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IN this paper an attempt is made to describe the sluicing operations on the tin fields of north-eastern Tasmania. No claim is made to completeness, for much of the ground has already been covered, and nothing is to be gained by needless repetition. On this account some portions of the subject have obviously received but scanty attention in order that others may be rather more fully dealt with; for instance, figures referring to the accuracy of various methods of valuing alluvial deposits, particulars of efficiencies, and water duties on both overburden and drift; also, the system of recording water distribution, &c.The plans of the tin-streaming shed, sluice and feed·race, and overburden tail-race represent types of the most modern design.The principal alluvial deposits being worked at the present time are situated either in the ancient or modern bed of the Ringarooma river or its tributaries. This river flowed in a north-easterly direction, receiving numerous tributaries on either bank, and finally emptying into Boobyalla harbour. The most important of these tributaries, from a mining point of view, are the Cascade, Main creek, Weld and Frome rivers (which unite just before joining the modern Ringarooma), Wyniford river, and Bradshaw's...

Jan 1, 1911

By P Standish

Qualitative risk assessment methods are not well suited to considering complex systems and potential interactions of new technology. As part of supporting tier one mining organisations and international industry groups, the author and colleagues have innovated processes to help provide better solutions to sites/companies considering a move to implementing proximity detection and collision avoidance systems. The process identifies required operating states for the system. By applying a combination of research and team-based analyses, a rigorous identification of credible failure modes which could cause these states to be lost, is identified. Finally, required business inputs, expressed in practical terms are distilled from regulator, industry, organisation and site in a way which clearly addresses the failure modes and so retain the required operating states. These business inputs identify improvements for site arrangements (EMESRT levels 1 to 7) before identifying functional requirements for technological collision avoidance solutions (levels 8 for advisory and 9 for autonomous). The paper presents a case study synthesised from multiple sites analyses and will provide guidance on where to find additional resources to assist in making the best possible transition to better equipment and road network solutions.

Jun 22, 2022

By Drew GJ

Smelting is a process in which heat is applied to ores to produce metals. Impurities are removed by segregation in the slag, or converted to gases or sublimates and discharged up the flues. Mate- rials delivered into the smelter have generally been previously concentrated or processed at the mine, and the size of their particles, and also their chem- ical composition, greatly affect the smelting proc- ess. Some impurities are more difficult to remove than others, and are more objectionable in the finished product. The first metal mine in Australia was opened near Glen Osmond in South Australia in 1841, for silver-lead ore. It was followed by the Kapunda Mine for copper in 1844 and by the very signifi- cant Burra Mine, also for copper, in 1845 (Figure 1). A major part of their ores could not be exported profitably for smelting in England and Wales where the large smelters were then located. In addition to treating ores from Cornwall these also smelted ores from recently opened mines in Cuba, Chile, and Mexico. The Welsh smelting process (Figure 2) was developed over a period of years to utilise Welsh coal to treat copper ores particularly from Corn- wall. The first step consisted of a calcination to remove sufficient sulphur from sulphide ores so that subsequent melting operations would produce copper matte, a copper-iron-sulphide which melted at about 1050¦C. Subsequently refined to white metal with the addition of carbonate and oxide ores when these were available, and often through an intermediate step of blue metal, this matte was finally oxidised to pure copper, or as pure as it could be made in those days. The movement of metal towards greater purity was matched by a reverse flow of slag, carrying reducing quantities of copper, so that the slag rejected from the first melting process carried the minimum quantity of copper. Chemical analysis was virtually unknown. Materials were assayed in the laboratory by a small scale smelting process, and the purity of the final refined copper was judged b} the ease with Mhich it could be hammered into thin sheets.

Jan 1, 1987

IT is intended in this paper to present in broad outline to the members of the Institute a short account of the conditions and operations that constitute what is, variously known as Subterranean Warfare, Military Mining, or Tunnelling. Realizing ,the magnitude of the operations, and the varied and minute details met with in them on,the Western Front, it is the writer's intention to confine these notes to operations carried out by the First Australian Tunnelling Company. In so doing there is no wish to detract from the very fine records of the Second and Third companies it is to be hoped that members of the Institute (or others) who were with these companies will write accounts of their doings-the former in the water-logged areas to the south of Armentieres, and later in the sand-dunes at Lombardzee, and the latter in the chalk area of the Lens coal...

