Experimental determination of CePO4 and YPO4 solubilities in H2O–NaF at 800°C and 1 GPa: implications for rare earth element transport in high‐grade metamorphic fluids

Monazite (CePO₄) and xenotime (YPO₄) are important accessory minerals in metasediments. They host significant rare earth elements (REE) and are useful for geochronology and geothermometry, so it is essential to understand their behavior during the metasomatic processes that attend high‐grade metamorphism. It has been proposed that F‐bearing fluids enhance solubility and mobility of REE and Y during high‐grade metamorphism. We assessed this possibility by determining the solubility of synthetic CePO₄ and YPO₄ crystals in H₂O–NaF fluids at 800°C and 1 GPa. Experiments used hydrothermal piston‐cylinder and weight‐loss methods. Compared to the low solubilities of CePO₄ and YPO₄ in pure H₂O (0.04 ± 0.04 and 0.25 ± 0.04 millimolal, respectively), our results indicate an enormous increase in the solubility of both phosphates with increasing NaF concentration in H₂O: CePO₄ solubility reaches 0.97 molal in 20 mol.% NaF, and YPO₄ shows an even stronger solubility enhancement to 0.45 molal in only 10 mol.% NaF. The greatest relative solubility increases occur at the lowest NaF concentration. The solubilities of CePO₄ and YPO₄ show similar quadratic dependence on NaF, consistent with possible dissolution reactions of: CePO₄ + 2NaF =  CeF₂⁺ + Na₂PO₄^? and YPO₄ + 2NaF = YF₂⁺ + Na₂PO₄^?. Solubilities of both REE phosphates are significantly greater in NaF than in NaCl at equivalent salt concentration. A fluid with 10 mol.% NaCl and multiply saturated with fluorite, CePO₄, and YPO₄ would contain 1.7 millimolal Ce and 3.3 millimolal Y, values that are respectively 2.1–2.4 times greater than in NaCl‐H₂O alone. The results indicate that Y, and by extension heavy rare earth elements (HREE), can be fractionated from LREE in fluorine‐bearing saline brines which may accompany granulite‐facies metamorphism. The new data support previous indications that REE/Y mobility at these conditions is enhanced by complexing with F in the aqueous phase.     

Sourcing Iron Age softstone artefacts in southeastern Arabia: results from a programme of analysis using Inductively Coupled Plasma-Mass Spectrometry/Optical Emission Spectrometry (ICP-MS/OES)

Iron Age softstone vessels manufactured in southeastern Arabia are widely distributed across that region and in lesser amounts throughout Western Asia. Results from a pilot programme of analysis using Inductively Coupled Plasma Mass Spectrometry/Optical Emission Spectrometry on vessel fragments from two southeast Arabian sites are presented. These results indicate the existence of geochemically distinct groups that are separated by both transition metals and rare earth elements. While this indicates the potential for the application of the provenance postulate in softstone analysis, these promising results need to be further tested by an expanded programme of analysis which includes quarry fragments.     

Petrographic and geochemical analysis on the provenance of the Middle Bronze and Late Bronze/Early Iron Age ceramics from Didi Gora and Udabno I, Eastern Georgia

We report thin section petrographic and geochemical analysis of a total of 20 Middle Bronze, Late Bronze/Early Iron Age ceramics excavated from Didi Gora and Udabno I located in the Eastern part of the Republic of Georgia and 31 clay samples from eight different regions in the surrounding areas of the sites. The major and trace element compositions of the ceramics and clays were determined using a wavelength dispersive X-ray fluorescence technique. The results indicate that the ceramics were manufactured from local clays in Eastern Georgia, mainly from two local clays without any preference of one of the sources during the Middle Bronze, Late Bronze/Early Iron Age.     

Spatial analysis of the coincidence of rare vascular plants and landforms in the Carolinian zone of Canada: implications for protection

Assessing biodiversity in natural landscapes continues to be a focus of attention. While some researchers assess the value of predictive features, such as land‐form, others examine concentrations of rare species, seeking insight into their significance. In this paper I examine two inter‐related concepts. I explore the distributions of rare species on the landscape, assessing correlations between landform, numbers of rare species, and protected areas. I also examine the role of protected sites in maintaining biodiversity. Using records of rare plant collections for the south‐western portion of Ontario (the Carolinian zone) that were compiled as part of the Atlas of Rare Vascular Plants of Ontario project, and combining these with a) a map of the landforms of south‐western Ontario and b) the locations of protected areas within this region, an analysis was made of the spatial coincidence of rare vascular plants, landforms and protected areas. The findings here indicate that protected areas are critically aligned with the distribution of rare vascular plant species. While protected areas occupy less than 2 percent of the study region, approximately 20 percent of the 4379 unique rare plant records analyzed (representing 170 of the 293 rare species in the database or 68%) were collected from a protected site. In addition, while 42 percent of the rare vascular plant records occur on a single landform type, sand plains, sand plains occupy only 18 percent of the region. And while 24 percent of the study region is composed of till plains, less than 2 percent of the rare plant collections were found on this landform. Significantly, four land‐forms, representing 50 percent of the study region, support over 80 percent of all rare plant collections. L'évaluation de biodiversité dans les paysages naturels continue d'être un point de mire. Pendant que certains chercheurs estiment la valeur des caracteristiques prédictives, telles que des formes de relief, d'autres examinent les concentrations d'espèces rares pour comprendre leur signification. Dans cet exposé, j'examine deux concepts intereliés. J'explore les distributions d'espèces rares dans le paysage, évaluant les corrélations entre les formes de relief, les nombres d'espèces rares, et les sites protégés. J'examine aussi le rôle des sites protégés dans la conservation de biodiversité. La coïncidence spatiale des plantes vasculaires rares, formes de relief, et sites protégés a été analysée. L'analyse utilise, en partie, l'inventaire de collections de plantes rares pour une région dans le sud‐ouest de l'Ontario. Cet inventaire a été compilé pour le projet Atlas of Rare Vascular Plants of Ontario. L'analyse totale combine cet inventaire avec (a) une carte des formes de relief dans le sud‐ouest de l'Ontario et (b) les emplacements des sites protégés dans la même région. Les resultats indiquent que les sites protégés sont fortement alignés avec la distribution d'espèces rares. Alors que les sites protégés occupent mains que 2 pour cent de la region étudiée, environ 20 pour cent des 4379 plantes rares uniques analysées (représentant 7 70 des 293 espèces rares dans la banque de données ou 68%) se trouvent sur des sites protégés. De plus, alors que 42 pour cent des plantes rares se retrouvent sur un seul type de forme de relief (plaine de sable), ce type occupe seulement 18 pour cent de la région. Et alors que les plaines constituent 24 pour cent de la région, mains que 2 pour cent des plantes rares se retrouvent sur celles‐ci. Fait révélateur, quatre formes de relief constituent 50 pour cent la région étudiée mais elles soutiennent plus que 80 pour cent des plantes rares.     

Computer programmes for the correction of matrix effects in the XRF analysis of glass,ceramics and related silicate systems

The quantitative analysis of glass, ceramics and related silicate systems by means of energy dispersive X-ray fluorescence spectrometry is considered and problems arising from the selective absorption of X-rays in multi-element specimens are discussed. A computer programme written in FORTRAN and based upon a “semi-fundamental parameters” approach to the correction of matrix effects in glass and chemically similar materials is fully described. Model data are provided to enable the programme to be run and tested. An “empirical coefficients” computer programme for the quantitative analysis of silicate systems is outlined and the limitations of this type of programme are pointed out. The importance of adequate sample preparation prior to X-ray spectrometric analysis is stressed.