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By Pierre Gy

"Abstract - This paper deals with industrial complexes such as: (1) a mine producing metal-bearing ore and a furnace(s)/converter(s) where the ore is melted into metal, either directly, or after a mineralurgical concentration; and (2) quarries producing the raw materials required for the manufacturing of cement and the kilns to which they are fed.Each mine or quarry operation results from the exploitation of a mineral deposit. This deposit is never homogeneous. The raw materials which are extracted from the mine/quarry can never be safely fed to a "process" such as a cement kiln or a metal smelter, because the devices involved lack the flexibility required to absorb a very inhomogeneous feed. Furnaces and kilns are known to be very sensitive, sometimes dangerously so, with regard to deviations from a certain ideal feed composition.The purpose of this paper is to present the conditions required to optimize the operation of such a complex, so as to maximize the production, the quality of the product, as well as the profit generated. Two key operations are involved: sampling (to know accurately the materials being dealt with) and bed-blending (to achieve the desired degree of homogeneity). The theories of sampling and bedblending have been developed by the author and presented in various books (Gy, 1992, 1998)."

Jan 1, 1998

By A. Abadías Llamas, N. Bartie, M. Stelter

Evaluating the economic viability as well as the sustainability of the Circular Economy (CE) system requires a deep understanding of the distribution of all elements, compounds, alloys, materials etc. in flows. In this paper, the circularity of the copper value chain, including primary and secondary processing, is rigorously evaluated. The studied system comprises the metallic copper production from primary sources (from mineral to metal), copper-containing commodity production (copper is mixed with other metals) and copper recycling through secondary smelting to close the loop. This is linked to photovoltaic (PV) panels and battery storage. A simulation model of this system is created using HSC Sim, considering more than 30 elements (and its various compounds), 180 unit operations and 800 flows. From the mass and energy balances obtained through the simulation, an exergy analysis is conducted to evaluate the resource consumption from a second law (entropy) perspective. Additionally, these results are complemented through a Life Cycle Assessment (LCA), the recovery of technology elements and by-products is discussed, while quantifying the losses through the value chain. Through the digitalization of the complete system, a better CAPEX and OPEX understanding of the metal recovery and losses can be obtained, as well as the associated resource consumption and environmental impacts. New flowsheets and technologies can be evaluated. Several scenarios show how the resource consumption and the environmental impacts are affected by the recovery of different materials to produce different products. INTRODUCTION A key challenge of the circular economy (CE) is the linkage and optimization of both resource and energy efficiency of the (renewable) energy infrastructure and the resource cycle depicted by Figure 1 simultaneously. In addition, the CE requires the linkage of all stakeholders as shown by Figure 1. This has been discussed in some detail by Reuter and Bartie (2019) and Reuter et al. (2019). Copper and all its associated technology elements is one of the key enabling metals that is an economical copper colored thread through CE society (Reuter & Kojo, 2014). The Metal Wheel (Figure 2) shows the linkage of and recovery of various elements associated with copper and other carrier metals. This reveals that copper acts as an important carrier metal because of its properties i.e. the wealth of technology elements it carries from geological ores, but also its capacity to act as solvent of valuable elements and thence a key closer of various complexly connected element and material cycles when these technology elements are released during copper refining. The same applies to all other carrier metals of modern CE society as shown for example recently in a lead policy brief (Blanpain, Reuter & Malfliet, 2019).

Jan 1, 2019

By E. S. Moore

"The Michipicoten-Goudreau area, bordering on the northeast corner of lake Suferior, has had a tectonic history related to that of the geosyncline occupied by this lake. This basin has been a major structural feature in the Canadian Shield since at least late-Precambrian time. It has been extensively faulted and was the centre of great igneous activity in the Keweenawan feriod . Many of the faults, folds, dykes, and sills in the surrounding regions tend to head directly or indirectly into this basin. Some of the faults in the Michipicoten-Goudreau area appear to run under the eastern part of lake Superior just as the large Keweenaw fault in Michigan extends into the lake on the south side. Some of these faults may even be extensions of or counterparts of the faults on the south side of the lake. Another set of faults in the Michipicoten-Goudreau area runs nearly transverse to some of these major faults, and it is evident that in some places movement has recurred at a later time on faults formed in an early period.STRATIGRAPHYThe rocks of this area, with the exception of Pleistocene and Recent formations, are all Precambrian:"

