Dissolution rates of small forsterite spheres in superheated melts of basalt, andesite and rhyolite composition have been measured at 1300°C, atmospheric pressure. The rate is constant (83 µm hr−1) in the basalt, regardless of run duration. In the andesite the initial dissolution rate is 200µm hr−1, followed by a decrease to a constant value of 16µmhr−1 in 2–3 hours. Dissolution rate in the rhyolite decreases from an initial value of 1.7 to <0.1 µmhr−1 over 280 hours and never reaches a constant rate. Once the rate of dissolution has become constant, the film of contaminated melt that forms in melt about a crystal does not thicken with time, indicating attainment of a steady-state condition. Steady state is attributed to natural convection arising from the difference in density between the film of contaminated melt surrounding a crystal and that beyond. The density difference is approximately 2% of the density of the rock melt.

The mildy peralkaline Eikeren-Skrim granite belongs to the Permian magmatic province of the Oslo rift, south-east Norway. Euhedral quartz crystals from the abundant miarolitic cavities contain primary inclusions of partly crytallized silicate melts and coexisting primary, aqueous fluid inclusions. Micro-thermometric measurements give maximum estimates for the granite solidus of 685–705°C. Quenched silicate melt inclusions are not peralkaline, have normative Or/Ab weight ratios of 1.15–1.44 (compared to 0.49–0.80 in whole-rock samples) and F and Cl contents of 0.1 and 0.21–0.65 wt. %, respectively. Coexisting magmatic fluid inclusions are highly enriched in Na, Cl, S and to some extent K. These chemical characteristics are the results of late-magmatic melt-mineral-fluid interaction in the miarolitic cavities.

The effects of (OH)/F substitutions on thermally induced reactions in the apophyllite group have been investigated using TGA and DTA methods, supplemented by X-ray diffraction, infra-red and other techniques to identify the products of reaction. The samples studied cover the range between fluorapophyllite and hydroxyapophyllite, and include some unusual ammonium varieties. The presence or absence of fluorine exerts a major control on thermally induced reactions, not only during low-temperature dehydration, but also on high temperature recrystallization reactions up to 900°C+. All apophyllites dehydrate in two stages, the first being loss of a proportion of the water with only minor distortion of the crystal lattice, whereas the second results in total collapse into an amorphous material. Higher fluorine concentrations stabilize the structure, shifting dehydration reactions to higher temperatures, and permitting more water molecules to be lost during the first stage without destruction of the structure. Fluorine is not lost during the second-stage dehydration, as previously believed, but most is retained and influences subsequent recrystallization reactions.

Dehydrated hydroxyapophyllites remain amorphous until ca. 900°C, when high-temperature wollastonite crystallizes. Fluorapophyllites initially form a metastable CaF2.SiO2 phase by 700°C, low-temperature wollastonite by 800°C, both disappearing above 900°C when fluorine loss occurs and high-temperature wollastonite is produced. TGA and DTA provide simple methods of distinguishing between hydroxy- and fluorapophyllites.

Ammonian apophyllites, with up to 25% of the stoichiometric K+ replaced by NH4+ (in the samples studied), can be recognized by their DTA patterns, the endothermic peak for the second stage reaction being significantly reduced, and that for the first, dehydration, stage being correspondingly enhanced. Such samples have weight losses well above the calculated water content, the excess being due to evolution of ammonia. Ammonian varieties also have an extra infra-red absorption band at 1460 cm−1.

