Compositional Variation in Wolframites from the Barroca Grande Mine, Portugal: Evidence for Fault-Controlled Ore Formation

D. A. Polya
Department of Geology, The University, Manchester M13 9PL

Abstract: The major and trace element composition of over 40 wolframites from the Barroca Grande mine of the Panasqueira W-Sn-Cu quartz-vein hosted orebody have been determined by electron probe microanalysis.

The hübnerite content of wolframite is largely uniform (12 to 20 mol. %) throughout most of the mine, suggesting relative uniformity in composition of the main stage ore-forming fluids. However, wolframites show a striking pattern of enrichment in niobium adjacent to major sub-vertical fault zones. Typical wolframite Nb2O5 contents are below 1000 ppm, whilst values greater than 1000, 2000 and 4000 ppm are generally only found in wolframites less than 50, 30, and 10 metres respectively from major sub-vertical faults. This strongly suggests that some of these fault zones acted as major pathways for hydrothermal fluid migration during ore formation. The idea that the greisened cupola at Panasqueira was the sole major pathway for fluid movement is discounted.

Keywords: wolframite • niobium • Barroca Grande mine • Panasqueira • Portugal

Mineralogical Magazine; September 1988 v. 52; no. 367; p. 497-503; DOI: 10.1180/minmag.1988.052.367.08
© 1988, The Mineralogical Society
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