Ashley, P.M., Lottermoser, B.G., Collins, A.J., Grant, C.D., 2004. Environmental geochemistryof the derelict Webbs Consols mine, New South Wales, Australia. Environ. Geol. 46,591–604.

Aykol, A., Budakoglu, M., Kumral, M., Gultekin, A.H., Turhan, M., Esenli, V., Yavuz, F.,Orgun, Y., 2003. Heavy metal pollution and acid drainage from the abandonedBalya Pb–Zn sulfide Mine, NW Anatolia, Turkey. Environ. Geol. 45, 198–208.

Bain, J.H.C., Withnall, I.W., Black, L.P., Etminan, H., Golding, S.D., Sun, S.S., 1998. Towardsan understanding of the age and origin of mesothermal gold mineralisation in theEtheridge Goldfield, Georgetown region, north Queensland. Aust. J. Earth Sci. 45,247–263.

Barton Jr., P.A., Bethke, P.M., 1987. Chalcopyrite disease in sphalerite: pathology andepidemiology. Am. Mineral. 72, 451–467.

Bethke, P.M., Barton Jr., P.A., 1971. Distribution of some minor elements betweencoexisting sulfide minerals. Econ. Geol. 66, 140–163.

Bird, G., Brewer, P.A., Mackin,M.G., Balteanu, D., Driga, B., Serban, M., Zaharia, S., 2003. Thesolid state partitioning of contaminant metals and As in river channel sediments ofthe mining affected Tisa drainage basin, northwestern Romania and easternHungary. Appl. Geochem. 18, 1583–1595.

Blanchard, M., Alfredsson, M., Brodholt, J., Wright, K., Catlow, C.R.A., 2007. Arsenic incor-poration into FeS2 pyrite and its influence on dissolution: a DFT study. Geochim.Cosmochim. Acta 71, 624–630.

Bluteau, M.C., Demopoulos, G.P., 2007. The incogruent dissolution of scorodite: solubility,kinetics and mechanism. Hydrometallurgy 87, 163–177.

Bowell, R.J., Rees, S.B., Parshley, J.V., 2000. Geochemical predictions of metal leaching andacid generation: geologic controls and baseline assessment. Geology and OreDeposits: The great Basin and Beyond Proceedings, 2, pp. 799–823.

Brown, D., Salzsauler, K., Verburg, R., Sifuentes, R., Aranda, C., 2009. Geochemical charac-terization of waste rock using field kinetic testing at the Antamina mine. 8th Interna-tional Conference on Acid Rock Drainage (ICARD) and Securing the Future: Mining,Metals & the Environment in a Sustainable Society, pp. 311–321.

Buckby, T., Black, S., Coleman, M.L., Hodson, M.E., 2003. Fe-sulfate-rich evaporativemineral precipitates from the Rio Tinto, southwest Spain. Mineral. Mag. 67, 263–278.

Buckley, A.N., Woods, R., Wouterlood, H.J., 1989. An XPS investigation of the surface ofnatural sphalerites under flotation-related conditions. Int. J. Miner. Process. 26,29–49.

Bureau of Meteorology, 2013. www.bom.com.au.Caruso, B.S., Bishop, M., 2009. Seasonal and spatial variation of metal loads from natural

flows in the Upper Tenmile Creek Watershed, Montana. Mine Water Environ. 28,166–181.

Cook, N.J., Ciobanu, C.L., Pring, A., Skinner, W., Danyushevsky, L., Shimizu, M., Saini-Eidukat, B., Melcher, F., 2009. Trace and minor elements in sphalerite: a LA-ICP-MSstudy. Geochim. Cosmochim. Acta 73, 4761–4791.

Craw, D., Falconer, D., Youngson, J.H., 2003. Environmental arsenopyrite stability anddissolution: theory, experiment and field observations. Chem. Geol. 199, 71–82.

