The Piriá aluminous lateritic profile: mineralogy, geochemistry and parent rock

Abstract

ABSTRACT:Relatively small aluminous lateritic deposits are abundant in the northeast and northwest parts of the Pará and Maranhão states, respectively. Most of them hosts aluminum phosphate mineralization forming hills and plateaus that stand out in the topography of the undulating plains of this region. The Piriá ridge is one of those topographic features, covered by lateritic iron crusts that have been studied in the 1970s as part of iron ore exploration campaigns and recently for phosphates prospection. This study improves the knowledge about the evolution of the lateritic Piriá deposit and demonstrates its relationship with the most evolved laterites of the Amazon, known as mature laterites, which formed major ore deposits during the Paleogene. Samples of a 17 meter-deep borehole were investigated through mineralogical (X-ray diffraction -XRD, optical and electron microscopy) and chemical methods (inductively coupled plasma mass spectrometry -ICP-MS, inductively coupled plasma optical emission spectrometry -ICP-OES and X-ray fluorescence -XRF). The studied lateritic profile comprises a clay bauxitic horizon overlaid by an aluminous iron crust. Upwardly continuous dissolution of kaolinite occurs with the formation of gibbsite, as the result of intensive leaching, resulting in a higher Al2O3 content in the crust. The continuous formation of hematite from goethite resulted from the transition to more arid conditions. Anatase is a newly formed mineral (100-400 nm crystallites), showing a gradual increase, following the increase in TiO2 content, which is high and indicative of a mafic parent rock, confirmed by the Ti × Zr dispersion pattern. Prominent zoning in the lateritic profile is characterized by the mineralization in bauxite and augelite and abrupt chemical transition between the horizons, marked by a decrease in Si and increase in Fe content from the bottom to the top of the profile. These features are compatible and indicative of mature laterites formed in Amazon during the Paleogene. KEYWORDS:Gurupi region; mature laterites; bauxite. RESUMO: Depósitos lateríticos de pequeno porte são frequentes no nordeste do Pará e noroeste do Maranhão. A maioria está mineralizada em fosfatos de alumínio e ocorre em morros e platôs, que se destacam na planície rebaixada dessa região. A Serra do Piriá é uma dessas feições, estando recoberta por couraças ferruginosas, alvo de explotação na década de 1970 e de recente prospecção de fosfatos. Este trabalho buscou aprofundar o conhecimento sobre a evolução laterítica do depósito Piriá e demonstrar sua compatibilidade com os lateritos mais evoluídos da Amazônia, conhecidos como maturos, os quais constituem grandes mineralizações formadas durante o paleógeno. Investigaram-se amostras de um furo de sondagem com 17 m de profundidade, por meio de análises mineralógicas (difração de raios x -DRX, microscopia ótica e eletrônica) e químicas (espectrometria de massa por plasma acoplado indutivamente -ICP-MS, espectrometria de emissão óptica com plasma indutivamente acoplado -ICP-OE...

Geochemical characterization of the largest upland lake of the Brazilian Amazonia: Impact of provenance and processes

“…The positive correlation between Zr and REE indicates their preference for zircon. However, Ti is also positively correlated with REE, the same elements that correlates to Zr, suggesting that both zircon and anatase have accumulated together in the lateritic profile (Santos et al, 2016). The very similar distribution of Zr and SiO 2 in the SW portion of the LTI1 and the decrease in their concentrations towards the center of the lake are probably a function of hydraulic sorting of heavy minerals.…”

Genesis of the “soft” iron ore at S11D Deposit, in Carajás, Amazon Region, Brazil

“…10B and anatase -Fig. 10F), which are insoluble and usually immobile under surface conditions (Jiang et al 2005, Santos et al 2016. Furthermore, the distribution curves of the chondrite normalized REE values show the geochemical signature of BIF (Fig.…”

“…The contribution of laterite weathering has been demonstrated by Costa (1991), Costa et al (2005a), Horbe and Costa (2005), Costa et al (2009), Costa et al (2011), Costa et al (2014), Santos et al (2016), Costa et al (2016), and Oliveira et al (2016). Also, these authors described the intense weathering due to the lateritization process and intense erosional activity in the ore deposits located in the Carajás and Amazon region.…”

Petrological and Statistical Studies of the Limbiko Bauxite Deposit, Republic of Guinea

“…The gibbsitic bauxites, essentially Tertiary or younger [6], are found mainly in a tropical region characterized by a hot and humid climate [3]. Diaspora has been found as a minor component in several types of bauxite in which it is accompanied by gibbsite and boehmite [28] suggested that diaspora is the stable phase under the surface under climatic conditions and that gibbsite and boehmite are metastable, the presence of which is largely due to slow transformations. Alumogoethite, found in many bauxite deposits, is a substitute for Fe in goethite and soil [29].…”