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The Mount Marion lithium-tantalum pegmatite deposit is located ~40 km SW of Kalgoorlie, Western Australia (#Location: 31° 4' 28"S, 121° 27' 48"E).
The Mt Marion pegmatites was first discovered during a regional mapping program by the Geological Survey of Western Australia in 1913. The Hampton Plains Mining syndicate mined the pegmatite in 1956 on a small scale. They were mapped in detail by Western Mining Corporation (WMC) in 1960 as part of a continuing exploration effort between 1960 and 1964, followed up with a drilling program between 1971 and 1986. WMC delineated 'reserves' of 1.49 Mt @ 1.67% Li2O in the No.1 deposit. On the basis of the reserve and other testing, a preliminary study estimated a possible production of 5000 t of lithium carbonate per annum in a 10 year mine life operation. However, no mining took place, and the leases were surrendered. Subsequently, further work was undertaken by Associated Minerals, and a pre-feasibility study was completed by in 1996. Pilot test work produced spodumene concentrates grading at 6.5 to 7% Li2O, with lithium recoveries of between 75 and 83%. No mining was undertaken, although a test plant was constructed. Subsequently, the deposit was held by a private individual, with no further significant exploration activities conducted until purchased by Reed Resources Ltd. in 2009. Reed Resources explored the other pegmatites of the cluster and identified a JORC compliant resource of 14.8 Mt @ 1.3% Li2O for 0.2006 Mt of contained Li2O, including both No.s 4 and 6 deposits as well as No.1. Reed Resources Ltd. entered into a joint venture with Mineral Resources Ltd in late 2009, and then with Jiangxi Ganfeng Lithium Co. Ltd. in 2015, such that each held 13.8, 43.1 and 43.1% respectively in 2016. In September 2015, the resources were estimated to be 23.24 Mt @ 1.39% Li2O in 6 deposits. Construction of a mine commenced in Dec 2015, with commissioning in mid 2016 and the first blast in April 2016.
The mineralised pegmatites at Mt Marion are located within the NW to NNW striking Archaean Saddle Hills Greenstone Belt, ~2.5 km to the NE of the syn-tectonic Neoarchaean Depot Granodiorite. The pegmatites appear to be associated with a flexure and series of splays from the NNW to NW trending Karramindie Shear Zone, on the eastern side of the Coolgardie Domain, within the Kalgoorlie Terrane of the Archaean Yilgarn Craton.
The immediate hosts to the Mt Marion pegmatites are metamorphosed, strongly sheared, Neoarchaean fine to very fine mafic rocks/basalts of the greenstone belt, located on the eastern limb of a tight, faulted antiform. These basalts are bounded to the east by a suite of metamorphosed ultramafic volcanic rocks, separated by a NNW-SSE trending splay of the Karramindie Shear Zone, that branched off the main shear zone to the south where the latter begins its flexure to the NW. The ultramafic volcanic rocks are separated from the NNW trending Zuleika Shear to the east by a wedge of metamorphosed siliciclastic sedimentary rocks. To the east of the Zuleika Shear zone there is a broad suite of felsic volcanic rocks.
The antiform has a core of metamorphosed siliciclastic sedimentary rocks. The western limb of this structure includes narrower bands of basalt and ultramafic volcanic rocks in that order, westward. The sedimentary and basaltic bands are separated by another splay of the Karramindie Shear Zone, which is located along the SW margin of the ultramafic volcanic rocks at the contact with a further wedge of biotite rich metamorphosed siliciclastic rocks that separates the latter from the Depot Granodiorite.
To the south, the Karramindie Shear Zone trends NNW-SSE, before curving to become NW-SE, over which interval the splays mentioned above branch to continue the main NNW trend. The main shear after swinging to be NW-SE over an interval of ~7.5 km, curves again to trend north-south, before resuming its normal NNW trend.
A series of >10 separate, sub-parallel, NE-SW (averaging ~50°), to locally NW, trending mineralised pegmatites define a NNW-SSE aligned, >6 km long mineralised corridor of >6 'deposits' at Mt Marion. These pegmatites dip at between 10 to 30°NW. The bulk of these are located between and/or within the splays of the Karramindie Shear Zone from the point where they branch from the main structure, although the southern most, No. 4 Deposit, is within the ultramafic volcanic rocks, several km south of the main series of splays.
The observations above are based on available geological mapping published by the Western Australian Department of Mines and Petroleum via their online GeoVIEW.WA GIS. These observations suggest the pegmatites exploited transtensional weaknesses caused by sinistral transcurrent movement on the Karramindie Shear Zone and its splays, within the more competent basalts. However, it should be noted that the No. 4 Deposit pegmatites, as well as being south of the main zone of splay faulting are hosted within the ultramafic suite.
These NNW to NW trending faults and related fracture zones disrupt and intersect the continuity of the pegmatite bodies. Locally a set of conjugate secondary faults and fractures, largely trending NW and NE, also dissect, truncate and modify the geometry of the pegmatite bodies.
