130 The N.Z. Journal of Science and Technology. [June 
ore consisted of 44 fines,” which blocked the furnace. In consequence the 
experimental work was resumed at the request of the Under-Secretary of 
Mines. 
Two iarge samples, about 1 cwt. each, were obtained by Mr. T. 0. 
Bishop, Inspecting Engineer of Metalliferous Mines. The first represented 
the average ore being mined at that time. It consisted of a silicified 
breccia, mingled with clay rock. The chief mineral present was cinnabar 
(red) with a little metacinnabarite (black), and the accessory minerals 
were iron-pyrites and magnetite, both in small amounts only. It assayed 
mercury, 0-75 per cent. The second sample consisted of fine material, 
already referred to. It contained much more clay than the first sample, 
but was similar in other respects, and assayed mercury, 1-44 per cent. 
The solution recommended by Thornhill is sodium sulphide 4 per cent., 
caustic soda 1 per cent. ; and it was at once apparent that direct treatment 
of the ore by a solution of this nature would be very costly. If, however, 
the cinnabar could be concentrated prior to treatment the quantity of 
solution required would be considerably reduced, and the cost lessened 
proportionately. Concentration experiments were therefore made. 
Water concentration did not prove satisfactory, as some of the cinnabar 
was in a state of very fine division and was carried away. Oil flotation 
was then tried, and some preliminary tests, made in a separating-funnel, 
were very encouraging. A parcel of the ore was then sent to Mr. A. H. V. 
Morgan, Director of the Waihi School of Mines, where a small 44 Case ” 
cell, with mechanical agitation, had been installed. The chief difficulty 
was the large amount of clay in the ore. The addition of sulphuric acid, 
which is customary in many plants, did not help concentration. Lime, 
which was recommended by E. G. Stowell and W. H. Coghill in a paper, 
44 Experimental Flotation of Low-grade Quicksilver-ore ” (Mining and 
Scientific Press, vol. 120, 1920, p. 117), greatly improved the extraction, but 
it was difficult to judge from the appearance of the froth when the cinnabar 
ceased to be carried over, and the tendency was to collect a rather large 
bulk of concentrate. Caustic soda was somewhat better than lime, but 
the best results were obtained with the addition of caustic soda and 
common salt, in the proportions of 1 lb. and 2-5 lb. respectively per ton 
of ore treated. The salt, being an electrolyte, apparently caused an 
agglomeration of the colloidal clay particles, and a clean separation of 
sulphide and gangue resulted. The oil used was a eucalpytus-oil produced 
by the Tasmanian Eucalyptus Company, Melbourne ; amount, 0*25 per 
cent., or 5 lb. per ton of ore. The ore was ground to pass 100-mesh. 
The following table gives a few examples of the results obtained : — - 
Sample. 
Plllp. 
Oils and Chemicals. 
Per 
Cent. 
Per Cent. Hg by Assay. 
Per Cent. 
Extraction. 
Concen¬ 
trate. 
Head. 
Cone. 
Tail. 
By Cone. 
By 
Tails. 
A 
1 : 12 
0*1% eucalyptus + 2 lb. 
lime per ton 
7-00 
0-76 
8-88 
0-07 
81-8 
91-4 
T3 
1 : 12 
0*3% eucalyptus + 2 lb. 
h 2 so 4 
2-30 
0-76 
14-14 
0-33 
42-8 
56-6 
C 
1 : 12 
0”05% eucalyptus + 1 lb. 
NaOH 
5-30 
0'68 
10-60 
0-09 
82-6 
87-4 
D 
] : 10 
0*25% eucalyptus + 1 lb. 
NaHO + 2*5 lb. NaCl 
3-85 
1-42 
31-50 
0-17 
85-5 
88-0 
