Multi-stage mobilization and remobilization of mineralization in the broken hill block, Australia

Ore Geology Reviews, 2 (1987) 247--267

247

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

MULTI-STAGE MOBILIZATION AND REMOBILIZATION OF MINERALIZATION IN THE BROKEN HILL BLOCK, AUSTRALIA ROBERT

G. B A R N E S

New South Wales Geological Survey, Department of Geology and Geophysics, University of New England, Armidale, N.S. W. 2351 (Australia) (Accepted for publication March 17, 1986)

Abstract Barnes, R.G., 1987. Multi-stage mobilization and remobilization of mineralization in the Broken Hill Block, Australia. In. B. Marshall and L.B. Gilligan (Editors), Mechanical and Chemical (Re)mobilization of Metalliferous Mineralization. Ore Geol. Rev., 2: 247--267. The Proterozoic Willyama Supergroup of the Broken Hill Block in western New South Wales, Australia, hosts a wide range of mineral deposits with commodities such as Pb, Ag, Zn, W, Cu, Co and Sn. The diversity and time relationships shown by the deposits reflect the long and complex geologic history of the area. Four broad categories of deposits have been recognized: stratiform, stratabound, vein, and intrusive-related. The stratiform deposits, including the well-known Broken Hill-type, are concordant and syngenetic, whereas the three epigenetic classes are largely the products of the partial or complete mobilization/remobilization of syngenetic mineralization. Stratigraphic and metallogenic data demonstrate that a wide range of potential sources exists for metals in the stratiform mineralization within the sequence. Stratiform mineralization occurs both as discrete mineral deposits and as pervasive, background disseminations, principally in the middle levels of the Willyama Supergroup stratigraphic sequence. The stratiform mineralization changes from predominantly Fe, Cu, Co in the Thackaringa Group to Pb, Ag, Zn, W in the Broken Hill Group, and finally to minor Sn above the Broken Hill Group. Localized remobilization of primary ore has occurred in many stratiform deposits. Some masses of mineralization have been physically remobilized during deformation while others contain features suggestive of fluid movement during the waning stages of high-grade metamorphism. In places, more extensive remobilization has produced discordant stratabound deposits. Some deposits are associated with igneous bodies derived from anatexis of the Willyama Supergroup metasediments and metavolcanics. These deposits are possibly the products of metal-scavenging by melts and associated hydrothermal fluids, all (metals, melts, fluid~) being derived from the metamorphic sequence. Retrogression, both regionally, and in narrow retrograde schist zones, closely followed the 1660 Ma high-grade metamorphism, and also occurred during a later thermal/deformational event at about 520 Ma ago. Hydrothermal activity associated with both episodes of retrogression resulted in the formation of a range of vein types. During the last major episode of hydrothermai activity, retrograde schist zones were the main conduits for hydrothermal fluids which leached metals from the sequence to produce the well-known, low T--P, Thackaringa-type silver--lead bearing siderite- quartz veins.

0169-1368/87/$03.50

© 1987 Elsevier Science Publishers B.V.

248 Introduction The Broken Hill Block in western New South Wales, Australia, is a metamorphic complex containing mixed metasedimentary, metavolcanic and minor proportions of igneous (largely anatectic) rock types (Stevens and Willis, 1983). The Block has been subject to at least two amphibolite--granulite facies metamorphic events (e.g., Phillips, 1980; Gulson, 1984) and has been complexly d e fo rmed with at least two deformations during high-grade metamorphism (e.g. Majoribanks et al., 1980). Retrogression followed high-grade metamorphism and also occurred during a later thermal event dated at 520 ± 40 Ma ago (Harrison and McDougall, 1981). A major, detailed lithological and metallogenic mapping program, undertaken by the New South Wales Geological Survey over the past decade, has established a consistent stratigraphic sequence in the rocks of the Broken Hill Block (Stevens et al., 1980; Willis et al., 1983; see Fig. 1). The metallogeny changes upwards through the sequence from F e - Cu--Co--(U, Au) to Pb--Ag--Zn--W and finally to Sn (Barnes, 1980a). The observations and interpretations presented in this paper derive largely from the author's field descriptions of over 2000 occurrences of mineralization in the richly mineralized

Broken Hill Block (Barnes, in press). In addition to the huge and well-docum e n t e d Broken Hill Main Lode (e.g. Johnson and Klingner, 1975; Plimer, 1979) the many small mineral deposits contain commodities which include Pb, Ag, Zn, Cu, W, Sn, Co, Ni, Pt, U, Au, Fe, Be and Bi (Barnes, in press). The deposits fall into four broad categories: (a) stratiform; (b) stratabound; ( c ) v e i n ; and (d) intrusive-related. Mineralization evolved into its present forms through four main processes. Firstly, base metals were deposited with the sediments and volcanics of the Willyama Supergroup, both as discrete deposits and as background disseminations. Secondly, the original stratiform mineralization was mobilized and remobilized (definitions after Marshall and Gilligan, this volume) to varying extents during metamorphism and deformation, such that, in places, stratabound deposits were generated. Thirdly, magmatic fluids were generated within the Broken Hill Block, and, in some instances, incorporated metals from the surrounding sequence. Fourt hl y, hydrothermal activity, late in the geological history of the area, leached metals from the c o u n t r y rocks and existing deposits, and redeposited them in veins. This was the final stage of "recycling" (mobilization and remobilization) of the original metals.

Robert Barnes was educated in Sydney and undertook his geological studies on a New South Wales Department of Mineral Resources scholarship through Macquarie University. After graduating with Honours in 1972, he began work in the Metallics Division of the N.S.W. Geological Survey, undertaking regional metallogenic studies in southeastern N.S.W. In 1975, he transferred to Broken Hill as part of a state government project to produce detailed lithological and metallogenic maps of the Broken Hill region. Results of this project have been published mainly in Department of Mineral Resources publications. In 1985, he obtained his Master of Science degree from the University of New South Wales for work on the regional and stratigraphic setting of mineralization in the Broken Hill area. Rob continues to work for the New South Wales Geological Survey, and in 1983 transferred to Armidale in northeastern N.S.W. where a regional resource assessment programme is being carried out.

249

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LOCALITIES 1. Pinnacles mlne 2, Ettlewood ; 3, Corruga ; 4. Sisters 5, Sentinel 6, Great Eastern mine 7, Big Hill 8. Great Vugh mine 9. Silver King mine 10. Hores mine 11. Diamond Jubilee mine 12. Thackaringa mines 13. Mount Robe mine 14. Lily Extended mine 15. Barrier Queen mine t6, King Gunnia mine TT, Waukeroo tinfield 18. Mulga Springs 19. Mount Darling Creek

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250 Features of major deposit types

