Abstract
The field investigations of the iron beach sand deposits along the coast of the Pacific ocean from Mukawa to Horobetsu were carried out in the autumn of 1954. The iron placers occur along many shores and often produce by concentration from an elavated beach. More or less of the iron sands are seen all along many shores of the coast in the district, but the comparatively rich layers have only limited development being restricted mainly to the vicinities of Mukawa, Tomakomai, Shiraoi, Ponayoro, Noboribetsu and Horobetsu in where the last one is noteworthy and is now mined. In general the thickness of iron sand rich layers varies from 5 to 30cm, though that of the layer at Horobetsu reaches 50cm. The size of the magnetite grains is about 0.03mm in average, and the general contents of Fe and TiO2 in the iron sands are 25-45% and 2-5% respectively. The mineral and rock grains associated with the magnetite sand are hypersthene, augite, olivine, hornblende, plagioclase, biotite, quartz, garnet, ilmenite, chromite, andesite, hornfels, radioralian chert, etc. The parent source of these sand garins is probably in the adjacent volcanic rocks though some of them may be ordinarily derived from the older rock series in the Hidaka district.