Carbonates of the magnesite-siderite series have been found and analysed in carbonatites from the Lueshe, Newania, Kangankunde, and Chipman Lake complexes. This series has been represented until now only by a few X-ray identifications of magnesite and three published analyses of siderite and breunnerite (magnesian siderite). Most of the siderite identified in carbonatites in the past has proved to be ankerite, but the new data define the complete solid-solution series from magnesite to siderite. They occur together with dolomite and ankerite and in one rock with calcite. The magnesites, ferroan magnesites and some magnesian siderites may be metasomatic/hydrothermal in origin but magnesian siderite from Chipman Lake appears to have crystallized in the two-phase calcite + siderite field in the subsolidus CaCO3-MgCO3-FeCO3 system. Textural evidence in Newania carbonatites indicates that ferroan magnesite, which co-exists with ankerite, is a primary liquidus phase and it is proposed that the Newania carbonatite evolved directly from a Ca-poor, Mg-rich carbonatitic liquid generated by partial melting of phlogopite-carbonate peridotite in the mantle at pressures >32 kbar.

An occurrence of yellowish green to green dufrenite in iron-formation from Proterozoic metamorphites on Kangnas farm near Aggeneys, Bushmanland, South Africa is described. The mineral formed by reaction between iron oxides and hydroxides and a phosphate, probably apatite. It was identified by its characteristic X-ray diffraction pattern, but microprobe analyses presented here indicate that the chemical compositions are extremely variable.

Manganian andalusite occurs abundantly as porphyroblasts in manganiferous metasediments subjected to contact metamorphism under hornblende hornfels facies at the contact of a picrodolerite dyke near Manbazar, Purulia District, India. The Mn2O3 content of andalusite varies from 13.2% to 19.17%, corresponding to 14.8 and 21.14 mole per cent of ‘Mn2SiO5’ respectively. Based on the analysis showing maximum amount of Mn2O3 in andalusite, the mineral formula may be represented as follows:

Other minerals in the assemblage are muscovite, manganophyllite, spessartine, piemontite, quartz, braunite, hematite and rutile. The manganian andalusite is completely fresh and appears to have formed at the expense of spessartine, piemontite and braunite during contact metamorphism. The manganian andalusite probably formed at about 600°C at around 3 kbar pressure. This is another rare example of andalusite with very high Mn2O3 (and Fe2O3) as well as that of an occurrence of abundant manganian andalusite.

Coesite has been found as an inclusion in garnet from the Mengzhong eclogite in Donghai county, northeastern Jiangsu province, eastern China. The host eclogite occurs closely associated with regionally developed gneiss and was formed under P-T conditions of about 810°C and more than 28 kbar.

Fluid inclusions in the progressively metamorphosed rocks of the Joroinen-Sulkava area, located in the south-eastern end of the Raahe-Ladoga zone near the Archaean-Proterozoic boundary, southeastern Finland, fall into four main categories: (1) H2O-rich, (2) CO2-rich, (3) mixed H2O-CO2 and (4) CH4-N2 inclusions. The samples were collected from quartz veins associated with different deformation phases (D2-D4) and from metapelites. The progressive stage of metamorphism took place mainly during the D2 deformation. The age of metamorphism and D2 deformation becomes younger with increase in metamorphic grade from amphibolite to granulite facies.

Regional distribution of the different fluid types indicates a change in fluid regime from H2O to CO2-dominant during the progressive stage of the metamorphism. H2O entered preferentially into the anatectic melt. The possibility of CO2 infiltration from deeper crust can not be excluded, because granulite facies rocks occur most probably below the lower grade zones. A zone enriched in CH4-N2 fluids is located near the lineament zones caused by the D3 deformation. This fluid type dominates the Au-bearing D2–D3 quartz lenses in the K-feldspar-sillimanite zone. Density data of early CO2 inclusions in combination with estimates of metamorphic temperatures (645–750°C) in the different metamorphic zones indicate a pressure range of 3.0–4.5 kbar, which is consistent with data derived from mineral geobarometry. The diversity of fluid types encountered in the D2–D4 quartz veins are a result of the passage of different fluids through veins at different times without re-equilibrating with the wall rocks. However, it is supposed that the CH4-N2 fluid is derived from a CO2-rich fluid with XCH4 ⩽ 0.4 by re-equilibration during its passage through the rocks.

