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By F. Heivilin

Little did I know, in 1977, that when the A. P. Green Refractories Raw Material Manager showed me 5-6 burlap bags with samples of calcined high alumina bauxite in their testing lab that this was the start of China moving to be the number one user and producer of calcined refractory bauxite. According to Ted Dickson in his August 2008 Industrial Minerals article China produced about 4 million tons of calcined bauxite in 2007 using 2 million tons themselves. They imposed an export limitation of 970,000 tons in 2007 and 940,000 tons in 2008. A 10% growth will take up the difference between exports and production in 4 years. Two of these years are gone. It will take only 4 more years to eliminate the export quota in home use. Then they will be importing unless they increase production. Guyana was exporting over a half million tons in 1975 and sold less than 70,000 tons in 2002. Basai Metals Group bought Guyana?s deposits and is rose to 250,000 tons in 2007 and expects to produce 280,000 tons in 2008. PRICES According to the USGS Prices dropped from $172/per ton for Guyana calcines in 1980 just after the start of Chinese production to $122 in 1985. Guyana prices averaged around $120/ton from 1985 to 2005. China?s price dropped as low as $45/ton in 1995 undercutting Guyana and making it virtually impossible for anyone to get into the market. The price suddenly escalated to $550/ton FOB China in the summer of 2008 when China actually cut its exports in half. The price dropped in the fall as orders dropped. This is a four to five fold price increase. Is this a shortage of bauxite or a monopoly? Australia dropped out of the market in 2008 and Surinam, controlled by Alcoa, is not participating right now. Will these two come back in to make up the difference? Will the price hold up so they can make a profit? [ ] The low prices have undoubtedly affected the prices of the 60 and 79% alumina bauxite which can hold down the quantity of 80% plus calcined refractory needed in the world market. China is starting to upgrade lower quality bauxite up to 90% alumina. With high prices kaolin alteration to high alumina comes into play. The calcined bauxite is also used for proponents, Brown fused alumina, and abrasive grades which compete with Refractories. These and the tightness of supplies needed for metallurgical will hold prices up. TONNAGE China is the number one supplier and consumer of high alumina calcined bauxite in the world. Basai Metals Group Guyana (BMGG) is owned and controlled by Basai Minerals Group of China. This appears to be the second largest supplier. Australia has dropped production and Brazil is just starting to expand. It appears China is going to replace some of exports caused by the Export License 940,000 ton maximum in 2008 by raising Guyana?s (BMGG) production of calcined refractory grade bauxite. Companies exceeded restriction in 2007. Fines have been imposed for 2008. In August 2008 they appear on line to meet the 2008 quota. After August prices have dropped off as orders dropped due to the recession. Guyana was the largest producer in 1975 with 769,000 tons which decreased to less than 79,000 tons in 2002. The U. S. is a small part of the world production. I have used the United States charts to represent world imports because I have little data on what other countries import and pay FOB for their bauxite. China started exporting calcined 80% plus refractory bauxite to the United States in 1979 with 24,000 tons. By 1985 they were the number one importer with 169,000 tons. Guyana who had been number one in shipments to the United States gradually decreased to 36,000 tons in 2006. Guyana has been purchased by China BMGG and will increase there production to over 200,000 tons in 2009. Australia shut down production in 2008 and Surinam has elected to not send any Calcined bauxite to the United States. Imports to the United States from 1978 to present are as follows: [ ] Refractories are important because they affect 96% of the GNP. During the cold war we had stockpiles of 80% refractory grade bauxite

Jan 1, 2009

By Robert G. Ditchburn

The Mariana arc is an ~1,400-km-long intraoceanic arc that marks the southern extension of the Izu-Bonin arc, and is host to 62 ?volcanic centers? of which at least 27 (21 submarine) are hydrothermally, or volcanically active. A surface ship cruise in early 2003 mapped the distribution of hydrothermal plumes emanating from these centers, followed by remotely operated vehicle (ROV) cruises with ROPOS in 2004 and Jason II in 2006. With the exception of one volcano (East Diamante), none of the vent sites visited by the ROVs were host to sulfide mineralization. Rather, they were characterized by high sulfidation mineral assemblages dominated by native sulfur. The sulfur was seen marking the vicinity of vent sites, or as sulfur ?chimneys? (e.g., NW Eifuku and Nikko), or more spectacularly as ?lakes? of molten sulfur, either occupying the summit crater of the volcano (e.g., Nikko), or perched on the flanks of the volcano, near the summit (e.g., Daikoku). Gas (H2S and CO2) was discharging through the molten sulfur. Evidence for these lakes to have either been substantially ?deeper? in their recent past (e.g., Nikko), or existing at other volcanoes (e.g., Seamount ?X?) is given by remnant ?pillars? of native sulfur that are reminiscent of rock pillars in lava lakes found along mid-ocean ridges.

