University of Wollongong Thesis Collections University of Wollongong Thesis Collection

University of Wollongong Year 

Regolith geochemical exploration in the Girilambone District of Benjamin R. Ackerman University of Wollongong

Ackerman,Benjamin R, Regolith geochemical exploration in the Girilambone District of New South Wales, PhD thesis, School of Earth and Environmental Sciences, University of Wollongong, 2005. http://ro.uow.edu.au/theses/523

This paper is posted at Research Online. http://ro.uow.edu.au/theses/523

NOTE

This online version of the thesis may have different page formatting and pagination from the paper copy held in the University of Wollongong Library.

UNIVERSITY OF WOLLONGONG

COPYRIGHT WARNING

You may print or download ONE copy of this document for the purpose of your own research or study. The University does not authorise you to copy, communicate or otherwise make available electronically to any other person any copyright material contained on this site. You are reminded of the following:

Copyright owners are entitled to take legal action against persons who infringe their copyright. A reproduction of material that is protected by copyright may be a copyright infringement. A court may impose penalties and award damages in relation to offences and infringements relating to copyright material. Higher penalties may apply, and higher damages may be awarded, for offences and infringements involving the conversion of material into digital or electronic form.

Chapter 3

CHAPTER THREE - GEOLOGY, MINERALISATION AND REGOLITH SETTING

3.1 Introduction The name 'Girilambone' is of aboriginal origin and means the place of falling stars. It has been home to various mining and exploration efforts since the late 1800s, which have endured times of low profitability and relative wealth. In the early 1990s Nord Pacific Resources (Nord) and Straits Resources Limited (Straits) formed a joint venture to mine the Murrawombie open pit of the Girilambone mine under the control of the jointly owned Girilambone Copper Company. Mining activities at this time exploited leachable copper resources amenable to conventional open cut mining methods and Solvent Extraction - Electro Winning (SX-EW) processing technology. In 1997, mining commenced at Girilambone North, also exploiting a leachable copper resource which was subsequently processed at the SX-EW plant some 4 km to the south. Mining at the Girilambone North mine ceased in mid 2000, although processing of remaining ore continued until 2003. The Tritton copper deposit was discovered in 1995 by the Nord and Straits exploration joint venture using the SIROTEM technique. Subsequent exploration and resource delineation drilling has identified a significant copper and minor gold resource at Tritton. Development of the Tritton mine commenced in the first quarter of 2004 and further exploration by current owners Tritton Resources Limited is underway.

The mineral wealth contained within this region is well documented. Recent initiatives by the NSW Department of Mineral resources and other research bodies, coupled with advances in geophysical and geochemical exploration techniques and increased commodity prices, has renewed interest in the region which represents a potential target for future mineral exploration and development.

3.2 Location The small town of Girilambone is located in central west of New South Wales, approximately 620 km west of , and 44 km from the rural town of via the . The Girilambone mine is situated 4 km to the west of town at latitude 31o 16' S and longitude 146o 53' E and the Girilambone North deposits which form the focus of much of this study, are located approximately 4 km north of the Girilambone mine.

65 Chapter 3

The Tritton copper deposit is located 24 km south-west of the Girilambone mine along the Yarrandale Road en route to . Both study sites lie within the Coolabah 1:100 000 topographic map sheets and the 1:250 000 topographic map sheet and metallogenic map (Figure. 3.1).

Figure 3.1 Location of the Girilambone district, New South Wales.

Nyngan

3.3 Landuse and Climate Landuse is predominantly for agricultural purposes with extensive wheat and grain crops, cotton, cattle and sheep grazing. The landscape consists of flat to gently undulating surfaces, with extensive low lying ridges formed in more resistant lithologies e.g. quartzite and minor volcanic units, developed throughout the region.

The Girilambone region is classified as having a sub-arid climate with mean daily temperatures ranging from 19oC to 34oC in the summer (January), and from 4oC to 16oC in winter (July) as measured from Nyngan Airport. Annual rainfall is approximately 445 mm per annum with slight summer maximum rainfall (Commonwealth Bureau of Meteorology, 2003).

3.4 Geological Setting

66 Chapter 3

In a regional context, the study area lies within the western portion of the Palaeozoic Lachlan Orogen, one of three orogenic systems developed in New South Wales as part of the eastern Neoproterozoic to Mesozoic Tasman Fold Belt System, and is situated on the eastern margin of the Cobar Basin. The ‘Girilambone Group’ metasediments and metavolcanics form the main lithology throughout the region (Figure 3.2).

Figure 3.2 Geology of central New South Wales showing the location of the Girilambone Zone (GZ) in relation to other components of the Tasman Fold Belt system. After Fergusson et al. (2005).

The complex geological history of New South Wales has been widely studied and strongly contested by many workers, with varying evolutions being proposed. There is agreement however that the Lachlan Orogen formed within a complex oceanic accretion-subduction setting with stepwise accretion of deformed oceanic sequences, volcanic arcs and micro continents (Glen, 1995; Scheibner et al., 1999; Bierlein et al., 2002). From the Cambrian to the Early Carboniferous, continental development and oceanic retreat prograded from west to east. At this time deformation, consolidation and subsequent cratonic development associated with the Kanimblan Orogeny (Early Carboniferous) terminated orogenic growth of the continental lithosphere (Suppel et al., 1998). Prior to cratonisation, the Lachlan underwent a series of episodic deformation events which resulted in four main lithologies;

67 Chapter 3 two of which occur in the Girilambone district as Ordovician to Early Devonian turbidites and Silurian to Early Devonian granitoids, volcanics and sediments.

Geological history of the Lachlan Orogen and in particular the Girilambone district in a regional context is important in understanding the metallogenic relationships within the study area and a brief discussion follows herein. As will be discussed in more detail within this chapter, the origin of Girilambone copper mineralisation is a contentious issue. Providing a setting for emplacement of copper deposits within this area is therefore fundamental to the understanding of copper and gold ore genesis.

