Zircon and cassiterite U-Pb dating identifies the first Early Cretaceous Sn deposit in Fujian: Implication for tin mineralization potential in the southeastern coastal belt of South China

Abstract

The Xiayi Sn deposit, located in the Sanming city, southeast China, is the largest Sn deposit in Fujian province. The mineralization mainly consists of cassiterite-bearing veinlets and stockworks, and it is spatially associated with the granodiorite porphyry. Despite its economic significance, few studies have been carried out, and the mineralization age remains unknown. In this paper, we present the first geochronological data on the cassiterite and the associated granodiorite porphyry, Hf isotope of the zircon, and trace element compositions of cassiterite from the Xiayi Sn deposit. These data give precise age of the Sn mineralization and constrain its relationship with the granitic intrusion. Zircon U-Pb dating of the ore-related granodiorite porphyry yielded the age of 138.3 ± 1.8 Ma, which agreed well with the cassiterite U-Pb age of 136.5 ± 1.4 Ma, documenting the genetic link between the Sn mineralization and granitic magmatism. Zircon εHf(t) ranged from −4.5 to −1.8 with a weighted mean of −3.4 and the Hf model ages (TDM2) vary from 1.31 to 1.47 Ga with a mean value of 1.40 Ga. These data indicate that the granodiorite porphyry originates from the partial melting of the crustal materials of Mesoproterozoic basement and show the addition of mantle-derived materials, similar to typical Sn mineralized granite in the southeastern coastal tin belt and Nanling tungsten-tin belt. Besides, cassiterite from Xiayi deposit show clear CL-bright and CL-dark sector zonation in the cathodoluminescence images. LA-ICP-MS trace element analyses of cassiterites indicate a high Ti and Fe but low Nb and Ta contents in both CL-bright and CL-dark sector zones, while the W content is significantly high in the CL-dark zone and low in the CL-bright zone. Cassiterite trace element compositions together with the mineralization pattern and alteration assemblages indicate that Xiayi is a porphyry tin deposit. These results provide proof of the extension of the southeastern coastal Sn metallogenic belt and offer potential breakthroughs in tin deposit exploration in southwestern Fujian Province.