Geological formation environment and mineralization age of the Daehyun sericite deposits in Bonghwa-gun, Gyeongsangbuk-do: Introduction of the new type in South Korea

This study is carried out to interpret the geological formation environment of the Daehyun sericite deposits located in Socheonmyon and Seokpomyon, Bonghwagun, Gyeongsangbukdo. The Daehyun sericite deposits are distributed in the unconformity plane between Proterozoic Hongjesa granite and Paleozoic Jangsan Quartzite of Joseon System, and also are distributed in the conjugate area of several faults and fractures. The ore body deposited in the unconformity shows an irregular layered type extended to several hundreds meters of length. But the ore body deposited in the fault and fracture system shows small scale lens and pocket type by the selective alteration in a limited space. Generally the deposit formed in the unconformity is characterized by the larger scale. Al2O3 and K2O are increased and SiO(2 )and Na2O are decreased with an increase of alteration intensity, which is the result controlled mainly by the sericitization. Rb, U and Th show an increasing tendency and Sr and Ba do the decreasing tendency with an increase of alteration intensity. In particular, Cr is highly enriched in the strongly sericitic altered rocks. The ages of K-Ar of sericite and U-Pb of uraninite occurring in this deposit are 336 to 212 Ma, which show the very wide age range. But considering the oldest age, the age data indicate that the deposit might be formed in Carboniferous Period. The Daehyun sericite deposit belongs to Paleozoic hydrothermal sericite deposit. In particular, the deposit formed in unconformity can be called as Paleozoic unconformity type hydrothermal sericite deposit. Major alterations are characterized by sericitization, chloritization, and silicification and this deposit was formed by the most dominant sericitization. The origin of hydrothermal solution formed this deposit is not related to the igneous activity which emplaced the Proterozoic Hongjesa granite and not to the intrusion activity of pegmatite, and it was formed by the Paleozoic Carboniferous hydrothermal activity. This study can be applied to the exploration of hydrothermal clay resources with the similar deposit type.