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Deposit Synonyms
Aorangi Gem; Buicks Claim; Coxs Claim; Hog Bay; Kangaroo Island Amalg. Gem Syndicate; Kangaroo Island Chinastone And Clay Co.; W.A. Kingsborough
Mineral District
Deposit Summary
pegmatite to 80m wide worked for gem tourmaline, feldspar, kaolin and silica. Host was Kanmantoo Group metasandstone and schist. Tourmaline blue and green-coloured, kaolin poor quality. Depth of weathering generally to 126m.
Deposit Description
DUDLEY, mine located on a pegmatite, ~10 km south-east of Penneshaw, and was worked during the 1890s for gem tourmaline, and from 1905-10 for feldspar, kaolin and silica. The pegmatite outcrop trends NE for 550m, is up to 80 m wide. Its appearance and mineralogy are variable from a coarse-grained, perthitic microcline feldspar-quartz-muscovite rock to graphic granite and aplite, often with accessory tourmaline and rare traces of garnet. The pegmatite intruded into Kanmantoo Group metasandstone and schist during the Delamarian Orogeny.
Gem quality tourmaline, mostly blue and green-coloured is associated with coarse muscovite and/or quartz crystals in pods and veins that are often elongate parallel to the strike of the pegmatite body. Best finds are in the "gem shaft area," and confined to clay-filled vughs, often at depths >2m. The gemstones included a 43 carat, clean, dark blue crystal 47mm long by 10mm wide. Kaolin occurrences derived from weathered parts of the pegmatite were restricted and of poor quality. Depth of weathering was variable, generally to 126m RL.
In 1987 23 costeans to 2m depth were excavated across the strike of the pegmatite. The trenches were geologically logged, and selected intervals chosen for bulk samples. Several zones of tourmaline mineralisation were reported, particularly at the northern end of outcropping pegmatite.
In 2016 Entia Gems and jewellry completed costeans parallel to the pegmatite trend and on selected target zones including area E1, the "gem shaft area." Gem quality tourmalines were recovered from 2 zones in this area in host coarse pegmatite, along with minor coarse mica, and smoky quartz. Washed and seived samples returned grades of fractured, weathered green elbaite and blue indicolite tourmaline crystals ranging in size from 0.2 - 3cm. Also minor recovery of unfractured tourmaline needles, with 1 gemmy green elbaite 10.2mm x 5mm.
Discovery Year
? 1890
Commodities
Feldspar, Kaolin, Tourmaline, Silica
Ore Minerals
Beryl, Elbaite, Kaolinite, Microcline, Plagioclase, Quartz, Tourmaline
Gangue Minerals
Apatite, Muscovite
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