Ore Geology Reviews 41 (2011) 112–121 Contents lists available at ScienceDirect Ore Geology Reviews j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o r e g e o r ev The Catalão I niobium deposit, central Brazil: Resources, geology and pyrochlore chemistry Pedro Filipe de Oliveira Cordeiro a,⁎, José Affonso Brod a, b, Matheus Palmieri a, c, Claudinei Gouveia de Oliveira a, Elisa Soares Rocha Barbosa a, b, Roberto Ventura Santos a, José Carlos Gaspar a, Luis Carlos Assis c a b c Universidade de Brasília, Campus Darcy Ribeiro ICC Central, Instituto de Geociências, Brasília-DF, 70910-900 Brazil Universidade Federal de Goiás, Campus Samambaia, Instituto de Estudos Sócio-Ambientais, Universidade Federal de Goiás, Goiânia-GO, 74001-970 Brazil Anglo American Brazil LTDA, Avenida Interlândia 502, Setor Santa Genoveva, Goiânia-GO, 74672-360 Brazil a r t i c l e i n f o Article history: Received 24 March 2010 Received in revised form 23 June 2011 Accepted 24 June 2011 Available online 22 July 2011 Keywords: Catalão I Carbonatite Phoscorite Nelsonite Pyrochlore a b s t r a c t The Catalão I alkaline–carbonatite–phoscorite complex contains both fresh rock and residual (weatheringrelated) niobium mineralization. The fresh rock niobium deposit consists of two plug-shaped orebodies named Mine II and East Area, respectively emplaced in carbonatite and phlogopitite. Together, these orebodies contain 29 Mt at 1.22 wt.% Nb2O5 (measured and indicated). In closer detail, the orebodies consist of dike swarms of pyrochlore-bearing, olivine-free phoscorite-series rocks (nelsonite) that can be either apatite-rich (P2 unit) or magnetite-rich (P3 unit). Dolomite carbonatite (DC) is intimately related with nelsonite. Natropyrochlore and calciopyrochlore are the most abundant niobium phases in the fresh rock deposit. Pyrochlore supergroup chemistry shows a compositional trend from Ca–Na dominant pyrochlores toward Ba-enriched kenopyrochlore in fresh rock and the dominance of Ba-rich kenopyrochlore in the residual deposit. Carbonates associated with Ba-, Sr-enriched pyrochlore show higher δ18OSMOW than expected for carbonates crystallizing from mantle-derived magmas. We interpret both the δ18OSMOW and pyrochlore chemistry variations from the original composition as evidence of interaction with lowtemperature fluids which, albeit not responsible for the mineralization, modified its magmatic isotopic features. The origin of the Catalão I niobium deposit is related to carbonatite magmatism but the process that generated such niobium-rich rocks is still undetermined and might be related to crystal accumulation and/or emplacement of a phosphate–iron-oxide magma. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Brazil is the largest niobium producer in the World due to mining of residual deposits overlying the Araxá and Catalão I and II carbonatite complexes. These deposits represent more than 85% of the world's niobium supply. Although these complexes have been mined for more than 30 years, data from the Araxá niobium deposit is virtually unavailable and information on the Catalão I (Cordeiro et al., 2010, 2011) and Catalão II (Palmieri, 2011) deposits was published only recently. Not only general information is restricted but genetic interpretation of these niobium deposits is limited to “weathering of carbonatite related rocks” (Carvalho and Bressan, 1981; Gierth and Baecker, 1986). Cordeiro et al. (2010, 2011) studied the primary fresh ore and determined that pyrochlore occurs mostly in apatite- and magnetite-rich rocks that crosscut previous phoscorites and phlogopitites. According to ⁎ Corresponding author. Tel.: + 55 61 38779639. E-mail address: cordeiropfo@gmail.com (P.F.O. Cordeiro). 0169-1368/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.oregeorev.2011.06.013 the classification of Yegorov (1993) for olivine-poor member of the phoscorite series these unusual rocks are named nelsonite. At Catalão I, nelsonites are intimately associated with dolomite carbonatites and form two main swarms of densely-packed thin dikes near the center of the complex (East Area and Mine II orebodies). The direct relationship between phoscorite-series rocks and niobium mineralization in fresh rock has also been suggested in the Catalão II (Palmieri, 2011) and Araxá niobium deposits (Nasraoui and Waerenborgh, 2001). Although it is only the second largest niobium deposit in Brazil, Catalão I is the best understood. Mining of the Catalão I residual deposit started in 1976 with a reserve of 19 Mt at 1.08 wt.% Nb2O5 (Hirano et al., 1990; Rodrigues and Lima, 1984) and was discontinued in 2001 with a remaining residual reserve of 9.65 Mt at 1.19 wt.% Nb2O5 (our data) while mining focused on the Boa Vista mine in Catalão II. Recent modeling of the fresh rock deposit indicate a unpublished resource of 21.8 Mt at 1.22 wt.% Nb2O5 for the East Area orebody and 7.2 Mt at 1.23 wt.% Nb2O5 for the Mine II, adding up to a total reserve of approximately 29 Mt at 1.22 wt.% Nb2O5 for the Catalão I complex. In this paper we studied drill core samples from the fresh rock Catalão I deposit collected between depths of 100 and 500 m. Our 113 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 main aim is to describe the deposit and provide information on pyrochlore chemistry in order to establish the main crystal chemistry features and substitutions. We also compare Catalão I pyrochlore chemical composition with that of Lueshe (Nasraoui and Bilal, 2000), Oka (Gold et al., 1986; Zurevinski and Mitchell, 2004) and Sokli (Lee et al., 2006) to contribute for a broader model of pyrochlore evolution in carbonatite complexes. Finally, we address some points of significance for the bearing of magmatic processes in the origin of a phoscoriterelated niobium deposit. 2. Niobium deposits Most commercial niobium is from carbonatite-related sources, but minor production comes as a byproduct of tantalum and tin mining in pegmatites. In Table 1 we compiled and updated data from Woolley and Kjarsgaard (2008) on the World's niobium reserves. When possible, we report only measured, indicated and historical reserves, hence several resources listed in Table 1 are smaller compared to what is found in the literature. There are several carbonatite related niobium deposits worldwide, comprising residual and/or fresh rock resources, but only the Boa Vista (Catalão II), CBMM (Araxá) and Niobec (Saint Honoré) deposits are currently in production (Fig. 1). The number of untapped niobium deposits in Africa and the general lack of information on the Brazilian underground resources is noteworthy. Detailed information on Brazilian carbonatite-related deposits is given by Biondi (2005), but an equivalent study of African niobium deposits is still to be made. 3. The Alto Paranaíba Igneous Province (APIP) The APIP is a NW trending province of Late-Cretaceous alkaline igneous rocks intruding Neoproterozoic rocks of the Brasília Belt, between the NE border of the Paleozoic Paraná Basin and the SW border Fig. 1. Grade-tonnage data showing metal grades (wt.