600 
a sence of calcareous tufa, is quite erroneous. Hot waters issuing from volcanic rocks 
usua ly deposit siliceous sinter, and that alone, the lime being carried off in solution by 
t le waters, and usually present in veiy minute quantity. Calcareous deposits under 
^c eircumste.nces are rare exceptions,* and not the rule. The facts described in your 
Keport seem to offer conclusive evidence in favour of your theory.” 
As has already been mentioned, numerous dykes of diabasic doleritef intersect the 
country-rock. Hot one, however, is met with in the auriferous deposit. Had the latter 
been merely the siliceous skeleton remaining after the removal of the pyrites from the 
pyritous quartzite, the dolerite dykes would still be present to attest the original identity 
o the two masses. But there is at least one clear instance of a dolerite dyke intersecting 
country-rock (in No. 1 Tunnel, one hundred and twenty feet north of the 
shaft sunk from No. 5 Floor) and not intersecting the overlying sinter (in the south 
branch of the Freehold Tunnel, only thirty-five feet higher) ; showing that the sinter 
and ironstone were deposited on, and were not altered portions of the pyritous quartzite 
country-rock. It is hardly credible that the highly auriferous siliceous and ferruginous 
material now being worked represents merely a weathered condition of the pyrites with 
w ich the quartzite country-rock is so highly charged, and which is so poor in gold. 
gain, the fact that the sinter is mainly a hydroits silica is an argument against its being 
the skeleton produced by the solution of masses of pyrites from an anhydrous quartzite. 
Tor some distance around the Mount, the country -rock is frequently impregnated 
With aluminous, sihceous, and ferruginous material. Some portions of this rock were 
Bo far gone that on my first visit to Mount Morgan (1881) I imagined them to represent 
eposits from the overflow of the thermal spring, an idea which I have since abandoned, 
at oug it is likely enough that the influence of the thermal spring may have assisted in 
the decomposition of the adjacent rocks for some distance, and some of the easily soluble 
mineral matter may have percolated into the superficial portions of the adjacent rocks. 
The gold of Mount Morgan is probably the purest that has ever been mined. 
Dr. A. Leibins, of the Sydney Mint, says it assays as high as 997 per cent. The gold 
^ process of chlorination, but its recovery from the recently discovered 
ao in ores J has proved to be a much slower process than its extraction from the 
siliceous and ferrnginous. 
_My reasons for classing the Mount Morgan Gold Mine as Tertiary are the 
rollowing : — 
That the deposit left by the thermal spring is newer than the altered stratified 
rocks through which it has burst is obvious ; and that it is even newer than the much 
later date when the dolerite dykes filled up fissures in the stratified rocks, is proved by 
the fact that the dykes are clearly seen in some instances to be covered over by the 
siliceous, aluminous, and ferruginous deposits of the spring. 
But yet another circumstance helps us in our endeavour to ascertain the age 
of the outburst of the Mount Morgan hot spring. About a mile to the west of the 
•mountain ’ is a mass— apparently about one hundred and fifty feet in thickness— of 
horizontal bedded sandstone, undoubtedly the ‘ Desert Sandstone.’ It rests, apparently, 
at this point, on a mass of diabase, but in other places it may be seen lying on the 
upturned^ edges of quartzite and greywacke strata, similar in character to those of the 
country around Mount Morgan. The base of this Formation is a fine volcanic dust. 
The upper beds are coarsely gritty, and for the most part siliceous, varying from white 
* The Einasleigh Thermal Spring is one of the exceptions. See Chapter xxxvi. 
T See Notes by Messrs. Edgeworth David and Anderson above quoted. 
. . ores, I understand, rarely exceeds thirty per cent, of the whole, 
being siliceous sinter. 
the remainder 
