Fluid inclusion data and geochemical evidence lead to a genesis of Ba-F (Pb-Zn) lodes of the Spanish Central System as related to fluid mixing of hot (>300 °C), low saline (<0.6 molal), Na-K deep fluids and cool (<100 °C), oxidized, more saline (>2.8 molal), Na-K-Ca-Mg brines of phraeatic origin. Ore formation took place at relative low depth and temperatures (from 270 to 120 °C) in a regime of increasing fO2, (Ca + Mg)/Na ratio and pH of the fluids towards the surface. Such evolution destabilizes the chloride metal complexes, allowing for the precipitation of Zn and Pb carried by the deep solution.

Vertical fluorite-baryte zonation is explained in terms of mineral solubilities. Fluorite deposition in the deeper mineralized zone is related to a slight increase of mCa2+ of the fluid in the lower part of the fluid mixing zone; further increase of mCa2+ and mMg2+ towards the surface promotes fluorite dissolution. Increase of fO2 in the shallow part of the hydrothermal system promotes the oxidation of , resulting in baryte formation.

We propose an ore genesis related to fluid mixing in shallow hydrothermal systems associated with an extension of Permo-Triassic age. Such interpretation is in agreement with the present day ideas for the genesis of many of the Ba-F deposits in the Hercynian Belt of Europe.

The Neves-Corvo mine opened officially in December 1988 and it is already the biggest producer of copper in the Iberian Pyrite Belt (IPB). Tin production started in 1990. The ore deposits of the IPB are related to felsic submarine volcanism which developed during the lower Tournaisian to the middle Visean. At the end of the first phase of Hercynian deformation in the middle Westphalian, the ore deposits were affected by low-pressure metamorphism producing schistosity and prehenite-pumpellyite greenschist facies assemblages in the volcanogenic sediments of the IPB.

The unique nature of the mineralogy of the Neves-Corvo deposit compared with other IPB deposits is mainly a result of the introduction of later Cu-rich hydrothermal solutions to the primitive ore pile and the presence of tin mineralisation. The cupriferous ores are rich in tetrahedrite-tennantite, stannite, kesterite, stannoidite and mawsonite.

Cassiterite occurs in Neves-Corvo: (a) as thin layers of euhedral crystals in cupriferous ores, partially replaced by chalcopyrite; (b) in the schistosity of a banded black shale chalcopyrite hanging wall formation; (c) as metre-sized lenses of massive cassiterite overlying the cupriferous ores.

The ore textures at Neves-Corvo are complex, due to intergrowths of fine colloform pyrite with the base metal minerals. Because of the low grade of metamorphism, colloform, geopetal and soft-sediment diagenetic features are preserved in the ‘complex ores’. These ‘complex ores’ have contents of 0.5% Cu, 1% Pb and 5.5% Zn. In copper-rich ores (7.9% Cu and 1.4% Zn), replacement of the primary ore by chalcopyrite has obliterated most of these textures and produced fine chalcopyrite-tetrahedrite-pyrite intergrowths. The textures clearly indicate the genesis of these ores but they impose a practical problem in recovery of the metals. There is no clear correlation between these textures and the ore classification used at the mine, but an understanding of the textures is vital since the ‘complex ores’ require fine grinding to achieve liberation and the fine grinding adversely affects the froth flotation processing of the ore.

The implications of the complex sulphide textures for ore beneficiation have been studied using reflected light microscopy, with determination of modal analyses and grain-size distributions of free particles and middlings from concentrates and tailings.

The outcome of a one-year intensive study is that the ore microscopy laboratory at the mine now produces daily information about the textures of the feed ores so that metallurgical engineers can optimise the performance of the ore dressing plant.

The infrared spectrum of kegelite has been measured and is discussed. The infrared spectra of 1 : 1 molar mixtures of leadhillite with pyrophyllite or with muscovite resemble the spectrum of kegelite, the chemical formula of which is a 1 : 1 stoichiometric sum of those of pyrophyllite and of the leadhillite polymorphs. Kegelite is not a physical mixture of these species, but its structure may be an interlayering of phyllosilicate and leadhillite-like structures within the unit cell. The unit cell parameters of pyrophyllite-1Tc and the leadhillite polymorphs are compatible with each other and can be combined to give a cell with parameters close to those of the kegelite cell. A structural model for kegelite on these bases is suggested, which is also consistent with its thermal analysis. The formula of kegelite can be written as Pb8(SO4)2(CO3)4(OH)4(AlOH)4(Si4O10)2.