Stratiform deposits Stratiform deposits form an original part of the Willyama Supergroup sequence. They are commonly siliceous horizons which are interpreted as metamorphosed exhalites or other types of chemically deposited sediments. The main features of these deposits are: (a) host rocks are predominantly bedded metasediments, or gneisses with probable bedding; (b) they tend to be tabular to lenticular, are usually narrow but relatively extensive along strike, and are mostly folded; (c) the mineralization is predominantly concordant with bedding or lithological layering in the host rocks; (d) internal layering is common, and is parallel to the boundaries of the mineralization; (e) the deposits have been subject to high-grade metamorphism and, as a result, show granular polygonal textures; and (f) the nature of the mineralization is intimately related to its stratigraphic position. The types of stratiform mineralization recognized in the Broken Hill Block and the commodities they contain are: (1) Broken Hill-type (Pb, Ag, Zn): lead--silver--zinc mineralization in quartz--gahnite rock, garnet--quartz rock and similar lode rock types; (2) miscellaneous stratiform horizons related to Broken Hill-type (Fe, Pb, Ag, Zn): included are garnet-quartz rock, banded iron formation, quartz--fluorite rock and other lode rock types with minor mineralization; (3) Ettlewood-type (Pb, Ag, Zn, Cu, W): layered calc-silicate rock bearing sulphides or scheelite; (4) Corruga-type (W, Cu, Pb, Ag, Zn): irregular garnet--quartz--epidote-amphibole rock associated with basic gneiss and containing scheelite or base-metal sulphides; (5) Sisters-type (Fe, Cu, Co): quartz--magnetite iron sulphide rock together with minor copper mineralization; (6) Great Eastern-type (Pyrite, Cu, Co): granular quartz--iron sulphide (+garnet) rock containing copper and/or cobalt mineralization; (7) Big Hill-type (Pyrite, Co): pyrite (+cobalt) in plagioclase--

quartz rock; and (8) irregular quartz--garnet-epidote--amphibole rock similar to Corrugatype, but having minor base-metal mineralization and no tungsten.

Stratabound deposits Stratabound deposits are locally transgressive but remain closely stratigraphically controlled. They appear to have formed from the mobilization/remobilization of disseminated to massive stratiform mineralization over distances of tens to hundreds of metres within specific stratigraphic positions. Types of stratabound deposits described by Barnes (1979, 1980a, b, 1983a, b) are: (a) Silver Kingtype (Pb, Ag, Zn, Cu, Au, W): base metalbearing, grossly concordant quartz bodies, and associated base-metal mineralization disseminated in amphibolite; (b) Hores-type (W): tungsten in quartz--muscovite--tourmaline pegmatites, or as disseminations within quartz--feldspar--biotite (+garnet) gneiss or tourmalinite; and (c) Diamond Jubilee-type (Cu, Au): copper--gold mineralization in pyritic quartz lenses in migmatite.

Vein deposits Vein deposits have sharp boundaries, are commonly discordant to lithological layering, and have distinctive mineral assemblages. Most veins have not undergone high-grade metamorphism but many show the effects of retrogression and shearing. Although having little stratigraphic control, they exhibit distinct geographic distribution patterns. The main types of vein deposits are: (a) Thackaringa-type (Au, Pb); silver-lead bearing siderite--quartz veins; (b) copperbearing siderite--quartz veins (Cu}; (c) Mount Robe-type (Pb, Ag, Zn, Cu, F): lead--silver-zinc--copper-bearing quartz--fluorite veins; (d) other lead-bearing quartz veins not included in the types above (Pb, Ag); (e) copper-bearing quartz veins, copper in schist zones, or copper disseminated in schist (Cu); (f) pyrite-bearing quartz veins with very

251 minor or no base metals; (g) laminated pyritebearing quartz veins; and (h) gold-bearing pyritic or cupriferous quartz veins (Au, Cu, pyrite).

Intrusive-related deposits Mineralization in this category occurs as: (a) irregular masses at, or near, the contact of various intrusive rocks with their host rocks; and (b) disseminations within intrusive rock types. The mineralization is genetically associated with rock types which intruded the metasediments and metavolcanics of the Willyama Supergroup. The intrusions and their related deposits, a number of which are broadly stratabound, formed after high-grade metamorphism, but some have been weakly affected by retrogressive processes. The main types of intrusive-related mineralization are: (1) disseminated cassiterite in pegmatites (Sn); (2) platinoid--copper--nickel mineralization in ultrabasic intrusive rock (Pt, Cu, Ni); (3) m a g n e t i t e - p y r i t e occurrences in granitic intrusive rock, or as veins or pods in metasediments (Fe, pyrite); and (4) pegmatitic and aplitic rock containing radioactive minerals (U, Th). Relationships of mineralization to stratigraphy Mineralization occurs throughout the stratigraphic sequence in the Broken Hill Block, but the vast majority of deposits occupy the central parts of the stratigraphic sequence within the Thackaringa and Broken Hill Groups (Fig. 2). The main types of mineralization at various stratigraphic levels are described below.

Clevedale Migmatite and Thorndale Composite Gneiss These are the oldest recognized stratigraphic units exposed in the Broken Hill Block. They comprise leucocratic quartzofeldspathic

and metasedimentary composite gneiss and are interpreted as immature clastic sediments with minor interbedded sodic and basic volcanics (Willis et al., 1983). Mineralization in these units is limited to minor stratiform quartz--iron oxide/sulphide horizons and, in some areas, copper-bearing and Thackaringatype veins.

Thackaringa Group The Thackaringa Group contains abundant quartzofeldspathic gneisses, including major bodies of "granite gneiss", and sodic plagioclase--quartz granofels with interbedded composite gneiss, metasediment, and basic gneiss. The first widespread chemically deposited siliceous horizons, and other disseminated to massive stratiform mineralization, were developed particularly in the Himalaya and Cues Formations. The major types of stratiform mineralization developed in the Thackaringa Group are: (a) layered horizons of quartz--magnetite + iron sulphide + copper minerals +-minor gold; (b) granular horizons of quartz--iron sulphide + garnet + copper minerals; (c) granular to layered garnet-rich horizons with rare basemetal mineralization; (d) quartz--gahnite horizons with rare base metals (with the major exception of the 200,000 t Pinnacles mine, a Broken Hill-type deposit); and (e) disseminated to massive cobaltiferous pyrite mineralization in plagioclase- quartz granofels. These have been described by Barnes (1980a) and Barnes et al. (1983), and in the case of type (e) by Plimer (1977). The characteristic features of this stratiform mineralization are: (1) the abundance of Fe, occurring as magnetite, pyrite or pyrrhotite; (2) the presence of copper and cobalt (and lesser antimony, arsenic, gold and uranium); (3) the general absence of abundant Pb--Zn mineralization (with the exception of the Pinnacles deposit and the Sentinel quartz--magnetite body); and (4) the presence, surrounding some " l o d e " horizons, of garnet,

252

WlLLYAMASUPERGROUPSTRATIGRAPHY OLDEST. . . . . .T.ha.ck.anri.ga. . . . . . Group . . . . .~. . . . . . . . . . .

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MI Robe ~ype Lead sliver zinc copper quartzfleer,re veins

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253

chlorite, biotite or cordierite, which may collectively represent metamorphosed alteration zones.

Vein mineralization is abundant in the metasediment-rich units of the Thackaringa Group, but is comparatively rare in the felsic metavolcanic units.