Danyushevsky, L., Robinson, P., Gilbert, S., Norman, M., Large, R., McGoldrick, P., Shelley,M., 2011. Routine quantitative multi-element analysis of sulphide minerals by laserablation ICP-MS: standard development and consideration of matrix effects.Geochem. Explor. Environ. Anal. 11, 51–60.

David, C.P.C., 2003. Establishing the impact of acid mine drainage through metal bioaccu-mulation and taxa richness of benthic insects in a tropical Asian stream (thePhilippines). Environ. Toxicol. Chem. 22, 2952–2959.

DeSisto, S.L., Jamieson, H.E., Parsons, M.B., 2011. Influence of hardpan layers on arsenicmobility in historical gold mine tailings. Appl. Geochem. 26, 2004–2018.

Diehl, S.F., Smith, K.S., Desborough, G.A., Goldhaber, M.B., Fey, D.L., 2003. Trace-metalsources and their release from mine wastes: examples from humidity cell testsof hard-rock mine waste and from Warrior Basin coal. National Meeting of theAmerican Society of Mining and Reclamation Symposium, Billings, MT,pp. 232–253.

Diehl, S.F., Koenig, A.E., Hageman, P.L., Smith, K.S., Fey, D.L., Lowers, H.A., 2007. From themicro to the macroscale: a textural and chemical perspective of characterising waste-rock material. Proceedings of the 2007 Society for Mining, Metallurgy and Exploration(SME)AnnualMeeting andExhibit, and the 109thNationalWesternMiningConference,Denver, Colorado. Society for Mining, Metallurgy and Exploration Inc., United States,Preprint 07-021, pp. 1–16.

Diehl, S.F., Hageman, P.L., Smith, K.S., 2008. What is weathering in mine waste? Mineral-ogic evidence for sources of metals in leachates, Chapter A. In: Verplanck, P.L. (Ed.),Understanding Contaminants Associated With Mineral Deposits: U.S. Geological Sur-vey Circular, 1328, pp. 4–7.

DME (Queensland Department of Mines and Environment), 2008. Report on Value Engi-neering Study, Remediation of Abandoned Federation and Glencoe Mines, Croydon.

Dold, B., 2003. Speciation of the most soluble phases in a sequential extraction procedureadapted for geochemical studies of copper sulphide mine waste. J. Geochem. Explor.80, 55–68.

Downing, B.W., Madeisky, H.E., 1997. Lithogeochemical methods for acid rock drainagestudies and prediction. Explor. Min. Geol. 6, 367–379.


Drahota, P., Filippi, M., 2009. Secondary arsenic minerals in the environment: a review.Environ. Int. 35, 1243–1255.

Edraki, M., Baumgartl, T., Fletcher, A., Mulligan, D., Fegan, W., Munawar, A., 2009. Hydro-geochemical evolution of an uncapped gold tailings storage. In: Wiertz, J., Moran, C.(Eds.), Proceedings of the 1st International Seminar on Environmental Issues in theMining Industry. Santiago, Chile.

Edraki, M., Forsyth, B., Baumgartl, T., Bradshaw, D., 2012. Geochemistry of tailings andseepage from three tailings storage facilities in Australia— uncapped, capped, and ac-tive tailings. Proceedings of the Life-of-Mine Conference, Brisbane, Australia,pp. 269–277.

Egiebor, N.O., Oni, B., 2007. Acid rock drainage formation and treatment: a review. AsiaPac. J. Chem. Eng. 2, 47–62.

Evangelou, V.P., Zhang, Y.L., 1995. A review: pyrite oxidation mechanisms and acid minedrainage prevention. Crit. Rev. Environ. Sci. Technol. 25, 141–199.

Fandrich, R., Gu, Y., Burrows, D., Moeller, K., 2007. Modern SEM-based mineral liberationanalysis. Int. J. Miner. Process. 84, 310–320.

