Search Documents

By W. J. Birch, M. Kirke

Despite increasing competition from mechanical methods of tunnelling, the drill and blast method is often still the most viable method of excavating tunnels in strong and abrasive rock. To advance a tunnel using drill and blast, explosives are loaded into boreholes in the rock and detonated according to a prearranged sequence. On detonation of the explosive, the rock is fractured and displaced from its original position, leaving behind the desired void. Among the secondary effects of a tunnel blast are ground vibrations caused by elastic disturbances that propagate away from the blasted tunnel face. The possibility that such ground vibrations may cause permanent damage to property and substantial nuisance has generated significant opposition to the use of drill and blast, particularly in urban areas. It is therefore essential that the blasting engineer is able to predict Peak Particle Velocity (PPV) vibration levels at locations in the vicinity of the blast site. Such predictive capability enables the engineer to design blasts so as to ensure that ground vibrations can be kept within acceptable levels. The objective of this project was to analyse data obtained from the ground vibration monitoring program undertaken during the drill and blast excavation of a hard rock tunnel in Central England. Seismograph recordings of tunnel blasts contain a vast amount of information that cannot possibly be expressed using a single PPV value. The main focus of the study was to investigate whether predictive capability could be improved by using scaled distance models derived for selected PPV components relating to specific detonator timings in a given tunnel round. This study has established a method of analysis that can unlock this information for predictive purposes. By permitting the extraction of sub-event Peak Particle Velocity (PPV) values and allowing Scaled Distance (SD) models to be derived for individual period numbers or groups of period numbers, the method has the potential to vastly improve PPV prediction from tunnel blasting. The method established could also help diagnose blasting problems and help target blast design modifications, resulting in improved efficiency and excavation rates.

Jan 1, 2005

By A Goldstone, T Maton

The Golden Cross Mine is located on the North Island of New Zealand, at the base of the Coromandel Peninsula, approximately 8 km northwest of Waihi. The project is operated as a Joint Venture with Coeur Gold New Zealand holding 800/0 and Viking Mining Limited with a 20% interest. The past open-pit and underground gold and silver producer has been in the reclamation phase of the operation for approximately 2.5 years and is now nearing completion. Although rehabilitation of the site is a regulatory requirement, the Closure Plan has been enhanced by the ongoing commitment of the Joint Venture to establish a sustainable land use for the site by commissioning engineered facilities designed to last for perpetuity. The Joint Venture identified six significant design features that were key to successful rehabilitation. These were the controlled placement of acid generating waste rock into engineered disposal sites; the design and placement of sealing layers over the waste rock disposal sites; the design and construction of diversion drains; the establishment and management of vegetation to protect the oxygen diffusion layer; a partial capping of the tailings to accelerate consolidation adjacent to the tailings dam embankment, and the implementation of a cyanide recovery circuit to recycle cyanide from the tailings prior to disposal. Another key to success for the project involved genuine consultation with all parties participating in the planning, evaluation, and consenting of the closure process at Golden Cross. The local and regulatory community has been widely represented in the Joint Venture's operating and closure plans throughout the history of the mine. Participants include: Regional and District Councillors and staff members, professional peer reviewers, environmental groups, local residents of the valley, and Iwi. This overall commitment to the project has resulted in a world-class rehabilitation program for the first modern metal-mine closure in New Zealand and we believe that collectively, the work done at Golden Cross is helping to set a standard for the success of future programs within the extractive industry.

