Search Documents

By Y Li

An ilmenite ore from the Murray Basin was initially characterised using combined X-ray Fluorescence Spectroscopy (XRF), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Electron Probe Microanalysis (EPMA) techniques. XRF analysis showed the ilmenite sample contained 58.7 wt per cent TiO2 and 26.2 wt per cent Fe2O3. Major impurities included: Cr2O3 (4.5 wt per cent), Al2O3 (2.7 wt per cent), SiO2 (1.9 wt per cent), Mn3O4 (1.5 wt per cent) and MgO (1.1 wt per cent). Manganese and magnesium were present as solid solution components within the ilmenite lattice while the elevated Al2O3 and SiO2 levels were due to separate aluminosilicate gangue minerals. Chromium was associated with discrete chrome spinel gangue phases of variable composition, (Fe,Mg)(Cr,Al)2O4. Quantitative XRD analysis of the sample identified rutile (12 per cent), ilmenite (11 per cent), and pseudorutile (67 per cent) as the main titanium-containing phases and chrome-rich spinels (seven per cent) as the major impurity phase. Minor quartz, aluminosilicates, zircon and monazite were also present. The ilmenite was mixed with synthetic graphite, pressed into pellets and reduced carbothermally in nitrogen at 1200 and 1400°C with C/O molar ratio of 1.2. Titanium oxide in the ilmenite was converted to titanium oxycarbonitride. Iron oxides were reduced to metallic iron. The Changes of impurities as a result of reduction was examined by SEM and EPMA analyses. Iron and chromium oxides within Fe-rich chromite were reduced to form a Fe-Cr-C alloy. Mg-rich chrome spinels were partly reduced at 1200°C. Zircon particles were not reduced at 1200°C, but were significantly reduced at 1400°C, with the particles becoming porous and the silicon being removed.

Oct 5, 2011

By J Pan, C M. Tang, D Q. Zhu, C C. Yang, S W. Li, Z Q. Guo

The short process of electric furnace steelmaking with direct reduction iron (DRI) as raw material is an important process for smelting high-quality and special steels. In order to prepare high-quality DRI, the pellets with basicity of natural basicity and 0.4 were prepared from magnetite concentrate (MR=0.09, MR=0.4) and hematite concentrate (HR=0.02, HR=0.4). Based on the HYL method, the gas-based direct reduction experiments were conducted under the condition of rich hydrogen (H2/CO = 2.6). The reduction index (RI), reduction swelling (RSI), cold compressive strength (CCS), and phase changes of the pellets were systematically studied. The results show that the RI of four kinds of pellets is greater than four in the temperature range of 800~950°C. For the magnetite pellets, at a fixed reduction temperature, the RSI increases and then gradually decreases, reaching a peak between 50 per cent and 80 per cent. Moreover, the RSI enhances with the increase of the reduction temperature. In general, the RI, RSI, and reduced CCS of the MR=0.09 pellets are better than those of the MR=0.4 pellets. For the hematite pellets, the maximum RSI decreases from 23 per cent to 17 per cent during hydrogen-rich reduction, while the compressive strength increases from 500 to 1070 Nꞏpellet-1. The main reason is that the glass phase generated by the increase of basicity adheres to the surface of hematite grains, hindering the contact between reducing gas and particles. As a result, the apparent activation energy is reduced, which is not conducive to the reduction process. In addition, the glassy phase attached to the hematite reduces the migration rate of Fe2+/Fe3+, resulting in a difference in the reduction expansion rate of hematite in the inner and outer layers of the pellet. Thus, concentric cracks are formed inside the pellets, the RSI increases and reduced CCS decreases.

