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By Crockford GI

Some twelve months of operation at Mount Lyell, using two large diameter ball mills as a two-stage grinding circuit indicated a short- fall in the grinding capability compared with design criteria. Breakage, particularly at coarser sizes, was less efficient than with the previously used grinding circuit comprising a large number of smaller diameter mills. This paper describes both old and new equipment, puts forward the facts as they are presently known, and lists the attempts made to overcome the problem.

Jan 1, 1978

Taiwan is situated between Ryukyu and the Philippines with 35,960 sq. km of area, being slightly larger than Belgium It has roughly a spindle-shaped outline with a longitudinal axis extending in a roughly north-south direction. Geologically, Taiwan is extremely complex in terms of its tectonic setting in the convergence zone between the Asian continent and the Philippine Sea Plate. To the east of Taiwan, the Philippine Sea Plate subducts beneath the Ryukyu island arc, and to the south of Taiwan the Philippine Sea Plate overrides the Asian plate along the Manila Trench. Taiwan, therefore, occupies an unstable region between these two well-defined subduction systems of opposite polarity (see the following block diagram).

Jan 1, 1987

Precious metal mineralization at the North Arm goldfield in SE Queensland occurs in the Triassic North Arm Volcanics, a sequence of andesite to rhyolite, pyroclastic and epi- clastic rocks deposited in a continental envir- onment. This unit displays a well-defined fracture system on Landsat imagery, including several arcuate structures which may represent former calderas. Two of the latter are associ- ated with zones of hydrothermal alteration, breccias and anomalous precious and volatile metal values. At the North Arm prospect, alter- ation is zoned from outer propylitic into exten- sive sericitic, although K-feldspar alteration is prevalent in the rhyolite. A zone of advanced argillic alteration is also present at Mt. Ninderry, SSE of North Arm. Alteration involves depletion of Na, Ca and Sr, and vari- able enrichment of S, As, Au, Ag, Hg and Mo. K and Rb are strongly enriched in K-feldspar altered zones. Precious metal mineralization occurs in veins, stockworks and hydrothermal breccia zones, and pervasive low grade Au-Ag dispersion is found throughout the sericitic and K-feldspar altered rocks. Veins and brec- cia interstices contain abundant quartz (common- ly banded), minor pyrite, calcite and sericite, with traces of silver grading to electrum, frei- bergite, naumannite, allargentum, marcasite, chalcopyrite and sphalerite. Mineralogical and geochemical characteristics are consistent with that found at volcanic-hosted epithermal precious metal deposits, particularly with the low-sulphur/adularia-sericite type.

Jan 1, 1987

The necessity for good management and economic working in our mines and ore-dressing sheds is impressed upon us by the present low prices of all our metals. Silver, lead, copper, and tin have all suffered a heavy decline during the last six or twelve months, and many mines have been shut down simply on account of the low market value of the ore produced. After fully considering the position of the mining industry. I am convinced that considerable improvements will have to be made to make it as prosperous as it ought to be. The most obvious of these improvements are good management, good machinery, and as little interference by directors as possible. If these conditions are insisted upon and carried out efficielltly a poor mine may have a chance to weather the storm.There is no doubt that the present depression is the refilult of over-speculation and general loss of confidence by which the whole commercial system has been affected, and every branch has suffered more or less, mining not excepted. It has suffered heavy losses in the past, and the future is not over bright we are, therefore, compelled to be careful in everything by which mining is affected and savings can be secured.

Records of ex-solution intergrowths with tetrahedrite as a component are rare. Intergrowths of this nature of tetrahedrite with galena have been described by Guild (1917) and Schneiderhohn (1922), and in Broken Hill ore by Stillwell (1926), but both Schneiderhohn (1922) and Gruner (1929) have commented specifically on the apparent absence of exsolution intergrowths of tetrahedrite and chalcopyrite, despite their frequent association in ores, and their related atomic structures. Schwartz (1942), reviewing the literaturerelating to ex-solution among ore minerals, lists only two instances of such intergrowths, one an occurrence of lamellae of chalcopyrite oriented along the octahedral planes of tentantite (the arsenical isomorph of tetrahedrite), the other of blebs of tetrahedrite in stannite. The only other possible instance of such intergrowths known to the author is the record of "pseudoeutectic" intergrowths of tetrahedrite with chalcopyrite and with bornite in a silver pitchblende ore from the Great Bear Lake district of Canada (Furnival,1939).Some interest attaches, therefore, to the two occurrences described below of tetrahedrite showing ex-solution relationship, in one instance with chalcopyrite, and in the other with bornite.TETRAHEDRITE-CHALCOPYRITEAn intimate intergrowth of tetrahedrite and chalcopy-rite, apparently the product of unmixing of a solid solution of...

