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By G B. Arehart, J L. Mauk

Quartz veins from the Martha Hill epithermal gold-silver deposit, Waihi, commonly exhibit crustiform banded textures. Visual differences observed between bands are primarily the result of a 1 to 1500 ¦m variation in quartz grain size. Quartz band textures are dominated by anhedral interlocking quartz mosaics, commonly associated with minor adularia and sulphide phases; these textures are interpreted to be products of amorphous silica crystallisation. The occurrence of rhombic adularia suggests that prolonged boiling influenced parent fluids. In contrast, the presence of coarsely crystalline bands, made up of subhedral to euhedral quartz grains, infers primary crystal growth from solution; evidenced by the occurrence of growth-zoned quartz within these bands. There is a narrow range of 3.3ë in d18Oquartz between maximum and minimum isotopic values for the deposit. Significant overlap in d18Oquartz values are observed between the Martha and Welcome lodes. However, statistically significant and commonly systematic differences do occur between individual bands analysed in most samples. Temperature fluctuations may be the dominant factor responsible for observed inter-band variation.

Jan 1, 1995

By M. M. Foss

Geophysical methods are gaining acceptance in the evaluation of coal mine ground control condition. The use of in-seam seismic investigations has contributed significantly to the body of information concerning ground control feature identification and analysis. Seismic methods have been used successfully in locating voids, faults, fracture zones, roof and floor rock interfaces, and more recently in characterizing in-seam stress distribution. Seismic tomography is an effective tool in data interpretation for several of these applications, but as is the case with other engineering application of geophysical techniques, there are limits as to how much substantive information can be interpreted from a given data set. This paper discusses some of the applications of in-seam seismic geophysical tomography, and the limits to which the transformation from raw data to information should be taken.

Jan 1, 1995

By J. A. Pontius

The Cresson Deposit is located in central Colorado within the historic Cripple Creek Mining District. The deposit has moved from its initial discovery in 1990 to full production in less than five years (current reserve nearly two million ounces). This accomplishment required a great deal of cooperative teamwork between the exploration, development, permitting and corporate groups. Nowhere was this cooperation more evident than in the construction of the geologic block model. The detailed modeling of gold and its metallurgical characteristics formed the foundation upon which critical financial and design decisions were based.

Jan 1, 1995

Risk Management has been applied relatively slowly in the mining industry. Except for the risk concept application in financial considerations, the application of Risk Management in safety management has been far from satisfactory. When applied it was treated in a global occupational safety and health sense. Regardless of how much the mining industry has progressed over the years it is still, in many respects, `state-of-the-art' business. The safety aspects of mining are well known and yet little understood by the public. Regardless of what has been achieved so far and how much effort has been put into it, mining is regarded as an unsafe and somehow rude business. Safety records of the mining industry vary from State-to-State. Latest mining related disasters in PNG and Queensland and some other fatal accidents support this public perception. They purport a need for change in managing safety in the mining industry. The latest mining fatalities have raised the issue: What must be done to improve safety standards? Duty of care, risk management and system engineering concepts can provide some answers. Risk Management principles which have been advocated for some time provide many answers and explanations and can make safety management more constructive and workable. What has been missing so far is that this concept has neither been applied nor has been modified for its practical application and purpose on a larger scale. A risk management approach to the management of safety and health in the mining industry is addressed, herein. This approach does not attempt to provide the solution. It does, however, provide a basic understanding of what Risk and Risk Management are all about. Rational management of risk is addressed in the life cycle and system contexts. A system of continuous improvement is applied. There is always a chain of events, outcome, exposure, consequence(s), and consequence(s) value(s). It means that development of an event takes place in time and space. Dynamic circumstances have been created in or within the system. It is a decision-making process designed to provide a methodology which is directed not toward a mathematical model but toward easy use and application in dynamic working environment, by decision-makers who can be anybody from either a risk taker or a risk creator. The emphasis is placed not only on arriving at the best practical, possible and fair decision but also on structured and systematic acquisition of knowledge about the system, its hazards and associated risks, hence increasing the decision maker's ability to manage the decision-making process related to the management of risk.

Jan 1, 1995

A back-propagation model, which is typical of the models used in the science of artificial neural networks, was applied to the prediction of gossans from the southeast area of Habei Province in China. A success rate of 100 per cent was achieved. The results show that the neural-network approach is good, and that it can be used effectively in the prediction of multi metallic deposits.

