To reduce exploration costs in the mining districts rich in showings (copper, lead, zinc, precious metals) by optimizing the methods for selecting the main bodies.
Work has been carried out to establish exploration criteria and methods to locate metal rich zones in the South Iberian Pyrite Province, possibly the largest massive sulphide province in the world. The research was centred on a study of the geological sequence hosting the volcano massive sulphide (VMS) deposits, as well as on the mineralogical, chemical and structural characteristics of the mineralization, and the results have made it possible to establish a predictive model of massive sulphide distribution throughout the province. The development of a specific geographical information system made possible a very efficient, objective and systematic multidataset processing that takes into account both classical exploration data (ie gravimetry, geochemistry) and the geological characteristics of the massive sulphide mineralization and its environment. This enabled a ranked anomaly map to be produced for the exploration area. The work carried out has established that:
no characterization is possible of a specific mineralizing volcanic event among the acidic volcano sulphide (VS) facies presumed to be closely linked to the mineralization. Nevertheless, all the acidic volcanites of the VS show rare earth element (REE) patterns typical of sulphide hosting volcanites;
from the standpoint of mineral paragenesis and lead isotopic signatures, no difference can be seen between the pyritic and the polymetallic orebodies. Nevertheless, the mineralogy, Pb isotopic signature and palaeostructural context can be used for identifying a doubtful mineralized occurrence as a positive indicator of a massive sulphide stockwork;
no direct relationship can be determined between the polymetallic character of a gossan and that of the original sulphide mineralization;
the distribution of massive sulphide deposits and associated mineralization could be structured in kilometre long alignments showing specific metallogenic characteristics;
within a delimited exploration area, multidataset processing enables better focusing on priority anomalies.
In order to define parameters for high metal contents which will make it possible to prepare enrichment guides, the following will be studied:
the palaeostructural anomalies likely to serve as drains in hydrothermal phenomena;
volcanic development across the province and its connection with the mineralisation observed;
the petrochemistry of the acid volcanic systems supporting mineralisation, and of their basic companions, as well as their effect on mineralisation;
the parameters revealing geothermal palaeogradients;
the mineralogical zoning and the geochemical haloes of the hydrothermal columns and the emanation levels synchronous with, or subsequent to, the sulphide bodies;
the variations of isotopic compositions of the lead in the minerals reflecting differences in the sources of the hydrothermal systems;
the petrochemistry of the chemical precipitates accompanying or following the deposition of the mineralisation, which might indicate the tenor of the ores;
the relationships between different reference bodies, high and low in base metals and precious metals respectively, in the South Iberian province.
The work programme will consist of the following stages.
Firstly, modelling of deposits characteristic for their high content of base metals and precious metals. This modelling is envisaged for the following deposits: Chaparitta, Pena de Hierro, Rio Tinto in Spain and Gravio, Serra Branca, Breijo and Sao Domingos in Portugal. A summary sheet will be prepared for each of these deposits containing a grading system for the parameters of high tenors and the corresponding guides.
Secondly, preparation of summary sheets on several deposits selected across the province: Herrerias, 3 bodies in the Tharsis region, Le Zarza, Aznalcollar, La Joya, Nerva, San Miguel, San Telmo, and Lomero Poyatos. The aim is to put the study of the guides on a regional basis.
Thirdly, the guides obtained in the first 2 stages will be tested on zone 7 (according to the numbering adopted by the Spanish Mines Directorate in the South Iberian province). This zone contains several types of pyritic deposits, sometimes polymetallic (copper, lead, zinc, precious metals), as well as some lenticular deposits of manganese and some chert and chloritite levels. The method adopted will comprise some lithostructural and lithogeochemical sections oriented by a remote sensing survey. With this survey, and a structural analysis at ground level, it will be possible to assess the importance of palaeostructure in the studies.
Fourthly, the multidata analysis results (geology, geophysics, geochemistry) available, or obtained from zone 7, will be processed using th Syner GIS software for presentation in the form of thematic maps in which the most promising zones will be plotted.
Lastly, sampling at the surface and on drill cores will be carried out in Portugal on the Gaviao, Serra Branca, Breijo and Sao Domingos deposits, in order to undertake the same type of studies on ores and the surrounding rocks.
Funding SchemeCSC - Cost-sharing contracts