Search

Organic matter in Archean hydrothermal cherts may provide an important archive for molecular traces of the earliest life on Earth. The geobiological interpretation of this archive, however, requires a sound understanding of organic matter preservation and alteration in hydrothermal systems. Here we report on organic matter (including molecular biosignatures) enclosed in hydrothermally influenced cherts of the Pleistocene Lake Magadi (Kenya; High Magadi Beds and Green Beds). The Magadi cherts contain low organic carbon (n-alkanes, hopanes, and polycyclic aromatic hydrocarbons (PAHs) indicate that a fraction of the bitumen has been thermally altered to early or peak oil window maturity. This more mature fraction likely originated from defunctionalization of dissolved organic matter and/or hydrothermal petroleum formation at places of higher thermal flux. Like the bitumens, the kerogens also show variations in thermal maturities, which can partly be explained by admixture of thermally pre-altered macromolecules. However, findings of archaea-derived isoprenoid moieties (C20 and C25 chains) in kerogen pyrolysates indicate rapid sequestration of some archaeal lipids into kerogen while hydrothermal alteration was active. We posit that such early sequestration may enhance the resistance of molecular biosignatures against in situ hydrothermal and post-depositional alteration. Furthermore, the co-occurrence of organic matter with different thermal maturities in the Lake Magadi cherts suggests that similar findings in Archean hydrothermal deposits could partly reflect original environmental conditions and not exclusively post-depositional overprint or contamination. Our results support the view that kerogen in Archean hydrothermal cherts may contain important information on early life. Our study also highlights the suitability of Lake Magadi as an analog system for hydrothermal chert environments on the Archean Earth.

This work focuses on the hydrothermal synthesis of Na-P1 zeolite by using a kaolinite rock coming from Romana (Sassari, Italy). The kaolin is calcined at a temperature of 650 °C and then mixed with calculated quantities of NaOH. The synthesis runs are carried out at ambient pressure and at variable temperatures of 65 and 100 °C. For the first time compared to the past, the Na-P1 zeolite is synthesized without the use of additives and through a protocol that reduces both temperatures and synthesis times. The synthesis products are analysed by X-ray diffraction, high temperature X-ray diffraction, infrared spectroscopy, scanning electron microscopy and inductively coupled plasma optical emission spectrometry. The cell parameters are calculated using the Rietveld method. Density and specific surface area are also calculated. The absence of amorphous phases and impurities in synthetic powders is verified through quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The results make the experimental protocol very promising for an industrial transfer.

Crystallization of zeolite Li-A(BW) from kaolinite (Standard Porcelain by the IMERYS Minerals Ltd) through a conventional hydrothermal treatment is here achieved for the first time with no additives as reported in the literature. Moreover lower kaolin calcination temperatures and lower synthesis temperatures are tested and verified in this work. The synthesis process is rather simple as the reaction of kaolinite with alkali occurs very readily after calcination of at 650 °C. Metakaolin is mixed with calculated amount of aluminum hydroxide and lithium hydroxide and the experiment is performed at ambient pressure and 180 ± 0.1 °C. Li-A(BW) is characterized by powder X-ray diffraction, high temperature X-ray diffraction, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, thermal analysis and infrared spectroscopy. Calculation of cell parameters (through Rietveld Refinement) and density, specific surface and pore size are also achieved. The amount of amorphous phase in the synthesis powders is estimated with quantitative phase analysis using the combined Rietveld and reference intensity ratio methods. The results become notably attractive in view of a possible industrial transfer of the synthesis protocol.

