Special Feature“Japan, the Land of Gold.” How True Is the Old Legend?
But why was such a big gold deposit discovered only in the 1980s? And, could there be similar deposits elsewhere, waiting to be discovered?
Scientists want answers to these types of questions, so they are examining the mine’s geological structure, and trying to learn how the gold was deposited there. One scientist, Dr. Watanabe Yasushi of the National Institute of Advanced Industrial Science and Technology (AIST), explains: “The gold at Sado and Konomai formed more than 10 million years ago, but the deposits at Hishikari are only about 1 million years old, which is relatively young geologically speaking. The rock above had still not been eroded, so the veins were not exposed on the surface. That is why they were discovered only recently.
“The type of deposits at Hishikari give us a clue to use to discover gold somewhere else. You see, in a volcanic part of the world like Japan, molten magma rises up, and that magma may contain gold and silver. They make a hydrothermal fluid in the magma. The fluid rises higher and boils, and then, as it cools, the minerals in it settle and form veins in the rock. At the same time, the hydrothermal fluid in the upper part of the veins reacts with the surrounding rocks, making them metamorphic. That metamorphic rock could be a marker indicating the presence of gold.”
There is another clue, one that is easier to recognize: the water at hot springs. Watanabe says that recent research has shown that, “in hot spring locations where the water contains a lot of naturally occurring chlorine, and the pH level is neutral—in other words, the water is neither acidic nor alkaline—there’s a good chance that there could be some hydrothermal gold and silver deposits deep underground.” Of course, the 65 °C water bubbling up near the Hishikari gold mine meets those conditions.
Japan is known worldwide for its magnificent hot springs, so it could be that many more gold deposits are still lying underground.
Japan Oil, Gas and Metals National Corporation (JOGMEG) has explored for gold using the results of this research. The company has not discovered any veins at a grade high enough to make a profit because of the high cost of extracting minerals in Japan. The rich Hishikari mine is still an exception, and more effective exploration and extraction techniques are needed.
The search continues. Deep under the ocean off Japan, hydrothermal deposits have been found over the last few years, and scientists keep trying to discover more about the location and structure of their mineral veins.