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By S. R. Hutchins

Several refractory sulfide and carbonaceous gold ores were examined to determine whether microbial pretreatment could be used to enhance gold recovery. Test samples were biologically leached using unique, thermophilic microorganisms to solubilize iron sulfide minerals. Gold recovery from sulfide ores and concentrates was enhanced following pretreatment with the thermophiles; responses varied widely for the individual materials. Although bioleaching had little effect on the preg robbing characteristics of the carbonaceous gold ores, cyanidation of the bioleached residues yielded higher gold recoveries than cyanidation of the native ore. By combining bioleaching with abiotic processes designed to inhibit preg robbing, gold recoveries of 83-98% were obtained from carbonaceous ores yielding 10-50% gold recovery by direct cyanidation.

Jan 1, 1987

By R. Owens, C. Roos, B. Hill, S. Rosenthal

It is common practice, and even legally required in many jurisdictions, to design two-lane haul roads in open pit mines to three and a half times the widest dimension of the haul trucks operating on the road. In open pit gold mines with high strip ratios, the road width has a significant impact on the economics of a design. It is possible to minimize the flattening of the highwall if the road width is reduced, assuming the width used is not needed to flatten the slopes for geotechnical purposes. With the use of autonomous haulage and pullouts, it may be possible to operate safely and efficiently on a reduced road width of two times the width of the hauling equipment.

Mar 2, 2022

By Bill S. Taylor

Dutch State Mines [D.S.M] introduced the Heavy Medium Cyclone into the United States for cleaning fine coal about three decades ago. Since that time the general industry practice has been to deslime the raw coal at 28 Mesh (0. 59mm) size. The plus 28M material is fed to the Heavy Medium Cyclone for cleaning, and the 28M x 0 fraction is processed by other means (e. g. flotation or hydrocyclones). This approach recognized that 28M was the smallest size particle that could be easily rinsed on vibratory screens without excessive loss of magnetite, and without blinding of sieve bend and vibratory screen decks. Another reason for the 28M de-sliming was to avoid excessive contamination of the media with non-magnetic coal, shale, or clay fines. The most undesirable of these contaminants is the sub-micron size clay particles (2) that greatly increase the viscosity of the media and reduce the numerical maximum level that the media specific gravity can obtain due to the lower specific gravity of clay with respect to magnetite. The higher the fugitive clay content, the more severe the preceding problems become. During the last 30 years, many conventional Heavy Medium Cyclone Plants have been built throughout the world. In the United States, the initial cyclone plants were confined to the production of high quality metallurgical coal where lower gravities of separation were required than could be obtained from the conventional hydraulic or air separation processes. In recent years a large and ever-increasing number of preparation plants producing steam coal have started utilizing Heavy Medium Cyclone technology due to the environmental pressures being encountered to produce low sulphur coal. Due to the inherent characteristic of many coals of having a lower pyritic sulphur content at lower specific gravity fractions, many applications and markets are appearing for separating steam coals at much lower specific gravities than have been historically normal in the United States. Therefore. Heavy Medium Cyclones are being utilized to a much greater degree in this field, due to the flexibility of low separating gravity ability coupled with high efficiency when high percentage of near gravity material is present.

Jan 1, 1978

By Jr. Raleigh

As part vi the development of the Coal Quality Expert (CQRN) --a computer program capable of predicting the impacts of coal quality on power plant performance, costs, and emissions control--several nationally important coals are being characterized to augment the coal quality database associated with the software. The project is sponsored by the U.S. Department of Energy and the Electric Power Research Institute (EPRI) under the Clean coal Technology Program. Since 1989, CQ Inc. (a subsidiary of EPRI) has characterized seven bituminous coals from Alabama, Illinois, Kentucky and Oklahoma and six sub-bituminous coals from the Powder River Basin (PRB) in Montana and Wyoming. Coals from the PRB region--being burned more frequently in Midwestern and southern power plants to reduce emissions of sulfur oxide compounds--can sometimes contain significant concentrations of potentially toxic elements. Although no limits were imposed on air toxics emissions from fossil-fuel fired utilities by the Clean Air Act Amendments of 1990, future regulations may be implemented at the conclusion of Federally-mandated emissions studies. One possible result is that any increased utilization of coals, including those from the PRB, may depend on the potential for removing toxic trace elements prior to combustion.

