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By Yuting Xue, Danqing Gao, Brijes Mishra

Heterogeneity and discontinuity significantly affect rock strength. For accurate stability prediction, intact rock behavior is imperatively included in rock mass behavior. However, past research largely used arbitrary scaling approaches to produce rock strength. This paper considers a stochastic approach in order to determine the strength of a rock. Based on the laboratory data, a MATLAB® with extreme value stochastic model generates a database for each physico-mechanical property. Then FLAC® simulates laboratory-sized rock specimens. The grids developed in the numerical model can in turn develop random material properties in MATLAB®, which researchers then applied to the final FLAC® model. Model runs simulate the approach performed in the laboratory. The results from the model indicate that a stochastic approach produces strengths that are lower than a deterministic approach. Failure modes for each specimen are different, similar to observations in the laboratory. In addition, random density also influences the failure mode, highlighting the importance of stochastic analysis in rocks.

By J. A. Hrabik

The feasibility of mining deep phosphate deposits by a borehole mining system was compared with mining by proven conventional techniques. An economic comparison of the borehole mining system with conventional dragline and bucket wheel excavator mining systems was completed at various mining depths and production rates. Hypothetical phosphate deposits, with various overburden thicknesses and reserve tonnages, were defined. Geologic conditions necessary for the application of the borehole system were identified. Discounted cash flow analyses based on derived capital and operating costs were used to generate rates of return and product prices. Borehole mining was found to be more economical where overburden thickness was 46 m (150 ft) or greater. However, at 15- and 30-m (50- and 100-ft) thicknesses, conventional surface mining was more economical. Overburden thickness has a great effect on the economic feasibility of the conventional mining systems but less effect on the economics of borehole mining. Economies of scale are only realized in conventional mining, since larger equipment is used to achieve greater production, whereas increased production from borehole mining is achieved using additional equipment units. A comparison of the environmental effects of borehole and conventional surface mining systems showed that borehole mining is environmentally more desirable.

Jan 1, 1987

By E. J. Meets, C. F. Meyer

Bord and pillar mining at shallow depth (400 m approx. maximum) is widely used in South African coal mines. One of the problems encountered in extracting coal in this manner is the ventilation of advancing bord and pillar headings. The traditional ventilation methods of force, exhaust and overlap (force/exhaust) are reasonably effective but tend to be both cost and labour intensive. Ducting often restricts the available free area of roadways thus impeding the transport of coal and other materials inbye the coal production section. Due to the above facts, ductless fans are currently being used to minimize the amount of ducting required in advancing sections. Two different types of fans are used, namely, vortex fans and the so-called `jet' fans. Vortex fans were developed from the fan blade design used for vertical take-off aircraft. The fans have the capability of delivering air over distances of about 30 m in the underground situation without any ducting attached to it. Jet fans are standard axial flow fans fitted with outlet reduction pieces which increase the velocity pressure at the discharge to such an extent that the air delivery distance is improved to almost match that of vortex fans. The paper describes some applications of both these fan types in advancing bord and pillar sections.

Jan 1, 1993

By Keith Whiting

The Van Stone zinc-lead mine is located in northeastern Washing- ton in Stevens County. It is about 24 km (15 miles) south of the Canadian border and 48 km (30 miles) west of the Idaho line. The deposits occur in late Cambrian age limestones and dolomites of the Metaline Formation. The bedding controls the trend of the zones containing the lenses of zinc-lead mineralization. The Van Stone property and vicinity is almost entirely covered with glacial drift averaging perhaps 6 m (20 ft) in thickness. Outcrops are very sparse. Outcropping gossan with zinc mineralization was first discovered by George Van Stone in 19 13, in what is now known as the South Ore Zone. Only minor trenching was done at that time. The property was idle until the mid- 1920s when Hecla Mining Co. drove several short adits and performed minor diamond drilling. In 1938, Willow Creek Mines of Nevada Inc. acquired the Van Stone plus adjacent parcels and commenced drilling on the known South Ore Zone. In the course of an expanded drilling program, the nonoutcropping North Ore Zone was discovered and was drilled out along a N30°E strike for about 305 m (1000 ft), beyond which point no mineralization was intersected.

