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By R. L. Bullock

For many years, the combined efforts of machinery manufacturers and mine operators have endeavored to achieve greater productivity from the men involved and the machinery and capital invested, by developing methods to drill blast holes more effectively. Obviously, this means much more than simply developing a drill that will drill a single hole faster. Considerable attention over these years has also been given to methods of carrying and positioning the drilling machine on versatile jumbos, whereby the man's time can he better utilized by the faster drilling machines. Likewise, the art of blasting to utilize the holes that were drilled to achieve the maximum amount of fragmented ore and the methods of moving the broken ore have also progressed. But each phase of the production cycle just described must be made to balance with the other phases of the work. Obviously, major breakthroughs in only one phase don't always generate more "rock in the box" per manshift. Yet, through the persistent effort of the machinery developers and the researchers, the progressive attitudes of mine managers, backed by corporate capital investments, and battle after battle at the operating level, progress is made. Then, if the innovated system is good enough to "stick", in a few years it becomes the system that the newer method must replace, after the same repeated struggle. This is the situation that many mine operators find themselves in today, Looking at their production cycle, which is assumed to be efficient and balanced between drilling, blasting and materials moving capabilities, they tend to guard any visable disruption of the balance of that day's production, and many would prefer to maintain the status quo indefinitely. Yet, if history repeats itself, we can expect any major breakthrough in the cycle to trigger other innovations in the

Jan 1, 1975

By R. H. King

Recently, the North American mining industry experienced a severe recession, forcing managers to take dramatic steps to cut costs and compete in the difficult international market. Some of these steps were closing mines, reducing work forces, renegotiating wage agreements, and purchasing the most productive equipment. Managers are now looking beyond these traditional avenues and are focusing more on advanced technology. In the present environment, it is essential that mine operators obtain the maximum use of capital expended on equipment. However, mine workers do not obtain maximum efficiency or productivity from equipment because the adverse and hazardous mine environment impedes human performance. Also, the efficient use of large, complex machines calls for levels of precision that many times are beyond the capability of even highly trained miners. A possible solution to this problem is a machine that mines without operators - autonomous mining machines. However, numerous problems confront researchers who are attempting to develop such equipment. Some mining tasks are not always composed of a series of cyclic motions readily performed by factory floor robots. In addition, mining takes place in the geological environment where conditions are highly variable and unpredictable. As a result, these machines must be able to sense and adapt to variations in operating tasks and environment. Considerable autonomous vehicle research has been completed, especially for defense. However, autonomous vehicle (AV) technology has not advanced to practical application yet (King, 1988) and mining research is necessary in areas: representing mining specific knowledge; •analyzing and reasoning about sensor data in the mining environment; and •discovering completely new mining methods or new approaches to existing methods that become apparent when we remove the constraints imposed by the necessity of human operators. A specific machine, the LHD, can be used to show the problems for researchers who are attempting to develop autonomous machines for mining. This author chose the LHD because it can borrow concepts developed for autonomous navigation by military programs. But considerable mining research is also required. Furthermore, studies done at the Henderson mine, in Colorado, show autonomous LHD 's promise cost and safety benefits (King, 1988). At Henderson, LHDs load ore from draw points, tram to an ore pass, dump and return, or switch to another draw point. An autonomous LHD must sense vehicle position along the route, relate sensor data to stored-map information, to determine location, follow drift center lines, plan paths between dump position and initiate appropriate control commands, sense vehicle operating status and vehicle health, key on features or targets for special tasks like high speed turns, perform end of travel tasks (loading and dumping), and detect and avoid obstacles. These goals are similar to those for shuttle cars, trucks, and front-end loaders. Therefore, much of the technology is transferable. Each Henderson LHD extracts six to 40 dippers from each of a series of draw points. The LHD transports the ore to an ore pass within 55 m (180 ft) of the draw point, making the longest round trip 110 m (360 ft). The LHDs have very fast hydraulic dumping and loading systems that reduce the round trip cycle to less than one minute. Even though the LHD is capable of 500 trips per shift, the average production is 300 dippers. Man trip and lunch reduce available operating time to 6.5 hours per shift. Mucking difficulties (setting large boulders aside), operator breaks for activities like talking shop, and cleaning and smoothing roads further reduce operating time. Supervised autonomy can reduce the number of operating units by increasing operating time per shift since computer controlled machines can operate during lunch and between shifts and reduce operator errors. If dippers per shift increase from 300 to 350 (long-range goals are 500 dippers per shift), constant production requires only 10 operating LHDs and two spares. Manpower requirements drop from 24 to four by controlling five machines from one workstation. A review of technology available from the Autonomous Land Vehicle, the Advanced Ground Vehicle Technology, the Ground Surveillance Robot, and other programs, show the following differences between others work and mining industry needs: •If we focus initially on mobile haulage vehicles, we can navigate from a map. We do not need to explore. •We can modify the environment to reduce the navigation requirements. •We have a harsher environment than any of the research programs have encountered. •Our equipment must operate faster and more precisely than present AVs. •Our equipment must operate reliably over long periods of time. •We must have better onboard machine health monitoring and diagnostics. •The AV programs do not address geosensing. •The major AV programs are not cost-effective. For example, we cannot afford the computer power for robust image processing, yet. To computer control an LHD, we must replace the guidance and monitoring skills of experienced operators with sensors, computing hardware, interfaces, and several software mod¬ules. Experienced operators avoid collisions and load efficiently in piles that may contain oversize muck. Collision avoidance without an operator requires sensing all obstacles in the draw

