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Shear-hosted base metal mineralisation at the DanaPeaks, Murchison Mountains, Fiordland, New ZealandA Allibone a , P Ashley b , D MacKenzie c & D Craw ca Rodinian Pty Ltd, Queanbeyan, NSW, Australiab Earth Sciences, University of New England, Armidale, NSW, Australiac Department of Geology, University of Otago, Dunedin, New Zealand

Available online: 22 Dec 2010

To cite this article: A Allibone, P Ashley, D MacKenzie & D Craw (2010): Shear-hosted base metal mineralisation at theDana Peaks, Murchison Mountains, Fiordland, New Zealand, New Zealand Journal of Geology and Geophysics, 53:4,271-294

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Shear-hosted base metal mineralisation at the Dana Peaks, Murchison Mountains, Fiordland,

New Zealand

A Allibonea*, P Ashleyb, D Mackenziec and D Crawc

aRodinian Pty Ltd, Queanbeyan, NSW, Australia; bEarth Sciences, University of New England, Armidale, NSW, Australia; cDepartment ofGeology, University of Otago, Dunedin, New Zealand

(Received 29 December 2009; final version received 26 May 2010)

Darran Suite dioritic, tonalitic and granodioritic plutonic rocks and schistose Loch Burn Formation volcaniclastic rocks in thecentral Murchison Mountains at the Dana Peaks have been affected by widespread biotite-sericite-chlorite-albite-quartz-pyrite9carbonate9epidote/clinozoisite9titanite/rutile9actinolite alteration. More intense, paler coloured sericite-albite-quartz-pyrite9carbonate alteration is concentrated along orange weathered shear zones. Alteration assemblages are transitionalbetween those commonly referred to as propylitic, potassic and phyllic. Altered rocks contain anomalous concentrations ofcopper, lead, zinc and silver over an area of c. 2.5�6 km. Metal concentrations 2�5 times those typical of Darran Suite plutonicrocks and the Loch Burn Formation are commonly associated with more extensive weak to moderate intensity alteration.Higher metal grades up to c. 0.5% copper, 1% zinc, 1.3% lead and 30 ppm silver are concentrated in or adjacent to the 1�5mwide, more intensely altered shear zones which contain entrained lenses of pyritised country rock, breccias and quartz9K-feldspar9chlorite9carbonate9hematite9tourmaline veins. Some mineralised rocks also contain traces of tungsten(2�7 ppm), arsenic (B5�35 ppm) and tellurium (0.2�5.4 ppm). Most samples lack detectable molybdenum (B3 ppm), gold(B0.004 ppm) or bismuth (B0.2 ppm), with atypical higher values (40, 0.03 and 50 ppm, respectively) generally restricted to themost intensely altered and/or deformed rocks. The mineralised rocks show a close spatial and temporal relationship with severalnarrow ductile shear zones that probably developed in the Early Cretaceous between c. 128 and 110Ma. Mineralised shear zonesform minor splays off larger shear zones that are part of a major intra-arc fault system, active along or near the boundarybetween inboard and outboard parts of the Median Batholith at this time. Traces of similar lead mineralisation are present at thehead of the Mid Burn c. 8 km to the northeast along strike on the same regional-scale fault system as the Dana Peaks locality.Fluids and metals are likely to have been derived from metamorphism of the Loch Burn Formation and/or adjacent plutonicrocks. A magmatic hydrothermal origin is considered unlikely as the metal assemblage lacks Mo, Bi, Au, Sn and W and theadjacent plutonic rocks probably crystallised several million years or more before alteration and mineralisation.

Keywords: copper; Dana Peaks; Dana Tonalite; Fiordland; lead; Loch Burn Formation; Murchison Intrusives; MurchisonMountains; Plateau Pluton; propylitic; pyrite; sericite; shear zone; silicification silver; zinc

Introduction

Basement rocks of the Fiordland region comprise a large

variety of plutonic and metamorphic rocks, many of which

formed in a subduction-related arc environment near the

paleo-Pacific margin of Gondwana during the Carboniferousand Jurassic-Early Cretaceous (Kimbrough et al. 1994; Muir

et al. 1995, 1998; Tulloch & Kimbrough 2003; Allibone et al.

2007, 2009a, b; Scott 2008; Scott & Palin 2008; Tulloch et al.

2009). Many well-known mineralised terranes, such as the

Ordovician-Silurian Macquarie Arc in eastern Australia(Walshe et al. 1995; Cooke et al. 2007; Glen et al. 2007)

and mineralised plutonic rocks of western North and South

America (Titley & Beane 1981; Seedorff et al. 2005; Sillitoe

2000), formed in similar settings around the margin of the

paleo-Pacific basin during the Phanerozoic. Such environ-ments are commonly highly prospective for intrusion-related

mineralisation of several styles (Thompson et al. 1999; Cerny

et al. 2005; Meinert et al. 2005; Seedorff et al. 2005).

The similar geologic setting of Fiordland and many cir-

cum-Pacific mineralised terranes suggests economic concen-

trations of metals should also be present in the Fiordland.Despite the apparently favourable geological setting for

mineral deposit formation, occurrences of mineralised rocks

in Fiordland are rare. The quartz veins that host historic

gold workings in Paleozoic metasedimentary rocks of south-

west Fiordland remain undated but may have developed

during metamorphism prior to Carboniferous plutonism in

the surrounding area between c. 356 and 349Ma (Williams

1974; Allibone et al. 2007; Tulloch et al. 2009). However,

minor mineralised veins hosted by Early Cretaceous gran-

itoids in this area (Gollan 2006) indicate some mineralisa-

tion in southwest Fiordland accompanied by Mesozoic arc

magmatism. Sub-economic concentrations of magmatic Fe,

Ti, Cr and Ni occur within some mafic-ultramafic layered

intrusions in eastern and central Fiordland (Main 1973;

Morrison 1973; Williams 1974; Codling 1977; Hancock

*Corresponding author. Email: rodinian@msn.com

New Zealand Journal of Geology and Geophysics

Vol. 53, No. 4, December 2010, 271�294

ISSN 0028-8306 print/ISSN 1175-8791 online

# 2010 The Royal Society of New Zealand

DOI: 10.1080/00288306.2010.498406

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1977). Weakly anomalous gold was detected in one mafic-ultramafic intrusion at Mt George during unsuccessfulprospecting for platinum group elements (Mitchell 1996).A syngenetic origin has been ascribed to isolated narrowbands of Fe, Cu, Pb and Zn-bearing sulphides within someearly Paleozoic metasedimentary rocks of Fiordland (Park1924; Williams 1974). Zones of patchy, weak, propyliticalteration with trace chalcopyrite in northeast Fiordland arethe only sign of possible porphyry Cu mineralisationdetected to date in Fiordland (Pirajno 1981). Other minorcopper occurrences in northeast Fiordland are related tometamorphism, not igneous intrusion (Craw et al. 1997). Tinas cassiterite has only been recorded as a detrital heavymineral in Cenozoic sedimentary rocks adjacent toFiordland (Hutton & Turner 1936).

Recent remapping of Fiordland by GNS Science duringthe QMAP project (1:250 000 scale) involved extensive newfieldwork and confirmed the general dearth of mineralisedrocks. In this paper we document the geologic setting,petrography, paragenesis and geochemistry of unusualhydrothermal base metal sulphide occurrences in the DanaPeaks area of the Murchison Mountains.

Regional geologic setting

The Fiordland region comprises the largest area of plutonicand medium- to high-grade metamorphic basement rocks inNew Zealand. The western and central parts of Fiordlandare underlain by Western Province metasedimentary rocksof Gondwanan affinity and the inboard part of the MedianBatholith emplaced between the Cambro-Ordovician (c. 500Ma) and Early Cretaceous (c. 115 Ma) (Fig. 1) (Mattinsonet al. 1986; Gibson & Ireland 1996, 1999; Hollis et al. 2003,2004; Tulloch & Kimbrough 2003; Allibone et al. 2007,2009a, b; Tulloch et al. 2009). The eastern third of Fiordlandis underlain by the outboard part of the Median Batholithemplaced between the Carboniferous (c. 340 Ma) and theEarly Cretaceous (c. 116Ma) (Fig. 1) (Kimbrough et al.1994; Muir et al. 1998; Mortimer et al. 1999; Scott & Palin2008; Allibone et al. 2009a). Inboard parts of the batholithintrude early Paleozoic metasedimentary rocks and clearlyhave an autochthonous relationship with early Paleozoiccontinental Gondwana. Outboard parts of the batholithappear to lack early Paleozoic metasedimentary basementand may be either autochthonous or allochthonous to theearly Paleozoic Gondwana continental margin (Scott2008; Allibone et al. 2009a). Minor amounts of Jurassic-Cretaceous metamorphosed andesitic and dacitic volcani-clastic rock, bedded epiclastic conglomerate, sandstone andsiltstone, and rare lavas included in the Loch Burn Forma-tion and Largs Group occur in the outboard part of theMedian Batholith in eastern Fiordland (Fig. 1) (Williams1978; King 1984; Blattner & Williams 1991; Ewing et al.2007; Scott et al. 2008).

