Search Documents

By J M. Parr, P M. Herzig, J B. Gemmell, S D. Scott

PACMANUS is an actively-forming seafloor analogue of volcanic-hosted massive sulfide orebodies, situated on the crest of an andesite-dacite-rhyodacite ridge overlying rifted older arc crust in a back-arc basin. Hydrothermal deposits range from Mn-oxide crusts to Cu-Zn-rich massive sulfide mounds and chimneys containing significant Au and Ag. Preliminary data suggest a substantial magmatic component to fluids and metal sources, and we speculate that PACMANUS is the cap to a complete hydrothermal system including subvolcanic and intrusive-related mineralisation.

Jan 1, 1995

The New Zealand Steel Ironsand Slurry Pipeline was successfully commissioned in February 1986. The project includes 18 km of high pressure, polyurethane lined buried pipe. McConnell Dowell Constructors Limited has developed a coupling which has allowed this pipeline to be fully welded. The design and development of the coupling and its application on this project is discussed.

Jan 1, 1986

By B M. Washington, R R. Lovel, G J. Sparrow, M J. Fisher-White

"Work in CSIRO with several Australian ores has shown that?by heating a high-phosphorus goethitic iron ore and then leaching with caustic or acid, the phosphorus levels in the ore can be lowered to a commercially acceptable value of around 0.08 weight per cent phosphorus (P). With increasing heating temperatures up to 1300¦C, the extent of phosphorus removal increased. This is considered to be associated with mineralogical changes in the iron oxide phases in the ore during the heating.Little phosphorus was removed from four high-phosphorus goethitic iron ores containing 0.12 - 0.16 weight per cent P in leaches with boiling water. However, leaches with sulfuric acid removed ten to 20 weight per cent of the phosphorus and leaching with sodium hydroxide removed even more phosphorus to produce leach products containing between 0.08 and 0.12 weight per cent P from three of the ores.After heating at 300¦C, leaches at a low pulp density of 0.5 weight per cent solids with 1 - 5 M NaOH and 0.1 - 1 M H2SO4 gave leach products with 0.06 - 0.09 weight per cent P. The lixiviant concentration required and extent of phosphorus removal depended on the ore. At a higher pulp density of 25 weight per cent solids, leach residues with between 0.07 - 0.14 weight per cent P were obtained.More phosphorus was removed from ores heated at 900¦C. Leaches at both the low and high pulp densities, with 1 - 5 M NaOH and 0.1 - 1 M H2SO4, gave leach products with 0.05 - 0.09 weight per cent P. However, the lowest phosphorus levels were obtained after heating the ores at 1200 or 1300¦C and leaching with 1 M NaOH or 0.1 M H2SO4. Leach residues with 0.02 - 0.06 weight per cent P were obtained, even from leaches at the higher pulp density of 25 weight per cent solids. Leaching tests on heated samples under heap leaching conditions at ambient temperatures have shown that phosphorus levels can be reduced to similar levels to that achieved in an agitation leach within ten days.CITATION:Fisher-White, M J, Lovel, R R, Sparrow, G J and Washington, B M, 2013. Effect of temperature on removal of phosphorus from Australian Goethitic iron ores, in Proceedings Iron Ore 2013, pp 373-380 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Aug 12, 2013

By D Kepert, M Absalom, N Nitschke, C Fowers

The discovery of the Nyidinghu Iron Ore Deposit totalling 2.46 Bt of resource continues FortescueÆs highly successful exploration record of discovering multi-billion tonne deposits under cover with little to no surface expression. Since inception in 2003 Fortescue have discovered and delineated the Christmas Creek and Cloudbreak deposits in the Chichester Range totalling 3.38 Bt and 3.25 Bt in the Solomon region. Together with other deposits Fortescues resource portfolio now approximates 10 Bt of hematite - goethite mineralisation.The Nyidinghu deposit is situated on the southern margin of the Fortescue Valley, 35 km south of FortescueÆs Cloudbreak mining operations on the north margin of the valley. Nyidinghu comprises approximately 70 per cent BID martite - goethite mineralisation hosted by the Brockman Iron Formation and 30 per cent CID beneath alluvial outwash of the Weeli Wolli Creek in to the Fortescue Valley. Minor DID mineralisation occurs at the deposit margins.BID mineralisation is strongly controlled by the pre-existing NE/SW trending Weeli Wolli Fault system and bounded to the north by the Poonda Fault. Both fault systems are interpreted to have had a long and complex history commencing pre Ophthalmian Orogeny (ca 2.2 Ga) and remaining intermittently active through the Proterozoic.CID at Nyidinghu is the downstream continuation of the combined Weeli Wolli/Marillana CID palaeochannel system being mined by Rio Tinto and BHP Billiton at Yandicoogina and Yandi, respectively.Exploration commenced in August 2010 with the inaugural resource announcement of 1 Bt being made just six months later. To date over 1700 RC and 85 diamond core holes have been drilled forming the basis for the resource of 2.46 Bt and ongoing feasibility studies. Current exploration activities continue to delineate new mineralisation at Nyidinghu with an ultimate target tonnage of 3 Bt.CITATION:Fowers, C, Kepert, D, Absalom, M and Nitschke, N, 2013. Discovery, geology and structural setting of the Nyidinghu iron ore deposit, Hamersley Province, Western Australia, in Proceedings Iron Ore 2013 , pp 81-90 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 12, 2013

