The Ulu Rompin iron deposits are located in an area of rugged topography in the State of Pahang, Malaya. There are several high grade primary ore bodies and superficial sheets of lateritic ore. The area is underlain by sheared alkalic rhyolite lavas and tuffs in which there are small lenses of sedimentary rocks, carbonates being the most important. There are several small stocks of hornblende granodiorite which probably merge into one larger parental mass at depth. The Bt Ibam ore body, which is the largest, is a tabular mass of magnetite in a highly magnesian gangue, originally chlorite and actinolite but now largely altered to talc. Underneath the ore there is a thin intermittent layer of calcic skarn, while massive chlorite appears along parts of the hanging wall. A short distance below the footwall there is granodiorite. The Bt. Batu Puteh deposit is magnetite associated with calcite marble, and at Bt. Hitam magnetite is found just above granodiorite. At Bt. Pesagi and BT. Sanlong the primary ore is haematite with very little magnetite. These bodies are located in shear zones in the volcanic rocks, and are not associated with calcic or magnesian minerals. All the ore bodies and country rocks have been pyritized, and other sulphides and sulphosalts have impregnated the Bt. Ibam body. These have produced zones, contaminated by copper and zinc, and to a lesser degree bismuth and lead. Hypogene and supergene alteration have extensively affected the iron ores and rocks and caused some redistribution of the impurity elements. The iron ores probably originated in the cooling granodiorite magma and were transported as chlorides or chloride complexes. The control over the loci of mineralization was partly lithological - magnetite bodies in calcic and magnesian rocks, and partly structural - haematite bodies in shear zones.

Column chemistry element purification methods were optimised for separation of Cu, Fe and Zn from geological samples taken from hydrothermal ore-forming systems. The method presented produces high-purity elemental separates at -100% recovery, ensuring absence of column-induced isotopic fractionation. Variation of Fe isotope ratios within two different mineral deposit types was investigated. In the West Cumbrian hematite, isotopic variability due to intermineral, redox and biological fractionation is likely absent, allowing identification of fluid flow and mineral precipitation effects. Isotopic ratios span >2.4%, with a trend toward lower values in primary mineralisation close to fluid conduits. This is interpreted to reflect Rayleigh-type distillation during kinetically-controlled hematite precipitation, with ∆56Fefluid-hematite ≈ 0.90%0. Secondary hematite, containing Fe sourced by dissolution of primary mineralisation, showed similar light isotope enrichment. Iron sulfide samples from the Lisheen Zn-Pb deposit, Ireland, were studied to assess the potential of Fe isotope analysis for tracing Fe source and mineralisation influences in a complex massive-sulfide deposit. Here, Fe isotope variation is correlated to paragenetic stage. Preore sulfides retain diagenetic compositions, locally overprinted by red sandstone-derived Fe. Main stage sulfides have a silicate-derived Fe signature, modified by kinetic mineral precipitation, reflecting evolution of the hydrothermal system from shallow to deep flow through time. Laboratory experiments were conducted to better understand the behaviour of Fe isotopes during transfer of Fe from silicate rocks into hydrothermal solutions. Basalt and granite powders were leached with HCI or oxalic acid solutions, with supernatant aliquots retrieved over a 7 day period. Initial aliquots showed significant enrichment of light isotopes, commonly ∆56Ferock-fluid >1.50%0. Fractionation magnitudes decreased over time, to apparent steady-state at ∆56Ferock-fluid ≈ 1.0 - 0.5%0. This study demonstrates the importance of kinetic processes during mineral precipitation, and the potential for future Fe isotope studies for gaining fundamental insight into many aspects of hydrothermal ore genesis.

