No description available.

Gossans, the brightly coloured oxidation products of sulphide mineralised rocks, have acted as an exploration target for base and precious metals and sulphur for thousands of years. They are easily identified from remote sensing and field-based reconnaissance, and once found may be drilled to determine the character of mineralisation below. The number of targets drilled could potentially be reduced if gossans overlying significant mineralisation can be discriminated from their field relations, mineralogy and geochemistry. Previous such studies have focussed on porphyry-type systems, with less attention on the generally much lower tonnage volcanogenic massive sulphide (VMS) deposits. However, VMS continue to provide an economically important source of metals in Europe and elsewhere. The Troodos Massif in Cyprus was chosen for this study as it hosts a currently active Cu mine along with historically worked VMS, is little deformed and has a relatively well understood geological framework. Of particular interest are secondary Cu deposits (SCUD) which form due to weathering of primary massive sulphides (PMS). These can be worked at relatively lower financial and environmental cost, and at much lower grades (down to around 0.1 % Cu). The only currently mined SCUD in Cyprus is the Phoenix ore body at Skouriotissa, which lies immediately adjacent to, and structurally below the Phoukasa PMS. The questions addressed in this study are: 1) Do Cypriot PMS that were mined for Cu show original Cu enrichments, or is their elevated Cu content a result of supergene enrichment to form an SCUD? This was addressed by comparing the mineralogical, chemical and S isotopic compositions of PMS mined for Cu with those mined for pyrite only from across the Troodos; 2) Do gossans formed from Cu-rich sulphides show distinctive mineralogical and chemical signatures? The characteristics of gossans known to overlie prospective sulphide bodies were compared with those from barren PMS; 3) What circumstances promote the formation of SCUDs? In particular, did sulphide oxidation occur on the sea floor or in a terrestrial environment? It was considered likely that SCUD formation may require sea floor oxidation because this will result in limited Cu dispersion, due to both sharp pH and redox gradients and limited fluid flow when compared with terrestrial weathering, where the depth to the water table can be considerable. The question was addressed by comparing the field relations, chemistry and S and O isotope compositions of gossans thought to have formed on the sea floor (Skouriotissa - Phoenix) with those generated in a terrestrial setting (Kokkinopezoula, Mathiati and Sia). The remnants of primary VMS deposits mined for Cu in Cyprus (Phoukasa, Sia and Troulli) almost exclusively contain primary Cu sulphides such as chalcopyrite. Secondary Cu sulphides, mainly chalcocite and covellite, are only present in significant concentrations at Phoukasa and Troulli, with Cu oxides being found in Phoenix. At Phoukasa, secondary Cu sulphides have a mean δ34S = 3.69±0.08 ‰ similar to primary pyrite and chalcopyrite (mean δ34S = 3.78±0.08 ‰) suggesting formation from Cu-rich fluids that scavenged S from primary sulphides. Sulphide material collected from copper mines has Cu = 840 to > 10,000 ppm at Phoukasa; 167 to 3573 ppm at Sia; 288 to > 10,000 ppm at Troulli, while the Cu-barren deposits have generally lower Cu grades (Cu = 170 to 433 ppm at Kokkinopezoula; 327 to 1303 ppm at Mathiati north). There are no systematic differences in the S isotope compositions of pyrite between deposits mined for Cu and those not (average δ34S = 1.68, 3.74 and 7.1 ‰ for Cu-rich Sia, Lysos and Phoukasa, and 5.03 and 3.70 ‰ for Cu-poor Kokkinopezoula and Mathiati North sulphides, respectively). No consistent chemical differences (including chalcophile elements) could