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By Juan Mori Arellano

El presente texto describe la evolución de la tecnología con sus limitaciones iniciales en su aplicación, el cambio cultural de una empresa en cuanto a sus necesidades de conocimientos, la globalización de los mercados y el alto nivel competitivo que ha permitido adoptar diferentes esquemas de mantenimiento con el fin de aumentar la eficiencia en equipos de carguío superficial.

Mar 1, 2017

By Amado Yataco

El presente texto describe el panorama de las inversiones durante el período 2008-2017 a través de tres períodos: 2008 Enero 2017; 2016 Enero 2016 y Enero 2017. De acuerdo a este contexto, las inversiones mineras declinaron sin un ingreso significativo. Sin embargo, dado el número de megaproyectos mineros de clase mundial y las reservas mineras se plantean algunas medidas que coadyuven a la más pronta recuperación de las inversiones en los dos rubros más destacados: Maduración, ejecución de proyectos y exploraciones.

Mar 1, 2017

By Robert Burgess, Dale Gill, Jaco Steyn, Bill Kyslinger

"With mining, especially coal extraction, comes the necessity of supporting the roof. Since the 1950s, the primary method for roof support has been the use of roof bolts. Roof bolting is considered one of the most hazardous jobs in underground coal mining. In 2004, there were 3,405 injuries reported to the U.S. Mine Safety and Health Administration (MSHA). Of those injuries, 17 percent were associated with bolting machines (593 injuries). The majority of the injuries resulted from rock falling from supported roof. However, injuries involving a part of the body being struck by, or caught between, during bolting and drilling occurred with relatively high frequency (Burgess and Steiner, 2007).Roof drilling and bolt installation is labor-intensive and repetitive. These labor-intensive and repetitive requirements can lead to cumulative trauma. Operators are expected to perform a considerable amount of lifting, carrying, bending, reaching and stretching. Back and shoulders become sore from bending and twisting to install bolts or lift and position drill steels, wrenches and bolts. Confined operator spaces also contribute to difficult and awkward working positions for the operators (Cornelius and Turin, 1998).In South Africa, the majority of the roof bolting machines used are “man-in-position” style machines (Fig. 1). This puts the operator in close proximity to where the drilling and bolting process is performed. When proper operation procedures are followed, it has been proven to be a very effective, productive and safe system. The MSHA-certified automatic temporary roof support (ATRS), canopies and dust collection system of Fletcher bolters all provide the operator with unparalleled protection. However, there are some occupational hazards inherent to the zone located next to the drilling and bolting zone. This has led some customers to request relocating the operator away from this zone. The idea being that the operators will no longer be located in the face area, greatly reducing their exposure to dust, noise, machine and geological hazards."

Mar 1, 2017

By N. Bat, N. Sarantsatsral

Blasthole sampling practices were investigated at the Erdenet copper and molybdenum mine in Mongolia to address grade reconciliation issues. The goal of the study was to determine if the particle size distribution (PSD) of blasthole cuttings was accurately reflected in the samples. The study additionally examined if the measured grade was related to the particle size of samples. Using a sector sampler specifically designed to collect samples for the study, six large samples were collected from three blocks following a specialized protocol. Each sample was split into nine size fractions, ranging from larger than 12 mm to smaller than 63 µm. Copper and molybdenum grades were determined for each of the size fractions. For comparison, nine samples were collected from the same blocks following the standard mine sampling protocol. These samples were also split into the same nine size fractions. As with the other samples, grades were determined for each of the size fractions. The results showed that the PSD in the samples collected following the standard operating procedure varied significantly from sample to sample. This variation was much lower for the samples collected following the specialized protocol. Loss of fines was also indicated in the standard mine sampling process. These observations suggest that the standard sampling protocol did not consistently capture the PSD. The copper and molybdenum grades increased as particle size decreased, regardless of the sampling protocol used. This observation underscores the importance of the PSD of a sample being representative of the true PSD. Given the low number of samples in the study, it is not a strong conclusion that the standard sampling protocol captures the PSD inconsistently. However, it could be taken as a caution. On the other hand, the grade versus PSD relationship is more certain, given that it was observed regardless of the sampling method used.

