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By C. R. Stephan

The Mine Safety and Health Administration's (MSHA) Ventilation Division continues to evaluate proposed explosion-resistant seal designs. There are currently eleven specific designs for explosion-resistant seals that are suitable for construction in underground coal mines. Seal construction in operating mines must be equivalent to those constructed in the Experimental Mine during the explosion testing program. Accidental failures of seals have occurred due to explosion pressures below 138 Kpa (20 psi). The possibility exists that the failed seals were not properly constructed. Also, conditions in the vicinity of the seals may change. Water may accumulate against the seals, heave or sag may cause detrimental effects on the seals, and sloughage of the ribs may negate hitching. If seals are not properly installed or maintained, they could fail when subjected to explosion pressures. If seals fail for any reason, the possibility exists for explosion propagation throughout large areas of the mine. There could be catastrophic consequences to an event of this nature. This report will present a limited discussion on the construction of each of these seals and will address related issues.

Jan 1, 2001

By Heribert F. Broicher, Arne Volland

The application of remote sensing techniques combined with fluorescence spectroscopy is realised in analytical devices called LIF Analysers. The analysis of laser-induced fluorescence facilitates non-destructive, non-contact, on-line and real-time rock identification and quality control of bulk solids in transport. LKAB of Sweden was the first company to test LIF Analysers in the Kiruna Mine for bulk sorting of run-of-mine ores depending on the phosphorus content. Other applications tested in Germany so far are quality control of limestone (iron and/or dolomite content) and rock identification in lignite mining. Of special interest also is rock identification in diamond mines for dilution control. The paper summarises the present state of the application of LIF Analysers.

Jan 1, 2003

By J G. Webster-Brown

The Tui Mine is located near Te Aroha at the base of the Coromandel Peninsula. It was a lead-zinc mine, which closed in 1973 due to declining concentrate prices, high overheads, and high mercury levels in the ore. The site was abandoned, leaving behind an acid rock drainage generating system, including a sulfide-rich tailings dam which has since caused pollution of Tui Stream, as well as open adits and waste piles which drain predominantly into the neighbouring Tunakohoia Stream. At the AusIMM conference in 2003, Harvey and Webster-Brown presented water quality results from the Tui mine site and lower stream catchments in 2002. In April 2006, Environment Waikato undertook remediation works to stabilise the dam and reduce acid drainage entering Tui Stream. In this study, water quality results from the Tui mine site and lower stream catchments are again being determined, in order to compare with the pre-remediation results. Preliminary data collected for summer indicate a minor but consistent improvement in water quality in the lower stream catchments, although lower Tui Stream continues to exceed ANZECC (2000) aquatic life guidelines for Cd, Cu, Pb and Zn. This slight improvement may be due to a decrease in the flow of ARD into Tui Stream, as there does not appear to have been an improvement in quality of the contributing ARD waters.

Jan 1, 2007

By L. D. Tracy

This is the third of the series of reports on coal-mine royalties and leasing conditions in Illinois. The results of the study of District VI were published as Serial No. 2726, January, 1926, and those of District VIII as Serial No. 2745, April, 1926, of the Bureau of mines. The counties of Macoupin, Sangamon, and Montgomery, which are three of the principal coal-producing areas in the northern part of District VII, have been chosen for this report because these counties cover an entirely different part of the State than do the two districts already covered. Some leases in, Randolph and Washington counties are included as they are in the southern part of the district, and the data happened to be readily available.

Jan 1, 1926

By R. Y. Wan

Low grade sulfidic-carbonaceous refractory ore from Newmont Gold Company's Carlin deposit was microbially pretreated. The biological pretreatment process gave partial oxidation of the sulfidic components of the refractory ore but the preg-robbing carbon continued to be active resulting in approximately zero cyanide gold extraction. A 495 ton pilot plant test heap was conducted using acidic thiourea leach following biooxidation. Activated carbon and cation exchange resin adsorption were tested for gold recovery from the thiourea pregnant solution. The results obtained from the test heap were not satisfactory. Gold extraction was low due to slow reaction kinetics which was caused by relatively large particles and very low winter temperatures. Problems existed in the thiourea-test heap and are discussed in this paper. An alternative heap leach process using thiosulfate has been successfUl at the pilot scale for gold extraction following biooxidation pretreatment of refractory sulfidic-carbonaceous ores.