In understanding the consequence of existing law, and the likely implications of its reform, it is necessary to comprehend the logic of the situation that the law provides individual decision makers and how that situation would be adjusted by reform. In particular, the way in which natural resources, including minerals, are used and managed is influenced by the definition and structure of property rights that the law provides. Property rights are enforceable claims to use or to benefit from resources. An example is a mining licence that allows its holder to extract minerals in a specified area. Property rights establish the structure of incentives, opportunities and constraints within which resource use decisions are made, ie the logic of the situation, and hence influence the use and management of resources. The extent and type of mining in New Zealand, for example, reflects the rights that miners have to extract minerals, and their rights to benefit from mining as against their duties to compensate landowners and pay royalties. This paper describes the characteristics of minerals that are relevant to the definition of property rights, analyses the implications of alternative property right arrangements and describes the existing situation.

Jan 1, 1988

The Century zinc-lead-silver deposit has a geological resource of 118 million tonnes averaging 10.2% zinc, 1.5% lead and 36 g/t silver. It lies approximately 250 krn NNW of Mt Isa in NW Queensland, Australia, and is hosted by middle Proterozoic age siltstones and shales of the Lawn Hill Formation. Within the orebody, most mineralisation occurs selectively within black shale units as fine grained sphalerite and galena lamellae with minor pyrite and siderite. The black shale units are separated by weakly mineralised sideritic siltstone horizons. The deposit is unmetamorphosed and only weakly deformed, displaying excellent lateral stratigraphic and grade continuity. The deposit is mostly overlain by younger Proterozoic sediments and later Cambrian age limestone cover and only a small proportion of the mineralisation crops out. Mineralisation has a subtle surface expression without a classic gossan profile, probably due to the low iron sulphide content of the ore. These factors contributed materially to the length of time between the first recognition of lead-zinc-silver mineralisation in the area by prospectors in the 1880s, to the discovery of the orebody by CRA Exploration Pty Ltd (CRAE) in April 1990.   Small scale prospecting and mining continued in the area from the date of the first mining lease in 1887. Post 1950, the deposit area was also included within nine separate regional exploration titles prior to CRAE's title acquisition in 1987. CRAE's original exploration strategy was partly pragmatically and partly conceptually inspired, but the eventual discovery only partly conformed to the original conceptual model. The deposit was found higher in the stratigraphy than the original target position, with unexpectedly low total sulphide content relative to other known deposits.   The discovery soil anomaly was located by the CRAE's first regional orientation traverse line in the area, but was not drill tested for three years. The discovery sequence at Century has strong elements of persistence, technical competence and some luck. It demonstrates that even in well explored terrains (by conventional standards) the exploration story can never be said to be over. The foreshadowed development of an economic resource at Century will hopefully inspire continued commitment to 'brownfields' exploration by mining companies, and demonstrate to external regulators the importance of genuine multiple land use strategies and the need for continued access to land for exploration and mining purposes.

