Thermodynamic data are constrained by the interrelated thermodynamic equations in addition to the observational measurements and their uncertainties. The consequence is a network of thermodynamic properties that can be evaluated for their internal consistency. In this study, three fluoride minerals that can cause high fluoride concentrations in groundwaters are evaluated for their solubilities and their internal thermodynamic consistency with calorimetric, isopiestic and electrochemical measurements: fluorite, CaF2, cryolite, Na3AlF6, and villiaumite, NaF. This evaluation involves the three solids and 13 aqueous species, the free ions of Ca2+, Na+, Al3+ and F–, and the hydroxido and fluorido complexes of Al3+, and the CaF+ ion pair. For the fluorite–cryolite–villiaumite–aqueous species network, the number of components is minimal, and the solubility studies are mostly of high quality. Re-evaluations of original data using PHREEQC helps to broaden the quantitative evaluation of thermodynamic properties and to resolve apparent discrepancies. A check on this thermodynamic network shows that through a careful appraisal of the literature, a highly consistent set of values can be derived. The resultant infinite-dilution solubility-product constants at 25°C and 1 bar are: for fluorite solubility, logKsp = –10.57 ± 0.08; for cryolite solubility, logKsp = –33.9 ± 0.2; and for villiaumite solubility, logKsp = –0.4981 ± 0.003.

The recently developed fluorite (U–Th)/He thermochronology (FHe) technique was applied to date fluorite mineralization and elucidate the exhumation history of the Mazandaran Fluorspar Mining District (MFMD) located in the east Central Alborz Mountains, Iran. A total of 32 fluorite single-crystal samples from four Middle Triassic carbonate-hosted fluorite deposits were dated. The presented FHe ages range between c. 85 Ma (age of fluorite mineralization) and c. 20 Ma (erosional cooling during the exhumation of the Alborz Mountains). The Late Cretaceous FHe ages (i.e. 84.5 ± 3.6, 78.8 ± 4.4 and 72.3 ± 3.5 Ma) are interpreted as the age of mineralization and confirm an epigenetic origin for ore mineralization in the MFMD, likely a result of prolonged hydrothermal circulation of basinal brines through potential source rocks. Most FHe ages scatter around the Eocene Epoch (55.4 ± 3.9 to 33.1 ± 1.7 Ma), recording an important cooling event after heating by regional magmatism in an extensional tectonic regime. Cooling of the heated fluorites, as a result of thermal relaxation in response to geothermal gradient re-equilibration after the end of magmatism, or exhumation cooling during extensional tectonics characterized by lower amount of erosion are most probably the causes of the recorded Eocene FHe cooling ages. Oligocene–Miocene FHe ages (i.e. 27.6 ± 1.4 to 19.5 ± 1.1 Ma) are related to the accelerated uplift of the whole Alborz Mountains, possibly as a result of the initial collision between the Afro-Arabian and Eurasian plates further to the south.

Some important and interesting data on the O, C and Sr isotopic compositions of rocks associated with the Bayan Obo Fe-Nb-REE deposit have been reported by Le Bas et al. (1997). However, a number of points relating to the interpretation of these data, and also to the terminology adopted, are worthy of further discussion. The essence of this discussion is that some of the geochemical and isotopic signatures found at Bayan Obo are not exclusively consistent with an igneous origin. A replacement hypothesis involving deep-sourced fluids could also explain the pattern of data, if minor carbonatitic intrusions into a sedimentary sequence are considered.