Jan 1, 1995

By Golding D

The Charters Towers goldfield is located in the centre of a Lower to Mid-Palaeozoic igneous complex where schistose, amphibolite-grade metamorphic rocks were intruded by multiple phases of medium grained granodioritic rocks. Several generations of mafic and felsic dykes also occur. Two distinct mylonites cut all but the youngest granitoids. Gold mineralisation occurs in quartz veins located in brittley reactivated mylonite and in sympathetic fissures in the undeformed granitoids. The gold-quartz veins occur in complex, gouge-filled, 2.5m thick zones, with minor sulfides, surrounded by zoned phyllic and propylitic alteration assemblages. Four main vein systems are each restricted to separate granitoids or contain oreshoots near granitoid contacts. No genetic relationship between the granitoids and the vein systems can be documented. The early mylonitic fabrics and the granitoid contacts played an important role in ground preparation and in the localization of oreshoots. Non mylonitized granitoids also served as favourable hosts for many of the lodes. Whole rock values of 180 of the granitoids range between 6.5 and 7.9 per mil. Hydrothermal vein quartzes have 180 values between 12.2 and 15.7 per mil. Mylonite quartzes have values of 8.4 per mil. Variation in 180 values of quartzes is in part related to granitoid host rock type.

Jan 1, 1987

By V. Blet

Rare earth elements (REE) are regarded today as highly critical raw materials but currently lack suitable recycling processes. A combined hydro- and pyrometallurgical process aimed at REE recovery from used NdFeB permanent magnets was recently developed by the CEA. The process integrates the physico-chemical treatment of magnets, followed by a solvent extraction step for the recovery and intra-REE separation using a selective extractant. A subsequent pyrometallurgical treatment via molten chloride salt electrolysis allowed the isolation of pure Dy metal. Technical-economic assessment and life-cycle analysis were also conducted. Following this first successful demonstration, a new project aimed at the recovery of REE from end-of-life nickel-metal-hydride batteries is currently being developed in association with industrial and academic partners. The project aims at evaluating from an experimental and economic perspective different processes converging at the production of value-added products such as cermet materials for catalytic applications, purified REO concentrates, or metallic alloys.

CHAIR: I see a great many safety men in the audience and I hope you will all take part in using up the time that we have left. The point brought up by all was the necessity of education. It is very hard to know just how this is going to be done. We get very little encouragement to do this. At a recent meeting at Rock Springs, 100 in attendance, and most of them mine officials. Another condition which contributes to accidents is the labor turnover in many of our States. With many companies I am told from actual statistics the labor turnover is 125 per cent. Each field has different mining conditions so that men coming from one field are not always familiar with the mine conditions in the field they come to. These are conditions which have to be overcome. WM. LITTLEJOHN: Mr. Harrington brought up the subject of sprinkling. I will try to tell what we are doing at the Utah Fuel Company camps. Our dust at Castle Gate is the most inflammable gas that has yet been tested at the Pittsburgh station of the Bureau of Mines, so it is up to us to use every precaution to keep it down. I will try to tell what we are doing regarding sprinkling from tanks. We now have in operation two tanks in our locomotive roads, one in Castle Gate, one in Sunnyside. These tanks are something like 500-gallon tanks with pump on one end of truck which gets its power from the power wire and has a half circle perforated pipe on the other end of tank. This is simply hooked on to the locomotive. When the pump is started up it throws a fine spray of water all around which wets the roof, the sides and floor. We found this very successful from an economical as well as a working standpoint. A roadway that we probably would have had to pay a man at least two shifts for, covering the full distance, with the ordinary hose and spray, we can do in half a day and do it more thoroughly. We are also figuring on at the present time using the same system on rope haulage ways, which of course will have to be run by a reel from the feed lines, handling say four hundred feet each way before reconnecting. We haven't got it finished, but are working on it at the present time. MR. COLBURN: I would like to say a few words -about this question of education. Education was mentioned by all three sections of the Safety Committee. Education regarding safety might be divided into two branches. One branch is for the official at the mine to keep him acquainted with the latest developments in safety equipment and safety methods. The other part of education is for the workmen. The United States Bureau of Mines is co-operating in both directions. Safety Clubs are organized around the Bureau of Mines First Aid Training, but it is the idea to expand those clubs and teach the miner the advantage of such-things as the closed safety lamp, and also the regulations that have been made for his safety. In Illinois we can't operate with the closed lamp, because the miners in that section of the country are not educated to the advantages of the safety lamp. Another form of education has been taken up by the National Safety Council, consisting of voluntary organizations similar to the Institute, to which all mining men are invited to attend. Such conferences nave been held in the Lake Superior district, in Butte, and in Globe, Arizona, this year. These are to be extended throughout the coal mining regions. CHAIRMAN PRYDE: The Union Pacific Coal Company has also built two tank cars of 600 gallons capacity each. The tanks are connected with hose, so that water can flow from one tank to the other. A centrifugal pump is mounted on a truck, and connected to the front tank. This pump takes its power from the trolley wire. The discharge from the pump is perforated, so that it sprays the floor and sides of the entries. We expect to use this water train on main haulage ways where we have no sprinkling line.