Jan 1, 1991

By J. Humphries

With today?s turbulent markets and unprecedented global opportunities, the need to optimize net present value and internal rates of return from capital investments has never been greater. To help address the need, this paper presents an overview of the key processes and strategies for achieving maximum return from capital projects. Best practices discussed address stage gate management for project evaluation, selection, and oversight, project execution efficiency, value improving practices, operational readiness, and operational excellence. The paper also includes a model of key metrics and benchmarking with tips for application. [ ]

Jan 1, 2011

By Arthur A. Brant

Your chairman has asked me to deal with questions of education relative to our present and projected trends in the field of mineral expiration. First comes our definition of education--and education is not the merely formal acquiring of academic knowledge, but the understanding, using and projection of knowledge into our channels of life and thought activity. This past year makes us realize the extent to which price and economic cut-off may stimulate or curtail exploration,, But exploration does not consist solely in the discovery of sources of material. There is just as inspiring and imaginative a territory in the develop¬ment of uses and application--and no one in our base metal industry but would hope that our educational processes would fertilize those springs of inspiration that lie dormant in us all, toward the- imaginative conception of new uses--lead roofing cloths or felts, non-tarnishable copper utensils, further zinc solid state application. Thus an educational pattern should seek to develop imagination and thinking beyond--the possibility of that small but oh so difficult step just ahead of the existing,

Jan 1, 1959

By Naeimeh Shabani, Hamid Mirzaie, Javid Sadeghi, Hoda Jafarizadeh-Malmiri, Afshin Javadi

Iron oxide nanoparticles (Fe3O4 NPs), despite their small size, are stable and have a large surface area that allows for absorption and removal of ions as well as turbidity in a short period of time. Thus, the present study addressed the synthesis and characterization of Fe3O4 NPs synthesized using the co-precipitation method and evaluated their effect on the coagulation process in water treatment. The Fe3O4 NPs characteristics were evaluated as follows: magnetic properties were measured using a vibrating sample magnetometer (VSM), surface area using Brunauer–Emmett–Teller (BET), crystal phase using X-ray diffraction (XRD), and morphology using field emission scanning electron microscopy (FESEM). In addition, the effects of the synthetic Fe3O4 NPs on the turbidity reduction of water in various pH levels were evaluated. The synthesized Fe3O4 NPs were without any impurity in the sizes of 22–32 nm, surface area of 99.6 m2/g, pores’ mean diameter size of approximately 10.6 nm, and maximum magnetic saturation of 66.21 emu/gram (emu/g). Using 0.2 g of synthetic Fe3O4 NPs with an initial turbidity of 17 NTU and pH of 6 could reduce all water turbidity (100%). Considering the cheap and facile production and separation, as well as the possibility to reuse them and reduce the sludge water content, iron oxide Fe3O4 NPs can be effectively used for turbidity reduction in the water treatment process.