The Nkout (Cameroon) and Putu (Liberia) oxide facies iron ore deposits comprise fresh magnetite banded iron formation (BIF) at depth, which weathers towards the surface, forming high grade martite–goethite ores. This study aimed to improve the mineralogical understanding of these deposits in order to predict their metallurgical responses. It concentrated on developing the QEMSCAN® technique and testing its application to these ore types, but also used a variety of other analysis methods. The QEMSCAN® species identification protocol was developed to include three goethite entries: goethite/limonite, phosphorus-bearing and aluminium-bearing goethite. QEMSCAN® was also used to distinguish between the iron oxides using their backscattered electron signals. To test the correlation between the mineralogy and metallurgical characteristics, magnetic separations were carried out. The samples were divided into 4 main groups based on their whole rock Fe content, determined by XRF analysis, and their degree of weathering: enriched material, weathered magnetite itabirite, transitional magnetite itabirite and magnetite itabirite. Quartz and Al oxide and hydroxide minerals such as gibbsite are the major gangue minerals in the magnetite BIF and martite–goethite ores respectively. From the QEMSCAN® analysis it was concluded that the iron oxides are closely associated and liberation of them individually is poor. Liberation increases when they are grouped together as iron oxide. Chamosite concentrations > 6 wt. % significantly lower liberation of the iron oxides. From the metallurgical testing, it was concluded that iron oxide modal mineralogy gives an indication of iron recovery but other QEMSCAN® data such as mineral association and liberation could be important especially if the iron oxide minerals are not liberated. Grain size and instrument characteristics also affect recovery of iron minerals. There is no evidence to show that there is any structural control on the BIF mineralisation at Nkout because metamorphism has significantly affected the lithological characteristics. The BIF mineralised zones occur as stacks with no particular stratigraphic relationship. Alteration and stratigraphy are the main controls on the martite–goethite ores. These results are applicable to most other BIFs so that as direct shipping ores are exhausted, the approach used here can help to develop the lower grade portions of the deposits.

Les smectites riches en fer appelées nontronite jouent un rôle majeur dans de nombreux processus biogéochimiques à la surface de la Terre. La compréhension de ces processus requiert une caractérisation cristallochimique détaillée de ces minéraux, avec notamment une connaissance précise du statut du fer. Les signatures spectrales du fer structural des nontronites ont été étudiées par spectroscopie infrarouge (IR), Mössbauer et XPS. La mise en évidence de ces signatures a été possible grâce à la synthèse hydrothermale à 150°C d’une série de nontronites avec une large gamme de teneur en [4]Fe(III). Les caractéristiques spectrales IR permettent d'effectuer une estimation robuste de la quantité de [4]Fe(III) tétraédrique présente dans la structure de la nontronite. Ces synthèses ont également permis de faire le lien entre la cristallochimie des nontronites synthétiques et la spéciation aqueuse du Si, Fe et Na. Les calculs de la spéciation aqueuse du Si montrent que l'augmentation des espèces anioniques H3SiO4-(aq) et H2SiO42-(aq) liée à l'augmentation du pH, favorise l'incorporation du Fe(III) dans les sites tétraédriques de la nontronite. La stabilité de ces nontronites dans les conditions de synthèse a ensuite été étudiée en fonction du temps. Une transformation minéralogique a été mise en évidence, amenant à la dissolution de la nontronite au profit d'un assemblage aegirine et hématite. Ces résultats montrent clairement que les nontronites synthétisées sont transitoires dans le système étudié. / Iron-rich smectites named nontronite are playing a great role in lot of biogeochemical processes at the Earth's surface. To better understand these processes a characterization of iron status in nontronites is required. Spectral iron features in the nontronite structure were studied by infrared (IR), Mössbauer, and XPS spectroscopies. IR characteristic fingerprints of Fe(III) allowed to obtain a detailed overview of the crystal-chemistry of this minerals, notably a robust estimation of the tetrahedral [4]Fe(III) content of the nontronite. This study was possible thanks to an experimental approach using hydrothermal synthesis (150°C) of a series of nontronites with a wide range of [4]Fe(III) content. These syntheses allowed to assess the link between the crystal-chemistry of synthetic nontronites and the aqueous speciation of Si, Fe, and Na. The aqueous speciation calculations indicated that the increase in anionic species H3SiO4-(aq) and H2SiO42-(aq) linked to the increase in pH, favored the incorporation of Fe(III) in the tetrahedral sites of nontronites. The stability of nontronites versus time was also studied. A mineral transformation was evidenced with the formation of the aegirine and hematite through the dissolution of nontronite. These results revealed that the synthetic nontronite are transitional in this experimental syntheses.