Southwestern Sardinia, Italy, hosts several skarn, W–Sn–Mo greisen and hydrothermal deposits related to a 289±1 Ma Late Variscan granite suite. Among them, the most representative scheelite-bearing skarns belong to the San Pietro and Sinibidraxiu localities, in the Monte Tamara area, Sulcis region. The San Pietro deposit is a typical calc-silicate skarn whereas Sinibidraxiu is a sharply bounded orebody hosted in a marble unit. Optical petrographic observations and compositional data of major and trace elements were obtained for samples from both localities. San Pietro data suggests evolution from an oxidising prograde skarn stage (andradite–diopside, hematite and scheelite), to progressively more reducing conditions from the early retrograde (magnetite–cassiterite) to the late sulfide stage (arsenopyrite, stannite, molybdenite, Bi sulfosalts and Zn–Cu–Pb–Fe sulfides); Sinibidraxiu has diffuse carbonate–quartz intergrowths pseudomorphic over an early mineral assemblage with fibrous habit, followed by abundant ore mineral precipitation under reducing conditions (scheelite, arsenopyrite and Pb–Zn–Cu–Fe sulfides). Geothermometers indicate a comprehensive temperature range of 460–270°C for the sulfide stages of both deposits. The differences between the two deposits might be controlled by the distance from the source intrusion coupled with the different reactivity of the host rocks. The San Pietro mineralogy represents a more proximal skarn, contrasting with more distal mineralogical and chemical features characterising the Sinibidraxiu orebody (lack of Mo–Sn–Bi phases; LREE–MREE–HREE signature of scheelite). This investigation contributes for the first time to the identification of a W–Sn skarn system in SW Sardinia, thereby suggesting the Monte Tamara area and its surroundings as favourable for further exploration.

The appearance of Beaker pottery in Britain and Ireland during the twenty-fifth century bc marks a significant archaeological horizon, being synchronous with the first metal artefacts. The adoption of arsenical copper, mostly from Ireland, was followed by that of tin-bronze around 2200 bc. However, whilst the copper mine of Ross Island in Ireland is securely dated to the Early Bronze Age, and further such mines in the UK have been dated to the Early and Middle Bronze Age, the evidence for the exploitation of tin ores, the other key ingredient to make bronze, has remained circumstantial. This article contains the detailed analyses of seven stone artefacts from securely dated contexts, using a combination of surface pXRF and microwear analysis. The results provide strong evidence that the tools were used in cassiterite processing. The combined analysis of these artefacts documents in detail the exploitation of Cornish tin during this early phase of metal use in Britain and Ireland.

The Cape Cross–Uis pegmatite belt, Damara Orogen, north-central Namibia hosts multiple Ta–Nb- and Sn-oxide-bearing pegmatites. Columbite-group minerals, tapiolite, cassiterite and minor ixiolite and wodginite occur in abundance within pegmatites and display various compositional and internal structural mineralogical variations. Ta–Nb oxides display various zonation patterns indicative of multiple crystallisation phases, whereas cassiterite is dominantly homogeneous with minor euhedral columbite-group mineral inclusions. Ta–Nb oxides are mostly rich in Fe, with fractionation patterns in the columbite quadrilateral being sub parallel to the Ta/(Ta + Nb) axis; increasing Ta/(Ta + Nb) with little change in Mn/(Mn + Fe), which is consistent with classical trends in beryl-to-spodumene rare-element pegmatites. In addition, these trends suggest that co-crystallising minerals compete with Ta–Nb oxides for elements such as Mn, preventing Ta–Nb oxides from attaining Mn-rich compositions during the fractionation process. Cassiterite shows similar fractionation patterns with Fe > Mn and notable increases in the Ta content. Minor-element substitution in Ta–Nb oxides shows sharp decreases with increasing fractionation supporting the hypothesis that newly stabilised co-occurring minerals compete with columbite-group minerals for certain elements. Tapiolite shows the same minor-element trend, however, only for Sn and Ti suggesting cassiterite was a dominant competing mineral. Although crystallisation of Ta–Nb oxides from an aqueous fluid at the late-stages of pegmatite genesis is highly debated, significantly elevated Ta contents in metasomatised country rock, compared to unaltered country rock, may give new insight, suggesting that Ta may indeed partition into, and be transported by, an exsolved aqueous fluid. However, further studies of the country rock metasomatic contacts are required as currently the dataset is limited. The degree of fractionation as depicted by Ta–Nb and Sn oxides within pegmatites, indicate that a zonation from primitive to evolved pegmatites surrounding granites is not present and that pegmatites are probably not related to granites in the typical parent–daughter relationship.