Broken Hill Group The Broken Hill Group consists of a highly variable mixture of psammopelitic to pelitic metasediments, quartz--feldspar-biotite-garnet gneiss ("Potosi-type" gneiss), leucocratic quartzofeldspathic gneiss, basic gneiss and various types of metamorphosed chemical sediment. Major environmental changes accompanied the transition from the Thackaringa Group to the Broken Hill Group (Willis et al., 1983); they include a significant decrease in acid volcanism, an increase in tholeiitic/dacitic volcanism, and a change from feldspathic volcaniclastic shelf sediments to well-bedded, deeper-water turbidites. Willis et al. (1983) suggested that the Broken Hill Group was deposited during late rifting. The Broken Hill Group contains the bulk of the Pb, Ag, Zn and W mineralization in the Broken Hill Block, and many deposit types show a close association with basic gneiss and "Potosi-type" gneiss. The major types of stratiform mineralization are: (a) Broken Hill-type deposits (Pb, Ag, Zn) (Fig. 3); (b) Corruga-type deposits (W, Cu, Pb, Zn); (c) Ettlewood-type calc-silicate mineralization (W, Zn, Pb); and (d) various garnet-rich rocks, banded iron formation and tourmalinites.

In addition to the stratiform mineralization, the Broken Hill Group contains stratabound Silver King-type deposits in the Mount Robe area, the Hores-type stratigraphically controlled pegmatoid and disseminated tungsten deposits, and abundant vein deposits. These types of mineralization have been described by Barnes (1980a)and Barnes et al. (1983).

Sundown and Paragon Groups Only minor amounts of stratiform mineralization are in the metasedimentary units overlying the Broken Hill Group. This mineralization comprises very minor quartz-gahnite horizons and tourmalinites, and lowgrade tin disseminations in the Paragon Group (see below). Most mineralization exists as veins of various types, although these are almost completely absent in many areas. Tin-bearing pegmatites are broadly stratabound in metasediments overlying the Broken Hill Group in the Waukeroo tin field, northeastern Broken Hill Block. Similar tin-bearing pegmatites (Lishmund, 1982) occur in the same stratigraphic units in the Byjerkerno area of the Euriowie Block north of the Broken Hill Block.

Summary The stratigraphic and metallogenic data demonstrate that a wide range of potential sources of metals exists in the stratiform

Fig. 2. The stratigraphic setting of mineralization in the Broken Hill Block (modified after Barnes, 1980a). Under "Main C o m m o d i t y " , c o n t i n u o u s lines show the main concentrations of the metals, and dashed lines, the subordinate concentrations. In all o t h e r sections, the main occurrences are portrayed as black-filled columns, and minor occurrences as o p e n columns. The figure shows that: (a) Fe, Cu, Co mineralization is c o n c e n t r a t e d in the Thackaringa Group; (b) Pb, Ag, Zn, W mineralization is c o n c e n t r a t e d in the Broken Hill Group; (c) stratabound deposits contain similar c o m m o d i t i e s to their stratiform equivalents at similar stratigraphic levels and probably represent localized remobilization; (d) veins are spread through the sequence, but nevertheless, concentrate at those levels containing pre-existing stratigraphically controlled mineralization; and (e) intrusive-related mineralization consists of Sn and U pegmatites which may have mobilized from disseminated mineralization, m a g n e t i t e - - p y r i t e masses in anatectic granites which show little relationship to stratigraphic position, and Pt, Cu, Ni-bearing ultrabasic serpentinites which have intruded the sequence.

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mineralization within the sequence. Metals occur as discrete deposits, as sparse disseminations (values of 50--200 ppm Pb, Zn and Cu are c o m m o n in basic gneisses for example, W.J. Stroud, pers. commun., 1985)~ and in various types of " l o d e " horizon (Barnes et al., 1983). In addition to the stratiform mineralization, there are stratabound, vein, and intrusive-related mineralizations at stratigraphic levels corresponding to those in which stratiform mineralization is most abundant. Evidence of the mobilization and remobilization of mineralization Localized remobilization

The stratiform mineralization in the Broken Hill Block has been subject to the same amphibolite--granulite metamorphism as the host stratigraphy, but the effects of metamorphism and deformation on this mineralization vary widely. Many horizons show localized remobilization; in some instances, this occurred during high-grade metamorphism, whereas in others, remobilization was associated with retrogression. Some chemically precipitated horizons (such as banded iron formation) have retained finescale layering, have metamorphosed isochemically on a layer to layer basis (Stanton, 1976), and rarely include coarser-grained remobilized material. Other horizons, including many quartz--gahnite--garnet horizons and q u a r t z - i r o n oxide/sulphide horizons, have recrystallized to form sub-equigranular textures, and only preserve coarse layering (Barnes et al., 1983).

In many places, the granular, usually siliceous, lode horizons contain coarsegrained, cross-cutting lenses of recrystallized material which, although containing similar minerals to those in the surrounding horizons, do not have a polygonal, granular texture. This localized recrystallization of various stratiform types of mineralization has commonly produced bodies of mineralization containing two, or more, distinct textural variants; for example: (a) Quartz-gahnite rocks (interpreted to be siliceous, sulphur-poor, meta-exhalites; Barnes et al., 1983) generally have a well-developed polygonal texture and contain a wide range of minor and accessory minerals, including sulphides, as granular layers, or as intergranular disseminations. Some bodies also contain large patches of coarse-grained, white quartz with gahnite euhedra and scattered coarse-grained sulphide patches. These coarsegrained patches are generally confined within the granular rock, but "veins" extending into the surrounding host rocks have been observed. (b) Stratiform, finely layered, g a r n e t quartz--apatite horizons contain, in places, concordant and transgressive quartz-sulphide veinlets which can comprise up to 30% of the rock. An excellent example occurs at Piesses Nob, 15 km northeast of Broken Hill. The coarse-grained quartz veinlets do not have the high-grade polygonal metamorphic textures of the surrounding garnet--quartz-apatite rocks and are interpreted as localized remobilization of some of the components of the garnet--quartz--apatite rocks after highgrade metamorphism. Similarly, crosscutting, coarsely recrystallized white quartz patches in

Fig. 3. T h e d i s t r i b u t i o n of B r o k e n Hill-type deposits in t h e B r o k e n Hill Block ( e x c e p t for t h e s o u t h e a s t c o r n e r w h i c h includes t h e L i t t l e B r o k e n Hill area a n d was n o t part of this study). T h e d i s t r i b u t i o n of B r o k e n Hill-type d e p o s i t s very closely follows t h a t of t h e B r o k e n Hill G r o u p rocks (see Fig. 1) a n d is o n e of t h e best pieces of e v i d e n c e d e m o n s t r a t i n g t h e s t r a t i f o r m n a t u r e of this m i n e r a l i z a t i o n . Similar s t r a t i g r a p h i c a l l y c o n t r o l l e d d i s t r i b u t i o n p a t t e r n s are r e c o g n i z e d for o t h e r t y p e s of s t r a t i f o r m a n d stratab o u n d deposits. T h e s y m b o l s i n d i c a t e c o m p a r a t i v e sizes of deposits, f r o m d e p o s i t s w i t h no p r o d u c t i o n to t h e B r o k e n Hill Main Lode. Most d e p o s i t s have p r o d u c e d less t h a n 1 0 0 0 t of ore. Bars t h r o u g h s y m b o l s i n d i c a t e strike. ( F r o m Barnes, in press.)

