Yinnietharra Dravite mine (South Open Cut), Tomkap tourmaline mines (Soklich), Yinnietharra, Upper Gascoyne Shire, Western Australia, Australiai

Regional Level Types
Yinnietharra Dravite mine (South Open Cut)	Mine
Tomkap tourmaline mines (Soklich)	Group of Mines
Yinnietharra	Station (farming)
Upper Gascoyne Shire	Shire
Western Australia	State
Australia	Country

A well-known locality for very large and well-formed dark brown dravite crystals. The deposit was discovered in 1918. A. Soklich claimed the mining lease and started mining in 1968. During the initial period of mining (January 1969 to January 1971) more than 12 tons of dravite crystals were produced for specimens. More recently (2010) the mineral lease has been taken up by Tom Kapitany, who renamed it Tomkap tourmaline mine, produced more specimens and provided some of the following information.

It consists of two pits 1km apart roughly parallel on strike north-north west. Brown dravite occurs at the south pit, and black dravite in the north pit.

The dravite is found in a phlogopite-plagioclase schist on Morrissey Hill in the Gascoyne Province of the Precambrian Shield of Western Australia (Bridge et al., 1977). Associated pegmatites cut across strike of the tourmaline-bearing schists. Regional metamorphism and deformation of metasediments with highly hydrothermally altered zones allowed tourmaline crystals to form in the mica schists, possibly with boron derived from underlying pegmatites. Dravite rarely has associated apatite crystals up to 125mm. Dravite crystals up to 7kg have been found. There are different zones existing in 2 contact zones producing smaller crystals and central zone producing giant dravites.

The main south deposit is about 5 meters wide and runs for a few hundred meters. The existing pit is about 30 meters long and had a very curious, friendly goanna living in there. The pit contains highly fluorescent chalcedony under both UV and short wavelengths, and exists in fracture lines to the surface.

Most of the brown dravite specimens on the market come from the Soklich mining period (1968-1971), with crystals found sporadically within pods. Near surface crystals were of poor quality due to fracturing, commonly encrusted by secondary opal and carbonates from weathering.

Better quality material occurs at 3-6 metres below the surface. The crystals appear opaque but have minor translucence, vitreous lustre, often indented with small booklets of mica (although most specimens on the market have these removed). Some of the specimens are very large, to a few kg. They occur as single and intergrown crystals. Plagioclase as poikilitic inclusions are commonly found in the dravites aligned as flattened laths sub-parallel to the principal axes of the dravite crystals. Inclusions can also include phlogopite, subhedral rutile, apatite, zircon and fluorite.

Crystal forms present include a hexagonal prism, trigonal prism, and rhombohedral terminations. There was initial confusion amongst collectors, as crystals are almost equidimensional, or equant, with short prismatic zones terminated by rhombohedra, superficially resembling the dodecahedral morphology of garnets.

In Fetherston, J.M., Stocklmayer, S.M., Stocklmayer, V.C. (2017) Gemstones of Western Australia, second edition. Geological Survey of Western Australia, Mineral Resources Bulletin 25, 356 pages, it is reported that:

"At the Yinnetharra North deposit, 1.5 km to the north of the Yinnetharra dravite openpit, schorl or black tourmaline was originally reported. In more recent years, it has been established that all tourmaline in this area is black dravite, with an MgO content of 9.85%. The Yinnetharra North deposit, on former mineral claim MC09/215, is in a black phlogopite schist containing large, euhedral black dravite rhombohedra, many with double terminations and internal zoning visible in thin section. Maximum crystal size is recorded as 60 mm in diameter and 23 cm in length".

Other Regions, Features and Areas containing this locality

References