TiO₂ in the coastal sands of Brazil

Brazil is a major titanium province hosting the minerals ilmenite, leucoxene, anatase, and rutile in very large scale geological settings. Brazil contains huge carbonatite complexes that host anatase and perovskite. The Brazil craton contains igneous and metamorphic complexes, such as rutile-bearing eclogites that contain up to 10% rutile. However most of those complexes are highly retrograded, altered, and/or of insufficient volume and grade to be sources of titanium ore minerals.

The very long Brazil coastline with enormous stretches of sand is a prime environment for the formation of heavy mineral sand deposits. Certain climatic zones are excellent for caus-ing alteration of ilmenite and the enhancing of its titanium grade. In Bahia state, huge re-serves containing high grade ilmenite (~60% TiO₂) are identified (Pratiga area). There is also an operating heavy mineral mine at Mataracas. Clearly, sectors of the Brazil coastal region contain all the geological parameters necessary for the development of heavy mineral sand deposits that contain higher grade ilmenite.

In the period 2008 to 2012 GEUS and DuPont sampled deposits/localities along ca. 4000 km of Brazilian coast with the focus to locate occurrences of +60% TiO₂ ilmenite and to under-stand how and where deposits of such ilmenite are formed in Brazil. A total of 143 samples were analyzed via Computer Controlled Scanning Electron Microscopy (CCSEM) at the GEUS labs. Of those, 70 are from the Gurupi River area and other DuPont programs con-ducted before 2008. 44 have been collected by GEUS as part of the regional sampling program and 26 are from the Pratiga and Punta do Mota deposits just south of Salvador.

The analyses of the samples show that +60 % TiO₂ ilmenite is found at several locations along the Brazil coastline and that there are sizable accumulations of titanium minerals that are not being mined, e.g. at Pratiga south of Salvador. At Pratiga, the Bahia State Geologi-cal Survey has identified about 266 million tons of sand with 2.6 % titanium minerals and zircon (ca. 3.1 % total heavy minerals). CCSEM of samples collected in the Pratiga deposit during the present program average 61.7 % TiO₂ for ilmenite and for all titanium minerals, 69.1 % TiO₂. The local authorities have been active in trying to promote mining of the depos-its at Pratiga and address environmental issues. However, at the time of writing, it is not clear how mineral rights could be obtained nor if development is possible.

The formation of high grade ilmenite (> 60 % TiO₂) is dependent on a number of factors, but chief among them is climate. On the northern coast of Brazil there is a shift from east to west where the dry climate in the east can be coupled with low TiO₂ ilmenite and immature heavy mineral assemblages whereas to the west, close to the very humid climate in the Amazon basin, high TiO₂ grade ilmenite occurs together with mature heavy mineral assemblages (e.g. without mafic silicates). In general, most of the Brazilian coastal sand deposits are mature.

Kaolinite rich sandstones belonging to the Tertiary Barreiras Formation occur near the Brazilian coast. Such sandstones that are altered to kaolin rich deposits also contain high grade ilmenite and a very mature heavy mineral assemblage. Cretaceous sandstones in the Amazon Basin are also deeply altered and kaolinized and characterised by very mature heavy mineral assemblage and high TiO₂ ilmenite. When such deposits are reworked the grade of the ilmenite is inherited. This is probably the case for ilmenite deposits in both the Gurupi River area and the Pratiga area both with Cretaceous or Tertiary sandstones in the hinterland.

During the last ½ million years at least 5 episodes of sea level high stands affected coastal processes in Brazil. Beach deposits developed during those episodes are common in Brazil. Where Pleistocene elevated beaches have been exposed to the intense weathering climate of Brazil, the contained ilmenite has a high TiO₂ grade.