Samples from a traverse across the Blå Måne Sø perthosite unit in the Tugtutôq Central Complex of the Gardar province, South Greenland have been examined for cathodoluminescence characteristics, microporosity and δ18O isotopic values. Reddening of cathodoluminescence colours in alkali feldspars (normally blue) from the unit may be correlated with increased microporosity of the feldspars as determined using scanning electron microscopy. δ18O values of all samples lie within the range of values expected of juvenile fluids, independent of the level of alteration indicated by cathodoluminescence studies.

Observations are consistent with previous suggestions that levels of alkali feldspar microporosity and levels of fluid alteration (as determined by cathodoluminescence of alkali feldspars) are related phenomena. Oxygen isotope ratios suggest that the fluid is largely juvenile in origin, with, perhaps, some meteoric (low δ18O) component.

The western Rhodope massif contains a significant number of ‘battery grade’ Mn-oxide deposits which are best developed in the area near Kato Nevrokopi, Drama district, N. Greece. Economic Mn-oxide ore concentrations are confined to fault zones and related karsts in marbles. The mineralisation has formed by weathering of hydrothermal veins that were genetically related to Oligocene magmatism.

At Kato Nevrokopi, progressive and continuous weathering of primary, hydrothermal veins of rhodochrosite, mixed sulphide, quartz and ‘black calcite’ (calcite and todorokite) has resulted in the formation of the assemblage MnO-gel-(amorphous Mn-oxide)-todorokite-azurite-goethite-cerussite in the veins and the assemblage MnO-gel-nsutite-chalcophanite-birnessite-cryptomelane-pyrolusite and malachite and amorphous Fe-oxides in karstic cavities.

The fs2 and fO2 of the hydrothermal fluids increased with time. The breakdown of the hypogene Mn-carbonate was aided by the production of an acidic fluid due to the oxidation of sulphides. Precipitation of the supergene ores was caused by neutralisation of the fluids due to reaction with the host marble and to mixing of relatively reduced fluids with oxygenated surface water in a fluctuation water table regime. Zinc was also mobile during weathering and became concentrated in the intermediate Mn-oxides, effectively stabilising their structures. The mineral paragenesis records the progressive oxidation of the ore and the appearance of less hydrated Mn-oxides, low in alkalis and alkaline earths.

The amygdaloidal carbonatite lavas at Qasiarsuk have a primary phenocryst assemblage of calcite, fluor-apatite and magnetite set in a groundmass of calcite, apatite and iron oxides, and minor dolomite. Cathodoluminescence reveals a complex history, both for the major minerals which show zonal growth, and for important Nb and REE accessory phases which include pyrochlore and perovskite. The REE reside in fluor/hydrous-carbonates included exclusively in apatite. These REE minerals are similar to synthetic phases from hydrothermal experiments, but probably crystallised in equilibrium with a late-stage volatile-rich carbonate melt. Apart from low-temperature alteration, the rocks have been little disturbed since their extrusion during the earliest phase of development of the Gardar Alkaline Igneous Province.

The Mari Rosa mine lies within a low-grade Precambrian alternating series of black shales and metagreywackes in the Spanish Hercynian massif. There are two generations of mineralized veins: V2, gold-(stibnite)-bearing quartz veins, parallel to the main cleavage, and V3, stibnite-bearing quartz veins which postdate the main deformation event.

Four main types of inclusions have been identified. Type I, II and IV are aqueous-carbonaceous inclusions, with variable degrees of filling, while type III are non-aqueous and typically single-phase at room temperature. Except for type I (absent in V3), similar inclusions have been observed in both V2 and V3 veins. Gas compositions are always characterised by CH4-N2-CO2 assemblages, ranging from CO2-rich mixtures in the earliest inclusions (type I), to N2-rich mixtures in the latest inclusions (type IV).

Gold precipitation in V2 veins can be related to type I inclusions at T > 380°C (TH = 300–380°C). A subsequent drop in XCO2 and cooling are recorded in type II and III inclusions, interpreted to be the result of unmixing of a previously homogeneous fluid derived from type I. This boiling would provoke the precipitation of stibnite at 300°C and 1 kbar. The type IV inclusions, which are the richest in H2O, represent a late fluid circulation at lower temperatures (TH = 190–280°C).