Feb 1, 2017

By R. E. Vivas, J. A. Villa

"Located in the state of Colima, Peña Colorada is one of the largest iron ore operations in Mexico. The project is owned in equal parts by ArcelorMittal and Ternium. Though boasting a production capacity of 4.1 Mt/a (4.5 million stpy) of concentrate per year, Peña Colorada is faced with declining ore grades. In order to respond to this situation, Peña Colorada had to expand production even further. This expansion created various challenges that were overcome by the adoption and application of new technology. Examples of these technological innovations are discussed in detail in this article and include improvements in geo-modeling, mine planning, and mine operations. The successful implementation of these technologies paid for itself many times over, and has led to significant improvements in production and performance, while lowering the operating costs and reducing the variance between planning and execution.Project overviewPeña Colorada is a mining company that produces about 30 percent of the iron ore in Mexico. This project generates about 1,200 direct jobs and 3,000 indirect jobs, making a significant contribution to the local economy. Similarly, Peña Colorada invests in its local communities through numerous educational programs, scholarships, university agreements, social development, environmental agreements, etc. Peña Colorada’s operations consist of an open pit mine located in Minatitlán and a pellet plant located in the port city of Manzanillo, as shown in Fig. 1. Technological innovationsMost mining projects around the world typically follow the logic of “mining the next best ore.” Consequently, head grades tend to decline over the life of the mine. In the case of Peña Colorada, a decline in head grade combined with a decline in iron ore prices forced the operation to adapt to a new business environment and adopt new technologies to face these challenges. However, the first step along this process was to increase the confidence and reliability of the resource model. This task involved additional drillhole campaigns coupled with more detailed modeling techniques. Once the block model was completed, new optimization studies and production schedules were evaluated with new optimization tools that improved many aspects of the mine plan. The Peña Colorada block model has undergone 3 expansions to reflect additional information not available in the past. The model has expanded to the East and Southwest. The latest model expansion increased the total number of benches to 98 as a result of positive exploration results. Similarly, new geotechnical studies were prepared, which provided new guidelines for pit slope design, and new technology was implemented to monitor ground movement and slope stability. Two sectional block model views in Hexagon Mining’s MineSight 3D, along with the pit designs and geologic solids are shown in Fig. 2."

Feb 1, 2017

By A. Noble

"Froth flotation circuits are widely used throughout the mineral processing industry for the concentration of fine particles. It had been estimated that nearly 2 Gt (2.2 billion st) of ores are treated globally each year using this versatile separation process (Fuerstenau, 1999). Due to the high feed tonnage, a large economic incentive exists for flotation plant operators to optimize the performance of this critical processing circuit. Prior to the 1950s, the optimization of flotation circuits primarily involved the manual adjustment of operating variables based on visual observation and sporadic sampling (Lynch, Harbort and Nelson, 2010). During the next several decades, however, the advent of improved on-line instrumentation coupled with the rapid development of high-speed microprocessors allowed the industry to develop more advanced control systems that could quickly adjust operational parameters in response to disturbances in ore characteristics and plant flows. These early online controls typically involved feedback loops designed to stabilize cell performance through the automatic manipulation of process variables such as pulp levels, gas rates and chemical dosages. The set-points for these controllers were often set by plant operators based on one or more operator objectives, such as maximizing throughput, recovery or grade. More recently, these regulatory controllers have been interfaced with high-level data display and management systems that provide operators with the ability to better optimize flotation plant performance based on mathematical models and rule-based algorithms (Greet, 2010).While tremendous strides have been made during the past several decades, even the most modern flotation plants are still faced with the long-standing question: “What are we trying to optimize?” From an operator perspective, some common responses include “Maximize tonnage of saleable concentrate” or “Maximize metals recovery at a customer-specified market grade.” These replies may or may not reflect those of management, who often focus on economic goals such as “Maximize profits for each operational unit” or “Maximize rate of return for all corporate assets.” Unfortunately, these high-level objective statements do not always translate well into practice due to the disconnect between plant operating protocols and product value. Attempts have been made by industry to overcome this issue using various types of optimization routines such as linear programming or other optimization engines. While this approach does have some merit, these blind routines require considerable input data and interpretational expertise and provide little or no fundamental insight that can be used to drive improvements in concentrator performance."