The Dana Peaks are located in eastern Fiordland, inthe outboard part of the Median Batholith (Fig. 1). Themineralised zones are hosted by plutonic rocks of theJurassic-Cretaceous Darran Suite and volcaniclastic meta-sedimentary rocks of the Loch Burn Formation (Fig. 1)(Scott et al. 2008; Allibone et al. 2009a). U-Pb zircon datingby several methods indicates the Darran Suite in easternFiordland was emplaced between c. 230 and 128Ma (e.g.Kimbrough et al. 1994; Muir et al. 1998; Scott & Palin 2008;Allibone et al. 2009a). Loch Burn Formation rocks on theeastern side of the Dana Peaks were intruded by DarranSuite quartz diorite at 157.691.4Ma, indicating they weredeposited before this time (Scott et al. 2008).

Mineralised rocks are located within or adjacent to anetwork of ductile shear zones that likely form part of aregional-scale transpressional fault system active between c.128�105Ma. This fault system encompasses similar struc-tures on Stewart Island (Allibone & Tulloch 2008), theGrebe Shear Zone in southern Fiordland (Fig. 1; Scott 2008)and the Indecision and George Sound Shear Zones innorthern Fiordland (Klepeis et al. 2004; Marcotte et al.2005; Allibone et al. 2009b). Within Fiordland this trans-pressional fault system was active during c. 120�110Ma.Constraints on the age of this fault system include theminimum U-Pb zircon ages of affected plutonic rocks(Klepeis et al. 2004; Marcotte et al. 2005; Allibone &Tulloch 2008; Scott 2008) and Ar-Ar thermochronologicalstudies of micas and K-feldspar within deformed rocks(Scott 2008).

Methods

Initial field reconnaissance of the Dana Peaks area wascompleted in March 2006 and January 2007 during theQMAP 1:250,000 geological mapping program in Fiordland(Turnbull et al. 2010). More detailed mapping of the mostintensely altered and mineralised rocks was undertaken inFebruary 2009. The mineralised rocks are well exposed insteep gullies and buttresses across the Dana Peaks, provid-ing a continuous cross-sectional view from northwest tosoutheast (Fig. 2). Similar rocks are exposed on the nextridge crest to the southwest (Fig. 2). Intervening sides andfloors of most valleys and cirques are covered with scree andmoraine, so lateral extensions of mineralised zones can onlybe inferred (Fig. 2). Grid references refer to the NZMS260map series based on the 1949 New Zealand map grid.

Petrographic observations were made on 67 polished thinsections of representative rock types encompassing the leastaltered and least deformed to strongly altered, deformed andvariably mineralised with sulphides. Sample numbersprefixed OU are housed in the collection of the Departmentof Geology, University of Otago. Sample numbers prefixedP are housed in the PETLAB collection of GNS Science(http://pet.gns.cri.nz/).

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Fig. 1 Regional geology of Fiordland and location of the Dana Peaks in the Murchison Mountains, after Allibone et al. (2007, 2009a, b).Mineralised rocks at the Dana Peaks are hosted by plutonic and volcaniclastic rocks of the Darran Suite in the outboard part of the Median

Batholith.

Shear-hosted base metal mineralisation 273

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Fig. 2 Geologic map of the Dana Peaks area. Altered and mineralised rocks are located between shear zones on either side of the DanaPeaks. More intense alteration is localised along and adjacent to several narrower ductile shear zones between these two larger structures.Less intense pyrite-bearing propylitic-potassic alteration occurs over a wider area within the Dana Tonalite, Plateau Pluton and Murchison

Intrusives. Orientations of structural elements are summarised in lower hemisphere stereographic projections.

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A range of rock chip samples, 100�500 cm3 in size,reflecting the variety and intensity of alteration and miner-alisationwere assayed for a suite ofmetallic elements (Table 1)by SGS laboratories in Townsville, Australia. Gold concen-trations were measured using fire assay method FAA505.Concentrations of Cu, Pb, Zn, As, Sb, Mo, Bi and Ag weremeasured using inductively coupled plasma-atomic emissionspectroscopy (method ICP40Q) after sample dissolution in amixed acid digest (HF-HClO4-HNO3-HCl). Concentrationsof Sn, W and Te were measured using inductively coupledmass spectroscopy (method IMS40Q), again following thefour acid near total digest of the sample material.

Bulk rock major and trace element chemical data wereacquired for suites of variably altered specimens using fieldand laboratory X-ray fluorescence (XRF) techniques. Thelaboratory XRF data are listed in Table 2. Outcrop sampleswere analysed in the field using an Innov-X Systems XPD-4000 portable handheld XRF Analyser. This is a small,lightweight (B2 kg) field portable instrument that emitsX-rays generated from an internal X-ray tube. When asample is placed in front of the instrument’s window, ashutter opens and X-rays emitted from the tube are absorbedby the atoms in the sample. The electrons surrounding theseatoms then fluoresce and release energy that is reflected backand read by the unit’s detector. The detector measures thetotal counts received for a particular wavelength of energythat is specific to each individual element. The unit wascalibrated using Alloy Certified Reference Materialsproduced by Analytical Reference Materials International(ARMI), and the calibration verified using Soil CertifiedReference Materials produced by National Institute ofStandards and Technology (NIST). The excitation sourcefor this analyser is a 10�40 keV, 5�50 mA, W anode X-raytube and the detector is a thermo-electrically cooled Si PINdiode with a resolution of B280 eV. Measured elementsheavier than phosphorus mostly have detection limits in therange 50�150 ppm. The following precision ranges wereobtained: Fe 2�4% of the measured total, Ti 6�25%, Mn5�32%, Zr 4�27%, Rb 5�30%, Sr 3�20%, Cu 8�31%, Pb5�30% and Zn 6�30%. The outcrop was analysed by thehandheld XRF at c. 1 m intervals. Where possible, the leastweathered and flattest outcrop surface was used for analysis(a spot typically B2 cm diameter) but many surfaces wereirregular and moderately to highly weathered. Hand samplescollected in the region were analysed under similar condi-tions for direct comparison to the analyses obtained from theoutcrop. All samples were analysed using the unit’s soilanalytical mode, which was regularly calibrated with astandardisation clip supplied by the manufacturer. Analysistimes ranged from 15 to 30 s.

Host rocks at Dana Peaks

Mineralised rocks in the Dana Peaks area are hostedby parts of the Loch Burn Formation, Dana Tonalite,

Murchison Intrusives and Plateau Pluton (Fig. 2) (Alliboneet al. 2009a). The Dana Peaks themselves are underlain bythe Dana Tonalite which is separated from the MurchisonIntrusives immediately northwest of the Dana Peaks by athin sliver of Loch Burn Formation (Fig. 3). The PlateauPluton and Murchison Intrusives underlie areas southwestand west of the Dana Peaks, respectively. Altered andmineralised rocks extend eastwards as far as the shear zonewhich marks the western margin of the main extensive beltof Loch Burn Formation in the Murchison Mountains. Westof the Dana Peaks, altered and mineralised rocks locallyextend as far as the northwest shear zone (informal name)within the Murchison Intrusives.

Granodiorite from the Murchison Intrusives near thewestern margin of our study area was emplaced at c. 137Ma (Fig. 2) (Ramezani & Tulloch 2009; Allibone et al.2009a, TIMS U-Pb zircon). Loch Burn Formation south-east of the Dana Peaks is intruded by 157.691.4Madiorite, indicating deposition of the former before this time(Scott et al. 2008, LAICPMS zircon). The age of thePlateau Pluton and Dana Tonalite are unknown. However,marginal dikes of the Plateau Pluton cut more mafic partsof the Murchison Intrusives, implying that the former alsohas an Early Cretaceous or younger emplacement age. Therelationship between the Dana Tonalite and Plateau Plutonis unclear. They may be in intrusive contact, or twoslightly different phases of the same intrusive event.Regional descriptions of the Murchison Intrusives, PlateauPluton and Dana Tonalite are given in Allibone et al.(2009a) and of the Loch Burn Formation in Scott et al.(2008).

