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Radioactive minerals

by  Rebecca Priestley

When the Second World War ushered in the atomic age, the race was on to find uranium to make nuclear weapons and fuel nuclear power stations. New Zealand joined the search, and the discovery of uranium deposits on the West Coast in 1955 raised hopes of enormous wealth.


Prospecting for uranium

Radioactive minerals

A small number of naturally occurring minerals give off invisible radiation as they gradually decay into a more stable form. The term radioactivity was coined by the French physicists Marie and Pierre Curie, who investigated this property in the late 19th century. Radioactivity in rocks and minerals is due to the presence of tiny amounts of radioactive elements, particularly uranium and thorium.

Uses

Radioactive elements have a range of applications in medicine and agriculture. In the first part of the 20th century scientists theorised that they could be used to generate heat for power stations, and to build a powerful type of bomb. Trace amounts of uranium compounds are found in almost all rock, soil and water, and one uranium isotope (U-235) is highly radioactive. For use in nuclear reactors and weapons, natural uranium must first be enriched with U-235. This form of uranium is capable of sustaining a chain reaction, releasing large amounts of heat.

During the Second World War, uranium was used to make the bomb that was dropped on the Japanese city of Hiroshima on 6 August 1945, and to make plutonium for the bomb dropped on the city of Nagasaki three days later. Development of nuclear power followed and uranium became a sought-after global commodity that would take the world – including New Zealand – into the atomic age.

The wartime search

New Zealand’s first uranium survey was inspired by the British and American demand for uranium for their nuclear weapons programmes in the Second World War.

Ernest Marsden, head of the Department of Scientific and Industrial Research (DSIR), initiated New Zealand’s first uranium survey during the war. In 1943, British and American scientists began work on the Manhattan Project to isolate U-235 and make an atomic bomb. While the UK had initiated a Commonwealth search for uranium in 1942, they did not consider New Zealand promising enough to include in the survey. Marsden, however, planned his own search for radioactive minerals in the South Island.

In the winter of 1944 a team of DSIR physicists assembled at the Dominion Physical Laboratory in Wellington to prepare equipment for the survey. The following summer, two teams of geologists and physicists began secretly exploring the South Island. Each was armed with a large, unwieldy Geiger counter – used to detect radioactivity.

An earlier study of New Zealand soils and rocks had suggested that granitic rocks and the beach sands derived from them would be the most likely source of uranium and other radioactive minerals. Although radioactivity levels were low, the DSIR teams found the most significant levels in the black sand concentrates of the West Coast gold dredges, and spent two months working on the Gillespies Beach dredge sands near Franz Josef.

Field day

Physicist Jim McCahon became an unwitting target while searching for uranium on the West Coast:

‘It was very hot so we worked most of the time nearly naked, and any time a cloud came over the sun we were free feed for the sandflies. When we had been there 10 days Ernie Marsden came to see how we were getting on. We told him of the sandfly troubles. He went away to his car and came back with a bottle labelled dimethyl phthalate – the stuff that is nowadays called ‘dimp’. He had bludged this from the airforce up in the islands and he gave it to us for protection. It was an absolute godsend.’ 1

First voyage of the New Golden Hind

In March 1945 the DSIR chartered the government ship New Golden Hind, and the secret uranium survey was extended to the granitic rocks of Fiordland. The scientists on board investigated the eight sounds from Milford Sound to Nancy Sound, but failed to find any promising sources of radioactive minerals.

In August 1945 the United States dropped atomic bombs on Hiroshima and Nagasaki. In recognition of the military and economic importance of uranium, New Zealand’s Atomic Energy Act was passed on 7 December 1945 to give the state full ownership and control over uranium and other radioactive elements.

Second voyage of the New Golden Hind

In January 1946 a second New Golden Hind expedition – this one was not secret – continued the survey in the southern sounds from Preservation Inlet up to Nancy Sound.

Once again, they found no significant radioactivity. Over the course of the two-year survey, the scientists had tested the radioactivity of rocks and beaches along nearly 1,600 kilometres of coast, the sands and gravels from more than 100 streams and rivers, and the concentrates from more than 20 sluicing and gold-dredging claims in Nelson, Westland, Otago and Southland. While uranium-bearing minerals – including some previously unknown to science – were found concentrated in tailings left by West Coast gold dredges, the quantity and concentration was considered insufficient for a mining venture.

Footnotes
  1. Jim McCahon, personal recollection, recorded 14–16 August 1998. › Back

West Coast uranium rush, 1955–56

By the mid-1950s uranium was in hot demand to fuel the developing nuclear weapons and energy programmes in the United States and the United Kingdom. Following advice from the United States Atomic Energy Commission, in December 1954 New Zealand’s Geological Survey enlisted the help of amateur and weekend prospectors with the publication of a booklet, Prospecting for radioactive minerals in New Zealand.

The booklet provided information on the field properties of radioactive deposits, and on likely places to find them. For those not able to pay for a Geiger counter, there were simple instructions on how to make one. Uranium prospecting was promoted as a weekend or summer hobby.

