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By S. Rajendran

India?s interest in the resources of the deep seabed particularly the manganese nodules in the Indian Ocean can be traced back to the Indian Ocean Expedition of 1960 ? 65. The collection of Manganese Nodule samples from the Indian Ocean in January 1981 aroused considerable interest within the scientific community. Following several surveying expeditions, the Central Indian Ocean was identified as the most promising area for exploitation. India was accorded ?Pioneer Investor? status and further research and development programs were launched to establish the techno-economic viability of deep seabed mining. India has also shown considerable progress in the field of development and testing of methods for processing the nodules. The Department of Ocean Development manages the program.

Jan 1, 2003

By I. E. Teymenson, N Fedunets

Mining-metallurgical complex is the base of any economics and influences directly on practically all branches of world economics. Therefore the task of estimation and selection of investment decisions in mining industry adequate to modern market conditions and the task of decreasing multidimensional alternatives selection uncertainty are very actual. An uncertainty of investment alternatives is explained by a number of reasons, main of which are a presence of several investors types, an unstable situation on the market and an absence of evident relations between appraisal criteria used. Maximum increasing of formalization and objectivity of information technologies applied for an estimation permits to reduce the uncertainty of investment variants estimation. A number of principled innovations, allowing to solve the task of decreasing of multidimensional alternatives selection uncertainty, are introduced into the information technology of estimating and selecting investment decisions in mining-metallurgical branch, developed by us. In the article the necessity of including a cognitive model into developed selection mechanism, which allows to take into consideration inter-influences of used critera, has been grounded. Besides, the forecasting model considering interconnected time rows has been applied for increasing the world conjuncture forecast quality. Further in the article main metrics types have been characterized and application of weighted Chebyshev’s metrics as the most compromised from all studied metrics for variants selecting has been proved, and also the developed procedure of directional search of effective compromise decisions has been described. Brief characteristic of designed instrumental means of multi-criteria variants estimation and selection finalizes the article. In conclusion expedience and efficiency of using the developed information technology for reduction of multidimensional alternatives selection uncertainty have been grounded.

Jan 1, 2003

By K. Regl, J. Berneder

"AMAG investigated different aspects to improve the resistance against grain coarsening in aerospace alloys during recrystallization and was successful in finding several opportunities to minimize this effect. The studies show that one aspect to counteract grain coarsening is the chemical composition and subsequently all phases that are formed during homogenization. Starting with a fine grain (~ 50 µm) can lead to a final grain size of few mm. On the other hand with a coarse initial grain size (approximately 150 µm) and the right chemical composition the grain size can stay almost constant despite different deformation steps. Additional we investigated different sequences for the component production to eliminate the problem of grain coarsening as a coarse grain has a detrimental effect on product performance.INTRODUCTION In the aircraft industry, aluminium sheets are most commonly deformed in their soft state, followed by solution heat treatment and natural or artificial aging. If the preceding deformation is in a critical amount, during the recrystallization at solution heat treatment grain coarsening can occur. A subsequent deformation to this condition leads to an orange peel surface, which requires additional polishing. Next to this extra effort the coarse grain size produces a drop in the mechanical properties, often below specification limits. If there is no subsequent deformation, this effect is not visible and without destructive testing there is no possibility to detect the error. As mentioned before, this effect occurs during recrystallization, which is a process that is driven by the stored energy in the microstructure. The two most important aspects for an increase of the stored energy are the increase of the grain boundaries fraction (smaller grain size) and the increase of the dislocation density caused by deformation. The increase in dislocation density during the deformation arise from trapping of existing dislocations and from the generation of new dislocations. During recrystallization all grains are built completely new, so all dislocations are removed (Humphreys & Hatherly, 2004). There are three requirements for recrystallization:"

