100 
GAYNDAH GOLD FIELDS. 
MOUNT SHAMROCK. 
This o-oldfield is a comparatively new field, and its output appears for the first 
time in 1877^ as 3,348 oz. of gold from 3,151 tons of stone crushed. In the same year 
5 tons of bismuth ore were exported. , j. 4 . 
Mount Shamrock is a low hill about 145 feet in height above the level of Didcot 
Creek, which runs at its foot on the eastern side. The hiU. consists almost entirely of a 
dark-coloured massive slate, which is intersected by dykes of porphyry. It was on 
the summit of this hill, close to where their shaft now is, that the prospectors firs 
discovered the gold in a piece of iron-stained stone lying at the surface. 
Mount Shamiiock Prosuectino Claim. 
In a shaft 30 feet deep “ the following materials were passed through, in the 
order mentioned, in layers, all of which were dipping away steeply to the east 
“1. A breccia consisting of angular fragments of a fine-grained aluminous and 
siliceous rock, cemented together with a hard cement of oxide of iron and silica, 
throughout which are numerous blebs of quartz. 
“ 2. A yellow oclire coiitalning a fair percentage of oxide of bismuth. 
“ 3. A brown iron ochre with veins of crystallised glassy quartz running 
through it. „ , , i i 
“ These ochres form the principal part of what has been passed through in tne 
shaft. The two together must be at least 8 feet to 10 feet in width, and they contain 
numerous veins and bunches of oxide of bismuth. 
“ 4, Earthy red Inematite, with siliceous veins containing also broken particles 
and blebs of glassy quartz. _ _ 
“ All these materials contain gold in considerable quantity, the gold in some 
places being beautifnlly crystallised. 
“ Much doubt has been expressed as to the nature of this deposit. Both from 
the character of the stone and the regular manner in which it strikes and dips, I 
am of opinion that it is a lode, the breccia being formed by the breaking up and 
subsequent cementing together of particles of the walls and matrix of the lode. 
The fissure in which the lode is formed appears to have acted as the channel for 
the passage of water of hot springs to the surface, for all the materials, the 
crystallised gold, the hard siliceous and iron cement of the breccia, and the ochreous 
materials are such as would have only been formed by deposition from solution 
in water. _ ^ i f 
“ The gold appears to be especially associated with the bismuth, tor the veins oi 
oxide of bismuth are exceptionally rich. A small sample of the oxide assayed by 
Mr. Hamilton contained 62 per cent, of metallic bismuth and 252 oz. of gold per ton o 
the material. , , i 
“ A dyke of white felspar-porphyry can bo traced down the hill from a poin 
immediately south of the shaft in a west-north-west direction. It is very probable that 
this dyke may have influenced the richne.ss of the lode at this point. 
“ 111 No. 1 and No. 2 North small quantities of gold have been found associated 
with the porphyry dyke. , , , , , . a 
“ Mount Melville consists of massive blue slates and hardened sandstones, 
intersected by dykes of felspar-porphyry of a similar character, and probably » 
continuation of those met with in the northern part of Mount Shamrock. A 
