IN-SITU LA-ICP-MS CASSITERITE U–PB DATING OF THE NEVES CORVO CU-SN DEPOSIT, IBERIAN PYRITE BELT

The Neves Corvo deposit is located in the Portuguese part of the Iberian Pyrite Belt (IPB), which is the biggest metallogenic province of volcanic massive sulphide deposits in the world. The deposit is the second most important copper mine in Europe and the richest ore deposit ever found in the IPB. It contains more than 300 Mt of massive sulfides and is unique because of its extremely high Cu (average 8% Cu, with large volumes exceeding 20% Cu) and Sn (up to 65% Sn) grades. Based on Rb-Sr and Re-Os isotopes for sulfide ores, the obtained formation ages were 347±25 Ma and 358±29 Ma, respectively. These ages have considerable errors and can not be used to define the timing of mineralization precisely. We present laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating results of cassiterite from three different ore types, fissural, massive sulfides and rubané ores, to place tight constraints on the timing of mineralization. These cassiterite grains, which have moderately high U (1.5–42.5 ppm) and Pb (0.2–23.9 ppm) contents, are euhedral to subhedral crystals and are closely intergrown with chalcopyrite, pyrite, sphalerite, stannite and quartz. Cassiterite from the fissural ore and the massive ore yield Tera–Wasserburg (TW) U-Pb intercept ages of 366.3±8.8 Ma (n=20, MSWD=1.3) and 368.8±9.7 Ma (n=16, MSWD=1.8), respectively. Two samples from the rubané ore, yield TW U–Pb intercept ages of 369.3±6.3 Ma (n=19, MSWD=0.61) and 367.6±8.6 Ma (n=19, MSWD=0.9). These ages confirm a close temporal relationship between tin mineralization and felsic magmatic events (354–384 Ma) in this region and the age consistency within analytical uncertainty confirms that the tin ores in different types were generated in coeval. Our new geochronological data indicate all ore bodies in the Neves Corvo formed at about 368Ma and temporally and genetically associated with the upwelling of the felsic magmas.