Feb 1, 2017

By Erick Lino

Como parte del proceso extractivo de la minería, se generan materiales de desmonte que deben ser almacenados en topografías bruptas y planas dependiendo de la capacidad de almacenamiento que requiera el proyecto. La geometría y los taludes de estas estructuras deben ser diseñados tomando en cuenta las propiedades de resistencia del desmonte de mina. Por ello, el presente texto describe la importancia de la caracterización geotécnica de este material con el objetivo de diseñar el depósito de una unidad minera en condiciones estáticas y dinámica.

Feb 1, 2017

"Iron ore is the source of primary iron for the world’s iron and steel industries. Its production can be reported as crude ore, usable ore or iron content of ore. Historically, the U.S. Geological Survey (USGS) used reported crude ore production from China in tabulations of world iron ore production while other countries have typically reported their production in terms of usable iron ore. When China’s crude ore production was tabulated with usable ore production from other countries, world iron ore production totals have been overestimated by 10 percent to a high of content and may include products such as concentrates, direct-shipping ore, pellets, and sinter.• Iron content, also referred to as metal content or grade, denotes the amount of elemental iron in the crude or usable ore.BackgroundIron ores consumed in the steel industry typically require an iron content greater than 58 percent before being considered commercially usable. Iron ores that are not commercially usable must undergo beneficiation to raise the iron content. Approximately 98 percent of the world’s usable iron ore production is consumed in blast furnaces to make pig iron, which is further processed to make steel.High-grade iron ore mines can supply usable iron ore, known as direct-shipping ore, to blast furnaces, with minimal physical processing and no beneficiation. With direct-shipping ore, the reported production for crude ore and usable ore are the same. Ore from low-grade deposits must undergo beneficiation to increase the iron content before it can be used by the steel industry. In this instance, the mined material is called crude ore and post-beneficiation concentrates are called usable ore; the amount produced will be less than the crude ore amount. With the notable exceptions of countries such as Australia and Brazil, most of the world’s iron ore deposits are low-grade and require beneficiation."

Feb 1, 2017

By Chee Theng

"Keep calm and carry on mining. That has long been the conventional wisdom in the mining industry, a largely cyclical one that has weathered roller-coaster booms and busts. But in the years from 2002 to 2016, an unprecedented steep rise in commodities prices that lasted a decade and then took a sharp turn downward had made it hard for gold and silver miners to stay the course.“The last 15 years highlighted some of the structural and inherent challenges that our industry has, from product price uncertainty to long lead times to the capital intensity of our business,” said Mitchell Krebs, president and chief executive officer of Coeur Mining, who was the luncheon speaker at the American Exploration & Mining Association’s 122nd Annual Meeting held Dec. 5-9, 2016, in Reno, NV.Looking back, Krebs said, “We were given this enormous gift of a commodities super cycle, and the industry kind of blew the opportunity.” While gold prices rose 319 percent and silver prices rose more than 200 percent over the 2002 to 2016 period, the XAU index of 30 gold and silver mining companies’ stock prices went up by only 20 percent.Entering 2016, precious-metals prices have made a comeback, with gold rallying strongly from a six-year low at the start of the year. This time, the industry is ready. Companies are leaner and meaner, with lower costs, reduced debt and an increased focus on higher grades and quality ounces. Although opportunities were missed in the past, the industry has got its act together and is now well positioned to take advantage of a price upswing and even to show profits when prices fall, as they did in August 2016, pushed down by a strong dollar."

