Search Documents

By Shiro Ishii

When construction sites are in a densely- populated area or near roads, railroad or river, restrictions upon the ways of handling and using explosives such as dynamite and large demolition equipment are being increasingly stringent, in consideration of environmental pollution such as noise, vibration, dust, flyrocks etc., and safety precaution. In view of this, the development of safe and pollution-free technology for demolishing rocks at mines and reinforced concrete structure at building sites is strongly required. To meet such requirements, the demolition by means of expantion of mineral substances has been considered long before. Recently with the demolition technique using non-explosive demolition agent developed by ONODA CEMENT CO., LTD., holes are drilled into substances to be demolished, such as rocks and concrete before-hand. Then, slurry of such agent mixed with an appropriate quantity of water is poured into the holes. It hardens and expands with the passage of time, and the expansive stress reaches more than 3m/m2 in 10 to 24 hours. This expansive stress causes the material to crack. In this article, descriptions of the non- explosive demolition agent, BRISTAR manufactured by ONODA CEMENT CO., LTD., TOKYO, JAPAN, are given briefly with regard to its physical and chemical properties and its method of use; and the way it is used at an actual construction site is reported.

Jan 1, 1982

By T. M. Storer

Much has been written and many discussions held on the virtues (and evils?) of a Company-owned motor fleet. Almost invariably these dialogues take a generalized form and thereby lose something since the individual circumstances, geography and philosophy - particularly in diverse industries, is never quite the same. In considering the nature of my remarks today, I felt a departure from the general approach might be in order, and in lieu of that, will attempt to present a concise picture of how we in the Lehigh Portland Cement Company view this problem and the steps we have taken in our efforts to solve it. At the outset a word may be in order about the Lehigh Company itself, what we do, and the problems that confront us specifically as well as the cement industry at large. We are primarily a manufacturer of portland cement operating 10 plants with a total annual capacity of about 23,000,000 barrels. We market this material in 30 states, shipping both from the plants directly as well as through a system of 18 distribution terminals. About 150,000 truckloads of cement are shipped to customers each year.

Jan 1, 1969

By John E. Miller

In recent years there has been increasing concern in the mining industry over the availability and high cost of diesel fuel to support mining operations. Unit Rig & Equipment Co. has been deeply involved with the development and testing of the newest designs for trolley assist. Beginning in dune 1980, Unit Rig modified and commissioned six 156 metric ton (170 short ton) trolley assist haulage trucks at two mine locations in South Africa. Operating haulage trucks with General Electric GTA 15E/776 drive systems were chosen for the tests since this size of truck represented the majority of the population of large size haulage trucks and the greatest technical development problems. Test operations have proven the feasibility of equipment designs in actual operation and preliminary economic data has convinced the operators to proceed with planning to modify their entire mining operation to use trolley assist. The initial capital investment incurred for trolley assist can be recovered in a short period of time. Following this quick capital recovery, mines will continue to realize lower operating costs through increased productivity and lower diesel consumption.

Jan 1, 1980

By Donald I. Bleiwas

The U.S. Bureau of nines evaluated the potential availability of tungsten from 57 tungsten mines and deposits in 19 market economy countries (1). The 38 properties that were producing at the time this study was performed contain approximately 375,000 tons1 of W03 (tungsten trioxide). The total estimated recoverable resource from all properties studied, both producers and nonproducers, was 1.2 million tons W03 (demonstrated level). Approximately 143,000 tons of W03 is recoverable from producing properties with costs at or below the January 1983 market prices. The study indicates that by 1990 production from currently operating mines in market economy countries will decrease as their demonstrated resources become exhausted. Some of this potential decline may be offset by lower than anticipated levels of market demand, discoveries of additional resources at producing mines, development of other known deposits, and/or discoveries of new deposits. Development of new tungsten resources in market economy countries will likely result in costs higher than exist at currently producing properties. The People's Republic of China has been steadily increasing production and export of tungsten in various form and currently supplies about 25 pct of U.S. imports. China's tungsten mines are large, high-grade operations capable of producing at relatively low cost. These factors, coupled with China's apparent need for foreign exchange, could lead to further expansions of production and exports from China, with a consequent increased dependence by market economy countries on China for tungsten requirements and a threat to the survival of the market economy countries' tungsten industries.

