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By P Maillet, A J. Crawford, S M. Eggins

TheFiji Islands are remnants of a once continuous Solomon-Vanuatu-Fiji-Tonga volcanic arc (the Vitiaz arc), located at the boundary between the Indian-Australian and Pacific plates. They record a history of: (i)                  arc volcanism the late Eocene to late Miocene, (ii)                an extensive magmatic response to arc rifting (5.5 - 3.0 Ma) during which volcanism was dominated by shoshonitic to tholeiitic basalts, and as rifting continued, (iii)               a transition from arc to intraplate volcanism.   The Hunter Ridge-Hunter Fracture Zone separates the inactive South Fiji Basin from the actively spreading North Fiji Basin, and has been considered to be a transform zone, almost parallel to the motion vector of the Australian plate. However rocks dredged during the 1993 æAlizeÆ cruise, from along the northern part of the Hunter Ridge are typical arc tholeiites, and therefore demand that subduction has occurred beneath the Hunter Ridge sometime during the last ~5 Ma. The Kadavu Island group, south westernmost Fiji, lies at the north-eastern end of the Hunter Ridge-Hunter Fracture Zone, and possibly results from oblique subduction of South Fiji Basin oceanic crust, which may have accompanied the anticlockwise rotation of Fiji during opening of the North Fiji Basin. These islands consist dominantly of 3.4 - 0.5 Ma old medium-high K andesites and dacites, with many traits typical of subduction-related volcanics, ie predominance of intermediate members (55 - 65% SiO2) no Fe enrichment, TiO2<1%, and negative Nb-Ta anomalies. These features contrast strongly with volcanics from elsewhere in Fiji around this time, where volcanic centres produced Om-like intraplate olivine basalts. The Kadavu Islands become gradually younger to the southwest, and show a significant decrease in K2O with time. The north easternmost islands (Astrolabe islands) containing the oldest rocks (~3 Ma) have shoshonitic affinities and are considered to be of similar age and composition to the youngest shoshonites found elsewhere in Fiji.

Jan 1, 1995

By C J. Hogan

Increasing demand for fine grinding to improve mineral liberation and metal recovery and the need for stricter control of the environmental impact of tailings deposition poses problems for tailings disposal. This has led to an increasing number of investigations of properties of tailings and their disposal. This paper describes laboratory model testing undertaken on Macraes mine flotation tailings to provide information on tailings behaviour under conditions of subaerial deposition. The in-place density or 'dry density' of the impounded tailings and the impoundment depth relationship are important for utilisation of the available impoundment storage facility and results of dry density to depth relationships are given for the Macraes mine tailings impoundment.

Jan 1, 1993

Neither the copper orebodies nor the zinc-lead-silver orebodies at Mount Isa were formed syntectonically as has been claimed for the last 20 and 10 years respectively. Both orebody types were cogenetic, coeval, and formed early during the sedimentation and diagenesis of the host formation. The copper orebodies are interpreted as having formed diagenetically at hand specimen scale, syngenetically at formation scale. The zinc-lead-silver orebodies are interpreted as having formed primarily by sedimentary means at both hand specimen and formation scales.

Jan 1, 2000

By G B. Arehart

The Midas epithermal system is one of the larger low-sulfidation epithermal vein systems discovered in the western US in recent years, containing in excess of 3 Moz of gold (premining). The deposit is spatially and temporally related to bimodal volcanism in the Northern Nevada Rift; dates on igneous rocks (16 - 14.7 Ma) bracket the age of high grade veins (15.3 Ma). Hydrothermal alteration at Midas is typical of epithermal systems, comprising proximal potassic through distal propylitic assemblages; in contrast to many epithermal systems, Midas has minimal development of wallrock illite/sericite. Mineral assemblages are clearly zoned on the vein structures that acted as focal planes for fluid upflow. Geochemical zoning patterns also show this zoning. Metals were deposited in open-space veins as the result of boiling of hydrothermal fluids; multiple episodes of crustiform mineral deposition are documented in the vein textures. The major vein minerals include quartz, adularia, calcite, selenides and sulfides, with electrum as the primary ore mineral. REE patterns for vein material are similar to patterns for coeval rhyolites, but distinctly different from patterns of the host rocks. Stable isotope data are consistent with meteoric water as the dominant ore fluid. Combined REE and stable isotope data suggest that fluid from which the main ore-bearing stage of the veins was deposited was slightly lower pH than other stages.