Jan 1, 2000

By M. M. Poulton

Universities are not immune from the large number of retirements facing the mining industry. Department heads anticipate that we will need to replace all of the senior mining engineering faculty in the U.S. by 2020. Long term studies of Ph.D. completion times and success rates indicate that in Engineering disciplines in the U.S., the ten year completion rate is 65% at best and the four year completion rate is less than 8%. We do not have accurate data on completion rates and times for mining or metallurgical engineering Ph.D. students in the U.S. but students self-report their expected completion times are around 4 years. National data on doctoral students indicate that younger, full time students with sufficient financial support have a higher probability of success in completing their degrees in a timely manner. Students in Eastern U.S. mining engineering programs are on average 32 years old, 85% are full time, and the gap between support and cost of attendance is $5,000 per year. Students in Western U.S. programs are on average 38 years old, 78% are full time, and the financial gap is $8,483. Further, it appears that domestic graduate students are not very geographically mobile. The current demand for new faculty is higher in Western programs but the longer term retirements are higher in Eastern programs. While all Ph.D. students who responded to the 2010 survey indicated an interest in a faculty position at some point in their careers, very few were applying for the open positions. Over the past 35 years for which data could be obtained, the maximum number of Ph.D. students enrolled in mining engineering in the U.S. is 115 with a maximum of 27 degrees granted in one year. On average 89 students are enrolled in doctoral programs in mining engineering in the U.S. with average degree production of 15 Ph.D.s per year.

Jan 1, 2012

Whilst the fossil fuel-based power industry moves towards carbon capture and storage (CCS) or so-called 'geosequestration', the minerals industry should adapt to reap the benefits of the new technology. If CCS becomes viable, the door is open to potential key developments in mineral processing. For example, truly continuous steelmaking could at last be realised using natural or manufactured gas combined with generic melt circulation. Iron ore fines would form a thin molten layer moving countercurrent to the gaseous reductant on one side of a melt circulation loop with efficient post-combustion without deleterious effects of slag accumulation on the other. This eliminates oxygen steelmaking because carbon has no access to the circulating molten iron. Steelmaking merely requires addition of the appropriate low level of carbon and in-line impurities removal to meet product specification. Concerning non-ferrous smelting, nothing short of virtually zero gas emission will be acceptable in the future. For dolomite-hosted Zn/Pb sulfide ores, typified by those in the Carpentaria region of Northern Australia, the way forward proposed is sulfur fixation at the mine site employing the highly exothermic reaction of SO2 with dolomite, followed by encapsulation of sulfated dolomite in fused ore slag. This releases enough energy for direct ore smelting to individual metal products. However, without CCS the strategy would be unacceptable because of greenhouse gas emissions. The scheme is advocated for direct ore smelting at McArthur River. As a result, the environmental problems of disposal of flotation tailings are avoided. Also, highly energy intensive ultra-fine grinding is eliminated, as indeed froth flotation itself, with overall very significant energy savings and exceptionally high increases in metals recovery. Zinc and lead recoveries approaching 99 per cent are predicted to be entirely feasible.

Sep 13, 2010

By G J. Delemontex, N J. Grigg

Pre-concentration of precious metal and base metal ore types is becoming more relevant with the discovery, development and operation of many lower grade deposits around the world. The fluctuations in metal prices expose many mines to risks especially dealing with low and variable ore grades.Pre-concentration, the process of concentrating the valuable metal into a smaller mass yield, effectively results in the introduction of higher feed grades to milling circuits. Gangue Rejection, the removal of lower S.G. waste rock from the circuit not only results in higher downstream grades but also potentially removes harder, non-valuable mineral, providing significant power savings within the circuit. The pre-concentration or ‘gangue rejection’ process offers a number of benefits when considering the treatment of marginal ore deposits, especially if it can be performed at a coarse crush size; these benefits include a reduction of the operating costs and the feed of more metal units to the mill.Gekko Systems has effectively utilized the Inline Pressure Jig (IPJ) to pre-concentrate the valuable metal, achieving high primary recoveries into a range of mass yields resulting in upgrade ratios between 2 and 10 times.This paper explores the benefits of pre-concentrating ‘marginal’ ore deposits prior to the milling circuit; the selective rejection of ore types that may affect either the recovery or comminution process, and also looks into the potential to effectively reduce the ‘cut-off’ grade when considering the mine planning process. Case studies of projects using the IPJ to pre-concentrate and reject gangue are also included.Pre-concentration and gangue rejection provide the potential to develop marginal ore deposits, thus providing higher grades, less gangue and more metal at a lower operating cost to producers.CITATION:Grigg, N J and Delemontex, G J, 2015. The pre-concentration of precious and base metal deposits using the Inline Pressure Jig – higher feed grades and more metal, in Proceedings MetPlant 2015, pp 296–310 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 7, 2015

