Evidence for an Early Cretaceous mineralizing event above the basement/sediment unconformity in the intraccratonic Paris Basin : paragenetic sequence and Sm-Nd dating of the world-class Pierre-Perthuis stratabound fluorite deposit

LETTEREvidence for an Early Cretaceous mineralizing eventabove the basement/sediment unconformity in the intracratonicParis Basin: paragenetic sequence and Sm-Nd datingof the world-class Pierre-Perthuis stratabound fluorite depositMorgane Gigoux1,2&Guillaume Delpech1&Catherine Guerrot2&Maurice Pagel1&Thierry Augé2&Philippe Négrel2&Benjamin Brigaud1Received: 22 October 2014 /Accepted: 22 April 2015 /Published online: 3 May 2015#Springer-Verlag Berlin Heidelberg 2015AbstractWorld-class stratabound fluorite deposits are spa-tially associated with the basement/sediment unconformityof the intracratonic Paris Basin and the Morvan Massif inBurgundy (France). The reserves are estimated to be about5.5 Mt of fluorite within six fluorite deposits. In this study,we aim to determine the age of the major fluorite mineraliza-tion event of the Pierre-Perthuis deposit (1.4 Mt fluorite) by acombined study of the paragenetic mineral sequence and Sm-Nd dating on fluorite crystals. Fluorite occurs as isolatedcubes or filling geodes in a Triassic, silicified, dolomitic for-mation. Threefluoritestagesassociated with sphalerite,pyrite,galena, barite, and quartz have been distinguished using opti-cal, cathodoluminescence, and scanning electron micro-scopes. Seven crystals of the geodic fluorite stage were ana-lyzed for their rare earth element (REE) contents and their147Sm/144Nd and143Nd/144Nd isotopic compositions. Thenormalized REE distribution displays homogeneous bell-shaped patterns for all the geodic fluorite samples with aMid-REE enrichment over the Light-REE and Heavy-REE.The147Sm/144Nd varies from 0.3108 to 0.5504 and the143Nd/144Nd from 0.512313 to 0.512518. A six-point Sm-Nd isochron defines an age of 130±15 Ma (initial143Nd/144Nd=0.512054, MSWD=0.21). This Sm-Nd iso-chron provides the first agefor the stratabound fluorite