Jan 1, 1923

By J. T. Clancey

The potential inadequacy of natural gas reserves to supply projected requirements in the 1980's has been pointed out.(1,2) As a result, interest has arisen in the development of new, potentially low-cost processes for the conversion of coal into high BTU gas. In June, 1964, the office of Coal Research (U. S. Department of interior) and Consolidation Coal Company (now a subsidiary of Continental Oil Company) entered into a contract to continue work on coal gasification utilizing the Consol CO2 Acceptor Process. Work under this contract has been specifically directed toward the use of lignite as the carbonaceous feed, although the process is also applicable to non-caking subbituminous coals. The primary objective of this work was to establish the technical feasibility in continuous bench-scale equipment, of the novel features of the C02 Acceptor Process. Secondary objectives were the testing of commercially obtainable acceptors and the design and economic evaluation of a commercial facility. The bench-scale process development has been completed successfully and the construction of a large pilot plant at Rapid City, South Dakota, has been authorized. It is the purpose of this paper to review the technology of this new gasification process and to present the current projected economics of a plant producing 250 MM SCFD of pipeline quality gas.

Jan 1, 1969

By Bruce A. Kuyper

Routine core drilling at the Cove deposit failed to confirm gold-silver grades and length of intercepts observed in reverse circulation drilling. A drilling program was designed to ascertain whether the disparity was due to problems with reverse circulation drilling techniques, core drilling techniques, or the erratic nature of the gold-silver mineralization. Special sampling devices and core drilling methods were employed. Data obtained from core-reverse circulation twins showed that down-hole contamination during reverse circulation drilling accounted for much of the variation between reverse circulation and core drill results. Down-hole contamination occurred as a result of high ground-water inflows eroding friable vein material from hole walls.

Jan 1, 1991

By Geoffrey Gilbert

A study of specimens shows that the key to both oxidation and enrichment at Duck-town is the behavior of pyrrhotite, which is in part dissolved and in part replaced by marcasite. Enrichment takes place chiefly at the expense of marcasite. THE material that forms the basis of this paper was collected in the spring of 1922, during a ten-day visit to Ducktown by the writer in the company of Prof. L. C. Graton. The time available for the work was far too short to allow anything like a thorough study of the deposits, and structural and stratigraphic questions, though they have an important bearing on the origin of the primary ores, were necessarily left untouched. Attention was focussed on the zone of oxidation and enrichment; and by devoting most of our time to the upper levels, open pits, and old workings, and examining the deeper levels only thoroughly enough to obtain a fair idea of the nature of the primary sulfide ore, we were able to make a reasonably complete survey of the various orebodies. With this field work for a background, the writer later made a study, in the Harvard laboratories, of the specimens obtained during the visit. As some of the facts brought to light by this study appear to be new, it seems worth while to set forth the outstanding features and a proposed explanation of them. Much of the Ducktown material that is obviously of greatest significance, as regards oxidation and enrichment, is soft and crumbly. Notwithstanding the desirability of gaining from such material all possible information as to its mineral composition and textural relationships, but little has heretofore been learned regarding it; but, by suitable preparation of this material in connection with the present study, it has been possible to examine it under the microscope without any disturbance of its texture and about as satisfactorily as if it were hard, fresh ore. The information thus gained has contributed measurably to the results set forth in this paper.