Sep 18, 2023

The æMountain Camp reefÆ at Alford's mine, Wakamarina,Marlborough, had no recorded gold production although assays of 5 - 26 g/t were reported, but it did produce c. l000 kg of scheelite. The lode consists of a lower massive quartz layer, and upper, cm-banded, ribboned quartz layers, and has a very low sulphide content. Within the massive layer, relict early fine-grained mosaic quartz with idioblastic scheelite is surrounded by recrystallised granoblastic coarse-grained quartz with calcite and plagioclase, in which an original ribbon banding texture is mimiced by strings of tiny inclusions. In both the banded and massive layers, rounded quartz grains, created by cataclastic milling of grain margins and along syn-vein fractures, have been partially annealed within later quartz overgrowths. Late fibrous quartz and calcite fill brittle cross fractures.   Deformation events D1 and D2 are associated with mid-late Jurassic metamorphism of the Pelorus Group, D2 producing the main regional schistosity (S2, and the earliest scheelite. D3 is an extensional mylonitic shear event that formed the dominant schistosity in Alford's mine (S3). The quartz lode was emplaced within the mylonite by a series of individual dilation pulses (D4). The D5 event caused crenulation of the S3 mylonite, kink banding and chevron folding of the S2 schist and S3 mylonite, and reverse faulting, rodding and cross-fracturing with late fibrous quartz-calcite veining of the D4 quartz lode.   Fluid influxes during successive dilations of D4 fractures progressively caused recrystallisation of earlier quartz bands on the footwall, annealing and recrystallisation of quartz along milled crystal margins and fractures, and deposition of minor sulphides. There was thus a dynamic interplay between fault dilation, lode fracture, fluid influx, lode band deposition, and lode recrystallisation. Illite-Kfeldspar al ¦ 2 Ma (K/Ar), c.30 Ma after metamorphism.

Jan 1, 1996

By V S. Mutton, M J. Shearer

"The current economic challenges faced by the mining industry led to a review of options for reducing the cost of ventilation control devices (VCDs). The VCDs at the Mount Isa Mines site operated by Glencore in Queensland typically experienced significant damage on the operating levels and required expensive replacements. Ventilation controls can become damaged by the effects of stope firings. This paper discusses the nature of blast wave effects, giving consideration to distance from the firing and changes in mine geometry. The time taken to adjust the airflow on the operating levels with the current VCDs resulted in the loss of productivity opportunities. The mine site engaged an equipment supplier to collaborate on the development of a high-strength regulator to control the required airflows within its underground workings.The strengthened regulator proved to be cost-effective and provided additional benefits, including ease of use, simplicity of installation and speed of change in the control of available ventilating airflow. An added advantage of the re-engineered regulator compared to contemporary VCDs is its flexibility, which includes the ability to easily move mobile equipment into different ventilation districts where required without the need to remove the VCD from its location. This paper describes both the innovation and environmental sustainability approaches followed when developing the new regulator for its implementation at the site.CITATION:Shearer, M J and Mutton, V S, 2015. Advanced ventilation control – an analysis of innovation and environmental sustainability, in Proceedings The Australian Mine Ventilation Conference, pp 55–62 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Aug 31, 2015

Background A recent development in many industries,' including the mining industry, has been ever increasing acceptance and adoption of extended (12-hour) shifts and compressed work cycles compensated by more time off work by employees between cycles. In the Western Australian mining industry development of `long-distance-commute' (LDC) coincided with adoption of 12-hour rotating shifts. Preludes to LDC were the `construction-style' rosters with two crews plus allowance for annual and sick leave relievers working the statutory 13 consecutive shifts followed by one shift off. Crews rotated day to night shift weekly or at fortnightly intervals. Average hours of 72 to 78 per week were common. The author had personal experience working these rosters in the East Pilbara of Western Australia from 1977 to 1982. Workers tolerated these rosters until a suitable combination of frustration, boredom, despair and the `Five Grand Fever' triggered them to `pull the pin' and head for relaxation in Bangkok, Manila, Nimbin, or Margaret River according to their personal tastes.

