Epithermal vein and carbonate replacement deposits in Cunningham Gulch are located within the western San Juan Tertiary volcanic field in southwestern Colorado. The Pride of the West epithermal vein system is hosted within the intracaldera facies of the Sapinero Mesa Tuff, a voluminous ash-flow tuff that erupted from and resulted in the formation of the San Juan Caldera at 28 mybp. The Pride of the West vein system is developed along a radial fracture formed during resurgence of the San Juan Caldera prior to eruption of the Crystal Lake Tuff (27.5 mybp). This eruption led to the concomitant collapse of the Silverton Caldera, nested within the larger San Juan Caldera. The Pride of the West, Osceola, and Little Fanny mines are positioned near the intersection of the Pride radial fracture system and the buried structural margin of the San Juan Caldera, suggesting that ore concentration was controlled by this structural setting. Large limestone blocks of the Mississippian Leadville Formation are incorporated into the intracaldera fill volcanics in the mine area. These blocks appear to have been engulfed within mudflow breccias of the Tertiary San Juan Formation (32.1 mybp). They were then emplaced in their present structural position within a caldera-collapse breccia which caved from the oversteepened margin of the San Juan Caldera. Regional propylitic alteration of the hosting volcanics to a chlorite-calcite-pyrite assemblage preceded vein-associated alteration and mineralization. The veins are enveloped by a narrow phyllic alteration assemblage of quartz, sericite, illite, kaolinite, and pyrite. The veins are comprised of sphalerite, galena, chalcopyrite, pyrite, hematite, magnetite, quartz, pyroxmangite, calcite, and minor barite. Substantial bodies of replacement ore are present where the vein structures intersect the limestone blocks; the mineral assemblages of the replacement deposits are identical to those of the feeding vein structures. Commonly, replacement textures are spectacular concentrations, especially the "zebra ore" which primarily consists of regularly spaced, alternating bands of sulfides and quartz. These "zebra" laminations are stratigraphically controlled and appear to represent replacement of a depositional or diagenetic fabric. Main ore-stage mineralization began with widespread deposition of quartz with or without pyrite, followed by sphalerite, chalcopyrite, and galena. Post ore-stage brecciation and silicification events are evident and were followed by deposition of calcite and minor barite during the waning stages of the hydrothermal system. The distributions of Fe, Mn, Pb, and Ca suggest a lateral component of fluid flow from northwest the southeast, away from the structural margin of the Silverton Caldera. Fluid inclusion data from both vein and replacement-type sphalerite and quartz indicate that mineral deposition occurred over a range of 200 to 312°C (mean 243°C) from solutions containing 1 to 5% total salts. The high base metal to precious metal content of the ore, the phyllic alteration assemblage, and the temperature and composition of the ore-forming fluid indicate that the mine workings are within the lower portion of a fossil geothermal system. / text

Equilibrium relations between garnet and orthopyroxene have been investigated by reversal experiments in the range of 20-45Kb and 975-1400°C in the FeO-MgO-Al₂O₃-SiO₂(FMAS) system. The Fe-Mg exchange reaction seems to have little or no compositional dependence at these conditions. The experimental results can be fitted adequately by the linear relation: ln K(D) = 2243/T°K - 0.9522 at 25Kb where K(D) = (X(Fe)/X(Mg))ᴳᵗ/(X(Fe)/X(Mg))ᴼᵖˣ. Combination of the available data for the mixing properties of garnet and V° for the Fe-Mg exchange reaction with the above experimental results yields the following geothermometric expression for the common natural assemblages that can be represented essentially within the system CaO-MnO-FeO-MgO-Al₂O₃-SiO₂. T°K = (1968 + 11P(Kb) + 1510(X(Ca)+X(Mn))ᴳᵗ)/(ln K(D) + 0.9522). The stability field of pyrope+quartz, defined by the reaction pryope+quartz=opx+sill, has been calculated as a function of P,T,X(Fe)ᴳᵗ in the FMAS system using the reversal experimental data of Perkins (1983) in the MAS system, and the present data on K(D)(Fe-Mg) between garnet and orthopyroxene. This reaction is very sensitive to pressure and compositional effects. Combination of P,T conditions for the garnet stability and that defined by (K(D)(Fe-Mg))ᴳᵗ⁻ᴼᵖˣ yields a simultaneous solution for both P and T of equilibration of garnet and orthopyroxene in the presence of Al₂SiO₅ and SiO₂. The effect of FeO on Al₂O₃ solubility in orthopyroxene in equilibrium with garnet has been determined experimentally at several pressures at 975 and 1200°C. These data have been modeled to develop a thermodynamic method for the calculation of Al₂O₃ in orthopyroxene as a function of P,T and composition. The Al₂O₃ isopleths have moderate P-T slopes, and provide virtually the only means of determining the pressure of mantle derived rocks.

