Academic literature on the topic 'Mineralogy|Metallurgy'

“Image analysis” refers to the general family of computational techniques which are concerned with the extracting of quantitative information from images captured in digital form. Such techniques have been in use for several years in areas such as biology and metallurgy, but have been slow to find wide use in the microscopic areas of Earth Sciences. Notable exceptions have included applications in the areas of mineral processing and sedimentary petrography.The impetus for the meeting held jointly by the Applied Mineralogy Group of the Mineralogical Society and the Geological Information Group of the Geological Society of London in September 1993, was an attempt to take stock of the spread of digital image analysis techniques into the domain of the mineralogist and petrologist.

Andres Manuel Del Rio was born in Madrid in 1764 and died in Mexico City in 1849. He studied mineralogy, geology, metallurgy, and mining engineering at the Royal Academy of Mines of Almaden and the Patriotia Seminary of Vergara. In 1871, with a stipend from the Spanish Crown, he continued his studies in Paris, Freiberg, Chemnitz, and other scientific centers throughout Europe, particularly in metallurgy. In 1794 at the invitation of Don Fausto Delhuyar, who together with his brother Juan Jose Delhuyar discovered tungsten in 1783, Andres Manuel Del Rio went to Mexico where he was a professor at the SahooZ of Mines for more than fifty years, until his death. In 1801, while analyzing a lead mineral from Zimpan, Hidalgo, Mexico, he discovered a.mew element that he called pancuronium or erythronium, because of the red colors, aharaateris·tia of its salts. In 183Z, the Swedish chemist NiZs Gabriel Sez>fstz>IJm z>edisaovered erythronium in an iron ore from Taberg, Smaland, Sweden, and named it vanadium in honor of the Scandinavian goddess Vanadis.

Determining whether or not a gold gravity circuit should be installed in a gold plant requires a prediction of how much gold will be recovered. This has always been a difficult task because recovery takes place from the grinding circulating load, in which gold's behavior must be described.<br>A population-balance model (PBM) to predict gold gravity recovery was developed at McGill University in 1994 (Laplante et al, 1995). The objective of this research was to make this PBM user friendly. This was achieved in two different ways. First, the behavior of gravity recoverable gold (GRG) in secondary ball mills and hydrocyclones was described by two parameters, tau and R-25mum, and these parameters were linked to the circulating load of ore and the fineness of the grinding circuit product, for easy estimation. Second, the database of simulations produced by the PBM was represented by two multilinear regressions (one for coarse GRG, the other for fine GRG) linking the predicted GRG recovery to the natural logarithm of tau, R-25mum , the size distribution of the GRG and the recovery effort (Re ), defined as the proportion, in %, of the GRG in the circulating load recovered by gravity. Re was found to be the most significant parameter, tau the least. The GRG size distribution, represented either by two (coarse GRG) or three (fine GRG) points on the cumulative passing curve, has a significant impact on recovery. A total of twenty different GRG size distributions were used to generate the simulation database.<br>The multilinear regressions were tested on four case studies, and found to predict GRG recovery well within the precision with which the GRG content can be measured, a relative 5%. Whenever size-by-size recovery data are available, the PBM itself would be used; if not, the simpler regressions would be preferred.

This research documents the use of a 7.6 cm laboratory Knelson Concentrator (LKC) to determine the amount of gravity recoverable gold (GRG) content in ores and evaluate the performance of gravity circuits, with an emphasis on high gangue density. Two approaches were used to minimize the effect of the high gangue density in estimating the GRG content, oversize removal and 2:1 ratio dilution with silica flour.<br>The amount of GRG was determined in four ore samples with an established protocol, yielding values of 35% to 78% of total gold.<br>Results from the Angnico-Eagle La Ronde Division (AELRD), Louvicourt and East Malartic mills suggest that the typical Knelson-based gravity circuit which can recover one half to two thirds of GRG from low density gangues will only recover one third to two fifths of the GRG from high density gangues. Simulation of gold recovery at AELRD showed that the high circulating loads, 700--1100%, were a significant factor in reducing gold recovery by gravity. (Abstract shortened by UMI.)