Jan 1, 2018

By A. Bayer, T. Klopfer

"As a leading global strategy consultancy, Roland Berger Strategy Consultants firmly believe that the issue of sustainability is at the core of every business activity. Thus, strategies to enhance corporate sustainability (CS) are an essential cornerstone in the consultancy's approach to develop and implement new strategic concepts for the clients. In this paper, the authors conclude that innovation is the only solution possible to guarantee growth and welfare gains while achieving sustainable development. More efficient and effective ways are necessary to enable technical and social breakthroughs. To illustrate Roland Berger Strategy Consultants's vision on CS, four selected cases from the basic resources, energy and utilities sectors are presented. They demonstrate that the implementation of a CS strategy does not only refer to CEO spheres and are by no means just a moral justification for current business practices. Rather they show that the decision to opt for these new ways also opens up multiple opportunities."

Jan 1, 2005

Most orebodies have one or more boundaries which are gradational, where the decision to stop mining is based on an economic cut-off. To maximise profit, this cut-off grade must be chosen correctly. It is necessary to review cut-off grades regularly, as the optimum cut-off grade changes with time, and major changes are hard to implement in a working mine without disruption to production schedules.Whenever a cut-off grade is used, there will be errors in its application caused by errors in the estimation of block grade. These can be minimised by stringent quality control in sampling and by the use of kriging, which attempts to minimise the absolute errors in grade estimation. The kriging method used should produce the most accurate estimates of marginal grade blocks - this will not necessarily be the technique that gives the best overall prediction of head grades.

Jan 1, 1993

By J J. L du Plessis

Escalating energy and electricity costs have become one of the biggest expenditure drivers in mining operations. During the last eight years, energy costs have trebled when expressed as a percentage of total running cost in South African mines. Power consumption on mines is controlled by three main strategies, namely load clipping where energy use is reduced for parts of the day, load shifting where energy use is shifted to other parts of the day, and energy efficiency where energy use is reduced permanently.To reduce the operating costs of ventilating and cooling underground mines continuously, system optimisation studies must be completed. A part of this paper describes methods that can be used to reduce energy usage by optimising cooling and ventilation systems during planning and in existing operations using network simulation models that accurately reflect the current and planned ventilation conditions. These models are used to examine various options for improving the overall ventilation and cooling efficiency. Furthermore, an overview of refrigeration and cooling practices, and ventilation strategies is presented.Ventilation-on-demand and cooling-on-demand strategies have the potential to reduce both the capital and operating costs associated with mine ventilation and cooling systems. In addition, it has been proven that modern strategies and energy-efficient tactics are technically feasible.It is also important that the correct equipment selection is made. This must be based on the best technology with the highest energy efficiency. Where equipment replacement is being considered, energy efficiency must be one of the key decision drivers.In this paper a number of studies were presented and from the experience and the data presented it is clear that a large financial benefit is possible through optimising ventilation and cooling during the planning of mines or within an existing operating mine.CITATION:du Plessis, J J L, 2015. Strategy and tactics implemented to achieve energy-efficient ventilation and cooling of mines, in Proceedings The Australian Mine Ventilation Conference, pp 9–18 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 31, 2015

By Charles L. Karr

Researchers at the University of Alabama in cooperation with the U.S. Bureau of Mines have developed adaptive process control systems in which genetic algorithms (GAS) are used to augment fuzzy logic controllers (FLCs). GAS are search algorithms that rapidly locate near-optimum solutions to a wide spectrum of problems by mimicking the search procedures of natural genetics. FLCs are rule based systems that efficiently manipulate a problem environment by modeling the "rule-of-thumb" strategy used in human decision making. GAS and FLCs can be combined to produce powerful, efficient, and robust adaptive control systems. To perform efficiently, such control systems require a control element to manipulate the problem environment, an analysis element to recognize changes in the problem environment, and a learning element to adjust to the changes in the problem environment. I" this paper, the details of an ongoing research effort to develop and implement an adaptive process control system for a column flotation unit are discussed.