Jan 1, 1993

By C. L. Lin

A PC image-based on-line coarse particle size analyzer has been developed to measure particle size distributions under plant situations where overlapped particles are being transported on a moving belt conveyor. Although previous testing had shown satisfactory performance of this image-based system for separated particle size measurements (the non-overlapped case), it was necessary to modify original algorithms in order to solve the overlap problem and make the system suitable for plant operations. On-site testing has been conducted at a large copper concentrator in the southwestern U.S. for further investigation of the overlap problem.

Jan 1, 1995

By James E. Lawver

The agriculture industry has made great strides during the past decade to increase agriculture yields through increased use of fertilizers. Increased use of fertilizers may prevent or at least delay mass starvation due to the alarming increase in world population. Phosphate was added to soil as a plant nutrient in the forms of calcined bones at least 2 000 years ago, (1) and man has used phosphate minerals as a source of fertilizers in one form or another for at least 100 years. During 1977 the world produced about 116 million metric tons of phosphate rock, with about 86% used for fertilizers and another 4% for animal feed supplements. More than three-fourths of the total production comes from the United States, Morocco, and the Soviet Union. From a mineral beneficiation point of view, the major sources of phosphate rock and the methods of beneficiation can be classified as follows. Marine deposits not containing appreciable carbonate minerals, marine deposits requiring a francolite carbonate mineral separation, igneous deposits not containing appreciable carbonate minerals, and igneous deposits, requiring an apatite carbonate mineral separation.

Jan 1, 1978

By J. P. Fitzgerald

This paper is an accumulation of information on the geology, mineralogy and mining of the Hectorite clay deposit owned by NL Chemicals (U.S.A.), Inc. The mine is located in San Bernardino County, California approximately 35 miles east of Barstow and 1-1/2 miles south of U.S. Highway 40. The region is known as the Mojave Block which is a region bound by the San Andreas fault zone to the southeast and the Garlock fault zone to the North. The faults of both zones are active, vertical faults along which movements are mainly horizontal. Most of the faults within the Mojave Block are high angle faults which trend northwest. They are considered part of the San Andreas fault system and are a result of the right- lateral movement characteristic of this system. The east-trending faults are also high angle faults, along which movement has displaced rock units vertically. Manix fault is the only mapped fault that shows evidence of left slip which is characteristic of the Garlock sys tem to the North.

Jan 1, 1986

By Bern Klein, Rafael Fernandes de Mesquita, Fatima Regina Ney Matos, Andre Xavier

"193 United Nations members are signatories of the 17 Sustainable Development Goals (SDGs). Even though it does not make it legally binding to the country members, the SDGs establishment incites national and managerial frameworks to achieve the SDGs. The mining industry inserts itself in this context by its global presence and frequent location within ecologically sensitive and less developed areas. This paper aims to consolidate the state of academic research on mining, sustainability and sustainable development, by organizing the results of previous studies within a systematic review on the SDGs set. To do so, the ISI Web of ScienceTM Core Collection database was chosen as a database of record, as it is one of the most widespread databases of academic journals. We have used all years available in the ISI database, from 1945 to 2016 (for complete years). The systematic review process comprised of five steps: (i) to search terms [(“sustainability” or “sustainable development”) and mining] on the database and to apply filters of criteria; (ii) organizing papers; (iii) metrics and relations between papers and authors; (iv) classification of the results through content analysis techniques; and (v) synthesis. The results were divided in two groups: the highly cited and the most recent papers, to include papers that have academic impact and those which show the newest contributions to the field. The results showed that, in spite of a growing amount of publications in the past years that relates to mining and sustainability, the main focus of these publications are still on the environmental dimensions of the UN goals. This suggests that more practical and academic work in the mining sector are required to fill in the blank spaces regarding the other set of goals that compose the SDGs framework.Introduction A total of 193 United Nations members are signatories of the 17 Sustainable Development Goals (SDGs). Even though it does not make it legally binding to the country members, the SDGs establishment incites national and managerial frameworks to achieve the SDGs. The mining industry inserts itself in this context by its global presence and frequent location within ecologically sensitive and less developed areas (Atlas 2016). The goals are important because they add common targets for different countries and easily establish discernible criteria for it (Costanza et al 2016). A forward-looking approach like the SDGs would be able to attach the sustainable development framework with profitable activities taken by the mining companies (Starke 2016). This paper aims to consolidate the state of academic research on mining, sustainability and sustainable development, by organizing the results of high impact previous studies and recent publications, within a systematic review, on the SDGs set. By doing so, the results can portray the actual concern and the lacks that the academic field had on this subject in comparison to the UN contemporary agenda."

