Phosphatization of basaltic rocks from Sal Island, Cape Verde Archipelago: A microtopochemical approach using synchrotron radiation X-ray fluorescence

M.O. Figueiredo; T. Pereira da Silva; J.P. Veiga; P. Chevallier

doi:doi:10.1051/jp4:20030108

Issue		J. Phys. IV France Volume 104, March 2003


Page(s)		399 - 402
DOI		https://doi.org/10.1051/jp4:20030108

J. Phys. IV France 104 (2003) 399
DOI: 10.1051/jp4:20030108

Phosphatization of basaltic rocks from Sal Island, Cape Verde Archipelago: A microtopochemical approach using synchrotron radiation X-ray fluorescence

M.O. Figueiredo^{1, 2}, T. Pereira da Silva^{1, 2}, J.P. Veiga^{1, 2} and P. Chevallier³

¹ Cryst. & Miner. Centre, IICT, AI. D. Afonso Henriques 41-4°, 1000-123 Lisboa, Portugal
² CENIMAT, Fac. Sci., New Univ. Lisbon, Quinta da Torre, 2829-516 Caparica, Portugal
³ LURE, Centre Universitaire Paris-Sud, bâtiment 209C, 91405 Orsay, France

Abstract
The geochemical processes involved in phosphorous enrichment of volcanic rocks under shallow seawater are not yet fully understood. As a contribution to this problematic, a detailed chemical characterization of phosphatized basaltic hyaloclastites assigned at Sal Island, Cape Verde archipelago, was undertaken using synchrotron radiation X-ray fluorescence. The mineralogical constitution of the samples was characterized by combining X-ray diffraction and electron microprobe data. Micromappings of metallogenetically significant components and other mobile chemical species were obtained. A positive correlation between Br plus Sr, on one side, and As plus Cr and Zn, on the other, is pointed out and brief comments are presented on the selective up-take of chemical elements in close dependence from the mineral assemblage formed by phosphatization.