This thesis focuses on the geochemistry of secondary minerals, mainly calcite but also others such as fluorite and Ca/Al silicates, precipitated throughout the last 1.5 billion years in fractures of crystalline rock, SE Sweden. The work was based on previous reconnaissance studies and has been possible thanks to access to high-quality drill cores and associated mapping data provided by the Swedish Nuclear Fuel and Waste Management Co (SKB). Concentrations of rare earth elements (REEs) and occasionally other metals were determined in a variety of secondary minerals from fractures (mainly open systems) and veins (mainly sealed systems) and in primary minerals from the bedrock. Stable-isotope composition was measured in the secondary minerals. The overall aim was to define the sources, uptake and fractionation of REEs in calcite, and a few other co-genetic minerals, precipitated throughout the geological history under conditions ranging from hydrothermal to low temperatures. Collectively, the findings of the individual studies show that there is no easy and straightforward control of REE abundance and fractionation in calcite and other minerals in fractures and veins in crystalline bedrock settings. For example, the REE features in calcite vary extensively within sub-generations of single vein-precipitating events, on micro scale in transects across individual veins, and unsystematically over the geological history characterised by successively decreasing temperatures of mineral formation. Although the REE content in, and release from, the crystalline bedrock can have an influence on REE distribution in calcite and other minerals, it is of overall minor importance within a given bedrock domain. The main advantage of determining REEs in secondary minerals in fractures and veins in crystalline rock is therefore, as revealed in this work, to assess the character and evolution of the conditions (including features of the paleofluids) during confined mineral-precipitating events.

Dissolved compounds and ions, including mineral elements and products of microbial metabolism, are present in many cheeses in relatively high concentrations. These dissolved substances may precipitate from the aqueous phase of cheese to form sparingly soluble crystals that can impart a crunchy, gritty, or sandy texture on the cheese. In the present work, optical and diffractometric methods were optimized for use with cheese samples to identify crystal phases in several cheese varieties. These techniques, which included powder X-ray diffractometry (PXRD), single crystal X-ray diffractometry (SCXRD), and petrographic microscopy (PM) have traditionally been used on geological specimens that are quite different from the cheese samples used in the present study. Nonetheless, these techniques were successfully used to gain valuable insight into crystal development in cheese. Powder X-ray diffractometry was optimized to minimize the occurrence of artifacts that may occur due to the high water content and low crystallinity of some cheese samples. The use of enhanced sample preparation techniques facilitated the identification of organic and inorganic crystal phases such as tyrosine, leucine, brushite (CaHPO4·2H2O), and calcite (CaCO3) in hard and soft cheeses. SCXRD was used to determine the crystal structures of ikaite and struvite, which had been tentatively identified in washed-rind cheese using PXRD. PM was used to observe morphological and optical properties of crystals in white mold cheese and washed-rind cheese. In two subsequent aging studies, PXRD was used to determine the approximate timing of crystal nucleation in the rinds of white mold cheese and washed-rind cheese. These observations were paired with inductively coupled plasma-atomic emission spectroscopy (ICP-AES) data to demonstrate that the onset of crystallization in the rinds coincided with a diffusion phenomenon in which mineral ions diffused from the center of the cheese and became concentrated in the rind. PM observations demonstrated that maximum crystal size in the rinds generally increased as aging progressed. These observations will be useful in future work that investigates the impact of crystallization on sensory properties of cheese.