Jan 1, 1995

By Jorge Rubio, Luis Valderrama, Carlos Pérez

This work describes the effect of the degree of energy transferred to the pulp, during the conditioning stage, on gold flotation fines recovery, grade and kinetics, with three types of frother (Dowfroth 250, pine oil and MIBC) and amyl xanthate as collector. Best results show an increase in 24% recovery and 50% in concentrate grade, depending on the intensity of conditioning and type of frother (better with Dowfroth 250). For low or intermediate energies (0.5-1.5 kWhlm3 pulp), the fine particles adhere to larger ones, increasing the recovery due to a mixture of carrier (pyrite, in this case) and autogeneous carrier flotation and at higher shear (2-3 kWhlm3 pulp), gold fine particles aggregate themselves. These phenomena are demonstrated by measurements of flotation rate, true flotation (flotation by actual particle-bubble adhesion), and by the amount of entrained particles. Alternatives for this type of pulp conditioning and mechanisms involved are discussed.

Jan 1, 1995

By Kang-In Rhee

A series of processes to recover the gold from electronic scrap which contains initially about 200-600 ppm Au have been developed. First, mechanical beneficiation including shredding, crushing and screening was employed. Results showed that 99 percent of gold component leaves in the fraction of under 1 mm of crushed scrap and its concentration was enriched to about 800 ppm without incineration. The scrap was leached in 50% aqua regia solution and gold was dissolved completely at 60°C within 2 hours. Other valuable metals such as silver, copper, nickel and iron were also dissolved. This resulting solution was boiled to remove nitrous compounds in the leachate. Finally, a newly designed electrolyzer was tested to recover the gold metal. More than 99% of gold and silver were recovered within an hour in electrowinning process.

Jan 1, 1995

By John E. Hamak

The identified helium resources of the United States were estimated by the U.S. Bureau of Mines at 617 Bcf, as of December 31, 1992. This includes 285 Bef of demonstrated reserves, 85 Bcf of demonstrated marginal reserves, and 37 Bcf of demonstrated sub-economic resources. The identified resources also include 166 Bcf of helium in inferred reserves and inferred marginal reserves and 44 Bcf in inferred sub-economic resources. The identified helium resources contained on Federal lands are approximately 172 Bcf, including 32 Bcf in underground storage in the Cliffside Gasfield near Amarillo, TX. Undiscovered helium resources in the United States are estimated at a most likely volume of 104 Bef, with a maximum volume of 249 Bcf and a minimum volume of 41 Bef. Also reported are 51 Bcf of helium in nonconventional and low-helium-content natural gases. Extraction of helium in the United States occurs mostly from natural gases produced from the Hugoton gas area in Kansas, Oklahoma, and Texas, and the Riley Ridge area in southwest Wyoming. Helium extracted from natural gas in the United States in 1992 was 3.3 Bcf. Some shortfalls in helium supply may occur in about 5 to 10 years.

Jan 1, 1995

By G. R. Corbett

The introduction of roof bolts to Phalen Colliery in the Sydney Coalfield, Nova Scotia (annual output of 2Mt) has been successfully implemented in maingate and tailgate entries over the last four years. Monitoring of the roof bolted areas continues to be an integral part of the quality control program as the results are utilized to maintain safety and to aid in long-term design strategies. Although all gateroads in the Phalen Colliery have converted to roof bolts as their primary means of support, the majority of intersections which intersect the main slopes remain supported by large steel structures. Several intersections within the Phalen Colliery were monitored as they were created by the mining process. A comparison is made between intersections supported with only traditional 6.4 to 6.7 m steel structure and intersections supported by 2.44 m fully resin encapsulated roof bolts in conjunction with 7.6 m fully cement grouted cable bolts. Detailed monitoring was conducted using CA NM ET's intrinsically safe sonic probe extensometer datalogger which has the ability to read up to sixteen probes simultaneously at programmed intervals. The density of the data from the datalogger has allowed a better understanding of the deformation of cable bolted intersections than was possible with manual monitoring. Test results have helped mine operators to design safer cable bolted intersections.