Jan 1, 2017

By J. Kretschmann, K. Sakamornsnguan

"Sustainable development is an influential ethical concept in modern mining management. However, the concept is not culturally neutral because it is based on Christian, Western values. These values can be very different from traditional values in emerging mining countries like Thailand, where Buddhist values are dominant. When applying the concept of sustainable development, these differences should be taken into account. Different values imply different interpretations of ‘good mining’. They have a significant impact on how mining operations are evaluated, perceived, operated and managed. This paper attempts to integrate Buddhist principles with approaches of the sustainable development concept. When local values are appreciated and maintained, mining companies and their external stakeholders can identify objectives and approaches that match with their own values and contexts. Practices based on this integrated ethic can help to promote sustainable mining and to minimize communication risks for enterprises in mining countries like Thailand. INTRODUCTION The objective of this paper is to integrate Buddhist principles to the application of sustainable development concept to mining activities. The structure of this paper is divided into four parts. An introduction provides basic information about Thailand, its mining industry and the role of Buddhism on the past development. The second part compares the differences between the sustainable mining framework and the implications of Buddhist principles on mining. In the third part, the core Buddhist teachings are integrated into the sustainable mining framework. This is followed by conclusions in the last part. THAILAND, BUDDHISM, AND MINING Thailand is a constitutional monarchy state in Southeastern Asia with a population size of around 65 million [1]. Its GDP in 2013 was 391 billion USD [2], predominantly deriving from manufacturing (38%), trade, transport and communication (24%), agriculture (8%) and mining and construction (4%). Still the largest part of the Thai workforce (39%) is working in the agricultural sector. The remaining part of the workforce is equally distributed across services, manufacturing, and mining and construction sectors. [3]"

Jan 1, 2015

By J. G. Nalven

On July 1, 1999, most domestic metal mines will have to report releases of toxic chemicals into the environment for the first time as required by SARA Title 313. Some of these reportable releases will appear huge in relation to reports by other industries. The reasons for the potentially large reportable releases, special considerations for mining operations, and strategies for dealing with the reports are described. Data composited from experience with several mining companies is presented in the context of a typical gold mine.

Jan 1, 1999

By H. Y. Sohn

Considering the two most important issues the ironmaking industry faces today, i.e., energy consumption and greenhouse gas emissions, it would be advantageous to utilize the concentrate-size raw materials directly without pelletizing or sintering, especially without the use of coke. This plenary lecture describes two such processes developed at the University of Utah. One is the Flash Ironmaking Technology (FIT) and the other is a moving-bed process for continuous ironmaking with gaseous reduction of iron ore concentrate (MBIT). These technologies are designed to produce iron directly from iron concentrate without requiring pelletization/sintering and cokemaking in two significantly different temperature ranges. They take advantage of the high reactivity of the concentrate particles and will considerably reduce energy consumption and carbon dioxide emissions compared with the current processes. The process of the development from the conception of the idea, to kinetic feasibility establishment, to laboratory flash furnace, and finally to the operation of a prototype facility for the development of the FIT is discussed. The development of the MBIT also started with the formulation of the process concept, followed by kinetics feasibility establishment, and the design of a potential industrial reactor. The results of economic analyses on the FIT are briefly described.