Foster, A.L., Brown Jr., G.E., Parks, G.A., Tingle, T.N., 1998. Quantitative speciation of arsenicin mine tailings using X-ray absorption spectroscopy. Am. Mineral. 89, 553–568.

Franco, S., Kadletz, O., Stevens, R., Nguyen, X., Reid, M., Scougall, J., McLean, R.,Stutsel, M., Long, T., 2010. Strategic framework for managing abandoned minesin the minerals industry. Ministerial Council on Mineral and PetroleumResources (MCMPR), p. 44.

Gasparon, M., Smedley, A., Jong, T., Costagliola, P., Benvenuti, M., 2007. Acid mine drainageat Mount Morgan, Queensland (Australia): experimental simulation and geochemicalmodeling of buffering reactions. In: Cidu, R., Frau, F. (Eds.), IMWA Symposium: Waterin Mining Environments, pp. 433–436.

Giere, R., Sidenko, N.V., Lazareva, E.V., 2003. The role of secondaryminerals in controlling themigration of arsenic and metals from high-sulfide wastes (Berikul gold mine, Siberia).Appl. Geochem. 18, 1347–1359.

Goodall, W., 2008. Automated mineralogy in the prediction of acid rock drainage: acces-sible mineralogy using QEMSCAN. Proceedings of the 2008 Society for Mining, Metal-lurgy and Exploration (SME) Annual Meeting and Exhibit, Salt Lake City, Utah, UnitedStates.

Gore, D.B., Preston, N.J., Kirstie, A.F., 2007. Post-rehabilitation environmental hazard of Cu,Zn, As and Pb at the derelict Conrad Mine, eastern Australia. Environ. Pollut. 148,491–500.

Gray, N.F., 1997. Environmental impact and remediation of acid mine drainage: amanagement problem. Environ. Geol. 30, 62–71.

Harries, J.R., 1997. Acid Mine Drainage in Australia: Its Extent and Potential Future Liabil-ity. Supervising Scientist, Canberra (94 pp.).

Harris, D.L., Lottermoser, B.G., Duchesne, J., 2003. Ephemeral acid mine drainage at theMontalbion silver mine, north Queensland. Aust. J. Earth Sci. 50, 797–809.

Harvey, M.C., Schreiber, M.E., Rimstidt, J.D., Griffith, M.M., 2006. Scorodite dissolutionkinetics: implications for arsenic release. Environ. Sci. Technol. 40, 6709–6714.

Hudson-Edwards, K.A., Edwards, S.J., 2005. Mineralogical controls on storage of As, Cu, Pband Zn at the abandoned Mathiatis massive sulphide mine, Cyprus. Mineral. Mag. 69,695–706.

Hudson-Edwards, K.A., Jamieson, H.E., Lottermoser, B.G., 2011. Mine wastes: past, presentand future. Elements 7, 375–380.

Hutchison, B.J., Brett, D., 2006. Savage river mine — practical remediation works. 7th In-ternational Conference on Acid Rock Drainage (ICARD), pp. 810–819.

Irwin, R.J., Van Mouwerik, M., Stevens, L., Seese, M.S., Basham, W., 1997. Environ-mental Contaminants Encyclopedia Cadmium Entry. National Parks Service, Colarado,US 88.

Jambor, J.L., 1994. Mineralogy of sulphide rich tailings and their oxidation products. In:Blowes, D.W., Jambor, J.L. (Eds.), The Environmental Geochemistry of SulphideMine Wastes. Mineralogical Association of Canada, Short Course Series, 22,pp. 59–102.

Jambor, J.L., Dutrizac, J.E., Groat, L., Raudsepp, M., 2002. Static tests of neutralizationpotentials of silicate and aluminosilicate minerals. Environ. Geol. 43, 1–17.

Jambor, J.L., Dutrizac, J.E., Raudsepp, M., 2007. Measured and computed neutralizationpotentials from static tests of diverse rock types. Environ. Geol. 52, 1019–1031.

