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Th e mineral ilmenite (FeTiO3) is an important component of heavy-mineral placer deposits and constitutes the largest volume of valuable mineral in such deposits. Th e minerals zircon (ZrSiO4) and rutile (TiO2), which occur in lower concentrations than ilmenite in the deposits, have a greater value per ton – c. 1100 and 900 $/ton respectively – compared to ilmenite that ranges from 100 to 200 $/ton depending on its composition. Other minerals such as staurolite, sillimanite, amphibole and garnet are generally also present in placer deposits, but are of minor or no commercial value and, e.g. amphibole needs to be separated from the valuable heavy minerals which adds to the production cost. Ilmenite is more valuable as a raw material in titanium dioxide manufacture if the titanium content is enhanced by natural leaching of the iron component. When exploring for potentially economic heavy-mineral placer deposits, both the variation in composition and distribution of ilmenite are of interest. Accordingly, it is also important to understand not only the concentration of heavy minerals in the ground but also the abundance and composition of the individual minerals. Th e source (provenance), route and mechanism of transport from source to potential reservoir sandstones are of interest when attempting to understand petroleum systems in sedimentary basins. Heavy minerals in reservoir sandstones contain a wealth of information about their formation that characterises their source. Th us a database with the characteristics of possible sediment sources is a key tool to investigate the distribution, composition and other characteristics of the heavy minerals in a given area. Both heavy-mineral exploration and locating off shore petroleum reservoir sand sources are relevant in northern Brazil. In June 2011, the Geological Survey of Denmark and Greenland in cooperation with Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil set up a project to sample and analyse in situ Cretaceous sandstones, sands in river beds and sands from the coastal sediments. Th e results were entered into a database of heavy-mineral compositions and properties. Th e variation in the distribution of the heavy minerals as well as their composition were determined for 34 samples from northern Brazil using computer-controlled scanning electron microscopy (CCSEM; Keulen et al. 2012). U-Pb ages of detrital zircons were determined by laser ablation inductively coupled plasma mass spectrometry (for analytical procedures see Frei et al. 2006). Four samples for the U-Pb age determinations came from Cretaceous sandstones, two from river beds and two from beaches.

Composition of ilmenite and provenance of zircon in northern Brazil