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.
Résumé
LETTER
Evidence for an Early Cretaceous mineralizing event
above the basement/sediment unconformity in the intracratonic
Paris Basin: paragenetic sequence and Sm-Nd dating
of the world-class Pierre-Perthuis stratabound fluorite deposit
Morgane Gigoux
1,2
&
Guillaume Delpech
1
&
Catherine Guerrot
2
&
Maurice Pagel
1
&
Thierry Augé
2
&
Philippe Négrel
2
&
Benjamin Brigaud
1
Received: 22 October 2014 /Accepted: 22 April 2015 /Published online: 3 May 2015
#
Springer-Verlag Berlin Heidelberg 2015
Abstract
World-class stratabound fluorite deposits are spa-
tially associated with the basement/sediment unconformity
of the intracratonic Paris Basin and the Morvan Massif in
Burgundy (France). The reserves are estimated to be about
5.5 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 a
combined study of the paragenetic mineral sequence and Sm-
Nd dating on fluorite crystals. Fluorite occurs as isolated
cubes 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 their
147
Sm/
144
Nd and
143
Nd/
144
Nd isotopic compositions. The
normalized REE distribution displays homogeneous bell-
shaped patterns for all the geodic fluorite samples with a
Mid-REE enrichment over the Light-REE and Heavy-REE.
The
147
Sm/
144
Nd varies from 0.3108 to 0.5504 and the
143
Nd/
144
Nd from 0.512313 to 0.512518. A six-point Sm-
Nd isochron defines an age of 130±15 Ma (initial
143
Nd/
144
Nd=0.512054, MSWD=0.21). This Sm-Nd iso-
chron provides the first age
for the stratabound fluorite