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By O Dahl, I M. Platten, E J. Sides

Many narrow-vein gold deposits are characterised by a high to extreme nugget effect and the presence of coarse gold. They rank amongst the most difficult of deposits to produce an accurate and precise resource estimate. This contribution presents a case study from the Nalunaq Gold Mine in Southern Greenland. The mine commenced operation in May 2004 and is currently operating at a rate of 400 tonnes per day, to produce about 100 000 oz gold per annum from a total resource base of 1.2 Moz. Mineralisation is characterised by quartz veins that are hosted within a shear zone that is continuous over about 1000 m. The principal orebody is the Main Vein structure, which ranges up to 3 m in width, maintains an average dip of 35¦SE, and contains significant gold grades (1000s g/t Au). Gold particles are often visible, with 25 per cent being greater than 250 microns in size. Variography using underground development samples indicates a nugget effect of about 75 per cent. For the 2005 resource estimate, a 2D metal accumulation ordinary kriged block model was used to produce a global grade for the Target and South Blocks of the Main Vein. Grade control chip-channel samples are collected from æshantyÆ drive footwalls, and used as the basis for both the kriged block model and to determine the grade of individual stope blocks by peripheral weighted averages. Geology plays a key role in mining efficiency, given the locally variable nature of the ore zone.

Jan 1, 2006

By Floyd JM

Pilot plant trials showed the effective ness of the submerged lance SIROSMELT technology for altering the composition of iron blast furnace slags as a preliminary step to produc- tion of formed materials. Mixtures of oil and air were injected into a bath of liquid slag to provide the heat required for melting the additives and to provide very turbulent conditions which resulted in complete dissol- ution of added fluorspar within one minute and almost complete dissolution of silica in two minutes. Sulphur lost during injection was readily made up by addition of pyrite or pyrrhotite. A stable foam could be readily made and broken down and the foamed slag appeared suitable for extrusion or forming into shapes.

Jan 1, 1979

By Raczej I, Defant M

Pre-Miocene igneous rocks from the Phili pine island arc are characterised by 87Sr/86Sr and 143Nd/144Nd ratios typical for intra-oceanic island arcs where sediment involvement in the magma genesis was minor. Lead isotopic ratios are similar to Indian Ocean MORB (Mukasa et al., 1986a,b). Pliocene to recent volcanics, however, have more radiogenic Sr and Pb and less radiogenic Nd, except for the volcanics of the Bicol Arc, which have similar isotopic signatures as the Pre-Miocene rocks. We suggest that Pre-Miocene magmas and Bicol-Arc magmas have been generated in response to the subduction of the Philippine Sea Plate, their isotopic characteristics reflecting the composition of Philippine Sea crust. The Bataan arc magmas may reflect the larger amounts of sediments available for subduction in the South China Sea, while magmas of the Mindoro Arc, which are characterised by the most radiogenic Sr and least radiogenic Nd, may have been contaminated by slivers of the Mindoro-North Palawan terrane, which have been carried down to mantle depths after the collision of this terrane and the Philippine arc in Miocene (McCabe et al., 1982). This interpretation implies that Nd (and by inference other REE) can migrate from the subducted slab to the mantle wedge. Thus, variable Nd-isotopic ratios in island arc magmas (e.g. Sunda, Lesser Antillas) may not he a primary feature of the mantle wedge but a consequence of the release of Nd from the subducted slab.

Jan 1, 1987

This paper describes the programing and specification requirements which affected the choice of excavation methods on the Melbourne Underground Rail Loop (M.U.R.L.). The various methods that were chosen are briefly described, and the three most used are compared in more detail. Excavation rates, cycle times and other statistics are compared for full face tunnel boring, full face drill and blast, and heading and bench using a road header excava- ting machine. The length of tunnel excavated is sufficient to enable meaningful statistics to be presented and the significant specifi- cation and geological factors are described to weight the statistics where necessary for purposes of comparison. Average tender prices are given for excavation and primary support to indicate the reimbursement sought by contractors to carry out this type of tunnelling.

Jan 1, 1981

This paper examines the various stages of development and design work which were necessary to develop the cemented rock fill system for copper mining at Mount Isa. The reason for a cemented sand fill development program together with details of the test work undertaken are briefly outlined. The testwork associated with the selection of a suitable local rock to supple- ment the cemented hydraulic fill is discussed, as is the method for underground placement and mixing of the graded rock with the cemented hydraulic fill. The design features of the final system which incorporates a graded rock handling system and a cemented hydraulic fill reticula- tion system is outlined.

Jan 1, 1973

Radioisotope X-ray and neutron techniques of analysis can be used for the determination of a wide range of elements in minerals. The most important applications of these techniques to the mineral industry are for on-stream analysis of slurries and solids, and for geological assay. The radioisotope X-ray techniques are the more developed ones and two installations for on-stream analysis are in routine use in mineral processing plants in Australia. Neutron techniques are being developed, and should prove valuable for geological assay of large numbers of mineral samples, for borehole logging, and for specific on-stream analysis when the cost of the equipment is warranted.

