Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales

Ore Geology Reviews, 1 (1986) 259--313

259

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

METALLOGENY AND TECTONIC DEVELOPMENT OF THE T A S M A N FOLD BELT SYSTEM IN NEW SOUTH WALES P.R. DEGELING

j , L.B. GILLIGAN

2 , E. S C H E I B N E R 2 and D.W. S U P P E L 2

' Alkane Exploration N.L., 16 Spring Street, Sydney, N.S.W. 2000 (Australia) 2 Geological Survey o f New South Wales, Department o f Mineral Resources, P.O. Box 5288, Sydney, N.S.W. 2001 (Australia) (Accepted for publication May 15, 1986)

Abstract

Degeling, P.R., Gilligan, L,B., Scheibner, E. and Suppel, D.W., 1986. Metallogeny and tectonic development of the Tasman Fold Belt System in New South Wales. In: E. Scheibner (Editor), Metallogeny and Tectonic Development of Eastern Australia. Ore Geol. Rev.. 1: 259--313. The northwestern corner of New South Wales consists of the paratectonic Late Proterozoic to Early Cambrian Adelaide Fold Belt and older rocks, which represent basement inliers in this fold belt. The rest of the state is built by the composite Late Proterozoic to Triassic Tasman Fold Belt System or Tasmanides. In New South Wales the Tasman Fold Belt System includes three fold belts: (1) the Late Proterozoic to Early Palaeozoic Kanmantoo Fold Belt; (2) the Early to Middle Palaeozoic Lach!an Fold Belt; and (3) the Early Palaeozoic to Triassic New England Fold Belt. The Late Palaeozoic to Triassic Sydney--Bowen Basin represents the foredeep of the New England Fold Belt. The Tasmanides developed in an active plate margin setting through the interaction of East Gondwanaland with the Ur-(Precambrian) and Palaeo-Pacific plates. The Tasmanides are characterized by a polyphase terrane accretion history: during the Late Proterozoic to Triassic the Tasmanides experienced three major episodes of terrane dispersal (Late Proterozoic---Cambrian, Silurian---Devonian, and Late Carboniferous-Permian) and six terrane accretionary events (Cambrian--Ordovician, Late Ordovician--Early Silurian, Middle Devonian, Carboniferous, Middle-Late Permian, and Triassic). The individual fold belts resulted from one or more accretionary events. The Kanmantoo Fold Belt has a very restricted range of mineralization and is characterized by stratabound copper deposits, whereas the Lachlan and New England Fold Belts have a great variety of metallogenic environments associated with both accretionary and dispersive tectonic episodes. The earliest deposits in the Lachlan Fold Belt are stratabound Cu and Mn deposits of Cambro-Ordovician age. In the Ordovician Cu deposits were formed in a volcanic arc. In the Silurian porphyry C u - A u deposits were formed during the late stages of development of the same volcanic arc. Post-accretionary porphyry Cu--Au deposits were emplaced in the Early Devonian on the sites of the accreted volcanic arc. In the Middle to Late Silurian and Early Devonian a large number of base metal deposits originated as a result of rifting and felsic volcanism. In the Silurian and Early Devonian numerous Sn--W, Mo and base metal--Au granitoid related deposits were formed. A younger group of Mo--W and Sn deposits resulted from Early-Middle Carboniferous granitic plutonism in the eastern part of the Lachlan Fold Belt. In the Middle Devonian epithermal Au was associated with rifting and bimodal volcanism in the extreme eastern part of the Lachlan Fold Belt. In lhe New England Fold Belt pre-accretionary deposits comprise stratabound Cu and Mn deposits (preFarly Devonian): stratabound Cu and Mn and ?exhallte Au deposits (Late Devonian to Early Carboniferous); and stratabound Cu, exhalite Au, and quartz--magnetite (?Late Carboniferous). S-type magmatism in the Late Carboniferous--Early Permian was responsible for vein Sn and possibly Au--As-.Ag--Sb deposits.

260 P R. Degeling graduated (B.Sc.) from the University of Newcasth., m 1968. iie worked as an exploration geologist in Papua New Guinea and Western Austraha unlil 1970 and then as a senior mine geologist at Mount lsa unlil !972. From 1972 unt~il 1984 he worked in the New South Wales Geological Surw~y (m th,,, metallogenic mapping programme. He is now employed by Alkane l~:×plorati(m N.I., as their exploration manager.

L.B. Gilligan holds the degrees of B.Sc. from the University of New South Wales, Sydney, and M.App.Sc. from the New South Wales Institute of Technology. He has been with the New South Wales Geological Survey since 1970 and has been involved with Survey's 1:250,000 metallogenic mapping programme of the State and has worked extensively on volcanogenic and remobilized sedimenthosted base-metal deposits in New South Wales. His current position is Senior Geologist, North Eastern Region, in the Geological Survey and is responsible for the coordination of metallogenic mapping of the New England Fold Belt.

Dr. E. Scheibner completed his undergraduate (1958) and post-graduate (1964) studies at the J.A. Comenius University, Bratislava, Czechoslovakia. He taught at the same university as lecturer, senior lecturer during 1958--1966 and docent 1967, and carried out regional research of Western Carpathians, mainly in the Pieniny Klippen Belt. In 1968 after a brief period with the Technical University in Zurich, Switzerland, he joined the New South Wales Geological Survey, where he is now a Principal Research Scientist. His main interest is in regional geology, tectonics, remote sensing and in the application of these to metallogeny in general, and specifically in Eastern Australia and Southwest Pacific. Some of his longer overseas experiences include 10 months spent in 1964 with a geophysical expedition in Afghanistan and 3 months in Saudi Arabia in 1983 working on a synthesis of the Arabian Shield.

D.W. Suppel holds degrees of B.Sc. from the University of Sydney and M.Sc. from the University of New South Wales, Sydney. He joined the New South Wales Geological Survey in 1964. He has worked mostly on metalliferous mineral deposits and has been involved in the Survey's 1:250,000 metaUogenic mapping programme. Currently he is Principal Geologist in the Geological Survey, supervising the Survey's programmes in the Southern Region of New South Wales and taking part in organization of the Survey's metalliferous mineral investigations throughout the State.

2(; 1 Volcanogenic base metals, when compared with the Lachlan Fold Belt, are only poorly represented, and were formed in the Early Permian. The metallogenesis of the New England Fold Belt is dominated by granitoid-related mineralization of Middle Permian to Triassic age, including Sn--W, Mo--W, and Au--Ag--As Sb deposits. Also in the Middle Permian epithermal Au--Ag mineralization was developed. During the above period of post-orogenic magmatism sizeable metahydrothermal Sb-Au(--W) and Au deposits were emplaced in major fracture and shear zones in central and eastern New England. The occurrence of antimony provides an additional distinguishing factor between the New Enghmd and Lachlan Fold Belts. In the New England Fold Belt antimony deposits are abundant whereas they are rare in the Lachlan Fold Belt. This may suggest fundamental crustal differences.

Introduction This is the first a t t e m p t (Degeling et al., 1984) to s tu d y the metallogeny of New South Wales using the c o n c e p t of tectonostratigraphic terranes. The application of this concept to the tectonic d e v e l o p m e n t of the Tasman Fold Belt System (TFBS) started only recently ( F lo o d and Fergusson, 1982; Harrington, 1983; Powell, 1983a, b, 1984b; Scheibner, 1983, 1985a; Basden et al., 1985; Cawood and Leitch, 1985) and hence our discussion is only of a preliminary nature. The review o f the tectonic d e v e l o p m e n t of the Tasman Fold Belt System in New South Wales is based on a paper (Scheibner, in press), in which the tectonic d e v e l o p m e n t of the Tasmanides is discussed in time slices (tectonic stages) which are also illustrated by way o f palaeogeographic maps. For each time slice a brief outline of metallogeny follows the tectonic description, and location o f representative deposits is shown on the palaeogeographic maps. The advances in plate-tectonic t h e o r y and the understanding o f regional geolo~,5, have enabled a m e n d m e n t s to be made to the earlier-proposed plateteetonic models for Eastern Australia (cf. Scheibner, in press). Because there exists a detailed description o f mineral deposits of New South Wales (cf. M ~ k h a m and Basden, 1975) and even more detailed descriptions contained in the interpretative e x p l a n a t o r y notes to the 1:250,000scale metallogenic maps o f New South Wales published by the Geological Survey, we will limit the a m o u n t of detailed description in this paper.

It is possible to classify the metal deposits in the Tasmanides in relation to terrane accretion as pre-, syn- or post-accretionary. Pre-accretionary deposits were form ed at passive or active plate margins before the onset of terrane accretion. Their genesis is mainly related to terrane dispersal in settings of extension, rifting, break-up and seafloor spreading. During terrane dispersal, metals were derived from the mantle or scavenged from crustal rocks. Syn-accretionary deposits form ed during collisional terrane accretion, largely by remobilization of earlier deposits or mobilization and concentration of earlierdispersed mineralization. New deposits seem to have f o r m e d from m e t a m o r p h i c and ot her h y d r o t h e r m a l fluids focussed along suture zones. Post-accretionary deposits are of two main types: (1) those formed by metamorphic: and ot her h y d r o t h e r m a l fluids inherited from earlier collisional accretion and focussed along suture zones; and (2) those related to stitching plutons* of varied nature. In the first t ype of deposits the metals were scavenged from crustal rocks, whereas in the second t y p e metals were derived from crustal and subcrustal sources, i.e., the region where the melts of the stitching plutons formed. Sources of data Basic stratigraphic and ot her geologic data for the Tasmanides arc contained mainly in recent publications and accompanying papers *Stitching plutons are defined as those which were emplaced alter terrane accretion and which stilch together tectonostratigraphic terranes.

262

in this volume. The interested reader is primarily directed to Cas (1983}, Collins et al. (1982), Cooper and Grindley 11982), Crook (1980), Crook and Powel! (1976), Flint and Parker (1982), Geological Society of Australia (1971), Geological Survey of New South Wales Metallogenic Map Series 1:250,000 scale, Queensland Geological Survey (1975), Harrington and Korsch (1985a~ b), Henderson and Stephenson (1980), Korsch (1977), Korsch and Harrington 11981), Leitch (1974), Markham and Basden {1975), Owen and Wyborn {1979}, Packham {1969, 1973), Parkin (1969), Pickett (1982). Plumb (1979), Pogson (1972), Powell (1983a, b, 1984a, b), Roberts et al. (1972), Rutland (1976~, Scheibnet (1976, 1978, 1985a, b), VandenBerg (1978), Veevers (1984), Von der Borch (1980), Webby {1978), White and Chappell (1983), Williams (1978) and references quoted in these publications. Structural framework This paper discusses only the Tasman Fold Belt System in New South Wales. In this state the system comprises the following {Figs. 1 and 2): three orogenic belts, a foredeep {foreland basin), and a possible, but concealed, continuation of a foreland fold and thrust belt. The three orogenic belts differ in the timing of their tectogenic processes, namely the conversion of pre-cratonic tectonic provinces into transitional provinces Can episode of molassic sedimentation), and final cratonisation, i.e. conversion into a neocraton (cf. Scheibner, 1976). The K a n m a n t o o Fold Belt (KFB} occurs in northwestern New South Wales, northwest of the Darling Depression and east of the paratectonic Adelaide Fold Belt (Scheibner, 1972a). Large tracts of this orogenic belt are concealed below the Cenozoic Murray Basin, but aeromagnetic anomalies (Tucker and ttone, 1984}, thought to reflect extensions of the Stavely Greenstone Belt (VandenBerg and Wilkinson, in Cooper and Grindley, 1982}, appear to link, beneath the basin, equi-

valent exposures in northwestern N.S.~V., and thus delineate the eastern margin of t,h~, KFB. The KFB developed from a Late Proterozoic to Early Palaeozoic pre-cratonic province con taining deep-water turbiditic st.rata, sore, volcanics, and shallow-water sediment.s clos,,~ to basement inliers. The pre-cratonic development was terminated by the diachronous Middle Cambrian to l,~arly Ordovician Delamerian Orogeny (Thomson, in Parkin, 1969). Transitional tectonic, shallow-marine to continental sedimentation started locally in the Middle Cambrian both in N.S.W. (Powcll ct al., 1982) and in Tasmania (Collins and Williams, this volume), and terminated in the Early Ordovician. Sedimentation and volcanism associated with the development of the adjacent Lachlan Fold Belt {I,FB) subsequently affected the region of the KFB. During the Early Dewmian (?latest Silurian), continental to shallow-water sedimentation occurred in grabens (Grampians} in Victoria (VandenBerg, 1978), where it was preceded by extrusion of rhyolites, whereas in the (C,o o t a w u n d y beds) in N.S.W. (described by Webby, in Cooper and Grindley, 1982) it was associated with felsic and lesser marie andesitic to felsic volcanism (G. Neef, pers. commun., 19841. Middle Devonian to Early Carboniferous continental elastics were part of a larger molassic sheet of sediments which may have connected with similar accumulations farther east, After the continent-wide Carboniferous Alice Springs -- Kanimblan Orogeny the KFB behaved as a neocraton. The Kanmantoo Pre-cratonic Province probably continued farther north into Queensland, but this area is almost completely concealed by the Late Carboniferous to Cenozoic TransAustralian Platform (;over (Geol. Soc. Aust., 1971) and it is difficult to separate the Early Palaeozoic fold belt from the Middle Palaeozoic one. For this reason, an all-embracing name, the Thomson Fold Belt (TFB), was introduced by K irkegaard (1974). By convention the boundary between the KFB and TFB could be taken along the

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Darling River Lineament or the major Bouguer gravity change in northwestern New South Wales. The east-verging Stawell--Bendigo Foreland Fold and Thrust Belt of Cox et al. (1983) might continue northward from Victoria across the Murray River Lineament, but if this is correct, this belt is concealed under the Murray Basin. It is linked in a stratotectonic sense to the KFB as its foreland basin, but with respect to deformation it is

linked to the early development of the Lachlan Fold Belt. The Lachlan Fold Belt ( L F B ) is a complex orogenic belt. its Early Palaeozoic history culminated locally in the formation of a Late Ordovician to Early Silurian collisional belt during the Benambran Orogeny (Pogson, 1982; Scheibner, 1982). The Melbourne Trough (VandenBerg, 1978) was an area of turbiditic sedimentation during this event and this lasted into the Middle Devonian. In con-

265 trast, the Silurian is generally absent in the region west of the Gilmore Suture (Scheibner, 1982), and basin formation with some volcanic rifting occurred here during the Early Devonian. From the Middle Silurian to the Middle Devonian the region east of the Gilmore Suture became a complex back-arc area. This back-arc area was changed by the Middle Devonian Tabberabberan Orogeny, the effects of which diminish from the southeast to the northwest (Powell, 1983a). Subsequent diachronous molassic sedimentation lasted from the late Early Devonian to the Early Carboniferous and was terminated during the Kanimblan Orogeny, which converted the LFB into a neocraton. The New England FoM Belt (NEFB) is the youngest fold belt of the Tasmanides. It is separated by its foredeep, the Sydney-Bowen Basin, from the other orogenic belts to the west. The pre-cratonic development was complex and started in the Cambrian (Cawood, 1976}. The NEFB contains composite Early to Late Palaeozoic volcanic arc-fore arc basin-accretionary prism complexes, which have been intruded by syn-kinematic, but mainly post-kinematic granitoids. The dew.qopment of the fold belt was punctuated by Middle Devonian and Middle to Late Carboniferous deformations, and was terminated by the broad Hunter--Bowen Orogeny spread over the period between the Middle Permian to the Late Triassic (Day et al., 1978, 1983; Leitch, 197,i; Korsch and Harrington, 1982). Cratonization progressed from south to north. Post-kinematic igneous activity lasted into the Mesozoic. The latest Carboniferous to 'triassic Sydney --Bowen Basin represents a platform cover on the older foM belts to the west. During the later stages of terminal deformation, the NEFB was thrust over the S y d n e y - B o w e n Basin along the Hunter--Mooki--Goondiwindi Thrust System. Probably one of the most characteristic features of the Tasmanides is the widespread orogenic plutonic activity (Richards, in Henderson and Stephenson, 1980; White and Chappell,

1983). While some granites can be related to hypothetical B-subduction processes, a large proportion of crustal melting is difficult to explain this way because of the large area involved. It has been suggested that some of these granites were related to thrust pile-up of marginal basin fill with consequent crustal thickening, and melting (Pogson, 1982; Scheibner, 1982). while others were related to melting associated with rifting (Wyborn, 1977; Collins et al., 1982; Barron et al., 1982).