256 some granular, cupriferous, quartz--iron sulphide garnet horizons are believed to be remobilized. Excellent examples exist at the Coultra copper mine in the southern Broken Hill Block. (c) Layered calc-silicate rocks have generally retained fine-scale bedding features through high-grade metamorphism (Edwards, 1958; Stroud et al., 1983). However, these rocks contain, in places, transgressive, coarsegrained, quartz--sulphide veins or coarsely recrystallized calc-silicate patches rich in sulphides or scheelite. Barnes (1983b) again interpreted these as remobilization. (d) Within the plagioclase---quartz granofels of the Thackaringa Group are pyrite accumulations occurring as disseminations through to nearly massive sulphide lenses several metres wide. These lenses are usually concordant, but at several localities (e.g. Bald Hill, Great Vugh mine) irregular masses up to several metres wide transgress bedding, and appear to represent material remobilized during deformation. (e) Irregular masses of coarse-grained sulphides (known as "droppers") occur in the footwall of the Broken Hill orebody. The droppers are up to 12 m wide, and project to about 120 m below the orebody (e.g. MacKenzie, 1968; Maiden, 1976). Other examples of remobilized material in the Broken Hill orebody include sulphide masses which have moved, en masse, into fold hinges for example, during the peak and waning phases of high-grade metamorphism (see Plimer, this volume). Many of the textural and structural features previously attributed to processes such as metasomatism (e.g. Stillwell, 1959; Hodgson, 1975) are more probably a result of the high-grade metamorphism of very large, chemically unusual ore lenses. Temperatures may have exceeded 600°C for up to 60--70 Ma (Gulson, 1984). During this metamorphism, the orebodies, with their sulphide-rich lenses, were squeezed and thickened into fold hinges, and lost most of their primary textures. It is also possible that parts of the Broken Hill orebodies partly

melted during metamorphism (Lawrence, 1973; Plimer, this volume). Some metahydrothermal veins (Lawrence, 1968) may have formed during retrogression. (f) Corruga-type tungsten deposits contain coarse-grained irregular textural phases with metamorphic minerals such as garnet, and finer-grained, layered calc-silicate rock. The coarse-grained phases c o m m o n l y dominate over finer-grained calc-silicate rock and, in places, form transgressive veins extending up to several tens of metres away from the stratiform calc-silicate bodies (Barnes, 1983b). In the above examples, the remobilized material is coarser grained than the source material and lacks high-grade, polygonal, metamorphic textures. But in many cases, high-grade metamorphic minerals, such as gahnite and garnet, are enclosed within remobilized material, which is concentrated in the source horizons. The observation of these relationships at many widespread localities suggests that localized remobilization of mineralization from syngenetic source horizons occurred throughout the Broken Hill Block. The textural and mineralogical features of the remobilized material suggests that remobilization t o o k place after metamorphism had produced a granular groundmass in the surrounding rocks, but before highgrade metamorphic conditions finally subsided. Some of the remobilization may have occurred during retrogression.

Larger-scale mobilization In addition to localized remobilization of mineralization within stratiform horizons, there is evidence that disseminated mineralization was mobilized to produce stratabound deposits. Silver King-type deposits are stratigraphically controlled within the thin Broken Hill Group in the Mount R o b e area of the northern Broken Hill Block. They consist of granular to vein-like, locally discordant, base metal-bearing, quartz lenses which seem unrelated to chemically deposited stratiform

257

horizons (other than tourmalinites), and were consequently classified as vein deposits by many earlier workers. However, detailed examination revealed the deposits' close stratigraphic control, and showed that some lenses of mineralization were conformable

with amphibolite host rocks. Further, bedded tourmalinites (possibly meta-exhalites; Barnes, 1980b; Slack et al., 1984), occur with some of the deposits which have similar, though not identical, lead-isotope ratios to those in Broken Hill-type deposits (Reynolds,

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Fig. 4. 2°TPb/2°~Pb vs. 2°6Pb/2°4Pb for mineral deposits in the Broken Hill Block. There is little spread in ratios of Broken Hill-type deposits, but a small spread in stratigraphically controlled deposits which have remobilized phases. The spread is probably due to a mixing of small amounts of radiogenic lead with Broken Hill-type lead during the localized remobilization. Ratios in lead from vein deposits lie along a mixing line and appear to be the result of mixing of stratiform lead types and radiogenic lead as suggested by Richards (1971).

258 1971; Barnes, 1979; Gulson et al., 1985; see Fig. 4). All of these data suggest that the deposits formed (probably during the final stages of high-grade metamorphism) by the mobilization of mineralization originally disseminated in the amphibolites and associated rocks. Stratabound tungsten deposits of the Yanco Glen area in the northeastern Broken Hill Block (see Barnes, 1983b) also appear to have formed from mobilization of disseminated low-grade mineralization. The deposits mainly occur as structurally controlled, locally discordant, quartz-rich pegmatoids within units of quartz-feldspar--biotite--(garnet)-gneiss. They are always close to bedded tourmalinites; but at Hores mine, concordant lenses of disseminated scheelite and pyrrhotite [hosted by quartz-- feldspar-biotite--(garnet) gneiss] are located within a few hundred metres of the pegmatoids (Barnes, 1980a, 1983b). Exploratory drilling of these lenses has shown that they extend for several hundred metres (W. Laing, pers. commun., 1985). The tungsten deposits, which always occur at stratigraphic levels equivalent to those of Broken Hill-type and Corruga-type deposits, in some cases yield anomalously high lead values and contain rare gahnite mineralization. Formation of the pegmatoids was possibly facilitated by the presence of boron in the environment since this substantially reduces the solidus temperature of granitic melts (Chorlton and Martin, 1978; Pichavant, 1981). Tungsten and other metals therefore appear to have been mobilized from the immediately adjacent metal-rich sequence. Tin-bearing pegmatites occur in the metasedimentary sequence stratigraphically above the Hores-type tungsten deposits in the Yanco Glen area where a distinct tungsten-tin subprovince exists. Barnes (1980a, 1983a) suggested that the tin might be derived from the surrounding metasedimentary sequence, and this is supported by the discovery (J. Main, pers. commun., 1983) of several distinct

lenses of metasediments containing 50 to 500 ppm tin. The tin is associated with magnetiterich metasediments, but the host-mineral phase, although not cassiterite, has yet to be established (W. Laing, pers. commun., 1985). The discovery of these lenses supports the suggestion that localized mobilization of metals into hydrous melts is possible. It also supports the contention (Plimer, 1980) that components not readily accommodated by silicate structures (as shown by their association with the residual fractionation of an anatectic melt), are the first components to partition into the anatectic melt. As with the tungsten-bearing pegmatites, abundant tourmaline in the environment may have facilitated this partitioning. The tin-bearing pegmatites commonly cross-cut S1 and $2, and some are emplaced along and possibly deformed by an $3 (Corbett, 1979). Further, the pegmatites predate the post-S3 Adelaidean unconformity which lies just to the east. These relationships indicate that the pegmatites formed after the high-grade metamorphism which accompanied D1 and D2, but before cessation of the third major deformation in the area. The deposits probably formed about the same time as nearby, but genetically unrelated, intrusions of Mundi Mundi-type granite, since the thermal episode which produced the granite may also have led to the formation of the pegmatites. Other examples of stratigraphically controlled discordant mineralization are the pyritic copper--gold Diamond Jubillee deposits in the northwestern Broken Hill Block, and the uranium-bearing pegmatites in the Thackaringa area. The pegmatites are similar to those at Radium Hill and elsewhere in the Olary Block, South Australia (Rayner, 1960). In a study of thorian brannerite mineralization in sodic granitic rocks and associated sodic felsic gneisses in the Crockers Well area, South Australia, Ashley (1984) suggested that field, mineralogical and chemical data support derivation of the granitic rocks from the gneisses by anatexis during high-grade meta-

