Evidence for the Mechanism of the Reaction Producing a Bournonite-Galena Symplectite from Meneghinite

Ni Wen, J. R. Ashworth and R. A. Ixer
School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

Abstract: In vein material from the abandoned copper mine at Dhurode, County Cork, Republic of Ireland, the sulphosalt meneghinite is partly replaced by later minerals, notably a symplectite of galena and bournonite. Mineral analyses and proportions indicate that the bulk Pb/Sb ratio in the symplectite is almost identical to that of the meneghinite. It is inferred that Pb and Sb were the relatively immobile elements whose short-range segregation controlled the scale of symplectite intergrowth, during a diffusive replacement reaction in which Cu and S were added from the vein-forming fluid. This is the second sulphosalt-bearing symplectite for which immobile elements have been identified. In both cases, the inferred replacement reaction causes a volume increase, approximately 15% in the present example.

Keywords: symplectite • meneghinite • bournonite • replacement • Ireland

Mineralogical Magazine; June 1991 v. 55; no. 379; p. 153-158; DOI: 10.1180/minmag.1991.055.379.01
© 1991, The Mineralogical Society
Mineralogical Society (www.minersoc.org)