Jan 1, 1984

By James A. Bloom

To operate the Morris Fork Preparation Plant with a closed water circuit has been an elusive goal for Union Carbide. The benefits of a closed circuit have never been questioned. The removal of fine solids from washery water makes possible the recirculation and reuse of the water. Heavy media drag tanks and other separating machines perform better and more consistently with washery essentially free of fine solids. Finally, the production of a clarified effluent makes unnecessary the sludge ponds usually associated with a coal preparation plant. Why then do I say elusive? Because, since plant design was completed in 1970 we have been in hot pursuit of an ever-growing fine solids problem. In four years the minus 28 mesh material in the plant feed has nearly doubled. The replacement of conventional sections with continuous mining machines has led to a lowering in size and quality of product from the mine. In addition, increasing emphasis underground on roadway clean-up has contributed to the fines problem.

Jan 1, 1975

By Carrie Smith

In 1972, in Denver, CO, five women with a shared goal joined forces to create the first formal space for women in the mining industry: Women in Mining USA (WIM USA). When the organization first took shape, few could have predicted that a small gathering of women would grow into one of the most influential organizations that would advocate for inclusion in the industry. Now, more than 50 years later, the group remains a vital network for professionals across the United States with a diverse array of membership and chapters.

Jan 1, 2026

By S. Afrouz, C. Keles, W. R. Reed, E. Sarver, T. Akinseye, A. Greth, L. Pan, F. Animah

The resurgence of severe lung disease among U.S. coal miners has not only highlighted the need for improved dust controls, but also the need for an improved understanding of dust characteristics and monitoring strategies [1]. Following up on prior work by the National Institute of Occupational Safety and Health (NIOSH) to demonstrate a novel wet dust collection system on a roof bolter [2], the current study explores the effect of that system on dust characteristics and uses interlaboratory comparisons to comment on analytical methods. Results indicate the wet system did not appreciably affect the composition or size of respirable dust in the vicinity of the operating roof bolter. However, the system does appear to have substantial benefits for the operator. NIOSH has already shown it can reduce the respirable dust mass concentration to which the operator is exposed during dustbox cleanout [2,3], which is a frequent maintenance activity that can re-aerosolize dust, and new results here indicate the silica and silicates content in this dust may also be reduced, thereby reducing the overall hazard. Moreover, regarding analytical methods, excellent correlation was demonstrated between measurements of quartz mass, taken first by NIOSH and then by a university laboratory, using direct-on-filter Fourier transform infrared (FTIR) analysis. This method is the basis for envisioned “end of shift” silica monitoring (quartz is the predominant form of crystalline silica in coal mines) [4]. For particle-level analysis by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), there was more variability in results generated by two independent university laboratories.

Mar 1, 2024

By J. B. Hedrick

Rare earths were not mined in the United States in 2008. However, processing of intermediate rare-earth concentrates continued throughout the year at the Mountain Pass Mine in California. Consumption of refined rare-earth products increased. U.S. rare earth imports were primarily from China, with lesser amounts, in decreasing order, from France, Hong Kong, Japan, Austria and Russia. The United States imported 100 percent of its supply of yttrium metal and compounds primarily from China. United States In 2008, lanthanide concentrates were processed by Chevron Mining Inc. (previously Molycorp Inc.) at its mine site at Mountain Pass, CA. Chevron Mining sold its entire holdings in the rare earths mine to Molycorp Minerals LLC in September and operations continued at the site through-out 2008. Major uses for these mineral commodities were in automotive catalytic converters, petroleum fl uid-cracking catalysts, permanent magnets, glass-polishing compounds, ceramics, metal-alloying additives, phosphors and recharge-able batteries. Three domestic companies produced and sold lanthanide intermediate concentrates and refined products. Chevron Mining sold its interests in the Mountain Pass Mine to Molycorp Minerals LLC on Sept. 30, 2008. Molycorp Minerals LLC is an investment company owned by Resource Capital Fund IV L.P., Pegasus Partners IV, LP, The Goldman Sachs Group Inc., Traxys North America LLC, Carint Group LLC and Mark Smith. The Molycorp operation previously mined the rare earth fluocarbonate mineral bastnäsite by hard-rock surface methods, and the mine remained on care and maintenance in 2008. Molycorp maintained significant stocks of bastnäsite concentrates, intermediate concentrates and high-purity rare earth compounds at its operations at Mountain Pass. In October 2007, Chevron Minerals completed phase one of its three-stage plan and restarted the rare earth separation plant at Mountain Pass. The company also processed intermediate rare earth concentrates from existing stocks during the first three quarters of 2008. Molycorp Minerals LLC maintained production in the last quarter of the year. The mine at Mountain Pass has been closed since 1998. Future plans are to restart processing of stockpiled bastnäsite concentrates followed by reopening of the mine.

