Search Documents

By J. E. Quinn, S. Wolstencrof, K. H. Soldenhoff

Ion Exchange (IX) using Strong Base Anion Exchange (SBA) resins is conventionally used to purify uranium from sulfuric acid pregnant leach solutions (PLS), particularly when uranium grades are relatively low. However, the presence of chloride in the PLS interferes negatively with conventional SBA based IX processes, by reducing the uranium loading on the resin. Chloride can be present in the PLS due to the use of saline bore or seawater in leaching, or chloride containing leach/IX reagents. ANSTO has been examining strategies to combat this problem for several years. ANSTO previously reported that a recently developed high-capacity SBA resin was capable of extracting uranium efficiently from saline leach liquors produced at Boss Resources’ Honeymoon in-situ recovery mine in South Australia. The resin was tested successfully in a 2017 Field Leach Trial carried out onsite in the existing wellfield area. While the piloting was extremely promising, the elution was more challenging, with eluate tenors limited to 2 g/L U3O8 using NaCl. This is due to the resin’s strong affinity for the uranium complex, which makes it difficult to elute efficiently by standard methods. In this paper, we describe a novel elution process developed for strong base resins that significantly improves upon conventional methods. The process, developed by ANSTO, is based upon conversion of the extracted uranyl sulfate species to uranyl carbonate, followed by elution with sodium chloride. The loading and elution process was demonstrated in continuous locked-cycle piloting conducted at ANSTO in 2019. The results were excellent, with eluate tenors of 8–9 g/L U3O8 achieved from Honeymoon PLS containing 50 mg/L U3O8, with very little transfer of impurities. In subsequent test work, the eluate was shown to be amenable to uranium peroxide precipitation. The results represent a huge step forward for the purification of uranium from saline leach liquors.

Jan 1, 2020

By J. A. C. Fortescue

"Reconnaissance geochemical mapping, based on the chemical analysis of waters, stream, and / or lake sediments had its origin in geochemical prospecting surveys carried out in New Brunswick during the 1950s. More recently, reconnaissance geochemical surveys carried out by government agencies for mineral resource appraisal purposes have been seen as a special case of regional geochemical mapping which is carried out with the aim of describing geochemical patterns f or elements which may he interpreted for mineral resource appraisal, environmental or geological purposes. The interpretation of pal/ ems on regional geochemical maps is based on the concepts of landscape geochemistry, in this paper, the regional approach 10 geochemical mapping is described with reference to an experimental regional geochemical survey which was completed in southwest Ontario during 1981-82. II is concluded, on the basis of data pal/ems for one element only (i.e. arsenic), that the new approach has much potential for solving modern problems in geoscience.""If things don 'I alter they will stay as they are... An old adage.IntroductionDuring the past hundred years topographic, geological, and geophysical maps have been made for all, or nearly all, of Ontario. During the past thirty years these maps have become related as components of what is now called geoscience. Geoscience maps at the regional (i .e. 1 :250,000) scale are often used together to solve general problems in earth science especially in relation to prospecting, or mineral re source appraisal."

Jan 1, 1986

By R. S. Adhikari

The changes in defects patterns or in element condition index during visual inspection of bridges are primary concerns for inspectors. This paper presents a new approach for change detection of defects in bridges by identifying changes in texture patterns through spectral analysis of digital images. The commonly used method for change detection is image differentiation. This subtraction method requires images to be of same size, scale, and rotation. However, no two images are same in real practices. Thus, image registration is required to align images and to produce change maps. This process is tedious and it is difficult often to achieve a good registered image. But, the change detection task can be readily modeled in frequency domain for texture patterns discrimination and also for quantifying their properties. This paper proposes a novel approach for change detection by transforming digital images into Fourier spectrum. In new coordinate system, 1-D signature functions can be drawn which facilitates easy comparison of textures in different directions. The proposed methodology provides useful tools for comparison of inspection history graphically and quantitatively. In practice, expensive sensors are used to detect subtle change in defect patterns. The proposed method can be used to detect any subtle change in defect patterns using digital images at much lower cost.