% Nb) for carbonatite-related niobium deposits (please refer to Table 1 for references). Stars are deposits in production and circles represent resources. of the Archean São Francisco Craton. The province origin is attributed to the initial impact of the Trindade Mantle Plume beneath Central Brazil at ca. 85 Ma. According to Gibson et al. (1995) and Thompson et al. (1998), thinning of the lithosphere under the Brasília Belt allowed mantle plume heat to penetrate by conduction and advection causing melting of readily fusible, K-rich parts of the lithospheric mantle. Xenoliths of perovskite-rich pyroxenite (bebedourite) and pyroxenite in APIP kamafugite lavas and pyroclastics are analogous to ultramafic rocks occurring in the carbonatite complexes, thus providing evidence of the intimate association between kamafugites and Table 1 Comparison of carbonatite-related niobium deposits (adapted from Woolley and Kjarsgaard, 2008). Complex Country Status Style Association Resources Reserve Mt Nb2O5% Nb% Main references St-Honoré Araxá Canada Brazil Active mine Active mine Primary Residual Nb + REE Nb+Fe+P Measured and indicated 32 462 0.56 2.48 0.39 1.73 Catalão II Brazil Active mine Residual Nb Probable reserve 3.4 1.67 1.17 Lueshe Sukulu Oka Congo Uganda Canada Past producer Past producer Past producer Residual Residual Primary Nb P + Nb Nb 30 230 37.5 1.34 0.25 0.53 0.94 0.17 0.37 Catalão I Brazil Residual Nb+Fe+P 19 1.08 0.76 Catalão I Araxá Tapira Bonga Brazil Brazil Brazil Angola Past producer and resource Resource Resource Resource Resource Primary Primary Residual Primary Nb+Fe+P Nb+Fe+P Nb Nb 29 940 166 824 1.22 1.6 0.73 0.48 0.85 1.12 0.51 0.34 Bingo Mrima Congo Kenya Resource Resource Residual Residual Nb + P Nb + REE 13 75 3.3 0.7 2.31 0.49 Ondurakorume Namibia Resource Primary P+Nb+REE 8 0.3 0.21 Mbeya (Panda Hill) Aley Bone Creek (Fir) Argor Tanzania Resource Primary Nb + P 125 0.3 0.21 Canada Canada Resource Resource Primary Primary N+P+REE Ta + Nb 20 23.1 0.7 1.14 0.49 0.80 Canada Resource Primary Nb+P+Zr 62.5 0.52 0.36 Martison Lake Canada Resource Residual P + Nb Measured and indicated 62.2 0.34 0.24 Nemegosenda Lake Seis Lagos Canada Resource Primary Nb Inferred 49.9 0.43 0.30 Brazil Resource Residual Nb Measured and indicated 2.47 1.73 www.iamgold.com (Resources 2009) Rodrigues and Lima (1984), Hirano et al. (1990) http://www.cbmm.com.br/ (conference paper by Guimarães and Weiss) Deans (1966) Deans (1966); van Straaten (2002) http://www.niocan.com/ (Technical Report February 10 2010) Rodrigues and Lima (1984), Hirano et al. (1990) This paper Issa Filho et al. (1984) Melo (1997) Pena (1989); Kamitani and Hirano (1991) Woolley (2001) Deans (1966); Notholt et al. (1990); Pell (1966); Woolley (2001) Verwoerd (1967, 1986); Woolley (2001) Deans (1966); Woolley (2001); van Straaten (2002) Richardson and Birkett (1996) www.commerceresources.com (Technical Report June 20 2007) Stockford (1972); Woolley (1987); Sage (1988) Woolley (1987); www.sedar.com (Technical Report May 31 2007) www.sarissaresources.com (Technical Report July 2009) Justo and Souza (1986) Measured, Indicated and historical reserves Measured and indicated Indicated 239 114 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 carbonatites in the APIP (Brod, 1999; Brod et al., 2000, 2001). Those authors argued in favor of a common subcontinental lithospheric mantle origin for kamafugites and the parental magma of APIP complexes (phlogopite picrite). The temporal and spatial association between these alkaline rocks defines a kamafugitic–carbonatitic association in the APIP, similar to those occurring in Italy (Stoppa et al., 1997; Stoppa and Cundari, 1995) and China (Yang and Woolley, 2006). APIP carbonatite complexes also host phosphate (Araxá, Catalão I and II, Tapira and Salitre), titanium (Serra Negra, Salitre, Tapira and Catalão I), and rare earth (Catalão I) deposits, as well as occurrences of vermiculite, copper, barite and magnetite. Thus, the APIP is of great economic interest and can provide key information for mineral exploration of carbonatite-related deposits. 4. The Catalão I Carbonatite Complex The Catalão I Complex (Fig. 2) is located in Central Brazil at 18°08′ S, 47°48′W, near the cities of Catalão and Ouvidor. The complex has intruded quartzites and schists of the Late Proterozoic Araxá Group as a vertical pipe with a diameter of ~6 km at surface, creating a domelike structure. The age of the intrusion is reported by Sonoki and Garda (1988) as 85 ± 6.9 Ma (K–Ar, phlogopite). The complex can be divided into an outer zone dominated by phlogopitite and an inner zone composed mostly of dolomite carbonatites and phoscorite-series rocks. The outer zone comprises phlogopitites and rare dunites, pyroxenites and bebedourites (perovskite-rich pyroxenites). Phlogopitite is interpreted as the result of interaction of former ultramafic rocks with carbonatite fluids (Brod et al., 2001). Ultramafic relicts within phlogopitite, which sometimes retain the original mineral assemblage unaffected by fluid alteration, are a very strong evidence for phlogopitization. The dominance of phlogopitite over other rock types in the outer zone attests to the extremely intense carbohydrothermal alteration that occurred in the complex. Fig. 3. Combination of an Ikonos image showing the roughly circular Mine II open pit and a 3-D model of the Mine II and East Area orebodies. The inner zone is composed of magnetite–apatite-rich rocks and carbonatite. The Catalão I fresh rock deposit is intimately related to these rocks and can be divided into Mine II and East Area orebodies (Fig. 3). Mine II is a roughly oval, pipe-like body, 200 m long and 100 m wide, hosted mainly by dolomite carbonatite. East Area is an L-shaped orebody, 400 m long, 200 m wide hosted by phlogopitite. Both orebodies are open at depth and deep drilling confirmed their extension at until a depth of at least 800 m. Fig. 4 shows the general pipe-like geometry of East Area and Mine II orebodies. Despite their shape, the orebodies do not represent single, homogeneous pyrochlore-bearing magnetite–apatite rocks, but rather dike swarms up to 2 m wide and plugs up to 10 m wide. The main Nb-mineral within the orebodies is pyrochlore. Aside from pyrochlore modal content, ore grades are also controlled by Fig. 2. Geological sketch of the Catalão I Complex. The fresh rock niobium deposit occurs in the center of the complex comprising the nelsonite unit. Adapted from Brod et al. (2004). P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 115 Fig. 4. Schematic model of the fresh rock niobium ore, where apatite nelsonite P2, magnetite nelsonite P3, and dolomite carbonatite DC crosscut phlogopitite. The detail shows the common textural feature of DC pockets. frequency and width of nelsonite dikes and can be largely diluted by barren wallrocks (Fig. 5A, phlogopitite). Because of their dike-like, plug-like and vein-like shape, these terms are used in a generally descriptive sense. The occurrence of magnetite–apatite rich rocks, named phoscorite, in carbonatite complexes was