Jan 1, 1996

The Myra Falls minesite, of Westmin Resources Limited, is located at the geographic centre of Vancouver Island, within the confines of Strathcona Provincial Park. The operation includes two active underground mines, II-W and Lynx, together with a modem 3650 1/d milling facility. Recent exploration successes will lead to the commissioning of a third mining area in late-1993 - The Battle/Gap Mine. These ore deposits are complexly metal-zoned volcanogenic massive sulphides of Devonian age, hosted in the Myra Formation of the Sicker Group volcanic assemblage. Three distinct felsic volcanic units are defined within the 450 metre thick Myra Formation. They are, from oldest to youngest, the H-W Horizon, the LMP Horizon and the Upper Rhyolite Unit. Massive sulphide mineralisation occurs throughout the property in the H-W and LMP Horizons. There are a number of orebody types, including polymetallic massive sulphides, polymetallic disseminated sulphides, zoned pyritic massive sulphides, elastic sulphide zones and stringer sulphide zones. Individual orebodies range in size from 10 000 tonne zinc-rich polymetallic lenses to the ten million tonne, zoned massive sulphide H-W main lens. The property has been in continuous operation for 26 years, producing over 13 Mt of ore averaging 2.2 g/t Au, 64.0 g/t Ag, 1.9 per cent Cu, 0.6 per cent Pb, and 5.6 per cent Zn. Current geological reserves stand at 12.5 Mt at a comparable grade, including 4 Mt of recently discovered high grade ore in the Battle and Gap Zones. Mining and milling methods have evolved over time to enable successful extraction and milling of these complex ores. Change is on-going with the recent conversion of the H-W Mine to large-scale bulk mining methods, and the development of effective computerised ore reserve calculation and mine planning tools. These changes, in concert with successful exploration techniques that led to recent high grade ore discoveries, have breathed new life into the operation and should assure its present and future viability.

Jan 1, 1993

By N J. Beukes, S T. Netshio, M O. de Kock

The Thabazimbi iron ore deposit comprises a series of stratabound orebodies, on average 18 - 25 m thick that are aligned along the faulted basal contact between the Penge Iron Formation and dolostones of the Malmani Subgroup, Transvaal Supergroup. Field geological relationships and petrographic observations suggest that the formation of high-grade iron ores took place after contact metamorphism related to the intrusion of the Bushveld Complex (2.06 Ga) but before the deposition of red beds of the Waterberg Group at ca 1.9 Ga. Hard, high-grade iron ores are predominantly composed of martite and microplaty hematite. Goethite is restricted to supergene-modified ores close to the Late Cretaceous û Early Cenozoic Old African land surface. At depth, the high-grade hematite ores interfinger with low-grade dolomite-hematite and calcite-hematite ores. Iron oxides (martite, microplaty hematite) present in these low-grade ores are texturally indistinguishable from those in the associated high-grade ores, ie ore formation is genetically associated with carbonate metasomatism. Microthermometric studies of fluid inclusions in sparitic carbonates and rare megaquartz reveal their hydrothermal origin. Two compositionally distinct aqueous fluids of shallow crustal origin are identified, namely a Ca-Na-rich high-salinity brine (26 wt per cent NaClequivalent, TH ~160¦C), and an aqueous Mg-K-bearing fluid of intermediate salinity (8.3 - 12.6 wt per cent NaClequivalent, TH~120 - 150¦C). The results confirm that high-grade hematite orebodies at the Thabazimbi deposit owe their origin to an event of extensive oxidative carbonate metasomatism (calcification), similar to that recognised at other important high-grade iron ore deposits in the world. Hydrothermal ore formation is both structurally and lithologically controlled. Size and quality of the orebodies was improved by Late Mesozoic-Cenozoic deep lateritic weathering as carbonate-hematite ores were enriched to friable high-grade ores, but this supergene modification is second in importance compared to the primary event of hydrothermal ore formation.

