The Malines Cambrian carbonate-shale-hosted Pb-Zn deposit,France: Thermometric and isotopic (H,O) evidence for pulsating hydrothermal mineralization |
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| Authors: | A Charef S M F Sheppard |
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| Institution: | (1) Centre de Recherches Pétrographiques et Géochimiques, B.P. 20, 54501 Vandoeuvre-lès-Nancy Cedex, France |
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| Abstract: | Microthermometric, stable isotope (D/H, 18O/16O), and Raman spectroscopic data are given for four different mineralization events located beneath a Triassic unconformity. These events include the Pb-Zn-bearing KII mineralization which fills geodes and fractures in the main karstic mineralization KI and the F mineralization which fills fractures in the Cambrian carbonates and shales. Post-KI, pre-KII, and F mineralization fluids were hot ( 150°C), moderately saline (10 equiv. wt% NaCl), and precipitated red dolomite. Subsequently, equally hot but more saline (20 equiv. wt% NaCl) fluids deposited white dolomite and then sphalerite of the F mineralization; they were followed by another generation of dolomite at about 70°C from fluids with about 15 equiv. wt% NaCl and, even later, barites (165°C, 10 equiv. wt% NaCl). Variation in the homogenization temperature with salinity for the different dolomite generations suggests that the hot saline fluids were repeatedly diluted by a cooler, less-saline fluid. The fluids are interpreted to be of formation-water origin having possibly developed in the deep levels of the Rhone basins to the southeast, which was at least 3 km thick at the time of mineralization (post-Hetangian). The inferred metal-bearing hot brines were probably episodically expulsed during the dewatering of the basin, depositing their mineralization in the more permeable fault and karstic zones associated with the uplift of the St. Bresson horst. Cold surface waters probably invaded the mineralized zones between the pulses of hydrothermal solutions. This hydrothermal model with the introduction of sulfides can account for the precipitation and dissolution textures associated with the hydrothermal mineralizations. |
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