Natrocarbonatite lavas erupted from hornitos T37B and T49B at Oldoinyo Lengai (Tanzania) during 23–30 July, 2000 are unusual in containing sylvite and fluorite microcrysts together with fluorite-nyerereite intergrowths. The latter are relatively coarse grained and exhibit granular textures indicative of slow crystallization rates relative to those of their host subaerial lavas. Fluorite microcrysts are considered to be derived by the fragmentation of the fluorite-nyerereite clasts. Sylvite microcrysts contain inclusions of ferroan alabandite [(Mn0.67-0.71Fe0.33-0.29)S] and are poor in Na (1.9–7.7 wt.% Na; 6.1–23.4 mol.% NaCl). Intergrowth and microcrystal fluorite contains 1–3.5 wt.% Sr. Intergrowth nyerereite has a composition similar to that occurring as bona fide phenocrysts. The groundmass of lava erupted from hornito T37B contains nyerereite microphenocrysts (4–8 wt.% BaO) that are epitaxially mantled by barian nyerereite (12–20 wt.% BaO). The latter are compositionally and texturally distinct from the groundmass phase X, which is considered to be a burbankite-group mineral. The fluorite-nyerereite clasts are considered to be derived from the magma chamber underlying hornitos T37B and T49B, and thus representative of some of the products of crystallization of natrocarbonatite magma under hypabyssal conditions. The origins of the sylvite microcrysts cannot, as yet, be determined.

Diagenetic palaeotemperatures determined from aqueous fluid inclusions can be affected by re-equilibration during burial heating. Calculations based on the observed behaviour of inclusions in fluorite under external confining pressure allows prediction of the temperatures and depths of burial necessary to initiate re-equilibration of aqueous inclusions in the common size range 40 to 4 µm. Heating of 20° to 60°C over the initial trapping temperature may cause errors of 10° to 20°C in the homogenization temperature. This suggests re-equilibration may cause aqueous inclusions in carbonates to yield a poor record of their low-temperature history, but a useful record of the maximum temperature experienced by the host rock. Previous work suggests inclusions containing petroleum fluids will be less susceptible to re-equilibration.

The Tinderet volcano (19.9 to 5.5 Ma), located within the Kavirondo rift in Kenya, contains blocks of carbonatite lavas with calcite, minor apatite, fluorite, spinel-group minerals, accessory perovskite and 'plumbopyrochlore'; nyerereite is present as inclusions in the perovskite. At least four types of calcite are present in the carbonatite lavas; they differ in morphology, composition and origin. The dominant variety is secondary type-II calcite, which is enriched in sodium (up to 1.1 wt.% Na2O) and strontium (up to 1.3 wt.% SrO). The spinel-group minerals are manganese-bearing and include Mn-rich magnetite, magnesioferrite and jacobsite. Oxygen isotope data for bulk carbonatite samples (δ18O = +16.2 % to +22.6 % VSMOW) support a low crystallization temperature for the secondary calcite. Petrographic, mineralogical and isotopic data indicate that the Tinderet carbonatites are similar to natrocarbonatites from the Oldoinyo Lengai and Kerimasi volcanoes that have altered and recrystallized to form calcite carbonatites. These data support the hypothesis that some of the Tinderet carbonatites were originally alkali-rich rocks which contained primary nyerereite.

The fluorite vein deposits of the Southern Alps (Northern Italy) exhibit similar geotectonic, paragenetic, and textural characteristics permitting useful comparison between their fluid inclusions and REE systematics. Due to differing post-crystallization deformation, primary fluid inclusions can only be observed in the northernmost deposit (Rabenstein/Corvara). Here, fluorite precipitated from highly saline H2O-NaCl-CaCl2 solutions containing appreciable H2S. During vein formation the fluids changed from low salinity (≈7 wt. % NaCl equiv.) and medium temperature (Th ≈ 230°C), corresponding to the precipitation of early quartz, towards high salinity (≈20 wt.% NaCl equiv.) and lower temperatures (Th ≈170°C during the deposition of late-stage fluorite. This was accompanied by an increase in Ca in solution.

REE distribution patterns for the northern deposits are very uniform suggesting a similar source, a large-scale homogeneous fluid system, and fluorite precipitation under reducing conditions. By comparison the southern deposits exhibit contrasting patterns documenting a more complex history, probably due to their remobilization from an earlier mineralization. None of the fluorites shows a ‘primary’ magmatic REE distribution pattern, thereby favouring a genetic model for fluorite mineralization involving the leaching of suitable rock units by formation waters.

