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With the post-war expansion of mmmg activities on its Western group of mines, the management of Lake View and Star Limited has commenced a project for the improvement of underground ventilation.The major part of this project is to provide adequate return airways for the ventilation of the deep levels. To this end, the Ivanhoe South Extended shaft is being enlarged, and ultimately an exhaust fan with a capacity of 180,000 cu. ft. of air per minute will be installed at the shaft collar.Prior to 1932, the shaft was used exclusively for baling water from the 800 and 2,000 ft. levels. These two levels are the only ones connected to workings from the Horseshoe lease. After the installation of pumping plant at the Horseshoe Main Shaft, baling was discontinued, and the water was graVitated from dams to the pumps on the 1,000 and 2,000 ft. levels.Water makes into the shaft, through a series of fault planes, between the 600 and 1,500 ft. horizons. The total flow is 16 gal. per minute, of which approximately 7 gal. per minute graVitates to the 800 ft. level. As a big proportion of the water dropped uncontrolled through the shaft, a downcast current of air approximating 20,000 c.f.m. was induced. This air ventilated a limited area of workings in the Horseshoe lease, between the 2,000 and 2,360 ft. levels.In 1938, it was decided to reverse the direction of the airflow in the shaft. Work was carried out to pipe the...

Jan 1, 1948

By R Castroviejo, F Segundo, C Brea, J-C Catalina, H-J Bernhardt

Optical microscopy is a basic but still indispensable tool for examining mineral parageneses in ores. The design and concepts behind the reflected light ore microscope have obviously not been subject to spectacular technical evolutions in the last decades. However, digital imaging capabilities have opened new and stimulating perspectives for automated mineral identification. Recent works in developing multispectral image analysis (Pirard, 2004) have demonstrated its superior potential with respect to conventional colour imaging, but at the same time reconciliation with spectroscopic databases such as the Quantitative Data File III (Criddle and Stanley, 1993) still needs a more in-depth investigation as well as the possibility to extend both imaging and spectroscopy into the near infrared domain. In this paper, the authors present results gained from multispectral imaging in the range between 400 and 1000 nm together with spectrophotometric data from the QDFIII database, with an emphasis on minerals that cannot be easily distinguished in the visible spectrum.

Jan 1, 2008

By D Akis, A Clark

The Lihir gold operation, located in the New Ireland Province of Papua New Guinea (PNG), approximately 900 km north of Port Moresby, was commissioned in 1997 under the management of the Lihir Management Company, a subsidiary of Rio Tinto. This management period ended in 2005 with Lihir Gold Limited (LGL) becoming self-managed. LGL is now the largest listed company in PNG and a top tier mining company in Australia. The focus of the operation since 2005 has been to take advantage of strong market conditions to increase cash flow while driving operating costs into the lowest quartile of gold producers. During this period production has increased through capital expansions, most notably with the addition of a flotation circuit, and through culture change and efficiency improvements. The next step forward for the Lihir operation is a major plant upgrade to increase production to an average of around one million ounces per annum by matching the ore processing rate to the ore mining rate. The key benefits of this project will be the addition of approximately 240 000 ounces per annum of gold production, the access to an additional one million ounces of gold and the ability to meet all stockpiling requirements. The Lihir operation has come out of the boom period in a strong position, is undertaking a major upgrade at a time when prices are low and labour is available, and will be positioned to take advantage of future opportunities as they arise.

Jan 1, 2009

By A B. Christie

In Northland, Coromandel, Taupo and Canterbury, weathering and hydrothermal alteration of Cenozoic volcanic rocks has resulted in the formation of various types of clay deposits. Subtropical weathering of rhyolite in the Matauri Bay area (Matauri and Mahimahi deposits) in Northland has formed high quality halloysite deposits. The Matauri Bay halloysite is mined and processed to produce reputedly æthe world's whitest clayÆ that commands a high price in niche ceramic markets. In the Coromandel, some argillic alteration zones contain kaolinite clays (at Hahei) and advanced argillic alteration zones contain kaolinite-gibbsite-pyrophyllite assemblages (at Pumpkin Hill and Lookout Rocks). In addition to known halloysite and kaolinite clay deposits, there is also economic potential for smectite clays produced by hydrothermal alteration of volcanic rocks. Bentonite (mainly ferriferous-beidellite) is mined from weathered basaltic ash in Miocene lake beds at Coalgate in Canterbury.   We have compiled interim mineral deposit profiles for bentonite in basaltic ash, halloysite in rhyolite, kaolinite in altered rhyolitic rocks, kaolinite-gibbsite-pyrophyllite clays in advanced argillic alteration zones and for smectite clays in argillic alteration zones. These deposit profiles include geological and mineralogical attributes, which are linked to the underlying volcanic, hydrothermal and weathering processes that have produced the clay minerals from their source volcanic rocks. Further work on refining the deposit profiles includes characterising the composition of selected deposits to determine spatial trends in mineralogy and geochemistry.