Loch Burn Formation

The 250m wide slice of Loch Burn Formation between theDana Tonalite and Murchison Intrusives immediately westof the Dana Peaks (Fig. 3) comprises deformed andaltered schistose rocks. Primary textures are commonlypreserved to varying degrees in less deformed domains1�5m across, between higher strain zones. Relict texturessuggest that matrix-supported coarse-grained volcaniclasticfragmental rocks are the dominant primary lithologies inthis part of the Loch Burn Formation. Coarse fragmentalrocks are accompanied by minor volumes of porphyriticdacite and finer grained sandstone and siltstone. Rem-nants of transposed bedding are locally discernible,principally as variations in the size and proportions ofrelict centimetre-decimetre scale clasts. The matrix con-tains abundant 0.5�2mm grains of plagioclase, porphyriticvolcanic rocks, rare quartz grains and finer grainedvolcaniclastic material. Possible volcanic rocks are plagi-oclase-phyric, rarely with quartz, and have a fine-grained,relatively felsic groundmass. While these rocks mightrepresent coherent lava, it is also possible that they arelarge clasts in a coarse fragmental rock. The bulk

Shear-hosted base metal mineralisation 275

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Table 1 Assay data for altered and/or mineralised samples of the Dana Tonalite, quartz-rich sulphide-bearing veins and sericite-albite-carbonate-quartz altered shears nearthe margins of the Loch Burn Formation on the western side of the Dana Peaks (Grid references and other sample data can be obtained from the online GNS science

PETLAB database; analytical procedure codes refer to methods employed by SGS laboratories; BLD: below level of detection)

Element Au Te Cu Pb Zn As Sb Mo Bi Ag Sn W

Method FAA505 IMS40Q ICP40Q

ICP40Q/

AAS41Q

ICP40Q/

AAS41Q ICP40Q ICP40Q ICP40Q ICP40Q ICP40Q IMS40Q IMS40QLower limit of detection 0.01 0.2 5 5 5 5 5 10 10 1 0.5 0.1Upper limit of detection 1000 1000 10000 10000 5000 10000 10000 100 1000 1000

Units ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm

Weak to moderately altered countryrock

P76233 BLD 0.2 71 20 192 35 BLD BLD BLD BLD 0.7 3.3P76234, epidote-rich alteration,pyrite veins, diorite protolith

0.03 0.8 555 41 208 5 BLD BLD 10 BLD 2 3.8

P76238 BLD BLD 15 32 209 BLD BLD BLD BLD BLD 1.6 2.5P76256, granite protolith BLD 0.4 26 40 82 BLD BLD BLD BLD BLD 5 2.1P76257, weakly altered leuco diorite BLD 0.3 31 17 95 BLD BLD BLD BLD BLD 1.6 2.5

Massive pods of strongly albite-carbonate� /-sericite altered rock

P76241, extremely strongly altered

country rock

0.03 0.2 114 4450 10010 24 BLD BLD BLD 2 2.2 3.9

P76227, strong alteration, mmsericite shears

BLD 0.3 41 67 241 30 BLD BLD BLD BLD 1.9 6.8

P76229, strong alteration, mmsericite shears, granitoid protolith

BLD 0.2 23 42 254 17 BLD BLD BLD BLD 1.8 3.9

Quartz vein samplesP76242, quartz vein with galena BLD 5.4 11 13740 68 BLD BLD BLD 50 27 BLD 0.5P76252, quartz vein with pyrite,

chalcopyrite, and sphalerite

BLD BLD 1140 41 3270 BLD BLD BLD BLD BLD BLD 0.5

Sericitic shear zones

P76251, sericitic shear zone BLD 1.7 19 419 220 BLD BLD BLD BLD BLD 1.2 2.3P76253, sericite quartz pyrite shearzone, with similar veinlets

BLD 0.5 25 211 641 BLD BLD BLD BLD BLD 1.9 4.2

P76258, sericite quartz shear andquartz vein

BLD 0.2 24 24 60 12 BLD 40 BLD BLD 4.6 4.7

Background 0.004 0.001�0.01 30�80 10�40 10�80 1�5 0.1�0.2 1�3 0.1�0.2 0.04�0.1 2�3 1�2

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mineralogyoftheLoch

BurnFormationsuggests

adacitic

protolith

.Chemicalanalyses

implyacompositio

nalrange

betw

eenbasaltic

andesite

anddacite,

with

dacite

most

widesp

read(Table2).

MurchisonIntrusives

Hornblende9

clinopyroxenediorite,h

ornblendequartz

dior-

iteandtonalite

arethemostcommonlith

ologies

inthearea

immediately

west

oftheDanaPeaks.Minorrela

tively

mafic,

hornblende-biotite-b

earinggranodiorite

andweaklyplagio-

clase

porphyritic

micro

diorite

makeuptherem

ainder.

Intrusivecontacts

betw

eenunitsrangefromsharptograda-

tional.Individualintrusionsrangefromdikesafew

deci-

metres

thick

tosmallplutonsthatcro

poutoverseveralsq

uare

kilometres.

Thecompositio

nalrangein

theMurch

ison

Intrusives

issim

ilarto

other

DarranSuite

rocksin

the

surroundingarea.However,

theproportio

nofdiorite

togranodiorite

ishigherattheDanaPeaks(Allib

oneetal.

2009a).Outsid

ethevariousshearzonesdescrib

edbelow,the

Murch

isonIntrusives

are

either

massiv

eoronly

weakly

foliated.

PlateauPluton

ThePlateauPluton(Allib

oneetal.2009a)southoftheDana

Peakscomprises

medium-grainedequigranularpaletonalite,

granodiorite

andminorgranite.

Outsid

ethevariousshear

zonesitismassiv

eandunfoliated.Granodiorite

atNZMS260

2085922E,5539620Ncontainsrareovoidenclavesofmicro

-diorite

similartosomefinergraineddikeswithinthenearby

Murch

isonIntrusives.

DanaTonalite

TheDanaTonalite

(Allib

oneetal.2009a)isweaklyaltered

andfractured

throughout,andisthemostpervasively

altered

unitintheDanaPeaksarea.Remnantsofweaklyporphyri-

ticto

equigranular,medium-to

fine-grained,subhedral-

euhedralplagioclasegrainsoccu

rwidely

withintheDana

Tonalite.

Atonalitic

compositio

nissuggested

bythehigh

modalproportio

nsofplagioclase

andgenerallack

of

prim

ary

K-feld

spar.Subordinatequartz

diorite

andrare

granodiorite

arealso

presen

t.Minorprim

ary

biotite

and

traces

ofhornblenderem

ainintheleastaltered

samples

but,

elsewhere,

prim

ary

mafic

minerals

havebeen

pseu

do-

morphed

byphyllosilica

tes,epidote,

carbonate,

pyrite

and

titanite.

Rhyodacite

andmicro

granitoiddikes

Murch

isonIntrusives

northwest

oftheDanaPeaksare

locally

cutbyporphyritic

rhyodacite

andmicro

granodiorite

dikes2�20macro

ss.These

dikesaregenerally

parallel

tothefoliationbutarethemselv

esalso

stronglyfoliated.They

containplagioclasephenocrysts

inrecry

stallised

andaltered

Table 2 Laboratory XRF analyses of the Dana Tonalite and Loch Burn Formation. Major element compositions are reported as wt% values. Trace elements (As�Zr) arereported as ppm

Pluton Rock type Sample SiO2 TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O P2O5 LOI Total As Ba Ce Cr Cu Ga La Nb Nd Ni Pb Rb Sc Sr Th U V Y Zn Zr

Murchison Intrusives microdiorite OU80669 64.20 0.71 16.52 4.59 0.18 1.51 2.84 6.02 2.83 0.36 1.08 100.84 0.5 736 70 4 2 19 27 9 27 3 19 78 7 461 13 4 59 23 199 255

Dana Tonalite leuco-granodiorite OU80681 72.00 0.31 14.39 1.81 0.06 0.69 1.48 4.06 4.01 0.09 1.34 100.24 0.5 597 59 5 516 16 26 4 17 7 36 113 2 321 22 5 31 15 87 166

Dana Tonalite sheared zone OU80671 71.51 0.59 15.74 1.87 0.07 0.44 0.14 3.52 4.78 0.15 1.59 100.40 0.5 1216 43 2 41 25 25 15 19 4 1241 142 5 90 17 3 36 17 242 352

Dana Tonalite biotite tonalite OU80670 61.45 0.82 16.56 6.05 0.12 2.12 4.23 4.18 3.00 0.25 1.92 100.70 0.5 726 49 5 16 19 15 4 20 4 15 88 11 545 9 3 105 24 76 162

Dana Tonalite tonalite OU80677 64.43 0.75 15.91 4.58 0.42 0.80 0.60 3.87 5.43 0.29 2.91 99.99 1 1476 89 1 21 18 50 14 41 6 535 135 6 162 12 4 44 23 689 110

Dana Tonalite tonalite OU80672 63.00 0.65 16.57 3.70 0.28 1.03 2.99 4.71 4.51 0.27 3.10 100.81 3 1299 66 2 4 20 31 11 25 2 20 107 7 347 13 3 50 22 160 132

Dana Tonalite quartz diorite-tonalite OU80680 57.24 1.05 18.51 6.06 0.09 3.73 4.28 3.58 2.16 0.25 3.22 100.17 0.5 368 36 20 16 20 1 1 11 11 25 74 21 712 8 1 242 17 77 70

Dana Tonalite tonalite OU80679 68.08 0.54 15.64 2.65 0.06 0.59 0.77 5.53 3.25 0.20 3.52 100.83 0.5 681 73 5 5 18 35 9 27 5 44 83 4 264 15 3 39 22 68 285

Dana Tonalite quartz diorite-tonalite OU80675 58.40 1.21 17.15 6.98 0.11 2.10 1.05 3.76 3.50 0.61 3.72 98.59 0.5 261 24 33 17 20 B1 2 10 12 23 39 19 677 6 1 256 14 88 75

Dana Tonalite tonalite OU80674 73.55 0.50 15.73 3.25 0.20 1.33 1.84 5.89 2.18 0.14 4.19 108.80 0.5 533 77 2 35 17 40 12 29 3 149 67 4 301 16 3 34 24 80 333

