Phosphate nodules containing two distinct assemblages in the Cema granitic pegmatite, San Luis province, Argentina: Paragenesis, composition and significance
- 1 August 2012
- journal article
- research article
- Published by Mineralogical Association of Canada in The Canadian Mineralogist
- Vol. 50 (4), 913-931
- https://doi.org/10.3749/canmin.50.4.913
Abstract
Nodules of Fe-Mn phosphates are common in the outer core zone of the Cema pegmatite, San Luis Range, Argentina. Two different complex phosphates associations have been distinguished in these nodules. One of them is beusite-wyllieite-sicklerite-rich (BWS), with varulite and stanekite among the main products of replacement, Fe/(Fe + Mn) values between 0.46 and 0.48 for sicklerite, and MgO values up to 2.14 wt%. The other association is lithiophilite-sicklerite-rich (LS), with varulite and hureaulite among the main secondary products, lower Fe/(Fe + Mn) values, in the range 0.37-0.39 for lithiophilite, and lower MgO contents, invariably below 1 wt%. According to the mineral-chemistry data of these Fe-Mn phosphate nodules, a higher temperature of crystallization is proposed for the BWS association compared to the LS one. The Mn enrichment observed in these phosphates, in a pegmatite that is not highly fractionated, could be explained as a result of the early crystallization of other Fe-(Mg-Mn)-rich minerals, such as schorl, in the border and wall zones of this pegmatite. The crystallization of this silicate would have strongly depleted the activity of Fe in the remaining pegmatite-forming melt.Keywords
This publication has 7 references indexed in Scilit:
- Nomenclature of the tourmaline-supergroup mineralsAmerican Mineralogist: Journal of Earth and Planetary Materials, 2011
- Chemical variations and significance of phosphates from the Fregeneda-Almendra pegmatite field, Central Iberian Zone (Spain and Portugal)Tschermaks Mineralogische und Petrographische Mitteilungen, 2010
- THE ASSOCIATION QINGHEIITE - BEUSITE - LITHIOPHILITE IN THE SANTA ANA PEGMATITE, SAN LUIS, ARGENTINAThe Canadian Mineralogist, 2009
- TOURCOMP: A program for estimating end-member proportions in tourmalinesMineralogical Magazine, 2008
- PHOSPHATE ASSEMBLAGES FROM THE BRISSAGO GRANITIC PEGMATITE, WESTERN SOUTHERN ALPS, SWITZERLANDThe Canadian Mineralogist, 2008
- Mn-rich graftonite, ferrisicklerite, staněkite and Mn-rich vivianite in a granitic pegmatite at Soè Valley, central Alps, ItalyMineralogical Magazine, 2007
- Origin and internal evolution of the Li-F-Be-B-P-bearing Pinilla de Fermoselle pegmatite (Central Iberian Zone, Zamora, Spain)American Mineralogist: Journal of Earth and Planetary Materials, 2005