Search Documents

By Lawrence D. Meinert

Abstract-Most large skarn deposits are zoned in both space and time relative to associated intrusions. Zonation occurs on scales from kilometers to micrometers, and reflects infiltrative fluid flow, wallrock reaction, temperature variations, and fluid mixing. The most spectacular examples of skarn zonation usually occur at the skarn-marble contact, where transitions between monomineralic bands can be knife sharp. Other small-scale examples occur in zoned veins and individual mineral crystals. Although, visually striking and scientifically interesting, in mineral exploration these small-scale variations are less useful than deposit- or district-scale zonation. In most skarn systems there is a general zonation pattern of proximal garnet, distal pyroxene, and vesuvianite (or a pyroxenoid such as wollastonite, bustamite, or rhodonite) at the marble front. As well, individual skarn minerals may display systematic color or compositional variations within the larger zonation pattern. Such patterns are reviewed for 14 well-studied examples of Cu, W, Sn, Au, and Zn-Pb skarns. In addition, many deposits have endoskarn or other alteration of the associated intrusion, and recrystallization or other subtle changes have occurred in the surrounding wallrocks. Copper skarns, such as Mines Gaspé in Quebec and Big Gossan in Irian Jaya, have high ratios of garnet:pyroxene and are zoned outward from the intrusion, to garnet, to pyroxene, to massive-sulfide replacement and vein deposits. Garnets in Cu skarn are Fe-rich and change from dark red-brown near the intrusive contact to paler brown, green, or yellow in distal locations. Pyroxenes in Cu skarns are pale and diopsidic near the intrusion, and become darker and more Fe- and Mn-rich away from the intrusion. Tungsten skarns, such as Salau and Costabonne in France and Pine Creek and Garnet Dike in California, have intermediate ratios of garnet:pyroxene, are more extensive vertically and along strike than perpendicular to the intrusive contact, and have zonation patterns commonly complicated by overprinting of metamorphic lithologies. In W skarns, garnet is commonly subcalcic and the pyroxene is Fe-rich, reflecting particularly reducing wallrocks or great depth of formation. Tin skarns, such as Dachang in China and Moina in Australia, also can have subcalcic garnet and Fe-rich pyroxene, but this reduced mineral assemblage typically is due to an association with reduced S-type granites. Tin skarns differ from most other skarn types in having a late greisen stage that may replace earlier Sn-bearing calc-silicate minerals, thus liberating Sn to form cassiterite. Many high-grade Au skarns, such as Hedley in British Columbia and Fortitude in Nevada, have low ratios of garnet:pyroxene and are associated both with reduced plutons and reduced wallrocks. Goldrich zones occur in Fe-rich, pyroxene-dominant, distal skarn. Zn-Pb skarns, such as the Yeonhwa- Ulchin district in Korea and Groundhog in New Mexico, have low ratios of garnet:pyroxene and generally form distal to associated intrusions. These skarns also are zoned from proximal garnet to distal pyroxene and pyroxenoid (bustamite-rhodonite), with significant zones of massive sulfides within and beyond skarn. Manganese enrichment of most mineral phases, particularly pyroxene, is characteristic of distal zones. Fundamental controls on skarn zonation include temperature, depth of formation, composition and oxidation state of associated plutons and wallrocks, and tectonic setting. Most W skarns form at relatively great depth, 5 km to 20 km, with extensive high-temperature metamorphic and metasomatic mineral assemblages. In contrast, most other skarn types are relatively shallow, <10 km and mostly <5 km, with limited, lower temperature metamorphic aureoles. Differences in oxidation state correlate well with different skarn zonation patterns, particularly garnet:pyroxene ratios and compositions, and can be used in both classification of and exploration for s

