3rd European SEG Student Chapter’s Conference

Metallogeny and Magmatism of the North Massif Central

Budapest, 2011. 10. 13.

Emődy Kincső & Fekete Szandra

• ESSCCO: European SEG Student Chapter’s Conferenceevery two years in a different country

• 3rd ESSCCO: 23-26 August, 2011, Institut Polytechnique LaSalle Beauvais (France-Oise)

• Participants from Ukraine, Switzerland, Hungary and France

Mark Hannington and the participants of the 3rd ESSCCO

August 23rd: lecture series– Presentation of the SEG Student Chapter and

discussions

Francois Denivelle (LaSalle France)

Participants in the lecture hall

Doctor Mark Hannington (official lecturer of the SEG) from the University of Ottawa: “The Mettalogeny of Western Pacific Submarine Volcanic Arcs”

Invited speakers gave a talk:

• Invited speakers gave a talk:

• Doctor Philippe Boulvais from the University of Rennes: „New approaches to isotope geochemistry in metallogeny”

• Doctor Eric Gloaguen from the University of Orleans: „Introduction to the field trip, The granites and rare metal pegmatites (North Limousin)

After the presentations...

...students were looking round inside the Institut Polytechnique...

...teachers were drinking some beer...

... and we had dinner together.

• 24-25, August: Field Trip to the North Limousin

Eric Gloaguen is talking about the geology of the field trip area

The rare metals pegmatites of the North Limousin

Geology of the North Limousin:

-Northwestern part of the French Massif Central

-The inner orogenic domain of the mid-European Variscan belt (collision zone between the Baltica and Gondwana)

-Polyphased deformation, four main tectonic stages (Eo-, Meso-, Neo-, Late-Variscan) and two main stages associated with granitoid magmatism (Meso- and Neo-to Late Variscan)

Localisation of the field trip area (from Charlier et al., 2002)

European Variscans

Zonation of the Variscan Europe,metallogenous element association

• In the Limousin area the most important granitoid magmatism occurred in the Neo-to Late Variscan geotectonic stages

– widespread peraluminous muscovite + biotite granite and leucogranite (Limousin type) magmatism, 325+/-10 Ma

– rare metals magmatism: very small bodies of HP

peraluminous lepidolite muscovite leucogranites, rich in Ta, Nb, Sn, W and U (Rare Metal Granites, RMG), pegmatites, rhyolites, 317-310 Ma

• Most deposits ( rare metals, W-Sn, Au) are related to Neo- to Late Variscan (325-305 Ma) peraluminous granites

– linked to the „metalliferous peak”, 300 Ma– Ta, Nb, Sn, Li, Be deposits are disseminated within

the RMG– RMG occur: (~3-4 km depth)

• pegmatitic veins• small granitic stocks• sheets• ryolitic dykes

Origin of the rare metals is felsic magmatism

-high-phosphorus RMG (Montebras, Beauvoir)-peraluminous intermediate phosphorus granite (Chavence)-ryolitic dyke (Richemont)-lepidolite subtype pegmatite (Chedeville)-beryl-columbite subtype pegmatite (Ambazac Mount, Crozant)

Structural map of the Limousin area (from Gebelin et al., 2007.)

• „A pegmatite is a coarse grained igneous rock having a grain size of 3 cm or more. Mostly pegmatites are granitic in origin, that is they are composed of granite and its constituents like quartz, feldspar and mica. In addition to these basic minerals there are also generally rare earth elements. ” (http://www.gemandmineral.com/peg.html)

The Ambazac Mounts LCT pegmatites

Limoges (http://maps.google.com/)

Ambazac Mt. located 20 km north to Limoges

The Ambazac Mounts pegmatites(issue XIV of the „Regne Minéral” magazine)

• In the Monts d’ Ambazac area is the granitic complex of Haute-Vienne, composed by three granites:– La Brame– Chateauponsac– St. Sylvestre

• Several pegmatites hosting rare metal are associated with the granite of St. Sylvestre The Ambazac Mounts pegmatites

(issue XIV of the „Regne Minéral” magazine)

• 3 types of pegmatites, 3 different geochemical domains, results from a continous magmatic evolution

– Main Group: western part, potassic and sodi-potassic pegmatites

– NE Group: alkalin-sodi-potassic leucogranite host lepidolite subtype pegmatite, and some of the sodi-potassic pegmatites (beryl-columbite subtype)

– Larmount Group: eastern part, alkalin-sodic leucogranite

Localisation of Chèdeville -La Cheze Lépidolite petalite RM pegmatite on the southren

border of the Saint Sylvestre granite (Raimbault, 1998)

• On the first day of the field trip (August 24th) we visited Chabannes and Margnac LCT-type, beryl-columbite subtype pegmatites

– These pegmatite are parts of a dyke swarm known in the western part of the Saint-Sylvestre granite

– Chabannes pegmatite was the last mined pegmatite– heterogenous body, concentric structure

Marginal z. External z. Internal z. Quartz core and Blocky z.

Schematic section of the Margnac pegmatite (Patureau, 1982; 2002)

• marginal zone : thin banded aplitic succession; albite,muscovite, Q + apatite, grt, zircon, zinnwaldite

external zone : cm pink K-feldspar, albite, grey Q, musc., and biotite + yellow beryl, zinnwaldite; graphic and „pine tree” texture

internal zone : inside the external zone, with substitution of K-feldspar by white albite by sodic metasomatose; rare elements minerals: rare lepidolite, zinnwaldite, beryl, columbite-tantalite, triphylite (LiFePO4), Triplite ((Mn,Fe)2(PO4)(F,OH)), amblygonite, turquoise, apatite

Muscovite testacée

• blocky zone: pink perthitic microcline (up to 1 m), albite, Q; geodes and•quartz core: mainly grey Q,+ beryl, microcline, muscovite

• After the field we went to a very friendly village to spend the night there.

Sauvagnac

• On the 2nd day we went inside the Chèdeville – La Chaze LCT-type, lepidolite-subtype pegmatites

– pentalite-lepidolite-albite dyke, 1200 m long, SW-NE int he southern part of the Saint Sylvestre granite

– enriched in rare metals (Li, Rb, Cs, Ta, Sn)– main lithium minerals : lepidolite

(K(Li,Al)3(Si,Al)4O10(F,OH)2 and petalite (LiAlSi4O10)

– well-developed internal structure: coarse upper zone and an aplitic lower zone

Coarse upper zone

Lower aplitic zone

Lower aplitic zone

– Repetation of the zonation provides evidence of multiple batches of magma

– Nb-Ta mineral characteristics are different from those of the granitic rockspegmatites are more Mn-rich

– There is no evidence of their direct derivation from the Saint Sylvestre granite (age of Chèdeville pegmatite has been dated at 309+1 Ma (Ar/Ar on lepidolite) vs. Saint Sylvestre granite (324+4 Ma)

Participants inside the Li-rich Chèdeville pegmatite

The Rhyolitic dyke of Richemont

• The Rhyolitic dyke of Richemont

– 5 km long and 5 m width outcrop– Age: 313+3 Ma– Rhyolite belongs to the high phosphorous

peraluminous RMG group– Typically strong enrichment in Ta, Nb, Li, Be, F, P– Idiomorphic quartz and muscovite phenocrysts are

dispersed in a devitrified homogenous matrix– Texture imply a very fast cooling of the intrusion

We are looking for the rhyolitic dyke outcrop

The rhyolitic body is in this bush

Goodbye party

August 26th, Paris:

Andriy, Gautier, Kincső & Szandra in front of the Notre Dame

Mélanie, Andriy, Kincső & Szandra over the Sain

Thank you for your attention!