New Zealand’s first uranium find

In the Buller Gorge two bush-clad peaks – Mt Cassin and Mt Jacobsen – are named after the prospectors Frederick Cassin and Charles Jacobsen, who in November 1955 discovered uranium in the road cutting near Hawks Crag.

The sprightly septuagenarians had finished their day with a few drinks in the Berlins Hotel and, on the drive home, stopped to relieve themselves at the side of the road next to Batty Creek. Here Jacobsen put the Geiger counter on the rock face. The counter ticked wildly and the needle went off the scale. The excited pair spent the night at the Berlins Hotel, returning to Batty Creek the next morning to gather rock samples and take them to Wellington.

Cassin and Jacobsen’s find excited the media and other prospectors, especially as Cassin claimed that they had found one of the most highly radioactive deposits in the world.

Uranium fever hits the West Coast

Reports of Cassin and Jacobsen’s find gave other prospectors clues on where to look. By 14 November there were two new uranium finds, both close to Reefton – and a new air of hope and prosperity on the West Coast. Hotels presented parting guests with radioactive rock fragments; shop windows attracted customers with displays of uranium-bearing rock; and the Berlins Hotel had its busiest afternoon’s trade since the gold rush 90 years earlier.

By 23 November more detailed analysis showed that the high levels of uranium oxide in Cassin and Jacobsen’s initial samples were anomalous; further samples from the same location contained only one-quarter to one-hundredth of the first samples’ levels. Their discovery was found to come from a small volcanic dyke rich in radioactive zircon. The surrounding rock – the unusual sedimentary deposit called Hawks Crag Breccia – contained scattered patches of uranium-bearing minerals that had previously been overlooked.

Rewards under the Atomic Energy Act

In recognition of their discovery, in 1956 Cassin and Jacobsen were each awarded £100 under the Atomic Energy Act 1945. An amendment to the act in 1957 established a new schedule of rewards and in 1958 a further £400 each was awarded to Charles Jacobsen and the estate of the late Frederick Cassin in acknowledgement of the first discovery of uranium in New Zealand.


Uranium prospecting, 1956 onwards

Following Frederick Cassin and Charles Jacobsen’s find, prospectors began to search for the rock called Hawks Crag Breccia. In May 1956 prospectors employed by Buller Uranium, a subsidiary of the Nelson company Lime and Marble, reported three finds of radioactive boulders and outcrops in the lower Buller Gorge. Uranium Valley, a Westport company, found uranium at the Fox River mouth and in the Paparoa Ranges inland from Punakaiki.

Government support

Over the next four years the New Zealand government granted more than £35,000 to the West Coast search for uranium. Buller Uranium used their grants to cut tracks in the steep Buller Gorge bush, make clearings for helicopter airdrops, and set up and supply four prospecting camps. Prospectors expanded their search, tramping through the rainforest with geological hammers, slashers, compasses and Geiger counters. Uranium Valley built huts at two locations in the Paparoa Ranges, carrying supplies by helicopter, packhorse and on the backs of the prospectors to bases at Bullock Creek and Pororari.

United Kingdom Atomic Energy Authority

A confidential agreement between the Crown, the United Kingdom Atomic Energy Authority (UKAEA) and Buller Uranium was signed on 11 March 1959. The UKAEA was to investigate the Buller Gorge uranium deposits, and would have first right of refusal over any uranium found in New Zealand. High above the north side of the Buller Gorge, the UKAEA set up a camp with bunkhouse, drilling equipment and a rock crusher. Between September 1959 and March 1960, 10 short adits, or tunnels, were drilled by jackhammer. Chemical analysis, however, revealed that concentrations of uranium oxide were too low to support underground mining operations. In August 1960, after spending £17,775 on uranium prospecting on the West Coast, the UKAEA terminated their agreement.

Renewed interest – and decline

When the New Zealand Electricity Department’s 1964 Power Plan suggested that a nuclear power station would be needed in the 1970s – using uranium fuel worth about $10 million a year – Lime and Marble Ltd resumed their push to prove the West Coast’s uranium deposits. Others were interested too. In 1967 Australian company CRA Exploration spent over A$37,000 exploring the West Coast, including conducting a helicopter scintillometer survey to measure radiation intensity, but found no new uranium prospects.

Over the next decade, several companies undertook exploration programmes (some subsidised by the government), but the results were disappointing. The grade of mineral-bearing rocks was very low, and no new areas of radioactivity were found. By 1980 uranium was no longer considered important for New Zealand. A substantial natural gas field had been discovered offshore from Taranaki, and nuclear power stations had been deleted from the New Zealand power plan in favour of gas turbines.

In 2005 ownership of New Zealand’s uranium resources remained with the Crown, and under a 1996 minerals programme issued through the Crown Minerals Act 1991, prospecting, exploration and mining of uranium minerals is no longer permitted.


Hononga, rauemi nō waho

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How to cite this page: Rebecca Priestley, 'Radioactive minerals', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/radioactive-minerals/print (accessed 8 December 2019)

He kōrero nā Rebecca Priestley, i tāngia i te 12 Jun 2006