be identified between gossans overlying Cu-rich as opposed to barren PMS. Gossans overlying the Lysos and Sia Cu-rich PMS, however, show an enrichment in Pb and Zn not observed in other gossans, and umbers, which are chemical sediments associated with VMS systems, often overlying gossans, show strong Cu enrichments in the vicinity of Cu-rich PMS. Umber samples from near the Cu-rich Phoukasa sulphide body contain > 10,000 to 35,400 ppm Cu, while those around Cu-poor Mathiati North contain 669 to 819 ppm Cu. There were no differences in the S isotope compositions of gypsum from sulphide bodies which were Cu-rich (δ34S = 5.9 to 6.9 ‰ for Sia, Phoukasa and Troulli) and Cu-poor (δ34S = 5.0 to 7.3 ‰ for Kokkinopezoula, Mathiati North). Regarding the environment of formation of SCUDs, an initial submarine oxidation of the Phoukasa VMS is considered likely as it is immediately overlain by marine pelagic sediments, while all other deposits studied are overlain by volcanics. In addition, volcanics in the vicinity of Phoukasa show large negative Ce anomalies (Ce/Ce* = 0.90 to 0.38, average = 0.71), consistent with sea floor alteration, compared with other localities such Kokkinopezoula (Ce/Ce* = 0.89 to 1.08, average = 0.97) and Sia (Ce/Ce* = 0.92 to 1.03, average = 0.99). Unfortunately, the S isotope composition of gypsum could not be used to determine the nature of the gossan-forming environment. Gypsums from all locations (average δ34S = 6.74±0.08 ‰) have δ34S values similar to, but slightly 34S enriched compared with their associated sulphides (average δ34S = 2.9±0.08 ‰) which indicates that their S isotope signature largely reflects that of S released during sulphide oxidation, as opposed to evaporation of sulphate-rich waters or direct precipitation from a similar solution (i.e., seawater). However, the oxygen isotope composition of gypsum (average δ18O = 6.2 ‰) from Sia (average δ18O = 2.4 ‰) reflects a mixture of atmospheric O (δ18O = 23.6 ‰) and Mediterranean meteoric water O (δ18O ≈-5.0 ‰), indicating a terrestrial environment of formation. Gypsum from Skouriotissa has an average δ18O = 6.6 ‰ which most likely indicates a combination of seawater and seawater-dissolved O (δ18O ≈23.5 ‰), despite some overlap with the composition of meteoric water and atmospheric O. In summary, it is proposed that the currently unique nature of Skouriotissa as hosting the only major SCUD in Cyprus is due largely to initial sea water alteration of the Phoukasa PMS resulting in limited Cu dispersion and localised Cu enrichment within the primary ore body. Subsequent uplift and alteration of the Phoukasa PMS led to the formation of a relatively high grade SCUD in the Phoenix deposit. The main outcomes of the study are a series of models for the development of gossans and associated lithologies in terrestrial and seafloor weathering environments in Cyprus. These incorporate a new term (retali) for acid leached volcanics in the footwall of PMS, and exploration-relevant field, mineralogical and chemical criteria for their discrimination from gossans, which overlie PMS. In agreement with an existing model, the formation of the Phoenix SCUD is interpreted as having been due to the downward migration of Cu-bearing acid fluids from the seafloor oxidation of the upper parts of the Phoukasa deposit. Secondary Cu mineralisation is thought to have taken place within the relatively reducing environment below the water table in lavas stratigraphically below the Phoukasa deposit. That the formation of SCUDs may require seafloor sulphide oxidation, and that this can be recognised in the mineralogy and chemical compositions of associated volcanics and gossans, provides new exploration criteria for SCUDs. However, it should be noted that the Phoenix deposit was the only SCUD examined in this study, and that this model should therefore be tested elsewhere.

