The layered agpaitic nepheline syenites (kakortokites) of the Ilímaussaq complex, South Greenland, host voluminous accumulations of eudialyte-group minerals (EGM). These complex Na-Ca-zirconosilicates contain economically attractive levels of Zr, Nb and rare-earth elements (REE), but have commonly undergone extensive autometasomatic/hydrothermal alteration to a variety of secondary mineral assemblages. Three EGM alteration assemblages are recognized, characterized by the secondary zirconosilicates catapleiite, zircon and gittinsite. Theoretical petrogenetic grid models are constructed to assess mineral stabilities in terms of component activities in the late-stage melts and fluids. Widespread alteration of EGM to catapleiite records an overall increase in water activity, and reflects interaction of EGM with late-magmatic Na-, Cl- and F-rich aqueous fluids at the final stages of kakortokite crystallization. Localized alteration of EGM and catapleiite to the rare Ca-Zr silicate gittinsite, previously unidentified at Ilímaussaq, requires an increase in CaO activity and suggests post-magmatic interaction with Ca-Sr bearing aqueous fluids. The pseudomorphic replacement of EGM in the kakortokites was not found to be associated with significant remobilization of the primary Zr, Nb and REE mineralization, regardless of the high concentrations of potential transporting ligands such as F and Cl. We infer that the immobile behaviour essentially reflects the neutral to basic character of the late-magmatic fluids, in which REE-F compounds are insoluble and remobilization of REE as Cl complexes is inhibited by precipitation of nacareniobsite-(Ce) and various Ca-REE silicates. A subsequent decrease in F– activity would furthermore restrict the mobility of Zr as hydroxyl-fluoride complexes, and promote precipitation of the secondary zirconosilicates within the confines of the replaced EGM domains.

Moskvinite-(Y), Na2K(Y,REE)Si6O15, is a rare mineral, which until now has only been described from its type locality Dara-i-Pioz, Tajikistan. At Ilímaussaq moskvinite-(Y) was discovered in a drill core from Kvanefjeld, where it occurs as a replacement mineral associated with a mineral belonging to the britholite group. The composition was determined by a combination of electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry analyses. The empirical formula based on 15 oxygens is Na1.94K0.99(Y0.94Yb0.03Er0.03 Dy0.03Ho0.01Gd0.01) ∑1.05Si5.98O15. The coexistence of an almost pure Y and a light rare-earth element (REE) mineral is interpreted as fractionation of REE and Y during the replacement of an earlier formed REE mineral. Theoretical calculations of the observed replacement of feldspathoids by natrolite show that the generated fluid would have pH > 8, which inhibits large scale mobility of REE. In addition, a K-Fe sulfide member of the chlorbartonite-bartonite group is for the first time observed in Ilímaussaq where it occurs where sodalite is replaced by natrolite and arfvedsonite by aegirine. The sulfide incorporates the S and some of the Cl generated by the alteration of sodalite, whereas the K and Fe originates from the replacement of arfvedsonite by aegirine.

Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of production and political issues, most notably a near monopoly in supply from China. Red mud, the waste product of the Bayer process that produces alumina from bauxite, represents a potential secondary resource of REE. Karst bauxite deposits represent the ideal source material for REE-enriched red mud as the conditions during formation of the bauxite allow for the retention of REE. The REE pass through the Bayer Process and are concentrated in the waste material. Millions of tonnes of red mud are currently stockpiled in onshore storage facilities across Europe, representing a potential REE resource. Red mud from two case study sites, one in Greece and the other in Turkey, has been found to contain an average of ∼1000 ppm total REE, with an enrichment of light over heavy REE. Although this is relatively low grade when compared with typical primary REE deposits (Mountain Pass and Mount Weld up to 80,000 ppm), it is of interest because of the large volumes available, the cost benefits of reprocessing waste, and the low proportion of contained radioactive elements. This work shows that ∼12,000 tonnes of REE exist in red mud at the two case study areas alone, with much larger resources existing across Europe as a whole.

Continuous development of advanced technologies has created increasing demand for rare-earth elements (REE), with global emphasis on identifying new alternate sources to ensure adequate supply. Ore deposits containing physically adsorbed lanthanides are substantially lower grade than other REE deposit types; however, the low mining and processing costs make them economically attractive as sources of REE. To evaluate the commercial potential for the recovery of REEs from ion-adsorption deposits in a systematic manner, a standardized procedure for REE leaching was developed previously. Using this procudure it was found that, regardless of variations in ore origin and REE content, all REE consistently reached peak extraction levels under ambient conditions with fast kinetics. Various techniques to improve the REE extraction through process variations were also investigated: it was found that decreasing the L:S ratio, re-using leachate on fresh ores and counter-current leaching were all capable of increasing REE concentrations in the resultant leachate, albeit at the expense of REE extraction levels. In addition, the water content trapped in the leached material was found to contain significant amounts of REE and residual lixiviant requiring thorough washing of the solid residue.