Jan 1, 2005

Recent legislation in the environmental field gives the mining industry an opportunity to take timely action to address its image. Shifting the focus away from mining (the activity) to minerals (the resource) will enable the mining industry to stand on equal footing with other industries and will help minimise the vulnerability to political and interest groupsÆ interference.

Jan 1, 1993

By McKay AD

The bulk of Australia's uranium resour- ces was delineated in the last 18 years when a total of $563 million (1984 dollar values) was spent on uranium exploration. Australia's share of the low-cost Reasonably Assured Re- sources in the World Outside the Centrally Planned Economies Area (WOCA) increased from 1.5% in 1967 to 29% by the end of 1984 and its share of the low-cost Estimated Additional Resources (Category I) then stood at 25%. As of December 1984, Australia's uranium resour- ces were estimated by the BMR to be: Cost range US$80/kg U (US$30/lb U301) Reasonably Assured Resources 463 000 t U Estimated Additional Resources(I) 251 000 t U Cost range US$80-130/kg U (US$30-50/lb U308) Reasonably Assured Resources 63 000 t U Estimated Additional Resources(I) 126 000 t U The increases in Australia's resources was sustained by a group of large and rela- tively high-grade deposits which were disco- vered during the period 1969 to 1975. Austra- lia's share of the low-cost resources was also enhanced by a contraction of WOCA's low-cost resource base due to escalation of production costs for smaller low-grade deposits. Most of Australia's uranium resources are contained in the Proterozoic unconformity- type deposits of the Alligator Rivers uranium field and the stratabound deposit at Olympic Dam on the Stuart Shelf. Most of the remain- der of Australia's uranium resources is con- tained in calcrete-type deposits. Less than 10% of Australia's uranium resources are in sandstone-type deposits. Total Australian production to the end of 1984 amounted to 26 241 t U, representing 3.4% of WOCA's cumulative production. Aus- tralia's share of WOCA's annual production has steadily increased from 1.3% in 1977 to 11.2% in 1984 (4390 t U). The increases in Austra- lian production took place in the face of reductions of production in WOCA countries, principally the US, from a record level of 43 988 t U in 1980 to about 39 000 t U in 1984. New low-cost production centres, mainly in Australia and Canada, have partly compen- sated the decline in US production. The Department of Resources and Energy (1985) reported that Australian exports of yellowcake are expected to reach 10 000 t U308 (8480 t U) by 1993/94, representing an in- crease of about 13% oer annum.

Jan 1, 1986

By J E. Nethery

At the Red Dome and Mungana deposits in north Queensland, Australia, it is proposed that mineralisation and alteration developed as a 'telescoped' overprinting continuum, ranging in style from hypothermal to epithermal, reflecting the major changes that developed in the regional setting over the period circa 325 - 290 Ma. Regional assessment suggests that this also applies to many other precious and base metal deposits within a 40 km length of the host Siluro-Devonian Chillagoe Formation.   A ten stage paragenetic sequence of structural preparation, multi phase intrusion and associated mineralisation, alteration and brecciation is postulated for the Chillagoe district.

Jan 1, 1995

By K J. Thompson

This paper describes the work which has been undertaken at the Ohai coalfields in Southland to restore overburden heaps during past opencast mining operations, and procedures which have been adopted to ensure that restoration is achieved concurrent with present opencast mining activities. The system implemented for the treatment of wastewater from opencast mining operati6ns is also described.

Jan 1, 1981

Dynamics of Three Phase Contact Line Motion in Liquid-Liquid-Solid Systems - Impact of Surface Roughness

Sep 13, 2010

Longwall mining originated in the early 18th century in the county of Shropshire in England, where it was known as the longway method. Its name implies the extraction of the seam over a long continuous length or wall of exposed coal. Until the late 19608 and early 1970s the use of the longwall system with a few exceptions was confined to the United Kingdom and Europe. It was not until the early 19708 that the highly productive longwall faces we now know, were developed and the application of the longwall system extended to Australia, South Africa, United states of America and other parts of the world. The modern longwall face has three major components, namely: +         the machine to break and load the coal +         the face conveyor; +         and a system of roof support.   This paper reviews the development of longwall mining technology. The parameters directly influencing the production 'of a modern longwall face are considered, as are the possible constraints to the further development of the longwall system.