Aug 1, 2013

By D. R. Reeves

This paper describes the geophysical Jogging of coal that is being carried out for the National Coal Board in the United Kingdom. An explanation of the technique is given and results are presented showing estimations of seam thickness to within ±0.5 in. and ash content to accuracies of ±2.5 per cent. The basic method of interpretation is outlined and some conclusions regarding the conditions of roof and floor material which may be deduced from the logs are explained. An indication of future developments in this field, including the identification of coal type and moisture content, is given.

Jan 1, 1971

By R. M. Graves, C. B. McKenzie, D. Barbour, D. W. Desnoyers

"Abstract -The prospective Tulks volcanic belt hosts five significant massive sulfide deposits, Tulks Prospect, Tulks East, Jack's Pond, Daniel's Pond and Victoria Mine, as well as numerous showings and indications throughout its 70 km outcrop length. Regionally, the 498 Ma sequence consists dominantly of felsic pyroclastic rocks and flows with interbedded mafic volcanic units and fine­ grained sediments, commonly graphitic. Contemporaneous granitoid rocks occur in the south half of the belt. Rocks usually display a strong NE-SW, steeply dipping, penetrative foliation and other shear-related high-strain fabrics. Facing directions are normally northwest, although there is local evidence of folding. Sulfide bodies and their alteration systems are deformed and shape-modified in the style of ambient strain.The Tulks, Tulks East and Jack's Pond prospects appear to occupy a similar stratigraphic level, on or near the contact between a thick felsic pile and an overlying broad, conductive package of graphitic sedimentary rocks. AU are pyritic deposits with well-developed footwall alteration systems. The Tulks prospect comprises four polymetallic lenses totalling 750 000 t. Three lenses constituting more than 6 000 000 t of sulfide mineralization are indicated at Tulks East but only the 210 000 t ""B"" lens contains significant base metals. Jack's Pond consists of a very extensive, zoned alteration complex in which four lenses of massive to semi-rnassive pyrite + chalcopyrite are known.The central part of the system, characterized by Mg chlorite and carbonate, is enveloped by pervasive sericitization and capped by intensely silicified and pyritized volcanics. The sulfide lenses are interpreted as part of the footwall zone and are beneath that part of the system most likely to host polymetallic massive sulfides.Daniel's Pond differs from the other prospects in such fundamental ways as metal content, associated alteration and structural setting. The deposit comprises strongly tectonized, Ag-rich, Zn-Pb mineralization distinguished by a pronounced Ba-As-Sb signature. Mineralization is confined to a narrow, north-south high-strain zone which separates unstrained mafic volcanic rocks to the east from well-foliated felsic rocks. The deposit Jacks an extensive alteration halo and at its north end is associated with a lens of barren, undeformed massive pyrite.The Victoria Mine deposit, the most cupriferous of the five, is related to a moderately dipping structure that separates well-foliated Tulks volcanic rocks from an overlying, Jess deformed volcanic­ sedimentary sequence that may be as young as 462 Ma. The structure is also the locus of black chlorite, dolomite and quartz alteration. Structurally remobilized precursor sulfide mineralization is one possible source for the deposit."

Jan 1, 1993

By P. L. Claessens, S. Belisle, C. Bowen

"Use of zinc shot feed is a well-established procedure among North American electro-galvanizers. This form of zinc is easy to handle and relatively inexpensive when compared with zinc oxide. This paper reports results on the kinetics of zinc shot dissolution in traditional pure zinc solutions and in electrolytes used for the plating of nickel/zinc alloys. Despite the cementation of minor amounts of nickel in the latter solution, acceptable dissolution rates of the zinc shot can be achieved through proper adjustment of the solution velocity. Under these conditions, the nickel shell produced by cementation is continuously abraded, exposing the underlying zinc.IntroductionThe use of insoluble, noble metal-containing anodes rather than soluble zinc anodes for the operation of high current density electro-galvanizing lines has gained almost universal acceptance. Two major reasons for this trend are:• improved control of the process by virtue of constant inter-electrode distance; and• increased productivity because the operation of the lines does not require the relatively frequent interruptions for replacement of consumed anodes .The results of the principal anode and cathode reactions are, respectively, depletion of the zinc content of the electrolyte and the increase on its acidity;"