Jan 1, 1969

The mathematical modelling of rock fragmentation by blasting is one of the most difficult and challenging problems of applied mathematics. Not only is complex mathematics required but there is incomplete understanding of the basic physics and chemistry involved. The possibility of getting the physical basis of a model correct by simple mathematical and experimental procedures is demonstrated for the novel process of fragmenting rock by high-pressure arc discharges. While the importance of obtaining the correct physical basis for a model is emphasised, high-pressure arc induced fragmentation of rock is shown to be a powerful laboratory tool for the study of blasting.

Jan 1, 1990

By S Paciornik, G Schinazi, M H. de Pinho Maur-cio, M B. Vieira, O da Fonseca Martins Gomes, D T. Wagner

Vale (previously CVRD û Companhia Vale do Rio Doce) evaluates the microstructure of sinters in order to understand their characteristics and behaviour in the agglomeration process, and the correlation with conventional quality parameters. Efforts on image analysis development are in progress between Vale and PUC-Rio in order to improve both the qualitative and quantitative evaluation of a representative portion of material. In the present work, digital microscopy techniques were developed allowing this kind of assessment. Employing a motorised and computer controlled optical microscope, low magnification mosaic images covering complete sinter samples were automatically obtained. The mosaics provide a powerful qualitative overview of the whole sample while allowing low resolution quantitative evaluation of the major phases. In addition, quantitative results for phase fractions were compared for the same sample regions at three magnifications (5x, 10x and 20x objective lenses). A single field (1 x 1) at the lowest magnification corresponds to mosaics of 2 x 2 and 4 x 4 images at the higher magnifications. The automated system allows perfect registration between the mosaics and the single image. Changes in phase discrimination were evaluated as a function of optical resolution, and phase fractions obtained by interactive segmentation of the image histograms were compared. While finer dark phases, eg silicates, were only visible with the best optical resolution, coarser phases such as haematite and pores were measured at all resolutions. For haematite, magnetite, ferrite and pores, the largest relative error in area fraction, between the images obtained with the 5x and 20x lenses, was 12 per cent. The results for silicate were less accurate with a relative error of 44 per cent. The results indicate that digital microscopy provides a flexible method for qualitative and quantitative evaluation of these materials.

Jan 1, 2008

By Jensen B

The approach of using the Coward Triangle for the analysis of flammable mine gas mixtures has been examined for its application, to the flammability of coal dust/gas/air mixtures. Explosible lean limit and rich limit concentration data for dust/methane/air mixtures are examined and illustrated using co-ordinate geometry. It is concluded that a three-dimensional envelope representing hybrid explosible mixtures can be drawn. The dimensions of this explosive zone will vary with the characteristics of the coal dust and the gaseous composition of the mine atmosphere. Further research is needed to establish these dimensions for important mined seams.

Jan 1, 1994

This study begins with the semivario- gram modelling of variables rutile grade and clay content from a beach sand rutile deposit. This is followed by two dimensional block kriging. The deposit was divided into blocks of 30 x 30 x 1.5 m dimensions and the kriged estimate together with the associated kriging variances for each variable within each block were determined. Finally, using the results of the krig- ing program and considering the acceptable limit of clay content together with the cutoff grade for rutile, a method for optimization of mineable thickness and hence the tonnage of ore was applied and the results were dis- Cussed.

Jan 1, 1986

By Millett R

In January 1989, Western Mining Corporation (WMC) acquired the Perseverance and Rocky's Reward orebodies and associated infrastructure from the Agnew Mining Company (AMC). AMC had closed the operation in August 1986 and it had been on care and maintenance since that time. To return the operation to full production as quickly as possible it was planned to mine the Rocky's Reward orebody by opencut mining and treat this ore whilst the underground Perseverance workings were rehabilitated. Removal of overburden from Rocky's Reward thus commenced immediately with a target of April 1989 for delivery of the first ore to the concentrator. Extensive rehabilitation and upgrading of the concentrator commenced in late January, and continued in stages for an 18 month period. The first stage consisted of overhauling all existing equipment and completing a crusher upgrade commenced by AMC prior to the mine closure. During this period, it was necessary to recruit a workforce and re-establish all the required support structure. In late April the plant commenced commissioning trials on mullock. The first ore was crushed on the 11th May 1989 and concentrate produced the following day. From May 1989 to June 1990 the plant was producing nickel concentrate whilst further upgrading continued. During this period, the flotation capacity was tripled by installation of a bank of eight Wemco 144L flotation cells in rougher-scavenger duties and two 12 metre by 2 metre diameter columns in cleaning duties. The existing vacuum drum filters were replaced by two Larox PF32 pressure filters, eliminating the need for solar drying and allowing the flash drier to be fed direct from the filters. These, along with a major borefield expansion and further work to the crusher increased the nominal plant capacity from 600,000 to 1,000,000 t/yr. The plant achieved the 1,000,000 t/yr rate in April 1990.