reported by several authors (Krasnova et al., 2004 and references therein) and due to their rarity, nomenclature remains problematic. A discussion on phoscorite series rocks is provided in Krasnova et al. (2004). We favor an adapted version of the nomenclature of Yegorov (1993) as used by Cordeiro et al. (2010, 2011). Therefore, phoscorite is an olivine-, phlogopite-, apatite- and magnetite-bearing rock and nelsonite is a phlogopite-, apatite- and magnetite-bearing rock. In Catalão I, the phoscorite-series can be divided into two stages, according to mineral chemistry and modal mineralogy. Early-stage phoscorites are grouped under the P1 unit (Fig. 5B). Their main characteristics are a) breccia structure; b) emplacement as small plugs and dikes; c) no obvious direct relationship with carbonatite; d) olivine occurs as altered to minute tetra-ferriphlogopite, indicating interaction with carbohydrothermal fluids; and e) pyrochlore is rare (although this stage is an important source of apatite for the Catalão I residual phosphate deposit). Late-stage P2 and P3 units (Fig. 5B and C) are nelsonites and represent the bulk of the fresh rock niobium mineralization. Nelsonites can be distinguished from early-stage phoscorites by a) emplacement as dikes and small plugs; b) occurrence of internal pockets of dolomite carbonatite; c) no visible evidence of carbohydrothermal alteration; d) absence of olivine; e) abundant pyrochlore, reaching up to 50 vol.% in some samples. Dolomite carbonatite is abundant, but up to 15 m wide plugs and up to 2 m wide dikes of calcite carbonatite occur. Phoscorite is intensely crosscut by dolomite carbonatite dikes, which originates the breccia-like aspect of these rocks. Widespread alteration of olivine crystals within phoscorite to tetra-ferriphlogopite suggests that the inner zone was also affected by carbohydrothermal fluids. Nelsonite, on the other hand, shows no sign of metasomatic alteration, indicating that its emplacement occurred later, after the widespread alteration event. Carbonatites, particularly dolomite carbonatites, dikes and plugs are widespread in Catalão I and are especially abundant within P1. One particular set of dolomite carbonatite, designated here DC, is intimately related to P2 and P3 and may occur within them as centimetric to metric pockets as well as dikes and plugs. DC can be easily discriminated from earlier generations of dolomite carbonatites by the absence of olivine and presence of pyrochlore and ilmenite. 4.1. Primary ore Fig. 5. Main rock types of the Catalão I Nb-deposit. A. Phlogopitite with relicts of the original ultramafic rock cut by a magnetite nelsonite dike (P3) with dolomite carbonatite (DC) pockets. B. Coarse-grained phoscorite (P1), cut by P3 dikes with DC pockets. C. Equigranular apatite nelsonite (P2) with DC pockets. Primary (fresh) rock ore in Catalão I is represented by nelsonite dikes, but subordinate DC dikes with more than 1% modal pyrochlore occur. P2 nelsonite is apatite-rich and its essential silicate phases are tetra-ferriphlogopite crystals with phlogopite cores. Apatite is prismatic, frequently zoned with cores surrounded by a fluid inclusions-rich rim. Magnetite is interstitial and may contain very thin (ca. b0.01 mm) ilmenite lamellae. P3 is magnetite-rich (apatite/magnetite b0.8 vol.%) and its essential silicate phase is tetra-ferriphlogopite. In contrast to P2, aluminous phlogopite cores are virtually absent. Apatite is prismatic to rounded, but also occurs as aggregates of anhedral crystals, usually associated with massive anhedral magnetite clusters. Magnetite forms interstitial masses and may reach up to 71 vol.%. Dolomite carbonatite (DC) occurs as pockets within nelsonites and also as independent dikes and veins. Although other dolomite carbonatite phases occur in the complex, the variety genetically related to nelsonites crosscuts all rock types. DC dikes are believed to 116 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 Fig. 6. Textural characteristics of nelsonites pyrochlore. A. P2 nelsonite with subhedral, brown to orange pyrochlore. B. P3 nelsonite with anhedral to subhedral brown to orange pyrochlore. C. Sector zoning in pyrochlore from DC. D. P2 aggregates within DC, crossed polars. (Mag = magnetite; Apt = apatite; TFP = tetra-ferriphlogopite; Carb = carbonate; Pcl = piroclore). represent the product of extraction of carbonatite from the nelsonite crystallizing assemblage (Cordeiro, 2009). The pyrochlore content in DC varies, but it is hardly more than 5 vol.%. Pyrochlore from P2 and P3 nelsonites are texturally similar and generally fine-grained. They occur as anhedral to subhedral brownish or yellowish crystals often showing optical zoning (Fig. 6A, B). DC pyrochlore is often euhedral to subhedral and may occur as inclusions in ilmenite, together with betafite and columbite, and in magnetite (Cordeiro, 2009). It is medium- to fine-grained, often optically zoned (Fig. 6C). Aggregates of pyrochlore and apatite occur within DC (Fig. 6D). The abundance of Nb over other B site elements classifies Catalão I pyrochlore supergroup minerals within the pyrochlore group (Fig. 7). Pyrochlore representative compositions are shown in Table 2. Data published by Fava (2001) indicates that more than 95% of all Catalão I fresh rock pyrochlore exceeds 0.5 apfu and therefore should have the prefix fluor. However, we haven't analyzed fluorine and Atencio et al. (2010) suggest prefixes should be droped in face of lack of data to avoid misclassification. Therefore the first prefix won't be used in this paper. 5. Pyrochlore chemistry Pyrochlore composition was determined by WDS using a CAMECA SX-50 electron microprobe at the University of Brasília. The analytical conditions were beam diameter 2 μm, 20 kV, 20 nA and two minute count times. Detection limits varied between 0.01 and 0.05 wt.%, except Nb and Ta (0.07%) and La, Ce and Y (0.2%). The pyrochlore general formula is A2−mB2X6−wY1−n·pH2O (Atencio et al., 2010; Lumpkin and Ewing, 1995). The A site is occupied by large anions such as As, Ba, Bi, Ca, Cs, K, Mg, Mn, Na, Pb, REE, Sb, Sr, Th, U and Y. The B site comprises smaller and highly charged cations such as Nb, Ta, Ti, Zr, Fe3+, Al and Si (Zurevinski and Mitchell, 2004) and rarely W+ 5 (Caprilli et al., 2006). The Y and X anions can be O, OH and F. Vacancies are common in the A and Y sites. In this paper, pyrochlore has been calculated to produce a total of 2 cations in the B site (Wall et al., 1996). Pyrochlore classification is originally described by Hogarth (1977) but an up to date CNMNC-IMA-approved nomenclature was published by Atencio et al. (2010). The new nomenclature is composed of two prefixes and a root name based on the content of Y, A and B sites. The Y site content (cation, anion, H2O or vacancy) determines the first prefix and the A site content refers to the second prefix. The dominant element in the B site determines the root name: pyrochlore (Nb), microlite (Ta), roméite (Sb), betafite (Ti) and elsmoreite (W). Fig. 7. Triangular Nb–Ti–Ta pyrochlore classification scheme (Atencio et al., 2010; Hogarth, 1977, 1989) showing fresh rock pyrochlore as black circles. Outlines for pyrochlore compositions from the Catalão I residual deposit (square pattern, Fava, 2001), Oka (gray, Gold et al., 1986; Zurevinski and Mitchell, 2004), Sokli (solid black outline; Lee et al., 2004, 2006) and Salitre (dotted black outline, Barbosa, 2009) are shown for comparison. BET = betafite, PCL = piroclore, MCL = microlite. 