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1 New Zealand Journal of Geology and Geophysics ISSN: (Print) (Online) Journal homepage: Mineralogy, geochemistry and origin of hydrothermal alteration and sulphide mineralization in the disseminated molybdenite and skarn-type copper sulphide deposit at Copperstain Creek, Takaka, New Zealand Antoni Wodzicki To cite this article: Antoni Wodzicki (1972) Mineralogy, geochemistry and origin of hydrothermal alteration and sulphide mineralization in the disseminated molybdenite and skarn-type copper sulphide deposit at Copperstain Creek, Takaka, New Zealand, New Zealand Journal of Geology and Geophysics, 15:4, , DOI: / To link to this article: Published online: 20 Jan Submit your article to this journal Article views: 248 View related articles Citing articles: 13 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 03 December 2017, At: 21:50

2 Nd MINERALOGY, GEOCHEMISTRY AND ORIGIN OF HYDROTHERMAL ALTERATION AND SULPHIDE MINERALIZATION IN THE DISSEMINATED MOLYBDENITE AND SKARN-TYPE COPPER SULPHIDE DEPOSIT AT COPPERSTAIN CREEK, TAKAKA, NEW ZEALAND ANTONI WODZICKI N.Z. Geological Survey, Department of Scientific and Industrial Research, Lower Hutt, New Zealand (Received 19 October 1971) ABSTRACT Overturned Paleozoic quartzo.feldspathic and pelitic schists, amphibole schists and calc-silicate rocks were regionally metamorphosed to the lower amphibolite facies and intruded by granodiorite near a major thrust fault during the Cretaceous. Ex tensive hydrothermal alteration and sulphide mineralization are associated with the grandodiorite intrusion. Alteration of the non-calcareous rocks resulted in the formation of an outer zone characterised by muscovite ± albite, and an inner zone characterised by microcline and muscovite; and in the addition of large amounts of potash and sulphur and minor amounts of molybdenum. Alteration of the calcareous rocks resulted in the formation of an outer zone characterised by tremolite-actinolite, epidote ± talc, an intermediate zone characterised by diopside, and an inner zone by andradite, magnetite ± hedenbergite; addition of large amounts of silica, iron oxide and sulphur and minor amounts of alumina and copper; removal of large amounts of lime and C02; and both redistribution and removal of some magnesia and ti tania. The mineralogy and oxygen isotope fractionation between co existing magnetite and quartz suggest that the temperature in the more intensely altered rocks reached at least 500 c. Factors which influenced localisation of sulphide mineralization were the presence of (1) a major fault, (2) calcareous rocks, and (3) a granitic intrusive exposed near its apex. INTRODUCTION The Copperstain Creek sulphide deposit occurs in the catchment of Copperstain Creek and the upper reaches of Mineral Creek. Both creeks are small tributaries of the Pariwhakaoho River, approximately 9 km northwest of Takaka (Fig. 1). The sulphide mineralization occurs largely in calc-silicate rocks and highly altered quartzo-feldspathic schists that have been intruded by small granitic stocks near a major reverse fault. The deposit comprises one of the larger areas of sulphide mineralization in New Zealand and is a good example of a skarn type of deposit. The deposit has been diamond drilled by Lime and Marble Ltd. and later by Kennecott Explorations (Australia) Pty Ltd., and the cores kindly made available by these companies have greatly assisted in the present study. N.z. Journal of Geology and Geophysics 15 (4): Gcology-ll

3 600 NZ. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 ISLAND o Post Paleozoic 1 I ~ Permian ~ Undifferentiated ~ Onekaka Schist ~ Arthur Marble LEGEND Ordovician-Silurian o 5 10 L ~I ~lkm ~;';~ I Bay Schist fitttil Cambrian ~ k V '\ ~I Granite Intrusives _ Thrust Faults FIG. I-Geological map, generalised after Grindley (1961), showing regional setting of Copperstain Creek area.

4 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 601 The mineralization at Copperstain Creek was first described by Bell et at. (1907), who reported a 15 m mineralized band extending along strike for about 240 m and "consisting of a highly pyritized altered schist and micaceous carbonate" containing some chalcopyrite. Williams (1965, p. 226) states that the mineralization straddles 300 m of stratigraphic thickness, and quotes an otherwise unpublished report written by Dr A. G. W. Whittle who considered that the sequence of rocks appear to be metamorphosed and metasomatised micaceous sandstones, impure marbles and basic igneous rocks, and that the sulphides within the metasediments are probably of sedimentary origin. The present study has shown that small granitic stocks intrude the metamorphic rocks and are genetically related to the sulphide mineralization. The paper describes the structure, mineralogy, petrology and geochemistry of the deposit. An attempt is made to define as far as possible, the physical and chemical conditions prevailing during alteration and mineralization. The origin of the deposit and the factors that appear to favour the localisation of mineral deposits of this type in north-west Nelson are discussed. REGIONAL GEOLOGICAL SETTING The mineralized zone near Copperstain Creek lies within a belt of Lower Paleozoic metamorphic rocks which strike approximately north-south, are overturned, and dip steeply to the west. The Pariwhakaoho River a,rea has been mapped by Grindley (1961; 1971), and a generalised geologic map is shown in Fig. l. According to Grindley (1971) the oldest rocks in this area ave the Bay Schists which crop out in the upper reaches of the Pariwhakaoho River, are late Middle to Upper Ordovician, and consist of dark, pelitic biotite and garnet bearing schists interbedded with occasional bands of quartzite. The Bay Schists are structurally underlain to the east by the Arthur Marble which is Upper Ordovician and consists of grey-white calcite marble with only minor impurities of quartz, phlogopite, tremolite-actinolite, talc and fuchsite. Further to the east, the Arthur Marble is structurally underlain by the Onekaka Schist which is Late Ordovician-Silurian and consists of pelitic garnet biotite schists, quartzites, amphibolites and, in the vicinity of Copperstain Creek, of calc-silicate skarns. Lenses of Arthur Marble occur along the Golden Bay Fault which cuts Onekaka Schist near Copperstain Creek. Grindley (1971) considers that movements along the fault was initiated prior to Lower Devonian, during. a period of northward thrusting and nappe formation in north-west Nelson. At this time Lower Paleozoic rocks of the Pariwhakaoho River area were folded into a recumbent syncline and the Golden Bay Fault was a low angle thrust along which Arthur Marble lenses were tectonically emplaced. Refolding of the rocks prior to the emplacement of the Karamea Granite resulted in the steepening of the Golden Bay Fault and the Lower Paleozoic rocks. On the Parapara Ridge, at the headwaters of the Pariwhakaoho River, the Bay Schists are unconformably overlain by Permian conglomerate, sandstone

5 602 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 and siltstone. The Permain rocks are metamorphosed to the same rank as the underlying Lower Paleozoic rocks showing that metamorphism is post Permain. Approximately 0.5 km east of Copperstain Creek the Onekaka Schist is intruded by a stock of garnet-bearing biotite-muscovite adamellite (Onahau Granite), which, according to Grindley (1971), is part of the Separation Point Granite and is probably Cretaceous. Several dikes, sills and small stocks (Richmond Hill Porphyry) intrude the Permain and Lower Paleozoic rocks, which Grindley (1971) considers have been contact-metamorphosed by the Onahau Granite and were probably intruded during the main deformational phase of the Rangitata Orogeny. Near Copperstain Creek similar intrusions are associated with the alteration, metasomatism, and sulphide mineralization described in this paper. GEOLOGY OF THE COPPERSTAIN CREEK AREA General Setting The geology of the Copperstain Creek-Mineral Creek area is shown on Fig. 2. The rocks have been divided into four main lithologic units, namely: marble, quartzo-feldspathic and pelitic schist, calc-silicate skarn and amphibole schist, and granodiorite. Except for the granodiorite intrusions these rocks have undergone,regional metamorphism. Associated with the intrusions is a zone of alteration and sulphide mineralization which occurs to the west of the Golden Bay Fault, and is elongated parallel to the strike of the fault and to the prominent foliation in the metamorphic rocks. In the following sections the structure, mineralogy and petrology of the regionally metamorphosed rocks and the intrusive rocks are described, and the mineralogical and chemical changes brought about during alteration are discussed. Regionally Metamorphosed Rocks The regionally metamorphosed rocks strike approximately north-south and dip steeply westward. Two foliations can be seen within the schistose rocks. The first foliation Sl, is roughly parallel to the bedding and dips between 30 and 80 west. A weak lineation L1, plunges approximately down-dip and is associated with the Sl foliation near the headwaters of Copperstain Creek. A younger foliation S2, strikes north-north-east, dips steeply, and is found in the lower reaches of Copperstain Creek and in the Pariwhakaoho River. Intersection of these two foliations gives rise to a second lineation L2 which plunges south at Rocks that occur both within and outside the altered area are the marble, quartzo-feldspathic and pelitic schist, and amphibole schist. The calc-silicate rocks are only present within the altered zone, where the effects of regional metamorphism have been strongly modified.