Jan 1, 1954

By D. J. Hutchinson, M. Lato, M. Diederichs

Light Detection and Ranging (LiDAR)-based applications for geomechanical purposes have recently proven to be a highly reliable and accurate form of remote analysis and documentation. The ability to remotely collect, process and evaluate rockmasses for structural geomechanical applications has benefits ranging from safety to efficiency, and provides a permanent record that can be assessed before and after an excavation has been completed. With the collaboration of Queen’s University and Rio Tinto, the Iron Ore Company of Canada (IOC) mines in Labrador City, Newfoundland and Labrador, evaluated the practical application of the I-Site 4400 LiDAR equipment, in conjunction with the Vulcan geotechnical module for geomechanical purposes. The project provided a comparative analysis between conventional hand-mapping and digital analysis. The analysis indicates that digital mapping could be employed as an active tool within the general geotechnical workflow, where results would be used in pit wall and rockmass support designs. As well, the field work enabled the generation of effective operational guidelines and protocols to maximize scanning efficiency.

Jan 1, 2009

By R. B. Barlow, J. A. C. Fortescue

Originally developed for use in mineral exploration, regional geochemical mapping based on stream (and lake) sediment sampling is showing broader application in other areas of the earth sciences and in environmental science. The purpose of this paper is to focus attention on the role of regional geochemical mapping in relation to geological and environmental studies. This is achieved using a descriptive equation for the chemical composition of a stream-sediment sample and then relating it to the use of successive approximations in geochemical and environmental investigations. The procedure is further qualified with reference to time and process in the formation of regional geochemical patterns. Examples are included of studies based on stream sediments related to bedrock geology, surficial geology, ecology and man's effect on the geochemistry of the environment. The range of applications of regional geochemical mapping in earth and environmental studies is outlined and some conclusions drawn regarding the future development of geochemical mapping under Canadian conditions.

Jan 1, 1980

By A. Galip Ulsoy, K. V. S. Sastry

"This review paper is intended to provide, the mineral process engineer with an introduction to the concepts, terminology. and practice of mineral process control. It also provides an extensive sampling of the vast body of literature relevant to this topic. The topics discussed include the principles of automatic control, instrumentation, mineral processing unit operations, process modeling and simulation, and process and plant control. IntroductionEconomically accessible higher-grade ores are being rapidly depleted, and at the same time the demand for mineral raw materials continues to increase. Mineral recovery from the remaining low-grade or finely dispersed ores requires grinding for liberation. High energy consumption during grinding and poor efficiency associated with the beneficiation of fine minerals are two important problems facing the mineral industry . These problems, coupled with advances over the last 10 to 15 years in the areas of process modeling, instrumentation, computer technology and control theory, have made automatic control of mineral processing systems an important research area(23,52,66,67,120,129,152)."

Jan 1, 1981

By V. Itkin

"Three methods were tested for the beneficiation of aluminum scrap, generated by heavy medium separation of non-ferrous automobile scrap residue. These were: crushing in a shredder followed by screening; grinding in a ball miff followed by screening; and eddy current separation. The best results were obtained with the grinding-screening method. IntroductionThe usual method of aluminum alloy reclamation from non-ferrous automobile scrap residue consists of a two-step heavy medium separation to remove materials lighter than and heavier than aluminum. The resulting aluminum scrap still contains over 15% impurities such as stones and glass, heavy rubber, insulated copper wire , plastics and heavy metals entrapped by macerated aluminum piece s, composite fragments, etc.(2). Upon melting, these impurities create difficulties and yield a low ingot recovery-65% to 70%, hence small foundries avoid this material.There are a number of ways to improve the quality of aluminum scrap such as:(1 ) crushing of the scrap, which powders the brittle content , a major impurity component, followed by screening out of the dust(2) eddy current separation , which removes metals from the material flow, and(3) implement better methods for density separation.The eddy current separation and two variants of the comminution-screening technique were studied by Intermetco Ltd., Hamilton , Ontario."

