Geology and hydrogeology Resources (Department of National Resources 1976), the Water 2000 Study (Department of Resources and Energy 1983) and the 1985 Review of Australia's Water A. Laws Resources (Department of Primary Industries and Energy 1987). Most other reports on groundwater in the area are Introduction unpublished reports covering work carried out to locate water supplies for individual pastoral leases, This section of the report outlines the geology and the Main Roads Department, and town water hydrogeology of the area. Its purpose is to provide a supplies, operated by the Water Authority of Western description of the origin and nature of groundwater Australia. Other unpUblished reports review the water resources within the survey areaf and a practical supplies for the towns of Mt Magnet, Cue, and guide to where they may be located, their salinity, and Meekatharra. general guidelines on how they may be developed. For assistance on the siting of bores or any particular supply, pastoralists and other land users should contact the Director, Geological Survey of Western Australia, Department of Minerals and Energy. Physiography The pastoral industry is one of the major users of The Upper Murchison River Catchment is part of groundwater in the area. Because there is a regional the drainage basin of the Murchison River, and is water-table, and over more than 60% of the total area situated in the Yilgarn Craton (previously termed the the water-table is less than 15 m below ground level, Yilgarn Block) of Western Australia. more than 2000 bores and wells have been constructed throughout the area. However, the distribution of The major physiographic features are shown in stock bores and wells does not reflect solely the Figure 22. Most of the drainage in the area covered by availability of groundwater, but also the different this report, falls within the south-east corner of pastoral value of the land for stock, and its carrying Jutson's (1950) Murchisonia, and drains towards the Indian Ocean. A small, south-eastern part of the area, capacity. is in Salinaland, which drains inland into salt lakes, Consequently bores and wells tend to be more such as Lake Austin. concentrated on areas of alluvium rather than in the thinner, topographically higher, colluvial soils, or in Within the area of Murchisonia there is a marked areas of bedrock outcrop. difference between the topography formed from bedrock of Phanerozoic and Archaean age. Phanerozoic sedimentary rocks occur in the north­ west of the area, and topographically the area is Previous investigations generally monotonous and flat. There are scattered low hills and a few isolated mesas of duricrust, which Detailed comments on previous geological are more or less overlain and surrounded by sand plains. investigations are given in the relevant 1:250,000 Dunes and playas occupy a broad palaeodrainage in Explanatory Notes (Belele-Elias 1982, Byro-Williams the Yarra Yarra Creek area (Figure 22). In general, 1.R. ef a1. 1983, Cue-De La Hunty 1973, Watkins ef al. areas of high and low relief are related to structural 1987, Glenburgh-Williams S.J. ef a1. 1983, Glengarry­ features within the Phanerozoic bedrock. Elias ef a1. 1982, Kirkalocka-Baxter ef a1. 1983, Murgoo­ Baxter 1974, Robinson Range-Elias ef a1. The Archaean terrain is characterised by very 1980, Sandstone-Tingey 1985, and Yalgoo-Muhling shallow alluvial 'valleys' which, to an observer on the ground are so broad and so gently inclined as to ef al. 1977). In 1990 a major report on the geological evolution and mineralisation of the Murchison appear to be flat plains between distant hills. The hill Province was published (Watkins and Hickman 1990), ranges are often flanked by stony pediments which whilst the adjoining Western Gneiss Terrane was shed run-off onto very broad sheetwash plainS. Above mapped in detail by Gee ef a1. (1981, 1986) and Myers the pediments are low rocky hills of bedrock, or (1988). Summaries of the geology can be obtained breakaways over deeply weathered, duricrust-capped from Memoir 3 (Geological Survey of Western bedrock, which lie on the interfluves or at the heads of the main drainage lines. The duricrust remnants are all Australia 1990). that remain of a once continuous Early Tertiary Apart from brief early reports on water supplies for lateritic surface, which has become eroded during mines and batteries in the area (Maitland 1908, Clarke Quaternary times. 1916, and Ellis 1936a, 1936b, and 1953) and later The topography over the areas of outcrop varies reports that concentrated on groundwater in the according to the rock type. The granitoids typically calcrete drainages (Sanders 1969a, 1969b, 1971, 1973a, form large monoliths and extensive uplands of flat 1973b) regional reports on groundwater are limited to pavements, whilst basalt generally produces rugged, Berliat (1957); Morgan (1965); and Baxter (1972). rounded hills. Prominent strike ridges are formed Broadscale regional assessments were made of the from outcropping iron formation and metaperidotite, groundwater resources of this and surrounding areas while felsic volcanics tend to produce gently as part of the 1975 Review of Australia's Water undulating plains. 