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7 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 603 Marble Marble occurs as north-south trending lenses near Copperstain Creek. It is white to pale grey, shows no sedimentary features, and in the upper reaches of Copperstain Creek, has a weak foliation which dips parallel to the Golden Bay Fault and to the S1 foliation in the Onekaka Schist. The marble consists predominantly of calcite and contains varying but minor amounts of quartz, phlogopite, and fuchsite. The calcite is coarse grained, equigranular, and commonly shows bent twin lamellae. The quartz and mica are finer grained and commonly occur along calcite grain boundaries. The mica flakes are often bent while the quartz grains have strong undulose extinction. The northern lens of marble is in fault contact with the Onekaka Schist and drill holes penetrating its western margin show that a brecciated zone occurs at the contact. The marble in the footwall of the fault has not been affected by the alteration found in the hanging wall, showing that some displacement post-dates igneous intrusion and the associated alteration. In the southern lens of marble, contacts with the Onekaka Schist have not been faulted after the emplacement of the granodiorite and the associated alteration. This contact is gradational over about 3 m, and part of the marble has been altered. The coarse crystalline marble is very similar to the Arthur Marble, which crops out towards the headwaters of the Pariwhakaoho River, and is correlated with it. It differs markedly from the calc-silicate skarn of the Onekaka Schist, which crops out nearby, in that it contains only minor silicates and has only been locally affected by alteration and sulphide mineralization associated with intrusion. Amphibole Schist Amphibole schists that have not been affected by the alteration and sulphide mineralization are present as a thick layer approximately 0.5 km west of the mapped area. They are dark green, medium to coarse grained, and have a well developed foliation and lineation. They are interbedded with minqr schist and quartzite, and in the altered area, with calc-silicate rocks. The amphibole schists consist of hornblende, plagioclase and minor biotite, epidote, sphene and ma~netite (Table 1, Fig. 3). The hornblende is pleochroic with X yellow, Y olive green, Z bluish green and IX = 1'638, (J = 1'650, Y = 1'665. It has a sieve texture containing inclusions of plagioclase. The plagioclase is An3Q and shows weak normal zoning. Biotite is pleochroic with X yellow, Y and Z brown, y = 1'622, and according to Rimsaite (1967, p. 35) contains 18% Fe as FeO. The amphibole sch;sts are in the amphibolite facies and comprise a conformable member within the Onekaka Schists. Quartzo-Feldspathic and Pelitic Schist Schists that have been subjected only to regional metamorphism, occur both east and west of the altered and mineralized zone near Copperstain Creek. The schists are interbedded with minor quartzite and amphibole Geology-9

8 0-0 ~ TABLE i-mineralogical modes (percent by volume) Acces- Retro- Alteration Mineral Olig Qtz Bio Musc Py Kfel Scap sory grade Minerals Minerals (a) Granodiorite '--< Transi- 0 tional be- e ~ tween {NO, Samples Apat Calc Z >- unaltered Range % tr 5 Zirc t"" rocks and Average % tr 5 0 Zone 1 "'l {NO, samples Apat Anal Q Zone 2 Range % tr-l tr Moly ttl Average % t"" (b) Peliti: a:1d quartzo-fe!dspathic schist >- Z :Mineral Stau Gar Chi Olig Qtz Epid Bio Musc Py Alb Scap Kfcl I::' Q Sph Chi ttl 0 {NO, Samples Tour "CI unaltered Range % O-tr Apat ::c >< Average % tr 2 tr 70 tr 15 Vl 12 {NO, Samples Sph Chab, Stil n Vl Zone 1 Range % O-tr tr Apat Thorn Average % 50 tr (No. Samples Sph Anal, Stil Zone 2 L Range % O-tr tr-30 tr-40 tr Apat Average % 50 tr Moly Z N 0 Cl -< ~ r... \h

9 (c) Amphibole schist Z 9 oh Mineral Bde Olig Qtz Bio Epid Sph Py Trem- Alb Scap Kfel Act t:) {NO, Samples Sph Chi unaltered Range % tr 2 Average % tr 2 {NO, Samples Sph Stil, Anal Zone 1 Range % tr-30 O-tr tr Natr I () Average % tr Calc 0 (d) Calc-silicate skarn Mineral Calc Qtz Epid Trem- Py Bio Talc Alb Olig Scap Kfel Dio Bed Gar Mag IJl Act C t'" Zone 1 '0 {NO, Samples Apat Stil Chab ::c Range % tr-l Sph Calc 6 ttj Average % rs=pi~ Sph Stil Anal 0 ttj Zone 2 Range % tr NatrChab. '0 Average % tr 2 tr 20 Calc 0 [j) No. Samples Chal Chi.::::; Zone 3 Range % tr-l0 tr Calc Average tr >-1 Abbreviations used: Act - actinolite, Alb - albite, Anal- analcite, Apat - apatite, Bio - biotite, Calc - calcite, Chab - chabazite, Chal- chalcopyrite, Chi - chlorite, Dio - diopside, Epid - epidote, Gar - garnet, Bed - hedenbergite, Bde - hornblende, Kfel - Kfeldspar, Mag - magnetite, Molymolybdenite, '" >- Musc - muscovite, Natr - natrolite, Olig - oligoclase, Py - pyrite, Qtz - quartz, Scap - scapolite, Sph - sphene, Stau - staurolite, StH - silbite, Talc - talc, Thom - thomsonite, Tour - tourmaline, tr - transitional, Trem - tremolite, Zirc - Zircon. ~ N n ~ '0 '0 ttj ~ >- >- '" G\ 0 VI

10 606 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL, 15 Mineral Oligoclase Quartz Biotite Muscovite Pyrite K feldspar 'ScapoI" Unaltered Granodiorite -1-- Zonet Zone 2.J _----- Pelitic Ouartzo.. Feldspathic Schist Staurolite Gamel Chlorite OUgoclase Quartz Epidote Biotite Muscovite Pyrite Albite" $capolite K feldspar Hornblende OHgoclase Quartz Biotite Epi~e Sphene F')rite TremoIite ACtinolite Alb.. ScapoIne K feldspa< -Calc.. "Quartz Epidote Tremoljte- Actinolite 0_ F')rite Biotite Talc Albite ScapoI" K feldspar [);opside ".00 Gamet Magnetite Unaltered -.- -f f Amphibole ~ ~ ~ '- 1-- Schist Zone 1 Zone 2 Zooe c~c ' ? I- --- FIG. 3-Mineralogical changes occurring during alteration of rocks in Copperstain Creek area.

11 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 607 schist, and in the altered area, with calc-silicate skarn. They are light grey to brown biotite schists, the more pelitic rocks containing garnet and occasionally staurolite porphyroblasts. Both the SI and S2 foliations are developed in the schists and where they occur together, the southward plunging lineation L2 is also present. The mineralogical mode of the schist is summarised in Table 1 and Fig. 3. Typical mineral assemblages present are: staurolite, almandine, biotite, muscovite, quartz, plagioclase; almandine, biotite, muscovite, quartz, plagioclase, chlorite; in the pelitic rocks, and biotite, muscovite, quartz, plagioclase, epidote, in the quartzo-feldspathic rocks. Staurolite, garnet, and some chlorite occur as subhedral porphyroblasts. The staurolite and garnet have a sieve texture and contain round inclusions of quartz which are frequently arranged in an S pattern suggesting that the crystals grew during SI deformation. The garnet has a unit cell edge, a = and n = 1"805 and according to Winchell (1958) is almandine-rich. Biotite is pleochroic with X yellow, Y, Z deep brown, y averages about 1'630 and according to Rimsaite (1967, p. 35) contains 21 % Fe as FeO. The micas have grown along both SI and S2 and impart strong foliation to the rocks. Plagioclase is approximately An 2o - 25 and is only rarely twinned. Some of the rocks have suffered mild retrograde metamorphism and garnet is partly altered to a fine grained inter growth of chlorite and biotite. The schists are in the staurolite zone of the amphibolite facies. They are conformable with the Arthur Marble towards the headwaters of the Pariwhakaoho River, but are in fault contact with it near Copperstain Creek. Granodiorite Intrusions The granodiorite occurs as small stocks and sills within the catchment of Copperstain Creek (Fig. 2). Most of the intrusive rocks have been strongly altered, but a few narrow sills cropping out towards the headwaters of the creek have escaped maj or alteration, and most of the original mineralogy and texture have been preserved. The less altered,rocks are dark grey, are distinctly porphyritic and, in the narrower sills, have a weak foliation parallel to the intrusive contacts. Occasional xenoliths of country rock are found in the granodiorite. The unaltered granodiorite consists dominantly of quartz, plagioclase, orthoclase, microline, biotite and muscovite and traces of zircon (Table 1, Fig. 3). It contains subhed.ral plagioclase (Au 25 ) and less commonly orthoclase, phenocrysts in a fine grained groundmass consisting of anhedral equigranular intergrowths of quartz, plagioclase and microcline, and subhedral micas with preferred orientation. The phenocrysts have weak normal zoning, while the ground mass plagioclase is homogeneous in composition. Biotite is pleochroic with X light yellow, Y and Z reddish brown, y = 1"630 and according to Rimsaite (1967, p. 35) contains 21% Fe as FeO. It contains tiny inclusions of zircon surrounded by strong pleochroic haloes.