Feb 1, 2017

By Amado Yataco

"La minería es la actividad económica que genera el mayor porcentaje de impuestos y contribuciones al país. Bajo esta perspectiva, el presente texto determina la influencia de las exportaciones mineras en la evolución del tipo de cambio (soles &US$) y, en una etapa preliminar, inferir cuál es el aporte indirecto de la actividad minera al sostenimiento del Producto Bruto Interno Nacional (PBI)."

Feb 1, 2017

By Diego Benites Negrón

El presente texto describe los resultados de la caracterización mineralógica de 28 muestras con contenido en sulfosales de plomo y cobre de origen hidrotermal provenientes de la sierra central del Perú. Por ello, se busca caracterizar la mineralogía de la zona con énfasis en las sulfosales y el aporte de la plata que esta pueda contener. Asimiso, se realizaron análisis mineralógicos por difracción de rayos X a fin de conocer las especies minerales no metálicas.

Feb 1, 2017

By Augusto V. Ramírez

"El presente texto revisa algunos aspectos de la historia minera en los Andes Centrales -particularmente la negociación minera de Aguas Calientes, ubicada en Casapalca. La mina data de 1917, cuyo propietario fue Ricardo Bentín Sánchez. Asimismo, se revisa los antiguos procesos de extración y ventilación, la oficina de concentración, enfermedad y accidentes de trabajo y los aspectos sociales de la vida en Aguas Calientes. "

Feb 1, 2017

By Chee Theng

"In 2013, Coeur Mining had more than $55 million in general and administrative (G&A) costs and less than $100 million in cash flow. This year, its G&A costs stand at $30 million, down by more than 40 percent, its all-in sustaining costs have shrunk by more than 30 percent, and its cash flow is above $200 million. To realize this, the company aggressively reduced both its corporate overhead cost and operating cost and repaid more than $300 million in debt.The more robust balance sheet meant the precious-metals producer was well positioned to reap the rewards of an upsurge in commodity prices in the early part of 2016. Its stock price soared from $1.75 in January to $15.98 in August. Although the stock price has since dropped to around $9 due to a stronger dollar and a more hawkish Federal Reserve that recently raised U.S. interest rates, shifting the opportunity-cost argument away from buying gold and silver, Coeur remains attractive to analysts in light of its prudent spending and improved fundamentals.Focus on balanced portfolioCoeur is the largest primary silver producer and one of the largest gold-producing companies in the United States and one of the largest silver companies in the world. Incorporated in 1928, the U.S.-listed company has a total of five operations: three in the United States, one in Mexico and one in Bolivia. About two-thirds of its revenue comes from the United States.The company is conscientious about having a balanced portfolio, so no single mine accounts for more than about 30 percent of its business. Being in three different jurisdictions provides further diversification, and its revenue split of about 60 percent from gold and 40 percent from silver gives it some metals mix. This year, it expects to produce about 466 t (15 million oz) of silver and 10.3 t (330,000 oz) of gold."

Feb 1, 2017

By Venancio Astucuri

"El presente texto describe las cuatro competencias que debe poseer un ingenierio de minas para un desarrollo sostenible de la minería. Dichas competencias se dividen en personales, académicas, profesionales y de ingeniería. Este grupo de competencias pueden ser usados también para un proceso de autoevaluación, donde cada uno pueda medir sus competencias con el fin de determinar brechas y superarlas, de forma que las empresas puedan plantear requisitos mínimos para sus diferentes posiciones laborales y, finalmente, para que en las instituciones educativas, estos puedan diseñar de forma adecuada sus respectivos planes de estudio."

Feb 1, 2017

By Scott Rodibaugh

El presente trabajo describe las aplicaciones representativas de la PPC (pressure-powered centrifugue) en minería, diseño básico, función y la experiencia de aplicación de OEM de motores. Asimismo se detallará ejemplos de desempeño de campo de la PPC como experiencias en un sistema hidráulico de camión minero, un motor diésel de camión minero y una trituradora de mineral que lleva el circuito de lubricación. De otro lado, se abordan los métodos de análisis de laboratorio para detectar los rasgos clave del fluido y evaluar la condición del contaminante.