The chain of Late Subhercynian granitoids can be traced along the Srednogorie-Istranca-Pontid belt. The Demirköy pluton outcrops in the Istranca segment. The rocks of the pluton range from diorite through grandiorite to perthite granite with granodiorite predominating. On the basis of 25 chemical analyses, the intrusive setting of the granitoid has been investigated. Calcic to calc-alkaline and peraluminous to metaluminous character indicate a subduction-related origin. Low to moderate concentrations of the large-ion lithophiles (LIL), high field strength elements (HFS), light rare earth elements (La, Ce) and low HFS/LIL ratios indicate a mantle-derived magma with subduction-related enrichment. Trace element discrimination diagrams such as Rb/Zr-Nb, Rb/Zr-Y, Rb-SiO2 and Rb-(Nb + Y), are particularly indicative of normal arc-setting for the samples.

The Demirköy granitoid is chemically indistinguishable from the Upper Cretaceous granitoids of Strednogorie to the west and the Pontids to the east. This extensive maximum of plutonism can be considered as a time marker in the northern Tethys subduction system.

Combined structural and textural studies of the quartz veins of the Panasqueira W-Cu-Sn deposit of central Portugal have revealed the presence of coeval forms of crack-seal and cavity-fill mineral textures. The textures result from the dilational and infilling histories of brittle fractures produced within the host rock by the intrusion of pressurised fluids. Crack-seal textures were produced wherever or whenever crystal growth rates matched or were greater than fracture dilation rates, whereas cavity-fill textures developed wherever or whenever dilation rates were quicker than those of crystal growth. Rates of dilation within the blade-like fissures were naturally lowest at the edges, where types of crack-seal textures were produced, and highest in the cores, where cavity-fill texture formed. During propagation the linkage of adjacent echelon blades, by the rupture of the host-rock straps (bridges) between them, enhanced dilation rates and led to the widespread development of cavity-fill textures. Within the composite fissures so produced, environments in which types of crack-seal textures could form were restricted to the fissure margins and to areas where the tensile strain was sympathetically shared between closely spaced fissures. Textures and minerals characteristic of each fracture environment were able to form simultaneously within the fracture system.

The oxygen and hydrogen isotope composition of hydrothermal fluids associated with the Variscan granites of southwest England has been inferred from analysis of various silicate minerals (predominantly quartz) and by direct analysis of fluid inclusions within quartz and fluorite. These data have been combined with the results of a fluid inclusion study to develop a model for the origin and evolution of hydrothermal fluids in the region. Magmatic fluids expelled from the granites had compositions in the range δD = −65 to −15‰, and δ18O = 9 to 13‰. Respective temperature, salinity, fluid δD, and fluid δ18O values for the (i) early Sn-W mineralization, (ii) later Cu-Pb-Zn sulphide mineralization, and (iii) latest ‘crosscourse’ Pb-Zn-F mineralization are: (i) 230–400 °C, 5–15 wt.% NaCl equiv., −39 to −16‰, and 7.0 to 11.2‰, (ii) 220–300 °C mostly 2–8 wt.% NaCl equiv., −41 to −9‰, and 2.3 to 8.1‰, and (iii) 110–150 °C 22–26 wt.% NaCl equiv., −45 to +2‰, and −1.8 to +5.5‰. These data highlight the important role of both magmatic fluids exsolved from the crystallizing granite, and basinal brines circulating within restricted fracture systems.

The crystal structure of fedotovite, K2Cu3O(SO4)3 has been determined, space group C2/c, a 19.037(6), b 9.479(2), c 14.231(5) Å, β 111.04(3)°, Z = 8, Dx = 3.09 g/cm3. The main units of the fedotovite structure are formed around two additional oxygen atoms and consist of edge-sharing [OCu4] tetrahedra and four [SO4] tetrahedra attached to them. The units are further connected by two [SO4] tetrahedra, building distinct layers parallel to the yz plane. These layers are interconnected by potassium atoms. In the fedotovite structure, the three kinds of copper atoms are fivefold (4 + 1) coordinated to oxygen atoms with a strong Jahn-Teller effect. The coordination polyhedra of Cu1 and Cu2 atoms are distorted and flattened orthorhombic pyramids with Cu-O distances varying from 1.912 to 2.333 Å, the sixth neighbour of the both atoms is the copper atom lying at 2.975 and 2.981 Å for Cu2 and Cu1 respectively. The coordination environment of the Cu3 atom is a distorted elongated orthorhombic pyramid with four Cu-O distances from 1.943 to 1.961 Å, a fifth at 2.558 Å, and further sixth and seventh neighbours (oxygen and copper atoms) at 2.809 and 2.806 Å, respectively.