Jan 1, 1986

By Masami Nakamoto

Controlled thermolysis of gold(I) thiolate complex, [C14H29(CH3)3N][Au(SC12H25)2], at 180 °C for 5 h under an N2 atmosphere produces novel gold nanoparticles passivated by alkyl groups derived from the precursor complex, the TEM photograph of which shows spherical particles with average diameter 26 nm. Since Brust et al. reported the two-phase reduction of AuCl4 - by NaBH4 to afford monodispersed gold nanoparticles passivated by alkanethiolate ligands (1), plenty of preparative investigations on gold nanoparticles (2,3) and its surface modification (3,4) have appeared, because of their potential applications in microelectronics (5). However, those preparative methods generally involve the reduction of AuCl4 - by reducing agent NaBH4 in the presence of suitable organic stabilizers such as alkanethiol (1-4), phosphane (5), quarternary ammonium salts (6), surfactants (7) or polymers (8). On the other hand, O?Brien et al. recently reported the preparation of organically capped gold nanoparticles at 190 °C, where tri-n-octylphosphine oxide and/or n-octadecylamine are used both as a reaction medium and as a passivating ligand (6), but this procedure also needs NaBH4 as reducing agent. Our strategy of novel preparative method of gold nanoparticles is the combination of reductive elimination of thiolate ligands and simultaneous attachment of organic moiety on the growing nuclei. Gold(I) thiolate complexes with ammonium cations were useful for our preparative method. We now report the controlled thermolysis of gold(I) thiolate complexes, [R(CH3)3N][Au(SC12H25)2] and [R(CH3)3N][Au(SC6H4-p-R?)2] (R= C14H29, C12H25; R?= C8H17, CH3), under an N2 atmosphere, where the powder of gold(I) thiolate complexes completely melts to afford the precursor liquid and then the liquid gradually decomposes. In spite of no use of reducing agent and solvent, reduction reaction is thermochemically induced to afford novel gold nanoparticles passivated by alkyl groups rather than by alkanethiolate ligands. Figure 1a shows a typical transmission electron microscopy (TEM) image of gold nanoparticles prepared by thermolysis of [C14H29(CH3)3N][Au(SC12H25)2] at 180 °C for 5 h, indicating a controlled growth of spherical gold nanoparticles. As shown in Fig. 1b, these spherical gold nanoparticles display the size distribution ranging from 5 to 50 nm. Although the particle size is larger than that of thiol-derivatized gold nanoparticles (less than 5 nm) prepared by NaBH4 reduction (1-3), the aggregation of gold nuclei is smoothly regulated and the growth of core gold is limited to be 26 nm in average diameter in spite of thermal procedure.

Oct 1, 2003

By Alireza Sarafi, Alijan Aftabi

"A hydrocyclic system used for mineral separation at the laboratory scale results in the separation of more than 90% of micas. The system functions only by water and might offer advantages where other methods of mica separation are not available. INTRODUCTIONVarious methods for the separation of micas, wollastonite, and garnet, e.g., screening, flotation, magnetic separation, and heavy liquids, are well known (e.g., Spence, 1929; Bates,I960; Gillson et al., 1960; Benjamin, 1971; Connor and Kolhnar, 1991; Collings and Andrews, 1991). However, where these methods are not available, the separation of micas by a hydrocyclic system developed by Sarafi and Aftabi (1991) may prove to be economic. This note is a brief description of the hydrocyclic system. Minerals and MethodFor testing the recovery of mica and other minerals from different rocks (garnet-mica schist, skarn, and pegmatite), standard minerals were tested first, and then rock samples. Pure mineral standards were prepared from coarse-grained samples of pegmatite, mica schist and skarn; the grain size of the minerals separated was more than I cm. The Hydrocyclic System and Mineral SeparationThe hydrocyclic system is shown schematically in Figure 1. In the first step in mineral separation, mineral and rock samples were crushed, milled, and then sieved to minus 250 plus 125 microns. Approximately 10 gm to 25 gm of the sample were inserted in decanter Dt • The motor pwnps, M1 and M2, were then turned on and the water valve rl was opened. At this time, water was flowing turbulently (30 em3/sec. to 50 em3/sec.) and minerals were separated according to their crystallographic nature, density and!or habit. The fInal separation was done by exit valves r2, r3 and r4, while the motor pwnps were still operating. After each experiment, the rt , r2' r3 and r4 valves were closed and the motor pumps were turned off. Following this, minerals in each decanter and the mter were collected, dried and weighed. The whole time of the experiment was optimized to be about 10 minutes, but varied from 3 to 15 minutes for micas and garnets. respectively."

