Implication of halmyrolysis in migration of REE during formation of ferruginous sedimentary rocks in Uzelga massive sulphide deposits, Southern Urals (Russia)

摘要

Ferruginous sedimentary rocks associated with the Devonian Uzelga VHMS deposits of the southern Urals formed by cold seawater interaction (halmyrolysis) of hyaloclastic material with intercalated carbonates and sulphides. These units have been previously interpreted as either "jasperites", "gossanites" and "umbers". They have been investigated using REE geochemistry in both bulk samples and laser ablation inductively coupled plasma mass-spectrometry. In carbonate-rich hyaloclastic sediments the REE contents decrease in the following order: hyaloclastites → partially hematitized hyaloclastites → hematite-quartz aggregates. The REE contents in jasperites are therefore always much lower than in primary hyaloclastites. The REE patterns in most gossanites and umbers were preserved with the exception of a pronounced negative Ce-anomalies. The REE-behaviour is dependent on the presence of anion complexes available during sea-water/rock interaction. The presence of CO_3~(2-) and HCO_3~- in carbonate-bearing hyaloclastites promotes the formation of soluble carbonate REE-complexes and the migration of the REE into the subalkaline seawater during interaction of seawater with carbonaceous hyaloclastites.