Jan 1, 1991

By Yu. A. Polozov, V. A. Lagunov, O. Yu. Lushinkova, Yu. I. Svirskiy, Eh. Ya. Kipko, Roy A. Williams

4.1 THE GENERAL COMPOSITION AND PROPERTIES OF CLAY-BASED GROUTS Clay-based grouts are visco-plastic systems; they are made by adding structure-forming reagents to a clay mineral mortar. Small amounts of cement and various chemical ad¬ditives constitute the reagents. If necessary, fillers also are added. The distinguishing feature of clay-based grouts is that throughout their entire stabilization period they do not form a crystallized structure as does cement grout. The structure of stabilized clay-based grouts does not deteriorate during minor rock movement or upon the initiation of blast¬ing during the construction of a shaft or a drift. Because they can possess good rheological properties during the ini¬tial structure-forming period relative to cement grouts, clay¬based grouts are not easily eroded from large fractures and karstic cavities by flowing ground water. In addition, their finely dispersed clay particles facilitate a greater fracture penetration capacity, especially in dual porosity rocks. Numerous investigations of the structural-mechanical and rheological properties of clay-based grouts by STG have demonstrated that the most effective grouts for pre¬venting the inflow of ground water into underground work¬ings are grouts that have a cement content of 8 to 10% (90 to 120 kg/m3) of the clay grout by mass. The grout should have a density of 1.18 to 1.30 T/m3. Various additional substances and chemicals can be added as additional fillers and structure-forming reagents. In pure ground water at temperatures above freezing, sodium silicate in the amount of 0.8 to 1 % by mass normally is the only structure-forming reagent that is necessary if the proper clay is selected and if it is available. The production process for making clay-based grout is divided into two stages: 1) the production of an initial clay mortar with specified properties and 2) the production of a clay-cement additive grout mixture using the initial grout along with the structure-forming reagents, including the ce¬ment. The properties of clay-based grouts depend on the phys¬ical-mechanical properties of the initial clay mineral, the properties of the cement and the properties of the chemical reagents that are added. 4.1.1 TECHNOLOGICAL PROPERTIES OF CLAY-BASED GROUTS The dynamic shear stress' To, the viscosity 11, the static shear stress2 0, the maximum shear stress of the structured that the rheological and structural-mechanical prop¬erties of clay-based grouts must fall within the following limits: the dynamic shear stress To = 50 to 200 Pa; the viscosity -9 = 0.02 to 0.07 Pa sec; the static shear stress 0 = 150 to 600 Pa; the plasticity strength Pm of the structure one minute after preparation (according to P.A. Rebinder's method) equals 150 to 500 Pa. The plasticity strength 10 days after preparation is ? 0.15 MPa. The general relationship of the change in the structural strength of clay-based grouts relative to stabilization time is shown in Fig. 32. The figure shows that the structure-form¬ing process for clay-based grouts is characterized by three stages. These stages correspond to the time periods required for conducting the principal operations during the injection of the grout into a fractured aquifer as described below. Stage I, corresponding to the time period T1, reflects the small development of structural strength during early stabi¬lization. During this time, the structural strength must not preclude the capability to pump the grout. The time Tl must correspond to the length of pumping time from the moment water is shut off and mixing occurs until the pump stops forcing the grout through the manifold block and pipeline into the fractured rock as described subsequently herein. Stage II, corresponding to the time interval T2, reflects a sharp but controllable increase in the structural strength of the grout. The length of time period T2 is controlled by the addition of appropriate reagents. Stage III produces the final value of the structural strength. This final strength is used to design the dimensions of the isolation curtain. Consequently, the development of grouts is guided by two principal criteria: 1) the grout must develop the highest possible structural-mechanical properties and 2) it must be able to be pumped by a piston pump prior to final stabili¬zation. Successful grouting depends to a large extent on the correct design of a grout for each specific case. It is impor-