Jan 1, 1991

By Lightfoot BW, Bultitude-Paull J

The Sirosmelt top submerged lancing system has many applications in the smelting of base metal and complex materials. It has particular advantages for smaller scale smelting and the treatment of recycle materials in smelters where its low capital and operating costs and its operational flexibility are of immediate benefit. The system can be fueled by oil, gas or coal, as well as by mixtures of fuels. For many applications, the use of coal as a fuel has operating cost advantages over oil and gas, but conventional pulverised coal feeding systems entail very large capital expenditure and this militates against the use of coal. The methods available for improving on conventional technology for coal firing of Sirosmelt systems are discussed and operating experience with alternative systems are outlined. The use of coal as a reductant in the Sirosmelt system is also discussed.

Jan 1, 1987

By Vynne J. F

Drill monitors for rotary blasthole drills have been available to the mining industry since the 1970s. The early monitors were pen strip chart recorders that were developed for the oil drilling industry and adapted to mining. They recorded drilling parameters such as depth, pull-down pressure, torque, RPM, and hailing air pressure. While these recorders could generate a large volume of paper, the amount of useful data was minimal. The data was not summarised and required an engineer to interpret the chart traces. Being a mechanical recorder, the devices were also susceptible to frequent failures. Modem electronics, and the development of the personal computer and its associated software have radically changed the type of instrumentation that is now available for blasthole drills. Perhaps more important is what can be done with the data. The PC allows the logged data to be analysed, summarised, and a variety of reports to be generated. The reports can be customised to meet the specific requirements of the mine and reduce the amount of time that is required to interpret the data. There is also an increased awareness in the mining industry of the importance of production drills. Blasthole drills have typically been the piece of production equipment that received the least amount of attention in a surface mine. Management focussed on the trucks and shovels or draglines. This situation is changing, and therefore the benefits that can be derived from monitoring drill performance are being recognised. Potential economic benefits of installing drill monitors have been documented in previous papers (Peck and Vynne, 1992). Mines are finding that pay-back periods of less than twelve months and rates of return in excess of 30 per cent are not uncommon. These benefits include the following: 1. Reduced overdrilling; 2. Increased rate of penetration; 3. Helping to locate coal seams; 4. Identification of weak and strong zones; 5. Reduce geophysical logging; 6. Optimising blasts; 7. Improved fragmentation and diggability; 8. Decreased coal dilution; 9. Increased bit life; 10. Reduced maintenance costs; 1 I . Improved accuracy of data and reports.

Jan 1, 1995

By Scott B. R

Bougainville's copper mine is located on the west slope of the Crown Prince Range on Bougainville. A high grade copper concentrate is produced for sale to overseas customers. Production planning which was originally based on pilot plant data has developed progressively since commissioning of the concentrator in 1972. Pilot plant data and mine sampling have been supplanted by the correlation of concentrator performance with ore sources, as the basis for short term planning. The influence of accurate sampling is reflected in 1. hourly shift control, 2. the daily milling statement, 3. the prediction of the characteristics of ore from various mine locations, 4. production reconciliation, and 5. the control of copper losses. The mechanical and electrical failures of the original sampling system emphasized the need for a reliable, automatic sampling facility. The development of a pneumatic drive mechanism, which has now been fully field tested, was undertaken.

Jan 1, 1976

The South Mine, property of Broken Hill South Limited, is situated at Broken Hill, NSW, Australia, towards the southern end of the main lode. The leases (MLs 7 and 8) cover a length of 2400 feet along the lode outcrop and the workings extend, at this date, to a depth of 1940 feet below the collar of the original main shaft and to 825 feet below sea level. Mining operations have been continuous for about 58 years and during this period nearly 12.5 million tons of ore have been mined. The monthly tonnage extracted approximates 30 000 tons in normal times.The ore is a mixed sulphide containing galena and marmatite; the gangue minerals are principally calcite, rhodonite, quartz and garnet. A typical assay for a monthly period is 14.4 per cent Ph, 5.6 ozs Ag, and 11.6 per cent Zn. The whole of the ore is concentrated on the property by combined gravity and flotation methods. The lead and zinc concentrates produced are railed to other centres for the extraction of the contained metals.

