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By Bernhard C. Koch, Richard W. Hutchinson, Bernhard Free

The Tertiary Silverton caldera collapsed asymmetrically to the southwest 27.5 m.y. ago. Resurgent volcanic activity is expressed by a quartz-monzonite stock at the southern caldera margin and by the Red Mountain porphyry stock in the northwest of the caldera which were emplaced at 25 m.y. and 11 m.y. b.p., respectively. The apical Eureka graben formed between 27.5-22.5 m.y. ago and transects the Silverton caldera southwestward. In the northeast it terminates at the 22.5 m.y. Lake City caldera margin. This graben as well as caldera faults provide dominant structural control for base and precious metal deposits. The epithermal gold mineralization of the Gold King mine is proximal to the Red Mountain stock in the north central part of the caldera. Here, west-northwest striking faults related to the collapse of the caldera intersect northeast faults of the Eureka graben. Superimposed upon earlier base metal mineralization at 23 to 22.5 m.y. b.p., the 11 m.y. younger gold metallization was a distinct event at Gold King. Supergene enrichment of the hypogene precious metal assemblage resulted in a metal tenor of up to 3,016 g/t gold and 1,088 g/t silver. The deposit is hosted by quartz-latite tuffs, flows, and flow breccias of the Burns Formation. Veins, up to 5 m wide follow steeply southeast and northwest dipping structures of the Eureka graben. Subsidiary veins up to 2 m wide branch off the main lode and are termed "flat veins" because of their conformable strike but shallow dip of 45' to 50' toward the northwest. Meteoric water-dominated hydrothermal solutions generated by the Red Mountain stock ascended through intensely fractured, ferruginous

Jan 1, 1988

From a gathering storm of climate change based legislation that could potentially overwhelm the mining industry, to the nuts and bolts of mineral processing and just about everything in between, about 100 mining and mineral processing professionals heard it at all at the 60th annual Colorado MPD Meeting April 22-24 at the Broadmoor in Colorado Springs, CO. With a sweeping agenda under the banner ?What in the world is new in mining and metallurgy? attendees were treated to four sessions and 21 presentations that covered the range of mining industry issues. Bill Reid, president, chief executive officer and director of Gold Resources Corp., spoke about his company?s El Aquila gold project in Mexico. With five projects in Mexico, Gold Resources Corps. is aiming to become a low-cost gold and silver producer. Its flagship property, the El Aguila gold project, is a high-grade gold and silver property with significant base metal credits of copper, lead and zinc. Production of the El Aguila project was targeted for mid-2009. Reid said that three high-grade deposits have been discovered at the El Aguila project. They include the high-grade ?manto? style El Aguila openpit deposit, the El Aire high-grade polyme-tallic vein system, which is underground, and the underground La Arista high-grade polymetallic vein system. The project is located 120 km (75 miles) south-east of the capital city of Oaxaca, Mexico. Reid said the property has yielded several exceptional gold and silver surface samples, including a 36-g/t (1.1 oz/st) gold sample and a 3,100-g/t (90 oz/st) silver sample. Other properties that Gold Resource Corp. has are:

Jul 1, 2010

By Satid Therdkiattikul, Donald A. Dahlstrom

Many gold ores are known to be refractory so that conventional cyanide processing will result in serious losses of gold and silver values. A significant percentage of these refractory ores contain aresenopyrite and the gold and silver is usually encapsulated within this matrix as well as the pyrite matrix. Normally the values can be recovered as flotation concentrates because of the sulfide compounds with recoveries of over 90% and at very good grades. In order to free the gold and silver, the sulfide matrix must be destroyed. This can presently be achieved by (1) pressure­temperature leaching (2) roasting and (3) bacterial leaching. All of them have advantages and disadvantages as well as an obviously increased cost for the each processing method. However, the increased gold and silver recovery should and must more than offset this cost. It is believed that gold recovery should be well over 90% from the concentrate so that overall recovery from the ore should be in the 90-95% region. All three processes must consider pollution control of both sulfur and arsenic to prevent contamination of air, water or land through improper waste disposal. This paper will concern only bacterial leaching and its necessary control of effluents and solids. Sulfur does not appear to be a problem as the element is oxidized to sulfate and is precipitated with an acceptable solubility. Other important improvements that must be controlled are arsenic and iron which are present as significant values (1-12 g/1 of arsenic, 20-40 g/1 of iron). In addition much smaller values of base metals, aluminum and magnesium can be present as well as other elements depending on the ore and these must be low enough after treatment to meet EPA regulations.