Summary: Raman spectroscopy is a widely used method in geoscience fields. Using a portable Raman spectrometer is possible to identify different materials, Raman spectrometer will participate in the survey the Martian surface. Its use is widely applied in mineralogy. There was measured a set of dark, green and some bright minerals of different mineralogical system groups that have been assessed the applicability of the chosen detector excitation at 785 nm mainly off-road equipment. The obtained spectra were measured off-road equipment ahura and delta nu at excitation 785 nm and laboratory equipment InVia Renishaw and there were used lasers at excitaion of 785 nm and 514 nm. It was set of these minerals: Prehnite, Sulphur, Tyrkenit (howlit), Pyroxene (diopside), Libethenite, Toutmaline (verdelite), Dioptas, Klinoklas, Langit, Jadeit, Pseudomalachit (ehlit), Actinolite, Epidote, Augite. Some minerals were measured off-road equipment acquired spectrum, witch corresponded with laboratory measurements, the spectra of other optical properties due to their ambiguous. Keywords: Raman spektroscopy, portable Raman spectrometer, mineralogy, dark and green minerals

A research report submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Master of Science, Johannesburg, August, 2014. / Efflorescent minerals are a common feature of the soil surface in seasonal environments where evapotranspiration (ET) exceeds precipitation (P), and are formed by the evaporation of salt solutions from the soil during periods of drying. On the Highveld gold fields, ET exceeds rainfall by approximately two-and-a-half times during the dry season, and soils overlying acid mine drainage and along polluted stream banks can become covered by distinctively coloured mineral efflorescent crusts. Whereas some efflorescent minerals are relatively insoluble and present a negligible environmental hazard (for example, gypsum), others may be readily soluble and contain high concentrations of potentially toxic metals (for example, copiapite, jarosite and uranyl sulphate). During periods of rainfall, such salts are washed further afield and into surface water bodies and act as sources of episodic pollution. The presence of some efflorescent minerals can be detected from their characteristic reflectance signatures using remote-sensing (RS) of the electromagnetic spectrum. The species of efflorescent minerals present is a useful indication of the spatial extent of sub-surface contamination, and also of the chemical conditions of the substrate, in particular the concentration of total dissolved solids, pH and redox conditions. The aim of this study was therefore to assess the use of remote-sensing on indicator efflorescent minerals as a cost-effective aid in the spatial mapping of acid rock-drainage polluted soils and water-bodies. This study describes the range of efflorescent crusts identified on different land-use areas and soil classes in a Highveld gold-mining region. Crusts were first measured in-situ under natural sunlight using a portable analytical spectral radiometer (ASD) as well as using X-ray diffraction (XRD). They were then dissolved in deionized water and the resulting salt solutions allowed to evaporate prior to analysis under controlled lighting conditions. Spectra were post-processed and compared with iv geological spectral reference libraries. The salt solutions were also analyzed for metal and sulphate content and the results were used to establish evaporation models from which mineral precipitation could be predicted. Minerals identified in the visible near-infra red (VNIR) region included iron oxides (hematite and goethite), and the sulphate mineral jarosite. In the short wave infra-red (SWIR) region clay minerals of the smectite group were dominant. Gypsum and Al-Mn-Mg-Na sulphate salts were identified in the SWIR region as mixtures occurring with clay minerals. Minerals identified in the VNIR-SWIR region were all confirmed by X-Ray diffraction (XRD). Upon dissolution, geochemical modeling revealed that gypsum and jarosite are the most common minerals expected to precipitate. The precipitation of gypsum and jarosite indicates persistent acidic conditions after dissolution of mineral salts. Gypsum and jarosite were also accurately identified by hyper-spectral spectroscopy and confirmed by XRD and geochemical modeling. Agreement between spectral interpreted minerals and geochemically precipitated mineral phases demonstrated the ability of hyper-spectral data in detecting efflorescence minerals on the soil surface. Using partial least squares regression (PLSR) combined with bootstrapping, reflectance spectrum was significantly correlated with geochemical variables.