Jan 1, 2008

By Peter G. Zambas

In planning an underground room and pillar mine, the selection of the shaft or portal location and the orientation of the main haulage arteries is of paramount importance, particularly in view of the high dependence of the cost of truck haulage on the proper definition of these parameters. In an effort to facilitate this selection a computer program was written which, by relating the truck characteristics to the areal configuration of the property or ore-body, derives the volume-weighted total fuel and time requirements for hauling ore from every panel within the property to a specified portal or shaft location through a predetermined gridwork of haulage drifts. By varying the size and orientation of the gridwork and the location of the portal or shaft access, an infinite number of configurations can be investigated. The results of this analysis can be plotted to indicate the optimum conditions.

Jan 1, 1971

By Håkan Stille, Kjeld Boye-Møller, Lars Lundström

BACKGROUND Forsmark Power Station is a nuclear power plant under construction at the Baltic abt 120 km north of Stockholm. Investigations on the Site were started in 1969. Areas were reserved for a maximum of 6 units of which the buildings for two of them, Unit 1 and 2, were nearly finished in 1976, when the investigation for Unit [3], here presented, was carried out, cf Fig. 1. [ ]

Jan 1, 1979

By P. W. Conrad, C. Todd, N. West, R. Kramer

"Surface subsidence caused by both underground room-and-pillar mining operations and solution mining operations have each been studied separately, but never combined. In 2008, FMC Minerals began using solution mining at its Westvaco Mine as a secondary extraction method in an area that had been previously mined using the room-and-pillar mining method. Mining regulations require that subsidence associated with underground mining activities be monitored and measured annually. Researchers at Montana Tech were able to develop a relationship between measured surface mine subsidence and solution mining that can be used at the Westvaco Mine to estimate the production of trona from solution mining operations. PROJECT BACKGROUND FMC Minerals (FMC) has increased the production of trona from its Westvaco Mine near Green River, Wyoming, using solution mining as a secondary extraction method in an area previously mined using the room-and-pillar method. The area of interest was mined until 2001 with the use of a borer miner at a depth of approximately 1,600 feet. Currently, FMC determines the amount of trona produced using its solution mining operations by measuring the dissolved solids pumped from the mine. This approach, however, does not account for the location from which the trona was removed. The location from which the trona was removed and the size of the cavern created by the solution mining operations is important to FMC’s mine planning. FMC believed that with proper investigation of the subsidence at the Westvaco test site, a correlation might be found that would allow for the use of surface subsidence measurements to estimate the amount and location of trona production from the solution mining activities. The primary goal of this project, conducted by Montana Tech, was to find a relationship between the measured subsidence and the solution mining activities. The project attempted to model the relationship between the measured subsidence and the solution cavern using Salt_Subsid, an existing subsidence software package from the Solution Mining Research Institute (SMRI), to determine the program’s usefulness for locating and developing the cavern created by solution mining activities. The project also attempted to develop an equation that could be used to predict solution trona production based on measured subsidence. The data used in this study were collected over a seven year period, 2008 through 2014."

Jan 1, 2016

By K Louie

When BHP Copper's Lower Kalamazoo Project commenced production in January 1997, two of the four original hoists had been converted to hoist ore from the Lower K level. Conversions on these hoists not only allowed hoisting from a much deeper level, but also created a higher hoisting efficiency and higher capacity as well. Conversions included new drums, new cables, SCR drives and other solid state control technologies not available when the original hoists were installed. Two of the original hoists were installed in the 1950's and the other two were installed in the 1970's.

Jan 1, 1998

An information system (I/S) plan is a means for establishing and communicating the direction the organization intends to take to provide the information required for achievement of organizational goals and objectives. The rapid advancements in information technology, the increasing complexity of systems, and the growing dependence of mining companies on these information systems have emphasized the need for more comprehensive I/S planning. This subsection explores this need, the role I/S planning can play within a mining company, and finally describes a methodology for development of an I/S plan.