Jan 1, 1993

By D. J. Sweet, B. Seymour, T. M. Emery, M. Armatys, J. P. Bourgeois, W. Johnson

The Spokane Mining Research Division (SMRD) of the National Institute for Occupational Safety and Health (NIOSH) has partnered with a narrow vein, hard rock underground mine to research the effects of the binder content on the elasticity and post-peak ductility of cemented hydraulic backfill (CHB). This is part of a larger study to enhance the long-term integrity of ground support in underground mines. As mining advances deeper and stresses increase, CHB mix designs will benefit if they can be modified to handle higher levels of strain which are induced by an increased stope closure, typically affected by a reduction in stope width and increased mining depth, or through dynamic loading resulting from a local seismic event. This portion of the research examined the impact of reductions in binder and their impact on Young’s modulus, peak strength, and post-peak ductility.

Mar 2, 2022

By David E. Thompson, Daniel J. Dobbels

INTRODUCTION The planning process for projects requiring construction of tunnels in urban environments can be highly complex and involves interaction with professionals of many disciplines. Typically the initial step in the planning process is to establish basic design criteria for the tunnel or tunnel system consistent with its intended purpose. Such criteria might include acceptable tunnel geometry, minimum and maximum slope or other associated criteria. Ideally, once the basic criteria have been established, the next step in the process might include establishing technically feasible horizontal and vertical alignment and shaft siting alternatives and developing "ball park" construction and operational cost estimates for the alternatives. Comparisons can then be made regarding the relative technical and economic merits of the alternatives and the most favorable alignment(s) are selected for further study or preliminary design. Typically the last and perhaps the most important task that is conducted during the planning stage includes identifying issues and potential problems to be addressed during the design and construction stages of the project. Many issues warrant consideration during the planning phase of a tunneling project. For the purposes of this paper, these issues can be divided into two broad categories: technical and non-technical. Important technical issues include, among others, general design criteria, geotechnical and geoenvironmental issues, and constructibility issues. Important non-technical issues include, among others, right-of-way and easement related considerations, project scheduling constraints, both short and long term environmental impacts and overall cost/benefit aspects of the project. With respect to influence on the planning process, these two groups of issues often cannot be separated completely. For urban tunneling projects, however, it is most often the case that the non-technical

Jan 1, 1991

By Brian T. Hamilton, Richard Piliounis, Cian Murphy

"The Eglinton-Crosstown Light Rail Transit line is a 19-kilometre corridor with a 10-kilometre underground portion currently being constructed by Metrolinx in Toronto through a densely populated urban environment. Tunneling works are being completed through two separate design-bid-build contracts that include consideration for a phased handover to a follow on contractor who will take ownership of the tunnels, including warranties, and will complete the stations and remainder of the system through a PPP delivery model including maintenance of the system for 30 years. Warranty provisions, settlement apportionment, tunnel leakage, potential delays and conflicts between contractors are just some of the risks the team managing tunnel contract integration had to consider when developing the PPP contract. This paper will present an overview of how these risks were assessed and allocated through the contracts and the strategies adopted to minimize risks to Metrolinx while ensuring successful procurement was maintained. INTRODUCTION The Big Move is a 25 year, $50 billion ($-CAD) plan for coordinated and integrated transportation in the Greater Toronto and Hamilton Area (GTHA) in Ontario, Canada. This plan has been initiated by Metrolinx, a division of the provincial government of Ontario, and its vision, goals and objectives are rooted in creating a high quality of life; a thriving, sustainable and protected environment; and a strong, prosperous and competitive economy for the GTHA. The Big Move will triple the length of rapid transit service in the GTHA to 1,725km, significantly increase the percentage of the GTHA population living within two kilometers of rapid transit, reduce commute times to an average of 77 minutes per person per day and decrease greenhouse gas emissions from passenger transportation per person by 29%. Work is currently underway on several projects and more than $16 billion ($-CAD) of the planned investment has already been committed. A key project that forms part of this commitment is the Eglinton Crosstown Light Rail Transit (LRT) Project which is being delivered in the City of Toronto under Metrolinx’s Rapid Transit (RT) Program. This complex and sizeable undertaking has been broken into a number of separate contracts comprising: LRT Vehicles contract; Eglinton West Tunnels Project; Eglinton East Tunnels Project; and a Public-Private-Partnership (PPP) contract to complete the underground stations, at-grade stops, all rail infrastructure and systems and to maintain the entire system for 30 years. The PPP contract, which includes an initial capital portion of approx. $5.1 billion ($-CAD), has recently been awarded to Crosslinx Transit Solutions, a Special Purpose Vehicle (SPV) consortium comprised of SNC Lavalin, Aecon, Dragados and EllisDon."

