Londonderry Li deposit, Nepean, Coolgardie Shire, Western Australia, Australiai

Regional Level Types
Londonderry Li deposit	Deposit
Nepean	Urban area (Historical)
Coolgardie Shire	Shire
Western Australia	State
Australia	Country

"At Londonderry, south of Coolgardie, a large microcline feldspar pegmatite dyke… is a potential source of the lithium minerals lepidolite and petalite." (Geol. Austral. Ore Deposits, 1953, page 76).

"Located near Nepean, Bouchers, and Miriam deposits. A feldspar quarry located 19 km South of Coolgardie." (Bridge & Pryce, 1974).

Frasers Find on Mindat is the old name for the Londonderry deposit, named after Hugh Fraser, who discovered it in 1909. Also known in its early days of mining from 1929 as Scahill's Quarry.

The deposit contains two quarries and two large white mullock hills. It has been a source of many specimens over the years. Four known pegmatite sheets called Londonderry Feldspar Quarry, Lepidolite Hill, Tantalum Hill and Bon Ami.

Mining first took place in 1929 by the Australian Glass Manufacturers Company for microcline feldspar.

In 1947 the second quarry was opened for feldspar mining, while quarry 1 reverted to petalite mining.

By 1948 the quarries had produced 37,535 tonnes of microcline, 72 tonnes of beryl and 320 kilograms of tantalite-columbite.

Australian Glass Manufacturers Company was purchased by the Australian Consolidated Industries in 1974, then Unimil Pty Ltd purchased the quarry in 1980. They mined the deposit irregularly until 1987. The mine was nearly exhausted, and they battled to find a market for the material, which was often contaminated with other minerals.

In 1986, Commercial Minerals Ltd purchased the quarries for $40,000 with the intention of switching their operations from the Mukinbudin Feldspar Quarries, which were nearing exhaustion. After much exploratory work, the deposit was viewed as uneconomic, placed under care and maintenance, and then their licences surrendered in 1999. A small operation crushing mullock for road gravel continues at the site.

The pegmatite is complex, accounting for the range of species. From the top down, the zones are:

- a border zone of fine-grained albite-quartz-garnet,
- albite-quartz-muscovite zone,
- microcline-quartz-muscovite zone in quarry 2,
- petalite quartz and petalite-quartz-albite-muscovite zone in quarry 1,
- albite-quartz-muscovite zone mixed with albite-quartz-beryl,
- quartz-microcline-Li-micas,
- albite-microcline-quartz-muscovite zone,
- and a footwall border zone of fine-grained albite-quartz-garnet.

Specimens of petalite are most likely from the mining process and are large cleavage blocks, transparent, white to pearly white. Petalite pseudomorphs are likely from the dumps, and are often misidentified by dealers, so a brief description follows, from most to least common:

- Albite-quartz or albite (also known as hornstone) are fine-grained white rocks showing a crystal orientation to the c-axis of the original petalite cleavage.

- Quartz-cookeite and quartz-albite pseudomorphs are soft fine-grained in lilac, light green or multicoloured.

- Prehnite-quartz pseudomorphs are 80% prehnite, and by hand analysis look like solid prehnite, light green, transparent to 4 cm.

- Eucryptite-quartz pseudomorphs were first discovered here in 1963, are pale pink and more rarely dark glassy brown, and fluoresce a pale begonia colour under short-wave UV light.

- Eucryptite makes up the majority of some specimens.

- Rarest are spodumene-quartz pseudomorphs and are fine-grained and grey.

Various other species are found, the descriptions of some found below:

- Pictures exist of ixiolite black fan-shaped intergrown crystals from a centre point to 7 cm in length.

- Minor ferrocolumbite and ball zinnwaldite.

- White, light green, yellow and pinkish beryl crystals to 17 cm, although good crystals are rare.

- Purple ball trilithionite, usually advertised just as "lepidolite". "Lepidolite" is common in pegmatites of the region. Specimens previously listed as "lepidolite" from this locality have all proved to be trilithionite. This was confirmed by EDS analysis.

- Bavenite was discovered here in 1948 and initially misidentified as a new species, duplexite. It pseudomorphs beryl crystals within a matrix of cleavelandite, and also as pearly white to light green fan-shaped interlocking crystals and finally in bow-tie format.

- Bityite is found associated with bavenite as grain-sized reflective plates, also discovered here in 1948 and misidentified as a new species bowleyite.

- Peter Bridge discovered moraesite in the mullock in 1956, as tufts of delicate needles, and at the time it was only the fourth known occurrence of the species.

- In 1977, Peter Bridge also discovered a new species from material collected in the 1940s, and together with Jiri Just analyzed the species, but their paper was never published. In 1981, Marshukova et al. published a paper on the species and the IMA approved the name natanite (FeSn(OH)6). There are many other species in collections from these quarries.

- The Simpson Mineral Collection of the Western Australian Museum contains specimen MDC 4862 (identified as bismoclite) from this location.

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References