259 morphism. The davidite-bearing pegmatites of the Thackaringa area might have a similar derivation.

mineralization may have various retrogressive events.

formed

during

Origins of metals in vein mineralization

Timing of mobilization/remobilization The foregoing examples of larger-scale mobilization and localized remobilization suggest that mobilization/remobilization of mineralization resulted from metamorphic and pseudomagmatic processes over a considerable time-span. In particular, the presence of two textural phases, each with high-grade metamorphic minerals (e.g., gahnite, garnet) in many of the chemically deposited lode horizons, requires that some remobilization of mineralization accompanied the waning phases of high-grade metamorphism. The extent of the time-span may be obtained from radioactive dating of the high-grade metamorphic peak and waning conditions. Thus, the high-grade metamorphic peak occurred at 1660 Ma ago (Shaw, 1968; Reynolds, 1971; Gulson, 1984), but the slowly cooling rocks did not fall below about 500°C until about 1570 Ma ago (Harrison and McDougall, 1981). This suggests that intermediate metamorphic conditions (~>500°C) persisted for at least 90 Ma and is consistent with Gulson's (1984) estimate that high-grade metamorphism lasted for up to 70 Ma. Within this metamorphic time-frame, there was clearly ample opportunity for many mobilization/remobilization events. Conceivably, some mobilization/remobilization accompanied the formation of the second of two sillimanite schistosities (Laing et al., 1978), and/or later episodes in a sequence of episodes in which quartzofeldspathic segregations were formed (Brown et al., 1983). The intrusion of Mundi Mundi-type granite at about 1490 Ma ago may have triggered formation of locally derived hydrous magmas which formed the tungsten and tin-bearing pegmatites in the Yanco Glen area. Other lenses of mobilized/remobilized

Vein deposits with commodities including Ag, Pb, Cu, Zn and Au are widespread in the Broken Hill Block. Most veins post-date high-grade metamorphism, but some have been affected by retrograde metamorphism. The veins in the Broken Hill Block have formed predominantly by the translocation of metals in pre-existing mineralization, which was not necessarily concentrated in discrete mineral deposits. Much vein-type mobilization/remobilization occurred during a thermal pulse which affected the Broken Hill Block about 520 +40 Ma ago (Harrison and McDougall, 1981) and raised temperatures to about 350°C. However, earlier and later veinforming episodes have been recognized (Barnes, 1983a): (a) Laminated pyritic quartz veins which formed pre-retrograde metamorphism; these usually show substantial recrystallization and mylonitic textures. (b) Many copper-bearing quartz veins, which formed syn-retrograde metamorphism; these show a weak to strong foliation defined by aggregates of chlorite, biotite or muscovite and, in general, parallel the retrograde schistosity in the host rocks. Many barren quartz veins and some Pb--Zn bearing types also fall into this category. (c) Siderite--quartz veins and some barren quartz veins which are post-retrograde metamorphism and shearing. Type (a) veins are described in detail in Barnes (1980b); types (b) and (c) veins are discussed more extensively below.

Thackaringa-type veins Of the veins in the Broken Hill Block, the Thackaringa-type veins, which belong to type (c) above, have been the most studied (e.g., Kenny, 1922; Lawrence, 1967; Both, 1978; Barnes, 1980a, b). They are generally narrow

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(0.1--2 m) and are composed essentially of siderite, quartz and argentiferous galena. The veins occur in shallow-dipping faults and joints which crosscut the retrograde schistosity in the host rocks. They are amongst the youngest geological features of the Broken Hill Block. The T h a c k a r i n g a t y p e veins show little stratigraphic control but are limited to distinct geographic areas which are bounded by major schist zones, faults or lineaments (see Fig. 5). They have no geographical association with Broken Hill-type or other leadbearing mineralization, but occur in, or adjacent to, strongly retrogressed Broken Hill Group or Thackaringa Group sequences. They appear to have formed by mobilization of metals disseminated in the sequence, or less probably by remobilization of components in massive sulphide bodies (King, 1958; Lawrence, 1967; Both, 1978; Barnes, 1980a). Evidence for mobilization is provided by: (a) An absence of identified igneous source rocks. (b) The lead- and sulphur-isotope characteristics of the veins; these are compatible with derivation of at least some sulphur and lead from Broken Hill-type mineralization (e.g., Reynolds, 1971; Both and Smith, 1975). However, lead (Cooper, 1970), and sulphur, oxygen and carbon isotopic studies (Dong et al., in prep.)~ indicate that mobilization involved a significant input of components other than those in pre-existing disseminated mineralization. The components include

radiogenic lead, and carbon and oxygen possibly derived from meteoric or seawater. (c) Stratigraphic association; despite lacking a distinct geographical association with Broken Hill-type deposits, the veins are concentrated in retrogressed parts of sequences which host most lead-bearing mineralization. This relationship is also apparent on a regional scale. The Olary and Euriowie Blocks, respectively west and north of the Broken Hill Block, contain the same Willyama Supergroup sequence as that at Broken Hill (Willis et al., 1983). However, because the Broken Hill Group, which hosts most of the lead-zinc mineralization in the Broken Hill Block, is absent or only poorly developed, Thackaringa-type deposits are correspondingly rare or absent. Both and Smith (1975) and Dong et al. (in prep.) report homogenization temperatures of primary inclusions (interpreted to be filling temperatures) in the range 150°--200°C. These data, and the occurrence of the veins in shallowly dipping structures, suggests that the veins formed under low T--P conditions, possibly close to the surface. Copper-bearing siderite--quartz veins, which also belong to type (c) above and are grouped with Thackaringa-type veins, occur in discrete clusters in the Mount Gipps and Oakdale areas (Barnes, in press). They characteristically contain little or no lead, silver or zinc. In both areas where the veins are concentrated, stratiform horizons of cupiferous quartz--iron sulphide mineralization typify

Fig. 5. The distribution of Thackaringa-type galena-bearing siderite--quartz veins in the Broken Hill Block. Several major centres of c o n c e n t r a t i o n are recognizable and are labelled on the map as: (a) Thackaringa; (b) Silverton and U m b e r u m b e r k a ; (c) A p o l l y o n Valley; (d) P u r n a m o o t a H.S. and Mayflower; and (e) Maybell. Each centre is associated with major faults or lineaments with a coplanar retrograde schistosity, but the deposits themselves usually occur in minor faults or lineaments cross-cutting the retrograde schistosity. The veins are c o m m o n l y a b u n d a n t adjacent to the major structures as well as within their boundaries. However, some areas are totally devoid of Thackaringa-type deposits suggesting that the deposits f o r m e d f r o m localized h y d r o t h e r m a l cells. Dong et al. (in prep.) have shown that the sulphur isotope characteristics in particular centres are recognizably different f r o m those in o t h e r centres. The distribution pattern of the Thackaringa-type deposits can be c o m p a r e d to that of the copper-bearing quartz veins (Fig. 6) which pre-date the Thackaringa-type veins. Symbols indicate the comparative sizes of deposits; t h e y range f r o m deposits with no p r o d u c t i o n to deposits which produced several hundred t h o u s a n d tonnes of ore. Strike is indicated by bars. ( F r o m Barnes, in press.)