Jan 1, 2016

By Peter L. Comanor

At Getchell, Nevada a thousand tons per day mill for extracting gold from an ore containing orpiment and realgar was operated several years until early 1967. A cyanide process with a roaster was used in the processing of the ore. Mill wastes were contained in tailings ponds, in which the concentration of arsenic, currently, is one per cent or higher, Studies were conducted determining the effect of the tailing wastes on the Upper Sonoran vegetation of the area. Grid and line-intercept techniques were employed to obtain botanical informatics of the area surrounding the tailings ponds. Data of the per cent ground cover, species frequency, and plant vitality as a function of distance from the tailings ponds was collected. The data was compared to other botanical data collected from a control site outside the influence of the tailings ponds. In an attempt to isolate naturally occurring factors for varying plant communities from hose induced by factors derived from the close proximity of the tailings, soil cores were taken along the line-intercepts at intervals of 30 meters. The cores were analyzed for several compounds and elements needed for growth, or known to inhibit growth. Specific physical parameters of the soil samples were also taken. The paper describes the impact made by mill wastes containing large amounts of arsenic on the Upper Sonoran vegetation of the Getchell region. Described in detail are the techniques used to make the correlations between the plant communities and the influences of mill wastes.

Jan 1, 1974

By N. G. W. Cook

The conventional cyclic system of deep-level mining by drilling and blasting gives rise to an inadequate degree of stope sorting when mining thin reefs. This results in poor utilization of the capital facilities of a mine in the form of shafts, haulages, airways and associated equipment. Continuous and controlled removal of the thin gold-bearing portion of the reefs would permit better stope sorting and hence greater utilization of capital facilities. Results of experiments to develop hard rock cutting machines for mining are reported and the benefits which could be derived from their use are discussed.

Jan 1, 1969

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

By H. E. Rowen

I hope my title is not confusing; even more so that I am not. Actually pelletizing and sintering, meaning both the formation of pellets and the hardening of them, are closely related to each other and to phenomena of nature. Figure. 1 This many-celled porous structure, frozen as it was at the fusion temperature and was being frothed by fast-moving gases, may be considered a typical piece of sinter. The same structures have been found in natural ores.

Jan 1, 1962

By Robert G. Ditchburn

The Mariana arc is an ~1,400-km-long intraoceanic arc that marks the southern extension of the Izu-Bonin arc, and is host to 62 ?volcanic centers? of which at least 27 (21 submarine) are hydrothermally, or volcanically active. A surface ship cruise in early 2003 mapped the distribution of hydrothermal plumes emanating from these centers, followed by remotely operated vehicle (ROV) cruises with ROPOS in 2004 and Jason II in 2006. With the exception of one volcano (East Diamante), none of the vent sites visited by the ROVs were host to sulfide mineralization. Rather, they were characterized by high sulfidation mineral assemblages dominated by native sulfur. The sulfur was seen marking the vicinity of vent sites, or as sulfur ?chimneys? (e.g., NW Eifuku and Nikko), or more spectacularly as ?lakes? of molten sulfur, either occupying the summit crater of the volcano (e.g., Nikko), or perched on the flanks of the volcano, near the summit (e.g., Daikoku). Gas (H2S and CO2) was discharging through the molten sulfur. Evidence for these lakes to have either been substantially ?deeper? in their recent past (e.g., Nikko), or existing at other volcanoes (e.g., Seamount ?X?) is given by remnant ?pillars? of native sulfur that are reminiscent of rock pillars in lava lakes found along mid-ocean ridges.

