Excavated Items from the Ruins of the Sado Magistrate's

A Government Office That Was Also a Refinery

In 1603 the Tokugawa shogunate set up an administrative seat at Aikawa, on a terrace of raised ground above the Sea of Japan on Sado Island. From here it governed the whole island and, above all, the gold and silver coming out of the mountains behind the town. Sado was tenryo, land held directly by the shogunate rather than by a regional lord, because the metal mattered that much.

What set the Sado Magistrate's Office apart from any other provincial bureau was its second life as a factory. Inside the same walls as the courtrooms and clerks' rooms stood the yoseseriba, a workshop where ore was crushed, sorted, and smelted, and where the shogunate even struck its oval koban gold coins. Law and metallurgy shared one address.

The buildings are long gone. They burned, were rebuilt, and burned again, and what endured of the original compound lay beneath the soil. Between 1994 and 1998 archaeologists opened the entire site. Out of the ground came the two halves of the office at once: the lacquer bowls and writing tablets of daily administration, and the mortars, nozzles, and lead of the refinery floor.

In 2011 the national government selected 928 of these finds as an Important Cultural Property in the category of archaeological materials. The collection is curated at the Aikawa Local History Museum, a short walk downhill from the site itself.

Why 928 Buried Objects Earned National Protection

Mining sites are seldom excavated in Japan, and the objects they yield are rarer still. That scarcity is part of what gives the Sado assemblage its standing. Few other digs anywhere in the country let you follow, artifact by artifact, how a major Edo-period mine was run from day to day.

The collection is valued because it holds two stories in one trench. One is bureaucratic. Wooden tablets known as mokkan carry the names of magistrates and served as shipping labels; ceramics from the first half of the 17th century fill out the picture of a town at its peak. The wares include Chinese porcelain from the Zhangzhou and Jingdezhen kilns alongside Japanese pieces from Hizen, Mino, and Bizen, the imported and domestic tableware that circulated when Aikawa swelled to a population said to approach fifty thousand.

The other story is industrial. Mortars, troughs, and furnace fittings record the work of pulling precious metal from rock. Archaeologists even found refining structures lying below the office floor: bellows nozzles and rod-shaped clay pieces older than the office itself, proof that someone was already smelting on this spot before 1603.

Taken together, the finds let researchers reconstruct both the administrative face of the office and the gold-and-silver refining carried out at the yoseseriba. That dual record is the reason the collection ranks so highly.

Seven Tons of Lead, Lost for Two Centuries

One find draws the eye before any other. In a pit on the south side of the office, excavators uncovered a stack of 172 lead plates, sitting about 1.1 metres down. Each plate runs roughly 70 centimetres long, 26 wide, and 5 thick, and weighs close to 41 kilograms. Stacked together, they come to about seven tons of metal.

Lead was no afterthought on Sado. It was the working material of the island's refining method, called cupellation (haifukiho in Japanese). Crushed ore is melted together with lead so that the lead binds to the gold and silver; the resulting alloy is then heated on a bed of ash, the lead soaks away into the ash, and the precious metal is left behind. No lead, no refining.

The plates carry a small mystery. Records such as the Sado Nendaiki chronicle suggest they were buried as an emergency reserve in 1641. When officials came back to dig the reserve out in 1718, short of lead for the furnaces, they failed to recover all of it. The plates that came up in the 1990s are most likely the share that stayed lost underground for the better part of three centuries—until a trowel found them again.

The lead is the headline, but the supporting cast is just as telling. Paired upper and lower mortar stones once ground ore to powder; wooden boats, tubs, and well over a thousand grinding stones came from the workshop. Set these beside the lacquer bowls, the braziers, and the everyday wooden clogs, and the collection swings between the clerk's desk and the smelting floor in the space of a single display case.

Around the Site

The excavated items belong to the Aikawa Local History Museum, but the place to feel their context is the reconstructed Sado Magistrate's Office a few minutes uphill. Rebuilt in 2000 from excavation findings and old drawings, it presents the offices and courtyards of the goyakusho and, on a lower terrace, the yoseseriba. Visitors slip off their shoes to walk the 33-mat great hall, then step outside to turn one of the stone mortars by hand and feel the labour behind every gram of gold.

The whole hillside repays a slow afternoon. Just below sits the Kitazawa flotation plant, a vast concrete ruin from the modern mining era, and the lanes of Aikawa still trace the boomtown that grew up around the metal. For an orientation before you climb, Kirarium Sado near the harbour lays out the four centuries of the mines in film and exhibits.

All of it gained a new frame in July 2024, when "Sado Island Gold Mines" was inscribed on the UNESCO World Heritage List, recognized for sustaining sophisticated hand-worked mining and refining into an age when much of the world had already mechanized. The 928 objects from the magistrate's office are among the most concrete witnesses to that distinction.