Accretion o f allochthonous terranes and orogenic activity In orogenic belts for which active platemargin settings can be documented, all the terranes b e y o n d the autochthonous miogeoclinal or paratectonic zone fringing a cratonic foreland should be considered "suspect" (cf. Coney et al., 1980; Williams and Hatcher, 1982). They are "suspect" in that they may have originated remote from the regions where they now occur. This means that some of these diverse crustal fragments could be allochthonous tectonostratigraphic terranes. The presence of such terranes in the Tasmanides has been suggested only recently (Flood and Fergusson, 1982; Seheibner, 1982, 1983, 1985; Powell, 1983a, b, 1984b; Cawood, 1983; Harrington, 1983; Cawood and Leitch, 1985) ef. Fig. 3. Some of these terranes will be mentioned below. In the Tasmanides the episodes of terrane accretion and orogenic activity appear to haw.' been closely related. While continuous deformation occurred in arc-trench gap areas, episodes of stronger deformation affecting limited areas (e.g., Powell, 1983a, b) punctuated the tectonic development. These distinct, often diachronous, orogenic' episodes may have resulted from changes in the mode of B-subduction (Mariana- versus Chilean-types), closure of marginal basins, and collision of volcanic arcs and microcontinents (tectonostratigraphic terranes). Major orogenic episodes were followed by rearrangements of stratotectonic units or the formation of new ones

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at the active plate margin, and it is assumed that these localized changes were the consequence of the rearrangement of major plate movements and interactions. The following orogenic episodes or events were important during development of the Tasmanides: Delamerian (Middle Cambrian to Early Ordovician), Benambran {Late Ordovician to Early Silurian), Quidongan (Middle Silurian), Bowning (Early Devonian), Tabberabberan (Middle Devonian), Kanimblan (Carboniferous), and Hunter--Bowen (Middle Permian to Triassic).

Tectonic development and metRUogenesis of the Tasman Fold Belt System in,,New South Wales La te Precam brian developmen t

Evidence for pre-Cambrian break-up and seafloor spreading associated with the separation of microcontinents, has been discussed recently (Scheibner, in press). This event preceded the distinctive episode of extension at the Cambrian/Precambrian boundary

267

(Plumb, 1979; Von der Borch, 1980; Veevers, 1984; and others). Both these extensional events represent terrane dispersal. The paratectonic Adelaide Fold Belt (Parker, 1983) developed from a continental margin rift zone which had many hallmarks of an aulacogen (Von der Botch, 1980). It was oriented obliquely to the continental margin and was opposite the Murray Salient in the Tasmanides. This salient was either an e m b a y m e n t in the continental margin or developed during subsequent collisional movement of t h e Victorian Microcontinent (see below). If we accept the modified continental

margin and aulacogen model of Von der Borch (1980), we could speculate that the prolonged Late Proterozoic rifting and extraarch basin formation (Von der Borch, 1980 Rutland et at., 1981) were related to continental break-up farther east than the subsequent Cambrian break-up that localized the ensimatic Kanmantoo Trougb at the continental margin (Fig. 5). Progressive continental break-up resulted in separation of microcontinental blocks of unknown size by one or more marginal seas with some oceanic crust (Fig. 4). Such oceanic crust would have subsequently become gravitationally unstable and, together with the

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26~ interacting hypothetical Ur-Pacifie oceani(' plate, would have led to the formation of an active plate margin. Unfortunately little is known in N.S.W. a b o u t rocks which ~'ould have formed at this active plate margin. More data on the Late Proterozoic rocks in the Kanmantoo Fold Belt are available from Tasmania (of. Collins and Williams, this volume). The Wonominta beds present in northwestern N.S.W. (Rose and Brunker, 1969) comprise a m e t a m o r p h o s e d complex of graywackes, slates, magnetite cherts and some basic volcanics, and could have formed m an active plate margin setting. However, according to Leitch et al. (1985) and K.J. Mills (pers. eommun., 1985) the Wonominta beds comprise at least these different ro('k complexes. In the Kayrunnera terrane lFig. 3) the Wonominta beds are considered to be of Early Cambrian age. In the Tibooburra terrane they could be Cambrian to Ordovician (B.D. Webby, pers. commun., 1985). In the Wertago terrane multiply deformed Wonominta beds are beneath a metamorphosed sequence of sediments and minor basic volcanics, which are thought to be of Late Proterozoic (Adelaidean) age. The Adelaidean strata in turn conformably underlie Early Cambrian metasediments. Hence Mills suggests that the multiply deformed Wonominta beds are preLate Proterozoic in age. However, this is not y e t supported by isotopic dating. We could still be dealing with a Late Proterozoic or()genic domain similar to R o c k y Cape region in Tasmania (cf. Collins and Williams, this volume). In the following chapter the term Wonominta beds sensu stricto refers to the lowermost multiply deformed sequence. Deposits in the Wonominta beds sensu stric to (p re-A delaidean ) In the Wonominta beds mineralization is restricted to scattered occurrences of copper, lead--zinc and gold (Barnes, 1975). At the Ponto and Grassmere mines (Fig. 4, deposits 1 and 3) (in all subsequent references to mineral deposits shown on figures, deposit

numbers are shown in italics), COpl~er oc(:ur~: in tabular iron-rich banded quartzite bodies which are conformable with cleavage. I'he lodes are in a sequence of low-grade metasediments and metamorphosed mafic voicanics. The copper mineralization is considered to be of Besshi t y p e (of. Sawkins, 1976), and may have formed in a pre-accretionary, marginal sea setting. Lead--silver mineralization is in quartz--s'iderite veins at the Nuntherungie silver field (Fig. 4, 2). The origin of these deposits is not known, although they probably are of fault-fill type (Barnes. 1975!. and therefore syn- or post-accretitmary in character, and could be related t.o the Palaeozoic history of the region. Early Palaeozoic development

The Early Palaeozoic rock complexes in Eastern Australia indicate that by earliest Cambrian time a well-developed West Pacifictype active plate margin existed here (see Scheibner, in press, fig. 5). Cambrian plate interactions and Early Palaeozoic terrane accretion

The possible arrangement of stratotectonic units in the area of present-day New South Wales and adjacent regions during the Early Cambrian is shown in Fig. 5. To the north the Kanmantoo--Glenelg Marginal Basin was either interconnected across the Darling River and Cobar-Ingle: w o o d Lineaments (fracture zones) with the narrow Bancannia Trough (Scheibner, 1972a) or with the White Cliffs Basin (K.J. Mills, pers. commun., 1984). This trough was in the area of the Wonominta Recess which developed possibly from a continental margin promontory. East of the Bancannia Trough was the hypothetical Mount Wright Volcanic Arc (Mount Wright Volcanics; cf. Packham, 1969; Scheibner, 1972a; Edwards, 1979). The Early Cambrian Mount Wright Volcanic Arc volcanics and younger intrusions have strong aeromagnetic expression, which

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together with the positive anomalies caused by the basement rocks in the Wonominta Complex characterize the Kanmantoo Fold Belt. A well-developed complex magnetic ridge can be traced in subsurface in the Murray Basin area along the continuation of the "Stavely Magnetic High" in Victoria (cf. VandenBerg and Wilkinson, in Cooper and Grindley, 1982; D. Tucker, pets. commun., 1985). This magnetic high terminates in the Scopes Ranges and appears to be offset from the magnetic anomalies in the Mount Wright and Wertago terranes by the Darling River Lineament. To the east of the Mount Wright Volcanic Arc was the White Cliffs Basin in which the Copper Mine Range beds (Pogson and Scheibner, 1971) accumulated.

Relationships of the Girilambone Group and Jindalee beds (Fig. 5), a flysch-like complex with possible dismembered ophiolites, remain uncertain. Contrary to earlier ideas (Scheibner, 1972a), perhaps these rocks are closely related to the Molong Microcontinent and its development, rather than the region to the west. At the Australian active plate margin, diachronous orogenic deformations preceded by mild episodic tectonic activity c o m m e n c e d in the Middle Cambrian and continued into the Ordovician. These orogenic: deformations were named the Delamerian Orogeny in South Australia {Thomson in Parkin, 1969), and the same name has been used in Victoria and N.S.W. (Scheibner, 1972a; VandenBerg, 1978).

270

Ordovician; cf. Milnes et ai., 1975: l{.ichard:and Singleton, 1981) were eml)laced n()t oniy in the inverted Kanmantoo-Glene]g Mar~inai Basin (Kanmantoo--Glenelg belt), hut als,~ in the old eraton (cf. Thomson, u', Parkin. 1969). The orogenic belt which resulted from the deformation of the Early Cambrian actiw, plate margin has been referred ~,(~ as the Kanmantoo Fold Belt (Scheibner, 1972a, b, 1978). In Queensland the slightly younger complexes were cratonized by tlw Middh: Ordovician and formed the con:, of the T h o m s o n Fold Belt (Murray and Kirkegaard, 1978; Day et at.,1983). The late orogenic (transitional tectonic) Middle Cambrian to Early Ordovician sediments of the Kanmantoo orogen are mostly

During this orogeny, inner marginal seas (Kanmantoo--Glenelg and Bancannia on the mainland and Dundas in Tasmania) were closed and inverted by collisional movement of the inner microcontinents with attached volcanic arcs. In effect this represented accretion of tectonostratigraphic terranes (Scheibner, 1983, 1985). Retrograde metamorphism affected the Preeambrian craton (e.g. the 520-+ 40 Ma thermal pulse in the Broken Hill Block; Harrison and McDougall, 1981) and the paratectonic cratonic cover was deformed. This deformation resulted, for example, in formation of the Adelaide Fold Belt in South Australia (Thomson in Parkin, 1969; Rutland et al., 1981; Parker, 1983). Orogenic granites (Late Cambrian to Early

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271 shallow-marine to continental (cf. Cooper and Grindley, 1982), and comprise the Gnalta Shelf (Fig. 6). On the Victorian Microcontinent a wide sheet-like foreland basin developed above the earlier orogenic complexes (Cox et al., 1983). This included perhaps the Stawell, but mainly the Ballarat (Bendigo) and Melbourne depositional areas (VandenBerg, 1978, and in Cooper and Grindley, 1982). It is possible that these Victorian belts continue into New South Wales and are concealed under the Murray Basin.

Deposits in the K a n m a n t o o Fold Belt in N e w South Wales The volcanic arc character of the Mount Wright Volcanics suggests potential for the occurrence of pre-accretionary volcanogenic massive sulphide deposits. Gold deposits situated at Tibooburra, Warratta, Mount Browne and perhaps those at Koonenberry Gap and Cawkers Well are located in this Fold Belt (Fig. 9, 1--5, respectively) b u t are related to younger intrusives.

Ordovician stratotectonic units Figure 6 shows the distribution of main Ordovician stratotectonic units in their present configuration. The Molong Volcanic Arc has a western G o o n u m b l a segment (Bowman et al., 1983) which is separated by a belt of turbiditic sediments and the Young Anticlinorial zone (Fig. 2) or terrane (Fig. 3) from the main eastern Molong segment from which subsequently the Capertee segment splits away. Recently, Packham (1985) suggested that these G o o n u m b l a and Molong segments represent sinistrally displaced parts of an originally narrower arc. He also suggested that the meridional gravity ridge in the Sydney-Bowen Basin (Fig. 2) represents the third displaced segment of the Molong Volcanic Arc. We favour an interpretation (Bramall and Qureshi, 1984) that this gravity ridge

reflects a younger, Mid-Late Palaeozoic volcanic chain (see Figs. 8 and 9). Starting possibly in the latest Cambrian, but definitely by the earliest Ordovician (Sherwin, 1979}, the Molong Volcanic Arc developed east of the Victorian Microcontinent. It can be traced from the N.S.W./ Victorian border northward to the Cobar-Inglewood Lineament (Fig. 6). Its relationship to the Mount Windsor Volcanic Arc in Queensland (Day et al., 1983} is not known. Most authors of published models (Oversby, 1971; Scheibner 1972b, 1974a; Packham, 1973; Cas et al., 1980; Crook, 1980; Powell, 1983a, b, 1984b) agree on a model in which the Ordovician volcanics in New South Wales formed a volcanic island arc bordered on the west by a marginal sea (Wagga Marginal Basin} and an open ocean (Monaro Slope and Basin) on the east. Such a model was mainly based on the analogy that the Ordovician volcanics are similar to those which characterize volcanic island arcs. Geochemical data (L. Wyborn, 1977; Owen and Wyborn, 1979; I. Clarke, pers. commun., 1985) from the rocks of the Molong Volcanic Arc indicate that the volcanism had a dominantly shoshonitic character. Minor tholeiitic basalts and island arc tholeiites occur in the southern part of the arc (L. Wyborn, 1977; Owen and Wyborn, 1979). In the northwestern part of the arc, around Parkes, shoshonites are prevalent, but K-rich calc-alkaline andesites and basalts, and minor trachytes also occur (I. Clarke, pers. commun., 1985}. The uncertainty a b o u t the origin of modern shoshonitic suites (of. Johnson et al., 1978) has led to reservations a b o u t the validity of a subduction model for the Molong Volcanic Arc (cf. Owen and Wyborn, 1979}, and also to the suggestion that these volcanics were related to Ordovician rifting and fracturing of continental crust in a marginal plateau environment (L. Wyborn, 1977). We favour a converging plate-margin setting. In the Southwest Pacific, modern shoshonites occur mostly in areas where there is some older continental-type crust. Coulon and Thorpe (1981)