Jan 3, 1924

By C. Geier

Previous mine incidents show weaknesses in mine rescue preparedness from poor training in decision making, leadership and incident command center (ICC) protocols. Computer simulations offer a larger range of training opportunities for mine rescue teams focusing on exploration and communications. The mine rescue simulator developed by the Colorado School of Mines and Rite Solutions Inc. utilizes four computers for the instructor and team, with the instructor monitoring the team?s progress. As the team explores, it relays information back to the Fresh Air Base, which then reports to the ICC. This forces a three-step communication procedure, enhancing the team?s overall communication skills and developing ICC protocols. The simulator is decision-based, demanding team decisions be made quickly. Upon completion, teams commented positively. Generally, participants said that the simulator is useful for learning how to communicate and make decisions during mine rescue emergencies. This mine rescue simulator improves team training, providing effective communications practice with an easy setup and no production interruption.

Feb 1, 2014

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Jan 12, 1959

By Rich A. Lamb, Paul J. Axtell, Michael K. Muchard

"Since 2010, the Minnesota Department of Transportation (MnDOT) has performed eight full-scale compressive load tests on large-diameter pipe piles at four different project locations across the state. All of the piles were 42-in diameter, open-ended pipes driven to practical refusal on sedimentary bedrock with D125-32 diesel hammers from three separate manufacturers. The rapid load test method in general accordance with ASTM D7383-10 (Statnamic method) was used along with high-strain dynamic testing and subsequent signal matching. Results of these tests indicate that the axial nominal resistance of these piles in compression is not controlled by geotechnical considerations when driven with an appropriately sized hammer and installation criterion. Rather, the predominantly elastic load-deflection behavior of the piles under compressive load suggests the axial nominal compressive resistance is controlled by the structural capacity of the pile. In all instances, the rapid load tests indicated a nominal resistance exceeding that produced by high-strain dynamic tests due to insufficient hammer energy to fully mobilize resistance. In all cases, the hammers used were able to easily install the piles through the soil overburden. Mobilizing a larger hammer simply to demonstrate high-strain dynamic resistance is not economical or practical. This paper presents the subsurface conditions at each location, the ensuing test results, and the ramifications for future projects in Minnesota utilizing large-diameter open-ended pipe piles.INTRODUCTIONThe Minnesota Department of Transportation (MnDOT) has recently performed eight full-scale compressive load tests on large-diameter pipe piles at four different project locations across the state. The four project locations described in this paper where pile load testing was performed are shown in Figure 1 and exist in the southeastern portion of Minnesota. The projects are all major bridges crossing the Mississippi River in three instances and the St. Croix River just above the Mississippi River in the other instance. The first project is the TH 61 Mississippi River crossing in Hasting, MN where two load tests were conducted. The second is the TH 36 St. Croix River crossing in Stillwater, MN where two load tests were performed. The third project is the I-90 Mississippi River crossing in Dresbach, MN where three load tests were conducted. The final project is the TH 43 Mississippi River crossing in Winona, MN where one load test was performed."

Jan 1, 2017

"Injection technology has been an important subject from the early days of ladle metallurgy until the present. During the last decade, there have not been many publications in the area of injection technology. It is the author's opinion that with the challenge to find new solutions especially to environmental and energy related problems as well as better understanding of phenomenas from computer modelling, a new era of inventive injection technology developments is at hand. This is illustrated in the article with examples from six different areas where MEFOS is or have recently carried out R&D work related to issues from the injection technology field. IntroductionThe boom in injection technologies came with the introduction of ladle metallurgy treatment during the '70s and '80s. Since then, the theories and principles have been thoroughly laid down by a number of scientists and also published at several early SCANINJECT conferences.Not many new technologies/applications have been presented during the last ten years. This might lead one to believe that everything is known and done. Those, like MEFOS, who are challenged to find technological solutions to a number of environmental problems and energy saving issues in the pyrometallurgical field are, however, continuously faced with the task of developing new injection technologies.Especially, the call for sustainable technologies to solve environmental problems is a challenge for metallurgists all over the world and it will surely induce a revival of injection technologies. So, in order to encourage all injection experts, let us share some new experiences and let us encourage each other's creativity to solve some of the demands of the future society.The following show some examples of technologies under development, or recently tested."

