Vein systems interpreted from the viewpoint of brittle and ductile behaviors of rocks

a case study of the Akenobe polymetallic deposit, Southwestern Japan.

Abstract

Vein systems of the Akenobe Cu-Pb-Zn-W-Sn deposit, Hyogo Prefecture, are devided into two types, i.e., B-type and D-type based on their fracture patterns (Fig. 3) and modes of emplacement (Fig. 4). The system of B-type consists of veins whose strikes are N10-20°W, N40-50°W and N70-80°W, and the boundary between a vein and a country rock is clear. Most of veins in the Sekiei area, and Shirogane veins in the Kanagidani area belong to this type. On the contrary, the system of D-type is not characterized by the distinguishable strikes, and is accompanied with disseminated ores along a vein. Chiemon veins in the Daiju area, and Ginsei veins in the Kanagidani area belong to this type. Rock mechanics suggests that the veins of B-type were formed by the brittle failure of country rocks, and that those of D-type by the ductile deformation. This implies that we must take into account the ductile behavior of rocks as well as brittle one for discussion on the formation mechanism of fracture systems.