Jan 1, 1920

By R R. Anand

Recent research by CRC LEME from an Australian mineral exploration perspective, has focussed on regolith architecture and mechanisms of geochemical anomaly formation, within transported regolith. Methods have been developed for the rapid production of regolith-landform maps which is the starting point for understanding regolith architecture in the third dimension. Methods for development of 3D regolith models are less well advanced, and require integration of all available geological and geophysical datasets, but still with a heavy reliance on drill-hole information. The base of the transported regolith û the unconformity û remains the most important regolith boundary for geochemical sampling in transported regolith terrains. A new generation portable spectral logger, employing a broader spectrum can interpret important features from drill chips within the regolith. This allows internal architecture, redox fronts and the all-important interface to be objectively identified. Transported lateritic components can provide vectors to mineralisation in depositional regimes. Palaeomagnetic and new radiometric methods which date individual phases of the regolith provide evidence of different episodes, each characterised by different geochemical dispersion patterns in transported regolith. Along with lateritic residuum, calcrete is prime sampling medium. Calcrete is probably enriched in gold through physical and biological processes, rather than straight chemical processes. In South Australia, the lowermost calcrete layer buried within the depositional regime, especially where it lies directly over the silcrete layer at the buried interface, is the desired sampling medium. Certain gum trees, with deep roots in transported regolith have been shown to record anomalous values of gold and basemetals in leaves, twigs and bark. Anomalous metals in acid-sulfate soil seeps can also provide a window through sedimentary cover in respect of mineralisation in the basement. A number of Yilgarn occurrences of gold anomalies in transported cover, strongly infer hydromorphic and biological mobilisation of gold. This inference is supported by micro-analyses of regolith mineral hosts in hardpans and mottled sediments, which show gold and pathfinder elements prefer to reside in goethite and specific types of clay minerals. This creates anomalies in specific mineral phases. However the inference that that these are sites of mobile or labile metal ions remains enigmatic. Similarly there is inconclusive evidence that selective extractions will provide an anomaly not otherwise detected by conventional total dissolution methods. Hydrogeochemistry is a promising exploration tool for basemetal exploration. The importance of microbes in both the dissolution and precipitation of gold in the Australian regolith is demonstrated. We are on the verge of identifying the functional gene sequence of individual active microbes. A consideration of possible mechanisms for creating anomalies in soils above transported regolith, presents difficulties in facilitating upward movement of ions from the watertable to the surface. Perhaps the best avenues of research lies with surrogate soil gases, and biotic transfers.

Jan 1, 2004

In presenting the paper, Mr. Davey quoted subsequent work which yielded k, at miscibility gap composition, of about 50.We can confirm the authors' findings for k j 300 for nearly pure tin to k 2 about 50 (average 47) from our own experience and from repeat experiments on materials described by the authors, at 1150°C.During laboratory-scale trials we also found confirmation of the authors' view that it is more difficult to reach equilibrium from the high-iron (in slag) side than from the low-iron (high-tin) side. Working from the high-iron side tends to yield results that point to a high k, leading to optimistic values of iron/tin ratio in final slags. In practice the smelting of a tin concentrate, unless it is exceptionally low in tin and high in iron, must yield initially a tin-rich slag and therefore equilibrium can only be reached from the "tinny" side.

Jan 1, 1967

In order to understand the technique, basic theoretical principles of radiation emission and in- strumentation theory are reviewed. Methods of surveying, reduction of data and interpretation are outlined. Other applications of the technique (e.g. in airborne geological mapping), as well as its specific use in uranium exploration, are discussed. By means of case history-type examples the successful applicant of gamma-ray spectrometry, as a tool in Australian mineral search, is demonstrated.

Jan 1, 1969

By B Murphy, S O’Connell, J L. Heath

In the 1989 best-seller The 7 Habits of Highly Effective People, the author, Stephen Covey, highlights the importance of maintaining not only ‘production’, but also, ‘production capacity’. When operating a modern flotation concentrator, production is often measured in terms of concentrate tonnage, tonnes milled and plant utilisation. There are very few metrics that focus directly on flotation equipment condition in relation to performance, which is analogous to Covey’s production capacity principal. It is evident on many mine sites that flotation equipment condition is not monitored on a proactive basis and that the prevailing culture is to wait for a failure, before addressing an issue.This paper discusses examples of how poor equipment condition can lead to production loss through poor metallurgical performance. Actual examples are given where these problems have occurred in operating plants. An outline is provided on how metallurgical and maintenance departments can work together to protect production capacity and gain more from existing equipment.CITATION:Murphy, B, O’Connell, S and Heath, J L, 2014. Maximising value through maintaining your flotation equipment, in Proceedings 12th AusIMM Mill Operators’ Conference 2014 , pp 71–76 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 1, 2014

