Header
Accueil du site > Publications > Interplay of magmatic and diapiric environments in the Djebel El Hamra (...)

Interplay of magmatic and diapiric environments in the Djebel El Hamra Pb-Zn-Hg ore district, northern Tunisia

Abidi, R. ; Marignac, C. ; Deloule, E. ; Hibsch, C. ; Gasquet, D. ; Renac, C. ; Somarin, A.K. ; Hatira, N. ; Slim-Shimi, N., Mineralium Deposita

Interplay of magmatic and diapiric environments in the Djebel El Hamra Pb-Zn-Hg ore district, northern Tunisia

Abidi, R. ; Marignac, C. ; Deloule, E. ; Hibsch, C. ; Gasquet, D. ; Renac, C. ; Somarin, A.K. ; Hatira, N. ; Slim-Shimi, N.

Mineralium Deposita, 2021, 57, 35-60

Abstract :

The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred in the Triassic dolostone : stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals ; stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression to extension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition : one low-salinity (L1, 3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, 22 wt% eq. NaCl) solution which originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement was also involved in the Pb-Zn deposition. The δ34S values from a cluster of sulfates around +16‰, show a Triassic evaporate source. The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR) ; however, crystallization in a closed system resulted in a range of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemical sulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena (207Pb/204Pb : 15.595 to 16.193, 206Pb/204Pb : 18.673 to 18.939, 208Pb/204Pb : 38.330 to 40.572) point to local contributions (sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at a depth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermal fluctuations.

Voir en ligne : https://doi-org.insu.bib.cnrs.fr/10...




publié jeudi 6 janvier 2022