By C. O. Aksoy, H. Kose, K. Heasley, E. Yalçin

"In Turkey, the growing demand for lignite has resulted in increased lignite production and an emphasis on improving underground recovery. This has resulted in a gradual increase in the application of the retreat longwall mining method and also in the extraction of the safety pillars protecting permanent underground structures (drifts, shafts) in mines prior to their abandonment.Extracting these safety pillars presents a special hazard to mine employees and the stability of the mine. Often subjected to high stresses, the behaviour of these pillars is not always predictable. Special care must be taken to ensure that infrastructure does not collapse prematurely, and that working conditions remain safe. Otherwise the extraction must be halted, and the remaining coal lost.This investigation reports on a study of the stability of safety pillars during the final extraction phase of the Hustas mine in Soma, Turkey.” The model construction was based on mine plans, and material properties were derived from physical properties testing. Observed subsidence effects from other mining events were used to calibrate the overburden lamination thickness.The model results compared well with surface physical disturbance occurring as a result of mining, as well as with conventional longwall stress redistribution theory and underground observations. The study has shown that properly calibrated models can be useful in assessing mine safety during remnant pillar extraction. The LAMODEL results demonstrate the convenience of this easy to use software."

Jan 1, 2004

By Efrem R. Reeves, David C. Byrne

This study was conducted as part of a project involving the evaluation of a new type of noise exposure monitoring paradigm. Laboratory tests were conducted to assess how “nonstandard” dosimeter microphones and microphone po­sitions measured noise levels under different acoustical condi­tions (i.e., diffuse ?eld and direct ?eld). The data presented in this article re?ect measurement differences due to microphone position and mounting/supporting structure only and are not an evaluation of any particular complete dosimeter system. To varying degrees, the results obtained with the dosimeter microphones used in this study differed from the reference results obtained in the unperturbed (subject absent) sound ?eld with a precision (suitable for use in an ANSI Type 1 sound level meter) 1/2 -inch (12.7 mm) measurement microphone. Effects of dosimeter microphone placement in a diffuse ?eld were found to be minor for most of the test microphones/locations, while direct ?eld microphone placement effects were found to be quite large depending on the microphone position and supporting structure, sound source location, and noise spectrum.

By Michael Day, Paul Kos, Scott Brinton

A hydrogeologic characterization and impact analysis was performed for a proposed quarry at the Hitch Rack Ranch located in the Little Turkey Creek watershed southwest of Colorado Springs, Colorado. Continuous multiple channel tubing, nested piezometers, stream flow measurements, and mapping of known seeps were used to define the three-dimensional potentiometric distribution and areas of groundwater recharge and discharge. Water balance considerations, mass balance calculations, and potentiometric response to earth tides and barometric fluctuations confirmed that the granite fracture system in the ridge area of the proposed quarry has an extremely low bulk hydraulic conductivity resulting in minimal groundwater discharge to sustain the baseflow of Little Turkey Creek. The Little Turkey Creek valley forms the major conduit for groundwater flow exiting from the upper part of watershed underlain by granite. This conclusion has significant implications with respect to mine planning to minimize projected impacts to the hydrologic system and preserve this recharge component to downgradient Denver Basin sedimentary deposits.

By Oliver Bowles

Under a cooperative agreement between the Bureau of Mines, the United States Geological Survey, and the United States Bureau of Standards, a study of the stone-quarrying industries of the country was begun in 1914. The results of investigations made have been published from time to time.1 During the World War the Bureau of Mines centered its attention on problems relating to national defense, and detailed studies of stone-quarry problems were not undertaken except for an investigation of labor saving at limestone quarries, reported in Technical Paper 203, which related to a question of military importance. Since the return of peace, the high cost of materials and labor has made more imperative than in prewar times the conduct of investigations for aiding the quarrying industries in every way possible to adopt more economical methods and to utilize the most efficient labor-saving equipment. The publications already issued have had a wide demand, and in the interest of the quarry industries the bureau proposes to issue additions to the series as rapidly as funds are available. In an endeavor to promote economy and the reduction of waste in the slate industry, a study of slate quarrying was begun in 1920 and covered a period of about two years. Sixty-five active quarries were visited, and a detailed study made of all problems bearing on their successful operation. Field study was supplemented by a study of all information available in books or published articles on slate quarrying.