Jan 1, 1993

By S. S. Mauney

Natural and synthetic colors are used in almost every facet of our daily lives as a means of communication and expression. Natural ochres, umbers, hematites, and magnetites were once used in their crude or semi-processed state for their pigment value in construction products and low-end coatings applications, while yielding, in recent years, to synthetically produced iron oxides for more sophisticated products. Today, through innovative mining, processing, and marketing techniques, natural iron oxide pigments are once again gaining strong inroads into products and markets requiring precise chemical and physical characteristics. With our focus on environmental consciousness and resource conservation, value added natural iron oxides provide an economical and responsible alternative to our color needs.

Jan 1, 1993

By Foreback T. G.

The McKinley Mine is a large strip operation sup-plying coal to several utility and industrial customers. The mine reserve comprises many coal seams of varying quality and thickness. Erosion of the terrain has created coal out-crop lines that are encountered frequently with associated deviations in quality. Due to the complex nature of the coal reserve and the various customer quality requirements, coal quality control is a primary consideration and a constant challenge at the McKinley Mine. This paper will discuss the practices employed to ensure that the available coal meets contract specifications.

Jan 1, 1994

By J. Gauntt

Calcium carbonate is one of the most widely used industrial minerals in applications like cement, lime, agriculture, power plant fluegas desulfurization (FGD) and construction aggregates. Most applications are generally high-volume and low value ($9/t or $10/st) or less free-on-board (f.o.b.) mine site) uses of this material. Specialty uses of ground calcium carbonate (GCC) are typically referred to as ?performance mineral? or ?extender and ?ller? applications. Primary specialty markets for GCC include paper and plastics as well as a number of construction applications including joint compounds, carpet backing, paint, and adhesives, caulks and sealants (ACS). Other important specialty applications for GCC include rubber, food and personal care products. A new and growing application for GCC is in nonwoven fabrics, where this mineral replaces a small percentage of the polymer. Typical specialty applications for GCC are color sensitive and require extremely white/bright materials. Although deposits of limestone are located in most states, high brightness resources are relatively rare and controlled by a limited group of suppliers.

By Weijie Wei, Jinwang Zhang, Shengli Yang

In longwall top-coal caving (LTCC) mining with an inclined seam, the recovery rate is low and equipment stability is poor due to the unbalanced top-coal drawing process. To address these problems, this paper proposes the dynamic group caving method (DGCM), whose basic premise is that when the drawn volume of top coal from a support reaches about half, the next support begins drawing top coal, and the drawing process between the two supports is half done. Using particle flow code (PFC), the caving mechanism of top coal under DGCM was investigated. The results are of significance to realize high efficiency and precise caving in LTCC mining with an inclined seam.

By Panshi Xie, Yan Chen, Shaogang Wu, Yang Hang

In order to realize the intelligent mining of coal seam with large dip Angle, this paper adopts the methods of large proportion variable Angle loading threedimensional physical simulation experiment, numerical simulation and field measurement with digital twin technology. The hydraulic support with large dip Angle and large mining height is used as the prototype to design the physical entity model of 1:5 hydraulic support, combined with modeling and graphics rendering technology. Angle, displacement and load sensors were selected and placed to realize the data channel between the lower machine and the upper computer of the digital twin system, so that the position and load data of the physical entity model and the twin model of the laboratory hydraulic support could be shared in real time. Moreover, the multi-dimensional dynamic and static load transfer law and the position evolution characteristics of the support and surrounding rock under different inclination angles were analyzed. The results show that: with the increase of the Angle of the working face, first, the initial support force required by the support decreases, and the damage degree of the roof increases; When the roof is soft, the lifting operation can avoid the instability of the support to a certain extent. Second, under the action of positive pressure, the load of the top beam under different angles is balanced; Under the backpushing action, the load in the upper inclined area of the shield beam increases gradually, while the load in the lower inclined area decreases gradually. Under the lateral push, the load changes periodically, and the load in each cycle is increased compared with that in the previous cycle. Third, the numerical simulation analysis shows that the load on the lower bracket is less than that on the upper bracket, and the load on the bottom of all the columns is greater than that on the middle and upper brackets. In order to reduce the impact of the columns on the bottom plate or the base, it is necessary to improve the anti-subsidence ability of the base. Finally, according to the research results, the improvement and optimization measures of the support are put forward, and the field test shows that these measures effectively solve the problems of sinking, sliding and tipping of the support in the working face with large inclination Angle, and obtain good application results.

