Ambligonite - Montebrasite from Divino das Laranjeiras – Mendes

AMBLYGONITE - MONTEBRASITES FROM DIVINO DAS
LARANJEIRAS - MENDES PIMENTEL PEGMATITIC SWARM, MINAS
GERAIS, BRAZIL III. SECONDARY PHOSPHATES
Ricardo SCHOLZ1, Joachim KARFUNKEL2, Vladimir BERMANEC3, Geraldo Magela
da COSTA4, Adolf Heirich HORN5, Luiz Antônio Cruz SOUZA6 & Essaid BILAL7
1
Departamento de Geologia, Instituto de Geociências, Programa de Pós-Graduação em
Geologia, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil –
[email protected]
2
Departamento de Geologia, Instituto de Geociências, Universidade Federal de Minas Gerais,
Belo Horizonte, MG, Brasil – [email protected]
3
Mineralogy and Petrology Institute, Faculty of Sciences and Mathematics, University of
Zagreb, Zagreb, Croatia - [email protected]
4
Departamento de Química, Instituto de Ciências Exatas e Biológicas, Universidade Federal de
Ouro Preto, Ouro Preto, MG, Brasil - [email protected]
5
Departamento de Geologia, Instituto de Geociências, Centro de Pesquisa Professor Manoel
Teixeira da Costa, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brasil –
[email protected]
6
Escola de Belas Artes, Centro de Conservação e Restauração, Universidade Federal de
Minas Gerais, Belo Horizonte, MG, Brasil – [email protected]
7
Ecole Nationale Supérieure des Mines de Saint Etienne, SPIN, Instituto Héliopolis,
[email protected]
SECONDARY PHOSPHATES
The Divino das Laranjeiras – Mendes Pimentel pegmatitic swarm is internationally know
since the 1940 decade, when 3 new minerals have been discovered in the Córrego Frio
pegmatite: brazilianite (Pough & Henderson 1945) and scorzalite and souzalite (Pecora & Fahey
1949). Later, many other secoundary phosphates related to amblygonite-montebrasites have been
described (Cassedann & Baptista, 1999; Lindberg, 1958; Leavens et al. 1990; Ribeiro, 1996;
Karfunkel et al. 1999).
Eosphorite, childrenite and ernstite
Eosphorite
-
(Mn2+,
Fe2+)Al(PO 4 )(OH) 2 H 2 O)
and
childrenite
(Fe2+,
Mn2+)
Al(PO 4 )(OH) 2 H 2 O) form as alteration products of primary pegmatitic phosphates such as
amblygonite-montebrasite (Moore 1973) and triphylite (London & Burt 1982). Although they
are usually associated with pegmatites, they can occur in other environments like in Pb-Zn
deposits of Stari Trg, Trepča, Kosovo (Bermanec et al 1995).
140
Ernstite – (Mn 1-x 2+, Fe x 3+)Al(PO 4 )(OH) 2-x O x – was described by Seelinger & Mücke
(1970) as an alteration (oxydation) product of childrenite. Controversy concerning the genesis of
the mineral was shown by Alves et al. (1980), who indicated that childrenite reists the oxydation;
however, Braithwaite & Cooper (1982) describe an excess of Fe3+ in relation to Fe2+ due to
supergenic alteration. Ginsburg & Voronkova (1950) report a complete oxydation of Fe2+ to Fe3+
of specimens from Kasakstan.
Eosphorite, childrenite and ernstite are common minerals in pegmatites of Divino das
Laranjeiras – Mendes Pimentel. The first two are associated with amblygonite-montebrasites,
mainly as dissolution cavity fillings or grown on their faces. Other allied minerals are zanazziite,
roscherite, fluorapatite, hydroxylherderite and brazilianite. Ernstite has been identified in 1
pegmatite of the region: João Firmino. It occurs in late alteration/substitution bodies together
with hydroxylherderite, muscovite and montebrasite.
Roscherite and Zanazziite
Roscherite - Ca(Mn2+,Fe2+) 2 Be 3 (PO 4 ) 3 .2H 2 O - was first described by F. Slavik as a
hydrated phosphate of calcium, iron, manganese and aluminium (Lindberg, 1958). It crystalize
as granulate masses of green to brownish color and is usually associated with other secondary
phosphates (e.g. eosphorite, gormanite, montebrasite, fluorapatite, and frondelite).
The studied samples from the João Firmino mine are monoclinic, space group C2/c, in
agreement with datas presented by Lindberg (1958). However, Fanfani et al. (1975), studying
samples from Foote Mine (North Caroline), indicate a triclinic symmetry.