Dana Tonalite Porphyritic tonalite OU80678 60.05 0.63 17.06 4.41 0.26 1.74 2.13 4.03 3.93 0.22 5.53 99.99 0.5 888 64 1 35 21 30 7 27 3 38 116 7 279 11 3 77 18 92 216

Loch Burn Fm volcaniclastic OU80673 61.62 1.03 17.99 4.83 0.25 1.89 1.38 6.17 3.27 0.37 1.61 100.41 0.5 867 101 1 4 21 47 15 42 2 103 90 12 432 11 3 71 26 488 364

Loch Burn Fm Porphyritic volcaniclastic OU80666 50.74 1.44 19.34 11.17 0.32 4.40 2.97 3.56 3.33 0.49 3.00 100.76 2 1575 37 19 2 24 6 9 23 22 41 90 23 581 5 3 282 25 293 153

Loch Burn Fm Epiclastic sandstone OU80668 59.18 1.14 17.58 6.66 0.08 2.06 0.59 2.38 5.06 0.38 4.38 99.49 0.5 855 60 3 28 24 33 11 30 4 72 123 14 99 6 2 151 21 221 277

Loch Burn Fm crystal-lithic volcaniclastic OU80667 58.05 1.20 17.07 6.98 0.11 2.07 1.05 3.78 3.48 0.60 4.86 99.25 2 1331 117 3 12 24 64 15 53 2 19 100 12 162 6 3 153 26 218 305

Loch Burn Fm Plagioclase phyric volcanic OU80682 62.40 0.89 15.20 6.70 0.03 2.54 0.35 2.44 1.10 0.35 5.83 97.83 0.5 231 53 6 124 32 25 13 24 15 674 34 9 100 11 2 59 16 102 414

Shear-hosted

basemetalmineralisation

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groundmasses composed originally of plagioclase, K-feldspar, quartz, small amounts of ferromagnesian materialand FeTi oxide. Similar dikes cut plutonic and volcanicrocks in northwest Stewart Island (Allibone 1991), suggest-ing that the dikes in the Dana Peaks area are part of aregion-wide swarm emplaced late in the history of theoutboard part of the Median Batholith.

Shear zones

General characteristics of shear zones at the Dana Peaks

More strongly altered and mineralised rocks are localised inand adjacent to shear zones that occur throughout the DanaPeaks area (Figs. 2, 3), and all rocks in the Dana Peaks areahave undergone deformation and alteration of primaryminerals to some extent. Away from macroscopicallystrongly deformed zones, plutonic rocks tend to be massivewith well-preserved igneous textures and partially preservedigneous mineralogy. However, even apparently undeformedrocks in outcrop display evidence of incipient deformation,including partial recrystallisation and grain-size reduction ofcoarser igneous plagioclase and quartz and widespreadreplacement of ferromagnesian phases by chlorite, greenbiotite and pyrite.

The gradation from less to more deformed plutonic rocksis marked by an increase in the intensity and penetrativecharacter of the foliation. In weakly deformed plutonicrocks, secondary minerals tend to be concentrated alongirregularly shaped microshears and extensional fractures instrain shadows, commonly adjacent to coarser relict plagio-clase and secondary pyrite grains. The concentration ofaligned, elongated alteration minerals in microshears andstrain shadows indicates that secondary mineral growth wassynchronous with deformation.

In more strongly deformed plutonic rocks, coarser relictigneous plagioclase is reduced to isolated, irregularly shapedporphyroclasts surrounded by a fine anhedral mosaic ofquartz, albite and recrystallised/replaced ferromagnesianand FeTi oxide minerals. The foliation is defined by alignedphyllosilicates and elongated aggregates of epidote orcarbonate9quartz. The foliation commonly wraps aroundporphyroclastic plagioclase grains and their associatedpressure shadows. In the most strongly deformed rocks(whether of plutonic or volcaniclastic origin), irregular toelongated foliated masses commonly dominated by sericite/muscovite coalesce to form a penetrative planar shear fabric.Locally, these white mica-rich masses grade into planarbiotite-epidote9chlorite and carbonate-rich aggregates.

Where examined for this study, the shear zone at thewestern margin of the main body of the Loch BurnFormation in the Murchison Mountains (Fig. 2) is generallyunmineralised although minor pyrite occurs locally. Othersegments immediately east of the Dana Peaks that wereobserved from a distance have a rusty reddish colour,

suggesting that pyrite may be more common in these parts

of the shear zone. Several other locally mineralised ductileshear zones cut the Dana Tonalite, Plateau Pluton and

Murchison Intrusives (Figs. 2, 3), but the largest are theDana Shear Zone immediately west of the Dana Peaks and

the northwest shear zone (informal name) along the ridgebetween the Snag and Ettrick Burns (Fig. 2). They consist of

1�250m wide zones of foliated rock with a NNE�NE strikeand moderate to steep westward dips (Figs. 2, 3).

Dana Shear Zone

The Dana Shear Zone can be traced intermittently forc. 8 km along strike (Figs. 2, 3). Towards its northern end it

juxtaposes Dana Tonalite against dioritic rocks of theMurchison Intrusives. A 250m wide, 1�1.5 km long slice of

schistose LochBurn Formation is confined to theDana Shear

Zone between theMurchison Intrusives andDana Tonalite inthe centralDana Peaks (Fig. 3). Southwest of theDanaPeaks,

theDanaShearZone bifurcates into several subparallel 1�4mwide ductile shears several hundred metres apart, which cut

the Plateau Pluton (Fig. 2). Isolated outcrops of Loch BurnFormation on ridge tops several kilometres southwest of the

Ettrick Burn may mark southerly extensions to the Dana

Shear Zone (I. Turnbull pers. comm. 2008). The DanaShear Zone dips moderately to steeply towards the northwest

(Fig. 3), and a southwest-plunging obliquemineral elongationlineation is locally developed (Fig. 3). Altered andmineralised

rocks occur widely within and adjacent to the Dana Shear

Zone and in nearby narrower, less continuous, shear zones(Figs. 2, 3).

The Loch Burn Formation within the Dana Shear Zone

consists of variably foliated micaceous schist in whichseveral generations of foliation are recognisable (Fig. 4A).

An earlier metamorphic foliation defined by chlorite, sericiteand biotite is preserved in 1�10m scale, less-deformed

domains (Fig. 4A). The early foliation is cut by a spaced,anastomosing shear foliation that is also defined by chlorite,

sericite and biotite, and is generally subparallel to the

metamorphic foliation. The shear foliation is more intenselydeveloped within 1�5m wide zones where it dominates the

rock fabric (Figs. 4A, B). These particularly stronglyfoliated, locally protomylonitic, rocks contain elongated

aggregates rich in one or more of sericite/muscovite, biotite,

epidote, chlorite or carbonate. A marked increase in theamount of disseminated pyrite accompanied by traces of

base metal sulphides characterises the more intenselysheared zones. These form prominent orange-brown stained

elongated outcrops on steep faces on the western flanks ofthe Dana Peaks. A subordinate shear fabric locally cuts

across the prominent shear foliation but merges north-

westwards with the shear foliation itself (Fig. 4A). Laterbrittle faults lie subparallel to, but cut and disrupt, the

dominant shear foliation (Fig. 4C).

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Northwest shear zone

The northwest shear zone (Fig. 2) locally separates hetero-geneous Murchison Intrusives from Plateau Pluton granitoidrocks, but in the north the shear zone is located wholly within

theMurchison Intrusives. The northwest shear zone also dips

moderately to steeply northwest, and contains a widespread

west to southwest-plunging mineral elongation lineation.

Variably sheared rocks persist structurally down-section

Fig. 3 Detailed geologic map of the area around the Dana Peaks where altered and mineralised rocks are most common. Mineralisation hasaffected the Murchison Intrusives, Loch Burn Formation, Plateau Pluton and Dana Tonalite, particularly where these units are cut by the

Dana Shear Zone and adjacent narrower and less continuous shear zones. Orientations of structural elements in the Dana Shear Zone areshown in the lower hemisphere stereographic projection. The plunging nature of the most strongly mineralised rocks within the Dana ShearZone is indicated with an inset sketch section A-B.

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towards the Dana Peaks between the northwest and Dana

Peaks shear zones, where the two structures converge

(Fig. 3).Mineralised rocks extend as far as the northwest shear

zone where it is closest to the Dana Shear Zone (Fig. 2).

Further west, the northwest shear zone is flanked by

unmineralised massive plutonic rocks locally affected by

the patchy weak chlorite, epidote and sericite alteration

typical of much of the Murchison Intrusives (Allibone et al.

2009a).

Fig. 4 Outcrop scale geologic relationships between alteration, veining, and deformation. (A) Cross-section across the core of the DanaShear Zone within schistose rocks of the Loch Burn Formation in the region of NZMS260 2085250 5540360. (B) Outline of dismembered

quartz 9 K-feldspar 9 hematite veins within the Dana Shear Zone, at location indicated in (A). (C) Outcrop sketch of shear-relatedmineralised pod and veins and post-mineralisation faults at location indicated in (A).

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Minor shears and altered fractures within theDana Tonalite

Most outcrops of Dana Tonalite are cut by 1�2mm wide

sericite9chlorite9biotite seams spaced 1�10 cm apart.