21 80 km Sheet calcrete l0J~ Rock outcrops and fringing scree slopes D Main drainage and associated flood plains I??I~H Colluvial arid alluvial sheet wash piedmont plains 6-~::-~J Saline lakes M:m~W~m:1 Sand plain 000 0 0 Drainage basin boundary Physiographic division Figure 22. Physiographic provinces and units in the survey area. 22 The south-east part of the study area falls within (Watkins 1990, Watkins and Hickman 1990). To the Jutson's Salinaland, and is dominated by a generally north, north-west, and west the Murchison Province is flat to gently undulating topography, with sandy in tectonic contact with the Narryer Gneiss Complex surfaced Quaternary plains. Drainage is to the south­ of the Western Gneiss Terrane (Myers 1990), whilst to east into saline lakes. The physiography of the eastern the north-east the granite-greenstone rocks are part of the area, and land further to the east is overlain unconformably by sediments of the Nabberu described in Mabbutt (1963). Basin. In the north-west sediments of the Carnarvon Basin occur (Figure 23). The generalised stratigraphy is slUnmarised in Table 4, and the geology and structure in Figure 24. Drainage More than 80% of the drainage in the area is exorheic, draining to the west into the Murchison, Wooramel, and Greenough River catchments, and subsequently to the Indian Ocean. The remainder of Stratigraphy and structure the area has an endorheic drainage system to inland The area underlain by the Murchison Province salt lake systems. consists of a series of greenstone sequences and suites of granitoids. To the north and north-west these abut All drainages are ephemeral. The Murchison River the N arryer Gneiss Complex, which consists of two is very intermittent, but may flow for long periods groups of gneisses. In the north-east and west, these after heavy rainfall. Generally the major drainages rocks are overlain by Proterozoic sedimentary rocks, have broad flood plains, some of which have been and further to the west are unconformably overlain by discontinuously incised by narrow channels. Penman sediments. In the western part of the shldy area, the bed of the Murchison River follows a more deeply incised The greenstone belts trend NNW to NNE, and are sinuous course and is probably a fault-controlled surrounded by the more extensive granitoid subsequent stream along this stretch. Williams I.R. et intrusions. They are shown on Figure 23 as al. (1983) noted the unusual junction of the Roderick undifferentiated mafic and ultramafic rocks, consisting and Murchison Rivers and relate this to a fault­ of basalt, amphibolite, gabbro and dolerite. They have controlled dam near the junction of the rivers, which been deformed by large scale foldmg and are dissected has been subsequently breached. The west-flowing by faults. Most of the belts occur in the east and south­ tributaries of the Murchison River and the upper part east of the study area. of the river itself are consequent streams. The granitoid rocks show variable composition and Elongate and dissected sheets of valley calcrete texture, and include biotite granite, muscovite granite, occupy parts of the trunk drainages (Figure 22), and tonalite, adamellite, granodiorite, and granophyre. some are 1 to 2 m or more above the present ground They intrude the greenstone belts and are widespread level, indicating that there has been widespread in the western and central part of the area. erosion of the calcrete since its formation. Further to the east the trunk drainages of the Yalgar and Hope The Narryer Gneiss Complex consist of rnigmatite, Rivers follow probable palaeodrainage lines gneiss, schist, and quartzite of Archaean age, and have developed on the duricrust during the early Tertiary been derived mainly from granite and, to a lesser (Elias 1982). extent, metasediments, dykes, sills, and layered intrusions. On the southern boundary of the complex, To the south-east the palaeodrainage system is between the Whela and Murchison Rivers, schist and represented by saline drainages and salt lakes, with metasediment of the Jack Hills Group crop out as a gypsiferous mud flats and small parabolic banks of prominent linear range. calcareous and gypsiferous sands, surrounded by sand sheets, salt flats, and sheets of calcrete. Lower Proterozoic sediments of the Glengarry Sub­ basin of the N abbern Basin occur in the north-east where they unconformably overlie the Archaean basement, whilst Late Proterozoic sediments of the Regional geology Badgerrada Group occur as a small intracratonic basin in the western part of the area, overlying Archaean basement, and abutting Permian sediments of the General features Carnarvon Basin. For the purpose of this report the geology has been summarised and simplified, on the basis of its The Permian sediments of the Carnarvon Basin hydrogeological significance (Figure 23).