Jan 1, 1991

By Jose R. Hernandez-Aguilar

"This paper revisits data from previous studies (Hernandez-Aguilar, 2010, 2011) to better understand the link between metallurgical performance and bubble size (Db) in the collection (pulp) zone of full-scale flotation systems. To obtain conclusive evidence exclusively related to the collection zone, the experiments were designed in those studies to control both the bubble generation method and the influence of the froth zone on the overall metallurgical performance in industrial and pilot-scale flotation columns. The results showed that generating small (1 mm) bubbles had a significantly higher beneficial effect on the recovery of coarse (> 75 µm) particles compared to the effect on fine (< 16 µm) particles. It was observed that, under certain practical conditions, the recovery of liberated coarse particles was close to zero, but could be recovered almost completely by reducing bubble size. The evidence revealed an apparent inconsistency of the so-called “k–PSb” model: at constant froth recovery, increasing Sb did not always result in higher recovery, as the model predicts. Overall, the evidence showed that it was not the Sb but the bubble size that proved to be a more reliable link to metallurgical performance. Only under highly suboptimal bubble size conditions (Db = 3 mm) did the froth zone seem to play a role, possibly reflecting an effect of pulp-zone bubble size on froth stability. However, for the most part, both the bubble generation method and the froth zone played inconsequential roles. An empirical model that better describes the kinetics of particle collection is proposed.INTRODUCTIONStudies showing the link between metallurgical performance and the interactions of bubbles and particles in the collection (pulp) zone of industrial flotation systems are scarce. A common belief among a number of mineral processing practitioners considers that “small” bubbles are favourable to recover “small” particles and that, conversely, “larger” bubbles are more efficient at floating “coarse” particles. However, perceptions like this are often substantiated by anecdotal evidence rather than by rigorous data analysis. What is the optimum bubble size for a particular case, how operating conditions can be adjusted to control a target bubble size, and whether the bubble size needs to be changed in the first place to optimize the operation of a flotation plant are questions that usually remain without solid answers.The studies reported by Hernandez-Aguilar (2010, 2011) were, in part, performed to test the effect of bubble size on flotation response and, thus, help address some of the above questions. The focus of the studies was to optimize the metallurgical grade-recovery performance of the Cu-Mo separation plant at Teck’s Highland Valley Copper mine (HVC). The outcome was compelling and significantly valuable: consolidated production data showed that in 2008 – the year when the recommendations from the studies started to be implemented – the Mo plant recovery was 89%, and gradually increased to 92% and 94% in 2009 and 2010, respectively, along with an increase in Mo concentrate grade. (Note: these production figures were not included in the publications quoted above; however, they were shown during an oral presentation at the 43rd Annual Meeting of the Canadian Mineral Processors in 2011.)"