These seams are progressively more common towards both

larger shear zones described above and smaller discontin-

uous 1�20m wide shear zones within the Dana Tonalite

itself. Although these smaller shear zones generally strike

northeast, discordant foliation surfaces at a high angle to

this also occur locally, resulting in intersecting and mutually

crosscutting structures (Fig. 5).

Alteration and mineralisation

Hydrothermal alteration and mineralisation were imposedon all rock types during and after development of the shearzones in the Dana Peaks area. Four principal styles ofalteration and/or mineralisation are recognised:

(1) disseminated sulphides and propylitic-potassic-phyllicalteration typical of shear zones and adjacent less-deformed rocks;

(2) pods of massive albite-carbonate altered rock withdisseminated sulphides which occur in and adjacent tosome shear zones;

(3) quartz-rich veins;(4) albite-carbonate-pyrite9sericite altered breccias.

All four styles occur in close proximity in some outcrops,

with gradation from one type to another. All four alteration

and mineralisation types apparently formed approximately

synchronously, although the breccias formed in the later

stages of the alteration process.

Alteration and mineralisation of shear zones and adjacentless deformed rocks

Hydrothermally altered rocks crop out over several square

kilometres in the vicinity of the Dana Peaks (Fig. 2).

Plagioclase was initially replaced by albite and subsequently

by one or more of sericite/muscovite, epidote, green biotite,

carbonate and chlorite. Most ferromagnesian phases have

been replaced by aggregates of one or more of sericite/

muscovite, epidote/clinozoisite, green biotite, chlorite, minor

pyrite, titanite and/or rutile and locally by carbonate. More

mafic protoliths such as diorite tend to contain larger

concentrations of biotite, chlorite and epidote, with minor

actinolite, rutile and titanite, whereas more felsic protoliths

commonly have a larger proportion of sericite/muscovite.

Pyrite is scattered through the matrix of altered rocks and is

the most common sulphide mineral. Trace amounts of

chalcopyrite form inclusions in pyrite in rare samples (e.g.

P76228). Secondary magnetite and tourmaline are rare and

apparently restricted to the altered rocks of the Loch Burn

Formation.The presence of biotite suggests alteration under biotite

grade metamorphic conditions similar to those documented

in the larger belt of Loch Burn Formation rocks immedi-

ately east of the Dana Peaks (Scott et al. 2008). The greenish

colour of biotite may reflect crystallisation under relatively

oxidising conditions, consistent with its common coexistence

with epidote.Undeformed and weakly deformed rocks generally

contain the assemblage albite, sericite, green biotite,

chlorite, epidote, carbonate, titanite and pyrite. As the

intensity of deformation increases the relative amounts of

epidote, chlorite and biotite decrease, whereas the relative

amounts of carbonate, sericite and pyrite increase. Mineral

(A) (B)

Fig. 5 Structural relationships between veins and foliations at the outcrop scale. (A) Equal area stereoplot showing the orientation of poles toquartz 9 K-feldspar 9 carbonate 9 chlorite 9 hematite 9 sulphide veins associated with altered and mineralised shear zones. (B) Equalarea stereographic projections showing the orientation of chloritic fractures and foliation surfaces within areas of weak propylitic-potassic

alteration.

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assemblages in the most intensely deformed rocks are

dominated by sericite, pyrite, quartz, and albite9carbonate.

carbonate. Increasing deformation intensity correlates

with a decrease in the diversity of alteration mineral

assemblages.Some more strongly altered shear zones appear

‘bleached’ and superficially could be described as ‘silicified’

or having phyllic (quartz-sericite-pyrite) alteration. How-

ever, generally there is little petrographic evidence of the

pervasive hydrothermal introduction of quartz, and all the

bleached rocks retain albite. Even in the most strongly

deformed and altered zones, hydrothermal alteration was

not completely feldspar-destructive. The pale colour is due

to the paucity of dark alteration minerals such as biotite and

chlorite. Definite silicification is only recognised at the

metre-scale, where relatively massive protolith material is

replaced by fine-grained quartz.K-feldspar forms narrow irregular rims and lobate

irregular patches that partly overprint older relict plagio-

clase grains in some samples of the Dana Tonalite.

K-feldspar may have formed during the final stages of

magmatic crystallisation from a tonalite-derived magmatic-

hydrothermal fluid or during the hydrothermal event

responsible for the later propylitic alteration. However, as

K-feldspar with this texture has not been observed in

plutonic rocks away from the zone of altered rocks at

Dana Peaks, it is interpreted as having formed during an

early stage of the same hydrothermal event as the more

extensive propylitic alteration.Some samples show textural evidence of more than

one phase of alteration. Rims and irregular patches of

K-feldspar which overprint relict plagioclase grains are cut

by micaceous microshears with propylitic and biotite

potassic alteration assemblages. Pyrite growth appears to

have spanned deformation. Early pyrite is surrounded by

anastomosing mica grains and strain shadow overgrowths of

silicate gangue minerals. Pyrite later grew across the fabric

in some microshears.Rock chip samples of undeformed and weakly deformed

Dana Tonalite and Murchison Intrusives diorite affected by

propylitic and biotite potassic alteration contain up to

550 ppm Cu, 40 ppm Pb, 210 ppm Zn, 35 ppm As and

0.03 ppm Au (Table 1). Minor chalcopyrite inclusions in

some pyrite account for some if not all of the Cu, and pyrite

is the likely host for As at concentrations above the few

parts per million typical of unaltered Darran Suite plutonic

rocks elsewhere in Fiordland and Stewart Island (Allibone

et al. 2009a). Rock chip samples of more strongly foliated

sericite-rich shears contain up to 420 ppm Pb, 640 ppm Zn

and 1.7 ppm Te (Table 1). Pb and Zn values higher than

those typical of unaltered Darran Suite rocks reflect the

presence of minor galena and sphalerite in the more strongly

altered and deformed rocks.

Massive albite-carbonate altered pods

Massive podiform zones of more intensely carbonate-albite9quartz-rich altered rock developed locally in andadjacent to more strongly sheared zones. These pods aregenerally no more than a few metres wide and 1�10m long,typically elongated parallel to the shear foliation in the hostrock. The pods are best developed in the strongly shear-foliatedLoch Burn Formation in the Dana Shear Zone (Figs. 3 and4A, C), but others occur adjacent to red-weathering shearswithin the Dana Tonalite. The margins of the pods arediffuse and irregular at the 1�10 cm scale. The pods formdistinctive erosionally resistant brown-weathered outcrops,the brown colour suggesting the carbonate has an ankeriticcomposition.

The pods contain 2�5% disseminated pyrite, much ofthe sphalerite and galena and a smaller proportion of thechalcopyrite found in the altered rocks at the Dana Peaks.Total volumes of base metal sulphides generally do notexceed c. 1%. Rock chip samples contain up to 114 ppm Cu,0.45% Pb, 1% Zn, 30 ppm As and 0.03 ppm Au (Table 1).Base metal sulphides within the strongly altered pods occuras disseminated individual grains, as 1�4mm sized blebscomprising several grains elongated parallel to the shearfoliation in the adjacent foliated rocks, and as inclusions inpyrite.

Veins

Irregular quartz veins cut across the host rocks in closeproximity to shear zones. The veins are typically gash-like,with tapering shapes that thin to sharp tips towards theshear zones. The veins have a wide range of orientations butfall into two general groups: veins subparallel to the shearfoliation and veins at a high angle to the shear foliation witha generally gentle ENE dip (Fig. 5A). The veins are mainlyhosted in less-deformed rocks on the margins of shear zoneswhere they cut the weakly developed shear foliation. Someveins that extend into the shear zones cut the shear foliationand are weakly deformed. Others are strongly deformed andwere boudinaged during progressive shearing (Fig. 4B).These relationships indicate that vein formation spannedat least the later stages of deformation.

Veins are dominated by coarse milky quartz with a rangeof subsidiary minerals including K-feldspar, chlorite, biotite,pyrite, Mn-bearing ankerite, and hematite. Rare galena,sphalerite, chalcopyrite and pyrrhotite are present insome veins (e.g., at NZMS260, 2085254 5540368). Chalco-pyrite and pyrrhotite occur as inclusions in sphalerite andthe base metal sulphides locally replace previously fracturedpyrite in the veins, suggesting mineralisation may haveoccurred in several stages. One vein also contains scatteredrosettes of tourmaline. K-feldspar-bearing veins are parti-cularly abundant in the Dana Shear Zone (Fig. 4B). Thepresence of K-feldspar in some of the earlier deformed veinssuggests it formed during early hydrothermal K-feldspar

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alteration of plagioclase rims in nearby tonalite. Rock chipsamples of vein material contain up to 0.11% Cu, 1.37% Pb,0.33% Zn, 5.4 ppm Te and 27 ppm Ag (Table 1). The Ag ismost likely contained in galena as no discrete Ag-richminerals were observed.