A thesis submitted for the degree of Doctor of Philosophy in the Faculty of Science at the University of the Witwatersrand. / The present thesis is divided into three parts. The study described in Part I arose out of a request by the Chamber of Mines Mining Research Laboratory to the National Institute for Metallurgy to undertake a preliminary study of whether it would be feasible, in Witwatersrand conglomerates, to carry out rapid delimitation of areas rich in gold and/or uranium at the rock face, a procedure which would permit areas of rich ore to be removed selectively by means of the "rock-cutter". The approach adopted in this study was essentially geochemical, while conventional mineralogical techniques (macro-auto radiographs , thin section and polished section analyses) provided a control. The samples were drawn from the Vaal Reef at Hartebeestfontein and Zandpan and from the Ventersdorp Contact Reef at Venterspost, and were analysed quantitatively for gold, silver, uranium, pyrite, muscovite, pyrophyllite, chlorite, quartz, iron, potassium, nickel, titanium, zirconium and chromium. The intensity of the interrelationships between the elements and minerals analysed for was examined statistically by means of correlation covariance and factor analysis programmes written for an IBM 360/50 digital computer. A sympathetic relationship -- defined as significant positive correlation (with a correlation coefficient r> 0. 7) -- was found to exist between gold and uranium in both the Vaal Reef and Ventersdorp Contact Reef samples. These findings suggest that gold and uranium can be removed Simultaneously by means of the rock-cutter, and that radioactivity can be used as an indicator for on-site delimitation of areas rich in gold. In the course of the study described in Part I, it became evident that little detailed mineralogical work had ever been done on the phyllosilicates occurring in the Witwatersrand System. Accordingly, certain phyllosilicates from Witwatersrand conglomerate bands and other sources were examined in detail, this study being described in Part II of the present thesis. This study called for detailed chemical, optical, X-ray crystallographic, infra-red, differential thermal and thermogravimetric analyses, the results of which are presented. The findings were examined in the light of variolls classification schemes that have bep proposed for the phyllosilicates. This investigation revealed the need for a universally acceptable system of classification for the phyllosilicates, which should preferably be drawn up under the auspices of the International Mineralogical Association to avoid the confusion that exists at present. Part III of the present thesis is devoted to a discussion and description of various analytical techniques that had to be modified or developed to meet th8 requirements of the studies described in Parts I and II. The techniques described include: (1) An X-ray diffraction method which was developed for the quantitative analysis of pyrite, muscovite, pyrophyllite, chlorite and quartz in crushed ore from Witwatersrand conglomerates. This method makes use of novacul iie as an external standard and of binary mixtures as analytical standards, and had a mean absolute error of 1. 1 %. This method may be expanded to permit analysis of an n-component mixture. (2) A whole rock pressed powder technique of X-ray fluorescence analysis which was used for the quantitative determination of iron, potassium, nickel, titanium, zirconium and chromium. This method makes use of internstional rock standards as external standards. Six computer programmes used for the computation of the analytical results and in the statistical and crystallographic calculations are also presented in Part III. / AC2017

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy / Raman and photoluminescence (PL) spectroscopy techniques were used to investigate the mechanical properties of diamond and cubic boron nitride (cBN) by optical means. Both these materials have extreme mechanical properties that make them the material of choice for many industrial applications, ranging from cutting and grinding to wire-drawing dies. The results obtained on single crystal diamond, polycrystalline diamond (PCD) and cBN are summarised below. Micro-Raman and photoluminescence (PL) spectroscopy were used to map the threedimensional (3D) stress and deformation distributions surrounding a plastic impression made in a synthetic, type Ib single crystal diamond. Using data from the Raman peak position, a 3D map of the stress contours surrounding