In 1577, under Hōjō rule, Takeda gold miners advanced oblique shafts toward existing vertical shafts. After the Hōjō clan's fall, it was inherited by Tokugawa mining operations and became a major gold-producing site in the Toi region.
The 1577 opening date and Takeda miners' involvement are uncertain; Izu City notes these 'are thought to be the case' without definitive confirmation.
Certainty: MediumHow far the account above is supported by the cited sources. It does not refer to the precision of the coordinates or the dating.
See it on the 1577 map