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C.—3

Humboldt describes a vein carrying cinnabar in Mexico in pitchstone porphyry, also other occurrences of the same ore in the eruptive rocks in that country. Cordazar states that the quicksilver ores of Mexico are everywhere found near the eruptive rocks. In Peru it is found in trachyte, near Cajamarca, and again at Avaviri. In America deposition is going on from the highly-heated waters of Sulphur Bank, California, and at the Steamboat Springs, Nevada; a hot stream also issues from the workings of the Valley Mine ; also hot moist gases emanate from certain workings of the Beddington Mine. At the Manzanita Mine, Colusa County, very hot springs exist a few hundred feet from the deposit, which itself contains free sulphur and other indications of solfataric action, though there seems to be no lava near by. In Mexico, also in the Guadalcazar district, free sulphur is associated with cinnabar. In Peru cinnabar is found at the Baths of Jesus, and close to the famous Huancavelica Mines are extensive hot springs. The above is given to show that there is a similarity in the formations where quicksilver is found in other parts of the world and that at Ohaeawai, where the basaltic rock joins on to the sandstones, and it is near the contact where the cinnabar deposit is found; here also it is not only seen in a vein or lode, but also the decomposed sandstone is impregnated with it in many places. There is therefore a probability of sufficient cinnabar being discovered to pay for working were it not for the obstacles there are to be encountered —namely, highly-heated water and the large emanations of dangerous gases. As to the composition of these gases, they have never yet been analysed, but in all probability they will be found to be a mixture of carbonic acid, carburetted hydrogen, sulphuretted hydrogen, and possibly nitrogen. These gases seem at the present time the most plentiful at the southern end of the company's workings. It may also be stated that G. F. Becker, who is well acquainted with the quicksilver-mines in America, says that he does not know of a single producing district in California and in other States where bitumen has not been found with cinnabar. Taking all these into consideration it is very questionable, if even a good cinnabar-lode is found at Ohaeawai, that it can ever be worked at a great distance below the surface. At the same time there may be a good deal of ore near the surface that could be taken out, but sufficient prospecting has not yet been done to prove whether that is the case or not. It may be as well to state that, should the workings continue to be carried on from shafts, great care will have to be exercised in making sufficient provision for the health of the workmen employed, and frequent inspections should be made to see that this is properly attended to. In regard to the origin of ores containing quicksilver, G. P. Becker states that in any one quicksilver-bearing region, such as the coast of California, or Inner Austria, it is difficult to avoid ascribing a common source to the ore. This source cannot be ascribed to the adjoining rocks, for they are most various ; on the other hand, granitoid rocks seem everywhere to underlie in the superficial more heterogeneous formations within a few miles of the surface. The evidence is overwhelming that in many cases quicksilver ores were deposited from thermal springs of volcanic origin ; and the analogy between the deposits is so great that, in the absence of positive evidence of a different origin, the probabilities are in favour of the hypothesis of a similar origin for all of them. This does not imply that all quicksilver deposits are of the same age ; those of Almaden, for example, seem to be far older than most, or perhaps any, of the Californian deposits. Assuming that the quicksilver ores have been deposited from hot springs due to voleanicism, it would seem that cinnabar might be classed as a volcanic emanation. In that case, however, one would look for this ore as the component of lavas and in craters. It is not certainly known to occur in this way, and if it exists in this association it must be very rare. It seems to follow that the volcanic springs must have leached the ores from deep-seated rocks of very wide distribution— i.e., either from the granitic masses or from some unknown infragramitic rock overlying the foci of volcanic activity. With reference to the cost of extracting mercury from its ores, this is a very cheap process ; instead of using the old-fashioned method of extracting it by decomposition in retorts by lime, the continuous fine ore-roasting furnace is now generally adopted. What is known as the Granzita or Hutton and Scott Purnace is the one now generally adopted. This furnace holds 45 tons of ore, and 36 tons are passed through every twenty-four hours. In working this furnace, 1 ton by volume of the spent ore is drawn alternately from each side every forty minutes, 2501b. being taken from each draw-hole, and a charge of 2,0001b. of raw ore and 201b. of coal is let down into the furnace. The firing is attended to every hour, three 4ft. lengths of good firewood being ordinarily added to each side of the fireplace during that period, and from one and a half to one and threequarter cords of firewood is thus burned every twenty-four hours. At the new Almaden Mine, in California, the average amount of mercury in the ore treated is said to be 1-66 per cent., and the cost of treatment per ton of ore is about 2s. Bd. It will be seen from this that the process of extraction is comparatively an easy one, and that very low-grade ores can be made remunerative if the cost of mining could be done at a reasonable rate; but the latter is the question which greatly affects the working of the cinnabar deposits at Ohaeawai. Judging from the quantity of mercury that has been leached out of the ore and condensed on and near the surface of the ground there must be a considerable deposit in the neighbourhood; at the same time, if it is at any great depth, the value of the deposit is not likely to compensate the company for the cost of extraction ; besides, the heat of the ground, together with the large quantity of gas, and, possibly, mercurial fumes in places, will make it very injurious to the health of the workmen employed. Annexed is a sketch-plan of the different workings and pools where the cinnabar deposits are at present being found, which will enable the report to be more clearly understood.