Oct 26, 2020

By Howard Brown

High purity, high brightness limestone deposits in the San Bernardino Mountains and Mojave Desert region occur in upper Paleozoic carbonate rocks which are part of an upper Precambrian and Paleozoic sequence that unconformably overlies crystalline basement. The Paleozoic strata are divided into formations and members, and correlated with strata of the inner Cordilleran miogeocline. The region has been affected by multiple Mesozoic intrusive, contact, and regional metamorphic events. Structure is complex, and includes polyphase Mesozoic folding and thrusting, and complex Cenozoic structures. The area continues to be seismically active. High brightness (white), high purity crystalline limestone deposits are uncommon because their formation is dependent on several geologic processes which include; 1) depositional environment, 2) contact and or regional metamorphism, 3) folding and faulting, 4) uplift and erosion, and 5) preservation through geologic time. The complex geologic history of the San Bernardino Mountains and Mojave Desert region has allowed the formation of several large high brightness, high purity limestone deposits which are currently being mined or will be mined in the future. Specialty Minerals, Inc. (formerly Ptizer), Pluess-Staufer (California), Inc. and Partins Limestone, Inc. produce high brightness, high purity limestone from several quarries in the San Bernardino Mountains. These active mines combined with undeveloped deposits controlled by Pluess-Staufer in the San Bernardino Mountains, New York Mountains, and Bristol Mountains in the Mojave area, contain proven and or indicated reserves sufficient to sustain production through the 21st century Detailed geologic mapping, intimate knowledge of stratigraphy, recognition of complex structures, sampling, drilling and assay data, are proven tools in the discovery and delineation of high brightness, high purity limestone deposits in the San Bernardino Mountains and Mojave Desert region of southern California.

Jan 1, 1995

By F. J. Sotillo

Mineral processing requires good classification of particles to attain an adequate separation of minerals. This is of utmost importance in the case of sulfide minerals. An ideal classification is obtained when particles are separated at a given mesh, which is fixed according to the characteristics of each sulfide ore. Under these ideal conditions, particles coarser than the mesh of separation are recovered in the underflow, whereas particles finer than the mesh of separation are recovered in the overflow. This paper presents the results of pilot plant tests that were performed on Ag-Pb-Zn and on Ag-Au Peruvian sulfide ores using a Density Separator, and the comparison of these results with those obtained using hydrocyclones, under similar operating conditions. The results show that the ratio of circulating load is reduced by 50% by using a Density Separator with respect to that obtained by using hydrocyclones. Moreover, the effect of the improvement in the separation efficiency obtained by using the Density Separator on the kinetics of flotation is also shown. Silver recovery of the Ag-Pb-Zn ore increased by 18% whereas gold grade in the concentrate of the Ag-Au ore is doubled.

Jan 1, 1998

By Joseph C. Hirschi

Mine engineers have been interested in building models that simulate mining operations since computers were introduced to the industry in the 1960s. Computer models enable operational scenarios to be evaluated without the need for actual field experimentation. Virginia Tech’s FACESIM and CONSIM, Penn State’s UGMHS, and KETRON’s CPMINE are perhaps the best known early models. Recently, SIUC has modified a Microsoft® Excel version of Virginia Tech’s Mathematical Model, calling it the SSP Model. It is used to quantify the significance of various controllable parameters. Productivity increases approaching twenty percent may be achieved where recommendations suggested by the model are applied.

Jan 1, 2005

Minerals contribute to the U.S. gross domestic prod-uct (GDP) at several levels?mining, processing and manufacturing finished products. In 2008, the estimated growth rate for the real GDP of the United States was 1.1 percent and the nominal GDP was about $14.3 trillion (Table 1). Trends in various sectors of the domestic economy are often reflected in mineral production and consumption rates. For instance, continued declines in the U.S. housing market during 2008 were reflected in further reductions in the production and consumption of cement, clays, construction sand and gravel and crushed stone (mineral commodities that are used almost exclusively in construction), and those associated with the related manufacture of goods, such as ceramic tile, heating and air conditioning equipment, paint, plumbing and sanitaryware, roofing, wiring and wallboard ? all used by the housing industry. The widespread effects of the slowing domestic economy became more apparent in the last three to six months of 2008 when prices for many mineral commodities declined sharply after reaching record highs earlier in the year, indicating significantly lower demand for those materials or products containing them.

Jan 1, 2009

By Edwarde R. May

The Flambeau volcanogenic massive sulfide deposit located in northwestern Wisconsin occurs within the southern lobe of the Canadian Precambrian Shield. The steeply dipping tabular body occurs in a complex pile of cyclic schistose intermediate to felsic fragmental volcanics. No chloritic alteration pipe is recognized but adjacent rocks have undergone magnesia metasomatism and subsequently were metamorphosed to the upper greenschist and lower amphibolite facies. Although modest in size the deposit is of special interest in that it has an extensive and well preserved supergene enrichment blanket. Economic minerals found within a pyritized quartz-sericite schist are chalcocite and bornite overlying primary chalcopyrite.

