Discovered July 1954 Operating Mine 1958-63 and 1976-82 Ore Processed 9,200,000 tonnes Average Grade U3O8 0.116% U3O8 Produced 4,091.8 tonnes (1st Period)
4,800.6 (2nd Period)
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Mary Kathleen is about half way between Mount Isa and Cloncurry, in far north west Queensland. The deposit was discovered in July 1954 by prospectors from nearby Mount Isa, soon after the discovery of the nearby Skal deposit sent hundreds of prospectors madly roaming the Mt Isa and Clonclurry countryside.
The uranium prospecting syndicate was led by Norman McConachy, Clem Walton, and included brothers Mick, Henry and John Walton, Jim Lankin, G Barnes and G Fox (1). They were prospecting 48 miles from Mt Isa, near the site of the old copper town of Rosebud, when they struck terrific radioactivity high on a ridge-based outcrop of conglomerate breccia. Surface indications were so rich that geiger counters went haywire - and so did the prospecting companies who came to bid for the lease. Their offers made some of the Northern Territory prospects look like a poor relation (see the history of Rum Jungle and South Alligator mines).
Australian Oil Exploration Ltd was given an option over the prospect for a cash offer of $500,000, plus twenty per cent of shares of any company floated, and five per cent of any ore produced.
The prospect, now named Mary Kathleen after Norman McConachy's wife who had died of cancer only a forthnight before the strike, became world famous. The deal was headline news and it bought a sudden switch of the uranium limelight to Queensland. Dozens of companies, including most of the major concerns in the Northern Territory, sent prospecting teams rushing to the Mt Isa-Clonclurry region to stake out prospecting leases. Even the North Australian Uranium Corporation (NAUC), discoverer's of the Sleisbeck uranium deposit in the South Alligator Valley, diverted a team from their Sleisbeck prospect to hunt for new Mary Kathleen's in the barren hills around Mt Isa.
In 1955 Mary Kathleen Uranium Ltd (MKU) was formed, with the majority (65%) of the shares held by the Rio Tinto Mining Company of Australia Limited (later to become part of CRA, and now just Rio Tinto). The remainder (35%) was held by Australian Oil Exploration Ltd (AOEL) (2).
By late 1957, however, AOEL was nearly bankrupt. Ric Dowling, one of the most powerful mining stockbrokers for the time, heard during a trip to London that AOEL were about to sell their share in MKU to RTZ. On his return to Australia Dowling sought the support of clients and associates to keep a stake in MKU in Australian hands. Kathleen Investments Ltd was floated to purchase the 35% share in MKU, controlled at the time by Roy Hudson and Ric Dowling (2). Kathleen Investments Ltd later acquired a 51% interest in Queensland Mines Ltd during 1965, the exploration company that found and developed the Nabarlek uranium deposit in Arnhem Land, NT (2).
A sales contract with the United Kingdom Atomic Energy Authority was signed in 1956. Mining commenced at the end of 1956 and the treatment plant was commissioned in June 1958. The project was developed by MKU at a cost of $24 million.
Beyond ascertaining that sufficient ore (at a grade of 0.16%) was available to meet obligations under the UK contract, the orebody was not fully proved up at this stage. (Initial reserves were later quoted at 7 million tonnes of 0.12% ore containing 12,000 tonnes of U3O8.) However it was evident that the mineralisation (3.0% rare earth oxides and 0.025% thorium oxide) really comprised a rare earths orebody containing uranium, and over the years various attempts were made to find markets for the rare earths as a co-product, to no avail.
In this first phase of operation from 1958 to 1963 Mary Kathleen treated 2.9 million tonnes of ore at an average grade of 0.13% to yield 4,082 t (4,500 short tons or 9 million pounds weight of U3O8) of uranium concentrate (then actually yellowcake - ammonium diuranate) containing 3,460 tonnes of uranium.
Initially the process was the conventional sequence of crushing, grinding, leaching with sulfuric acid, counter-current decantation, followed by ion exchange and extraction and drying. In 1960 electronic radiometric ore sorting was introduced to concentrate ore prior to crushing, with the result that the head grade feed increased from 0.17% to 0.24%.
Tailings were emplaced in a 12 hectare tailings dam in a small valley west of the plant. This overflowed into an evaporation pond of some 60 hectares.
With improvements in the treatment plant the contract was filled faster than the nine years originally envisaged, and hence in October 1963 the mine closed and the plant was put on care and maintenance. Some 2.8 million tonnes of 0.148% ore was identified then as remaining accessible by open pit mining, containing 4,246 tonnes of uranium oxide.
In the event, the mine remained closed for more than a decade. New contracts with utilities in Japan, Germany and USA for 4,740 tonnes of uranium oxide were negotiated early in the 1970s and recommissioning began in 1974. The company made a share issue to raise capital, and the Commonwealth Government, through the Australian Atomic Energy Commission underwrote this, thereby obtaining a 42% holding in the company. Conzinc Riotinto of Australia Limited, a successor of Rio Tinto Mining, held 51%, and the public 7%.
In the plant the ion exchange section was replaced with a more effective solvent extraction process and the mine and mill reopened in February 1976. The cost of refurbishment was $26 million.
At the end of 1982 the mine was depleted and finally closed down after 4,802 tonnes of uranium oxide concentrate had been produced in its second phase of operation. During the 12 years of operations about 31 million tonnes of material was mined, including 7 million tonnes of ore.
At Mary Kathleen, where operations ceased in 1981-2, one million litres of radioactive liquid was deliberately released in Febuary'84 from the mines evaporation ponds during an unexpectedly wet wet season.
Notwithstanding the minimal conditions imposed in relation to the 1954 leases, the company took the view that it should conform to relevant current environmental and occupational health standards. Consequently, before the recommissioning in 1976 a full environmental impact study was undertaken and this incorporated a rehabilitation plan for the 64 hectares of waste dumps, 29 hectares of tailings dam and 60 hectares of evaporation ponds. Mary Kathleen then became the site of Australia's first major rehabilitation project of a uranium mine, which was completed at the end of 1985 at a cost of some $19 million. In 1986 this work won an award from the Institution of Engineers Australia for environmental excellence.
The closure in 1982 and subsequent rehabilitation of the Mary Kathleen uranium mine is a classic case of economising at the environment's expense. The mining company covered the tailings with crushed rock instead of clay in order to save millions of dollars. The seepage of radioactive radium and thorium and toxic elements from the tailings will be much greater than if clay were used as an relatively impermeable barrier.
In the late 1980s, following relinquishment of the Mary Kathleen leases, MKU was liquidated.
Graphics and photo from a postcard available in Clonclurry, Queensland. The postcard says :
"Mary Kathleen Open Cut - Queensland's only uranium uranium mine. In the Cloncurry shire."
Bottom photo - Annual Reports, Mary Kathleen Uranium Ltd.
Information combined from the Uranium Information Centre and Friends of the Earth Sydney
submission to the Senate Select Committee Inquiry on Uranium Mining and Milling.
(1) - Ross Annabell, 1977, The Uranium Hunters, Published by Rigby Limited.
(2) - Trevor Sykes, 1978, The Money Miners - Australias Mining Boom 1969-1970, Published by Wildcat Press.
Page last updated - February 18, 2000.
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