Breccias

Albite-carbonate altered breccias developed locally wherequartz veins and strongly altered rockswere intensely fracturedand cemented with carbonate, sericite and pyrite. Scatteredsmall (B1m long) zones of albite-carbonate-pyrite alteredbreccia occur in the most strongly sheared parts of the DanaShear Zone. The most spectacular breccia occurs in a 100mwide shear zone cutting the Dana Tonalite (Fig. 6B) where azone of altered tonalite and unmineralised but variablyschistose tonalite at least 20 m wide has been extensivelydisrupted into blocks 0.1�5m across. The whole breccia has

been cemented with sericite and coarse-grained clusters ofpyrite up to 5 cm across. Later cataclastic deformation hassubsequently affected both the breccia clasts and matrix.

Geochemistry

Laboratory and field XRF techniques have been used toascertain the affects of alteration on the bulk rock chemistryof the Loch Burn Formation and Dana Tonalite. Nounaltered specimens of either the Loch Burn Formation orDana Tonalite were found in the vicinity of the Dana Peaks.Accordingly, the chemistry of altered Loch Burn Formationrocks from the Dana Peaks area is compared to metamor-phosed Loch Burn Formation dacite and rhyolite sampled inthe Stuart Mountains c. 10 km to the north (Ewing et al.2007) and to Paterson Group andesite lavas of StewartIsland (Allibone 1991) which have been correlated with theLoch Burn Formation. The chemistry of the altered Dana

Fig. 6 Sketches illustrating the field relationships of strongly altered zones in variably foliated and brecciated Dana Tonalite: (A) intersectingminor shear zones; (B) brecciated zone with post-mineralisation cataclasis.

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Tonalite has been compared with that of several potential

correlatives of Carboniferous and Mesozoic age from

adjacent parts of Fiordland. These include the Jurassic

to Early Cretaceous Darran Suite (Murchison, Hunter

and Hanging Valley Intrusives, Cleughearn and Plateau

Plutons), minor probable Carboniferous rocks included in

the Hunter Intrusives, the Carboniferous William Granite

and the Carboniferous Lake Roxburgh Tonalite.Silica contents of the Dana Tonalite vary between c. 57

and 74% (Table 2). Similar ranges in silica content character-

ise many unaltered intermediate to granitic plutons and suites

of intrusives in the surrounding parts of Fiordland that may

be correlatives of the Dana Tonalite (Allibone et al. 2007,

2009a). Variations in the chemistry of the unaltered plutonic

rocks reflect igneous fractionation processes rather than

alteration, and much of the variation in the chemistry of the

Dana Tonalite may also reflect igneous rather than alteration

processes.Nb/Y ratios and Ga contents of altered Loch Burn

Formation rocks from the Dana Peaks (Table 2) overlap

fields typical of calc-alkaline andesitic rocks and more

alkaline trachyandesites (Winchester & Floyd 1977). This

is consistent with the relatively high K2O contents of

Paterson Group andesites (Allibone 1986), and those Loch

Burn Formation samples analysed by King (1984), some

of which classify as high-K dacite and high-K rhyolite.

The altered Loch Burn Formation dacitic rocks analysed

during this study also have relatively high K2O contents,

despite evidence that K was removed from these rocks

during alteration (see below). Dana Tonalite Nb�Y

contents of 16�37 ppm (Table 2) are typical of volcanic

arc granitoids formed along active continental margins

(Pearce et al. 1984) and of the surrounding Darran Suite

(Muir et al. 1998; Allibone et al. 2009a). Y contents of the

Dana Tonalite (14�24 ppm, Table 2) are higher than thosetypical of most Separation Point Suite rocks, c. 90% of

which contain B14 ppm Y. Dana Tonalite Sr/Y ratios are

also generally typical of the Darran rather than the

Separation Point Suite, but these may have been modified

during mobilisation of Sr associated with alteration (see

below).A Pearce Element Ratio (PER) approach has been used

to analyse the cause of variations in the major element

chemistry of the altered Dana Tonalite and unaltered

potential correlatives (Pearce 1968; Stanley & Madeisky

1994). This approach avoids the problem of closure caused

by the expression of elemental variations in whole rock

analyses as relative proportions or weight %. In order to

undertake a valid PER analysis, the samples being

compared should be from a single closely related suite of

rocks. At least one conserved element which is not involved

in the process(es) which have affected rock chemistry is

also required.

Conserved elements in the Dana Tonalite and Loch BurnFormation

Variations in the concentrations of several high fieldstrength elements in both the Dana Tonalite and LochBurn Formation were examined to test whether anyrepresent conserved elements. Molar plots of P2O5 versusTiO2 (Fig. 7) indicate that the two elements have generallymaintained the same relative concentrations during bothigneous fractionation and alteration. The trend defined byboth altered and unaltered rocks passes close to the origin ofeach plot, especially when analytical uncertainties in therelatively low concentrations of Ti and P are also consid-ered. Scatter at higher contents of both oxides is a featureof some Hunter Intrusives and Dana Tonalite samples(Fig. 7A), and likely reflects decoupling of the fractionationof P and Ti-bearing minerals in some less common rocksricher in both elements. The coincidence of most DanaTonalite samples with the dominant trend in P2O5/TiO2contents implies that both elements were conserved andtherefore either can be used as the denominator in PERplots.

Alteration of the Dana Tonalite

Fig. 8 includes a series of chemical projections designed toillustrate the effects of igneous fractionation and alteration onthe bulk rock chemistry of the Dana Tonalite and possiblecorrelatives. Unaltered Jurassic-Cretaceous and Carbonifer-ous plutonic rocks from surrounding parts of Fiordlanddefine a clear trend parallel to that which would be expected ifvariations in the composition of these rocks were largelycontrolled by the fractionation or accumulation of feld-spar9biotite (Fig. 8A). Many less strongly altered specimensof the Dana Tonalite plot within this igneous fractionationtrend, implying their chemistry is still controlled by igneousfractionation. Alteration of these rocks was therefore largelyisochemical with respect to Ca, Na, K and Al. Other morestrongly altered samples of Dana Tonalite plot below and tothe right of this igneous fractionation trend and are char-acterised by compositions with excess Al over that containedin feldspar and biotite. Petrography (see above and Alliboneet al. 2009a) indicates that this Al is accommodated inmuscovite, as suggested by Fig. 8A. More intense alterationof the Dana Tonalite therefore appears to have resulted in anincrease in the amount of Al relative to K, Na and Ca. Thisimpression is reinforced by Fig. 8B which indicates that theK contents of unaltered rocks are controlled by variations inthe amounts ofK-feldspar andbiotite, whereas theK contentsof more strongly altered parts of the Dana Tonalite arecontrolled by variations in the amount of muscovite. Fig. 8Cindicates that the Ca contents of unaltered rocks and lessstrongly altered parts of theDanaTonalite are comparable. Aminor variation in the Ca content of these rocks likely reflectslimited igneous fractionation of hornblende and titaniterather than anorthite in plagioclase (note scale difference

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between Fig. 8C and other plots in Fig. 8). More strongly

altered samples ofDanaTonalite are depleted inCa compared

to the range of Ca contents typical of igneous fractionation

processes. Depletion in Ca is inferred to reflect albitisation of

igneous feldspar during alteration. Although small amounts

of ankeritic carbonate are associated with alteration through-

out much of the Dana Tonalite, this carbonate does not

contain sufficient Ca to offset that lost during albitisation of

igneous feldspar. Fe�Mg contents of the Dana Tonalite and

possible correlative unaltered rocks remain consistent

(Fig. 8D). This implies that no additional Fe and Mg above

that already present in the Dana Tonalite was required to

form pyrite, chlorite and ankerite during alteration.Isocon plots (Grant 1986) that compare the chemistry of

two more strongly altered Dana Tonalite samples with that

of an ‘average’ Darran Suite granitoid of similar SiO2content suggest removal of Ca and Sr and addition of Mn,

K, Rb, Pb, Zn and Cu during alteration (Fig. 9). Other

elements tend to scatter across the central axis of the isocon

plots without clear addition or removal during alteration.

The apparent addition of minor P and Ti to OU80677

(Fig. 9A) probably reflects a higher content of these two

elements in OU80677 than the hypothetical average Darran

Suite granitoid, rather than any net movement of P and Ti

during alteration. Addition of base metals is consistent with

the presence of galena, sphalerite and chalcopyrite in some

of the more strongly altered samples, including some

of those assayed by wet chemical techniques (Table 1).

Chemical analysis of other potential ore-related elements

within variably altered samples of the Dana Tonalite,

crosscutting quartz-rich veins, and sericitic shears indicate

that Au, As, Sn, W, Bi and Mo are not generally present at

values greater than those expected in intermediate to granitic

plutonic rocks (Table 1).

(A) (B)

Fig. 7 Ti and P contents of the (A) Dana Tonalite; (B) Loch Burn Formation (Table 2) and unaltered correlatives. Samples from both named

units tend to plot along lines that pass close to the origin, suggesting that P/Ti ratios remained constant during igneous fractionation andalteration and that both elements may have been conserved (see text for discussion).

