Olivine (ol) leucitite lavas from Northeast China contain hyalophanes with contrasting Ba-zoning patterns. The hyalophanes occur: (1) in a magmatic inclusion (DZ2n), consisting of barian-titanian phlogopite + hyalophane + leucite + sodalite, and (2) as a mantle surrounding a sanidine megacryst (DZ19). Hyalophanes contain 4.6-20.2 mol.% celsian (Cn). The DZ2n hyalophane is normally zoned with respect to Ba (decreasing Ba toward rim), whereas the hyalophane mantle of megacryst DZ19 is reversely zoned. DZ2n probably crystallised from an extensively evolved (>80 wt.% crystallisation) potassic melt derived from a primitive magma chemically similar to the host, at relatively low temperatures and pressures (e.g. T-720°C P∼2 kbar). Competition with barian-titanian phlogopite for Ba, and limited Ba supply from the residual melt are the main cause for the normal Ba zonation. Sanidine megacryst DZ19 originated as a high P-T product (e.g. T > 950°C P > 15 kbar) of an evolved leucite (lc) basanite/trachybasalt genetically related to ol-leucitites. Subsequently, it was incorporated into the host ol-leucititic magma at which point it was partially resorbed and then mantled by hyalophane. An increase in KBaaf/liq values with decreasing temperature and pressure and cocrystallisation of the hyalophane mantle with Ba-free phases may have caused the unusual reverse zonation.

Alternating eclogitic amphibolites, mica schists and orthogneisses in the Schobergruppe to the south of the Tauern Window suffered a post-Upper-Ordovician progressive deformation D1-D2 which produced parallel planar-linear structures in all the rocks. Zoned garnets, preferentially oriented zoned clinopyroxenes (Jd 35-42%) and albite (An 7-9%) give evidence of high-pressure metamorphism (550-650°C 14-16 kbar) of the metabasites. Ca-amphiboles crystallized during subsequent decompression. In a kyanite-staurolite-garnet mica schist 300 metres below the metabasites, garnetbearing assemblages grew synchronous with the development of foliations S1 and S2. Garnets are zoned with increasing XMg and decreasing-increasing-rcdecreasing Xca from cores to rims. Albitic plagioclase (An 1-3%) and micas are enclosed in garnet cores and rims, are in contact with garnet, and occur with garnet in microlithons. When these minerals are used for geothermobarometry, a prograde P-T evolution (460 to 680°C with coeval pressure variations which reach high-pressure conditions can be estimated. This suggests that garnet-plagioclase geobarometry with albitic plagioclase works in the relevant P-T field. Similar garnet zonation trends and a similarly shaped P-T path from mica schists of an adjacent region with late-Variscan cooling ages, points to an eady-Variscan age of the syn-D1-D2 high-pressure and subsequent amphibolite-facies metamorphism.

Low-salinity fluids (T > 200°C reduced S, modest CO2) and high geothermal gradients are common to many gold deposits and provinces. In contrast, host rocks, hosting structures, depth of formation (in the crust during deposition), subsequent metamorphic overprint, alteration mineralogy and isotopic signatures can vary dramatically within single deposits or provinces. Gold deposits with co-product base metals are an exception to the above comments, and probably relate to saline fluids.

The low salinity fluids inferred for major gold-only deposits are not easily explained by seawater, basinal brines, meteoric fluid or common magmatic processes. In contrast, metamorphic devolatilisation of mafic/greywacke rocks is one effective way to produce low-salinity metamorphic fluids with characteristics matching the gold fluids. Such an origin also explains the link to geothermal gradients.

The transition from chlorite—albite—carbonate assemblages to amphibole-plagioclase assemblages (commonly greenschist—amphibolite facies boundary) involves considerable loss of metamorphic fluid whose composition is buffered by the mineral assemblage, and is a function of P and T. This low salinity, H2O-CO2 fluid is evolved at T > 400°C commonly carries reduced sulphur, and may contain Au complexed with this sulphur. This auriferous fluid is likely to mix with other fluid types during times of elevated temperature, especially magmatic fluids at depth, and upper crustal fluids at higher levels.

