Rutile from Panasqueira (Central Portugal): An Excellent Pathfinder for Wolframite Deposition

Minerals

Filipe Pinto¹  Eleonora Carocci²  Andreï Lecomte²  Michel Cathelineau²  Christian Marignac³  Laurent Truche⁴ 

[1] Beralt Tin and Wolfram Portugal, 6225-051 Barroca Grande, Portugal;GeoRessources, Université de Lorraine, CREGU, rue Jacques Callot, F-54506 Vandoeuvre-lès-Nancy, France;GeoRessources, Université de Lorraine, Ecole Nationale Supérieure des Mines de Nancy, Parc de Saurupt, F-54042 Nancy, France;ISTERRE, Université de Grenoble-Alpes, F-38041 Grenoble, France;

关键词: W-rich Rutile;    sector zoning;    oscillatory zoning;    fluid source signature;    wolframite;    Panasqueira;   

DOI  :  10.3390/min9010009

来源: DOAJ

【 摘 要 】

Abundant W-rich rutile in the tourmalinized wall-rocks from the Panasqueira W-deposit appears to be a marker of the onset of the main wolframite depositing event. Rutile displays spectacular zoning, both sector (SZ) and oscillatory (OZ). An extensive set of compositional data obtained on crystals, beforehand studied using back-scattered electron images and X-ray maps, was used to address (i) the effects of SZ on differential trapping of minor elements, and (ii) the significance of the OZ in deciphering fluid sources and fluid circulation dynamics. Particular attention was paid to Sn, W (Nb, Ta) concentrations in rutile as pathfinders of the W deposition. Concerning the sector zoning, W is more incorporated than (Nb, Ta) onto more efficient faces, whereas Sn contents are nearly not impacted. The net effect of the sector zoning is thus a progressive increase of the relative weight of Sn from pyramid to prism faces, in combination with a less significant increase in the relative weight of Nb + Ta. The oscillatory zoning concerns most minor elements: W, Nb (Ta), Fe, V, Cr and Sn. In the frequent doublets, the clear bands are in general enriched in W relatively to the dark ones, whereas the inverse is true for Nb and Ta. The doublets may be viewed as the result of the successive influx of (i) a W-rich, Nb + Ta poor fluid, abruptly replaced by (or mixed to) (ii) a Nb + Ta-rich and W-poor fluid. The Nb + Ta-rich fluid could be in turn related to a rare-metal granite layer observed atop of the Panasqueira granite.

【 授权许可】

Unknown