117 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 Table 2 Representative compositions of pyrochlore group minerals from the Catalão I primary niobium deposit (b.d. = below detection limit; calcio = calciopyrochlore; keno = kenopyrochlore; natro = natropyrochlore). Sample 1782C 192B2 192B8 056-2 178-1 18303 3393C 157B06 157B2 230B2B 230B2B 149-1 0933 0561 18305 304B2 1706 170-4 230A2 1702 Type Unit Nb2O5 Ta2O5 SiO2 TiO2 ZrO2 UO2 ThO2 La2O3 Ce2O3 Y2O3 FeO MnO CaO BaO SrO Na2O Total calcio P2 59.26 b.d b.d. 4.64 2.05 b.d. 3.39 0.39 2.90 0.57 0.50 b.d. 14.31 b.d. 0.69 4.23 92.97 calcio P2 55.76 b.d. 0.16 5.59 0.90 b.d. 2.13 0.75 2.85 0.49 0.70 b.d. 14.46 0.24 1.06 3.83 89.07 calcio DC 59.93 b.d. 0.12 6.15 2.13 1.02 2.04 0.62 2.37 0.55 0.40 b.d. 16.14 b.d. 1.17 4.71 97.41 calcio P2 55.26 0.16 b.d. 3.67 0.26 0.19 1.44 0.87 3.09 0.34 0.31 b.d. 14.50 0.13 2.41 2.96 85.59 calcio P3 64.26 b.d. b.d. 3.91 1.78 0.14 1.12 0.95 2.47 0.45 0.86 b.d. 13.11 b.d. 2.29 5.94 97.32 calcio P3 63.14 b.d. 0.04 4.71 1.65 b.d. 1.13 0.68 2.00 0.46 0.46 b.d. 15.74 b.d. 1.59 6.09 97.81 calcio P3 63.39 b.d. b.d. 4.35 0.53 b.d. 2.40 0.71 2.72 0.53 0.20 b.d. 11.86 b.d. 2.35 5.93 95.04 calcio P3 63.39 b.d. b.d. 4.35 0.53 b.d. 2.40 0.71 2.72 0.53 0.20 b.d. 11.86 b.d. 2.35 5.93 95.04 calcio DC 68.71 0.28 b.d. 2.04 0.53 b.d. 0.22 1.63 3.26 0.57 0.18 2.00 9.87 b.d. 2.50 7.31 97.17 keno P3 59.99 0.81 1.20 3.16 b.d. 0.77 0.41 1.30 3.37 0.26 0.69 0.11 5.11 11.03 4.65 0.34 93.25 keno DC 50.10 0.77 2.93 5.27 2.44 1.01 2.15 0.32 2.91 0.40 4.47 b.d. 2.80 14.61 2.23 0.77 93.18 keno P3 62.17 0.57 b.d. 4.87 0.32 1.17 4.66 1.13 4.09 0.48 0.40 b.d. 8.51 2.81 2.03 1.16 94.43 keno P3 52.26 0.80 0.61 2.37 3.20 3.72 4.94 0.42 3.04 0.20 1.49 0.08 3.34 12.24 3.56 0.38 92.65 keno DC 63.96 0.81 1.10 1.26 0.75 0.12 0.74 0.92 3.54 0.68 0.77 b.d. 0.12 15.20 0.75 1.29 92.01 natro DC 72.56 1.61 b.d. 0.78 b.d. b.d. 0.19 0.37 0.73 0.39 0.18 b.d. 11.32 0.18 4.61 7.83 100.84 natro P2 63.76 0.37 b.d. 4.20 0.94 0.82 1.72 0.96 2.68 0.55 0.16 b.d. 12.05 b.d. 2.08 6.46 96.78 natro DC 52.85 0.92 b.d. 17.35 0.09 b.d. b.d. 0.35 0.24 0.20 4.22 0.90 10.98 b.d. 3.01 7.75 98.92 1.77 b.d. b.d. 0.18 0.05 2.00 1.73 b.d. b.d. 0.22 0.05 2.00 1.78 b.d. b.d. 0.20 0.02 2.00 1.78 b.d. b.d. 0.20 0.02 2.00 1.88 0.01 b.d. 0.09 0.02 2.00 1.75 0.01 0.08 0.15 b.d. 2.00 1.46 0.01 0.19 0.26 0.08 2.00 1.75 0.01 b.d. 0.23 0.01 2.00 1.70 0.02 0.04 0.13 0.11 2.00 1.83 0.01 0.07 0.06 0.02 2.00 1.94 0.03 b.d. 0.04 b.d. 2.00 1.77 0.01 b.d. 0.19 0.03 2.00 1.28 0.01 b.d. 0.70 b.d. 2.00 b.d. 0.02 0.02 0.06 0.01 0.04 b.d. 0.86 b.d. 0.08 0.70 1.79 b.d. 0.02 0.02 0.04 0.01 0.02 b.d. 1.02 b.d. 0.06 0.72 1.91 b.d. 0.03 0.02 0.06 0.02 0.01 b.d. 0.79 b.d. 0.08 0.71 1.73 b.d. 0.03 0.02 0.06 0.02 0.01 b.d. 0.79 b.d. 0.08 0.71 1.73 b.d. b.d. 0.04 0.07 0.02 0.01 b.d. 0.64 b.d. 0.09 0.86 1.73 0.01 0.01 0.03 0.08 0.01 0.04 0.01 0.35 0.28 0.17 0.04 1.03 0.01 0.03 0.01 0.07 0.01 0.24 b.d. 0.19 0.37 0.08 0.10 1.12 0.02 0.07 0.03 0.09 0.02 0.02 b.d. 0.57 0.07 0.07 0.14 1.09 0.06 0.08 0.01 0.08 0.01 0.09 0.01 0.26 0.35 0.15 0.05 1.14 b.d. 0.01 0.02 0.08 0.02 0.04 b.d. 0.01 0.38 0.03 0.16 0.75 b.d. b.d. 0.01 0.02 0.01 0.01 b.d. 0.72 b.d. 0.16 0.90 1.83 0.01 0.02 0.02 0.06 0.02 0.01 b.d. 0.79 b.d. 0.07 0.77 1.78 b.d. b.d. 0.01 b.d. 0.01 0.19 0.04 0.63 b.d. 0.09 0.81 1.78 calcio P2 62.66 0.15 b.d. 3.52 0.17 0.36 1.08 1.21 4.20 0.44 0.14 b.d. 9.02 0.35 2.78 5.59 91.67 calcio P2 61.68 0.33 0.61 3.15 0.13 0.59 1.09 1.14 3.42 0.32 0.94 b.d. 7.46 4.89 3.95 4.09 93.87 calcio P3 55.58 0.70 0.57 4.16 3.95 2.35 2.69 0.62 2.92 0.26 1.93 0.36 8.53 3.67 3.48 2.52 94.28 Structural formulae calculated based on ∑ B-site elements = 2 Nb 1.82 1.71 1.68 1.65 1.80 1.62 1.79 Ta b.d. b.d. b.d. b.d. 0.01 0.01 b.d. Si b.d. b.d. 0.01 0.01 0.04 0.04 b.d. Ti 0.17 0.22 0.28 0.28 0.15 0.20 0.20 Zr 0.01 0.06 0.03 0.06 b.d. 0.13 0.01 ∑B 2.00 2.00 2.00 2.00 2.00 2.00 2.00 site U 0.01 b.d. b.d. 0.01 0.01 0.03 b.d. Th 0.02 0.05 0.03 0.03 0.02 0.04 0.02 La 0.03 0.01 0.02 0.01 0.03 0.01 0.02 Ce 0.10 0.07 0.07 0.05 0.08 0.07 0.08 Y 0.02 0.02 0.02 0.02 0.01 0.01 0.01 Fe2 0.01 0.03 0.04 0.02 0.05 0.10 0.02 Mn b.d. b.d. b.d. b.d. b.d. 0.02 b.d. Ca 0.62 0.98 1.03 1.05 0.52 0.59 1.11 Ba 0.01 b.d. 0.01 b.d. 0.12 0.09 b.d. Sr 0.10 0.03 0.04 0.04 0.15 0.13 0.10 Na 0.70 0.52 0.50 0.55 0.51 0.32 0.41 ∑A 1.60 1.70 1.75 1.79 1.50 1.42 1.79 site Nb2O5 content varies from 50 to 70 wt.%. The average TiO2 content ranges from 3 to 5 wt.%, but may reach up to 17 wt.% in natropyrochlore inclusions in ilmenite from DC. Most analysis show low Ta2O5, ranging from b1 wt.% to a maximum of 2 wt.% in one grain from P2 and in pyrochlore crystals within DC ilmenite. ZrO2 and SiO2 reach up to 5 and 3 wt.% respectively. Pyrochlore from fresh rock nelsonite has Ca and Na as the main A site elements, ranging up to 19 and 8 wt.%, respectively. Therefore calciopyrochlore dominates in the Catalão I Nb deposit followed by natropyrochlore. Ba is one of the most common substitutes for both Na and Ca in this site and BaO content reaches 18 wt.% whereas SrO may reach 7 wt.%. The sum of the analyzed rare earth (La + Ce + Y) oxides varies from 3.5 to 6 wt.%. ThO2 is up to 6 wt.% but its average content is b2 wt.%. UO2 is up to 4 wt.%, averaging b1 wt.%. FeO may reach 3 wt.%, and MnO is always below 1 wt.%. Several analyses indicate the occurrence of kenopyrochlore (zero-valent-dominant pyrochlore) in the Catalão I Nb fresh rock deposit but according to data from Fava (2001) they are dominant in the residual ore. Several studies tried to explain the evolution of pyrochlore composition throughout magmatic evolution (Chakhmouradian and Williams, 2004; Hogarth et al., 2000; Knudsen, 1989). During the early stages of carbonatite magmatism Nb and Ta are probably transported as phosphate and fluorine complexes, which might explain the common correlation between the occurrence of apatite and pyrochlore (Hogarth et al., 2000; Knudsen, 1989). Knudsen (1989) argued that during the carbonatitic magmatism Nb is more soluble than Ta, which could explain the occurrence of Ta-rich pyrochlore in primitive magmas and Nb-rich, Ta-poor pyrochlore in more evolved, late stage ones. Hogarth et al. (2000) concluded that the normal path of evolution of pyrochlore in carbonatites is one of progressive enrichment in Na, Ca and Nb and depletion in Ta, Th, REE, Ti and U. A more detailed evolution scheme is proposed by Chakhmouradian and Williams (2004) where Th-enriched Ca–Na dominant pyrochlore evolves toward Ba–Sr-rich compositions in calcite–dolomite carbonatites from Kola carbonatite complexes. Pyrochlore from the Catalão I fresh rock deposit seems to fit well into the proposed scheme, but early Ta–Th–U enriched pyrochlore phases are not present. Pyrochlore analyses of several stages of Sokli phoscorites (Lee et al., 2004; 2006) confirm the trend of early Ta–U–Th pyrochlore toward evolved Ca–Na compositions. Thus, Ca–Na pyrochlore in P2 and P3 nelsonites and related DC dolomite carbonatites can be interpreted as belonging to a more evolved phase, similar to the late-stage D5 dolomite carbonatite phase in the Sokli complex. 