Krause, E., Ettel, V.A., 1988. Solubility and stability of scorodite: new data and furtherdiscussion. Am. Mineral. 73, 850–854.

Kwong, J.Y.T., 1995. Thoughts on ways to improve acid drainage and metal leaching pre-diction for metal mines. U.S. Geol. Surv. Water Resour. Rep. Invest. 95–4227.

Kwong, Y.T., Swerhone, G.W., Lawrence, J.R., 2003. Galvanic sulphide oxidation as ametal-leaching mechanism and its environmental implications. Geochem.Explor. Environ. Anal. 3, 337–343.

Liu, Y.G., Zhou, M., Zeng, G.M., Wang, X., Fan, T., Xu, W.H., 2008. Bioleaching of heavymetals frommine tailings by indigenous sulfur-oxidizing bacteria: effects of substrateconcentration. Bioresour. Technol. 99, 4124–4129.

Lottermoser, B.G., 2010. Mine Wastes: Characterization, Treatment and EnvironmentalImpacts, third ed. Springer-Verlag, Berlin Heidelberg.

Lottermoser, B.G., 2011. Colonisation of the rehabilitated Mary Kathleen uranium minesite (Australia) by Calotropis procera: toxicity risk to grazing animals. J. Geochem.Explor. 111, 39–46.

Lottermoser, B.G., Ashley, P.M., Lawie, D.C., 1999. Environmental geochemistry of the GulfCreek coppermine area, north-eastern New SouthWales, Australia. Environ. Geol. 39,61–74.

Lottermoser, B.G., Ashley, P.M., Costelloe, M.T., 2005. Contaminant dispersion at the reha-bilitated Mary Kathleen uranium mine, Australia. Environ. Geol. 48, 748–761.

Luís, A.T., Teixeira, P., Almeida, S.F.P., Ector, L., Matos, J.X., Ferreira da Silva, E.A., 2009. Im-pact of AcidMine Drainage (AMD) onwater quality, stream sediments and periphyticdiatom communities in the surrounding streams of Aljustrel Mining Area (Portugal).Water Air Soil Pollut. 200, 147–167.


http://refhub.elsevier.com/S0375-6742(13)00218-5/rf0370












































http://www.bom.com.au





























































































































Marescotti, P., Carbone, C., De Capitani, L., Greco, G., Lucchetti, G., Servida, D., 2007. Mineral-ogical and geochemical characterisation of open-air tailing and waste-rock dumps fromthe Libiola Fe–Cu sulphide mine (Eastern Liguria, Italy). Environ. Geol. 53, 1613–1626.

Moncur, M.C., Jambor, J.L., Ptacek, C.J., Blowes, D.W., 2009. Mine drainage from theweathering of sulfide minerals and magnetite. Appl. Geochem. 24, 2362–2373.

Mudd, G.M., 2005. An environmental history of uraniummining in Australia: a scientific re-view. Proceedings of the Australian Uranium Conference, Fremantle, WA, pp. 1–19.

Mudd, G.M., Patterson, J., 2010. Continuing pollution from the Rum Jungle U–Cu Project: acritical evaluation of environmental monitoring and rehabilitation. Environ. Pollut.158, 1252–1260.

Murciego, A., Álvarez-Ayuso, E., Pellitero, E., Rodríguez, M.A., García-Sánchez, A., Tamayo, A.,Rubio, J., Rubio, F., Rubin, J., 2011. Study of arsenopyrite weathering products in minewastes from abandoned tungsten and tin exploitations. J. Hazard. Mater. 186, 590–601.

Nordstrom, D.K., 2004. Modeling low-temperature geochemical processes. In: Drever, J.I.(Ed.), Surface and Ground Water, Weathering, and Soils. Treatise of Geochemistry:Elsevier Pergamon, Amsterdam, pp. 37–72.

Nordstrom, D.K., 2009. Acid rock drainage and climate change. J. Geochem. Explor. 100,97–104.

