Vesuvianite: A potential U-Pb geochronometer for skarn mineralization---a case study of tungsten and tin deposits in South China

Abstract

Vesuvianite is one kind of common U-bearing minerals in various skarns and skarn mineralization. As an early phase mineral, vesuvianite can be well preserved since it usually occurs at the front of skarn close to the marble and far away from the pluton, therefore, accurately determining its growth history can directly date hydrothermal activity in the skarn system, just like the zircon U-Pb geochronometer recording magmatic processes. In order to demonstrate reliability of the vesuvianite U-Pb geochronometer, we choose six vesuvianite samples from two skarn deposits in South China for the LA-ICPMS dating. Accordingly, the U-Pb dating of four vesuvianite samples from the Shizhuyuan W-Sn ore district yielded precise ages of 160.3 ± 1.2 Ma, 155.6 ± 2.6 Ma, 154.5 ± 3.1 Ma and 150.4 ± 3.1 Ma, respectively; these dates coincide well with the previously published ages of the relevant granite complex emplacement and hydrothermal mineralization in the region with the ages of ca. 160 Ma, ca. 155 Ma and ca. 150 Ma. The other two vesuvianite samples from the Furong Sn ore district yielded precise ages of 159.3 ± 1.8 Ma and149.1 ± 1.6 Ma，which are consistent with the multi-stage magmatic activities in the studied area with emplacement time of ca. 160 Ma and ca. 149 Ma. Theoretically, the site of the Ca2+ position in vesuvianite is slightly larger than that in intergrown grossularite, which gives the former a better ability to incorporate uranium. Therefore, vesuvianite with high uranium concentrations and relatively low common Pb is beneficial for obtaining precise results during the LA-ICPMS U-Pb dating, it is an ideal mineral for accurately determining the time of skarn formation and/or various skarn mineralization.