May 12, 2023

By Y. J. Wang

The selection of a shaft size for ventilation purposes is a classic problem of concern to mining engineers. This presentation is concerned with the sizing of conventionally-sunk circular shafts with concrete or shotcrete linings. Costs of sinking shafts of three different depths (from 500 feet to 1000 feet) and six different diameters (from 14 feet to 24 feet) were obtained through questionnaires to shaft contractors. The primary objective of the economic model presented is the balancing of detailed annual capital and operating costs to achieve the minimum overall cost of the shaft installation over its life. The economic model is similar to previous analyses but treats several of the individual cost categories in an updated fashion. Included in the paper is a detailed analysis of the effects of varying power costs on optimal shaft size. Also included are a statistical analysis of current shaft costs and comments on the choice between shotcrete and concrete linings.

Jan 1, 1977

By W. G. Pariseau

"The Crandall Canyon Mine (CCM) is located in the Wasatch coal field in central Utah. Extensive longwall mining at CCM preceded a decision to recover coal left in barrier pillars on each side of a set of main entries extending far into the mine. During mining in March 2007, a major bump occurred that led to cessation of mining in the barrier pillar on the north side of the mains and to the start of mining in the south barrier pillar. Subsequent loss of ground control in August 2007, through coal pillar bursts had tragic consequences with loss of six miners and shortly afterward three rescue team members. A U.S. Mine Safety and Health Administration (MSHA)report describes the events in detail (MSHA, 2008).An important lesson to be learned from CCM is the need to select a computer program suitable for pillar design. Computer programs are engineering tools and selecting the right tool for the job is essential. In this regard, minimum program requirements include capability for computing stress distribution within a pillar and adjacent roof and floor strata. The reason is simple: strength of rock is stress dependent; both vary from point to point in pillars and adjacent strata. Preferably, one should follow the evolution of stress as the mining plan is executed from start to finish to assure safety or to warn of a potentially hazardous situation developing as mining progresses.The approach to the problem posed by barrier pillar mining at CCM is conventional in the sense of applying well known finite element modeling techniques to analysis of a proposed mining plan. The engineering purpose is to evaluate the mining plan with respect to ground control questions including roof, floor and pillar safety. Results of previous two-dimensional finite element analysis indicated pillar safety was by no means assured (MSHA, 2008; Pariseau, 2008; Pariseau, 2011). Geometry of barrier pillar mining is limited in two dimensions for example, crosscuts are not seen in vertical cross sections. While three-dimensional analyses are preferred, even moderately sized regions often lead to very large problem sizes that exceed computer capabilities. However, a recent development in finite element modeling of tabular deposits allows for whole mine analysis in three dimensions. This technique involves a dual node - dual mesh concept. Both have been used separately in much earlier work, but are only now used in combination. It is possible to have an estimation of subsidence at a kilometer scale and details of stress, strain and displacement about barrier pillars, main entries and pillars, and so on at a meter scale (Pariseau, 2014). No compromise involving empirical formulas or similar guess work is required. Indeed, all calculations are based on first principles: physical laws, kinematics, and material laws. Effects of joints and in situ variability or uncertainty in strata properties, elastic moduli and strengths, may be included for greater realism. An important objective of the present study is to assess the role of three-dimensional pillar geometry in arriving at conclusions regarding barrier pillar mining versus two-dimensional results."

Jan 1, 2014

By Keith A. Heasley

Historically, the surface subsidence over underground coal mines has been predicted using empirical profile or influence functions which have little or no connection to the actual mechanics of the subsidence. Without a mechanistic basis, establishing the exact site-specific parameters to use in these empirical methods has been problematic. A practical subsidence predictive method based on mechanics has the appealing capability of allowing the determination of site-specific parameters from fundamental properties of the overburden with minimal field calibration work. This paper presents several case studies where a mechanics-based, boundary-element program is used to back-calculate the surface subsidence associated with various panels at several Northern Appalachian coal mines. The program used in this case study is called LAMODEL, and it incorporates a frictionless, laminated overburden into a general purpose displacement-discontinuity code primarily designed for calculating the stresses and displacements in coal mines or other thin scam or vein type deposits. In this paper, the program is used to calculate both the underground convergence and the resulting surface subsidence at five longwall panels and a room-and-pillar section. The fitted subsidence from the model is compared with the field measurements and analyzed. The results from the case studies in this paper demonstrate that the laminated model with calibrated properties can easily provide moderately accurate subsidence predictions and is fairly flexible for fitting measured subsidence. However, additional subsidence predictive case studies arc recommended in order to ultimately evaluate the potential of the laminated overburden model for practical subsidence prediction