the impression was generated, while the Raman width data yielded a map of the plastic deformation volume. The stress contours compare favorably with the resolved shear stress contours calculated for diamond. PL intensity maps of the zero phonon line (ZPL) associated with the [N-V]– defect centre at 1.945eV provide images of the extent of vacancy formation and movement during the impression process. Data concerning the position and width of the ZPL correspond well with the Raman results. Polycrystalline diamond (PCD) tools commonly consist of a PCD layer sintered onto a cobalt-tungsten carbide (Co-WC) substrate. These tools are used in diverse applications and both the magnitude and distribution of the stresses in the PCD layer affect tool behavior. These stresses in sample drillbits were investigated by means of micro-Raman spectroscopy. Cyclic annealing of a sample drillbit to 600 oC shows that the tool properties are retained after 5 cycles, while similar cycling to 800 oC resulted in a permanent decrease of the average surface compressive stress. This implies a reduction in the drillbit’s ability to resist crack formation and propagation and is thus a degradation of the tool properties. The method of Raman mapping of stress and deformation in diamond was also applied to single crystals of cBN. Indentations on cubic boron nitride (cBN) crystals and polycrystalline cubic boron nitride (PcBN) composites were mapped and the shifts of the cBN Raman lines from their unstressed positions used to quantify the residual stresses in the boron nitride due to the deformation brought about by the indentation. These were found to be of the order of 1 GPa. vi These measurements illustrated for the first time the use of Raman spectroscopy to study residual stresses in boron nitride. Defects in cBN were studied using photoluminescence spectroscopy at low temperature (< 10 K) of two types of cBN irradiated at ambient temperature with 1.9 MeV electrons. All the samples were small (<1 mm diameter) single crystals of cBN. Three defect centres (with narrow lines at 2.28 eV, 2.15 eV and 1.98 eV) were introduced in both the amber-coloured and blackbrown coloured samples by the irradiation. The amber coloured sample also showed a defect centre (at 1.65 eV) that is present before and after irradiation. Line shape analysis of the zero phonon lines of all three irradiation-induced centres showed that the lines are predominantly Gaussian in character, suggesting that linetype defects such as dislocations are a prevalent characteristic of these crystals. Raman spectroscopy of cBN single crystals as a function of temperature was performed over a wide temperature range from 4 K to 1373 K. The low temperature measurements extended the data previously reported in literature, as this data ranged from room temperature upwards. It was concluded from the shift of Raman peak position with temperature that both linear expansion and anharmonic effects were required to adequately account for the observed data. This is in agreement with previously published findings. Both 3- and 4-phonon processes were required to account for the observed linewidths as a function of temperature, again in agreement with literature. The results presented here and in the associated journal publications illustrate clearly how optical spectroscopy techniques can serve as non-destructive characterisation tools for the mechanical properties of ultra-hard materials.

O cobre está associado ao metabolismo de lipídios, sendo bastante importante na redução do colesterol, e à estabilidade oxidativa da carne, por fazer parte de algumas enzimas antioxidantes. Porém, quando na forma iônica, é considerado um elemento pró-oxidante. O cobre orgânico não apresenta esse efeito e, além disso, geralmente apresenta maior biodisponibilidade que fontes inorgânicas. Desse modo, o objetivo deste estudo foi determinar o efeito da suplementação com dois níveis e duas fontes de cobre (inorgânica e orgânica) sobre o desempenho, concentração de cobre no fígado, músculo e sangue, fermentação ruminal, parâmetros oxidativos e metabolismo de lipídios e colesterol. Trinta e cinco bovinos da raça Nelore em fase de terminação foram divididos em 5 grupos, com 7 animais por tratamento, conforme descrição: 1) C: Dieta controle, sem a suplementação adicional de cobre; 2) I10: suplementação de 10mg de Cu/kg de MS na forma de sulfato de cobre; 3) I40: suplementação de 40mg de Cu/kg de MS na forma de sulfato de cobre; 4) O10: suplementação de 10mg de Cu/kg de MS na forma de proteinato de cobre; 5) O40: suplementação