272 came to the conclusion that shoshonites form where the continental crustal thickness exceeds 20 km. We have to conclude that there must haw: been some earlier continental-type crust in the areas of Ordovician shoshonitic volcanism on the Molong Volcanic Arc. This crust could have originated during the previous orogenic episode, but it is considered more likely that it was a separated microcontinent - the Molong Microcontinent (Fig. 4). The CambroOrdovician Girilambone Group rocks and correlatives (Jindalee Group) could represent part of basement to the Molong Volcanic Arc. Another possibility is that they comprise an accretionary wedge related to eastward subduction below the Molong Volcanic Arc. On the east the Late Ordovician Rockley volcanics interfinger with the flysch-like sediments (Triangle Group) and no older basement is known. Most authors envisaged westerly dipping subduction under the Molong Volcanic Arc. ttowever, this is not completely conclusive. Some uncertainty with the westward subduction model is introduced by the apparent eastward younging of Ordovician arc rocks. The oldest rocks occur west of Parkes and the youngest on the east around Sofala and Rockley. If the above distribution is real and the conclusion of Dickinson (1973) about progressive migration of magmatic arcs away from the trench is correct, then subduction could have been towards the east. L. Wyborn (1977} noted an eastward progression of volcanics from tholeiitic through island-arc tholeiitic to shoshonitic in the southern part of the volcanic arc. This would support a model of eastward subduction. The Molong Volcanic Arc rocks occupy a composite terrane which is now bounded on the west by the Gilmore Suture (Scheibner, 1982). This is best documented in the south where the Gilmore Fault Zone (Basden, 1982) forms the boundary. This and other similar faults are reverse faults modified from thrusts by later deformation. The westward-dipping Gilmore Fault Zone and the gravity gradient

indicate that the Molong Microcontment with its overlying volcanic arc complex has underthrust the western marginal sea c o m p l e x 'l'h~:~ Gilmore Suture is complex, and slices ,,>f the: volcanic arc (Nacka Nacka complex, Basdet~, 1982; Basden et al., 1985} occur west; of the main dislocation. North of the l,achlan Riw:~r Lineament the Gilmore Suture may have two strands, the eastern one defined by slices of serpentinites and the Silurian Devonian Alaskan-type intrusions within the' Girilambone terrane. To the west of the Gilmore suture is the Wagga--Omeo terrane (Fig. 3}. lt, was an area of turbiditic basinal sedimentation, which m relation to the craton in the west and the Molong Volcanic Arc in the east has been interpreted as a marginal basin (Packham 1973), the Wagga Margin~ Basin (Scheibner, 1972b). New palaeontological data (Kilpatrick and Fleming, 1980) indicate that sedimentation started in the earliest Ordovician. If westward subduction under the Molong Volcanic Arc did occur, then the Wagga Marginal Basin had a back-arc basin setting and as such could be expected to be partly floored by oceanic crust, l towever, there is no direct evidence (e.g. presence of ophiolites) for this. [t has been argued above that some Precambrian oceanic crust could have been present between the Victorian and Molong Microcontinents. The fill of this basin was converted into the Wagga--Omeo Metamorphic Belt during the Late Ordovician--Early Silurian Benambran Orogeny. The belt is bounded by the Gilmore Suture on the east and by another collisional suture zone, the Kiewa Thrust (Fig. 7), on the west. In Victoria along the east-dipping Kiewa Thrust high-T/low-P Ordovician metamorphics (Omeo) intruded by synkinematic anatectic S-type granites are in contact with weakly metamorphosed Ordovician rocks of the Howqua Zone (Tabberabbera subzone) (VandenBerg, 1978). Recently Fergusson (1985) suggested that the so-called "Wonnangatta Line", west of the Kiewa Thrust is the major boundary dislocation.

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To the east of the Molong Volcanic Arc was an area of turbiditic sedimentation. In accordance with the model of westward subduction, these sediments were designated as deposited in the Monaro Slope and Basin (Scheibner, 1974a). They would mainly represent fore-arc basin fill (Crook, 1980). Farther east, perhaps in the South Coast region of N.S.W. we could expect to find the accretionary wedge rocks. The Wagonga beds, which contain some basic volcanics, could fulfil this role (Scheibner, 1974a, 1982). In the South Coast region, Powell (1983a, b) recently recognised Ordovician belts showing stripy-cleavage which he interpreted as characteristic of an accretionary prism setting (outer arc slope). Scheibner (1983, 1985)

suggested that these rocks possibly form an allochthonous terrane, the Narooma Terrane, and Powell (1984b) suggested that the basic volcanics could represent rafted-in oceanic island volcanics. Tectonic model for the Ordovician-Early Silurian and the Benambran terrane accretion The, following model could explain the distribution of discussed tectonic units. During the earliest Ordovician, and probably earlier, west-facing Mariana-type B-subduction developed east of the Molong Mierocontinent. The Molong Volcanic Arc formed on this block (terrane). The back-arc basin (Wagga Marginal Basin) was partly floored by oceanic

27i

Proterozoic, volcanic island arc toceanic: plateau). This hypothetical terranc, was subsequently partly subducted, and tectonically underplated the accretionary prism (Narooma Terrane) plus the eastern part of the Monaro Slope and Basin up to the [--S llllt~ (Whlt,e and Chappell, 1977). This underplated igneous material could have later become bhe source rock for the large l-type granite batholiths. After arrival (docking and accretion occurred later) of the hypothetical oceanic plateau, subduction was relocated {flipped) and eastward subduction west or [he ar,: started. This involved subduction of any oceanic crust formed in a back-arc basin setting during the Ordovician as well as any earlier oceanic crust present. After (.:onsump-

crust which formed during the Late Cambrian to Early Ordovician subduction and/or was a remnant from an earlier marginal sea between Victorian and Molong Microcontinents. To the east of the volcanic arc: was the fore-arc basin (Monaro Slope and Basin), and farther east the possible accretionary prism (Narooma Terrane) (Scheibner, 1972b, 1974a: Paekham, 1973; Cas et al., 1980; Powell, 1983b). During the Early Ordovician the volcanic arc was split east of Parkes and an inter-arc basin formed (Initial Cowra Trough). During the latter part of the Ordovician the Marianatype subduetion changed into Chilean-type. It is speculated that the change in the mode of subduction was caused by the arrival of a hypothetical intra-oceanic, probably Late

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275 tion of oceanic crust, B-subduction changed into A-subduction involving extended continental-type crust. This resulted in closure of the Wagga Marginal Basin. The volcanic arc collided and underthrust the marginal basin complexes (Wagga -- Omeo Metamorphic Belt.) and these in turn collided with the Victorian Microcontinent and overthrust it. The Gilmore and Kiewa Sutures came into existence. The deformation and thrust pile-up of the Wagga Marginal Basin fill resulted in high-T/low-P metamorphism, with areas of ultra-metamorphism which led to the formation of anatectic S-type granites (Pogson, 1982; Scheibner, 1982). Subsequent granite plutonism lasted throughout the Silurian for about 30 m.y. (Fagan, 1979). Many plutons were emplaced in environments affected by stresses caused by new plate interactions, subsequent to the Benambran collision (Fig. 8). During the Benambran collision (Orogeny) the hypothetical oceanic plateau on the east was aecretcd and it tectonically underplated the region east. of the I--S line (Scheibner, 1982; Glen and VandenBerg, 1985). In the area west of the Kiewa Suture the rocks of the H o w q u a subzone and the Wellington Greenstone Belt (el. VandenBerg and Wilkinson, in Cooper and Grindley, 1982), representing cover of the Victorian Microcontinent, were thrust westward. They form a structure which best could be described as a fold and thrust belt (Fig. 7). The sedimentation in the actual foreland basin (Melbourne Trough), protected by the rigid basement, was continuous. The collisional forces, however, were transmitted westward by the rigid basement and the east-verging Stawell--Bendigo Foreland Fold and Thrust Belt developed (Cox et al., 1983). In the Kanmantoo Fold Belt, this collision caused a weak metamorphic event (Milnes et al., 1977). Because of the small size of the plates involved in the Benambran collision, deformation did not reach the magnitude observed during major plate collision. Rapid uplift and erosion is indicated by the presence of Early Silurian granite clasts in Silurian conglomerates in

Victoria. The W a g g a - O m e o Metamorphic Belt remained mostly emergent during the Silurian. If we accept Packham's (1985) model of strike-slip displacement of the Molong Volcanic Arc resulting at least in its repetition, there is no need to postulate splitting and development of the "Initial Cowra Trough". The belt of turbiditic sediments east of Parkes between the G o o n u m b l a and Molong segments could represent a fore-arc or back-arc basin.

Pre-accretionary deposits in the Molong Mierocon tinen t The Girilambone Group contains a number of copper deposits of moderate size in the Girilambone and Tottenham districts (Fig. 6, 1, and 2, respectively). These are considered to be pre-aceretionary deposits in strata which, as noted above, may represent part of the basement of the Molong Volcanic Are (and therefore pre-Ordovician) or be related to subduction west of the arc (and therefore partly Ordovieian). The Girilambone Group is an extensive sequence of mostly deepwater flysch-type sediments interbedded with metabasic schist (?metabasalt), graphitie schist, and magnetite quartzite at Tottenham (Suppel, 1975a, 1977) and chloritic schist, graphitic schist, and cryptocrystalline quartzite at Girilambone (Smith, 1976). The strata are characteristically complexly deformed. The copper deposits are conformable pyritic chalcopyrite bodies which, at Tottenham, overlie metabasie schist units. In geological setting and character they resemble the Besshi-type deposits of Japan (Sawkins, 1976) and deposits in the upper Cambrian--Ordovieian volcanic and volcanosedimentary sequences of the Caledonides of Scandinavia (Vokes and Gale, 1976). The deposits might also be compared with the recently formed hydrothermal deposits of talc and pyrrhotite containing significant copper and zinc which occur in the Guyamas Basin in the Gulf of California. These cteposits formed in a thick turbidite sequence in a

276 young, partly sediment-filled graben with evidence of contemporaneous or near-contemporaneous volcanism in the form of diabase sills and possible laccoliths (Lonsdale and Lawver, 1980). Some distance to the south, possible correlatives of the Girilambone Group, the Jindalee Group (Basden, 1982) contain small manganese deposits of syngenetic origin in the Cootamundra area {Fig. 6, 3}.

Pre-accretionary deposits and deposits related to the Benambran accretion and plutonism in the Lachlan Fold Belt Pre-accretionary deposits. A large number of relatively small deposits formed in the andesitic rocks of the Molong Volcanic Arc in the northern part of the Lachlan Fold Belt (Fig. 6). According to Bowman et al. (1983) these occur as: (1) native copper, copper carbonates and/or copper sulphides in andesitic and shoshonitic lards, thought to be deposited by late-stage fumarolic activity towards the tops of volcanoes (manto-type deposits); (2) stratabound disseminated to semi-massive copper sulphide deposits in tuff; and (3) vein and stratiform gold and copper--gold deposits in shallow marine sediments, on submerged parts of the volcanic rises adjacent to volcanic centres and in sediment-filled calderas. The Molong Microcontinent split into three segments. Volcanism continued on these segments forming the Goonumbla, Molong and Capertee Rises. The same types of deposits as those in the Early Ordovician were formed in the Late Ordovician. Southeast of Parkes, relatively small stratabound manganese deposits were deposited in fine grained siliceous sediments {cherts and jaspers) and minor basic volcanics in the Initial Cowra Trough {Bowman, 1977). Syn-accretionary (Benambran) deposits. Most mineral deposits in the W a g g a - O m e o Metamorphic Belt are probably related to the plutonic activity commenced during the

Benambran Orogeny and which ,:,:mtinued throughout the Silurian. These deposits art~ considered to be mainly post-Bcnambmm, however, and will be discussed in a following section. Vein gold deposits are present throughout Ordovician flysch rocks in southern sections of the Lachlan Fold Belt and in some areas, for example near the Gilmore Suture, these deposits may have formed from hydrothermal processes associated with regional metamorphism and granite generation .'luring the Benambran Orogeny (Herzberger et al., 1978: Degeling, 1982).

Deposits related to late stages of the Molong Volcanic Arc Deposits occurring in the northwestern segment of the Molong Volcanic Arc probably formed during later stages of arc development after the Benambran collision. It is therefore difficult to decide whether they are syn- or post-accretionary in character. Porphyry copper deposits were originated in intrusive-extrusive dacitic complexes within Ordovician to Silurian andesitic sequences {Bowman et al., 1983). By far the largest deposits discovered to date are in the Goonumbla area near Parkes {Fig. 8, 2), where exploratory drilling to date has defined a resource in excess of 250 × 10 ~ MT with mean grades of 0.7% Cu and 0 . 2 8 g M T -I Au {Jones, 1985}. These are high-level volcanic to subvolcanic porphyry-type deposits of Middle Silurian age located in the centre of a former caldera (Jones, 1985}. Mineralization is associated with quartz monzonite intrusions into comagmatic shoshonitic, latitic and trachytic volcanics (Clarke, 1985). Other porphyry copper deposits are located to the east, but at least some of these are of probable Early Devonian age (see following section on deposits related to Devonian plutonism). At Peak Hill (Fig. 8, I) 27 km to the northeast of Goonumbla, gold mineralization of epithermal type occurs in a Late Ordovician to Early Silurian andesitic volcanic pile.

