Phase relations in the binary system anorthite-K-feldspar at 10 kbar were studied with a solid-media piston cylinder apparatus. The eutectic character of this system is confirmed, with the eutectic point located at An30Kf70 (± 3 mol%), and 1215 ± 15°C, 10 kbar. The mutual solubilities between anorthite and K-feldspar at the solidus are greatly increased at 10kbar compared with those at 1 atm. The maximum solubility of K-feldspar in anorthite is c. 5% at 1 atm, c. 18% at 10 kbar; and that of anorthite in K-feldspar is c. 3% at 1 atm, c. 7% at 10 kbar. The increased solubilities are attributed to the increase in the eutectic temperature at high isostatic pressures. The results imply increased ternary feldspar solid solutions at high pressures and support the existence of homogeneous feldspars with extensive ternary composition under high-P, T and anhydrous conditions.

Pyritic slates from the late Precambrian, Middle Dalradian Argyll Group Easdale Slate Formation, contain mainly quartz, muscovite and chlorite with variable amounts of dolomite, albite and paragonite. Slates from Easdale Island and Cuan Ferry contain pyrite porphyroblasts with δ34S = + 12 to + 16‰. The pyrite grew during a post-tectonic retrogressive event at the expense ofpyrrhotine which formed during the main regional metamorphism of the Grampian orogeny by reduction of diagenetic pyrite. Slate from Oban contains abundant diagenetic framboidal pyrite and small syn-tectonic pyrite porphyroblasts with δ34S = +22‰. This pyrite was not all reduced to pyrrhotine on metamorphism so there was little retrogressive growth of pyrite. Metamorphism appears to have homogenized local (cm scale at least) isotopic inhomogeneities and preserved an average seawater-sulphate-sulphide isotopic fractionation value. Middle Dalradian seawater-sulphate had a δ34S value of about + 35‰, so the small fractionations are appropriate for bacteriogenic reduction in bituminous sediments, the heavier sulphide in the case of the Oban slate indicating more rapid reduction of sulphate. Lower Dalradian Appin Group, Ballachulish slate contains pyrite with δ34S = +15±2‰ and is best interpreted as forming in the same manner as the Easdale slates of Easdale Island and Cuan Ferry; the sharp increase in late Precambrian ocean-sulphate sulphur isotope signature from +15 to > +30‰ therefore occurred by Lower Dalradian Appin Group times.

Palladium-bearing minerals from the Cauê iron mine, Itabira District, Minas Gerais, Brazil, are found in gold-rich jacutinga, a hydrothermally-altered Lake Superior-type carbonate-bearing oxide facies iron-formation. Palladium occurs as: native palladium with trace contents of Au, Fe and Cu; palladseite ((Pd,Cu,Hg)17Se15), which was found in the core of a grain of palladium; palladium–copper oxide ((Pd,Cu)O); and arsenopalladinite (Pd8(As,Sb)3), with inclusions of palladium–copper oxide. The palladium and palladium–copper oxide grains are coated with films of gold and commonly do not exceed 100 µm in width. These palladium minerals occur in hematite bands and in boudinaged bands of quartz and white phyllosilicate parallel to the S1 mylonitic foliation. Palladium-copper oxide also occurs as inclusions in gold grains which are strongly to weakly stretched parallel to S1.

Palladium mineralization is interpreted as synchronous with intense D1 shearing and contemporaneous with the peak of thermal metamorphism. At high oxygen fugacities and high temperatures (up to 600°C), Pd may have been transported as chloride complexes and deposited following changes in pH caused by mineralizing fluids reacting with jacutinga. Deposition may also have been prompted by the formation of insoluble selenide and arsenide–antimonide minerals and by the dilution of C1 concentrations in the mineralizing fluid. Textural studies, and the zonation observed in palladium and other hydrothermal minerals, suggest that oscillations in the physico-chemical conditions of hydrothermal fluids occurred during the mineralizing event.

Several field and laboratory studies have demonstrated that secondary Fe-bearing minerals such as goethite, lepidocrocite and mackinawite have a high capacity for the uptake of As, but little work has been carried out to examine the capacity of the mineral vivianite [Fe3(PO4)2·8H2O] for this element. We report here preliminary results of an experimental study designed to test the efficiency of As(III) and As(V) uptake by natural vivianite at acid, near-neutral and alkaline pH at T = 4ºC, which is representative of Lake Baikal-type environments, where natural vivianite is reported to occur. The vivianite takes up between 0 and 5% As(III), and between 21 and 45% As(V), from 200 ppb solutions of these As species. Further work at 25ºC and other solution concentrations, together with characterization of the post-sorption solids, will yield information on the efficiencies and mechanisms of As uptake by natural vivianite.