Ferromanganese (Fe-Mn) deposits constitute a ubiquitous mineral type in oceanic settings, with metal (Cu, Ni, Zn, Co, Pt) and rare earth element (REE) enrichments of potential economic interest. Routine analysis of trace elements by ICP-MS has advanced our understanding of the impact of hydrogenetic, diagenetic and hydrothermal processes on the mobility and interaction of high field strength elements (HFSE: Zr and Ti) and REE and yttrium (REY) with Fe-Mn oxyhydroxides. Recent discoveries in the French exclusive economic zone (EEZ) of Wallis and Futuna (southwest Pacific Ocean) have brought new insight into the formation of low temperature (LT) hydrothermal Mn deposits and lead us to reconsider the classification and discrimination diagrams for Fe-Mn deposits and ore-forming processes. Using a suite of LT hydrothermal Fe-Mn crusts from Wallis and Futuna, we investigate how contrasting genetic processes influence the distribution of metals (Mn, Fe, Cu, Ni, and Co), HFSE and REY in hydrogenetic, diagenetic, hydrothermal and mixed-type deposits from different environments in the global ocean. The interaction of the different metal oxide-forming processes indicates that: (i) enrichment of Co, HFSE and REY is favored by hydrogenetic precipitation, (ii) diagenetic processes produce higher Mn, Cu, and Ni concentrations with oxic remobilization in the sedimentary column, while suboxic conditions promote greater Mn and Fe remobilization that competes with the incorporation of Cu and Ni ions in nodules. HFSE and REY derived from seawater are usually low in diagenetic precipitates, which discriminate between hydrogenetic and diagenetic inputs within nodules, (iii) hydrothermal Fe-Mn deposits show strong depletion in HFSE and REY due to rapid formation and high contents of either Fe or Mn oxides. We present a new discrimination scheme for the genetic types of Fe-Mn deposits using a 10 ∗ (Cu + Ni + Co) − 100 ∗ (Zr + Y + Ce) − (Fe + Mn) / 4 ternary diagram. The use of HFSE and REY in the classification allows for a more robust discrimination of: (i) each ore-forming process with well-delimited fields, without overlap of metal-rich hydrothermal samples and hydrogenetic samples, (ii) oxic and suboxic diagenesis within nodules, (iii) trends between hydrogenetic and diagenetic end-members forming a continuum, and (iv) mixed genetic types such as the presence of hydrothermal particles within hydrogenetic crust layers. Alternatives are also explored to adapt our discriminative diagram to elements measurable by on-board instruments to aid in exploration at sea.

Orientadores: Lena Virgínia Soares Monteiro, Roberto Perez Xavier Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: Os depósitos Salobo e Igarapé Bahia representam importantes depósitos de óxido de ferro¿cobre¿ouro (IOCG) da Província Carajás. O depósito Salobo é hospedado por gnaisses do Complexo Xingu, granitoides da Suíte Igarapé Gelado e por unidades metasedimentares. Alteração hidrotermal formou rochas miloníticas ricas em grunerita¿almandina¿faialita¿magnetita¿(turmalina) e (grunerita¿almandina)¿magnetita¿biotita. O depósito Igarapé Bahia é hospedado por rochas metavulcanossedimentares do Grupo Igarapé Bahia e metassedimentares da Formação Águas Claras. Xenólitos embasamento ocorrem no depósito e forneceram idades de 2935 ±36 Ma (MSWD = 0,85), sugerindo uma crosta ensiálica prévia a instalação da bacia. Idades U¿Pb de zircão detritítico das metagrauvacas do Grupo Igarapé Bahia (2,82 ¿ 2,88 Ga e 2,94 ¿ 2,99 Ga) e da Formação Águas Claras (2,81 ¿ 2,89 Ga e 2,91 ¿ 3,03 Ga) apontam para predominância de fontes do embasamento mesoarqueano. Nódulos e layers de calcopirita em metarritmitos da unidade superior representam