Phenomenally large (up to 2 mm) oil-bearing and associated brine inclusions in fluorite from carbonate-hosted, epigenetic, fluorite-calcite-(baryte) deposits of the Koh-e-Maran area are investigated using a combination of microthermometry, UV-microscopy and FTIR microspectroscopy. The liquid hydrocarbon phase in primary ‘oil’ inclusions is brown in colour and is dominated by saturated, low molecular weight, aliphatic hydrocarbons.

Two types of mixed aqueous and ‘oil’ inclusions occur. Aqueous/oil types represent co-eval trapping of immiscible drops of oil and brine during primary growth. In oil/aqueous inclusions the oil appears to ‘wet’ the aqueous phase resulting in an odd ‘dish-shaped’ meniscus. The oil or liquid hydrocarbon part of the inclusion is primary but the aqueous part is thought to represent a secondary infill. The fluid inclusion evidence suggests that fluorite precipitated from a dilute (3.5 wt.% NaCl) brine at temperatures around 110–140°C in the presence of an immiscible liquid hydrocarbon phase dominated by saturated, light hydrocarbons. This ‘oil’ was present as an emulsion in the aqueous fluid and the phenomenal size of the inclusions is thought to reflect the large droplet size in the emulsion. Infiltration of a more saline, calcium-enriched brine into pre-existing oil inclusions resulted in complex oil-water inclusions showing a reversal in the nature and shape of the oil-water interface due to the presence of unspecifed surfactants in the brine which affected the wetting characteristics of the oil.

The homogenization temperatures and the presence of liquid petroleum inclusions are characteristic of Mississippi Valley-type (MVT) and manto-type fluorite deposits in many other parts of the world.

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.

The granites of Hong Kong comprise a variety of assemblages dominated by chemically evolved compositions. They are divided into two suites based on petrographic, geochemical, and age criteria. The oldest and most primitive intrusive units are deformed biotite-hornblende granodiorites and monzogranites of the Lamma Suite. These rocks are characterised by high CaO (1·4-2·7%), and low Nb and Y contents. The Lion Rock Suite (LRS) is dominated by relatively undeformed monzogranite with subordinate quartz syenite and comprises three subgroups. Granites of subgroup I are separated into coarse- and fine- to medium-grained lithologies. The fine- to medium-grained granites are predominantly fluorite-bearing with silica contents ranging from 75·5-78%. They are characterised by high total REE, Ga, F, Rb, Nb, and Y contents and yield a Rb-Sr whole-rock isochron age of 155 ± 6 Ma with an initial 87Sr/86Sr ratio of 0·7101 ± 0·0060 (MSWD = 4·6). Granites of subgroup II comprise a diverse range of compositions (SiO2 = 63–77%) and are characterised by highly variable trace element abundances. Coarse-grained granites yield an age of 148 ± 9 Ma with an initial 87Sr/86Sr ratio of 0·7060 ± 0·0006 (MSWD = 0·1). Granites of subgroup III are moderately to highly evolved (SiO2 = 72·5-77·9%) and the silica-rich compositions are marked by enrichment in Y, Nb, Rb and depletion in Ba and Sr. Rb-Sr whole-rock isochron ages for individual plutons vary from 138 ± 1 to 136 ± 1 and corresponding initial 87Sr/86Sr ratios are 0·7080 ± 0·0002 (MSWD = 1·2) and 0·7092 ± 0·0006 (MSWD = 0·4). Granites of the Lamma Suite and coarse-grained granites of LRS subgroup I are interpreted as synorogenic I-types, whereas those of LRS subgroups II and III are interpreted as late-orogenic to postorogenic, fractionated I-types. Fineto medium-grained granites of LRS subgroup I have distinctive A-type affinities and together with their association with quartz syenite indicate a transition from compressional to tensional tectonics.