Made available in DSpace on 2016-04-28T14:16:16Z (GMT). No. of bitstreams: 1 Andrea Bortolotto.pdf: 923414 bytes, checksum: b7aa6819938401f2b747e43d546e5665 (MD5) Previous issue date: 2012-10-18<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>On the one hand, this dissertation examines to what extent the Chemical knowledge and the knowledge that sprang from experiments conducted in mines contributed to a new proposal of identification and classification of minerals in the 18th century, a period in which the demand for metals expanded. On the other hand, it is an attempt to discuss the sources that were used in order to propose a new concept, which is neither a result of a simple aggregation of previous concepts nor their neglect. As a matter of fact, the new concept goes beyond that, as it entails previous knowledge by complementing and transforming it. To do so, we analyzed in what terms Johann Andreas Cramer (1710 1777) moved closer and further from the various concepts available in his time to put forth a new method of mineral assaying based on the chemical behavior of the bodies, which allowed him to identify, extract and classify minerals more precisely. Among these sources, two stand out: Georg Ernst Stahl and Herman Boerhaave, rather different sources, considered even paradoxical by many historians. Such analysis has revealed that in the History of Chemistry there were moments in which lines of thought moved away. Nonetheless, there were also moments in which they blended. That finding leads us to conclude that the History of Chemistry is to be evaluated in terms of non-continuous analysis without disregarding continuity, though<br>Nesta tese, buscamos verificar, por um lado, em que medida os conhecimentos químicos e os conhecimentos advindos dos trabalhos realizados junto às minas contribuíram para uma nova proposta de identificação e classificação mineral no século XVIII, época em que a demanda por metais era crescente. E por outro, discutir as fontes usadas para propor um novo conhecimento, que não se constitui apenas por simples adição de conhecimentos anteriores nem por seu completo abandono. Mais do que isso, o novo conhecimento traz em sua elaboração conhecimentos anteriores que além de se completarem, se transformam. Para tanto, analisamos em que medida Johann Andreas Cramer (1710 - 1777) se aproximou e se distanciou dos diversos conhecimentos disponíveis em sua época para propor um método de análise mineral baseado no comportamento químico dos corpos, o que permitiu identificar, extrair e classificar os minerais com mais precisão. Dentre essas fontes destacam-se duas, Georg Ernst Stahl (1659-1734) e Herman Boerhaave (1668-1738), fontes bem diferentes e consideradas opostas por muitos historiadores. Essa análise nos revelou que, na História da Química, houve momentos em que as correntes de pensamento se distanciavam, mas também momentos em que se completavam. Tal constatação nos conduz à conclusão de que a História da Química deve ser pensada em termos de análises não-continuístas, não desprezando, entretanto, suas continuidades

In a particle based geometallurgical model, the behavior of the particles can be used for forecast the products and quantify the performance of the different ore types within a deposit. The particle tracking is an algorithm developed by Lamberg and Vianna 2007 whose aim is to balance the liberation data in a mineral processing circuit composed by several processing units. Currently, this tool is being developed for the HSC Chemistry software by Outotec.The objective of this study is to understand and evaluate the particle tracking algorithm in a geometallurgical test for iron ore. To achieve this objective, the liberation data is balanced in a Davis tube test circuit. A total of 13 samples from Leveäniemi iron ore were process in a Davis tube circuit.The magnetite is the main mineral in the Leveäniemi iron ore samples. Its high recovery in the Davis tube circuit along with the V, Ti and Mn suggest that these elements are present in the magnetite lattice. These penalty elements in the iron concentrates cannot be avoided at the stage of mineral concentrations.The washing effect of the Davis tubes controlled by the rotational and longitudinal agitation of the tube perturb the particles agglomeration between the pole tips of the electromagnet. A higher agitation frequency and amplitude will wash away most of the gangue minerals and also fine grained magnetite.In this work, the particle tracking is depicted and implemented in a magnetic separation circuit for high liberated material. The liberation data was balanced in a way that the particle classes can be followed through circuit and their recoveries can be calculated. Nevertheless, the algorithm requires further validation and analysis of its limitations in terms of resolution and reproducibility.