Jan 1, 1976

By Bijan Taheri, Behrouz Maghsodi, Monireh Heshami, Reza Kohan

A common problem recently encountered with the increase in the rate of input feed at Enrichment Plant 2 of the Sarcheshmeh Copper Complex is the loss of value to the tails, translating to lower recoveries. The feasibility of the direct transfer of part of the high-grade concentrate from rougher stages to an appropriate position along the circuit was studied, and two positions were proposed for direct transfer of the concentrate. One position was the feed flow into cleaner cells, and the other was the feed flow into the recleaner cell. The results indicated that transferring the concentrate from the first unit of the rougher stage to the feed flow into the cleaner cells was feasible, with no limitations, while the second position required the installation of a set of hydrocyclones. It was found that the transfer of concentrate to the proposed positions not only addressed the problem of limited cell capacity, resulting in debottlenecking of the circuit, but also improved metallurgical separation efficiency up to 1.4%.

By Andrzej Frycz

The development of the theory of reliability creates more and more possibilities of its application in different domains of technics. The methods evolved to date, both theoretical analysis of the engineering systems and investigations techniques in practice can be put in use a d translated from one science to another one [1,3,7J . It needs to consider the specific of the different sciences. But it is necessary to take account of the specific characteristic of each line of science. The reliability investigations needs, justified in technical and economical viewpoint appear too in mine ventilation technics and systems. The mine ventilation system is a complex of workings and ventilation plants, which serve to supply the networks with a sufficient quantity of fresh air from the atmosphere and then carry off the vitiated air. The condition necessary for a ventilation system to perform definite task is the correctness of all its elements, that is a capability to preserve in a expected range of tolerance, the values of basic parameters. The element of a system which ceases to work correctly is called failed. The basic parameter of all elements of a ventilation system is the characteristic curve, pressure loss - air quantity relation ?p = f(Q) (1) This curve concerning the workings and ventilation stoppings is given by the formula: ?p = R Q2 (2) thus the resistance R (of the workings or stoppings) may be taken as a characteristic parameter. The course of this characteristic f(Q) will be given in a complex form in concern with fans, ejectors, air curtains. The failure of a ventilation plant or working is therefore an event, relying on a change of its characteristic, thus for a definite time the losses of the plant's or working's capability set in for the fulfilment of its function in the ventilation system. The failures are divided in viewpoint of their nature on sudden and progressive. We are in concern with the sudden failures which are characterised by a violent change of the ventilation element parameter for example a fall of roof, or silt up of the working, opening or failure of the ventilation stopping, the stand-off of the fan or ejector etc. We distinguish two kinds of failures on the viewpoint of their action on the air flow: the "opening" failure and "closure" failure. The prevalence of factors, which causes the failures is in connection with the intersection in the mine of roads of haulage, roads of underground transport of materials and lining elements, roads of people motion with airways, as also depends on the rock pressure reaction on the workings lining and plants placed there. Other factors will yet be decisive upon supply decay of fans, ejectors and curtains. The appearance of failure of the ventilation element is therefore of random nature and determines the change of the element, when it is passing from operating state to unoperate. Qualifying the ventilation system element to one of these states is easy, when the characteristic change is clear and occurs suddenly, that was assumed. The investigations conducted by Patrushev and Karnaukh [91 in concern with the ventilation stoppings resistance change in the case of their opening, had shown the possibility of resistance value change in the range of several hundreds higher.

Jan 1, 1980

By F. A. Molloy

As a result of feasibility studies made in 1975 a 3-0 seismic reflection survey was shot over part of the Veendam salt pillow during 1978-1979. The Zechstein salt pillow, located in the northeast of the Netherlands near the town of veendam, occurs at a depth of 1400 m and contains three carnallite rich horizons over an interval of 300 m below top salt. MgCl2 brines are produced from these layers as feedstock for a magnesia plant, which starts up in 1981. Prior to the acquisition of the seismic data four wells had been drilled. The thickness of the carnallitite layers encountered in these wells varied between 50 and 125 meters. In view of these variations it was necessary to obtain a reliable isopach of the different layers. The 3-0 seismic survey covered an area of ± 4x4 km with a sampling interval of 20 m in all directions. The data was recorded it an area array using a 120 channel instrument. Final presentation of the data was in the form of 3-0 migrated acoustic impedance cross sections. The quality and resolution of the seismic data allowed reliable structural and isopach mans to be made. It was shown that the carnallitite layers are continuous over the area surveyed, whilst local thickening is "fault" related. Having this information brine production locations could be choosen in the thicker parts, allowing maximisation of production potential whilst avoiding faults and fulfilling mining regulations. A subsequent benefit of this approach is the possibility of using the seismic data to predict ore grade. Using the available wells as calibration points the acoustic impedance response of the seismic at the well was matched to the ore grade found. From these points a synthetic section was made with varying ore grades. Pre¬liminary results are encouraging and the liability of this predictive tool will be evaluated in the light of future drilling.