3.4.1 Geological evolution From the latest Neoproterozoic to Cambrian, development of a well defined active convergent plate margin existed to the east of the Tasman Line and formed the continental margin of the Australian continental lithosphere (Scheibner et al., 1999). Up until the Ordovician the Girilambone region was essentially a deep marine environment (Glen, 1991a). To the west, westward migration of the oceanic lithosphere pushed deformed basin rocks onto the Australian continental plate creating the Delamarian Highlands, the initial stages of the Kanmantoo fold belt. At the edge of the continental margin, the Stawell marginal basin filled with sediment from erosion of the Delamarian Highlands, which created eastward prograding of the continental margin (Scheibner et al., 1999). The Kanmantoo region was later subject to post orogenic collapse and lithospheric extension which resulted in subsistence and deposition of shallow marine sediments to the east.

During the Ordovician, the Girilambone region existed as a deep marine environment with the active plate margin developed to the west of . Two shallow marine environments existed at Broken Hill, east of the Delamarian Highlands. A volcanic rise, due to intrusions and subduction related volcanics (volcanic arc), formed from Dubbo to Kiandra and extending to Victoria (Glen, 1991a). During this time, the Girilambone area was part of a back arc setting, with appreciable turbidite and pelagic sedimentation (Suppel et al., 1998; Scheibner et al., 1999) and the Girilambone Group was accreted in an inferred east-dipping subduction zone in the Wagga marginal sea (Fergusson et al., 2005). Up to 5 km of sediments were deposited within the ocean basin (Glen, 1991a), which was simultaneously undergoing subduction. Throughout the Girilambone area numerous

68 Chapter 3 felsic/ultramafic intrusive rocks, similar to Alaskan-type intrusive complexes (Suppel, 1974; Fogarty, 1998a) are believed to be products of Ordovician shoshonitic magmatism, intruded the deep marine sediments. Continued east-west compression during the Silurian at the convergent Australian continental margin saw renewed uplift and oceanic retreat. During this time, flat lying sediments were squeezed up, and broken into discrete blocks, which underwent erosion and appreciable sedimentation. The associated increase in lithostatic load of adjacent subducted blocks resulted in a rise in temperature and pressure conditions, leading to consolidation and low-grade metamorphism. At the base of the subducted oceanic lithosphere, melts developed as escaping gases created thermal gradients and magma upwelling (Glen, 1991a), resulting in extensive intrusion of magmatic complexes.

From the Late Silurian to Early Devonian the eastern part of the Australian plate underwent extension, and shallow marine environments dominated the Lachlan Orogen. The convergent plate margin lay in the New England area between the Palaeo-Pacific ocean and the Australian Craton, thus placing the Lachlan Orogen at this time in a back-arc setting (Glen et al., 1996). Widespread initiation of basins followed post orogenic collapse of Silurian granites and subduction of Ordovician metamorphosed sediments. Rapid sedimentation of uplifted blocks resulted in filling of deep water troughs gradually as the rate of subduction related to crustal extension lessened and a shallow marine environment developed (Glen, 1991a).

In the Early Devonian, renewed east-west compression and associated upheaval of pre- faulted blocks gave rise to development of small hills. In the Cobar region, localised compression and associated increases in temperature and pressure lead to the development of hydrothermal fluids rich in Au, Ag, Cu, Pb, Zn, Fe and Si. These fluids were concentrated during the folding and deformation of basinal sediments (Glen, 1991b).

From the Middle Devonian to the Early Carboniferous, enormous river systems developed on terrestrial flood plains. Substantial deposition of sandstone and conglomeratic lithologies ensued. The Kanimblan Orogeny of this period allowed the final deformation and contraction in which the Lachlan Fold Belt and Kanmantoo Fold Belt further to the west achieved their final form, emerging as neocratons (Scheibner et al., 1999).

69 Chapter 3

The most significant feature of the Lachlan Orogen development was that of plate convergence and easterly retreating subduction zones of weak lithospheric layers (Scheibner et al., 1999). The ‘thin skinned’ tectonics of Glen (1992) and other workers allowed for renewed basin development and orogenic collapse following crustal thickening at the convergent plate boundary in a back arc setting.

Powell (1983) first placed the development of the Lachlan Orogen within a back arc setting in which orogenic activity was concentrated at converging plate margins, which has subsequently been supported (Glen, 1995; Glen et al., 1996; Suppel et al., 1998) among others. Accompanying this model of Lachlan Orogen formation was magmatism associated with subduction of oceanic lithosphere. The notion that deformation and subsequent metamorphism was intraplate has since been argued by Fergusson & Coney (1992) and VandenBerg (1999). Thus differing magmatic sources have been proposed. The tectonic setting in which the Lachlan Orogen evolved, and more specifically the Girilambone copper deposits, is crucial to the understanding and assumptions made in assigning ore genesis and developing exploration strategies.

3.4.2 Regional geology The Ordovician Girilambone Group represents the oldest rocks and form the base lithology within the Girilambone region (Figure 3.3). These rocks form a northerly trending belt through the region confined within major north-south fault systems which are to the west the Rookery and Coonara Faults and the Tullamore and Gilmore ‘Suture’, and to the east by the Miandetta Line (Glen, 1995; Glen et al., 1996). The southern extent of these rocks is bound by the Lachlan River Lineament, beyond which the Wagga Metamorphic rocks crop out (Suppel, 1974). To the north and north-east, the Girilambone Group is concealed under the Great Australian Basin.

Lithologies identified in the area as part of the Girilambone Group sediments include strongly foliated, bedded and laminated quartz to quartzo-feldspathic sandstone, quartzite, shale, phyllite, chert minor mafic volcanics and intrusives (Gilligan et al., 1994; Fogarty, 1998a; Chan et al., 2003a). Much of the Girilambone Group has been classed as 'undifferentiated sediments' (Gilligan et al., 1994) and remains a relatively unknown group

70 Chapter 3 of lithologies, although there does appear to be some division between western and eastern areas (Fogarty, 1998a). Low-grade regional metamorphism has resulted in lower greenschist facies mineral assemblages, with higher grade metamorphism and deformation being recognised in the eastern portion of the Girilambone Group (moderate greenschist facies) (Chan et al., 2003a; Fergusson et al., 2005) with abundant chlorite, muscovite, quartz and minor epidote. The western part is commonly of low metamorphic grade and contains sedimentary structures indicative of turbidite deposition (Fergusson et al., 2005). However, it seems the division between the western and eastern lithologies (Fogarty, 1998a) is an inferred boundary only (Fergusson et al., 2005) as no surface exposure or occurrences in drilling has been documented. Figure 3.3 Regional geology of the Girilambone district showing mineralised occurrences and current exploration and mining tenements (after Fogarty (1998a)). Inset A depicts the location of

open pit workings of the Girilambone and Girilambone North mines, and the major northeast trending structures joining these areas (after Tritton Resources Limited (2003)).