Jan 1, 1995

By Ann M. Hagni

Flash reduction of zinc oxides is an alternative, environmentally safe method to leaching and electrowinning for zinc recovery. Zinc and lead are volatilized in a flash reactor, a non-hazardous residue is generated, and the fuel source is inexpensive coal in the flash reduction process. Results from experimental laboratory tests yielded low zinc recovery for this process. Mineralogical and textural characterization of the residues from the flash reduction tests for different feed materials and temperatures were conducted to determine the cause for the low zinc recovery. Reflected light microscopy, cathodoluminescence microscopy, scanning electron microscopy-energy dispersive spectroscopy, and X-ray diffraction were utilized in this applied mineralogical research. The original zinc calcine is composed primarily of fine-grained, iron-bearing zincite particles, 25-40 um in diameter, in a porous texture. Pellets processed at 1150°C were found to produce reaction rims of franklinite-magnetite-jacobsite solid solution that are 125-200 um thick and surround cores of unreacted iron-bearing zincite in a Zn-Fe-Si-Ca glass matrix. The reaction rims have subsequently oxidized to form an outer 10 ~m thick rim of hematite. Slags from calcines processed at 1275°C are primarily triangular particles with porous centers, cenospheres, and spheres of iron-bearing zincite, in addition to rectangular particles composed of non-porous franklinite-magnetite solid solution cores with iron-bearing zincite rims. Slag particles from calcine processed at 1200°C are predominantly 100-250 ~m triangular-shaped, spheres, and cenospheres containing fine-grained franklinite and franklinite-magnetite solid solution in an iron-bearing zincite matrix. Slag from calcine processed at 1300°C are also predominantly 1 00-250 um triangular-shaped, spheres, and cenospheres but contain coarser-grained iron-bearing zincite. The zincite in the penets and the slags typically contain 10-20% iron. Based upon these mineralogical observations, it is concluded that the significant amounts of iron in the zincite prevent volatilization of the zinc in the flash reduction process.

Jan 1, 1995

By J. Y. Kim

Lead ions originating from galena during processing of complex sulphide ores migrate to "cover" the surface of sphalerite and iron sulphide mineral particles, and cause poor selectivity in differential flotation. Generally in sulphide ore processing, the lead-activated minerals float in the Cu/Pb rougher circuit. Subsequently, surface lead complicates the zinc flotation circuit by lowering the concentrate grade due to the co-flotation of lead-activated iron sulphide minerals. The effect of lead in the differential flotation of sphalerite from Cu-Pb-Zn and Pb-Zn ores is discussed. Plant and laboratory test data are interpreted by determining the surface composition of individual grains of sphalerite and iron sulphide particles using two surface analytical techniques, Laser Ionization Mass Spectrometer (LIMS) and Time of Flight-Secondary Ion Mass Spectrometer (TOF-SIMS). Cationic and anionic species on the surface were analyzed to elucidate the phenomena.

Jan 1, 1995

By David L. Huston, Wouter Bleeker, Bruce E. Taylor, Ron Cook, Bob Stewart, Elizabeth R. Koopman

"Abstract—Detailed oxygen isotope mapping of rhyolites in and around the Kidd Creek mine indicates that the orebodies are associated with relatively low (<12‰) whole rock values that extend up to 200 m laterally from ore. The zone of low d18O values is overlain stratigraphically by a carapace of higher (>13‰) values that extends up to 1.5 km laterally from and 300 m to 500 m above ore. Immediately above the stratigraphically highest orebody this carapace is cut by a zone of lower d18O values extending from the ore zone. Zones of higher d18O values also occur in massive rhyolite bodies that occur in the footwall of the orebodies.The zone of low d18O values partly coincides with a Na2O depletion anomaly associated with hydrothermal alteration, except that the Na2O depletion anomaly has a greater lateral extent, and the low d18O anomaly extends farther into the stratigraphic hanging wall. These data suggest that d18O mapping may detect hanging wall alteration above massive sulfide bodies more effectively than conventional lithogeochemistry. Zones of high d18O values, which define zones through which large quantities of low-temperature hydrothermal fluids have passed, may also have usefulness in exploration.Oxygen isotope variations at Kidd Creek record three stages of a hydrothermal system that evolved in temperature with time, as follows: (1) an early, low-temperature event that produced rocks with high d18O values, (2) a high-temperature event that produced rocks with lower d18O values, and (3) a later, low-temperature event that also produced rocks with high d18O values. The high d18O signature of the massive rhyolite was recorded during early-stage, low-temperature (<200°C) alteration, and was probably preserved owing to decreases in permeability associated with low-temperature silicification. The low d18O signature of cherty breccia and chloritite was recorded during the thermal peak at >300°C. High d18O values in the carapace above the deposit were recorded as the hydrothermal system waned."

Jan 1, 1995

By P. Bevilacqua, G. Ferrara, M. C. Williams, T. P. Meloy

Tabling is an old environmentally friendly separation unit operation. This paper models shaking tables and explores the action and design of riffles on shaking tables. By reassessing riffle shape and riffle patterns, significant improvements in tabling performance appear feasible. While table sales appear at their nadir, a high-tech environmentally friendly table may have a significant market in the coming decade. Riffles on a shaking table impact particle separation. Particles are affected by riffles and their exit position on the table is dramatically changed, Riffle shape determines how much the riffle will influence a given material. Moreover, riffle patterns influence the concentration of a given material and its exit points on a table. This effect of riffle placement and design is modeled in a spreadsheet. Major performance and separation improvements may he expected by improved table design. Two physical laws of tabling have been derived. These laws aid in the design of sophisticated high-tech tables.