Individual pegmatites vary in strike length from approximately 300 to 700 m, and average 15 to 20 m in thickness, but vary locally from less than 2 to up to 35 m thick.
Lithium occurs as 10 to 30 cm long, and ~1.5 cm in diameter, pale pink, pale green or grey-white spodumene crystals [LiAlSi2O6 containing ~8% Li2O] within fine to medium grained pegmatites composed primarily of quartz, feldspar, spodumene and muscovite, without any significant zoning of mineral assemblages. These are the first recognised unzoned albite-spodumene pegmatites in Western Australia. The spodumene crystals are typically oriented orthogonal to the pegmatite contacts, and hence are mainly near-vertically aligned. Some zoning of the pegmatites parallel to the contacts is observed, with higher concentrations of spodumene occurring close to the upper contact.
A coarse grained pegmatite intrusive into coarse grained greenstones occurs at the northern end of the belt, and contains spodumene, quartz, feldspar, muscovite, columbite and beryl. It exhibits four well defined zones: i). quartz-spodumene; ii). quartz-spodumene-muscovite-feldspar (Lepidolite zone); iii). quartz-spodumene-muscovite-feldspar-columbite; and iv). pure feldspar. Spodumene crystals, which can reach lengths of as much as 1 m, and may be up to 30 cm in diameter, tend to be aligned vertically.
Each of the pegmatites does not appear to have been mineralised over its whole length.
Details of the individual pegmatites are as follows:
• Pegmatite No.1 occurs as a flat sheet averaging 17 to 21 m thick, dipping 15°W, and has eroded into two masses with a cumulative length of 335 m. It has a homogeneous granitic texture of quartz, microcline, albite and muscovite, with some pale green to white spodumene crystals up to 30 cms in length. A thin band of cleavelandite [quartz albite] occurs near the hanging wall and footwall, with holmquistite [Li2Mg3Al2(Si8O22)(OH)2] along the hanging wall contact. It contains 6.59 Mt @ 1.42% Li2O.
• Pegmatite No.2 is similar to No.1, and is 330 m long, dipping 30°W. Pegmatite No.2 West is a separate body with a 'V' shape in outcrop, pointing south, and is 30 m wide. Resources are No.2 - 2.31 Mt @ 1.45% Li2O, and No.2 West - 7.81 Mt @ 1.44% Li2O
• Pegamtite No.3 is a flat lying sheet, 4 to 14 m thick, with a strike length of 640 m. It contains spodumene crystals up to 1 m long, and has a core of quartz-spodumene-albite-muscovite containing 30 to 50% spodumene. Small sub-cm columbite-tantalite crystals are found with the albite in the core. The core is encapsulated by outer zones composed of microcline-quartz-plagioclase-muscovite.
• Pegmatite No.4 is similar to No.1, outcropping as a narrow curved north-south vein that is 6 to 8 m thick, dipping 10 to 25°W, is unzoned, and contains spodumene. It contains 2.3 Mt @ 1.3% Li2O.
• Pegmatite No.5 has a resource of 0.96 Mt @ 1.33% Li2O, over an area of 650 x 200 m.
• Pegmatite No.6 has a resource distributed over an area of ~600 x 175 m, and varies in thickness from 8 to 25 m. It has an internal barren interval of 2 to 10 m locally and dips westward. At its shallowest and thinnest to the east, it is 8 m thick and <10 m below the surface averaging 0.55% Li2O over the full width. Some 250 m west, the pegmatite comprises 18 m @ 1.24% Li2O, and a further 250 m is 21 m @ 1.76% Li2O from a depth of ~20 m. The western most intersection is 24 m @ 1.11% Li2O, but continues for at least another 250 m where it is at a depth of ~60 m below the surface and ~25 m thick. It contains 3.21 Mt @ 1.24% Li2O.
The individual deposits are distributed in the following order, from south to north: No.4, No.6, No.5, No.1., No.2 and No.2 West, and No.3. No.4 is 2.2 km SSE of No.6, which is 1 km SSE of No.5. No's 5, 1, 2 and 2 West are closely spaced, and N.3 is <1 km NW of No.2 West.
Published JORC compliant mineral resources as at May 2016 were as follows, based on a 0% Li2O cut-off (Neometals and Mineral Resources release 18 May 2016):
- Indicated resource - 10.5 Mt @ 1.45% Li2O, 1.33% Fe2O3;
- Inferred resource - 13.19 Mt @ 1.34% Li2O, 1.5% Fe2O3;
- TOTAL resource - 23.24 Mt @ 1.39% Li2O, 1.43% Fe2O3.
Details of the pegmatites and their mineralisation included in this summary are drawn from a range of sources, mostly releases by Neometals Ltd., the Mindat database and an analysts report by Ecclestone, C., 2014 of Hallgarten and Co., on Reed Resources.
The most recent source geological information used to prepare this summary was dated: 2014.
This description is a summary from published sources, the chief of which are listed below.
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