Jan 1, 2009

By Richard J. Waxweiler, Frank E. Lundin, Robert J. Roscoe, Victor E. Archer, Michael J. Thun, Joseph K. Wagoner

[Introduction] Since excess lung cancer mortality was first noted in the late 1800's among Joachimsthal-Schneeberg miners, there have been a number of studies of the long term health effects among various types of miners exposed to elevated levels of radon and its radioactive decay daughters. Substantial excesses of lung cancer have been noted among miners in the Joachimsthal mines (Sevc, 1976) , lead-zinc miners in Sweden (Axelson, 1979) , fluorspar miners in Canada (DeVilliers, 1971) , iron miners in Sweden (Renard, 1974) , uranium miners in Canada (Hewitt, 1976), and metal (Wagoner, 1963) and uranium miners in the United States (Lundin, 1971; Archer, 1976). The latter prospective cohort has also been shown to be at an excess risk of death due to tuberculosis, nonmalignant respiratory disease, and accidents when followed through September 30, 1974 (Archer, 1976). This report extends the followup of this cohort of miners through December 31, 1977 and expands the mortality analysis to investigate more cause-specific categories. [Methods] During the decade beginning with July, 1950, medical teams from the United States Public Health Service (USPHS) examined 3362 white and approximately 780 nonwhite males who had worked underground in uranium mines in the Colorado Plateau at least one month by January 1, 1964. Occupational, medical, and smoking histories were obtained during the examinations and often updated/confirmed during subsequent annual censuses of the miners conducted by the USPHS. The white miners now have been followed-up through December 31, 1977 using the Social Security Administration, Internal Revenue Service, direct telephoning and various other sources. Death certificates were obtained for the deceased and coded directly into the Seventh Revision of the International Classification of Diseases, Adapted, using the rules in effect at the time of death. Deceased miners for whom no certificate has yet been located were assumed dead on the date specified by the reporting agency, cause of death unknown. The uranium miners cohort was analyzed using a modified life-table system developed by the National Institute for Occupational Safety and Health (NIOSH). Person-years at risk of dying (PYAR) were calculated for each miner from his first USPHS medical examination date or date upon completion of one month of underground uranium mining if that was later. PYAR were calculated specific for five-year age groups, calendar periods, and periods after first underground uranium mining. The numbers of cause-specific observed deaths among the cohort occurring by December 31, 1977 were compared to the numbers of expected deaths. The expected deaths were calculated by multiplying the appropriate PYAR by the United States death rates for white males specific for five-year age groups, five-year calendar periods, and cause. The results were summed over the age and calendar period specific categories to obtain the total expected deaths for each cause. Standardized Mortality Ratios (SMR's) were calculated for each cause by dividing the observed number of deaths by the expected number of deaths and multiplying by 100. In some tables, two-sided 95% confidence intervals for the SMR's were computed using either Fisher exact confidence limits, if the observed frequency was less than eight, or approximate confidence limits, if the observed frequency was eight or greater, to indicate statistical significance. Because a priori hypotheses had been well established, one-sided lower confidence limits were used for tuberculosis, lung cancer, other nonmalignant respiratory disease (ONMRD), accidents, and total mortality. [Results] The cohort included 589 miners first examined in either 1950, 1951 or 1953; 753 first examined in 1954; 1235 first examined in 1957; 5 first examined in 1958; and 782 first examined in 1960. In Figure 1 the distribution of the cohort by first year of underground uranium mining indicates that 13.7% started before 1947 and would have thus had an opportunity to be followed beyond 30 years