Jan 1, 1997

By Walter S. White

The Michigan native-copper district has produced about 5,400,000 tons of copper since mining began in 1845. The copper occurs primarily as open-space fillings and replacements in amygdaloidal flow tops and conglomerate beds of the Portage Lake Lava Series, of middle Keweenawan age. Secondary minerals with which the copper is associated include microcline, chlorite, epidote, pumpellyite, prehnite, quartz, and calcite; zeolites, other than laumontite, are not abundant. A zonal pattern of the secondary minerals transects bedding and suggests regional metamorphism mainly to the grade of the prehnite-pumpellyite graywacke facies of Coombs. Most of the major copper deposits are near the upper limit of abundant quartz in this zonal pattern. The distribution of copper in both amygdaloid and conglomerate deposits is controlled partly by primary permeability of the rocks and partly by later tectonic fracturing that was concentrated in the mechanically weak flow tops and sedimentary beds. Ore shoots and deposits are therefore controlled partly by primary structural features, such as areas of thick and thin fragmental amygdaloid or the boundaries of conglomerate lenses, and partly by regional structure: a number of ore deposits are in synclinal downwarps. The copper-bearing solutions that formed the deposits were ascending. They may have come from a large concealed intrusive, or may have been driven out of the porous tops of lava flows when the rocks were compacted and metamorphosed at great depth in the central part of the Lake Superior syncline. The second hypothesis seems more consistent with the widespread distribution of the copper, its relation to mineral zoning that represents truly regional metamorphism, its native state, and the likelihood that copper deposition was later than most or all of Keweenawan volcanism.

Jan 1, 1968

By H. Sevim

An innovative approach in designing the haulage systems for underground coal mines is discussed in this paper. The haulage systems are formed by serially connected components. Therefore an economic and efficient design of the entire system is necessary. The computer model that uses a heuristic algorithm solves this design problem globally in a single run. It is a probabilistic model because it considers the probabilistic aspects of face operations. It is versatile because it can accommodate any type of mining and belt conveyor network configuration. The hoisting section can be used to design drum or friction hoisting systems for single or multiple level operations. These systems can have two skips in balance or a skip and a counterweight in balance. The model also has the option to internally determine the capacity of bunker(s) and shaft-bottom bin. The objective is to minimize the expected cost per ton of coal hauled from the coal faces to the surface. At the end of the paper is an example that illustrated the capabilities of the model.

Jan 1, 1987

By Richard L. Rains

In 1992, the Bureau of Mines evaluated mineral resources of the 34,043-hectare Caribou City and 41,943-hectare Stump Creek study areas in southeastern Idaho. No resources were delineated. The areas had been proposed for wilderness. Rocks underlying the study area are part of the Idaho-Wyoming Thrust Belt. At Caribou Mountain they have been intruded by diorite-monzodiorite. Where the intrusive rocks contact calcareous members of the thrust belt, skarn bodies have formed that host metal deposits. Gold, both placer and lode, occurs in the Caribou City area, and salt occurs in the Stump Creek area. Production records show 73.5 kg (2,363 ounces) of placer gold were produced; however, field studies indicate more than 2,000 kg (67,000 ounces) probably were recovered. Minor amounts of lode gold, silver, and copper were recovered from the hard rock mines. Production of salt from the Stump Creek study area in the 1860&apos;s was used by emigrants on the Oregon trail and also shipped to various mining districts for use in silver recovery. Oil and gas were drilled for, but all holes are plugged and abandoned. There are no current leases. Examined workings consisted of 25 adits, 3 shafts, 50 prospect pits, and extensive placer workings all in the northern tip of the Caribou City area, Current BLM records show 168 placer and 146 lode claims; 14 claims are patented.

Jan 1, 1993

By Alexander E. Morrow

Oxygen breathing apparatus for use in mines was introduced to the United States in 1907. Despite their intended purpose of safeguarding lives, the apparatus led to the deaths of many men because of inherent or developed defects in the equipment, lack of training,, physical shortcomings of wearers, and improper procedures. The Bureau of Mines pioneered in research and training to curb logs of life among users of such apparatus and promoted development of safer equipment and procedures. As a consequence, deaths have been far less frequent. In 1944 the Bureau issued Information Circular 7279, Loss of Life Among Wearers of Oxygen Breathing Apparatus. That publication listed the case histories of 26 deaths that had occurred since the introduction of such equipment to American mining. The author, the late G. W. Grove,3/ asserted that further loss of life could be avoided if good equipment were used, teams were properly trained, and the basic principles of safe procedure were followed. This publication is a sequel to I.C. 7279 and contains information on eight deaths among wearers of oxygen breathing apparatus that were overlooked in the original compilation. It also describes the single death that occurred since I.C. 7279 was published.