Jan 1, 1995

Platinum-group minerals (PGM) are recorded from a number of localities along theWaiau River, western Southland, and the south coast of the South Island, New Zealand. At each locality, small amounts of PGMs were recovered as by-products of historical gold mining operations. During the period 1890-1950 an estimated 1000-2000 oz. of æplatinumÆ were recovered from the region, the only area within New Zealand where PGM have been commercially exploited. The PGM suite of southern New Zealand consists of Pt-Fe alloys, IPGE (iridium subgroup, platinum-group elements) alloys, sperrylite (PtAs2), cooperite (PtS) and braggite ((Pt,Pd)S). The composition of Pt-Fe alloy exhibits considerable variation and two compositional populations are recognised. Some Pt-Fe alloy grains are chemically zoned. Iridium is the most abundant IPGE alloy phase and often contains considerable Pt, in contrast to osmium and ruthenium alloys. Cooperite and braggite grains are characterised by extremely low concentrations of Ni.   Exsolution of osmium and iridium from Pt-Fe alloy and Pt-Fe alloy from iridium is observed Several PGM host mineral inclusions which vary from single to poly-phase, display rounded to equant outlines and range in diameter from greater than 100 ¦m to less than 5 ¦m. Olivine and Ni-sulphide inclusions are only present within IPGE alloys. Pt-Fe alloy, cooperite, braggite and sperrylite host Cu-Fe sulphides, a wide variety of PGM, clinopyroxene, amphibole, magnetite and plagioclase within inclusions. Sperrylite also hosts Pd bismuthiotellurides, gold and several potassium-rich silicate phases. Similarities in inclusion phases and mineral chemistry from several localities suggest that the PGM are derived from a single (as yet unidentified), probably calc-alkaline magmatic source. This source is situated somewhere along the margins of the western Southland sedimentary basin where PGM liberated by erosion are transported down the Waiau River and dispersed eastwards along the coast by strong longshore currents.

Jan 1, 1995

The excavatability of the rock mass in a proposed open pit mine at Globe-Progress has been assessed. The rock mass was initially evaluated by determining variations in seismic velocity and by using the Revised Size-Strength Chart. These two assessments should be performed during the feasibility or early investigation stages of a project. A complete rock mass excavatability assessment using a suite of geological and geotechnical properties was then performed using three methods: RMR System; Modified Rippability Rating; and a productivity estimation method. These three methods should be applied during the investigation and design stages of a project. The preliminary assessments show that most of the open pit rock mass is expected to be rippable. The complete assessment differentiates weak, fair and good rock masses within the open pit. Weak rock mass exists along the Globe-Progress Shear zone, located along the northern and eastern pit walls and also in the western pit wall where the Chemist Shop Fault is located are both regions are expected to be diggable. Relatively weak rock mass also exists along the Globe-Progress Shear axial hinge. The Globe-Progress Shear limbs are generally fair to good rock where moderate to hard ripping should be expected.

Jan 1, 1996

Previous methods for measuring the flow of solids in Jnrdraulic conveying have not considered the important effects of slip velocity and particle concentration. In this paper an extension of the method proposed byShirato et al. (J. Chem. Engng. 'Japan, 1: 164-167) for determining mass flow in a vertical conduit is outlined.The present method consists of measuring' the volumetric flow of the slurry (by a magnetic flow meter for instance) and the density of the slurry in two pipe sections of different diameters. Effects of variation of slip withparticle concentration, not previously considered, are allowed.Problems involved in estimating the density of a slurry from differential pressure measurement are discussed.The major problem is the uncertainties in estimating frictional losses due to the wall in two-phase flows. The greater reliability of a more "direct" technique, such as by 'Y-ray absorption, for measuring solid concentration is emphasized.

Jan 1, 1971

The paper discusses the special mixing requirements for Metallurgical Plant Design and outlines the problems associated with the agitation in Mineral Processing Industry today. It also covers new applications such as state of the art large leach tanks and backfill for deep mining.

Jan 1, 2004

By J L. Mauk

Gladstone Hill, a volcanic-hosted low-sulfidation epithermal prospect in the Coromandel Peninsula, is less than 1 km from the world-class Martha Hill Au-Ag deposit. Gold-silver-bearing quartz veins occur in Late Miocene andesitic volcanic rocks of the Waipupu Formation that are extensively altered. The occurrence, spatial distribution and temporal relationships of hydrothermal minerals have been determined along two cross sections that transect the Amaranth, Gladstone, Cowshed and Moonlight veins. Quartz and pyrite are ubiquitous along these sections. Adularia and chlorite are widespread, but both are scarce in wall rocks adjacent to the Moonlight and Cowshed veins. By contrast, rare hydrothermal albite and epidote are restricted to wall rocks surrounding the Amaranth vein. Illite, which replaces adularia, is widespread and grades laterally eastwards into a zone of interstratified illite-smectite that envelops the Moonlight and Cowshed veins. During late-stage hydrothermal activity, rare calcite formed at depth and uncommon kaolinite and alunite formed at shallow levels. The overall clay mineral zonation with illite grading eastward into interstratified illite-smectite reflects paleothermal gradients of >220¦C to -170¦C towards the margin. The alteration assemblage of quartz, adularia, chlorite, albite, epidote, illite, interstratified illite-smectite and pyrite reflects formation from a near-neutral to weakly alkaline pH chloride water that contained low concentrations of CO2, Late calcite formed from very local descending steam-heated CO2rich water, whereas the rare assemblage of kaolinite and alunite formed from shallow steam-heated acid-sulfate water. Analysis of the available data indicates that the Martha Hill deposit and the Gladstone Hill area formed within a single large geothermal system. We infer that the Martha Hill deposit formed in the main upflow zone, whereas the Gladstone Hill area may have formed adjacent to this upflow zone.