Jan 1, 2005

Alluvial mining even of shallow deposits is often economically a marginal proposition and causes significant disruption of the land surface through the need for large scale excavation. In-situ leaching using chlorine-based solutions eliminates the need for excavation, the disruption of surface activities, and may greatly reduce processing costs and improve recovery especially of fine gold. A spreadsheet model has been developed to design and analyse the economics of in-situ leaching of alluvial deposits. In-situ leaching of shallow deposits may be achieved in a number of ways including solution infiltration via perimeter ditches or the use of injection and production wells. In most instances deeper alluvials may only be processed using well systems. Two deposits are analysed in this paper. The first consists of one metre of payable wash beneath one metre of overburden. Some thirty fields per year are treated processing 450 000 BCM per year at a cut-off grade of around $4/tonne ($8/rn3 or the gold value equivalent of 0.26 gh or 0.52 g/m3). The principal costs are well drilling and labour. Sensitivity analysis indicates that doubling the throughput halves the cost. The economics of the project are relatively insensitive to reagent costs and consumptions, and halving the recovery doubles the cut-off grade. Shallow deposits treated using the infiltration ditch system may be marginally cheaper and more conveniently managed although this depends on the relative cost of digging the perimeter ditches. In a second example, deep leads with one metre of wash beneath 30 metres of overburden necessitate significant drilling and feature reduced throughputs as a consequence. In the example chosen 30 fields a year are processed for an annual throughput of 65 000 tonnes costed at around $20/tonne (1.4 g/t Au equivalent, $40 /m3). Sensitivity analysis indicates that throughput, and drilling cost per metre are not important but there is a high sensitivity to recovery and to the depth to payable wash.

Jan 1, 1992

By X Zheng, P Manton

Pebble recycle crushing circuit performance at Telfer has historically fallen significantly short of the design product P80 of 12 mm. An investigation was undertaken to evaluate the current pebble crusher circuit performance, quantify the optimum performance achievable with the existing circuit and examine the impact of pebble crusher performance on the overall grinding circuit throughput. The primary objective of this investigation was to develop an operating strategy that could consistently deliver the finest possible pebble crusher product to maximise the overall plant throughput.The pebble crusher specific energy (Wc) was proposed as a key control variable for pebble crusher operation based on the results of plant survey work. Over the range of pebble crusher specific energies encountered at Telfer, a strong linear relationship was found to exist between Wc and the crusher product size. This direct linear relationship between specific energy and crusher product size remained constant regardless of how the change in specific energy was generated, ie through changes to the crusher closed side setting (CSS), feed rate, liner profile or moisture content. Key findings for the Telfer pebble crushing circuit were: each 0.1 kWh/t change in Wc resulted in a 4.9 per cent to 6.0 per cent change in plant throughput, each 1 mm change in pebble crusher CSS resulted in a 2.2 per cent to 2.6 per cent change in plant throughput, and 0.57 tonne of new feed was displaced for each tonne of crushed pebbles recycled to the semi-autogenous grinding (SAG) mill. The presence of an existing 3000 tonne pebble stockpile between the SAG mill and pebble crushers provides an opportunity to manipulate the feed rate to the pebble crushers independently of the SAG mill pebble production rate. This flexibility, along with excess pebble crushing capacity, enables the pebble crusher specific energy to be maximised the majority of the time. Pebble crusher specific energy has subsequently been incorporated as an online crusher control measure to assist in maximising plant throughput.

Jan 1, 2009

By Hayward P. G

Complex ores, characterised by intimate intergrowths between minerals, have previously been treated by flotation with limited success. The most common problem has been that the liberation size is often finer than the lower size limit for selection flotation. A technique has been developed in which the problem is overcome by the use of a selective agglomeration procedure in which the values are coalesced with oil to a size suitable for flotation prior to introduction into the flotation machine. A complex lead ore was characterised by QEM*SEM mineralogy as having a mean galena liberation size of 15 ¦m. The best recovery of lead at 50 per cent Pb grade by standard flotation was 53 per cent. After application of the procedure, 86 per cent recovery was obtained after a single cleaner step. The oil functions as a bridging liquid in the presence of conventional collectors which render the mineral oleophillic.

Jan 1, 1991

By Hellsten K, Eshuys E

The best long-term approach to exploration involves the use of extensive quality data and the integration of many different factors, methods and techniques. The successful exploration manager needs to integrate people, area selection and exploration methods, with the use of descriptive and genetic geological models. Based on a syn-metamorphic genetic model for Archaean gold, successful exploration in Western Australia requires the integration of data on anomalous gold, alteration, lithology and structure. Many other parameters such as geophysics, geochemistry and regolith studies provide additional, indirect information that needs to be integrated into the overall exploration programme. Timely access to research findings and ability to integrate these into immediate exploration has contributed considerably to the success of the gold industry in Western Australia since 1980. Extensive and deeper drilling, and the ability of computers to handle the volume of data generated have enabled effective testing of many more geological targets.