71 Chapter 3

Surface exposure of the Girilambone Group is poor and very little work has been done to resolve the stratigraphic and structural relationships within this unit. In the Girilambone area, outcrop is limited to open cut pits of the Girilambone and Girilambone North mines, several north-south trending quartzite ridges, Trig Hill to the east of the Girilambone mines and several small railway and road cuttings. A revised stratigraphy based on extensive drilling data and interpretation has been proposed by Fogarty (1998a) and is shown in Figure 3.4. However, given the scarcity of other investigations, this should be considered to hold true for the Girilambone area alone. Semi-pelitic and mafic schists form the ‘basement’ of the Girilambone Group sediments, which according to Fogarty (1998a) are unconformably overlain by the ‘Caro Schist’ composed of mafic schist and quartz greywacke lithologies. The Tritton Formation, consists of quartz wacke, sandstone and phyllite, which in turn overlies the Caro Schist. The Ballast Beds, previously interpreted to be part of the Girilambone Group (Brunker, 1969; Suppel, 1974), overlie the Girilambone Group and are composed principally of the Weltie Sandstone.

Figure 3.4 Stratigraphic relationships of rock units about the Girilambone district. Modified after Fogarty (1998a) and Shields (1996).

72 Chapter 3

Various chert layers are evident in the Girilambone sequence, namely the Alandoon Chert and Whinfel Chert of Gilligan et al. (1994) and other workers. Occurrence of microcrystalline silica is closely associated with mineralised bodies throughout the Girilambone region. Previously, these cherty units were given the name ‘Pink Quartzite member’ and interpreted to represent a single stratigraphic marker. However, Fogarty (1998a) has since found evidence in various deposits of this pink quartzite at various stratigraphic levels elsewhere in the Girilambone stratigraphy. Furthermore, occurrence of the pink quartzite in thin section has indicated a low temperature hydrothermal origin (Fogarty, 1998a).

Previous workers have included the Ballast Beds as part of the Girilambone Group (Brunker, 1969; Suppel, 1974), although now, these lithologies are believed to overlie the Girilambone Group sediments (Fogarty, 1998a). There is very little fossil evidence collected throughout the region to suggest detailed age constraints. Middle to Late Ordovician conodont fossils have been located in the western portion of the Girilambone Group sediments (Iwata et al., 1995). Based on the lithological similarity with known Ordovician rocks in the area the Girilambone Group sediments have been assigned an Ordovician age similar to other parts of the Lachlan Fold Belt, although there may exist areas of older basement rocks of Cambrian age (Brunker, 1969; Shields, 1996; Fergusson et al., 2005). Recent work by Fergusson et al. (2005) has defined a metamorphic cooling age of ca 435 Ma for moderate grade metamorphic rocks and slates from the Tottenham and Girilambone regions, by 40Ar/39Ar geochronology of muscovite grains.

Three broad categories of rock type have been identified in the area. The most abundant being the flysch-type sediments of the Girilambone group and overlying Ballast Beds, which would have originally been deposited as sandstone, greywacke and argillaceous sediments (Suppel, 1974). Subsequent deformation and associated metamorphism has altered them to lower greenschist facies assemblages. Intrusive rocks in the form of intermediate to basic dykes and granitic bodies form the other main rock types within the area. Near Girilambone, basement schists of the Girilambone beds are intruded by syntectonic and post-tectonic granitoids and intermediate mafic and ultramafic Alaskan- type intrusive rocks, dolerite sills and later stage quartz gabbro dykes (Fogarty, 1998a). The intrusive granites are of Silurian age with numerous occurrences to the north and further

73 Chapter 3 south of the study area. Various workers (Pogson & Hilyard, 1981; Glen & Hutton, 1983), have assigned ages of approximately 420 Ma to these granite units throughout the region and ages as old as 440 Ma have been obtained (Warland, 1991).

To the west, the Early Devonian Cobar Supergroup overlies the Girilambone sediments and Ballast Beds, occurring as variably folded and deformed thinly bedded turbidites (Glen, 1987). Lithologies at Cobar and throughout the Girilambone district are essentially similar, although deformation is generally greater in the east and decreases to the west where the Girilambone beds and Cobar Supergroup are similarly deformed (Brunker, 1969). The Girilambone Group sediments represent an earlier period of deposition of Ordovician age.

3.4.3 Girilambone North Lithologies within the vicinity of the Girilambone North mine are predominantly laminated schistose psammites and pelites, micaceous quartzites, rare serpentinite and metamorphosed igneous rocks. Relict bedding depicted by alternating psammitic and pelitic layers is evident within the Girilambone North mines (Fergusson et al., 2005). All lithologies in the mine environment have been metamorphosed to low- to mid-greenschist facies with common chlorite, sericite, muscovite, haematite and quartz mineral assemblages. Mineralisation in the Girilambone North deposits is hosted within the Caro Schist, interpreted to be the basal unit of the Tritton Formation (Fogarty, 1998a) which is underlain by mafic basement schists.

A major fault line striking 330° and dipping at 50° to the north-east is visible in the eastern wall of the Murrawombie pit (Girilambone mine). This fault continues north-west through the western margin of the Girilambone North pits and for a further 18 km to the north-west (Fogarty, 1996). This zone forms a corridor of deep seated reverse faulting into which serpentinite and dolerite dykes have intruded into local lithologies at various locations (Fogarty, 1998a). Mineralisation in the vicinity of the Girilambone and Girilambone North mines follows this zone which is represented by anomalous copper geochemistry (Figure 3.3, Inset A).