277 Clarke and Krynen (1985) suggested that the mineralization is the result of a subvolcanic, comagmatic intrusion into the pile, and that it represents the upper part of a p o r p h y r y system. The age of the mineralization, therefore, could be Early (or Middle) Silurian. Age data are lacking, however, and an Early Devonian age cannot be discounted and the intrusive source in fact could be related to the K-rich magmas which gave rise to the Yeoval batholith a short distance to the east. Recent mapping and mineral exploration has delineated a narrow belt of andesitic volcanics, volcaniclastics and dioritic intrusions of (?)Ordovician to Silurian age flanking the Gilmore Suture on the east, extending from West Wyalong in the north to Temora in the south (Suppel et al., 1985, and in prep.). Additional volcanic sequences to the south, in the Junee area, are possible correlatives. These volcanics host a number of epithermal gold deposits notably the Gidginbung deposit (Fig. 8, 4) near Temora, discovered in 1983. The age of mineralization at this deposit, from dating of alteration minerals, is reported as Middle Silurian (Lessman, 1985). The tectonic setting of these deposits remains to be clarified. While these are situated apparently on Molong Volcanic Arc basement, the host rocks may have formed as part of development of the T u m u t Trough in the Middle Silurian (Suppel et al., in prep.). Therefore, the deposits could be regarded as pre-accretionary related to Silurian terrane dispersal rather than post-accretionary related to Benambran collision. Early Palaeozoic in the New England Fold Belt In the New England area, Cawood (1976, 1980) described Early Palaeozoic strata unconformably beneath the Early Devonian fore-arc sequence (Tamworth Group). The oldest sediments of late Middle Cambrian to early Late Cam brian age were derived from a volcanic arc. The well-documented accretionary prism complex (Woolomin Formation,

cf. Cawood, 1980) is pre-Early Devonian (Leitch and Cawood, 1980). Recently M.A. Lanphere (pets. commun., 1983) obtained Late Ordovician (444Ma) K--Ar ages on micas from blue schists at Port Macquarie (Barton et al., 1976). All these data point to an Early Palaeozoic convergent plate setting (Leitch, 1982), but it is difficult to relate it to the Ordovician model of the Lachlan Fold Belt. As already mentioned, Packham (1985) proposed transform displacement of the Ordovician Molong Volcanic Arc, and one segment he considered to be preserved below the Sydney--Bowen Basin (Meandara Gravity Ridge; Bramall and Qureshi, 1984). A more probable candidate is the gravity ridge (Namoi Gravity Ridge) under the Tamworth Belt. At, present it will be useful to treat the Early Palaeozoic rocks in the Peel Fault Zone as a suspect allochthonous terrane, Copes Creek Terrane (Scheibner, 1983, 1985) or Wisemans Arm Terrane of Cawood and Leitch (1985). Silurian to Early Carboniferous development o f Tasmanides The Silurian rock record indicates that subsequent to the Late Ordovician--Early Silurian Benambran Orogeny there was a major rearrangement of the active plate margin of eastern Gondwanaland (Fig. 8). New South Wales--Victorian segment during the Middle to Late Silurian In general, major changes occurred in the region between the Gambier -- Beaconsfield and Darling River Lineaments (Fig. 1) with most significant changes between the Darling River and Murray River Lineaments (Fig. 8), which functioned as transform fracture zones. With the exception of the Melbourne Trough, Early to early Late Silurian sediments arc absent west of the Gilmore Suture. In the Melbourne Trough south of the Murray River Lineament, sedimcntation between the Ordovician and Silurian was continuous and similar to that of Eastern Tasmania (of.

27S Ramsay and VandenBerg, this volume). East of the Gilmore Suture, during the Middle and Late Silurian several nearmeridional extensional volcanic rifts and troughs formed (Fig. 8). At least one of these troughs, the T u m u t Trough, was partly floored by ophiolites (Ashley et al., 1979). Judging from the large thickness of sediments in the Hill End and Cowra Troughs (cf. Packham, 1969) extensive thinning of the crust is indicated. Although there is no direct evidence, new crust may have been created locally by dyking or diffuse seafloor spreading. These troughs had at the outset the character of volcanic rifts or volcano-tectonic depressions containing some Kuroko-type massive sulphide mineralization (Gilligan et al., 1979). Volcanism in rifts was bimodal, though dominantly felsic. Subsequently, these troughs were filled predominantly by turbidites which initially were quartz rich and later became lithic and volcaniclastic, plus pyroclastic (Packham, 1968; Cas, 1978a). Locally, deep-water emplacement of silicic lavas has been d o c u m e n t e d (Cas, 1978b). Marginal trough facies include olistostromes and slump deposits (Crook and Powell, 19761. The intervening ridges, rises, or highs were sites of shallow-water sedimentation (some carbonates} and submarine to subaerial volcanism. Some of these volcanic piles of Sand I-type character (Owen and Wyborn, 1979; Wyborn et al., 1981) were intruded by comagmatic granites. On the rises, which had previously been the site of Ordovician arc volcanism, Siluro-Devonian p o r p h y r y - t y p e mineralization was associated with felsic igneous activity (Bowman et al., 1983). The stratigraphy and lithology of all these Silurian rocks has recently been described (Pickett, 1982: Cas. 1983). New England Fold Belt region during the Silurian Late Silurian calc-alkaline volcanics, volcanic sediments, limestone, and chert in the Queensland portion of the New England Fold Belt provide evidence for an intra-oceanic

volcanic island arc, which has been called tht:. Calliope Island Arc by Day et al. (1978) isee "also Murray, this volume). The mair', dew~l opment of this are took place during theDevonian. It is possible that this volcanic: arc continued farther south into N.S.W., and due to subsequent displacement occurs west of the Tamworth Belt, concealed beneattl younger sediments. In N.S.W., to ti~e east of the hypothetical continuation of this volcanic arc, coralline limestone blocks and slices of uncertain origin occur, perhaps representing guyot cappings. The limestone sli,::es are associated with major faults and serpentinites in the Woolomin Formation. 'Fhe Woolomin Formation, a sequence dominated by cherts and basic volcanics, has been interpreted t)y most authors to be the remains of a subduction complex. Detailed descriptions tlave only recently been provided by Cawood (1980). Limestone blocks occur also as clasts in the Devonian Wisemans Arm Formation (Leitch and Cawood, 1980). Marsden (1972) suggested that ti~e SiluroDevonian Calliope Volcanic Arc in Queensland was separated by a marginal sea from the regions to the west. A similar marginal basin (Murruin Basin) possibly existed in the south (Scheibner, 1974a), and hence the whole New England region, at least for part of ;,t~is time, could have been a separate terrane. Deposits and metallogeny of Silurian rocks in the New England region will be discussed together with younger pre-accretionary deposil;s. Tectonic models for the Middle t~J Late Silurian It is perhaps premature to suggest a tectonic model which would satisfactorily explain 'all the different tectonic settings in Eastern Australia deduced from scattered and often sketchy data, especially if the New England region was a separate super-terrane. Recently, Powell (1983b, 1984b) proposed a tectonic model envisaging a simple and constant plate geometry during the transition from the [,ate Ordovician to Silurian palaeo-

27,(} geography and this puts southeastern Australia into regional dextral shear. He compared the region of the Tasmanides during Silurian -Devonian to the present western North America characterized by a wide Basin and Range Province. Arguments against this model have been discussed recently (Scheibner, in press). We are still inclined to follow the earlier model (Scheibner, 1976) in which the major palaeogeographic changes during the Silurian south of the Darling River Lineament were the consequence of "stepping o u t " of subduction (a new subduction zone) to the east. The problem is that the first evidence for this new subduction arrangement, the Calliope Volcanic Arc, commenced in the Late Silurian, while the earliest extensional basins farther south in the Lachlan region had started to form in the Middle Silurian. This could reflect northward progression of the subduction. Another complication is that the previously mentioned New England region could have been a distant separated terrane. If a model, in which the Calliope Volcanic (island) Arc, despite its possible distant. separation, was the frontal volcanic arc, is accepted, then all the Lachlan region would have been in a back-arc position. Such regions are characterized by extension. If the subduction was oblique, besides extension due to roll-back of the subduction zone, a transtensional c o m p o n e n t would also have been generated, and such a tectonic regime is indicated by available data for the region east of the Gilmore Suture. Insufficient structural data and the effects of Devonian to Carboniferous deformations, which severely distorted the original shape of the Middle to Late Silurian extensional traughs, make it difficult to deduce reliably the sense of transtension.

Deposits related to Silurian terrane dispersal and Silurian plutonism in the Lachlan Fold Belt Pre-aecretionary deposits. During the Silurian, a range of pre-accretionary deposit types formed in the Lachlan Fold Belt.

Stratabound base-metal deposits lie within Silurian felsic volcanic rocks and marine sediments 'along the margins of the Hill End Trough (for example, Mount Bulga, Fig. 8, 3) and within the Captains Flat Trough (Woodlawn and Captains Flat, Fig. 8, 6 and 7). As noted above, these deposits are similar in many respects to the Kuroko deposits in Japan (Lambert, 1979). They have been the subject of numerous studies (e.g., Gilligan et al., 1979; Ramsden and Ryall, 1979; Ayres, 1979; Ayres et al., 1979; Seecombe et al., 1984). The copper deposits in the Tumut Trough occur in a belt characterized by a greater abundance of andesitic and basic rocks than the other troughs Ramsden l in Ramsden and Ryall, 1979) considered that the basic composition of the unit which hosts the Basin Creek deposit (Fig. 8, 5), suggests that the mineralization is not of Kuroko type. Podiform chromite deposits occur in the Coolac Serpentinite, part of the Coolac Ophiolite Suite thought to represent oceanic crust of the Tumut Trough floor (Ashley et al., 1972; Basden, 1982). These deposits are cumulates within the serpentinite which has been tectonically emplaced as a narrow belt along the eastern margin of the T u m u t Trough.

Deposits related to granitic plutonism. The widespread granitoid emplacement in the Lachlan Fold Belt in the Late Silurian and Early Devonian resulted in the formation of numerous mineral deposits. The Silurian and Early Devonian granitoids can be divided into three northerly trending belts (Fig. 10). These are (Suppel and Degeling, :I 982a, b): (1) A western belt of mainly S-type granitoids, with some younger leucogranites (including possible A-type granitoids and some I-type granitoids). Granite related mineral deposits mostly contain tin and tungsten (Fig. 11). (2) A central belt of both S- and I-type granitoids containing small tin--tungsten, tungsten--molybdenum and copper-- iron deposits. The Gilmore Suture marks the

280

tungsten-bearing granitoids may h a v e been derived by partial melting of the flys('h rocks of the W a g g a - O m e o Metamorphic Belt, whereas the source of the S-type ~ranito~d.~ to the east may have been a pre-Ordovic:ian. more plagioelase-rich sequence (Fa~an, 1979; Wyborn and Chappell, 1979). A number of leucogranites occur in ~he t.in---tun~sten belt and it is possible that some (ff these are younger A-type granites, although this (:annot, be determined until trace-element data a~c available. Plimer {1982) has suggested that A-type granite is the source of tm mineralization at Doradilla, in the north ~1" [;he belt (Fig. ]1, l ) .

boundary between the central and western belts (Fig. 12). (3) An eastern belt of I-type granitoids which contain m o l y b d e n u m and copper--l e a d - z i n c - s i l v e r deposits. The boundary of this belt with the central belt is the I--S line of White et al. {1976) (Fig. 13). The limited whole-rock (:hemical data available suggest that the S-type granitoids differ in composition across the belt. The t i n tungsten deposits of the western belt occur in a northerly trending zone of granitoids in the west, which have lower calcium and potassium and perhaps higher silica than those to the east in the western and central belts (Suppel and Degeling, 1982b). The t i n -

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Early to Middle Devonian in the Lachlan and K a n m a n t o o Fold Belts Major changes occurred in this region during the earliest Devonian (compare Figs. 8 and 9). Immediately to the east of the Gilmore Suture, the Tumut Trough in N.S.W. (Crook and Powell, 1976; Basden, 1982) and the Cowombat Rift in Victoria (see Ramsay

and VandenBerg, this volume) were closed and inverted and their fill was deformed and metamorphosed. Silurian granites were unroofed during the latest Silurian to earliest Devonian Bowning event (cf. Packham, 1969). At about the same time, to the west of the Gilmore Suture, formation of the Darling Basin was accompanied by rift-related

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282

volcanism along much of its eastern margin and in the adjacent Mineral Hill " t r o u g h " . The Mineral Hill " t r o u g h " was characterized by volcanism in a generally shelf-like area of sedimentation. Farther west, in the region of the K a n m a n t o o Fold Belt in northwestern N.S.W., rift-related volcanism developed (Cootawundy beds). The Adavale Basin and the eastern side of the Anakie lnlier in the Thomson Fold Belt in Queensland also conrain Early Devonian volcanics (Murray, this volume). South of the Darling River Fracture Zone, now a lineament, felsic volcanics predominate, whereas those of intermediate composition are absent. Minor basic rocks in the Darling Basin (Mount Hope Trough, volcanic cauldron or volcano-tectonic depression) reflect bimodal rift volcanism (Barton et al., 1982). To the north of the Darling River Lineament, mafic-intermediate volcanics (basaltic andesites) occur as well as felsic rocks in the C o o t a w u n d y beds (G. Neef, pers. commun., 1984). Mafic andesites present in the Louth Block of the Darling Basin around L o u t h and Bourke (encountered during mineral exploration drilling) were previously ascribed to the Ordovician; however, an indeterminate bryozoan fauna of younger aspect is associated with them (J.W. Pickett and D.W. Suppel, pers. commun., 1984). Marie continental andesitic and felsic volcanics (Gumbardo Formation; Galloway, 1970) also occur in the Adavale Basin and on the eastern side of the Anakie [nlier (cf. Day et al., 1983). Near the Cobar--lnglewood Lineament the rifts appear to be symmetrically arranged, trending northwest-southeast to the north and northeast-southwest in the south (cf. Fig. 9). The north-northwest-trending Mineral Hill Trough, which is close to the Gilmore Suture, is an exception to this pattern. During the Early Devonian basin formation in the Darling Basin, rifts and pull-apart structures appear to have been associated with dextral master faults, whereas a sinistral sense is indicated for the Mineral Hill Trough (Scheibner, 1983; Glen et al., in prep.). In-

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tensive volcanism in the Darling Basra oc.. curred south of the Lachlan River Fracture Zone, now a lineament (Sc.heibm~r ai~d Stevens, 1974) and to the north or the Darling River Fracture Zone. In the Mineral Hill Trough, by way of contrast, v(~lcanism developed between these lineaments. In the; eastern part of the Darling Basin, mainly in the Cobar Basin, but to a lesser extent in the Mount Hope and Rast Troughs, large thicknesses (up to 10km) of mainly mrbiditic sediments accumulated (luring the Early Devonian, while shallow-water facies dominated elevated blocks and areas to the west (Glen, 1982b; Glen et al., in prep.~. The Cobar Basin and Mount Hope and Rast Troughs, despite large thicknesses of sedimentary fill, show relatively positive Bouguer anomalies, perhaps reflecting crustal thinning during basin formation and underplating by denser material (Scheibner, 1983). This interpretation has been used to extend the suspected rifts towards the southwest (Fig. 9) into areas concealed beneath the Late Carboniferous to Cenozoic platform cover. Early Devonian granites comagmatic with the rift volcanics occur in the Darling Basin (Mount Hope Trough; of. Barron et al.. 1982), while the tectonic setting of the Tibooburra Granite in northwestern N.S.W. (410Ma) (Shaw, in Cooper and Grindley, 1982) is unknown. The Silurian palaeogeography, east of the Gilmore Suture, with the exception of the Tumut Trough, continued without much change into the Early Devonian and lasted generally into the Emsian. Plutonic activity increased during the Devonian, with emplacement of large I-type batholiths east of the I--S line during the Early to Middle Devonian (White and Chappell, 1983). The southern part of the Lachlan region, as well as experiencing plutonism, was also strongly affected (folding and strike-slip faulting) by the Middle Devonian Tabberabberan event (Packham, 1969), giving rise to the Tabberabberan Highlands which became the source of molassic elastics (Powell, 1984b). While this event had

285 diminished effects towards the north and west in N.S.W. (Powell and Edgecombe, 1978; Powell and Fergusson, 1979; Powell et al., 1980: Glen, 1982a), pre-cratonic facies were replaced by transitional tectonic molassic facies everywhere in the Lachlan region.

