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By Pina P, Pereira MJ

The increasing exhaustion of raw materials entails the exploitation of poorer orebodies where the target mineral occurs frequently in a very fine dissemination. Consequently it is necessary to grind more and more fine to achieve an adequate mineral liberation. In other words, it is of fundamental importance to know what size one should grind in order to avoid the following detrimental situations: 1. Excessive grinding - giving rise to the generation of ultra-fine slime particles which may be lost in the ulterior concentration process and simultaneously leading to higher energy consumption. 2. Incomplete grinding - giving rise to insufficient liberation and consequently leading to considerable losses of the valuable components in the tailings. Although this issue constitutes one of the most important steps in mineral processing, little research has been done compared to other processes, mainly due to the fastidious experimental work required. This paper describes a complete and integrated system of image analysis, where some algorithms to determine automatically the degree of li beration, for different levels of grinding, are proposed. These algorithms, mainly based on mathematical morphology theory were tested with images obtained from polished sections of different grain size fractions. Cases studies on a complex sulphide ore from an important copper and tin deposit located in the South of Portugal are discussed. Samples of the unbroken ore are also studied by image analysis to predict the degree of liberation obtained according to the fineness of grinding.

Jan 1, 1993

By Terry R. Neumann

During 1983, U.S. Bureau of Mines personnel examined mines, prospects, and mineralized zones to evaluate the mineral resources and potential of the Funeral Mountains Wilderness Study Area (WSA), Inyo County, California. Eleven mineral properties and two mineralized zones were examined during this study. Of these, six are within the study area and seven adjacent. There are no active mines, in the WSA, nor is there evidence of past production from any claim within the study area. The WSA contains no identified mineral resources. However, occurrences of bentonite, zeolites, and strontium were found in the area. There is little likelihood for resource development of any occurrence in the WSA. The area, in the Basin and Range Physiographic Province, is dominated by a Paleozoic marine sequence. Segments of Tertiary continental fluviolacustrine sediments, including volcaniclastic rocks, abut and overlie the Paleozoic rocks in fault controlled basin areas. Significant concentrations of bentonitic clay and zeolites occur as alteration products in Tertiary tuffaceous sedimentary rocks. However, they are generally low-grade, thin, and discontinuous, precluding commercial development. Limestone, quartzite, and sand and gravel in the area are suitable for many types of construction uses, but similar deposits outside the WSA are closer to markets. No energy resources have been identified in the WSA.

Jan 1, 1984

By S A. Campbell

There has been a reduction of coal production in the United States due to environmental pressure and the increased use of natural gas. This reduction will require coal producers and consumers to make decisions on whether to sample more to verify contract quality or sample less in an effort to cut costs.CITATION:Campbell, S A, 2014. The shrinking coal market in the US – sample more or sample less?, in Proceedings Sampling 2014 , pp 3–6 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 29, 2014

By John Jiang, Brian R. Hart, Stamen S. Dimov, Aparup Chattopadhyay, Barun K. Gorain

"This paper presents a systematic approach to metallurgy diagnostics using an integrated gold deportment methodology developed for complex refractory gold and copper-gold ore bodies. Quantification of gold deportment for these ore bodies is a challenging task due to reasons such as lower grades, high variability of visible and invisible gold content in different sulphides and iron oxide phases, significant presence of disseminated and composite carbonaceous matters along with associations of various copper sulphide phases. Some case studies are presented in this paper to demonstrate the value of a high confidence gold deportment methodology in developing insights for problem diagnostics and to identify opportunities for metallurgical improvements. A holistic approach involving different fields of expertise is critical for successful development and delivery of solutions for complex ore bodies.INTRODUCTION Studies were initiated on various complex ore deposits and also on samples representing various process streams. These complex copper-gold single refractory, double and triple refractory gold ores are mainly composed of silicates and/or carbonates with moderate amounts of clay and mica, along with minor amounts of sulphides and organic carbonaceous matter. Variable proportions of visible gold and “invisible gold” (sub-microscopic gold) were noted in different mineral phases for various ore types and process stream samples. Invisible gold commonly occurs as solid solution or as colloidal-sized particles in different sulphides and other phases for different refractory ores. The dominance of invisible gold and presence of highly preg-robbing along with finely disseminated carbonaceous matters adversely affects gold recovery in flotation and leach circuits for most of these double and triple refractory ores. This paper discusses applications of an integrated gold deportment technique developed for different types of gold and copper-gold ores, namely, complex copper-gold, double and triple refractory gold ores (Chattopadhyay & Gorain, 2014; Chattopadhyay et al., 2016). Various process streams from flotation and gold leaching circuits were investigated. Different concentrates and tailings samples from flotation circuits whereas feed and discharges from pressure oxidation (POX) and carbon-in-leach (CIL) residues were used from gold processing circuits."