Jan 1, 1996

By C Mroczek, B Mitchell

Perilya Broken Hill, from its inception, has budgeted for more than 2.0 million tonnes per year from the Southern Operations. This tonnage was planned to come from in excess of 100 stopes per year in a remnant mining environment with numerous mined voids and consequent mining challenges. To mine an average of two stopes per week requires patience, flexibility and detailed knowledge to best manage the potential risks and hazards. The evolution of the Perilya Broken Hill Mine Planning Process has necessitated the establishment of a process to identify and manage these risks during the planning stage in a reliable but efficient manner. This process is to ensure that vital steps for each stope are not missed, and that each personÆs work can be tracked by other members of the team. This paper outlines the planning process from resource to stope closure.

Jan 1, 2005

By R Simonato

It is now recognised that rotary sample division is by far the best laboratory tool for extracting subsamples from a lot of material. In terms of sampling theory, rotary division, by virtue of the fact that it can extract many increments from the lot during the division process, radically reduces the variance due to distributional heterogeneity in the sample being divided. There are a number of occasions in sample preparation when it is necessary to extract a subsample of a target mass. To do this with rotary dividers taking a fixed fraction of the starting mass is a tedious task. In response to this problem, a variable split sample divider has been designed and built for the mineral industry. This paper discusses the utility of the device and presents test data showing that the machine is capable of making accurate mass split while overcoming segregation in the material being divided.

Jan 1, 2008

By S Mitra, D O’Dea, N Barrett, S, T Honey, M M. Hoque

The steel industry is currently exploring hydrogen-enriched blast furnace operations as a means to reduce the greenhouse gas emissions. However, there is a need to investigate the gas permeability behaviour of mixed burdens comprising of lump and sinter as the current knowledge regarding their behaviour is limited, particularly with regards to hydrogen enrichment. In the present study, a series of interrupted softening and melting (S&M) under load tests were carried out in a hydrogen rich gas environment (~15 per cent) in the temperature range from 1000 to 1300°C by placing different types of ferrous ore layer including Newman Blend Lump (NBLL), sinter and sinter-NBLL mixed burden in between two coke layers. X-ray computed tomography (CT) was then used to scan the interrupted test samples. Scanned images were first analysed using an image processing workflow implemented in ImageJ and the material simulator GeoDict (v2022) to segment different phases such as coke, ferrous and void based on their grey scale values. A quantitative analysis was then performed on the segmented images to estimate the phase volume fraction as well as bed permeability. Bed void fraction thus obtained agreed well with the bed contraction data obtained from the S&M test. It was further noted that both ferrous layer void fraction and bed permeability decreased linearly with increasing temperature for all ore samples. The mixed burden voidage changed in a similar fashion to the sinter, demonstrating a high temperature interaction between the two materials

Sep 18, 2023

By L O. Filippov, I V. Filippova

Subsea massive sulfide deposits have particular mineralogical compositions and textural features differentiating them from onshore ore. When extracted from salty water and exposed to the air, massive sulfide samples strongly oxidise and soon become covered by thin layers of iron, copper and zinc-rich sulfates and oxides, as well as elemental sulfur. The textural properties vary according to the degree of maturity and the sample position within the hydrothermal deposit. Because of the variation of secondary mineralisation and porosity level, sea floor massive sulfides respond differently from terrestrial ore to processing methods. Froth flotation, commonly applied to separate all types of sulfides from the gangue minerals, is one possible treatment technique to process sea floor ore. Sulfide recovery rate is, in most cases, excellent (>90 per cent). However, separation of the various mineral phases is difficult to obtain even when applying known methods used for onshore ore. Moreover, the flotation behaviour decreases dramatically with time of conservation, even when the samples were stored in a confined environment. High pH range, which is a good way to depress pyrite and therefore to favour the flotation of copper and zinc sulfides, does not have the same effect on subsea ore. Consequently, careful flotation procedure should be elaborated to obtain efficient mineral separation for this specific marine ore.CITATION:Filippov, L O and Filippova, I V, 2015. Processing of subsea massive sulfide ores by flotation – similarity and features with terrestrial ores, in Proceedings Third International Future Mining Conference, pp 239–244 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 4, 2015