The cathodoluminescence (CL) of cassiterite (SnO2) from the paragenetic sequence in the lodes at South Crofty Mines has been used in the interpretation of the processes which govern mineral deposition. Luminescence is controlled by the substitution of Ti, Fe and W for Sn in the cassiterite lattice. Ti and W behave as luminescence activators whereas Fe quenches luminescence. The observed colours and intensity of the luminescence are believed to result from the interplay between these effects. Successive generations of cassiterite formed during the separate stages of paragenetic evolution show different luminescence colours. These are believed to reflect changes in bulk composition of the fluid, which is indicated by the systematic variation in the composition of tourmaline in the associated gangue.

CL also reveals details of growth and deformation in individual crystals. Growth textures observed in CL are broad concentric growth banding, oscillatory zoning and sector zoning. Sector boundaries often show a zig-zag form which is indicative of competitive growth of adjacent crystal faces. Interpretation of CL textures is used to support the hypothesis that cassiterite growth took place under two main regimes. These are, firstly, conditions in which fluid pressure decreased abruptly when tectonic reactivation caused dilation of parts of the lode fracture system and secondly, conditions of sustained hydraulic pressure within fractured vein fill. In tectonically induced fractures the crystals are stubby, have non-equivalent growth faces and are commonly tetragonal bipyramidal forms in which sector zoning is invariably present. In hydraulic fractures crystals take a predominantly tetragonal prismatic form. Thus, it is believed that growth under these contrasting conditions leads to distinctive morphology and zoning in cassiterite, providing a basis for typomorphic characterisation.

In the Ordovician Snowdon Volcanic Group caldera quartz-magnetite-hematite-pyrite assemblages occur in a breccia vein in rhyolitic tuff and vein swarms in basalt. The veins developed pre-cleavage. Elevated levels of tin and tungsten in the veins, and of fluorine in the wall rocks, suggest a magmatic contribution to the mineralising fluids. The chemistry of the veins differs from that of the base-metal sulphide veins found elsewhere in the caldera.

Based on geological studies, 141 rock analyses and 5 trace element analyses of metabasites, the present paper deals with the rock association, chemical features, protolith formation and the original tectonic settings upwards through the Lower Proterozoic metamorphic strata in the Dabieshan-Lianyungang area, in the south-east of the North China Platform. The results of the study indicate that the lower and middle parts of the metamorphic strata comprise terrigenous clastics, phosphoritic and aluminous sedimentary formations which formed under stable continental margin conditions. In the middle-upper part a calc-alkaline volcano-sedimentary formation under the active continental margin was developed. The Lower Proterozoic meta-strata of sedimentary-volcanosedimentary origin from bottom upwards suggest that the tectonic evolution of the south-eastern margin of the North China Platform is a process from stabilization to mobilization. This process suggests a northward subduction of the Yangtze Plate under the North China Plate during the later part of the early Proterozoic.

Cathodoluminescence (CL) petrography of nepheline syenites of the Igaliko complex, Gardar province, South Greenland shows that sodalites possess embayed contacts against nepheline, and have formed by a process of metasomatic replacement. This texture is demonstrated clearly by CL, since sodalite luminesces bright orange and nepheline is poorly luminescent. The transformation from nepheline to sodalite results in a volume change which leads to a network of fractures in which deep-blue luminescent fluorite is precipitated. Fluorite is formed since the chlorination process involved in the transformation causes localised reductions of the salinity of the fluid and therefore a decrease in the solubility of fluorite. Sodalite-fluorite textures observed using CL allow sodalites of secondary origin in alkaline igneous rocks to be identified.

Nephelines and sodalites, when observed using scanning electron microscopy, possess small micropores. By analogy with recent work on alkali feldspars, pervasive alteration of nephelines may occur by fluid flow assisted by a permeable micropore network.