|Magnesite mineral information
Magnesite is an important industrial center mineral magnesium carbonate (MgCO3)
Pure magnesite is theoretically 47.8% magnesia (MgO) and 52.2% carbon dioxide (CO2)
It is the source of two thirds of the world's magnesium oxide (MgO), 25% is obtained from sea water, the rest comes mainly from brines.
Magnesite deposits in South Australia
Three main types of magnesite deposits occur in South Australia:
Sedimentary deposits: occur as intermediate layers in the dolomite of the Adelaidean Skillogalee age. This formation extends from the Torrens Gorge near Adelaide, the Leigh Creek-Marree area in the northern Flinders Ranges.
The magnesite was deposited as a chemical precipitate in shallow, marginal marine lagoons and mudflats, and occurs predominantly as cryptocrystalline particles 1-5 to the size. Much has been of storm tides and in intraformational conglomerates thinly interbedded with dolomite reworked. The thickest development of magnesite is along a strike length of 120 km, northwest of Leigh Creek (Figure 1, opens in new window). Here, the calcium content of the magnesite beds is relatively high, ranging from 2% at Mount Hutton to 4.5% in Screechowl Creek, with calcium present, as dolomite or magnesium calcite.
Talc and quartz are present in small quantities.
Replacement deposits: Irregular bodies coarsely crystalline sparry magnesite have been formed by metasomatic replacement Balcanoona Formation dolomite near Balcanoona and in the Mount Fitton-Mount Livingston area.
Residual deposits: Small deposits of magnesite are superficial on magnesium-rich dolomite of the Hutchison Group on Eyre Peninsula and developed on Skillogalee Dolomite near Robertstown. Although some lumps relatively pure (94-97% MgCO3), the deposits are thin and discontinuous.
Flinders Ranges sedimentary deposits
Copley (as well known Camel Flat)
The deposit is located 5 km from Railway Station route west of Copley. The first recorded mining was in 1919, but the main period of activity was from 1940 to 1955 as FH Faulding & Co. Ltd extracted 6000 t for the pharmaceutical and chemical stress.
The deposit comprises 60 magnesite beds, 0,05-3.0 m thick over a length of 1.5 km within the upper 300m of the Skillogalee dolomites. The average chemical composition of the central zone (21 beds in a total of 13.4 million is 89.4% MgCO 3 (42.7% MgO).
Myrtle Springs-Mount Hutton
At the Myrtle Springs deposit, 30 km by road northwest of Leigh Creek (Figure 1, opens in new window) magnesite has removed over a length of 400 m from four magnesite beds of 1 m thickness dipping 65 º east.
Approximately 30 000 tonnes were mined in 1983-84 for water filtration in Queensland alumina refinery, but annual production since 1990, an average of 700 tonnes, mainly for agricultural purposes and rockwool manufacture. This deposit and raw lease at Mount Hutton along strike to the southeast, were purchased from SAMAG in 2000. Detailed mapping and subsequent drilling has established continuity of the sedimentary sequence for a total strike length of 14 km between the two groups of leases.
The 120 m thick sequence comprises 52 magnesite beds 0.1 to 2.4 m thick deposited an average of 42.9% MgO with dolomite. The measured resource 18.3 Mt
A diamond drilling program of Pima Mining in 1998 defined a resource with a strike length of 2.5 km with a 240 m thick sequence with 47 magnesite beds 0.1 to 2.1 m thick deposited with dolomite. The average magnesite grade is 42.7% MgO.
A diamond drilling program of Pima Mining in 1998 defined a resource with a strike length of 6.9 km with a 124 m thick sequence with 45 magnesite beds 0.1 to 2.9 m thick deposited with dolomite. The average magnesite grade is 42.8% MgO, and the measured resource 4 Mt
The deposit is 35 km west along station tracks from Farina. Leases have been produced by FH Faulding & Co. Ltd. from 1964 to 1980, when a total of 5,000 tonnes held. The deposit lies in a shallow depression basin 4.3 km long and 2.0 km wide. Outcrop is generally subdued, and the sequence is not fully exposed. A diamond drilling program of Pima Mining in 1998 defined a resource that is stored a sequence of up to 350 m thick, thick with 23 magnesite beds with dolomite from 0.3 to 11.0 meters. The average magnesite grade is 40.0% MgO, and the measured resource is 23.7 Mt
Screechowl Creek - West Mount Hut
A 93 m thick sequence with 25 magnesite beds 0.2 to 3.9 m thick deposited with dolomite, is exposed in the deeply cut banks Screechowl Creek, 105 km north-west of Leigh Creek. Detailed mapping has established continuity of the sedimentary sequence for a total strike length of 18 km.
Southern Flinders Ranges
Skillogalee dolomite deposits of the southern Flinders Ranges (Mundallio, Port Germein Gorge) are thinner and are hosted larger mining problems than in the northern Flinders. BHP produced 4500 t from shallow open cuts and underground workings in these deposits in the 1940s and 50s.
Flinders Ranges replacement deposits
Access is over 110 km of unpaved road east of Copley. The deposit is now within the Gammon Ranges National Park, a total of 20 Mt is inferred in four orebodies in the Weetootla Gorge area. The only production of a 660 t trial parcel from exploratory tunnels in 1956. The package was analyzed as 95.7% MgCO3, CaCO3 0.7%, 0.8% SiO2, 1.8% and 0.5% Al2O3, Fe2O3.
Mount Fitton and Mount Livingston
Small deposits of similar material as the Balcanoona are deposit at Mount Fitton and Mount Livingston known, ~ 60 km to the north.
The Robertstown deposits, 115 km east-northeast of Adelaide, are the most important deposits of this type. Recorded production since 1916 is ~ 20 000 t. The deposits are discontinuous and of variable degree, with a superficial cap nodular magnesite to 1 m deep Skillogalee dolomite with fracture-fillings extension 2-3 m below the surface.