12 608 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 The granodiorite intrudes the quartzo-feldspathic schists, amphibole schists and calc-silicate skarus. It was mostly intruded as sills parallel to the SI foliation, but the largest stock in the Moly Creek catchment has a definite cross-cutting relationship with the surrounding metamorphic rocks. The intrusive rocks have not been affected by either the SI or S2 foliation. Hydrothermal Alteration and Sulphide Mineralization Rocks that have undergone hydrothermal alteration and sulphide mineralization lie in a zone that runs roughly north-south through Copperstain Creek, parallel to the SI foliation in the metamorphic rocks and to the strike of the Golden Bay Fault. The granodiorite, the quartzo-feldspathic and pelitic schists, and the amphibole schists and calc-silicate skarus have been affected. Each of these rock types has been subdivided into two or three zones based on the nature of the hydrothermal alteration, which is described in the following sections and summarised on Table 1 and in Fig. 3. Granodiorite The alteration in the granodiorite has been divided into two zones. The less intensely altered zone 1, is largely restricted to sills in the upper reaches of Copperstain Creek and is characterised by minor secondary muscovite, pyrite and calcite. The secondary muscovite occurs as randomly oriented porphyro-blastic grains which have a sieve texture and contain inclusions of quartz. The muscovite grew largely at the expense of plagioclase, probably after the intrusive rock had solidified. Pyrite is disseminated throughout the rock, whereas calcite occurs largely as cross-cutting veinlets. The remainder of the intrusive rocks have undergone the more intense alt,eration of zone 2 which is characterised by secondary microcline and muscovite. The rocks have largely recrystallised, are medium grained and white to pale grey. The narrower sills still retain the original weak foliation. The larger intrusives have been fractured in an apparently random fashion, and the fractures filled with secondary quartz and sulphides. The dominant minerals are quartz, plagioclase, orthoclase, microcline, biotite, muscovite, occasional scapolite, minor pyrite and traces of apatite and molybdenite (Fig. 3 and Table 1). Primary quartz, microcline, biotite and muscovite remained stable during alteration. The biotite is lighter brown, however, and has an appreciably lower refractive indices (y = 1'593-1'610) than in the less altered intrusives, and according to Rimsaite (1967, p. 35) contains 9-14% Fe as FeO. Where the alteration intensifies, plagioclase has been increasingly replaced by secondary microcline, so that in the most strongly altered intrusive rocks no plagioclase remains. The groundmass is completely recrystallized and develops a granoblastic texture, whereas the microcline replacing some plagiocla~e phenocrysts retains the original phenocryst outlines. Fine grained muscovite partly replaces the orthoclase phenocrysts and the remaining plagioclase, while microcline remains largely unaltered. Scapolite is restricted to narrow sills adjacent to calcareous rocks, especially in diamond drill hole 1, where it replaces plagioclase. It co-exists with quartz, microcline, biotite and muscovite. It has e = 1'547-1'549, '" = 1'575-1'577, and approximates in composition to

13 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 609 Me 55 (Deer et al. 1963, Vol. 4, p. 329). Secondary quartz occurs along occasional veinlets often with minor pyrite. Euhedral to subhedral pyrite is also disseminated throughout the altered rock, while the minor amounts of molybdenite occur largely along joint and parting planes. Quartzo-Feldspathic Schists The schists in the altered zone are dominantly quartzo-feldspathic and no relict garnet or staurolite, typical of the pelitic lithology, weve seen. They have been divided into two alteration zones (Table 1, Fig. 3). Zone 1 is characterised by the presence of secondary muscovite ± albite, and occurs around the periphery of the altered area. The rocks are white to grey and still retain the original foliation. The dominant minerals in this zone are quartz, muscovite, biotite, pyrite, albite, occasional scapolite, while minor epidote, apatite and sphene are sometimes present (Fig. 3 and Table 1). Primary quartz, muscovite, biotite and epidote have remained stable during alteration. The biotite is lighter brown and has lower refractive indices (y = 1 610) than in the unaltered schists and, according to Rimsaiie (1967, p. 35), contains 14% Fe as FeO. Plagioclase is replaced by secondary muscovite, and in some instances by albite or scapolite. Muscovite has developed with cleavage parallel to the regional metamorphic foliation (Sl), so that it is difficult to distinguish secondary from primary muscovite. However, the marked increase in the abundance of muscovite in the zone 1 schists and the concurrent disappearance of plagioclase, shows that some has crystallized during the hydrothermal alteration. Albite occurs in about half the samples and is restricted to the outer periphery of the zone where it replaces plagioclase. Large sieved scapolite porphyroblasts with numerous round quartz inclusions replace plagioclase. Subhedral pyrite is disseminated throughout the schists, and also occurs with quartz in veinlets which are generally parallel to the Sl foliation. A 30 cm wide Ag-Pb-Zn lode occurs on the periphery of zone 1 schists approximately 500 m to the north of the mapped area (Fig. 1). The lode is parallel to the foliation in the schists and consists of quartz, sericite, pyrite, sphalerite and galena. Sphalerite and galena show a mutual boundary relation and were probably deposited together. Both replace the earlier formed pyrite. ' Zone 2 schist is characterised by the presence of secondary microcline and muscovite. It occurs near the core of the altered zone and is freguently in contact with the granodiorite intrusions. The rocks are white to light grey. Foliation originating during regional metamorphism can still be recognised in most samples, but because of more intense recrystallization it is not as strongly evident as in zone 1 schists. The dominant minerals in this zone are quartz, microcline, muscovite, b;otite and pyrite, while minor amounts of epidote, apatite and sphene also occur (Table 1, Fig. 3). Quartz, muscovite, biotite and epidote remain stable during zone 2 alteration. As in zone 1 the biotite is lighter brown and has lower refractive indices (y = ) than in the equivalent unaltered schists and according to Rimsaite (1967, p. 35) contains 8-141Jc

14 610 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 Fe as FeO. No plagioclase remains in these rocks and its place is taken by microcline which occurs in granoblastic intergrowth with CJuartz. As in zone 1, subhedral pyrite occurs together with secondary quartz in veinlets and also disseminated throughout the rock. Minor molybdenite occurs along joint surfaces near the larger granodiorite intrusions. Amphibole Schists and Calc-silicate Skarns These two rock types occur alon.'s a zone that runs approximately northsouth within the catchment of Copperstain Creek, west of the Arthur Marble lenses. They have undergone intense alteration which has strongly modified their mineralogy, texture and chemistry. The rocks are subdivided into three alteration zones based on mineralogical changes within the calc-silicate skarns. Amphibole schists, which are interbedded with the calc-silicate horizons, are restricted to the least altered zone. Zone 1 is least altered and is generally separated from granodiorite intrusions by mor,e intensely recrystallized rocks. It consists of interbedded amphibole schists and calc-silicate skarns, the latter comprising approximately 80% of the rocks in the zone. The amphibole schists are dark green, coarse grained and show a strong Sl foliation. They are characterised by actinolite-tremolite, epidote and in contrast to the calc-silicate rocks, an absence of calcite (Table 1, Fig. 3). Typical mineral assemblages in this zone are: actinolite-tremolite, epidote, pyrite (quartz), (albite), (biotite); actinolite-tremolite, epidote, pyrite, scapolite (quartz), (albite), (biotite); actinolite-tremolite, epidote, pyrite, scapolite, microcline, (quartz), (albite), (biotite). Of the minerals present in the regionally metamorphosed amphibolites, only quartz, biotite, epidote and sphene remained stable during alteration. The altered rocks are, however, much richer in epidote than the unaltered ones, and the biotite is much lighter brown in colour, and probably approaches phlogopite in composition. Taking the place of the hornblende are the low alumina amphiboles tremolite and actinolite, the former being the more common. Actinolite is very pale green and has a = 1'620, f3 = 1'630, Y = 1'649 and according to Deer et at. (1963, Vol. 2, p. 257) has a ratio Mg: (Mg + Fe+ 2 + Fe+ 3 + Mn) of approximately 0'75. Albite takes the place of oligoclase, though it is present in smaller quantities than in the unaltered amphibolites. Pyrite is disseminated throughout the rocks. Scapolite occurs as large porphyroblastic grains and has a birefringence of 0'025, and approximates in composition to Me 60 (Shaw 1960, p. 252). It contains numerous inclusions of tremolite or actinolite which remain orientated parallel to the original Sl foliation. Microcline occurs as porphyroblasts with inclusions of amphibole, and in pod shaped segregations with quartz and pyrite. The calc-silicate skarns in zone 1 are light to dark green depending on the ratio of calcite to dark minerals in the rock, and show a moderately strong Sl foliation. It is characterised by the presence of actinolite-tremolite, epidote, and occasionally talc in place of epidote and amphibole (Table 1, Fig. 3). In contrast to the calcite-free amphibole schists of this zone, the calc-silicates