Early to Middle Devonian in the N e w England region The Silurian palaeogeography continued into the Devonian in the New England region. In addition to the Calliope Volcanic Arc and its continuation, the Baldwin Volcanic Arc (Veevers et al., 1982) in N.S.W., shelf sedimentation characterized by volcanic detritus to the east (Yarrol Shelf in Queensland and Tamworth Shelf in N.S.W.) can be recognized. This shelf belt is usually interpreted as a forearc basin (Leitch, 1974, 1975; Day et al., 1978; Crook, 1980; and others). There appears to be a change from intermediate to felsic rocks with time (Crook, 1964), probably reflecting maturing of the volcanic arc. Pelagic and turbiditic sediments and basic volcanics of ophiolitic character occur to the east of the Yarrol and Peel Fault Zone Systems (thrusts). The pelagic and turbiditic sediments are interpreted as part of an accretionary prism [Wandilla Slope and Basin in Queensland (Day et al., 1978), and Woolomin Slope and Basin in N.S.W. (Scheibner, 1972b, 1 9 7 4 b ) ] . The name Woolomin Slope and Basin should not be used for the Devonian because the Woolomin Formation is of pre-Early Devonian age (Leitch and Cawood, 1980), and instead the name Cockburn, deriw;d from the Devonian Cockburn Formation (Cawood, 1980), will be used. :\ late Middle Devonian event, which correlates with the Tabberabberan Orogeny in the Lachlan region, affected the Calliope Island Arc. The marginal sea (Marsden, 1972) which separated the New England region from the rest of the Tasmanides, in the west, was closed not only in Queensland but also in N.S.W. (Murruin Basin). Some granitoids were

emplaced in the Calliope Island Arc. Local unconformities and disconformities (cf. Korsch and Harrington, 1981) are an expression of this event in the Tamworth belt.

Tectonic models for the Early to Middle Devonian The tectonic models previously discussed for the Late Silurian also apply to the Early to Middle Devonian. It can be speculated that the mode of subduction changed from Mariana- into Chilean-type, probably due to the arrival and subsequent accretion of a hypothetical terrane, perhaps an oceanic plateau, at the Australian plate margin. This feature has not been identified with certainty, but Solomon and Griffiths (1972) suggested that the Lord Howe Block was a Precambrian crustal block which collided with the Lachlan orogen. The collision causing the Tabberabberan event (folding, strike-slip faulting and plutonic activity) seems to have progressed from south to north, with deformational effects dying out. northward and westward in N.S.W. This collision resulted in the progressive emergence of the Lachlan orogen, giving rise to widespread subsequent molassic deposits that accumulated in late orogenic transitional tectonic basins. The onset of molassic sedimentation was diachronous progressing from the craton towards the zone of collision. The convergent margin in the New England region continued into the Late Devonian. Powell (1984b) suggested that an eastwardmigrating heat source under the Lachlan region can explain the distribution of orogenic granitoids. However, whereas the general easterly younging is valid for the eastern part of the Lachlan region, opposing trends are present in Central and Western Victoria and elsewhere. Increase in crustal thickness due to the Tabberabberan collision probably contributed to the associated plutonism, but no widely accepted model for the genesis of igneous activity has been put forward.

Deposits related to Devonian t errane dispersal, Devonian plutonism, and the collisional Bowning and Tabberabberan even ts Deposits related to terrane dispersal. Large (several millions to tens of millions of tonnes) base-metal and gold deposits are situated in fine-grained sedimentary rocks in the Cobar Basin at Cobar (Fig. 9, 7 and 8). There is sharp disagreement a b o u t the origin of these deposits. They exhibit strong structural control and in most deposits ore lenses are aligned in cleavage. The sediments contain little or no evidence of volcanic activity, although contemporaneous volcanism was widespread in shelf environments to the east and south of the basin. Sangster (1979} suggested that the deposits exhibit metal zoning and are exhalative, plus sub-exhalative (feeder zone) in character, an interpretation strongly opposed by O'Connor i1980). Suppel (1984) also suggested that the deposits are exhalative and were formed within a major basin of intracratonic character, possibly by solutions generated at depth by magmatic activity or high heat flow within the basin which, as suggested above, may have resulted from crustal thinning and underplating by denser material. Water released during subsequent greenschist metamorphism may have caused substantial metahydrothermal remobilization of mineralization into the strong slaty cleavage. Schmidt (1983) favoured a replacement origin for the Elura silver-l e a d - z i n c deposit at Cobar (Fig. 9, 9) with rupturing of an anticline allowing upward escape of metal-bearing basinal brines. Glen (1984) and Glen et al. (1985) suggested that the Cu-~-Au deposits are epigenetic and formed in hydraulically generated fractures associated with faults focussing hydrothermal fluids generated during regional metamorphism. The source of the metals is thought to be disseminated sulphides (or somewhat enriched sources) in the sedimentary pile or in the basement. Glen suggested a Carboniferous age for the regional metamorphism and thus

formation of the deposits at Cobar. which m this model, would be post-accretionary. Kirk (1983) "also considered that mine!"aiizati~.)i~ formed during Carboniferous regional mete.,. morphism and deformation. The contemporaneous Early l)ew~nian felsic volcanic sequences in the ('oi~ar region contain volcanogenic ba.~e metal dnd gold deposits in the Mount l-lope and Shutt.leton areas to the south of Cobar (Fig. 9 . . ! 0 and 11) and in the Canbelego area t.o the east (deposit 12) (Gilligan and Suppei, 197S; Barton et al., 1982; Suppel and Gilligan~ 1983; Gilligan, 1983). The felsic volcanics in the Mineral Hill "Trough" are i)robably slightly older than those at Canbelego and Mount Hope. The volcanics in the Mineral Hill Synclinorial Zone (see Fig. 2) contain base metal and gold deposits at Mineral Hill and Boona (deposits 13 and 14) (McClatchie, 1971). Deposits related to plutonism. As noted above, Early Devonian granitoid bodies occur in the Lachlan Fold Belt, notably in the east, and these host numerous small deposits. At least some of the porphyry copper deposits on the Molong Rise could be Early Devonian in age. The Copper ttill deposit (Fig. 9, I7) has been interpreted as Early (or Middle) Devonian age on stratigraphic grounds (Chivas and Mutter, 1975; Chivas, 1976). Host intrusions at Yeoval and Cadia (Fig. 9, 16 and 17) have Early Devonian radiometric ages (Gulson and Bofinger, 1972, Ambler et al., 1977, respectively). The magmas with which the porphyry copper deposits are associated could have been formed by later melting of the rocks of the mature Molong Volcanic Arc (Suppel and Degeling, 1982b). Dioritic intrusions may be the source ~)f some gold mineralization in stratabound and disseminated deposits in Ordovician andesitic sequences on the Molong Rise, for example, at Junction Reefs (Leahey, 1981) and Browns Creek (cf. Taylor, 1983; Fig. 9, 19 and 20). Alaskan-type intrusions within the Giri-

287 lambone Group, near the eastern of the two northern strands of the Gilmore Suture mentioned above, were emplaced in the Early Devonian. Intrusions near Fifield very probably were the source of alluvial platinum in the district (Fig. 9, 15). In the Kanmantoo Fold Belt, copper deposits occur in fault zones and veins at Wertago {Fig. 9, 6) in both Early Devonian sediments {Cootawundy Beds) and in the Wonominta Beds. These deposits are situated close to mineralized {?)Devonian quartz porp h y r y intrusions, which are post-accretionary deposits with respect to the Kanmantoo Fold Belt, but resulted from possible rift volcanism and plutonism associated with the described limited terrane dispersal in the Lachlan Fold Belt. In the eastern segment of the Lachlan Fold Belt, the Early- {?)Middle Devonian Bindook complex represents a major caldera structure (Fergusson, 1980). At Yerranderie {Fig. 9, 21), silver lodes occur close to a crater rim and in adjacent pyroclastic rocks of the volcano.

Late Devonian--Early Carboniferous in the Kanmantoo and Lachlan Fold Belts In northwestern N.S.W. and eastern South Australia, major subsidence of certain crustal blocks occurred within the K a n m a n t o o Fold Belt and resulted in accumulation of over 4 k m of molassic continental clastics, including red beds {Bancannia and Renmark Troughs; Fig. 14). These continental elastics are similar to the coeval clastics in the Lachlan Fold Belt (Packham, 1969; Evans, 1977). The so-called Lambian Transitional Tectonic Province molassic rocks in the Lachlan Fold Belt are preserved in superimposed synclinoria (Scheibner, 1976). They comprise some marine facies in the east, but are mainly continental clastics, including red beds (Conolly, 1969a, b). Controversy exists as to whether they formerly constituted a continuous sedimentary blanket (Powell, 1984b) or were isolated intramontane basins (Conolly, 1969a,

b; Cas, 1983). Onset of sedimentation was diachronous, and this to some extent helps to define three main basinal areas: the Barka Basin in the west (Glen et al., in prep.; formerly the Ravensdale Terrestrial Basin of Scheibner, 1974a), the ttervey Basin to the east (Conolly, 1965a), and the Lambie Basin farther east (Conolly, 1969a, b). It is possible that during the Late Devonian all these basins, including regions to the west in the Kanmantoo Fold Belt, formed a wide blanket as suggested by Powell (1984b). Sedimentation in the Barka Basin started in latest Early to early Middle Devonian (Glen 1982a), whereas in the east sedimentation commenced in the Frasnian (Conolly, 1969a, b; Roberts et al., 1972). Sedimentation was preceded on the South Coast of N.S.W. during the late Givetian or early Frasnian by volcanic rifting which resulted inthe Eden--Comerong --Yalwal Rift (McIlveen, 1974). Bimodal volcanics are intercalated with continental and marine strata in the rift (Steiner, 1975; Fergusson et al., 1979). Associated with this rifting are A-type granitoids {Collins et al., 1982). The greatest thickness, 4.7 kin, of preserved sediments appears to be around Taralga in N.S.W. (Powell and Fergusson, 1979) indicating more intensive basin formation. Here, according to Powell, the upper part of the section contains volcanolithics derived from an eastern volcanic arc, which he correlated with either the frontal arc in the New England region or a second arc west of it. It is assumed that the upper limit of the Lambian rocks is the same as that in northwestern N.S.W. where Evans (1977) identified Early Carboniferous spores. The Kanimblan event during the Early Carboniferous caused metamorphism, folding, and faulting, and converted the Lachlan Fold Belt into a neocraton (Packham, 1969; Powell, 1976).

Late Devonian--Early Carboniferous in the New England region Subsequent to the Tabberabberan accretion

288 of the composite New England Terrane. an Andean-type continental volcanic arc (arch} developed along the western margin of the New England region. In Queensland it has been named the Connors--Auburn Volcanic.' Arc or Arch (Day et al., 1978), whereas its continuation in N.S.W. is concealed beneath the Sydney--Bowen basin. Powell (1983a, 1984b) suggested that this arc continued farther south, just east of the Lambie Basin, and was the source of the volcanolithic detritus for the upper part of the Lambie C,roup rocks. In the northern segment (Connors Arch), massive andesite flows predominate over felsic rocks and locally abundant basalts. In the southern segment {Auburn Arch) the felsic rocks predominate, with locally abundant andesites (Marsden, 1972; Day et al., 1978). The volcanolithic detritus derived from the N.S.W. portion of the arc indicates that it was of andesitic to dacitic character {Crook, 1964; Powell, 1984b). To the east of this volcanic arc {arch) the fore-arc basin had the character of an unstable shelf. The sediments in the fore-arc basin were dominated by volcaniclastics derived from the arc and interbedded primary volcanics {Crook, 1964; Marsden, 1972). During the widespread marine transgression in the Early Carboniferous, distinctive oolitic limestone formed locally. The oolites were redeposited and transported eastward into a deeper shelf and slope environment and enable dating of otherwise mostly sterile flysch sequences {Fleming et al., 1974). The fore-arc basin passed eastward into a continental slope and ocean basin environment which in Queensland is referred to as the Wandilla Slope and Basin. Day et al. (1978) used the name Woolomin Slope and Basin for its extension in N.S.W. However, as mentioned above the name Woolomin is not appropriate and should be replaced by the name Cockburn for Devonian complexes and Texas for Carboniferous complexes. The name Texas has been used previously (Scheibner, 1972b, 1974a) and it (.'an be

expanded into Texas--Coffs Harbour Slope and Basin to include the most typical region. The typical rocks of this zone comprise cherts and metabasalts, but the ~equencc mostly consists of volcaniclastic and quartz arenites deposited by turbidity currents and are interbedded with massive argillite.~. Slump deposits are also common. Fergusson !1982a, b) has described melange.s and imbricate structures from the Coffs Harbour Block in N.S.W. and suggested that these rocks represent an accretionary prism. Re.deposited oolites and Early Carboniferous fossil fragments from the fore-arc basin occur in some parts of this accretionary prism and help in stratigraphic correlations ~Fleming et al., 1974). The Early to Middle Carboniferous Kanimblan event, which so profoundly affected the rest of the Tasmanides, had only a mild localised expression in the New England region, with major changes taking place during the Late Carboniferous. In the Yarrol Shelf, during the late Early Carboniferous marine regression, the area of sedimentation decreased. The waning of the arc vok:anism was reflected in a change of prow~nance of the detritus from volcanic to igneous (based on quartz type; Day et al., !978; Roberts and Engel, 1980). In the N.S.W. portion, felsic volcanism with rare andesites continued. In the fore-arc basin in N.S.W. shallow-marine sedimentation was limited to the eastern part of the shelf, while elsewhere continental sedimentation predominated (Roberts and Engel, 1980}.