The Lone Star porphyry copper deposit in the Safford District of southeastern Arizona was discovered in the late 1800's but never mined on a large scale. In addition to typical copper oxide species such as chrysocolla, the upper part of the deposit has zones of mineralization in which the chemical assays of core samples have higher amounts of copper than can be visually assigned to the observed copper-bearing minerals. The goal of this study is to identify the Cu-bearing minerals, which is crucial because the efficiency of the extraction processes is strongly dependent upon the mineralogy. Samples from seven cores with a range of copper contents and observed copper minerals were collected for analysis. Elemental compositions have been determined by X-ray fluorescence spectrometry and show a large variability in copper content (ranging from 360 ppm to 4.7 wt. %). Mineral assemblages were determined by optical microscopy, energy dispersive spectroscopy on the scanning electron microscope, and X-ray diffraction analysis and show varying concentrations of possible Cu-hosting minerals such as chlorite, biotite, iron oxides/hydroxides, and clay. Copper element maps were created for selected samples using an electron microprobe and areas of elevated copper concentration were more closely mapped with quantitative analyses taken of many points. This identified some common copper minerals that were simply too small to be seen in hand sample. However, several other minerals also contain high concentrations of Cu including chlorite and biotite (up to 19.3 wt. % CuO), iron oxides/hydroxides (up to 5.2 wt. % CuO), and clay (up to 7.3 wt. % CuO). While it has been determined that there is copper substitution into the structure of these minerals, transmission electron microscope analysis shows some of the copper in the chlorite and biotite is in native Cu blebs between the phyllosilicate sheets. The iron oxides and hydroxides are nanometer-sized particles with large surface areas for adsorption of copper. This presents a multi-phase system of copper minerals that cannot be seen during normal core logging. The presence of ore-grade concentrations of copper in the oxidized zone is likely due to insufficient acid production, as Lone Star is a sulfur-poor deposit, and the neutralizing effect of the andesite that hosts the deposit.

The Cassenha Hill copper-gold prospect is situated in the Catabola area, Huambo Province, southwestern Angola. Geologically, the prospect is part of the Angolan Central Eburnean Zone (CEZ) and consists of Paleoproterozoic metasedimentary rock sequences which have been intruded by Eburnean granitoids at ± 2.1 Ga. The prospect itself comprises an area of 180 Km2 and has been intermittently explored since 2005 by Rift Valley Resources (RVR) and its associates. The Cassenha Hill prospect is characterized by the occurrence of partially altered and highly oxidized metasedimentary rocks (meta-mudstone, meta-siltstone, carbonate-rich rock, meta-sandstone, breccia, and quartzite), and altered isolated granitoids. This study represents the first detailed study of the prospect and aims to shed light on the characteristics of the various rock types (i.e., host and barren rocks), their source/provenance, styles of alteration, and the origin and/or type of the fluid responsible for the mineralization. Techniques applied include borehole core logging, petrography, whole-rock geochemistry (XRF and ICP-MS), and stable isotope geochemistry on samples collected on the surface and from exploration boreholes drilled as part of RVR exploration program. Overall, the petrographic and geochemical studies undertaken in the rocks of the Cassenha Hill prospect indicate the following: (1) The rocks are moderately to strongly fractured; (2) The rocks have experienced weak to moderate chemical weathering; (3) The rocks are compositionally immature and originated from felsic provenance; (4) The rocks are sulfur-poor, and lacking in sulfide minerals (5) The rocks are enriched in LREE and LILE elements and depleted in HREE and HFSE elements; (6) The mineralization is associated with chloritization alteration and predominantly occurs within and/or at the edges of quartz/chlorite-rich veins/fractures and is not restricted to any rock type. Two ore stages could be identified, namely, hypogene ore (stage I) consisting of pyrite ± chalcopyrite ± other copper sulfides, and supergene ore (stage II) consisting of malachite ± azurite ± chrysocolla, which represents the prevalent mineralization at the prospect. The δ 18O value of quartz veins range from +12.81 to +13.53‰, while the δD of chlorite minerals range from -51 to -45‰. Therefore, assuming fluid-rock interaction took place at ≈ 350oC, due to the presence of quartz, the fluid had δ 18OH20 values of about +8‰, which are typical of magmatic waters. On the other hand, at a temperature of ≈ 350oC, and with the difference between chlorite and water being -33.5‰, such fluids would have had δDH20 values of about -20‰ (δ 18OH20= -4‰), which are typical of meteoric waters. Although the various mineral phases have yielded different isotopic signatures, this study suggests that water is ultimately of meteoric origin but exchanged with hydrogen-poor magmatic rock, thus maintaining the meteoric signature. The continuous influx of meteoric waters within the fracture system led to the development of copper oxides such as malachite, azurite and chrysocolla, which possibly originated from the insitu oxidation of the hypogene sulfides. This signature, together with other field, petrographic and geochemical observations allows one to, tentatively, suggest that the Cassenha Hill prospect represents an extension of a polymetallic vein-type of porphyry Cu deposit that has been subjected to supergene processes at the weathering profile.