A new occurrence of barium silicates has been found in unmetamorphosed sedimentary rocks of central North Greenland. Two different barium minerals have been identified, the Ba-feldspar hyalophane, and an unknown and hitherto undescribed hydrated Ba-silicate with an anhydrous chemical composition identical to cymrite but with about 4 moles of water in the mineral structure. Both silicates are found in a black organic-rich chert sequence in close association with baryte. No replacement textures are observed between the three Ba-minerals.

The hydrated Ba-silicate in the unmetamorphosed rock sequence of the Navarana Fjord area is considered to represent a member in a sequence of Ba-silicates from the unknown Ba-silicate with four H2O in the structure (BaAl2Si2O8·4H2O), through cymrite with one H2O (BaAl2Si2O2O8·H2O) to celsian with none (BaAl2Si2O8). This sequence might reflect the continuous release of water during prograde diagenesis and metamorphism. The association between chert and Ba minerals in the sedimentary rocks of the Navarana Fjord area is believed to reflect an addition of silica and barium by hydrothermal solutions.

Veins developed during contact metamorphism associated with the emplacement of the Cornubian granite batholith contain both H2O-rich and CO2-rich fluid inclusions. Microthermometric data indicate that unmixing of a low-CO2, low-salinity fluid occurred at 400–200°C and 1000–500 bars to produce low-density CO2-rich vapour and saline aqueous fluids (8–42 wt. % NaCl equivalent). Decrepitation-linked ICP analyses show that the cation composition of the brines is dominated by Na, K and Ca, but that significant amounts of Li, Sr, Ba, Fe, Mn, Zn and B are also present. Bulk volatile analyses confirm the dominance of CO2 over N2 and CH4 in the vapour phase, with CO2/N2 molar ratios of 15.3–28.7 and CO2/CH4 molar ratios of 66.9–292. The relative abundance of nitrogen suggests an aureole-derived ‘organic’ component is present.

The source of the fluids is ambiguous as they are intermediate in composition between ideal ‘magmatic’ and ‘metamorphic’ end-members. It is proposed that this is due to mixing of the two types of fluid in the contact aureole during granite intrusion. A model is suggested in which magmatic-metamorphic circulation occurred synchronously with granite emplacement and subsequently evolved to a meteoric-dominated system with the bulk of the ore deposits forming in response to the influx of meteoric fluids.

Ilmenites from alkaline basic dykes in the Gardar province, south Greenland have Zr contents up to 3850ppm and Nb contents up to 1030ppm. These elements substitute for Ti in the octahedral site. These are amongst the highest recorded Zr and Nb contents for ilmenites, giving distribution coefficients (Kdilmenite/matrix) for Zr up to 11.6 and Nb up to 70.3. Fractionation of ilmenite may thus have a dramatic effect on residual Zr and Nb contents. These effects are discussed in relation to the use of trace element tectonomagmatic discrimination diagrams.

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.

High-resolution transmission electron microscopy of biogenic carbonate minerals is hampered by a lack of stability during exposure to the electron beam. However, aragonite in bivalve shells may be successfully imaged using a modification of the ‘minimal-exposure technique’ of Williams and Fisher (1970). Diffraction patterns taken before and after beam exposure indicate that the aragonite remained stable during imaging. The procedure described here should prove useful for further studies of the ultrastructure and/or the diagenesis of biogenic carbonate minerals.

New chemical data show that the two main granite types (G1 and G2) cannot be discriminated, but that microgranite sheets/dykes (G3) are significantly different and more evolved, largely as a result of biotite, accessory mineral, and plagioclase fractionation. The Lundy granite is similar to other Tertiary granites of Scotland and Ireland, in age, setting, possible high-temperature mineralogy, relationship to basic magmatism, and REE patterns. These features and a highly evolved chemistry suggest derivation from an unexposed more ‘primitive’ granite that, in turn, had a basaltic parentage. However, similarities with the nearby S-type Hercynian granites, such as high aluminium saturation index (and normative corundum), high trace alkali, Nb, and F contents, low Zr, and high initial Sr ratio suggest a significant crustal component. The problem is resolved by proposing either mixing of silicic magma derived by strong fractionation of basaltic magma with anatectic magma from a pelitic/semi-pelitic crustal source, or fractionation of basaltic magma heavily contaminated by assimilated crustal material. Both origins would yield the high REE contents and fiat REE patterns of a ‘primitive’ granite magma. Fractionation, perhaps of hornblende initially, and later, of biotite and accessory minerals together with feldspars, would produce the small volume of highly fractionated Lundy granite.