Jan 1, 1994

By M. X. Yao, C. D. Opris, P. C. Patnaik, R. Liu, X. J. Wu

Two cobalt-based superalloys, Stellite 694 and Stellite 712, were functionally graded with reinforcement of titanium-carbide particle for high-temperature wear/corrosion applications. The designed composite specimens were fabricated using powder metallurgy (P/M) technique, combined with hot isostatic pressing (HIP). Calorimetric effects of the alloy powders were investigated using the differential scanning calorimetry (DSC) technique, which provided the basis of the sintering cycles designed. The phases present in the microstructures of the materials were analyzed using SEM and X-ray diffraction. The wear resistance of the materials was evaluated on a pin-on-disc tribometer. It was demonstrated that adding titanium-carbide particles to the alloys has increased significantly their wear resistance. It was also found that the HIP process had improved the density of the sintered specimens and thus enhanced their wear resistance.

Jan 1, 2004

By Jennifer Pakula

Productivity improvements in underground mining are becoming harder to find. Most mines quickly identify deficiencies in their processes and then struggle to make productivity gains beyond that plateau. One way to increase productivity in this situation is to modify existing methods of operation. Vale?s Stobie Mine has been in operation since the late 1800?s employing a variety of mining methods. Many mining advances have been incorporated over time. With the advent of mechanized rubber tired equipment, sublevel cave mining was introduced to allow economic extraction of a large low grade area. Additional productivity gains were seen in the sublevel cave area with the introduction of preloading production drill holes. In preloading, the holes are loaded with bulk emulsion ahead of the production cycle and then primed for blasting as needed. The introduction of preloading, although giving the Stobie sublevel cave process an overall productivity gain, saw an increase in oversize due to the collar priming technique employed. Handling oversize material prohibited the operators from handling additional units of optimally sized material. Prepriming, adding detonators at the toe and midcolumn of the production holes during the preloading process, was identified as a change that could reduce the formation of oversize. This paper describes the introduction of prepriming to the sublevel cave mining method and focuses on the process Stobie employees followed to ensure a safe transition to this productivity improvement.

Nov 1, 2011

By So-Yeong Lee, Moosang Lee, Seung Hwan Ahn, Ho-Sang Sohn, Jongshin Chang

It is necessary to understand the characteristics, phase changes and chemical reactions of flue dusts introduced from a furnace to an off-gas line in order to achieve the stable operation and the improvement. This study is to develop the dust reaction model for chemical reactions of dusts in an uptake shaft of smelting furnace and a waste heat boiler. Phase equilibria and reaction paths in this system were determined by thermodynamic calculation with experimental and industrial data. The oxidation reaction rate of dusts was determined by the gas film mass transfer controlling. And the sulfation reaction rate was evaluated by the unreacted shrinking core model. Kinetic parameters were estimated by reference data including industrial ones. The present study with the developed model shows various effects of temperatures, dust particle sizes, and O2 gas partial pressures on dust reactions. INTRODUCTION The flue dusts from a copper smelting furnace move along a furnace off-gas stream into an uptake shaft and a waste heat boiler (WHB) and electrostatic precipitator(s). It is necessary to control the dust quality in order to stabilize the operation because the sticking behaviors differ depending on the phase of dusts. Phase changes of dusts are caused by chemical reactions at given conditions such as temperature and partial pressure of gases. Therefore, it is required to understand the phase changes and chemical reactions of dusts in order to perform the improvement and stable operation. The present study carried out the investigation to understand their fundamental knowledge. Especially, this study was focused on the kinetics of chemical reactions of flue dusts, developed the model. In particular, the scope of development and utilization of the model was defined as the uptake shaft of the Mitsubishi S furnace and the S-WHB radiation section in the Onsan smelter. Information needed for the modeling work referred to data from these processes.

Jan 1, 2019

By K. Woo

The increasing move to block cave mining methods (including sublevel and panel caving) to access deeper and lower grade ore deposits as near surface sources become exhausted raises questions as to the extent and magnitudes of caving-induced subsidence as it may affect strain-sensitive infrastructure on surface. Predicting these surface deformations is difficult as they tend to be discontinuous and asymmetric due to large movements around the cave controlled by geologic structures, rock mass heterogeneity and topographic effects. Of further impediment is the sparse number of case histories available, in which actual subsidence measurements are reported to provide guidance and empirical constraints for subsidence calculations. This study reports the development of an exhaustive and comprehensive database of available (i.e. public domain) subsidence data from block cave mining operations from around the world.