In recent years, automated mineralogy has become an essential tool in geometallurgy. Automated mineralogical tools allow the acquisition of mineralogical and liberation data of ore particles in a sample. These particle data can then be used further for particle-based mineral processing simulation in the context of geometallurgy. However, most automated mineralogical tools currently in application are based on two-dimensional (2D) microscopy analysis, which are subject to stereological error when analyzing three-dimensional(3D) object such as ore particles. Recent advancements in X-ray microcomputed tomography (µCT) have indicated great potential of such system to be the next automated mineralogical tool. µCT's main advantage lies on its ability in monitoring 3D internal structure of the ore at resolutions down to few microns, eliminating stereological error obtained from 2D analysis. Aided with the continuous developments of computing capability of 3D data, it is only the question of time that µCT system becomes an interesting alternative in automated mineralogy system. This study aims to evaluate the potential of implementing µCT as an automated mineralogical tool in the context of geometallurgy. First, a brief introduction about the role of automated mineralogy in geometallurgy is presented. Then, the development of µCT system to become an automated mineralogical tool in the context of geometallurgy andprocess mineralogy is discussed (Paper 1). The discussion also reviews the available data analysis methods in extracting ore properties (size, mineralogy, texture) from the 3D µCT image (Paper 2). Based on the review, it was found that the main challenge inperforming µCT analysis of ore samples is the difficulties associated to the segmentation of the mineral phases in the dataset. This challenge is adressed through the implementation of machine learning techniques using Scanning Electron Microscope (SEM) data as a reference to differentiate the mineral phases in the µCT dataset (Paper 3).

Several deposits in the Mt Isa - Cloncurry region have been studied, including those held by Australian Resources near Selwyn (Plume, Slate Ridge, Mobs Lease and Straight Eight),in particular, with respect to cobalt and gold mineralisation. Cobalt is associated with pyrite, pyrrhotite and arsenic sulfosalts. Other cobalt deposits in the Eastern Fold Belt of the Mt Isa Block were studied; these include the Queen Sally, Lorena and the Great Australia mine. Varying styles of Co-bearing mineralisation were encountered. In the Queen Sally mine a curious vanadium - substituted heterogenite has been found. This is only the world's second reported occurrence of this mineral of the halotrichite group. At the Great Australia, primary Co mineralisation has been shown to be confined to one generation of cobaltian pyrite. Several generations of pyrite are noted for this and other deposits.<br>Master of Science (Hons)

Thesis (PhD) -- Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: The process route for the production of base and platinum-group metals from natural sulfide ores commonly requires the conversion of high-iron furnace matte into an iron-lean converter matte. This is followed by pre-treatment through cooling of the iron-lean molten matte, physical processing of the solidified matte and hydrometallurgical metal extraction. Lonmin is the third largest producer of platinum-group metals in the world and utilizes Peirce-Smith converters for blowing high-iron furnace matte with air to a final iron concentration or endpoint. The molten matte is water granulated and solidification occurs via fast-cooling. The solidified matte is ground in a closed circuit ball mill with hydrocyclone classification and subjected to first stage atmospheric leaching. The specification of an ideal or desirable converter iron endpoint requires careful consideration. Most importantly, it must ensure the crystallization of converter matte with mineralogical qualities that are within the setpoints of the downstream unit processes and techniques. An