The Sanru vein outcrop located about 500 m west of the project boundary was discovered in 1917 by local prospectors. Six Au-Ag mine workings are recorded on the government geological survey maps covering the project area. Production (1925-83) from the Sanru vein system located just off the western edge of the project totals 190 Koz of gold, at an average grade of 7.3 g/t Au,  and 1.09 Moz of silver, at an average grade of 42 g/t Ag¹. A government moratorium on mining lead to the closure of the mine in 1943.

More recent exploration was undertaken by the Australian company, Austpac Gold N.L. from 1989 to 1994², and in the late 1990’s by the MMAJ³ as part of a regional metallogenic study which included regional geophysical surveys and drainage sediment sampling.  A MMAJ gravity survey mapped northeast Hokkaido in detail with a survey station spacing of about 700 m. Processing of the raw data defined numerous basin and caldera features that are spatially associated with district epithermal mineralization. Austpac identified two prospects along strike from the Sanru mine in the vicinity of the Jugosen-zawa workings, which lie within the current Sanru Project. Due to dwindling exploration funds and an appreciating yen, no further work took place at the this time, and the land was ultimately relinquished.

Systematic regional drainage sampling by the MMAJ was undertaken in 1997 across the current Sanru license extents.  Data for four elements (Au, As, Hg, Cu) from more than 70 sample sites within the project area have been obtained by Japan Gold. These indicate five major areas of coincident gold-arsenic anomalies³ (note the raw analytical data upon which published geochemical maps are based is not available).

Three areas (Bifuka, Piyashiri and Monsanru) highlighted in the drainage survey were followed up with further work in 1998, which consisted of geological mapping and soil sampling. A siliceous zone discovered in the northeastern portions of the project area returned low-level gold anomalies along a northeasterly trend based on MMAJ data (soil geochemical maps). No follow-up work on this anomaly was attempted at the time.