<報文>釜石鉱山新山鉱床における鉱石の帯状分布とその成因

概要

論文の詳細を見る
The zonal distribution of oxide (magnetite) and sulfide (pyrrhotite-chalcopyrite) ores was studied mineralogically and a probable explanation for its origin was tried on the thermodynamics of skarn and ore minerals in a postulated NaCl acid hydrothermal system. The genetic order of magnetite, hexagonal pyrrhotite, monoclinic pyrrhotite and pyrite in an increasing order of sulfur content is well explained by assuming that the ore-depositing process continued under the condition of falling temperature. The localized deposition of oxide and sulfide ores in different places is a result of the difference in mineralogical environment between the two zones. Since grandite and hedenbergite differ from each other in the oxidation state of their constituent Fe, an isothermal switchover from magnetite deposition to pyrrhotite deposition was prompted in the hedenbergite skarn, but hindered in the grandite skarn. Another isothermal transition from Fe-S-O mineral deposition to chalcopyrite deposition cannot take place without a decrease in both Fe^<++> and H^+ activities below the respective certain values. The decrease in those activeties in the ore solution must have been performed through its reaction on the limestone. This is supported by the fact that the copper ore-shoots are limited to the periphery of the hedenbergite skarn along its boundary to the survived limestone.
東北大学の論文
1981-10-20