Gold Exploration in Japan

by Jun-ichi ISHIKAWA

Gold has been actively produced since the old days in Japan.
It is recorded that gold dust was gathered in Miyagi prefecture in 749. In the twelfth century, Oshu-Fujiwara dynasty formed an independent kingdom, mainly on Hiraizumi, in the northeast region of Japan. And it depended on the gold dust, which was the local special product. If gold dust was found by a curve of a river accidentally, placer gold was mined at the vicinity.
In the times when Kublai Khaan governed China, Marco Polo (Italian) wrote that Japan was "a country of gold" in his memoirs.

The Middle Ages
Abe gold mine (central part of Honshu) was owned by the Imagawa family in 1472. Sedimentary gold deposits were mined there at first.
These deposits are divided into the two following types.
1."Kawakin":. placer gold in rivers and streams.
2."Shibakin":. placer gold in sand under a gravel layer of terrace deposit.
At these deposits, sand including gold dust was carried away on straw mats, and heavy gold dust of a specific weight, which sunk to the bottom, was gathered. If a "Shibakin" deposit had a large-scale, miners dug the basement gallery. Such miners were considered to be part of a special engineering group.
And miners innovated techniques to operate the following type of deposit.
3."Yamakin":. Quartz vein including gold.
Gold was extracted from ore by "cupellation". Gold ore was crushed into powder, and it was mixed with lead. And it was burnt on a plate made from animal bone. Lead was oxidized or melted into a plate, and gold was left. After that, Europeans came to Japan and taught Japanese the amalgamation.
The main gold mines at final stage of the Middle Ages in Japan were Kurokawayama, Sado, Abe, Toi, and Takatama etc.
Gold veins were found by looking at upper streams of placer gold.
However, as veins decreased, miners began to search veins by observing the topography, the hue or plants in mountains. Some of them made explanations based on their experiences and on the interacting principles of Yin and Yang.
Some of these methods and explanations are reasonable and have meaning, but some are superstitious and fanatical. The primitive, absurd and delusive nature worship has been believed in Japan, and it is powerful, for example as "Shinto", even now.
Therefore, people had doubtfully associated with such prospectors.
Prospectors of ore veins are called "Yamashi" in Japan. This word has other meanings (speculator, swindler etc.) by the above reasons.
However, Shin-en Sato (1769-1850) is appreciated by his detailed natural observation of mining areas, even now.

The Modern Ages
The modernization in technology had a large influence in the development of mining. However, it took a long time to install geological knowledge for the exploration of ore deposits.
In Japan, around 1874, less than 100kg of gold was produced. However, it produced 500kg, in 1887, and 1200kg in 1898. It was immediately due to the progress of refinement technology.

In 1898, placer gold was discovered in Bankenai, Hokkaido. Gold rush occurred in Hokkaido. Gold dust collectors gathered at the Sea of Okhotsk coast. Farmers and fishermen sometimes looked for placer gold, too. It is recorded that 200g of gold was taken on a daily basis. But, just after the discovery,all of gold dust was taken.

Kisaburo Imahori was interested in many kinds of ore. His specimens were enormous. And he noticed that quartz grains were often with placer gold along the rivers in Hokkaido.
He obtained some quartz samples from the Mobetsu river, and he explored along the river. Imahori thought that there were gold veins in the upper streams of the Mobetsu river. He told Eizo Okino (fisherman) about his thought. And Okino discovered an outcrop of gold ore. This developed into the Konomai mine.

The price of gold did not change as much as other prices, because it could be changed into paper money. The production decreased in the time when prices of general commodities were high.
Large gold deposits were sketched in detail. However, it was difficult to observe the total images of the deposits. Even if the geological factor of a place was similar to some gold deposits, it might be uneconomical in the case of the low gold component. Therefore, it was difficult to discover a promising deposit by only thinking of the geological situation of the area.

A kind of massive sulfide ore, including Cu, Pb, Zn, is known in English by its Japanese name "Kuroko" (black ore). It often includes gold and silver. But it was known after World War II that the ore was formed by submarine dacitic volcanic activity in neogene.

Mr.Mishima was a farmer in Hiroshima prefecture, western area in the Main Island of Japan. He was curious about not only agriculture but also mining. He was testing many kinds of limestone and agalmatolite in 1949. He found that a white vein in a new garden consisted of quartz and some gold in 1953. He was exploring in the mountains for several years, and found a new promised outcrop. He opened a new gold mine, called Kabutoyama Mine, in 1963. The gold deposits are white quartz veins in the Paleozoic.

The Hishikari gold vein deposit, in Kyushu, was found in 1981. It has highly prized gold ore, and is still being mined at present. The deposit was formed with Tertiary and Quaternary volcanic activity.
Therefore some of the unknown gold deposits may be formed with new volcanoes.

Current Promising Areas
We are interested in the South Fossa Magna. The Fossa Magna which means "huge ditch" in Latin.
According to the recent theory, there is a huge geological crack in the middle of the ditch, in the Main Island of Japan, and some magma chambers may have risen.
The east area of the Asian Continent rose almost 25 million years ago, and there were a lot of cracks. Huge amount of lava erupted from the cracks. These volcanic activities made gold veins in the Sado mine that historically produced the second highest amount of gold in Japan. In general, gold veins, which were formed by volcanic activity on land, have high gold contents with a large scale.
The Sea of Japan had begun to open almost 16 million years ago. And Fossa Magna became the sea. The volcanic activity continued at the bottom of the sea. Kuroko deposits were formed at this time.
And Hokkaido Island has some promising areas. We are analyzing the data and extracting detailed survey areas in the island.

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