Vol.3 No.4 2011

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Research paper : Investigation of the distribution of elements of the whole of Japan and their applications (N. Imai)−274−Synthesiology - English edition Vol.3 No.4 (2011) 6 Geochemical map of Japan and its implications (Behaviors of elements in nature and in human activities)This study produced geochemical maps showing distributions of 53 elements in sea and land areas. It is necessary to interpret each elemental behavior according to its circumstances because its behaviors in nature and in human activities might differ from those of other elements. Here, we describe geochemical maps of chromium and mercury, which have characteristic features in terms of their respective distributions. Please refer to individual reports in the literature for details related to other elements and features of elemental distribution in respective regions[16]-[20].6.1 Geochemical map of chromium (Cr)Figure 5-1 shows the geochemical map for chromium. The two red lines in Hokkaido and Shikoku (areas of high Cr concentration) in this figure are noticeable first. A remarkable high-Cr concentration region of more than 200 ppm exists along the median tectonic line. The tectonic line crosses from west to east of the Shikoku and Kinki regions, reaches the Tokai and Kanto regions and another crosses the center part from north to south in Hokkaido. This prevalence is thought to result from the green rocks and ultra-basic rocks distributed along these regions that contain chromium and nickel in very high concentrations. The red area of high concentration in the sea is apparent in the coastal areas of off southern Hokkaido and Hokuriku. The most remarkable area is along the Hime River in Itoigawa, where the northern end of the Fossa Magna in Hokuriku District is located. The high concentration region of chromium on land extends to the sea. A high concentration region of chromium along the Hime River on land continues to the deep sea valley. Therefore, the detritus of the serpentine, which contains chromium in high concentration moves from the Hime River to the Toyama deep sea valley in the sea. This figure also portrays the topography of the seabed in this region. It is readily apparent that a deep sea valley exists in the north of Hime River and that the sediment flows from the Hime River along this valley to the sea.6.2 Geochemical map of mercury (Hg)Figure 5-2 shows the geochemical map of mercury. The mercury concentration is remarkably high in the region where large-scale mercury deposits such as Itomuka mine in Hokkaido and Yamato mine on the Kii Peninsula exist. Furthermore, the concentration of mercury is high around big cities such as Tokyo and Osaka on the land, and concentrations are high in Tokyo Bay, Ise Bay, and Osaka Bay. This prevalence is affected by anthropogenic influences from cities with large populations. This figure also shows geochemical maps of Kyushu, Hokuriku, and Kinki regions. The high concentrations of mercury off the coast of Niigata and in the Yatsushiro Sea and western Kyushu are visible in the figure. It is possible that the influence of the past mercury pollution remains in these high-concentration regions. The high concentration of mercury in the northern sea around Sado is considered to reflect the influence of the Sado gold mine in the past. The high concentrations of mercury in Ise Bay and Osaka Bay in the Kinki region are thought to be influenced by large-scale Yamato mercury deposits in the Kii Fig. 5-1 Geochemical map of chromium (Cr) of Japan, Hokuriku and Hokkaido regionsA high Cr concentration region is apparent along the median tectonic line and the tectonic line in the center of Hokkaido. The high concentration region extends from Hime River to the sea.Fig. 5-2 Geochemical map of mercury (Hg) of Japan, Kyushu, Hokuriku, Kinki regionsHigh Hg concentrations off the coast of Niigata and in the Yatsushiro Sea reflect the influence of past mercury pollution. That in the sea off northern Sado reflects the influence from gold mines in the past. The high concentrations in Tokyo Bay, Ise Bay, and Osaka Bay are attributable to anthropogenic influences from the nearby large cities.Submarine canyonHokurikuHokkaidoHigh concentration along the tectonic lineHime RiverChromium CrHokurikuKyushuKinkiIse BayOsaka BaySadoMercury HgOffNiigataYatsushiro SeaFig. 5 Elucidating elemental behavior in nature and human activities using a geochemical map

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