Occurrence and genesis of bicchulite and tilleyite skarns at the Sakae adit, the Akagane mine, Iwate Prefecture

Abstract

The Sakae deposit of the Akagane mine is a pyrometasomatic copper deposit formed along the boundary between limestone and gabbro. At a part of No. 4 orebody in the deposit, were found so-called hightemperature skarns characterized with tilleyite, spurrite and gehlenite. The occurrence of these skarns suggests that they were formed from limestone by the reaction with gabbroic magma, but have suffered intense alteration by the later ore-forming hydrothermal solution related to granitic intrusion. Gehlenite is observed only as pseudomorph, and is completely decomposed to bicchulite with vesuvianite and xanthophyllite. Tilleyite is also partly altered to calcite and foshagite. This occurrence provides a rare example of an overlapping of the ore skarn formation (WATANABE, 1960) with the primary skarn formation (TILLEY, 1951). Chemical composition data on bicchulite, the third occurrence in the world, tilleyite and foshagite, are given with X-ray powder diffraction patterns.