15 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 611 do not contain any scapolite or microcline. Since the calc-silicate rocks do not occur outside the mineralized zone, their pre-alteration mineralogy is not known, but since the regional metamorphism reached the amphibolite facies, they may have contained diopside (Winkler 1967, p. 109). Typical mineral assemblages in this zone are: calcite, tremolite-actinolite, epidote, (biotite), (quartz), (albite), (sphene), (apatite) ; calcite, talc, pyrite, (quartz), (apatite), (sphene); calcite, talc, pyrite, magnetite, chlorite. The first assemblage is by far the most common, while magnetite and chlorite occur together in only one sample. Preferred orientation of the amphiboles and biotite and segregation of minerals into calcite, quartzepidote, and ferro-magnesian rich bands are parallel to the SI foliation. Tremolite and actinolite are present in approximately equal proportion but never in the same sample. The actinolite is pleochroic with X light yellow and Y and Z light green, has IX = 1'620, f3 = 1'631, Y = 1'648 and according to Deer et al. (1963, Vol. 2, p. 257) has a ratio of Mg: (Mg -+ Fe+ 2 + Fe+ 3 + Mn) of approximately 0'75. Epidote is colourless and has IX = 1'718, f3 = 1'728, Y = 1'736 and according to Deer et al. (1963, Vol. 1, p. 203) contains 16 mole percent Ca2Fe+3Si3012(OH). Biotite is pleochroic with X almost colourless and Y and Z very li~ht brown, and y = 1'592, which according to Rimsaite (1967, p. 35) indicates 8% Fe as FeO. Talc occurs as randomly orien1jed fine grained aggregates, but only in samples that do not contain tremolite-actinolite, epidote or albite, suggesting that it only formed in alumina-free rocks. Subhedral pyrite is disseminated throughout this zone. In Zone 2 the calc-silicate skarns are fine to medium grained, are li,ght to dark green, and are characterised by the presence of diopside (Table 1, Fig. 3). Samples containing only minqr diopside are foliated parallel to the SI foliation but intensely recrystallized rocks that contain a high proportion of pyroxene are massive. The diopside bearing rocks are restricted to the vicinity of DOH 1. To the north, east and west they are bounded by zone 1 calc-silicates, while to the south they grade into zone 3 calc-silicates. Typical mineral assemblages present in zone 2 are: calcite, diopside, tremolite-actinolite, epidote, pyrite, plagioclase, (quartz), (biotite), (sphene); calcite, diopside, tremolite-actinolite, epidote, pyrite, microcline, (scapolite), (sphene). Diopside occurs as large porphywblastic grains and often contains small inclusions of epidote. It is colourless, has IX = 1'668, f3 = 1'677, Y = 1'704, Z /\ c = 40 and according to Deer et al. (1963, Vol. 2, p. 62), is close to pure diopside in composition. The proportion of calcite, quartz and actinolite-tremolite decreases from zone 1 to zone 2, and the probable diopside-forming reaction is: tremolite + 3 calcite + 2 quartz = 5 diopside + 3 CO2 + H 20 Actinolite, epidote and biotite have similar optical properties in zones 1 and 2. Scapolite and microcline only occur immediately adjacent to feldspar

16 612 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 porphyry dikes which also contain these two minerals. Pyrite is disseminated throughout the zone. Zone 3 comprises the most intensely altered calc-silicate rocks in the area. It is characterised by the presence of garnet, ma,'snetite and occasionally hedenbergite (Table 1, Fig. 3). The rocks are white to pink depending on the ratio of garnet to quartz and calcite present. The rocks do not show any foliation, are medium to coarse grained, and have a patchy appearance due to the uneven distribution of garnet, epidote, magnetite etc. Typical mineral assemblages in zone 3 are: calcite, garnet, magnetite, pyrite, (epidote); calcite, garnet, magnetite, pyrite, hedenbergite, (epidote). In additioa 3 samples from DDH C-1 that do not contain garnet or ma,'snetite have been shown within this zone in Fig. 2 because the pyroxene present in these rocks is hedenbergite rather than diopside. Calcite, epidote and quartz remain stable in zone 3, but the proportion of epidote is considerably less than in zones 1 and 2, the proportion of calcite is less than in zone 1, while the proportion of quartz is considerably higher than in zones 1 and 2. The epidote is pleochroic in yellow, and has a = 1'730, {3 = 1-752, Y = 1'777 which are higher than in zones 1 and 2 and according to Deer et at. (1963, Vol. 1, p. 203) correspond to 30 mol percent CaeFeo+3Si301z(OH). The garnet is pink, has n = 1'84, a unit cell edge a = 12'015, and according to Winchell (1958) is andradite-rich. The hedenbergite is fine grained and generally partly altered to chlorite. The refractive indices are higher than for diopside in zone 2, it is light green, and has Z 1\ c = 49 and is probably ferrosalite-hedenbergite in composition. Pyrite and magnetite are disseminated throu,'shout the zone. Pyrite in places rims the magnetite, but no evidence for replacement was seen. Actinolite-tremolite is present only in minor quantities in three samples, suggesting that the stability limit of these minerals has been reached; a reaction of the type Ca 2 (Fe, Mg)5SisOn(OH)2 + 3CaCO:; + 2 SiOz = 5 Ca (Fe, Mg)Siz06 + 3C0 2 + HzO may have occurred. However, because the concentration of both iron and silica increases considerably from zone 2 to zone 3 (see later section) reactions of the type: 3CaCO~ + Fe 2 0:; + 2Si0 2 = Ca3FezSi~OlZ + 3C02 and/or + 4CaC03 2FeP3 + 2FeO 5Si0 2 = Ca~Fe2Si:;012 + CaFeSi Fe C0 2 (Deer et at. 1963, Vol. 1, p. 92) may also have occurred. In general, the calc-silicate rocks in the Copperstain Creek area are characterised by an andraditic garnet and pyroxene which varies in composition from diopside to ferrosalite or hedenbergite, and according to Zharikov's (1970) classification, are limy skarns. The scarcity of plagioclase, K feldspar and scapolite in the calc-silicate rocks in Copperstain Creek however, suggests that the activities of soda and potash were lower than in the limy skarns considered by Zharikov (1970).

17 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 613 Retrograde Alteration Minerals that crystallized after the climax of the alteration include calcite, quartz, chlorite and numerous zeolites. All rock types and alteration zones have been affected to some degree. Chlorite is most widespread in zone 3 of the calc-silicates. Here garnet in some samples is partly replaced by a strongly pleochroic bright green chlorite. Hedenbergite is very susceptible to alteration and more than 750/( of it is replaced by a pleochroic brown chlorite. Ferro-magnesians in other alteration zones have been unaffected by retrograde alteration. Quartz and calcite occur in cross-cutting vein lets and pods, often with zeolites and minor pyrite. Very often crystals are euhedral suggesting that the minerals grew in cavities. Zeolites are common in all the rock types except zone 3 calc-silicates, and their occurrence is summarised in Table 1. Generally, they occur in crosscutting vein lets, but stilbite often replaces scapolite and albite in zone 1 schists and amphibole schists. Post Alte-ration Faulting Five faults that post-date alteration and mineralization have been mapped in the Copperstain Creek area (Fi~. 2). One occurs along the western boundary of the northern lens of Arthur Marble and is marked by a 1-2 m brecciated zone wh;ch strikes north-south and dips W. The fault is parallel to the pre-devonian thrust along which Arthur Marble lenses were tectonically emplaced and subsequently steepened (Grindley 1971). It is probably part of the Golden Bay Fault as mapped by Grindley (1961). The brecciated zone separates zone 3 calc-silicate skarns frem unaltered Arthur Marble, showing that some displacement post-dates the alteration. A small thrust fault crops out near the southern end of the northern Arthur Marble lens. It dips 45 E and displaces both the unaltered Arthur Marble and the highly altered Onekaka Schist. Two steeply dipping faults that strike N 65 E crop out near the centre of the mapped area. Both have narrow crush zones (5-20 cm) and displace alteration zones in the Onekaka Schist and granodiorite intrusions. The displacement along both faults may have been either left lateral or downward on the north side with respect to the south side of each fault. However, because an exact matching of lithologies on either side of these faults is not possible they both probably have a considerable vertical component in their displacement. A near-vertical fault that strikes N 30 E also crops out near the c-entre of the mapped area, and is associated with an intensely fractured zone up to 10 m wide. It cuts the two N 65 E striking faults and displaces the Arthur Marble, the granodiorite and the Onekaka Schist with its alteration zones. It is the youngest fault mapped in the area. The Arthur Marble and the adjacent zone 3 calc-silicates can be matched quite closely on either side of the fault, suggesting that the displacement was predominantly right lateral.