additional consideration is for the final blown converter matte to achieve an optimum bulk concentration of the base metals Ni and Cu and platinum-group metals Pt, Pd, Rh, Ru and Ir. Mattes characteristic of variable iron endpoints were regularly produced at the Lonmin converter plant section. Uncertainty by plant metallurgists in knowing the desirable iron endpoint, particularly within the context of the Lonmin base metal refinery, and poor control has had detrimental effects on the mineralogical quality of the final matte and hence on the processing characteristics of the solidified matte particles downstream. A desirable iron endpoint required investigation, selection and implementation at Lonmin. The primary focus of this study was therefore to quantify the effect of a specific iron endpoint on the mineralogy and mineral chemistry of solidified converter matte. A fundamental examination of the solidification process upon cooling was regarded as critical to an in-depth understanding of the attained mineralogy and mineral chemistry as a function of a specific iron endpoint. It became equally important to quantify the effect of the resultant mineralogy, and hence iron endpoint, on the physical property of mineral structures in relation to downstream grinding, liberation and leaching characteristics. Despite considerable industry context, limited in-depth and coherent studies on the effect of a specific iron endpoint on fast-cooled converter matte systems were found in both industrial and scholarly literature. Previous findings in literature offered a limited quantitative understanding of the effect on mineralogy and mineral chemistry. Phase and cooling equilibria of multi-component, iron endpoint specific Ni-Cu-S matte systems were also not fully available. These would have been particularly useful in understanding the complexities of converter matte solidification as a function of iron endpoint. Physical property knowledge of converter matte mineral structures was hardly available and even less so in relation to grinding, liberation and leaching processes. A comprehensive investigation was therefore required to address these extensive knowledge gaps with respect to fastcooled converter matte systems in an industrial framework. Three Peirce-Smith converter production samples, representative of the extent in variability of iron endpoints attained at the converter plant, were used in a systematic investigation coupled to a novel combination of modern analytical techniques, computational thermochemistry and metallurgical testwork. The modern analytical techniques included the application of high resolution transmission electron microscopy and focused ion beam scanning electron microscopy tomography. Computational thermochemistry was applied through the use of MTDATA phase diagram software. Metallurgical testwork involved laboratory batch grinding at various specific energies. Closely associated leach experiments were also considered relevant to this wide-ranging investigation. The Peirce-Smith converter samples investigated were indicative of mattes that attained specific endpoints of 5.17%, 0.99% and 0.15 weight% Fe. The highest combined bulk concentration of the important base and platinum-group metals was achieved in the matte which attained a specific iron endpoint of 0.99%. The mineralogy of all three converter mattes was dominated by nickel sulfide mineral structures matched to the natural mineral of heazlewoodite. Mineral structures of copper sulfide, NiCu-alloy, spinel and OsRu-alloy were also constituents of the different converter mattes. The attainment of a specific iron endpoint was found to result in measurable mineralogical differences with respect to relative mineral abundances, external morphological characteristics and mineral chemistry. The mineralogical differences were particularly distinct between mineral structures of the high (5.17%) and low (0.99% and 0.15%) iron mattes. Subtle mineralogical differences were evident between mineral structures of the low iron mattes. The 0.99% Fe matte