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.

This paper is based on microprobe analysis (Ta, Nb, Fe, Mn, Ti, W, Sn) and Fe3+ EPR spectra of cassiterite samples from 14 tin deposits from the Iberian Hercynian Massif. The interpretation of microprobe data, atomic ratios (Fe+Mn)/(Nb+Ta), and Fe3+ EPR spectra reveal that the coupled substitution: 3Sn4+ = (Fe,Mn)2+ + 2(Nb,Ta)5+ is dominant in cassiterites from pegmatites, and high-temperature quartz veins and in the dark zones of cassiterites.

The mechanisms:

2Sn4+ = Fe3+ + (Nb,Ta)5+ and

Sn4+ + O2− = Fe3+ + OH−

are dominant in those from medium-low temperature quartz veins and in the light zones of cassiterites.

In the Yichun granite complex (SE China), columbite group minerals, microlite and cassiterite are the main Nb, Ta, Sn-bearing minerals. They are mainly concentrated in the uppermost albite-lepidolite granite. Rutile is the only Nb, Ta-bearing phase in the geochemically primitive muscovite-zinnwaldite granite. The chemical evolution of the columbite group minerals (the most abundant and commonly zoned Nb, Ta-bearing minerals) indicates a complex crystallization history of the host granites with: (1) fractional crystallization at depth, reflected by a strong increase of Mn/(Mn+Fe) ratios with a moderate increase of Ta/(Ta+Nb) ratios from the muscovite-zinnwaldite granite to the Li-mica granite and then the most fractionated topaz-lepidolite granite; and (2) emplacement of successive magma batches corresponding to the different units of the granite complex with progressive crystallization of each unit, mainly reflected by a strong increase of Ta/(Ta+Nb) ratios with moderate variation of Mn/(Mn+Fe) ratios during the growth of the zoned crystals. The data are compared with those from the RMG of Ezzirari (Morocco), Montebras, Beauvoir and Chèdeville (France).

Bismuthinite-bearing quartz veins from the Alston Block of the North Pennine Orefield are all close to, or above, the Rookhope and Tynehead cupolas of the buried Weardale Granite. They are uniform in composition and paragenesis and are earlier than the main fluorite-baryte-galena-sphalerite mineralization of the orefield. Rhythmical crystallization of quartz, chalcopyrite and minor pyrite is followed by fluorite-quartz-chalcopyrite-minor sphalerite-altered pyrrhotite mineralization. Early tin-bearing (up to 0.29 wt.% Sn) chalcopyrite encloses trace amounts of bismuthinite (Bi2S3), synchysite (CaREE(CO3)F2), argentopentlandite (Ag(FeNi)8S8) (close to being stoichiometric), pyrrhotite, cubanite and cosalite (Pb2Bi2S5), while early pyrite carries monoclinic pyrrhotite (close to Fe7S8) and tungsten-bearing cassiterite (up to 1.03 wt.% WO3). Bismuthinite is macroscopically visible and is associated with native bismuth and small, fine-grained, spherical aggregates that qualitative analysis suggests may be cosalite crystals. Synchysite and more rarely monazite, xenotime and adularia are intergrown with bismuthinite. These mineralogical data form part of the basis for an increasing awareness of the contribution of the Weardale Granite to the early phases of mineralization in the Alston Block.