18 614 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 CHEMICAL CHANGES DURING ALTERATION Partial chemical analyses of samples from various lithologies and alteration zones are shown in Tables 2 and 3 and the location of samples analysed for major elements is shown in Fig. 1 and 2. Silica, titania, alumina, iron oxide, magnesia and lime were analysed by X-ray fiuoresoence, and soda and potash were analysed by flame photometry. United States Geological Survey standard rocks were used as standards. Cu, Pb, Zn and Mo were analysed by Lime and Marble Ltd. and Chemistry Division DSIR, using atomic absorption and emission spectroscopy respectively, while sulphur analyses were done gravimetrically by Chemistry Division. Exact comparison of the chemical composition of different alteration zones is not possible because of the extremely heterogeneous nature of the various metamorphic rocks. However, it is possible to determine semi-quantitatively some of the major chemical changes that occurred during alteration, particularly where these have been accompanied by obvious changes in the mineralogical modes. TABLE 2-Chemical composition Total Approx. Alteration Sample SiO 2 TiO 2 AI.o 3 Fe as MgO CaO Na 2 0 K.O S CaC0 3 No. Fe (vol.%) (a) Granodiorite Unaltered Zone Zone Zone Zone Zone Av. Zone (b) Pelitic and Quar tzo.jeldspathic schist Unaltered Unaltered Av. Unaltered, Zone Zone Zone Zone Zone Av. Zone Zone Zone Zone Zone Zone Av. Zone

19 No.4 WODZICKI -COPPER SULPHIDE DEPOSIT, TAKAKA 615 TABLE 2-Chemical composition-continued Total Approx. Alteration Sample SiO. TiO. AI.O. Fe as MgO CaO Na.O K.O No. Fe,O. S CaCO. (vol.%) (c) Amphihole Schist Unaltered Zone Zone Zone Zone Zone Zone Av. Zone tr (d) Calc-siltcate Skarn Zone <0.05 Zone Zone Zone Av. Zone < Zone < Zone < Av. Zone < Zone <0.05 Zone Zone <0.05 Zone Zone < Zone <0.05 Zone Av. Zone < iwajor Element Distribution in Non-calcareous Rocks The non-calcareous rocks in the Copperstain Creek area include granodiorite, amphibole schist and the pelitic and quartzo-feldspathic schist. The trends of the chemical changes in these rock types are probably similar, but it is only from the pelitic and quartzo-feldspathic schists that the whole range of samples from completely unaltered to highly altered were available for study (Table 2). The concentration of silica, titania, alumina, iron oxide, ma,'snesia and lime in the schists do not appear to change greatly during alteration. The slightly lower silica and lime contents and the somewhat higher alumina, iron oxide and magnesia of zone 2 rocks may simply be a reflection of a slightly more pelitic nature of these samples.

20 616 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 TABLE 3-Average minor and trace element composition of alteration zones Alteration Length of drill hole intersection ppm % (in metres) eu Pb Zn Mo S (a) Granodiorite Zone (b) Pelitic and quartzo:feldspathic schist Zone Zone (c) Amphibole schist and calc-silicate skarn Zone Zone Zone Potash more than doubles in concentration in the altered rocks and this correlates WIth the formaci on of secondary muscovite in zone 1 and of secondary microcline in zone 2. Soda possibly decreases in concentration in zone 1, and increases again in zone 2_ In zone 1 the soda is largely present in albite and scapolite, while in zone 2 it is probably in scapolite and in solrd solution in the K feldspar. The concentration of sulphur increases markedly in the altered rocks and it is present largely in pyrite which is disseminated throughout the altered rocks. The decrease in the iron content of biotites during alteration suggests that pyrite may have formed by the reaction: Fe-rich biotite + sulphur = Fe-poor biotite + pyrite. No chlorine analyses were carried out, but the presence of occasional scapolite in the altered rocks shows that chlorine was added to the noncalcareous rocks. Major Element Distribution in Calc-silicate Skarns Chemical changes in the calc-silicate rocks are more intense than in the non-calcareous a'ssemblages, and by and large different elements have been affected (Table 2). Silica concentration increases considerably with increasing intensity of alteration, zone 3 containing twice as much silica as zone 1. This is accompanied by an increase in the ratio of silicates to calcite, and in zone 3, by a marked increase in modal quartz. Titania and alumina increase in concentration in zone 2 and then decrease again in zone 3. These changes are marked by the virtual disappearance of sphene in zone 3 and an increase in modal epidote in zone 2. Total iron increases markedly with increasing intensity of alteration, zone 3 containing three times as much total iron as zone 1. In zone 3 this increase can be correlated with the presence of iron-rich minerals such as andradite, hedenbergite, an iron-rich epidote, magnetite, and abundant pyrite.

21 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKi. 617 The concentration of magnesia possibly increases in zone 2 and then decreases markedly in zone 3, while calcium decreases with increasing intensity of alteration. This correlates with the high proportion of magnesium-rich minerals in zone 2 (tremolite-actinolite and diopside), the absence of magnesium minerals in zone 3, and a decrease in modal calcite from zone 1 to zone 3 (Table 1). Soda and potash remain uniformly low throu.<shout the alteration zones. This correlates with the almost complete absence of alkali-bearing minerals in the calc-silicate skarns. The concentration of sulphur increases markedly with increasing alteration. The presence of magnesium-rich minerals (tremolite, Fe-poor actinolite, talc, diopside) in zones 1 and 2, suggests that pyrite may have formed by a reaction of the type: Fe-rich silicate + sulphur = Fe-poor silicate + pyrite however, this is not possible to prove since no unaltered calc-silicate rocks are present in the area. No analyses have been carried out for carbon dioxide, but the decrease in modal calcite (Table 1) with increasing alteration shows that CO 2 has been lost from the system. Zonation of Ore Elements A strong correlation exists between the distribution of ore elements and the lithology and degree of alteration (Table 3). Thus molybdenum is concentrated in zone 2 of the granodiorite and to a lesser extent in zone 2 of the pelitic and quartzo-feldspathic schist, copper is concentrated in zone 3 and to a lesser extent in zone 2 of the calc-silicate skarns, and high concentrations of lead and zinc are only known in a Ag-Pb-Zn lode in the outer periphery of zone 1 schists. Vertical Zonation In addition to lateral zonation, there is evidence that vertical mineralogical and chemical zonation is also present in the Copperstain Creek area. If the interpretation that displacement along both the N 65 E striking faults has been down on the north, is correct, then each of the blocks A, Band C (Fig. 2) which are separated by these faults, represents a different depth at the time of granodiorite intrusion. Thus block A represents the shallowest exposed level where only narrow sills of granodiorite occur, block B an intermediate level where a thicker sill intrudes the metamorphic rocks, and block C the deepest exposed level where a small cross-cutting stock is found. The distribution of copper, lead, zinc, molybdenum and sulphur in the various litholo~ies and alteration zones in blocks A, Band C is shown in Table 4, while the probable pre-fault distribution of rock types, alteration zones, and copper and molybdenum mineralization is summarised in the diagrammatic cross-section in Fig. 4. In the schists, zone 2 is widely,developed in the deeper levels, while in the relatively shallow level exposed in block A it is very restricted. In the cajc-silic~te skarns. Z01lf> :1, Pf'"S;,ts in ~ 1t three levels, but zone 2 appears to be restricted to the highest level exposed.