Zanazziite – Ca 2 (Mg,Fe2+)(Mg,Fe2+,Al) 4 Be 4 (PO 4 ) 6 (OH) 4 .6H 2 O – has been described by
Leavens et al. (1990) from the Ilha mine, Taquaral county, in north of Minas Gerais. These
samples are usually associated with montebrasite and eosphorite. X-ray diffraction of samples
from the Gentil pegmatite in the studied area indicate a monoclinic symmetry and a C2/c spacel
group.
Herderite - Hydroxylherderite
Herderite and Hydroxylherderite represent end members of the isomorphous series
Herderite - Hydroxylherderite. They were discovered by Haidinger in 1828 and by S. Penfield in
1894, respectively (Leavens et al. 1978). Palache et al. (1951) divided this serie into 2 members.
These minerals form during late crystallization stages as hydrothermal alteration products of
141
beryl and beryllonite (Leavens et al. 1978). Moore (1973) describe temperatures between 350C200C as characteristic for late hydrothermal fluids.
Hydroxylherderite occur in all pegmatites of Divino das Laranjeiras - Mendes Pimentel
area, that are rich in montebrasite. Crystalls have a flat prismatic habitus, usually twinned after
{100}, sometimes {100} conjoint with {001}. In fresh samples its color is light yellow, however
it has sometimes a white alteration rim. In the Piano pegmatite pseudomorphs of
hydroxylherderite substituting eosphorite are common.
Samples with an alteration rim have been studied by x-ray diffraction and by EPMA).
These studies point towards a mixture of muscovite and hydroxylherderite in the altered zone.
Chemical analyses in the EDS mode show absence of fluorine, reforcing the definition as
hydroxylherderite. Infrared spectroscopical studies reafirm the results, due to the presence of two
well defined bands in the interval 3567cm-1 and 3605 cm-1, indicating the presence of OH- in the
structure of this mineral.
Brazilianite
Pough & Henderson (1945) were the first to describe and denominate a hydrated, sodium
phosphate from the studies area, as brazilianite - NaAl 3 (PO 4 ) 2 (OH) 4 . The mineral is quite rare
and most specimens on the mineral market come from this area. Besides the Córrego Frio
pegmatite, brazilianite is known from at least a dozen localities in the region, with the Telúrio
pegmatite outstanding at present time. Brazilianite occur as green to yellow-greenish monoclinic
crystalls, often in gem quality (cuttable), up to 3 cm long. Together with fluorapatite,
montebrasite, hydroxylherderite, beryllonite, eosphorite, Mn rich siderite, albite, muscovite,
casiterite and quartz.
Beryllonite
Beryllonite
–
NaBePO 4
–
crystallize
in
the
monoclinic
system
with
a
pseudoorthorhombic habitus, usually as hydrothermal alteration product of beryl and
amblygonite-montebrasites (Moore 1973).
In the Divino das Laranjeiras - Mendes Pimentel area beryllonite has been described only
from two pegmatites (Telírio and Roberto). The mineral occurs together with secondary
phosphates like brazilianite, hydroxylherderite, montebrasite poor in fluorine, childreniteeosphorite and fluorapatite, besides other non phosphatic minerals (e.g. muscovite, quartz and
142
albite). The colorless transparent crystalls, up to 3 cm in diameter have an extreme short
prismatic habitus. Twinning is common and many specimens are of gem quality.
Infrared spectroscopy show a non-hydratic structure with absence of transmittance band
at the interval 3600 cm-1 to 3400 cm-1 . In the 1150 cm-1 to 1150 cm-1 interval occur most
transmittance bands due to the PO 4 tetrahedra. The cation Na and Be2+ are responsible for
transmittance bands in the interval 775 cm-1 to 480 cm-1.
Fluorapatite, hydroxylapatite and carbonate-hydroxylapatite
Of the apatite group, fluorapatite (Ca 5 (PO 4 ) 3 F) and hydroxylapatite (Ca 5 (PO 4 ) 3 (OH)) are
the most common minerals. In pegmatites fluorapatite occurs as a primary phosphate, as well as
during the whole pegmatitic-hydrothermal evolution from 780C to 125C (Moore 1973).
Hydroxylapatite, as well as carbonate-hydroxylapatite (Ca 5 (PO 4 , CO 3 ) 3 (OH)) are common in
late crystallization stages and form as hydrothermal alteration products of primary phosphates
(Campbell & Roberts 1986).