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the Thackaringa Group, whereas stratiform Pb--Zn mineralization is absent. This association suggests that the metals in the veins were derived relatively locally, perhaps in restricted cells of circulating hydrothermal fluids, and that the concentration of copper in the veins reflects the predominance of copper (over lead, zinc and silver) in the surrounding stratigraphy.

Copper-bearing quartz veins Copper-bearing quartz veins, which belong to type (b) above, are more widespread than Thackaringa-type veins (see Fig. 6). Their close similarity to other base metal-bearing, pyritic, and barren quartz type (b) veins, means that conclusions about the copperbearing veins are equally applicable to these other types. Copper-bearing quartz veins have been briefly described by Came (1908), Dickinson (1972), Barnes and Stevens (1975) and Barnes (1980a, b). The most common and economically important veins are 0.5--2 m wide, and up to several hundred metres long; they usually comprise en-echelon lenses which parallel the retrograde schistosity in large retrograde schist zones. They have an internal layering defined by the foliae of phyllosilicates and/or quartz grainsize variation caused by zones of recrystallization. These en-echelon relationships and internal fabrics show that the veins formed before the retrograde deformation ended. In some instances, several episodes of hydrothermal activity can be recognized. For example, at the Lily Extended mine within the Thackaringa-Pinnacles retrograde schist zone, cross-cutting relationships suggest that two sets of essentially barren quartz veins

preceded the formation of a body of nearly massive sulphide (pyrite with minor chalcopyrite). Shearing of the barren quartz and massive sulphide in the ongoing retrograde event produced a quartz pebble or durchbewegung (Vokes, 1969) texture. The concentration of syntectonic barren and base-metal-bearing veins within the retrograde schist zones is consistent with hydrothermal fluids being present during shearing and retrogression. It is conceivable that an early retrograde event followed the high-grade metamorphic peak, and involved an influx of aqueous fluids possibly generated by the crystallization of partial melts (Corbett and Phillips, 1981). These fluids might have formed the earliest laminated and deformed veins that have been assigned to type (a) above. Large volumes of fluids, which may have included meteoric and/or seawater, were also present during the retrogression dated at about 520 Ma ago (Vernon and Ransom, 1971; Etheridge and Cooper, 1981). The chemistry of the retrogression involved substantial depletion of silica and potassium in the schists of the retrograde zones (Etheridge and Cooper, 1981). In addition, substantial amounts of Ca and Mg, possibly from seawater, are present in fluid inclusions in some veins (Dong et al., in prep.). The fluids present during active retrogression were probably instrumental in leaching and transporting base metals from source rocks and depositing them in type (b) quartz veins, but fluids of a simpler composition and lower temperature were responsible for the postretrograde, type (c), Thackaringa-type veins. As concluded by Etheridge and Cooper (1981), a long history of localized deformation and retrogression characterises the planar

Fig. 6. T h e d i s t r i b u t i o n of c o p p e r - b e a r i n g q u a r t z veins. A l t h o u g h less a b u n d a n t t h a n t h e T h a c k a r i n g a - t y p e veins, they are m o r e widespread. T h e c o p p e r - b e a r i n g q u a r t z veins, a n d o t h e r base m e t a l - b e a r i n g q u a r t z vein types, o c c u r a l m o s t exclusively w i t h i n t h e b o u n d a r i e s of c o n t r o l l i n g r e t r o g r a d e schist z o n e s or faults, are o r i e n t e d parallel t o the r e t r o g r a d e schistosity, a n d are c o m m o n l y foliated. Most f o r m e d d u r i n g active retrogression. S y m b o l s indicate t h e c o m p a r a t i v e sizes of deposits a n d range f r o m d e p o s i t s w i t h n o p r o d u c t i o n t o deposits w h i c h p r o d u c e d several tens of t h o u s a n d s of t o n n e s of ore. Strike is i n d i c a t e d b y bars. ( F r o m Barnes, in press.)

264 shear zones; their conclusion is consistent with field observations of multiple veinforming episodes. Introduced mineralization

Mineralization derived from outside the original sediments and volcanics of the Willyama Supergroup is limited to irregular pockets and disseminations of platinoid-c o p p e r - n i c k e l minerals in, and adjacent to, serpentinized ultrabasic intrusive rocks {Barnes, 1980a; Stroud et al., 1983). The ultrabasic rocks occur in major retrograde schist zones and are themselves sheared and affected by retrograde metamorphism. The intrusives probably have a mantle source, and their presence in the Broken Hill Block may be an expression of deep mantle upwelling with resultant high heat flow which could explain the rifting, volcanism, highgrade metamorphism, complex deformation, and even subsequent hydrothermal activity present in the Block. Minor copper mineralization in the Barrier Queen area, northwest of the Pinnacles mine, may have derived its copper from the shearing of nearby, weakly mineralized, ultrabasic dykes. Conclusions

The long and complex history of the Broken Hill Block (see Stevens, 1986) is reflected in its mineral deposits (see Fig. 7). The special geologic and tectonic conditions which led to the formation of the vast Broken Hill orebodies were part of a process of evolution of mineralization from Fe, Cu, Co, (U, Au)-rich types, through Pb, Ag, Zn, W-rich types, and finally to a Sn-rich type. Metals were deposited widely throughout the area in concentrations ranging from stratiform discrete deposits to very low-grade disseminated mineralization. During high-grade metamorphism and

deformation, the various types of chemically deposited mineralization developed distinctive fabrics, and were, in places, partly mobilized and concentrated, or remobilized, to yield irregular transgressive coarse-grained zones. More extensive remobilization of massive sulphides t o o k place in relation to the Broken Hill orebodies and several massive pyrite bodies in plagioclase--granofels. More extensive mobilization and concentration of disseminated mineralization formed some distinctive strata-bound deposits such as the Silver King-type. Much of this mobilization and remobilization occurred during the waning phases of high-grade metamorphism. Localized hydrous melts concentrated tungsten and tin disseminations from metavolcanics and metasediments, respectively, and thereby produced stratigraphically controlled pegmatitic deposits. This mobilization occurred following high-grade metamorphism and deformation, and may have been associated with the intrusion of Mundi Munditype granites about 1490 Ma ago. Retrogression during the waning phases of high-grade metamorphism was particularly intense in retrograde schist zones which focussed large fluid flows; some vein deposits may have formed at this time. Many of the retrograde schist zones were reactivated during a thermal and deformation pulse at about 520 Ma ago. Large volumes of fluids were again focussed through these zones and formed various base metal-bearing and barren quartz veins. The last major geologic event to affect the Broken Hill Block was the formation of the low T--P Thackaringa-type silver--lead siderite--quartz veins which occurred after the retrograde deformation had ceased. The spatial distribution of deposits and the metal associations in stratabound, vein and some intrusive-related types provide strong evidence that almost all of the epigenetic deposit types in the Broken Hill Block formed by mobilization and remobilization processes.

