02 - A FLUOR-POOR WAVELLITE IN PHOSPHATE-RICH IRON CRUSTS IN AMAZON - 05-29-2020 GMGA - Grupo de Mineralogia e Geoquímica Aplicada - http://gmga.com.br 02 - A FLUOR-POOR WAVELLITE IN PHOSPHATE-RICH IRON CRUSTS IN AMAZON http://gmga.com.br/02-a-fluor-poor-wavellite-in-phosphate-rich-iron-crusts-in-amazon/ 10.31419/ISSN.2594-942X.v72020i1a2MLC Marcondes Lima da Costa1*, Alessandro Sabá Leite2, Ronny Kaden3, Herbert Poellmann3, Nilson F. 4 5 Botelho , Daniel Chaves Santos 1Instituto de Geociências (IG), Universidade Federal do Pará, Belém, Brazil, [email protected], [email protected] 2PPGG/IG, Universidade Federal do Pará, Belém, Brazil, [email protected] 3Universität Halle-Wittenberg, Halle an der Saale, Germany, [email protected] 4 Instituto de Geociências, Universidade de Brasília, Brasília, Brazil, [email protected] 5Phosfaz, Bonito, Pará, [email protected] *Corresponding author ABSTRACT The minerals of the alunite supergroup, which comprises aluminum phosphates and sulphates (APS), which in turn constitute the groups/series of crandallite-goyazite, woodhouseite-svanbergite and wardite- millisite, involve more than forty minerals, which are formed under the hydrothermal to supergenic conditions. Among the supergenics are the lateritic formations, being the Gurupi region, or more precisely Northeast of Pará and Northwest of Maranhão, in the Eastern Amazon a world classic geological example. Here, in addition to the minerals of these groups or series, senegalite, augelite, variscite and also wavellite occur. The latter, however, is always restricted, while the others may form a characteristic horizon. At the Sapucaia phosphate mine in Bonito, Pará, this mineral is presented in beautiful centimeter druses. The work describes this mineral in terms of its morphological, crystallographic and chemical characteristics, highlighting its poverty in fluorine, and discusses why its formation is restricted in terms of volume and to aluminous phosphate iron crust, concluding that the wavellite is directly linked to the initial weathering alteration. 1 / 16 02 - A FLUOR-POOR WAVELLITE IN PHOSPHATE-RICH IRON CRUSTS IN AMAZON - 05-29-2020 GMGA - Grupo de Mineralogia e Geoquímica Aplicada - http://gmga.com.br Keywords: lateritic iron crust; crandallite-goyazite; woodhouseite-svanbergite; Sapucaia; Bonito; Gurupi. INTRODUCTION The geological occurrences of aluminum phosphates are frequent in the Earth's crust, normally associated with peraluminous rocks in different environments (Dill, 2001), and are currently denominated together with aluminum sulfates, APS (Aluminum Phosphates and Sulfates Minerals), with which are generally associated. APS comprises more than 40 species in the alunite supergroup alone (Dill et al., 1995, Jambor, 1999; Dill, 2001. The general formula of these alunite minerals is AB3(XO4)2 (OH)6, where A is a large cation (Na, U, K, Ag, NH4, Pb, Ca, Ba, Sr, REE) and B sites are occupied by cations of the x- elements Al, Fe, Cu and Zn. In nature, the anion (XO4) is dominated by P and S (Dill, 2001). The alunite supergroup comprises the series of crandallite, woodhouseite and wardite, among others. In the series of crandallite the most important minerals are, this mineral, and goyazite, florencite, gorceixite and plumbogummite; in the woodhouseite, this mineral and svanbergite; in the wardite series, wardite and millisite. The minerals from these series are frequent in lateritic aluminum phosphate deposits, with the Northeast region of Pará and Northwestern Maranhão (Costa & Costa, 1980; Costa et al., 1980, Oliveira & Schwab, 1980; Schwab et al., 1983, 1989, 1993; Pöllmann et al., 1987; Toledo et al., 2006; Costa et al., 2016), as the most significant example worldwide. Dill (1995, 2001) shows the wide range of environments in which these minerals can form and, therefore, demonstrates how frequent they are. In general, they are found as small occurrences, many of them even rare, associated with hydrothermal veins, in rocks such as phyllites and schists, mainly as venules and quartz veins; also in rocks modified by volcanic activities (Dill et al., 1995) and in tropical and paleosol soils, in cryptocrystalline, spherulite and acicular-radial and microcrystalline masses, and rarely as millimeter crystals in cavities. In addition, aluminum and aluminum-iron phosphates are known in recent organic accumulations, such as the guano deposits in Chile and Peru (Costa, 1979, 1982) and old ones in Romania in caves developed in limestone terrains (Costa, 1982; Polyak et al., 1996; Dill, 2001). In lateritic environments, complex solid solution series of these minerals occur, as already mentioned, but in addition to them, variscite, AlPO4.2H2O, wavellite, Al3 (PO4)2 (OH, F)3•5(H2O), augelite, Al2(PO4) (OH)3 and