Tectonic models for the Late Devonian-Early Carboniferous Most of the published tectonic models for the Late Devonian to Early Carboniferous {recently reviewed by Leitch, 1982; Day et al., 1983; Powell, 1984b; and Murray, this volume), envisage a convergent continental margin in the New England region {superterrane) which was accreted during the Tabberabberan and Carboniferous events. A continental volcanic arc /arch) developed in

289 the general zone of terrane accretion (suture). The fore-arc basin and the accretionary prism to the east of the arc indicate westward subduction. In contrast, however, Harrington and Korsch (1985a) suggested that this arc was west-facing (eastward subduction) and rejected the interpretation of Carboniferous rocks as representing an accretionary wedge put forward by Fergusson (1982a, b). The rest of New South Wales was characterized by transitional tectonism. There was widespread molassic sedimentation of predominantly continental facies with marine inc.ursions from the east, and rift-related volcanic (bimodal) and plutonic (A-type) activity. This development happened in a partly stabilised wide back-arc region which was dominated by the stresses generated by convergence, i.e. subduction of the hypothetical Pacific plate and rotation of the East Gondwanaland continental plate. This development terminated during the late Early and Middle Carboniferous Kanimblan event. Structures formed during this event indicate a general east--west compression, perhaps with some oblique component. However, structures (thrusts and nappes) present in the Amadeus Transverse Zone of Rutland (1976) in the centre of the Australian continent and formed during the generally coeval Alice Springs event indicate north--south compression. Recently Powell (1984a) interpreted major kink zones from the Tasmanides apparently post-dating east--west compressional structures as being a result of this same continental-wide north--south compression. Deposits related to Late Devonian rifting and plutonisrn and Kanimblan metamorphism, Lachlan Fold Bell Late Devonian rifting and plutonism. The subaerial felsic volcanic rocks of the Eden-Comerong--Yalwal rift zone host epithermal gold deposits, the largest being located in the Yalwal and Pambula areas (Fig. 14, 1 and 2; McIlveen, 1974; Wall, 1976). The source of

the related Late Devonian A-type granitoids on the South Coast of New South Wales is considered to be residual material from which earlier I-type granitoids had been extracted. A-type magmas may have an enhanced capacity to incorporate and transport metals. The granite at Whipstick {Fig. 14, 3), near Bega, may be an A-type intrusion and contains the comparatively large Whipstick molybdenite deposit (Suppel and Degeling, 1982b). Kanimblan metamorphism. There is some disagreement a b o u t the timing of regional deformation of the Hill End Trough. Powell et al. (1976) have suggested an Early Carboniferous (Kanimblan) age rather than a Mid Devonian (Tabberabberan) age. The large vein gold deposits at Hill End (Fig. 14, 4) possibly formed from solutions mobilized during formation of regional slaty cleavage in the Hill End Trough. As noted above, Kirk (1983), Glen (1984), and Glen et al. (1985) favoured a metamorphogenic origin for the large Cobar deposits and suggestect a Carboniferous age for the metamorphism. Pre-accretionary deposits in the N e w England Fold Belt Stratabound indigenous mineralization characterises the metallogenesis of the preaccretionary terranes of the New England Fold Belt. Three accretionary prism complexes have been recognized, viz. the preEarly Devonian Woolomin Formation (Leitch and Cawood, 1980), the Devonian Carboniferous "Sandon Association" (Cockburn Formation and Sandon beds), and the Carboniferous accretionary prism rocks in the Coffs Harbour Block (Fergusson, 1982). The Woolomin Formation (Fig. 8) is distributed east of the Peel Fault System and is characterized by chert, fine-grained elastics, jasper, and mafic volcanics, and may represent the superstrate to an ophiolite complex as is developed at Port Macquarie (Barron et al., 1976). Massive cupriferous pyrite deposits arc liberally distributed throughout the Woolomin

290

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Formation (Lusk, 1964; Fitzpatrick, 1975a, b) (e.g., Fishers copper mine, Fig. 8, 8). These deposits are intimately associated with mafic volcanics of tholeiitic affinity (Herbert, 1982), and chert and jasper, and are regarded as being of Cyprus-type (Fitzpatrick, 1975a, b; Herbert, 1982). Stratiform manganese deposits (oxides and rhodonite) in this complex are regarded as oceanic syndepositional chemical sediments (Fitzpatrick, 1975a, b). The "Sandon Association" (Korsch, 1977) (Sandon beds and Cockburn Formation,

Cawood; 1982, Fig. 14) comprises turbidites, chert and minor mafic volcanics. This association is juxtaposed to the east of the Woolomin Formation, and also occurs as fault blocks throughout much of central and southern New England. Stratabound cupriferous pyrite deposits have been recognized at a number of localities in the complex, e.g., Bundarra copper mine (Fig. 14, 5; Weber, 1975} and Greengate No. 1 {Fig. 14, 6; McKay, 1967). Stratiform manganese deposits are liberally distributed through these rocks in central

291 New England. Commonly, areally associated with the manganese deposits are gold-quartz veins and it has been argued (Gilligan, 1982) that there may be a genetic relationship where the gold was derived, late in the deformation history, from exhalite chert horizons spatially associated with the stratiform manganese deposits. The Carboniferous rocks of the northern Cells Harbour Block host both slcratiform, chert exhalite gold horizons (Dalmorton, Fig. 14, 7: Keevers and &rues, in press) and stratabound cupriferous pyrite mineralization (Nit. Browne copper mine; Fig. 14, 8). Extensive quartz- magnetite units have been identified but as yet are not precisely defined. Such units appear genetically relat.ed to both the gold exhalites and to stratabound copper mineralization. Numerous discordant gold--quartz vein deposits in the complex (Coramba--49rara gold field) probably are metahydrothermal in origin with the mineralization derived from various gold-exhalite horizons and pillow basalts (Keevers and Jones, in press; Gilligan et el., in prep.).

Late Carboniferous to Triassic development Late Carboniferous to Triassic. platform cover of the Tasmanides The Kanimblan event was followed by the early Late Carboniferous episode of continental and highland glaciation (Powell and Veevers, in Veevers, 1984). Subsequent deposition in the Kanmantoo, Lachlan, and Thomson Fold Belt. regions occurred in platformal epicratonic basins during the Late Carboniferous--Early Permian and Permian-Triassic, in typical Gondwana facies (Veevers, 19841. Continental to marine glacigene sediments are present in the Galilee and Cooper Basins and Lovelle Depression in Queensland and in basins mostly concealed beneath the Cenozoic Murray Basin (Fig. 16), in the three southeastern states. Some outcrops of glaeigene sediments are found in South Australia and Victoria, and in the

Tasmania Basin (of. Doutch and Nicholas. 1978; Veevers, 1984).

Late Carboniferous--Triassic post-kinematic igneous activity in the Lachlan Fold Belt Subsequent to the Kanimblan event, postkinematic l-type granitoids (Bathurst-type of Vallanee, 1969) were emplaced in the northeastern part of the Lachlan Fold Belt. Some volcanics (Rylstone Tuff) locally appear to have boon associated with them. Aeromagnetic data indicate that these granites occur in the subsurface beneath the Meso-Cenozoic cover farther north towards the Cobar--Inglewood Lineament (A. Agostini, pers. commun., 1984). Tectonieally, this igneous activity is p ~ t of the Lambian Transitional Tectonic Province and might be related to the increase of crustal thickness and deep crustal fract.uring associated with suspected transcurrent faulting (Seheibner and Stevens, 1974). Late Carboniferous post-accretionao, deposits, Lachlan Fold Belt Deposits associated with the Late Carboniferous I-type granitoids of the northeastern segments of the Lachlan Fold Belt (Fig. 15) exhibit a similar metallogenic character to the Early Devonian l-type granitoids of the Eastern Belt. The deposits contain molybd e n u m - c o p p e r - - t u n g s t e n (minor tin), lead-silver and gold (Stevens, 1975). Sydney--Bowen Basin During the latest Carboniferous and earliest Permian, west of the composite New England super-terrane a foreland basin (foredeep) dew,qoped spanning the zone of accretion. In Queensland, it is called the Bowen Basin and this unit continues into northern N.S.W., where it narrows north of Narrabri. The N.S.W. portion of this basin is known as the Sydney Basin. In the structural sense, the portion between Narrabri and the Liverpool Ranges to the south is referred to as the Gunnedah Basin, and farther south is named the Sydney Basin (sensu stricter.

292 In N.S.W., the relationship between the foredeep and the New England orogen is complicated. The foredeep was superposed on the frontal volcanic chain, and a close relationship is suggested with the fore-arc basin area. In the Gunnedah Basin, volcanism was widespread during the latest Carboniferous and earliest Permian, and there is good evidence for rift-related bimodal volcanism (Boggabri Volcanics and Werrie Basalt; Runnegar, 1970). In the northeastern part of the Sydney Basin, a northwest-trending depression developed during the latest Carboniferous, and fluvio-glacial sediments were followed by marginal marine sediments and interbedded volcanics (Mayne et al., 1974). In the southern part of the basin, glacigene and fluvio-glacial elastics were deposited in broad valleys, probably draining glaciated highlands to the west (Herbert, 1972). During the Early Permian a major transgression occurred which, according to Evans and Roberts (1980), was related to eustatic sea-level rise. This transgression resulted in widespread marine sedimentation in the Sydney -- Bowen Basin. At the basin margin, coal measures and other continental facies interfingered with marine facies. Volcanic activity during the Early Permian in New South Wales had a bimodal character with marie rocks predominating. Sedimentation increased rapidly east of the north-south trending "hinge line" through Mount Tomah (cf. Bembrick ct al., 1973; Herbert and Helby, 1980). During a b o u t the mid-Early Permian a major orogenic event occurred in the New England Fold Belt, and was expressed as a regression in the Sydney--Bowen Basin (Evans and Roberts, 1980). Connection between the Sydney and Bowen basins was interrupted (Runnegar, 1970) and widespread coal measures accumulated. This regression was followed by another transgression during the late-Early Permian reflecting a new eustatic sea-level rise (Evans and Roberts, 1980). During the Late Permian, marine regression was followed by deposition of coal

measures, and there was deposition of continental (mainly fluviatile) to marginai marirw facies during the Triassic. In N.S.W.. i h,' Sydney Basin was th(, main del)ocent(,r (Mayne et al., 1974: Herbert and Hell)y, 1980). The S y d n e y - - B o w e n basin was deformed during Late Triassic: time. The structures indicate an increase in intensity of defor. mation towards the orogen, which overthrust its foredeep along the H u n t e r -Mooki ...... Goondiwindi Thrust System (of. [3embrick et al., 1973).

Late Carboniferous--earliest Permian in the New England Region During the early Late Carboniferous in N.S.W., in the area of the previous frontal volcanic arc, volcanism continued, but with a changed character. Widespread ignimbrites, especially during the Late Visean, were interpreted (Scheibner, 1974a, 1976) as reflecting volcanic rifting (Ayr Volcanic Rift). Towards the east, close to the volcanic chain, sedimentation comprised continental and marginal marine facies, while elsewhere marine facies predominated (Roberts and Engel, 1980). Deposits of predominantly continental facies during the Namurian accumulated ira a narrow trough called the Ayr Basin (Scheibner, 1974a, 1976) or Werrie Basin (Evans and Roberts, 1980). According to Roberts and Engcl (1980), during the Namurian the central part of the New England region was uplifted to form the New England Arch of Campbell (1969). It is possible that the Peel Thrust developed at the western margin of the composite accretionary prism during this time, or alternatively during the later part of Late Carboniferous, when the accretionary prisms in the Woolomin--Texas and Coffs Harbour Blocks were folded and metamorphosed. The presently steeply east-dipping Peel Fault System had a complex history, including multiple upthrust and strike-slip movements (Crook, 1963). It is probably an old suture as indicated by diverse slices of Early

293

to Late Palaeozoic rocks present along it, and, also, it separates the composite accretionary prism and the fore-arc basin complexes. Multiple (Carboniferous and Permian) emplacement of serpentinites and other ultramafic and mafic rocks occurred along this structure. The Carboniferous age for early serpentinite emplacement, as originally suggested by Benson {1913), has now been supported by dating of nephrite associated with serpentinite south of Tamworth (279 and 2 8 6 M a recalculated t o new constants; el. Lanphere and Hockley, 1976). Following the Late Carboniferous deformation, S-type granitoid plutons of the Bundarra (286Ma) and Hillgrove (289Ma) suites were emplaced into the deformed

accretionary prism rocks (Shaw and Flood, 1981). The B u n d a r r a suite forms a belt parallel to the Peel Fault System and is probably related to thrusting along this suture (Shaw and Flood, 1981). According to Flood and Fergusson (1982), the structures and facing of the accretionary prism complexes in the Coffs Harbour and Texas Blocks indicate large-scale oroclinal bending probably caused by southeast dextral displacement of the southern part of the Queensland segment of the New England Fold Belt (Murray and Whitaker, 1982). This bending was accentuated by subsequent Late Permian and Triassic dextral displacement along the Demon Fault (Korsch ctal., 1978). The timing of this event as Late Carbonif-

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29 ,l erous to earliest Permian is further supported by the presence of unconformities at the base of the Permian sediments (Olgers and Flood, 1970; Runnegar, 1970; and othersl. The result of this event was the formation of the core of the New England Fold Belt (NEFB), which was subsequently strongly modified during the Permo-Triassic. Either immediately succeeding or perhaps contemporaneously with this orogenic event, an extensional feature, the Nambucca Basin, formed.

Early Carboniferous--Early Permian magmatism and related deposits Two extensive belts of S-type plutons were emplaced in Late Carboniferous--Early Permian times in New England. These are the western Bundarra Plutonic Suite and the eastern Hillgrove Plutonic Suite (Shaw and Flood, 1981). Metallization was apparently not extensively developed in association with the emplacement of these granitoids, although minor tin oecurs with the Bundarra Plutonie Suite and locally substantial gold--silver-arsenic--antimony mineralization is associated with the Hillgrove Plutonic Suite (Fig. 15). Much of the Bundarra Plutonic Suite has been deeply eroded and accordingly its metallogenesis is not easily determined, but sheetedvein tin mineralization has been recognized at Watsons Creek (Fig. 15, 1) associated with a phase of this suite. The Hillgrove Plutonic Suite likewise has been largely deeply eroded, with the exception of the Rockvale Adamellite which has been only shallowly unroofed. Here a genetic relationship appears to exist with vein arsenic-gold-silver--antimony mineralization (e.g., Tulloch silver mine, and Comet gold mine; Fig. 15, 2). Several other ttillgrove suite granitoids have mineral deposits proximally related. For example, the Hillgrove Au---Sb--W deposits (Fig. 17, 37) occur in and adjacent to the Hillgrove Adamellite; however, there is no evidence to indicate a genetic association. Cu--Au--As mineralization (Fig. 15, 4) is geographically associated with a Hillgrove

suite granitoid north of Dorrigo (Dm~darrabm Granodiorite) and there is a fair case ~o argu(, a genetic relationship.

Early Permian in the New Englanc~ Fold Belt The NEFB underwent major modifications during the Early Permian (Fig. 12). Marine sedimentation represented by shallow-marine facies encroached on all sides of the New England Arch (Runnegar, 1970). To the east. flysch-like sediments and argillites interbedded with rare pillow basalts were deposited in the Nambucca Basin. Some felsic volc.anics, possibly rift-related, occur in the western part of this basin. During the middle Early Permian, large areas of the NEFB were affected by the ]-tuntcr event (Carey and Brown. 19381. In N.S.W. the strongest effects can be observed east of the Peel Fault System. Deformation i;er~, was accompanied by shearing and regional metamorphism which locally reached the amphlbolite facies (Binns, 1966}. K/Ar ages were reset (Flood and Shaw. 1.977L Multiple deformation affected some areas, not.ably the fill of the Nambucca Basin (Ix, itch, 1978!. New emplacement of serpentinites occurred along • the Peel Fault System and other major dislocations. In the area west of the Peel Fault System, the Tamworth Synclinoriai Zone or Belt formed by deformation of the fore-arc basin. Typical are west-verging folds and thrusts (Voisey, 1959), and burial metamo)'phism (Crook, 1961). The whoh, belt was thrust over its foredeep (Sydney--Bowen Basin, Carey, 1934). According to Roberts and Engel (in press), in [he southern part of the Tamworth belt this thrusting was the consequence of gravitational gliding off the inner part of the rising fold belt. Crustal blocks were displaced along large .~t:rike-slip faults. 'the Hunter event was followed by emplacement of granites dated at 260--269Ma. Remains of late Early Permian marine sediments in the NEFB indicated that during the marine transgression, which affected the

295 foredeep, most of the fold belt remained emergent. These marine sediments occur in southeastern Queensland and northeastern N.S.W.