Jan 1, 1991

Promoters for Soap Flotation of Phosphate Minerals

Sep 13, 2010

A research project was commissioned by the Australian Coal Association Research Program (ACARP) to improve the understanding of tailgate strata mechanics and to provide a more rigorous engineering basis for tailgate support design. A deformation mechanism termed æskew roofÆ was defined which relates the regional influence of differential horizontal strata movement (shear) about longwall extraction to gateroads. Confirmation of the mechanism was achieved by field investigations which included measurement of the shear displacement along weak interfaces. Under geological and mining conditions where the skew roof mechanism operated, strata units were found to move progressively further towards the goaf with height into the roof. 3D numerical modelling was used to assess the major geotechnical factors controlling the mechanism and to determine appropriate support strategies within a æskew roofÆ environment including the role of cables versus standing supports. The skew mechanism is considered relevant to; all roadways in the vicinity of longwall extraction including the faceline itself, chain pillar design, and support design.

Jan 1, 2005

Low displacement fault zones often comprise a mesh of interlinked faults, extensional-shear and purely extensional vein fractures. Hydrothermal mineralisation localised around such structures testifies to their importance as conduits for fluid flow. Mesh structures are most commonly developed in situations approximating bulk pure shear but predominantly simple shear meshes also occur. They appear to develop through the infiltration of pressurised fluids into a heterogeneous rock mass with varying material properties. In some circumstances, mesh formation appears to be a precursor to the development of major through going faults. Mesh formation generally involves hydrofracturing (Pf > s3, at least locally) and the condition Pf ~ s3 to be maintained for the mesh to remain a high permeability conduit, requiring fluid over pressuring at other than shallow depths in extensional-transtensional regimes. The volumetric character of earthquake swarm activity appears to result from the passage of hydrothermal fluids through mesh structures, representing a form of distributed fault-valve action along suprahydrostatic hydraulic gradients arising from magmatic intrusion, compaction overpressuring, metamorphic dewatering, etc. Fluid redistribution in the crust is influenced by maximum hydraulic gradient (not necessarily vertical), by existing permeability anisotropy arising from bedding and other forms of crustal layering, and by structural permeability developed under the prevailing stress field. Strong directional permeability develops in the s2 direction, parallel to fault-fracture intersections within the mesh and orthogonal to fault slip vectors. In particular tectonic settings, stress-controlled permeability allows strongly focused flow through fault-fracture meshes with high potential for mineralisation. Favoured localities for mesh development include short-lived link structures along large-displacement fault zones such as dilational jogs, lateral ramps, and transfer faults.

Jan 1, 1995

By D J. Brake

There has been a strong trend over the past decade in hard rock mines towards the use of very high powered auxiliary (or secondary) fans; in many mines, the installed power for the secondary ventilation system now exceeds that of the primary ventilation system. This also reflects the trend to use two-stage auxiliary fans pushing air into a single ‘trunk’ duct that in turn splits into multiple branches with multiple outlets feeding multiple workplaces. This often produces a poor result in terms of face flows due to the high resistance, high leakage and badly managed duct outlets, as well as high fan capital and operating (power) costs, which in turn also results in a higher cost for the underground power reticulation/distribution systems. This paper explores the reasons why this trend exists and what ventilation practitioners can do to utilise less expensive systems that simultaneously deliver better workplace conditions. It includes a case study.CITATION:Brake, D J, 2017. Auxiliary ventilation design – why and how mines waste so much power on inferior systems, in Proceedings Australian Mine Vent Conference 2017, pp 27–34 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 28, 2017

Beneficiation of Iron Ore - Washing with Surface-Active Agent The stability of the dispersed phase in 10 wt per cent slurry of iron ore slime and fines was studied at pH 5 and different concentrations of surface-active agents. The behaviour of the dispersed phase of iron ore slime and fines is different for different surface-active agents. The improvement of iron value of slime and fines in the presence of surface-active agent is best realized at pH 8, where the Al2O3/Fe and Al2O3/SiO2 ratios in the concentrates are appreciably reduced. The polar functional group like -COO- interacts with hematite surfaces and forms outer- and inner-sphere surface complexes depending on the suspension pH and adsorbate.