Jan 1, 1981

By M. Misra, I. Anazia

The dispersion of oily collector has a significant effect on the flotation recovery of ultrafine coal. Generally, reagent dispersion is accomplished by mechanical mixing and/or ultrasonic agitation, followed by direct addition of dispersed collector into the flotation cell. Such dispersion and reagent addition techniques are invariably inadequate and nonselective. A new collector addition technique involving gas phase transport of atomized collector has shown improved results when compared to conventional reagent addition techniques. This technique involves atomization of the collector into the air stream. Under these circumstances, an aerosol is introduced into the flotation cell. Initially, the oil is dispersed within the air phase (continuous with respect to oil), and the air phase is dispersed within the pulp (continuous with respect to aerosol). In the flotation cell, the atomized oil droplets coalesce on the bubble's surface and create a de facto oil-encapsulated bubble. This approach provides excellent dispersion, increases selectivity, and, most significantly, increases the flotation rate of ultrafine coal. Atomization of collector/frother combinations yielded improved flotation recovery and maintained near uniform froth levels, which is a desirable feature in coal flotation. Microscopic examinations of the attachment of oil- coated bubbles at a coal surface were conducted by attachment time and contact angle measurements. Oil-coated bubbles attach at significantly faster rates and with a higher contact angle than oil-free bubbles.

Jan 1, 1988

By C. J. Greet

Grinding with an electrochemically inert grinding media (i.e., high chrome white iron) shifts the pulp potentials to more oxidising conditions, increases the dissolved oxygen content and reduces the EDTA extractable iron concentration when compared with milling with electrochemically active grinding media (forged steel). These changes in pulp chemistry produce cleaner particle surfaces, reduce reagent consumption, and increase concentrate grades and recoveries. This paper presents a robust laboratory test program that not only demonstrates the changes in the pulp chemistry, but also provide an indication of the magnitude of the metallurgical improvements that are possible. While laboratory studies are interesting, the proof is in the pudding! So, the paper provides an overview of plant trials conducted at several porphyry copper operations around the world: Newmont’s Cadia and Red Chris Operations, as well as Evolution Mining’s Northparkes Operation. These successful plant trials clearly demonstrate that selection of the right grinding media alloy will yield savings in grinding media consumption and reagent consumption as well as increases in revenue through improved copper and gold recoveries. However, many of the porphyry copper mines on the Eastern Pacific are copper-molybdenum deposits. The paper presents laboratory test results for typical copper-molybdenum operations and extrapolate these numbers to what might be expected should a plant trial occur.

Feb 1, 2025

By C. M. Marquardt

The materials handling systems in the large concentrating plants have required the employment of a considerable number of workmen, many of whom had very little to do except to act as watchmen to avoid bad spills at belt junctions and to operate tripper cars, shuttle belts, etc. Much time also was spent in watching bins to make sure they were properly filled. Approximately four and one-half years ago the author, Yin coopera¬tion with the engineering and supervisory personnel of The Anaconda Company at Anaconda, Montana, began to give this problem serious consideration. Prior to this the author had developed, at the request of The Anaconda Company, a transistorized resistance-sensitive probe relay system for detecting the level of ore in bins. With this system cables or chains were suspended from insulators above the bins and were of suitable length to determine the elevation of the ore in the bins.

Jan 1, 1962

By Emily Sarver, Cigdem Keles, Jonathan Gonzalez

The study re-examines respirable coal mine dust samples using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). It finds that SEM tends to overpredict the abundance of dust from rock strata and underpredict coal content, possibly due to coal-mineral microagglomerates (MAGs). The findings suggest that MAGs could be valuable in improving dust controls in mines.