Pre-accretionary deposits in the Early Permian complexes in New England Stratiform exhalative copper--lead--zinc-silver mineralization is developed at Halls Peak (Fig. 15, 5) in Early Permian felsic volcanics (Suppel, 1975b). It is unclear how these rocks and the contained mineralization evolved in their present position. Similar mineralization has been recorded from the Wauchope area (Huntingdon deposit; Gilligan and Brownlow, in prep.). Late Permian--Late Triassic in the New England FoM Belt Marine sedimentation during the Late Permian was very limited, whereas widespread igneous activity occurred throughout the NEFB. This igneous activity represents a Late Permian to Triassic magmatie arc (arch). In N.S.W., eale-alkaline, mainly felsic, volcanics are c o m m o n l y associated with cauldron subsidence structures (MePhie, 1982) which are intruded by subvoleanic granitoids. Large, massive (post-kinematic) plutons of A-type and I-type character have been grouped into several igneous suites {Shaw and Flood, 1981; Korseh and Harrington, 1981). Similar granitoids of Late Permian to Triassic, and occasionally Early Jurassic age occur throughout the NEFB and even farther north in the Hodgkinson--Broken River Fold Belt (Ri(:hards, 1980). During the Late Permian, deformation affected large areas of the NEFB and is well d o c u m e n t e d in the ,area of marine sedimentation in the Queensland--N.S.W. border region (Thomson, 1973; Murray et al., 1981). New rifting affected the NEFB during the Early-Middle Triassic. At the end of Middle Triassic new basins formed mainly in Queensland: the 'rarong, Callide, and lpswich or Clarence--Moreton Basins (Day et al., 1974). The Clarenee--Moreton (Ipswich)

Basin was filled by early rift volcanics, followed by deposition of coal measures (Day et al., 1974). Thinner coal measures accumulated in the other basins. The magmatic arch continued to develop, mainly in Queensland (Riehards, 1980). Further displacement of crustal blocks occurred mainly along north-south strikeslip faults; one of the best-documented being the dextral Demon Fault in northeastern N.S.W. (Korsch et al., 1978). During the Late Triassic the Bowen orogenic events occurred (Carey and Brown, 1938). Sedimentation terminated in the foredeep (Sydney--Bowen Basin) which had a transitional tectonic character, as well as in the NEFB, and the Gympie Basin was deformed (Day et al., 1974). After the Bowen event the NEFB behaved as a neocraton and subsequent sedimentation has platformal character.

Post-aecretionary deposits in the New England Fold Belt Post-accretionary plutonism has dominated the metallogenesis of the New England Fold Belt (Fig. 16). Granitoids dating from Middle Permian to Middle Triassic (--- ?Jurassic)have been responsible for an extensive range ot" vein, disseminated, stoekwork, and skarn deposits. Deposits of tin, tungsten, base metals, silver, gold, molybdenum, bismuth, and arsenic have resulted. In addition to this plutonism, felsic volcanism ill the Middle Permian has played an important role in the development of epithermal silver and gold vein, stockwork, and disseminated systems. The extensive fracture-controlled antimony, gold, and tungsten (scheelite) mineralization through central New England is probably, ill part, derived from the metamorphic reworking (leaching) of lower crustal rocks and the focussing of mineralized fluids along major fault, and shear zones. Shaw and Flood (1981) subdivided the post-orogenic granitoids of tile New England Fold Belt into four suites based on geochemical and isotopic commonality: i.e., Moonbi Plutonie Suite, Clarence River Plutonic Suite,

296

Uralla Plutonic Suite, and the Leucoadamellite Suite. In general terms, each of these suites has a characteristic metallogenesis. Additional geographic groupings of granitoids have been recognized which have a particular metallogenic and petrogenetic character, e.g., the Gundle belt of granitoids and the coastal granitoids. Hensel et al. (1982} recognized another suite in the southwestern part of New England, which he termed the Nundle Plutonic Suite. Plutonism was largely of l-type and I--S type (Shaw and Flood, 1981}, although Kleeman (1982) regarde( some of these authors' Leucoadamellite Suite to be of A-type. More recently, Hensel et al. (1985) argued that the above distinction between I-

and S-type (in the case of the previousiy dis.. cussed Hillgrove and Bundarra Plutoni.c Suites ! is only a reflection of the composition of the source rocks (felsic versus mark: voh:anogemc sediments ). The Moonbi Plutonic Suite and Clarence River Plutonic Suite are both l-type granitoids (Shaw and Flood, 1981). :['he Moonbi Suite is characterized by Mo--W metallogenesis, illustrated by the Attunga scheelite skarn {Fig. 17, I) and various Mo--W vein and disseminated occurrences in the Kootingal area {Fig. 17, 2}. A group of granitoids in northern New England also belongs to this suite and includes the Red Range and Kingsgate Granites [Kingsgate Mo--Bi pipes (Fig. 17, 19), and Deepwater Mo--Sn--Bi-W deposits (Fig. 17.

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the Bolivia Range, Mt. Jonblee, Nonnington, and Billyrimba Leueoadamellites [Bolivia Mo pipes (Fig. 17, 22), Jondol Mo pipe (Fig. 17, 23)]. This group of granitoids has a metal suite comprising major Mo, Bi, less W, :ks, Cu, Pb, Zn, and minor Sn. The Clarence River Plutonic Suite granitoids lie east of the Demon Fault and appear responsible for a variety of metallization types, e.g., skarn Fe and Cu at Fine Flower (Fig. 17, 3), vein Au _+Sb at Lionsville (Fig. 17, 4), and vein Au--Ag at the Lunatic Gold Field (Fig. 17, 5). The Uralla Plutonic Suite was regarded by Shaw and Flood (1981) as having more a mixed I--S character, perhaps representing a physical mixture of source rocks of both marie and felsic volcanogenic character (cf. ttensel et al., 1985). The Uralla Plutonic Suite granitoids are extensively distributed through central New England. The metallogenesis is characterized by Au--Ag--SI)--As as represented by the vein deposits at Uralla (Fig. 17, 6) and Tilbuster (Fig. 17, 7). The abundant placer gold at Uralla may originally have been derived from vein gold mineralization of this type. In terms of abundance of associated mineral deposits, the most important granitoids in the New England region are those of the Leucoadamellite Suite. This suite includes the following plutons and mineral deposits (see Fig. 17): the Gilgai Granite [Elsmore and Staniffer Sn deposits (10), Leviathan Sn deposit (9), and the Conrad base metals--Ag--Sn deposit (11)], the Mole Granite [Taronga (12) and Emmaville (13) sheeted vein Sn deposits, Torrington (14), The Gulf (15), Silent Grove (16), and Binghi (17) vein Sn deposits], and the R u b y Creek Granite [Wilsons Downfall (18) Sn deposit]. Kleeman (1982) regarded the Mole Granite to be an A-type granitoid, be also suggested the R u b y Creek Granite to be of the same type. This group of granitoids thus has a metal suite comprising major Sn; less W, Ag, Cu, Pb, Zn, As, Bi; and minor Mo.

In addition to the plutonic suites above, other granitoid belts of particular metallogenic and petrogenetic character have been identified, i.e., the Gundle belt of granitoids (Hensel et al., 1985; Gilligan et al.. in prep.), and the coastal granitoids (Gilligan et al., m t)rep.). The Gundle belt is a north-northwesterly trending group of essentially equant-shaped Triassic granitoids, including the Gundle and Glen Esk Granites, Carrai Granodioritc, Round Mountain Leucoadamellitc, and the Oban River Leucoadamellite(?). Their affinity is yet to be determined and at this stage are regarded as either I- or A-type. The two lastmentioned granitoids have been included by Shaw and Flood (1981) in their Leucoadamellit(: Suite, although their metallization appears to be more consistent with that of the Gundle belt i.e., Sn > = Mo versus Mo :~>Sn in the Leucoadamellite Suite. The Gundle belt includes skarns [Willi Willi (Fig. 17, 24), Gundle (25)], vein tin deposits [Gundle (25), Yooroonah (26)] and disseminated Mo deposits ]Guy Fawkes (27), Birdwood (28)]. This group of granitoids has a metal suite comprising major Sn: less Mo, :\s, W, Au, Cu, Pb, Zn: and minor Sb. The coastal granitoids arc a group of Middle Triassic -- {?)Jurassic magnetic granitoids developed along the coast between Kempsey and Coffs Harbour including the Smokey Cape Adamellite, Yarrahapinni Adamellite, and Valla Adamellite. These probable I-type granitoids have genetically associated Au--As lodes I Valla (Fig. 17, 29)], disseminated Mo [Yarrahapinni (30)1, and vein Ag deposits [Newee (::reek (31)]. This group of granitoids thus has a metal suit(: comprising major Ag, Mo; less Au, :ks; and minor Sb. The Nundle Plutonic Suite (Hensel et al., 1982) includes a range of small granitoids in southwestern New England. With regard to metallogenesis, the associations with the Nundle Suite may include Au--Sb--W (Fig. 17, 32) at Nundle (although unlikely), and several minor Cu occurrences (331. The

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Fig. 17. Deposits associated with the post-kinematic granitoids in the New England Fold Belt:.

Barrington Tops Granodiorite, the southernmost granitoid of the New England Orogen, has a genetic relationship with extensive Au mineralization in the Upper Hunter (Fig. 17, 34) and Copeland--Barrington gold fields (Fig. 17, 35). This genetic relationship may

not, however, require the granitoid to be the source of the metals but rather to provide the heat source for the generation of metamorphic--hydrothermal deposits (see Gilligan and Brownlow, in prep.}. High-level expressions of the post-orogenic

299 plutonism are evidenced by the Middle Permian epithermal Ag--Au deposits of the Drake area (Fig. 17, 36). Important vein gold--antimony deposits at Hillgrove (Fig. 17, 37), a n t i m o n y deposits at Taylors Arm (38), Munga Creek (39), Wild Cattle Creek (40) and Fishington (41), and minor gold occurrences at Enmore--Melrose t42) and Kookabookra (43) are all related to major fracture or shear systems. Preliminary lead isotopic data (B.L. Gulson, pers. commun., 1984) support a crustal origin for the a n t i m o n y deposits of central New England. Comsti and Taylor (1984) argued that the ltillgrove mineralization was probably of metamorphic--hydrothermal origin. A metamorphie-hydrothermal origin for most of the major a n t i m o n y deposits is favoured where major fault and shear zones have focussed the fluict flow (Gilligan et al., in prep.).

Tectonic models for the Late Carboniferous to Late Triassic development After the Kanimblan--Alice Springs event, most of Eastern Australia behaved as a ncocraton, with widespread platformal sedimentation commencing after the retreat of the continental and highland glaciation (Veevers, 1984). An active-plate margin setting was still present in the New England region, and postkinematic igneous activity occurred along nearly the whole length of the present eastern coastal region. Not enough attention has been devoted to the problem of basin formation in the platformal region of Eastern Australia, and no consistent kinetic model has been proposed for the whole region. Some of the basins, like the Renmark and Tararra Troughs, are parallel to major reactivated fracture systems (Darling River and Cobar--lnglewood Lineaments). The Oaklands Basin--Ovens Valley Graben appear to be framed by basement faults. Others, like the Cooper Basin, appear to follow the structural grain in the basement, which is well expressed in the gravity data. Evans and Roberts (1980) linked the formation of the platformal basins to a dextral shear

couple, i.e., Galilee Basin and Lovelle Depression, the sub-basins in the foreland basin (Sydney -- Bowen Basin), and the basins ill the orogenic New England region (Ayr or Werrie Trough, Grantleigh Trough, Berserker Graben, and others). This shear couple produced different effects on either side of an inferred northwest-trending transform fracture zone. This fracture zone is at present expressed as the Longreach--Roma gravity lineament. Most of the published tectonic models for the development of the NEFB envisage an active plate-margin setting, but interpretations differ in detail. Usually an Andean-type convergent margin is suggested for Carboniferous time, in contrast to an intra-oceanic arc for the Late Silurian--Devonian. Volcanism became rift-like in N.S.W., but waned in Queensland, to be followed by widespread post-kinematic plutonism in the region of the Carboniferous arc: and farther north in the already consolidated Hodgkinson Broken Riw.~r Fold Belt and its foreland. It is not clear if this long-lasting plutonism was related to subduction or not. During the latest Carboniferous to earliest, Permian a widespread ew~nt resulted in the formation of the core of the New England Fold Belt. The composite accretionary prism (comprising Early, Middle and Late Palaeozoic complexes including some high-P/low-T metamorphosed rocks) was thrust (Peel - Yarrol Fault System) westward over the fore-arc basin (Scheibner and Glen, 1972; Day et al., 1978). Some authors (Leitch, 1975; Crook, 1980) have compared this thrust to the Coast Range Thrust in California. However, a closer analogy exists with the obduction (thrust) of an accretionary prism over a volcanic arc, as suggested by Kroenke and Dupont 11982) for the Three Kings Rise (north of New Zealand). Obduction in the Three Kings Rise region appears to have been caused by an oceanic plateau which collided with the rise and choked the subduction zone. If a similar collision occurred in the NEFB, the colliding block has not yet been identified. The Bundarra Suite S-type granitoids are

300 parallel to the Peel Fault System and appear to be related to the thrusting along this fault system (Shaw and Flood, 1981). Some authors (Cawood, 1980; Crook, 1980) have suggested formation of syn-kinematic granitoids in the accretionary prism rocks due to subduction of a spreading centre causing high heat flow and partial melting. ]'his problem remains unresolved. Major displacement of crustal blocks bounded by strike-slip faults occurred, and yielded the well-developed block structure of the New England Fold Belt. The southeastern Queensland region was dextrally displaced in a southeasterly direction (Murray and Whitaker, 1982) causing the major oroclinal bending of the accretionary prism complexes, described by Flood and Fergusson (1982) from the Texas and Coffs Harbour Blocks. Subsequently or contemporaneously with the latest Carboniferous - e a r l i e s t Permian event, the ensimatic Nambucca Basin formed in N.S.W. Tectonic interpretations of this basin are contradictory. Evans and Roberts (1980) suggested basin formation in association with dextral shear, while Cawood (1982, 1983) proposed a sinistral transtensional origin during an episode of terrane dispersal. Scheibner (1974a, 1976) interpreted the Nambucca Basin as a marginal sea formed due to stepping out of the subduction zone, and t h o u g h t that deformation of the fill of this basin occurred during its closure by subduction. These rocks show multiple intensive deformation and burial metamorphism (Leitch, 1978). Leitch (1982), however, argued that these rocks do not show the imbricate structure typical of accretionary prisms. The large-scale structure remains unresolved and complete allochthoneity could be suspected. During the mid-Early Permian Hunter event the block structure of the NEFB was further enhanced. The strongest deformation, including regional metamorphism, occurred in the central part of the NEFB. Generally, east--west compression resulted in renewed thrust movement on the Peel - - Y a r r o l Fault