By C B. Smith, G L. Boxer, S W. Moss, A L. Jaques, V Lorenz, M J. Rayner

The Ernest Henry Iron Oxide Copper Gold deposit is hosted in a large dilation between two moderately dipping shear zones found in the footwall and hanging wall of the deposit. These shears are controlled by a large diorite intrusion to the north-east and south-west of the deposit, formed ~1660 Ma. A shear zone dubbed the ‘Interlens’ uncovered through underground workings truncates the main orebody into two lenses, and is hypothesized to have formed in conjunction with the Hanging Wall Shear Zone and Footwall Shear Zone. All three shears dip moderately to the SSE (50–140) from open cut exposures through to the current mining horizon approximately 800 m below the surface. Routine geological work and a capital drilling campaign has identified a significant flexure in these sub parallel ore bounding shears with increasing depth. A shift in shear orientation in the Interlens over approximately 100 m vertically from ~50° to the SSE to a steep, easterly trend (~85° to the east) is observed in both drill core and exposures in the underground workings. It is hypothesized the diorite intrusive to the south-west of the deposit controls the shear zone geometries at depth. The geometry of the Interlens mirrors the surface expression of the Proterozoic package of the orebounding shears to the south-west of the deposit, suggesting the surface geometries of the shear zones are consistent with depth. Additional drilling to explore the validity of this hypothesis is planned for the near future to better understand the structural controls on the Ernest Henry mineralisation with increasing depth.

Mar 22, 2022

By G Gibson, B Bessen

In coal preparation, large dense medium cyclones (DMC) at low pressure heads (typically 9D where D = cyclone diameter) are the norm. This contrasts with high density mineral applications where, largely for historical reasons, smaller cyclones at high heads are the standard. There are advantages in preferring large diameter cyclones at low heads, assuming that metallurgical performance does not suffer significantly. These include simpler plant layouts, easier maintenance, smaller spares inventories, reduced wear, reduced medium pumping demands, smaller buildings and overall lower capital and operating costs. In 2008, therefore, Xstrata Zinc decided to trial a single DSM-design 800 mm cyclone in one of its four DMC lines at Mt Isa, replacing the four 400 mm cyclones previously installed. Circumstances allowed a low head of 9.5 D to be trialled, compared with the existing 400 mm head of 21.5 D. This paper describes the trial, including tests using painted ore particles as tracers, estimates of yield and metal recovery, and wear monitoring. The larger unit performed well. There was no evidence that metallurgical performance in terms of metal recovery and waste reject rate suffered, and there was some evidence that it may have improved. Cyclone life increased, and preliminary data suggest that the replacement cost of the 800 mm cyclones is less than half that of the 400 mm units, and this is expected to improve. The plant layout and operability have also improved significantly. Xstrata has therefore decided to convert the whole plant to four low head 800 mm units, replacing the original 16 high head 400 mm units. The paper includes an explanation of the effect of static head on DMC separating force. It also reviews earlier research on diamond applications, and applies a general DMC process model to the Xstrata case, both of which confirm that large, low head cyclones are appropriate in mineral applications, contrary to conventional practice. Such units could significantly reduce both the capital and operating costs of DMC plants in mineral applications.

Jan 1, 2009

During the century past geologists have discovered an extraordinary range of mineral resources. It is somewhat surprising, in view of their success, to look back and find that geologists have been concerned through the entire time about the adequacy of resources to meet future needs. They continue to express concern. The basis of their concerns seems to rest as much in social issue as in evaluations of geology.Demand for mineral resources is driven by population and by per capita consumption. Both have grown steadily over the past century, and both continue to rise. In 1890 the global population was about 1.7 billion, people. It has now exceeded 5 billion and the growth rate is such that by the year 2000, the global population will be between 6~ and 7 billion. Demographic projections suggest the global population will approach 12 billion before a steady state is reached dnrino the centiirv ahead

Jan 1, 1990

By Azizan A

The paper presents the results of chlorination of beneficiated rutile and struverite (a tantalum-niobium bearing, rutile type mineral in alluvial tin deposits) by carbon tetrachloride in the range 623¦K to 773¦K. The chlorination of rutile could reach near completion at 773¦K in about an hour. The process was found to follow a modified pore-blocking law, with the basic reaction constant K varying inversely with the particle size, so that the basic process may be a reaction under interface control (chemical control) as modified by the pore blocking effect. The pore blocking factors for the various experimental conditions were evaluated and the predicted curves showed good agreement with the experimental data. In the case of Struverite, a similar kinetic behaviour was observed but the chlorination process was relatively slower than that in rutile. It was also observed that in struverite, niobium got chlorinated faster, followed by tantalum and titanium, indicating a good possibility of separation by chlorination using carbon tetrachloride.