Jan 1, 2017

By Han Yi

The coarse indium ingots produced by Shaoguan smelter contained a lot of impurities. In order to produce the high pure indium with the purity more than 99.99%, the appropriate refining processes were designed and the practice of combined application of Glycerin-KI process and electrolysis in Shaoguan smelter was introduced.

Jan 1, 2005

By F. C. Miller

The metallurgical fuel of Colorado, Utah, and New Mexico has been a Veiny tardy member in the caravan of western industrial progress. The history of western coke has naturally been closely related to the development of the metallurgy of iron and steel and the precious metals, in the State of Colorado. It was at Leadville, with a population of 300 in 1877, that the Sentinel was published by Richard S. Allen. The Sentinel gave very full accounts of the various mineral discoveries at the new town of Leadville, which found their way to the more widely circulated journals of the East, and attracted the attention of many people. At the close of 1878, a census slowed a total of 5040 persons. The first smelter was established in 1877, at Malta, two miles from Leadville, by A. R. Meyer, but was not successful. It was succeeded by the Harrison Reduction Works, in 1878. The La Plata began with one furnace in June, 1878, and in 1879 had four furnaces in active operation. These furnaces used charcoal for fuel, and, because of hot tops, suffered a tremendous loss in lead and silver. This difficulty was overcome by the erection of 50 single-bank 10-ft. beehive ovens at Crested Butte, Colo., in 1880. The slack coal sent to these ovens was very pure, and yielded a coke carrying as little as 4.5 per cent. ash. Among the pioneers in the Leadville district were Grant, Eddy, James, Billings, Eiler, and Dickson. To these men the West owes the present expansion of its mining industry, and the erection of metallurgical processes for the treatment of precious metals. On Mar. 1, 1876, Pueblo was connected to the Atchison, Topeka & Sank Fe by the Pueblo & Arkansas Valley branch. The first smelter was erected in Pueblo by Mather and Geist. This modest plant grew into the immense Pueblo Smelting and Refining Co., now a part of the American Smelting and Refining Co. Coke for these small furnaces was made from unwashed Engleville coal, in 186 single-bank 12-ft. ovens at El Moro, in the Trinidad district, and it was not uncommon for the percentage of ash to exceed the percentage of fixed carbon in the coke. On Jan. 23, 1880, the Colorado Improvement Co. consolidated

Jan 1, 1920

By E. T. Dumble

In continuation of the geological work begun in Sonora, Mexico, a partial account of which has already been given in the Transactions of the Institute,* a similar reconnaissance was made of Cochise county, Arizona, and a part of the Whetstone mountains. The investigation resulted in the identification of beds of similar age and character to those of the Sonora region, and in the discovery of interesting deposits, which, so far as I call ascertain from the literature at my command, have not been described heretofore. Route.—Starting from Nogales, we followed the railroad to Crittenden, and then drove to the southeastern slope of the Whetstones. After a brief examination of some reported coalbeds we continued our route, following the wagon-road between the Whetstones and the Mustang mountains to Huachuca, and eastward to Tombstone. Crossing the Dragoon mountains at South Pass, we traveled south and west by way of Turquoise and Antelope Spring into the road from Tombstone to Bisbee. Our route over the Mule mountains lay through Mule Pass and Bisbee, where we stopped a day or two. Thence, crossing Sulphur Spring valley, we drove around the southern end of the Swisshelms, and N. through the valley between these mountains and the Chiricahuas, to White river. From that point our way led through Rucker canon into the San Simon valley, then northward along the eastern face of the Chiricahuas, and by way of Fort Bowie to Willcox, Arizona, from which place we returned to Nogales. It was greatly regretted that the extremely wet weather prevented us from including in our examination the Huachuca