Paktunc, A.D., 2001. MODAN a computer program for estimatingmineral quantities basedon bulk composition: Windows version. Comput. Geosci. 21, 883–886.

Parbhakar-Fox, A.K., Edraki, M., Walters, S., Bradshaw, D., 2011. Development of a texturalindex for the prediction of acid rock drainage. Miner. Eng. 24, 1277–1287.

Parbhakar-Fox, A., Bradshaw, D., Lottermoser, B., 2013. Evaluating waste rock mineralogyand microtexture during kinetic testing for improved acid rock drainage prediction.Miner. Eng. 52, 111–124.

Plumlee, G.S., 1999. The environmental geology of mineral deposits. In: Plumlee, G.S.,Lodgson, M.J. (Eds.), The Environmental Geochemistry of Mineral Deposits Part A:Processes, Techniques andHealth Issues, Reviews in Economic Geology, vol. 6B. Societyof Economic Geologists, United States, Littleton, CO, pp. 71–116.

Savage, K.S., Tingle, T.N., O'Day, P.A., Waychunas, G.A., Bird, D.K., 2000. Arsenic speciationin pyrite and secondary weathering phases, Mother Lode Gold District, TuolumneCounty, California. Appl. Geochem. 15, 1219–1244.

Simpson, S.L., Batley, G.E., Chaiton, G.E., Stauber, A.A., King, C.K., Chapman, J.C., Hyne, R.V.,Gale, S.A., Roach, A.C., Maher, W.A., 2005. Handbook for Sediment Quality Assessment(CSIRO, Bangor, NSW). 126.

Skousen, J., Simmons, J., Ziemkiewicz, P., 2002. Acid–base accounting to predict post-mining drainage quality on surface mines. J. Environ. Qual. 31, 2034–2044.

Smart, R., Skinner, W.M., Levay, G., Gerson, A.R., Thomas, J.E., Sobieraj, H., Schumann, R.,Weisener, C.G., Weber, P.A., Miller, S.D., Stewart, W.A., 2002. ARD Test Handbook:Project P387A Prediction and Kinetic Control of Acid Mine Drainage. AMIRA, Interna-tional Ltd, Ian Wark Research Institute, Melbourne, Australia.

Smith, L.J., Neuner, M., Gupton, M., Moore, M., Bailey, B.L., Blowes, D.W., Smith, L., Sego,D.C., 2009. Diavik waste rock project: from the laboratory to the Canadian arctic.8th International Conference on Acid Rock Drainage (ICARD).

Smuda, J., Dold, B., Friese, K., Morgenstern, P., Glaesser, W., 2007. Mineralogical and geo-chemical study of element mobility at the sulphide-rich Excelsior waste rock dumpfrom the polymetallic Zn–Pb–(Ag–Bi–Cu) deposit, Cerro de Pasco, Peru. J. Geochem.Explor. 92, 97–110.

Stanton, M.R., 2005. Baseline laboratory studies of sphalerite (ZnS) dissolution: effects onaqueous metal concentrations and solubilization rates. In: Barnhisel, R.I. (Ed.), Pro-ceedings 22nd National Conference. American Association of Mining Reclamation,Breckenridge, CO, pp. 1155–1165.


Stanton, M.R., Taylor, C.D., Gemery-Hill, P.A., Shanks III, W.C., 2006. Laboratory studies ofsphalerite decomposition: applications to the weathering of mine wastes and potentialeffects on water quality. Paper presented at the 7th International Conference on AcidRock Drainage (ICARD), March 26–30, 2006, St. Louis MO. R.I. Barnhise. Published bythe American Society of Mining and Reclamation (ASMR), 3134 Montavesta Road,Lexington, KY, p. 40502.

Stanton, R., Gemery-Hill, P.A., Shanks, W.C., Taylor, C.D., 2008. Removal of zinc and tracemetal release from dissolving sphalerite at pH 2.0 to 4.0, Appl. Geochem. 23,136–147.