In Divino das Laranjeiras - Mendes Pimentel these minerals occur together with
brazilianite, eosphorite-childrenite, beryllonite, amblygonite-montebrasite, roscherite, zanazziite,
frondelite, herderite, hydroxylherderite and siderite. Crystalls are hexagonal, blue, green, pink,
white, or colorless, with a long or short prismatic habitus. They have been found mainly in late
substitution bodies or as alteration products pseudomorph after eosphorite.
THE PHOSPHATIC PARAGENESES IN THE STUDIES AREA
Primary phosphatic phases can be substituted partially or completely by late stage
processes and thus masquerade the chemical evolution of a pegmatite. Therefore, although a first
attempt, the following parageneses described below can help to establish a chemical evolution
scheme for the crystallization of phosphatic pegmatite minerals in the studies area.
The following phosphatic mineral assemblages in pegmatites with primary montebrasite
have been determined:
a – montebrasite Type I + fluorapatite
b – montebrasite Type II + fluorapatite
c – montebrasite Type II + montebrasite Type III + eosphorite
d – brazilianite + montebrasite Type III + fluorapatite + beryllonite
e – brazilianite + eosphorite
143
f – montebrasite Type III + eosphorite
g – montebrasite Type III + fluorapatite + hydroxylherderite
h – eosphorite + siderite + fluorapatite + hydroxylherderite
i – eosphorite + fluorapatite + hydroxylherderite + coockeite
j – eosphorite + roscherite
k – siderite + fluorapatite + hidroxylherderite
l – hydroxylherderite + carbonate-hydroxylapatite + crandalite
m – ernstite + roscherite
n – eosphorite + zanazziite + leucophosphite
o – hydroxylherderite + crandallite + moraesite.
The evolution scheme is shown in Fig. 1, and has been divided, according to the
phosphatic mineralogy, in 4 stages: (i) Primary with montebrasite rich in fluorine; (ii) a second,
metasomatic stage, at which fluorapatite and montebrasite Type II form through alteration of the
primary montebrasite; (iii) The evolution of the crystallization took place simultaneously with
the presence of hydrothermal fluids, which alterate the primary mineralogy, accompanied by
metasomatic processes. It corresponds to the more diversified phosphatic mineralogy and is
found in late substitution or alteration bodies; (iv) at the end of the hydrtothermal stage, under
influence of external agents (e.g. meteoric water) the last crystalization/alteration took place with
phosphatic minerals of supergenic origin.
DISCUSSION AND CONCLUSION
The results of our analyses supported by datas from the mineralogical literature showed
that amblygonite-montebrasites occur in about one third of all pegmatites from Divino das
Laranjeiras - Mendes Pimentel. Moreover, these minerals differ in their fluorine content and
allow to distinguish three types. Type I is of primary nature and occur together with the main
mineral constituents. Fluorine content is around 4-5%. The second type (Type II) could be
detected in late crystallization and substitution bodies, usually with dissolutions on cleavage
plans and without a well defined habitus. The fluorine content is in average 2.3-2.5%. Minerals
of the Type III amblygonite-montebrasites have a well defined crystallographical habitus and
occur as late crystallization products and in substitution bodies. They are associated with other
phosphates of late crystallization, like brazilianite, eosphorite-childrenite, and have an average
fluorine content lower than 1.1%.
144
Fig. 1. Evolution scheme of crystallization/alteration of phosphatic mineralogy in pegmatites rich in primary
montebrasite from Divino das Laranjeiras – Mendes Pimentel.
Although late cristallization and alteration can change the primary mineralogy and thus
have masqueraded partially the evolution of crystallization processes in a pegmatite, the authors
suggest to use these specific phosphatic parageneses as a possible clue for establishing chemical
evolution schemes in phosphatic pegmatites. As known from the specific literature and
confirmed by own analyses, the fluorine content decrease in amblygonite-montebrasites during
differentiation processes due to a substitution of F- by OH-. This led us to suggest the threefold
division of these minerals, related to three crystalization/alteration stages during the evolution of
a phosphatic pegmatite. Since there is a slight overlapping in the fluorine content of the different
types, the evolution scheme represent just an attempt to relate effects (fluorine content) to causes
(differenciation/alteration) in a complicated multy-system.
ACKNOWLEDGEMENTS
The authors wish to thank the following institutions for partial support:
FAPEMIG – Fundação de Amparo à Pesquisa do Estado de Minas Gerais;
CNPq – Conselho Nacional de Desenvolvimento Científico e Tecnológico;
CAPES – Coordenação de aperfeiçoamento de Pessoal de Nível Superior.