Jan 1, 1902

By F. Selig, A. S. Odeh

A second-order approximation to the exact solution of the diffusivity equation corresponding to the pressure build-up of a well producing at a variable rate is derived. This approximation is applicable when the well's shut-in time is larger than the total time elapsed since the well was first produced. The resulting equations are compact in form and easy to use. Thus, the need for Horner's' theoretically precise but rather laborious solution to the above problem is eliminated. In addition, these equations apply where the use of Horner's widely known approximate method is questionable. From a practical point of view, the reported method is best suited for analysis of drill-stem tests and short production tests conducted on new wells. INTRODUCTION The utility of drill-stem and short production tests in reservoir studies has long been recognized by the reservoir engineer. If interpreted correctly they could lead to a wealth of information upon which may depend the success or failure of reservoirs' analyses. Initial reservoir pressure and the average flow capacity are two quantities that are normally sought from a drill-stem and/or a short production test analysis. Pressures are the most valuable and useful data in reservoir engineering. Directly or indirectly, they enter into all phases of reservoir engineering calculations. Therefore, their accurate determination is of utmost importance. The flow capacity kh of the reservoir is indicative of its commercial capability. In addition, it can indicate the presence of a darnaged zone around the wellbore and, thus, the necessity for remedial measures. Of the several methods used to analyze drill-stem and short production tests, Horner's' method is by and large the most common. It applies to an infinite reservoir and or a limited reservoir where the effect of production has not been felt by the boundary. Horner's method makes use of the so-called "point-source" solution of the diffusivity equation. The point-source solution is approximated by a logarithmic function and the superposition theorem is utilized to give the familiar pressure build-up equation where is the shut-in time, q is in reservoir barrels per day and the rest of the symbols conform with AIME nomenclature. Eq. 1 was derived for a well which produced at a constant rate q from time zero to time t and was then shut in. In actuality, such a constant rate of production does not normally obtain. Therefore, a correction must be applied to Eq. 1 to account for the varying rates of production. Horner suggested two methods. The first, which results in a theoretically accurate solution, is rather lengthy and laborious and, thus, it is not suited for routine analysis. The second which has been termed a "good working approximation" is the one used by the majority of the reservoir engineers. In the second method, Eq. 1 is modified by simply introducing a corrected time t, and writing where q is the last established production rate prior to shut-in, and t, is obtained by dividing the total cumulative production by the last established rate. Horner's original paper does not give any indication that this method of correction is based on any theoretical justification. In addition, there is a question as to what constitutes the last established rate. In case of a drill-stem test some engineers use the average rate obtained by dividing the total fluid produced by the total flow time, while others calculate the average rate by dividing the total fluid produced by the last flow-period time. Obviously, different results obtain for the different flow rates used. Because of this, a simple method to the varying-rate case was developed which is theoretically sound and which defines clearly the flow rate and its associated time to be used in the calculations. The final equation arrived at is where q* and t* are a modified rate and time, respectively, and can be easily calculated. In addition, it is shown theoretically that Horner's approximate method, if used for a variable-rate case, gives the correct pressure but would not be expected to give the correct flow capacity. MATHEMATICAL ANALYSIS The general equation governing the flow of slightly compressible fluid in porous media may be written as The elementary solution to Eq. 4, representing an instantaneous withdrawal of Q units volume of fluid at the origin at t = 0, is known as the instantaneous sink

By Bernard Rachlin

In the mineral industry measurement of density or specific gravity of slurries is often necessary or highly desirable. To date the most successful method of measuring the specific gravity of various media is to hand weigh a constant volume sample of the slurry. This method is time-consuming, however, and is intermittent rather than continuous. Most density measuring instruments in use today are variations of three basic systems: air bubble tube systems, radioactive methods, and displacer systems. The high cost of the radioactive cell, combined with the precision electronic measuring that is required, limits the practical utility of this procedure to a small percentage of critical processes. In the air bubble systems clogging of the bubble tubes with solids has rendered this type of measurement completely ineffectual for many applications. Continuous or intermittent purging of the bubble tubes with air or water to prevent tube clogging has been tried but has not been very successful, especially in the heavy media process.