Jan 1, 1996

By C Grobler, M Recklies, G Jiang, I Taylor, M Morgan, G MacDonald, L Smith

The resource estimation of lateritic deposits, such as Aurukun, presents specific issues related to the lateral changes in thickness and elevation of the various horizontal layers (or zones) within the deposit where the x and y dimensions are orders of magnitude greater than the z dimension. The objective was to develop a three-dimensional (3D) block model that retained the vertical and lateral variation inherent in deposits of this type to allow full optimisation of the production plan without prior selection of an economic portion (enriched bauxite layers) of the profile at the resource estimation stage. The Aurukun bauxite deposit is held by Chalco Australia Pty Ltd (Chalco) and forms part of the world-class Weipa bauxite province, Cape York Peninsula, Queensland, Australia. The bauxite is predominantly pisolitic with an upper boehmite-rich zone and lower gibbsite-rich zone. The bauxite consists of both in situ and reworked domains, is overlain by a thin soil horizon and has kaolinite clay as a transitional base. A portable infrared mineral analyser (PIMA) was utilised on site, in addition to elemental assay, on each drill sample to determine the mineralogy, in particular levels of boehmite, gibbsite, kaolinite and reactive silica. As part of the scope of work, a field program was undertaken using large diameter Boart Longyear sonic drilling to acquire detailed density measurements across the deposit to allow compliance with Joint Ore Reserves Committee (JORC) reporting requirements. Interpretation of the stratigraphy was conducted on a hole by hole basis with definition of the zone layering based on stratigraphy, geochemistry and mineralogy. The zone boundaries were then modelled as 3D surfaces and used to constrain a block model. The block model estimation used the ordinary kriging method, with the estimation done in unfolded space and then refolded, therefore maintaining the zones irrespective of thickness or orientation. The unfolding process converts the real-world positions for both blocks and informing samples to a scaled position relative to the roof and floor of each zone. Analysis of the data and variography were also undertaken in unfolded space. The x and y dimensions are unchanged, but the z dimension is a relative position. The effect of the unfolding and limits on number of samples per hole is to æpushÆ the informing sample search sideways but within the stratification, rather than vertically. This honours the strong vertical zonation within the bauxite profile. The JORC Code requires that the stated resource must have æreasonable prospects for economic extractionÆ. This is a qualitative rather than quantitative definition. A number of selection criteria to define a resource roof and floor were developed in consultation with the project engineers and owners to meet these criteria. The vertical selection of material to include in the resource highlights the variation in the development (and destruction) of the bauxite profile from area to area within the deposit.

Jan 1, 2009

By Tuckey SH, Wake BA, Ariti J

Astute exploration on the northern Minahasa Peninsula, North Sulawesi, resulted in the discovery of the Toka Tindung, Pajajaran, Blambagan and Araren low-sulphidation quartz-adularia vein and stockwork gold-silver deposits. Combined, these deposits have estimated mineral resources in excess of I Moz gold at an average grade of 2.8 gAu/t and 7 gAg/t and are known as the Toka Tindung Gold Project. Gold typically occurs as fine grained electrum and is often associated with acanthite. The structurally controlled mineralised veins are hosted by Late Pliocene plagioclase and pyroxene-phyric basaltic andesite volcaniclastics and flows which form part of the Early Miocene to Pleistocene Sulawesi-East Mindanao Arc. Silica-adularia alteration dominates the volcaniclastic host of the Toka Tindung deposit. K-Ar dating of vein adularia indicates a 2.16 ¦ 0.04 Ma mineralisation age. Relatively narrow envelopes of silicification and argillisation surround the chalcedonic silica, quartz and adularia veins, stockworks and breccias at the other three deposits. Remnant hydrothermal breccias, chalcedony and anomalous arsenic, antimony and mercury indicate these gold deposits were part of a mineralised geothermal system.As of June 1997, Aurora Gold Ltd is finalising a feasibility study on exploitation of the four deposits and treatment of ore through a centrally located conventional CIP plant. Subsea tailings disposal is anticipated. Favourable metallurgy of the ore and logistics of the project area assist in minimising capital requirements.

