The source of Au and S of the orogenic gold deposits in the Llamas de Cabrera district (Iberian Variscan Massif)

Gómez-Fernández, F. and Cunningham, John and Caldevilla, P. and Herrero-Hernández, A. and Beard, Andy (2019) The source of Au and S of the orogenic gold deposits in the Llamas de Cabrera district (Iberian Variscan Massif). In: UNSPECIFIED (ed.) Proceedings of the 15th SGA Biennial Meeting, 27-30 August 2019, Glasgow, Scotland. Society for Geology Applied to Mineral Deposits, pp. 842-845. ISBN 9780852619636.

Abstract

Using optical scanning electron microscopy, electron microprobe and sulphur isotopic analysis, pyrite and graphite in black slates and volcanic rocks from Luarca Formation were studied. Four types of pyrite are present in the black slates. In ascending order according to their evolutionary degree: framboidal, framboidal evolved, subhedral macroscopic, and euhedral macroscopic pyrite. The content in Au, As and other metals are significantly higher in the framboidal than in the other pyrite types. The gold included in the pyrite and probably also in the organic matter would have been released during diagenesis and Variscan metamorphism, in order to form the orogenic gold deposits in the district. δ34S distribution in Luarca Formation pyrites is similar to that of sulphides from the gold deposits in the district, with mean values of 13.8‰ and 12.4‰ respectively, although in the pyrites from the black slates the variability range is wider. The data gathered are in agreement with the existence of two sulphur sources, marine sulphate and magmatic sulphur, the former being the main source of the sulphur involved in these processes

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