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AMAZONITIZAÇÃO EM GRANITO RESULTANTE DA INTRUSÃO DE PEGMATITOS

2000; Sociedade Brasileira de Geologia; Volume: 30; Issue: 4 Linguagem: Inglês

10.25249/0375-7536.2000304693698

ISSN

2177-4382

Autores

Hanna Jordt-Evangelista, Júlio Cesar-Mendes, Ana Luisa Cosso Lima,

Resumo

ANitCfrom Santa Maria do Itabira in Minas Gerais is cut by amazonite-bearing pegmatites., being.marginally.transformedinto a green granite due to à"rur"-"itiìut,*.}ti.pápér ¿""rr;irh;h; pññesánd the miniralògicäf añd chemical va-ria.tioñsinvolved in the transformation of the normal granite into a green granite.?h";;;;-*id'" peg"¡natite is composed of decimeter-large anrazonite clystals of intense green color, cleavelandite, biotite, qtrartz and small arìrounts ol blacli tourmaline, galena, fluorite xnd allatase.Th;;iü;ñ.*;,"s"ni.À.oniËï-i"i"p;;;J;¡áil;;;'"rrry pure albite, microcli¡e.withtriclinicities of 0.68 to 0.93, Fe-biotite and accessorv minerals.The rnean siO" couient'is ì4 weight'vo, but in {uirtz-pool iarnples it decreases to 62vo.MgO.i1,verv, l9w (l 0'05 weight o/o)' t¿;:ö:"" #hä.iä;;åù;iil;ii;-a-.s2,.À.i'ong í"goriu"Ë, on.,üoty"ouia be due to the retentiou orEu in the calcic plagioclases left over' in íesii8i8 rocks which generated the alkaline magma by parlial rnelting' ä,;ft;rity of the grón color in the granite.increasestowalds the pe"gmatite contact-Chemicallv this colol valiation is accompanied by an incrcase in the pb (and ro a lesser exrent also in Rb) .ont"nå,ïfriiãi;iiff";;t'r* "ò"ld be registéred fol the majoJ and other trace elements pb varies fronr 37 ppm r" 30iñ;; t;;hi;;g ¿õ¿-pórn i;i ti-'" '"irãr",iii".-ii is possible -that the-subsolidus intt'oduction of not onlv Pb but also of water from the pegmatite into the country rock was r".,pon.ìUi"for the genér'ation of H2O -.Pq pairs in the microcline, which are postulated in rhe current lirerarur.eo, u"initü" "ãur;;'f ;Ë g¡3gir ."1'or'oÏãi"oioult"si Considering tlíe Lelatively low temperatures.ofpegmatitic magmas and the massive structure of th;gionit" tfl"-,"åto.ã^ati"pro"".. òf amazonitization *aÑery efircieni since the ãtrreoles Iocally reached a width equal to the width of the pegmatite.Ke1,w6r¿r, amazonite,

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