Jan 1, 1999

By SANDEEP KUMAR JENA

This review work reports the recovery of potassiumfromdifferent rocks and mineral sources. The global demand for potassiumis rising consistently due to the growth of agricultural production. A major portion of the world potassium production is consumed in making of fertiliser; however, other uses include those in pharmaceutical, glass, ceramic, food and detergent industries. The availability of soluble potash minerals (sylvite, kainite and carnallite) in different countries like Canada, USA, Israel and Russia makes them as major potash producers, whereas agricultural-based countries like Liberia, Somalia, Central African Republic, Thailand, Indonesia and Malaysia including India meet their potassium requirement through import only. On the contrary, the availability of huge potassium-bearing rocks/minerals (like nepheline syenite, feldspar, mica, glauconitic sandstone) in these countries containing around 4–17% K2O would be a prospective for commercial production of potassium. The potassium recovery from minerals/rocks is very complicated due to the uniform distribution of potassium throughout the crystal structure. Different physico-chemical separation methods like bioleaching, chemical leaching, flotation and roast leaching have been discussed for the successful recovery of potash values from these rocks/minerals. However, the recovery of potassium from hugely available seawater using the chemical precipitation, solvent extraction,membrane separation and ionic exchangemethods is not cost-effective due to the low concentration of potassium.

Aug 31, 2020

By R. E. Murray

"It is a gloomy moment in the history of our country. Not in the lifetime of most men has there been so much grave and deep apprehension; never has the future seemed so incalculable as at this time. The domestic economic situation is in chaos. Our dollar is weak throughout the world. Prices are so high as to be utterly impossible. The political cauldron seethes and bubbles with uncertainty. Russia hangs, as usual, like a cloud, dark and silent, upon the horizon. It is a solemn moment. Of our troubles, no man can see the end." By now you, no doubt, are asking, 'Where did Murray get this bit of philosophy?' Well, I obtained it from an editorial entitled. "The Worst of Times", which was published in the Harper's Magazine in 1847. That's right, 1847! The parallelism between the situation in our country at this time and in 1847 is un- canny. But wait, there is one major exception the size of government. To my knowledge, the citizens of 1847 were not stifled by the extreme governmental excesses that we are experiencing today.

Jan 1, 1980

By Kanhaiya Mishra, Phanil. K. Mandal, S. K. Behera, P. S. Paul, Prashant Singh, C. N. Ghosh

The techno-economic and social benefits of cemented paste backfill (CPB) resulted in its wide acceptance by the mining industry. The Ordinary Portland Cement (OPC) remains the key binder but to diminish its economical constraints, suitability of alternate binders has been examined worldwide. The present study aimed to investigate the effect of partial replacement of OPC with fly ash on the CPB’s strength and to determine the most optimal mix to achieve the required strength (1 MPa at 28 days of curing) at the most cost-effective way using the Bayesian network (BN). The CPB mixes were prepared at 72 wt.% solid concentration with mill tailings (87–91%), OPC (6–13%), and fly ash (0–4%), and instantly after mixing, fresh (slump, bleeding, density) CPB properties were measured. The strength was tested at 7, 14, 28, and 56 days of curing and initially analysed through traditional model. The traditional models follow the aleatory principle and are considered not appropriate for geotechnical engineering. Hence, the BN model was developed and tested. The reliability of two classifiers in learning model structure was compared which gives Naïve Bayes as the highest reliable tool. The CPB’s strength is most sensitive to the OPC content. The most consistent mix(s) is mill tailings: 87–88%, OPC: 9–11%, fly ash: 1–4%. Adding fly ash at 89–91wt% mill tailings possesses high failure probability of the CPB. The collinearity test indicates that the fines percentage and chemical composition of CPB’s ingredients are highly correlated with its slump, bleeding, and strength development.