Sericitization in three separate pulses of the Rosses Granite Ring Complex, Co. Donegal, Ireland, has been investigated texturally and chemically using electron microscopy, electron microprobe and fluid inclusion thermometry. The sericitization, which is restricted to the cores of plagioclase, is associated with pores which are abundant in the cores, but absent in the margins. Alkali feldspar, although porous, is unaltered. Associated with the sericitization is alteration of the adjacent primary plagioclase within the cores of grains to a more sodic composition.

It is postulated that the sericitization resulted from the action of externally derived secondary hydrothermal fluids, which gained access to the pores in the plagioclase via now sealed microfractures, formed either by contraction during cooling of the Rosses Complex, or more likely by hydraulic fracturing by the fluids themselves. Limited fluid/rock ratios restricted the degree of sericitization within the host plagioclase, whilst an absence of alteration in alkali feldspar may have been due to the inaccessibility of pores in the alkali feldspar to the hydrothermal fluids at the time of alteration. Fluid inclusion data suggest that the fluids were of low salinity, and that the sericitization took place at an early stage in the cooling history of the Rosses Complex at temperatures between 400 and 600°C. It is further contended that greisenization in the Rosses Complex predated the sericitization and that the greisenization may have been due solely to volatile-rich late-stage magmatic fluids.

A new compositional variety of zirconolite characterized by high Mg, Al, Y2O3 and REE, and low Fe is described from a sapphirine granulite xenolith entrained in an intrusive norite body which was emplaced into the late Archaean (2520–2480 Ma) Vestfold Hills high-grade terrain during the early Proterozoic. The zirconolite, and similarly Mg-Al rich perrierite-(Ce), formed as a result of sanidinite facies partial melting of the particularly magnesian and aluminous sapphirine granulite xenolith during its incorporation into the c. 1170°C basic magma at c. 2240 Ma. The high REE compared to Al cations require that a previously unrecognized coupled substitution:

occurs in this zirconolite. Full chemical analyses are presented for zirconolite and perrierite from this unique occurrence.

A hygroscopic, soft, pink mineral was discovered in Sinjar town, west of Mosul city. Wet chemical and X-ray diffraction analyses proved that the mineral has a composition of calcium chloride dihydrate CaCl2·2H2O, which has not been known in nature before. It is therefore a new mineral, and is named sinjarite after its locality.

Tidal mudflats are locally enriched in heavy metals at the head of Strangford Lough in Northern Ireland, where drainage from the hinterland enters the sea lough via a tidal canal in an urban area. To characterize the metallic contaminants and investigate their provenance, heavy particles separated from stream, canal and estuarine sediments were analysed by electron microprobe and laser Raman microspectroscopic methods. Potential metal sources are mineralization in the catchment area and industrial or domestic pollution. Anthropogenic particles include metallic grains, alloys and compounds of Pb, Zn, Cu, Fe, Cr and Sn. Alteration of metallic particles includes de-zincification of brass in freshwater sediment and replacement of Cu wire by covellite in brackish to marine sediment. Mobility of Cu, Fe and S in canal and estuarine sediments is indicated by the authigenic growth of framboidal Fe sulphide on oxide substrates and of chalcopyrite rims on covellite. Intricate colloform and platy crystalline textures suggest a cyclical deposition of covellite and chalcopyrite under conditions of varying redox and salinity. Lead and Cr mobility in the contaminated estuarine sediment is shown by the authigenic formation on Pb-rich substrates of heterogeneous Pb- and Cr-rich sulphate-phosphate compounds and Pb-oxychlorides.

The crystal structure of franconite, NaNb2O5(OH)·3H2O, has been characterized by single-crystal X-ray diffraction using material from Mont Saint-Hilaire, Québec, Canada. Results give a = 10.119(2), b = 6.436(1), c = 12.682(2) Å and β = 99.91(3)° and confirm the correct space group as P21/c. The crystal structure, refined to R = 4.63% and wR2 =11.95%, contains one Na site, two distorted octahedral Nb sites and nine O sites. It consists of clusters of four edge-sharing Nb(O,OH)6 octahedra, linked through shared corners to adjacent clusters, forming layers of Nb(O,OH)6 octahedra. These alternate along [100] with layers composed of NaO(H2O)4 polyhedra, the two being linked together by well defined H bonding. The predominance of H bonding, essential to the mineral, results in a perfect {100} cleavage. Chemical analyses (n = 7) of four crystals give the empirical formula (Na0.73Ca0.13☐0.14)∑=1.00(Nb1.96Ti0.02Si0.02Al0.01)∑=2.01O5(OH)·3H2O (based on nine oxygens) or ideally NaNb2O5(OH)·3H2O. Franconite is crystallo-chemically related to SOMS [Sandia Octahedral Molecular Sieves; Na2Nb2−xMxO6−x(OH)x·H2O with M = Ti, Zr, Hf], a group of synthetic compounds with strong ion-exchange capabilities. Both hochelagaite (CaNb4O11·nH2O) and ternovite (MgNb4O11·nH2O) have X-ray powder diffraction patterns and cation ratios similar to those of franconite indicating that these minerals probably have similar structures.