The Penouta deposit is associated with a small Hercynian apogranite stock that intrudes Precambrian-Cambrian gneisses of the Ollo de Sapo Formation. Tin ore occurs as disseminations of cassiterite in the apogranite and as greisenized zones and quartz veins which traverse both the alkaline leucogranite and the surrounding metamorphic country rocks.

A fluid-inclusion study, utilizing microthermometric, crushing tests and Raman spectroscopic techniques on quartz from an intragranitic vein and a greisen of the host rock, indicates that the evolution of fluids was similar in both samples and occurred in the three main stages: The first stage is characterized by complex CO2 (CO2-N2-CH4-H2S) and complex CO2 aqueous (H2O-NaCl-CO2-N2-CH4-H2S) fluids of low salinity (Tm ice > −6°C), homogenization temperatures between 250 and 410°C homogenization pressures below 900 bars, and thermobarometric trapping conditions with temperatures below 700°C and pressures below 3250 bars. These fluids were probably responsible for the greisenization of the apogranite and wall rocks, and the precipitation of cassiterite. The second stage is represented by low-salinity aqueous solutions (H2O-NaCl) with Tm ice ⩾ −4.5°C, trapped at homogenization temperatures between 110 and 300 °C and homogenization pressures below 100 bars. This stage can be correlated with kaolinization. The third stage is characterized by higher salinity aqueous fluids (Tm ice ⩾ −16.5°C) containing Na+ and other cations, trapped at homogenization temperatures between 100 and 130°C and homogenization pressures below 5 bars. These fluids can be associated with the epigenetic or supergene phases of the orebody.

The formation of sulphide and cassiterite-bearing chlorite-rich greisens in the Navalcubilla granite has been modelled theoretically. Numerical simulation on the reaction of a hydrothermal fluid with a granitic rock predicts assemblages very similar to those found in nature, with progressive formation of muscovite, quartz, chlorite, microcline and plagioclase zones. The hydrothermal alteration of the rock produces a neutralization of the inflowing acid fluid, a drop in the fS2 and, to a lesser degree, an increment in fO2. During hydrothermal alteration, fS2 and fO2 change abruptly between metasomatic zones, but chlorite seems to control their major changes. Scheelite and cassiterite are concentrated in the internal zones, while sulphides are related to the more external zones. Fluid-rock reactions seem to be very effective for precipitating cassiterite and scheelite, even from very Sn and W-poor fluids. Appreciable amounts of sulphides are only expected in systems with high concentrations of base metals. Boiling and simple cooling of the fluids acidifies and oxidizes them but chemical changes are not strong enough to induce significant precipitation of ore minerals, at least when the temperature changes are small. Continued circulation of fluids along fractures with previously precipitated quartz + wolframite produces replacement of wolframite by scheelite and sulphides.

Analysis of stable isotopes in coexisting minerals has found wide application in the study of hydrothermal mineral deposits, particularly for elucidating the temperature and source of the fluid phase involved in mineralisation. For these purposes the temperature dependence of isotopic fractionation in several mineral-water systems has already been established (e.g. Friedman and O'Neil, 1977; O'Neil, 1986). Unfortunately, the oxygen isotope fractionation between cassiterite (SnO2) and water has not been adequately characterized, and this has hindered a full utilization of oxygen isotope data derived from studies of tin deposits (e.g. Harzer, 1970; Patterson et al., 1981; Kelly and Rye, 1979). Because of this situation, an attempt is made here to derive a relationship between temperature and the fractionation of oxygen isotopes (Δ) between quartz and cassiterite, based on the fractionations observed in naturally-occurring assemblages and independent temperature estimates.

Herzenbergite, SnS, was found in dykes in three granite pegmatite fields in north-central Sweden. It occurs as erratic replacements of cassiterite. The formation of herzenbergite was probably triggered by local interactions with fluids from sulphide-bearing graphitic schists located in the immediate vicinity of the pegmatite dykes.