Jan 1, 1996

By S. Jagdish

India ranks fourth in the world of iron ore production and exported 55% of the total iron ore production of 180.9 million tons in 2006-07. As per United Nations Framework Classification (UNFC), the total iron ore reserves in India is 25249 mt. This consists of about 14630 mt of Hematite ore and 10619 mt of Magnetite ore. While the deposits of magnetite iron ore are limited to the states of Karnataka, Andhra Pradesh and Tamil Nadu, hematite ore is available in abundance in Jharkhand, Orissa, Chhattisgarh, Karnataka and Goa. National Steel Policy, declared by government of India in 2005 envisages 110 million tons of steel production by 2020. This is likely to be revised upwards. Massive exploration work in iron ore is needed to convert the available resources of iron ore into reserve category. Steel Authority of India Limited (SAIL) produced more than 24.5 million tons of iron ore during 2006-07 and plans to produce 42.0 million tons per year by the year 2010-11 to meet the requirement for a hot metal production of 26.2 million tons. While processing iron ore, the challenge faced would be the reduction of the gangue materials ? alumina and silica. It is proposed to bring down alumina and silica in the iron ore to less than 2% each from the current level of 2.5%~3.5% each. Appropriate beneficiation schemes are being developed depending upon the mineralogical characteristics of iron ores at different mines in the country. The state-of-art beneficiation technologies like Hydro-cyclone, jigging, magnetic separation etc. will be incorporated. SAIL?s corporate plan envisages blast furnace burden of 15% iron ore lumps, 15% pellets and 70% sinter by 2010. This strategy opens up the opportunity of utilization of micro fines generated in the mining and beneficiation processes for pellet making. This also directs towards all together new technological approach to the beneficiation process. SAIL is planning to set-up three pelletisation plants of 2~3 mtpa capacity. Environmental issues like reduction in slime loss and utilization of dumped low-grade iron ore are very important. R&D Centre for Iron and Steel, SAIL has carried out extensive laboratory investigations in the above area. This will help in reducing the loss of valuable iron through slimes and also increase the iron ore resource base. Laboratory investigations indicate that low grade dumped ore fines with Fe: 55.5% can be upgraded to a product with Fe: 66.2% with about 48% recovery.

Jan 1, 2014

By Daniel J. Corkery

Mines in Canada and the United States are subject to regulations limiting ammonia, nitrate and nitrite levels in mine effluents released into the environment. The primary source of these nitrogen compounds is typically explosive used in blasting operations, as ammonium nitrate (AN) remains a significant component of most explosives used in the mining industry. The amount of AN entering a local water drainage system is related to site conditions, explosives used, explosive handling and blast efficiency. Mining operators acknowledge AN loss to mine water from blasting operations. However, the mechanisms by which ammonia, nitrite and nitrate are entering the water drainage system, or the relative contribution of specific mechanisms, may not necessarily be assessed or monitored adequately. Characterization of these mechanisms, through systematic investigations, allows a mining operation to focus its efforts on reducing AN loss. This paper outlines a strategy for investigating the mechanisms through which AN enters the mine water drainage system and methods to mitigate this loss. This strategy includes collection and analysis of data to identify and quantify the AN loss mechanisms, design and implementation of tests to mitigate this loss, and assessment of the results. Such investigations are not intended to be a separate one-time project, but part of a long-term process of continual feedback and optimization that is related to the collection and reporting of AN levels for regulatory purposes. The implementation of the strategy must be tailored to each mine?s requirements and existing conditions.

