The isotopic composition of sulphur and lead in the Zn-Pb mineralizations in the valle de Aran (central Pyrenees) and its metallogenic significance

The sulfur isotopic composition of sulfides from sedex-type deposits enclosed within Upper Ordovician rocks in the valle de Aran (Central Pyrenees) ranges from +3.5 to +15.1‰ in mineralizations enclosed in carbonates and from -2.7‰ to +5.5 in mineralizations enclosed in detritic rocks. These values suggest two different sources of sulfur: a heavy source of crustal origin, probably related to the reduction of seawater sulfate, and a lighter one, resulting from leaching of underlying detritic and/or volcanic rocks of Cambro-Ordovician age. Lead isotope composition of 6 galena samples have the following ratios: 18.02 ≤ 206Pb/204Pb ≤ 18.08; 15.66 ≤ 207Pb/204Pb ≤ 15.70 and 38.16 ≤ 208Pb/204Pb ≤ 38.29, similar to those reported for the Pierrefitte deposits (Central Pyrenees, France). These values are very homogeneous and suggest a lead source situated within the upper crust.