Ministry of Science and Technology of Croatia ( Project # 0119420).
145
REFERENCES
ADDAD, J.; SCHOLZ, R.; FIGUEIREDO, J.; XAVIER, E. S.; KARFUNKEL, J.; ROCHA, S. O. G.;
PINHEIRO, M. 2000. Caracterização química das turmalinas azuis-verdes de Divino das
laranjeiras, MG, por espectroscopia no infravermelho e mapeamento por microssonda. In: 23a
Reunião Anual SBQ. Anais... Poços de Caldas V.1.QM-009.
ADDAD, J.; SCHOLZ, R.; KARFUNKEL, J. & MARTINS, M. S. 2001. Mapas químicos por
microssonda eletrônica: caracterização e relação cor-substituição de minerais. In: 6º Cong.
Geoquímica Países de Língua Port. Anais... Faro, Portugal. p. 85-87.
ALMEIDA, F. F. M.; HASUI, Y.; BRITO NEVES, B. B. & FUCK, R. 1977. Províncias Estruturais
Brasileiras. In: VIII Simp. Geol. Nordeste, Anais... SBG Núcleo Campina Grande. p. 363-391.
ALMEIDA, F. F. M. 1981. O Craton do Paramirim e suas relações com o do São Francisco. In:
SIMPÓSIO SOBRE O CRATON DO SÃO FRANCISCO E SUAS FAIXAS MARGINAIS.
Salvador, SBG – Núcleo Bahia, p. 1-10.
ALVES, K. M. B., GARG, R. & GARG, V. K. 1980. A Mössbauer resonance study of Brazilian
Childrenite. Radiochem. Radioanal. Lett., 45(2):129-132.
BARBOSA, A. L. M.; GROSSI SAD, J. H.; TORRES, N. & MELO, M. T. V. de. 1966. Geologia da
região do Médio Rio Doce. SBG, Núcleo RJ. Publ. N.2. 11p.
BERMANEC, V.; SCVNICAR, S. & ZEBEC. V. 1995. Childrenit and crandallite from the Stari Trg
mine ( Trepca, Kosovo): new data. Mineralog. and Petrol., 52: 197-208.
BRAITHWAITE, R. S. W. & COOPER, B. V. 1982. Childrenite in south-west England. Mineralog.
Mag., 46: 119-126.
BRITO NEVES, B. B & CORDANI, U. G. 1991. Tectonic evolution of South America during the late
proterozoic. Precambrian Research, 53: 23-40.
CASSEDANNE, J. P. & BATISTA, A. 1999. The Sapucaia pegmatite – Minas Gerais, Brazil. Mineralog.
Rec., 30(5): 347-366.
CAMERON, E. N., JAHNS, R. H.; McNAIR, A. H. & PAGE, L. R. 1949. Internal structure of granitcs
pegmatites. Econ. Geol., Monogr. 2, 115p.
CAMPBELL, T. J. & ROBERTS, W. L. 1986. Phosphate minerals from Tip Top Mine, Black Hills,
South Dakota. Mineralog. Rec., 17(4): 237-254.
ČERNÁ, I.; ČERNÝ, P. & FERGUSON, R. B. 1972. The Tanco Pegmatite at Bernic Lake, Manitoba. III.
Amblygonite-Montebrasite. Can. Mineralog. 11:643-659.
CORREIA NEVES, J. M., MARCIANO, V. R. P. R. O., LENA, J. C. & PEDROSA SOARES, A. C.
1987. Fosfatos do tipo crandalita (plumbogumita, goyazita, gorceixita) resultantes do
intemperismo de amblygonita de pegmatitos de Coronel Murta (nordeste de Minas Gerais) e seu
significado paleoclimático. An. Acad. Brasil. Ciênc., 17(1): 42-52.
FANFANI, L., NUNZI, A., ZANAZZI, P. F. & ZANZARI, A. R. 1975. The crystal structure of
roscherite. Tschermaks Mineral. Petrogr. Mitt., 22 (3-4): 1266-277.
FISHER, D. J. 1958. Pegmatite phosphates and their problems. Amer. Mineralog. 43(3-4): 181-207.
FRANSOLET, A. M. & TARTE, P. 1977. Infrared spectra of analyzed samples of the amblygonitemontebrasite series: a new rapid semi-quantitative determination of fluorine. Amer. Mineralog.,
62: 559-564.
GINSBURG, A. & VORONKOVA, N. V. 1950. Oxychildrenite a new mineral of theiron-manganesealuminium phosphate group. Dokl. Akad. Nauk SSSR, 72: 145-148. In: Zbl. Miner. I, 162, 1950.