Jan 1, 1922

The Bureau of Mines in the Department of the Interior is increasingly concerned with the safety and health of personnel engaged in coal-mining operations, particularly below ground. The Bureau is also concerned with improving the utilization of domestic mineral resources, and reducing the environmental impact of mineral operations. One obvious way to improve safety and minimize health hazards would be to eliminate coal mining entirely by bringing the energy value of the coal to the surface in some other way, such as by partially burning it underground to form combustible gases and bringing these gases to the surface, where their energy content can be put to use. This technique might also improve the utilization of the coal resource. ? Accordingly, the Bureau of Mines, interested in re-evaluating underground coal gasification technology in terms of current and expected conditions in the United States, requested Arthur D. Little, Inc., (ADL) to appraise the technology to determine: ? Whether the current (1971) state of the technology offers a technically feasible method for gasifying coal underground that is applicable to the reserves of bituminous and lower rank coals in the United States. ? Whether a program of research and further development of the technology could ultimately make it a technically feasible alternative to current open-pit and underground coal mining operations. ? What the nature and cost of further research and development work in the technology should be.

Jan 1, 1971

By T. Mudder, R. Cellan, R. Waterland, J. Whitlock, B. N. Nelson

The effectiveness of anaerobic in-situ biological treatment for the immobilization of selenium, molybdenum, and uranium in an alluvial aquifer was examined using long-term column tests. A series of organic substrate and nutrient combinations were tested to determine removal effectiveness, optimum supplement concentrations and ratios. Final column testing was conducted to determine the chemical stability of the treatment by-products/treatment compounds by dosing the columns continuously with elevated redox untreated alluvial groundwater.

Jan 1, 2002

By D. D. Southworth

In 1987, the Bureau of Mines initiated a mineral assessment of the 5.7 million-acre Valdez Creek Mining District (VCMD). Following a literature search and interviews with persons knowledgeable about deposits within the district, limited on-site field visits were made to various deposits. Present within the district are the industrial minerals limestone, argillite, granite, basalt, perlite, zeolite, and sand and gravel. At least six limestone deposits of potentially economic size and grade are known to exist within the district. Adjacent to the Parks Highway and marginal to the district, a limestone deposit is currently being mined as a source of agricultural lime. A perlite occurrence near Yacko Creek was evaluated but proved not to be of industrial grade. The sand-and-gravel resources of the district are vast, but high silt content renders many of the glacial deposits unsuitable for use in construction applications.

