New data on the Gongo Soco palladium-oxygenated compounds are presented for the first time since the work of Johnson and Lampadius (1837). A variety of PdO species is documented, always in association with Cu, Fe and Mn, and includes Pd(OH)2 or PdO.H2O, and phases with metal excess in relation to oxygen, interpreted as metastable. Their remarkable occurrence in ‘ouro preto’ (black gold) and jacutinga (auriferous itabirite/iron ore) is the result of mertieite-II alteration. It involves leaching of Sb and As, limited removal of Pd, and incorporation of Cu, Mn and Hg into PdO species. The locus of Hg-bearing PdO species in microfractures parallel to the enclosing gold-mineralized shear band suggests at least one low-temperature hydrothermal generation. The presence of a halite crystal attached to gold testifies to the involvement of Cl-saturated hydrothermal fluids in the oxidizing environment of jacutinga formation.

Zincian högbomite has formed by hydrous alteration of spinel and biotite in a lens of highly aluminomagnesian sapphirine-bearing granulite-facies rocks. The högbomite forms chestnut-brown {0001} flakes 1 mm across. ε = 1·827, ω = 1·852 (− 0·002). Analysis: BeO 0·10, SiO20·65, Al2O3 59·69, TiO2 5·37, Ga2O3 0·23, Nb2O5 0·01, Fe2O3 5·24, SnO2 0·06, NiO 0·04, ZrO2 0·03, MgO 7•69, Sc2O3 0·01, CoO 0·11, ZnO 3·08, FeO 17·52, In2O3 0·05, MnO 0·12. The pattern of d-spacings is anomalous. Other högbomites from the region have exsolved from cordierite or titaniferous opaque oxides.

Microthermometric characteristics of metamorphic to hydrothermal fluids and microfracturing were studied in a contact zone between metamorphic series and peraluminous granites, located in the southern part of the Mont Lozère pluton (Massif Central, France). Four major stages of fluid production or migration have been recognized: (1) N2-CH4 (±CO2)-rich fluids related to the metamorphism of the C-bearing shales, occurring as fluid inclusion along the quartz grain boundaries; (2) CO2-CH4-H2O vapours or liquids, with homogenization temperatures of 400 ± 20 and 350 ± 50°C respectively, related to the first hydrothermal stage produced by the late peraluminuous intrusions; (3) aqueous fluids having low salinities and Th in the range 150–330°C; (4) low-temperature aqueous fluids.

It is shown that the percolation of hydrothermal fluids occurs through a dense set of microfissures on a microscopic scale. The different stages of fluid percolation have been investigated by relating the deformational events to the observed fracturing. The nature of the hydrothermal fluid has been deduced by studying the trails of fluid inclusions. Analysis of the relationships of the fluid inclusion trails (F.I.T.) with structures associated with plastic deformation show that their propagation is independent of the intracrystalline anisotropies. Combined studies of their orientation in space and their microthermometric characteristics show that: (1) according to the direction, several generations of fluids are distinguished within each sample on the basis of their physical-chemical characteristics; they correspond to different stages of the hydrothermal activity and to different directions of micro-crack opening; (2) in bulk isotropic media (granite), fluid inclusion trails are essentially mode I cracks which can be used as excellent markers of paleostress fields; however, in bulk anisotropic media (quartz lenses in mica schists) the migration directions of the fluids are mostly dependent on the local reorientations of the stress fields.

The study of the contact zone between granites and a metamorphic series submitted to local abnormal heat flows shows that fluid characteristics are significantly different in the two environments. Migration of carbonic fluids from mica schists towards granites occurred but is relatively limited, whilst aqueous fluids mixed in variable amounts with carbonic fluids in the metamorphic zone.

The mineral deerite is restricted in occurrence to blueschist facies meta-ironstones. From the ideal formula of Si12O40(OH)10 there are a limited range of substitutions: Ti and V for Fe3+ and Mn on the Fe2+ site. In the present survey of deerite compositions from the majority of deerite localities the maximum substitutions have been 2Ti and 3Mn in the above formula. There is an at present unexplained anomaly in the totals of a number of the analyses indicating that there may be variations away from the ideal formula towards increased hydroxyl and decreased cation contents.