Jan 1, 1946

By D Wardiman, R Benton, D Sims, T Carr, V Singh

The Kencana underground gold mine comprises two world-class epithermal vein deposits located in the North Maluku province of Indonesia on Halmahera Island. The K1 deposit has a recent extensive mining history, whilst development of the K2 deposit is in progress. Kencana epithermal vein zones have a relatively simple planar geometry dipping 25 to 45¦ towards the East and extend 400 to 600 m along strike and down dip. True width ranges from 1 m to 20 m. Economic gold grades are generally associated with two distinct mineralisation styles: Main Zone û continuous material characterised by classic epithermal vein textures including crustiform/colloform chalky white quartz- adularia sulfide banded and brecciated veining typically grading 10 to 40 g/t Au. Bonanza Zone û semi-continuous identifiable zones within the Main Zone. Characterised by brecciated quartz-adularia sulfide banded vein æginguroÆ material typically grading 80 to 200 g/t Au. Associated with this æBonanzaÆ zone are gold grades averaging around ten times higher than the surrounding Main Zone. At the resource evaluation stage, these deposits are typically drilled on approximately 25 m by 25 m spacing. This drilling density is usually adequate to allow robust estimation of global resources, including the lateral definition of æBonanzaÆ style mineralisation. It appears intuitive at the resource definition stage to separately model the æBonanza ZoneÆ using deterministic methods such as manual interpretation and wireframing. Inevitably, however, such deterministic methods result in a simplified version of reality. Whilst the geologistÆs interpretation of the overall vein volume and lateral extent of æBonanzaÆ mineralisation has proven to be remarkably accurate, close-spaced sampling and mapping of the K1 orebody has shown that this style of mineralisation exhibits extreme short-scale geometric and spatial variability. A consequence of this short-scale geometric and grade variability is the significant uncertainty with reporting these Resources and Reserves at relatively small reporting time periods such as monthly production periods. The mining method employed at Kencana often involves extracting the full width of the mineralised vein with multiple mining passes over several months. In the past it has proven difficult to achieve accurate production budgets and forecasts at Kencana as any given mining schedule based on the resource model is acutely sensitive to the quantity and location of æBonanzaÆ material. Moreover, the degree of uncertainty or risk associated with a mining schedule significantly increases as the reporting time period becomes smaller. A further deficiency of deterministic methods for geometric modelling is the inherent lack of ability to derive confidence intervals for quantifying uncertainty and risk. The use of conditional simulation techniques can help overcome this deficiency. Geostatistical conditional simulation techniques have been applied at Kencana in an attempt to model and quantify geological and grade variability in the upcoming K2 orebody based on the experience to date with mining the K1 orebody. At Kencana, conditional simulation has provided a successful means to quantify uncertainties and risks associated with various data densities and reporting time periods. The results of this project have provided managers and planners with a clearer understanding of the likely variances and risks associated with predicting gold metal production at key reporting time periods based on data at the resource model level of resolution. With corporate requirements to adhere to mining budgets/quarterly schedules, this type of analysis allows a more scientific approach to estimating grade uncertainty in the mining schedule. Until now this has been difficult to quantify due to the extreme gold metal variability. The availability of this type of analysis allows a time-efficient rationalisation on redesigns of the mining shapes and effective communication of the likely uncertainties involved.

Jan 1, 2009

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 D S. Nicholson, T Marshall

Reserves of high-grade quartz gravel, lignite and timber suitable for the production of silicon metal and ferrosilicon on large scale occur within 40 miles of Bluff Harbour. Undeveloped hydroelectric power resources on the Clutha River are located within 50 miles of the most promising quartz gravel deposits while opencastable lignite, potentially suitable for electric power production, occurs in the same locality as the quartz gravels. A preliminary study of production economics indicates that the commercial feasibility of silicon/ferro-silicon production would depend mainly on the cost of electric power, total capital cost of plant, and the market value of the products. The proximity of Bluff Harbour is advantageous for the export of products.

Jan 1, 1971

The Olympic Dam Project constitutes a major resource of Copper and Uranium and has been under intensive evaluation since the discovery in 1975.A 500 metre deep rectangular shaft has been sunk into the deposit and this has been followed by 8400 metres of level, incline and decline development. 5 surface ventilation raises have also been constructed.Large scale trackless equipment is used to carry out the development, and productivity statistics are given.The paper describes the functionalised system used in the development program and discusses the maintenance support, and services required to carry out these works.The objectives of the Exploration Development program and the satisfactory results obtained from this work are also discussed.