was characteristic of a significantly higher NiCu-alloy relative abundance, compared to the 5.17% Fe matte. The NiCu-alloy structures were found to act as the primary collectors of the economically significant platinum-group metals. Mineralogical observations were used to develop an understanding of the underlying mineralization mechanism of NiCu-alloy structures. High-fidelity color and grayscale 3D reconstructions were produced of the resultant mineralized structures. It was shown theoretically that variations in iron endpoint specific starting compositions of oxygen-free liquid matte systems alter the solidification pathway towards the eutectic. Moreover, a quantitative understanding of liquid phase solidification of the high and low iron matte systems, including oxygen, was developed to within ±2.5 oC. Most of the specific energy available for grinding was expended breaking the nickel sulfide matrix, particularly of the high iron matte. The breakage rates of copper sulfide mineral structures in the 5.17% Fe matte were calculated to be higher than in the 0.15% Fe matte at 25kWh/t specific energy. The degree of copper sulfide liberation was shown to be higher for the 5.17% Fe matte than for the 0.15% Fe matte at the same specific energy of grinding. A higher degree of Ni extraction and Cu cementation could be achieved when leaching low iron matte particles. The production of converter matte attaining a specific iron endpoint of 0.99% was found to be the most suitable with respect to endpoint selection criteria. A practical iron endpoint range of 1.6% to 1.0% was recommended for the production of converter matte with a resultant mineralogical quality within the constraints of the Lonmin base metal refinery. This study offers an integrated understanding of base and platinum-group metals production as a function of a desirable iron endpoint at Lonmin. This was not previously available in metal production literature. New technology for the monitoring and consistent control of such a practical iron endpoint range can subsequently be implemented.<br>AFRIKAANSE OPSOMMING: Die prosesroete vir die produksie van onedel en platinumgroepmetale uit natuurlike swawelertse vereis gewoonlik die omsetting van ’n ysterryke hoogoondmat in ’n ysterarm omsettermat. Hierna volg voorbehandeling deur die afkoeling van die ysterarm gesmelte mat, fisiese verwerking van die soliede mat, en hidrometallurgiese metaalekstraksie. Lonmin is die derde grootste produsent van platinumgroepmetale ter wêreld en gebruik Peirce-Smith-omsetters om ysterryke hoogoondmat met lug te blaas totdat dit ’n finale ysterkonsentrasie- of ystereindpunt bereik. Die gesmelte mat word met water granuleer, en solidifikasie vind deur middel van snelafkoeling plaas. Die soliede mat word in ’n geslotekringbalmeul met hidrosikloonklassifikasie gemaal en aan eerstestadium- atmosferiese loging onderwerp. Die spesifikasie van ’n ideale of gewenste ystereindpunt verg deeglike oorweging. Bowenal moet dit verseker dat die omsettermat kristalliseer met mineralogiese eienskappe wat binne die setpunte van die eenheidsprosesse en - tegnieke verder af in die prosesstroom val. ’n Bykomende oorweging is dat die uiteindelike geblaasde omsettermat ’n optimale massakonsentrasie van die onedel metale Ni en Cu en die platinumgroepmetale Pt, Pd, Rh, Ru en Ir moet bevat. Matte met die kenmerke van wisselende ystereindpunte is gereeld by die Lonminomsetteraanleg geproduseer. Die onsekerheid van metallurge by die aanleg oor die gewenste ystereindpunt – veral binne die konteks van die Lonmin-raffinadery vir onedel metale – sowel as swak beheer het ’n nadelige uitwerking gehad op die mineralogiese gehalte van die uiteindelike mat, en dus ook op die verwerkingskenmerke van die soliede matdeeltjies verder af in die prosesstroom. Die bepaling van die gewenste ystereindpunt het sorgvuldige ondersoek, seleksie en toepassing deur Lonmin vereis. Hierdie studie is dus hoofsaaklik uitgevoer om die uitwerking van ’n spesifieke ystereindpunt op die mineralogie en minerale chemie van soliede