Fluids, together with alteration and ore mineral assemblages, were studied in representative hydrothermal gold-bearing quartz veins from the western part of the Variscan belt in France (La Bellière, Montagne Noire district, Villeranges-Le Châtelet district, and Limousin province). Petrographic studies of the relationships between ores, fluid inclusions, microfracturing and quartz textures show that chronological and genetic relationships between gold deposition and fluid trapping may be very complex and difficult to establish for veins which show multi-stage fracturing and shearing. Systematic studies of secondary fluid inclusions in microcracks and recrystallized zones of the early quartz veins indicate two contrasting physical-chemical conditions: 1 relatively high temperature (250–400°C) and pressure (>1 kbar) event with CO2-CH4-H2S-N2 (±H2O-NaCl)-rich fluids related to the early sulphide deposition; 2 lower temperature (150–250°C) and pressure with aqueous fluids related to the late native-gold-sulphide (or sulphosalt) assemblage, which constitutes the economic ores in some deposits.

In deposits where gold occurs predominantly in a combined state within arsenopyrite and pyrite (Châtelet and Villeranges), primary fluid inclusions in authigenic quartz combs cogenetic with arsenopyrite are almost purely aqueous (H2O-NaCl) and have a low salinity (1–4 wt. % NaCl). P-T conditions (150–250°C), nearly hydrostatic pressures) are similar to those of the second stage in the multi-stage quartz veins.

Consideration of chemical equilibria in the C-O-H-N-S system using microthermometric and Raman spectrometric analysis for the fluids, together with data obtained from mineralogical studies, show that during gold deposition, fO2 was below hematite-magnetite buffer at Villeranges and around the Ni-NiO buffer at La Bellière and Montagne Noire. fS2 calculations based on H2S analyses are in good agreement with mineral assemblage estimates and close to that fixed by the pyrite-pyrrhotite boundary at high temperature. Ore fluid pH was significantly lower than in the host rocks as shown by the complete alteration of the host rocks into a quartz-K-mica assemblage. The data illustrate that during the late Hercynian, fluid circulation evolved from high P-T conditions, in some cases linked to late magma intrusions, towards conditions typical of later hydrothermal systems of the geothermal type.

A zeolite found in a soil profile developed in Danian chalk was studied. The results showed that it is a heulandite, temperature-stable to above 600°C with a Si/Al ratio of 2.88 and almost completely K-exchanged. The mineral probably formed under burial diagenetic conditions in the chalk formation.

The unstable glassy component of the Oligocene tuffaceous sediments of the Metaxades area, Thrace, Greece, has undergone extensive zeolitic diagenetic alteration. The authigenic minerals occur as crypto- to micro-crystalline aggregates making up most of the matrix in the altered tuffs and as precipitates in cavities produced by dissolved glass fragments. Glass-shard pseudomorphs are ubiquitous and most of them are partly filled by one or more of the minerals smectite, heulandite, mordenite and silica.

The heulandite group zeolites are mostly high-silica calcium-rich heulandites showing intermediate thermal behaviour between most heulandites and clinoptilolites. Their Si/Al ratios are similar to clinoptilolite (4.74–5.19) but their divalent/monovalent cation ratios (1.5–3.24) are partly superposed onto the ratios of heulandite group 1 and 2 and differ considerably from the values of the relevant ratio in clinoptilolite. Rare K-rich clinoptilolite crystals have been identified in one sample only.