Jan 1, 1996

By Vito J. Colangelo

The primary object of this study was to determine the effect of ferrite and its orientation upon the mechanical properties of a precipitation -hardening stainless steel with particular attention to the short-transverse properties. The investigation consisted of Jour major parts : the preliminary investigation of billet properties, the effect of forging reduction and ferrite content upon mechanical properties, the effect of notch orientation upon impact strength, and the relationship of heat composition to ferrite content. Low ductility and impact strength in the short transverse direction were found to he associated with the orientation and shape of- the ferrite plates. It was also determined that impact strength varied with notch orientation. The test values obtained with the notch perpendicular to the plane of the ferrite plate were lower than those obtained in the notch-parallel condition. The over-all investigation showed that high ferrite contents in general had a deleterious effect upon mechanical properties and that the ferrite content could he minimized by exercising rigorous control of the heat composition. A careful balance of elements, nitrogen in particular, must he maintained in order to reduce the formation of ferrite. THE precipitation-hardening stainless steels were developed to fulfill a need for high-strength corrosion-resistant alloys. In the annealed condition they are soft and ductile and possess many of the desirable characteristics of the austenitic stainless steels. In the hardened condition, the alloys exhibit the high strength and hardness of the martensitic stainless steels. The alloy under consideration in this investigation has a nominal composition as follows: C Mn Si Cr Ni Mo N 0.13 0.95 0.25 15.50 4.30 2.75 0.10 The hardening mechanism is identical to that of other hardenable steels in that it depends upon the transformation of austenite to martensite. This alloy because of its annealed structure and its ability to be hardened combines the desirable forming and corrosion properties of the austenitic grades with the high hardness and strength levels attainable with the hardenable grades. The reason for this apparent duplicity of proper- ties can be explained by considering a basic metallurgical difference between the hardenable stainless steels and those of the austenitic group. Both types are austenitic at 1800°F but, while the martensitic grades transform to martensite upon rapid cooling to room temperature, the austenitic grades remain austenitic even when cooled to temperatures below room temperature. The major difference then is in the degree of austenite stability. This stability can quantitatively be described by the Ms temperature. The Ms is defined as that temperature at which austenite begins to transform to martensite. The austenitic grades for example may be cooled to -300°F without producing significant quantities of martensite. The hardenable stainless steels on the other hand have an Ms temperature in the vicinity of 400" to 700°F. In cooling to room temperature, these alloys traverse the entire Ms-Mf range and show almost complete transformation to martensite. The semiaustenitic stainless steel, however, occupies an intermediate position with respect to its austenite stability. The analysis is so balanced that the Ills temperature lies at or slightly above room temperature. The resulting alloy retains much of its austenite at room temperature and yet responds to hardening heat treatments. Achieving this delicate balance of elements is therefore of great importance. Slight imbalances of the equivalent Cr-Ni ratios frequently result in the presence of 6 ferrite. It is the effects of this ferrit with which we are concerned, more specifically the effect of the quantity and ferrite orientation upon mechanical properties, particularly ductility. PROCEDURE A) Preliminary Investigation of Billet and Forging Properties. In order to determine the effect of ferrite on billet properties, billet stock from three heats with various ferrite contents was utilized. Tensile specimens were obtained in the transverse and longitudinal directions from this material and heat-treated as shown in Tables I and 11. Forgings were made from these same heats, the purpose being to determine what effect, if any, the ferrite might have upon the mechanical properties. These forgings were made in such a manner as to elongate the ferrite in the longitudinal and transverse directions. The method of forging was as follows. A section was cut from a 6-in.-sq billet of Heat A and flat-forged to 1-1/2 in. thick. Working was done from one direction only with no edging passes as shown

Jan 1, 1965

By N Kreutzman, A Moilanen, V Palosaari

Carboxymethyl cellulose, CMC, is widely used in mineral processing as a flotation depressant, mainly for the depression of carbonate and talcaceous gangue in the flotation of Cu-Ni sulfide and PGM ores. Although CMC is a common depressant that can be used in the flotation of different ores, understanding of the interaction mechanisms between CMC and mineral particles in different flotation circuits and different pulp conditions is still limited. Electrokinetic measurements, microflotation and laboratory-scale flotation tests were carried out to optimise the action of CMC depressants in the flotation of a PGM ore. Standard and new CMC brands produced and characterised by Noviant were used in the study. Pure talc and chlorite minerals and a low-grade PGM ore composite were used as test materials. A laboratory flotation test evaluation was performed using the recovery-grade relationship and double value index (DVI) calculation to estimate the effects of both valuable and harmful components on the product value. Solution conditions play an important role in the depression of gangue minerals such as talc. The most favourable conditions for MgO depression were found to be mildly acidic in which conditions the electrostatic repulsion between the CMC molecule and talc is minimised. Similar effects were obtained with electrolytes that affect the conformation of the CMC molecule and the mineral surfaces. In addition to the control of chemical conditions in the pulp, CMC molecules were modified to optimise structural variables. The new CMC brands developed in this work showed significant potential to improve flotation performance, particularly when pulp conditions are controlled.

