Prospecting specularite-haematite resources with ETM+ and field data, Marampa iron occurrence, northern Sierra Leone

摘要

Marampa iron occurrence in northern Sierra Leone is hosted in the Precambrian of the West African Craton. Several iron ore prospects have been identified here by geological, geophysical and geochemical surveys. The Marampa rock units are dominated by massive beds of specularite-schist interstratified with quartz-micaschist which hosts the specularite-haematite mineralization. In this study, Crosta techniques and Band ratios are applied on ETM+ data to map alteration minerals in Marampa. The results show that, band ratios of 3/1 and 5/4 effectively enhanced areas with ferric-oxide and ferrous-bearing minerals, respectively. Crosta technique on the other hand was effective in mapping areas with hydroxyl-bearing minerals. Alteration anomalies were modeled and overlain with the deposit map of Marampa. The result of the overlay shows that, iron-oxides mapped with the band ratio 3/1 mostly occur within tailings deposits, whilst those (ferrous) mapped with band ratio 5/4 are most consistent with the primary orebody. Six zones of ferric and ferrous anomalies were randomly checked in the field and all occurred in the vicinity of previously mapped iron resources. Rock samples at depths of 2–5m were collected from the inspected ferric/ferrous anomalies for XRF geochemical analysis. Laboratory results for the tested field samples obtained an average feed of 30.7%Fe. This is a 98% correlation to the established 31.2%Fe average grade of the Marampa resource which has a cut-off of 15%Fe as at 2011. It is concluded that, applying band ratios on ETM+ data is effective in prospecting specularite-haematite and in differentiating between ferrous and ferric oxide occurrences.