Based on field observations, compositions and paragenetic relationships of coexisting authigenic minerals and the absence of critical phases such as laumontite, analcime or authigenic albite, it is suggested that the Metaxades pyroclastic rocks underwent burial diagenesis intermediate between Iijima's (1978) zones II and III commonly developed in silica saturated environments.

The upper Proterozoic Cuiabá group of Mato Grosso, Brazil, is composed of low-grade clastic meta-sediments which have been folded by several successive tectonic events. Three generations of quartz veins are associated with the structural evolution of this area. The first veins are deformed by the main tectonic phases and show a complex deformational patterns. The second set is parallel to the cleavage and was formed syntectonically during the main folding phase, whilst the last quartz veins are related to a later stage of deformation. A systematic study of fluid inclusions in relation with a statistical study of microstructural markers (fluid inclusion trails, opened microcracks) was carried out on quartz veins from three localities. On the basis of microthermometric studies and Raman spectrometry analysis, four differents types of fluids have been distinguished, each trapped in specific fluid inclusion trails: (i) CO2-rich liquids and vapours (Lc, Vc) at Casa de Pedra, (ii) Lc and Vc inclusions with variable amounts of CO2, CH4, N2 in the vapour phase at BR-70, (iii) CH2-N2-rich vapours (Vn-m), and (iv) aqueous inclusions (L) with variable salinities representing the last fluid generations at all localities.

At Casa de Pedra and BR-70, most fluids are observed within the three generations of quartz veins, indicating an important fluid circulation associated with the last phase of brittle deformation. Fluid inclusions of type (iii) and (iv) are oriented along several well defined directions. The study shows the importance of integrated microstructural and fluid-inclusion studies for understanding the geometry and chronology of fluid circulation.

Damaraite, ideally 3PbO.PbCl2, is a new mineral which occurs with jacobsite, hausmannite, hematophanite, native copper, an unnamed Pb-Mo oxychloride, calcite, and baryte, in specimens from the Asis West section of the Kombat mine, Namibia (South West Africa). Damaraite is colourless and transparent with a white streak, and adamantine lustre. It is brittle with an irregular to subconchoidal fracture and a cleavage on (010). The mineral has a low reflectance, a weak bireflectance, barely discernible reflectance pleochroism, from grey to slightly bluish grey in some sections, and is weakly anisotropic. Reflectance data in air and in oil are tabulated. Colour values relative to the CIE illuminant C for the most strongly bireflectant grain are, for R1 and R2 respectively:

It has a VHN50 of 148 (range 145–154) with a calculated Mohs hardness of 3. X-ray powder diffraction studies give the following parameters refined from the powder data: orthorhombic; space group Pma2, Pmam or P21am; a 15.104(1), b 6.891(1), c 5.806 (1)Å; V is 604.3 (4)Å3 and Z = 3. Dcalc 7.84 g/cm3. The strongest six lines of the powder pattern are [d in Å (I) (hkl)]: 2.902 (10) (121,002); 2.766 (10) (510,221); 2.877 (9) (411); 3.164 (6) (401); 3.135 (6) (220); 1.747 (b) (313,721,531). The name is for the Damara sequence which hosts the Kombat deposit.

Pollucite is a silicate mineral of the rare element caesium, occurring in granitic pegmatites. Experiments have been carried out at 450, 600, and 750°C, 1.5 kbar, to study the equilibrium between pollucite, albite and the co-existing hydrothermal solution. When pollucite co-exists with albite, the alkaline composition of the solution is buffered. The Cs/Na ratio of the solution has been determined to be 0.11 at 450°C 0.22 at 600°C and 0.23 at 750°C. Pollucite contains about 15 mol.% of sodium, whereas albite is almost purely sodic. In nature, pollucite with more than 82 mol.% caesium has never been found. This can be explained by the absence of solutions in granitic pegmatites having a higher Cs/Na ratio than those determined by us.