The polyphase evolution of a late Variscan W/Au deposit (Salau, French Pyrenees): insights from REE and U/Pb LA-ICP-MS analyses

Abstract

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-grained scheelite skarn related to contact metamorphic and metasomatism between the intrusion and the adjacent carbonate rocks. The second type is represented by massive sulfides accompanied by coarse-grained scheelite, apatite, and electrum. This syn-kinematic mineralization is found enclosed within the skarn ore but occurs also within the granodiorite stock along major ductile–brittle shear zones. REE contents of scheelite and apatite from the two types of mineralization show differences suggesting that the two types derived from two different fluids. U/Pb dating on zircon, apatite and scheelite illustrates that magmatic zircon and apatite formed at 295\u2009±\u20092\xa0Ma during emplacement and cooling of the granodiorite intrusion. These are cogenetic to the fine-grained scheelite skarn. Hydrothermal apatite from massive sulfide ores yields a younger age of 289\u2009±\u20092\xa0Ma, whereas closely associated coarse-grained scheelite yields a consistent although less precise age of 284\u2009±\u200911\xa0Ma. These results suggest that the late massive sulfide ore with abundant coarse-grained scheelite and electrum is related to the emplacement of an underlying, more evolved intrusion, accompanied during its ascent by the development of steeply dipping reverse-dextral shear zones.