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Rapid fluid inclusion data
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The pegmatites in the French Massif Central contain rare metals,
tungsten, tin and uranium and have been extensively researched. In
the past they have produced tin, tungsten and uranium, but at
present they are actively mined for industrial minerals including
clay. A comprehensive summary of these deposits is in the
field trip guide book for the 13th SGA meeting, Nancy, France,
2015.
Rare metal, W and U deposits and related granites from the
NE French Massif Central.
by Michel Cuney and Christian
Marignac 2015 (155 pages)
A few of the quartz samples in this study show weak low
temperature decrepitation near 270 C indicating the presence CO2
rich fluids, but such fluids seem to be of minor amounts. Other
pegmatite deposits (eg Tanco,
Canada) often show more prominent CO2 fluid
contents. There are many variations in the quartz decrepitation
features between 350 C and 550 C indicating multiple fluid events,
but the significance of these events is not clear from this data.
The feldspar sample from the Beauvoir clay pit (2506D) is
interesting as it shows that inclusions have been preserved in the
feldspar and the weak low temperature decrepitation at 250 C shows
that CO2 rich fluids were present during feldspar
formation. Such CO2 rich fluids seem to have been less
abundant during quartz formation at this same location.
Pegmatite samples from the French massif central show interesting
variations over this large area, but they mostly lack CO2
rich fluids. It is not clear from this limited data if fluid
inclusion decrepitation data correlates with economic
mineralization or mineral exploration potential.
Only rare centimetre-sized fragments of quartz were present at La
Puelle quarry, present in late stage vugs. Both samples show
significant low temperature decrepitation at 280 C, indicating the
presence of CO2 rich fluids. But these fluids may
post-date the main pegmatite crystallization event.