Mario Luiz de Sá Carneiro Chaves

Ion microprobe Pb–Pb dating of carbonado, polycrystalline diamond

Abstract We report in situ ion microprobe Pb–Pb dating of quartz, rutile and clay mineral inclusions and matrix part of polycrystalline diamonds, ‘carbonado’ derived from a Proterozoic conglomerate in diamond-bearing deposit of Minas Gerais in Brazil together with U–Pb ages of zircons also extracted from the deposit. Thirty four spots on seven quartz grains located in the cavity of the GM01 carbonado yield 207Pb/206Pb isochron age of 3247±800 Ma (2σ; MSWD=0.75) and six spots on three rutile inclusions give the age of 3916±1300 Ma (2σ; MSWD=0.092). Seven spots on three clay mineral inclusions of the DO3 carbonado show common lead compositions while four spots on matrix define 207Pb/206Pb isochron age of 3811±1800 Ma (2σ; MSWD=0.012). Seventy six spots on seventy zircon grains derived from the same conglomerate show three major U–Pb concordant ages of 2151±17 Ma, 2692±20 Ma and 2931±22 Ma with two concordant zircon outliers of 1726±58 Ma and 3599±12 Ma. The youngest age is consistent with the formation age of 1750–1700 Ma in the Proterozoic conglomerate estimated by other workers. The 3.6 Ga zircon is the oldest record in the South American platform. It may be detrital in origin and reflect the remnant of an Archean craton. The Pb–Pb age of quartz and rutile inclusions in GM01 carbonado and that of DO3 carbonado matrix are 3315±720 Ma and 3811±1800 Ma. The matrix age is consistent with Pb–Pb age of 2.6–3.8 Ga of Central African carbonados in the literature, suggesting a close genetic relationship between Brazilian and African carbonados.

Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, from Eduardo mine, Conselheiro Pena, Minas Gerais, Brazil: Second arsenate in the laueite mineral group

Abstract Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1-2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm3. The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition (n = 4, WDS, calculated for the condition Fe2+:Fe3+ = 1:2, H2O for the ideal structural formula, wt%) is: FeO 11.50, Fe2O3 25.56, CaO 15.41, As2O5 33.51, H2O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe2+0.98Fe3+1.96[(AsO4)1.79(PO4)0.31](OH)1.52·8.08H2O. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(1̅21), 3.158(32)(13̅0), 2.960(39)(022̅), 2.884(35)(1̅31), 2.680(29)(2̅11), and 2.540(23)(2̅10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P1̅) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), γ = 102.30(2)°, V = 347.1(2) Å3, and Z = 1. Gladstone-Dale compatibility is -0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.

Grenvillian age magmatism in the Southern Espinhaço Range (Minas Gerais): evidence from U-Pb zircon ages

This paper describes the first in situ occurrence of a volcanic rock with maximum deposition age of ca. 1.16 Ga suggesting a Grenvillian (~ 1.4 - 1.0 Ga) magmatic event in the Southern Espinhaco Range. Sample Vul-1A is intrusive within the Archean Basement Complex, and is characterized by a brecciated structure, with clasts of schists, banded iron formations (BIFs), volcanic and granitic rocks, in a very fine to medium-grained matrix. Petrographically, it has a basic nature with alkaline tendency, defined as a basaltic trachyandesite to trachybasalt, with volcaniclastic aspects. Zircons recovered from the matrix of this rock showed three types of ages: Archean ages (mainly between 2.9 - 2.7 Ga), Paleoproterozoic ages (2.2 - 1.8 Ga), and the most important, Grenvillian ages (1.20 - 1.16). Geochemical data showed that this unit is not similar of the post-Espinhaco meta-basic rocks (Pedro Lessa Suite), dated at 1.0 - 0.9 Ga. If the occurrence of an igneous rock of that age is confirmed, with such facies aspect, it reinforces the idea that similar magmatic processes possibly of explosive type occurred during the last syn-rift phase of the Espinhaco basin evolution. Our geochronological data may have identified the possible source of the Grenvillian detrital zircons from the Sopa-Brumadinho Formation, and suggest that these volcanic processes were coeval and recurrent during the sedimentation of this unit.