Jan 1, 1981

By W. Robert Power

Stone is considered by many to be the premium material for beauty and durability in all kinds of construction. Its use dates to the dawn of civilization and only buildings made of stone have survived from ancient times. The use of stone relative to other materials declined from the beginning of the present century reaching a low point in the third quarter, but there has been a resurgence in the use of stone in construction during the past decade, due probably, to new techniques for producing stone, a greater recognition of its beauty and durability, and greater affluence among consumers. The aesthetic appeal of stone is attested to by the many attempts to simulate it in synthetic materials. Today, natural stone is considered by many to be the ultimate in aesthetic appeal, durability, and ease of maintenance. Consumption of dimension stone has increased dramatically during the past decade. The US Bureau of Mines reported that the total value of US consumption in 1978 was $1 13 million and that total imports were valued at $65 million in 1979 (Anon., 1980). In 1989 consumption of domestic dimension stone was valued at $208.3 million and imports at $525 million. This dramatic increase occurred after demand had decreased at an average rate of 2.5% in the two decades prior to 1978 (Anon., 1980). More than half of the imports come from Italy, but production of dimension stone has increased worldwide spectacularly. Meaningful statistics on dimension stone are hard to acquire. The finished piece of stone is a highly value-added product, but stone may be sold as rough blocks, sawed slabs, or finished product. The same piece of stone may therefore be sold and reported three or more times. Furthermore, although the quantity of stone is most commonly reported in tons, stone cladding is more often sold by the surface area and at the same price for different thicknesses. By any measure, however, the production and consumption of dimension stone has increased dramatically during the past decade. A significant indication of the resurgence of stone was the introduction of two new trade publications during the 1980s. Stone World (Tradelink Publishing Co., Inc., Oradell, NJ), introduced in 1984 is published monthly and Dimensional Stone (Dimensional Stone Institute, Inc., Woodland Hills, CA), introduced in 1985 is published monthly. Both magazines provide useful information on new technology, market trends, producing areas and companies, and other information not previously available.

Jan 1, 1994

By Song Jiang, Xianzhi Tan, Minjie Lian

"The ground water heat pump system lades underground hot water which can be heated or cooled by heat exchanger in water source heat pump air conditioner. This system replaces the model of heating of air-conditioning by refrigerator and boiler. In this paper, the formation conditions of hot water energy in Shan Dong are analyzed in order to achieve the purpose of energy conservation and emissions reduction by taking full advantage of water resources such as water pouring and return water of beatification during the productive process of underground metal mine. In order to analyze the issue better, the paper points out some ways and methods for geothermal water often used in underground metal mine. This paper also presents the advantages of the technology of water source heat pump that is applied into underground metal mine. Here is a case study of comprehensive utilization of water source in a certain underground metal mine in Ji Ning. This mine, according to its own actual situation, designs heat pump heat exchange system which is used for indoor heating of buildings and bath for staff. It turns out that the system can save 23% water per year, cut down 3.303 million KW electric energy, and reduce 4160t emission of carbon dioxide. It is concluded that the technology of water source heat pump has broad application prospects in underground metal mine. Therefore, the results show that it is an ideal way to change the present structure of cooling and heating source in metal mine.Introduction In recent years, overuse of fossil fuels has posed a grave threat onto the environment, which makes renewable energy a more important status in energy structure. Development and utilization of renewable energy has become an important direction. Water source heat pump technology is to use solar energy stored in water as cold/heat source to convert energy. Currently, this technology has been widely used in some advanced countries. However, due to facers of implementation technology and component costs, there is still a gap in water source heat pump technology between China and these advanced countries. According to (Blum et al 2011) that after in-depth study, water source heat pump technology has developed rapidly in China recently, and the gap is gradually reduced. Groundwater source heat pump system as a kind of high efficiency, energy-saving and environmentally friendly technology in recent years, more and more get the people's attention. At the same time, its practical application has also been rapid development. Based on (Ni et al 2015) that According to the relevant departments of the prediction, the technology will become the 21st century the most efficient heating and cooling technology."

Jan 1, 2017

By George H. Roseveare

Early flotation dealt primarily with the bulk concentration of sulphide minerals or the separation of one sulphide from another and was referred to as oil flotation because oils and fats were used as reagents. The separation or concentration of one nonmetallic mineral from another developed later with the use of fatty acids. Fatty acids are organic acids present usually as glycerides in tall oil and oils of fish, peanut, cottenseed, soya beans and ethers of veg¬etable and animal origin. Some, of these oils and their derivatives were used by the Phoenicians as early as 600 B.C. in making soap, and the use of such reagents in mineral dressing is referred to as "soap flotation". The first use of oleic acid for the recovery of minerals was the early agglomeration process.' The coarse particles of ore, from 1/16 to 1/4 inch diameter, were coated with large amounts of soap or oil and after screaming from the gangue were recovered by screening, hydraulic or table classification. In 1886, a patent was issued to Mrs. Carrie Everson in which the essential feature was the constituted commingling of pulverized ore, fat or an oil, either animal, mineral, or vegetable, for the purpose of effecting .a. union of the free metal or metallic portion of the ore with such admixed material whereby the same may be changed in subsequent separation of quartz or other rock therefrom by washing or other suitable means. The patent mentions the use of red, cotton seed, caster, sperm and linseed oils, In the early use of collectors the amount of oil for froth flotation was often 2 to 6 per cent by weight of the ore rather than pounds per ton.

