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Isotope geochemistry (S, C, O, Sr, Pb) of the Chaudfontaine mineralization (Belgium)
| Content Provider | Semantic Scholar |
|---|---|
| Author | Dejonghc, L. |
| Abstract | Investigations on S, C, O, Sr, and Pb isotopes in ores, gangue, and country rocks of the Chaudfontaine ore deposit confirm that interbedded barite and white sparry calcites are cogenetic. They emphasize the marine origin of S and the nonmarine origin of the metals. They underline the important role played by the bacterial reduction at the site of deposition. Hypotheses concerning the source of the metals and the nature of the brines involved in their transportation are briefly discussed. Isotope geochemistry is a powerful tool in deciphering the petrogenesis of rocks in general and of ore deposits in particular. However, some metallogenists are not wholly convinced of the merits of this technique. Indeed, in some cases, results based on a small amount of data have led to premature conclusions. In other cases, conclusions have been drawn without taking into account all the geological constraints. Sometimes, detailed isotope studies on several different elements have resulted in contradictory conclusions (Routhier 1980, p. 170-171). Isotope geochemistry should thus be used with caution and the isotope results should be considered in conjunction with all other avalaible data. These few unfortunate examples should not, however, make us forget the numerous cases for which the contribution of isotope geochemistry has been essential. The synthetical works of Fritz (1976) on C and O isotopes, Sangster (1976) on S and Pb isotopes, and KSppel & Saager (1976) on U, Pb and Th isotopes constitute fruitful contributions. This study demonstrates the usefulness of the integration of several isotope systems, both stable (S, C, O) and radiogenic (St, Pb), in understanding the genesis of a sedimentary barite ore deposit, i.e., that of Chaudfontaine (Belgium). The Chaudfontaine ore deposit and its geological environment The Chaudfontaine ore deposit (Dejonghe 1979, 1985) is situated within the Verviers synclinorium (Graulich et al. 1984; Graulich & Dejonghe 1986) which is subdivided into three tectonic subunits, i.e., the Herve massif, the Vesdre massif, and the Theux tectonic window. A detailed geological map of the Chaudfontaine area is presented in Fig. 1. The bedrock is exclusively made up of sedimentary rocks of various ages (from Lower Devonian up to Silesian) and of various lithologies (alternating sandstones, shales, and carbonates, see Fig. 1). This region is tectonically complex: It is cut by numerous overthrust faults, and an overthrust sheet (Ch+vremont) is pinched between the Vesdre and Herve massifs. Two NS geological cross sections (Fig. 2) illustrate the tectonic pattern of the area, which consists of a succession of wide synclines and narrow anticlines with frequently fractured or even faulted axial planes. A comparison of these two parallel sections, 375 m apart, gives an appreciation of the tectonic variations of this area. The position of the mineralized level of Chaudfontaine is plotted on each of the cross sections. The ore deposit is characterized by the alternation of strongly mineralized layers, barren beds, and various combinations of these two extremes. The ore is chiefly made up of barite with accessory pyrite, sphalerite, and galena. Under the microscope, scarce small inclusions of chalcopyrite and bravoite have also been identified (Dejonghe 1978; Dejonghe et al. 1985). The main forms of the barite crystals as well as the sedimentary structures in which they occur have been described by Dejonghe (1979, 1985). The orebody has been intersected by three drill holes (enumerated by the Geological Survey of Belgium as 134 E 303, 134 E 310, and 134 E 396, Fig. 1). The drill sites occupy the vertices of a right-angle triangle, the right-angle sides of which measure 180 and 375 m in length. The orebody is located on the two flanks of a faulted anticline shown in Fig. 2 at vertical depths between 180 and 210 m. In the three drill holes the mineralization is situated at the same stratigraphic level, i.e., at the top of the Frasnian. More precisely, using the terminology of Coen-Aubert & Lacroix (1979), it is located at the top and above the second Phillipsastraea biostrome of the Aisemont Formation. The fluid inclusions of the barite have been studied by Dejonghe et al. (1982 b) and Dejonghe (1985). All the syngenetic inclusions are single phase at room temperature. The lack of a gas bubble requires a very low filling temperature, certainly below or'equal to 50°C (Sabouraud et al. 1980). The mean salinity deduced from the histogram is 16.5 equiv. wt% NaC1. At their highest concentrations, the brines have reached salinities of up to 23 equiv, wt% NaC1. If the salinities of the Frasnian seas were identical to those of the present-day seas, it would correspond to a mean concentration by evaporation of about one-fifth of the original volume (Sabouraud-Rosset 1976, p. 72). In drill hole 134 E 396, at two levels (between 195.50 m and 196.45 m and between 202.70 m and 202.90 m), barite is accompanied by very white sparry calcite, which is locally |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://page-one.springer.com/pdf/preview/10.1007/BF00206317 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