This is a study of the supergene mineralogy of the San Xavier West mine located in the Pima mining district, Pima County, Arizona. The number and composition of secondary species collected are found to be closely related to the relative amounts of the various primary minerals and to the manner in which they were emplaced in the host rock. Supergene mineral species were selected that appeared to be in equilibrium with their environment, and certain assumptions are made concerning the stability fields of these minerals. The equilibrium conditions in most cases can be narrowed and often closely defined by combining the stability fields of several secondary minerals. On this basis, two acid environments and one alkaline environment are found to exist and are separable on the basis of mineralogy. The fields of chalcanthite and melanterite define a highly acid environment while those of goslarite and malachite define an environment of lower acidity. The association of calcite, rosasite, hemimorphite, and malachite indicate an alkaline environment. The acidity of the environments is principally determined by the amount of pyrite present, and pH may be lower than 3 if pyrite is abundant and reactive carbonate material lacking. Also, knowledge of stability relations allowed the history of enrichment and subsequent oxidation to be followed in a case where a transitional species had been removed from reaction by inclusion with gypsum.

La connaissance minéralogique et géochimique des gisements de nickel latéritique est sans aucun doute plus approfondie que celle de leur structuration. En effet, le profil d’altération oblitère le réseau de fracture affectant la roche mère sous-jacente, pourtant indispensable pour l’évaluation de la ressource car elle contrôle l’essentiel de l’altération et donc la libération du nickel. La Nappe des Péridotites de Nouvelle-Calédonie constitue un objet exceptionnel d’étude de la fracturation au sein d’une ophiolite mantellique car le soulèvement majeur et les phases d’érosion subséquentes, qu’elle a subis du Miocène à l’Actuel, ont permis de mettre au jour la structure en trois dimensions. Cependant, la facilité d’accès à la ressource fait qu’à ce jour assez peu d’études structurales ont été conduites sur les gisements, ou le plus souvent, sont restées confidentielles. L’objectif de cette étude est de mieux comprendre l’influence de la structuration de l’ophiolite sur la genèse des gisements de nickel latéritique en Nouvelle-Calédonie. Cette étude multi-échelle a porté sur l’ensemble de la Nappe des Péridotite et se scinde en deux volets : 1) une étude structurale de terrain, et 2) l’interprétation de données d’électromagnétisme nouvellement acquises. Cette campagne de géophysique héliportée a été effectuée sur trois zones minières représentatives des différents types (morphologiques et génétiques) de gisements rencontrés en Nouvelle-Calédonie (les massifs de Koniambo et du Kopéto-Boulinda et au sud, la zone de Plaines des Lacs – Goro - Port-Boisé).L’analyse de la fracturation des péridotites est primordiale pour comprendre les chemins de migration des eaux météoriques et donc les variations d’épaisseur du profil d’altération. Une approche minéralogique et texturale est nécessaire afin de distinguer les différents épisodes de fracturation et de remplissage statiques ou cinématiques, et permet de proposer une chronologie relative. À la suite de cet inventaire, il est possible d’identifier ces objets sur les profils d’électromagnétisme. Cette analyse permet de visualiser la géométrie des structures jusqu’à une profondeur de 300 m et montre un lien direct entre les approfondissements du profil d’altération et la présence de certaines fractures. Ainsi, il apparait clairement que les eaux météoriques empruntent des chemins préférentiels fonction de la morphologie générale du massif elle-même issue des structures héritées.La géométrie des structures visualisées par la géophysique, combinée aux observations de terrain, permet de mieux appréhender la complexité du système. A l’issue de ce travail, il est possible de replacer chacun des types d’objets observés dans leur contexte géodynamique et ainsi de restituer l’histoire de l’ophiolite depuis l’accrétion océanique jusqu’à son émersion à l’Oligocène. Un modèle révisé de la genèse des gisements de nickel en Nouvelle-Calédonie est présenté et de nouveaux guides d’exploration sont proposés. L’électromagnétisme s’avère être une méthode particulièrement adaptée pour visualiser la géométrie globale du profil d’altération et constitue une aide substantielle à la prospection et la modélisation des gisements de nickel. / The mineralogical and geochemical understanding of lateritic nickel ore deposits is undoubtedly better constrained than their tectonic structure. Indeed, the fracture network of the underlying bedrock is typically