On the Geology and Ore Deposit of the Ani Mine Akita Prefecture, Japan
1958 Volume 8 Issue 30 Pages 193-209
Details
1958 Volume 8 Issue 30 Pages 193-209
1) The Ani Mine area is composed mainly of pyroclastic and igneous rocks. The lower members of the sedimentary rocks are fresh water sediments, whereas the upper members are marine. The igneous rocks represent cycles of subalkalic igneous activity, each of which ranges from basic to acidic and has transitional phases with the preceding and succeeding cycles.
2) Geological structures are characterized by block movements. Faults are, classified into several groups. Fold structures can be demonstrated by tracing the geologic horizons. Two directions of major fold axes are recognized. From these studies it is concluded that the prominent structural features of this area are fault movements, either related to a domal structure formed by intersection of two fold axes, or occurring along the contact of igneous intrusions. Basaltic rocks are often found in places having the domal structure, therefore it is inferred that their intrusion also was controlled by this structure.
3) The Hikiwari, Magi, Atago and Yukuchinai beds are correlated to members of the Daijima formations and the Kobuchi basalt is correlated to the members of Nishikurosawa on the basis of stratigraphic and palaeontological data and the cycles of igneous activity.
4) Ore deposits in basaltic rocks, which are the most favorable wall rocks, are more . concentrated in places forming the domal part of the basaltic rocks than in any other part of them.
5) Generally speaking, veins are more persistent in igneous rocks than in sedimentary ones. Even so the largest one persists less than 200 meters in depth. Width of veins having some relation to the character of veins are in the scope of 7 to 120 centimeters.
6) Wall rocks differ greatly in favorability for ore deposition. Favorability of several kinds of wall rocks is shown quantitatively in Table 2 by percentage of the amount of minable ore reserve.
7) Ore shoots are controlled by clayey materials and have some relation to the curvature of a vein surface.
8) There is much that we have yet to study about genesis of ore deposition: the mechanism of faulting and fracturing, and the process of mineralization.