Jan 1, 2001

By C G. Ryan, T P. Mernagh, S R. Hunns, R A. Both, R R. Large, J B. Gemmell

 The Hellyer and Mt. Chalmers deposits are mound-style volcanic-hosted massive sulphide (VHMS) deposits in Australia. Textural, petrographic and microthennometric investigations of fluid inclusions in the Hellyer stringer system indicate that Type I, primary, liquid-vapour inclusions are 10 - 15 J.UIl in size, and yield homogenisation temperatures of 170 - 220¦C in early 2A veins, 165 - 322¦C in main-stage 2B veins and 190 - 256¦C in late-stage 2C veins. These data suggest a waxing and waning thermal history. However, the average salinity remained between 8 - 11 NaCl equiv. wt % in all Stage 2 veins. At Mt Chalmers, Type I inclusions up to 20 urn are found in quartz from the mineralised zone, and these inclusions yielded homogenisation temperatures of 160 - 268¦C and salinities of 5 - 8 NaCl equiv. wt %. Laser Raman spectroscopic (LRS) analysis indicates the presence of CO2 (<1 mole %) in the Hellyer and Mt. Chalmers VHMS systems. Semi-quantitative SEM/WDS microprobe analyses of fluid inclusion decrepitates indicate that the Hellyer and Mt Chalmers ore fluids were enriched in potassium and calcium but depleted in magnesium relative to seawater. PIXE microanalysis of fluid inclusions in quartz also indicates a significant base metal concentration in these fluids. Cation composition and higher salinities relative to seawater suggest that recycled seawater alone cannot be the sole source of the ore fluids. High base metal content and the presence of CO2 in the fluid inclusions imply that magmatic input of ore metals during seawater leaching of the footwall volcanic pile is a distinct possibility.

Jan 1, 1995

By S Adamson

Morphological analysis of alluvial gold recovered from the same segment of a placer by four common commercial methods indicates that gold shape and the presence of quartz intergrowths or sulphide overgrowths substantially influence the recovery efficiency of each method. The amount and types of gold saved by each method varies according to the different hydrodynamic conditions under which each of the methods operates. Reverse circulation drilling has the lowest efficiency and preferentially loses moderate-high flatness gold and intergrown or overgrown gold particles with relatively low density. Gravity riffle, hydraulic riffle, and jigcentrifugal concentrator systems respectively save progressively more of these problematic gold morphotypes, but still lose significant and sometimes substantial amounts (of profit) to the tailings. Because of the differences in recovery efficiency, reverse circulation drilling probably underestimates the grade of most placers and may have resulted in bypassing several economic deposits. Losses to tailings by commercial recovery plants arise from inadequacies in fundamental plant design features. These inadequacies compromise plant efficiency by limiting the ability of plants to simulate the wide range of hydrodynamic conditions necessary to operate effectively throughout placer systems. Incorporation of sand pumps and multiple recovery methods into the more sophisticated plants only partly overcomes these inadequacies. At best, efficiency will be maximised in a few segments of the placer determined by individual plant design, and will decrease progressively upstream and downstream of those segments. Without prior knowledge of the morphological characteristics of the gold to be mined, it is difficult to choose the most appropriate plant design, or to estimate what proportion of the gold will be recoverable by any given plant. If the relevant relationships are not considered beforehand, the recovery plant is likely to lose a significant proportion of the gold, and sacrifice maximum profit.

Jan 1, 2001

By M J. Begbie, K B. Sporle

The Golden Cross low sulfidation epithermal deposit produced approximately 750,000 ounces of Au from two ore zones: the underground Empire Vein System and the open pit stockwork. The Empire Vein System has at least eight stages of vein formation: (1) sulfide veins, (2) black veins, (3) massive veins, (4) banded veins, (5) thin white veins, (6) crumbly veins, (7) massive/platy calcite veins, and (8) flattened rhomb calcite veins. Gold mineralisation occurred relatively early in the lifetime of the system, dominantly during 2 through 4. The late calcite veins (7 and 8) and early sulfide veins (1) are barren. The vein system formed in a dominantly extensional environment, though some compressional faulting may have also existed during vein formation. There is no evidence for significant strike-slip faulting during vein formation, highlighting the fact that explorationists should pursue on-site structural patterns rather than fashionable models.