Gold deposits in Archaean greenstone belts exhibit good evidence of low salinity, H2O-CO2 fluids of T > 300°C these include examples from Canada, Australia, Brazil, Zimbabwe, India, and South Africa. Turbidite-hosted (slate-belt) deposits exhibit similar evidence for such fluids but commonly with appreciable CH4; the Victoria and Juneau (Alaska) goldfields are examples. The Witwatersrand goldfields also show evidence of low salinity, H2O-CO2 fluids carrying reduced sulphur and gold, but their distribution and timing are not well established. Epithermal (sensu lato) gold deposits have evidence for low salinity fluids carrying Au and S, but are much more diverse in character than those from the previously mentioned gold provinces: this probably arises from mixing of several fluid types at high crustal levels. Together these four types of gold provinces account for over 80% of the primary gold mined to date.

Pyrite, the most widespread and abundant of sulphide minerals in the Earth's surficial rocks, commonly constitutes the primary opaque phase in ore deposits. Consequently, an understanding of the behaviour of pyrite and its relationships with coexisting phases during the metamorphism of pyritebearing rocks is vital to the interpretation of their genesis and post-depositional history. Metamorphism is commonly responsible for the obliteration of primary textures but recent studies have shown that the refractory nature of pyrite allows it to preserve some pre-metamorphic textures. Pyrrhotite in pyritic ores has often been attributed to the breakdown of pyrite during metamorphism. It is now clear that pyrrhotite can be primary and that the presence of pyrrhotite with the pyrite provides a buffer that constrains sulphur activity during metamorphism. Pyrite-pyrrhotite ratios change during metamorphism as prograde heating results in sulphur release from pyrite to form pyrrhotite and as retrograde cooling permits re-growth of pyrite as the pyrrhotite releases sulphur. Retrograde growth of pyrite may encapsulate textures developed during earlier stages as well as preserve evidence of retrograde events. Sulphur isotope exchange of pyrite with pyrrhotite tends to homogenise phases during prograde periods but leaves signatures of increasingly heavy sulphur in the pyrite during retrograde periods.

Lamproites with high MgO, high SiO2 affinity are abundant only in SE Spain where the Cancarix outcrop (in the province of Albacete) occurs. The rocks of Cancarix are peralkaline, saturated to oversaturated in silica, very high in K2O, Th and LREE. The mineralogy and petrography show some variations which depend on the conditions of emplacement and rate of cooling of the magma. The following phases may be present: olivine, phlogopite, K-amphibole, clinopyroxene, sanidine, orthopyroxene, apatite, and, in minor amounts, Cr-spinel, minerals of the pseudobrookite group, ilmenite, roedderite, dalyite, carbonate, analcime (probably pseudomorphous on leucite), a silica phase, rutile, pyrochlore (?), britholite (?) and glass. The lamproites of Cancarix contain Cr-Zrarmalcolite, which is typical of lunar basalts and which has been found also in kimberlites. The composition of early magmatic spinel and the occurrence of Cr-Zr-armalcolite indicate low oxygen fugacity for the primitive magma and related mantle source, in agreement with recent experimental data on lamproitic systems. The redox conditions changed during crystallisation, leading to increase of the Fe3+/Fe2+ ratio in the system. During the later stages of crystallisation, the residual melts/fluids were depleted in alumina and enriched in several components, e.g. Na, Zr, Fe, REE, C1, etc. stabilising Na-Fe-clinopyroxene, dalyte, arfvedsonitic rims around K-richterite and other alumina-free phases which, on a chemical basis, have been identified as britholite and pyrochlore. Rough comparison with experimental systems and the geochemistry of the rocks suggests that the magma was generated at shallow depth (≪20 kbar) in the lithospheric mantle, which, after early depletion, underwent strong enrichment in many 'incompatible' elements.

Ultramafic to marie plutons in the Olyutor Range, North Kamchatka, represent the magmatic roots of a late Eocene arc, related to the westward subduction of the Komandorsky Basin beneath the Asian continental margin. Olyutor Range plutons are concentrically zoned with cumulate dunite cores mantled by a wehrlite-pyroxenite transitional zone and, in turn, by a narrow gabbroic rim.