Jul 14, 2022

By Kevin Vander Tuig, Tim O’Rourke, Rick Vincent, Doug Lopata, Kellie Rotunno, Dan Dobbels

"The Northeast Ohio Regional Sewer District (NEORSD) was required under the Federal Clean Water Act and U.S. Environmental Protection Agency’s (U.S. EPA) Combined Sewer Overflow (CSO) Control Policy to develop a Long Term Control Plan (LTCP) to reduce or eliminate overflows from its permitted CSO outfalls. The LTCP was completed in 2002. Key components of the plan include: 26 miles (42 km) of deep storage and conveyance tunnels providing a total CSO storage volume of 325 million gallons (MG) (1.2 billion liters); over 30 miles (48 km) of consolidation sewers to route CSO control flows to the tunnels; and associated diversion/inflow control structures and drop shafts. Final design and construction of the initial phases of the LTCP are completed or underway. Advanced planning of the final phases began in April 2013. This paper summarizes this advanced planning process and, specifically, how hydraulic performance and tunnel design and construction considerations were balanced to eliminate unnecessary projects and shafts, reduce implementation risks, and reduce program costs by approximately $650 million. BACKGROUND The Northeast Ohio Regional Sewer District (District) serves an area of approximately 350 square miles (SM) (907 km2), including combined (81 SM; [210 km2]) and separate (269 SM [697 km2]) sewer systems that discharge to three wastewater treatment plants in the greater Cleveland area. The service area, shown in Figure 1, is divided into three districts—Easterly, Westerly, and Southerly—each having its own interceptor system and treatment plant, ranging in wet weather treatment capacities from 100 to 735 million gallons per day (MGD) (378.5 million to 2.8 billion L/day). The system includes 124 permitted combined sewer overflow (CSO) outfalls overflowing into the region’s tributary streams, Cuyahoga River, and Lake Erie."

Jan 1, 2016

By J. D. Miller

The sedimentary western phosphate deposits of Idaho, Montana, Utah, and Wyoming tend to be calcareous and generally carry a significant amount of dolomite along with collophanite. In some cases, such as the Smokey Canyon Mine, Afton, Wyoming, the ore will also contain mudstone, and in this case the aluminosilicate minerals (clay, feldspar, etc.) together with some dolomite are floated from the collophanite in column flotation cells with an amine in order to meet product specifications (31 % P205) (Service et al.). In other cases, such as the SF Phosphates Limited Mine, Vernal, Utah, the ore is treated by traditional fatty acid flotation of the collophanite with mechanical flotation cells (Weber, 1986). Preliminary tests have now been conducted to evaluate air-sparged hydrocyclone (ASH) technology for the flotation of western phosphate ore. For this preliminary study, samples were taken from the hydrosizer overflow stream (18-21 % P205) at the SF Phosphates Limited Plant in Vernal, Utah for scavenger flotation testing with the 2-inch ASH system in laboratories at the University of Utah. Selected design and operating variables are being studied, and the initial results show that satisfactory separations can be achieved by high-capacity ASH flotation at appropriate operating conditions. For example, with single-stage ASH flotation 80% recovery can be obtained with a scavenger concentrate grade of about 26% P2O5. These results are comparable to, or better than, those obtained at SF plant operations with conventional flotation cells and suggest that ASH flotation technology can be used to good advantage in the phosphate industry. Of course, research should be continued to consider other process streams, optimize the separation efficiency, and evaluate larger diameter ASH units.