5.1. Chemical evolution of pyrochlore The range of P2 and P3 pyrochlore chemical compositions overlaps widely and we could not find an applicable chemical criterion to 118 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 discriminate pyrochlores from the two units. According to Cordeiro et al. (2010) other minerals from P2 and P3, such as phlogopite and apatite, aren't discernible from each other. This suggests only minor chemical differences in the magmas that produced the two units. Therefore, the compositional spread seen in our data might be related to factors such as a) zoning (Chakhmouradian and Mitchell, 2002; Hogarth et al., 2000); b) hydrothermal alteration (Chakhmouradian and Mitchell, 1998; Geisler et al., 2004); c) weathering (Lumpkin and Ewing, 1995; Wall et al., 1996). Chakhmouradian and Zaitsev (1999) point out that several types of pyrochlore may be found in the same complex or even within the same facies. Hence, in order to address the compositional variation we need a classification criterion other than lithology. Lumpkin and Ewing (1995) argued that A site large cations such as K, Ba and Sr can be useful in the identification of pyrochlore chemical variation because their occurrence is related to the host rock alteration. Accordingly, we adopted a division based on the variation of the A site content, allowing us to discriminate between three pyrochlore groups (Fig. 8): a) calciopyrochlore; b) natropyrochlore; and c) kenopyrochlore. The occurrence of vacancy in pyrochlore from the fresh rock deposit is an important feature of its evolution. Vacancy, sometimes accompanied by Ba-enrichment, was attributed to alteration at Sokli (Lee et al., 2006), to hydrothermal overprint at Oka (Zurevinski and Mitchell, 2004) and Lueshe (Nasraoui and Bilal, 2000) and to both oscillatory zoning and alteration in the Bingo carbonatite (Williams et al., 1997). The trend from calciopyrochlore and natropyrochlore toward kenopyrochlore illustrated in Fig. 8 is related to the exchange of Ba for Ca + Na, and consequent vacancy, in the A site. Similar trends can be found in Lueshe (Nasraoui and Bilal, 2000) and Bingo (Williams et al., 1997) pyrochlore, described as product of weathering, and in Kola carbonatites pyrochlore (Chakhmouradian and Williams, 2004), as derived from supergene or low-temperature hydrothermal alteration. An additional trend from calciopyrochlore toward natropyrochlore can be considered. Despite considerable scatter, calciopyrochlore, natropyrochlore and the fields of Oka and Salitre fresh rock pyrochlore show an overall alignment to the 1:1 line in a Na vs. Ca diagram. This trend is even more marked in crystal core composition from the Catalão I weathered pyrochlore deposit (Fava, 2001). Taking into account that most natropyrochlore are inclusions in ilmenites from the last stage of magmatic evolution in the deposit (DC unit) and that ilmenite is one of the last minerals to crystallize, natropyrochlore formed at such stage would represent the most evolved pyrochlore composition. Therefore, we interpret that the negative correlation of Ca and Na represent the evolution from earlier calciopyrochlore toward a late stage natropyrochlore. 5.2. Comparison with pyrochlore from the residual deposit Pyrochlore chemistry from the Catalão I fresh rock and residual deposits shows no clear differences in the B site, but some important substitutions occur the A site. Fava (2001) described the mineralogical characteristics of pyrochlore from the residual deposit developed over Catalão I nelsonites and carbonatites and concluded that weathering induced substitutions in the A site and originated bariopyrochlore, renamed here as “Ba-enriched” kenopyrochlore according to the nomenclature of Atencio et al. (2010). On the other hand, Catalão I fresh rock and residual Ba-enriched kenopyrochlore are different from each other. Fresh rock crystals show a negative Sr–Ca correlation that leads toward Sr-enriched kenopyrochlore and the same correlation occurs in the residual deposit pyrochlore crystal cores (Fava, 2001). However, the majority of pyrochlore in the residual deposit is Ba-enriched kenopyrochlore that lack a negative Sr–Ca correlation. These features suggest that different processes originated fresh rock kenopyrochlore and the residual deposit kenopyrochlore. We suggest that the chemical shift from calciopyrochlore and natropyrochlore toward kenopyrochlore in the Catalão I fresh rock deposit is due to interaction with hydrothermal fluids that also carried Sr. Later weathering-related fluids originated the residual deposit Baenriched kenopyrochlore by depleting pyrochlore from Ca and Na. With weathering progression even Ba is eventually leached from pyrochlore leading to its destruction and consequent formation of secondary Nb-enriched minerals in the soil (Wall et al., 1999). 6. Carbon and oxygen isotopes Carbon and oxygen isotopes from DC pockets dolomite (Table 3) were analyzed to establish a correlation with the pyrochlore chemistry (Fig. 9). Carbonates were extracted from pockets with a manual tungsten-carbide drill to avoid interference from different carbonate generations or contamination with external sources. Oxygen and carbon Fig. 8. Ternary plots of Ca, Na and A site vacancy. Compositional pyrochlore fields of other deposits are shown for comparison. Data sources as in Fig. 7, plus the Bingo field from Williams et al. (1997). 119 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 Table 3 Representative analysis of carbon and oxygen isotopes of carbonates from pyrochlore-bearing DC pockets. Sample 056 056E 93 093G1 178G1 178G2 192G1 Type δ13CPDB δ18OSMOW Carbonatite − 5.53 11.80 Carbonatite − 5.86 20.23 DC pocket in P2 − 5.38 19.99 DC pocket in P2 − 5.53 10.42 DC pocket in P2 − 5.85 15.92 DC pocket in P2 − 5.16 11.06 DC pocket in P2 − 6.14 8.59 isotope data were obtained reacting carbonate samples with 100% H3PO4 at 72 °C, using a Gas Bench II System connected to a Delta V Advantage gas-source mass spectrometer at the University of Brasília. Results are expressed in delta notation, relative to the PDB (carbon) and SMOW (oxygen) standards. Data from Table 3 show that gray fresh dolomite (093 G1, 056) has a mantle-like carbon- and oxygen-isotope signature, interpreted as magmatic, whereas white brittle dolomite in the same samples has higher δ18OSMOW values than gray calcite and is interpreted as affected by low temperature H2O-rich fluids probably of meteoric origin. The same fluids are likely to have altered pyrochlore, leaching Ca and Na and leaving vacancy while partially replacing them with Ba. This hypothesis is supported by comparison between calciopyrochlore or natropyrochlore cores with Ba-enriched kenopyrochlore rims, suggesting fluid interaction. This would be consistent with general alteration models (Wall et al., 1999). 