From differences between the mineral compatibilities of deerites from the higher-grade Franciscan exotic block blueschist localities and those from more conformable Alpine blueschists, in conjunction with previous work on the experimental stabilities of the low-pressure/low-temperature hydrous iron silicate minerals, it has been possible to map the form of the low-pressure deerite stability field involving reactions of greenalite or minnesotaite or grunerite with magnetite and quartz. Within the deerite stability field, further deerite-forming reactions involve the breakdown of riebeckite and the hydrous incompatibility of magnetite with quartz; both are very dependent on the activity of sodium. A low-pressure stability to 4 kb at 200 °C and 6 kb at 300 °C are estimated from these low-temperature breakdown reactions. This fits in well with the high-pressure deerite stability determinations of Langer et al. (1977).

Th-rich (up to 18.4 wt% ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na0.39LREE0.19Th0.12Ca0.05Sr0.02)Σ0.77(Ti0.76Nb0.27)Σ1.03O3. The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi2O6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (Å) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) Å. The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations (‘ceriobetafite’). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE2O3 and ThO2 contents. Both ‘ceriobetafite’ and belyankinite were formed due to metasomatic alteration of loparite.

The 3.5 Ga Bon Accord Ni deposit occurs within the lowest serpentinized mafic–ultramafic lavas of the Barberton Greenstone Belt (South Africa). Though now completely mined out, it comprised a suite of rare Ni-rich minerals that led to its interpretation as either an extraterrestrial body or as an oxidized fragment of Fe-Ni alloy originating from the terrestrial core. In this study, we draw on detailed petrographic observation and mineral chemical data, as well as previous work, to re-evaluate these ideas. The balance of evidence, from thin section (<1 mm) to regional (∼10s of km) scales, appears to support an alternative origin for Bon Accord, possibly as an oxidized Ni-sulfide deposit formed in association with ocean floor komatiite eruptions.

Fluid flow through a two-dimensional fracture network has been simulated using a discrete fracture model. The computed field-scale permeabilities were then compared to those obtained using an equivalent continuum approach in which the permeability of each grid block is first obtained by performing fine-scale simulations of flow through the fracture network within that region. In the equivalent continuum simulations, different grid-sizes were used, corresponding to N by N grids with N = 10, 40, 100 and 400. The field-scale permeabilities found from the equivalent continuum simulations were generally within 10% of the values found from the discrete fracture simulations. The discrepancies between the two approaches seemed to be randomly related to the grid size, as no convergence was observed as N increased. An interesting finding was that the equivalent continuum approach gave accurate results in cases where the grid block size was clearly smaller than the 'representative elementary volume'.

The existence and relationships of hydrated forms both to one another and to anhydrous CaSO4 have been studied by X-ray methods. Detailed study of the hemi-hydrate reveals its true cell to be monoclinic and does not confirm the previously suggested polymorphism.

Dehydration studies of the dihydrate and hemi-hydrate are reported; cyclic dehydration and hydration of single crystals of the latter show a variable temperature interval between the formation of γ-CaSO4 and the reconstitution of the hemihydrate at approximately constant humidity. An explanation of this behaviour is offered, and the structural implications of the results of the dehydration studies are discussed.

Experimental melting equilibria at 1 kbar PH2O are reported for three early Tertiary granites from Skye and one from Rhum, together with a quartz monzonite from Ardnamurchan. The Hebridean Province leucogranites show cotectic melting behaviour, whilst associated ‘primitive’ (mostly adamellitic) acid plutons have silicate liquidi ∼ 925 °C and plagioclase liquidi ∼ 875 °C. At such high temperatures the morefusible crustal rock types of the region would be almost completely molten. If the Tertiary ‘primitive’ acid magmas were simple crustal melts, they would inherit the incompatible element ratios of their sialic progenitors. This is demonstrably not so. Minor element ratios in these plutons are consistent with extensive fractional crystallization during the evolution of their magmas. But it is, in most individual instances, extremely difficult to specify, either by thermal or geochemical arguments, whether (1) fractional crystallization followed sialic contamination of basic magmas or (2) mixing occurred between fractionation residua and sialic melts. Both the minor element ratios and cotectic melting behaviour of the Hebridean Province leucogranites are consistent with the view that they are products of extreme fractional crystallization of (sial contaminated) more-basic magmas. Nevertheless, it is clear—when the sequence and timing of emplacement of acid magmas within individual intrusive centres is considered—that very complex polycyclic combinations of fusion, fractionation, and re-fusion were involved in the evolution of these granites.