22 618 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 TABLE 4-Minor and trace element composition of alteration zones in blocks A, B, and C (see Fig. 2 and text) Length of Alteration drillhole intersection ppm % (in metres) Cu Pb Zn Mo S Zone 1 Zone 2 Block A (a) Granodiorite (b) Pelitic and quartzo-feldspathic schist Zone Zone (c) Amphibole schist and calc-silicate skarn Zone Zone Zone Blo"k B (a) Granodiorite Zone 1 Zone (b) Pelitic and quartzo-feldspathic schist Zone Zone (c) Amphibole schist and calc-silicate skarn Zone Zone 2 Zone Blo"k C (a) Granodiorite Zone 1 Zone (b) Pelitic and quartzo-feldspathic schist Zone 1 Zone (c) Amphibole schist and calc-silicate skarn Zone 1 Zone 2 Zone

23 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 619 LEGE [Yl Granocilont calc Slhcal s i t B:::E Arthur rbl :-;::-. > 200ppm 1:-;::1> 3000ppmCu FIG. 4-Schematic vertical cross-section through Copperstain Creek area showing zones of high copper and molybdenum concentration. The concentration of lead and zinc remains rather uniformly low within the three blocks of the mapped area. Molybdenum is strongly concentrated in the gra'1odiorite stock and to a lesser extent in the adjacent zone 2 schists, in the deepest level exposed, but decreases markedly in concentration upward. Both copper and sulphur are concentrated in the two higher levels of zone 3 calc-silicate skarns, and decrease in concentration downwards towards the main granodiorite stock in block C. Metasomatic Transport Approximate estimates of the quantity of material transported during alteration are possible, provided that the following assumptions and condi tions are made: (a) Major and ore element analyses in Tables 2 and 3 give the approximate compositions of the various litholo:5ies and alteration zones. (b) Using the average element abundances in various crustal units of Turekian and Wedepohl (1961), the concentrations of copper, molybdenum and sulphur in unaltered schist are 30, 1, and 1300 ppm, in unaltered feldspar porphyry 30, 1 and 300 ppm, and in the unaltered calc-silicate 40, 1 and 700 pp respectively. (c) The major element composition of unaltered and zone 1 calc-silicates is the same. (d) The area between the upper reaches of Copperstain Creek and Mineral Creek where alteration has not been mapped, is left out of the calculation. (e) Amphibole schists within zone 1 of the calc-silicate skarns are ignored since they only comprise a small proportion of the total rock. (f) The specific gravities (based on the average modal composition and estimated specific gravities of minerals) of the granodiorite, schist, and zones 1, 2 and 3 of the calc-silicate skarns are 2-7, 2-7,3'0,3'1 and 3'3 respectively. Geology-IO

24 620 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 Based on the above, the weight of elements gained or lost from the various lithologies and alteration zones have been calculated and are shown in Table 5 and schematically in Fig_ 5. The most striking feature of the metasomatic changes is the marked difference in the mobility of elements in the calcareous and non-calcareous assemblages. In the non-calcareous rocks potash and sulphur, to a lesser extent soda, and to a minor extent molybdenum, were transported over considerable distances while the distribution of the other major elements and copper remained essentially unchanged. TABLE 5-Chemical changes (in tons per Vertical Metre) in the various alteration zones and in the whole mapped area Whole Total Rock Si0 2 Ti0 2 AI Fe as MgO CaO Na 2 0 K 2 0 S Cu Mo Fe (a) Granodiorite Zone Zone Zone2 390 (b) Pelitic and quartzo:feldspathic schist (c) Calc-silicate skarn Zone Zone Zone Total v > K 2 0 / IL '..!.:;.-j M~O Mo f - -'- '7--Ti02 1 V Y - --;. -I Cu I I ~+-->-- 8,02 I V V I I 1 Granodiorite y V Fe I I V y ~s-----l~s-'---l---s~~: ~ K 2 0 Calc-silicate skarn Pelitic and quartzofeldspathic schist zone 2 FIG. 5-Diagrammatic representation of metasomatic changes occurring during alteration.

25 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 621 In the calc-silicate skarns silica, iron oxide, lime, sulphur, possibly lesser amounts of alumina, magnesia and titania, and minor amounts of copper were transported over considerable distances, whereas, except for an addition in the immediate vicinity of some granodiorite dikes, the distribution of the alkalies remained unchanged. The marked difference in the mobility of elements in the calcareous and non-calcareous rocks probably reflects the composition of the hydrothermal fluids. In the calcareous rocks the fugacity of CO 2 was probably higher than in the non-calcareous rocks, while, in the non-calcareous rocks the common occurrence of scapolite shows that the C1- activity was significant. Burnham (1967) has shown experimentally that the ratio CO 2 /C1- strongly influences the solubility of elements in hydrothermal fluids. Where the CO 2 fugacity is high, the solubility of the alkalies is depressed to a far greater extent than that of silica and alumina, causing alkalies to remain immobile during silica and alumina metasomatism, while high C1- activity enhances the alkalies at the expense of silica and alumina. The present study would suggest that a high CO 2 fugacity may also en chance iron, titania, magnesia and copper solubilities, while high Cl- activity may also enchance the solubility of molybdenum, though experimental evidence for this is lacking at the present time. Direction of Migrtttion and Source of 'Mobile' Constituents Some of the chemical changes that occured during alteration can be accounted for by a redistribution of elements within the altered rocks. Thus referring to Table 5 and Fig. 5 titania and magnesia in the calc-silicate skarns may have been transported from zone 3 to zone 2, while soda in the schists may have been transported from the lower temperature region of zone 1 to the higher temperature region of zone 2, in accordance with the experimental findings of Orville (1963). Other constituents may have been lost from the altered rocks. Thus lime and carbon dioxide, which show a net decrease in concentration in zones 2 and 3 of the calc-silicate skarns, were probably transported out of the area of study, presumably by hydrothermal fluids. Silica, iron, sulphur, copper and possibly alumina in the calcareous rocks, and potash, sulphur and molybdenum in the non-calcareous rocks, however, show a net gain in the altered rocks and must have been introduced from an outside source. The most obvious source for these constituents is a crystallising magma, and the roughly zonal distribution of mineralogical and chemical changes round the intrusions, supports this possibility. The small stocks and sills cropping out in the Copperstain Creek area however, do not in themselves seem to be adequate sources for such large amounts of introduced material, and it is considered likely that the altered area is underlain by a larger intrusive body of granitic rock from which most of the introduced material was derived. Further evidence for the magmatic source of the hydrothermal fluids is the sulphur and oxygen isotope composition of hydrothermal minerals in the altered area.

26 622 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 TABLE 6-Sulphur isotope analyses Sample No. Rock Type Alteration Mineral 8 S" Granodiorite Zone 2 pyrite 1.4 ± Granodiorite Zone 2 pyrite Granodiorite Zone 2 pyrite 1.5 ± Schist Zone 1 pyrite 2.5 ± Schist Zone 2 pyrite Schist Zone 2 pyrite 1.4 ± amphibolite Zone 1 pyrite 1.6± amphibolite Zone 1 pyrite 1.5 ± calc-silicate Zone 2 pyrite 1.1 ± calc-silicate Zone 3 pyrite 0.3 ± calc-silicate Zone 3 pyrite 2.5±0.1 Av. pyrite 1.5 Ag-Pb-Zn lode Zone 1 galena -0.8 ± 0.1 in schist sphalerite 1.7 ± 0.3 pyrite 2.2 ± 0.3 Analyst: Dr T. A. Rafter, Institute of Nuclear Sciences, DSIR, New Zealand. The IlS'" values of the disseminated pyrite in the altered rocks are shown in Table 6 and the location of the samples in Fig. 2. The very minor variability of the results suggests a uniform sulphur source while the near zero IlS H values are generally considered to indicate a magmatic souroe. The oxygen isotope composition of calcite from the Arthur Marble, and calcite, quartz and magnetite from the altered calc-silicate skarns are shown in Table 7 and the location of the samples in Fig. 2. The values of quartz and magnetite from zone 3 calc-silicate skarns average 12'7% and 0'7% respectively. Assuming that the quartz and magnetite were in isotopic equilibrium with the hydrothermal fluid at c (the quartz-magnetite temperature, see next section), then according to the magnetite-water fractionation curves shown in Fig. 2 of Friedrichsen (1971) and the quartz-water fractionation curves in fig. 4.2 of Taylor (1967) the Il value of the hydrothermal water with which they coexisted was 9'4. This is close to the value for magmatic water, which according to Taylor (1967) varies between 7'5 and 9'0, thus supporting a magmatic origin of the hydrothermal fluid. CONDITIONS DURING REGIONAL METAMORPHISM AND ALTERATION Regional Metamorphism Experimental investigation of the stability of almandine (Hsu 1968) and staurolite (Hoschek 1969) indicate that the temperature during regional metamorphism was probably in excess of 500 c (Fig. 6), while the presence of chlorite in some almandine bearing rocks suggest that P-T conditions were close to the chlorite + quartz = almandine + vapour equilibrium (curve 1). According to the experimental work of Richardson (1968), the absence of chloritoid also suggests that the temperature was greater than