Feb 1, 2017

"When boring a tunnel, homogeneous hard rock is the exception rather than the rule. While contractors can set goals such as meters per month and performance incentives, it is also prudent to plan for difficult ground. A properly designed tunnel boring machine (TBM) can tackle fault zones, water inflows, squeezing ground, or whatever the risk may be. The alternative is not a good one: modifying the machine in the tunnel after bad ground is encountered. Not only does this result in increased downtime, but it also needlessly exposes the crew to the tunnel conditions. In the worst case scenario, the entire operation grinds to a halt.However, an accurate GBR cannot always be obtained, particularly for mountainous, high cover tunnels in remote locations. And even with a thorough GBR, unforeseen geological events can occur. What can be done in these situations? Difficult Ground Solutions (DGS) is ground investigation system with a suite of options that can be added to a shielded hard rock machine or dual-mode, Crossover machine to better enable advance when conditions are unknown or difficult conditions are anticipated.DGS consists of a set of integrated features tailored to a specific project’s geology. The main components of the system allow for ground investigation ahead of the TBM, increased monitoring and methods to keep a machine shield from becoming stuck.In fault zones and squeezing groundIf fault zones or squeezing ground are known or suspected, or if there is even a possibility of encountering them, this can greatly affect the TBM operation. Shielded machines protect the crew from the surrounding rock, and they can bore and line a tunnel efficiently, but in fault zones and converging material their shields can be their downfall. Avoiding a stuck machine is paramount to project success. DGS employs several features to avoid the problem of a machine becoming stuck. The first of these is multi-speed cutterhead drives. These drives effectively give the machine multiple modes of operation—high speed, low torque for hard rock, and low speed, high torque for difficult ground. Designing a machine with high-torque, continuous boring capabilities allows that machine’s cutterhead to restart with break-out torque in difficult ground. The net effect is that the machine can keep boring in the event of a face collapse and can bore through fault zones and running ground where the potential for cutterhead jamming exists. Going one step further, multi-speed gearboxes give the machine the ideal earth pressure balance- (EPB-) type torque if larger sections of soft ground are anticipated.Secondly, TBMs can get through squeezing ground and faults using Continuous Shield Advance. This design utilizes a stepped shield configuration — where each successive shield is slightly smaller in diameter — to avoid becoming stuck in converging ground. External shield lubrication is an added insurance against becoming stuck, using a series of radial ports that can pump Bentonite into the annular space to act as a lubricant in squeezing material.As a last effort, if a machine has already become stuck the TBM can utilize augmented, or “super” thrust. Additional thrust jacks can be added to supply an extra boost in a short stroke, generating enough force to break loose a trapped shield."

Jan 12, 2017

By Kim B. Shedd, Erin A. McCullough, Donald I. Bleiwas

"The earliest known use of cobalt was to make blue glass in Mesopotamia before 2000 B.C.E. Since then, innovations across many diverse industrial sectors transformed cobalt into an essential commodity for contemporary society. The physical and chemical properties of the element cobalt and its alloys and compounds make them indispensable for a variety of applications, including aircraft engines, hybrid electric vehicles, machine tools, missile guidance systems, petroleum refining and smartphones. As a major industrialized nation, the United States is a leading consumer of cobalt and cobalt-containing products. However, with few exceptions, U.S. cobaltcontaining ore deposits are of low cobalt grade. Historically, U.S. cobalt mine and refinery output have not met domestic cobalt demand. As a result, U.S. cobalt chemical and alloy producers need to procure most of their cobalt from the international market, which can become susceptible to supply risk.The 1978 Cobalt Crisis illustrates supply risk. At that time, the Democratic Republic of the Congo (DRC) (then known as Zaire) was the world’s leading producer of mined and refined cobalt. An insurgent invasion of the country’s copper-cobalt mining region during a period of high cobalt demand and low producer inventories caused a temporary supply shortage in the international market. The monthly average cobalt spot price increased from $18/ kg ($8/lb) before the crisis to $99/kg ($45/lb) seven months later. The high price and concern about potential disruptions in supply prompted manufacturers to reduce or substitute for cobalt where possible, and encouraged increased recovery of cobalt from scrap. The DRC has regained its position as the leading producer of mined cobalt globally and continues to be characterized by high governance risks (U.S. Central Intelligence Agency, 2015; World Bank, undated). This article will present current and historical world cobalt production trends, which can help inform discussion about the variety of international supply chain risks consequential to its trade."