Oct 1, 2010

By H. Gumede

The challenges of noise emission in the mining industry are well known. These challenges are exacerbated by the increasing trend towards mechanized mining, and there is general consensus that an effective industry-wide Buy Quiet initiative (BQI) will significantly assist in reducing noise-induced hearing loss by minimizing noise at its source. In its endeavours to improve the health of workers, the MOSH Noise Team has facilitated development of a proposed strategy and structure for a BQI. Extensive consultation with stakeholders resulted in support for the initiative. The MOSH Noise Team was advised to solicit the contributions of consulting mechanical and electrical engineers (CM&EEs), whose support is viewed as critical for realization of the initiative, since elimination of noise at source is an engineering challenge, and most procurement standards and specifications are set and managed by engineers. A workshop with CM&EEs and their representatives, as well as group environmental engineers (GEEs), confirmed the urgent need for the initiative and provided valuable insights. The workshop used obstacle based planning techniques to identify the factors on which the success of this BQI will depend. Most potential obstacles to the implementation revolved around proper scoping, leadership commitment, and companies? adherence to the initiative. Lack of involvement by the relevant stakeholders and economic issues were also identified as potential obstacles. Delegates at the workshop felt that the successful implementation of the industry-wide BQI, will depend on the mining industry addressing the specific obstacles. The most critical and urgent issue was identified as the formation of a properly constituted industry-wide BQI task team that includes representatives from critical stakeholder groups and which is mandated and empowered to drive the initiative.

Jan 1, 2014

By Rick W. Bellenie, Ronald L. Woolf

The Gregg River mine is located 40 kilometres (25 miles) south of Hinton, Alberta, approximately 330 kilometres (205 miles) west of Edmonton and lies against the Front Range of the Rocky Mountains.

Jan 1, 1994

By Norman O. Lotter

Drill core is preferred as the sample material for metallurgical and mineralogical characterisation and flowsheeting of an orebody. The question arises as to how to do this at the economic optimum, since geologists have several other strategic uses for their drill core. The limiting factors are the cost of extra drilling for the metallurgical testwork and the need to preserve the drill core record. In this study, the representative sampling of drill core at an economic optimum for metallurgical testing is addressed. This phase of the drill core work is preceded by earlier drill core characterisation - for which other appropriate sampling protocols are used - that has provisionally categorised the orebody into geometallurgical units. In stratified sampling of drill core, use is made of a version of the stratified approach to compound distributions proposed by Cochran in 1946. Use is made of Gy’s 50-piece minimum sample mass model to estimate minimum requisite sample mass. In the case where sampling and testwork are required on a Lifeof- Mine blend of a given ore deposit, whereby defined ore types or geometallurgical units are present, the sample mass requirement is significantly reduced by working from drill-core at the geometallurgical unit level. A case study using Raglan drill core is discussed. Using nickel as an indicator paymetal, and sampling at a fundamental variance level of 8%, the minimum sample masses for disseminated sulphides, net-textured sulphides, and massive sulphides are 3.80, 7.37 and 4.39 kg respectively. When the same drill-core is sampled as a Life-of-Mine mixture without knowledge of the geometallurgical units, the minimum sample mass increases to 84.28 kg. It is thus possible to assemble a representative Life-of-Mine sample of drill-core more economically, at the same time validating its representativity. Equivalent calculations for copper, platinum and palladium are discussed, with outcomes consistent with this finding. When all four paymetals are considered, one selects the largest minimum mass out of all four cases. This results in minimum sample masses of 11.67, 74.90 and 175.16 kg for disseminated sulphides, net-textured sulphides and massive sulphides respectively. The simulated Life-of- Mine blend would require a minimum sample mass of 377.33 kg to cover all four paymetals.

Jan 1, 2010

The authors describe two stratiform intrusions within a two miles thick ophiolite belt, one of the many ophiolite (serpentine) belts of the eugeosynclinal sequences of the Kalgoorlie System (metamorphic age c.2700 million years). Unusually good evidence of gravitational differentiation involving cumulates for an Alpine type peridotite-gabbro intrusion has been obtained, in spite of modifications of the original igneous rocks imposed by regional metamorphism. Unmetamorphosed relics of cumulate rocks are a surprising feature of this occurIfence.'fhe differentiation process reflected in the layered sequences is compared to that of the Stillwater Intrusion, Montana. Phase, cryptic and rhythmic layering are recognized. The economic significance of this study lies not only in the possibility of nickel mineralization in this ophiolite belt, but also in that much detailed information on the nature of these belts, which is difficult to obtain in the case of the more altered and sheared rocks of the belts carrying gold and nickel ore deposits nearby, is gathered from the Yilmia occurrences.