27 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 623 TABLE 7-0xygen isotope analyses relative to SMOW analytical precision +0.2% Sample No. Rock Type Alteration Mineral Il 0 1 " Arthur Marble not altered calcite calc-silicate Zone 1 calcite 12.7 quartz calc-silicate Zone 1 calcite 10.7 quartz calc-silica te Zone 2 calcite 11.9 oligoclase calc-silicate Zone 3 calcite 13.4 quartz 12.9 magnetite calc-silicate Zone 3 calcite 10.5 quartz 12.5 magnetite 0.1 Analyst: Dr I. Devereux, formerly of the Institute of Nuclear Sciences, DSIR, New Zealand. 8 (')~(31 7 FIG. 6-Experimentally determined reactions: I-Chlorite + quartz 6 ~ almandine + vapour (Hsu (4) 1968), 2-Chloritoid + silli.d -"" 5 manite ~ staurolite + quartz + vapour (Richardson 1968), ::J 4 3-Chlorite + muscovite ~ (/) (/) staurolite ~ + biotite + quartz ~ 0. + vapour (Hoschek 1969), 'U 3 (j 4-Staurolite + muscovite '5 + quartz ~ Al silicate + biotite "" 2 + vapour (Hoschek 1969). Shading indicates possible conditions of regional meta morphism DC 500 c. The pressure d~ring metamorphism is more difficult to estimate, but according to Richardson (1968), the absence of cordierite in the pelitic rocks su.ggests that the total pressure was greater than 3'5 kb. If this is so, then the temperature was probably about 550 c. Alte-ration Experimental data on the formation of talc (Metz 1970), diopside (Metz and Puhan 1970) and wollastonite (Greenwood 1962) are shown in Fig. 7, and make it possible to place some limits on the temperatures prevailing during alteration of the calc-silicate skarns and the adjacent schists. The mole fraction of CO 2 in the hydrothermal fluids is not known, but extreme high or low values are unlikely. Most of the metamorphic reactions that took place during alteration of the calc-silicates produced CO 2, but this was undoubtedly diluted considerably by water both from the diopside forming

28 624 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL i zone1 /',/ Zone 2 Zone 3 3o0L-----~----~~--~~----~O~ 8~--~1 0 Mole Fraction Xco2 FIG. 7-Isobaric equilibrium curves for the formation of talc, diopside and wollastonite: 1-3 dolomite + 4 quartz + 1 H20 ~ 1 talc + 3 calcite + 3 C02 (Metz and Puhan 1970), 2-1 tremolite + 3 calcite + 2 quartz ~ 5 diopside + 3 C H~O (Metz 1970), 3-Calcite + quartz ~ wollastonite + C02 (Greenwood 1962; Harker and Tuttle 1956). Shading indicates possible conditions during the formation of zones 1, 2, and 3 in the calc-silicate skarns. reaction (reaction 2 in Fig. 7), and by the large amount of water that was necessary to bring about the intense metasomatism. On the other hand, the absence of wollastonite even from the most intensely altered rocks of the zone 3 calc-silicate skarns, suggests that the CO 2 mole fraction was probably not below 0'1, since under these conditions the stability fields of diopside and wollastonite approach each other closely. The total pressure during alteration is also not known, but referring to Fig. 7 it is evident that in zone 1 of the calc-silicate skarns where talc is stable, the temperature was probably above 350 c, while in zone 2 where diopside is stable the temperature was probably above 500 c. The temperature in zone 3 was probably higher than in zone 2, but the stability field of wollastonite was not reached. Temperature prevalent durin.:5 alteration can also be estimated from the fractionation of oxygen isotopes between co-existing oxygen bearing minerals, and from the fractionation of sulphur isotopes between co-existing sulphide minerals. The oxygen isotope compositions of calcite, quartz and magnetite from the altered calc-silicate skarns, are shown in Table 7, and the location of the samples in Fig. 2. Quartz and calcite are obviously not in isotopic equilibrium since in samples P31465 and P30894 the /l018 values of calcite are higher than those of quartz. Although the samples analysed show no obvious retrograde effects, retrograde alteration forming late calcite, chlorite and zeolites is common in the altered rocks, suggestin.:5 that the isotope composition of calcite may have changed during waning hydrothermal alteration. According to the quartz-water and magnetite-water fractionation curves shown in Fig. 2 of Friedrichsen (1971, p. 29), the temperature at which quartz and magnetite crystallized in zone 3 calc-silicates was approximately 500 c, this being in fairly good agreement with the temperature estimated from the mineralogy.

29 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 625 The sulphur isotope composition of pyrite, galena and sphalerite from the Ag-Pb--Zn lode in zone 1 schists in Galena Creek (Fig. 1) are shown in Table 6. Because textural evidence suggests that the pyrite is earlier than the galena and sphalerite, temperature is estimated from sulphur isotope fractionation between galena and sphalerite. From the theoretically derived curve of Sakai (1968) and the experimentally derived curves of Kajiwara et al. (1969) and Grootenboer and Schwarcz (1969), the temperature of galena and sphalerite deposition was 350 o c, 325 c and 225 c respectively. These estimates vary widely but all indicate a temperature lower than that estimated from mineral equilibria for zone 1 schists and zone 1 calc-silicate skarns in the Copperstain Creek area. This suggests either that the temperature in the oat::r periphery of the alteration was lower than in the Copperstain Creek area, or that the galena and sphalerite were deposited during the waning of hydrothermal activity. Limits can also be placed on the oxygen and sulphur fugacities prevailing during the deposition of pyrite and rna.'snetite in zone 3 calc-silicate skarn assuming that the temperature was between 527 c and 627 c and taking into account the textural evidence for equilibrium between the two minerals. From Fig. 8 where the stability relations between oxides and sulphides of iron have been calculated from entropy and enthalpy data of Kubaschewski and Evans (1958), the fugacity of oxygen was evidently between and atm., while the sulphur fugacity was between 10-4 and 10 1 atm. The presence of K feldspar and muscovite in zone 2 schists and of muscovite with albite in zone 1 schists, makes it possible to put some limits on the activity ratios K+ /H+ and Na+ /H+ in the hydrothermal fluids, provided it is assumed that total pressure was 1 kb and temperatures in zone 1 and zone 2 schists were c and c respectively. Referring to fig. 1 of Hemley and Jones (1964, p. 548), under the assumed conditions the activity rat:o K + /H + in zone 2 schists would be approximately 10 2 Furthermore, referring to fig. 6.7 of Meyer and Hemley (1967, p. 215) the coexistexe of albite and muscovite in zone 1 schists shows that the activity ratio K+/H+ was b:'!tween 10 2 and 10 2.\ and the activity ratio Na+/H+ was between loa a:ld This suggests that the K+/H+ activity ratio was of the same order in both zone 1 and zone 2 of the schists and that the change from a K feldspar-b:'!aring assemblage to an assemblage without K feldspar was largely due to a fall in temperature Jog f 02 o FIG. 8-Stability relations of some iron oxides and sulphides as a function of f02' fs2' and temperature. Solid lines at 527 c. Dashed lines at 627 C.

30 626 N.z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL. 15 K-AR AGES OF REGIONALLY METAMORPHOSED AND ALTERED ROCKS K-Ar ages of whole rocks and separated minerals from regionally metamorphosed amphibolite and schist and from altered schist and granodiorite reported by Hulston and McCabe (1972) are shown in Table 8, and the location of the samples in Fig. 2. Rocks that have only undergone regional metamorphism (33464 and 31481) give whole rock, hornblende and biotite ages of m.y., their near concordance suggesting that this is TABLE 8-K-Ar ages of whole rocks and minerals from the Copperstain Creek area K-Ar Sample No. Rock Description Sample Age (m.y.) Regionally metamorphosed rocks Hornblende - plagioclase amphibolite Whole rock: 93 Hornblende: Staurolite - garnet - biotite - muscovite - plagioclase- Whole rock: 88 quartz schist. Biotite: 97 Granodiorite Quartz - microcline - biotite muscovite intrusive. Whole rock: 92 Zone 2 alteration. Biotite: Quartz - microcline - biotite - muscovite intrusive. Whole rock: 98 Zone 2 alteration. Biotite: 106 Altered schist Quartz - microcline - biotite - muscovite schist. Zone Whole rock: 92 2 alteration. Biotite: 97 ~Muscovite : Quartz - microcline - biotite - muscovite schist. Zone Whole rock: alteration. Biotite: Quartz - microcline - biotite - muscovite schist. Zone Whole rock: alteration. Biotite: 135 close to the true age of regional metamorphism. Two strongly altered samples of granodiorite (33465 and 33428) and one alfered schist (33456) also give reasonably conformable K-Ar ages which are similar to the ages of the regionally metamorphosed rocks, suggesting that the period of granodiorite intrusion and alteration was near contemporaneous to regional metamorphism. In the remaining altered schist samples (33426 and 33427), however, whole rock and biotite ages differ widely and both are higher than in the other sampl'es. There are two possible explanations for this wide variation in K-Ar ages: (a) The oldest ages, 135 m.y. (the maximum biotite age), or even 203 m.y. (the maximum whole rock age), represent the closest approximation to the age of alteration and possibly regional metamorphism, the younger ages being due to varying degrees of argon loss at a later time. or (b) The ages between 90 and 100 m.y. date the regional metamorphism and alteration, which were approximately coeval, whereas the anomalously high ages of samples and are due to excess radiogenic argon introduced during alteration.