Jan 1, 1979

By Yi Luo, FENGLIANG WU

Explosions and fires originated from longwall gob due to the formation of methane-air mixture have been a severe threat to coal miner’s lives.Many numerical studies on coalmine fire and explosion hazards have focused on the airflow in roadways and mine gobs. However, most of these studies isolate the gob from its surrounding roadways, and the network analysis and the CFD method are applied independently tomodel the two classes of airflows. This approach greatly limits the ability of simulatingmine ventilation flow, especially unable to consider the effects of gob boundary conditions on air exchange between the gob and the surrounding airways. An innovative finite tube method (FTM) is developed to couple the one-dimensional mine ventilation network (MVN) and the 2D/3D gob flow field (GFF). In FTM, GFF is discretized into a finite number of flow tubes each of which is formed by any two adjacent stream lines. These tubes, representing the gob’s field flow, connect the MVN into a new coupling network. To solve the coupling model betweenMVN and GFF, an iterative solution technique is developed inwhich the MVN analysis is used to evaluate the boundary pressures for GFF simulation and in turn the FTM feeds the GFF results back to the coupling network. Based on the FTM approach, a model for gas migration in gob has been established for delineating the hazard zones of explosive methane concentration and spontaneous combustion. A computer program is developed to implement the FTM simulation. An illustrative example with five flow tubes representing the GFF is created to verify the stability and convergence of the FTM solution process. A simulation example also indicates that the accuracy of FTM is improved by 12% compared with previous method. Results of an application case show that the program is capable of quantitatively evaluating the gob’s risk zones prone for spontaneous combustion and gas explosion as well as performing risk analysis for various ventilation scenarios.

