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Abstract
The deposits of Rio Tinto are located in the Spanish segment of the Iberian Pyrite Belt and are hosted within felsic porphyritic volcanic rocks and tuffs. The orebodies comprise a spectrum from sedimentary exhalative (San Antonio) to sub-sea floor replacement of the volcanic host rocks (Filon Norte); the two largest masses (San Dionisio and Filon Sur) are closely associated with black shale and probably formed by partial replacement of these units in an anoxic setting. Alteration associated with ore deposition is typified by marginal sericitic (white mica) alteration, and central chloritisation and silicification in a multi-phase alteration history. Structures formed during initial plate convergence may have acted as controls on ore deposition, and evidence of such controls is retained in the distribution of various elements in the sulphide deposits. Tectonism followed the mineralisation, and overprinted previous extensional events and resulted in the development of slaty cleavage in the pelitic rocks with partial remobilisation of sulphides, and tight folds with associated shearing of the southern limb.
The author wishes to thank the management of EMED Mining Public Ltd and in particular Harry Adams (Managing Director) and Ron Cunneen (EMED Chief Geologist) for permission to publish this work. Thanks are also due to EMED colleagues John Ingram and Angelo Farci for discussions on various aspects of the project, and to Daniel de Oliveira and Gul Seddel for constructive reviews. Editorial comments by Neil Phillips improved the final presentation and are gratefully acknowledged.