CONTROLE DO MINÉRIO DE ESPODUMÊNIO EM PEGMATITOS DA MINA DA CACHOEIRA, ARAÇUAÍ, MG

Authors

  • Júlio Cezar Pimenta Romeiro Mestre em Geologia pela UFMG; Companhia Brasileira de Lítio, Araçuaí, MG
  • Antônio Carlos Pedrosa-Soares CPMTC-IGC-UFMG; Pesquisador do CNPq

DOI:

https://doi.org/10.18285/geonomos.v13i1e2.137

Abstract

The focused pegmatites belong to the Cachoeira Group, a spodumene-rich pegmatite population ofthe Araçuaí Pegmatite District, located in the north region of the Eastern Brazilian PegmatiteProvince. The Cachoeira Mine (CBL-Companhia Brasileira de Lítio) is located in the low valley ofthe Piauí River, east of Araçuaí town, Minas Gerais. The structural control of the pegmatites andrelated variations in spodumene grain size are important factors for mine planning. The pegmatitesof the Cachoeira Mine are non-zoned bodies with very few and small replacement pockets. Theyintruded along two different NE-striking surfaces of medium- to high-angle dip: the NW-dippingschistosity and the SE-dipping fracture cleavage. Systematic measurements show that the generalaverage size of spodumene crystals decreases with depth (i.e., the deeper the pegmatite segment, thesmaller the crystal size), but spodumene modal contents remain similar in different depths. Enrichmentin coarse-grained spodumene crystals occurs in shallow-dipping pegmatite segments. The increasingin spodumene crystal size, from lower to upper depths, can be related to decreasing in viscosity of thesilicate melt in response to accumulation of rising aqueous fluids towards the top of the pegmatite.The same effect can be expected for places of fluid swimming, such as the shallow-dipping pegmatitesegments. Fluids, like H2O and F, act by lowering the viscosity that, in turn, assists crystal growth. K/Rb and K/Ba ratios obtained from microcline crystals, associated to the spodumene, decrease graduallyfrom the bottom to the top of the pegmatites. Such increasing (to the top) in Rb and Ba also suggestsfluid enrichment in the same way of the increasing size of spodumene crystals.

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Published

2013-02-17

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Artigos