Jul 10, 2020

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

8.1 INTRODUCTION Under room and pillar mining if the extraction ratio is low, (i.e., < 50%) a pillar can support the overburden without collapse and there will be no surface subsidence whatsoever. In other words, if the pillar sizes are properly determined to support the overburden weight, the roof strata cannot cave and there will be no surface subsidence, provided the entry width is small and properly reinforced so that a continuous roof fall leading to piping or the total collapse of the roof does not occur. Under the prevailing mining conditions in the US if only development mining is em¬ployed in room and pillar mining (i.e., no pillar extraction), the extraction ratio is usually less than 50% and generally no surface subsidence will occur. If pillar mining is employed, surface subsidence may occur, depending on the extraction ratio and the size of the remnant pillars (or stumps) left in the gob. The higher the extraction ratio, the smaller the stump pillars left behind in the gob. As the size of the stump pillars becomes smaller, the possibility of their support¬ing the roof without collapse is smaller. If all stumps are crushed completely, the roof will collapse and surface subsidence will occur. Again, whether surface subsidence occurs, it depends on whether the remaining stumps can support the overburden or not. Therefore, since the weight of the overburden which the stump pillars have to support is proportional to the mining depth, a fixed¬size stump pillar can support the overburden at a shallow depth, but will collapse under greater depths. In this context extraction ratio is not the only parameter for determining whether surface subsidence will occur. Furthermore, during pillar mining a pillar can be cut away in many ways to finally reach the same extraction ratio. Therefore, the safest way to determine whether or not sur¬face subsidence will occur in room and pillar mining is to compare the strength of all stump pillars in the panel of interest with the weight of the overburden that the pillars have to support. If they are too small to support the overburden, surface subsidence will occur. Under normal mining practices the characteristics of surface subsidence profiles vary with methods of mining. In the US there are two types of coal mining methods, i.e., longwall and room and pillar mining. Longwall mining is indisputably a total extraction method, but different percentages of coal recovery are achieved in room and pillar mining. Recovery is much higher for sections with pillar extraction than those without pillar extraction. For those without pillar extraction, coal recovery increases with increasing entry width or decreasing pillar size. For those with pillar extrac¬tion, the total coal recovery depends on the amount of coal ex¬tracted from each pillar which is in turn dependent on the roof conditions and methods of pillar extraction. Bauer and Hunt (1981) analyzed the characteristics of the subsidence profiles due to the three types of mining methods in Illinois. Fig. 8.1 shows the range of locations associated with the following profile features: profile edge, maximum tensile curvature, maximum slope, maxi¬mum compressive curvature, and maximum subsidence. The scat¬ter of the data increases with decreasing percentages of extraction. The profile is much sharper for longwall mining and becomes milder as percentage of extraction decreases; for longwall mining the profile edge is always beyond the opening, while in room and pillar mining it may fall within. The location of maximum tensile strain moves outward, while that of the maximum compressive strain moves inward as the percentage of extraction decreases and the maximum subsidence decreases with decreasing extraction ra¬tio. The general concepts discussed in this chapter may not apply to the entry development sections between two longwall panels where roof caving in both panels are very severe and overlap each other. Consequently, it must be treated differently. 8.2 CASE STUDIES Kohli et al. (1982) described several case studies on surface subsidence due to room and pillar mining with pillar extraction. In one case, the seam was 6 ft thick and ranged from 650 to 800 ft deep. The panel was 720 ft wide (Fig. 8.2) and was developed with seven entries. Each entry was 18 ft wide and the pillars were driven at 88 ft center-to-center between entries and crosscuts. Dur¬ing retreating, two additional pillars (pillars J and K) were devel¬oped, two blocks ahead of the pillar line, to take the barrier pillar, 160 ft wide, between panel No. I and No. 2. Pillar extraction began by taking a central slice across the whole panel, beginning from pillar 0 through J. After that, each pillar was sliced by 6 wing-slices, 3 on each side, leaving 4 stumps, 2 on each side. One of each pair was triangular shaped approximately 6 ft wide by 26 ft long. The other was trapezoidal, 26 ft long by 16 ft and 10 ft wide at the upper and lower bases, respectively. This resulted in a total extraction ratio of 85% within the panel. Obviously the stump pillars were not large enough to support the overburden and col¬lapsed completely. The final subsidence profiles were rather smooth, just like those under total extraction (Fig. 8.3). The max¬imum subsidence on Lines A and B was about 3 ft for an average mining height of 6 ft, but the locations of the maximum subsidence were skewed toward panel No. 1. Along Line D, the central por¬tion was flat-bottomed, but the maximum subsidence was only 2 ft, mainly because Line D was only two blocks from the right-side edge. Notice in every profile there was heaving of as much as 0.3 ft, beyond the edges above the solid coal. In another case (Fig. 8.4), the seam was 6 ft thick under 650 to 850 ft cover. Three panels, 710, 400, and 350 ft wide, respec¬tively, were extracted side by side. The entries were 18 ft wide and the pillars at 88 ft center-to-center between entries and crosscuts. Pillar extraction was practiced the same way as described previ¬ously. According to the mine maps, there was no barrier pillar left between the adjacent panels. Thus after extraction the three panels formed a common gob of more than 1460 ft wide. This was re¬flected in the development of the subsidence profile along the county road. After Panel No. I was mined, the maximum subsi¬dence of 1.2 ft occurred at Monument No. 1. This was increased to 1.6 ft after the extraction of Panel No. 2 and went to a further 1.8 ft after the extraction of Panel No. 3. The final maximum subsidence of 4.3 ft occurred at Monuments No. 6 through No. 8, while the remaining portion of the county road showed rebound. However it must be noted that the subsidence profiles were rather bumpy and fluctuated, perhaps an indication of the irregular stump pillars that were left and crushed at various time after mining. Moebs (1982) surveyed the subsidence profiles of four room

Jan 1, 1992

By Justin Kolster, Donald Benjamin, Kyle White

Expansion of the Plum Island Wastewater Treatment Plant requires interconnection of three operating pump stations using only two existing 10-ft diameter shafts for access. These two existing shafts require additional support to allow access 130 feet below grade. Interconnection requires rehabilitation of an existing tunnel, excavation of two new tunnels, and abandonment of additional existing tunnels. Construction has discovered unexpected conditions at all three connection points. The CMAR contracting method has effectively accommodated project team discussion, value engineering decisions, and allocation of risk during preconstruction and construction phase services.

Dec 1, 2022

By Richard E. Otoo, Evan J. Owen, Virginia T. McLemore

Disruption in critical minerals supply chains has resulted in the evaluation of various types of mineral deposits for critical minerals potential. Much of the study on critical minerals focuses on occurrence and characterization, but little research has addressed what concentrations of critical minerals in a mineral deposit are required to make an exploration target into an operating mine. Understanding the cut-off grades of ore deposits being actively mined is one criterion to determine if concentrations in an exploration target are high enough. Cut-off grade is defined as the minimum amount of mineral contained in a ton of ore that is sent to the processing plant. Among many factors, cut-off grade depends upon the size and type of the deposit and mining operation, the processing technique, and market prices. This research does not aim to define cut-offs for determining if a mineral deposit is economic. Rather, it defines estimates of concentrations of critical minerals that could be considered good enough for further exploration. For example, ~2% total rare earth oxide (TREO) is the cut-off grade for Mt. Pass carbonatite, but 500 ppm TREO could be an exploration target for coals.