Jan 1, 2016

By L. Dubourg, H. Habibi, D. Rasmussen

The combination of laser welding with Gas Metal Arc Welding (GMA W) forms the hybrid laser-OMA W welding. This process is an attractive tool with a high potential in welding lightweight structures, especially for aluminum alloys. For five years, this technology has increasingly attracted interest in both, industry (aeronautics, automobile, metal industries producing large structures) and academia (universities and research centers). Hybrid laser-OMA W welding process is generally accepted for its robustness, efficiency and flexibility. Coupling of a deep-penetrating laser beam with the heat and molten metal feeding of GMA W significantly expands the original welding application range of lasers. Its main advantages compared to the two individual components are deep and stable weld penetration, gap-bridging ability improvement, low distortion and easy filler metal addition. Hybrid welding allows a much wider groove tolerance compared to laser welding, especially for aluminum welding. Moreover, the reduction in distortion decreases the post-welding rectification needed and makes the assembly easier. In addition, if metallurgical factors are critical, the weld composition can be balanced with filler metal, decreasing the hot cracking susceptibility of some aluminum alloys. The combination of these two welding processes can also improve the weld bead shape quality (including the elimination of undercut), possibly reduce the porosity and increase the welding speed. This article reviews the recent works about the laser-OMA W hybrid welding of aluminum alloys. After a brief presentation on the interaction mechanisms between a laser beam and an electric arc, the paper depicts the typical welding parameters and experimental methods along with their characteristics.

Jan 1, 2006

By A. J. Stapleton

"This paper gives a brief description of the occurrence and development of the Needle Mountain mine at Gaspe Copper Mines, Limited and describes the trackless mining equipment used in this highly mechanized underground operation.Maintenance of the trackless equipment is considered in detail, with particular emphasis on scheduling and control, examination and inspection. All maintenance is carried out in an underground garage, and the facilities for maintenance and field repairs are also described. Maintenance costs are given for various units and the figures for different types of loading and haulage units are compared to support the trend toward larger units and the increasing use of rubber-tired loaders."

Jan 1, 1969

By Boyd Davis, Brook Zaback

"Among the first published papers from Prof. Torstein Utigard was work on imaging the aluminum electrolysis process and in-situ measurements of aluminum in cryolite melts. He and Prof. Jim Toguri used an x-ray radiographic technique to measure interfacial tension of aluminum drops. Publications using this equipment for aluminum electrolysis spanned from 1985 to 2006. As well, other methods were used to better understand electrolysis in molten salts, including hot-stage microscopy, direct observations from above the bath and water modeling techniques. For chloride systems (for magnesium and lithium), it is possible to see side-on the electrolysis using a quartz cell. In honour of Prof. Utigard’s contribution to this field, this paper presents a summary of work on visualization of molten salt electrolysis, including work done at the authors’ labs and others around the world. The paper will summarize key findings and their possible impact on molten salt electrolysis."

Jan 1, 2015

By A. Fahr, T. Byczkowski, M. Genest, C. Mandache

"Layered aluminum structures assembled with rivets are often found in aircraft fuselage. These structures are exposed to various mechanical loads and a range of environmental conditions that contribute to their ""aging"". The rivet holes are the source of stress concentrations and the location of crack nucleation and growth. Detection and sizing of second and third layer cracks under fasteners represent a major challenge for non-destructive evaluation (NDE) technicians. Electromagnetic methods are currently the most feasible NDE techniques that are capable of successfully inspecting such structures. However, different probe lift-offs, due to protruding rivets and paint coatings, or interlayer separations, due to sealant or air gaps, pose difficulties in detecting and sizing cracks. In addition, the use of conventional eddy current technique is limited due to the inverse relationship between the probe spatial resolution and its field penetrability. In this paper, we present an alternative approach that overcomes the previously mentioned shortcomings by using pulsed eddy current excitation and magnetoresistive sensor pick-up. Various signal manipulations are employed for defect detection and quantification."

Jan 1, 2006

By M. H. Fathi

The aim of this work was to prepare the metallic coatings on 316L stainless steel dental implant and evaluate the corrosion characteristics and thus the biocompatibility of the uncoated and metallic coated dental implants and comparison of the effect of the type of coatings on biocompatibility. Three types of metallic coatings including Tantalum, Niobium, and Titanium coatings were made using physical vapor deposition process on 316L stainless steel dental implant. Structural characterization techniques including; X-ray Diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Analysis were utilized to investigate the microstructure and morphology of the coatings. Electrochemical potentiodynamic tests were performed in two types of physiological solutions at 37±1 °C in order to determine and compare the corrosion characteristics. All three types of metallic coatings had a positive effect on improvement of the corrosion behavior so that the coatings could increase the corrosion resistance of 316L stainless steel and this trend was independent to the type of physiological environment. Biocompatible metallic coatings could decrease the corrosion current density that is a distinct advantage for prevention of ion release. This can improve the biocompatibility of the implant and, consequently prevention of tissue damages, inflammation and irritation and obtained desirable histopathological response.