Jan 12, 2017

By S. E. Vanderslice, J. A. Hummer

"The results of laboratory evaluations were used to compare the potential of two alternative, biomass-derived fuels as a control strategy to reduce the exposure of underground miners to aerosols and gases emitted by diesel-powered equipment. The effects of fatty acid methyl ester (FAME) biodiesel and hydrotreated vegetable oil renewable diesel (HVORD) on criteria aerosol and gaseous emissions from an older-technology, naturally aspirated, mechanically controlled engine equipped with a diesel oxidation catalytic converter were compared with those of widely used petroleum-derived, ultralow-sulfur diesels (ULSDs). The emissions were characterized for four selected steady-state conditions. When fueled with FAME biodiesel and HVORD, the engine emitted less aerosols by total particulate mass, total carbon mass, elemental carbon mass and total number than when it was fueled with ULSDs. Compared with ULSDs, FAME biodiesel and HVORD produced aerosols that were characterized by single modal distributions, smaller count median diameters, and lower total and peak concentrations. For the majority of test cases, FAME biodiesel and HVORD favorably affected nitric oxide (NO) and adversely affected nitrogen dioxide (NO2) generation. Therefore, the use of these alternative fuels appears to be a viable tool for the underground mining industry to address the issues related to emissions from diesel engines, and to transition toward more universal solutions provided by advanced engines with integrated exhaust aftertreatment technologies. IntroductionDiesel engines have been the workhorses of modern society for industrial and transportation enterprises. Diesel engines of all generations are extensively used in a variety of light-, medium- and heavy-duty applications in underground mining operations around the world. Fuels obtained from various sources and with wide-ranging chemistries have been combusted in diesel engines. However, the bulk of the currently used fuel can still be traced to nonrenewable petroleum sources. The petroleum-derived diesel fuels are primarily made up of saturated acyclic hydrocarbons (parafins or alkanes), aromatic hydrocarbons (arenes or aryl hydrocarbon), and unsaturated hydrocarbons with double bonds (olefins and alkenes). Improvements in the quality of petroleum-based diesel fuels was identified in federal regulations as an important piece in resolving the puzzle of diesel engine emissions (Environmental Protection Agency, 2001, 2004). The reduction of U.S. diesel fuel sulfur content below 15 ppm had the effect of lowering sulfate emissions and enabling the development and implementation of catalyzed emissions control technology across a wide spectrum of applications."