Feb 1, 2024

By Raymond E. Riethmann

El clasificador de espiral fue diseñado originalmente para circuitos cerrados de molienda. Desde entonces se ha aplicado con éxito a otros trabajos de clasificaci6n donde se necesita realizar un corte de dos productos. Inherentemente a las cualidades especiales de este cla- sificador está especialmente preparado para: clasificar, lavar, o agotar materiales tales como minerales, roca fosfática, arenas, carbbn, conchas de ostra y sales fosfáticas. Presentamos ahora las características de operation, flexibilidad de diseiio y líneas maestras para una apropiada aplicación.

Jan 1, 1982

By J. B. Boisvert, O. Leuangthong, T. Acorn

Optimizing final pit limits for stochastic models provides access to geologic and economic uncertainty in the pit-optimization stages of a mining project. This paper presents an approach for optimizing final pit limits concurrently over all realizations in a stochastic model and using a risk-management framework to manage the geologic and economic uncertainty. A heuristic pit optimizer is used to find multiple uncertainty-rated pit shells. These uncertainty-rated pit shells follow the mean-variance criterion to approximate the efficient frontier for final pit limits. Stochastic dominance rules are then used in a risk-management framework to further eliminate suboptimal solutions along the efficient frontier. This results in a smaller set of final pit shells that can be further analyzed for production scheduling. Additionally, the original solutions are analyzed for changes in the mining limits, and two regions are targeted as potential regions for further exploration.

By Robert A. Cortese, Carrie E. Lucci

Mine Safety and Health Administration (MSHA) regulations require underground coal mine operators to dust their mine corridors with an inert material to prevent coal dust explosions. The most commonly used material is pulverized limestone. Current practice to determine compliance with MSHA regulations requires the coal mine foreman or an MSHA inspector to collect samples of the deposited dust, a mixture of coal dust and limestone rock dust, for above ground laboratory analysis. To expedite this process, the U.S. Bureau of Mines has developed two instruments to facilitate the inspection and rock dusting processes, the explosibility meter and float dust deposition meter. The explosibility meter is a hand-held instrument which provides an in situ measurement of the explosible nature of homogeneous mine dust samples. The float dust deposition meter measures the mass loading density of the top layer of coal or limestone dust deposited on the mine floor during mining operations by the ventilation air. It may also be used to automate trickle rock dusting equipment. The operation of each device is based on the difference in the optical reflectance between the light limestone dust and the dark coal dust. The principal of the explosibility meter is based on the observation that, for a fixed coal volatility, the optical reflectance of dust mixtures is relatively constant at the limit of flammability, and independent of the coal dust particle size.