Jan 1, 2007

By E. I. Robinsky

"In light of the recurring spills and failures of conventional tailings disposal pond dams, a brief review of the Thickened Tailings Disposal (TTD) system is presented. It is shown that by the process of thickening the tailings to a heavy slurry prior to disposal, it is possible to create a self-supporting deposit of tailings and to eliminate the typical superimposed settling pond. These features, together with the ability to reclaim the disposal area even as mining continues, preclude an ecological disaster. IntroductionMine tailings spills are really not such rare occurrences. They have been happening on many continents, in many countries. Neither Canada nor the United States have been spared. In Ontario, the most recent spill occurred at a closed-down tailings disposal area in Matachewan, in 1991.Such continuing disasters could be avoided if a different approach were taken to the disposal of tailings wastes. The recent failures at the Los Frailes mine in Spain, the Omai mine in Guyana, and the Marcopper mine in the Philippines, will hopefully shake up the industry to consider other methods of disposal. The reason why the failure of a conventional tailings disposal dam is so environmentally disastrous is not the dam itself, but the fact that the dam retains a mass of very loose unconsolidated tailings and a great deal of water, or process fluid1. If the dam fails, the contents liquefy completely as they flow through the breach. In this liquid state, they can flow many miles downstream. If the dam itself were built of tailings material, as is often the case, it too would liquefy and join the flow.The reason the material is so loose in the first place is that it has been discharged into a pond filled with water. The tailings particles drift down through the water, their weight reduced by 50% due to buoyancy, to form a loose structure, like a “house of cards,” or lakebottom mud. It doesn’t take much of a shock to collapse the material into a liquefied state."

Jan 1, 1999

By Richard E. Barrett

SOME YEARS AGO I was associated with a mining operation which, because of its isolated location, burned wood for heating purposes. Year after year the tractors and tucks hauled the cordwood in from the edge of the ever-growing clearing. Each year the cartage costs became greater. The degree to which transportation distances affect the economics of fuels obviously varies with many factors, but the main criterion is the amount of heat a unit weight of the fuel will produce. For in-stance, wood is limited in most cases to a haulage distance of a few miles. Coal can be shipped hundreds of miles, whereas petroleum and gas ?can be transported thousands of miles. The world is now on the brink of having a new fuel -uranium. It has the virtue of being so concentrated that transportation costs can, for all practical purposes, be disregarded.

Jan 1, 1958

By David Eichenberg

A154S A154N After 3 Years of Mining ?Current mining Level A154S 280RL ?110 Vertical metres of A154S ?Current mining Level A154N 300RL ?100 Vertical metres of A154N ?Variations in Kimberlite Volume ?Ore Types and Plant Production

May 1, 2006

By Yi-xin Zhoa

The characteristics of coal bumps are analyzed based on the microseismic data from No.8935 workface in Xinzhouyao coal mine, Datong Mining Group. The geology of this workface is characterized by the thick sandstone roof and coal seam, both with relative higher stiffness and strength. In order to investigate the mechanism and precursors of coal bumps occurred in No.8935 workface, the locations of microseismic, the relationship of microseismic energy and frequency and the spectrum of microseismic signals are analyzed. The result shows that the coal bumps in No.8935 workface were mainly induced by the seismic caused by roof failure. The coal pillar near the goaf is more easily to bump. The statistics results indicate that the coal bumps were mainly occurred in the gate road near the pillar, less than 50m ahead of mining face and located in the hard roof adjacent with coal seam. Moreover, the frequency, energy, b-value and frequency spectrogram of microseismic events were found to decrease before coal bumps. It was found that the frequencies of the microseismic events before coal bumps mainly concentrate upon 5~60Hz. The sudden decreasing of frequency and increasing of amplitude of microseismic events can be regarded as a precursor of coal bumps.