uma mineralização singenética coeva à deposição do Grupo Igarapé Bahia no Neoarqueano. A composição isotópica de enxofre dessa geração de calcopirita (+0,29 e +1,56¿) e os seus elevados conteúdos de Ni, Co e Bi apontam para enxofre e metais lixiviados das rochas metavulcânicas da unidade inferior. Extensas zonas de alteração hidrotermal com rochas ricas em (turmalina)¿carbonato¿magnetita e (turmalina)¿carbonato¿clorita envelopam a mineralização IOCG. Geocronologia U¿Pb em monazita forneceu idade 2559 ±34 Ma no corpo Alemão. A assinatura geoquímica de minério com elevados valores de ?ETR e conteúdos significativos de U, Mo, Sn, W, Y, Nb e Sr são característicos da mineralização IOCG. No depósito Salobo, fluidos em equilíbrio com grunerita (?18OH2O = +6,66 a +7,96¿, ?DH2O = ¿10,65 a ¿1,33¿), granada (?18OH2O = +6,88 a +7,77¿) e turmalina (?18OH2O = +4,11 a +6,41¿, ?DH2O = ¿15,40 a +5,12¿), a 429 ±45 ºC, e fluidos em equilíbrio com biotita (?18OH2O = +7,16 a 7,96¿, ?DH2O = -36,96 a -21,93¿) e quartzo (?18OH2O = +6,88 ± 0,35¿), a 520 ± 45 ºC, apresentam composição semelhante à da água magmática. No depósito Igarapé Bahia, fluidos associados com a formação de turmalina (?18OH2O = +5,54 a 6,24¿, ?DH2O = ¿46,98 a ¿32,70¿) e calcita (?18OH2O = +1,68 a +3,10¿; ?13CCO2 = ¿9,04 a ¿4,65¿, 398 ± 85°C) também evidenciam fontes magmáticas. A participação de fontes externas no Igarapé Bahia é marcada pela clorita (?18OH2O = +2,13 e +3,41¿). Isótopos de enxofre apontam para fontes magmáticas no depósito Salobo (¿0,37 e +1,63¿) e externa para o Igarapé Bahia (+1,36 e +5,35¿). Isótopos de boro em turmalina nos depósitos Salobo (+3,4 a +17,0¿), Igarapé Bahia (+3,4 a +14,6¿), Furnas (+13,1 a +17,2¿), Grota Funda (+8,2 a +13,6¿) e GT-46 (+5,4 a +6,4¿) sugerem a participação de fontes híbridas, que incluem salmoras derivadas de fluidos hidrotermais submarinhos e/ou evaporação da água do mar associada com boro proveniente de salmoras magmáticas. A sobreposição de episódios de mineralização de Cu¿Au reflete os diversos eventos tectônicos e magmáticos do Domínio Carajás Abstract: The Salobo and Igarapé Bahia deposits represent important iron oxide-copper-gold (IOCG) deposits at Carajás Province. The Salobo deposit is hosted by gneiss from the Xingu Complex, granites from the Igarapé Gelado suite and by metasedimentary units. Hydrothermal alteration formed grunerite¿almandine¿fayalite¿magnetite¿(tourmaline) and (grunerite¿almandine)¿magnetite¿biotite mylonitic rocks. The Igarapé Bahia depositi is hosted by metavolcanosedimentary rocks from the Igarapé Bahia Group and metasedimentary sequences from the Águas Claras Formation. Basement xenoliths occur within the deposit with ages of 2,935 ±36 Ma (MSWD = 0.85), evidencing the presence of an ensialic crust prior to rifting. U-Pb ages in detrital zircon of the metagraywackes of the Igarapé Bahia Group (2.82 ¿ 2.88 Ga e 2.94 ¿ 2.99 Ga) and of the Águas Claras Formation (2.81 ¿ 2.89 Ga and 2.91 ¿ 3.03 Ga) point to mesoarchean basement sources. Chalcopyrite nodules and layers within metarhytmites of the upper sequence represent a syngenetic mineralization coeval with deposition of the Igarapé Bahia Group in the Neoarchean. Sulfur isotopes in this chalcopyrite generation (+0.29 and +1.56¿) and elevated contents of Ni, Co and Bi suggest that sulfur and metals were leached from the metavolcanic rocks of the lower sequence. Zones of hydrothermal alteration with (tourmaline)¿carbonate¿magnetite and (tourmaline)¿carbonate¿chlorite envelop the IOCG mineralization. U-Pb geochronology in monazite yielded ages of 2,559 ±34 Ma in the Alemão orebody. Ore geochemistry signature at IOCG mineralization exhibit elevated ?ETR values and expressive contents of