2021 Volume 71 Issue 1 Pages 25-34
In the late Cretaceous accretionary complex of the northern Shimanto belt, OPS (Ocean Plate Stratigraphy) mélanges consisting of slabs originated from oceanic crusts are intercalated within coherent units, and host small–scale volcanogenic massive sulfide deposits as its constituent member. The Akinokawa deposit, one of such deposits, characteristically produces cupriferous sulfide ores having concentric tubular structures of a diameter of several centimeters. The structure consists of rhythmic repeating of bands of fine pyrite/quartz, chlorite and chlorite/quartz. In each band, columnar rutile and aggregate of fine rutile are crystallized. Although titanium is one of the HFSEs (High Field Strength Elements) and is considered to be insoluble and immobile during low temperature metamorphism and alteration, these kinds of occurrences of rutile don't indicate in situ replacement products of titanium oxide minerals and/or titanium bearing silicate minerals, but precipitated from titanium bearing hydrothermal fluid in hydrothermal pathways. Titanium might be originally supplied by dissolution of titanium oxide minerals such as titanomagnetite and ilmenite in basaltic host rocks.
