Cassiterite U–Pb, mica 40Ar–39Ar dating and cassiterite trace-element composition of the Furong tin deposit in the Nanling Range, South China

Abstract

The Furong tin deposit (530,000 t Sn @ 0.8% Sn) is located in the southern part of the Mid–Late Jurassic, multiphase, granitic Qitianling batholith in the Nanling Range, South China. The spectrum of tin mineralization comprises skarn, chloritized granite, greisen, and quartz vein types, of which the skarn type is the most important. Cassiterite U–Pb dating provided Tera-Wasserburg lower intercept ages of 157.1 ± 1.5 Ma and 156.3 ± 1.5 Ma for skarn-type mineralization, 158.1 ± 1.4 Ma and 158.7 ± 1.6 Ma for chloritized granite-type mineralization, 155.8 ± 3.4 Ma for greisen-type mineralization, and 160.1 ± 1.7 Ma for quartz vein-type mineralization. These ages overlap with each other and define a pooled weighted mean age of 157.9 ± 1.1 Ma (2σ) for the tin ore system. Hydrothermal phlogopite from tin skarn and muscovite from tin greisen yielded younger 40Ar–39Ar plateau ages of 154.3 ± 1.9 Ma and 150.0 ± 1.5 Ma, respectively, which may reflect resetting due to post-ore fluid circulation. Distinctive cathodoluminescence textures and trace-element patterns of various cassiterite types indicate that the four ore types resulted from pulsed ore-forming fluids and changes in temperature in a single magmatic-hydrothermal system. In combination with the geological characteristics, the geochronological and trace-elemental data of cassiterite indicate that the formation of different ore types at Furong was associated with the most fractionated and latest alkali-feldspar granite of the Qitianling batholith, and resulted from the specific interactions of the ore-forming fluids with their granite and limestone host rocks.