Jan 1, 2008

By M. Szatkowski

The studies conducted by Laplante and coworkers (1983,1984) with flotation of galena and quartz, showed that the rate of flotation reaches a maximum value for a certain intermediate value of the air flow rate. A similar, though less pronounced, effect of the air flow rate on the selectivity was also observed. Luttrell and coworkers (1985) showed that the size of air bubbles has a significant effect on both rate and selectivity of coal flotation. These two studies used flotation tests in which no froth layer was formed. This note describes effects of the air flow rate and bubble size on the rate constant and selectivity of coal flotation, using a mechanical laboratory machine with a froth layer allowed to form. Experimental A raw, dry ground Illinois coal was used in flotation tests. The size distribution and ash content of the samples are : Particle size (µm) Weight (%) Ash (%) +600 4.30 41.7 600/200 43.05 19.0 200/74 22.25 16.0 - 74 30.40 24.0 average 20.8 No. 2 fuel oil with a concentration of 200 g/t of feed and M.IBC with concentrations of 11, 22, and 33 mg/L of pulp (128, 256, 384 g/t, respectively) were used as flotation reagents. Tap water with a natural pH of 7.0 to 7.8 was used throughout the tests. No other reagents were used. The starting concentration of coal in the pulp was 86 g/L. A standard flotation machine with the pulp volume of 5 L was used in experiments. Three different air flow rates were employed, resulting in three air escape velocity values of 14, 30, and 70 cm/min. The air escape velocity (AEV) was calculated as the ratio of air flow rate (Qa) to the slurry surface (Ss) in the machine. For a comparison, the upper limit of air escape velocity values used in commercial size flotation machines is between 70 and 100 cm/min (WEMCO, 1983). A machine consisting of a generator of fine bubbles and a separatory column, described elsewhere (Szatkowski and Freyberger, 1985), was used for some tests where bubble size lower than that generated in the standard machines was required. Prior to a flotation test, a batch of coal was mixed with water in the flotation cell for at least 10 minutes to ensure that all coal was thoroughly wet. Then the specified amount of fuel oil was added and the pulp was conditioned for five minutes. The specified amount of MIBC was added 15 seconds before the end of conditioning. After air flow was opened, flotation products were collected for 0 to 30, 30 to 60, and 60 to 120 second intervals. Content of the combustible material in samples was determined by subtracting the ash content from 100%. A photographic technique was used to determine initial distributions of bubble size generated by the flotation machines. Bubbles generated in water containing the prescribed amount of the frother but no solids were photographed against a black background. The average diameter and standard deviation were then calculated for each set of flotation conditions. The method gives results reproducible within k 5% of the average bubble size. Table 1 contains information about the measured bubble size distributions expressed by the average bubble diameter (Db) and the standard deviation ( SD ) . Results and discussion The general formula for calculating the flotation selectivity is: o = recovery of coal/recovery of ash (1)

Jan 1, 1988

By V. B. Achanti

This paper deals with the effect of various bit geometric parameters on failure characteristics of rock material. Improvement of rock cutting efficiency of continuous mining machines has been an interesting research topic for the last few decades. In the current study, an automated rotary rock cutting simulator, duplicating a continuous miner, was utilized to study these parameters in the laboratory. Improvement of bit performance in terms of its life, cutting efficiency, dust production and energy consumption has drawn wide spread attention over the years. Research shows that optimizing bit parameters can result in efficient fragmentation of rock. Indiana limestone rock material was utilized in this study while bit tip angle, bit tip size, bit spacing, depth of cut and cutting velocity of rotary drum were varied to investigate the failure characteristics. The cutting pressure, penetrating pressure and the depth of cut were monitored on the simulator during the cutting process. Air borne dust and settled dust were measured for each experiment. Then, the specific airborne dust and specific energy were determined for the each type of bit. Triaxial tests were carried out to correlate the failure angle of the rock in static case to dynamic cutting process failure. The physical and mechanical properties of the rock were also determined in order to assess their influence on the wear characteristics of each bit.