Correianevesite, Fe2+Mn22+(PO4)2·3H2O, a new reddingite-group mineral from the Cigana mine, Conselheiro Pena, Minas Gerais, Brazil

Abstract Correianevesite, ideally Fe2+Mn22+(PO4)2·3H2O, is a new reddingite-group mineral approved by the CNMNC (IMA 2013-007). It occurs in a phosphate-rich granite pegmatite that outcrops near the Cigana mine, Conselheiro Pena, Rio Doce valley, Minas Gerais, Brazil. Associated minerals are: triphylite, lithiophilite, frondelite, rockbridgeite, eosphorite, vivianite, fairfieldite, leucophosphite, cyrilovite, phosphosiderite, etc. Correianevesite occurs as grayish-brown to reddish-brown transparent bipyramidal crystals up to 4 mm in size. The streak is white, and the luster is vitreous. Mohs hardness is 3½. Cleavage is poor on (010). Fracture is laminated, uneven across cleavage. The measured density is 3.25(2) g/cm3; the calculated density is 3.275 g/cm3. The mineral is biaxial (+), α = 1.661(5), β = 1.673(5), γ = 1.703(5), 2Vmeas = 70(10)°, 2Vcalc = 65.6°. The IR spectrum confirms the presence of H2O. The Mössbauer spectrum shows the presence of two sites for Fe2+ and one site for Fe3+ occupied in the ratio Fe12+:Fe22+:Fe3+ = 39:55:6. The chemical composition is as follows (electron microprobe, H2O determined by gas chromatography of ignition products, Fe apportioned between FeO and Fe2O3 based on Mössbauer data, wt%): MnO 29.21, FeO 21.74, Fe2O3 1.54, P2O5 34.59, H2O 12.6, total 99.68. The empirical formula, based on 11 O apfu, is H5.78Mn1.70Fe2+1.25Fe3+0.08P2.015O11. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 5.08 (43) (020), 4.314 (28) (002, 210), 3.220 (100) (221, 202), 3.125 (25) (122), 2.756 (35) (103, 230), 2.686 (25) (222, 113), 2.436 (22) (123), and 2.233 (23) (411, 331). The crystal structure is solved (R1 = 0.0176). Correianevesite is orthorhombic, space group Pbna, a = 9.4887(2), b = 10.1149(2), c = 8.7062(2) Å, V = 835.60(3) Å3, Z = 4. The refined crystal-chemical formula is: (Fe2+0.72Mn2+0.20Fe3+0.08)(Mn1.48Fe2+0.52)(PO4)2 (H2O,OH)3.

Kimberlito Canastra-1 (São Roque de Minas, MG): geologia, mineralogia e reservas diamantíferas

The research on the primary diamond sources in Brazil started in the 1960 years and had its highest achievement with the discovery of the mineralized Canastra-1 kimberlite which is the first Brazilian primary deposit having economic contents. This pipe surfaces in the Serra da Canastra (Canastra Range) near the sources of the Sao Francisco River. The intrusion is made up of two blows lined along NE-SE, which is the regions structural trend defined in the metasedimentary rocks of the Canastra Group. The smaller blow is nearly circular with an area of approximately 0.8 ha and has only negligible diamond content. The SE blow has almost 1.0 ha and is mineralized with an average content of 12 to 18 ct/100 tonnes of rock. There are also significant differences in the petrographic facies of the two bodies, which is homogeneous in the NW blow while the SE blow is heterogeneous, with the occurrence of a mixture of several facies. The short distance between the blows justifies the assumption that they join in depth, therefore being apophyses of the same intrusion. The mineral chemistry of the indicators showed a strong resemblance with some diamondiferous African kimberlites. Data from experimental mining indicated an excellent quality for this kimberlites diamonds, with US

Pauloabibite, trigonal NaNbO3, isostructural with ilmenite, from the Jacupiranga carbonatite, Cajati, São Paulo, Brazil

180-200/ct estimated average value.