The solidi of the samples studied experimentally, together with published data, show a progressive rise in temperature as the compositions of the rocks diverge from the minimum melting composition in NaAlSi3O8-KAlSi3O8-SiO2 at 1 kbarH2O. This relationship is important when considering the likely nature of sialic contamination of basic to intermediate continental magmatic suites fed through reservoir systems which are swarms of dykes and, or, sills. Because salic low-solidus crustal rock types also show near-cotectic melting behaviour, the composition of the contaminant may be strongly biased towards these (usually minor) crustal units, rather than the ‘bulk’ or average crustal composition.

The crystal structure of seeligerite, Pb3IO4Cl3, from the San Rafael mine, Sierra Gorda, Chile, was solved in the space group Cmm2, and refined to R = 3.07%. The unit-cell parameters are: a = 7.971(2), b = 7.976(2), c = 27.341(5) Å, V = 1738.3(6) Å3 and Z = 8. The crystal structure consists of a stacking sequence along [001] of square-net layers of O atoms and square-net layers of Cl atoms with Pb+ and I+ cations located in the voids of the packing. As is typical of cations with a stereoactive lone-pair of electrons, Pb2+ and I5+ adopt strongly-asymmetrical configurations. Pb2+ cations occur in a variety of coordination polyhedra, ranging from anticubes and monocapped anticubes to pyramidal ‘one-sided’ coordinations. I5+ is coordinated by a square of four oxygen atoms: I1 and I3 exhibit a ‘one-sided’ coordination, whereas I2 has square-planar coordination.

The TEM investigation has revealed additional superlattice reflections (which were not registered by X-ray diffraction (XRD)) in the hk0 diffraction pattern of seeligerite based upon a 0.158 Å-1 square net, which can be interpreted as arising from a 20-cation super-sheet motif (12.6 Å x 12.6 Å), likely related to a further level of Pb-I order superimposed upon the 8-site motif identified by XRD.

A chrysotile disc is proposed as the fundamental seed structure for the formation of chrysotile asbestos fibres, polygonal serpentine fibres and polyhedral lizardite spheres. The curvature, fivefold symmetry and hydrogen-bonding alignment of the layers in the seed disc control the formation of the 15 or 30 sectors in polygonal serpentine and the orientations of the planar arrays of 15 or 30 radial crystals in polyhedral serpentine. A polygonized disc precursor to polygonal fibre formation has been observed at an arrested stage of growth in a synthesis experiment.

The stability of synthetic connellite has been determined at 298.2K (25 °C) and 105 Pa, using solution methods. For the reaction 1/37{62H+(aq) + Cu37Cl8(SO4)2(OH)62.8H2O(s) ⇌ Cu2+(aq) + 8Cl−(aq) + 2SO42−(aq) + 70H2O(l)}, log KH+ is equal to 6.44(2). This result has been used in turn to calculate a value for ΔfG°(1/37Cu37Cl8(SO4)2(OH)62.8H2O, s, 298.2K) of −423.7±6.6 kJ mol−1. During the synthesis of connellite, claringbullite sometimes forms as a metastable phase. This solid recrystallizes to connellite if kept in contact with the reaction solution. The results have been used to construct an equilibrium model for the formation of connellite in relation to other common secondary copper (II) minerals. Connellite crystallizes from solution over an appreciable range of conditions. This result is consistent with the observed widespread occurrence of connellite, though as a very minor phase, in the oxidized zones of cupriferous sulfide ores.

The structure of a synthetic end-member wairakite (CaAl2Si4O12·2H2O) has been determined using Rietveld analysis of high-resolution, synchrotron X-ray powder diffraction data, and 29Si and 27Al magic angle spinning nuclear magnetic resonance spectroscopy. The framework in the synthetic sample is more disordered than that in natural wairakite. Ca is distributed over the cavity cation sites M2, M12A, M12B in the approximate proportions 0.8:0.1:0.1, respectively, with M11 being vacant. 29Si MAS NMR data are consistent with about 80% of the Si occupying tetrahedral T11 and T12 sites linked to two Al atoms [Q4(2Al) silicons]. Tetrahedral and cavity cation site disorder are coupled so that Al mainly occupies T2 sites, with Ca in M12A and M12B being balanced by Al in T12A and T12B; T11A and T11B sites appear to only contain Si, in agreement with the M11 site being vacant. The crystal chemistries of the wide range of stoichiometries which crystallize with the leucite/pollucite structure-type are also reviewed, with particular attention being paid to the tetrahedral ordering configurations present in these phases, and the implications to crystallographic phase transitions.

