The columbite-group minerals from granitic pegmatites of the Pampean Ranges: A panoramic view.

GALLISKI M. A. CERNÝ P.

Salta

Congreso; XIV Congreso Geológico Argentino; 1999

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:1; mso-generic-font-family:roman; mso-font-format:other; mso-font-pitch:variable; mso-font-signature:0 0 0 0 0 0;} @font-face {font-family:"WP MultinationalA Roman"; panose-1:2 2 6 4 5 5 5 2 3 4; mso-font-charset:2; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:0 268435456 0 0 -2147483648 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:none; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:EN-US; layout-grid-mode:line;} a:link, span.MsoHyperlink {mso-style-noshow:yes; mso-style-unhide:no; color:blue; text-decoration:underline; text-underline:single;} a:visited, span.MsoHyperlinkFollowed {mso-style-noshow:yes; mso-style-priority:99; color:purple; mso-themecolor:followedhyperlink; text-decoration:underline; text-underline:single;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:72.0pt 2.0cm 72.0pt 2.0cm; mso-header-margin:72.0pt; mso-footer-margin:72.0pt; mso-paper-source:0;} div.Section1 {page:Section1; mso-endnote-numbering-style:arabic;} --> THE COLUMBITE-GROUP MINERALS FROM GRANITIC PEGMATITES OF THE PAMPEAN RANGES: A PANORAMIC VIEW. Galliski, M.A., IANIGLA-CRICYT-CONICET Avda Adrián Ruiz Leal s/n Parque General San Martín, 5500 Mendoza, galliski@lab.cricyt.edu.ar ;    „erný P., Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada, p_cerny@Umanitoba.CA   Over 400 chemical compositions generated by EMPA for WO3, Nb2O5, Ta2O5, TiO2, ZrO2, SnO2, ThO2, UO2, Sc2O3, As2O3, Y2O3, Sb2O3, Bi2O3, MgO, CaO, MnO, FeO, ZnO, PbO, and 80 cell parameters refined on natural and heated samples of columbite-group minerals (CGM) from 30 rare-element-class granitic pegmatites are evaluated. The data show the diversified crystal chemistry and geochemistry of the group in the Pampean Ranges. The more evolved CGM range from manganocolumbite to manganotantalite and occur in petalite subtype pegmatites of the El Quemado pegmatite field. Possible lepidolite-subtype pegmatites from the Altautina and La Estanzuela pegmatite fields have almost the same Nb/Ta and Fe/Mn ratios. The CGM from spodumene-subtype pegmatites from Salta to San Luis show a wide range of variation and different evolutionary trends for each pegmatite. In general, CGM range from manganocolumbite to manganotantalite; the data plotted in the FeNb2O5-FeTa2O5-MnNb2O5-MnTa2O5 quadrilateral  show oblique, upward, bifurcated or ill-defined fractionation trends. In beryl-type pegmatites of LCT signature, CGM have very variable compositions from ferro- to manganocolumbite or locally tantalite, but the range of variation is rather limited. In the northern part of the Pampean Ranges, the Fe/Mn and Nb/Ta ratios are lower than, e.g., in the Comechingones pegmatite field. The only two known albite-type pegmatites known to date from the El Totoral pegmatitic field have zoned CGM with intermediate compositions in terms of both the Nb/Ta and Fe/Mn ratios, whereas the rare-earth-type pegmatites of the Conlara pegmatite field have manganocolumbite with relatively high Mg, Y, Sn, W and U contents. The chemistry of CGM in the beryl-type pegmatites from the Punilla pegmatite field correspond to ferrocolumbite enriched in high-field-strengh trace elements.  The structural state of investigated CGM is variable, ranging from cation-disordered to moderately cation ordered.