May 1, 2009

By Y. Buro

The Bachelor Lake gold deposit occupies an ESE-trending, SW-dipping, silicified shear zone with hematitic alteration. It transects NE-trending, steeply dipping Archean volcanic formations and the O'Brien granite. Major W-SW and N- NE-trending faults have affected the ore zone and the emplacement of the granite intrusions. Movements along the WSW set may have opened the fractures filled by the mineralization. Gold is generally associated with pyrite. Its source, whether a granitic pluton or a volcanic sequence, is undetermined, but the granite probably provided the concentrating mechanisms through heat and hydrothermal solutions.

Jan 1, 1984

By Göran Bäckblom

The Swedish mining companies LKAB and Boliden, the equipment supplier Atlas Copco, the general contractor NCC and the specialist company Reflex joined forces in 2005 to advance the field of rock technology for the purpose of mining and underground construction. The creation of the company Rock Tech Centre is part of the strategy developed by the Swedish mining industry to strengthen co-operation with industry, academia and society. This paper outlines the current R&D strategies developed for the industry in general, discusses what focus areas are selected and provides some details on the current RTC project portfolio, especially faster and better drifting.

May 1, 2006

By Chao Yang, Liguo Tian, Yan Yang

"The Jinfeng gold mine is one of the three gold mines that Eldorado Gold has in China and it is the second largest gold mine in China. The mine is located in a relatively remote and mountainous area in the southwestern Guizhou province. The orebody is similar to the Carlin type deposit in Nevada. The mill throughput was designed to treat 3,600 tones per day. The ore comes from open pit mining and underground mining, and is fed to one-stage jaw crushing. The crushed ore is stockpiled, reclaimed and then fed to the SABC grinding circuit. After classification with hydrocylones, the ore is floated, and the resultant concentrate is oxidized biologically in a process known as BIOX®. The oxidized concentrate is then washed in a CCD circuit and finally leached with cyanide in a CIL circuit for gold extraction. Jinfeng produces about 180,000 oz of gold per year.This paper introduces operations and modifications of SABC circuit over the past three years, and then describes some technical characteristic of the SAG mill and other circuits in the processing plant.Major modifications and improvements on the SABC circuit are described in the paper, including:1. Impacts of grinding ball and mill liner with respect to material selection, quality, hardness, manufacturing methods, and interactions between mill liner and grinding ball.2. Effect of milling operation parameters on milling efficiency.3. Impacts of SAG mill scats and modifications of grate size to improve mill throughput.4. Design and construction of a pebble crushing system, and recycle the crushed scats to the SAG mill to improve mill throughput.With the above-mentioned modifications, 20% increase over the design in mill throughput has been realized over the past three years, and operating cost has been significantly reduced. However, some issues still remain, and thus process modifications and technical innovations are still needed."

Jan 1, 2012

By B. R. Casement

"Managing safety on the basis of after-the-fact reaction to accidents, can never be more than partially successful. Injuries will occur as long as the underlying potential for them still exists. Unless unsafe actions and conditions are systematically decreased, no program can have more than a short-term success.The pro-active Bullmoose loss control process, instead, focusses on heightening awareness of work habits, to prevent incidents by reducing their potential.Any safety program will be doomed to failure if the development of safe work habits depends on the safety supervisor or a safety committee. At Bullmoose the focus is on the critical actions out of which losses emerge. The successful application of performance-related feedback is achieved by taking safety, health, and environmental concerns into consideration on every level, and, by doing the right thing in every job done.What is an Exceptional Loss Control Program?If an accident in an organization creates a flurry of interest, resulting in ""cracking down"" on violations for a short period of time then an ""exceptional"" loss control program exists. Unfortunately, exceptional here does not refer to the effectiveness of quality of the program but to the fact that the organization is managing loss control by exception. The degree of management attention in an ""exceptional"" safety program varies over a period of time, remaining low as long as the rate of losses stays within management's acceptable control limit (Fig. I). When the losses rise above this, management becomes motivated to begin ""exceptional"" efforts to manage losses. When the rate falls again to within the accepted limit, efforts to control losses take a back seat.Such a strategy guarantees that losses will be tolerated or ignored as long as the actual rate is below the acceptable limit. Simply to lower the limit would not reduce losses, but would result in an increased number of flurries of management attention to loss control. This ""on-again, off-again"" style of management teaches supervisors and others that basic loss control is not as important as are statistics."