Shields (1996) identified two prominent periods of deformation in the Girilambone lithologies about the Girilambone Mine. An intense S1 cleavage at 60°-70°/080° believed

74 Chapter 3

related to the major 330° to 360° trending fault and a less intense S2 fabric at 60°/050° were identified in the Murrawombie Pit. Fergusson (2005) later inferred up to four deformations from mapping of lithologies within the Murrawombie pit, Hartman’s Pit of Girilambone North, local rail cuttings and surface exposures around Girilambone. According to

Fergusson (2005), deformation manifests as a slaty-style cleavage (S1) steeply dipping to the north and striking in an easterly direction; a steeply dipping east to south-easterly dipping differential layering (S2) major foliation; well defined and prominent moderately west dipping crenulation cleavage (S3) and localised weak crenulation cleavages (S4). Figure 3.5 (Fergusson et al., 2005) shows structures mapped in the Hartman’s open pit mapped in conjunction with the present study.

Figure 3.5 Structural elements of the Hartmans open pit, Girilambone North. After Fergusson et al. (2005).

75 Chapter 3

3.4.4 Tritton The rocks at Tritton are composed of moderately folded lower greenschist facies pelitic schists, phyllites, mafic schists, greywacke and quartzite. Figure 3.6 depicts a schematic representation of the Tritton ore deposit and host lithologies in cross-section. Mafic schists occur in the foot and hanging walls about the mineralised zones, which are separated into Upper and Lower ore zones. Several late-stage porphyritic dykes having intruded the sequence and crosscut the upper zone of mineralisation (Berthelsen, 1998).

At the base of the stratigraphy identified in drilling, there are a series of siliceous and chloritic schists, mafic schists and greywacke which represent the footwall of mineralisation of the Tritton copper deposit. These rocks are not unlike others seen throughout the region, with similar lithologies noted in the Girilambone Mine (Fogarty, 1998a) and are equivalent to ‘basement schists’ of the Girilambone Group. Basement rocks are typically chlorite±carbonate±epidote altered (Berthelsen, 1998) and considerably more intensely altered than the overlying lithologies. The ‘Mine Schist’ is a green crenulated chloritic schist/phyllite, with 20-30% quartz veining. This unit marks the very top of the ‘basement schists’, the upper contact of which has a sharp contact with the overlying quartzite unit.

Figure 3.6 Schematic cross section of the Tritton Copper Deposit, looking NE. (1) and (2) refer to base of complete oxidation and top of un-weathered rock respectively.

76 Chapter 3

At Tritton, mineralisation is mainly confined to siliceous envelopes referred to as ‘quartzite’ units which vary in thickness from 20 to 150 m (Berthelsen, 1998). At lower levels, quartzite is commonly inter-layered with less silicified greywacke and phyllitic schists. Intense hydrothermal brecciation is evident in quartzite units of the Tritton deposit, which Berthelsen (1998) suggests has allowed sufficient pathways for transporting mineralising fluids and subsequent precipitation of massive sulfides.

Schists immediately above the mineralised Upper ore zone are termed the ‘hanging wall schist’, and chlorite-sericite schists and phyllite are closely associated with mineralisation within the quartzite unit. A series of porphyritic dolerite dykes 0.5 to 5 m in thickness, cross cut the upper zone of mineralisation in a north-south direction (Berthelsen, 1998).

3.5 Mineralisation The Lachlan Orogen is host to four major metallogenic provinces with characteristic metallogenic associations (Bierlein et al., 2002) of which the Cobar Girilambone deposits are most likened to rift basin-related sediment-hosted Cu-Pb-Zn deposits. Common metallogenic mineral associations in the Cobar and Girilambone mineral deposits include Cu-Au, Cu-Pb-Zn and Pb-Zn-Ag. Glen & Fleming (2000) have suggested that ‘Girilambone style’ mineralisation is significantly different from copper and gold mineralisation in the Ordovician intra-oceanic Macquarie Arc or the base metal and gold association in the Late Silurian to Early Devonian (Cobar style mineralisation).

The Cobar and Girilambone mineralised province is one of the richest mineralised areas of New South Wales with polymetallic gold, copper and silver deposits. There are over 250 known mineralised occurrences within the Cobar 1:250,000 map sheet, the majority of which are focussed about several historical mining and exploration centres, namely Cobar, Hermidale, Mt Boppy, and Girilambone (Gilligan et al., 1994).

Major styles of mineralisation in the Girilambone area have been reviewed by Chan et. al. (2003a) and various mineral occurrences noted by Kenny (1928), Rayner (1969), Suppel (1974), Gilligan et al. (1994) and Fogarty (1998a). In the Girilambone district, the most notable deposits include Murrawombie, Hartman’s, Larsen’s, and North East open pits and the Budgerigar, Tritton and Budgery copper deposits, all of which are associated with

77 Chapter 3 primary pyrite-chalcopyrite mineralisation. Minor sphalerite, pyrrhotite and tenorite may accompany this mineralisation (Rayner, 1969).

Similarities for Girilambone-style mineralisation have been drawn with that of the Cobar mineral deposits, particularly for the Tritton deposit (Berthelsen, 1998). Cobar-style mineralisation is hosted by moderately deformed Early Devonian thinly-bedded turbidites. Structurally controlled epigenetic hydrothermal Cu, Au, Pb, Zn and Ag mineralisation form steeply plunging, narrow and elongate pipe-like ore bodies, the occurrence of which is concentrated about major fault structures (Glen, 1987, 1991a; Stegman & Pocock, 1996) and is closely associated with strong silicification. Glen (1991b) suggests that structures developed during the inversion of the Cobar basin have in places acted as fluid pathways and traps for mineralising fluids. While the deposits of the Girilambone district appear genetically similar to those of the Cobar mineral field, a distinction is realised in the age of the Girilambone mineralisation, which is thought to be of Ordovician age. Carr et. al. (1995) assigned an Ordovician age (435-460 Ma) to sulfide mineralisation from Tottenham, to the south of Girilambone and hosted within Girilambone Group lithologies, based on Pb- isotope geochronology. Furthermore, Pb in this system was found to be derived from the mantle and a possible Besshi-type origin was proposed. However, no samples from the Girilambone mines were included in Carr et al. (1995), thus extrapolation of these data to the Girilambone deposits is tentative.