concealed beneath a thick weathering profile. However, this fracture network strongly controls weathering and ultimately nickel release from peridotites, thus improving its knowledge appears critical in the evaluation of nickel resources. In New Caledonia, the Peridotite Nappe is a particularly outstanding case study because Early Miocene to Recent uplift and subsequent erosion allow the structure of a mantle ophiolite to be observed in three dimensions. However, due to the easy access to nickel resources, only a few structural studies have been undertaken, or remained confidential. The main objective of this study is to better constrain the role of the fracture network of the Peridotite Nappe in the genesis of New Caledonia’s lateritic nickel ore deposits.A multiple-scale study of the whole Peridotite Nappe has been performed following two main parts: i) field-based structural observations and analyses; and 2) interpretation of new acquired heliborne electromagnetic data. The latter focused on three mining areas (massifs of Koniambo and Kopéto-Boulinda; and, Plaine des Lacs – Goro - Port-Boisé), which are representative of the different types (morphologic and genetic) of nickel ore deposits encountered in New Caledonia.The study of the fracture network is essential in the understanding of the migration of meteoric waters and thus thickness variations of the weathering profile of peridotites. A mineralogical and textural approach has been undertaken to distinguish the various steps of fracture development on the basis of static or synkinematic infill events and eventually allowed a relative chronology to be proposed. Following this inventory, it has been possible to identify these objects on electromagnetism profiles. This analysis allows visualizing the geometry of controlling fractures at depth and reveals a direct link between deepening of the weathering profile and the fracture network. Ultimately, it clearly appears that meteoric waters use preferential pathways that in turn depend on the geomorphology of each massif, which originate from the inherited fracture network. The combination of geophysical data interpretation and field observations allow a better understanding of the complex nappe structure. Our results allow every described tectonic object to be replaced in its geodynamic setting and thus the full ophiolite history to be restored, from oceanic accretion to emersion in Oligocene. A refined model for the genesis of New Caledonia’s lateritic nickel ore deposits is proposed, as well as additional metallotects for exploration. Electromagnetism appears to be appropriate for describing the overall geometry of the weathering profile and can be useful in prospecting and modelling nickel ore deposits.

Pendant l'Eocène Moyen, dans la région du désert d'Atacama, Nord Chili, la mise en place de porphyres et la déformation synchrone de la Précordillère aboutissent à la formation de clusters importants de dépôts de cuivre supergènes et exotiques, actuellement en cours d'exploitation. La formation de ces dépôts métallifères résulte de l'interaction entre la tectonique, l'érosion et le climat. La nature et la chronologie de ces interactions sont encore débattues. Ce travail de doctorat se concentre sur la quantification des processus géomorphologiques, tectoniques et érosifs, sur le versant ouest des Andes, autour de 23°S dans le District minier Centinela situé dans la Précordillère. Vingt-neuf nouvelles données thermochronologiques basse-température et leur modélisation indiquent que les porphyres cuprifères mis en place à faible profondeur durant l'Eocène moyen étaient déjà exhumés près de la surface à l'Oligocène moyen. Il existe un intervalle de temps de cinq millions d'années entre l'exhumation du porphyre qui constitue la source primaire de cuivre et le dépôt secondaire de cuivre dans le district de Centinela daté par les méthodes 40Ar/39Ar et K/Ar. Cette relation suggère que les dépôts de cuivre secondaires ont eu lieu lorsque les reliefs étaient déjà aplanis. Un dépôt exotique cuprifère syn-sédimentaire s'est formé dans le bassin continental du district Centinela. Des échantillons de sable ont été prélevés entre 135 et 13 mètres de profondeur dans les mines El Tesoro et Mirador. Les concentrations en 10Be et 21Ne de quatorze nouveaux échantillons ont permis de déterminer l'âge du dépôt et de contraindre les paléo taux de sédimentation des derniers 14 Ma. L'étude permet de dater le dépôt exotique à ~12 Ma et suggère qu'il a eu lieu lors d'une quiescence des taux d'érosion, confirmant l'idée que les dépôts supergènes de cuivre en milieu aride ont lieu après l'aplanissement des reliefs. Ces résultats confirment aussi que les taux d'érosion ont drastiquement chuté après 10-12 Ma, quand l'hyperaridité s'est établie. Ce travail de thèse illustre la balance nécessaire entre l'exhumation