265

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Fig. 7. Schematic space--time plot showing the evolution of present types of mineralization by multi-stage mobilization/remobilization. The diagram summarises the events, and time and spatial relationships, leading to the present distribution of mineral deposits in the stratigraphic sequence at Broken Hill. The age and spatial relationships are generalizations which do not apply to all deposits of particular types. The original stratiform mineralization underwent metamorphic mobilization/remobilization predominantly during the waning stages of high-grade metamorphism. Some stratabound deposits formed at this time. Mobilization of tin and tungsten into localized anatectic hydrous "magmas" occurred during the waning stages of high-grade metamorphism, or during a thermal pulse associated with the intrusion of Mundi Mundi-type granites. Uranium-bearing pegmatites probably also formed at these times. The formation of veins by the mobilization of disseminated mineralization, and the remobilization of metals in deposits, occurred in several episodes. Retrogression followed high-grade metamorphism and was also associated with a thermal pulse at about 520 Ma ago; veins formed from fluids focussed through retrograde schist zones during each of these episodes. The retrograde schist zones later acted as conduits for fluids which formed the geologically youngest deposits, i.e., the Thackaringa-type siderite--quartz--galena veins.

Acknowledgements

References

Thanks are due to my colleagues in the New South Wales Geological Survey, and J.D. Kleeman who provided useful discussions and comments. The manuscript was critically reviewed by J.A. Anderson, G.M. Bradley, B. Marshall, K.H. Wolf, and B.P.J. Stevens. Diagrams were prepared by M. Roach. The permission of the Secretary, Department of Mineral Resources, New South Wales, to publish this paper is acknowledged.

Ashley, P.M., 1984. Sodic granitoids associated with uranium--thorium mineralisation, Crockers Well, South Australia. Mineral. Deposita, 19: 7--18. Barnes, R.G., 1979. Some base metal deposits in the Mount Robe area: their classification and relevance to lead isotope interpretation. New South Wales Geol. Surv., Quart. Notes, 34: 5--14. Barnes, R.G., 1980a. Types of mineralization in the Broken Hill Block and their relationship to stratigraphy. In: B.P.J. Stevens (Editor), A Guide to the Stratigraphy and Mineralization of the

266 Broken Hill Block, New South Wales. New South Wales Geol. Surv., Rec., 20(1): 33--70. Barnes, R.G., 1980b. A metallogenic study of the Purnamoota--Yalcowinna 1:50,000 sheet, northern Broken Hill Block. New South Wales Geol. Surv., Rep. GS 1980/116 (unpubl.). Barnes, R.G., 1983a. Mineralization of the Broken Hill Block. In: Broken Hill Conf., 1983. Australas. Inst. Min. Metall., Conf. Set., 12: 71--79. Barnes, R.G., 1983b. Stratiform and stratabound tungsten mineralisation in the Broken Hill Block, N.S.W.J. Geol. Soc. Aust., 30: 225--239. Barnes, R.G., 1986. A summary record of mineral deposits in the Broken Hill Block (excluding the southeastern-most portion). New South Wales Geol. Surv., Rec., 22(2): 367. Barnes, R.G. and Stevens, B.P.J., 1975. Other metalliferous deposits. In: N.L. Markham and H. Basden (Editors), The Mineral Deposits of New South Wales, New South Wales Geol. Surv., Sydney, N.S.W., pp. 80--86. Barnes, R.G., Stevens, B.P.J., Stroud, W.J., Brown, R.E., Willis, I.L. and Bradley, G.M., 1983.5. Zinc, manganese and iron-rich rocks and various minor rock types. In: B.P. Stevens and W.J. Stroud (Editors), Rocks of the Broken Hill Block: Their Classification, Nature, Stratigraphic Distribution and Origin. New South Wales Geol. Surv., Rec., 21(1): 289--323. Both, R.A., 1978. Remobilization of mineralization during retrograde metamorphism, Broken Hill, New South Wales, Australia. In: W.J. Verwoerd (Editor), Mineralization in Metamorphic Terranes. Aft. Geol. Soc., Spec. Publ., 4: 481--489. Both, R.A. and Smith, J.W., 1975. A sulphur isotope study of base metal mineralization in the Willyama Complex, western New South Wales, Australia. Econ. Geol., 70: 308--318. Brown, R.E., Stevens, B.P.J., Willis, I.L., Stroud, W.J., Bradley, G.M. and Barnes, R.G., 1983. 3. Quartzofeldspathic rocks. In: B.P. Stevens and W.J. Stroud (Editors), Rocks of the Broken Hill Block: Their Classification, Nature, Stratigraphic Distribution and Origin. New South Wales Geol. Surv., Rec., 21(1): 127--226. Carne, J.E., 1908. The copper mining industry in New South Wales. New South Wales Geol. Surv., Miner. Resour., 6 : 4 2 5 pp. Chorlton, L.B. and Martin, R.F., 1978. The effect of boron on the granite solidus. Can. Mineral., 16: 239--244. Cooper, J.A., 1970. Lead isotope classification of the A.B.H. Consols and Brownes shaft veins at Broken Hill, N.S.W. Australas. Inst. Min. Metall., Proc., 234: 67--69. Corbett, G.J., 1979. Structure, metamorphism and stratigraphy of part of the Willyama Complex near Yanco Glen, N.S.W. Ph.D Thesis, Univ. of New

South Wales, Broken Hill, N.S.W. (unpubl.). Corbett, G.J. and Phillips, G.N., 1981. Regional retrograde metamorphism of a high-grade terrain: the Willyama Complex, Broken Hill, Australia. Lithos, 14: 59--73. Dickinson, K.J., 1972. Mining history of the silver, lead, zinc and copper mines of the Broken Hill district to 1939, excluding the Main Line of Lode. New South Wales Geol. Surv., Bull., 2 1 : 9 6 pp. Dong, Y.B., Both, R.A., Barnes, R.G. and Sun, S.-S., in prep. A regional stable isotope and fluid inclusion study of vein type mineralization in the Willyama Complex, Broken Hill, New South Wales. Inst. Min. Metall., London (submitted). Edwards, A.B., 1958. Amphibolites from the Broken Hill district. J. Geol. Soc. Aust., 5(1): 1--32. Etheridge, M.A. and Cooper, J.A., 1981. Rb--Sr and whole rock chemical changes during retrogression in a shear zone at Broken Hill, Australia. Contrib. Mineral. Petrol., 78: 74--84. Gulson, B., 1985. Uranium--lead and lead--lead investigations of minerals from the Broken Hill Lodes and Mine Sequence rocks. Econ. Geol., 79: 476--490. Gulson, B.L., Porrit, P.M., Mizon, K.J. and Barnes, R.G., 1985. Lead isotopic signatures of stratiform and strata-bound mineralization in the Broken Hill Block, New South Wales, Australia. Econ. Geol., 80 : 488--496. Harrison, T.M. and McDougall, I., 1981. Excess 4°Ar in metamorphic rocks from Broken Hill, New South Wales: implications for 4°Ar/39Ar age spectra and the thermal history of the region. Earth Planet. Sci. Lett., 55(1): 123--149. Hodgson, C.J., 1975. The geology and geological development of the Broken Hill lode in the New Broken Hill Consolidated mine, Australia. Part III. Petrology and petrogenesis. J. Geol. Soc. Aust., 22(2): 195--213. Johnson, I.R. and Klingner, G.D., 1975. The Broken Hill ore deposit and its environment. In: C.L. Knight (Editor), Economic Geology of Australia and Papua New Guinea. 1 --Metals. Australas.. Inst. Min. Metall., Monogr., 5: 467--491. Kenny, E.J., 1922. Description of individual mines. In: E.C. Andrews (Editor), The Geology of the Broken Hill District. New South Wales Geol. Surv., Mere. Geol., 8: 219--294. King, H.F., 1958. Notes on ore occurrences in highly metamorphosed Precambrian rocks. Australas. Inst. Min. Metall., F.L. Stillwell Anniv. Vol., pp. 143--167. King, H.F. and Thomson, B.P., 1953. The geology of the Broken Hill district. In: A.B. Edwards (Editor), Geology of Australian Ore Deposits. 5th Empire Mining and Metallurgical Congress, Australia and New Zealand, Publ., 1: 533--577. Laing, W.P., Marjoribanks, R.W. and Rutland, R.W.R.,