U, Mo, Sn, W, Y, Nb and Sr. In the Salobo deposit, fluids associated with grunerite (?18OH2O = +6.66 to +7.96¿, ?DH2O = ¿10.65 to ¿1.33¿), garnet (?18OH2O = +6.88 to +7.77¿) and tourmaline (?18OH2O = +4.11 to +6.41¿, ?DH2O = ¿15.40 to +5.12¿), at 429 ± 45 ºC, and fluids in equilibrium with biotite (?18OH2O = +7.16 to 7.96¿, ?DH2O = -36.96 to -21.93¿) and quartz (?18OH2O = +6.88 ±0.35¿), at 520 ± 45 ºC, fall into the magmatic water field. In the Igarapé Bahia deposit, fluids in equilibrium with tourmaline (?18OH2O = +5.54 to 6.24¿, ?DH2O = ¿46.98 to ¿32.70¿) and calcite (?18OH2O = +1.68 to +3.10¿; ?13CCO2 = ¿9.04 to ¿4.65¿, 398 ± 85°C) also point to magmatic sources. External sources in the Igarapé Bahia deposit is constrained by chlorite (?18OH2O = +2.13 e +3.41¿). Sulfur isotopes point to magmatic sources at Salobo (¿0.37 and +1.63¿) and external sources for Igarapé Bahia (+1.36 and +5.35¿). Boron isotopes in tourmaline at Salobo (+3,4 to +17,0¿), Igarapé Bahia (+3,4 to +14,6¿), Furnas (+13.1 to +17.2¿), Grota Funda (+8.2 to +13.6¿) and GT-46 (+5.4 to +6.4¿) evidence the participation of exhalative fluids and/or evaporated seawater brines associated with magmatic brines. These results suggest that seawater and magmatic boron sources took part in the mineral system during distinct Neoarchean tectono-magmatic events separated in time Doutorado Geologia e Recursos Naturais Doutor em Ciências CNPQ 481969/2013-6 CAPES 2016/13162-7 FAPESP 2016/13162-7

Orientadores: Roberto Perez Xavier, Diego Fernando Ducart Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: O setor leste da Província Aurífera de Alta Floresta (PAAF), contexto meridional do Cráton Amazônico, centro-norte do Estado de Mato Grosso, hospeda mais de uma centena de depósitos e ocorrências auríferas que ocorrem na forma de veios, stockworks ou disseminados. Neste setor da província, o depósito Pé Quente representa um dos melhores exemplos de ouro disseminado associado à sulfeto. Descrições de testemunhos de sondagem e petrografia apontam biotita granodiorito como o litotipo hospedeiro da mineralização aurífera. A rocha hospedeira foi afetada por diferentes tipos de alterações hidrotermais espacial e temporalmente sobrepostas representadas por restrita alteração sódica com albita, ampla alteração potássica com feldspato alcalino, carbonatação, alteração fílica com sulfeto disseminado e venular, cloritização, silicificação e propilitização. As zonas mineralizadas, disseminada e venular, são compostas pela assembleia pirita, calcopirita, rutilo, galena e hematita, além de fases ricas em Ag, Te e Bi. Estas mineralizações são aparentemente sobrepostas por um veio de quartzo polimetálico (teor de Au > 30 ppm) com esfalerita, calcopirita, galena e pirita. Os dados obtidos no balanço de massa revelam que na alteração fílica, em comparação com a alteração potássica, houve acréscimo nos elementos móveis Ca, Fe, K, Mg, Na, Li, Ba, Rb e Sr e, imóveis Nb, P, Ta e Ti (exceto Hf, Th e Y). Análises de química mineral em conjunto com espectroscopia de reflectância em amostras mineralizadas provenientes da zona de alteração fílica identificaram as micas brancas fengita e muscovita indicando ampla ocorrência de reações do tipo Tschermak e comprimentos de onda da ligação Al-OH de 2211-2213 nm para os termos ricos em K+ e, entre 2214-2221 nm para os termos enriquecidos em Fe2+ e Mg2+. No grupo das cloritas foram identificadas as variedades: (1) ferro-magnesiana classificada como ripidolita/brunsvigita/diabanita e, clinocloro-Fe/ clinocloro Fe-Al com comprimentos de onda da ligação Mg-OH entre 2339-2349 nm e; (2) magnesiana classificada como brunsvigita/diabanita/penninita e, clinocloro-Fe/clinocloro com comprimentos de onda entre 