A thermodynamic prediction of the Gibbs free energy of formation (ΔGfo) of nukundamite (empirical composition Cu5.5FeS6.5) was made in order to specify whether the nukundamite + chalcopyrite or the bornite + pyrite assemblage is stable in the Cu-Fe-S system. The results of calculations using previously reported data of ΔGfo values of some Cu-Fe-sulphide minerals in equilibrium with nukundamite indicate that the total free energy of the nukundamite + chalcopyrite assemblage is appreciably higher than that of the bornite + pyrite assemblage in the temperature range 250–400°C. This means that nukundamite + chalcopyrite is a metastable assemblage under common ore-forming conditions.

The occurrence of nukundamite is not uncommon in the Fijian kuroko deposits in contrast to the Japanese kuroko deposits. A thermochemical treatment for this phenomenon leads to the interpretation that the black ore containing nukundamite in the Fijian deposit was formed under relatively highsulphidation and low-pH conditions. This suggestion is in good agreement with the present experimental result that the bornite + pyrite assemblage was produced in the temperature range 350–250°C by using near-neutral hydrothermal solutions.

Nearly boron-free kornerupine is locally abundant in pods or lenses of coarse-grained, non-foliated, Mg- and Al-rich rocks that occur at high metamorphic grades in early Proterozoic metapelitic rocks from the Reynolds Range, Northern Territory, Australia. This is the third reported occurrence of boron-free kornerupine worldwide. The samples consist almost entirely of coarse-grained kornerupine and its breakdown products sapphirine, cordierite, and gedrite or orthopyroxene. The kornerupine contains only 0.45 wt.% B2O3, corresponding to 0.098 B atoms per 22 (O, OH), and closely approximates 11:10:11 in terms of molar ratios of (MgO + FeOtotal):Al2O3:SiO2, with XMg = Mg/(Mg + Fetotal) = 0.874. The unusual textures and bulk compositions of the rocks in the pods are interpreted to have resulted from metasomatism and high-grade metamorphism (750 to 800° and ∼ 4.5 kbar) of precursors that may have included sedimentary Mg-rich clays. Rocks containing boron-poor, and relatively boronrich kornerupine (2.18 wt.% B2O3; XMg = 0.892) are separated in outcrop by as little as 10 m of the foliated cordierite-quartzite country rock and other rock types, suggesting that the compositions or amounts of the metasomatic fluids varied on a local scale.

Replacement phenomena in amblygonite–montebrasite in rare-element pegmatites from the Karibib-Usakos area, Namibia, have been investigated using the electron microprobe. The first African occurrence and analysis of the very rare mineral natromontebrasite NaAl(PO4)(OH,F) is reported from the Daheim pegmatite. In the Okatjimukuju pegmatite, montebrasite has been replaced by a number of phases including crandallite CaAl3(PO4)2(OH)5·H2O and brazilianite NaAl3(PO4)2(OH)4. In one example, montebrasite has been almost completely replaced by brazilianite which has also been found to contain not only crandallite but also its solid solution analogues: goyazite SrAl3(PO4)2(OH)5·H2O and gorceixite BaAl3(PO4)2(PO3OH)(OH)6. Apatite is common at the contacts with montebrasite and associated minerals and texturally is intimately intergrown with crandallite, goyazite and gorceixite at Okatjimukuju. The occurrence of these minerals offers insight into the chemistry of post-magmatic fluids in these pegmatites.

The Molteno meteorite was seen to fall in South Africa in 1953. It is a howardite, with pyroxene varying from En76Fs22Wo2 to En38Fs58Wo4 and then to En33Fs26Wo41. Also present are twinned plagioclase (An 84·4%) and small quantities of olivine (Fa 12%), troilite, nickel-iron (Ni 4%), ilmenite, and an aluminian chromite with 0·71% V2O3. A bulk analysis and analyses of the metal, troilite, and combined silicates and oxides are given.