Characteristics and in situ U-Pb dating of rutile in Xiadian, Jiaong gold provience, eastern China

Hydrothermal rutile U-Pb dating is an effective method to determine the age of gold mineralization, however, the multiple genesis of rutile limits its application in gold mineralization process and chronology. The Xadian gold deposit in Jiaodong has a wide range of rutile types, which is ideal for identifying the rutile genesis and determining the age of gold mineralization. The rutile in this deposit is distributed in clusters, and commonly intergrown with hydrothermal minerals such as electrum, pyrite, chalcopyrite, sphalerite and molybdenite, and developed metasomatic texture and irregular zonation, indicating that it is of hydrothermal origin. Two types of hydrothermal rutile were identified by BSE and EPMA analysis, one is high W content rutile (W content range from 1.672% to 6.125%, mean 3.480%) and the other is low W content rutile (W content range from 0.002% to 0.788%, mean 0.204%). In the early stage of gold mineralization, the decomposition or rebalancing of Ti-rich or Ti-containing minerals leads to the precipitation of low-W rutile, and the hydrothermal fluid carries refractory elements and some high field-strength elements in the ore-forming stage. The ions in the hydrothermal fluid, such as V3+, W6+, Fe3+, Cr3+ and Nb5+, substitute the Ti4+ in the early low-W rutile to form the high-W rutile, mainly via 2M(3+) + W6+ <-> 3Ti(4+). The high W rutile in the Xiadian gold deposit is usually associated with hydrothermal minerals in quartz-metal sulfides stage, and the LA-ICP-MS trace element analysis results show that the W content exceeded 7000x10(-6) and the Zr content ranged from 200x10(-6) to 600x10(-6). After comprehensive analysis, high W rutile is determined to be of hydrothermal origin, which is closely related to gold mineralization. In addition, the LA-ICP-MS U-Pb dating results of low-W rutile is 119.3 +/- 8.4Ma (2 sigma, n=17, MSWD=2.9), which provides a new constraint for the mineralization age of the Xiadian gold deposit.