Jan 1, 1969

By Stanton RL

Stratiform lead-zinc mineralization in the Soldiers Cap Group and Kuridala Formation of the Mount Isa Inlier is closely associated with iron-rich sedimentary units or "iron formation", and has many similarities to the Broken Hill deposit in New South Wales. Both the Soldiers Cap Group and the Kuridala Formation have been intensively explored for deposits of this type since the early nineteen- seventies. A mineralized belt of at least eight significant prospects has been identified, of which the Pegmont deposit is the largest and best known example. In most cases the mineralized horizons contain banded galena and sphalerite within a gangue of predominantly quartz-garnet- pyroxene-amphibole rock, sometimes containing a variety of other metamorphic silicates, and apatite. Chemically, the mineralized horizons are distinguished by higher than usual levels of one or more of total Fe, MnO, CaO and P205. Interpretation of patterns of mineral- ization within the belt is based on the Pegmont deposit, where a model of base metal sulphide deposition within restricted basins of iron-rich chemical sediment has been developed (Stanton and Vaughan, 1979). Broadly, the model envisages the deposition of higher grade lead-rich mineralization in the basin centre position, lower grade zinc- rich mineralization in a basin intermediate position, and much weaker copper-rich mineralization in a basin edge position. These three positions reflect a laterally continuous arrangement of silicate microfacies within the original iron-rich sediment.

Jan 1, 1984

The overall mineral assemblage of the Broken Hill orebody is similar to that of a skarn. However unlike the classical skarns it does not represent contact metamorphism of pre-existing limestone beds. It is a stratiform accumulation of exhalative-sedimentary silica, sulphides, (Ca, Fe, Mn) silicates and carbonates, fluoride and phosphate that has later undergone regional metamorphism. The resulting development of coarse-grained quartz, sphalerite, galena, rhodonite, bustamite, mixed carbonates, fluorite, apatite and many minor phases has produced a sulphide-rich skarn- like mass that like many others of its kind, might best be referred to as a stratiform skarn. Recent investigations of occurrences of this type are showing that the incidence of concentrations of particular metamorphic minerals in and adjacent to such orebodies are closely related to bedding and to former sedimentary facies patterns. From this it appears that the mineral assemblages may be used to deduce not only the nature of the materials laid down in the beds, but also the physico-chemical conditions under which sedimentation took place. Several stratiform deposits, including Broken Hill, are used as examples to show that variations in these conditions may have a profound influence on the subsequent response of the rock to regional metamorphism and hence on the mineral assemblages that finally develop.