de 40mg de Cu/kg de MS na forma de proteinato de cobre. A suplementação com cobre proporcionou maior concentração e acúmulo de Cu no fígado (p<0,05), sendo a maior média observada para o tratamento O40, porém, o status de Cu no músculo e no soro não foram alterados pelos tratamentos. A maior atividade da ceruloplasmina (p<0,05) foi observada para o tratamento I40. Não houve efeito significativo (p>0,05) para ganho de peso diário, ingestão de matéria seca, eficiência alimentar, rendimento de carcaça quente e fria, perda pelo frio, espessura de gordura subcutânea e área de olho de lombo dos bovinos, entre os tratamentos controle e suplementação com cobre inorgânico ou orgânico. O pH ruminal, os ácidos graxos voláteis e o nitrogênio amoniacal também não foram influenciados (p>0,05) pelos tratamentos. Em geral, a suplementação com cobre alterou o perfil de ácidos graxos da carne (p<0,05), com aumento na proporção de ácidos graxos insaturados em detrimento dos ácidos graxos saturados. Não houve efeito de tratamento para TBARS (substâncias reativas ao ácido tiobarbitúrico) no fígado e na carne embalada a vácuo (p>0,05), porém houve redução nos valores de TBARS na carne dos bovinos suplementados com Cu para as amostras dispostas no Display Life (tratamentos I40 e O40, p=0,06), e na atmosfera modificada (tratamentos I10, I40, O10 ou O40, p<0,05), em relação ao tratamento controle. A suplementação com Cu (tratamentos I40 e O40) aumentou a atividade da SOD (superóxido dismutase) (p<0,05), em relação ao tratamento controle, mas não influenciou a atividade da GSH-Px (glutationa peroxidase) (p>0,05). Não houve efeito da suplementação sobre triglicérides e colesterol no sangue; entretanto, em geral, houve redução da concentração de colesterol no músculo L. dorsi (p<0,05), em relação ao tratamento controle, através da redução (p<0,05) da concentração de GSH e da relação GSH/GSSG. / Copper is associated with lipid metabolism, becoming very important in reducing cholesterol, and with oxidative stability of meat, because it is part of some antioxidant enzymes. However, when in the ionic form, is considered a pro-oxidant element. The organic copper did not exhibit this effect and, besides, presents higher bioavailability than inorganic sources. Thus, the aim of this study was to determine the supplementation effect of two levels and two sources of copper (inorganic and organic) on the performance, Cu concentration in liver, muscle and blood, ruminal fermentation, oxidative parameters and metabolism of lipids and cholesterol. Thirty-five Nellore cattle in the finishing phase were divided into 5 groups with 7 animals per treatment, as described: 1) C: control diet, without additional Cu supplementation; 2) I10: 10mg Cu/kg DM, as Cu sulfate; 3) I40: 40mg Cu/kg DM, as Cu sulfate; 4) O10: 10mg Cu/kg DM, as Cu proteinate; 5) O40: 40mg Cu/kg DM, as Cu proteinate. Supplementation with copper provided higher Cu concentration and accumulation in the liver (p<0.05), with the highest mean observed for the O40 treatment, nevertheless the Cu status in muscle and serum were not affected by treatments. The highest activity of ceruloplasmin (p<0.05) was observed for the I40 treatment. There was no significant effect (p>0.05) for daily weight gain, dry matter intake, feed efficiency, hot and cold carcass yield, cold loss, backfat and loin eye area of cattle, among control treatment and supplementation with inorganic or organic copper. Ruminal pH, volatile fatty acids and ammonia were not influenced (p>0.05) by treatments. In general, copper supplementation altered the meat fatty acid profile (p<0.05), with an increase in the proportion of unsaturated fatty acids over saturated fatty acids. There was no treatment effect for TBARS (thiobarbituric acid reactive substances) in liver and meat vacuum packed (p>0.05), but there was a reduction in TBARS values in meat from cattle supplemented with Cu for samples prepared on Display Life (treatment I40 and O40, p=0.06), and modified atmosphere (treatment I10, I40, O10 and O40, p <0.05), compared to the control treatment. Supplementation with Cu (treatment I40 and O40) increased the activity of SOD (superoxide dismutase) (p<0.05) compared to control treatment, but did not influence the activity of GSH-Px (glutathione peroxidase) (p>0.05). There was no effect of supplementation on triglycerides and cholesterol in blood, however, there was a reduction in cholesterol concentration in L. dorsi muscle (p<0.05) compared to the control treatment, by reducing (p<0.05) of GSH concentrations and the GSH/GSSG ratio.