Dec 1, 1956

By Michael J. Taylor

Introduction A prime goal in the design and operation of uranium milling waste or tailing disposal systems is to mitigate adverse effects of tailing liquid on the adjacent groundwater. Adverse effects are often defined as modifying the groundwater quality in such a manner as to have detrimental health effects on downstream users. To accomplish this goal, the following three types of systems are employed with regard to the seepage and groundwater aspects of waste disposal: Type I Systems Seepage is allowed to occur unabated from the tailing disposal facility. Detrimental radionuclides and chemical elements are prevented from causing adverse downstream effects by natural purification actions in the subgrade geologic materials and the near zone groundwater. Monitoring is required to assure the predicted natural purification is occurring. The consequences of seepage loss is minimal since the m be predicted with current investigation and analytical techniques and can be evaluated as to effectiveness during operations. Type II Systems Seepage is partially retained in a waste impoundment or leakage from a designed retention system is anticipated. Natural purification is relied on for controlling migration of detrimental radionuclides or chemical elements, or contingency planning is employed to collect and return the tailing liquid to the impoundment. Installation efforts and concern for escape of tailing liquid are greater than for Type I systems, but extra precautions to preclude all seepage are not implemented. Monitoring is required to detect leakage and/or assure the natural purification of escaping tailing fluid. The consequence for accidential excusions are moderate, and will be excessive only if massive system failure occurs. Type III Systems Seepage is totally restricted by a costly system constructed and operated with extra care. Natural

Jan 1, 1980

By Bukeikhanov D. G, Syedin V. F, Sagyngaliyev K. S

The present paper describes a method of simulating deposits of com- posite structure by means of computers. The method employs mathematical tech- niques to study the openworks zone formation dynamics in open-pit mines with any mode of the works front ad- vance as well as to determine, on oriented graphs,the optimal direction of openworks expansion.

Jan 1, 1977

By Pratama Mochamad Rizki, Andika Satya

High-risk area in open-pit mining should always be monitored by the operational supervisor because of its nature. One of this type is the soft soil dump area. Due to the unstable bearing capacity of the soil, it’s highly possible for us to find cracks in the area. This paper aims to build computer vision which able to detect truck’s distance from safe limit allowed during dumping activity. The system will warn the truck’s driver if the truck has crossed that predetermined safe limit.

Jun 25, 2023

By Hakan Gurgenli

Many coal seams have weak shale immediate roofs that cause ground control problems. Therefore, it is important to know the properties of these shales so that preventive measures can be developed in advance. However, it is sometimes hard to understand this rock type due to its unpredictable behavior. A good example of this situation is found in two shale coal mine roofs located in the Illinois coal basin (Herrin No. 6 seam). Although, these mines are located very close to each other, one of them has many roof falls, whereas the other has no measurable ground control problems. The aim of this paper is to explain why and how one shale roof behaves worse than the other. Laboratory tests, including point load strength index, slake durability index, moisture activity index, weatherability index, water content determination, swelling strain and x-ray diffraction tests were performed to analyze the shale properties. According to these analyses, some useful correlations were found between the engineering properties, moisture-sensitivity indices, and weathering properties. Finally, mine and support design considerations based on the test results were discussed and recommendations to prevent ground control problems were given.