Jan 1, 2011

By A. Roca, G. Ríos, I. Ruíz, M. Cruells

Flash Smelting Furnace (FSF) hot dust-laden is cooled in a waste heat boiler (WHB) and then dedusted in electrostatic precipitators (ESP’s) before being treated, together with the Peirce Smith Converters off-gases, in the sulfuric acid plants for SO2 removal. FSF dust is sulfated by SO2 and O2 in the WHB. Typically, 70% of the dust from the FSF drops in the WHB while the remainder is caught in the ESPs. The collected dust is recycled to the FSF for Cu recovery. Some smelters have developed hydrometallurgical treatments to recover Cu from the dust; impurities, such as As and Bi, are bled as leach plant residues. This paper presents a study (laboratory scale), of leaching the FSF dust, generated in Atlantic Copper Smelter using the weak acid bleed from the gas scrubbing/cooling section (GSCS) of sulfuric acid plants. Leaching was performed with 0.5 mol L-1 sulfuric acid concentration, 60ºC, and a solid/liquid ratio 1/3. After leaching, H2O2 was used for arsenic and iron oxidation. pH was adjusted for precipitation of arsenic and iron as scorodite or as scorodite and arsenical jarosite. The precipitation was carried out at 95ºC during 3-6 h. Liquids after precipitation are suitable for subsequent treatments of electrolysis. INTRODUCTION The copper smelter dusts are usually recirculated totally or partially to the flash furnace. This practice increases the amount of impurities feeding the furnace. Some authors have developed processes for treatment of these materials for copper and zinc recovery and for arsenic, antimony and bismuth inertization. The processes for the treatment of copper smelter dusts can be pyrometallurgical (Yu, 1987; Carter, Vance, Aldridge, Zaw, & Khoe, 1994; Fu, Jiang &Wang, 2000), hydrometallurgical, or mixed processes (Yin et al, 1992; Mulale, Mwema, & Mashala, 1999; Gorai, Jana, & Khan, 2002). Hydrometallurgical processes have been extensively studied and, in some cases, applied to an industrial scale. The most important chemical reagent proposed for leaching the dusts has been sulfuric acid (Roman-Moguel, Plascencia, Pérez, & Garcia, 1995; Gabb, & Evans, 1997; Larouche, 2001; Morales, Cruells, Roca, & Bergó, 2010; Cáceres, Cruells, Morales, & Roca, 2012; Ecometales, 2013; Yang, Fu, Liu, Chen, & Zhang, 2017). Processes developed in alkaline media, and in some cases with the presence of sulfide, have also been carried out (Gabler, & Jones, 1988; Morales, Hevia, & Cifuentes, 2009; Alguacil, Garcia-Diaz, Lopez, Rodriguez, & Alonso, 2013), as well as by using a bioleaching process (Massinaie, Oliazadeh, & Seyed Bagheri, 2006; Bakhtiari, Atashi, Zivdar, Seyedbagheri, & Fazaelipoor, 2011).

Jan 1, 2019

By A. Dadgar

The adsorption kinetics of AuBr4 on Dowex ® -21K ion-exchange resin were studied and found to be independent of the initial gold, bromine, and base metals concentrations. A commercially-available undivided hypochlorite generating cell was used to generate bromine from simulated mixed halide (Br-/CI-) solutions. Electrolyses were performed with solutions containing very low Br' ion concentrations. The current efficiencies were 80-90%, and Br- ion utilization was maximized. A detailed economic assessment was made considering the capital and the operating costs for a 1000 mtpd gold ore processing plant. The toxicity and discharge levels of bromide, bromine, and cyanide were compared from a detailed analysis of the published literature data. Comparing bromine vapor with hydrogen cyanide gas for a given length of exposure, the lethal concentration of bromine is about 3 times less than hydrogen cyanide. The toxicity of sodium bromide is similar to that of sodium chloride. Acute poisoning to bromides and chlorides is rare because of their low toxicities. The allowed discharge levels of Br-, Br2, and CN- in fresh water are 250, 0.1, and 0.005 mg dm-3, respectively.

Jan 1, 1992

By Olav Mellgren

Part I. The interaction between potassium ethyl xanthate and lead salts has been studied thermo-chemically. It is shown that ethyl xanthate reacts with lead carbonate, basic carbonate, thiosulfate and sulfate according to principles of simple chemistry, whereas reactions with lead sulfite, metasulfite, basic thiosulfate and hydroxide at high pH are associated with secondary reactions. A new compound "xanthogen thiosulfate" is postulated. Part 11. Adsorption of ethyl xanthate on galena has been studied quantitatively and thennochemi-cally. It is shown that an ion-exchange mechanism governs the adsorption process and that the heat of adsorption of xanthate on galena is equivalent to the heat of reaction of ethyl xanthate with bulk lead salts. It is concluded that the entropy content of the surface "compound" on galena is different from that of a corresponding bulk lead salt. Alkali depression is in part shown to be due to the instability of the xanthate-galena system at high pH and to the formation of basic lead salts. Sulfate and carbonate ions are shown to have a stabilizing effect on the xanthate-galena system. PARTI. THERMOCHEMISTRY OF ETHYL XANTHATE AND OF ITS REACTION WITH LEAD SALTS In the past little attention has been paid to the chemistry of lead xanthate. It is known that xan-thates form slightly soluble compounds with lead and that suspensions of lead xanthates in alkaline solution decompose rather readily.' The solubility of lead ethyl xanthate is of the order of 2.6 x 10-6 moles per 1. At increasing pH the xanthate concentration of a saturated solution contains more xanthate. Thus at pH 11 this xanthate content is about 100-fold larger than at pH 7.1 Xanthates are known to be consumed when added to a suspension of slightly soluble lead salts such as lead sulfate and lead carbonate. It is unknown to what extent this xanthate consumption is due to a simple chemical reaction because, frequently, observations are made which reveal secondary reaction products in such reactions. Thermochemical study of the reaction between xanthate and lead salts offers a means to clarify the significance of these reactions as the enthalpy changes can be accurately predicted from heat of formation of lead salts in pure solution reactions. In the present work the heats of formation of lead ethyl xanthate from potassium ethyl xanthate and lead salts are determined and some thermochemical aspects of xanthate in solution are studied. The results of these investigations are presented in Part I. In Part II the heat of adsorption of ethyl xanthate on galena surfaces is presented. All enthalpy changes were measured directly in a microcalorimeter. Calorimeter: The calorimeter used for measuring enthalpy changes was similar to that used by Redinha and Kitchener2 which was based on a description by Derbyshire and Marshall.3 Other useful references4,5 are listed. A sketch of the calorimeter