omsettermat te kwantifiseer. ’n Grondliggende ondersoek na die solidifikasieproses by afkoeling is as noodsaaklik beskou vir ’n diepgaande begrip van die verworwe mineralogie en minerale chemie as ’n funksie van ’n spesifieke ystereindpunt. Mettertyd het dit egter ewe belangrik geword om die uitwerking van die gevolglike mineralogie, en dus die ystereindpunt, op die fisiese eienskappe van minerale strukture met betrekking tot maling-, vrystellings- en loogprosesse verder af in die prosesstroom te kwantifiseer. Ondanks heelwat bedryfskonteks, het nóg bedryfs- nóg vakkundige literatuur veel diepte- en samehangende studies oor die uitwerking van ’n spesifieke ystereindpunt op snelafgekoelde omsettermatstelsels opgelewer. Vorige bevindinge in die literatuur het boonop ’n beperkte kwantitatiewe begrip van die uitwerking op mineralogie en minerale chemie getoon. Die fase- en afkoelingsekwilibriums van ystereindpuntspesifieke Ni-Cu-S-matstelsels met veelvuldige komponente was ook nie ten volle beskikbaar nie. Dít sou veral goed te pas gekom het om die kompleksiteite van omsettermatsolidifikasie as ’n funksie van ystereindpunt te verstaan. Kennis van die fisiese eienskappe van die minerale strukture van omsettermat was kwalik beskikbaar, terwyl selfs minder inligting oor maling-, vrystellings- en loogprosesse opgespoor kon word. Daarom was ’n omvattende ondersoek nodig om hierdie beduidende kennisleemtes met betrekking tot snelafgekoelde omsettermatstelsels in ’n nywerheidsraamwerk aan te vul. Drie Peirce-Smith-omsetterproduksiemonsters wat die wisselende bestek van ystereindpunte by die omsetteraanleg verteenwoordig, is in ’n stelselmatige ondersoek gebruik, tesame met ’n vernuwende kombinasie van moderne ontledingstegnieke, gerekenariseerde termochemiese bewerkings en metallurgiese toetswerk. Die moderne ontledingstegnieke sluit onder andere in hoëresolusie-transmissie-elektronmikroskopie (HRTEM) en gefokusdeioonstraalskandering-elektron-mikroskopie (FIB SEM) tomografie. Die gerekenariseerde termochemiese bewerkings is met behulp van MTDATAfasediagramsagteware uitgevoer. Metallurgiese toetswerk het die maling van laboratoriumlotte teen verskillende spesifieke energieë behels. Nou verwante loogproefnemings is ook as relevant vir hierdie omvattende studie beskou. Die bestudeerde Peirce-Smith-omsettermonsters het op matte met spesifieke eindpunte van 5.17%, 0.99% en 0.15 gewig% Fe gedui. Die hoogste gekombineerde massakonsentrasie van die belangrike onedel en platinumgroepmetale is in die mat met ’n spesifieke ystereindpunt van 0.99% gevind. Die mineralogie van ál drie omsettermatte is oorheers deur die minerale strukture van nikkelsulfied, wat met die natuurlike mineraal heazlewoodiet ooreenstem. Die verskillende omsettermatte het ook die minerale strukture van kopersulfied, NiCu-allooi, spinel en OsRu-allooi bevat. Daar is bevind dat die verkryging van ’n spesifieke ystereindpunt tot meetbare mineralogiese verskille in die relatiewe volopheid van minerale, die eksterne morfologiese kenmerke sowel as minerale chemie lei. Die mineralogiese verskille was veral duidelik te sien tussen die minerale strukture van die ysterryke (5.17% Fe) en ysterarm (0.99% en 0.15% Fe) matte. Fyn mineralogiese verskille is ook tussen die minerale strukture van die ysterarm matte bespeur. Die 0.99% Fe-mat het tipies beduidend meer NiCu-allooi as die 5.17% Fe-mat bevat. Die NiCu-allooistrukture tree oënskynlik op as die hoofversamelaars van die ekonomies belangrike platinumgroepmetale. Mineralogiese waarnemings is gebruik om ’n begrip te ontwikkel van die onderliggende mineralisasiemeganisme van NiCuallooistrukture. Die gevolglike gemineraliseerde strukture is met behulp van driedimensionele rekonstruksies met hoë kleurgetrouheid sowel as in grysskaal voorgestel. Daar is teoreties aangetoon dat variasies in ystereindpuntspesifieke beginsamestellings van suurstofvrye vloeibare matstelsels die solidifikasieroete na die eutetikum wysig. Daarbenewens is die vloeifasesolidifikasie van die ysterryke en ysterarm matstelsels, wat suurstof insluit, op