Fluid flow through the sedimentary cover in northern Switzerland recorded by calcite–celestite veins (Oftringen borehole, Olten)

Abstract

Abundant veins filled by calcite, celestite and pyrite were found in the core of a 719 m deep borehole drilled in Oftringen near Olten, located in the north-western Molasse basin, close to the thrust of the Folded Jura. Host rocks are calcareous marl, argillaceous limestone and limestone of the Dogger and Malm. The d 18 O values of vein calcite are lower than in host rock carbonate and, together with microthermometric data from fluid inclusions in vein calcite, indicate precipitation from a seawaterdominated fluid at average temperatures of 56-68°C. Such temperatures were reached at the time of maximum burial of the sedimentary pile in the late Miocene. The depth profile of d 13 C and 87 Sr/ 86 Sr values and Sr content of both whole-rock carbonate and vein calcite show marked trends towards negative d 13 C, high 87 Sr/ 86 Sr, and low Sr content in the uppermost 50-150 m of the Jurassic profile (upper Oxfordian). The 87 Sr/ 86 Sr of vein minerals is generally higher than that of host rock carbonate, up to very high values corresponding to Burdigalian seawater (Upper Marine Molasse, Miocene), which represents the last marine incursion in the region. No evidence for internally derived radiogenic Sr (clay minerals) has been found and so an external source is required. S and O isotope composition of vein celestite and pyrite can be explained by bacterial reduction of Miocene seawater sulphate. The available data set suggests the vein mineralization precipitated from descending Burdigalian seawater and not from a fluid originating in the underlying Triassic evaporites.

Raman spectra of water in fluid inclusions: I. Effect of host mineral birefringence on salinity measurement

“…The salinity obtained by microthermometry on two‐phase LV inclusions had a mean of 3.6 ± 0.4 mass% NaCl eq. . Lamellar crystals of barite were found in vugs in Pilar de Jaravia (Betic Cordillera, Spain) iron deposits, in association with hematite, goethite, celestite and gypsum .…”

U–Pb dating of mineral deposits: From age constraints to ore-forming processes

“…However, in the absence of these hydrothermal minerals (which is not uncommon), other minerals listed in Table 2 with non-negligible amounts of common Pb can be called on. Titanite or allanite can provide excellent dates for skarn (Chiaradia et al 2008;Deng et al 2014;Chelle-Michou et al 2015;Deng et al 2015b) and IOCG deposits (Skirrow et al 2007;Smith et al 2009;Haller et al 2011). Ore-stage calcite or apatite may sometimes represent the only minerals suitable for U-Pb dating at MVT deposits (Grandia et al 2000) or some REE-P deposits (Huston et al 2016).…”

The origin of celestine–quartz–calcite geodes associated with a basaltic dyke, Makhtesh Ramon, Israel

“…Although the ratios also match that of Early Cretaceous seawater, the timing of magmatism in the Negev and seawater-derived Sr has been used to explain celestine mineralization elsewhere (Yan & Carlson, 2003; Hoareau, Monnin & Odonne, 2010; de Haller et al . 2011; Tisato et al 2012), the composition of fluid inclusions in the Ardon geodes indicate that they were not precipitated from seawater-derived fluids. Evidently, the Sr originated from within the Ardon Formation.…”

“…1990; Scholle, Stemmerik & Harpøth, 1990; Yan & Carlson, 2003; de Haller et al . 2011; Ehya, Shakouri & Rafi, 2013), sometimes by as much as 20‰. This disparity is sometimes explained by enrichment of the heavier isotope due to sulphate reduction (although no solid evidence is provided for such processes) and, in other cases, it remains unaccounted for.…”