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Alteration of the Loch Burn Formation

Pearce element ratio plots of Loch Burn Formation and

Paterson Group samples (Fig. 10) show trends indicative

of igneous fractionation of feldspar and/or biotite and

alteration to muscovite and chlorite. Paterson Group

andesites and the least-altered samples of the Loch Burn

Formation define separate trends, indicating that they

formed from different magmas whose evolution was

controlled by the igneous fractionation of feldspar9biotitebiotite (Fig. 10A). More strongly altered samples of theLoch Burn Formation contain larger amounts of Alrelative to Ca, Na and K than can be accommodated infeldspar or biotite, reflecting partial removal of the alkaliand alkali earth elements during alteration (Figs. 10A, B).One sample of Loch Burn Formation from the StuartMountains has a similar chemistry to the Dana Peakssamples, suggesting that it may also be altered or that

(A) (B)

(D)(C)

Fig. 8 Pearce element ratio plots showing variations in the chemistry of the Dana Tonalite and unaltered potential correlative plutonic rocks

based on laboratory XRF data in Table 2 and Allibone et al. (2009a) (see text for discussion). The hornblende compositional trends shownare for a ‘common’ hornblende composition (Deer et al. 1966) in which two moles of Al are accompanied by 2 moles of Ca and 4 moles ofFe � Mg. Note the larger scale used for plot C compared to plots A, B and D.

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greenschist facies metamorphism has locally mimicked theeffect of alteration on rock chemistry. This is consistentwith petrographic descriptions of Loch Burn Formationrocks in the Stuart Mountains which suggest metamorph-ism may not have been isochemical (Ewing et al. 2007).Some altered samples have Al/K ratios greater than thoseof muscovite. Variations in the ratios of Al to K, Ca andNa in these rocks suggest their high Al/K ratios are due tochlorite (Fig. 10B) rather than albite alteration (Fig. 10A).However, Fe�Mg contents are similar to those inunaltered rocks, implying little introduction of Fe andMg during alteration. Ca contents of most Loch BurnFormation samples are particularly low, probably reflect-ing the effects of plagioclase replacement by albite duringalteration and metamorphism.

Isocon plots (Grant 1986) that compare the compositionof more and less strongly altered samples of the Loch BurnFormation suggest that alteration involved the removal ofMn, Na, K, Ca, Sr, Ba and Rb and the addition of Pb, Cu,Mg and perhaps Fe (Fig. 11) (note Cu data is not availablefor sample 17758). Changes in major element contents arereflected in the relatively large amounts of chlorite asso-ciated with alteration.

Tape and compass traverse lines were established overtwo of the main mineralised shears in the Dana Shear Zoneand over a third shear zone hosted in the Dana Tonalite(MacKenzie et al. 2009). Results from one shear zonewithin the Loch Burn Formation are shown in Fig. 12.Elevated Rb/Sr ratios correspond to areas of greatersericite alteration within more intensely sheared rocks,suggesting removal of Sr relative to Rb during alteration.Areas of elevated Fe content correspond to some areas ofelevated Pb and Zn (Fig. 12). However, the Pearce element

ratio plots suggest that alteration is associated with little or

no introduction of Fe (Fig. 10). The apparent enrichmentin Fe recorded by the field XRF analyses probably reflectsconcentration of Fe in a 1�3mm thick zone along theoutcrop surface during weathering. Anomalous Pb and Zn

values may also be concentrated in supergene goethite atthis site. The field XRF technique is therefore capable ofidentifying thin zones of supergene enrichment on the

surfaces of rocks that might not otherwise appearobviously mineralised. Specimens of these rocks can thenbe collected in preference to other altered rocks which are

less strongly mineralised. Other higher Pb values between10�11m along the sample profile correspond to elevatedRb/Sr ratios implying galena is present within some areas

of stronger sericite alteration.

Discussion

Controls on the location of altered and mineralised rocks

Alteration and mineralisation are most intensely developedin the Dana Shear Zone where it bends c. 408 in strike andhosts a c. 1 km long by 200m wide wedge of Loch Burn

Formation schist (Figs. 2, 3). Alteration intensity dropstowards the northeast and southwest where the sliver ofin-faulted Loch Burn Formation schist pinches out. Outside

the Dana Shear Zone, the extent of alteration and miner-alisation in the Dana Tonalite and Murchison Intrusives isprobably controlled by smaller related faults, fractures and

shear zones. Some of these smaller structures may link theDana Shear Zone to the major shear zone on the easternmargin of the Dana Tonalite (Fig. 2) as they appear to be in

those parts of the Dana Tonalite and Murchison Intrusives

(A) (B)

Fig. 9 Isocon plots comparing the composition of two strongly altered Dana Tonalite samples (OU80677, OU80678) with an ‘average’Darran Suite rock, based on laboratory XRF data. The composition of the latter was obtained by calculating an average value for theconcentration of each element in laboratory XRF analyses of Darran Suite rocks in Allibone et al. (2009a) that fall within the range of SiO2contents typical of the Dana Tonalite.

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within c. 1 km of the bend in the Dana Shear Zone. They

may therefore have provided pathways for fluid between

shear zones on either side of the Dana Tonalite and within

the biotite zone Loch Burn Formation further to the east

(see below). The occurrence of hydrothermal mineral infill in

fracture networks and strain shadows is interpreted to

indicate that deformation and fluid flow were synchronous.Shear zones which control the location of altered and

mineralised rocks in the Dana Peaks area form part of a

regional-scale transpressional fault system active between

c. 128 and 105Ma throughout Fiordland and Stewart Island

(Marcotte et al. 2005; Allibone & Tulloch 2008; Scott 2008).

Within Fiordland, the age of this transpressional fault

system is more tightly constrained to between c. 120 and

110Ma by the minimum age of affected plutonic rocks

(constrained by U-Pb zircon dating, Klepeis et al. 2004;

Marcotte et al. 2005; Allibone & Tulloch 2008; Scott 2008)

and Ar-Ar thermochronological studies (Scott 2008).

Oblique southwest-plunging lineations in the Dana and

northwest shear zones (Figs. 2, 3) are oriented similarly to

those in the Grebe Shear Zone in southern Fiordland and

related structures on Stewart Island (Scott 2008; Allibone &

Tulloch 2008), supporting the inferred correlation of these

structures. Fluids responsible for alteration and mineralisa-

tion in the Dana Peaks area are therefore inferred to have

moved through a small segment of this regional-scale fault

(A)

(C) (D)

(B)

Fig. 10 Pearce element ratio plots of Loch Burn Formation and Paterson Group samples based on laboratory XRF data in Table 2 XRFanalyses in Ewing et al. (2007) and Allibone (1991). The hornblende compositional trends shown are for a ‘common’ hornblende

composition (Deer et al. 1966) in which two moles of Al are accompanied by 2 moles of Ca and 4 moles of Fe � Mg. (see text fordiscussion).

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system in the Early Cretaceous, after the onset of transpres-sional deformation in western New Zealand at c. 128Ma.The presence of altered rocks with galena near the shearzone which bounds the western side of the Loch BurnFormation in the Stuart Mountains c. 10 km north of theDana Peaks (Fig. 1) (Turnbull, unpublished data) suggestssimilar fluids were focused through other segments of thisfault system at this time.

Sources of metals and hydrothermal fluid

Some inferences as to the likely source of the hydrothermalfluid responsible for alteration and mineralisation at theDana Peaks can be made from field relationships andradiometric dating. Structural relationships imply thathydrothermal fluid circulation and metal transport occurredduring region-wide transpressional deformation in the EarlyCretaceous. Other studies have constrained the age of thisdeformation in Fiordland to between c. 120 and 110Ma (e.g.Klepeis et al. 2004; Marcotte et al. 2005; Scott 2008).Mineralisation at the Dana Peaks therefore also likelyoccurred during this time.

The chemistry of plutonic rocks in the Dana Peaks areaindicates that they are all members of the Darran Suite(Allibone et al. 2009a; Table 2), emplaced before c. 128Ma,rather than the younger Separation Point Suite which wasemplaced between c. 125 and 105Ma (Muir et al. 1998;Tulloch & Kimbrough 2003; Allibone et al. 2009a). TypicalDarran Suite rocks include a granodiorite from theMurchisonIntrusivesB1 km west of the Dana Peaks, which crystallisedat c. 137Ma (Allibone et al. 2009a), and diorite whichintruded the Loch Burn Formation southeast ofthe Dana Peaks at 157.691.4Ma (Scott et al. 2008). Thehydrothermal fluid responsible for alteration and mineralisa-

tion is unlikely to have been derived from the Dana Tonalite,

Plateau Pluton or the Murchison Intrusives as they all

probably crystallised before c. 128Ma, at least c. 8 Ma

before the onset of transpressional deformation synchronous

with mineralisation. This is consistent with the generally low

levels of Mo, Bi, Sn, Au andW (rarely above background) in

mineralised rocks at the Dana Peaks (Table 1). Elevated

levels of one or more of these elements would be expected in

granitoid-related systems.Metamorphosed Loch Burn Formation rocks juxtapo-

sed against the eastern side of the Dana Tonalite are an

alternative source of hydrothermal fluid derived frommineral

breakdown reactions during metamorphism. These rocks are

characterised by biotite zone, greenschist facies metamorphic

assemblages similar to alteration assemblages at the Dana

Peaks, albeit without the sulphide minerals present in the

altered rocks. The general similarity of alteration and

metamorphic assemblages is thus compatible with a meta-

morphic fluid source. Such fluids may have been able to

access rocks outside the main body of Loch Burn Formation

in the Dana Peaks area, where the structure of Early

Cretaceous transpressional shear zones is more complex.