Jan 1, 1998

By R H. Sibson

The gold province of Otago occupies an area of upwarped basement, the Otago Schist, comprising predominantly quartzofeldspathic and volcanogenic metasediments. This assemblage is the product of collisional tectonic deformation and associated metamorphism, mainly to lower greenschist facies, during the Rangitata Orogeny (200-100 Ma). Historically this region has produced 240 tonnes of gold, 4% (10 t.) of which was from the mining of Cretaceous goldquartz mineralised vein systems. Auriferous vein systems in the Otago Schist are mainly hosted within NW trending normal fault-fracture arrays, however NW trending reverse fault-hosted vein systems also occur. We propose that the Late Cretaceous-mid Tertiary Otago Schist structure represents a regional anticlinorium containing flexural folds of at least two wavelengths. The anticlinorium structure has been quantified by determining variations in angular discordance between schistosity and the Otago Peneplain, a Late Cretaceous-mid Tertiary erosion surface covering most of the Otago district. A structural model for the evolution of the post-collisional anticlinorium requires the cooling surficial zone (carapace) of a retrograding metamorphic belt to behave as an elastic lid. Erosion of topographic load on the carapace drove isostatic uplift, which was greatest in the tectonically thickened core of the orogen. In this way differential uplift produced flexural deformation in the elastic carapace, expressed as a large scale arching of the orogenic belt. Flexure created tangential longitudinal strains in the outer-arc, leading to extension and the formation of mineralised normal faults. These structures are separated by a neutral surface from shortening and associated mineralised reverse faults in the inner-arc. Our structural model predicts that the distribution of auriferous lodes should be localised about zones of maximum flexural curvature, where the tangential longitudinal strains are highest. As a result, NW-SE hinge regions separating schistosity dip domains in the Otago gold province may have new found significance as potential exploration targets.

Jan 1, 1995

By Larkin F, Farrer E, McGhie R. R

The Electrolytic Zinc Company of Australasia Limited commenced productive operations during February, 1936, at the- Rosebery and Hercules mines, which are situated near Rosebery, Tasmania. At this time it was decided that before re-organizing the steel sharpening shop a test should be made of the relative merits of conventional drill-steel and detachable bits. For this purpose Ingersoll-Rand type"I" thread centre hole.jackbits were selected and seventy-two of these were tested against conventional steel. Results indicated that, under the conditions pertaining at these mines, j ackbits should prove more economical than conventional drill-steel bits, and that a large-scale test, under working conditions, should be made. This was done by gradually replacing conventional drill-steel with jackbits at the Rosebery mine. Results were satisfactory and by the end of 1936 both mines were using only the jackbits.

Jan 1, 1939

Alluvial gold was found in the Terawhiti area, West of Wellington, in the 1850s. This led to the discovery of reef gold. Periods of minor 'gold fever', company flotations, and mining activity occured between 1869 - 1973, 1881 - 1986, and in the late 1880s, with one final company active in 1911 - 1914. 1n the early 1980s, further field work was carried out. No viable mining operations resulted from any of this activity.

Jan 1, 1993

A fundamental component of grade control at Tarmoola Mine has been the monitoring of assaying through quality assurance programs. The programs have concentrated on issues related to accuracy and precision of leachwell and fire assay techniques, sample preparation and grade variability within a sample. An outcome of monitoring has been identification of shortcomings in the application of assaying techniques to Tarmoola ore types that contain coarse particulate gold. Leachwell has shown satisfactory precision since introduction as the primary assay technique in October 1998 but leachwell accuracy and recovery through comparison with fire assay techniques has identified bias. A bias toward higher fire assays in grades above 2 g/t invoked an investigation into the cause of the discrepancy between leachwell and fire assay. Testwork evaluated Leachwell assay recovery by varying leach time duration, which showed that by increasing the leach time improved recovery significantly. Monitoring of leachwell against fire assay had shown that a leachwell (200 g) with a one hour leach has under-called grade when compared with fire assay by up to 18 per cent, on average, for Tarmoola ore types. Alternatively, optimisation of the leachwell assaying technique using a 200 g pulp and a two hour leach has returned, on average, higher assays than fire assay by up to eight per cent. Testwork on screen fire assays, duplicate assays and fire assay to extinction has demonstrated assay variability associated with coarse, particulate gold. The variability and distribution of gold in Tarmoola ore types has emphasised the importance of high quality sample preparation for leachwell assaying to ensure liberation of gold to leaching solutions. Assay quality assurance protocols are vital to assay data integrity and enable confidence in delineation of ore-waste boundaries and provide early recognition of problematic assaying periods and isolation of grade control practices, which depart from performance standards critical to the operation.