et les taux de précipitation pour former des minéralisations secondaires de cuivre et les conserver. / During the Middle Eocene in the Atacama Desert region (northern Chile), the intrusion of porphyries and the synchronous deformation of the Precordillera resulted in the formation of important clusters of supergene and exotic copper ore deposits that are currently exploited. Such metal ore deposits result of the interaction of tectonics, erosion and climate, for which both timing and relations remain debated. This PhD study focuses on the quantification of geomorphological, tectonic and erosive processes to understand their relationship in the Andean western slope around 23°S in the Centinela district in the Precordillera. Twenty-nine new low-temperature thermochronological data and their modelling indicate that shallow porphyry copper emplaced during mid-Eocene were quickly exhumed near the surface by the early Oligocene. There is a five million years-long time gap between the exhumation of primary source of copper and the ~25-12 Ma range of existing 40Ar/39Ar and K/Ar ages of secondary mineralization in the District. This suggests that supergene copper related deposits occurred when the reliefs where already flattened. A syn-sedimentary exotic copper mineralization was deposited in an intra-mountainous basin in the Centinela District. We sampled sand at different depths between 135 and 13 meters in the Tesoro and Mirador open-pit mines, one of them including this exotic deposit. The 10Be and 21Ne concentrations of fourteen new samples were used to determine the exotic deposit age and to constrain the paleo-sedimentation rate for the last 14 Ma. The study dates the exotic deposit at ~12 Ma and suggests that this mid-Miocene exotic layer occurred during an erosive quiescence, confirming the view that supergene copper mineralization occurs during a stage of slower geomorphic activity in arid environments. The results also confirm that the erosion rates drastically dropped after 10-12 Ma, when the hyperaridity was established. This study highlights the necessary balance between exhumation and precipitation rates required to form secondary copper.

No description available.

The Pilbara region of Western Australia hosts the Hamersley Province, an area of abundant iron ore resources located in the lower Hamersley Groups, Brockman and Marra Mamba Iron Formations. This study consists of a geotechnical and a geochemical and mineralogical investigation into the Banded Iron Formation (BIF) and shale deposits of the lower Hamersley Group that reside in the pit walls of RTIO mines in Western Australia. Areas throughout Tom Price, Paraburdoo, Marandoo and West Angelas iron ore mines are geotechnically investigated for rock mass conditions through the use of the Slope Mass Rating (SMR) classification system and through point load and slake durability testing. Selected samples from these areas were then geochemically and mineralogically tested by X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and microscopic analysis, to determine the geochemical and mineralogical changes of BIF and shale as they alter and weather through hypogene and supergene alteration and Recent weathering. It was found that the most efficient method for determining the alteration and/or weathering of lower Hamersley Group BIF and shale deposits was by the use of a chemical alteration index, calculated from enriched and depleted major elements in the BIF and shale as they alter and weather. It has been suggested here that this Pilbara Iron alteration index can be calculated efficiently and effectively from geochemical testing in intervals down boreholes throughout future or developing open pit mines to assist in estimating slope stability conditions. It is also suggested that many boreholes should be analysed in section or in 3D space to create cross sections or block models showing the varying extent of alteration and weathering throughout the area being studied. From the geotechnical investigation, it was found that the weakest region, in terms of pit slope stability, were the highly and extremely altered and/or weathered regions with Pilbara Iron alteration indices of between 61 and 80, and 81 and 100, respectively. If these zones are identified, slope stability analysis can be focused on these geotechnically vulnerable areas. Slope stability analysis should be completed by using a suitable technique, such as by the use of SMR, which, along with other risk identification measures, will identify potentially unstable areas and suggest the required course of action. Further hazard and risk analysis should be undertaken in potentially unstable areas and remedial measures undertaken as appropriate. Thereby, the Pilbara Iron alteration index can be used in the Hamersley Province as a predictive tool for pit slope stability.