7. Genetic implications The dike-like emplacement of nelsonites and its relationship with DC pockets is an important feature of the Catalão I Nb deposit, suggesting a magmatic origin for the Nb-ore. Cordeiro et al. (2011) showed that DC pockets within nelsonites have mantle-like C- and Oisotope signatures and suggested Rayleigh fractionation and magmatic degassing as important processes for the evolution of such rocks. The authors' results have also shown that metasomatism and weathering played a role in the carbon and oxygen isotopic variations of DC carbonates, albeit unrelated to the formation of pyrochlore. Accordingly, we interpret the occurrence of pyrochlore in nelsonites and dolomite carbonatite as an igneous process. The genesis of late-stage phoscorite-series rocks, and therefore of the Catalão I fresh rock niobium deposit, is still a matter of controversy. Krasnova et al. (2004) argues in favor of AFC and/or liquid immiscibility in generating phoscorites. Lee et al. (2004) described chemical discrepancies between Sokli carbonatites and related phoscorites as evidence for immiscibility that generated both a carbonatite and a phoscorite melt. However, the authors point out that experimental evidence for such process is still lacking. The best evidence we could find for the occurrence of phoscorite melts is given by Panina and Motorina (2008). They studied melt inclusions from the Krestovskii carbonatite complex, in the Maimecha– Kotui province, Russia, and suggested a carbonatite immiscibility event that originated alkali-rich phosphate melts. Evidence of Fe–P–Ti-rich melts exists in carbonatite-unrelated settings such as the andesitic Antauta subvolcanic complex in Peru (Clark and Kontak, 2004). The authors describe Fe-rich melt inclusions that are interpreted as derived from nelsonite-like magma, indicating that such unusual magmas may indeed occur naturally. Formation of cumulates is another possible mechanism in the generation of apatite–magnetite rich rocks. Mitchell (2005) argues that potential niobium ore rocks in carbonatites do not represent liquid compositions nor reflect the Nb content of the parental magma. Based on melt inclusion data, Veksler et al. (1998) argue that crystal fractionation resulted in the formation of calcite carbonatites, which evolved to forsterite–apatite–magnetite–phlogopite carbonatites with subordinate phoscorite cumulates and dolomite carbonatites. According to Downes et al. (2005) the Kola Alkaline Province phoscorite–carbonatite rocks series are the result of complex differentiation of an extremely phosphorous and iron enriched carbonate–silicate melt. They also favor the formation of cumulates as a mean of generating phoscorites. Fig. 9. Comparison between pyrochlore composition and carbon–oxygen isotope signatures of carbonates within the same pocket. Note that pyrochlore rims from samples 093 and 056 have systematically higher A site vacancies than corresponding cores. In sample 056, the core is calciopyrochlore and the rim is Ba-enriched kenopyrochlore, while samples 192B and 178 show only a slight Ba-enrichment and little vacancy. Carbon and oxygen isotopes show that samples with kenopyrochlore rims have wider variation in the δ18OSMOW content while less altered samples preserve the original composition. Stable isotope fields are from Cordeiro et al. (2011). 120 P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 At this stage we are unable to determine which of the described mechanisms was involved in the formation of the Catalão I fresh rock niobium deposit. Despite the occurrence of phosphate melts within carbonatite complexes, crystal accumulation is likely to be involved in the generation of nelsonites. DC pockets within nelsonite dikes are sometimes interconnected and low viscosity carbonatite lava could flow in the open space. Apatite, pyrochlore, magnetite and phlogopite (i.e. nelsonite) could crystallize in situ until all open spaces were filled and flow would stop. Such mechanism could explain both the occurrence of DC pockets and the related pyrochlore-bearing magnetite–apatite-rich rocks. Whereas magmatic controls were vital in the formation of the fresh rock niobium deposit, weathering played an important role in its enrichment, consequently forming the residual deposit. All rocks within the Catalão I Complex are easily weathered compared to the country-rocks (fenites and quartzites). The dome-like structure prevents erosion and allows the establishment of very thick soil cover over the alkaline rocks. On average, soil depth is 80 m, but reaches at least 150 m over phoscorite-series rocks. A similar pattern occurs at Seblyavr in the Kola Alkaline Province, Russia (Balaganskaya et al., 2007) where a weathering crust up to 200 m deep is developed over phoscorite-series rocks in the intrusion core. We believe that the abundance of fractured easily-weathered carbonatites, either as dikes cutting early-stage phoscorites or as DC pockets within nelsonites, contributed to the development of such deep soils and the generation of the residual deposit. 8. Conclusions 1) The pipe-like niobium orebodies at Catalão I consist of dike swarms of late-stage phoscorite-series rocks (nelsonites) that cut previous phlogopitite and carbonatite. 2) Weathering of such rocks originated the residual deposit, where leaching of carbonates induced a residual concentration of pyrochlore and other weathering-resistant phases. 3) Catalão I phocorite-series rocks can be divided into phoscorites (P1), and the niobium ores apatite nelsonite (P2) and magnetite nelsonite (P3). The mineralization can be classified as Nb (+Fe + P) on the grounds of high modal content of apatite and magnetite. Dolomite carbonatites (DC) associated with nelsonites are a subordinate source of pyrochlore but their grades are comparatively low, hardly above 0.3 wt.% Nb2O5. 4) The dominance of calciopyrochlore over other Nb-bearing phases in the fresh rock deposit and its chemical variability are independent of lithology. This indicates that pyrochlore formation chemical conditions were similar in P2, P3, and DC. 5) Substitution of Na–Ca for Ba in the fresh rock pyrochlore structure, leading to the formation of Ba-enriched kenopyrochlore, and the high δ 18OSMOW signature of the associated carbonates suggest interaction with hydrothermal fluids. These fluids affected nelsonites but had no role in the formation of the fresh rock niobium deposit itself. 