Late Cretaceous magmatism and related metallogeny in the Tengchong area: Evidence from geochronological, isotopic and geochemical data from the Xiaolonghe Sn deposit, western Yunnan, China

Xiaolonghe is a poorly studied greisen-type tin deposit that is hosted by biotite granite in the western Yunnan tin belt. The mineralisation-related metaluminous and weak peraluminous granite is characterised by high Si, Al and K and low Mg, Fe and Ca, with an average A/CNK of 1.02. The granite is enriched in LILEs (K and Rb), LREEs and HFSEs (Zr, Hf, Th, U and Ce) and depleted in Ba, Nb, Sr, P, and Ti, with zircon epsilon(Hf)(t) = -10.8 to -7.5 (T-DM2 = 1.61-1.82 Ga). These characteristics indicate that the magma was generated by the partial melting of a thickened ancient crust. LA-ICP-MS U-Pb dating of igneous zircon and hydrothermal cassiterite yield ages of 71.4 +/- 0.4 Ma and 71.6 +/- 4.8 Ma, respectively. The igneous biotite and hydrothermal muscovite samples show Ar-Ar plateau ages of 723 +/- 0.4 Ma and 70.6 +/- 0.2 Ma, respectively. The close temporal relationship between the igneous emplacement and hydrothermal activity suggests that the tin mineralisation was closely linked to the igneous emplacement. The delta O-18 and delta D) values for the deposit range from +3.11 parts per thousand to 4.5 parts per thousand and from -127.3 parts per thousand to -94.7 parts per thousand, respectively. The hydrothermal calcite C and O isotopic data show a wide range of delta C-13(PDB) values from -5.7 parts per thousand to -4.4 parts per thousand, and the delta O-18(SMOW) values range from +1.4 parts per thousand to +11.2 parts per thousand. The delta S-34(V-CDT) data range from +4.8 parts per thousand to +8.9 parts per thousand for pyrite, and the Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios range from 18.708 to 18.760, from 15.728 to 15.754 and from 39237 to 39.341, respectively. The stable isotopic (C-H-O-S-Pb) compositions are all similar to those of magmatic and mantle-derived fluids, which indicate that the ore-forming fluids and materials were mainly derived from magmatic sources that were accompanied by meteoric water. The tin mineralisation in the Xiaolonghe district was closely associated with the Late Cretaceous crustal-melting S-type granites that formed during the subduction of the Neo-Tethys oceanic lithosphere. Combined with the tin deposits in the Southeast Asian tin belt, Tengchong block and Central Lhasa, we interpreted that a giant intermittent tin mineralisation belt should be present along the Asian Neo-Tethys margin. (C) 2016 Elsevier B.V. All rights reserved.