Jan 1, 1995

By K. Fuenkajorn, S. Serata

Discussion by S. Serata and K. Fuenkajorn Background Results of the above study in the August 1991 issue of Mining Engineering offer valuable lessons in the solution of cutter-roof problems. The original study plan was initiated by the discussion authors to solve the problems using the "stress control method" of mining (Serata 1976, 1982; Serata, Carr and Martin, 1984; Serata and Gardner, 1986; Serata, Gardner and Preston, 1986; Serata, Gardnerand Shrinivasan, 1986; Serata and Kikuchi, 1986; Serata, Preston and Galagoda, 1987) However, the plan and the planner were changed to the arrangement reported in the paper. The change was considered reasonable at the time due to the mine engineers' uncertainties about the stress control method. Consequently, the basic principle of the study was shifted from the original stress control method to the method described in the paper, which will be called the "yield pillar method" for the purposes of this discussion. The paper convinces the reader that the yield pillar method fails to solve the cutter-roof problems. This doesn't mean that the stress control method also fails. Actually the contrary is true, as discussed below. Limitation of the yield pillar method The paper illustrates clearly how poorly the yield pillar method performs in solving the problem. The reason for this failure is the lack of the protective stress envelope needed to stabilize the cutter roof. Unfortunately, the protective envelope cannot be formed properly without utilizing the stress control method of mining. Changing the pillar size does not make much difference in the roof stability. Stress measurement The key issue is how to form the global stress envelope to make the gate entries safe for production. Therefore, measuring the stress condition of the ground around the mine opening is critically important to solving the cutter-roof problem, regardless of the method applied. With regard to the stress measurement, there is a serious question as to the reported stress state of [6 i = -51.7 MPa (-7499 psi), G2 = -44.5 MPa (-6458 psi) and 63 = -30.8 MPa (-4465 psi)]. It is mechanically impossible to have such a stress state at any location in the mine ground since the known initial vertical stress [o,,] is less than or equal to 800 psi. There may be a large stress state in the [61] direction, but that is possible only at the expense of the [63] value. Having the above stress tensors in the mine is simply impossible. The questionable, reported stress values could be attributed to the application of the overcoring method, which tends to produce erroneously large stress values in the extremely nonelastic mine ground. Stress control method The paper should be considered as a major contribution demonstrating the limitation of the yield pillar method. At the same time, the paper does not disprove the stress control method. However, in comparing the paper with stress control studies conducted in other similar failing grounds, the stress control method appears to be able to solve the problem more effectively. Therefore it is advisable that the mine not give up its efforts to solve the problem. [•] References Serata, S., 1976, "Stress control technique - An alternative to roof bolting?," Mining Engineering, May. Serata, S., 1982, "Stress control methods: Quantitative approach to stabilizing mine openings in weak ground," Proceedings, 1st International Conference on Stability in Underground Mining, Vancouver, BC, Aug. 16-18. Serata, S., Carr, F., and Martin, E., 1984, "Stress control method applied to stabilization of underground coal mine openings," Proceedings, 25th US Symposium on Rock Mechanics, Northwestern University, June, pp. 583-590. Serata, S., and Gardner, B.H., 1986, "Benefits of the stress control method," invited paper, American Mining Congress Coal Convention, Pittsburgh, PA, May 7. Serata, S., Gardner, B.H., and Shrinivasan, K., 1986, "Integrated instrumentation method of stress state, material property and deformation measurement for stress control method of mining," invited paper, 5th Conference on Ground Control in Mining, West Virginia University, Morgantown, WV, June 11-13. Serata, S., and Kikuchi, S., 1986, "A diametral deformation method for in situ stress and rock property measurement," International Journal of Mining and Geological Engineering, Vol. 4, pp. 15-38. Serata, S., Preston, M., and Galagoda, H.M., 1987, "Integration of finite element analysis and field instrumentation for application of the stress control method in underground coal mining," Proceedings, 28th US Symposium on Rock Mechanics, Tucson, AZ, pp. 265-272.

Jan 1, 1993

By H. Hinds

Plant testing of DuPont's Activator Technology in the vat leach circuit of the Homestake mine shows increased gold recoveries of 3-5%. Activators are catalysts of gold dissolution in cyanide solution. DuPont received the patent for this technology in January, 1996. The test was run in the west sand plant alternating control and activated vats to reduce the variability in head grade and cyanide consumption. Activated vats had gold in the preg solutions earlier, higher gold recovery, and lower gold residuals. Activator addition did not adversely affect mill operations or the environment. Optimization of the technology continues.