Jan 1, 1998

The floatability of a bituminous coal in NaG solutions was evaluated using a modified Hallimond tube to delineate the role of the electrostatic interaction between bubbles and particles in determining the coal hydrophobicity. Zeta potential measurements showed that bubbles are negatively charged in the entire pH range tested, while coal particles are positively charged below pH 6.0 and negatively charged above it. Also, both sodium and chloride ions were confirmed to act as indifferent ions without any specific effects for both coal particles and bubbles. Flotation as a function of pH exhibited a maximum and minimum at low salt concentrations which is shown to be determined mainly by the coal hydrophobicity as measured by a new hydrophobic levitation technique. At high salt concentrations (above 0.1 mole/dm3), the flotation without such maximum or minimum is controlled by the electrostatic interaction between the bubble and the particle.

Jan 1, 1992

By G. Almgren

With the exception of sublevel caving, the most common method of underground mining in Sweden is the "cut-and-fill" method. It is normally used for mining non-ferrous metals , and' is used extensively in the complex sulfide ore mines of the Boliden Company in north and central Sweden as well as the mines of the STORA and Vieille Montagne Companies in central Sweden. All in all, the cut-and-fill method is used in 13 of Sweden's 45 mines. As the mines are relatively small, the volume of ore mined by this method represents only about 5 % of the total ore production in Sweden. The commercial value, however, is much large than this percentage would imply. The production volumes and grades of some typical mines are shown in Table I. As seen, when rated internationally, the grades are comparatively low. The prices are set according to ?international metal prices? as dictated by the London stock exchange, and in lieu of governmental support, rational management methods are critical in order to achieve satisfactory profit.

Jan 1, 1975

By W. Setzepfandt, J. Henneke

PREFACE Debris disposal can very often be a severe problem and major restriction on tunnel boring projects, especially for small diameter tunnels and in underground mines. Hydraulic transport could provide a suitable solution. Investigations have therefore been made in connection with a full-scale project of 4.8 km length and 2,3 m diameter, to obtain the required technical and economical data for planning an optimized transport system, e.g. for a tunnel boring drivage of 6 - 7 m diameter in underground coal mines. INTRODUCTION The Radau-Tunnel, chosen for the investigations, has been designed for transferring flood peaks between the rivers Radau and Grosse Romke in the Harz-Mountain of Lower Saxony. A DEMAG TVM 20/23 H tunnel boring machine was used to drive the tunnel on a rising gradient of 0,53 %. The rock consisted of shale and hornblende (55 %), granite (15 %), diabase (15 %), chert (8 %) and gabbro (7 %). The project has been sponsored by the Federal Ministry of Research and Technology.

Jan 1, 1981

By III Cocanour

The line scan video photometer is a personal computer (PC) based, software-driven instrument which is used for the real time, on-line analysis of industrial process streams. The novelty of the instrument lies in the integration of its various components: (l) a true Red/Green/Blue (R/G/B) color video camera; (2) a unique, line-scan color sample and hold technique which provides a 4 to 20 mA analog signal to a commercial 12 bit analog to digital (A/D) converter; (3) software which converts data through a color absorbance algorithm to correlate elemental color to concentration; and (4) software-based control which utilizes color data, along with temperature and conductivity data to control process equipment. The photometer can be used for noninvasive analysis wherever color hues are representative of process variables such as chemical concentrations or mineralogy color reflectance. The line scan video photometer has been successfully demonstrated in solvent extraction/electrowinning (SX/EW) and ball mill circuits of copper producers.