Stomberg, B., Banwart, S., 1999. Weathering kinetics of waste rock from the Aitik coppermine, Sweden: scale dependent rate factors and pH controls in large column experi-ments. J. Contam. Hydrol. 39, 59–89.

Tarras-Wahlberg, N.H., Nguyen, T.L., 2008. Environmental regulatory failure and metal con-tamination at the Giap Lai Pyrite mine, Northern Vietnam. J. Environ. Manag. 86,712–720.

Tauson, V.L., Babkin, D.N., Parkhomenko, Y., Menshikov, V.I., 2004. On the mechanism oftrace-element uptake during the hydrothermal growth of sulphide mineral crystals.Crystallogr. Rep. 49, 149–157.

Texeira, E.C., Rodrigues, M.L.K., Alves, M.F.C., Barbosa, J.R., 2003. Study of the geochemicaldistribution of heavy metals in sediments in areas impacted by coal mining. In: Locat,J., Galvez-Cloutier, R., Chaney, R., Demars, K. (Eds.), Contaminated Sediments: Charac-terisation, Evaluation, Mitigation, Restoration and Management Strategy Perfor-mance. Proceedings of the Second International Symposium on ContaminatedSediments (Quebec City, Canada, May 26–28, 2003). ASTM International, WestConshohocken, PA, pp. 72–86.

Tran, A.B.., Miller, S., Williams, D.J., Fines, P., Wilson, G.W., 2003. Geochemical and miner-alogical characterisation of two contrasting waste rock dumps— the INAPwaste rockdump characterisation project. 6th International Conference on Acid Rock Drainage(ICARD), pp. 939–948.

Tremblay, G.A., Hogan, C.M., 2001. Mine Environment Neutral Drainage (MEND) Manual5.4.2d: Prevention and Control, Canada Centre for Mineral and Energy Technology,Natural Resources Canada, Ottawa (352 pp.).

Unger, C., Lechner, A., Glenn, V., Edraki, M., Mulligan, D.R., 2012. Mapping and prioritisingrehabilitation of abandonedmines in Australia. Life-of-Mine Conference 2012, Brisbane,Australia, pp. 1–14.

Urbano, G., Melendez, A.M., Reyes, V.E., Veloz, M.A., Gonzalez, I., 2007. Galvanic interactionsbetween galena–sphalerite and their reactivity. Int. J. Miner. Process. 82, 148–155.

Van Eck, M., Child, R., 1990. Croydon gold deposits. In: Hughes, F.E. (Ed.), Geology andMineral Deposits of Australia and Papua New Guinea, the Australian Institute of Miningand Metallurgy, Monograph. , 14, pp. 979–982.

Vik, E.A., Bardos, P., Brogan, J., Edwards, D., Gondi, F., Henrysson, T., Jensen, B.K.,Jorge, C., Mariotti, C., Nathanail, P., Papassiopi, N., 2001. Towards a frameworkfor selecting remediation technologies for contaminated sites. Land Contam. Reclam.9, 119–128.

Weisener, C.G., Smart, R.St., Gerson, A., 2004. A comparison of the kinetics andmechanismof acid leaching of sphalerite containing low and high concentrations of iron. Int.J. Miner. Process. 74, 239–249.

White, W.W., Lapakko, K.A., Cox, R.L., 1999. Static test methods most commonly used topredict acid mine drainage: practical guidelines for use and interpretation. In:Plumlee, G.S., Lodgson,M.J. (Eds.), The Environmental Geochemistry ofMineral DepositsPart A: Processes, Techniques, and Health Issues, Reviews of Economic Geology, vol. 6A,pp. 325–338.






































































































Documents

Identification of acid rock drainage sources through mesotextural classification at abandoned mines of Croydon, Australia: Implications for the rehabilitation of waste rock repositories