Jan 1, 1997

By Bastiawarman Rifki, Nugraha Nico, Priatna Anton

The Deep Mill Level Zone (DMLZ) is one of the underground mines operated by PT Freeport Indonesia (PTFI). DMLZ is located approximately 1,500 m below ground level, where dominant rock types are skarn and diorite. The DMLZ mine and layout was designed based on the previous mine located above ground, the Deep Ore Zone (DOZ). The DOZ mine, located approximately 1,000 m below ground level, was a proven success, with a maximum capacity of 80K tonnes per day. During the production ramp up, which started in 2015, the DMLZ experienced several seismic events. The most significant event occurred in January 2018 with a recorded magnitude of more than 2.0 Mw, which resulted in a 14-month delay of the undercutting until March 2019. The significant event in January 2018 required the DMLZ to apply several adjustments related to the mining plan to help ensure it could continue development and achieve production target safely. This paper will describe the changes in the DMLZ mine plan as a response to the seismic activity at the mine, the reason behind the decisions being made to change the mine plan and strategy, as well as strengths and weaknesses between the previous plan compared with the new plan.

Apr 26, 2022

You have been involved with research activities in froth flotation and size reduction. What do you think the future holds for these technologies? Froth flotation and size reduction are essential processing steps common to almost all current mineral-processing operations. The most significant recent advances in both of these technologies have been in the increased size of equipment and in some alternative machine designs, such as the column cells and the high-pressure roller mills. I believe that the next major area of improvement in size reduction will be at least partially driven by an improved awareness of controlling the conditions that influence the efficiency of particle breakage. This would include factors such as water-chemistry influences, the influence of fines from classification, chemical grinding additives and better rheology control. In froth flotation, significant changes are currently taking place in the plant use of frothers. Also, there will be an increasing number of new collector chemistries for certain types of flotation, such as with oxide minerals, oxidized mineral recovery in sulfide systems and improved selectivity with certain sulfide mineral systems. You have been active in implementing new engineering technology in industry. What do you think will be the technological future of mineral processing? Being involved in the invention and industrial implementation of new technology has been one of the most positive experiences of my career. I also have had the unique experience of working in the chemical and petroleum industries as well as in mineral processing. In my opinion, the future of mineral processing will be an exciting, wonderful work area in which to be involved. The development of new technology in minerals processing offers a special challenge compared, for example, to that of chemistry or chemical engineering. In successful industrial innovation involving minerals, having a sound theory is not enough. Instead, what is required is a valid blend of a good idea, meaningful laboratory characterization and, most key, the experience necessary to adjust the plant in such a way to incorporate the idea. The complexity of engineering systems that contain solids, liquids and gases, as well as highly variable natural mineral properties, means that nothing new comes easily. In some cases, it has been difficult to explain how processes practiced in industry for decades actually work, in terms of physical and chemical fundamentals. On the other hand, when a new idea is successfully implemented, the economic and professional returns can be very rewarding. I know of no more challenging field of engineering than minerals processing. What is your view of the future of the minerals industry in general? The need for minerals, metals and coal will be with us for decades to come. In many aspects, the minerals industry became global much earlier than some of the other industrial sectors that are currently experiencing globalization. I believe that fair international competition is beneficial to the users of minerals, metals and coals and to those involved in producing such materials. The key word here for a global economy to work is "fair." So the various playing fields involved such as finance, profit return, regulation and labor should be relatively level for all the players involved. Competition is an amazing driving force for innovation. This has been true in the minerals industry during the last few decades. The mining industry is producing more at less cost per unit than ever before in our history. I anticipate that this trend will continue as long as the global political situation remains relatively stable.