Deposition of the minor amounts of base metal sulphides and

pyrite at these sites would have been prompted by decreases in

temperature and pressure during post-metamorphism stress

relaxation.A source for the base metals associated with the altered

rocks at the Dana Peaks remains undetermined. Possibilities

include the breakdown of igneous minerals in either the

Darran Suite plutonic rocks or in the Loch Burn Forma-

tion, or derivation from early disseminated volcanogenic

sediment-hosted base metal mineralisation in the Loch Burn

Formation (although no such mineralisation has yet been

(A) (B)

Fig. 11 Isocon plots comparing the composition of strong (OU80682) and weak (OU80666) altered Loch Burn Formation samples from the

Dana Peaks to an apparently unaltered Loch Burn Formation dacite lava (sample 17758) from the Stuart Mountains described by Ewinget al. (2007). The dacite lava has a silica content comparable to the dacitic volcaniclastic rocks in the Dana Peaks area.

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identified). Craw et al. (1997) describe chalcopyrite occur-

rences in northern Fiordland that they infer formed where

similar metamorphism affected Cu-rich mafic plutonic

rocks in the Plato Volcanics, east of the Median Batholith.

The Cu-rich character of these mineralised occurrences

compared to the Pb and Zn enriched Dana Peaks occur-

rences may be a reflection of a different source rock

chemistry, since the Plato Volcanics and minor related

intrusions have background Cu contents of 50�200 ppm.In contrast, although no Cu data is available for

unaltered Loch Burn Formation, two andesite lavas from

the correlative Paterson Group on Stewart Island contain 15

and 58 ppm Cu, respectively (Allibone 1991) and Darran

Suite plutonic rocks around Dana Peaks contain

B2�156 ppm Cu with most samplesB50 ppm Cu (Allibone

et al. 2009). Some of the superficially similar alteration in

plutonic rocks of the Darran Mountains in northeast

Fiordland (Pirajno 1981) may also have a metamorphic

origin. However, primary segregations of magmatic Cu

in mafic intrusive rocks in this area may be the source of

traces of Cu associated with hydrothermal alteration,

rather than the source being metamorphosed volcanic rocks.There are mineralogical and structural similarities

between the Dana Peaks shear-hosted alteration and

(A)

(B)

(C)

(D)

(E)

Fig. 12 Results of field traverses across altered and mineralised shears in the Dana Shear Zone using field-portable XRF (location in Fig. 4).

Sketch (A) shows rock types and chemical profiles (B�E) are at the same scale. Estimates of background (unmineralised) concentrations ofelements are indicated with ranges for the least-altered rocks (grey boxes).

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mineralisation and that of the sediment-hosted base metaland gold deposits of the Cobar district, New South Wales.In the Cobar district, large-scale hydrothermal fluid flux isinvoked from metamorphic basement and basin sourcesduring basin inversion, with strong focusing of fluid intohigh-strain structural sites where mineralisation subse-quently took place (Lawrie & Hinman 1998; Stegman2001). The alteration mineral assemblages at Dana Peaksare analogous to those found in many Cobar-type deposits(e.g. chlorite, sericite/muscovite, Fe-bearing carbonate,quartz and albite), although proportions vary probablydue to differences in host rock types (e.g. volcaniclasticsand granitoids versus fine-grained siliciclastic sedimentaryrocks). The sulphide mineralogy found at Dana Peaks isalso similar to that found in Cobar-type deposits, but theproportions of sulphide and amount of quartz9carbonateveining are considerably less at the Dana Peaks. This isinterpreted as reflecting lower fluid/rock ratios and perhapslower salinity fluids being involved at Dana Peaks.

The apparent lack of hydrothermal mineral deposits in muchof Fiordland

The apparent paucity of mineral deposits in Fiordland mayreflect its mid- to deep-crustal level of erosion throughout allbut the far southwest parts of Fiordland. Data in Tulloch &Challis (2000), Scott (2008) and Allibone & Tulloch (2008)suggest that Jurassic to Early Cretaceous plutons in theoutboard part of the Median Batholith (including the DanaPeaks area) were emplaced in the mid crust at c. 10�20 kmdepth. Many inboard parts of the Median Batholith furtherwest were metamorphosed at pressures of 12�18 kbar,implying depths of c. 50�70 km (Blattner 1976; Oliver 1977;Newton & Perkins 1982; Bradshaw 1989; Ireland & Gibson1998; Clarke et al. 2000; Daczko et al. 2001, 2002, 2009;Klepeis et al. 2004; Allibone et al. 2005, 2009b;De Paoli et al. 2009). Any porphyry, epithermal or otherintrusion-related hydrothermalmineral deposits related to thearc plutonic rocks which dominate Fiordland are likely tohavebeen removed by erosionduringuplift from these depths.

Mesothermal lode Au deposits in the far southwest cornerof Fiordland are the only economically significant metallicmineralisation found to date in Fiordland (Williams 1974).Metamorphic pressures in this part of Fiordland probably didnot exceed thoseunderwhich cordierite is stable (B c. 4 kbar at15 km depth, Pattison et al. 1999, 2002), and this may explainthe preservation of minor intrusion-related Au-base metalvein occurrences in the area (Gollan 2006).

In contrast, numerous porphyry Mo prospects asso-ciated with Early Cretaceous Separation Point Suite por-phyry plugs are preserved in less deeply eroded parts of theWestern Province in the northwest South Island, on theopposite side of the Alpine Fault to Fiordland (Tulloch &Rabone 1993). The widespread presence of Separation PointSuite rocks in Fiordland (Muir et al. 1998; Tulloch &

Kimbrough 2003; Allibone et al. 2007, 2009a, b) suggeststhat similar porphyry mineralisation may once have beenpresent in the Fiordland region before Cretaceous-Cenozoicuplift and erosion. Higher crustal level volcanic andhyperbyssal rocks potentially prospective for epithermaland porphyry-style deposits in Fiordland are now restrictedto the Loch Burn Formation and Largs Group (Williams1978; Mortimer et al. 1999).

Conclusions

Hydrothermally altered shear zones in the Dana Peaks areaof the Murchison Mountains, Fiordland, contain anoma-lous metal concentrations and are particularly enriched inPb, Zn and Cu. Hydrothermal alteration was structurallycontrolled by shear zones and the mineralogy and structuralstyle of mineralisation was partly controlled by host rocklithology, as summarised in Fig. 13.

The most prominent metalliferous alteration affected athin fault-bounded sliver of Loch Burn Formation juxta-posed between plutonic bodies on the Dana Shear Zone.The Loch Burn Formation contains schistose volcaniclas-tic rocks with propylitic-potassic alteration assemblages.Localised more intense alteration within this shear zone isdominated by sericite, albite and pyrite in 1�10m scale pods.Higher metal grades up to c. 0.5% copper, 1% zinc, 1.3%lead and 30 ppm silver are concentrated in or adjacent toseveral 1�5m wide intensely sericite-quartz-pyrite-alteredshear zones, in entrained lenses of silicified and pyritisedcountry rock, in breccias and in quartz9K-feldspar9chlor-chlorite9carbonate9hematite9tourmaline veins. Minera-lisation accompanied the development of a near-pervasiveshear foliation that lies subparallel to the pre-exisitingmetamorphic foliation in the Loch Burn Formation.

Darran Suite dioritic, tonalitic and granodioritic plutonicrocks have also been affected by propylitic-potassic altera-tion, with associated localised metal enrichment. Mineralisa-tion-related foliation development is less prominent inplutonic rocks, and shear deformation was dominated bycataclasis and brecciation. An early stage of potassic altera-tion in some parts of the Dana Tonalite involved growth ofpotassium feldspar rims on plagioclase grains.

Transport and deposition of fluids and metals in theDana Peaks area coincided with the development oftranspressional shear zones between c. 120 and 110Ma, atleast c. 8Ma after the emplacement of adjacent plutonicrocks. Mineralised shear zones are minor splays off largershear zones that form part of a major intra-arc fault systemactive along or near the boundary between inboard andoutboard parts of the Median Batholith at this time. Basemetals associated with the altered rocks may have beenleached and concentrated in fluids generated during thebreakdown of igneous minerals in either the Loch BurnFormation and/or the adjacent plutonic rocks as part ofshear zone-related metamorphism.

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Acknowledgements

This research was funded primarily by Foundation for Research,

Science and Technology via University of Otago. The mapping on

which part of this paper is based was also funded by the

Foundation for Research, Science and Technology under contract

CO5X0401 to the QMAP programme. Initial fieldwork was

assisted by James Scott who found the first piece of galena in the

Dana Peaks area. Comprehensive reviews by David Skinner and

Robert Scott resulted in many improvements to the paper. We

would like to thank Doc Sutherland, Gaven Burgess, Carol Brown

and Ian and Angela Buick of Southwest Helicopters and Kim

Hollows of Fiordland Helicopters for logistic support. Damien

Walls and Kat Lilley assisted with the collection of laboratory

XRF data. Brent Pooley provided polished thin sections.

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