Yowah & Koroit

on . Posted in Queensland Opal Mines

Yowah NutHome of the Yowah Nut

Yowah township is situated 165 km West of Cunamulla and has a friendly population of around 100 people. A bore was sunk in 1912 for the mining settlement and has never failed since. There is a fossicking area for visitors, caravan park, golf course and numerous retail outlets and Opal cutters willing to help educate newcomers!

The greater Yowah Area also known as Cunamulla Mining Field, encompassing Koroit Opal Field, produces a whole sub-species of Boulder Opal, known generically as Yowah Nuts . The best examples reveal highly-prized solid cores of gem crystal. These small ironstone boulders or 'nuts' are found thickly embedded in the pipeclay band which varies in thickness from 15 centimeters to 60 cms.
 

This marvellous form of Boulder Opal includes a number of different nodule shapes and sizes which contain kernels of concentrically patterned and Boulder Opal Matrix. The first lease was registered at the Yowah in 1884.
 
yowahnutkernels.jpg yowah_nut_conglomerate.jpg

The earliest reference to the Yowah fields tells of the discovery of Opal in an area now known as the Water Claim at Whiskey Flat. Later, in 1893, Opal was found in the area known as Southern Cross. This area was taken up by a company headed by Mr Bond. Work continued until the death of the manager. In 1901 this lease of 1000 feet by 1000 feet was taken up by a group of Germans. From 1902 to 1906 approximately 100 miners were working on the field.

An extension of the Water Claim at Whiskey Flat was known as Evans Lead or the Great Extended. Mr C.F.V. Jackson, assistant government geologist, in October 1902 reported in the Opal Mining Industry:

‘The discovery of Opal at the Great Extended was made by Mr Evans when deepening an old shaft that had been left by some former prospector, and it is now one of the richest deposits which is being worked in Queensland. It was first held as a claim, but owing to disputes was subsequently taken up as a mining lease No.6 by Evans and T.C.Wollaston. This is now the only mineral lease for Opal which holds good.’

Black Gate followed with the discovery of Opal on Dynevor Downs in 1894. Nearby mines include Leopardwood.

Geology at Yowah Opal Field

At the Yowah field precious opal occurs in siliceous ironstone nodules generally referred to as "Yowah Nuts". Nuts range in size from about 5mm to 200mm across, are spherical or ellipsoidal in shape, showing alternate concentric rings or bands of light and dark brown siliceous ironstone. Rarely, there is a solid kernel of precious opal inside - which is the ultimate find.

The nuts are found in bands (150 to 600mm in thickness) at depths up to 20m in a ferruginous sandstone, and are commonly associated with claystone lenses. The main level is located near the contact between the sandstone and underlying mud/claystones, but scattered nodules, and in some cases another productive level is encountered above it. The lateral continuity of the nut bands is somewhat difficult to predict owing to the irregular bedding of the strata. Sandstone at its contact with the mudstone is more ferruginous and cemented by partial opalisation into a hard band, which may also contain opal as seams and pipes.

Koroit

Koroit opal fields are situated (80km NW of Cunamulla) 50 miles north-east of Yowah, as the crow flies!

Opal was discovered here in 1897 by Lawrence Rostron, the manager of Tilboroo station, Eulo. Rostron formed a mining syndicate which initially met with little success. In 1900 a larger syndicate formed which included most of the original eight-members who after several years of hardship merged with a group of Glasgow investors to be known as the Scottish & Australian Opal Mines. They carried out more extensive work to a greater depth and soon had a find estimated at between £800 to £900.

The syndicate's 10 men had dug 150 mine shafts by the end of 1904. Five were over 50ft deep and six were waterholes holding as much as 45,000 litres. Having tunneled a total distance of 1560 ft. by pick and shovel, 300ozs of medium grade and 30ozs of top grade free pipe opal were found. They also took one and quarter tons of selected boulder opal and boulder matrix - the newly prized type of opal!

At that time thirty or forty men were working the field, however the lack of water made the field a trying place. During the 1970's the field was deserted. Today this one of the most vibrant Opal producing fields.

Koroit Opal is world renowned for its hardness and beauty amongst consumers and opal experts. Koroit produces seam opal, brilliant nut opal and incredibly beautiful matrix picture stones. The famed red jasper-like 'boulder band' is etremely hard and also capable of revealing brilliant faces of colour from thin horizontal veins of opal. 

The fields encompass the 3-Mile and Boobara Station, including the Red StarFiery Comet and Holloways, Piglets mines. 

Testimonials

Sue-White opals29 June 2013
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Opalminded recommend opalsinformation6 June 2010
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Fri, Apr 16, 2010 
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5 April 2010
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