Feb 1, 2025

By John Newby, Mahmood Khwaja, Bernard Theron, Janice McGovern, Bernard Catalano, Michael S. Schultz

Launching a full-size pressurized-face Tunnel Boring Machine (TBM) in difficult ground conditions is always challenging. Recently, few projects have innovated the process by scaling the trenchless method of pipe jacking, and modified steel bell approach, to facilitate the launching of a full-size TBM without the need for large and deep trenches, starter/tail tunnels, or for incrementally installing supporting gear as the machine advances. This paper presents three such projects; evaluates the post-bid contractor proposed modifications; details the innovative use of pre-cast pipe segments to facilitate machine launch; and, provides an overall assessment of the benefits, challenges and lessons learned related to the modified approach.

Jun 13, 2021

By Howard J. Haselhuhn

"The effectiveness of reagent adsorption onto hematite ore particle surfaces is critical during beneficiation to promote effective selective flocculation and dispersion and increase iron oxide recovery. The relationship between aqueous calcium in the process water and the effectiveness of common iron ore dispersants has never before been studied. The nature of common dispersants was studied in the presence and absence of calcium in the process water. The settling behavior of hematite-rich iron ore at pH 11 was assessed in the presence of calcium and inorganic dispersants: sodium silicate, sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and organic dispersant ethylenediamenetetraacetic acid (EDTA). It was found that inorganic dispersants are ineffective at a pH of 11 without activating the surface sites of the ore particles with calcium. Organic dispersants, however, were found to be effective with and without surface site activation.IntroductionThe United States produced 54 million metric tons of concentrated iron ore in 2011 (Jorgenson, 2013). Over 8 Mt were produced using a process known as selective flocculation and dispersion (CCI, 2011). The grade of this ore is slowly depleting, making it imperative that processing efficiency improves. To increase processing efficiency, a complete understanding of the effects of chemical reagents in the process must be acquired. This process relies heavily on dispersants to disperse iron oxides from gangue minerals in settling processes. The mechanism that these dispersants use to disperse the ore and its relationship to calcium in the process water has never been studied. The following extended abstract summarizes the relationship between aqueous calcium in process water and the effectiveness of common iron ore dispersants at dispersing hydrated hematite ore. These tests were carried out at a pH of 11, as this is a typical pH used to ensure dispersion in selective flocculation and dispersion processes."

Jan 1, 2015

By Scott Burchmore, Jason Emery, Michael Melville

This paper presents best practice data management for monitoring of extensometers in Australian underground coal mines. This work is based on the combined experience of the authors and the available literature. The information and ideas presented herein are a culmination of many years of database development founded from mine site-based ground support design, underground inspections, extensometer data management and data analysis. Each author has more than ten years’ experience as a practicing geotechnical engineer at several operating industry wide research project focused on utilizing mechanical extensometer data for data analytics and machine learning. Principal hazard ground control management plans, stipulated in Australian coal mining legislation, outline the mandatory installation of ground monitoring devices during routine mining activities. After 20+ years of data gathering the barrier to implementing modern data analytics remains the challenges imposed by inconsistent data structure and data quality. This inconsistency is still routinely found between sites, companies and mining regions. Through the relatively simple application of a standardized database structure, the potential to shift from simplistic tracking of trigger levels, siloed at individual sites, to an industry standard method for compilation & comparison of monitoring data is enabled.

Jun 25, 2024

By F. Milton Lewis

In this paper an attempt has been made to review the cost trends in producing copper by conventional milling. smelting and hydro-metallurgical means during the last five years. The primary objectives of this cost analysis are to provide a base for future projections as well as to indicate which cost items are more volatile in their influence on overall cost of producing copper.

Jan 1, 1977

By İsmail İnce

The purpose of this study is to investigate the index-mechanical properties of igneous rocks by using the electrical resistivity method. Electrical resistivity, index (P-wave velocity, dry density, and porosity), and uniaxial compressive strength values of 48 different igneous rock samples were measured in the laboratory. Simple regression analysis was performed between index-mechanical properties and electrical resistivity values. Strong exponential and logarithmic correlations were found between electrical resistivity and the index-mechanical properties of the igneous rock samples.

