Fenites associated with carbonatite complexes : a review

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Carbonatites and alkaline-silicate rocks are the most important sources of rare earth elements (REE) and niobium (Nb), both of which are metals imperative to technological advancement and associated with high risks of supply interruption. Cooling and crystallizing carbonatitic and alkaline melts expel multiple pulses of alkali-rich aqueous fluids which metasomatize the surrounding country rocks, forming fenites during a process called fenitization. These alkalis and volatiles are original constituents of the magma that are not recorded in the carbonatite rock, and therefore fenites should not be dismissed during the description of a carbonatite system. This paper reviews the existing literature, focusing on 17 worldwide carbonatite complexes whose attributes are used to discuss the main features and processes of fenitization. Although many attempts have been made in the literature to categorize and name fenites, it is recommended that the IUGS metamorphic nomenclature be used to describe predominant mineralogy and textures. Complexing anions greatly enhance the solubility of REE and Nb in these fenitizing fluids, mobilizing them into the surrounding country rock, and precipitating REE- and Nb-enriched micro-mineral assemblages. As such, fenites have significant potential to be used as an exploration tool to find mineralized intrusions in a similar way alteration patterns are used in other ore systems, such as porphyry copper deposits. Strong trends have been identified between the presence of more complex veining textures, mineralogy and brecciation in fenites with intermediate stage Nb-enriched and later stage REE enriched magmas. However, compiling this evidence has also highlighted large gaps in the literature relating to fenitization. These need to be addressed before fenite can be used as a comprehensive and effective exploration tool.This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant No 689909

INFLUENCE OF PAVEMENT SURFACE CHARACTERISTICS ON NIGHTTIME VISIBILITY OF OBJECTS

Vehicle headlights do not light enough of a roadway length for safe nighttime driving at higher driving speeds. Therefore, particularly on highways with high traffic levels, fixed roadway lighting enables safe nighttime driving conditions. Roadway lighting design has evolved over the years from the illumination method, which is based on the amount of light falling on the road surface, to the luminance- and visibility-based methods that are in use today. Visibility of an object on the roadway is directly related to the contrast between the object and its surroundings. In nighttime driving situations, the pavement acts as the background for most objects on the road. Therefore, reflectance characteristics of the pavement are important in visibility-based roadway lighting design processes. Currently, pavement reflectance characteristics are incorporated through four standard reflectance tables (r-tables) developed to represent portland cement concrete, open-graded asphalt concrete, seal coat, and dense friction coarse asphalt pavements. In this research, the computer program STV developed by M.E. Keck, which calculates pavement luminance and visibility level, was used for a sensitivity analysis to evaluate how the pavement type and the standard r-tables influence these parameters. The analysis was conducted for fixed roadway lighting situations without the influence of vehicle headlights. Results from the sensitivity analysis indicated that standard r-tables are not sufficient to model the whole spectrum of pavement surfaces encountered in practice. An analysis of pavement reflectance data collected by the Road and Transportation Association of Canada revealed that asphalt-based pavements tend to increase their specularity and brightness with age, whereas portland cement concrete pavements display a decreasing trend