Unconformity-related mineralization and fluid transfers in the northern Aquitaine Basin (France) revealed by fluid inclusions and S-Sr isotopes studies
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引用次数: 0
Abstract
In sedimentary basins, unconformity between basement and sediments is the ideal site where fluids from different sources can flow and mix, initiating the formation of ore deposits. In western Europe there are numerous F-Pb-Zn-Ba (±Ag, Ge) basin-hosted deposits located near the unconformity between Mesozoic Basins and the Variscan basement as for example the deposits of the Vendée Coast (France) containing fluorite, baryte, pyrite and quartz. Here, microthermometric data on the primary fluid inclusions of these minerals indicate salinity ranging from 1 to 20 wt% eq. NaCl and homogenization temperatures between 100 and 390 °C. We interpret these data as resulting of a fluids circulation in the ore deposit zone, with an early incursion of basin brines expelled by the leaching of Hettangian evaporites buried several tens of kilometers away, followed by an ascent of basement-derived fluids and, finally, a recharge of seawater. In other French deposits, the δ34S isotopes of baryte are also consistent with a source of fluids from buried evaporites. The 87Sr/86Sr ratio of baryte demonstrates a crustal source of elements associated with brines-leached base metals and FBa. The process of buried-derived evaporites brines altering the basement along the unconformity is ubiquitous in all unconformity deposits in France.
With our results, we confirm that the basin deposits in the Southeastern Massif Central occur along structures formed during Tethys rifting at around 200 Ma, whereas in the Western part they form at ca. 145 Ma in link with the opening of the Bay of Biscay. This highlights that these basin-hosted deposits are preferentially formed during extensional activity in rifting settings, rather than in compressive settings.
期刊介绍:
Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics.
Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to:
define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas.
analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation.
evaluate effects of historical mining activities on the surface environment.
trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices.
assess and quantify natural and technogenic radioactivity in the environment.
determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis.
assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches.
Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.