Jan 1, 2007

Dilution in underground coal operations can be underestimated by up to five times during feasibility studies, with disastrous economic consequences. Every one per cent of stone waste introduced can reduce an in situ specific energy of 25 MJ/kg by some 0.25 MJ/kg and increases the abrasiveness of the run-of-mine coal. Where a wash plant is not in place, penalties imposed for not meeting contractual specifications alone can amount to some $A 1 million per year. This paper presents a method for monitoring, reporting and ultimately controlling dilution in an underground coal mining operation and presents the dilution trends from a continuous miner/longwall mine over an eight year period. The overall dilution level for the mine can be back-calculated by comparing the run-of-mine coal quality to the predicted in situ, undiluted quality. However, this will not identify the actual contaminant types, areas of the mine responsible for the dilution and the reasons for the dilution. This additional information is essential for controlling dilution to acceptable levels. Quality and horizon control using existing sampling information is generally only adequate for longer-term control purposes, and is not suitable for monitoring mining-induced dilution. The cost of close-spaced surface drilling to collect the information necessary for short-term control is prohibitive, particularly for deeper mines. However, much of this data can be collected through underground channel sampling and horizon control measurements taken during continuous miner development and longwall extraction. The mine runs the risk of not meeting contractual quality specifications and of increased equipment wear if this additional information is not available and the sources of dilution cannot be controlled. The information can also be used to plan longwall extraction heights on a short-term scale with resulting improvements in productivity.

Jan 1, 2003

By C P. de Jager, J J. Taljaard

Over the past 75 years, the mining of platinum has predominantly focused on the Merensky Reef horizon in the western Bushveld region of the Bushveld Igneous Complex (BIC) of South Africa (Figure 1). The orebody is relatively flat dipping at 10¦ to 25¦, narrow tabular in shape and has been mined to a maximum depth of some 1600 m within Anglo Platinum. This has resulted in the installation of up to four generations of shaft systems as mining progressed into reserves at greater depth. In recent years, with the improvement in processing technology and improved economics, in particular with the improved price of palladium, the mining of the UG2 Chromitite Reef is proving economically viable. The UG2 Chromitite Reef occurs below the Merensky Reef in the succession and the normal separation varies from 15 m to 400 m, with the largest separation between the reefs occurring in the eastern region of the BIC. The UG2 Chromitite Reef horizon is now being accessed from existing Merensky mining infrastructure by cross-cutting back through the stratigraphy where appropriate, or by establishing new decline cluster systems from surface, along the extensive strike length of the various mining properties. These declines are generally established utilising mechanised mining techniques. This paper gives an overview of the techno-economic approaches considered and evaluated for the selection of the optimum mining and shaft systems. More specifically, the paper reviews the design parameters used, techno-economics, conveyor versus haul alternatives, logistics simulations, capital costs, system performance, time to market or ramp-up success, important system differences and lessons learnt.

Jan 1, 2005

The Closure Risk model was developed as a new tool to aid decision makers in the complex area of mine closure. It uses a simple analytical technique that allows the decision maker to simplify what is often a complex mine closure process into more easily managed sub components. This systematic approach ensures that critical factors in the closure process are not overlooked. It also allows the most important issues to be highlighted. The model can also be used to produce quantitative estimates of risk by weighting and prioritising the issues to produce the Closure Risk Factor (CRF). Field trials at several mine sites in the Northern Territory of Australia in 2001 tested the model. The trials confirmed that the model has significant potential as a tool for decision-makers to assess in a structured, systematic manner, the major closure risks at individual mine sites. The risks include not only environmental impacts but safety and health, community, legal, financial, technical and other issues. The trials confirmed the value of a team-based approach and the inputs of key staff including environmental, production, mine planning, and community liaison personnel as well as mine management. Although the usefulness of the qualitative component of the model was established, it was found that, due to the influence of subjectivity, the utility of the prototype model to determine quantitative risk was of limited value. Using a continuous improvement approach, improvements to the model were sought. A refined model, incorporating the Australian Standard 4360 definition of risk and facilitated in-house risk assessment sessions was developed and tested against the data obtained in the field trial. This model, while maintaining the qualitative strengths of the original, allows more accurate absolute and relative quantitative scores to be calculated. This in turn facilitates comparisons between the issues at a single site as well as between different mines.

