Paleomagnetic constraints on mineralization age of the Nansatsu-type gold deposits in southern Kyushu, Japan

Abstract

Two mineralization stages, stage I and stage II, have been identified from textural, mineralogical and crosscutting relationships in gold ore from the Nansatsu-type gold deposits of Kasuga, Iwato and Akeshi. Mineralization age of each stage in each deposit was determined with paleomagnetic methods on 432 specimens from 312 oriented samples. As results, mineralization ages of stage I in these deposits fall in the same period, the reversed polarity subchron of 4.18-3.58 Ma, and those of stage II are limited in the normal and reversed polarity subchrons of 3.58-3.22 Ma. Contrasting with previous results based only on K-Ar ages, our conclusion shows that these Nansatsu-type gold deposits were formed contemporaneously.