Jan 21, 2022

By R. E. Cook

"Mineral deposits require substantial amounts of energy to transport and be processed into usable form and, as such, present a real processing challenge in that the deposits are never homogeneous and orebody compositional characteristics are all over the map. Extracting the desired mineral(s) from the deposit at sufficient profit margin, despite severe fluctuations in market price, requires process automation architecture capable of supporting an integrated enterprise solution. Such an architecture will encompasses the activities of individuals, process units, process areas, plant level activities, mine management and business planning, and accounting systems. Key to the automation process is the aspect of value generation. This article brings together the various requirements for the automation of a mining enterprise and presents the different aspects of how to obtain value across the entire mining operation.Minerals’ processing sites are historically long lived, with 20-year life-of-mine not uncommon and 75 years not unheard of. Considering that hardware technology advancements are introduced every six months, or less, it is prudent to select process automation systems that adhere to “open” industrial standards versus proprietary based systems. In the minerals processing industry, the key to survival is driving the cost of production per unit volume to the lowest possible level and provide enough profit to sustain operations. Control system architecture and business information technology are rapidly becoming important tools in the quest for productivity. Getting key dynamic business performance information at the right time to the right person or process unit is crucial to successfully achieving corporate goals. The process automation architecture selected must, therefore, be able to integrate to the various networking enterprises and business systems.The mining industry is generally known as an extractive industry that is physically oriented with respect to operations and the activities in which workers engage. Large numbers of people performing manual tasks in difficult surroundings, produce variable outputs. But times are changing – and so are industry best practices. While the nature of work still consists of activities such as ore extraction, ore movement, ore concentration, refinement and logistics, automation innovations are starting to change the nature of many of the production steps. The industry has transitioned from requiring more physical activities by workers to more information management, automated control and collaboration within the operation. Humans are good at situational intervention and nonlinear reasoning and do best when empowered with an overall production perspective. Machines and automation are good at repetitive functions, steady state operation, and managing transitions. Thus, a combination of advanced technology solutions, reliable and useful information and full human contributions are necessary to mining operations for value generation."

Jan 1, 2015

By Paul M. Jr. Musgrove, Thomas D. Henderson, Mark B. Nesbitt

Introduction History. Vat leaching operations began in October 1953. Since that time, about 4.2 million tpy of oxide ore averaging 0.72% copper have been treated. Economic conditions, improved operating methods, and increased production facilities have allowed the ore grade to be reduced over the years. The average ore grade was 0.84% Cu during the 1950s, 0.68% in the 1960s, and was 0.50%, or below, during the 1970s. By 1961 some 35 million tons of oxide ore had been removed from the mine, exposing the underlying sulfide ore body. A 5,000¬ tpd concentrator was constructed and put into operation to treat the sulfide ore in November 1961.1 The original crushing plants were used for both oxide and sulfide ores, but by adding a third crushing shift, six days per week, the total ore treated was raised from 12,000¬17,000 tpd. Dwindling oxide ore reserves prompted expansion of the concen¬trator to 13,500 tpd in 19672 so that exhaustion of known reserves of both ores would occur at nearly the same time. Again, no additional crushing facilities were added during the expansion. It was anticipated that the treatment rate of oxide ore would be reduced from 12,000 to about 9,000 tpd. Instead, the addition of two crushing shifts per week and improved operating procedures have increased the treatment rate to 26,500 tpd-13,000 tpd to the leaching plant and 13,500 tpd of sulfide ore treated in the concentrator. Geology. The Yerington ore body is a disseminated porphyry copper deposit where a quartz monzonite porphyry intrusive contains the major part of the ore values, with some copper mineralization found in the adjacent granodiorite and other rocks. The geology of the Yerington Mine was aptly described by J. R. Wilson (Mining Congress Journal, June 1963). The ore body is one of few porphyries where geologic conditions were optimum for the formation of an important concentration of oxidized ore with minimum economic effect of secondary enrichment. The principal mineral in the oxidized zone is chrysocolla, which irreg¬ularly occurs dispersed throughout the rock and as narrow seams along fissures. The grade of the ore in the oxidized zone is generally the same as in the primary sulfide below, although some massive concentrations do occur as vein-like fissures and as filling of breccia zones. Cuprite, tenorite, melaconite, malachite, and azurite occur but are not abundant. Lying between the chrysocolla horizon and the primary sulfide is a transition zone whose limits are irregular but seldom with vertical range exceeding 50 ft. Chalcocite, cuprite, melaconite, native copper, and chrysocolla occur superimposed on the primary sulfides. Chalcocite replacement of chalcopyrite, as well as secondary chalcocite, do occur. The primary sulfide minerals are chalcopyrite and pyrite, with minor amounts of bornite and covellite. There are no appreciable gold or silver values, and molybdenite has rarely been noted.