Jan 1, 1983

GENERAL GEOLOGICAL DESCRIPTION The uranium mineral appraisal herein described was made for an ore deposit in New Mexico. The uranium mineralization occurs as roughly tabular to lens-shaped deposits of varying thickness within the sandstone of the Jackpile formation of Jurassic age. The mineralization occurs at several horizons within the Jackpile formation, but is not always confined to specific beds. It often transgresses across stratigraphic layers, as demonstrated when attempting correlation of uranium gamma anomalies between adjacent drill holes. Preferred mineral trends have been established in some parts of the deposit, but are not always predictable when attempting to extrapolate beyond the zones defined by drill hole sampling. MANAGEMENT OF DRILL HOLE SAMPLE DATA All of the drill hole sample data used in the appraisal were obtained from interpretation of gamma-ray logs. A brief description of gamma-ray log sampling is given in Chapter 2. Two preliminary steps are involved in preparing gamma-ray logs into sample data normally acceptable for computer manipulation. 1) The gamma analog trace produced by the downhole probe must be digitized, i.e., counts-per-second (CPS) are recorded for each 0.15 m (1/2-ft) interval across the gamma-ray anomaly. The work is usually done on a "digitizer" while following the analog trace with an electronic stylus on a special tablet or table. The other alternative is to do the work manually. Some of the newest downhole logging equipment produces a magnetic tape output which can be read by a computer. 2) The gamma-ray CPS values must then be converted to equivalent U308 assay values, taking into consideration all appropriate correction factors. The US Atomic Energy Commission, now part of the Department of Energy, developed the theory and algorithm for this conversion in the 1960's, and though the work can be done manually, it is best done with the GAMRED (gamma-reduction) computer program. Fig. 14-1 illustrates a typical analog trace produced by the probe instrumentation, including gamma-ray trace (left), self-potential electric log (center), and resistivity log (right). Fig. 14-2 shows a form of the computer output after the analog data has been digitized to 0.15-m (1h-ft) intervals and converted to percentage U308 values for the same hole. The U308 grade bar graph on the right permits rapid visual inspection of anomalous values by depth and elevation. The converted U308 sample data were next processed by the SURVEY program that assigned to each assay interval [0. 15-m (1h-ft)] an X Y Z coordinate, taking into account all deviations indicated from downhole survey information. The output file of the SURVEY program was listed on the line printer for examination by project geologists, and also became the main input file for the URAN/ COMP compositing program, which is designed to group individual 0.15-m (/-ft) U308 sample values into larger intervals representing discrete anomalous zones according to a series of specified parameters entered into the program by the user. Composite U308 intervals were computed by the URAN/COMP computer program, the logic of which may be briefly described as follows: Step 1 The program searches for the highest U308 value in the hole and builds a composite by adding the highest grade interval on either side so long as the added value is greater than a minimum acceptable grade, and the total composite, after addition, meets minimum GT (grade times thickness) constraints. Step 2 The program loops back to find the next highest assay value in the hole not already included into a composite, until all anomalies above minimum cutoff grade are composited. Step 3 Individual composites are combined if they are closer than a specified minimum waste thickness, and the resultant composite grade still meets GT minimums.

Jan 1, 1980

By A. Hynes, T. Skulski, D. Francis

The Archean volcano-sedimentary succession in the LG-3 area has undergone two phases of deformation and has been metamorphosed to upper greenschist and amphibolite facies. Marine, fine-grained sediments and mafic pyroclastics comprise the lowest observed stratigraphic unit. These sediments are overlain by a thick sequence of submarine basalts and minor basaltic andesite. The lavas are characterized by high Al/Al+Si, Ti values, low Mg numbers and flat REE profiles (lOx chondrite). A sedimentary prism of coarse elastics which was deposited close to an exposed plutonic highland, overlie the volcanics. Massive lavas of basaltic andesi te and associated volcano-sediments comprise the uppermost stratigraphic unit. These lavas are characterized by high Mg numbers, Ni, Cr, LREE (lOOx chondrite) but low Ti, Al/Al+Si and HRee. The supracrustal rocks were intruded by tonalites and tonalitic gneisses.

Jan 1, 1984

The Myally Beds, Surprise Creek Beds and Mount Isa Group form the upper part of the Proterozoic Western succession of rocks in northwest Queensland. The latter two units are partly equivalent, and are important for their base metal content at Mount Isa and elsewhere. The arenaceous Myally Beds lie unconform- ably or disconformably below the Mount Isa Group and Surprise Creek Beds; they contain four mappable units which were deposited on a broad, shallow shelf washed by east-trending currents. Emergence of the Myally shelf initiated a series of parallel, possibly intra- cratonic, troughs to the east and west. In the east, the Surprise Creek Beds were deposited between the emergent shelf and base- ment rocks, and consist of a shelf and trough facies divisible into 7 and 10 units, respectively. Trough sediments are continuous north-south, and show turbidite character- istics; algal dolomite characterizes the shelf facies. To the west in the Mount Isa trough, an orthoquartzite facies, the Warrina Park Quartzite, defines the base of the Mount Isa Group. Hinge zones between the shelf and trough environments are marked by east-west facies changes, and provide a focus for later major north-south faulting. However, some penecon- temporaneous faulting near Mount Isa is best explained as complex post-depositional faulting of a disconformable sequence. Subsidence and deposition in the Mount Isa trough continued for a longer period than in the Surprise Creek trough, allowing accumulation of lead and zinc deposits in the upper half of the sequence. The Surprise Creek Beds appear equivalent to the lower half of the Mount Isa Group, and are probably not prospective for lead and zinc. Turquoise and possible other secondary copper minerals are widespread in the Warrina Park Quartzite and equivalents in the Surprise Creek Beds, and further investigation of these formations seems warranted.