Jan 1, 1967

By W. U. Reimold, R. Armstrong, R. G. Charlesworth

For many years rockbursts have plagued the mining industry. Although much research has gone into studying this phenomenon only a small proportion of it has been on the actual source mechanism. A study was recently carried out to compliment the previous work done on the micro-structure of these features and to compare it to the micro-structures seen on shatter cones, from meteorite impacts. Both optical and electron-microscopy were used during the study. Samples were collected from rockburst sites by the CSIR Miningtek Rockburst Investigation Unit, and from the collar of the Vredefort Impact Crater. In the optical-microscopy study, the pinnate fractures observed in previous studies were seen in the shatter cones, through all the material. In the rockburst samples, the fractures were observed only in the quartz grains. Quartz micro-crystals were present in the rockburst samples and appeared to be the product of comminution rather than crystallisation. Cataclasite was present on rockburst and shatter cone fracture surfaces. The observations of the shatter cone surfaces with the scanning electron microscope are in agreement with previous work, including the observed presence of melt features, spherules and spheroidal material. The deformation in the rockburst samples is concentrated in the quartz grains, highly complicated with brittle features like sub-conchoidal structures and step structures present. A quartz spherule was identified on one rockburst sample and rhombic-dodecahedra type micro-crystals were present and seen fracturing off quartz grains. It is clear that the rockburst and shatter cone fracture surfaces are quite different; the shatter cone deformation is equally distributed across the sample and involves plastic-deformation, while the deformation in the rockburst material is concentrated in the quartz grains and, with the exception of spherule formation, is brittle. This study agreed with the current explanation for the formation of the rhombic-dodecahedra, and disproved the possibility of it being coesite or fine-grained meta-chert. Although there is no definite evidence of the mechanism of formation of the spherule, it is believed to be the product of vaporization and condensation, and the presence of this material indicates the extreme conditions under which this event occurred.

Jan 1, 2003

By Mishark Nnabuchi

A heterojunction of PbS - CuS thin film has been grown on glass slides by SGT. The films were annealed for 1hr at temperature of 373K and 423K respectively. The optical properties were characterized using a UNICO UV - 2102 PC Spectrophotometer at normal incidence of light in the wavelength range of 200 - 1000nm. The minimum percentage transmittance was observed to be 34% for sample A and 25% for sample B within the same optical region. The band gap energy was determined from the spectra to be 2.05eV for sample A and 1.85eV for sample B which gave a band shift of 0.20eV. It can thus be concluded that the optical properties of the films within the VIS - UV - NIR can find application in solar thermal technology, particularly as antireflection coating, window materials and as good materials for selective solar cell fabrication.

Jan 1, 2010

Every automatic citizen is an automatic recipient of a miner's right under the present Mining Act (Chapter 195), but this alone does not entitle any automatic citizen to mine for minerals on any land, even his customary group's land. Without complying with requirements of the Mining Act, any automatic citizen who engages in mining solely on the basis of a miner's right would be mining illegally. He would also be engaged in illegal mining if he mines on customary or other non-government land. Even if mining is legally pursued by an automatic citizen, he does not acquire ownership of minerals without first making the required royalty payments to the State.