Jan 1, 2003

Over the past 18 months the De Beers Consolidated Mines Ltd operations have made a concerted effort to move away from using the traditional shock tube initiating systems. These systems are being systematically replaced by the use of electronic delay detonators (EDD). Various trials were conducted in both host rock and kimberlite rock masses to improve tunnel advance as well as to optimise delay timing during trough openings (Ngoma et al, 1999; Mohle, 1999; Baltus, 2000). The high cost of EDDÆs, when compared with traditional initiation systems, led to a number of detailed studies being conducted on the mines where EDDÆs were being used. These studies aimed to quantify the additional benefits when blasting with electronic detonators. The studies showed that the change was justified on the basis of increased quality control and reliability gained through the use of EDDÆs. However, these benefits attract other related benefits, like fragmentation control, and backbreak reductions. When compared to the shock tube initiating systems the increased development face advance and the reduction of oversize during production blasting using EDDs, compared favourably to the less costly systems. As blasting engineers gained experience and confidence in the use of the system bigger blasts were initiated in mass under-cut blasts and slot raise development, by using multiple hole firing and second delay periods between holes. In the open pit and sublevel open stope mining methods the control of the fragmentation distribution and the effect of the mass of explosive detonated during a blast is detrimental to the loading and hauling production rates and the stability of the rock mass behind the blast. With a stable rock mass the bench cutting can be executed to establish steeper overall slope angles leading to large cost savings due to a reduction in waste stripping. It is the purpose of this paper to indicate through quantification that the use of the EDDs as an initiating system improves all-round blasting performances and assists in meeting customer requirements. The customer being the ore treatment plant.

Jan 1, 2001

By G Davies, D Dunn, C Mawdesley, O Bertoli

The coal industry in Australia has been actively working in recent years towards the (re)integration of geostatistical techniques to the process of coal resource estimation. The benefits of using geostatistical techniques, over the current interpolation algorithms in use in coal modelling packages used to generate the grid estimates, need to be illustrated for the methodology to gain a broader acceptance in the coal industry. This paper focuses on the benefits gained at BHP Billiton Mitsubishi AllianceÆs Saraji mine for the estimation of the total product yield value at a 9.7 per cent product ash cut-off of a particular seam of the Saraji deposit. In order to perform this comparison, the results of the alternative estimation methodologies need to be benchmarked, which in most situations is achieved through the reconciliation of the estimates against production and/or process plant reconciliation data. Unfortunately, this benchmarking was not possible as no reconciliation data for the area of interest in the chosen seam was available, as it has not been mined at the time of the study. Where no reconciliation data is available, an alternative method is to use conditional simulations as the benchmark for comparison. The simulated values can be regarded as ærealityÆ, and the alternative estimation methodologies, based on a sampling of the underlying ærealityÆ, can then be compared using the simulated ærealityÆ as the benchmark for comparison.

Jan 1, 2009

By J du Plessis, W Marx

The FutureMine Collaborative Research Initiative has been successfully completed after three years of activity. The main objective of this initiative was to provide applications of research previously undertaken in the DeepMine initiative in terms of realistic solutions to problems facing gold mining operations as they reach for depths beyond 3500 m below surface. The FutureMine initiative was subdivided into four broad streams of technological expertise: rock engineering and seismicity; mining engineering and orebody management; software and communications and ventilation, cooling and refrigeration. This paper presents a summary of research output in this last area of expertise. Broadly, research in mine ventilation, cooling and refrigeration was directed in areas related to the recirculation of air, cyclical use of ventilation and cooling systems, air scrubbing technology, optimisation of chilled water reticulation, obtaining direct cooling at the workface, improving underground refrigeration systems through dry air-cooling and water heat rejection systems and a number of software simulation programs to be used in specific applications and as a tool assisting real-time monitoring of underground environmental conditions.This paper describes in broad terms the outcomes from this section of the research program and proposes ways in which some of these technologies may be combined synergistically in novel systems aimed at maintaining acceptable environmental conditions while reducing the impact on the profitability of operations.