sowat ±2.5 oC gekwantifiseer. Die meeste van die spesifieke energie wat vir maling beskikbaar was, is gebruik om die nikkelsulfiedmatriks te breek, veral vir die ysterryke mat. Berekeninge toon dat die breektempo’s van die minerale strukture van kopersulfied by die 5.17% Fe-mat hoër was as by die 0.15% Fe-mat teen ’n spesifieke energie van 25 kWh/t. Die mate van kopersulfiedvrystelling was hoër by die 5.17% Fe-mat as by die 0.15% Fe-mat by dieselfde spesifieke energie vir maling. ’n Hoër mate van Ni-ekstraksie en Cu-sementasie is verkry toe ysterarm matdeeltjies geloog is. Wat eindpuntseleksiemaatstawwe betref, is die produksie van ’n omsettermat met ’n spesifieke ystereindpunt van 0,99% as die mees geskikte aangewys. ’n Praktiese ystereindpuntbestek van 1.6% tot 1.0% word aanbeveel vir die produksie van ’n omsettermat met ’n gevolglike mineralogiese gehalte wat binne die perke van die Lonmin-raffinadery vir onedel metale val. Hierdie studie bied ’n geïntegreerde begrip van die produksie van onedel en platinumgroepmetale as ’n funksie van ’n gewenste ystereindpunt by Lonmin. Hierdie inligting was nie voorheen in literatuur oor metaalproduksie beskikbaar nie. Nuwe tegnologie vir die monitering en konsekwente beheer van so ’n praktiese ystereindpuntbestek kan dus op grond hiervan in werking gestel word.

The iron-nickel alloy phase transformations and metal-silicate reactions that occurred in relatively unshocked, types 4–6 ordinary chondrites were investigated using several approaches. Laboratory cooling experiments were used to study kamacite nucleation and growth during cooling. When polycrystalline taenite cools to temperatures of kamacite stability, kamacite allotriomorphs form at the taenite grain boundaries. If the taenite is phosphorus-saturated, intragranular (Widmanstatten) kamacite needles will form after small amounts of undercooling. However, phosphorus-free alloys will undercool more than 200°C without forming intragranular kamacite precipitates. A monocrystalline, phosphorus-free taenite particle will remain homogeneous as it cools through the taenite + kamacite field and will transform to martensite without a composition change. Metallographic techniques were used to study the microstructures and phase compositions of metal particles in relatively unshocked ordinary chondrites. Chondritic metal particles had widely varying bulk compositions after chondrite aggregation, but experienced intergrain homogenization and taenite grain growth during prograde and peak temperature metamorphism. Taenite grain growth was extensive in types 5 and 6 ordinary chondrites, resulting in many monocrystalline taenite particles. The phase transformations that occurred during cooling depended on whether taenite (phosphorus-poor) was polycrystalline or monocrystalline. Polycrystalline taenite particles experienced small amounts of undercooling within the taenite + kamacite field and transformed to “zoned taenite + kamacite particles” by the diffusion-controlled reaction, taenite → taenite + kamacite. Monocrystalline taenite particles experienced more than 200°C of undercooling; they remained homogeneous and metastable (iron-supersaturated) during cooling. The monocrystalline taenite particles cooled below the martensite-start temperature, and transformed to “zoneless plessite particles” by the taenite → martensite → tetrataenite + kamacite reaction. The occurrence of zoned taenite + kamacite particles and zoneless plessite particles within the same ordinary chondrite is compatible with cold accretion followed by prograde and retrograde metamorphism. The importance of metal-silicate reactions in ordinary chondrites was investigated by analyzing olivine crystals near olivine-metal interfaces. Olivine fayalite concentrations decrease by approximately 2 mole % near zoned taenite + kamacite particles, and increase by approximately 2 mole % near zoneless plessite particles. Chemical thermodynamic modeling shows that silicate-metal reactions occurred during slow cooling due to variable amounts of taenite undercooling.