Microprobe analyses were made to infer the source of 
detrital tourmalines from the Mid to Late Carboniferous 
turbiditic deposits of the Baixo Alentejo Flysch Group 
(BAFG) of the South Portuguese Zone

Dias, Patrícia

Fernandes, Paulo

Jorge, R. C. G. S.

Rodrigues, B.

Universidade do Algarve

Goldschmidt Conference Abstracts 
Mineralogical Magazine  www.minersoc.org 
1740 
Discrimination of sediment samples 
for forensic application using REE 
A. RODRIGUES, A. GUEDES*, H. RIBEIRO, B. VALENTIM 
AND F. NORONHA 
Centro de Geologia da Universidade do Porto e Departamento 
de Geociências, Ambiente e Ordenamento do Território, 
Faculdade de Ciências, Universidade do Porto, Rua do 
Campo Alegre 687, Porto, Portugal 
(*correspondence: aguedes@fc.up.pt) 
 
The geochemical signature of sediments is currently used 
as trace evidence in forensic investigations. In this research, 
geochemical studies have been carried out on Portuguese 
coastal sands aiming to ascertain its use for forensic purposes.  
Rare Earth Elements (REE) concentrations were 
determined on samples collected on three coastal areas 
surrounded by different geological contexts, namely 
limestone, granite and metasediment. Eight sand samples were 
collected along transects perpendicular to the coastline, in 
beach and dune from each site. Each sample was manually 
collected with a plastic spade from the surface sediment, at a 
depth of approximately 0-5cm. From the sediment samples a 
standardized particle size fraction of <150 µm was obtained 
by dry sieving method and subsequently grinded to minimise 
the variation in the geochemical properties due to particle size.  
The REE composition fraction was determined using four 
acid digestions ultratrace ICP-MS analysis at ACME labs 
(Canada), and concentrations calculated. Although the 
measured REEs concentrations can be compared directly for 
forensic purposes a normalisation reported to condrite 
meteorites was performed [1]. 
A REEs normalised concentration and a hierarchical 
cluster analyses were performed to obtain discrimination 
between samples. They reveal differences between samples 
associated with different geological context, and permitted the 
discrimination between samples surrounded by granite from 
samples surrounded by limestone and metasediments. It was 
also possible to discriminate some of the samples based on 
their REE concentration and profile. 
 
This research was supported by Project PTDC/CTE-
GEX/67442/2006 of FCT (Portugal). 
 
[1] Taylor & McLennan (1985) Blackwell Scientific 
Publications, 312p. 
 
Geochemical signatures in detrital 
tourmalines as indicators for 
sediment provenance: The Baixo 
Alentejo Flysch Group, South 
Portuguese Zone 
B. RODRIGUES1*, P. DIAS2, R.C.G.S. JORGE3 
AND P. FERNANDES1 
1CIMA, University of the Algarve, Campus de Gambelas, 
8005-139 Faro, Portugal 
(*correspondence: bmgrodrigues@sapo.pt, 
pfernandes@ualg.pt) 
2CIG-R, University of Minho (patriciasdias@gmail.com) 
3CREMINER LA/ISR, Dep. Geologia, Fac. Ciências da 
Universidade de Lisboa (rjorge@fc.ul.pt) 
 
Microprobe analyses were made to infer the source of 
detrital tourmalines from the Mid to Late Carboniferous 
turbiditic deposits of the Baixo Alentejo Flysch Group 
(BAFG) of the South Portuguese Zone. A representative group 
of greywacke samples covering the whole range of the BAFG 
ages was collected for this study. Tourmalines have brown to 
brownish gray colors and do not show any optical zonation. In 
the Fe-Mg-Al diagram, the tourmalines fall into the fields of 
Ca-poor metapelites, metapsammites and quartz-tourmaline 
rocks. Microprobe analyses revealed a range of values 
between schorl and dravite end members, being closer to the 
latter, with variable contents of X-site vacancies (0.05-0.255 
apfu), Ca (0.078-0.2 apfu), Na (0.627-0.924 and Al (5.746-
6.622 apfu). The Fe/(Fe+Mg) and Na/(Na+Ca) ratios range 
from 0.32-0.45 and 0.79-0.91, respectively. 
The presence of well-rounded tourmaline grains suggests 
that they could have derived from a source located at a great 
distance from the sedimentary basin, or from reworked 
sedimentary rocks. The occurrence of few euhedral grains 
indicates minor contribution from first cycle sediments. 
Together, these data suggest that the detrital BAFG 
tourmalines derived from multiple sources with the 
predominance of rocks with a felsic composition.  
 