Garnet is a widespread minor accessory mineral in the Late Proterozoic Elat-Quarry granite of southern Israel and is more abundant in the associated pegmatite and aplite. All garnets are dominated by almandine and spessartine end-members. Granite-hosted garnets are zoned with relative enrichment of Mn in the core and Fe in the rim. The chemistry of the garnet in the pegmatite and aplite are comparable to the rim compositions of garnets in the granite, but with a slight Fe-depletion at the rims. Geochemical parameters for the granite indicate fractional crystallization largely of an S-type source magma to a peraluminous composition.

In the highly evolved granite magma, Fe is relatively diminished, and only small amounts of biotite can crystallize. Manganese becomes a compatible element forming Mn-rich garnet (cores), and reducing the Mn content in the magma, subsequently leading to Fe-enriched rims. The greater abundance of garnet in the pegmatite and aplite (and its larger crystal-size in the former) relate to the enhanced presence of a hydrous fluid within the magma. The tendency for garnet crystals to concentrate in bands is much more developed in the pegmatite than in the granite, and is associated with the effects of hydrofracturing (fracture-filling), and the crystallization of coarse-grained alkaline feldspars.

From the Buranga pegmatite, Rwanda, three occurrences of eosphorite-childrenite series minerals are described in assemblages of Li-Fe-Mn-bearing phosphates and in relationship with quartz-feldspar masses in close association with these assemblages.

Electron-microprobe analyses of these terms (Mn,Fe) AlPO4(OH)2 · H2O afford the following Fet/(Fet + Mn) ratios: 0.548, 0.341, and 0.200. However, thanks to an investigation of the refractive indices and pleochroism, the presence of ferric iron is demonstrated and an oxidation phenomenon, similar to that previously known in rockbridgeite, is suggested to explain the existence of oxidized eosphorite. The oxychildrenite problem is raised again.

The Fet/(Fet + Mn) ratios characterizing the eosphorite sensu lato would be correlated with the Fe and Mn content of the associated major phosphates, the chemical analyses of which are also provided. The investigation of the structural relationships shows that eosphorite might form a paragenesis with montebrasite and that these phosphates replace Na- or K-feldspars by a hydrothermal process. Owing to the apparent dependence of the chemical properties of the couple eosphorite-montebrasite on those of the earlier-formed phosphates, it seems likely that the formation period of eosphorite-childrenite series minerals was prior to the oxidation and ferrisickleriteheterosite formation.

A number of diorite complexes occur within the Channel Islands region, notably on Jersey, Alderney, and particularly Guernsey. Much of northern Guernsey is made up of the largest of these complexes (fig. S1), the Bordeaux diorite. In the north-western part of this diorite, around Chouet, a complicated association of plutonic rocks occurs. Although the field relationships in this area are sometimes difficult to interpret—this is often the case in diorite complexes—three separate groups of rocks may be distinguished within the association: a diorite group; a granodiorite group; and an inhomogeneous suite of rocks (fig. S2).

The widespread diorite group consists predominantly of an even-grained diorite, which is relatively homogeneous but which occasionally grades into an acicular diorite, the latter often containing pods and veins of appinite. The granodiorite group is the least common, occurring as bodies which are interpreted as intrusive sheets and bosses within the even-grained diorite, but occurring as angular blocks within the inhomogeneous suite of rocks. The granodiorite invariably contains rounded diorite xenoliths. The inhomogeneous suite consists of a variety of rocks from patchy, dark diorite, through quartz diorite to tonalite. Commonly, these rock types are intimately associated, often showing gradational contacts with each other and frequently with the more basic portions occurring as ‘xenolithic’ material within the more acidic portions. At contacts between the inhomogeneous suite and the even-grained diorite certain features (e.g. lobate margins and pipe-like structures) indicate that the diorite must have been close to its solidus temperature at the time of emplacement of the inhomogeneous suite. The field relationships between the three groups are interpreted as indicating that the diorite group was emplaced first, followed by the granodiorite group, with both of these clearly pre-dating the inhomogeneous suite.