Jan 1, 2005

By D Pepper

Despite the limited literature regarding the pressure filtration of mine tailings (compared to the large number of papers published each year on paste thickening of tailings) the number of mines dry stacking filtered tailings is approximately equal to the number of mines storing tailings in paste form. Main drivers for filtering tailings are: water recovery, future rehabilitation costs for tailings storage area and permitting requirements. In arid climates, the cost and scarcity of water justify the capital and operating costs associated with pressure filters. Further justification for filtered tailings is the potential for progressive reclamation of the dry stack, which can proceed earlier and faster than the reclamation of a tailings dam.Filtered tailings must be transported to the storage area by trucks or conveyors. For dry stacking, 70 - 80 per cent solids content (by mass) is typically acceptable, however the primary goal is to provide a filter cake that is consolidated and dry enough to prevent bridging and build-up on the materials handling equipment. It has been observed that high average solids contents (~70 per cent) can be achieved while the centre of the filter cakes is still wet and sticky, presenting challenges for the transportation of the solids. Appropriate controls must be in place to ensure consistently easy to handle solids are discharged from the filter.FLSmidth has installed two fine coal tailings dewatering systems in the United States. One of these systems incorporates a Deep Cone Thickener« upstream of the filter press to minimise the amount of water that must be filtered, while the other tailings filter press is fed by a high rate thickener. The operation and performance of these filters is discussed and compared to the lab testing used to size the full-scale equipment.CITATION:Pepper, D, 2012. Operation of filter presses for tailings dewatering, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 241-246 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By A K. Bayer

When the human eye fails in the evaluation of quality parameters in the extraction of minerals the use of laser-induced fluorescence analysis (LIF) can supply more detailed information on the composition of rocks. On the basis of measurements of selected raw materials engineering concepts for the use of this method in the mining industry as an innovative system for horizon control of mining machines will be described and the most important analysis parameters, influencing factors and interference variables are presented.

Jan 1, 2003

A study of the effect of nickel on the cupellation process has shown that a very low "nickel limit" must be imposed for cupellation (0·08 grams nickel or 0·05 grams when copper is present). In the presence of slightly greater amounts of nickel, lead tends to spreadon the cupel with detachment of drops from the main lead pool. In crucible fusions nickel contaminates the lead button to a small extent, and this contamination is increased.in the presence of either iron or copper. Nickel also causes "shotting" of the lead, this effect being more apparent in the presence of iron.Both the spreading during cupellation and the shotting during crucible fusion are considered to be caused by adsorption of insoluble NiO at the Pb-PbO interface, lowering the interfacial tension.Excess litharge crucible charges are' fused at 116boC. to eliminate shotting. A brief· soaking in molten basic litharge slag effectively reduces the nickel content of lead buttons. The solubility of silver in litharge slags is considerably decreased in the presence of nickel. Corrections can be applied for silver losses in slags but these corrections are not as accurate as with copper ores.INTRODUCTIONThis paper on the effects of nickel on fire assays for silver is the second of an intended series describing investigations into the fire assaying method.In the first paper, discussing the effect of copper on fire assaying processes (Guerin, 1957), it was shown that certain elements, because of their relatively low affinities for oxygen, will tend to contaminate the lead button during crucible fusion and scorification. Nickel, having a slightly greater affinity for oxygen than has lead, would be expected to be oxidized and slagged readily, and would not be expected to appear in the metal phase (lead button) to any appreciable extent. Thus, judged solely on this basis of...

Jan 1, 1960

By M Tessier, M Pahkala, L Sletmoe

The Red Lake mine is one of the richest gold mines in the world. The primary mining methods are overhand and underhand cut and fill. Starting in 2003, Goldcorp initiated an expansion program at the mine. The expansion includes a new 6.55 m diameter hoisting shaft currently under construction. The shaft will be driven to a length of over 2180 m. The shaft will be used as a primary ventilation intake to the mine. In addition to the new hoisting shaft, a return air raise is being driven approximately 1690 m from surface. This raise will be a parallel return to the existing mine infrastructure. This paper describes the ventilation and climatic analyses performed in support of the expansion project. The study included a full mine ventilation survey, in situ rock mass measurements, analysing options related to mine layout, airway sizing calculations, air heating options, and climatic simulations. Specifications were prepared for an air heating system and main and booster fans. Analyses were also performed related to heat in the stoping areas namely caused by auxiliary fans and backfill with high cement content.

