Mineralogía magnética del depósito beachrock de Tunelboca (Ría de Bilbao, norte de España)Interrelación entre procesos sedimentarios naturales y desechos industriales ricos en hierro

Abstract

Rock-magnetic properties of the Tunelboca beachrock deposit (Bilbao estuary mouth, northern Spain) have been investigated to characterize its magnetic mineralogy and to obtain information about its genesis and evolution. This magnetic characte- rization has been performed by two complementary methods: on one side, in situ measurement of stratigraphic and surface magnetic susceptibility profiles; and on the other, a laboratory analysis of discrete samples (magnetic susceptibility, hyste- resis, remanence and high temperature thermomagnetic curves). The results indicate great abundance of magnetite derived from the iron present in the original industrial iron slag materials, as well as other iron oxy-hydroxides. Part of the original iron is also clearly detected in the samples, especially the most recent. This magnetic characterization allows us to use Tunel- boca as an end-member of extremely Fe-rich industrial waste products when comparing with our environmental magnetism data from modern intertidal sediments along the Bilbao estuary and other highly polluted estuarine settings in northern Ibe- ria. Due to the highly magnetic character of the Tunelboca materials, rock-magnetism reveals itself as a very useful tool to investigate this singular and spectacular example of a deposit formed by the interplay between natural sedimentary processes and anthropogenic industrial materials.