Fluid palaeo-circulation generated by the Pyrenean orogeny and its potential role in the formation of lead-zinc deposits in the Cévennes region: a modelling approach

Jost, Anne; Violette, Sophie; Macquar, Jean-Claude; Dromart, G.

doi:10.2113/175.4.317

Cited by 5 publications

(2 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…2005). This suggestion is consistent with recent hydrological modeling of fluid migration in the Cévennes region (Jost et al. 2004) that proposed that ore fluids probably circulated at depths in basements rocks and mixed with fluids in the overlying aquifers adjacent to the Cévennes horst.…”

Section: Discussionsupporting

confidence: 92%

Precipitation of lead–zinc ores in the Mississippi Valley‐type deposit at Trèves, Cévennes region of southern France

Leach¹,

Macquar²,

Lagneau³

et al. 2006

Geofluids

View full text Add to dashboard Cite

The Trè ves zinc-lead deposit is one of several Mississippi Valley-type (MVT) deposits in the Cé vennes region of southern France. Fluid inclusion studies show that the ore was deposited at temperatures between approximately 80 and 150°C from a brine that derived its salinity mainly from the evaporation of seawater past halite saturation. Lead isotope studies suggest that the metals were extracted from local basement rocks. Sulfur isotope data and studies of organic matter indicate that the reduced sulfur in the ores was derived from the reduction of Mesozoic marine sulfate by thermochemical sulfate reduction or bacterially mediated processes at a different time or place from ore deposition. The large range of d 34 S values determined for the minerals in the deposit (12.2-19.2& for barite, 3.8-13.8& for sphalerite and galena, and 8.7 to )21.2& for pyrite), are best explained by the mixing of fluids containing different sources of sulfur. Geochemical reaction path calculations, based on quantitative fluid inclusion data and constrained by field observations, were used to evaluate possible precipitation mechanisms. The most important precipitation mechanism was probably the mixing of fluids containing different metal and reduced sulfur contents. Cooling, dilution, and changes in pH of the ore fluid probably played a minor role in the precipitation of ores. The optimum results that produced the most metal sulfide deposition with the least amount of fluid was the mixing of a fluid containing low amounts of reduced sulfur with a sulfur-rich, metal poor fluid. In this scenario, large amounts of sphalerite and galena are precipitated, together with smaller quantities of pyrite precipitated and dolomite dissolved. The relative amounts of metal precipitated and dolomite dissolved in this scenario agree with field observations that show only minor dolomite dissolution during ore deposition. The modeling results demonstrate the important control of the reduced sulfur concentration on the Zn and Pb transport capacity of the ore fluid and the volumes of fluid required to form the deposit. The studies of the Trè ves ores provide insights into the ore-forming processes of a typical MVT deposit in the Cé vennes region. However, the extent to which these processes can be extrapolated to other MVT deposits in the Cé vennes region is problematic. Nevertheless, the evidence for the extensive migration of fluids in the basement and sedimentary cover rocks in the Cé vennes region suggests that the ore forming processes for the Trè ves deposit must be considered equally viable possibilities for the numerous fault-controlled and mineralogically similar MVT deposits in the Cé vennes region.

show abstract