Jan 1, 1997

By D J. Alchin

Most of South AfricaÆs high-grade iron ore resources are hosted within a fault-controlled structural basin in rocks of the Palaeoproterozoic Transvaal Supergroup in the Northern Cape Province of South Africa. Iron mineralisation occurs as individual orebodies in fault-bounded basins or as fold-controlled concordant lenses around an unconformity plane above the Kuruman Banded Iron Formation. The Sishen mine near Kathu and the beeshoek mine and Sishen South deposit near Postmasburg lie on the northern and southern border of a major domal structure known as the Maremane dome, respectively. The effects and structural constraints of at least three orogenic compressive episodes and several intermittent extensional episodes on the formation, erosion and preservation of iron mineralisation on the Maremane dome and surrounding environs were investigated. Ventersdorp impactogenal rift basin development at ~2.78 - 2.64 Ga, finalised with the deposition of the volcano-sedimentary Vryburg Formation during the thermal subsidence stage at ~2.64 - 2.6 Ga, and was followed by tectonic quiescence/stability and an extensive marine transgression across the entire Kaapvaal craton. The drowning event led to the formation of a carbonate platform with the deposition of the Schmidtsdrif and Campbellrand subgroups conformably above the Vryburg Formation at ~2.6 - 2.52 Ga. The initiation of distal (to the west of the Kaapvaal craton) off-craton oceanic rifting, causing submarine volcanism and associated hydrothermal activity, led to the deposition of initially manganiferous chert (Wolhaarkop Formation) followed by banded ironstone formations (Manganore Iron/Kuruman Formation) of the Asbestos Hill Subgroup at ~2.52 - 2.46 Ga. Initial passive margin rifting along the N-S oriented western edge of the Kaapvaal craton, initiated at the end of Ghaap Group time (during Koegas Subgroup deposition) at ~2.46 - 2.35 Ga, formed a prominent system of N-S striking, westerly dipping normal faults. Easterly directed crustal compression in post-Ghaap Group time in response to the Kalahari Orogeny (accretion of Rehoboth craton along western edge (Kalahari suture zone) of the Kaapvaal craton at ~2.35 - 2.24 Ma led to the formation of large-scale regional, N-trending F1-folds. Partial to complete inversion of the Koegas passive margin rift system (ie reverse dip-slip reactivation of the N-S striking normal fault system to high-angle reverse faults and dextral strike-slip reactivation of the Ventersdorp rift system developed in the Archaean basement), was followed by uplift, erosion and formation of a regional angular unconformity (Postmasburg unconformity). Uplift was accompanied by deposition of fluvio-glacial sediments of the Makganyene Formation (Lower Postmasburg Group) within an intracratonic peripheral foreland basin setting unconformable above Ghaap Group strata at ~2.35 - 2.24 Ga. Post-orogenic crustal relaxation and rifting caused extensional reactivation of the N-trending Palaeoproterozoic passive margin rift system and NE-trending Neoarchaean Ventersdorp impactogenal rift system, forming a fault-controlled depository for the volcano-sedimentary Upper Postmasburg Group at ~2.24 - 2.1 Ga. Deceleration in rifting was succeeded by thermal subsidence of the Upper Postmasburg Group rift, erosion, formation of a regional angular unconformity and deposition of clastic sediments of the Lower Olifantshoek Supergroup unconformable above Postmasburg Group strata at ~2.1 - 1.93 Ga. Renewed rifting led to the deposition of volcano-sedimentary units of the Upper Olifantshoek Supergroup within a rift system superimposed on the Postmasburg Group rift depository at ~1.93 - 1.83 Ga. Easterly directed crustal compression during the Kheis Orogeny at ~1.83 - 1.73 Ga led to renewed inversion of rift structures of the Postmasburg Group and Olifantshoek Supergroup depository, N-trending F2 folding and thin-skinned thrusting of older rock units eastwards over the cratonic cover, thereby utilising planes of weakness in the strata such as prominent unconformities and lithological contrast boundaries as principal dTcollements. NNW-directed crustal compression in response to Lomanian (Namaqua-Natal) Orogeny at ~1.15 - 1.0 G along the southern margin of the Kaapvaal craton, resulted in minor sinistral strike-slip reactivation of the N-S striking fault system, the formation of extensional NNW-SSE striking fracture/fault zones and the development of ENE-trending F3 folds forming a F2/F3 fold interference pattern. Post-Lomanian tectonic events (eg the Pan-African Orogeny at ~650 - 500 Ma, the Cape Orogeny at ~310 - 240 Ma, and the Gondwana breakup at 205 - 120 Ma), caused only comparatively minor extensional reactivation of the pre-existing fault systems. Iron mineralisation was ultimately preserved from erosion by Kheis Orogeny-related N-trending F2 synclines and Lomanian Orogeny-related ENE-trending F3 synclines, in particular areas of interference between F2 and F3 synclines representing comparatively deep semi-circular trough- like depressions, as well as in half grabens formed adjacent to reactivated westerly dipping N-S normal faults. Support for relating the iron and manganese mineralisation to structurally controlled hydrothermal fluid flow during the Kheis orogenic event has also been found, and ongoing research is aimed at confirming and refining the hydrothermal model for iron ore mineralisation in the Northern Cape.

