The Lava That Turned to Silver: Tasmania's Zeehan Field

On Tasmania's west coast, a small town called Zeehan sits above a tangle of underground passages so rich in silver that miners once called it the Silver City. Between 1882 and 1960, Zeehan's mines produced over 50 million ounces of silver, along with vast quantities of lead and zinc, all from a single system of volcanic vents that opened 360 million years ago.

The Rift That Opened

During the Devonian period, Tasmania was not yet an island. It was part of the eastern edge of Gondwana, where the crust was stretching and thinning. Near what is now Zeehan, a series of deep fractures opened in the Earth's crust, creating a network of pathways for hot, mineral-rich fluids to rise from the mantle.

These fluids carried dissolved metals — silver, lead, zinc, copper — leached from the surrounding rocks as they moved upward. When they reached the cooler, shallower parts of the crust, the metals precipitated out, filling cracks and cavities with veins of galena, sphalerite, and native silver.

The result was not a single massive ore body but a labyrinth of narrow, high-grade veins that snaked through the Devonian volcanic rocks. Miners followed these veins underground, sometimes for kilometres.

The Silver That Built a Town

Zeehan's boom years were brief but spectacular. By the 1890s, the town had 10,000 residents, 26 hotels, and a stock exchange. The Zeehan School of Mines and Metallurgy opened in 1893, training the men who would go on to develop some of Australia's largest mining operations.

But the ore was never easy to extract. The veins were narrow and erratic, pinching out without warning. Many mines closed within a few decades, unable to sustain production. The last major mine shut in 1960, and Zeehan's population dwindled to a few hundred.

What remains is a landscape scarred by old workings, mullock heaps, and rusting machinery — a visible record of the Devonian volcanic system that concentrated the silver.

The Volcanic Plumbing

The Zeehan field is part of a larger Devonian volcanic province that stretches across western Tasmania. The same tectonic forces that created Zeehan also produced the Mount Lyell copper deposit, the Renison Bell tin mine, and several smaller ore systems.

The silver at Zeehan did not come from a single volcanic eruption. It accumulated over millions of years as hydrothermal fluids circulated through a dying rift, depositing their metals in the fractures that opened as the crust cooled.

Unlike the massive, sulphide-rich deposits at Mount Lyell, Zeehan's veins are dominated by galena and sphalerite, with native silver often visible to the naked eye. Some specimens from the field contain silver in concentrations exceeding 10,000 grams per tonne — among the richest ever recorded.

A Window Into the Devonian Crust

Today, the Zeehan field is one of the best places on Earth to study how volcanic-hydrothermal systems concentrate metals in a continental rift setting. The veins are exposed in old mine workings, road cuts, and natural outcrops, offering geologists a three-dimensional view of the mineralising process.

The same Devonian volcanic rocks that host the silver also preserve a record of the tectonic forces that shaped Tasmania. The stretching and thinning of Gondwana's eastern margin created not only the Zeehan field but also the basins that would later fill with coal and the faults that would guide later mineralising events.

Zeehan's silver is a reminder that even small, narrow veins — if they are rich enough — can sustain a town, a school of mines, and a century of mining history.