Study on the mineralization age of the Akenobe Sn-Cu-W polymetallic deposit in southwest Japan

The northern part of Hyogo Prefecture in the southwestern Japan is a unique area having a number of large deposits that had produced various metals of industrial importance. For instance, the Nakaze deposit had been known for its extremely high-grade gold ore. The Ikuno deposit had been one of the major silver mines in Japan. Among them, the Akenobe deposit produced large amounts of tin, copper, zinc, and tungsten, as well as indium which is critical for electronic devices. The mineralization age of the deposit is a key constraint to discuss the ore genesis of such a polymetallic mineralization zone constituting large deposits of industrially important metals. However, the age of the Akenobe deposit was estimated only from the related igneous rocks by K-Ar dating, whereas a direct age determination of the metal veins has not been conducted yet. Here, we aim to directly determine the mineralization age of the veins by rhenium (Re)-osmium (Os) dating method. To apply the Re-Os dating to the veins of Akenobe mine, it is necessary to figure out the distribution of Re and Os within the ore samples. Therefore, we conducted Re-Os mapping by a Laser Ablation (LA)-Multi-Collector (MC)-ICP-MS at Ocean Resources Research Center for Next Generation, Chiba Institute of Technology. This instrument can detect extremely-low-concentrations of Re and Os simultaneously by using multiple ion-counting detectors equipped with discrete dynode type secondary electron multipliers. In the presentation, we will report the results of the Re-Os mapping using LA-MC-ICP-MS and mineralogical observation of the Akenobe ore samples, and discuss implications for the mineralization age in the Akenobe deposit.