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1978. Structure of the Broken Hill mine area and its significance for the genesis of the orebodies. Econ. Geol., 73(6): 1112--1136. Lawrence, L.J., 1967. Mineralogy and textures of Thackaringa sulphide ore. Australas. Inst. Min. Metall., Proc., 222: 85--94. Lawrence, L.J., 1968. The mineralogy and genetic significance of a Consols-type vein in the Main Lode Horizon, Broken Hill, N.S.W. Australas. Inst. Min. Metall., Proc., 266(1): 47--57. Lawrence, L.J., 1973. Polymetamorphism of the sulphide ores of Broken Hill, N.S.W., Australia. Mineral. Deposita, 8: 211--236. Lishmund, S.R., 1982. Non-metallic and tin deposits of the Broken Hill District. New South Wales Geol. Surv., Bull., 2 8 : 1 7 6 pp. MacKenzie, D.H., 1968. Lead lode at the New Broken Hill Consolidated Limited. In: M. Radmanovich and J.T. Woodcock (Editors), Broken Hill Mines -- 1968. Australas. Inst. Min. Metall., Monogr., 3: 161--169. Maiden, K.J., 1976. Piercement structures formed by metamorphic mobilisation of the Broken Hill orebody. Australas. Inst. Min. Metall., Proc., 257: 1--8. Marjoribanks, R.W., Rutland, R.W.R., Glen, R.A. and Laing, W.P., 1980. The structure and tectonic evolution of the Broken Hill region, Australia. Precamb. Res., 13: 209--240. Marshall, B. and Gilligan, L.B., 1987. An introduction to remobilization: Information from orebody geometry and experimental considerations. In: B. Marshall and L.B. Gilligan (Editors), Mechanical and Chemical (Re)mobilization of Metalliferous Mineralization. Ore Geol. Rev., 2: 8 7 - 1 3 1 (this volume). Phillips, G.N., 1980. Water activity changes across an amphibolite--granulite facies transition, Broken Hill, Australia. Contrib. Mineral. Petrol., 75: 377-386. Pichavant, M., 1981. An experimental study of the effect of boron on a water saturated haplogranite at 1Kbar vapour pressure. Contrib. Mineral. Petrol., 76: 430--439. Plimer, I.R., 1977. The origin of the albite-rich rocks enclosing the cobaltian pyrite deposit at Thackaringa, N.S.W., Australia. Mineral. Deposita, 12: 175--187. Plimer, I . R , 1979. Sulphide rock zonation and hydrothermal alteration at Broken Hill, Australia. Trans. Inst. Min. Metall., Sect. B, 88: 1 6 1 - 1 7 6 . Plimer, I.R., 1980. Exhalative Sn and W deposits associated with mafic volcanics as precursors to Sn and W deposits associated with granites. Mineral. Deposita, 15: 275--289. Plimer, I.R., 1987. Remobilization in high-grade metamorphic environments. In: B. Marshall and L.B. Gilligan (Editors) Mechanical and Chemical (Re)mobilization of Metalliferous Mineralization.

Ore Geol. Rev., 2 : 2 3 1 - - 2 4 5 (this volume). Rayner, E.O., 1960. The nature and distribution of uranium deposits in New South Wales. New South Wales Dept. Mines, Tech. Rep., 5: 63--101. Reynolds, P.H., 1971. A U--Th--Pb lead isotope study of rocks and ores from Broken Hill, Australia. Earth Planet. Sci. Lett., 12: 215--223. Shaw, S.E., 1968. Rb--Sr isotopic studies of the mine sequence rocks at Broken Hill. In: M. Radmanovich and J.T. Woodcock (Editors), Broken Hill Mines -- 1968. Australas. Inst. Min. Metall., Monogr., 3: 185--198. Slack, J.F., Herriman, N., Barnes, R.G. and Plimer, I.R., 1984. Stratiform tourmalinites in metamorphic terranes and their geological significance. Geology, 12: 713--716. Stanton, R.L., 1976. Petrochemical studies of the ore environment at Broken Hill, New South Wales: 1 -- constitution of "banded iron formation". Trans. Inst. Min. Metall., Sect. B, 85: 33--46. Stevens, B.P.J., 1986. Post-depositional history of the Willyama Supergroup in the Broken Hill Block, N.S.W. Aust. J. Earth Sci., 33: 73--98. Stevens, B.P.J. and Willis, I.L., ]983. Systematic mapping of rock units: a key to mapping and interpretation of the Willyama Complex. In: B.P.J. Stevens and W.J. Stroud (Editors), Rocks of the Broken Hill Block: Their Classification, Nature, Stratigraphic Distribution and Origin. New South Wales Geol. Surv., Rec., 21(1): 1--56. Stevens, B.P.J., Stroud, W.J., Willis, I.L., Bradley, G.M., Brown, R.E and Barnes, R.G., 1980. A stratigraphic interpretation of the Broken Hill Block. In: B.P.J. Stevens (Editor), A Guide to the Stratigraphy and Mineralization of the Broken Hill Block, New South Wales. New South Wales Geol. Surv., Rec., 20(1): 9--32. Stillwell, F.L., 1959. Petrology of the Broken Hill Lode and its bearing on ore genesis. Australas. Inst. Min. Metall., Proc., 190: 1--84. Stroud, W.J., Willis, I.L., Bradley, G.M., Brown, R.E., Stevens, B.P.J. and Barnes, R.G., 1983. 4. Amphibolite and/or pyroxene-bearing rocks. In: B.P.J. Stevens and W.J. Stroud (Editors), Rocks of the Broken Hill Block: Their Classification, Nature, Stratigraphic Distribution and Origin. New South Wales Geol. Surv., Rec., 21(1): 227-287. Vernon, R.H. and Ransom, D.M., 1971. Retrograde schists of amphibolite facies at Broken Hill, N.S.W. Geol. Soc. Aunt., J., 18(3): 267--277. Vokes, F.M., 1969. A review of the metamorphism of sulphide deposits. Earth-Sci. Rev., 5: 99--143. Willis, I.L., Brown, R.E., Stroud, W.J. and Stevens, B.P.J., 1983. The Early Proterozoic Witlyama Supergroup: stratigraphic subdivision and interpretation of high- to low-grade metamorphic rocks in the Broken Hill Block, New South Wales. Geol. Soc. Aust., J., 30: 195--224.