Feb 10, 2022

By S. Cotten

The regulations for current coal mine refuge alternative (RAs) require that there be sufficient life support to sustain survival of the maximum number of RA occupants for a minimum of 96 hours. This minimum duration assumes that rescuers can access the RA through the mine within four (4) days of the onset of the mine emergency. But what if mine rescue teams cannot reach the miners within the RA before the RA air supply is severely limited or exhausted? What could be done to extend the duration of the RA life support capability into the 97th hour and beyond? In addition, what might be done to enable more rapid rescue of the miners if they could not be reached through the mine in a timely manner? This paper describes a systems approach to address the potential need to extend the duration of RA life support beyond current design limits. New capabilities that need to be developed in advance of such a dire need include more reliable emergency communications, highly mobile and efficient drilling rigs, enhanced directional drilling techniques, and a standardized RA external life support interface along with RA internal design modifications to accommodate use of an external supply. The following sections describe the need, intent, and technology gaps associated with each of these capabilities. Government agencies and the mining industry should consider initiation of a program to investigate, design, and develop effective means of extending the current 96-hour time restriction on coal mine refuge alternative life support. The development process should begin with a focused study to refine the overall operational concept, investigate the current state-of-the art of critical technologies, identify specific technology development priorities, and make recommendations for a development program to provide in an organized, efficient, and timely manner a solution for extended refuge alternative life support and occupant rescue.

Jan 1, 2011

By G. Bonifazi

In the present work the possibility to utilize the morphometrical and morphological characteristics of an articulate solids system in a slurry flow to monitorate and to control a continuous process is considered. This goal has been reached by mean of an optical system able to acquire, to handle and to process the pictorial information derived by a suitable hardware architecture designed to realize the best lighting, focusing and sampling conditions for the examined flow stream domain. The procedure has been tested using different flow stream slurries coming from different sections of a beneficiation plant. A suitable strategy and a consequent software architecture has been set up in order to assure to the system the necessary speed and the stability to achieve correct on-line measurements and control.

Jan 1, 1994

By A. L. Crandell

History The Cortez Mining District has a long history of mining activity dating back to 1862. More recently, Cortez Gold Mines had operated a cyanide leach, counter current decantation (CCD) recovery gold mill from January 1969 to February 1976. This type of plant has been standard in the US for treating higher grade, finely disseminated gold in Carlin type ores. The mill was initially operated from 1969 to 1973 at 1.5 kt/d (1650 stpd) on oxidized ore from the Cortez ore body. In 1973, the mill was operated at 2 kt/d (2200 stpd) on softer, less oxidized, high clay ore from Gold Acres, located 13 km (8 miles) west of Cortez, NV. In February 1976, the oxidized portion of the ore body at Gold Acres was depleted and the mill ceased operations. Successful heap leaching of the lower grade portion of the ores was practiced at both Cortez and Gold Acres to supplement the milling operations. Valuable experience was gained in the operation of these two heap leaching programs (Duncan and Smolik, 1977). The ore heaps at Gold Acres and Cortez were releached with a limited crew from 1976 to 1979. The surge in the price of gold in late 1979 sparked an interest to incorporate new techniques into treating lower grade and less oxidized carbonaceous ores at Cortez. In early 1980, heap leaching was started on low grade oxidized dump material left from the earlier Cortez mining operation. By June of 1980, testwork was completed on the London Extension Dump, a low grade, mildly carbonaceous dump at Gold Acres. It was decided to convert the mill at Cortez from the conventional cyanide leach CCD recovery plant to a carbon-in-leach (CIL) recovery system. In May 1983, ore processing from the Horse Canyon deposit began. The Horse Canyon ore body contains both oxide and carbonaceous ores and is located 22.5 km (14 miles) from the Cortez mill. The Cortez CIL circuit was expanded to handle a blend of oxide and carbonaceous ores from Horse Canyon. Ore selection In the last quarter 1979, gold prices were increasing to a point where restarting the Cortez mill, idled since 1976, appeared imminent. Several previously explored geologic reserves at various stages of development were available as possible sources of feed for the mill. Initial metallurgical testing of dumps and tailings from earlier operations was completed, and previously uneconomic deposits were explored. It was decided to pursue sources of ore with the least lead time to production and those with the least capital cost requirements. A master plan was developed to bring the four profitable ore resources into production. The plan called for: • Heap leaching of waste dumps from the Cortez mining operation; • Restarting the mill to handle the waste dumps from the London

Jan 9, 1986