On the Contact Deposit of the Nakatatsu Mine, Fukui Prefecture.

Abstract

The contact zone bearing various kinds of skárn minerals, such as hedenbergite, grossularite, wollastonite, diopside and epidote, is located in the Palaeozic formations along the Ono-thrust fault which divides the Palaeozic formations from the middle Jurassic formations.
It is generally known that calcareous shales which belong to the Palaeozoic formations are most favourable for the formation of skarn minerals. Sulfide ore bodies are also predominate in these rocks.
The source of the ore has been supposed to be the quartz-porphyry which is distributed on the northern part of Senno-deposit but it is reasonable to consider that they were derived from the cryptobatholith underlying in the southern part of Ono-thrust fault.
The deposition of zincblende and galena took place in the pneumatolytic stage after the skarn minerals were crystalized. After deposition of the zincblende and galena hydrothermal mineralization followed depositing arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and some galena and zincblende.
In the later stage of the hydrothermal period, chalcedony, calcite and sericite were deposited with fine crystals of pyrite. The skarn minerals are restricted to the chemical compositions of country rocks and have no relation to the kinds of ore minerals.