System and in new emplacement ~)I"serpenLinites along this and other major faults. The former fore-arc basin (Tamworth Yarroi Belt) shows evidence of burial metamorphism increasing towards the inner part of the N EFB. and west-verging open t:() moderat,:,ly tight folds often are cut by reverse faults a~ld small thrusts. This structural style resembles that b; the foreland fold and thrust belts (,f other orogens. The NEFB was thrust over the t;ore deep along the Hunter .... Mooki ......(~oodiwin(ti Thrust System. Again the interpretation ()f the general sense of block displacements is most controversial. The above event could have resulted from terrane collision and accr~,tion in the region farther east. Recently, Cawood (1984) tried to correlate th(, tectonic development of the NEFB and the Rangitata Orogen in New Zealand, but many uncertainties remain. The subsequent tectonic development is characterized by the formation of a magmatic arc and by disruptive volcanic rifting and basin formation typical of transitional tectonism. The magmatic arc appears to have zoning of associated metal provinces (Weber and Scheibner, 1977) similar to that described from subduction-related arcs. Cawood (1984) argued for a close spatial relationship with plate convergence in the New Zealand orogenic region. This problem needs further assessment and analysis, and more data. The igneous activity and deformations appear to migrate northwards with time, suggesting an unstable migrating plate configuration, but no clear explanation is at hand. Obviously the NEFB is not a complete orogen, and parts essential for tectonic interpretation remain hidden in the marginal plateaux and microcontinents of the Southwest Pacific. Discussion

The Late Proterozoic to Triassic history of the Tasman Fold Belt System {TFBS) has been interpreted above in terms of several

301 episodes of terrane dispersal and terrane accretion. Each episode has a distinct metallogenic signature. We have traced the tectonic development of the TFBS from an initial Late Proterozoic breakup and terrane dispersal at the passive margin of Eastern Gondwanaland through a progressively more complicated active margin history. Separated microcontinents (terranes) responded independently to subsequent episodes of terrane dispersal and accretion. The microcontinents themselves tended to fragment during episodes of dispersal while the intervening basins were inverted during episodes of terrane accretion. During these events, mineral deposits evolved from a relatively simple assemblage to a much more diverse array of deposit types. The main changes occurred during the Silurian and Devonian periods in the Lachlan Fold Belt (LFB) and the Permian and Triassic periods in the New England Fold Belt (NEFB). These were the major episodes of felsic igneous activity, and most of the complex assemblages of mineral deposits in this part of the TFBS were formed as a consequence of this activity (see Fig. 18). Cupriferous pyrite deposits as at Grassmere (Fig. 18, association 1) and Girilambone (2), and other submarine volcanic exhalative deposits of oceanic affinities including manganiferous (15) and ferruginous cherts and jaspers, some of which may contain traces of gold, are possibly associated with the Late Proterozoic and Early Cambrian terrane dispersal in the region of the Kanmantoo and Lachlan Fold Belts. During the Ordovician, mineralization in the LFB, comprising mainly copper and gold deposits (Fig. 18, 13 and 20), was apparently restricted to areas of andesitic volcanism on the Molong Microcontinent. During the Benambran Orogeny and terrane accretion, the Kiewa and Gilmore sutures developed as thrust-faulted boundaries of the Victorian and Molong Microcontinents. Such suture zones in Western North America are c o m m o n l y coincident with important zones of gold

mineralization (Albers, 1982). In New South Wales, the Gilmore Suture appears to control gold mineralization, although the age of the deposits here is not clear. These sutures are zones of major crustal discontinuity which often have histories of repeated compression and rifting, and it is likely that mineral deposits may have formed over a protracted period. Mineralization along the Gilmore Suture may have a number of sources, e.g., metamorphic--hydrothermal fluids, deep circulating hydrothermal systems (with unknown juvenile water component) in various igneous and sedimentary rocks, and shallow circulating epithermal systems, both submarine and sub-aerial, genetically related to andesitic and rhyolitic volcanism (Fig. 18, 10} The Silurian and Early Devonian was mainly an episode of terrane dispersal with a localized accretionary event (Bowning Orogeny). During the Silurian, Sn-bearing granites were emplaced west of the Gilmore Suture (Fig. 18, 3), rifting and related volcanogenic base metal and gold mineralization occurred in the east. During the Early Devonian, rifting with possible base metal and gold mineralization t o o k place in the west in the Cobar region (7), whereas granites with base metals, gold, and m o l y b d e n u m were emplaced in the east (25). Silurian transtensional rifting affected both the Molong Microcontinent and the adjoining terrane to the east of the cryptic I--S suture. At least one of the troughs (Tumut Trough) has oceanic-type crustal basement, whereas the basement of the others had extended continental crust. Narrow bimodal volcanic belts framing the troughs indicate their rift character.The metallogenic character of these rifts varies. All contain volcanogenic gold and base metal deposits, but in the ensimatic T u m u t Trough copper--zinc deposits in andesitic volcanics (1l), together with an array of mineral deposits with oceanic crust affinities, are present. The troughs to the east have silver--lead--zinc--copper deposits associated with rhyolitic volcanics (23).

302

~o

FOLD

LACHLAN

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BELT

REFERENCE

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HYPOTHETICAL VOLCANIC ARC TECTONICALLY UNDERPLATED PROTEROZOIC VOLCANIC ARC

I

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Fig. 18. Principal igneous metallogenic associations, Tasman Fold Belt System in New South Wales. Number

Metal association

Example locality, district

Deposit type*

Grassmere Wertago Ardlethan--Tallebung ?Ardlethan Holbrook--Walwa

B ?Vk Gv Gv Gv

7 8 9 10 11 12 13 14 15

Cu Cu Sn, W Sn Pb, Ag, Zn; Mo, W, Bi; Sn, Ta Cu, Pb, Z n ; Au Cu, Pb, Zn; Au (Au, Sn) Cu Au Cu (Zn, Pb) Pt, Au Cu, Au Cu (Au) Cu, Mn

?Vk, Mb Vk Gv B E ?Vk, ?Vm J Vm, ?Seg Pc ?B, Sem

16

Cr

17 18 19 20 21

(Au; W, Sn) W, Mo, Bi (Sn); Cu, Fe Cu (Au) Cu, Au Au

Cobar Bobadah, Canbelego, Mt. Hope Tumbarumba Girilambone, Tottenham Temora (Gidginbung) Basin Creek Fifield Parkes (Goonumbla Rise) Goonumbla (Hoskins Formation, Jindalee Beds) Coolac (Young Granodiorite) Rye Park, Broula Cargo, Copper Hill (Molong Rise) Junction Reefs, Browns Creek

1 2 3 4 5 6

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Cy :

Vk: Vm: Scg: Sere :

Pc: Pm: E: Gv:

Gs:

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Au

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Cu, Mn, ?Au Cu, Mn Sn Au, Ag, As, ?Sb Sn, W, As, Ag Au, Ag, As, Sb Mo, W Au, Ag Ag, Pb, Zn, Cu Sn, Mo Mo, Ag, As, Au Av, Sb, Fe, Cu Sb Au Cu, Fe, Au Cr

Hill End Captains Flat, Woodlawn (Bathurst Granite ) (Bega Batholit h )

Mg Vk (iv (iv

Whipstiek Yalwal, Pambula Yerranderie Mount I)romedary (Great Serpenfinite Belt) Bundarra ("Sandon Association") Fishers mine ("Woolomin Association") Watsons Creek (Bundarra Plutonic Suite) Rockvale, Comet, Tulloch (Hillgrove Plutonic Suite) Torrington, Taronga, Wilsons Downfall, Elsmore (Leucoadamellite Plutonic Suite) Uralla, Tilbuster (Uralla Suite) Attunga, Kingsgate (Moonbi Plutonic Suite) Drake Halls Peak Willi Willi, Birdwood (Gundle belt) Valla, Yarrahapinni (Coastal belt) Lunatic, Fine Flower (Clarence River Plutonic Suite) Hillgrove, Taylors Arm, Fishingion, Munga Creek Enmore--Melrose, Kookabookra. Coramba- Orar~ Coramba--Orara (Gordonbrook Serpentinitc Belt)

Gv E E 1 C ?B, Se, Seg Cy, Sere (:iv (;v Gv Gv Gv, Gs, Pm l,: Vk Gv, Gs, ?Pm Gv, ?Pro Gv, ?Gs Ma

Mg ?B, Seg C

Besshi. Cyprus. Volcanogenic, felsic volcanics (commonly Kuroko-typc). Volcanogenic, intermediate volcanics (manto, stratabound and vein type). Exhalative goht. Sedimentary manganese. Porphyry copper. Porphyry molybdenum. Epithermal. Granitoid-related, vein type and associated alluvials. Granitoid-related, contact, skarn or replacement type. Diorite-related (?) stratabound replacement. Intrusive-related (other than granitoid-related). Cumulate. Metamorphic--hydrothermal antimony. Metamorphic- -hydrothermal gold. Met,amorphic--hydrothermal copper--lead--zincs-silver (gold).

In tile Early D e v o n i a n p l u t o n s o f intermediate c o m p o s i t i o n with p o r p h y r y - s t y l e gold and c o p p e r m i n e r a l i z a t i o n (19) i n t r u d e d the O r d o v i c i a n s h o s h o n i t i c volcanic sequences, on the n o w f r a g m e n t e d M o l o n g M i c r o c o n t i nent. G o l d - - c o p p e r and l e a d - z i n c r e p l a c e m e n t t y p e deposits f o r m e d w h e r e mineralizing intrusions encountered suitably reactive rocks. D u r i n g this time A l a s k a n - t y p e intru-

sions were e m p l a c e d along the G i l m o r e Suture. Alluvial p l a t i n u m was p r o b a b l y derived f r o m these i n t r u s i o n s (12). The d i s t r i b u t i o n of d i f f e r e n t granitoid t y p e s (A-, I-, M- and S-type) and their related mineral deposits reflect the n a t u r e o f their source rocks. The granitoids in the L F B in N.S.W. can be g r o u p e d into three belts. S o m e o f the larger deposits a p p e a r to be associated

304 with the A-type granitoids or S-type [eucogranitoids intruded during the Early Devonian in the west (Fig. 18, 4 and 5) and the Middle Devonian in the east (26). Middle l)evonian rifting in the east (Eden--Yalwal--Comerong Rift) was closely related to A-type magmatism and characterized by bimodal volcanism and epithermal gold mineralization ( 27). Later, during the Carboniferous Kanimblan deformation and metamorphism, mineralizing fluids of metamorphic origin may have resulted in some polymetaUic deposits, e.g. Cobar (6), and gold deposits, e.g., Hill End (22). The last significant metallogenic episode in the LFB was in the Middle Carboniferous with the intrusion of the Kanimhlan granitoids. In N.S.W., these granitoids are confined to the northeastern segment of the LFB. They are all I-types with a similar metal association to other I-types in the LFB (Mo -Cu--W, and Pb--Ag; Fig. 18, 24). The oldest element in the NEFB is an Early Palaeozoic accretionary prism, the Woolomin Formation, with oceanic crust-related metallogenesis, comprising stratabound Cu--Mn deposits (31 and 32). In the Late Devonian to Early Carboniferous, another accretionary prism was juxtaposed to the Early Palaeozoic prism. This, likewise, has associated Cu--Mn deposits (45) and possible exhalite Au occurrences. In the (?)Late Carboniferous, yet another accretionary prism was added. The associated mineral deposits comprise stratabound Cu, exhalite Au and quartz magnetite

(45). In the Late Carboniferous to Early Permian S-type plutonism occurred. In the west, the Bundarra Plutonic Suite has related minor tin (33), and to the east, the Hillgrow.* Plutonic Suite may have genetically associated Au-S b - A s - - A g deposits (34). Felsic volcanism in the Early Permian at Halls Peak produced small stratiform base and precious metal deposits (39}. In the Middle to Late Permian, felsic volcanism in the Drake area was accompanied by epithermal silver-gold mineralization (38). Middle to Late Permian magmatism was responsible for a diversity of mineral deposits,

although the deposit tyl)cs can t:, roiate(i to the particular granitoid suites, i.(, [iralla Plutonic Suite (I---S type, Au--S,h Ag--As: Fig. 18, 36), Moonbi Plutonic Suit.e (l-type, Mo--W--Bi; 37), Clarence River Plutonic Suite (I---?M type, Au---Sb--Cu--Fe; 42) and the Leucoadamellite Suite ( A- or [-type, Sn--W---As--Ag; 35). In the middle ']'riassic discordant belts of granitoids of l- ()r A-type character were emplaced in eastern New England. These comprise the Gundle belt (Sn--Mo, 40) and the coastal belt ( M o - A g .... As--Au, 41). During this episode of post-orogenic magmatism, sizeable metamorphic hydrothermal Sb--Au(- W) and Au deposits (43 and 44) were emplaced in major fracture and shear zones in central and eastern New England. In summary, the Kanmantoo Fold Belt has a very restricted range of mineral deposits whereas the Lachlan and New England Fold Belts have a great variety of meLallogenic environments associated with both accretionary and dispersive tectonic episodes. The metallogenesis of the Lachlan Fold Belt is characterized by relatively large (tens of millions of tonnes) base-metal deposits and porphyry copper--gold deposits, whereas the New England Fold Belt is dominated by granitoid metallogenesis. An additional distinguishing factor between the latter two fold belts is the occurrence of antimony deposits; in the New England Fold Belt they are abundant, whereas they are rare in the Lachlan Fold Belt, which may suggest fundamental crustal differences.

Acknowledgements We acknowledge contributions by marly authors of published and unpublished papers and specifically by our colleagues at the New South Wales Geological Survey who were involved in metallogenic mapping and regional studies. We all have benefited over the years from stimulating discussions with them. The final version of this manuscipt has benefited from critical reviews by Drs.Neville Markham,

305

Richard Glen and Karl Wolf. We thank Mr. Greg Stewart for drafting the figures. The tectonic part of the manuscript was typed by Mrs. Dora Lum and the whole manuscript was assembled by Mrs. Milly Farrell, whom we thank for typing the many versions. This paper is published with the permission of the Secretary, New South Wales Department of Mineral Resources, Sydney.

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