The polyphase evolution of a late Variscan W/Au deposit (Salau, French Pyrenees): insights from REE and U/Pb LA-ICP-MS analyses
Résumé
The Salau deposit, located in the Axial Zone of the French Pyrenees, is the most important tungsten deposit ever mined in France.Two types of mineralization, both closely associated with a granodiorite intrusion, are distinguished. The first is a fine-grainedscheelite skarn related to contact metamorphic and metasomatism between the intrusion and the adjacent carbonate rocks. Thesecond type is represented by massive sulfides accompanied by coarse-grained scheelite, apatite, and electrum. This synkinematicmineralization is found enclosed within the skarn ore but occurs also within the granodiorite stock along majorductile–brittle shear zones. REE contents of scheelite and apatite from the two types of mineralization show differences suggestingthat the two types derived from two different fluids. U/Pb dating on zircon, apatite and scheelite illustrates that magmaticzircon and apatite formed at 295 ± 2 Ma during emplacement and cooling of the granodiorite intrusion. These are cogenetic to thefine-grained scheelite skarn. Hydrothermal apatite frommassive sulfide ores yields a younger age of 289 ± 2 Ma, whereas closelyassociated coarse-grained scheelite yields a consistent although less precise age of 284 ± 11 Ma. These results suggest that the latemassive sulfide ore with abundant coarse-grained scheelite and electrum is related to the emplacement of an underlying, moreevolved intrusion, accompanied during its ascent by the development of steeply dipping reverse-dextral shear zones
Domaines
Géochimie
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