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SUMMARY:Making Sense of a Geological Dog's Dinner - Petrology and Petrogen
 esis of the Motzfeldt REE-Nb-Ta deposit\, South Greenland - Professor Adri
 an Finch\, University of St Andrews
DTSTART:20260310T120000Z
DTEND:20260310T130000Z
UID:TALK243067@talks.cam.ac.uk
CONTACT:Carrie Soderman
DESCRIPTION:There is much current interest in the critical resource potent
 ial of Greenland. The Motzfeldt deposit is being tipped as one of the worl
 d's largest Ta deposits\, also containing significant volumes of Nb and Ra
 re Earth Elements. Initial studies identified pyrochlore has the host of N
 b and Ta\, and the coexisting U in the pyrochlore was used to map the depo
 sit using radiometrics. Early mineralogical studies reported bastnasite (C
 eCO3F) in addition to pyrochlore\, leading some to classify it (mistakenly
 ) as a carbonatite-type deposit. However field studies showed that the hos
 t was a quartz syenite and that the mineralisation was spread over a wider
  area than the radiometric survey suggested. It became clear that Motzfeld
 t was a complex geological conundrum\, a deposit type for which a clear ge
 netic model did not exist.\n\nBig questions in economic geology include th
 e roles of extreme fractionation vs partial melting in generating extreme 
 melt compositions as well as the role and timing of fluid interaction. Thi
 s talk will run through how we picked apart the story behind the novel min
 eralisation. The target elements at Motzfeldt are hosted in the magmatic r
 oof zone and key to the siting of the mineralisation is the interaction be
 tween the magma and arenite in the roof. The mineralised units come from m
 ultiple sources\, including both extreme fractionates and partial melts\, 
 plus or minus hydrothermal interaction involving highly aggressive fluids 
 that transported REE and Nb. We were helped by the fact that Motzfeldt is 
 deeply dissected by recent glaciation giving superb 3D slices through the 
 roof zone. We now have a genetic model for syenite-hosted Ta-Nb mineralisa
 tion that is being applied to other similar deposits elsewhere in the worl
 d.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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