Fogarty (1998a) summarised several likely settings of ore genesis for Girilambone style mineralisation. The first was that of Besshi-type origin associated with mafic volcanism as proposed by previous workers, Carr et. al. (1995), Shields (1996) and Suppel et al. (1998). Other possible geneses include replacement of tufaceous or carbonate beds by silica and sulfur-rich fluids or as mineralisation associated with movement of hydrothermal fluids through shear zones which extended to basement (Fogarty, 1998a). Hydrothermal and skarn-type origins have also been suggested as having an exhalative origin in association with graphite and cryptocrystalline quartz (Fogarty, 1996). As mentioned previously, mineralisation at the Girilambone and Girilambone North Mines is concentrated about a northerly trending reverse fault and associated zone of anomalous geochemistry. Similarly, Tritton appears to be related to a structure trending 010° (Berthelsen, 1998). It has been suggested that mineralisation is genetically linked to the intrusive mafic bodies and

78 Chapter 3 associated intense silicification throughout the region (Shields, 1996; Fogarty, 1998a). Furthermore, mineralisation is closely associated with fault structures, which are thought to have provided fluid pathways for the mineralising fluid transport.

Primary sulfide mineralisation in the Girilambone district is characterised by massive pyrite-chalcopyrite lenses and disseminated mineralisation (Suppel et al., 1998). Chalcopyrite replaces earlier pyrite, which forms a disseminated halo about primary mineralised zones (Rayner, 1969). Mineralisation is closely associated with zones of chloritisation, siderite and epidote alteration, thin magnetite lenses, hematite alteration and intense silicification (Fogarty, 1998a), although not all deposits have these features. Steeply dipping quartzite ridges of intensely silicified greywacke form a close association with known massive sulfide mineralisation, which occur proximal to these ridges. Within the Girilambone and Hermidale districts, numerous obscure gossanous outcrops (or ironstones) exist which facilitated the discovery of earlier known mineral deposits e.g. Budgerigar. While anomalous copper values have been identified in near-surface bedrock for many of mineral deposits in the Girilambone district, previous investigations have not identified anomalous geochemistry associated with the Tritton copper deposit (Fogarty, 1998a).

3.5.1 Girilambone North deposits The Girilambone North Deposits are extensively mineralised over a strike length of about 1.2 km and about 400 m in width. Three deposits were mined from this vicinity, North East, Hartmans and Larsens East open pits, the latter two of which are investigated in the present study. Exploration in this area targeted supergene copper carbonates (malachite and azurite) and chalcocite mineralisation, treatable by SX-EW processing. Reserves estimated prior to commencement of mining of the Girilambone North deposits are indicated in Table 3.1. An additional combined primary chalcopyrite resource of the Girilambone North deposits has been estimated at 4.12 Mt at 0.96% Cu for 39 420 tonnes of contained copper (Fogarty, 1998b), and has been untouched by existing mining operations.

Copper mineralisation is hosted within the two main rock types at Girilambone and Girilambone North, a chlorite-sericite schist and a banded quartzite member (Shields, 1996). Alteration assemblages associated with the primary mineralisation include chlorite with lenses of epidote, siderite and magnetite. A classic supergene profile has formed

79 Chapter 3 above the base of complete oxidation which stands at approximately 84 m. Secondary mineralisation in the form of chalcocite, digenite and minor covellite form a ‘blanket’ near and below the present water table. Above the water table native copper developed in sheets in quartzite and schist foliations, and extensive malachite staining and minor azurite persist. Rare copper phosphates pseudomalachite and libethenite are found in the oxide zone, the distribution of which is attributed to weathering (Sharpe & Williams, 2000) although the occurrence of these minerals is more notable in the Murrawombie pit rather than Girilambone North deposits.

Table 3.1 Leachable ore reserves (proved and probable) prior to commencement of mining, Girilambone North mine. Adapted from Fogarty (1998a).

The Hartman’s open cut reveals a highly weathered ore deposit with appreciable hematite and goethite development. Ore mineralogy was principally chalcocite, which replaces chalcopyrite at the palaeo-watertable, with minor cuprite, bornite and covellite higher in the profile. Minor copper carbonate development in the form of malachite and azurite occurred in an elongate zone above the level of chalcocite enrichment. Chloritic schists commonly contain disseminated pyrite mineralisation at depth with minor chalcopyrite. No significant native copper was found during the mining of Hartman’s.

Larsen’s East mineralisation is hosted predominantly within weakly silicified semipelitic schists with minor mafic components, and occurs as a 250 m long, up to 46 m wide pyrite- chalcopyrite lens which strikes at 300° and dips moderately to the east (Fogarty, 1998a). While the primary mineralisation forms elongate moderately dipping ore bodies hosted by locally extensive shear zones, secondary mineralisation is generally flat lying and more extensive than the primary mineralisation from which it formed. Larsen’s East appears to be somewhat less weathered than Hartman’s due to the comparative lack of hematite alteration. However, siderite does form in the upper profile.

80 Chapter 3

3.5.2 Tritton The Tritton deposit consists of two zones of mineralisation, the upper and lower zone, each of which is continuous for up to 250 m in strike length, up to 35 m wide and is open at depth below 1000 m (Fogarty, 1998a, b). Mineralisation strikes at approx 028° and dips to the east at 20° to 70°, the uppermost extent of which reaches to approx 180 m below the present land surface. No surface geochemical expression has been found in soil and RAB surveys to date using conventional exploration element suites. High-grade mineralisation occurs as pipe-like massive sulfide zones. Chlorite, carbonate and epidote alteration assemblages are common throughout the Tritton deposit, with siderite alteration in the hanging wall closely associated with sulfide mineralisation. Epidote alteration is in places times so intense as to replace all other minerals (Berthelsen, 1998).

Mineralisation of the upper zone is wholly within a quartzite unit, with chalcopyrite replacing pyrite. A high-grade banded massive bornite and chalcopyrite pod occurs in the centre of this zone, with stringer and vein style mineralisation at the proximity of the upper zone (Berthelsen, 1998). The lower zone is situated below the main quartzite unit and is hosted within the lower mafic schist unit (Figure 3.6). Mineralisation occurs as banded massive sulfides with alternating pyrite- and chalcopyrite-rich layers.

Grades vary within the Tritton deposit, with copper grades in the upper zone generally quite high at approximately 5% Cu (and locally up to 20 - 30 % Cu), and may be as low as 1% Cu in the parts of the lower zone. Table 3.2 indicates the estimated reserves of the Tritton copper deposit, current for 2003 (Tritton Resources Limited, 2003).

