Hot tin mining

Q: In 1889, it was announced that the “only known continuous lode [of uranium
ore] in the world” had been found at the Union Mine in Grampound Road, Cornwall.
Does anybody know what happened to this deposit? There were plans to use the
uranium to replace gold in jewellery. Was this ever done? If so, it would add a
certain frisson to the Antiques Road Show.

A: Union mine is better known as South Terras Mine and is between the
villages of St. Stephen and Grampound Road. The mine was originally worked for
iron, and the uranium lode was discovered in 1873. The bulk of the ore, mainly
pitchblende, was worked out when the mine closed in 1900.

The mine was reopened several times and ore recovered from the dumps before
finally closing in 1929. A total of 736 tons of ore was produced, including 286
tons from the dumps. The early production was sent to Germany for making green
glass, and contained on average about 11 per cent U₃O₈,
although the best ore contained up to 36 per cent. The dumps used to be a
fruitful source of uranium ores for amateur geologists with army-surplus Geiger
counters.

South Terras was not the only mine in Cornwall to produce uranium. Trenwith
Mine, above St Ives, produced 694 tons of pitchblende and other ores over the
period 1911 to 1917. Recovery of the ore was mainly from the dumps, where it had
been discarded as worthless because it had originally been confused with black
copper ore. Radium, discovered by Marie Curie, was first isolated by her from
pitchblende from Trenwith Mine. The dumps were a plentiful source of stone for
local streets and houses. Now they provide hard core for the large car park that
occupies the mine site. One recent visitor was quite alarmed when he found
several rocks used in the car park walls to be radioactive, claiming that the
whole area should be cleared.

In the early part of this century, the dangers of radioactivity were not
appreciated and it was even considered beneficial. In the 1950s, an elderly
patient of one of the local doctors in St Ives was found to be keeping a large
box of pitchblende under his bed. At one time, the tailings of South Terras Mine
were offered for sale as “radioactive manure”, and a scheme was proposed to
promote a “radium spa” at St Ives, using water from springs in Trenwith Mine.
Although this never came about, the mine was the principal water supply for a
large part of St Ives until about 30 years ago, being used without any
treatment.

Christopher Hogg

Bodmin, Cornwall

A: Better known as South Terras or sometimes simply Uranium Mine, Union Mine
contained tin, iron and uranium ores, with traces of copper, nickel, silver,
zinc, arsenic, lead, bismuth and cobalt. The uranium lode was discovered in 1873
and was up to four feet wide.

I have not heard about the proposed uses of uranium in jewellery but almost
as alarmingly, attempts were made to sell the tailings to local farmers as a
radioactive fertiliser. This mine is known to mineral collectors and was always
regarded as a “hot” spot. I visited it several times during the 1970s and the
Geiger counter invariably read full-scale even before the main tips were
reached. Unfortunately I no longer possess this instrument and cannot remember
its range. On reflection, this is probably just as well.

Robert Bogue

Bere Alston, Devon