All of the iodine produced in the world, excluding that from "caliche" in Chile and sea weed, is collected from subsurface brines. The iodine in subsurface brines may be classified into the following two types; one of them is the iodine dissolved in brines accompanied by dry gas, and the other is gaseous brine occurring in the oil field region. The former is represented by iodine in Japan, which occurs in brine directly derived from sea water probably. The iodine content of this type brine is 143.5mg/l in maximum. A typical one of the latter type is iodine produced in Oklahoma, U.S.A. The iodine-bearing brines occur in the upper Paleozoic formations. The brines are characterized by their outstandingly high iodine contents.