6) We could not uniquely constrain the nelsonite formation process in Catalão I although it is clear that they are genetically related to carbonatite magmatism. Possible alternatives for the formation and evolution of these rocks are: (a) crystallization from a phoscorite magma (Lee et al., 2004, 2006); (b) crystal accumulation from a carbonatite magma (Veksler et al., 1998); and (c) crystal accumulation from a carbonated-silicate magma (Downes et al., 2005). Acknowledgments We are indebted to Anton Chakhmouradian, Nigel Cook and two anonymous reviewers for their helpful review of the original manuscript. This work was supported by the Brazilian Council for Research and Technological Development (CNPQ), through grants to the first author, JAB and ESRB, as well as by Mineração Catalão and the Anglo American Brazil Exploration Division. The University of Brasília is gratefully acknowledged for fieldwork support and access to laboratory facilities. References Atencio, D., Andrade, M.B., Christy, A.G., Gieré, R., Kartashov, P.M., 2010. The pyrochlore supergroup of minerals: nomenclature. Can. Mineral. 48, 673–698. Balaganskaya, E.G., Downes, H., Demaiffe, D., 2007. REE and Sr–Nd isotope compositions of clinopiroxenites, phoscorites, and carbonatites of the Seblyavr Massif, Kola Peninsula, Russia. Mineral. Pol. 38, 29–45. Barbosa, E.S.R., 2009. Mineralogia e Petrologia do Complexo Carbonatítico-Foscorítico de Salitre, MG, Unpublished Ph.D. Thesis, University of Brasília, Brazil. 432 pp. Biondi, J.C., 2005. Brazilian mineral deposits associated with alkaline and alkaline– carbonatite complexes. In: Comin-Chiaramonti, P., Gomes, C.B. (Eds.), Mesozoic to Cenozoic alkaline magmatism in the Brazilian Platform. Editora da Universidade de Sao Paulo: Fapesp, São Paulo, pp. 707–750. Brod, J.A., 1999. Petrology and geochemistry of the Tapira alkaline complex, Minas Gerais State, Brazil: Unpublished Ph.D. Thesis, University of Durham, U.K., 486 pp. Brod, J.A., Gibson, S.A., Thompson, R.N., Junqueira-Brod, T.C., Seer, H.J., Moraes, L.C., Boaventura, G.R., 2000. Kamafugite affinity of the Tapira alkaline–carbonatite complex (Minas Gerais, Brazil). Rev. Bras. Geociências 30, 404–408. Brod, J.A., Gaspar, J.C., Araújo, D.P., Gibson, S.A., Thompson, R.N., Junqueira-Brod, T.C., 2001. Phlogopite and tetra-ferriphlogopite from Brazilian carbonatite complexes: petrogenetic constraints and implications for mineral-chemistry systematic. J. Asian Earth Sci. 19, 265–296. Brod, J.A., Ribeiro, C.C., Gaspar, J.C., Junqueira-Brod, T.C., Barbosa, E.S.R., Riffel, B.F., Silva, J.F., Chaban, N., Ferrari, A.J.D., 2004. Geologia e Mineralizações dos Complexos Alcalino-Carbonatíticos da Província Ígnea do Alto Paranaíba. 42º Congresso Brasileiro de Geologia, Araxá, Minas Gerais, Excursão, p. 1 (29 pp.). Caprilli, E., Della Ventura, G., Williams, T.C., Parodi, G.C., Tuccimei, P., 2006. The crystal chemistry of non-metamict pyrochlore-group minerals from Latium, Italy. Can. Mineral. 44, 1367–1378. Carvalho, W.T., Bressan, S.R., 1981. Depósitos minerais associados ao Complexo ultramáfico-alcalino de Catalão I — Goiás. In: Schmaltz, W.H. (Ed.), Os principais depósitos minerais da Região Centro Oeste, 6. DNPM, Brasília, pp. 139–183. Chakhmouradian, A.R., Mitchell, R.H., 1998. Lueshite, pyrochlore and monazite-(Ce) from apatite–dolomite carbonatite, Lesnaya Varaka complex, Kola Peninsula, Russia. Mineral. Mag. 62, 769–782. Chakhmouradian, A.R., Mitchell, R.H., 2002. New data on pyrochlore- and perovskite-group minerals from the Lovozero alkaline complex, Russia. Eur. J. Mineral. 14, 821–836. Chakhmouradian, A.R., Williams, C.T., 2004. Mineralogy of high-field-strength elements (Ti, Nb, Zr, Ta, Hf) in phoscoritic and carbonatitic rocks of the Kola Peninsula, Russia. I. In: Wall, F., Zaitsev, A.N. (Eds.), Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province: Mineralogical Society Series, London, pp. 293–340. Chakhmouradian, A.R., Zaitsev, A.N., 1999. Calcite–amphibole–clinopyroxene rock from the Afrikanda Complex, Kola Peninsula, Russia: mineralogy and a possible link to carbonatites. I. Oxide minerals. Can. Mineral. 37, 177–198. Clark, A.H., Kontak, D.J., 2004. Fe–Ti–P oxide melts generated through magma mixing in the Antauta subvolcanic center, Peru: implications for the origin of nelsonite and iron oxide-dominated hydrothermal deposits. Econ. Geol. 99, 377–395. Cordeiro, P.F.O., 2009. Petrologia e metalogenia do depósito primário de nióbio do Complexo Carbonatítico-Foscorítico de Catalão I, GO. Unpublished M.Sc. Thesis, University of Brasília, Brazil, 140 pp. Cordeiro, P.F.O., Brod, J.A., Dantas, E.L., Barbosa, E.S.R., 2010. Mineral chemistry, isotope geochemistry and petrogenesis of niobium-rich rocks from the Catalão I carbonatite–phoscorite complex, Central Brazil. Lithos 118, 223–237. Cordeiro, P.F.O., Brod, J.A., Santo, R.V., Dantas, E.L., Oliveira, C.G., Barbosa, E.S.R., 2011. Stable (C, O) and radiogenic (Sr, Nd) isotopes of carbonates as indicators of magmatic and post-magmatic processes of phoscorite-series rocks and carbonatites from Catalão I, central Brazil. Contrib. Mineral. Petrol. 161, 451–464. Deans, T., 1966. Economic geology of African carbonatites. In: Tuttle, O.F., Gittins, J. (Eds.), Carbonatites. Wiley, New York, pp. 385–413. Downes, H., Balaganskaya, E., Beard, A., Liferovich, R., Demaiffe, D., 2005. Petrogenetic processes in the ultrmafic, alkaline and carbonatitic magmatism in the Kola Alkaline Province: a review. Lithos 85, 48–75. Fava, N., 2001. O manto de intemperismo e a química do pirocloro de Catalão I (GO): Um estudo preliminar: Unpublished M.Sc. Thesis, University of Brasília, Brazil, 124 pp. Geisler, T., Berndt, J., Meyer, H.W., Pollok, K., Putnis, A., 2004. Low temperature aqueous alteration of crystalline pyrochlore: correspondence between nature and experiment. Mineral. Mag. 68, 905–922. Gibson, S.A., Thompson, R.N., Leonardos, O.H., Dickin, A.P., Mitchell, J.G., 1995. The Late Cretaceous impact of the Trindade mantle plume — evidence from large-volume, mafic, potassic magmatism in SE Brazil. J. Petrol. 36, 189–229. Gierth, E., Baecker, M.L., 1986. A mineralização de nióbio e as rochas alcalinas associadas no complexo Catalão I, Goiás. In: Schobbenhaus, C., Queiroz, E.T., Coelho, C.E.S. (Eds.), Principais depósitos minerais do Brasil, 2. MME/DNPM, Brasília, pp. 455–462. Gold, D.P., Eby, G.N., Bell, K., Vallee, M., 1986. Carbonatites, diatremes, and ultra-alkaline rocks in the Oka area, Quebec. Geological Association of Canada, Mineralogical Association of Canada, Canadian Geophysical Union, Joint Annual Meeting, Ottawa'86, Field Trip 21: Guidebook, p. 51. P.F.O. Cordeiro et al. / Ore Geology Reviews 41 (2011) 112–121 Hirano, H., Kamitani, M., Sato, T., Sudo, S., 1990. Niobium mineralization of Catalão I carbonatite complex, Goiás, Brazil. Bull. Geol. Surv. Japn. 41, 619–626. Hogarth, D.D., 1977. Classification and nomenclature of the pyrochlore group. Am. Mineral. 