Jan 1, 2000

By D Matthews

With a brownfield project comes control integration challenges. The Khumani Iron Ore Mine’s second phase expansion posed a number of challenges as there was substantial brownfields work conducted. The fi rst phase was the compilation of the modifi ed process functional specifications for the project. The second phase was an audit on all of the operational sequences; this included a comparison between the SCADA sequences, sequential starts analysed from the historian data (with the potential for improvements made by the plant operators in manual start-ups) and what was proposed in the process functional specification. Differences, inclusions and missing equipment were highlighted. The third phase was the comparison of interlocking and control in the PLC with the updated process functional specification; this was done during the coding process. Running parallel to the three phases was the SCADA integration; tie-ins to the existing SCADA were conducted on maintenance days and shutdowns, in many instances with ‘dummy’ equipment to get the operational staff accustomed to the new interface. This paper details each of the phases, the success of this methodology as well as the pitfalls experienced.

Jul 11, 2011

By A Croll

A panel cave using LHDs for ore extraction came into production at Premier in 1990 at a depth of 630 metres below surface on the western side of the mine in the BA5 mining block. A post-undercut mining sequence was used with all development on both the undercut and production levels completed prior to the undercut being advanced over the pre-developed drawbells. Support and rock mass damage on the production level was extensive as the undercut moved overhead. Undercutting and coarse fragmentation created problems. The mining sequence was changed to an advance undercut with the minimum of development and support undertaken on the production level prior to the undercut moving overhead. Only once the abutment stresses had stabilised were drawbells developed and final support installed. The height of the undercut drill design was decreased from 18 to 13 metres. The changes resulted in markedly less rock mass and support damage on the production level. Lessons learned in the BA5 mining block on the 630 level were incorporated into planning and scheduling the BB1E mining block which came into production on the 732 metre level on the eastern side of the mine in 1996. An advance undercut mining sequence was planned, undercut height was minimised and undercutting parameters were optimised in terms of the BA5 experience. Numerous problems still occurred. As the undercut area increased in size severe spalling from the cave back resulted in vertical propagation of the cave to a height of 30 metres instead of the planned 13 metres. The resultant coarse fragmentation created secondary blasting problems and an excess of undercut ore that had to be loaded and trammed, slowed the rate of undercut advance. The planned mining sequence was compromised and considerable support and rock mass damage resulted on the production level below. Once these problems had been overcome the undercut advanced at the planned rate and continuous caving initiated at the predicted hydraulic radius. At a later stage the unexpected ingress of water hampered undercut drilling and slowed the rate of undercut advance in a section of the cave. Leads and lags between adjacent tunnels and the overall face shape could not be developed as planned. The rate of natural horizontal cave propagation exceeded the rate of undercut advance and three undercut drilling tunnels were extensively damaged. More tunnel development on the production level prior to undercutting than was planned resulted. The slow advance of the undercut and high abutment stresses caused extensive damage to installed support and the rock mass on the production level, 15 metres below. Experience in the BB1E mining block on the 732 metre level has taught that an advance undercut mining sequence reduces damage on the production level markedly. Extremely tight control on the rate of undercut advance, leads and lags between adjacent tunnels and overall undercut face shape as well as extraction ratio, tunnel development and support sequence on the production level below is required. Premier Mine plans to implement a block cave at a depth in excess of 1000 metres within the next decade. All the experience gained on current mining levels together with data collection and numerical modeling is being used to plan the proposed mining operation. The geotechnical challenge of mining at this depth in weak rock has been identified as the greatest risk to the project. Challenges centre around adopting the correct mining sequence, limiting the extent of rock mass damage associated with undercutting and effective support. The hydraulic radius needed to initiate caving, fragmentation, drawpoint spacing, secondary blasting and the possibility of seismicity are geotechnical concerns that are being addressed. Results to-date suggest that a pre-undercut mining sequence with all development and support on the production level carried out only after the undercut abutment stresses have passed overhead will have to be implemented.

Jan 1, 2000