Spinel is a common accessory mineral in these arc plutonics, and we present analyses of spinels from a range of lithologies. A continuous compositional trend is observed from Cr-spinel in the ultramafics to Cr-rich magnetite in marginal gabbros. Complex chemical zoning patterns within individual spinel grains suggest an interplay between fO2, fractionation, volatile content and subsequent sub-solidus reequilibration of spinel with co-existing silicates (mainly olivine).

In general, the spinels from magmatic arc environments are characterised by high total Fe and high Fe3+ contents compared to MORB and boninitic spinels and higher Cr-values relative to oceanic basin spinels. These differences imply a high oxygen fugacity during arc petrogenesis. Differences are also observed between plutonic spinels from arcs and low-Ti supra-subduction zone ophiolites. Low-Ti ophiolitic spinels are generally poorer in iron and richer in Cr, and hence are similar in composition and perhaps tectonic setting to fore-arc boninitic spinels.

Thermoluminescence (TL) studies of insulators, including crystals of minerals such as calcite, quartz or zircon, have resulted in the development of a wider range of applications in the fields of radiation dosimetry and archaeological and geological dating. Most conventional TL measurements are made by recording light emission during heating by means of broad-band optical filters and blue-sensitive photomultiplier tubes. Much more information may be gained by monitoring the details of the emission spectrum during thermoluminescence. TL spectra of minerals exhibit changes as a result of crystal purity, radiation dose, dose rate and thermal history. This paper exemplifies the additional information available as a result of spectral studies, and focuses on investigations undertaken by the University of Sussex TL group. Examples include work on calcite, fluorite, zircon and feldspars.

Ammonium analyses of representative rocks from the Rosses granite complex (Ireland) and their constituent mineral show that any variation of magmatic origin has been completely obscured by pervasive hydrothermal alteration. The altered rocks are strongly enriched in the ammonium ion, most of which is held by chloritized biotite and sericitized plagioclase. The present ammonium content of the Rosses granites averages 13 ppm, but the original ammonium content of the magmas is estimated to have been less than 5 ppm. Potassium feldspars may preserve a better record of the original magmatic ammonium content than the whole rocks or the biotites.

Mesothermal, gold-bearing quartz veins are widespread within allochthonous terranes of Alaska that are composed dominantly of greenschist-facies metasedimentary rocks. The most productive lode deposits are concentrated in south-central and southeastern Alaska; small and generally nonproductive gold-bearing veins occur upstream from major placer deposits in interior and northern Alaska. Oreforming fluids in all areas are consistent with derivation from metamorphic devolatilisation reactions, and a close temporal relationship exists between high-T tectonic deformation, igneous activity, and gold mineralization. Ore fluids were of consistently low salinity, CO2-rich, and had δ18O values of 7‰- 12‰ and δD values between −15‰ and −35‰. Upper-crustal temperatures within the metamorphosed terranes reached at least 450-500°C before onset of significant gold-forming hydrothermal activity. Within interior and northern Alaska, latest Paleozoic through Early Cretaceous contractional deformation was characterised by obduction of oceanic crust, low-T/high-P metamorphism, and a lack of gold vein formation. Mid-Cretaceous veining occurred some 50-100 m.y. later, during a subsequent high-T metamorphic/magmatic event, possibly related to extension and uplift. In southern Alaska, gold deposits formed during latter stages of Tertiary, subduction-related, collisional orogenesis and were often temporally coeval with calc-alkaline magmatism.

Metamorphosed stratabound iron- and base-metal sulphide deposits often exhibit microtextures in which fractures in cataclastically-deformed pyrite porphyroblasts are filled with matrix sulphides; chalcopyrite, sphalerite, pyrrhotite or galena. Discussions of such textures have mostly centred on whether solid-phase or fluid-phase mechanisms were responsible for the movement of the matrix sulphides.

The small Zn-Cu sulphide body at Gressli, in the central Norwegian Caledonides, shows these textural features to an extreme degree. Both chalcopyrite and sphalerite show heavy replacive relations to the cataclastically deformed metablastic pyrite, along fracture walls and grain boundaries. They also occur injected along the opened-up triple junctions of foam-textured pyrite. In addition, parts of the ore show patchy quartz with clear replacive relationship to all three sulphides, a feature not often reported from such ores. Such textures can be interpreted to support a mobilisation sequence chalcopyrite-sphalerite-quartz within the Gressli ore. Their extent and degree of development indicate that fluid-phase mobilisation of the three minerals must have played a dominant role. Chalcopyrite and sphalerite are most likely derived from within the ore-mass itself; an external source for the SiO2 seems most probable, in the form of metahydrothermal solutions moving along retrograde shear zones at or near ore-walls.