62, 403–410. Hogarth, D.D., 1989. Pyrochlore, apatite and amphibole: distinctive minerals in carbonatite. In: Bell, K. (Ed.), Carbonatites — Genesis and Evolution. Unwin Hyman, London, pp. 105–148. Hogarth, D.D., Williams, C.T., Jones, P., 2000. Fresh rock zoning in pyrochlore group minerals from carbonatites. Mineral. Mag. 64, 683–697. Issa Filho, A., Lima, P.R.A.S., Souza, O.M., 1984. Aspectos da geologia do complexo carbonatítico do Barreiro, Araxá, Minas Gerais, Brasil. In: Rodrigues, C.S., Lima, P.R.A.S. (Eds.), Companhia Brasileira de Metalurgia e Mineração, pp. 20–44. Justo, L.J.E.C., Souza, M.M., 1986. In: Schobbenhaus, C. (Ed.), Jazida de nióbio do Morro dos Seis Lagos, Amazonas. : Principais depósitos minerais do Brasil, 2. MME/DNPM, Brasília, pp. 463–468. Kamitani, M., Hirano, H., 1991. Important carbonatite–alkaline/alkaline complexes and related mineral occurrences in the world. Bull. Geol. Surv. Japn. 41, 631–640. Knudsen, C., 1989. Pyrochlore group minerals from the Qaqarssuk carbonatite complex. In: Möller, P., Cerný, P., Saupé, F. (Eds.), Lanthanides, Tantalum and Niobium. Springer-Verlag, Berlin-Heidelberg, pp. 80–99. Krasnova, N.I., Petrov, T.G., Balaganskaya, E.G., Garcia, D., Moutte, D., Zaitsev, A.N., Wall, F., 2004. Introduction to phoscorites: occurrence, composition, nomenclature and petrogenesis. In: Wall, F., Zaitsev, A.N. (Eds.), Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province. Mineralogical Society Series, London, pp. 45–79. Lee, M.J., Garcia, D., Moutte, J., Williams, C.T., Wall, F., 2004. Carbonatites and phoscorites from the Sokli complex, Finland. In: Wall, F., Zaitsev, A.N. (Eds.), Phoscorites and Carbonatites from Mantle to Mine: the Key Example of the Kola Alkaline Province. Mineralogical Society Series, London, pp. 133–162. Lee, M.J., Lee, J.I., Garcia, D., Moutte, J., Williams, C.T., Wall, F., Kim, Y., 2006. Pyrochlore chemistry from the Sokli phoscorite–carbonatite complex, Finland: implications for the genesis of phoscorite and carbonatite association. Geochem. J. 40, 1–13. Lumpkin, G.R., Ewing, R.C., 1995. Geochemical alteration of pyrochlore group minerals: pyrochlore subgroup. Am. Mineral. 80, 732–743. Melo, M.T.V., 1997. Depósitos de fosfato, titânio e nióbio de Tapira. Minas Gerais. In: Schobbenhaus, C., Queiroz, E.T., Coelho, C.E.S. (Eds.), Principais depósitos minerais do Brasil, 2. MME/DNPM, Brasília, pp. 41–56. Mitchell, R.H., 2005. Mineralogical and experimental constraints on the origin of niobium mineralization in carbonatites. In: Linnen, R.L., Samson, I.M. (Eds.), Rare Element Geochemistry and Mineral Deposits, 17. Geological Association of Canada, Canada, pp. 201–216 (Short Course Notes). Nasraoui, M., Bilal, E., 2000. Pyrochlores from the Lueshe carbonatite complex (Democratic Republic of Congo): a geochemical record of different alteration stages. J. Asian Earth Sci. 18, 237–251. Nasraoui, M., Waerenborgh, J.C., 2001. Fe speciation in weathered pyrochlore-group minerals from the Lueshe and Araxá (Barreiro) carbonatites by 57Fe Mössbauer spectroscopy. Can. Mineral. 39, 1073–1080. Notholt, A.J.G., Highley, D.E., Deans, T., 1990. Economic minerals in carbonatites and associated alkaline igneous rocks. Trans. Ins. Min. Metall. 99, 59–80. Palmieri, M., 2011. Modelo geológico e avaliação de recursos minerais do depósito de nióbio do Morro do Padre, Complexo alcalino carbonatítico de Catalão II, GO. Unpublished M.Sc thesis, University of Brasília, Brazil, 130 pp. Panina, L.I., Motorina, I.V., 2008. Liquid immiscibility in deep-seated magmas and the generation of carbonatite melts. Geochem. Int. 46, 448–464. Pell, J., 1966. Mineral deposits associated with carbonatites and related alkaline igneous rocks. In: Mitchell, R.H. (Ed.), Undersaturated Alkaline Igneous Rocks: Mineralogy, 121 Petrogenesis and Economic Potential: Mineralogical Association of Canada, 24, pp. 271–310 (Short Course). Pena, P.E., 1989. Perfil analítico do pirocloro (Nióbio), 2nd edition. DNPM, Boletim, 18 (59 pp.). Richardson, D.G., Birkett, T.C., 1996. Carbonatite-associated deposits. In: Eckstrand, O.R., Sinclair, W.D., Thorpe, R.I. (Eds.), Geology of Canadian Mineral Deposit Types: Decade of North American Geology, Geology of Canada, 8, pp. 557–566. Rodrigues, C.S., Lima, P.R.A., 1984. Carbonatite Complexes of Brazil: Geology. Companhia Brasileira de Metalurgia e Mineração, São Paulo. (44 pp.). Sage, R.P., 1988. Geology of carbonatite–alkalic rock complexes in Ontario: Argor carbonatite complex, District of Cochrane. Ontario Geological Survey, p. 41 (90 pp.). Sonoki, I.K., Garda, G.M., 1988. Idades K–Ar de rochas alcalinas do Brasil Meridional e Paraguai Oriental: compilação e adaptação as novas constants de decaimento. Bol. IG USP 19, 63–85. Stockford, H.R., 1972. The James Bay pyrochlore deposit. Can. Min. Metall. Bull. 65, 61–79. Stoppa, F., Cundari, A., 1995. A new Italian carbonatite occurrence at Cupaello (Rieti) and its genetic significance. Contrib. Mineral. Petrol. 122, 275–288. Stoppa, F., Sharygin, V.V., Cundari, A., 1997. New mineral data from the kamafugite– carbonatite association: the melilitolite from Pian di Celle, Italy. Mineral. Petrol. 61, 27–45. Thompson, R.N., Gibson, S.A., Mitchell, J.G., Dickin, P., Leonardos, O.H., Brod, J.A., Greenwood, J.C., 1998. Migrating Cretaceous–Eocene magmatism in the Serra do Mar alkaline province, SE Brazil: melts from the deflected Trindade mantle plume? J. Petrol. 39, 1439–1526. Van Straaten, P., 2002. Rocks for Crops: Agrominerals of Sub-Saharan Africa. International Centre for Research in Agroforestry, Nairobi, Kenya. (338 pp.). Veksler, I.V., Nielsen, T.F.D., Sokolov, S.V., 1998. Mineralogy of crystallized melt inclusions from Gardiner and Kovdor ultramafic alkaline complexes: implications for carbonatite genesis. J. Petrol. 39, 2015–2031. Verwoerd, W.J., 1967. The Carbonatites of South Africa and South West Africa. (Handbook) Geological Survey of South Africa. Verwoerd, W.J., 1986. Mineral deposits associated with carbonatites and alkaline rocks. In: Anhaeusser, C.R., Manske, S. (Eds.), Mineral Deposits of Southern Africa. Geological Society of South Africa, Johannesburg, pp. 2173–2191. Wall, F., Williams, C.T., Woolley, A.R., Nasraoui, M., 1996. Pyrochlore from weathered carbonatite at Lueshe, Zaire. Mineral. Mag. 60, 731–750. Wall, F., Williams, C.T., Woolley, A.R., 1999. Pyrochlore in niobium ore deposits. In: Stanley, C.J., et al. (Ed.), Mineral Deposits: Processes to Processing, Proceedings of the 5th Biennial SGA meeting and 10th Quadrennial IAGOD Symposium London, U.K. Balkema, Rotterdam, pp. 687–690. Williams, C.T., Wall, F., Woolley, A.R., Phillipo, S., 1997. Compositional variation in pyrochlore from the Bingo carbonatite, Zaire. J. Afr. Earth Sci. 25, 137–145. Woolley, A.R., 1987. The Alkaline Rocks and Carbonatites of the World. Part 1: North and South America. British Museum, Natural History, London. Woolley, A.R., 2001. Alkaline Rocks and Carbonatites of the World. (Part 3) The Geological Society, London. Woolley, A.R., Kjarsgaard, B.A., 2008. Carbonatite occurrences of the world: map and database. Geol. Surv. Can. 5796 (Open File Report). Yang, Z., Woolley, A., 2006. Carbonatites in China: a review. J. Asian Earth Sci. 27, 559–575. Yegorov, L.S., 1993. Phoscorites of the Maymecha–Kotuy ijolite–carbonatite association. Int. Geol. Rev. 35, 346–358. Zurevinski, S.E., Mitchell, R.H., 2004. Extreme compositional variation of pyrochloregroup minerals at the Oka carbonatite complex, Quebec: evidence of magma mixing? Can. Mineral. 42, 1159–1168.