Critical Elements in Supergene Phosphates: The Example of the Weathering Profile at the Gavà Neolithic Mines, Catalonia, Spain

Yael Díaz-Acha,Josep Bosch,Míriam Pastor,David Fernández-Lluch,Aleu Andreazini,Joan Carles Melgarejo,Marc Campeny,Susana E Jorge-Villar,Esperança Tauler,Cristina Villanova-De-Benavent,Iria Díaz-Ontiveros,Antoni Camprubí,Joaquín A Proenza

doi:10.3390/min10010003

Abstract

The essential role of Critical Elements (CE) in 21st century economy has led to an increasing demand of these metals and promotes the exploration of non-conventional deposits such as weathering profiles. The present work is focused on the study of a weathering profile located at the Archaeological Park of the Gavà Neolithic Mines, Barcelona, Catalonia, Spain. In the Gavà deposit, acid and oxidising meteoric fluids generated intense weathering during the early Pleistocene, affecting series of Llandoverian black shales and associated syn-sedimentary phosphates. The circulation of these acid fluids at deeper levels of the profile generated supergene vein-like mineralisations comprised of secondary phosphates (e.g., variscite, perhamite, crandallite, phosphosiderite) and sulphates (e.g., jarosite, alunite). This supergene mineralisation is significantly enriched in certain CE (e.g., Ga, Sc, REE, In, Co and Sb) that were mobilised from host rock components and later hosted in the crystal lattice of supergene minerals. Weathering processes and corresponding supergene enrichment of CE at the Gavà deposit could be used as an example to determine exploration guidelines of CE in weathering profiles and associated supergene phosphates worldwide.

Highlights

In 2017, the European Commission assessed a list of 61 raw materials on their criticality for the EU
The present study provides evidence of the supergene enrichment of critical elements in supergene phosphates produced by weathering
In the Gavà area, significant weathering processes involving acid and oxidising meteoric fluids occurred during the early Pleistocene affecting a series of Llandoverian black shales and associated syn-sedimentary phosphates

Summary

Introduction

In 2017, the European Commission assessed a list of 61 raw materials (including metallic ores, biogenic products and industrial minerals) on their criticality for the EU. The essential role of CE in the development of 21st century industry (e.g., electric cars, green energy production, LED lamps, optical fibre, etc.) led to an increasing demand of these metals in the last few years that will probably continue in the near future [2,3,4,5,6]. In this context, European governments promote the exploration of new resources of CE with special interest in the study of non-conventional mineral deposits that include secondary sedimentary formations such as weathering profiles [7], among others. The exploration of CE in this type of geological environments is mainly focused on the study of laterites in which significant concentrations of critical elements such as rare earth elements (REE), Sc, or platinum group elements (PGE) have recently been reported in different localities worldwide [8,9,10,11,12,13,14,15,16]

Methods

Discussion

Conclusion