Structural Localization of High-grade Sulphur Ores at the Zao Mine

Abstract

The sulphur and iron-sulphide ore deposits of exhalative replacement type at the Zao mine, Yamagata Prefecture, occur in andesitic lava flows and pyroclastic rocks of the Zao volcano. The important structural components distinguished in this mining area are fractured zones striking nearly N 10°W, in which sulphur deposits, solfataras and hot springs are found. These fractured zones were the main channel ways for the mineralizing solutions and gases.
Localization of high-grade sulphur ore bodies appears to have been controlled by the intersection of fractures with favorable beds such as tuff and tuff-breccia beds.