DIAMONDS IN AUSTRALIA.
As pointed out by Professor A. Liverside diamonds are found in the valley of the Horton or Big River, seven or eight miles from Bingera, under just the same conditions as at Mudgee. The diamond-bearing deposit is 2 to 3 feet thick, and occurs in isolated patches, the material which originally lay between having been denuded away. These patches of diamantiferous material are scattered over an area measuring four by three miles, in a valley, which is opened towards the north, but enclosed otherwise by the Drummond Range. The deposit consists of sandy and clayey material, and has probably been deposited in former times by the Horton River. The rocks of the locality are clay-slates of Devonian or Carboniferous age, and the sheet of basalt, which occurs in the neighbourhood, appears to overlie deposits similar to those now being considered. Here also the diamantiferous material is in places cemented together to form a solid conglomerate; it includes boulders and fragments of the underlying clay-slates, and, when clayey, contains crystals of gypsum. The associated minerals are practically the same as at Mudgee, barklyite is, however, here absent. Black tourmaline is regarded as a characteristic associate of the diamond, and its appearance is hailed with joy by the miners.
Diamonds occur here rather more plentifully; they are colourless or straw- yellow and small, the largest weighing only 2 6/8 carats. On an average only twenty stones are found in each ton of material, and a stock of 1,680 stones weighed no more than about 140 carats.
More recently diamonds have been discovered in the tin-gravels of the neighbourhood of Inverell, and their occurrence here appears to be sufficiently abundant to justify systematic working. Cassiterite (tin), quartz, sapphire, topaz, tourmaline, monazite, etc. are here associated with diamond; gold, however, is apparently absent. Several companies have been formed, and many thousands of stones, averaging 1/4 to 1/3 carat in weight, have been obtained from the different mines; the largest of these stones weighed 3 5/8 carats. From the Borah tin-washings, situated at the junction of Cope's Creek with the Gwydir River, 200 stones were obtained in a few months, the largest of which weighed almost 1 1/2 carats; while in the Bengonover tin-washings, only a few miles away, a stone weighing nearly 2 carats was found. Diamonds have also been found in most of the alluvial tin-workings on Cope's, Newstead, Vegetable, and Middle Creeks, in the Stanifer, Ruby, and Britannia tin-washings, and elsewhere in the same district.
All the occurrences of diamond in New South Wales, described above, are in secondary deposits of alluvial origin, in 1901, however, Mr. E. F. Pittman, the Government Geologist of New South Wales, has described its occurrence in what may perhaps be the mother-rock. At Ruby Hill on Bingera Creek, twelve miles to the south of Bingera, diamond has been found in the breccia filling a volcanic pipe. This breccia consists of angular fragments of clay-stone, felsite, basalt, eclogite, etc. with calcite, garnet, zircon, chrome-diopside, and other minerals; it bears a very striking resemblance to the diamantiferous material, which fills the Kimberley pipes, the principal difference being that it shows no sign of serpentinization.
Finally, we must mention the peculiar occurrence of diamond at Ballina, in New England, where solitary specimens have been found in the sands of the seashore. The diamond-bearing deposit is here exposed to the action of the waves of the sea, and the solitary specimens found in the shore sands have probably been washed out of the deposit by the waves.
The output of diamonds in New South Wales, as published in the official returns of the Department of Mines, amounted in 1899 to 25,874 carats, valued at £10,349 12s ($1,151,463).; in 1900, owing to lack of water, and the reconstruction of the mining company, there was a smaller output of 9,828 1/2 carats, valued at £5,663 ($630,023). Although a fairly considerable number of diamonds have been met with in New South Wales, yet the other Australian States are very poor in this respect; it is probable, however, that there will be important finds in the future.
In Queensland, conglomerates have been observed at Wallerawang and on the Mary River, which are remarkably like the diamond-bearing deposits of Mudgee and Bingera, no diamonds have, however, as yet been discovered in them. At other places in Queensland, namely, on the Palmer River and the Gilbert River, the precious stone has been found.
In South Australia about 100 stones have been found in the alluvial gold-washings of Echunga, twenty miles to the southeast of Adelaide; it was here that the octahedron of 5 5/16 carats, previously mentioned, was found. In Victoria a few diamonds were met with in 1862 in the Owens and in the Arena goldfields; a larger number of stones were found in the Beechworth district of the same State, upwards of sixty crystals, none however exceeding 1 carat in weight, having been collected. Diamonds have also been stated to occur in the neighbourhood of Melbourne, in association with ruby, sapphire, zircon, and topaz.
Finally, from Western Australia also, a certain number of diamonds have come, small crystals rich in faces having been found near Freemantle, in a sand containing zircon, ilmenite, quartz, red, yellow, and white topaz, and apatite. In 1895, it was reported that diamonds had been found in the northwest of the State, at Nullagine, in the Pilbarra gold-field; many leases have been taken up, but so far no important finds have been made. From 230 tons of auriferous ore treated in 1900 only twenty-five small diamonds were obtained.
Tasmania has been also added to the list of diamond producing places. According to old newspaper reports, a large number of stones were found at the end of the year 1894 in Corinna, one of the richest goldfields of the island. The reported occurrence caused a rush of thousands of diamond-seekers into Tasmania from the Australian mainland; many companies for the exploitation of the deposits sprung up, but apparently with no marked results.
Rafal Swiecki, geological engineer email contact
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