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Classification and nomenclature of the mine sequence at Rosebery has varied and developed with ongoing research and increased understanding (e.g., Hall et al., 1965; Braithwaite, 1972; Sainty, 1986; Berry et al., 1998; Gifkins, 2001; Corbett, 2002b; and Corbett, 2004). The present study uses nomenclature consistent with that of Corbett (2004).

From a hydrogeological perspective, it must be noted that all rock nomenclature refers to the relic rock type at deposition prior to diagenesis, deformation, metamorphism and metasomatism. Rock nomenclature, at Rosebery and in this thesis, is therefore not necessarily a description of the present form of the rock mass, particularly from a hydrogeological perspective. This qualification is important as, for example, the unsuspecting hydrogeologist reading this thesis might wrongly assume that pumice, sandstone or tuff could be highly permeable due to primary porosity. Other than the Pleistocene to Recent glacials, all units have been extensively altered and metamorphosed (Pwa et al., 1992; Khin Zaw, 1991; Green, 1983; Berry et al., 1998; and Gifkins, 2001) resulting in a crystalline rock mass which appeared to have little or no effective primary porosity in the unweathered state.

Preferential weathering of relic pumice clasts was observed at surface, with signs of porosity re-developing. This appeared to be limited to the upper regolith zone, within < 5 m of the surface. In addition, in many areas of the study area, the regolith zone is poorly developed and earlier (pre-Quaternary) regolith appears to have been removed by recent glaciation. The rock units of the study area are described below in some detail.

2.3.3.1 Cleveland/Waratah Association

The Cleveland-Waratah Association comprises quartzose feldspathic greywacke, pillowed basalt, mafic intrusives, red-brown shale and bedded chert (Williams 1989;

and Turner and Bottrill, 2001). The Cleveland-Waratah Association does not appear as outcrop within the study area, however, a mafic greywacke sequence of the Cleveland-Waratah Association outcrops on Colebrook Hill c. 4 km west of the study area (Corbett, 2002b). Using a 3D geological model (Pasminco Exploration et al., 2002) the Cleveland-Waratah Association is interpreted to occur at depth in west of the model domain.

2.3.3.2 Central Volcanic Complex

The Hercules Pumice Formation of the CVC contains both: (i) the transitional stratified volcaniclastics (hereafter referred to as the „host rocks‟); and (ii) the footwall volcanics (hereafter referred to as „footwall‟).

The host and footwall material are the most extensively studied materials in the area (e.g., Braithwaite, 1969 and 1972; Green et al., 1981; Green, 1983; Naschwitz, 1985; Corbett and Lees, 1987; Green, 1990; Lees et al., 1990; Khin Zaw, 1991; Pwa et al., 1992; and Martin, 2004). Gifkins and Allen (2001) described the footwall as a massive to weakly graded, feldspar-phyric pumice breccia. The footwall contains massive and disseminated ore at its top (ibid.). The footwall alteration zone also contains minor carbonate, tourmaline, pyrite and chalcopyrite (Green et al., 1981) as well as carbonate, and sericite, replacement of plagioclase phenocrysts in footwall rocks (Green, 1983).

The host-rock of the Rosebery deposit comprises: (i) transitional stratified volcaniclastics (interbedded crystal-lithic sandstone, siltstone and black mudstone); (ii) quartz-feldspar-biotite-phyric dacite sills; (iii) pumice breccia and sandstone; and (iv) massive sulphide mineralisation (Gifkins and Allen, 2001). Pwa et al. (1992) described the host-rock as containing disseminated pyrite, and being commonly siliceous, sericitic and chloritic; it is normally overlain by pyritic black slate. Martin

(2004) stated that the “majority of the gangue material in the sulphide ore comprises sericite, quartz, carbonate, barite, chlorite and minor rutile” and went on to say “that in ore affected by Devonian metasomatism, there may also be tourmaline, magnetite, haematite, garnet, fluorite and helvite present”.

The Kershaw Pumice Formation comprises primarily pumice breccia, pumice-rich sandstone and shard rich siltstone (Gifkins, 2001). The Kershaw Pumice Formation conformably overlies the Mount Black Formation above the Mount Black Fault (McNeill, pers. comm., 2006).