Fifty-nine specimens, chosen to give a representative sample of each of the three rock groups, have been analysed for major, minor, and a selection of trace elements and thirteen of these specimens have been analysed for REE. The chemistry of the analysed rocks confirms the division into three groups, with each group showing distinctive characteristics. Furthermore, chemical plots (e.g. Al2O3, P2O5, Cr, and Ni v. SiO2) show discontinuities and areas of overlap between each group which cannot be explained within the constraints of a single genetic model relating the three groups to each other. This argument is particularly strong for the relationship between the diorite group, which spans the range 50 to 59% SiO2, and the inhomogeneous suite, spanning the range 53 to 68% SiO2. In the area of overlap (53 to 59% SiO2) the two groups are geochemically different. Therefore, for a variety of reasons, including emplacement order, the geochemical characteristics of the groups and the lithological inhomogeneity which is associated only with the chemically intermediate members of the association (the inhomogeneous suite), three quite different and genetically unrelated liquids are required to generate the three groups of rocks.

The even-grained diorite shows chemical variation (e.g. with increasing SiO2, decreasing Al2O3, MgO, CaO, Sc, V, Cr, and Ni, and increasing Na2O, La, Nd, and Y) consistent with amphibole + plagioclase fractionation up to 55% SiO2. At 55% SiO2 several elements show a change of slope (e.g. FeO + Fe2O3, TiO2, Rb, Ba, and Zr) indicating the introduction of biotite as a fractionating phase. Increasing total REE content with increasing SiO2 throughout the even-grained diorite supports the contention that amphibole is an important fractionating phase. The higher TiO2, P2O5, Sr, La, Ce, Nd, and Y contents and negligible Cr and Ni contents of the acicular diorite suggest an origin by delayed crystallization of volatile-enriched portions of the diorite group magma.

The granodiorite group shows little geochemical variation. Members of this group contain detectable amounts of Cr and Ni, unlike virtually all members of the inhomogeneous suite. For this reason, and because of the field relationships, the granodiorite is considered to be genetically unrelated to members of the inhomogeneous suite and a separate liquid is thus required for its genesis. This liquid may have been the fractionated derivative of some other magma (though if this is so the ‘parent’ is entirely unrepresented at the present erosion level) or it may represent a direct crustal melt. Diorite xenoliths within the granodiorite are chemically similar to the even-grained diorite.

Despite the lithological complexity of the inhomogeneous suite, its geochemical unity is clearly established in that, for instance, virtually none of the members of the suite (including even the most SiO2-poor) contain detectable Cr and Ni. Moreover, geochemical variation within the group is rational (with the possible exceptions of Sr, Zr, and Ba) and may be explained in terms of a crystal fractionation model. However, the fractionation must have acted on a liquid itself unrelated to either the diorite or granodiorite group magmas. An additional complication is that later derivative liquids intrude into and partly digest earlier-formed semi-solids of the suite to produce much of the observed inhomogeneity. The phases which have controlled fractionation within the suite include plagioclase (established petrographically as well as geochemically) and hornblende. The role of apatite is uncertain. The fractionation of hornblende is particularly useful in explaining the change in REE contents within the inhomogeneous suite. Total REE contents increase from the dark diorite to the quartz diorite, but decrease from the quartz diorite to the tonalite with concomitant relative HREE depletion. This is taken to be a reflection of the changing hornblende/liquid partition coefficients for REE with increasing SiO2, which are less than one for liquids of basaltic and andesitic composition but greater than one for liquids of dacitic composition.

A spinel-phlogopite schist from the Mount Painter Province of South Australia forms part of a highly magnesium- and aluminium-rich unit and contains the minerals högbomite and taaffeite. Taaffeite nucleated in spinel during upper amphibolite facies metamorphism. During a subsequent upper amphibolite facies metamorphic event both spinel and taaffeite were partially replaced by högbomite. Chemical analyses of högbomite, taaffeite, and spinel are presented.

Transmission electron microscopy of several chondritic meteorites reveals exsolution products of two kinds in olivine. The coarser variety comprises particles that have nucleated heterogeneously on subgrain boundaries. Electron microprobe data confirm that these are chromite. The second variety, consisting of smaller precipitates distributed randomly, is interpreted as a homogeneously nucleated analogue of the first. It is potentially important as an indicator of cooling history. The aluminium-poor compositions of heterogeneously exsolved chromites suggest that some Cr may have entered tetrahedral sites in olivine during initial rapid crystallization from the melt.

Clinopyroxene crystals with complex lamellar intergrowths of orthopyroxene and garnet are described. The orthopyroxene lamellae are irrationally orientated within the clinopyroxene host although the optical relationships of these minerals are consistent with (100) exsolution in clinopyroxene. The intergrowth is nevertheless considered to be the result of exsolution processes. Possible modes of origin are reviewed together with the general significance of exsolved pyroxenes in eclogite- and granulite-facies associations.