599 
from the south-west nearly to the Crown Shaft, and the Gtrass-tree Tunnel (about 
seventy feet below the level of the I'reehold Tunnel) is driven from the south-east to 
the Crown Shaft.* 
The upper portion of the mountain consists of a deposit varying from red an 
brown haematite on the one hand to a frothy, spongy, cellular, siliceous sinter on the 
other, dfine gold is disseminated throughout the mass, but it varies considerably in 
richness. So far as the upper excavations show, the auriferous deposits are bounded to 
the south-west by a large kaolinised granitic dyke, but on No. 3 and No. 5 liloors the 
dyke intersects the auriferous deposits, some portion of the latter being found on its 
south-west side.f At the eastern end of the auriferous deposit, on the other hand, there 
are immense quantities of kaolinised rock, “ rich in gold — i.e., from i-oz. to 22 ozs. to 
the ton.” (Manager’s Eeport, 1st June, 1891.) No. 1 Tunnel discloses immense 
quantities of highly pyritous quartzite country -rock. Indeed, there is more pyrites than 
quartzite. 
Possessing (as will be seen from any plan of the workings) none of the 
characteristics of a “ reef,” as the term is generally understood, it becomes necessMy 
to seek for another explanation of the origin of the auriferous deposit. I am of opinion 
that the gold must have been precipitated in the ferruginous and siliceous sinter 
deposited by a thermal spring, which, charged with chlorine, dissolved the gold from the 
pyrites of such reefs as the “ Mundic Reef,” and from the pyrites with which the 
country-rock beneath and around the summit of the Mount is abundantly charged. 
Even if the gold was present in the pyrites of the country-rock in a very infinitesimal 
proportion, it might be collected by a thermal spring from such pyrites over a wide 
iirea. , . 
The occasionally angular condition of the sinter, and the tumbled condition of 
the ironstone masses (as evidenced by the deflection of stalactites from the vertical) 
would appear to indicate that explosive discharges of gases or steam occurred at 
intervals with sufficient violence to disturb the deposits accumulated by the thermal 
spring. 
Mr. A. W. Clarke, of Charters Towers, late Government Mineralogical Lecturer, 
has favoured me with the following Note on some speeimons from Mount Morgan - 
“ A very large proportion of the substance is soluble in strong potash solution, 
the residue being nearly pure crystalline silica. This is what ought to be expected of a 
siliceous sinter, as, of course, the silica would be hydrated and colloidal, and the presence 
of some quartz (or crystalline silica) in it is quite conceivable.” 
Mr. Walter H. Weed, of the United States Geological Survey, who has made a 
special study of the wonders of the Yellowstone National Park, writes me I as follows: 
“ The specimen of sinter which you enclosed is too small for satisfactory examination. 
It bears a striking resemblance to certain rhyolitic pumices from the Yellowstone, but 
lacks porphyritic crystals, while your observations regarding its occurrence render such 
an origin impossible, while another proof is easy in complete analysis. The sinter is 
not quite like anything in our collection from the Yellowstone, Iceland, or New' Zealand 
districts. It appears, however, to be a good sinter, and its vesicular or frothy nature 
indicates that it was formed at the surface. As to Mr. Cameron’s remarks (quoted on 
p. 5 of your Report of 1889), his objection to the thermal spring theory, based on the 
* An account of later workings and developments will be found in the W riter’s “ Third Keport on the 
Mount Morgan Gold Deposits.” Brisbane : by Authority : 1892. . , , m 
+ This is also the case in the “Freehold Stopes,’ a few feet above the level of the Grass-tree Tunnel. 
See “Third Report.” 
f In a letter dated 27th November, 1889. 