Jan 1, 1959

By Paul Gilmour

"The principal role of the geologist is to recognize the existence of phenomena before trying to explain them" - B.M. Keilau, 1825; A. Holmes, 1965 Some important groups of mineral deposits in the layered rocks of orogenic belts or greenstone belts occur in horizons characterized by the presence of exceptional amounts of silica, iron and carbon, with more or less significant amounts of manganese. Generally, the rocks involved are well banded. In practice, these five physical features - four compositional and one geometric - are found with many lithological guises. Iron formation, in the full, modern sense of the term (James, 1954), quartzite, ferruginous quartzite, chert, jasper, "tetsusekiei" (Horikoshi, 1969), tuffaceous jasper ("purple porphyry" - Anderson and Creasey, 1958, p. 36), ferruginous or graphitic shale, argillite, slate or schist, and hematitic tuff are but a few of the more familiar of the names that have been assigned to these rocks. Widely acknowledged and well-documented examples of metallic deposits found in such sediments include concentrations of iron and manganese and stratabound, polymetallic, massive pyritic sulfides. Less familiar examples include occurrences of asbestos (Miles, 1953; and Coetzee, et al., 1976), antimony (Coetzee, 1976), and perhaps stratabound deposits of Au-Cu-U-W-etc., such as Aitik in Sweden (Mining Magazine, 1975; and Nilsson, 1979) and Olympic Dam in South Australia (Roberts and Hudson, 1983). The case of gold is intriguing. An association between gold and iron formation has been identified at several famous deposits and districts, such as Yellowknife, N.W.T. (Morton, 1979), Homestake, S. Dak. (Sawkins and Rye, 1974), Vubachikwe, Zimbabwe (Fripp, 1976) and the Barberton district, R.S.A. (Hammerbeck, 1976). Yet a critical reading reveals the existence of many other hitherto unsuspected examples. The purpose of this note is to draw attention to that omission and the apparent explanation for it. It is not hard to detect the two most probable reasons for the discrepancy between reality and the record.Most occurrences of gold are associated, not with the familiar banded iron formation or interbedded magnetite and chert (technically, the magnetite-banded variety of the oxide facies), but with the enigmatic carbonate, sulfide and silicate facies of iron formation and/or with rocks evidently related to iron formation. All too commonly, the unfamiliar facies of iron formation have been identified by field and mine geologists and not a few researchers as products of regional metamorphism and hydrothermal alteration, as mafic igneous rocks, or as conventional sediments, ie., without regard to their intrinsically ferruginous nature. The justification for these two complementary assertions is largely to be found in the recognition of a characteristic suite of metals and minerals in gold deposits known to be associated with iron formations. Although, from a geological standpoint, a lithological association is more important than a mineralogical assemblage, the latter is the more likely of the two to be diagnostic. This arises from the different natures of mineral and rock classifications, The identification of a mineral or an element is a matter of fact. Owing to the genetic component inseparable from petrographic nomenclature, viz., "igneous": a rock (believed to have been) derived from a melt, the identification of rocks depends on inferences or conclusions about their mode of formation - conclusions that are commonly debatable and, all too often, involve subjective judgements. This is especially prone to be true, if - as at many of the gold occurrences in question - the host rocks have been metamorphosed and/or "altered". In the notes that follow greater weight has accordingly been assigned to elemental and mineralogical than to host rock composition. In other words, if, in a given gold occurrence, the suite of metals and minerals present conforms to the standards of the subject class, whereas the names assigned to host rocks do not, the latter will be viewed as suspect.

Jan 1, 1985

By J. W. Adams

This report surveys the efforts of six contractors to the U.S. Bureau of Mines with regard to their electromagnetic noise measurement programs. What has been done, what is planned, and evaluations and recommendations are given for each contractor. The main observation is that to date there is not sufficient knowledge of electromagnetic interference in mine environments to design a reliable communication system. This knowledge should be available by the end of June 1972 if certain planned programs are completed successfully. A major effort of this report is to establish parameters to be measured, units to be used, and workable formats for data presentation. This is given in Appendix A. Some details concerning equipment, procedures, locations, and sample data are included in Appendix B.