HOWTHORNE, F. C. 1998. Structure and Chemistry of Phosphate Minerals. Mineralog. Mag. 62(2):
141-164.
KARFUNKEL, J. RIBEIRO, S. H.; BANKO, A.; QUÉMÉNEUR, J. J. G.; SCHOLZ, R.; ADDAD, J.;
MARTINS, M.; KRAMBROCK, K.; PINHEIRO, M. V. B.; LADEIRA, L. O. LAMEIRAS, F. S.
& PEREGOVICH, B. 1999. Pegmatitos graníticos ricos em fosfatos e sua variabilidade
mineralógica: o exemplo de Linópolis, Minas Gerais. VII Simp. Geol. Centro-Oeste – X Simp.
Geol. Minas Gerais. Anais... Brasília. p.39.
LEAVENS, P. B.; DUNN, P. J.; & GAINES, R. V. 1978. Compositional and Refrative Index Variations
of the herderite-hydroxylherderite series. Amer. Mineralog., 63: 913-917.
146
LEAVENS, P. B., WHITE, J. S., NELEN, J. A. 1990. Zanazziite, a new mineral from Minas Gerais,
Brazil. Mineralog. Rec., 21(5): 413-417.
LINDBERG, M. L. 1958. The beryllium content of roscherite from the Sapucaia pegmatite mine, Minas
Gerais, Brazil, and from other localities. Amer. Mineralog. 43: (9-10) p.824-838.
LONDON, D. & BURT, D. M. 1982. Alteration of spodumene, montebrasite and lithiophilite in
pegmatites of the White Picacho District, Arizona. Amer. Mineralog. 67, p.97-113.
MOORE. P. B. 1973. Pegmatite phosphates: descriptive mineralogy and crystal chemistry. Mineralog.
Rec., 4: 103-130.
NALINI, H. A. 1997. Caractérization des suites magmatiques néoprotérozoiques de la région de
Conselheiro Pena et Galiléia, Minas Gerais, Brésil. École Nationale Superière des Mines, Saint
Etienne, France, Dr. Thesis, 237p.
NETTO, C.; ARAÚJO, M. C.; PINTO, C. P. & DRUMOND, J. B. V. 1998. Projeto Leste: Cadastramento
de recursos minerais, pegmatitos. Belo Horizonte: SEME/COMIG/MME/CPRM, 179p.
PAIVA, G. 1946. Províncias Pegmatíticas do Brasil. DNPM/DFPM, Rio de Janeiro, 78: 13-21.
PALACHE, C.; BERMAN, H. & FRONDEL, C. 1951. Dana’s system of mineralogy, 7th Ed., V.. II, Jonh
Wiley and Sons, New York, 286p.
PECORA, W. T. & FAHEY, J. J. 1949. The Córrego Frio Pegmatite, MG: Scorzalite na Souzalite, two
new phosphate minerals. Amer. Mineralog., 34: 83-93.
PEDROSA SOARES, A.C.; NOCE, C.M.; WIEDEMANN, C. & PINTO, C.P. 2001. The Araçuaí-WestCongo Orogen in Brazil: an overview of a confined orogen formed during Gondwanaland
assembly. Precambrian Research, 110: 307-323.
POUGH, F. H. & HENDERSON, E. P. 1945. Brazilianite, a new phosphate mineral. Amer. Mineralog.,
30: 572-582.
RIBEIRO, S. H. 1996. Caracterização mineralógica da região de Divino das Laranjeiras – Mendes
Pimentel (MG) com ênfase a seus depósitos gemíferos e minerais de coleção. Dissertação de
Mestrado. UFMG/IGC. 115pp.
SCHOLZ, R. ; ADDAD, J.; KARFUNKEL, J.; MARTINS, M.S.; BERMANEC, V.; KNIEWALD, G.;
FIGUEIREDO Jr., J. C. D.; SOUZA, L. A. C. & SOUSA, S. H. B. 2001. Caracterização
petrogenética e geoquímica de amblygonita-montebrasitas em pegmatitos de Divino das
Laranjeiras, Minas Gerais, Brasil. In: 6º Cong. Geoquímica dos Países de Língua Port. Anais...
Faro, Portugal. p. 88-91.
SEELINGER, E. & MÜCKE, A. 1970. Ernstit, ein neunes Mn2+Fe3+ - Phosphat und seine Beziehnungen
zum Eospghorit. Neuns Jahrb. Mineral., Mh.: 289-298.
147