[pt] As jazidas mundiais de minérios de ferro tendem ao empobrecimento dos teores de ferro, aumento das gangas (sílica, alumina, fósforo, etc.) e maiores ocorrências de minérios hidratados. Esta mudança vem gerando um esforço no sentido de aprimorar as técnicas de extração e beneficiamento. O fósforo é um contaminante que em certos teores provoca a fragilização dos aços, sendo, portanto, restritivo ao aproveitamento de importantes jazidas minerais, principalmente as ricas em minérios de origens intempéricas ou supergênicas. Vários trabalhos foram e estão sendo conduzidos visando desenvolver tecnologias capazes de reduzir o teor de P durante o processo de beneficiamento. Porém, até o momento não têm mostrado viabilidade econômica, face à escala de produção e a efeitos danosos ao ambiente. No caso da Samarco, os minérios foram gerados principalmente por processos de enriquecimento supergênico, nos quais é comum a presença de considerável goethita, que é apontada como principal mineral portador do fósforo. O objetivo deste trabalho foi, de forma original, a formulação de uma pelota para redução direta de forma que o fósforo se encontrasse fluxado em fases escorificadas. Essas fases, produzidas através de um adequado ciclo térmico de endurecimento e com composição química otimizada, resultaria em pelotas onde este elemento se mantivesse estável, tanto na produção do DRI quanto na fusão e refino oxidante deste no FEA. Para tanto foram realizados, além de uma ampla revisão bibliográfica, concebido um procedimento analítico original para quantificação apenas do fósforo liberado; planejado experimentos para: a avaliação cinética da migração deste fósforo em pellet feed, nas pelotas e no DRI quando submetido a diferentes aportes térmicos e auto-fluxagens; analise da influência das variáveis do processo de endurecimento sobre a liberação do fósforo e sua escorificação; e comprovação da estabilidade das fases escorificadas durante a redução, em escala de laboratório, e durante a fusão e refino conduzido em um FEA semi-industrial. Os resultados obtidos mostraram ser viável a produção de pelotas para redução direta com o fósforo auto-fluxado em fases estáveis. / [en] Actually the iron ore deposits in the world have the tendency to decrease the iron content, increasing the gangue (silica, alumina, phosphorus, etc.) and to further occurrence of hydrated ores. This change demands improvements in concentration processing techniques for feasible mining operations. The phosphorus is a contaminant that, in some contents, causes the embrittlement of steels, been, wherefore, a limitative to the use of important ore deposits, mostly regarding the weathered iron ores or supergene origins. Several studies were and have been conducted aiming to develop technologies capable of decreasing the P content during the beneficiation process. However, until now, the economic viability of such studies has not been feasible, considering the production scale and the harmful effects to the environment. In Samarco’s case, the mine geological formation is mostly supergene, which is responsible for the presence of the goethite ores, pointed as the main phosphorus carrier. The main point of this work was, with an innovating approach, formulate a new type of pellet addressed to direct reduction processes in a manner that the P could be fluxed into the slag phases. These phases, produced through an adequate thermal cycle of induration and with an optimized chemical composition, resulted in pellets with stable slags containing, as well as in the produced DRI and in the melted bath generated during the primary refining performed in the EAF. For this purpose, it was done, further to a wide bibliographic review, an original analytical procedure to quantify the released phosphorus and a series of planned experiments, such as: the kinetic evaluation of the phosphorus migration from the mineral phases of the pellet feed when subjected to different thermal treatments; analysis of the induration process variables which could affect the phosphorus release and its fluxing into the slag ; Finally, the stability of the fluxing phases during the reduction in a laboratory scale and the melting and refining process in a semi-industrial EAF, were performed. The obtained results showed the feasibility of this new approach produce DR pellets with self-fluxed phosphorus trapped in stable phases.