Innovative analytical and geophysical technologies for detecting polymetallic orebodies in southern Spain

The depletion of near-surface mineral resources in the Iberian Pyrite Belt (IPB) necessitates exploration for deeper orebodies. Surface geochemical an d geophysical techniques produce numerous anomalies, but the problem is to select those with genuine potential for polymetallic mineralization. A proj ect was undertaken, therefore, with the objective of developing an effectiv e, low-cost exploration methodology that would improve the chances of detec ting buried, potentially economic, polymetallic sulphide deposits within th e Iberian Pyrite Belt. The project centred on the development, testing and application of new geoc hemical and geophysical techniques combined with refined geological interpr etation. In practical terms, the work concentrated on the development of ne w exploration field tools, more powerful data-processing and modelling syst ems, a new inductively coupled plasma-mass spectrometry (ICP-MS) laser abla tion probe and a refined system of exploration methodology. The products of the project include: interactive, three-dimensional modelli ng software (MODGM-5D) for the integration of geological and geophysical da ta (gravity and magnetics); software for a downhole, three-axis electromagn etic probe system designed to detect conductive bodies within a radius of a bout 150 m of a barren borehole; a selective gas sampler capable of trappin g volatile organo-metallic compounds derived fi om underlying mineralizatio n; a powerful laser ablation mass spectrometer capable of producing multi-e lement and multi-isotopic analyses from solid geological samples; a regiona l geotechnical database for the Spanish part of the Pyrite Belt in which da ta from diverse sources are combined and incorporated into a geographical i nformation system; characterization of discriminant geochemical and mineral ogical criteria (including hydrothermal alteration and metal enrichment fac tors) for sulphide orebodies; and block-modelling of the Los Frailes polyme tallic sulphide orebody. The gas sampler and the three-axis electromagnetic probe are direct prospec ting tools used to investigate anomalies obtained by broader-scale geochemi stry and geophysical surveys. Gravimetric modelling software is a data inte rpretation tool that can be used for modelling the possible shapes and size s of known orebodies and for interpreting virgin anomalies. The ICP-MS lase r ablation probe is used in the detailed laboratory studies required for th e definition and control of geological selection criteria. Geological crite ria defined by the project, including structural modelling, identification of indirect markers of massive sulphide mineralization and studies of miner al assemblages associated with sulphide mineralization, are relevant to all stages of mineral exploration, from the selection of a potential mineraliz ed province or geological series to the evaluation of an orebody. The main aim of the project, to develop improved exploration techniques bas ed on new technological tools and an improved methodological approach, was fulfilled. Geophysical and analytical tools were developed as planned and p erformed well under field and laboratory conditions. The results of this pr oject should facilitate the identification of prospective ground in the Pyr ite Belt and increase the efficiency of exploration programmes. The project was coordinated by the BRGM (France) and the partners were SEIE MSA (Spain), Rio Tinto Minera S.A. (Spain), VG Elemental (United Kingdom), ITGE (Spain), the University of Southampton (United Kingdom), the Universit y of Huelva (Spain) and APIRSA (Spain).