New methodologies for volcanic-hosted copper sulphide mineralization on Cyprus: a GIS–prospectivity analysis-based approach

This report documents the results of a three-year collaborative research project between the British Geological Survey (BGS), The Natural History Museum, London (NHM) and the Geological Survey Department, Cyprus (GSD). It was funded by the Ministry of Agriculture, Natural Resources and Environment, Cyprus. The objectives of the programme were to develop new methodologies for the exploration and exploitation of cupriferous sulphide ore and re-establish metalliferous mineral exploration research on Cyprus and within the GSD. Initially the project only involved the BGS, the NHM and the GSD. However, early on, it became apparent that mining and mineral exploration companies held key datasets, needed to develop the new methodologies. Therefore, negotiations were conducted with the Hellenic Mining Company, Eastern Mediterranean Minerals and Hellenic Copper Mines . These established a framework for collaboration and all parties signed a confidentiality agreement. This allowed the BGS–NHM–GSD team to use proprietary data in their combined metallogenic–prospectivity analysis and the companies to have exclusive access to project results for six months after project completion. The project comprised five distinct components: • Technology transfer and institutional strengthening. • Development of new metallogenic models for ophiolite–hosted mineralization, including an examination of gold-rich epithermal-style mineralization associated with submarine basalts. • Mineralogical and metallurgical analysis of low-grade copper mineralization, with a review of solvent extraction electro-winning (SX-EW) technologies. • The use of legacy and new data at the regional to district scales for GIS-based prospectivity modelling. This included a reinterpretation of geophysical data. • A pilot study, using the prospectivity analysis, to define and test the mineralization potential of prospectivity anomalies. To facilitate technology transfer and institutional strengthening the project delivered a number of office and field-based seminars and workshops. These included training in the use of GIS for prospectivity analysis, examination of potential epithermal style mineralization, lectures on: (i) epithermal mineralization in the Aegean, (ii) VHMS mineralization in the Urals and (iii) SX-EW hydrometallurgical techniques—these were given to the Cyprus Society of Geologists and Engineers to ensure the widest dissemination. In addition, to give the project an international dimension, the prospectivity analyses were presented at two international conferences in Thessaloniki and Beijing. The project produced, using ArcSDM and a variety of geological, geophysical and remote sensing datasets, two prospectivity investigations: (i) a regional prospectivity map covering all of the Troodos Massif. This identified eight separate areas of high mineralization potential. The areas are generally located within 10 km of the boundary between the Troodos ophiolite and the autochthonous sedimentary cover sequences draping the ophiolite. (ii) A more detailed map focussed on an area of the northern Troodos. This identified drilling targets in the Memi–Alestos area. Key components to the prospectivity analysis undertaken by the project team included: (i) The digitisation of mineral occurrences and gossan distribution. (ii) The analysis of remote sensing data using band ratio image processing techniques to highlight regional alteration trends. (iii) The modelling and interpretation of airborne magnetic geophysics comprised the amalgamation of three generations of data into a single data set and the identification of lineaments and regions with positive and negative magnetic anomalies. In addition to the development of an ophiolite-hosted prospectivity GIS for the Troodos, the project addressed two new metallogenetic concepts for Cyprus—namely (i) The investigation of potential epithermal style VHMS mineralization using infrared spectroscopic and X-ray diffraction techniques. This study identified high temperature advanced argillic alteration phases and concluded that sub-seafloor boiling was responsible for some of the gold enrichment recorded in Cyprus-type VHMS mineralization (ii) The development of low-grade supergene Cu mineralization associated with massive sulphide mineralization. This showed that the favourable interplay between the mineralization and topography played an important role in the development of the large secondary low-grade orebodies. A strategy for exploring for such a supergene copper target would be to assess all surface gossans developed in topographic highs and seek potential downslope areas of mineralization—the use of high resolution digital elevation models provided by techniques such as LiDAR could be a way forward in this respect Professor John Monhemius, Imperial College London, undertook a review of the use of SX-EW hydrometallurgical techniques as applied to Cyprus. This study concluded that the decline in copper recoveries in the heap leach process used at Skouriotissa is due to increasing amounts of primary chalcopyrite, a refractory mineral that is very resistant to dissolution by oxidation, in the run-of-mine ore as mining gets deeper. Recent processes developed for the hydrometallurgical treatment of chalcopyrite all involve the use of extreme conditions, such as high temperature pressure leaching, ultra-fine grinding, or intensified bacterial leaching—these may not be appropriate for Skouriotissa and the best option for extending the life of the plant may be the discovery and exploitation of further reserves of supergene altered copper ores containing leachable copper oxide and secondary sulphide minerals This will allow production to continue using the heap leaching technology currently in use. If necessary, the effectiveness of this leaching method towards secondary copper sulphide minerals could be improved by introducing tanks for bacterially pre-oxidising the leach solutions under optimum conditions, prior to being sprayed on to the ore heaps. One key component of the project was to formulate and implement a pilot project based on the results of the regional GIS. The goal of the pilot project was to site a borehole to test if prospectivity analysis had the capability to predict the location of unknown mineralization. The application of a detailed prospectivity GIS using public domain and proprietary geophysical data focussed on the northern Troodos identified a high prospectivity zone in the Memi–Alestos region. Two boreholes were sited to test for the presence of mineralization beneath Upper Pillow Lava cover and one of these encountered over 20 m of argillically and propylitically altered lavas containing minor amounts of pyrite and chalcopyrite. This shows that prospectivity analysis approach used in this project could be a useful tool for locating buried VHMS mineralization on Cyprus. This is especially so when high-resolution geophysical data are available. In terms of future work, the project identified development in the following areas: • The need for national high-resolution geochemical and geophysical datasets to provide pre-competitive information for mineral exploration and environmental assessment • The development of fuzzy logic techniques for prospectivity mapping • Processing and interpretation of high-resolution airborne remote sensing dat