Geochemical characteristics and rare-earth element (REE)-bearing minerals of calc-alkaline granites in southern Myanmar were investigated to identify the minerals controlling fractionation between light and heavy REE (LREE and HREE) during magmatic differentiation and weathering. The granites were classified on the basis of the mineral assemblages into two contrasting groups: allanite-(Ce)- and/or titanite-bearing granites; and more HREE-enriched granites characterized by hydrothermal minerals including synchysite(Y), parisite-(Ce), bastnäsite-(Ce), xenotime-(Y), monazite-(Ce), Y-Ca silicate, waimirite-(Y) and fluorite. This suggests that allanite-(Ce) and titanite are not stable in differentiated magma and HREE are eventually preferentially incorporated into the hydrothermal minerals. The occurrence of the REE-bearing minerals is constrained by the degree of magmatic differentiation and the boundary of two contrasting granite groups is indicated by SiO2 contents of ∼74 wt.% or Rb/Sr ratios of ∼3–8. Fractionation between LREE and HREE during weathering of the granites is influenced by weathering resistance of the REE-bearing minerals, i.e. allanite-(Ce), titanite, the REE fluorocarbonates and waimirite-(Y) are probably more susceptible to weathering, whereas zircon, monazite-(Ce) and xenotime-(Y) are resistant to weathering. Ion-exchangeable REE in weathered granites tend to be depleted in HREE relative to the whole-rock compositions, suggesting that HREE are more strongly adsorbed on weathering products or that HREE remain in residual minerals.

Lithium mineralization is common in the Central Iberian Zone and, to a lesser extent, in the Galizia-Trás-OsMontes Zone of Spain and Portugal, occurring along a ∼500 km-long NNW-SSE striking belt. There are different styles of Li mineralization along this belt; they are mainly associated with aplite-pegmatite bodies and, to a much lesser extent, with veins of quartz and phosphate. Lithium mineralization in the Central Iberian Zone may be classified into four types: aplite-pegmatite dykes occurring in pegmatitic fields, Li mineralization associated with leucogranitic cupolas, beryl-phosphate pegmatites and quartz-montebrasite veins. The main Li minerals of these bodies include Li-mica, spodumene and/or petalite in the pegmatitic fields and leucogranitic cupolas; triphylite–lithiophilite in the beryl-phosphate pegmatites, and amblygonite–montebrasite in the quartz-montebrasite veins. The origin of these different styles of mineralization is considered to be related to differentiation of peraluminous melts, which were generated by partial melting of metasedimentary rocks during the Variscan orogeny. On the basis of paragenesis and chemical composition, the pegmatitic fields and Li mineralization associated with granitic cupolas record the highest fractionation levels, whereas the beryl-phosphate pegmatites and quartz-montebrasite veins show lower degrees of fractionation. There are a number of textural and mineralogical indicators for Li exploration in the Central Iberian Zone and in the Galizia-Trás-Os-Montes Zone, with the highest economic potential for Li being in the pegmatite fields.

The Zagros orogenic and metallogenic belt is characterized by the widespread occurrence of manganese and ferromanganese deposits. These deposits are spatially associated with radiolarian cherts and basaltic rocks, which cap the ophiolite sequences. The present work provides a review on the rare-earth element (REE) geochemistry coupled with major- and trace-element geochemical characteristics of the Nasirabad and Abadeh Tashk manganese deposits (associated with the Neyriz ophiolite), and Sorkhvand manganese deposit (associated with the Kermanshah ophiolite). These data are used to gain an insight into the primary ore-forming processes that control the deposition of manganese ores. All of the selected manganese deposits have consistently high Ba contents and low concentrations of trace elements (Co, Cu and Ni) with high Mn/Fe ratios typical of hydrothermal activity. A relatively low REE abundance, Lan/Ndn ratios (>3), and position on a Lan/Cen vs. Al2O3/(Al2O3 + Fe2O3) discrimination plot indicate a distal hydrothermal source for almost all of the selected manganese deposits. Most of the deposits are characterized by Ceanom < –0.1 which reflects the prevailing oxidative conditions during the deposition of manganese ores. Importantly, this is consistent with the occurrence of non-sulfide oxic Mn mineralization in all the manganese deposits of the Zagros orogeny. The comparison of the Sorkhvand, Abadeh Tashk and Nasirabad manganese deposits with other manganese deposits elsewhere in the world indicates that major- and trace-element characteristics, as well as the REE composition of the Zagros manganese deposits are analogous to those typical of hydrothermal deposits.