Jan 1, 1959

By K. J. Ma, L. Ma, J. Stankus

The paper’s intent is to evaluate pumpable foamed cementitious mine seal material by determining the shear strength of a generic foamed cement in the laboratory. The tests were conducted on three scales: small-size specimens, consisting of cylinders 4 in. in diameter or 3-in. prisms; double shear medium- size specimens, measuring 13 in. by 10 in.; and large-size specimens, measuring 6 ft by 4 ft by 4 ft. The small-specimen shear tests resulted in average peak and residual shear strengths of 128 psi and 56 psi, respectively. These values are fairly consistent with published shear strengths of foamed cementitious material. However, the other two types of shear tests did not achieve the shear strength of a typical pumpable foamed cementitous mine seal material. Based on the test results, the paper concluded that the structural analysis of cement foam seals should be based on their residual shear strengths, approximately 20 psi, determined from small laboratory-scale tests of the cement foam/concrete or rock interface, and not be based on their peak strengths.

Jan 1, 2015

By J. B. Hiskey

The principle oxide minerals of molybdenum are wulfenite (PbMoO4), ferrimolybdite (Fe2(MOO 4)3.nH2O), powellite (CaMoO4), and ilsemannite (Mo304). Wulfenite is found in Arizona, New Mexico, Nevada, Utah, California, and Montana. It is also found in the states of Sonora and Chihuahua, Mexico. Prior to 1915 wulfenite ores were the primary source of molybdenum. The solubility of wulfenite in hot sodium sulfide was first noted by Bonardi(1) during attempts to sulfidize wulfenite material prior to flotation. He identified lead sulfide and soluble sodium molybdate as reaction products. Bacon (2) sulfidized wulfenite in preparation for flotation and by X-ray analysis found the reaction product to be lead sulfide. Holmes(3) made an extensive investigation of the extraction of molybdenum from wulfenite concentrates by leaching. Nearly 100% molybdenum extraction was possible from -100 mesh samples leached for 15 min with 10% sodium sulfide solution at room temperature. Molybdenum extraction from -100 mesh samples after leaching 30 min at a temperature of 45°C using 2, 4, and 6% sodium sulfide was about 32, 79, and 98% respectively. The extraction showed little sensitivity to time, temperature, or particle size using 10" sodium sulfide solution.

Jan 1, 1976

By G. Ahuja

Tests were conducted to investigate the effects of cyclone geometry, operating conditions, and particle size on magnetite classification. The effects of these parameters on the partition curve for narrow size fractions were studied using a 25mm diameter cyclone cleaning -150 µ m coal. Additional tests were run to investigate the effects of geometry and operating conditions on the slurry, solid, and water splits. The relationship between the relative density of the underflow stream and the relative density of separation was also investigated. This paper presents the results from this study.

Jan 1, 1994

By John S. Harper

Can the mining industry in the United States accept the change and challenge of the "Now Generation" of entirely new high-performance automated transportation systems? Good Question! While there has been some revolutionary new thinking and product testing in mining, none has taken place in transportation of ore and waste. With one notable exception - DASHAVEYOR - not a single really new and 'unconventional' system has even been tried on a small scale in the hardrock mines in our country. Admittedly, U.S. equipment manufacturers share the responsibility for the slow progress in mine transportation systems in our country, since they have provided very litte leadership in design innovation or education. First, let me give you my definition of what is meant by the term "Advanced Transportation Systems". Then I will describe and compare such systems, emphasizing the strong and weak features of each as they apply to vertical and horizontal haulage. I will conclude by establishing the principal requirements for implementation of these types of systems in the mining industry in the United States.

Jan 1, 1969

By Charles G. Weakly, Alan M. Lander, Pamela B. Zohar, Robert W. Leonardson

The cluster of gold deposits at the Goldstrike property is located in the Northern Carlin Trend in northeastern Nevada (Fig. 1). At many mature mining camps like Goldstrike, exploration innovation and success may wane with time. In this regard, sufficient exploration drilling was conducted in the area immediately north of the ultimate pit crest and under the final planned pit wall to test for a major deposit. No indications of large deposits were found, however, the majority of drill holes did intercept mineralization. Mining along the northern pit wall exposed significant structurally controlled ore-grade mineralization that had been missed by exploration drilling. In 2002 and early 2003, the mine geology group added reserves to the pit and improved the definition of underground resources by targeting specific ore-controlling structures within favorable stratigraphic units by utilizing relatively inexpensive horizontal RC drilling from the pit wall. The widespread occurrence of mineralization to the north of the pit was re-interpreted to be an indication of continuity of these mineralized zones. In January 2003, 70 feet of 0.332 opt Au at a depth of 710 to 780 feet was intercepted in a dewatering well. This intercept was significantly thicker and higher-grade than average for the area, which confirmed the existence of high-grade structural continuity, and helped secure management support for additional exploration. A timely and cost effective solution was needed to confirm the potential of the area. Immediate follow-up drilling on tighter grid spacing was rejected in favor of improving the geology model. Exploration across the property would benefit from an improved geology model, but to provide results in a timely manner, the area to the north of the Betze pit was chosen as a starting point (Fig. 2).