Jan 1, 1995

By F. Rosenblum, P. Spira

"Self-heating of broken sulphide ore or waste rock underground can lead to ignition and cause serious problems in a mine operation. An extensive study has demonstrated that it is caused by oxidation of certain species of pyrrhotite. Self-heating was found to take place in two stages, first progressing from ambient temperature to 1000C with exothermic formation of elemental sulphur in the presence of moisture and oxygen, and proceeding to a second stage in which the sulphur oxidizes to SO2. Ignition may eventually follow. An apparatus was developed to assess the propensity of sulphide rock to self-heating and the potential for hazardous behaviour. The effect of temperature, time, rock size, and surface treatment with chemicals is presented. On the basis of these results, possible approaches for preventing a runaway reaction are suggested for further investigation.IntroductionThe oxidation of sulphide ore, waste rock or tailings backfill, which may cause hazardous conditions underground through heating, oxygen depletion and, in some cases, fire, is well documented (Farnsworth, 1977; Ninteman, 1978; Rosenblum et al., 1982; Reimers, 1987). The self-heating mechanism, nevertheless, has not been satisfactorily explained. The onset of heating from ambient temperature, in particular, has not drawn the attention of researchers. In the course of a previous study (Rosenblum et al., 1982) aimed at finding a method to assess the hazard from using sulphide tailings as backfill, the authors developed an apparatus to measure self-heating rate under controlled, near ambient conditions. This has since provided decisive information in backfill investigations in the Noranda Group.The test methodology devised for tailings failed to predict self-heating in a broken waste rock known to be active. Upon repeated testing, however, a freshly crushed sample began to exhibit appreciable heating and oxygen uptake (Fig. I). After 14 tests, the self-heating rate reached a plateau of about 4O°C/h and then fell progressively to < 5°C/h after 30 tests. It was hypothesized that weathering in the presence of moisture and oxygen during testing had caused the onset of self-heating. Active tailings, on the other hand, are exposed to natural surface oxidation and need not be weathered to show heating. Based on this finding, a new apparatus was developed capable of simultaneously weathering a sample of rock and monitoring its self-heating behaviour."

Jan 1, 1995

"The Cordillera contains numerous porphyry deposits and prospects, many containing economic quantities of copper, molybdenum, gold and tungsten. Over the lost twenty years, different phases of exploration have been driven by individual commodity prices and new discoveries. Exploration methods have remained largely unchanged since the 1960s and 1970s with the range of techniques chosen for each situation depending on the stage of the program, the type of porphyry target and the local environment. Improvements or changes to techniques have resulted from awareness of specific features in new deposits or regional problems. During the last ten years much of the emphasis has been on the re-evaluation of known porphyry deposits with more exploration in areas previously recognized as prospective. Re-evaluation of known deposits has resulted in increased reserves, often with improved gold grade, and the discovery of new zones. Several new deposits have been discovered including gold-only deposits of probable porphyry affinity.Research related to porphyry deposits has followed trends in exploration and has been directed toward the type of deposits that have been of current interest. In addition to research on specific deposits and areas, general research related to porphyry deposits has addressed three broad themes. The first theme involves the role of tectonic processes and the nature of source regions. Although different in detail, recent tectonic models suggest that a tectonic change or hiatus may be important for the generation of metal-rich magmas from various source regions and subsequent fractionation that permits volatile saturation. The second theme is based on magmatic processes, particularly the generation of a volatile phase enriched in metals. This research supports the general orthomagmatic model for porphyry deposits and has helped to define the influence of specific variables in the generation of different types of porphyry deposits. Finally, research on alteration and mineralization has provided evidence for different types of fluids and fluid processes involved in the formation of porphyry deposits. These data also support the orthomagmatic model but indicate additional complexity in magmatic-hydrothermal systems including the role of external fluids. Although important advances have been made, research has had a limited impact on exploration.Exploration and research on deposits that occur in the peripheral and upper parts of porphyry systems have been important over the last ten years. Although considerable advances have been made, the relationship of different styles of peripheral mineralization to magmatic processes in the core of the system remains ambiguous. An improved understanding of the processes that generate zoning, peripheral mineralization, and the surrounding alteration envelopes would be beneficial to exploration."