Neutron diffraction texture goniometry indicates that naturally deformed polycrystalline pyrite ores from Mt. Lyell (Tasmania) and Degtiarka (Ural Mountains) have weak lattice preferred orientations. During experimental deformation involving dislocation flow at elevated temperatures and pressures, these initial fabrics have been modified to produce new lattice preferred orientations.

Polycrystalline pyrite form Mt. Lyell (B-1) has an initial <111> - fibre texture perpendicular to a grain-size layering. After 24% shortening perpendicular to the <111> - fibre axis at 700°C a new, but weak <100> texture has developed parallel to the shortening axis. The Degtiarka pyrite (PN-6) initially has two weak fibre components. The somewhat stronger component is a <100>-fibre texture, similar to that in the experimentally deformed B-1 pyrite. The other one is a <111> - fibre texture similar to the intital B-1 preferred orientation. After 30% shortening oblique to both initial fibre axes at 600°C weak <110>- and <111>-fibre textures have developed. The experimentally produced fabrics have developed during deformation involving dislocation flow, dynamic recrystallisation and some microcracking. Intergranular sliding may also have been involved. Differences between lattice preferred orientations developed in the 600°C and 700°C experiments are interpreted to indicate a change in the dominant flow mechanism with changing temperature.

In comparison with other cubic minerals that have been deformed experimentally by dislocation flow mechanisms, the pyrite shows an unusually weak preferred orientation which can be detected only by means of neutron diffraction texture goniometry.

The symmetry of diamond is still sometimes questioned. Most people agree that diamond belongs to the space group Fdm and therefore to point group . Some however, on account of the existence of a few natural tetrahedral diamonds, have assigned diamond to the point group 3m. We report here on an X-ray topographic investigation, using both conventional and synchrotron sources, of eleven natural tetrahedral diamonds. Two large specimens (from the Alpheus Williams' collection) were studied and found to consist of two portions, unequal in size, that were twinned on a (111) plane. Another diamond (from Professor R. A. Howie's collection) was found to contain two non-parallel (111) twin planes with the diamond filling the space between them, giving the crystal a tetrahedral morphology. Four tetrahedral diamonds (selected by Tolansky) were shown to be either twinned on a (111) plane, or cleavage fragments consisting of one component of a made or single crystals that had been plastically deformed. Similar results were found for some diamonds from the Argyle Mine. Our findings are consistent with diamond belonging to the holosymmetric class () rather than to the hemihedral class (3m).

There is extensive textural evidence for sulphidation in the Middelvlei Reef of the Carletonville Goldfield, South Africa. Secondary iron sulphides have replaced sand- and pebble-sized elasts in conglomerate, as well as matrix material in both conglomerate and quartzite. Within the Middelvlei Reef there is a close correspondence between the intensity of sulphidation and areas of greater modal muscovite, and there is less sulphidation where chloritoid dominates. Both pyrite and minor pyrrhotite are widespread. The timing of the sulphidation appears to be post-depositional but the relative importance of diagenetic and syn-metamorphic processes cannot be determined using textural criteria. The absence of retrograde effects suggests that sulphidation occurred prior to or during peak metamorphism. The distribution and intensity of sulphidation and phyllosilicate alteration indicate that these processes may be more significant in the Witwatersrand than has generally been thought. These processes should be considered in all future genetic models.

Sulphide minerals and their analogues yield gases as a result of oxidation reactions. Even where sulphide minerals are in contact with mildly reducing groundwaters, S2- ions pass into solution and their dispersion patterns can be detected in soil as acid-released H2S. In more oxidising conditions, the metastable gases COS and CS2 are generated. Anomalous dispersion patterns of COS have been reported in soils above more than ten sulphide ore deposits, many of them concealed beneath transported exotic overburden. High concentrations of CS2 occur in the soils over several of the same deposits and uniquely reflect others. Anomalies of SO2 over sulphide deposits are confined to arid terrains. Certain anomalous dispersion patterns of arsenic and tellurium in soils are attributed to the generation and migration of unspecified gases from the oxidation of arsenide and telluride minerals.

