Maria Dos’s scientific contributions

Most of the lithic tools made during Prehistory in the Iberian Peninsula are mainly composed of three main siliceous rock types: chert, quartzite, and quartz. While the methodologies for the characterization and provenance of raw materials made on chert (and obsidian) have been developed with well-established and widely used protocols, the same does not apply to quartzite and quartz veins. Here we present recent developments in characterization and provenance analysis of quartzite and quartz through two case studies: (1) establishing and testing an analytical protocol for the quartzite available in the Côa River Valley region (Portugal) to be applied in future archaeological studies; (2) understanding the quartzite variability within the archaeological assemblage of the El Sotillo site (Spain). These two case studies allow us to highlight some of the main problems and challenges linked to the study of quartzite (raw material and lithic industry) in Paleolithic contexts.

A R T I C L E I N F O Keywords: Lithium pegmatite Metasomatism Geochemical halo Lithogeochemistry Psammitic and pelitic metasediments Geochemical exploration A B S T R A C T Fluid-assisted mass transfer and re-equilibration of mineral phases are common consequences of metasomatism associated with igneous intrusions. The addition and/or removal of chemical components in these environments may result in the generation of metasomatic aureoles, which can be recognized by their mineralogy and geochemistry. Due to an increasing demand for critical raw materials used in green energy technologies, rare-element granitic pegmatites have seen renewed interest in the mineral exploration industry. Granitic pegma-tites represent potential sources of critical commodities and geochemical studies of their related aureoles help to advance techniques in exploration targeting. Moreover, the role and timing of fluid exsolution during magma-tic-hydrothermal evolution in granitic-pegmatitic systems and concomitant element mobility remain highly debated. We present a prospect-scale systematic study of geochemical haloes generated by LCT (Li-Cs-Ta) family pegmatite dykes from the Fregeneda-Almendra Pegmatite Field, in the Central Iberian Zone of the Iberian Massif (Spain and Portugal). To understand the magnitude of metasomatic processes linked to these intrusions, we performed whole-rock mass-balance calculation of element gains and losses in variably metasomatized psam-mitic and pelitic host metasediments. The results show that F, B, Li, Rb, Cs, Sn, Be, Tl, As, W and S (±Mo, Ta) were carried by early exsolved and expelled aqueous fluids. The first evidence of element enrichment is recorded at distances of 4-5 times the thickness of the dykes, with exponentially increasing gains of those fluid-mobile elements proximal to the pegmatite margin. Enrichments that were detected farthest from the pegmatite margins were those of Li and Cs, followed by Rb and, to a lesser extent, Sn, F, B, Be, and Tl. The most evolved (fractionated) aplite-pegmatites generated the broadest haloes, with concentrations higher than 200 ppm Li, 30 ppm Cs, 300 ppm Rb, and 15 ppm Sn in the metasediments indicating proximity to a mineralized dyke. In addition, absolute gains of up to ~4000 ppm Li, ~1300 ppm Cs, ~1300 ppm Rb, and 170 ppm Sn in the host rocks could point to the presence of superimposed haloes from multiple evolved dykes.

The mechanisms involved in alkali-aggregate reaction and the characteristics of reactivity of some aggregates are not completely understood, although tens of thousands of mortar and concrete prisms have been tested in the laboratory and field exposure sites have been installed in a number of countries. Aggregates are the least well understood component in the alkali-aggregate reactions and, surely, the most difficult to assess. This happens not just because the materials used as aggregates are widely variable in origin, geological history, composition, texture and degree of alteration, but also because rocks that behave as innocuous in certain areas of the world appear to perform as reactive elsewhere. In consequence, the petrographic assessment of the aggregates is commonly not enough to classify an aggregate as innocuous or potentially reactive. In this paper questions are raised concerning slow reactive rock types, including suggestions about the possible forms of silica present and their identification.

The reactive forms of silica present in an aggregate depend on the origin and geological history of the rocks. The detection of specific reactive silica must be focused on characteristics such as the identification of polymorphs, the quantification of microcrystalline to cryptocrystalline quartz, and/or on the deformation manifestations for each aggregate. In this paper the types of sedimentary rocks usually exploited as aggregates for concrete, such as sandstone, greywacke, chert, siliceous limestone and mudstone, are presented. In addition, the rocks exhibiting low metamorphic grade are included when the sedimentary structure is still preserved and the features of metamorphic conditions are slight. The main characteristics of the sedimentary rocks regarding alkali-aggregate reactions are discussed and the importance of complementary methods for the detection of reactive forms of silica explained.