Jan 1, 1994

By Cousens DR, Benhamou M, French DH

Techniques appropriate to petrographic image analysis are being developed using digitized backscatter electron images of well characterized mineral assemblages obtained from a Cameca scanning electron microprobe. Emphasis is on developing descriptors for size, shape and association of mineral grains as these all convey important information concerning the nature of rocks and the processes that have operated upon them. Processes, for example, that could indicate the proximity of mineralization. For convenience, the work is being carried out on the PDP11/73 host computer of the electron micropt be, although it is recongnized that such a multi-user environment is not appropriate for practical image analysis. The eventual aim is to develop a low-cost microcomputer-based package for quantitative description of mineral textures and rock fabrics as an objective aid to the petrographic analysis of ores and host rocks.

Jan 1, 1989

By Carroll D. A

The mining and minerals industry has had and will undoubtedly continue to have a considerable impact on the development of this State. For the first 60 years of its history the colony of Western Australia made slow progress; its population in 1889 being only 43,000. However, as a-result of discovering gold at Coolgardie and Kalgoorlie the Eastern Goldfields alone had a population of 25,000 by 1897. The income generated by the gold mining industry allowed the Premier of the day, Sir John Forrest, and his Government to support the proposal put forward by the State's Engineer in Chief, C.Y. O'Connor, to construct a pipeline to carry water from the Darling Ranges to Kalgoorlie ; a distance of 600 kilometres. The demand for people knowledgeable in the science and art of mineral exploitation also prompted the State Government to establish a School of Mines in the Goldfields in 1902, where it has remained ever since. The gold mines of this region have been a major source of employment for over 70 years and there is no doubt of the fact that their continued prosperity minimised the effect of the world recession on Western Australia in the 1930's.

Jan 1, 1979

By Tyson G. R

A novel system has been developed using computer imaging techniques to make on-line measurements of material on a moving conveyor. Meas- urements of the mass or volume of conveyor materials are important in large open pit mining operations such as those operated by the State Elec- tricity Commission of Victoria (SECV). Such on-line measurements can be used for monitoring and controlling the production and transport of coal or overburden, and to assist in maintaining production levels. This paper describes a conveyor burden volume measurement system which is currently under development at the Research and Development Department of the SECV and although targeted initially for use in the Commission's open cut mines, the system is suitable for use on any open conveyor system. A basic developmental system has been built to demon- strate the viability of the technique used and further work on the system is planned. The measurement technique and the major components which have been developed as part of the system are described, some comparisons are drawn with other existing measurement systems and potential errors and future development are discussed.

Jan 1, 1989

From 1980 to February 1991 the Rosebery concentrator purchased ore from Aberfoyle's Que River Mine. Following the termination of the contract the concentrator reverted to treating Rosebery ore alone. Since that time it has become apparent that the circuit configuration employed was no longer optimum for zinc metallurgy. The circuit was designed to treat a difficult, slow floating sphalerite; however, the opposite was now found to be true. The sphalerite is fast floating and the circuit was cumbersome. During 1992 extensive circuit changes led to the provision of a simple open circuit flow sheet. The circuit is now easier for operators to understand and lends itself to improvements in process control. Middlings streams have been minimised, which produces a far more stable circuit. Significantly, it must be noted that the key to achieving potential results must lie in reducing variations within the process. A significant ore characterisation program has been undertaken, providing an insight into the metallurgical compatability of the ore to be mined. Using the information collected in this program, metallurgical recoveries and grades can now be predicted with a geater accuracy. Ore characterisation data suggests that an improvement from a 54 per cent zinc concentrate to a 57 per cent zinc concentrate should be achievable. By understanding the size-by-size mineral assemblage, a strategy for concentrate grade improvement has been developed. The requirements of the customer must in all cases determine the quality of the product. Pasminco is a fully-integrated zinc producer and as such significant gains can result by tailoring the concentrates to suit the Smelters.

Jan 1, 1993

Exploration risk increases with time, due to a general decrease in prospectivity as the more accessible deposits are found, and be- cause of rising costs and demands due to an improving standard of living. Risk is separated into financial risk, which increases sharply at the development stage, and the risk of failure which is at its peak at the outset of exploration. Risk is also divided into internal and external factors; some of the latter cannot be offset, viz. the systematic overall risk for any enterprise. The recently emergent risk embodied in withdrawal of large areas from exploration access is discussed. An appeal is made for objective multiple land-use policies to be applied so that land remains available at reasonable cost and with appropriate environ- mental safeguard conditions. Risks specific to gold exploration are discussed. As gold now accounts for over 50% of all mineral exploration, and most other metals are depressed, any sharp decline in gold will have grave effects on the ex- ploration industry. Gold exploration will become more difficult and expensive in about five years, after most of the readily accessible deposits in Australia are found. Government's role is important in pro- viding stability and basic data at reasonable cost. Exploration for specific minerals or of particular areas could be stimulated by extending the 150%.tax deductibility of R & D to aspects of exploration of strategic im- portance, particularly in the event of a downturn. Exploration is classic scientific research, at least through to the proving Stages.

Jan 1, 1987