Jan 1, 2007

The .subject of this paper is to briefly outline various methods of stockpiling and reclaiming, and the use of different types of bucketwheel re- claimers and stackers in these operations. The paper examines briefly the different types of bucketwheel equipment, their operations and relates them to different stockpile layouts, giving examples of their application in Australia.

Jan 1, 1973

A general review of grinding mill steel liner evolutions/developments in recent times. The driving force behind these developments has been the mill operators desire to minimise the nett cost of their operation. These developments have resulted from a team approach between supplier, operators and reline crews. The move towards larger diameter high aspect mills, faster mill speeds, pebble ports and the use of large diameter grinding media has affected the traditional liner designs, which is placing higher demands on the supplier to meet these new working parameters and expectations. Operators are also taking closer ownership in the liners being supplied, as demonstrated by the development of their own mill liner specifications. This paper outlines some of liner developments and changes undergone at various milling operations around Australia and overseas (such as Cadia Hill, Kidston, Ok Tedi Mining, PT Freeport, etc) and where to in the future?

Jan 1, 2000

By O. J. RICHARDS

The Wongawilli system of mining has been in use for over 30 years and has enabled high production rates and acceptable extraction ratios to be achieved in seams less than 4 m in thickness. A modification of the Wongawilli system has been developed to permit the use of a continuous miner and mobile equipment to extract a coal seam 6 m thick. Following physical and mathematical model studies the new mining method is now undergoing field trials at Collinsville, Queensland. Progress of the field trials to date has achieved 99% extraction of the upper slice by remote control operation of the continuous miner and established the feasibility of installing resin grouted wooden dowels in the coal floor to reinforce the coal septum. The method is explained in the text.

Jan 1, 1980

Optimum selection of explosives by means of monitoring explosive performance can lead to increased profitability through the control of fragmentation, a reduction in hangingwall and footwall damage and overall drill and blast costs. Studies conducted at the Mount Lyell Mining and Railway Company underground copper mine evaluated in situ the performance of four explosive types. Measurements included monitoring the levels of induced shock energy and the attenuation thereof with distance. The velocity of detonation (VOD) of these explosives was also measured using in-hole techniques. Assessment of these results, together with a knowledge of the rock mass strength, facilitated the selection of an explosive that was best suited to the given rock mass conditions.

Jan 1, 1995

One of the most praninent Bouguer anomaly features in the Broken Hill District is the long wavelength high of 10-15 ngals above background which forms a northeast trending, oval zone sane 15 km by 45 km with Broken Hill on its northern gradient. Rock density measurements and modelling indicate that this anomaly can be explained by the presence of generally relatively higher density meta- sediments extending from the surface to a depth of about 2000 m. The regional Bouguer anomaly data show that the Willyama Block and Euriowie Block are mostly overlain by a fairly smooth Bouguer anomaly high in the range 5-15 mgals, whilst the surrounding younger sediment covered areas, including the Mundi Mundi Plain, Murray Basin fringe and Bancannia Trough, are mostly overlain by lows which range to minus 30 mgals. Thus in terms of the gravity pattern the Willyama and Euriowie Blocks form a fairly continuous and haogeneous entity. However, the 5-10 mgals relative low over part of the Torrowangee Synclinorial Zone indicates that the Adelaidean System metasediments are in aggregate slightly less dense than the Willyama Supergroup metasediments. The low can be modelled to indicate a basement link between the Broken Hill and Euriowie Blocks at 1000-2000 m depth.

Jan 1, 1983