Sep 13, 2010

Goldfields (Tasmania) Limited operates a small, high-grade underground gold mine on the West Coast of Tasmania, 30 kilometres north of Queenstown. The main orebody, Zone 96, was discovered in 1989, with major development work commencing in 1993. The mine was officially opened in July, 1996. Initial production came from a shallow orebody known as the Sill Zone, some 50 - 150 m below surface, which was accessed by a 1 in 8 decline. Zone 96 lies between 350 m and 550 m below the surface and is accessed by a 402 m deep, 3.2 m diameter internal shaft from the collar level located 100 m below surface. The main ore extraction system in Zone 96 is mechanised cut and fill, using high density paste fill. Run of mine ore and waste are hoisted in a single 5.5 tonne overturning skip, then trucked from the underground collar to the gold plant ROM pad or waste dump, respectively. Ground conditions in the mine vary with orientation and proximity to major faults. The gold is contained in a sequence of strongly altered volcanic rocks adjacent to the Henty Fault. Most of the gold is contained in massive quartz, ranging in width from 0.5 m to 7 m, which has been subjected to substantial faulting. Average mineable grade is about 27 grams gold per tonne. Ore reserves in 1996 proved an initial mine life of approximately 4.5 years at 90 000 ounces gold per annum, with significant potential for additional resources from extensions to Zone 96 and adjacent zones. The lease is located in an environmentally sensitive area and a very high standard of environmental management is an essential part of the operation. This paper describes the relevant aspects of mining at Henty including grade control, ground support, backfill placement and environmental management.

Jan 1, 1998

Tonnage and grade are the principal reported components of mineral resource estimates but tonnage is a derivative of two more fundamental estimates; volume and bulk density. Typically, most of the effort in a resource estimation study is directed towards grade and volume, yet poor application of bulk density data to resource models can result in significant biases. The impact on tonnage estimates is easily recognised but poor density estimates may also introduce subtle biases into the grade estimates. Methods for measuring bulk density have been discussed previously. This paper focuses on the manipulation of bulk density data and the extension of bulk density from essentially point measurements to block estimates within resource models. Bulk density is a continuous, geologically controlled, spatial variable and should be treated as such. Issues such as combining data from multiple sources, sample support and the interdependence of bulk density and grade estimates must be resolved. The statistical and geostatistical techniques used for grade estimation are, under the right circumstances, equally applicable to bulk density. The importance of bulk density needs to be recognised. With robust raw data and correct estimation procedures, better estimates of bulk density can be obtained and both local and global tonnage and grade estimates can be improved.

Jan 1, 2000

Jan 1, 2004

Study on Desulfurisation and Deashing for Medium-High Sulfur Coal Using Shaking Table As important coal resources, medium- high sulfur accounts for a significant part of the coal reserve in China. The environmental regulations and fuel standard requires sulfur and ash to be removed before it is used, so as to save energy and decrease the emission. Therefore, the effective desulfurisation and deashing technologies are urgent needed. However, due to the local characteristics of the coal, specific technology with optimum operation parameters is required to develop for different local coal. Qinglong is a district of Guizhou Province, which has large medium to high sulfur contained coal reserve. In this paper, medium-high sulfur coal is sampled from Qinglong, Guizhou province. Some basic characteristics such as the mineralogical composition of the coal rock, the monomer existing state and the granulometric composition are determined by X-ray diffraction quantitative analysis and polarisation microscope analysis respectively. Adopting the classified feed method, shaking table tests show that the feed pulp concentration is 20 per cent, the stroke is 13mm, the frequency of the stroke is 380 per min, the cross slope is 3¦ and the volume of wash water is 5.2 L per min. Under such condition, aggregate processed coal yield is 72.87 per cent and sulfur content decrease to 1.31 per cent With shaking table technology of 'First stage rough and intermediate further fine benefication', the yield of concentrate coal increased from 72.87 per cent to 81.21 per cent, while the sulfur content reduced to 1.35 per cent.

Sep 13, 2010

During an eight month period, January to August 1978, nine bore holes were drilled in the Mikonui River gravels. On account of two rebores required from near bottom, the number of bores is in effect 11. Just on 1300 feet were drilled with an average depth of 120 feet. Depth varied from 102 feet to 133 feet. Penetration on average per hole value, varied from 7.4 to 16.4 feet per day. Gold values were even more erratic. Drill rig used was the Keystone churn drill manufactured locally by the Dispatch Foundary. It is skid mounted and requires a crew of two persons.

Jan 1, 1979