Jan 1, 1974

By I. Dimitrov, S. R. McCutcheon

"Industrial-grade limestone is found in both the Lower Silurian La Vieille Formation and Upper Silurian LaPlante Formation of the Chaleurs Group in northern New Brunswick. Currently, between 150 000 and 200 000 tonnes of limestone are produced per year from the proximal facies of the LaPlante Formation at the Sormany quarry of Elmtree Resources Ltd., located west of Bathurst.The proximal facies of the LaPlante Formation was deposited on the margins of tectonically uplifted Ordovician terranes. This facies comprises stromatoporoidal-algal bindstone intercalated with wackestone, packstone, and floatstone in variable proportions. The distal facies comprises calcareous shale and minor limestone deposited deeper offshore.Folding and faulting related to Middle Devonian Acadian tectonism have caused an increase in the apparent thickness of the limestone sequences, especially adjacent to the regional Rocky Brook-Millstream fault. Structural and stratigraphic observations indicate that some of the limestone bodies in the area have been tectonically displaced from their site of deposition.A variety of prospecting techniques was used to locate new limestone resources, including geological mapping, airborne and ground electromagnetic surveys, and satellite remote sensing. Clastic rock units above and below the LaPlante Formation have distinctive properties that help to trace the intervening limestone along strike. Because of water-saturated glacial cover, thick vegetation, and the small size of targets, airborne geophysical methods did not prove effective in delineating limestone beds, but aeromagnetic surveys helped map the underlying clastic unit. The remote-sensing data and especially high-resolution digital elevation models helped in identification of karst topography related to limestone."

Jan 1, 2007

By W. A. Padgham, H. Helmstaedt

Field evidence for current hypothe e about age and kinematic ignificance of gold-bearing hear zones in the Archean Yellowkni fe greenstone belt is reviewed , and it is concluded that major disagreements between previous workers are a direct result of differences in stratigraphic and tructural in terpretations of the Yellowknife Supergroup. Although goldbearing hear zone appear to be confined to the mafic volcanic pile of the Kam Group. it can be shown that shearing affected all supracru tal rocks, including the Jackson Lake Formation. now con idered to represent the youngest unit of the Yellowknife Supergroup. tructural ob ervations are incompatible with the hypothe is that the hear zones represent loci of ynvolcanic gravity sliding but are consistent with earlier conclu ions that shear zone development commenced with rotation of the volcanic pile and continued as re ult of lateral shortening broadly overlapping with the emplacement of granitoid batholiths. Shear Zones are common throughout the entire green tone belt. yet productive zone are confined to the Yellowknife Bay Formation of the Kam Group and localized where flow abut with a high angle again t the contact of the We tern Plutonic complex. However. no obvious tructural and lithological features have been recognized that are more favorable for gold deposition and distinguish the shear zones and flows of the area around the mines from those of other parts of the greenstone belt. The model that gold wa transported by metamorphic solutions and that hear zones were the firs t-order control for gold deposition provides no explanation for the trong localization of the depo it . As porphyries with elevated gold contents are present in and near ome of the mines. the possibility that gold was deposited from hydrothermal system around fel ic intrusion representing early phases of the Western Plutonic complex should be given erious consideration.

Jan 1, 1986