By L N. Loganathan

Risk exposure in tunnel projects is extremely high due to various factors such as variability of subsurface conditions, selection of inappropriate design and tunnelling methods, improper risk assessment on adjacent surface and subsurface structures and utilities, and inadequate contractual practices. The risks in tunnelling must be borne by the contractor, designer and the owner of a tunnelling project. There have been a number of improvements in the last ten to 15 years in the manner in which tunnel projects are developed and implemented in terms of their design, construction, financing and operations. One significant improvement has been the manner in which underground conditions and their risks are being managed. Owners are less willing to transfer the full responsibility to the contractor for managing the underground conditions, although this is a familiar manner in which underground major urban projects have been previously contracted and managed. The owners of tunnel projects in Singapore have advanced the risk management process for their projects through geotechnical interpretative baseline reports (GIBRs), geotechnical data reports (GDRs) and project specifications (PSs). This paper discusses industry practice and its development as well as the application during the preparation and use in Singapore on the Deep Tunnel Sewerage System (DTSS) and the Marina Coastal Expressway (MCE) project in Singapore. The DTSS trunk sewer is 48 km and ranges from 3.3 m to 6 m finished diameter up to 50 m below the ground. The underground conditions ranged from Old Alluvium, strengths of about 1 MPa to competent Bukit Tima granite, with strengths of over 230 MPa. The total route length of the MCE is about 5 km. About 3.6 km will be constructed underground, consisting of dual five-lane carriageways. The underground construction will be cut-and-cover, and 2.6 km will be constructed about 13 m underground, and 1 km of tunnel will range from 13 m to 24 m as the tunnel passes under a 420 m wide reach of Marina Bay, whose crossing will be constructed as a two-phase cofferdam.

Jan 1, 2008

By M BSckstr÷m

Acid rock drainage (ARD), commonly found in vicinities of sulfidic mines, possess properties capable of widely affecting the surrounding environment by acidification and heavy metal pollution. In most ARD treatments, various alkaline sources are used to neutralise the acid produced. Utilisation of highly alkaline fly ashes instead of raw materials is a cost-effective alternative, which lately have become increasingly popular. In laboratory batch experiments, neutralising capacity of fly ash was studied during 20 days. ARD was added to the fly ash once a day, for each increment the liquid to solid ratio (L/S ratio) was increased. At an early stage of the experiment (day 6, L/S ratio 12), the concentration of barium in solution unexpectedly increased by a factor of 50 (from 200 to 10 000 ¦g+l-1). This high concentration also sustained the following two days (L/S ratios 14 and 16) before dropping to the original level. pH showed a slight increase during these observations (pH 12.4 - 12.7). The phenomenon was also observed in a parallel and identical series. In addition to barium, aluminium and strontium clearly increased in the same manner, however not as much as barium. Furthermore, concentrations of chromium and molybdenum noticeably decreased at these distinct L/S ratios (12, 14 and 16). The behaviour of barium and subsequently strontium, aluminium, chromium and molybdenum is only partially understood. The decrease of chromium and molybdenum is suggested to be due to incorporation into the interlayer regions of hydrocalumite (Ca4Al2(OH)12(OH)2+6H2O), replacing the hydroxide groups, which also explains the increase in pH. Moreover, the increase of barium, strontium and aluminium could be attributable to dissolution of the silicate mineral celsian (Ba,Sr(Al2Si2O8)). Alternatively, barium and strontium increase could be explained by dissolution of a Ba,Sr(SO4)-solid solution and aluminium increase by dissolution of hydrocalumite or ettringite.

