Opalton and Mayneside Opal Fields 1902

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Geological Survey Office,
Brisbane, 1st May, 1902.
The Opalton Field, often called the Fermoy Field, is about 100 miles
further north. The nearest raihvay terminus is Winton, from which the field
is situated in a direct line 60 miles S.S.W., but it is almost just as easily
reached from Longreach. This field is also in the Opalton Mining District,
on Warnambool Downs Run, the mean rainfall being 12 inches, and the
minimum 3·5 inches.

The Opalton deposit, which was one of the largest and most extensively
worked in Queensland, was discovered m 1888, probably by some stockman of
Warnambool Downs finding opal on the surface. The gem, however, was
found before this date at Horse Creek, some ‘.!8 miles to the south-west, which
deposit was being worked in 1888 opal-mining of any importance was done at Opalton until 1893, when
some specimens were brought to Fermoy Station, and a man named McLenan
went out and commenced operations at what is known as the” Brilliant Claim.”
As a result of this first activity about £800 worth of opal was obtained.
Other finds were made, and Conway’s Claim was discovered in 1895, and a
small rush took place. In 1896 there are said to have been between 500 and
600 men on the- field. The rush was partly due to the good seasons prevailing,
and with abundance of horse feed and water available, the township was in a
flourishing condition.
The value of the total production is a matter which can only be guessed
at, but it would not be very far from the mark to ~ay that it must have been at
least £30,000 or £40,000. The field, however, is now practically abandoned
and, save for a few old residents, the township is deserted.

The police have been recalled, and there are not more than eight or ten
miner8 living at the old camp. A good many of them are engaged in searching
the old mullock heaps for stray stones. ‘l’here are several outlying prospecting
camps for which Opalton still forms a centre, but the whole number of miners
engaged in the district is only about forty-five.
The topography of this field is very similar to that of J undah, and the
shafts, which are of about the same average depth, were sunk through a similar
soft sandstone to the clay beneath. Boulders are found in the sandstone,
and weathering out on the surface. The greater proportion of opal was won
here from the old flats just to the east of the township, where the workings
or mullock heaps cover from 10 to 70 acres, and different portions of these flats
are known by various names of local significance. One of the richest claims
was probably that, known as the “. Little Wonder,” and the flat in this vicinity
for 8 or 10 acres is practically all worked out. The Little Wonder Claim
yielded opal to the value of £4,000.
Most of the mineral at Opalton occurred in the ordinary sandstone band,
but the “brick pipes” and ” pencil band” of the J undah Field were al8o found.
Numbers of other claims lie to the east of the Little Wonder, amongst others
the Brilliant, from which the first gems were won.
Conway’s Clairn is about a mile from the old flat towards the east and
south, and was a very rich deposit. Nearly all the mineral was found in one
claim, which is now surrounded by shafts which extend over nearly 3 acres.
The Bald Knob Workings are about 4 miles east of Opalton, and at present
two men are engaged there. A good deal of work was done here some years
ago for an output of £1,000 worth of opal. A great deal of common opal or
“schnide” was also obtained, some of it, though opaque and cloudy, being of
very fine appearance. A parcel of it is said to have been sold and sent
to Germany for making beads.
The Opalton miners have all been following the occupation for a number
of years, and most of them are provided with a lapidary’s wheel, wherewith
they cut and polish their gems. The field is dependent for its water supply
on the waterholes of a small creek which drains into Blue Bush Creek, a
tributary of Vergemont Creek, the waters of which flow to the Thompson River.
The supply from these holes is very poor, having at different time~ completely
given out, and water has been carted as much as 14 miles.
A number of Opalton miners recently determined to examine the country
to the south of Opalton, and for this purpose moved their camps to a place
called Mayneside, an old out-station where there is a large waterhole, and
where they intend to work in the vicinity of Horse Creek and Hyde Park
Creek. Not much had been accomplished up to the beginning of December
last, but it was hoped that with the season of storms approaching they would
be able to operate in a number of localities where work was carried on some
years ago.
The Horse Greek Mines are 25 miles south of Opalton in a direct line,
Horse Creek being a tributary of Hyde Park Creek, which runs into the Mayne
River, ultimately to the Diamantina. As already stated, this is the locality
where opal was first discovered in this district, probably the oldest mine
being that known as Cragg’s Mine, worked in 1888. The Poison Mine,
Carlyle’s Mine, and several others in the vicinity of New Year’s Creek are
about 7 miles further south.
The waterhole at Mayneside forms a convenient base from which these
may be reached, and where there were from fifteen to twenty men camping in
December last.

The Desert Sandstone rests horizontally, and with unconformability, on the
lower Cretaceous r0cks or Rolling Downs Formation.
Of the latter, Mr. Jack has stated* that it marks the position of a sea
which, in Cretaceous times, divided the Australian continent into two islands.
As will be seen from the geological map, it covers an area which may be
roughly stated at three-fourths of the total extent of the State. It extends
westward from the Paleozoic Range on the east coast, from near the heads of
the McIntyre in the south, to the Palmer in the north ; west of this line it
occupies the whole of the State, save where it is unconformably overlaid by the
Desert Sandstone, and where the Paleozoic rocks of the Cloncurry and of
De Little, Cairn, and Grey Ranges rise from beneath it like islands.
Westward and southward it extends across South Australia into Western
Australia and New South Wales, but except in Queensland it appears to be
covered to a considerable extent by tertiary rocks.
As follows from its mode of origin, the Rolling Downs Formation consists
of a series of sandstones, shales, and other sedimentary rocks.
Of the Desert Sandstone Formation, Mr  Tack states that, after the Rolling
Downs Formation had been laid down in the comparatively narrow sea which
connected the Gulf of Carpentaria with the Great Australian Bight, a considerable upheaval took place, and the denudation of the Rolling Downs Formation followed, and must have gone on for some time.
Unequal movements of depression then brought about lacustrine conditions on portions of the now uplifted bottom of the old deep-sea strait, and
in other portions permitted the admission of the waters of the ocean.
Finaliy a general upheaval placed the deposits of the period just concluded
in nearly the positions in which we now find them.
There is abundant evidence in Queensland that the upper Cretaceous
rocks of the Desert Sandstone Formation must at one time have covered almost
the whole of the Rolling Downs Formation, and occupied a similar area of about
three-quarters of that of the whole State, or 500,000 square miles.
Its denuded remains now occupy less than the twentieth part (25,000
square miles) of the area over which it originally extended.
The remaining portions of the Desert Sandstone are now only seen in the
form of low ranges, tablelands, and isolated fiat-topped hills, and such areas
of the formation occur at frequent intervals, chiefly within the limits already
defined in the western portion of the State. There are also other small
detached patches and a large area covering the greater portion of the Cape
York Peninsular.

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