Jan 1, 1985

By Zhao JC, Chen JJJ

A water/air model was developed to simulate the refining of molten aluminium by the sparging of gas through an impeller. The optimal gas dispersion depends upon selecting the correct gas rate for a given impeller rotational velocity to prevent flooding or channelling. Correlations illustrating this flooding behaviour exist for standard impellers within standard tank geometries. However the validity of these correlations has not been substantiated for gas dispersion in high temperature molten metals with non-standard tank and impeller dimensions.

Jan 1, 1995

The U.S. Bureau of Mines has developed a prototype cross well acoustic logging system and complementary tomogr`aphic image reconstruction software for the detection and delineation of abandoned underground mines and associated subsidence failure in relatively shallow environments. The logging system uses a piezoelectric, cylindrical bender as an acoustic source. A triaxial accelerometer assembly, designed to be rigidly locked in the borehole, is the receiver portion of the logging system. Both the source and receiver probes operate at high frequencies, thus providing short wavelengths capable of resolving small features in most rock types. A modified van with a dual-drum wireline winch, 4-channel data acquisition system, power amplifiers, and waveform generator supports field operation of the logging system. A field study was conducted at a test site in San Antonio, Texas, to demonstrate the cross well acoustic logging system. The underlying rock at the test site is similar to stratified sediments in coal measures. First- arrival travel times were interpreted by tomographic reconstruction of the velocity field in the two-dimensional cross section between the source and receiver boreholes. The resulting image correlates well with geological borehole logging data for the test site.

Jan 1, 1992

By Blair J. R

In the Bayer process, bauxite is leached with caustic soda, forming a solution of sodium aluminate, from which hydrated alumina is precipitated. The efficient operation of the continuous form of this process requires that the concentration of caustic soda be controlled. A computer simulation of the concentration of caustic soda has been conducted to provide information, regarding the dynamic behaviour of caustic concentration, which is not available from normal plant data. The basis of the simulation is a state- space model of an alumina refinery, linearized about the normal operating condition. The formulation of the model, with the relevant approximations and assumptions, is outlined. The simulation of the mudwash section of the. plant is described in detail. A continuous model of the mudwash, having time-varying coefficients, was driven using operating data from an alumina refinery. The modelled response showed reasonable agreement with the recorded plant response.

Jan 1, 1977

The influence of pulp potential on the flotation behaviour of sulphide minerals in laboratory batch flotation tests is discussed in terms of self-induced flota- tion, collector-induced flotation, and depression.' Assuming that the pulp poten- tial is controlled by the same factors that determine the genuine redox poten- tial, an attempt is made to interpret the experimental results in terms of potential-dependent reactions based on bulk thermodynamic data. Self-induced flotation is displayed by many sulphides in moderately oxidizing solutions but not in reducing solutions. The available evidence suggests that the hydrophobic entity could be sulphur produced by superficial oxidation of the mineral but this has not been established beyond dispute. In general, flotation is observed near the potentials at which sul- phur would be expected to form and the minerals which produce sulphur seem to float the most strongly. Collector-induced flotation is most conveniently studied on minerals which have only slight self-induced floatab- ility. The mineral-collector interaction is potential-dependent hence flotation is generally only observed in limited ranges of potentials. While the general form of the floatability-potential relationship is similar to that predicted from thermody- namic data close correspondence between predicted and experimental results is not always observed.

Jan 1, 1984

By Umar N

Traditional exploration has been undertaken by both local and overseas experts to discover tin deposits in Indonesia over almost 300 years. Indonesia is part of a tin belt which runs from Myanmar in the north through Malaysia to Singkep, Bangka, and Belitung islands in Indonesia in the south. The discovery of alluvial tin deposits is becoming harder as the more obvious geological targets are exhausted and topographical conditions become more difficult. New approaches are required to sustain successful exploration. There are indications that tin deposits can be found at depth on-shore as well as off-shore. These deposits are found associated with tough clays. On-shore tin exploration is hampered by swampy areas, while the off-shore search is often affected by difficult sea conditions. These factors lead to increases in the cost of exploration as well as the cost of subsequent production. Tin price fluctuations and environmental issues are also of major concern in the planning of the future operation of tin mining in Indonesia.