Bruno Rodrigues holds a PhD grant from the Portuguese 
Foundation for Science and Technology 
(n.° SFRH/BD/62213/2009). 


Geochemical signatures in detrital tourmalines as indicators for sediment provenance: the Baixo Alentejo Flysch Group, South Portuguese Zone

Sapientia

Goldschmidt Conference Abstracts Mineralogical Magazine  www.minersoc.org 1740 Discrimination of sediment samples for forensic application using REE A. RODRIGUES, A. GUEDES*, H. RIBEIRO, B. VALENTIM AND F. NORONHA Centro de Geologia da Universidade do Porto e Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre 687, Porto, Portugal (*correspondence: aguedes@fc.up.pt)  The geochemical signature of sediments is currently used as trace evidence in forensic investigations. In this research, geochemical studies have been carried out on Portuguese coastal sands aiming to ascertain its use for forensic purposes.  Rare Earth Elements (REE) concentrations were determined on samples collected on three coastal areas surrounded by different geological contexts, namely limestone, granite and metasediment. Eight sand samples were collected along transects perpendicular to the coastline, in beach and dune from each site. Each sample was manually collected with a plastic spade from the surface sediment, at a depth of approximately 0-5cm. From the sediment samples a standardized particle size fraction of <150 µm was obtained by dry sieving method and subsequently grinded to minimise the variation in the geochemical properties due to particle size.  The REE composition fraction was determined using four acid digestions ultratrace ICP-MS analysis at ACME labs (Canada), and concentrations calculated. Although the measured REEs concentrations can be compared directly for forensic purposes a normalisation reported to condrite meteorites was performed [1]. A REEs normalised concentration and a hierarchical cluster analyses were performed to obtain discrimination between samples. They reveal differences between samples associated with different geological context, and permitted the discrimination between samples surrounded by granite from samples surrounded by limestone and metasediments. It was also possible to discriminate some of the samples based on their REE concentration and profile.  This research was supported by Project PTDC/CTE-GEX/67442/2006 of FCT (Portugal).  [1] Taylor & McLennan (1985) Blackwell Scientific Publications, 312p.  Geochemical signatures in detrital tourmalines as indicators for sediment provenance: The Baixo Alentejo Flysch Group, South Portuguese Zone B. RODRIGUES1*, P. DIAS2, R.C.G.S. JORGE3 AND P. FERNANDES1 1CIMA, University of the Algarve, Campus de Gambelas, 8005-139 Faro, Portugal (*correspondence: bmgrodrigues@sapo.pt, pfernandes@ualg.pt) 2CIG-R, University of Minho (patriciasdias@gmail.com) 3CREMINER LA/ISR, Dep. Geologia, Fac. Ciências da Universidade de Lisboa (rjorge@fc.ul.pt)  Microprobe analyses were made to infer the source of detrital tourmalines from the Mid to Late Carboniferous turbiditic deposits of the Baixo Alentejo Flysch Group (BAFG) of the South Portuguese Zone. A representative group of greywacke samples covering the whole range of the BAFG ages was collected for this study. Tourmalines have brown to brownish gray colors and do not show any optical zonation. In the Fe-Mg-Al diagram, the tourmalines fall into the fields of Ca-poor metapelites, metapsammites and quartz-tourmaline rocks. Microprobe analyses revealed a range of values between schorl and dravite end members, being closer to the latter, with variable contents of X-site vacancies (0.05-0.255 apfu), Ca (0.078-0.2 apfu), Na (0.627-0.924 and Al (5.746-6.622 apfu). The Fe/(Fe+Mg) and Na/(Na+Ca) ratios range from 0.32-0.45 and 0.79-0.91, respectively. The presence of well-rounded tourmaline grains suggests that they could have derived from a source located at a great distance from the sedimentary basin, or from reworked sedimentary rocks. The occurrence of few euhedral grains indicates minor contribution from first cycle sediments. Together, these data suggest that the detrital BAFG tourmalines derived from multiple sources with the predominance of rocks with a felsic composition.   Bruno Rodrigues holds a PhD grant from the Portuguese Foundation for Science and Technology (n.° SFRH/BD/62213/2009). 

https://sapientia.ualg.pt/bitstream/10400.1/5121/1/Geochemical%20signatures%20in%20detritl%20tourmalines%20as%20indicators%20for%20sediment%20provenance.%20The%20Baixo%20Alentejo%20flysch%20group%2c%20south%20Portuguese%20zone.pdf

Geochemical signatures in detrital tourmalines as indicators for sediment provenance: the Baixo Alentejo Flysch Group, South Portuguese Zone

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