31 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA 627 The first alternative seems less likely since two of the most intensely altered rocks occurring only a few metres from the intrusive granodiorite give the oldest ages, while samples that show no evidence of alteration give the younger age. Furthermore, a concordant Rb-Sr muscovite, biotite and plagioclase age of 100 m.y. was obtained by Aronson (1968) from the Onekaka Schist in the Anatoki River some 6 km to the south of Copper stain Creek (Fig. 1) suggesting that the m.y. ages in this study approximate to the time of regional metamorphism. The second alternative appears to be more likely, although the site of the excess radiogenic argon in samples and is problematical. Biotite is ruled out as its age is lower than that of the whole rocks. K feldspar and muscovite are unikely sites; K feldspar is a mineral which loses argon very readily while muscovite in sample gives a younger K-Ar age than either the whole rock or the biotite. The remaining possibility is that the excess radiogenic argon originated through the degassing of rocks during metamorphism, and became trapped in fluid inclusions which formed during the intense alteration and metasomatism. FACTORS FAVOURING ORE DEPOSITION In the Copperstain Creek area, alteration zones are elongated parallel to the ancient thrust fault that runs along the Arthur Marble lenses, suggesting that this fault acted as a channelway for hydrothermal fluids. The calcsilicate skarns contain by far the highest concentration of copper and sulphur, while molybdenum is strongly concentrated in the granodiorite intrusions and in the adjacent zone 2 schists. The presence of a large granitic stock underlying the mineralized area is suggested by the widespread extent of the alteration and metasomatism in relation to the small size of the intrusives exposed at the present erosion level; the sulphide mineralization thus probably occurs near the apex of a larger granitic stock. On the basis of the zonal distribution of alteration and metasomatism around the exposed intrusions, and the oxygen and sulphur isotope composition of hydrothermal minerals, the dominant source of the introduced constituents (including copper, molybdenum and sulphur) was magmatic. The factors that probably influenced the localisation of the sulphide deposits in the Copperstain Creek area therefore appear to be: 1. The presence of a major fault which acted as a channelway for hydrothermal fluids. 2. The presence of carbonate-bearing rocks which acted as a locus for pyrite and chalcopyrite deposition. 3. The presence of a granitic intrusive exposed near its apex, which was the source of the constituents introduced during alteration, and acted as a locus for molybdenite deposition. Examples of ore occurrences in other parts of north-west Nelson (Fig. 1) where one or more of these factors appears to be important in the localisation of sulphide mineralization are given below. 1. Campbell Creek, where copper and pyrite mineralization occurs in calcs;licate rocks near a thrust fault and near a granite intrusion (N.2. Geological Survey 1970).

32 628 N.Z. JOURNAL OF GEOLOGY AND GEOPHYSICS VOL Elliot Creek and Knuckle Hill, where disseminated molybdenite mineralization occurs in small granitic stocks that intrude Paleozoic metasedimentary rocks. (N.Z. Geological Survey 1970.) 3. Johnston's United Mine, where sphalerite, galena, pyrite, chalcopyrite and tetrahedrite mineralization occurs along a low angle thrust contact between Ordovician and Cambrian schists (Grindley and W odzicki 1960). 4. Richmond Hill, where pyrite, chalcopyrite, galena and tetrahedrite mineralization occurs along narrow shears within a porphyry intruded near a thrust contact between Ordovician and Cambrian schists. (Grindley and Wodzicki 1960; Grindley pers. comm.). SUMMARY AND CONCLUSIONS 1. Overturned Paleozoic, quartzo-feldspathic and pelitic schists, amphibole schists and calc-silicate rocks were metamorphosed to the amphibolile facies and intruded by granodiorite near a major thrust fault. 2. A zone of intense hydrothermal alteration and sulphide mineralization extends parallel to the thrust fault and is related to intrusion. 3. Alteration of schists and granodiorik! are divided into two zones both of which contain quartz and biotite; a less intensely altered peripheral zone (1) characterised by secondary mas(qvite ± albite; and a more inte:1sely altered zone (2) characterised by secondary muscovite and K feldspar. 4. Alteration of calc-silicate rocks are divided into three zones all of which contain quartz and calcite; a less intensely altered peripheral zone (1) characterised by tremolite-actinolite, epidote, -+- talc; an intermediate zone (2) characterised by diopside; and an intensely altered zone (3) characterised by andradite, magnetite, -+- hedenbergite. 5. Sulphide mineralization is also zoned: molybdenite is largely restricted to altered granodiorite and adjacent zone 2 schists; chalcopyrite and pyrite are most highly concentrated in zone 3 calc-silicate skarns; while the only galena-sphalerite mineialization occurs in the periphery of zone 1 schists. 6. Metasomatic cha~1ges during alteration have been intense. In the calcsilicate s'<arns large amounts of silica, iron oxide and sulphur and lesser amounts of alumina and copper have been introduced; large amounts of lime and CO 2 have been removed; some magnesia and titania have been redistributed and some have probably been removed; and the distribution of alkalies has remained essentially unchanged. 7. In the non-calcareous rocks large amounts of potash and sulphur and minor amounts of molybdenum have been introduced; some soda has been redistributed b::tween the alteration zones and some has probably been removed; and the distribution of the remaining major elements has remained unchan,'sed. 8. The striking differences in the mobility of elements in the calcareous and non-calcareous environments probably reflects the difference in the chemistry of the hydrothermal fluids; in the calcareous rocks the CO 2 fugacity was probably high, while in the non-calcareous rocks the common occurrence of scapolite suggests that the activity of Cl- was high.

33 No.4 WODZICKI - COPPER SULPHIDE DEPOSIT, TAKAKA The close association of the granodiorite with the alteration and sulphide mineralization, and evidence based on the oxygen and sulphur isotope composition of hydrothermal minerals, suggest that the introduced constituents were magmatically derived, the major source probably being a large underlying granitic intrusive. 10. On the basis of mineralogy, the temperature prevailing during zone 2 and 3 alteration of the calc-silicates was probably greater than 500 c, while in ZO:1e 1 of the calc-silcates it was probably above 350 c. On the basis of quartz-magnetite oxygen isotope fractionation, temperature prevailing in zone 3 calc-silicates was approximately 500 c. 11. In zone 1 schists the activity ratio K + /H+ was probably about 10 2, while in zone 2 schists the activity ratios K+/H+ and Na+/H+ were 10 2 _ and 10"-10: 1. 3 respectively, suggesting that the change from the K feldsparmuscovite to a muscovite-bearing assemblage was largely due to a fall in temperature. 12. Thermodynamic calculations suggest that in zone 3 calc-silicates where pyrite and magnetite co-exist, the fugacity of oxy:sen was between and atm., while the sulphur fugacity was between 10-4 and 10' atm. 13. K-Ar age determ:nations suggest that regional me~amorphism, intrusion of feldspar porphyry and alteration were approximately coeval and date m.y. 14. Factors that probably influenced the localisation of sulphide mineralization are the presence of a major fault which acted as a channelway for hydrothermal fluids; the presence of calcareous rocks wh:ch acted as a locus for pyrite and chalcopyrite depcsition; and the presence of a granitic intrusion exposed near its apex, which was the source of the mineralization, and acted as a locus for molybdenite deposition. ACKNOWLEDGMENTS The writer wishes to acknowledge the co-operation of Lime and Marble Ltd. and Kennecott Explorations (Australia) Pty. Ltd., during this project. In particular the writer is grateful to these companies for making core samples and assay data available for study. A number of people, to whom the writer is most grateful, contributed materially to this paper: Mr ]. A. Ritchie for the sulphur analyses, Mr A. C. Wise for some of the trace element analyses, Mr ]. L. Hunt for the major element 3nalyses, Dr T. A. Rafter for the sulphur isotope determinations, and Dr 1. Devereux for oxygen isotope determinations. Mr P. R. L. Browne and Dr W. A. Watters read the manuscri!>t and offered many helpful suggestions ARONSON, REFERENCES J. L. 1968: Regional geochronology of New Zealand. Geochimica et Cosmochimica Acta 32: BELL, J. M.; WEBB, E. J. H.; CLARKE, E. DE C. 1907: The geology of the Parapara Subdivision. N.z. Geological Survey Bulletin 3. ll1p. BURNHAM, C. W. 1967: Hydrothermal fluids at the magmatic stage. Pp in BARNES, H. L. (Ed.): "Geochemistry of hydrothermal ore deposits". Holt Rinehart, New York.

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