Fluid flow, alteration and polysulphide mineralisation associated with a low-angle reverse shear zone in the Lower Palaeozoic of the Anglo-Brabant fold belt, Belgium

Piessens, K., Muchez, P., Dewaele, S., Boyce, A., De Vos, W., Sintubin, M., Debacker, T.N., Burke, E.A.J. and Viaene, W. (2002) Fluid flow, alteration and polysulphide mineralisation associated with a low-angle reverse shear zone in the Lower Palaeozoic of the Anglo-Brabant fold belt, Belgium. Tectonophysics, 348(1-3), pp. 73-92. (doi: 10.1016/S0040-1951(01)00250-5)

Abstract

In the Lower Palaeozoic rocks of the Brabant Massif (Belgium), a recently discovered polysulphide mineralisation is related to a low-angle reverse shear zone. This shear zone has been attributed to the main early Devonian deformation event. Data from boreholes and outcrops allow a detailed investigation of the alteration pattern and palaeofluid flow along this shear zone. Macroscopic observations of the mineralogy and quantitative changes in the phyllosilicate mineralogy indicate that this shear zone is characterised by an envelope of intense sericitisation and silicification. In addition, chloritisation is associated with this alteration. The alteration zone may reach a thickness of 250 m. Ore mineralisation occurred synkinematically and is spatially related to the shear zone, The mineralisation consists of pyrite, marcasite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, stibnite and smaller amounts of tetrahedrite and other sulphosalts, It is concentrated in quartz-sulphide veins or occurs diffusely in the host rock. The mineralising fluids have a low-salinity H2O- CO2-CH4-NaCl-(KCl) composition and a minimum temperature of 250-320 degreesC. The delta(18)O values of quartz vary between + 12.3parts per thousand and + 14.5parts per thousand SMOW, and deltaD compositions of the fluid inclusions in the quartz crystals range from - 65parts per thousand to - 35parts per thousand V-SMOW. The deltaD and the calculated 6180 values of the mineralising fluids fall in the range typical for metamorphic fluids and partly overlap with that for primary magmatic fluids, The delta(34)S values, between + 4.7parts per thousand and + 10.6parts per thousand CDT, fall outside the interval typical for I-type magmas. Important migration of likely metamorphic, fluids, causing a widespread alteration and a polysulphide mineralisation along a low-angle shear zone, has, thus, been identified for the first time in the Caledonian Anglo-Brabant fold belt.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Boyce, Professor Adrian
• Authors: Piessens, K., Muchez, P., Dewaele, S., Boyce, A., De Vos, W., Sintubin, M., Debacker, T.N., Burke, E.A.J., and Viaene, W.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Tectonophysics
• ISSN: 0040-1951