Jan 1, 1971

By L. Adler

A fairly complex analysis is required to select, or evaluate a piece of excavating and bulk handling equipment and obtain its performance. At present there is little agreement as to what specific points should be considered, and even less on what procedure to follow. This paper provides both of these in a consistent and direct form. The analysis applies to all types and sizes of equipment from the bulldozer and the continuous miner, to the B.W.E. The importance of the equipment characteristics, job activities, and work conditions are stressed and separate analytical stems are established in a flow chart for these. They are combined using suitability tests in the following steps: 1) problem statement, 2) natural conditions, 3) suitability guidelines, 4) appropriate equipment types, 5) operational activities, 6) encumbered space, 7) geometric design, 8) equipment sizing, 9) failure and limits, 10) performance and consumption, 11) public policy checks, and 12) costs and profitability. Public policy and economics while considered throughout receive emphasis towards the end. The procedure is iterative, containing distinct feedback loops. Specifying the steps and sequence provides a necessary structure which has long been overdue.

Jan 1, 1983

By H. C. Liang

Reverse osmosis (RO) and nanofiltration (NF) are widely regarded as being best available technologies (BATs) for removing contaminants of concern from water. In recent years, NF or RO treatment has increasingly gained more acceptance in the mining industry for treating mine water to remove a wide assortment of contaminants, either for meeting discharge standards or for internal re-use in mining processes. Consequently, the number of NF or RO membrane mine water treatment facilities has steadily increased. Although NF or RO membrane filtration can be a powerful tool in mine water treatment, especially when multiple contaminant removal is required, it also has many potential disadvantages. Besides the generally higher capital and operational costs for the high pressure membrane processes, organic constituents in mine water may foul the membranes, while inorganic compounds such as gypsum, calcite, or silica are liable to scale the expensive membranes if proper pre-treatment processes are not implemented. Additionally, because these membrane treatment processes generate a substantial reject or brine waste stream in addition to the clean treated water or permeate stream, brine management also needs to be considered carefully when deciding upon the viability of an NF or RO mine water treatment process. Because of these issues, it is important to conduct detailed analyses of the trade-off between selecting NF or RO vs. using chemical treatment processes when designing a mine water treatment facility.

Jan 1, 2012

By Efrem R. Reeves

Noise-induced hearing loss (NIHL) is the most common occupational illness in the United States, with 30 million workers exposed to excessive noise levels [NIOSH 1996] every day. Of particular concern is the mining industry; which has the highest prevalence of hazardous noise exposure of any major industry sector [Tak et al. 2009] and is second only to the railroad industry in prevalence of work-ers reporting hearing difficulty [Tak and Calvert 2008]. This document is for operators, safety personnel, and mechanics in the mining industry who are not specialists in noise control engineering or acoustics. Evaluations of successful and unsuccessful attempts at controlling noise on several large, underground metal mining machines are detailed to illustrate the basic principles of noise control. Once personnel understand the guidelines and principles of noise control, they will be able to ¦evaluate the extent of a noise problem; ¦determine the best approach to the problem; and ¦apply the most appropriate solution. Because of the insidious nature of NIHL, it can go unnoticed until a considerable loss of hearing has occurred. In some cases, diagnosis is delayed because an exposed individual claims to have become accustomed to the noise. In reality, that person may have already suffered irreversible hearing loss. Humans can hear sounds in the frequency range from about 20 to 20,000 Hertz (Hz). Within this range, NIHL usually begins in the frequency region around 4,000?6,000 Hz, the upper levels of the speech region. The first noticeable symp-toms include difficulty understanding higher pitched voices, such as the voices of females and children, and difficulty understanding certain consonant sounds, which are primarily high frequency in nature. The extent of NIHL varies depending on the level and duration of noise exposure and on an individual?s susceptibility; despite having similar noise exposure, individuals can experience differing degrees of hearing loss, or none at all. NIHL is almost always preventable. To reduce or eliminate the possibility of NIHL, an individual?s noise environment must be analyzed and appropriate action taken to reduce noise exposure.

Dec 1, 2009

By Douglas A. Anderson

The US Bureau of Mines, in RI 8507, has shown that blast vibrations at low frequency are more likely to cause damage and complaints than those at higher frequency. Since that publication in 1980, the Office of Surface Mining and many state and local regulatory authorities have incorporated frequency in their regulations for acceptable ground vibration from blasting. Even when frequency is not explicitly stated in regulations, it may become an issue in hearings or in court.