2330-2338 nm. A geotermometria da clorita (1) Fe-Mg que se encontra em paragênese com o sulfeto na zona fílica forneceu a temperatura média de cristalização de 370-250 °C a qual pode ser estimada como sendo a temperatura de aprisionamento do fluido mineralizante. Os corpos de minério Barba, Goiano e Gabriel, do depósito de ouro Pé Quente, constituem um sistema magmático-hidrotermal único alojado no biotita granodiorito com mineralização aurífera disseminada e venular crono-correlata à zona de alteração fílica representada por muscovita-fengita, clorita Fe-Mg, quartzo e sulfeto (pirita) Abstract: The eastern sector of the Alta Floresta Gold Province (AFGP) located in the southern Amazon Craton, north-central portion of the state of Mato Grosso, hosts a significant number of disseminated and vein-type gold and gold-base metals occurrences. In this sector of the AFGP, the Pé Quente deposit is one of the best representative examples of disseminated gold-sulfide deposit group. Drill core logging and petrographic descriptions reveal that the deposit is essentially hosted by a biotite granodiorite. This host rock has been mainly affected by early and restricted sodic alteration with albite, followed by extensive potassium alteration with alkali-feldspar and carbonate alteration, which is then overprinted by phyllic alteration with white micas-chlorite-quartz. The latter hosts the disseminated gold-sulfide mineralization. Post-mineralization alteration includes chloritization, silicification and propilitization. Disseminated and veinlet ore zones are composed of pyrite, chalcopyrite, rutile, galena and hematite as well as Ag, Te and Bi rich-phases. These styles of mineralization are superimposed by a gold rich (up to 30 ppm) quartz polymetallic vein containing sphalerite, chalcopyrite, galena and pyrite. The mass balance data shows that the phyllic alteration when compared with the potassic alteration is marked by an increase in mobile elements as Ca, Fe, K, Mg, Na, Li, Ba, Rb and Sr, and increase in immobile elements like Nb, P, Ta and Ti (except Hf, Th and Y). Mineral chemistry combined with reflectance spectroscopy in mineralized samples from the phyllic alteration zone identified white micas as phengite and muscovite indicating wide occurrence of Tschermak¿s reactions. Al-OH absorption wavelengths are recognized between 2211-2213 nm to K+ rich terms and between 2214-2221 nm to Fe2+ and Mg2+ enriched terms. For the chlorite the following varieties have been identified: (1) iron-magnesian-rich classified as ripidolite/brunsvigite/diabanite and clinochlore Fe/clinochlore Fe-Al with Mg-OH absorption wavelengths between 2339-2349 nm and; (2) magnesian-rich classified as brunsvigite/diabanite/penninite and clinochlore Fe/clinochlore with Mg-OH absorption wavelengths between 2330-2338 nm. The chlorite geothermometry applied to the (1) Fe-Mg variety associated with the gold-sulfide mineralization in the phyllic zone yielded temperatures between 370-250 °C which can be linked accordingly to the precipitation of gold. The several ore bodies that comprise the Pé Quente deposit, such as Barba, Goiano and Gabriel, may have been the result of a single magmatic-hydrothermal mineral system in which the disseminated and vein-type gold mineralization is coeval to the phyllic alteration stage represented by muscovite-phengite, Fe-Mg chlorite, quartz and sulfide (pyrite) Mestrado Geologia e Recursos Naturais Mestra em Geociências FAPESP 2016/04370-5

The mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood. We present a case study for high-temperature dolomitization of an Early Cretaceous (Aptian-Albian) ramp in Benicàssim (Maestrat basin, E Spain). In this area, seismic-scale fault-controlled stratabound dolostone bodies extend over several kilometres away from large-scale faults. This work aims at evaluating different Mg sources for dolomitization, estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the Benicàssim dolostones. Field relationships, stable 13C and 18O isotopes, as well as radiogenic 87Sr/86Sr isotopes, indicate that dolomitization at Benicàssim was produced by a high-temperature fluid (>80°C). 13C and 18O isotopic compositions for dolomite vary from+0.5 to+2.9‰ V-PDB and from+21.1 to+24.3V-SMOW, respectively. A Mg source analysis reveals that the most likely dolomitizing fluid was seawater-derived brine that interacted with underlying Triassic red beds and the Paleozoic basement. Geochemical models suggest that evolved seawater can be considerably more reactive than high-salinity brines, and the maximum reactivity occurs at about 100°C. Mass-balance calculations indicate that interstitial fluids with high pressure and/or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at Benicàssim. Instead a pervasive fluid circulation mechanism, like thermal convection, is required to provide a sufficient volume of dolomitizing fluid, which most likely occurred during the Late Cretaceous post-rift stage of the Maestrat basin. This study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes

Una sucesión de rocas con fósiles de organismos bentónicos en el depósito laterítico de níquel de Cerro Matoso S.A. (CMSA), localizadas en el extremo nororiental del cuerpo ultramáfico Denominado en proceso minero Pit6 a la altura del Banco 42, fueron estudiadas y analizadas Con petrografía, XRD, XRF y SEM. Estas rocas permiten precisar la génesis del yacimiento más importante de níquel en el país actualmente. La sucesión de rocas calcáreas autigénicas fosilíferas y depósitos hidrotermales identificados En la Tesis, precipitaron sobre la roca ultramáfica de Cerro Matoso en un ambiente submarino Euxínico caracterizado por la presencia de ventilas hidrotermales. Las rocas marinas están compuestas principalmente por siderita, bertierina, goethita y piroaurita Acompañadas de nimita, greenalita y tosudita entre otros minerales. Esta secuencia no continua, incluye de base a tope; siderita de cristalinidad gruesa a muy gruesa, Arcillolitas fosilíferas verdes, arcillolitas fosilíferas cafés, saprolito negro, canga de alta alúmina y canga mona. En algún periodo, alrededor de las ventilas hidrotermales en la roca ultramáfica de CMSA se Instaló una variedad de organismos extremófilos cuya cadena alimenticia comienza con microorganismos capaces de generar energía a partir de procesos anaerobios oxidantes de Metano y reductores de sulfato que a su vez alimentan gusanos tubulares y bivalvos en Relaciones simbióticas y quimiosintéticas. La fauna endémica encontrada en las rocas calcáreas y arcillolitas en el Pit 6 en CMSA está Compuesta por más de 30 especies incluyendo macro invertebrados como bivalvos Bathymodiolus cf. Thermofilus, Themiste dyscrita y gusanos tubulares indeterminados, Considerados el registro de actividad bentónica hidrotermal. Las elevadas concentraciones de azufre en el medio euxínico fomentadas por sistemas hidrotermales tipo ¨Black Smoker¨ generaron un enriquecimiento primario de níquel en Las rocas; el níquel un elemento altamente calcófilo pudo entonces formar sulfuros de Níquel para luego, posterior a la acreción de la peridotitas hacia finales del Cretácico En el noroccidente de Colombia, por procesos de concentración Residual y enriquecimiento Secundario generados por una fuerte meteorización química (i.e laterización) completar El enriquecimiento en níquel en el yacimiento laterítico. Abstract. A succession of rocks with fossils