A transmission electron microscopy (TEM) investigation was undertaken in order to elucidate the nature of the structural disorder in a tobelite specimen from the sedimentary rocks of the Armorican sandstones (western France). This structural disorder may be the origin of residual electron-density maxima in difference-Fourier maps reported previously in single-crystal XRD studies of tobelite. The TEM investigation of tobelite confirmed that it is the 2M2 polytype in subfamily-B, but the ordered sequence is interrupted by numerous stacking faults parallel to (001), for which the stacking vectors belong to both subfamilies-A and -B of mica polytypes, with a prevalence of the latter. Chemical heterogeneity depending on the Si/Al ratio and Na and Mg concentration was observed at the nanoscale among different mica lamellae in a single crystal. The observed variations are consistent with a change in mica chemistry leading to interlayer vacancies which may cause shortening of the interlayer separation, as revealed by the single-crystal structure refinements.

Volcanic rocks in south County Waterford include flow-top hyaloclastite, pillow lavas and peperite, which are formed typically by sub-aqueous eruption or intrusion into unconsolidated sediment. Element mobility in wet sediment during emplacement of volcanic intrusions was reconstructed on a variety of spatial scales using bulk-rock and mineral analysis. Magma-sediment and magma-water interactions enhanced hydrothermal alteration. The chemistry of chlorite was a function of mixing between an Fe-rich magmatic fluid and a Mg-rich meteoric fluid. Chlorite geothermometry yields temperatures of formation between 230 and 388°C compatible with other metamorphic indicators. Fluid inclusion microthermometric data from genetically-related mineralized quartz veins reveal a hydrothermal vein mineralization event that occurred at lower temperatures during the end stage of volcanic activity. A convection driven mixing trend reflects the trapping of co-existing brine with entrained seawater concomitant with, the late stages of emplacement of the Bunmahon Volcano intrusions.

The new mineral species ferrostalderite, CuFe2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as minute, metallic, black, equant to prismatic crystals, up to 50 mu;m, associated with dolomite, realgar, baumhauerite (?) and pyrite. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 24.2/25.4; 548.3: 23.7/24.7; 586.6: 22.9/23.8; 652.3: 21.0/22.0. Electron microprobe analyses give (wt.%): Cu 6.24(25), Ag 4.18(9), Fe 9.95(83), Zn 4.46(91), Hg 1.22(26), Tl 26.86(62), As 19.05(18), Sb 0.63(6),S 25.39(47), total 97.98(72). On the basis of 12 atoms per formula unit, the chemical formula of ferrostalderite is Cu0.75(2)Ag0.30(1)Fe1.36(10) Zn0.52(11) Hg0.05(1) Tl1.00(1)[As1.94(4)Sb0.04(1)]∑1.98(4)S6.04(4). The new mineral is tetragonal, space group I4̄2 m, with a = 9.8786(5), c = 10.8489(8) Å, V = 1058.71(11) Å3, Z = 4. The main diffraction lines of the calculated powder diagram are [d (in Å), intensity, hkl]: 4.092, 70, 211; 3.493, 23, 220; 3.396, 35, 103; 3.124, 17, 310; 2.937, 100, 222; 2.656, 19, 321; 2.470, 19, 400; 2.435, 33, 303. The crystal structure of ferrostalderite has been refined by Xray single-crystal data to a final R1 = 0.050, on the basis of 1169 reflections with F0 > 4σ(F0). It shows a three dimensional framework of (Cu,Fe)-centred tetrahedra (1M1 + 2 M2), with channels parallel to [001] hosting disymmetric TlS6 and (As,Sb)S3 polyhedra. Ferrostalderite is derived from its isotype stalderite M1CuM2Zn2TlAs2S6 through the homovalent substitution M2Zn2+ → M2Fe2+. The ideal crystal-chemical formula of ferrostalderite is M1CuM2Fe2TlAs2S6.

An oxide-silicate occurrence, containing >40 wt.% NiO whole rock and showing enrichment in the platinum-group elements and antimony, was investigated at high magnification. Many phases with grain sizes generally <100 μm were observed; electron microprobe analysis indicated that, although some of these are known minerals in Ni–Sb–As space (such as breithauptite and orcelite), most of them cluster around the following compositions: Ni3Sb, Ni3(Sb,As), Ni3As, Ni5(Sb,As)2, Ni7(Sb,As)3 and Ni11(Sb,As)8. Such phases have been observed in synthetic systems, but up to now not in nature. The data reported here therefore probably represent the compositions of new minerals.