Jan 1, 1991

The usefulness of laboratory studies - petrology and mineragraphy in the search for, and investigation of, mineral deposits should not be exaggerated, but it should not be overlooked, because such studies will always contribute to an understanding of the geology of the deposits, and can on occasions provide invaluable information not otherwise available. A few examples furnished by the investigations of the Mineragraphic Section of the Commonwealth Scientific and Industrial Research Organisation will show this.Petrology.In the early stages of the investigation of the King Island scheelite deposit, during the war, when the nature of, the deposit was not understood, a series of samples embodying the exposed rock types was submitted to the Mineragrap;hic Section for petrologicalexamination by the Mineral Resources Survey. It was at once apparent to the petrologist that the King Island scheelite ore was a contact metamorphic deposit, in which a series of argillaceous shales, calcareous shales, impure limestones and limestones had beenintensely metamorphosed. The shales had been converted to finegrained biotite and actinolite hornfels, according to their lime content, and the impure limestones to fine-grained diopside hornfels, garnetdiopside hornfels and garnet hornfels (calc-flint), the garnet being the lime variety grossularite. The limestones, however, after being first converted to marbles, had suffered intense pyrometasomatism, involving substitution of immense quantities ,of silica and' iron for lime and carbonate, and had been converted largely to a coarsegrained garnet rock, in which the garnet was the lime-iron variety, andradite. The silica and iron were derived from the mineralising solutions of the adja,cent ,granite. intrusion, responsible for the contact metamorphism, and were accompanied by tungsten and some molybdenum. The tungsten in the presence of so much mobile lime, was precipitated as schecelite, much of it finegrained and enclosed in or intergrown, with the andradite garnet or the quartz interstitial to the garnet.It was apparent that the King Island scheelite deposit, was a perfect example of selective pyrometallomatic replacement in a bedded contact metamorphic deposit. The bedded nature of the original rocks was preserved, and the scheelite was practically limited to the original limestone beds, 'Which had been so much more susceptible to replacement after recrystallization, than the other sediments. The further geological study of the deposit then resolved itself into the task of mapping the folding and faulting of the deposit, with bore cores to provide the stratigraphic sequence, and establish the number of scheelite-bearing beds.A second example is provided by a petrological investigation of the mineral composition and genesis of the talc deposits of the Gumeracha district of South Austral.ia, which was undertaken at the request of the South Australian ,Mines Department, in conjunctionwith mapping of these deposits. The field geologist mapping the deposits was experiencing some difficulty in interpreting the structure...

Jan 1, 1950

Two types of low-sulphidation epithermal mineralisation may be recognised in volcanic terranes. Chalcedonic Silica- Adularia-Illite type mineralisation is most common in rhyolitic terranes, whereas Crystalline Quartz-Illite-(Adularia- Kaolinite) type mineralisation is more typically formed in andesitic terranes. A third type of epithermal mineralisation, the high sulphidation or Vuggy Silica-Alunite- Kaolinite-Illite type, is also common in andesitic terranes. Episodic violent boiling, accompanying hydraulic fracturing and hydrothermal eruptions, characteristic of geothermal systems in rhyolitic terranes, is stressed for the formation of Chalcedonic Silica mineralisation. Such boiling of deeply circulating meteoric groundwater, with some magmatic fluid contribution, provides chalcedonic veining, episodic banding and brecciation textures, adularia stability, bladed calcite, and extreme loss of H2S from the fluid to cause major gold deposition. Crystalline Quartz mineralisation is probably caused by the mixing of shallow acidic groundwater with ascending deep geothermal fluids beneath andesitic strato- volcanoes. The cooling effect, oxidation, and increased acidity, overcomes the dilution effect, and results in quartz deposition, illite (and locally kaolinite) alteration, and precipitation of metals. Extensive formation of base-metal sulphides further enhances gold deposition. Violent boiling is restricted to local structural dilation sites, potentially producing high grade "bonanza" gold mineralisation.

Jan 1, 1991