Jan 1, 1993

By Neely H. Bostick

The primary and secondary organic matter in sedimentary rocks changes markedly when it becomes heated as a consequence of thick sediment accumulation and normal geothermal gradients, high geothermal gradients, hydrothermal fluids, or igneous events. Contact zones adjacent to small igneous dikes allow sampling of a single sedimentary bed that has been exposed to temperatures in a range as great as 30-500°C. Dike-heated rocks are, therefore, good sites for research on thermal effects because variation of the original organic matter is minimal, the range of heating is great, and the history of rock heating in a dike zone is relatively well established. In rare cases, such as at the dike near Wolcott, Colorado, described in this paper, the rock samples are sufficiently unweathered to allow analysis of secondary bitumens generated by the heating. We show by optical microscopy, scanning and transmission electron microscopy, and geochemistry the kinds of solid organic constituents in sedimen¬tary rocks and in ore deposits and the effects of heating. The primary phytoclasts that make up kerogen In sedimentary rock and in some ore deposits (pollen, resin, charcoal, humified woody remains, etc.) change in ways that are familiar to coal specialists. Progressive loss of moisture and other volatile matter yields residual kerogen that Is relatively higher in carbon and lower In oxygen and hydrogen, and has greater molecular or polymer ordering. In our contact zone examples, atomic H/C ratios of kerogen decrease from 0.8 (one case from 1.4) to 0.4, the hydrogen index from Rock-Eval pyrolysis decreases from 70 to 5, and the transformation ratio from Rock-Eval pyrolysis increases from 0.06 to 0.5 with increased heating. The visible effects of heating seen by scanning electron microscopy and light microscopy include formation of vesicles and flow structure, the development of optical anisotropy and mesophase, change of color, and increase in the refractive index, absorption, and reflectance. Some of these changes In primary organic matter are observed also in secondary organic matter, for example, in solid bitumens in sedimentary gold ores or In lead-zinc deposits. Quantification of color or absorption changes is difficult because it Is hard to make thin sections of organic matter with uniform thickness. However, natural objects with uniform thickness can be used. We show the colors of pollen In rocks from the Salton geothermal field at temperatures ranging from 100 to 300°C, and of pollen heated in laboratory bombs from 150 to 400°C. Measurement of vitrinite reflectance is a practical way to quantify thermal changes of kerogen and minerals of most sedimentary rocks because vitrinite is fairly widespread In sedimentary rocks of Devonian age and younger. For example, the reflectance of vitrinite rises from the regional level, as low as 0.4 % Ro, to more than 5% Ro adjacent to dikes that cut sedimentary rock. This is equivalent to the rank change from subbituminous coal to extreme meta-anthracite. The rise is most abrupt near thin dikes, but when the distance from the igneous contact is expressed as a ratio of dike thickness the reflectance rise is similar for all dikes. Controlled heating of vitrinite-bearing rocks In the laboratory provides a means to assign known temperatures to vitrinite-reflectance values. The derived plots of temperature In dike contact zones have the same shape and level as those predicted by heat theory, and the temperature lines extend toward dike contact temperatures that are about half those of most magmas, as expected if the intrusions did not flow past the sedimentary rock for a long time. The globular submicroscopic structure of vitrinite and Its heterogeneity, which we show by means of transmission electron microscopy, pose some problems In selecting a uniform type of vitrinite for measurement of thermal changes. At present, routine reflectance values of vitrinite dispersed in rocks have a relative uncertainty as great as 10%. Thermally caused chemical changes in the primary kerogen, especially decrease in the oxygen and hydrogen contents, lead to formation of secondary products in the contact zone. The measured changes of secondary organic products in these rocks include formation of peaks In concentration of total extractable organic matter and in hydrocarbons, and in the saturated/aromatic hydrocarbon ratio over the interval where primary organic hydrogen decreases most rapidly--then destruction or expulsion of these products at high temperatures. The odd carbon-number predominance of the C25-C31 n-alkanes In samples far from the dike disappears by about 1.3% Ro whereas the 13C: 12C ratios of the saturated and aromatic hydrocarbons increase over most of the thermal range. The saturated aromatic hydrocarbon ratio at first increases, corresponding to thermal generation of saturated hydrocarbons, then decreases in the most altered samples. One use of organic petrography, in addition to identifying organic fades or thermal alteration, is recognition of sample contamination such as the solid organic additives used in some drilling muds which may contaminate geochemical samples.

Jan 1, 2013