Table 3.2 Estimated resources and approximate metal content of the Tritton mineral deposit. Modified from Tritton Resources Limited (Tritton Resources Limited, 2003).

81 Chapter 3

In considering the paragenesis of the Tritton deposit, Berthelsen (1998) has suggested at least two periods of deformation followed by a three-stage sequence of sulfide mineralisation. Several fold generations are evident from drill core, with a bedding parallel foliation striking to 056° and dipping at 46° (S1) and an axial plane foliation striking 061° with a moderate to steep dip. A syn- to post-mineralisation shear zone separates the upper and lower zones of mineralisation, which has been reactivated and apparently displaced the mineralised zones. These folds are believed to have formed dilation zones in quartzite which has undergone brittle deformation during shearing, and provided suitable traps for mineralising fluids.

3.6 Landform and Regolith Setting The Girilambone area lies within the catchment of the northerly flowing Darling River and its tributaries, the Bogan River and the upper reaches of the Macquarie River. Drainage to the south of this region flows to the Lachlan River. Landforms in the area consist of erosional plains with a low relief of less than 9 m, and low undulating rises of less than 30 m relief. Topographic highs throughout the region are not more than 100 m from the land surface (approx. 250 m RL) and represent localised silicification and iron oxide induration (Cairns et al., 2001) and bedrock of more resistant lithologies, like silicified sandstones.

The region is typically mantled by an extensive blanket of colluvial and alluvial sediments and transported gravels, lithosols and red earth soils (Chan et al., 2003a). Soils are dominantly of the massive red earth type (typically sandy loam) which show little profile differentiation and are interpreted to have a significant aeolian content (Greene, 1992).

Outcrop and subcrop are generally found on elevated landscapes, with lower relief areas commonly forming on siltstones and displaying deeper weathering profiles (Cohen et al., 1996). Evidence for inversion of relief are found throughout the region (Pain & Ollier, 1995) and preserved palaeovalleys at various levels. Fluvial quartz-rich sediments are associated with northerly flowing alluvial palaeovalleys and infill previously incised palaeochannel systems which once traversed the landscape (Chan et al., 2003a). More recent alluvial channels cross-cut the palaeoterrain, with appreciable colluvial and alluvial sand, silt, clay and gravels.

82 Chapter 3

Lags are well developed across the region, and three morphological types have been identified by Alipour et al. (1996; 1997) as rough, blocky lithic lag; smooth pisoid lag and detrital lag being typical of various landforms. Onset of aridity in the Early Miocene saw the advent of increased bushfires, which contributed charcoal to the to the soil and drainage systems, and converted ferruginous lags to their maghemite bearing equivalents (Leah, 1996). Subsequent erosion has subjected these lags to various degrees of transport depending on the palaeo-drainage setting, and persist in palaeo-drainage channels which are readily identified by airborne magnetic surveys (Duk-Rodkin et al., 2003; Dehaan & Taylor, 2004). These palaeochannel lag deposits occur further west, and do not generally occur in the vicinity of the Girilambone and Tritton study areas.

Deep weathering profiles formed throughout the region are typically 60 to 80 m in depth dependant on lithotypes in which they form, and may extend to greater depths in shear zones. Classic weathering profiles are observed in areas, with well defined regolith boundaries identifiable down the profile. In general, weathered profiles are best developed towards the Cobar district on the Cobar Supergroup sediments (predominantly shales), and lesser developed in the eastern margin of the Girilambone Group sediments (Leah, 1996). Typically, weathered profiles have a variably ferruginised surface lag layer; red silty loam soil up to 1 m thick; a highly ferruginised zone passing into a saprolite mottled zone; well developed saprolite with quartz kaolinite assemblage; thin saprock horizon and low iron content bedrock (Chan et al., 2003a). Ferruginisation is typically well developed near the surface, although ‘lateritic’ profiles may not be fully developed. There is evidence of truncated profiles where the upper saprolite has been stripped by erosion at various locations including McKinnon’s and Elura Mines in Cobar (Cohen et al., 1996; Chan et al., 2003a).

3.6.1 Weathering history The weathering history and age of the Australian regolith has been postulated by many workers. Vasconcelos et al. (1994) describe a method of dating progressive oxidation events by 40Ar/39Ar and K-Ar analysis of potassium bearing manganese oxides. Using this method Vasconcelos (1996) determined the age of Mn-minerals in a preserved weathering profile from the Cloncurry district of northwestern Queensland as being pre 19 Ma. Similar ages have been obtained from dating of Mn deposits in Western Australia (Dammer et al.,

83 Chapter 3

1999) and several episodes of intense Tertiary weathering identified by 40Ar/39Ar and K-Ar dating of supergene Mn-oxides from the Groote Eylandt deposit, Northern Territory (Dammer et al., 1996). Elsewhere in eastern Australia, Pickett (2003) has identified laterisation of pre-Middle Miocene age (in Sydney) from the relationship between ‘lateritic’ surfaces and younger sediments and Bird and Chivas (1989) suggest an Early to Mid Mesozoic age for much of the Australian regolith.

The Girilambone and Cobar areas represent old weathering terrains, with a complex weathering history dating back possibly as early as the Jurassic (McQueen, 2004). Dating of other weathering events has been from Wilga Tanks, Elura, McKinnon’s and New Cobar mines (Chan et al., 2003a) which give a mainly Middle Miocene age of ferruginisation. Thus, investigations of weathering history by various workers in the Cobar and Girilambone areas has identified two periods of ferruginisation, these being Early Palaeocene and Mid Miocene. According to Chan et al. (2003a), these periods of weathering are equivalent to weathering phases dated previously in the Eromanga Basin.