Jan 1, 1992

By M. Akser, M. Tomas

Six Sigma is a methodology that uses a structured and disciplined approach to improve process performance (higher throughput, better recovery, lower cost, shorter cycle time, etc.). Specially trained people called “black belts” lead and manage Six Sigma projects. Black belts, with assistance from their team, ensure that projects follow the DMAIC (define, measure, analyze, implement and control) process phases. Timely completion of each project, with measurable deliverables, is key to Six Sigma’s significant financial success. Implementation of Six Sigma has been growing in recent years in a wide range of industries. The heavy mineral industry, like many other industries, could benefit from what Six Sigma has to offer. Specific Six Sigma project examples are included from DuPont’s Heavy Mineral Production Plant in Florida.

Jan 1, 2005

By C. O. Swanson

CALCULATING the average grade of a gold deposit is a problem that presents certain unique difficulties. Particularly troublesome is the fact that the average of the samples taken from a deposit is likely to be higher than the grade of the ore that is eventually mined, even when allowance is made for dilution and other factors resulting from the mining operations. It would seem that this situation is due to the presence in the deposits of structural peculiarities which have not been properly taken into account, since estimating the average grade of the broken ore produced from the deposits does not present the same difficulty. It is therefore evident that structural considerations are of prime importance in estimating the grade of a deposit. This fact is clearly realized and taken into account in cases where the boundaries of the orebodies and the variations within them are easily recognized. But in many gold deposits this condition is not satisfied, a circumstance which can be regarded as the main source of difficulty. Lacking definite information concerning the structure, we are apt to use certain procedures which are either empirical or based on general probabilities.

Jan 1, 1945

By R. L. Marek

The number of persons fatally injured in the petroleum industry in California in 1930 was 50, a decrease of 20.6 per cent from 1929, when 63 men accidentally lost their lives. The decrease in the number of fatalities for 1930 has caused the first downward trend in the fatality curve of the California petroleum industry since 1927 and is coincident with a period of little active development in new fields, the shutting in of many wells, and reduced activity in the older fields of the State. That a direct relationship exists between the number of accidental deaths and the rapidity of new field development is particularly emphasized by the fact that in 1929, a year of intensive field development in California, 48 men were killed in the drilling and producing division, whereas in 1930, a year of less development work, only 25 men were killed in this division. The figures for the average number of drilling and producing wells in 1930 decreased appreciably from, comparable figures for 1929 and a greater percentage of producing wells were shut-in in 1930 than in 1929.

Jan 1, 1931

By M. Hancer, J. D. Miller

It is known from soluble salt flotation practice that the K, Mg double salts of kainite (KClMgSO43H2O), and carnallite (KClMgCl26H2O) are difficult to float and must be converted to other salts such as schoenite (K2SO4MgSO46H2O) and sylvite (KCl) in order to recover potash values. The flotation characteristics of these double salts have now been confirmed in some detail by carefully controlled laboratory experiments with both cationic and anionic collectors. The experimental results are discussed in view of recent experimental findings regarding the flotation characteristics of simple salts, in which the flotation response was shown to be determined by the interfacial water structure and whether the salt could be considered to be a water structure maker or a water structure breaker. The same approach can be use to explain the flotation response of the potassium double salts ; schoenite, kainite, and carnallite. In addition, the sign of the surface charge of schoenite (K2SO4MgSO46H2O), was determined as a function of pH from nonequilibrium electrophoretic mobility measurements. Schoenite appears to exhibit three charge reversals (CR) which can be explained based on surface hydrolysis reactions. The flotation behavior of schoenite is further considered based on solution chemistry calculations, electrophoretic mobility measurements, and microflotation results.

Jan 1, 2001

By Nord L. Gale

The discovery of important new ore deposits of lead, zinc, copper and silver in 1955 in Southeastern Missouri has resulted in the development of a thriving mineral industry known as the "New Lead Belt" or "Viburnum Trend", to distinguish it from the older lead producing areas to the East. This region has recently become the world&apos;s largest lead producing district with production in 1970 reaching 432,576 tons or 74.4% of the entire United States lead mine production. The area is heavily forested with rolling hills dotted with numerous clear running streams in the Clark National Forest of the Missouri Ozarks. The location is within 70 miles of St. Louis, Missouri and has a natural abundance of water resources which provide an important recreational area for fishing, hunting, camping and other outdoor activities. Until this recent development, the area was sparsely populated and industrialization was almost unknown. The infusion of $150 million in mining capital has brought about a dramatic change in the economic structure of the area and will almost surely be accompanied by changes in its environmental picture. In an effort to maintain this bountiful national resource and to evaluate the changes occurring in surface water quality and aquatic life forms present, an inter- disciplinary research program at the University of Missouri has been undertaken with the support of the National Science Foundation. Research has been carried out to determine background values, establish natural baselines, and to evaluate the extent and causes of changes in streams effected by mine water discharges and wastewater from ore milling operations. The unique topography of the "New Lead Belt" area allows the channelization of milling and smelter wastes to separate stream systems (Figure No. 1) thus allowing measurements of the pollutional effects on an individual basis.