Jan 1, 2005

By R Pie, J Crusius, P Whittle, J J. McNee

The Main Zone and Waterline pit lakes at the Equity Silver Mine near Houston, BC (Canada) are the sites of an ongoing three-year government- and industry-funded research program. In order to assess the feasibility of various bio-remediation strategies, field-scale manipulations were conducted using enclosed mesocosms (limnocorrals). Two manipulation strategies were tested: addition of algal nutrients (phosphate and nitrate) to Main Zone Pit surface waters; and addition of algal nutrients (surface waters) and dissolved organic carbon (deep waters) to the Waterline Pit. Nutrient addition was conducted in order to stimulate algal production and enhance metal scavenging by biogenic particles, while dissolved organic carbon (ethanol) was added to increase oxygen demand and foster the development of sulfate reduction in pit bottom waters. Fertilisation resulted in rapid growth of natural phytoplankton populations in the surface waters of both pits. In the Main Zone Pit, the stimulation of algal growth resulted in the pronounced removal of both dissolved and total metals (Zn and Cu) from surface waters, with higher rates of metal removal being observed at higher nutrient additions. Metal removal could be attributed to the scavenging of dissolved metals by biogenic particles and subsequent particle settling. A similar pattern of removal from surface waters was observed in Waterline Pit (Zn and Cd). The addition of ethanol to deep waters in Waterline Pit was effective in promoting sulfate reduction in the lower layer. The development of reducing conditions resulted in near-quantitative removal of dissolved Zn and Cd, presumably as secondary metal sulfides. Iron, As and Ni profiles in Waterline Pit exhibited no evidence of removal from either surface waters or bottom waters. Collectively, the results demonstrate that the passive forms of bioremediation tested in these pit lakes may be effective for whole pit-lake remediation.

Jan 1, 2003

A formalised approach to risk management has been regulated in the United Kingdom (UK) since the Construction (Design and Management) Regulations 1994 (CDM) came into force in 1995. These regulations have recently been revised in 2007. In response to a series of significant claims around the world the UK insurance industry published a code of practice for risk management of tunnels in 2003, and that was followed by an international version in 2006. Probably one of the main contributions of this new approach is the recognition that health and safety risks can best be addressed early in the process, initially by the owner and then by the designers. One of the aims is to achieve elimination of risks by good design. The advantage of a risk-based approach to tunnel design is that all risks are considered explicitly, and any residual risks in the design are communicated clearly to the construction team. This paper looks at the implementation of this formalised approach to risk management with reference to the A3 Hindhead Project. The design has been undertaken in accordance with the requirements of the CDM regulations, and also in compliance with the Joint Code of Practice for Risk Management of Tunnel Works in the UK. An outline of the risk-based design process used is provided, including examples.

Jan 1, 2008

By M P. Schwarz

In recent years, computational fluid dynamic (CFD) modelling of mechanically stirred flotation cells has been used to study the complexity of the flow within the cells. In CFD modelling, the flotation cell is discretised into individual finite volumes where local values of flow properties are calculated. The flotation effect is studied as three subprocesses including collision, attachment and detachment. In the present work, these subprocesses are modelled in a laboratory flotation cell. The flotation kinetics involving a population balance for particles in a semi-batch process has been developed. From turbulent collision models, the local rates of bubble-particle encounters have been estimated from the local turbulent velocities. The probabilities of collision, adhesion and stabilisation have been calculated at each location in the flotation cell. The net rate of attachment, after accounting for detachments, has been used in the kinetic model involving transient CFD simulations with removal of bubble-particle aggregates to the froth layer. Comparison of the predicted fraction of particles remaining in the cell and the fraction of free particles to the total number of particles remaining in the cell indicates that the particle recovery rate to the pulp-froth interface is much slower than the net attachment rates. For the case studied, the results indicate that the bubbles are loaded with particles quite quickly, and that the bubble surface area flux is the limiting factor in the recovery rate at the froth interface. This explains why the relationship between flotation rate and bubble surface area flux is generally used as a criterion for designing flotation cells. The predicted flotation rate constants also indicate that fine and large particles do not float as well as intermediate sized particles of 120 - 240 ¦m range. This is consistent with the flotation recovery generally observed in flotation practice. The magnitude of the flotation rate constants obtained by CFD modelling indicates that transport rates of the bubble-particle aggregates to the froth layer contribute quite significantly to the overall flotation rate and this is likely to be the case especially in plant-scale equipment.