Aug 1, 2013

HIGH LAKE PROPERTY --HISTORYHISTORY -19501950??s ??Kennarctic Exploration discovers Exploration sulphides (A/B & (D Zones) at High Lake during helicopter reconnaissance exploration program.- -1991 93 Aber signs agreement to earn in to the High Lake Property from Kennecott. 63 holes drilled, primarily testing the known deposits. -2001 Wolfden purchases 100% interest in High Lake from Kennecott and Aber -2002 Wolfden performs helicopter borne TEM Survey over the High Lake Greenstone Belt. -2003 West Zone was discovered following UTEM & Gravity Surveys (performed by Teck Cominco ) over an airborne anomaly approx. 1km west of the known deposits. -2004 Wolfden awarded Bill Dennis Prospector of the Year

May 1, 2006

By C. H. Bertoni

"The Superior Province of the Canadian Shield is the largest gold producing area within Archean greenstone rocks in the world, with total production of over 140 million ounces of gold. One hundred and fifty-five mines have individually produced more than 8,000 ounces, although only a relatively limited number of deposits (33) produced more than one million ounces of gold. The output from these 33 deposits accounts, however, for 85% of total gold production. The majority of grades (68%) ranges between 0.10 and 0.30 ounce per ton, and there is no linear relationship between grade and tonnage.Development of new gold mines reflects the history of gold prices. However, the response to the latest increase in gold prices was not as marked. It is concluded that gold deposits are becoming increasingly more difficult to find and new exploration techniques are urgently required.IntroductionWith most of its production coming out of the Superior Province, the Canadian Shield is the largest producer of gold from Archean greenstone rock s in the world. In total gold production, the Superior Province is surpassed only by the paleo-placers of Witwatersrand and the placers of the USSR (Anhaeusser, 1976). There has been no attempt so far to compile the historical production of the Province as a whole in a single document. The aim of this work is to fill this gap, not only for the convenience of having a complete list of gold producers, but, more importantly, as a basis on which to study the tonnage and grade characteristics of these deposits."