Primary weathering and development of the ‘lateritic’ profile formed from the Late Cretaceous to late Middle Miocene (97-16 Ma) (Sharpe & Williams, 2000) by intense sub- aerial weathering of the low relief landscape in a tectonically stable regime. At this time, the climate was temperate to subtropical with episodic wetter climates and high global sea levels (Leah, 1996). Water tables move in response to climatic change and in periods of high water tables, no appreciable regolith development occurs below the water table beneath the influence of oxidation (Taylor & Eggleton, 2001) during wetter climates. It is important to note that leaching of trace metals from the upper profile during this period would have been extensive (Butt et al., 2000). As the water table dropped due to increasingly aridity, ‘lateritic’ development in the sub-aerial weathering zone resulted. Increasing aridity since the Middle Miocene was marked by falling water tables and weak secondary laterisation in the top of the weathered profile (Leah, 1996). Profile development and overprinting of various weathering features onto saprolite probably resulted during this time. Previous water-table stands may be evident in some profiles by lateral accumulation of Fe-oxides. Primary ‘lateritic’ profiles were extensively stripped and deeply incised to the level of saprock in the Late Miocene, which led to the development of truncated profiles evident throughout the region (Chan et al., 2003a). The significance of this is that the

84 Chapter 3 material in the upper portions of the profile has been dispersed through the palaeo drainage channels, which as has already been stated, are easily identified by the occurrence of transported maghemite gravels. Thus, while the presence of alluvial and colluvial mantles over truncated weathering profiles could mask mineralisation at depth, there may be some signature related to the mineralisation in the sediments and lag of the palaeo drainage channels. Evidence from an older profile of Jurassic age (180 Ma) has been found from palaeomagnetic dating of ferruginous mottles in the New Cobar pit. It has been suggested that these profiles represent much older weathering artefacts which have been preserved close to the surface, or been fortuitously buried and re-exposed (McQueen, 2004) and the limited occurrence of these profiles suggests appreciable erosional stripping since this time (Chan et al., 2003a).

3.7 Mining and Exploration History It has been recorded that copper was likely to be the first commercially mined commodity in NSW with operations in progress as early as 1844 (Kenny, 1928). During the period from 1870 to 1880 the Cobar district was highly prospected and many important discoveries were made at Cobar, Nymagee, Mount Hope, Girilambone, C.S.A. and Hermidale amongst other places (Kenny, 1928).

In the Girilambone region, copper was first discovered by Thomas Hartman, Charles Campbell and George Hunter in 1875 and production commenced in 1881 (Shields, 1996; Fogarty, 1998a). Ore grades were generally quite low, with some 80,000 tonnes of copper ore being mined intermittently at an average grade of 1.95% Cu (Fogarty, 1996), until a decline in the global copper prices in 1907 saw mining operations cease (Carne, 1908). Numerous shafts sunk in early mining times at Girilambone are close to resources defined more recently by Nord-Straits Joint Venture, in particular the Murrawombie pit occupies the site of the initial Girilambone mine and Larsen’s, Hartman’s and North East pits occupy the sites of Larsen’s Shaft, Hartman’s Shaft and Hunters Shafts respectively (Fogarty, 1996).

Exploration in the historical Girilambone mining area commenced in 1958, with diamond drilling to test strong magnetic anomalies conducted by Mining and Prospecting Services Pty Ltd, and confirmed the presence of ultramafic rocks at depth (Shields, 1996). The Utah

85 Chapter 3

Development Corporation and Seltrust Mining Corporation Pty Ltd acquired tenement from Girilambone to Hermidale following release of airborne geophysical survey by the Bureau of Mineral Resources in 1960. Exploration between 1963 and 1973 involved deep drilling in the vicinity of the Girilambone mine to define a copper resource of 3.315 Mt at 2.12% Cu. Rotary Air Blast drilling and bedrock sampling was also conducted by Utah at this time (Fogarty, 1996).

From 1974 to 1983, Seltrust Mining Corporation Pty Ltd drilled a single diamond drill hole and intersected massive pyrite mineralisation with minor chalcopyrite at approximately 300 m depth. Further to this, Sanidine NL conducted rapid reconnaissance magnetic induced polarisation survey over the area, identifying a significant shear zone in the area (Shields, 1996).

3.7.1 Girilambone North In 1989, Nord Australex Nominees Pty Ltd purchased 100 % of the prospect from Hunter Resources Limited. A combined reverse circulation and diamond drill hole program of the old Girilambone mine yielded favourable results (Shields, 1996). Further drilling identified a combined resource of 4.6 Mt at 0.88% Cu and mining commenced in 1993 under the management of the Girilambone Copper Company Pty Ltd, a joint venture between Nord Resources (Pacific) Pty Ltd (40%) and Straits Resources Ltd (60%). Further exploration as part of a joint venture in which Nord Resources and Straits Resources had equal interests was carried out through the tenement area including extensive airborne magnetic and radiometric surveys, geochemical sampling and ground geophysics. Subsequent drilling of 33,914 m of Reverse Circulation and combined diamond drilling for some 306 holes identified an extensively mineralised zone 1.2 km by 500 m in width approximately 3 km to the north of the Girilambone mine (Fogarty, 1995). This area became known as ‘Girilambone North’ and contained the Hartman’s, North East and Larsen’s East prospects, which have now been mined to completion.

3.7.2 Tritton Copper was first discovered at the Budgery group of mines in 1906 when a ‘pipe-like’ ore body of chalcocite, carbonates, native copper and cuprite, whereby according to Kenny (1928) 'Large and conspicuous masses of iron oxide at the surface indicated to the early

86 Chapter 3 prospectors the existence’ of the copper ore bodies. This group of mines included the Budgerigar, Budgerigar North and Bonnie Dundee mines from which production amounted to several hundred tonnes of copper from 1890 to 1910 (Fogarty, 1998b).

No further mineralisation was located in this vicinity until 1993 when intensive exploration to test the anomalous geochemistry, associated with the regionally extensive ‘Rockdale anomaly’, that the Tritton deposit was discovered. Transient electromagnetic surveys (SIROTEM) were conducted over the Budgerigar deposits and surrounds, which identified two highly anomalous late time conductors, Tritton and Budgerigar. Mineralisation of the Tritton copper deposit has subsequently been tested to 1000 m depth by 137 pre-collared deep diamond drill holes. Resource drilling has delineated a proven and probable resource of a 4.383 Mt at 3.1% Cu, 0.23 g/t Au and 9.93 g/t Ag.

Following further resource delineation, feasibility studies, mine planning and consent to mine, the Tritton copper prospect and associated mining rights were sold to Tritton Resources Limited in mid 2002 (Straits Resources, 2002). After successful capital raising in late 2003, Tritton Resources Limited is currently developing the Tritton Copper Mine by way of conventional box-cut and spiral decline.