Jan 1, 2006

By M. E. Wadswort, A. S. Peck

Infrared data disclose that phenacite reacts with oleic acid to form a chemisorbed oleate monolayer on the mineral surface. The absorption band characteristic of the antisymmetrical C = 0 oleate structure appears at a spectral wavelength of 1623 cm-'. Chemisorption also results in the displacement of OH- and silicate from the mineral surface. Infrared absorbance at 1623 cm-1 is correlated with float-ability at different pH for -60-mesh phenacite particles. Phenacite, Be2SiO4, is an ore mineral often associated with quartz, microcline, and chrysoberyl in pegmatites and mica schist. Experimental phenacite beneficiating processes have been confined principally to the flotation of low grade ores occur-ing in several mountain ranges of Utah and Nevada. The U.S. Bureau of Mines ' has recently reported on the separation of phenacite from ore deposits of Mount Wheeler, Nev. Infrared techniques were previously applied by the authors to characterize the role of sodium oleate and oleic acid in the flotation of several non-sulfide minerals.23 A parallel study was projected to the flotation of the orthosilicate mineral phenacite with oleic acid. Infrared spectra provided a 'molecular fingerprint' of the mineral surface and permitted identification of the reaction mechanisms. Infrared data were complemented with flotation and chemical tests. EXPERIMENTAL PROCEDURES The experimental procedures used in this investigation, for which data are presented in graphical or spectral form, are described in chronological test order. Phenacite crystals from Mt. Antero, Colo., were obtained from Ward's Co., Monterey, Calif. The crystals were fragmented in a porcelain mortar to -60 mesh and then pretreated with 0.5 molar HC1 for 15 min to remove iron. Then, the mineral particles were washed free of acid with distilled water and dried. Part of the dried material was ground to a fine powder with a Fisher Grinder using an agate mortar and pestle. Next, the powder was placed in a graduated cylinder and mixed with 500 ml of distilled water. The mineral in suspension was decanted from the settled fraction after 5 min, and the colloidal suspension was used for adsorption tests in which a high specific mineral surface area was required for adsorption and infrared analysis. Conditioning was performed in 50 ml glass centrifuge tubes for both infrared and flotation test determinations. Twenty ml of colloidal suspension was used for the infrared adsorption tests. One and a half g of deslimed -60-mesh HCl pretreated phenacite was added to 20 ml of distilled water for flotation conditioning tests. Six mg of oleic acid was used for each infrared adsorption test, and 0.2 mg of oleic acid was used for the flotation conditioning tests. HCl and NaOH were used for pH modification. The pulps were stirred at a speed of about 1500 rpm for 3 min. Then, the solids were separated out and either dried at 50°C or immediately transferred to a float cell. The pH of the residual liquid was determined with a Beckman Zeromatic pH meter. The flotation procedure is described as follows: 1) A 325-1111 glass micro-float cell was filled with distilled water. 2) Conditioned mineral was placed in the cell and the pulp was aerated through the glass fritted bottom at 7 psi pressure. 3) Floated mineral was skimmed from the cell with a glass slide until flotation ceased. (The end point was reached in all tests in less than 2 min.) 4) The flotation products were dried, weighed, and the recovery was calculated. Samples for infrared analysis were made into mulls using either oleic acid or series 13-21 Halocarbon oil obtained from Halocarbon Products Corp., Hacken-sack, N.J. The mulls were placed between two sodium chloride windows. A characteristic phenacite infrared band at 1868 cm-' was used as an internal standard for quantitative determinations in which absorbance at this position was quantified by the baseline-tangent method4 and related to absorbance at 1623 cm-'. The ratio obtained by dividing absorbance at 1623 cm-' by absorbance at 1868 cm-' was defined as an absorbance quotient for use in graphical presentation.

Jan 1, 1968

By Dennis R. Dolinar

In general, the direction of the maximum horizontal stress in the eastern United States is fairly well defined. However, the variation of the magnitudes of the horizontal stresses is not very well understood. Because the horizontal stresses cause severe ground control problems in underground coal and limestone mines throughout the eastern United States a more complete understanding of how the magnitudes vary would be useful for developing mine design strategies to combat horizontal stress related ground control problems. Therefore, in this National Institute for Occupational Safety and Health (NIOSH) study, the variation of the magnitude of the horizon stresses in sedimentary deposits in the eastern and Midwestern United States are examined with respect to two factors, the elastic modulus of the rock and the site depth. Stress measurements from thirty-seven sites are used in the evaluation. Examining the applied excess strains indicates that the eastern United States can be, separated into high and low strain zones. For most of the eastern United States the maximum applied excess or tectonic strain ranges from only 300 to 550 micro strains. However, there is one area, a portion of the Beckley seam in the central Appalachian region where the strains are significantly higher than the other regions. In this higher strain zone, the maximum applied tectonic strains range from 700 to 1,000 micro strains. Regression models for each zone based on the elastic modulus can explain between 83 to 85% of the variation of the maximum horizontal stress. Because one region, the northern Appalachian district, has strains that are about 20% higher than the other regions in the low strain zone, multiple strain models based on geographic regions were developed for the low strain zone that can explain 87 to 91% of the maximum horizontal stress variation with the elastic modulus. Depth was found not to be a significant causal factor in any increase in the horizontal stress even though the site depths ranged from 275 to 2,500 ft. Beyond a theoretical increase, based on Poisson’s effect and gravity, no other increase in the horizontal stress with depth can be justified with this data. The most significant factor controlling the variation of the maximum horizontal stress is the elastic modulus of the rock, not the overburden depth.

Measure tattling in cemented backfill when installation of bore-hole extensometers is not feasible. Problem To evaluate the amount of load that backfill carries during pillar recovery, information about how much the backfill settles after placement is often required. However, the composition of some backfills makes them difficult to drill and the installation of borehole extensometers almost impossible. Approach Bureau researchers have developed a vertical fill extensometer that can be cast in place as a stope is being filled. It consists of a baseplate, sections of steel pipe enclosed in loosely coupled polyvinyl chloride (PVC) pipe, and a top anchor assembly that contains a displacement transducer (fig. 1).