Jan 1, 1996

By H. Huang, R. N. Gow

"In Part I, Gibbs’ phase rule was applied to mass-balanced EH-pH diagrams for the Cu-As-S-H2O system. The diagrams were generated using the stoichiometry of enargite as a basis. In this study, the calculations were expanded to cover the stoichiometries of three other Cu-As-S minerals – tennantite, sinnerite and lautite – and compared with enargite. Stability regions within the resulting EH-pH diagrams were found to change with stoichiometry such that a particular mineral would predominate if its stoichiometry was used in the calculation. Solution speciation was also found to vary, with thioarsenate being the best example. This stoichiometric effect helps to explain results reported in the literature and would be difficult to realize if it were not for mass-balanced calculations. IntroductionA comprehensive thermodynamic review has been conducted on the aqueous copper-arsenic-sulfur (Cu- As-S) system (Gow et al., 2014, 2015a, 2016b; Gow, Huang and Young, 2016c). Data on the free energies of more than 100 species were collected from various authors, and thermodynamic databases collated to produce mass-balanced EH-pH diagrams using the thermodynamic equilibrium calculation software STABCAL (Huang, 2014). The full database is listed and discussed in Gow et al. (2015a). Diagrams were generated for enargite and confirmed with Raman spectroscopy using bulk mineral electrodes in order to identify reactions spectroelectrochemically. Theoretical calculations agreed well with the experimental results under alkaline conditions (Gow et al., 2015a), acid conditions (Gow et al., 2014) and alkaline sulfide leaching conditions (Gow et al., 2015b).In the present study, additional mass-balanced EH-pH diagrams were generated by changing the Cu-As-S stoichiometry from enargite (Cu3AsS4) to tennantite (Cu12As4S13), sinnerite (Cu6As4S9) and lautite (CuAsS). Regions for the thermodynamically stable species were shown to change with the four different mineral compositions. Potential leach conditions, both for co-dissolution and selective dissolution techniques, were examined for differences in predominant species according to changing copper-to-arsenic ratios, sulfur compositions and sulfur oxidation states."

Jan 1, 2016

By Lars Lövgren, Jörgen Jönsson

Heavy metals may be retained within deposits of sulfide minerals under oxidation and in the nearest recipients of drainage water by sorption to secondary iron precipitates. The extent of sorption is strongly influenced by solution pH and presence of complexing ligands, such as sulfate and natural organic acids. Desorption of metals and organidinorganic anions to recent secondary Fe precipitates, collected at the Kristineberg mine, Sweden, has been investigated under different geochemical conditions. Elemental composition and structural characterization (X-ray powder diffraction) indicate presence of schwertmannite. While metals such as Ni and Pb were fractionally desorbed from the precipitates under acidic conditions, oxyanions, e.g. arsenatdarsenite and sulfate were desorbed preferably under alkaline conditions. In a separate study the adsorption of NOM onto synthetic goethite was investigated. NOM adsorption showed a strong pH dependence, 95% was adsorbed at pH 3 and 40 % was adsorbed at pH 9. Addition of 2 mM of sulfate desorbed about 10 % of the adsorbed NOM.

Jan 1, 2000

By E. H. Christiansen

Gem-quality red beryl in the Wah Wah Mountains of southwestern Utah formed as a post-magmatic mineral in a topaz rhyolite flow. Unlike topaz, this beryl occurs along fractures in devitrified rhyolite, rather than in lithophysal vugs. The flow occupies a graben and perhaps a significant paleo-drainage. Beryl occurs at medial depths within the eroded flow, about 170 m below overlying mafic lava flows. Both beryl-bearing fractures and the host rhyolite show an unusual amount of argillic alteration compared with other topaz rhyolite flows. Alteration may be related to the incursion of surface water along shrinkage fractures within the flow. Whole-rock concentrations of CaO within the host rhyolite are very low (<0.01 % to 0.18%) compared with other topaz rhyolites and Be concentrations (about 20 ppm) are about average. Low Ca activities prevented fluorite precipitation and allowed Be transport as fluoride complexes. Beryl probably grew at subsolidus temperatures (-300-650°C), but above the temperature of kaolin development (200-300°C) as fluoride-rich vapors, released by devitrification, encountered fractures and mixed with vapors derived from surface water flowing through the fractures. Beryllium fluoride complexes reacted with water vapor, silica minerals, alkali feldspar, water, and Fe-Mn oxides along fractures to produce red beryl. Continued reaction of the cooling flow with surface water at lower temperatures probably produced a boiling, more acidic fluid that produced the argillic alteration. Consequently, eruption of low-Ca topaz rhyolite followed by entrance of surface water into medial portions of a devitrifying and still hot lava flow appear to be critical factors that led to red beryl formation.

Jan 1, 1996