3.8 Previous Geological Studies in the Girilambone District Extensive studies have been conducted in the region, although these have mainly been confined specifically to the mineral deposits and geology of the Cobar mineral field. While analogies and theories from studies of the Cobar area can at times be extrapolated to the eastern margin of the Cobar Basin in the Girilambone area, studies dealing specifically with the geology and mineralisation of Girilambone and its mineral deposits are limited. Considering also the poor surface exposure of the Girilambone Group lithologies and subsequent lack of mineral exploration in areas of deeper surface cover, the Girilambone Group sediments and associated mineral deposits remain a relatively poorly understood area of NSW.

Regional mapping in the Girilambone (and Cobar areas) cover regional regolith-landform mapping at 1:500 000 scale (Gibson, 1998), metallogenic occurrences and geology at 1:250 000 scale (Gilligan et al., 1994) and various scale regolith and geological mapping of

87 Chapter 3

T. Hopwood (Smith, 1971), Warland (1991) and Spry (2003) . Warland (1991) investigated the geology of the Hermidale and areas, mapping Ordovician Girilambone Group and Ballast Bed lithologies. Stratigraphic subdivisions of the Girilambone Group were proposed based on field evidence acquired from mapping, although they do not appear to have been retained in more recent studies of the area. Regolith landform mapping of the Byrock 1:100 000 map has been recently completed (Buckley, 2004) and geological mapping of the Cobar-Bourke regions is due to commence (Burton et al., 2004). However, regolith or geological mapping of the Girilambone area (Coolabah map sheet) is not anticipated in the near future.

More recently, the Girilambone and Hermidale districts have been the focus of extensive investigations by Chan et al. (2003a; 2003b), a joint project conducted by the Department of Mineral Resources of NSW (DMR) and the Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME). This study conducted shallow air core drilling along road transects in the Sussex-Coolabah areas, investigating regolith geology and geochemistry, and the potential for mineralisation beneath extensive basin cover. Geomorphological landscape evolution, palaeo-drainage, tectonic and weathering history were identified and a complex history of alluvial transport and deposition in the Cobar area inferred. Various other studies have stemmed from this work (Maly & Chan, 2002; Duk-Rodkin et al., 2003; McQueen, 2004; Scott & Le Gleuher, 2004).

In the Girilambone area itself there have been several studies by Fogarty (1995; 1996; 1998a; 1998b; 2001), Shields (1996) and Berthelsen (1998), who give detailed accounts of the geology and mineralisation in the vicinity of copper deposits throughout the Girilambone district. This literature is mainly confined to the Girilambone Mine, Girilambone North Mine and Tritton Copper deposits, the findings of which are discussed elsewhere in this chapter.

Other studies have presented detailed investigations of several of the mineral deposits in the Girilambone district. Pahlow (1995) focused specifically on the geology and geochemistry of Girilambone North deposits, geological mapping and petrographic examination of sulfide mineralisation. Various sampling media were examined for use in geochemical delineation of mineralisation. In particular biogeochemical sampling traverses

88 Chapter 3 were compared with lag and soil geochemistry, which were reported to define a broad multi-element response to mineralisation. Elvy (1998), Crane (2001), Sharpe and Williams (2000), identified supergene mineral species from the Murrawombie pit of the Girilambone Mine and an apparent zonation of these minerals in the weathered profile. Elvy (1998), further examined the copper species in groundwater solutions about the Girilambone and Girilambone North deposits and found copper to be stable as malachite-pseudomalachite phases, which are poorly dispersed at the present groundwater conditions. Hastings (2001) used spectral analysis with a Portable Infrared Mineral Analyser (PIMA) to determine the lithology, mineralogy and possible alteration assemblages associated with copper mineralisation of the Tritton copper deposit. Localised deep weathering (up to 150 m) along shear zones was encountered and the abundance of illite was used as an indicator of level of weathering. Similar methods were used by Chan et al. (2003a; 2003b) to define regolith boundaries in shallow air core drill holes.

3.9 Conclusions Ordovician turbidite sequences of the Girilambone Group form the most prolific lithology in the region, occurring as variably folded, deformed lower to mid greenschist facies schists, phyllites, slates, sandstones and quartzites. Later stage mafic dykes of dolerite and serpentine have intruded older Girilambone Group sediments, in addition to several large granitic bodies. Mineralisation occurs as structurally controlled polymetallic Cu+/-Au mineralisation within meta-sedimentary host lithologies, and is thought to be related to mafic intrusions of Ordovician age. Primary mineralisation is predominantly chalcopyrite and pyrite accompanied by accessory sphalerite with significant deposits located at the Girilambone and Tritton prospects. Supergene mineralisation which has formed the focus for recent exploration and mining at Girilambone and Girilambone North, is characterised by copper carbonates, chalcocite and native copper. Mining and processing of leachable copper ore ceased in mid 2003. The sulfide resources of the concealed Tritton Copper deposit have been delineated, and mine development is underway.

The Girilambone district has undergone a complex weathering history, with several periods of ferruginisation recognised. Poorly developed ferruginous upper layers have resulted in partially stripped weathered profiles within an erosional regime. Ferruginisation and regolith development is thought to have developed from the Cretaceous to late Middle

89 Chapter 3

Miocene in periods of warmer and wetter climates. Subsequent onset of arid conditions in the Late Miocene resulted in lowering of water tables and extensive preservation of deep regolith profiles of up to 100 m depth. Subsequently, occurrences of supergene mineralisation which represent a significant copper resource and exploration potential, have resulted from these weathering episodes.

The Girilambone district has been identified as a region of significant mineral wealth and exploration potential. Numerous mineral deposits have been located throughout the area, despite its being relatively under explored in modern times. A combination of poor surface exposure of local Girilambone Group lithologies and extensive colluvial and alluvial cover and in-filled deep palaeochannels has proved troublesome for mineral exploration in this area. Furthermore, the relative success and longevity of the Cobar mineral field has somewhat over-shadowed the Girilambone mineral deposits. Recently, the Girilambone area has received renewed interest with rising commodity prices, new mine developments, exploration and research throughout the region. With the advent of modern geochemical and geophysical exploration techniques, detailed regolith and bedrock mapping (currently underway) and an increased understanding of regolith processes and geochemical dispersion processes, this area holds significant exploration potential for copper and gold mineralisation.

90