The Mount Black Formation is dominated by dacitic lava overlain by rhyolitic lavas, pumice breccia, shard-rich sandstone and siltstone, pumiceous breccia, and crystal-rich sandstone (Gifkins and Allen, 2001). Pwa et al. (1992) describe the Mount Black Volcanics as mainly composed of weakly sericitised and chloritised dacitic to andesitic lavas. In the mine area they are in fault contact (Mount Black fault) with the host rocks and to the east, they conformably overlie the Sterling Valley Formation (Gifkins and Allen, 2001).

The Sterling Valley Formation is composed of andesitic to basaltic lavas and volcaniclastics units (Gifkins and Allen, 2001). The Sterling Valley Volcanics are exposed in only a few exploration holes due to their distal location relative to the Rosebery Deposit. The Sterling Valley Volcanics outcrop along the Murchison Highway and a small section of the upper Stitt River (Gifkins, 2001).

2.3.3.3 Western volcano-sedimentary sequence

The Western volcano-sedimentary sequence is comprised primarily of interbedded tuffaceous mass flow deposits, turbiditic sandstone, shard-rich tuffaceous mudstone, micaceous siltstone and graphitic black shale (Martin, 2004). The Western volcano- sedimentary sequence is taken to include the Farrell slates, and the White Spur

Formation (Martin, 2004). The White Spur Formation includes both the Hangingwall Volcaniclastics (hereafter referred to as the „hangingwall‟) and what is referred to locally as the „black slate‟ (a graphitic black shale). The hangingwall rocks are classified as sericitic quartz-feldspar-phyric epiclastic rocks (Corbett and Lees, 1987; Lees et al., 1990).

2.3.3.4 Tyndall Group

The Tyndall Group is composed primarily of crystal rich sandstone, volcanic breccia and volcanic conglomerate (Corbett and McNeill, 1986; and White and McPhie, 1996). The youngest part of the Mount Read Volcanic sequence (Corbett and McNeill, 1986), the Tyndall Group is conformably overlain by the Owen Group within the study area (Martin, 2004). The Tyndall Group outcrops in both: (i) the area down gradient of the mine; and (ii) at the southern extremity of the catchment (Figure 2.6).

2.3.3.5 Owen Group

The Owen Group outcrops in both the east and west of the catchment. The western Owen, the Stitt Quartzite, is composed mostly of massive quartzite and shale (McNeill, pers. comm., 2006). The eastern Owen is composed of terrestrial to shallow marine siltstone, conglomerate and sandstone (ibid.). In the east of the study area the Owen group meta-sediments outcrop as the dramatic 500 m high cliffs tht form the drainage divide at Mount Murchison on the West Coast Range (Figure 2.9).

2.3.3.6 Murchison Granite

The Cambrian Murchison Granite is an intrusive feature outcropping as close as c. 500 m to the east of the study area. Further-a-field is the Devonian granite pluton of Granite Tor, c. 8 km north east of Mount Murchison. The Murchison Granite varies from diorite to granite in composition (Polya et al., 1986). As the granites were

strictly beyond the catchment boundary, they were excluded from the hydrogeological model.

Figure 2.9 Mount Murchison. Looking north-west at the outcropping Owen Group; for scale, the tarn in the foreground is at an elevation of 750 m and the peak of Mount Murchison, slightly out of shot, is at 1275 m

2.3.3.7 Glacial deposits

The extent of the glacial deposits across the study area was mapped by Corbett and McNeil (1986). Glacials were observed in the present study to vary in composition from relatively impervious clays of fluvioglacial and lacustrine deposits to what appear to be extremely highly conductive moraine deposits. The glacial deposits are presently best observed in the Rosebery open-cut, rail and road cuttings, and on the Bobadil plain. Observation of drilling and excavations in the tailings dam areas also provided significant insight into the varied nature of the glacial deposits, as did the excellent review of local glacial material at the TME smelter site by East (1999). Although impervious clays are abundant, their lateral extent was observed to be limited. The resulting preferential flow which can be observed in cuttings around

clay layers translates to high flow rates and bulk permeability within the glacial units relative to the fractured rock bedrock.