Jan 1, 2005

Reliable sampling practices are the key to optimising the market value of a mining or chemical companyÆs stock. As a result, reliable sampling standards are needed. However, current standards on sampling present the æuniversalÆ Pierre GyÆs Sampling Theory in an ambiguous way. For example, the Total Sampling Error is divided into its basic components only in informative annexes, when it should clearly be the main body of the standard. Sampling standards are presently loaded with statistical concepts that actually belong in the annexes. Furthermore, many non-probabilistic sampling procedures are still mentioned which do not belong in a standard. The objective is not to criticise existing sampling standards, but to suggest better ones. Sections on the Sampling Theory should divide the Total Sampling Error into a sum of its nine basic components. Then, and only then, should they be addressed one at the time. Sections for establishing a sampling protocol should address the in situ Nugget Effect, the Fundamental Error, the Grouping and Segregation Error, the Long Range Quality Fluctuation Error, and the Periodic Quality Fluctuation Error. Sections for sampling methods, mechanical sampling, manual sampling, grab sampling, sampling of trucks, railroad cars, bags, and drums should be part of the critically important practical implementation of a recommended sampling protocol, called Sampling Correctness. It includes the increment Delimitation Error, the increment Extraction Error, the Weighting Error, and the Preparation Errors. Unless these errors are addressed one at a time, in an unambiguous way, the standard will remain ineffective in solving sampling problems for the industry. Therefore, a strategy is needed to create better standards required at the early stages of new projects, both by manufacturers of sampling equipment and by engineering firms. A logical sequence of important points that cannot be ignored in any sampling standard is presented. An analysis of the practical use of the words sampling uncertainty versus sampling error is recalled. Finally, as a practical example, an in-depth analysis of the correctness of cross-belt samplers is presented, and emphasis is placed on the correct ways to perform bias-tests for mechanical sampling systems.

Jan 1, 2005

Manganese ore has been mined from the Peak Hill Gold- field since 1948 and from the Pi'lbaraòGoldfield since 1954, and it is probable that some deposits- In and, near the Phillips River Goldfield will be mined at a future date', There are also several million tons of mariganiferous ;naterial which is too low in manganese. .co.ntent_ for . present requirements. The manganese deposits¦of Western Australia are mostly superficial. They hav' been formed during the Cainozoic Era by supergene enrichment ò6f Precambbrian: manganiferoius sediments, and by deposition from -solution on, or'in caves in, the Cain- ozoic land surface. The manganese in solution was derived from the weathering of Precambrian manganifer.ous s.edimexsts, None of the deposits are of hydrothermal origin, nor are they related to igneous rocks in any war, other than as ultimate source rocks. There is ho evidence-'t.o.:sugge,st that meta- morphism has been responsible for.the emplacement of any deposit. The tenor of the ore varies'aec'ording'to the quantity of gangue in the orebody and- also to the nature of the part- icular ore minerals. The main ore.mine.rals are the oxides pyrolusite and cryptomelane and the 'o'xide-silicate braunite. The main gangue minerals are hematite, limonite and quartz. The deposits of high grade oreò(-above.45 per cent Mn) range in size from 50 tons to many thousands of tons but most of them are in the 500-5,000-tons r .nge .

Jan 1, 1964

The methods employed in dressing 'the tin ore up to the required percentage of purity depend mainly on the type of ore crushed.These may be briefly divided into two distinct classes-viz., q, free: milling ore and a complex milling ore. In the former the ore is practically free from the common metallic sulphides, such as pyrites, mispickel, blende, galena, etc., and 1!' clean concentrate of 70 per cent metallic tin can be directly obtained in one continuous act of concentration; in the latter, however, in order to get a good extraction, it is only advisable to primarily concentrate up to 30 to 40 per cent. tin oxide, the rest being the sulphides of the metals. This concentrate is then roasted, re-ground, and re-concentrated up to 70 per cent. metallic tin on a separate set of tables.In the complex milling ore the tin is intermixed very closely with the sulphides, so that it becomes necessary to collect all the mineral present in order to obtain clean tailings. Stamp mills are the most popular machines for the primary crushing in the district, but whether they are invariably the best for the purpose is rather an open question. No doubt for some of the very tough chloritic ores they are the most efficient, but for a brittle quartzose ore, such as the free milling proposition usually is, the writer thinks Oornish rolls would well hold their own, especially when the tin occurs coarse, as is so often the case with this class of ore. Of course, the great drawback to stamps is the excessive quantity of tin slimed and slime tin is one of the problems of tin-dressing-while rolls give...

Jan 1, 1907