Jan 1, 1990

By Gordon R. Peeling

The Problem Five years after the consensus of the Whitehorse Mining Initiative the industry was losing public confidence Public opinion surveys ranked mining just above the tobacco industry Project opportunities were being lost to public and political opposition Operating practices called into question by a number of tailings dam failures CBC broadcast of "The Ugly Canadian" Our social licence was being lost

May 1, 2013

By Patrick Cahill, Jacob Miller, Nolan Mundwiller, Catherine Johnson

"The Experimental Mine at the Missouri University of Science and Technology is undergoing major developments. The underground workings are being expanded to include a ramp down to a second level which will comprise of larger opening and room sizes to better simulate modern mine layouts. Thisexpansion will enable the Experimental Mine to be utilized for many more generations. In addition, the new 15,000 sq. ft. Kennedy Mine Building is being constructed and will house the mine office,classrooms, and three laboratories to accommodate the mining and explosives engineering programs’ ever-increasing enrollment. With these new developments come an increasing need for safety and awareness in regards to explosives and blasting. This paper will utilize the Institute of ExplosivesMakers Safety Analysis of Risk (IMESAFR) software tool, to assess current magazine compliance withthe increased personnel limits and mine building location. Furthermore, this paper will assess theimplementation of a wireless blast warning system consisting of warning beacons and a centrally located siren which will be integrated with the construction of the Kennedy Mine Building. This warning system will provide the necessary precautions to safely conduct blasting-related experiential learningopportunities and research projects, and will enable facility staff to more efficiently oversee blastingoperations at the Experimental Mine. "

Jan 1, 2017

By Andrea Gambi, Giancarlo Olivucci, Maurizio Lenzi

"In the paper a criterion for the evaluation of the sharing of the lateral loads in a piled foundation is presented. It relies on the the compatibility condition between the rotation of the rigid pile cap and the rotations of the pile heads, following in that the criterion suggested by the Eurocode 8 - Part 5. This assumption leads to an analytical solutions which allows to deal with the sharing of the lateral loads and moments by means of two main interaction parameters only. A sharing domain is also derived and it shows the role played by the eccentricity of the lateral load on the values of the axial forces and of the bending moments at the head of the piles.INTRODUCTIONIt is well known that the interaction among soil, piles and foundation is one of the most complex subject to deal with in Geotechnical Engineering. Its rigorous study needs to employ suitable finite element software nowadays available and able to take into account the non linear behavior of the soil as a continuum and the inelastic response of the structure. A deep insight to the topic of the sharing of the loads cannot obviously renounce to this approach.On the other hand it is a daily need of the designers to have at their disposal simple tools that allow to make preliminary evaluations of the basic equilibrium conditions. To this purpose many methods of analysis have been developed in the past to face the sharing of the loads in a simplified version. The present contribution follows this way trying however to introduce some improvements that leads to find a solution that satisfies both the equilibrium of the forces and the compatibility of the movements (Lenzi, Gambi, Olivucci, 2002). The proposed model allows to identify the basic parameters which govern the sharing of the lateral load and it allows to perform also parametric analysis and quick checks that may be useful in the design of the piles."

Jan 1, 2005

By W. H. Emmons

MOST mineral deposits change as they are followed downward on their dips. Some of these changes are due to primary arrangement; different ores were precipitated at different depths when the deposits were formed. Other changes are due to weathering or secondary enrichment. The chief changes resulting from weathering, in the main, are understood and standard changes are recognized. The processes are relatively simple. They take place at ordinary temperatures and pressures and can be duplicated in the laboratories. Moreover, there are thousands of deposits available for study, because the processes take place near the surface where the development of mines is begun. The changes due to primary arrangement of the deposits of the metals are not so well understood. Deposition has taken place at higher temperatures and our knowledge of the chemistry of the processes leaves much to be desired. Very few experimental data are available. The deposits, moreover, offer fewer examples because many mines are not, developed to depths where the changes can be studied and a change to unprofitable material usually results in stopping work. Most, students of ore deposits now accept, as confirmed, the hypothesis that nearly all lodes and related deposits were formed by solutions originating in intrusive igneous masses. Outward from these masses, the deposits at many places are grouped in zones and the arrangement noted from the intrusions outward are commonly the reverse of the changes noted from the surface downward in a single lode. A study of the changes in groups of deposits, from the parent intrusion outward, will throw light on the changes to be expected in a single lode downward. Because the changes in series of deposits from the intrusive outward may all be observed near the surface, where more data are available, it is possible to increase the number of examples many fold and to apply the statistical method of study with greater confidence of avoiding error.

Jan 3, 1924