Jan 1, 2005

Risk management has taken on renewed vigor since the economic crisis of the late 2000s. The resources of governments, individuals, and corporations are being stretched to a point where only the most promising projects move forward. Risk management is a crucial part of the decision making process, yet it remains a broad term that includes disciplines from engineering to finance. A collaborative effort will be necessary to ensure that the most auspicious and appropriate projects are the ones moving forward. Risk management can be quantified to an extent by comparing the likelihood of an instance with the result of consequence of the instance occurring. In this manner it is possible to assign risk factors to instances and ultimately, begin to associate monetary value to the instance. Carbon sequestration is an emerging field that has a number of unique challenges. Risk management and mitigation must be an integral part of the overall picture. This begins with the planning and design phase, continues through implementation and production, site closure, and does not cease until termination of liability. The ability of carbon sequestration projects to successfully assess, mitigate, and recover from leaks will be a decisive characteristic of overall success. The costs of mitigation and failure will need to be analyzed on a test level, but will still need to be reliable enough to extrapolate to a commercial level operation. This paper will build a risk management profile based on case studies and field tests in Tennessee and Virginia. These tests are scheduled to commence in late 2013 and consist of small-scale injection tests in unconventional storage reservoirs with an emphasis on enhanced coalbed methane (ECBM) recovery and enhanced gas recovery. The ultimate goal will be to provide a clear and concise direction to move carbon sequestration from the test phase to commercial scale. While it is necessary from a risk management perspective to analyze all risk points, the scope of this paper will focus on pre-injection risk assessment for carbon dioxide (CO2) leakage potential. Despite the differences between the two tests, CBM compared to shale among other differences, a framework for analysis and mitigation can be developed pertaining to leakage risk. The probability of each type of failure will be assessed and analyzed, and plans to mitigate or reduce these risks will be reviewed.

Aug 1, 2013

By T. F. Tomb

on' January 6, ,1992, the Mine Safety and Health Administration (MSHA) issued an Advanced Notice of Proposed Rule Making (ANPRM) for diesel particulate (DP). The ANPRM identified five areas where the Agency was seeking additional information to assist in the rule making process. These areas were exposure 'limits, risk assessment, consideration of other information, sampling and monitoring methods, and feasibility. The period for submitting information relative to the ANPRM closed July 10, 1992. Prior to issuance of the ANPRM, the agency was involved in conducting studies to evaluate sampling and control technologies and to gather information with respect to occupational exposures to diesel particulate in underground mining operations employing diesel-powered equipment. Since issuance of the notice, additional studies have been conducted to provide supplementary information in these specific areas. Results of these additional studies indicate that average DP levels in coal mines not using aftertreatment range from 0.9 to 2.1 mg/m3. Aftertreatment devices can reduce these levels by approximately 50 to 90 percent. Studies conducted in metal and nonmetal mines showed average DP levels ranging from 0.3 to 1.6 mg/m3.

Jan 1, 1994

By J. Dean Warner

In 1984, as part of a project to evaluate Alaskan occurrences of certain critical and strategic minerals, the Bureau of Mines investigated a columbium-bearing regolith on upper Idaho Gulch, near Tofty, AK. The regolith is derived from weathering of a dolomitic marble and consists mostly of iron oxide minerals with accessory apatite, zircon, xenotime, rutile, monazite, and the columbium minerals aeschynite, columbite, and ilmenorutile. Two regolith lenses contain 340,000 lb of columbium resources at an average grade of 0.07 pct. Calculated composite concentrates from two regolith samples (approximately 200 lb each) contained 53 and 57 pct of the columbium at grades of 0.97 and 0.86 pct, respectively. In each case the grade could be improved to 1.1 pct Cb with a sacrifice of 9-pct recovery. The regolith's mineralogy, trace-element geochemistry, and similarity to descriptions of other columbium-enriched regoliths suggest that the underlying marble may be a carbonatite. The lack of associated alkalic igneous rocks and the stratiform nature of the regolith, however, may be interpreted as evidence for sedimentary origin of the marble. The marble and regolith are a lode source for some of the minerals in the Idaho Gulch placer deposit.

Jan 1, 1986