Jan 1, 1993

"“Developed by the CIM Sub-Committee, these guidelines are an addition to Guidelines Specific to Particular Commodities which are appended to the CIM Estimation of Mineral Resources and Mineral Reserves Best Practice Guidelines.Rock Hosted DiamondsJennifer Burgess, Consultant, Sechelt, BCNeil Buxton, WWW International Diamond Consultants Ltd.Darren Dyck, BHP Billiton Diamonds Inc., Kelowna, BCMartinus Oosterveld, (De Beers retired), Plettenberg Bay, South AfricaRichard Routledge, Scott Wilson Roscoe Postle Associates Inc., Toronto, ONMalcom Thurston, De Beers Canada, Toronto, ONPreambleDiamonds are produced commercially from intrusive rock, consisting of kimberlite and lamproite, and from alluvial and marine placer deposits. These guidelines apply to rock deposits; the term ""diamonds"" herein refers to natural diamonds; ""diamond deposits"" refers to diamonds hosted in kimberlite and lamproite rocks; and ""diamonds"" and ""stones"" are interchangeable.The CIM Best Practices General Guidelines for other commodities are also applicable to diamond deposits, however, because of diamond's distinguishing aspects, additional guidelines are appropriate as published in the CIM Guidelines for the Reporting of Diamond Exploration Results and these Best Practice Guidelines for estimating Mineral Resources and Mineral Reserves (MRMR).Diamonds differ from other minerals. Firstly, they occur as discrete particles in concentrations as low as parts per billion. Secondly, the release of diamonds from the kimberlite or lamproite host rock is a function of the excavation and treatment process. Thirdly, the value of diamonds varies from deposit to deposit and varies with stone size within a given deposit. These aspects must be considered when sampling, evaluating the resource and establishing the reserve of a depositThe product from metallic mineral mines is generally quite liquid in terms of number of potential buyers, and the commodity prices and price structure are published daily. In contrast, most diamonds are valued in the overall market context only 10 times a year in ""sights"" and the marketing of diamonds is dominated by a small number of organizations. Diamond valuation is more akin to industrial minerals valuation in that process recovery is important at the ""assay stage"", the impact on price of new goods arriving on the market must be evaluated, and product quality must be acceptable to potential buyers."

Jan 1, 2003

By Leslie F. Sawatsky

Failure of drainage works is one of the principal threats to the sustainability of mine closure facilities but the risk can largely be remedied by appropriate design of mine closure drainage facilities. The feasibility of sustainable mine closure facilities that avoid failure of drainage systems needs to be established during the early stages of mine planning, before mine disturbances make sustainable closure uneconomical. Experience in mine development shows there is often enough latitude in mine plan development to incorporate measures with neutral economic consequence and positive environmental benefit. Project managers need to resist the temptation to develop mine plans and closure drainage plans independently. Integrated mine planning with effective inputs by environmental specialists and drainage designers may affect the overall mine configuration, footprint and schedule. Key issues pertain to the end pit location, waste dump configurations, pit infill elevations, fluid impoundments, diversion channel routing and preservation of flows to receiving waters. Guidelines with illustrations of suitable practices are presented to assist mine planners.

May 1, 2004

By E. G. Langille

"The Premier mine; owned by Silbak Premier Mines; Limited; is 14 miles from Stewart at the head of Portland canal. Development of the property began in 1918; and since chat time a very large amount of gold and silver as well as some lead and copper have been produced from the mine.The area in the vicinity of the mine is underlain by greenstones tuffs, and sediments of Mesozoic age, belonging to the Bear River formation of the Hazelton group. These rocks are intruded by a stock 2 miles in diameter, composed of orthoclase porphyry and called the Premier porphyry. It sends numerous sill-like and dyke-like tongues into the Bear River formation, and is intruded in turn by a granodiorite outlier of the Coast Range batholith. The orebodies occupy fractures and fracture or shear zones. Primary ore consists chiefly of pyrite, galena, and sphalerite, with some chalcopyrite. The upper 300 feet, or locally 600 feet, contained presumably secondary silver minerals."

Jan 1, 1954