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Deposit Synonyms
Copley; Ml 3068; Ml 4998; Ml 5000; Ml 5001
Mineral District
Leigh Creek-Willouran Magnesite
Deposit Summary
0.3-2.6m thick beds of magnesite interbedded with siltstone and dolomite traced NW for ~8km OF strike. Production from 1947-2013 >60,000t. Resources ~10mt @ 43% MgO.
Deposit Description
MYRTLE SPRINGS, claims were taken out over beds of magnesite in the Myrtle Springs area in 1945, with tenure continuous until the 1990's. The beds were worked in a series of pits and quarries extending along the strike of the magnesite beds. The main bed was to 2 m thick, with mining proceeding by removal of overburden from the hanging wall, followed by mining in a long narrow slot to 8 m below plain level. The largest quarry was 100 m long x 3 m wide by 5 m deep, with a second quarry on ML's 4151-52 having dimensions 155 m long by 7 m wide by up to 8 m deep. First production was 105 tonnes in 1947, followed by 3,829 tonne from 1955-64, and 2,843 tonnes from 1970-83. In 1984-85 Commercial Minerals Ltd (now Unimin Australia Limited) carried out large-scale operations on the current mine site. A total of 12,848 tonnes (1984), and 17,876 tonnes (1985) were supplied to the aluminium industry in Queensland. After high rates in these two years, production dramatically decreased, and averaged less than 1000 tonnes/year thereafter. Mining was then carried out on a campaign basis as required. Total production from 1947-2013 was estimated at 61,000t.
The magnesite formed within an interpreted Neoproterozoic shallow water marine environment, where a characteristic repetitive lithogical sequence made up of dolomite, magnesite, siltstone and sandstone was deposited. Detailed mapping, together with imagery from airborne infrared hyperspectral survey (Hymap), flown in 1998, identified up to 17 potentially economic beds of magnesite common to both the Mount Hutton and Witchelina areas. They ranged up to 10 m in thickness, and were part of a much larger Mg-mineralised sedimentary package carrying up to 86 magnesite beds, only very few of which were discontinuous or lensoidal at deposit scale.
The detailed mapping of the mine showed 25 individual magnesite beds in 0.3-2.6 m thick beds of fine to medium grained, massive magnesite, and coarse, pelletal magnesite interbedded with dolomitic magnesite, laminated dolomitic siltstone and dolomite. The sedimentary sequence trends NW, dips 60-70 NE. The main magnesite units were traced NW for ~8 km along strike to Mount Playfair Well. There is a quartzitic dolomite marker bed along the eastern margin of the magnesite, with a similar bed of massive dolomite on the western margin. Nodular magnesite consists of fine grained magnesite of botryoidal and folded appearance. The nodular magnesite develops by replacement of magnesite mudstone and intraclasts during periods of sub-aerial exposure. Mosaic textures are apparent as a result of nodular growth on magnesite intraclasts. Indicated resources were 10 million tonne at 42.9 % MgO. Current production is from the Myrtle North quarry (MIL Resources Limited).
Discovery Year
~ 1945
Commodities
Magnesite, Dolomite
Ore Minerals
Magnesite
Gangue Minerals
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