Jan 1, 2008

By G Clarke

Commissioning of the Cannington processing plant began in October 1997. The nameplate capacity (of 1.55 million tonnes of ore per annum) was achieved relatively quickly. Since then (like many mines) the operation has strived to increase throughput and improve valuable metal recoveries, to offset declining head grades and lift the value of the operation. The processing plant now has the capability of treating over 3.2 million tonnes of ore per annum and in financial year 2005/06 the combined concentrate production exceeded 600 000 wet tonnes, approximately 80 per cent above concentrate output in the first full year of operation (at the design feed rate). This improved performance was achieved by making changes and additions to each of the major unit processes û primary grinding, flotation, leaching, filtering and paste fill preparation. The changes have included: adding a fines flotation circuit, expanding the grinding circuit, adding a pebble crusher, switching from continuous to batch leaching, building paste conveyors and decommissioning the column flotation cleaning circuits. This paper reviews these changes, outlines the current operating practices and discusses the challenges or opportunities that remain.

Jan 1, 2007

By J Darbritz

"This paper details the events leading up to a slope failure that occurred at Kalgoorlie Consolidated Gold Mines (KCGM) and the remediation method executed using rope access specialists.n January 2016, KCGM Fimiston Pit experienced a double bench wall failure where approximately 80 000 t of material fell from the wall that blocked access to a ramp and caused minor damage to equipment.The event was triggered by heavy rainfall and occurred along unfavourable eastward dipping structures that lead into weaker shale/porphyry bands, which in turn left more material on the face. A remediation plan was formulated that would allow for the continuation of open pit operations while a full geotechnical assessment of the failure area could be conducted. This was accomplished by means of rope access specialists who abseiled down the wall and blasted off the remaining overhang using a portable drill rig and prepackaged explosives.This paper provides a brief overview of the KCGM operations, how the instability was identified and monitored, details of the failure event, outcomes of the geotechnical assessment and details on the remediation work.Citation:Graf, C and Sullivan, R, 2016. The Journey to Steepening the Pit Slope Angle - Advancing the Effectiveness of Wall Control, in Proceedings Ninth AusIMM Open Pit Operators' Conference 2016, pp 104–114 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Nov 15, 2016

By B Taylor

The Perseverance deposit is the most southerly known economic copper/gold deposit within the Cobar gold field. The deposit is situated approximately 12 km to the south-southeast of Cobar and is essentially blind to surface with the top of economic mineralisation occurring 750 m below ground level.Based on the December 2010 resource estimate (inclusive of reserves and net of depletion) the deposit contains 3 011 000 tonnes at 6.1 g/t Au and 0.90 per cent Cu (590 000 oz of gold and 28 000 tonnes of copper). The deposit is comprised of four principal lenses, the Perseverance, Hulk, Zone B, and Hercules lenses. In excess of 90 per cent of the known resource tonnes are contained within the Perseverance and Hulk lenses. The deposit is shear related and hosted within lower Devonian rocks of the Cobar Basin. The competency contrast of rhyolites juxtaposed against sediments by the Peak-Perseverance shear is the principal control on mineralisation. Both the Perseverance and Hulk lenses are primarily hosted by brecciated rhyolites juxtaposed against Chesney formation sediments across the Peak-Perseverance shear. This faulted rhyolite sediment contact roughly defines the global orientation of the deposit. The Perseverance lens continues within the shear for up to several hundred metres beyond the extent of the faulted rhyolite sediment contact. Mineralisation within the shear beyond the faulted rhyolite contact zone is hosted by sheared silicified sediments. The Perseverance lens remains open at depth and to the south.The Zone B and Hercules lenses, which are significantly less important in tonnage terms, are hosted by rhyolite breccias within the main body of the rhyolite and appear to be only tenuously related to the Peak-Perseverance shear. Within the Perseverance lens, the presence of northeast trending high grade breccia veins developed oblique to the north-south trending shear system has led to the development of steeply north plunging high grade ore shoots within a globally north-south trending mineralised domain. These high grade shoots have limited horizontal continuity but significant down plunge extent.The presence of coarse gold and the resulting strongly skewed nature of the gold grades, in conjunction with controls on mineralisation which are not parallel to the mineralised domain, has led to predictive difficulties regarding stope performance.Strong heterogeneity of the gold content of the ore and geological controls on mineralisation which are not parallel to the global trend of the mineralisation impose a set of difficulties which sound geological control is helping overcome.

Aug 22, 2011