Department of Earth Sciences

In Portugal, mining waste needs to be identified, mapped and characterised from a physical and chemical point of view as the increase in demand for the use of “new” and “green” technology products is causing a global pressure on the supply of primary raw materials, and therefore increasing the need to find alternatives, such as secondary raw materials, for a more circular economy.
Based on this issue, the main goals of this study were to characterise the mineralogical and chemical composition of borehole logging samples collected from the two metal-rich fine tailings dams (FTD1 and FTD2A) located at the Panasqueira mine, central Portugal; to assess the compositional variation, regarding chemical affinity, between major and trace elements; and to verify whether or not the concentration of critical elements was anomalous, when compared to their upper continental crust abundance.
Two borehole loggings, of up to four meters of depth, were drilled in each FTD. The mineralogical analysis was done using the XRD (Philips PW3710) and the SEM-EDS (Zeiss Merlin with the Gemini II column) techniques, and the chemical analysis was performed using the XRF technique (Thermo Fisher Scientific NitonTM XL3t GOLDD+ and PANalytical Axios mAX).
Regarding the XRD technique, it was possible to identify quartz, muscovite, clay minerals and Fe-Mg carbonates in almost all of the six borehole logging segments analysed, three from each FTD. The inactive fine tailings dam (FTD1) also contains hubnerite and, probably, albite and pyrite, while the currently active fine tailings dam (FTD2A) also contains sphalerite and, probably, albite and galena. In order to study mineral composition using the SEM-EDS technique, a segment of a borehole logging from each FTD was selected and a mineral concentrate was prepared by gravity separation. The identified minerals for FTD1 include metallic minerals, such as pyrite, arsenopyrite and wolframite, and non-metallic minerals, such as quartz, mica and Mg-carbonates. The identified minerals for FTD2A include metallic minerals, such as arsenopyrite, pyrite, sphalerite, chalcopyrite, and trace amounts of galena and wolframite, and non-metallic minerals, such as quartz and mica. In relation to the critical elements for the EU, a small, but relevant, presence of Co related to pyrite, Ga and Ge related to mica, and Nb apparently related to sulphides and mica can be found in FTD1, and there is also a small, but relevant, presence of Ga related to mica in FTD2A.
Using a portable XRF spectrometer, it was possible to characterise the chemical variation, regarding the metals Cu, Zn, As, W, Sn and Pb, along all the segments from the four borehole loggings (two from each FTD). It is clear to see some similarities in the distribution of the metals in both of the FTDs, with Pb and Sn being the least abundant, followed by W and Cu. Regarding the other metals studied, Zn is the most abundant (reaching 22,240 ppm) in FTD1, while As is the most abundant (reaching 57,580 ppm) in FTD2A. The analytical data obtained by the XRF technique, using the benchtop spectrometer with the operation mode Pro-trace, shows anomalous concentrations of some critical elements, when compared to their upper continental crust abundance. The content of Ga is 2 times higher in FTD1 and 1.5 times higher in FTD2A; the content of Ge is 10 times higher in FTD1 and 6 times higher in FTD2A; the content of Sb is 8 times higher in FTD1 and 18 times higher in FTD2A; and the content of Ce is 2 times higher in FTD1 and 5 times higher in FTD2A. The Spearman’s rank correlation coefficient was used in order to evaluate the compositional variation regarding the chemical affinity between some major and trace elements. Apart from the expected mineral vs major elements relationship, positive correlations were confirmed between the more abundant critical trace elements and some abundant elements, which compose the main minerals of the paragenetic sequence, such as Ga with Al; Ge with Zn; Sb with Zn and As; and Ce with S, Fe and As.
Taking into consideration the chemical composition along the segments, it was possible to conclude that the elemental distribution is random in the first 4 meters of depth of each FTD. Regarding the chemistry of the whole rock samples, apart from the expected high concentration of W, Sn, Cu, Zn and Pb, there are some critical elements, such as Ga, Ge, Sb and Ce, with higher contents than the upper continental crust. The significant correlations found in this study allow us to relate the most abundant critical trace elements to some major “carrier” elements, thus allowing them to be assigned to the main “host” minerals of the paragenetic sequence. Therefore, Ga is related to mica, Ge is related to sphalerite, Sb is related to sphalerite and to As sulphosalts, and Ce is related to arsenopyrite.