Jan 1, 1983

By Kirsten Corin, Margreth Tadie, Cyril O’Connor, Jenny Wiese, Wonder Chimonyo

"Relating flotation performance to the electrochemical characteristics of a pulp remains a complex issue both in fundamental research and in practice. For example, in the case of thiol collectors different Eh values can result in the formation of the dimer or the metal thiolate which may or may not enhance the hydrophobicity of the mineral. Reducing or oxidizing conditions in a flotation system, viz. changing the Eh value, are usually manipulated to achieve an optimum flotation response by the control of pH and dissolved oxygen levels in the system. It is also possible to vary the potential by the addition of modifiers such as sodium hydrosulphide (NaHS), sodium hypochlorite (NaClO) or hydrogen peroxide (H2O2). The objective of the present study was to investigate the effect of the addition of the oxidising agents, NaClO and H2O2, on valuable mineral recoveries and grades in the flotation of sulphides from a PGM bearing Merensky ore. Batch flotation tests were conducted at pH 9.2, the natural pH of the system, in the absence and presence of a xanthate collector and Eh modifiers, viz. NaClO or H2O2. Most importantly in this way it was possible to vary Eh at constant pH and DO levels. The results indicate that in the absence or presence of xanthate the addition of H2O2 reduced both the recovery and grade of copper and nickel. In the absence of xanthate, the addition of NaClO improved the recovery of copper slightly and both the recovery and grade of nickel significantly, but in the presence of xanthate NaClO addition resulted in unchanged copper recovery and grade, but those of nickel were reduced. Based on anecdotal evidence that the addition of trace amounts of a potential modifier could improve flotation performance further tests were conducted the results of which suggest improved flotation performance.INTRODUCTIONIn the Merensky Reef, platinum group minerals (PGM) are commonly associated with base metal sulphides (BMS) and this has an effect on the way in which these minerals can be concentrated by flotation (Vermaak, Venter & Pistorius, 2004; Wiese, Harris & Bradshaw, 2005; Schouwstra, Kinloch & Lee., 2000). A major problem stemming from this association has been reported to be the loss of valuable minerals (PGM) associated with the loss of BMS (Wiese et al., 2005) during flotation. Shackleton (2007) suggested that PGMs behave in a similar manner to sulphides during flotation. Therefore, in order to recover the PGM, base metals are targeted. There is thus a need to investigate ways to improve the flotation performance of the sulphide minerals. The electrochemistry of the flotation of sulphide minerals has been studied for over half a century and there is consensus that sulphide minerals float only under a suitable redox environment (Heyes & Trahar 1979). This implies that reducing and oxidizing conditions during flotation of ores such as Merensky can be manipulated/varied to achieve an optimum flotation response.During flotation, sulphide minerals interact with thiol collectors in an electrochemical reaction to form hydrophobic species at the mineral surface (Finkelstein & Goold 1972; Rand & Woods 1984). The sulphide minerals are semiconductors and their interaction with collectors involves transfer of electrons. As such, a potential difference results which is responsible for driving electrons between reacting species (Fuerstenau, Jameson & Yoon, 2007). The magnitude of the potential difference affects the relative energies of charge carriers (electrons) at the mineral/solution interface hence controlling the direction and rate of charge transfer or rate of reaction (Bard & Faulkner, 2001). In a mixed mineral system the mineral/solution interface potentials account for the mixed potential which is critical to the process of flotation (Chander, 2003; Woods, 2003)."

Jan 1, 2016

By N. M. Steven, J. M. Moore, J. L. Kuyper

Abstract - Mineral exploration and research has led to the identification of four types of tungsten mineralization in the NE-trending, largely ensialic, inland branch of the late Proterozoic/early Paleozoic Pan-African Damara Orogen. The mineralization (mainly scheelite) occurs in a terrane (the Central Zone) that is characterized by multiple deformation, greenschist/amphibolite-facies metamorphism and numerous peraluminous S-type granitic and pegmatitic intrusions. The four major types of scheelite mineralization are (in ascending stratigraphie order of host rock): (1) thin (5 cm to 2 meter) quartz+ plagioclase+ diopside ± scapolite cale-silicate granofels with finely disseminated scheelite (scheelite-bearing granofels; SBG) developed as discontinuous intercalations within the cale-silicate rocks of the Khan, Spes Bona, Oberwasser and Kuiseb Formations (Nosib and Swakop Groups); garnet+ pyroxene ± vesuvianite + scheelite ± fluorite replacement skarns hosted by Okawayo, Karibib and lower Kuiseb Formation marbles in the aureoles of late tectonic, unmineralized leucogranites; metaturbidite-hosted scheelite- (and possibly wolfrarnite-) bearing tourmalinites, both stratiform and crosscutting, in the Kuiseb Formation located in the &apos;cleavage fronts&apos; of late tectonic granitoids; scheelite-bearing vesuvianite +quartz+ garnet skarnoid rocks (several hundred meters in length) in the calcareous metaturbidites of the upper Kuiseb Formation. These scheelite occurrences were discovered by the follow-up of a large number of tungsten anomalies located during a regional stream sediment sampling program. Detailed mapping, ultra-violet surveys and rock sampling proved to be the most effective surface exploration techniques for locating mineralization; soil sampling and geophysics were of almost no use. The largest, continuous scheelite-bearing skarn of economic interest, Otjua, has a drill-indicated reserve of 250 000 tonnes at 0.53 wt% W03 and 8 wt% CaF2.

Jan 1, 1994