Jan 1, 1973

By C. Ford, R. E. Salas Rojas, J. P. Contreras Rodriquez, S. A. Pierce

Heightened environmental consciousness has resulted in the development of various international accords dealing with natural resource management. This international awareness is now being translated into regional and local initiatives that proactively implement collaborative environmental management programs. One such program was recently initiated in northern Chile in recognition of the interconnection of Andean salars. Cooperative efforts between industry, governmental agencies and academic professionals have resulted in the implementation of simultaneous environmental monitoring of flora and fauna in the salars of northern Chile. This coordinated effort is leading to an improved understanding of the migratory patterns of South American fauna, as well as improved access to an expanded database for the multiple user groups associated with the Andean salars. The El Abra Mine is actively participating in these coordinated monitoring efforts.

Jan 1, 1999

By James P. Ulery, Frank E. Chase

Clay veins found in coal mines have caused numerous injuries and fatalities. These structures plague all phases of mining, including entry development, pillar recovery, and panel extraction. Clay veins also increase production costs and may disrupt or halt mining. These detrimental aspects have prompted the Bureau of Mines to investigate the physical characteristics of and roof instability problems associated with clay veins. This was accomplished by observing and mapping clay veins in surface and underground mines. The occurrence and origins of clay veins were also investigated to determine predictive capabilities. The investigators found that clay veins normally occur in more stable, less rapidly subsiding coal basins. Clay veins result when tensile stresses develop fissures which are later infilled. These fissures can be propagated by compactional processes and/or tectonic stresses active during and subsequent to coalification. The Bureau also found that associated faults, fractures, and slicken-side planes commonly parallel clay veins and disrupt the lateral continuity of the immediate and, sometimes, main roof. When clay veins parallel or subparallel the direction of face advance, the roof is segmented into cantilever beams, causing unstable conditions. Consequently, the strata on either side of the clay veins should be bolted and strapped together to form a beam.

Jan 1, 1987

By Mark S. Sanders

This report is a review and synthesis of the published literature dealing with personal equipment items used by low seam coal miners. This report reviews the following items of equipment: headgear, outer garments, respirators, cap lamp, gloves, knee pads, footwear, boots, helmets, ear protection, eye protection. Recommendations for further research and development are included.

Jan 1, 1978

By John R. McDonnell

The Valle Vidal Unit comprises 100,000 acres In Taos and Colfax: Counties, New Mexico. The unit was donated to the American public In 1982 by the Pennzoll Co. and is administered by the U.S. Department of Agriculture Forest Service as an addition to the Carson National Forest. During 1990-1991, the Bureau of Mines conducted a mineral Investigation of the unit as authorized by an Interagency Agreement (1987) Intended to assist the Forest Service to incorporate mineral resource data In forest plans. The Bureau reviewed literature and records concerning mineral resources and mining activity, and performed a field examination of mines, prospects, and mineral occurrences in and near the Valle Vidal Unit. The La Belle mining district encompasses most of the western part of the Valle Vidal Unit. The district was most active between 1893 and 1902, after the land grant was opened to prospecting and gold discoveries were reported. The discoveries were low grade, and eventually were abandoned. The Bureau&apos;s appraisal of the district determined that lode gold occurs primarily in fissure veins in volcanic rocks, and placer gold occurs In weakly cemented sedimentary rocks and alluvial sediments; but at a grade that is currently considered subeconomic. If the price of gold increases in the future, prospecting and exploration in the area may be renewed, but the activity would likely be limited due to "acquired land status" restrictions, which require mineral leasing and prohibit claim location in the Valle Vidal Unit.

Jan 1, 1992