Jan 1, 1996

By B Andrew, L Krois

Ground control systems, including ground control management, play an integral role in the effective and efficient extraction of copper ore at the Xstrata Copper û Mount Isa Copper Operations (MICO). Rock mechanics engineers and support technicians at Xstrata Copper have undertaken a wide range of investigations and actions over the past few years. Outcomes from this work have resulted in the evolution of ground control management practices on the site. Specific areas of improvement include the installation of efficient one pass ground control systems, greater application of sprayed concrete for areas requiring rehabilitation and the addition of new improved products, the removal of obsolete and less efficient products used in standard ground control practice. In some areas underground, the most effective methods to manage ground control hazards continue to be a variation on proven methods that have been in use for many years in the MICO. Ground control systems for developing through the basement contact zone are very similar to that developed in the late 1980s. Similarly, ground control systems have gone through repetitive evolution, whereby some systems fall in and out of favour subject to perceived costs. For example the pouring of concrete shuttering around drawpoints in poor ground conditions has recently been re-accepted as an effective means to manage this poor environment û despite having been previously cast aside as too expensive. Ground control management systems continue to evolve towards the goal of creating a workplace that is free of rockfall-related injuries and provide for higher levels of efficient and effective techniques by which ore is extracted from the ground.

Jan 1, 2005

By Wright J. K

A description is presented of the results of reduction experiments using a laboratory reduction apparatus in which simulation of the gas and temperature profiles which occur in direct reduction shaft furnaces is achieved using microcomputer control. The apparatus allows continously changing reduction conditions to be impressed on lump or pellet samples to simulate the environment that is experienced by iron ore burdens during their transit down the shaft of a direct reduction furnace. Three pellet samples and three lump ore samples were reduced in the apparatus. Comparative reduction curves and strengths after reduction for the materials were obtained over a range of reduction temp- eratures using Midrex-type gas compositions. The resulting reduction and strength curves show considerable variation in behaviour and reflect the physical and chemical variations in the individual ore and pellet types. A comparison is made of the reduction rates and modes of reduction of the samples reduced under "conventional" test conditions using a single unchanging gas composition and the simulated shaft furnace reduction conditions. It was observed that the course of reduction is very different in the two procedures and the major influence of temperature on the strength of the reduced product is noted.

Jan 1, 1987

By Corbett GJ

Comparisons between individual SW Pacific Rim gold deposits have facilit-ated proposal of a new classification of porphyry-related mesothermal gold deposit types. Carbonate base-metal gold systems form at relatively high crustal levels, peripheral to porphyry intrusions. There is a spatial assoc-iation with major structures which focus fluids from degassing porphyries at depth. Milled matrix intrusive breccias and extrusive maar volcano/ diatreme breccias form as a result of pre-mineralisation phreatomagmatic eruptions. These focus degassing magmatic fluids by the provision of fracture ground preparation, typically within competent host rocks, adjacent to the breccia bodies. Local dilational structures control the form of individual deposits which may contain bonanza gold grades at sites of fluid quenching and/or repeated mineral deposition.Early quartz veining and porphyry-related alteration is common and later gold mineralisation typically occurs in association with carbonate veining and Fe and base metal sulphides as Zn > Pb > Cu. The progressive cooling by mixing of the upwelling mineralised magmatic fluid with descending bicarbonate waters, produces characteristic zonations in carbonate compositions. These vary with distance from the porphyry source, from Ca through Mg, Mn and distal Fe types. Gold mineralisation is preferentially distributed within the Mn/Mg carbon-ates.

Jan 1, 1994

With the recent wider introduction of friction hoists of the Koepe type. for winding from depths of more than 3000 feet it has been found that failure by fatigue is the most common form of rope deterioration. Large numbers of wire breaks occur near the centre of the rope cross-section and it is difficult to detect these with certainty using the preferred d.c. magnetic test. For best results with conventional search coils their dimen- sions should be related to the typical wire break field pattern surrounding the longitudionally magnetised rope. The field of a broken wire was experimentally determined, using a Polish type MD6 Defectograph wire rope testing magnet and a short prepared length of rope with a movable simulated broken wire. The external field distortion perpendicular to the rope was measured by means of a gaussmeter and Hall probe. The advantages of this method are that terrestial magnetism and inherent rope "noise" have no effect on the results.

Jan 1, 1971

An airlift pump is fitted to the screw conveyor of a decanter type centrifuge in order to pump out soft cakes which are difficult to discharge from a standard decanter. The new patented2 design improves separation performance and allows more stable operation, particularly when operating the decanter as a thickener.

Jan 1, 1989

The paper describes the reasons for the development and for the selection of systems which were finally adopted; further estima- tion and design engineering problems, as well as experience with large screens in operation. Advantages, disadvantages and the final li- mits of screen dimensions are indicated.

Jan 1, 1984