Jan 12, 2017

By Bjorn Olsson

"Heavy impact. High frequency hammering. Extreme abrasion. Building on the experience of owning and operating its own mines, Ovako has developed a deep knowledge of how vital the right steel properties are in withstanding the extreme loads encountered in every part of the drill string. That is why Ovako’s product development process is focused on understanding the specific load cases and manufacturing operations associated with rock tools.The punishing conditions of percussive drilling can push the limits of most materials. And heavy mechanical loads are only the beginning. Highimpact energies at high frequency are a major source of fatigue. High temperatures result from impact energy losses. And abrasive, erosive and adhesive wear are constant risks. Handling any of these varying demands at a single point along the drill string is difficult enough — which makes optimizing for the entire drilling system an extremely complex challenge. Engineering for specific loadsOvako has specialized over many decades in analyzing the dominant loads for each of the parts and components used in rock tools, and testing for individual applications in its laboratories. The most critical fatigue properties are controlled through the steel metallurgy, and supported by performance measurements through extensive rotating bending fatigue (RBF) testing, along with special methods that combine impact load with various wear loads. The result is a fit-for-purpose steel with tightly controlled performance properties, making it possible for customers to precalculate the expected life time of their components for highly automated and repetitive processes Tailoring steels for the processing route.The same levels of control and predictability must be carried through to the customer’s own manufacturing processes. By ensuring minimal variations in chemical composition, everything from heat treatment and welding to automated machining can be carried out with high consistency. With precisely controlled material properties based on an existing processing route and exact load case, customers are able to minimize their total tool production costs while ensuring optimal performance for their end products. Development of Hybrid SteelBuilding on this experience in the mining industry, Ovako has developed a new steel family, known as Hybrid Steel, designed to meet the demands of high-stress, elevatedtemperature applications where mechanical and fatigue strength are critical. Traditionally, steels for these applications are produced by expensive small-batch processes. Hybrid Steel, however, enables high volume production at a competitive cost.The world of steel has traditionally been divided into clearly separated categories of tool steel, stainless steel and lower alloy engineering steel. Hybrid Steel is now challenging that division, offering attractive properties from all three categories."

Jan 12, 2017

By Mikael Ramström, Mark Board, Clayr Alexander, Wes Johnson

"The Coeur d’Alene mining district in northern Idaho was first discovered more than 130 years ago and has been the most prolific silver producer in the United States. The Lucky Friday Mine of Hecla Mining Co. (Fig. 1) is the oldest (76 years) and deepest mine in the district, producing approximately 725 t/day (800 stpd) from narrow, vertical lead-zinc-silver veins. Cut-and-fill stoping is currently employed at depths to about 2.3 km (7,500 ft) below ground surface, making it one of the three deepest mines in the western hemisphere. The #4 Shaft, a winze collared at approximately 1.8 km (5,900 ft) below surface and extending to a depth of nearly 2.9 km (9,600 ft), was recently completed to exploit the high-grade 30 Vein, whose resource has been identified to at least 3 km (9,700 ft) in depth.As with other deep mines worldwide, a number of challenging engineering issues occur, including: high in situ rock stress, squeezing ground, seismicity, high in situ rock temperature that requires refrigeration, diesel equipment that generates diesel particulate matter (DPM) requiring high ventilation airflow rates and long travel times for worker transport to mining areas.This article describes the methods that Hecla Mining Co. has employed during the past 50 years to combat these issues, with emphasis on the current efforts to implement continuous, mechanical mining with automated or teleremote operation and to introduce electric and battery-powered equipment to minimize refrigeration and ventilation requirements for the removal of DPMs.Geology and in situ stressThe host rock mass is an extremely thick sedimentary sequence (the Belt Series) that has been tilted vertically by mountain building. The rock mass in the current section of the mine consists of weak, heavily foliated argillites and stronger, bedded silty-argillites termed siltite. The vertical veins (80° to 85° dip) are parallel to the foliation with an approximate width of around 3 m (10 ft). There are two regional, vertical faults that parallel the vein; one forming the hangingwall of the orebody and one approximately 90 m (300 ft) in the footwall. Additionally, there are several thin, rough northdipping faults that occur in the footwall of the vein which terminate on the major vertical faults.Both the argillite and vein package rock have moderate strength, with uniaxial compressive strength averaging about 100 MPa (14,700 psi with a range from about 70 to 125 MPa), and are moderately abrasive, with CERCHAR abrasivity index of 2 to 3. The major in situ stress is horizontal and oriented in a northwest direction with magnitude about 1.5 times the vertical stress. Consequently, the Lucky Friday stress magnitude at depth is analogous to significantly deeper South African gold operations."

Jan 12, 2017