Diamantes do médio rio Jequitinhonha, Minas Gerais: qualificação gemológica e análise granulométrica

Abstract Pauloabibite (IMA 2012-090), trigonal NaNbO3, occurs in the Jacupiranga carbonatite, in Cajati County, São Paulo State, Brazil, associated with dolomite, calcite, magnetite, phlogopite, pyrite, pyrrhotite, ancylite-(Ce), tochilinite, fluorapatite, “pyrochlore”, vigezzite, and strontianite. Pauloabibite occurs as encrustations of platy crystals, up to 2 mm in size, partially intergrown with an unidentified Ca-Nb-oxide, embedded in dolomite crystals, which in this zone of the mine can reach centimeter sizes. Cleavage is perfect on {001}. Pauloabibite is transparent and displays a sub-adamantine luster; it is pinkish brown and the streak is white. The calculated density is 4.246 g/cm3. The mineral is uniaxial; n(mean)calc is 2.078. Chemical composition (n = 17, WDS, wt%) is: Na2O 16.36, MgO 0.04, CaO 1.36, MnO 0.82, FeO 0.11, SrO 0.02, BaO 0.16, SiO2 0.03, TiO2 0.86, Nb2O5 78.66, Ta2O5 0.34, total 98.76. The empirical formula is (Na0.88Ca0.04Mn2+ 0.02)SΣ0.94(Nb0.98Ti0.02)Σ1.00-O3. X-ray powder-diffraction lines (calculated pattern) [d in Å(I)(hkl)] are: 5.2066(100)(003), 4.4257(82)(101), 3.9730(45)(012), 2.9809(54) (104), 2.3718(88)(21̄3), 1.9865(28)(024), 1.8620(53)(21̄6), and 1.5383(30)(300). It is trigonal, space group: R3̄, a = 5.3287(5), c = 15.6197(17) Å, V = 384.10(7) Å3, Z = 6. The crystal structure was solved (R1 = 0.0285, wR2 = 0.0636 for 309 observed reflections). Pauloabibite is isostructural with ilmenite and is polymorphic with isolueshite (cubic) and lueshite (orthorhombic). The name is in honor of Paulo Abib Andery (1922-1976).

Raman and Infrared Spectroscopic Characterization of the Phosphate Mineral Lithiophilite—LiMnPO4

Os depositos aluvionares da bacia do Rio Jequitinhonha, em Minas Gerais, constituiram a fonte da maior parte dos diamantes produzidos no Brasil desde 1714 ate meados da decada de 1980. Essa importância historica e economica motivou a apresentacao dos dados quanto a granulometria e qualificacao gemologica dos diamantes nas areas de concessao das mineradoras Tejucana e Rio Novo. Em adicao, a amostragem adquirida em 14 pontos ao longo do rio e instrumental para a composicao de um banco de dados, tendo em vista a identificacao da origem de populacoes de diamantes. No mega-lote estudado, constituido por 186.052 pedras (17.689 ct), merece ser destacada a grande proporcao (82,2%) de diamantes gemologicos.

Pegmatito Gentil (Mendes Pimentel, MG) e suas paragêneses mineralógicas de fosfatos raros

Abstract The metal lithium is very important in industry, including lithium batteries. An important source of lithium besides continental brines is granitic pegmatites as in Australia. Lithiophilite is a lithium and manganese phosphate with chemical formula LiMnPO4 and forms a solid solution with triphylite, its Fe analog, and belongs to the triphylite group that includes karenwebberite, natrophilite, and sicklerite. The mineral lithiophilite was characterized by chemical analysis and spectroscopic techniques. The chemical is: Li1.01(Mn0.60, Fe0.41, Mg0.01, Ca0.01)(PO4)0.99 and corresponds to an intermediate member of the triphylite-lithiophilite series, with predominance of the lithiophilite member. The mineral lithiophilite is readily characterized by Raman and infrared spectroscopy. GRAPHICAL ABSTRACT

Almeidaite, Pb(Mn,Y)Zn2(Ti,Fe3+)18O36(O,OH)2, a new crichtonite-group mineral, from Novo Horizonte, Bahia, Brazil

Hundreds of pegmatitic bodies occur in the northern region of the State of Minas Gerais, several of these bodies producing gemologic and collection minerals. Such pegmatites are known by the mineral affinity with certain minerals species, groups or classes. The Gentil Pegmatite (Mendes Pimentel county) is characterized by the phosphatic mineral assemblage, and some of these minerals are rare or very rare in nature. Primary species are microcline, quartz, muscovite, almandine-espessartine, beryl, and triphylite as the main phosphate that was altered to an extensive paragenesis of secondary phosphates. In this list are noted brazilianite, frondelite, gormanite, hureaulite, lazulite, lithiophilite, purpurite, reddingite, woodhouseite, zanaziite, and matioliite, a species recently described in the Gentil Pegmatite.