Jan 1, 1997

By Gunnar Sparrman, Börje Ahlgren, Sten Rosenström

Starting in 1967 two major hydroelectric power projects have been implemented in East Africa viz. Kafue Gorge in Zambia and Great Ruaha in Tanzania. The two projects have similar characteristics and each consists of an underground power plant, a dam in connection with the power plant and a reservoir dam. The power plants are both designed and constructed according to principles applied in Scandinavia for a long time. Each consists of a headrace of a horizontal unlined rock tunnel with a length of about 10 km, vertical penstock shafts, machinery and transformer halls in large rock caverns and a tailrace of an unlined rock tunnel with a length of about 1 km. The head of the power plant of Kafue Gorge is 400 m, Great Ruaha 175 m, the capacity is 900 MW and 200 MW respectively. Both plants were executed in one stage, but building and erection works were made in two stages. However, the power plants show some interesting differences in design. The power plants are briefly described in the following, special regard being paid to the excavation works. GEOLOGY General The foundation of Eastern and Central Africa is made up of ancient crystalline rocks, consisting of sediments, lavas and intrusives, mostly intensively altered by repeated metamorphism. This repeated metamorphism - dynamic, ther-

Jan 1, 1979

By Gus H. Goudarzi

The apatite deposits in east-central Bahia, Brazil, are about 50 km east of Serra do Jacobina, between lat. 11° and 12° S. and long. 39°40' and 40° W. Apatite was found and examined at 15 localities in a mineralized belt that strikes about N.25° - 30 W. over a distance of about 100 km, but the size of the deposits has not yet been determined. Rocks of the region consist of a sequence of Precambrian migmatites and quartz feldspar paragneisses containing units of pyroxene-rich rocks, lenses of sillimanite-bearing quartzite, amphibolite zones, and calc-silicate marble lenses. Pegmatites and granites of probable anatectic origin (anatexite) are abundant. Faults are numerous. Clastic sediments of Tertiary and Quaternary ages cover most of the area; thus, outcrops of the Precambrian rocks are sparse. Trenches and pits have exposed mineralized zones as much as 10 m wide at some localities within the region. A layer of apatite at least 1 ½ m thick is exposed in a trench at Lagoa do Mel. At Rio do Peixe, vertical shafts have penetrated a mineralized zone, to a depth of as much as 13 m, of which about 25 percent is apatite. Apatite is massive or forms minute crystals, stringers, and disseminated grains in alkalic host rocks. At Apolinario, euhedral crystals of apatite are as much as 50 cm long and 30 cm in diameter. Associated minerals include vermiculite, biotite, scapolite, opal, chalcedony, epidote, montmorillonite, chlorite, kaolinite, sericite, magnetite, and limonite. Apatite is everywhere intimately associated with pyroxene-rich rocks, alkalic syenite pegmatites, and alkalic granite pegmatites. At Panelas-Retiro, apatite is associated with pegmatites, crystalline calcite (vein calcite), vermiculite, and pyroxene-bearing rocks. Analyses of samples show that the apatite is radioactive and rare-earth-bearing. Traces of vanadium and titanium were detected by spectroscopic analysis. The apatite was probably derived from phosphatic zones in the original Precambrian sedimentary rocks and has been crystallized and some mobilized by high-temperature regional metamorphism (higher amphibolite facies) into veins, pegmatites, and along certain preferred beds and fractures. Radiometric and geophysical surveys, in addition to conventional geological investigations, are planned to further investigate the nature and economic potential of the deposits.

Jan 1, 1972

By M. L. Maniocha

Most magnesia, MgO, whether of natural or synthetic origin, is utilized in its dead burned or periclase form as refractory linings for the production of steel. Continued research in refractory science combined with good refractory maintenance and improvements in steel making practice have resulted in decreased use of magnesia. To make up for this loss of business producers of synthetic magnesia have started to manufacture a variety of magnesium based chemicals that are utilized in many diverse industries and applications.

Jan 1, 1997