of benthic organisms were studied into lateritic nickel deposit of Cerro Matoso S.A. (CMSA), located in the northeastern part of the ultramafic body in the mining Process named Pit 6 at 42 Bench height, the rocks were analyzed with petrographic, XRD, XRF And SEM and allow pinpoint the genesis of the largest nickel deposits in the country today. The succession of authigenic limestone and hydrothermal deposits with fossils precipitated On ultramafic rocks of Cerro Matoso in a euxinic submarine environment characterized by the presence of hydrothermal vents. The marine rocks are composed mainly of siderite, berthierine and goethite accompanied by pyroaurite, niimite, tosudite and greenalite among others. This sequence is not continuous, from base to top includes; crystalline siderite coarse to Very coarse, fossiliferous green claystones, fossiliferous brown claystones, black saprolite, High Al2O3 canga and canga mona. Around hydrothermal vents activity in ultramafic rocks were installed a variety of extremophile Organisms whose food chain starts with microorganisms capable to generate energy from anaerobic processes of methane oxidizing and sulfate reducing which in turn feed tube worms and bivalves in chemosynthetic and symbiotic relationships. The endemic fauna found in the limestone and clays in the Pit 6 in CMSA is composed of More than 30 species including macro invertebrates as bivalves Bathymodiolus cf. thermofilus, Themiste dyscrita and indeterminate tubeworms, which logs benthic activity. The high sulfur level in an euxinic setting promoted by hydrothermal systems or ¨Black Smoker¨ Generated a primary nickel enrichment in the ore body, the nickel a highly chalcophile element Could form nickel sulfides and then by residual concentration processes and secondary nrichment Generated by strong chemical weathering (laterizationie) after the accretion of the peridotites in Northwestern of Colombia at late Cretaceous, was completed the nickel enrichment of the lateritic deposit. Additionally, the marine rock succession (basal sediments) and hydrothermal deposits acted as ¨ duricrust ¨ or trap preventing pit 1 profile of erosion and protecting lateritic nickel oncentrations In the ore body. Maestría

Los yacimientos epitermales del sector Almagrera-Herrerías parecen originados por un sistema hidrotermal asociado a celdas convectivas superficiales alimentadas por aguas meteóricas/marinas y magmáticas. La simulación matemática de un teórico sistema hidrotermal convectivo muestra la coincidencia entre las zonas mineralizadas conocidas con las zonas de descarga y acumulación de masa predecidas por el modelo. Todo ello, y la existencia de un sistema hidrotermal aún en activo, explica el interés de localizar zonas de descarga del sistema hidrogeológico actual, con el fin de profundizar en la génesis de los yacimientos conocidos y localizar posibles nuevos depósitos.

Critical properties of the NaCI-H₂0 fluid system are of fundamental interest to a variety of geochemical applications including fluid inclusion studies, numerical modeling of hydrothermal systems, and development of theoretical models for two·component fluid systems. Although many workers have expressed interest in NaCl·H₂0 fluid critical properties, most studies have been limited to small compositional ranges with little agreement among data sets at higher salinities. Critical densities are recorded in only one of these reports, and no studies have determined the locations of NaCl-H₂0 critical isochores (PT projections of critical densities). Furthermore, no studies to date have determined critical properties of NaCl·H₂0 solutions in excess of room temperature saturation (26.4 wt.% NaCl). Master of Science