more recently Senegalite, Al2(PO4) (OH)3•(H2O) (Johan, 1976; Costa & Reymão, 1984; Pöllmann et al., 1987) also stand out. These aluminum phosphates, however, can form economical mineral deposits in lateritic formations (Costa et al., 2016). The main lateritic occurrences in Senegal, the Christmas Islands, Australia, Ghana, Florida and Brazil (Capedcomme, 1953; Slansky et al., 1964; Flicoteaux, 1982; Costa,1982; Flicoteaux & Lucas, 1984; Dill, 2001) formed mainly from sedimentary rocks with phosphorites; in Canada, Australia, Gabon and Brazil (Costa, 1979, 1982; Schwab et al 1993) from magmatic rocks mineralized in apatite, and metamorphic in Brazil, Ghana, (Costa, 1979, 1982). In Brazil alone, lateritic aluminum phosphates have found a favorable environment to form, namely: exposure of in apatite mineralized primary rocks to hot and humid tropical conditions during the Cenozoic, which are essential for the establishment of intense tropical weathering, and in the Amazon region they reached their climax. Laterite formations mineralized in aluminum phosphates have been discovered in several areas of this region, however the biggest highlight is for the eastern portion of this region, the Northeast of Pará and the Northwest of Maranhão (better known as the Gurupi region, Figure 1), in its Atlantic coast zone and not so much from it (Costa, 1979, 1982; Costa & Costa, 1980; Costa et al., 1980; Oliveira & Schwab, 1980; Schwab et al., 1983, 1987; Costa et al., 1980, 2016), as previous mentioned. The first publication with reference to bauxite with phosphorus in the region (Pirocaua and Trauira) was presented by Shaw et al. (1925) and the first 2 / 16 02 - A FLUOR-POOR WAVELLITE IN PHOSPHATE-RICH IRON CRUSTS IN AMAZON - 05-29-2020 GMGA - Grupo de Mineralogia e Geoquímica Aplicada - http://gmga.com.br detailed pioneering publication on aluminum phosphates in the region by Brandt (1932), who recognized the lateritic terrain, but did not recognize the phosphates as lateritic, but as guano deposits. In this region, aluminum phosphates constitute the upper portion of the lateritic profile, forming a horizon up to more 10 m thick, extending up to 1.5 km in length. The most common aluminum phosphates are from the crandallite-goyazite, augelite, senegalite, wardite and variscite series. Wavellite is present, but always very restricted. Augelite and senegalite were found as mm crystals lining sub-centimeter cavities, but in general they are massive and constitute in some deposits a thick horizon rich in phosphorus. By the way, senegalite was an unknown mineral until 1976, when it was discovered in Senegal (Johan, 1976) as a rarity and later as an abundant mineral in the Gurupi region (Costa & Costa, 1980; Costa et al., 1980; Costa & Reymão, 1987; Pöllmann et al., 1993). Wavellite, on the other hand, seems much more restricted, does not develop a mineral horizon, like the others. It has recently been identified in millimeter to sub-millimeter-large crystals in cavities up to 20 cm inside of the aluminum phosphate iron crust from the Sapucaia phosphate deposit in Bonito, in the northeast of Pará (Costa et al, 2016, in this BOGEAM bulletin). On this occasion, the present work describes and discusses this occurrence in the context of lateritic deposits in the Gurupi region, but especially in the Phosphorues Rectangle “Santa Maria-Bonito- Ourém-São Miguel do Guamá”, in the northeast of the state of Pará (Figure 1). In fact, the current knowledge is a result of the pioneering research work of the Phosphates Project in the Northeast of Pará and the Northwest of Maranhão, financed by the Humid Tropic/CNPQ, started in 1976 with the active participation of the first author, since that time, and coordinated by the UFPA professor Manoel Gabriel Siqueira Guerreiro, already deceased, who unfortunately was not thrilled with the theme. 3 / 16 02 - A FLUOR-POOR WAVELLITE IN PHOSPHATE-RICH IRON CRUSTS IN AMAZON - 05-29-2020 GMGA - Grupo de Mineralogia e Geoquímica Aplicada - http://gmga.com.br Figure 1 – Location of the Sapucaia aluminum phosphate deposit, in the municipality of Bonito, northeast of the state of Pará and of the other known deposits in northeast of Pará and northwest of Maranhão (Gurupi region), with emphasis on the Rectangle Santa Maria-Bonito-Ourém - São Miguel, highlighting the most recent discoveries of aluminum phosphates in this area (smaller dots in red). Modified from Leite (2014). The phosphates from Sapucaia, at Bonito The phosphates of Sapucaia and Boa Vista deposits are located in the municipality of Bonito, in the northeast of the state of Pará, 140 km far from its capital Belém (Figure 1). These deposits were discovered and studied by Costa & Costa (1987, 1991) and investigated in detail by Leite (2014),