Unusual irregular galena crystals and whiskers were found in close proximity in some druse cavities from the Gradishtc hydrothcrmal lead-zinc deposit in the Madan ore district, Bulgaria. The following crystal forms were observed: (1) straight thin [110] whiskers and thicker needles; (2) kinked whiskers; (3) curvilinear whiskers; (4) complex tortuous whiskers composed of segments with varying directions—[110], [100], [211], (5) thicker irregular elongated crystals. Combinations of these forms occur also. The detailed SEM study shows that all these formations are single crystals of extreme anisometricity, bounded by octahedral and cubic faces as well as by stepped surfaces of these forms. Surface structures such as longitudinal grooves, jagged edges, striations, pits, etc., are abundant.

It is assumed that these highly non-equilibrium crystals with large surface areas were formed through rapid directed growth from highly supersaturated solutions under a diffusional regime. Such special environments arose in the ore veins as a result of tectonic shocks leading locally to a drastic volume increase and P and T decrease in the solutions.

Multi-element crush-leach analysis of H2O-CO2 inclusion fluids from a suite of six vein samples from gold-quartz veins in the Brusson district demonstrates that their solute chemistry (c. 5 wt.% NaCl equivalent) is dominated by sodium chloride with lesser amounts of calcium bicarbonate, potassium chloride and sodium bicarbonate. The samples have been analysed both for gas species (CO2, H2O, N2 and H2S) and for Na, K, Li, Rb, Ca, Mg, Sr, Ba, Fe, Mn, Zn, Pb, Cu, Al, As, B, SO42−, F, Cl, Br and I. The fluids contain appreciable H2S (>10−3 molal), which correlates with the contents of As, CO2 and B. Concentrations of many cations remain similar irrespective of wall rock, but there is evidence of leaching of Li, and possibly I, from some wall rocks. Large variations in the K-content of the fluid may result from precipitation of sericite. The bicarbonate concentrations in the fluids, estimated from charge imbalance, are substantially less than their total CO2 content when trapped as single phase fluids, indicating a low pH. Sulphate : sulphide ratios suggest relatively reducing conditions, which is consistent with Fe concentrations significantly greater than Mn.

The gold-quartz veins formed as H2O-CO2 fluids of modest salinity and very uniform composition ascended from depth. Halogen ratios of the fluids are consistent with an ultimate origin for these fluids from deep-penetrating surface or connate waters although such a model requires extremely low fluid : rock ratios, to account for the hydrogen isotope composition of many similar deposits. There is as yet insufficient reference data to use halogen ratios as a rigorous test for the alternative model of an origin for the fluid by metamorphic devolatilisation.

Carbonado and yakutite are both porous aggregates of polycrystalline micrometre-size diamond, with very different characters from those of monocrystalline diamond. The genesis of carbonado is very controversial, whereas yakutite is thought to have been formed by meteorite impact. Neutron activation analyses of trace elements in carbonado and yakutite indicate that their rare earth element (REE) abundance patterns have common characteristics: heavy REEs are not much depleted and a negative Eu anomaly is observed. These patterns are quite different from those of kimberlite and monocrystalline diamond and are similar to those of crustal materials such as shale, supporting the hypothesis of a crustal origin for carbonado and yakutite.

Chalcopyrite samples from Mt Isa, Australia have been experimentally shortened by up to 30% at temperatures up to 450°C at a constant confining pressure of 300 (400) MPa, and different strain rates in the range from 10-5 to 10-8 sec-1. After deformation, the X-ray pole figures show a maximum of (220/204) perpendicular to the compression axis for each of the samples, which has already been described for room temperature experiments by Lang (1968). The overlapping pseudocubic peaks of chalcopyrite can be separated into true tetragonal peaks by neutron diffraction texture analysis using a position sensitive detector combined with profile analysis (Will et al., 1989). The five investigated samples each show a combination of two or four main orientations of the crystallites, which represent neither a pseudocubic nor a tetragonal fibre texture.