Archaeological evidence for the earliest human presence in western Iberia is summarised and discussed.
Western Iberia is geologically characterised by magmatic and metamorphic rocks (Hesperian Massif) but also by siliciclastic and carbonate Mesozoic and Cenozoic formations. The geological context affects the distribution of Pleistocene archaeological sites, as the most of the archaeological evidence known today is located in river terrace formations or in karst deposits. Very few sites have been fully investigated; the older ones are tentatively dated as middle/late Middle Pleistocene. Recent results have been obtained using an archaeological and geomorphological approach carried out in the Portuguese region of Alto Ribatejo. Dating of the lithic assemblages found in fluvial terraces or in cave deposits indicates that the first human presence in Portugal is not older than the OIS 8–9. However, it remains difficult to explain
the long chronological gap between the archaeological evidences in western Iberia and the older sites in central and eastern Iberia, such as those in the Sierra de Atapuerca and Guadix Baxa areas.

The burial age of an alluvially deposited cobble pavement at the Tapada do Montinho archaeological site (east-central Portugal) is investigated using optically stimulated luminescence (OSL) dating. Measurements on the cobbles (quartzite clasts) were carried out on intact slices and large aliquots (∼8 mm) of quartz grains (63–300 μm), both recovered from the outer 1.5-mm surface of the cobbles. The recycling ratio, recuperation and dose-recovery tests show that the single-aliquot regenerative-dose (SAR) protocol is applicable to both rock slices and quartz grains; both have similar luminescence characteristics. The variation in the natural OSL signal with depth below the cobble surface using intact slices from two different cobbles shows that both were bleached to a depth of at least ∼2 mm before deposition. A model of the variation of dose with depth fitted to data from one of the cobbles gives a burial age of ∼19 ka and also predicts the dose-depth variation at the time of deposition. Ages based on rock slices suggest that one cobble surface, and the inner parts of two other cobbles experienced a resetting event at ∼45 ka, consistent with the age control. However, the surfaces of the other cobbles all record light-exposure events in the range 26 to 14 ka, suggesting that some of the cobbles were exposed to daylight perhaps more than once in this period. Given the shallow burial depth and unexpectedly young ages of the surrounding and overlying finer-grained sediment, it is suggested that phases of light exposure following surficial erosion are probably responsible for this underestimate. Nevertheless, it is remarkable that we can identify and quantify four events (two light exposures of different durations and two sequential burial periods) in the dose record contained within a single clast, and this suggests that the luminescence dating of rock surfaces may prove, in the future, to be at least as important as sand/silt sediment dating.

Novos dados sobre a Pré-história da zona do Cabo Espichel (Sesimbra, Setúbal), em resultado de vários anos de investigação, incluindo prospeções de natureza arqueológica, geoarqueologica e paleontológica e trabalhos de escavação pontual. Os autores incluem ainda observações sobre a fauna recolhida num concheiro e sobre estudo palinológico de cinco amostras sedimentares.

The three-day field excursion (8-10th September) will focus on the record of long-term drainage evolution of the Tejo River (English: Tagus (from Latin), Spanish: Tajo, French: Tage). The Tejo is a major European river system, draining a large part of the continental interior of Iberia to the Atlantic coast. It provides a long-term record of landscape evolution for SW Europe, controlled by tectonics, climate and eustatic variations over the last ~3.6 Ma (Pliocene-Recent).
The fieldtrip will start in Castelo Branco and end in Lisboa (~250 km), travelling along the Tejo valley. The itinerary and programme are given in Figs. 1a and b. Field sites in the upstream reaches will provide excellent opportunities to see: 1) the geomorphology of a spectacular river gorge where the Tejo River has cut through uplifted blocks of Palaeozoic basement; and 2) to examine and comment the sedimentology, stratigraphy, luminescence dating and archaeology of river terrace
landforms where the Tejo has incised into Tertiary deposits.
Collectively, upstream field locations will provide excellent opportunities to discuss climate and tectonic controls on this river system. Sites visited in the downstream region will focus on the Pleistocene, Holocene and historical evolution of the Tejo and its estuary, providing opportunities to discuss climate and human influences on river system dynamics.