Geological controls on refractory ore in an orogenic gold deposit, Macraes mine, New Zealand

Petrie, B. S.; Craw, D.; Ryan, C.G.

doi:10.1007/s00126-005-0467-y

Cited by 34 publications

(17 citation statements)

References 13 publications

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“…This association is so close that the gold commonly occurs encapsulated in As-bearing sulfide mineral grains at the micrometre or millimetre scale (Cathelineau et al 1989;La Brooy et al 1994;Petrie et al 2005). Whereas gold is commonly mined at grades B10 mg/kg, As concentrations in the same ore can be 100 or 1000 times higher (Bowell 1992;Petrie et al 2005;Salzsauler et al 2005). Hence, gold mines are commonly considered by environmental regulators to be highly contaminated with As, although since the As is entirely natural, the word 'contaminated' is inappropriate in this setting.…”

Section: Introductionmentioning

confidence: 96%

Climatic and compositional controls on secondary arsenic mineral formation in high-arsenic mine wastes, South Island, New Zealand

Haffert

Craw

Pope

2010

New Zealand Journal of Geology and Geophysics

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Recent and historic gold mines and mine wastes in the South Island of New Zealand have been exposed under a wide range of climatic conditions for up to 100 yr. The studied sites are in rain shadow areas east of the Southern Alps, and in wet areas west of the mountains. Arsenic concentrations in mine wastes are up to 20 wt% locally. The arsenic is primarily derived from arsenopyrite in gold-bearing ore, although roasting and oxidation of ore occurred at some mines. Arsenolite was a byproduct of roasting at two sites, and this was also discharged into mine wastes. Five secondary As minerals, scorodite, kankite, pharmacosiderite, zykaite, and bukovskyite, have formed in different mines and mine wastes during surficial oxidation and remobilisation. The minerals formed under different chemical and climatic conditions. Ferrihydrite with combined arsenate (up to 20 wt% As) occurs at all localities. Scorodite is the most common secondary As mineral, replacing arsenopyrite and/or arsenolite, and forming cement in mine wastes. Dissolution and precipitation of scorodite, which is strongly pH dependent, controls maximum dissolved As concentrations on a regional scale. Kankite has formed instead of scorodite in a persistently moist microclimate east of the mountains. Pharmacosiderite formed instead of scorodite on the 50 yr time-scale in mine tunnels at pH 7Á8. Pharmacosiderite is distinctly less soluble than scorodite in this groundwater setting at pH 7Á8, and apparently restricts dissolved As to B25 mg/L locally. Bukovskyite and zykaite form where dissolved sulfate concentrations are elevated and the host mine wastes are perennially damp.

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Section: Introductionmentioning

confidence: 96%

Climatic and compositional controls on secondary arsenic mineral formation in high-arsenic mine wastes, South Island, New Zealand

Haffert

Craw

Pope

2010

New Zealand Journal of Geology and Geophysics

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“…The HMSZ is different from other mineralised systems in east Otago because mineralisation accompanied contractional (thrust) deformation (angus et al 1997;Petrie & Craw 2005), whereas other principal gold-bearing systems (Fig. 1) occur in normal faults formed during regional extensional tectonics (McKeag & Craw 1989;MacKenzie & Craw 1993).…”

Section: Comparison To Hmszmentioning

confidence: 92%

“…1) and gentle (c. 15°) northeast dip subparallel to the pervasive foliation in the host schist (Teagle et al 1990;angus et al 1997). The shear zone has been described as a late metamorphic west-directed thrust zone, with abundant anastomosing shears, folds, and duplex stacks within the zone (Teagle et al 1990;Petrie & Craw 2005). The shear zone varies in thickness from 10 to 150 m measured perpendicular to the host schist foliation (Teagle et al 1990;Mitchell et al 2006).…”

Section: Regional Geologymentioning

confidence: 99%

“…3a). The metamorphic foliation has been deformed by syn-to late-metamorphic tight to isoclinal folds with rounded hinges and attenuated limbs (Petrie & Craw 2005), and fold hinges plunge gently southeastwards (Fig. 3a).…”

Section: Host Rocksmentioning

confidence: 99%

“…3a). These folds are most obvious in quartzofeldpathic horizons, where they cause local steepening of foliation and complex structure with disharmonic fold zones (Petrie & Craw 2005). …”

Section: Host Rocksmentioning

confidence: 99%

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Golden Bar gold deposit as an extension of the Hyde‐Macraes Shear Zone, east Otago, New Zealand

Jones

Craw

Norris

2007

New Zealand Journal of Geology and Geophysics

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The Golden Bar gold mine pit near Macraes, east Otago, was developed in Textural Zone (TZ) 3 of the Otago Schist, at least 100 m structurally up-section from the Hyde-Macraes Shear Zone. This study tests the hypothesis that the Golden Bar mineralised zone was an extension of the major Hyde-Macraes Shear Zone mineralisation system. The Golden Bar rocks have been extensively, but subtly, hydrothermally altered. Principal hydrothermal alteration effects are replacement of titanite by rutile, replacement of epidote by siderite and kaolinite, and addition of pyrite. Mineralised (gold-bearing) rocks within this hydrothermal alteration zone are volumetrically minor and include micaceous schist with disseminated pyrite and arsenopyrite, silicified micaceous schist, and quartz veins. The structurally lowest mineralised rocks occur in a well-defined foliation-parallel zone of black sheared rocks with abundant hydrothermal graphite and sulfide minerals. The top of the mineralised zone is defined by a duplex shear zone, c. 10 m thick, containing abundant silicified and sulfide-bearing schist that has been deformed into an imbricate stack. Between the lower shear and the upper duplex zone, shallow-dipping thick (metre scale) mineralised extensional quartz veins cut across schist foliation and extend for up to 60 m laterally. The Golden Bar mineralised rocks were emplaced during contractional deformation and this resulted in WNW-directed thrusting that controlled the formation of ore-grade zones. The deformation and mineralisation style at Golden Bar is essentially identical to that of the Hyde-Macraes Shear Zone that structurally underlies the Golden Bar zone. This inferred relationship between the Hyde-Macraes Shear Zone and Golden Bar mineralisation extends the overall structural thickness of this gold-bearing deformation zone to >250 m.

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Mining, Processing and Environment at Macraes

Craw

MacKenzie

2016

SpringerBriefs in World Mineral Deposits

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Geological controls on refractory ore in an orogenic gold deposit, Macraes mine, New Zealand

Cited by 34 publications

References 13 publications

Climatic and compositional controls on secondary arsenic mineral formation in high-arsenic mine wastes, South Island, New Zealand

Climatic and compositional controls on secondary arsenic mineral formation in high-arsenic mine wastes, South Island, New Zealand

Golden Bar gold deposit as an extension of the Hyde‐Macraes Shear Zone, east Otago, New Zealand

Mining, Processing and Environment at Macraes

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