Jan 1, 2005

By P. E. Lenz

In Nevada, large deposits of diatomite were formed during the Miocene / Pliocene in deep, alkaline lakes. Associated sediments are predominately fine-grained lacustrine with varying fluvial-clastic layers. Tephra layers are common, and probably served as a source of soluble silica for the extensive diatom colonies. Four companies are currently producing diatomite from Nevada deposits. Nevada ranks second to California in annual domestic production. Nevada diatomite is used in filter aids, fillers, absorbents, catalyst supports, and many other products. Economics and mineral reserves indicate that diatomite production in Nevada will be significant well into the next century.

Jan 1, 1993

By James L. McGregor

St. Joseph Lead Company has been paying incentive bonuses for well over 40 years. In 1958 almost half of St. Joe's 1,860 employees in Southeast Missouri received some form of incentive bonus in addition to their guaranteed wages. There are very few payroll jobs in St. Joe s Southeast Missouri organization that lend themselves to a reasonably good measurement of production or quality, or both, where an incentive bonus is not paid. The term "Incentive Bonus" is used to differentiate betwen bonuses that are based on quantity or quality of work, and those that are merely additional pay of a standard amount per hour or day because of an employee being temporarily assigned to some unusual task, An employee temporarily assigned to a job where the working conditions make the job performance unusually difficult or where a special skill is used is often given a bonus of some standard amount per hour or shift in addition to his usual rate. This is merely a convenient way of paying something extra without disturbing the normal rate structure. Actually, it is differential pay similar to that almost universally paid for evening and night shift work. Bonuses of that type are not being considered in this paper. The basic reason or theory for paying incentive bonuses 9s to get improved production at lower cost, Unfortunately, it is often difficult, if not impossible, to find a yardstick by which it can be definitely proved that a particular bonus plan is accomplishing its purpose, It becomes, then, a matter of judgment on the part of management personnel as to the value of the bonus plan. The fact that St. Joe Lead Company has continued to pay bonuses for over 40 yews and has increased the number of bonus schedules used attests to a definite belief that they are beneficial to the company's successful operations.

Jan 1, 1960

By Ward Sumner

The Jones Hill prospect is a Proterozoic age, volcanogenic, semi-massive to massive sulfide deposit. The deposit is located on the western edge of the Pecos greenstone belt in the southern Sangre de Cristo Mountains of northern New Mexico. The prospect is found in a block (West Block) of meta- igneous rocks, primarily diabase, metavolcanic rocks, and metasedimentary rocks (fig. 1). This assemblage is typical of lithologies found in the greenstone belt. Metamorphic grade is greenschist to lower amphibolite. The West Block is bound- ed on the west by Proterozoic age (1.7-1.4 b.y. by Rb/Sr), granitic plutons collectively called the Embudo granite, and on the east by Paleozoic sedimentary rocks, primarily sandstones, shales, and limestones of Mississippian and Pennsylvanian age. The mineralization occurs in a single horizon which has been overturned and cut into two blocks by a high-angle reverse fault (fig. 2). The mineralized horizon is found at the contact of felsic metavolcanic and rnetavolcaniclastic rocks with overlying intermediate metasedimentary rocks. The local stratigraphic sec- tion from bottom to top is as follows: 1) porphyroblastic quartz- sericite schist (originally a rhyolitic, subvolcanic intrusive); 2) quartz-sericite-chlorite-biotite schist (felsic metavolcanic and metavolcaniclastic rocks); 3) chlorite-talc-biotite-sulfide schist (altered felsic metavolcanic rocks); 4) carbonate-quartz-sulfide [ ] chlorite-tremolite-talc schist (mineralized exhalite); 5) quartz- chlorite schist (silicified tuff); and 6) amphibole-chlorite-feldspar- biotite schist (occasional mafic to intermediate metavolcanic flows).

Jan 1, 2013