Jan 1, 1995

By J. C. Norman

The United States was the world&apos;s largest producer and consumer of boron compounds during 1994. According to US Bureau of Mines (USBM) estimates, boron mineral concentrate and chemical production in the United States totaled about 1.05 Mt (1.15 million st), yielding 560 kt (617,000 st) of B203, for a total estimated value of $370 million. This production level was about 2% less than 1993 revised figures. The United States continued to provide nearly all of its own boron supply while maintaining a strong position as a source of sodium borate products and boric acid for export. Domestic employment in the mining and beneficiation of boron products during 1994 was 900 people, about the same as in 1993. USBM estimated total world production of boron of about 2.3 Mt (2.5 million st), yielding 1.1 Mt (1.2 million st) of B203. World production during 1994 was about the same as during 1993. USBM estimates US reserves to be about 210 Mt (231 million st) of ore and world reserves to be about 630 Mt (694 million st) of ore.

Jan 1, 1995

By K. I. Afewu, L. C. Woollacott

Little is reported in the literature that is directly useful for the interpolation film coefficients for the in-pulp adsorption circuits used in gold metallurgy. This can create a problem if the design or operation of these circuits is to be optimized by the use of simulation techniques. To address this problem, a study was undertaken on the influence of mixing intensity, scale, and geometry on the film coefficient in adsorption systems typical of the carbon-in pulp plants used for gold extraction. This, the first paper deals with the influence of these factors on the film coefficient and shows that the specific power to just disperse the carbon in the slurry is an important variable. This variable is also strongly dependent on mixing intensity, scale, and geometry-a dependence that is dealt with in the second paper in the series. From the informatlon obtained, practical scale-up procedures were developed. These procedures are considered to be applicable to resin-in-pulp as well as to carbon-In-pulp plants.

Jan 1, 1995

By Jeran Paul W., Michael A. Trevits

Subsidence data gathered by the U.S. Bureau of Mines over a series of longwall panels in the Pittsburgh Coalbed were studied to obtain insight as to the role of time in the subsidence process. It was found that subsidence began essentially with undermining and was completed within 1 year. The progress of the subsidence was dependent upon location above the panel. Subsidence in the central area of the subsidence trough, where subsidence is the greatest, was about 90 pct complete by the time the face had progressed a distance equal to one overburden thickness beyond a particular surface point. For a point over the rib of the longwall panel, the subsidence was only about 60 pct complete at this time. Data from three other sites in the northern Appalachian Coal Basin were analyzed to determine if an anomaly or the true characteristics of the subsidence process had been observed. All sites behaved similarly in the central portion of the subsidence trough. However, the subsidence of points over and adjacent to the ribs of the longwall panels was site specific. The fact that movement across the width of the panel was not uniform should be taken into account in assessing damages or the potential for damages resulting from mining-induced subsidence.

Jan 1, 1995

By R. J. Gochin, G. D. Schena

Mineral processing options and technical innovations should be financially assessed. Indeed technical feasibility alone does not offer an adequate process selection criterion. An appraisal by the use of engineering economics principles leads to a more efficient evaluation and selection of feasible mineral processing solutions. Financial consequences of different options synthesised by profitability indices allow better decision making. Selected examples derived from real world problems are used to illustrate the potential of engineering-economics methods applied to mineral processing.

Jan 1, 1995

By Bruce McKinstry

INTRODUCTION In June of 1992, the Bureau of Reclamation, United States Department of the Interior, awarded the contract for construction of the Sixth Water Aqueduct to the Fedrick-Redpath Joint Venture. This aqueduct, a segment of the Diamond Fork Power System, Central Utah Project, diverts water from Strawberry Reservoir into Sixth Water Creek and, when complete, will replace the old Strawberry Tunnel which was driven in the early 1900&apos;s. The new aqueduct is being built primarily as a result of deterioration of the old tunnel, but will also have a higher capacity and more positive control than the old tunnel as well as the capability to incorporate a turbine into the system at a later date. The Fedrick-Redpath Joint Venture is comprised of C.R. Fedrick, Inc. of Novato, California and J.S. Redpath Corporation of Tempe, Arizona. Fedrick, with its experience in pipelines and heavy construction, will construct the 4200 ft surface pipeline and flow control structure; Redpath, the managing partner, performed the underground work consisting of a 600 ft vertical shaft and 3300 ft tunnel. The project is located in the Uintah National Forest, approximately 20 miles east of Provo, Utah at a mean elevation of 7000 feet above sea level.

Jan 1, 1995