A Bahia tem sido, juntamente com Minas Gerais, Goiás e Rio Grande do Sul, destaque na produção de gemas naturais do Brasil, pais que detém grande parte das reservas mundiais desses bens minerais, com produção de gemas de qualidade reconhecidas internacionalmente. Os controles estatísticos registram a presença de mais de trinta variedades gemológicas em território baiano (Tavares et al, 1998). O quartzo é utilizado ultimamente em grande escala na produção de jóias. Isto se deve a sua grande abundância no território baiano, preços relativamente baixos de exploração, e a boa resposta do mesmo aos tratamentos térmico e de irradiação gema, visando mudanças ou o melhoramento da cor. As Serras do Espinhaço Setentrional e de Jacobina, bem como a região da Chapada Diamantina, concentram a maior parte das ocorrências de variedades, tanto coloridas como susceptíveis ao tratamento para induzir cor, deste mineral, o qual passou a ser visto como uma das principais matérias-prima para lapidários, comerciantes e joalheiros da região. Apesar da importância das mineralizações, existe uma carência de estudos científicos que abordem questões relacionadas com a evolução e controle geológico das mineralizações e com os tratamentos que são realizados para melhorar o potencial gemológico das regiões estudadas. Tendo em vista enriquecer o conhecimento deste potencial geológico do território baiano, a realização deste estudo representa um passo significativo no entendimento da evolução metalogenética das áreas estudadas, além de contribuir com o estudo geológico e gemológico das variedades coloridas do quartzo na Bahia. Os quartzos gemológicos estudados na Bahia encontram-se inseridos principalmente em ambientes hidrotermal, encaixados em rochas metareníticas e quartziticas do Supergrupo Espinhaço. A partir dos dados levantados em campo, pôde-se verificar que as mineralizações estudadas possuem um controle estrutural, e encontram-se posicionadas em fraturas de tração de baixo ângulo. Tais fraturas estão associadas com rampas de empurrão que se desenvolveram durante as deformações que culminaram com a estruturação do cinturão de dobramentos e cavalgamentos da Serra do Espinhaço. A cor da ametista é devido a presença de impurezas derivadas da família do ferro (FeO4)-4, e da radiação ionizante. O quartzo fumê desenvolve-se apenas com a presença de alumínio e lítio, e o fenômeno do \"centro de cor\" (defeito na estrutura cristalina causada pela falta de um elétron) é o responsável pela sua cor, onde o íon Al3+ ao substituir o íon Si4+ gera um desequilíbrio eletrônico que é compensado por íons de Li-. O citrino por sua vez, deve sua cor a uma combinação de AI-Li, semelhante ao do quartzo fumê. Os estudos também demonstraram que as aquisições de cores no quartzo obtidas através dos processos de irradiação gama e tratamento térmico, bem como a estabilidade das mesmas, estão amplamente condicionadas aos ambientes de formação dos cristais, e a presença de elementos químicos nos fluidos formadores dos cristais, os quais são responsáveis pela variação de suas cores. As características gemológicas encontradas demonstram que o quartzo baiano apresenta um elevado potencial comercial. Para o futuro sugere-se trabalhos de levantamentos geológicos e pesquisa mineral, desde que a exploração das gemas vem apresentando significativas reduções e limitações nas suas atividades minero-industriais, seja pela parcial exaustão das reservas conhecidas, ou pela necessidade de ampliá-las e, assim, incentivar novos investimentos. Pouquíssimos trabalhos com cunho gemológico tem sido publicados no Brasil com vista de esclarecer a correlação entre depósitos de quartzo e seu comportamento perante tratamentos de irradiação e de aquecimento. / Besides Minas Gerais, Goiás and Rio Grande do Sul, Bahia is worldwide known for its richness in minerals of industrial and gemological interest. Up to this day, more than 30 minerals of gemological use are known (Tavares et. al. 1998) One of the main gemological material is quartz, used currently in large amounts for jewelry due to its fair value and good response of color treatments by irradiation and heat. Most of the quartz is found and mined in the Espinhaço , Chapada Diamantina and Jacobina belts either as colorless quartz or as amethyst. The colorless variety is sometimes prone to treatments that induce color centers resulting in black (Morion), brown (Smoky), yellow(Citrine), green (Prasiolite) gemstones. Very few work exists dealing with the geological evolution, control of mineralization, estimation of quantities and possible treatments of these materials. The results of this work is a contribution to the knowledge of the metalogenic evolution of the studied areas and includes the location of all known occurrences of quartz from Bahia. It could be shown that most of the quartz from Bahia state is located mainly in a hydrothermal environment crosscutting the quartzites and arkosic rocks of the Espinhaço Supergroup. Field data showed strong tectonic control of the quartz veins, filling low angle traction fractures associated with the thrust belts that formed the Serra do Espinhaço mountain range. The fluids passing through these fractures deposited quartz, as amethyst (Breijinho de Ametista, Jacobina e Sento Sé), colorless and milky quartz and sometimes as citrine. The color of amethyst is due to substitutional iron with oxidation degree 4+, formed by irradiation of ferric iron contained in the tetrahedral of the quartz structure. Smoky colors are formed by irradiation of mainly Al containing quartz, whereas yellow and yellow green colors are formed by the presence of Al and Li. Few occurrences of colorless quartz forming a green variety by irradiation have been documented. Some preliminary results show that the type and intensity of color is determined by the specific environment of formation. More work is clearly needed to clarify the correlation of formation environment and color produced by irradiation and heat treatments.