Jan 1, 1985

By E. D. Attanasi, M. W. Bultman

Most statistical measures of mineral exploration continued downward in 1986. Prospects in 1987, however, appear to have brightened for exploration as the overall economic health of the mineral industry improved. The Society of Economic Geologists (SEG) survey of US and Canadian firms documents the marked decline in US mineral exploration since the early 1980&apos;s. From 1981 through 1986, the total exploration expenditure by US firms declined by more than 73% (Fig. 1). Exploration expenditures by US firms declined by 66%%. US based professional exploration staffs were slashed by 70% (Fig. 2). Also, many firms have written off some reserves because of weak markets or have not delineated new reserves to replace production. The Canadian government reported that between 1981 and 1986 Canadian molybdenum re¬serves had declined by 30%, lead and zinc reserves by 20%, and nickel and copper reserves by 15%. The SEG survey also shows the immediate impact of the decline in the dollar on US exploration expenditures abroad. Between 1981 and 1986 the share of the exploration dollar spent by US firms outside of the country declined by nearly one-half and exploration acreage abroad declined by 69%. The downward trend of the last six years may finally be near the end as a leaner and more efficient minerals industry starts to gear up for a period of increased activity. An industry survey reported to Mine Development Bimonthly (Metals Economics Group) indicates that mining firms were expected to increase exploration expenditures in 1987 by at least 10% above 1986 levels. Worldwide expenditures for 1987 by companies covered by the report were expected to top $800 million. It is the first time since 1984 that an increase in exploration expenditures was expected. Also, the US Bureau of Land Management reported a 30% increase in new mining claims for fiscal year 1987 over fiscal year 1986. The bulk of the increase in claims was in states having intense gold exploration, particularly Washington and Oregon. Much of the optimism is undoubtedly due to the increases in metal prices that occurred in 1987. Some of these increases include gold, average price up about 20%; copper, average price up 24%; aluminum, average price up 26%; and nickel, average spot price up 20%. The SEG survey shows precious and base metals accounting for 89% of the exploration expenditures in the US in 1986, up 52% from 1981. The US Bureau of Mines estimates that 80% of US exploration activity in 1986 was directed entirely at gold (1986 Minerals Yearbook). Worldwide exploration plans indicate the continued dominance of gold exploration. New programs were announced for Ghana, Malaysia, and Indonesia. Major new exploration programs were also launched for lead-zinc sulfides in Morocco, platinum and palladium in northwest Brazil, rare earth minerals in Greenland, diamonds in Indonesia, and heavy minerals off-shore Australia. Significant gold discoveries were made at Angels Camp in Oregon; South Africa, near Potchestroom; India, in the Chitradgra district; Northern Ireland near Mt. Speerin; Chile, San Cris-

Jan 5, 1988

By Timothy C. Richmond

The Stillwater District is located in south central Montana approximately 75 miles southwest of Billings, the state&apos;s largest city. It lies along the northeast front of the Beartooth Mountains and is within the boundaries of the Custer and Gelatin National Forests. The district contains some of the nation&apos;s most spectacular mountain scenery. Montana&apos;s highest peaks, including 12,799 foot Granite Peak, rise a few miles south of the area. Much of the district is located on a gently undulating plateau which averages 8500 ft. above sea level, broken by hills up to 10,000 feet and slashed by glacially carved canyons, some of which are more than 3,000 feet deep.(Fig. 1) Immediately to the north and east, the land falls away to the Great Plains, stretching unbroken to the Mississippi River. Two major tributaries of the Yellowstone River, the Stillwater and Boulder Rivers, traverse the area and several large streams originate in the district itself. Access to the high mountain country and the adjoining Beartooth Primitive Area is restricted to a few horse and jeep trails continuing from the terminus of improved roads in the bottom of the Stillwater and Boulder Valleys. Hunters, fishermen and cabin owners make intensive use of the area along its improved transportation routes, but hikers seldom venture more than three miles beyond the end of the roads. People from the Billings area are the most frequent visitors.

Jan 1, 1974