INVESTIGATION OF MINING IN CALIFORNIA.

Otago Witness, Issue 1343, 25 August 1877, Page 3

INVESTIGATION OF MINING IN CALIFORNIA.

Last week we gave the portion of Mr G. Thureau's first letter from California referring to Hydraulic Sluicing. We now give the remainder of it, treating on Quartz Lodes and Assaying. Mr Thureau was sent to California by the Sandhurst School of Mines :—: — QUARTZ LODES. In treating of the quartz lodes of California, it is necessary that I should say something of the character of the country rocks enclosing same, in order to make, if possible, comparisons between the similar formations which occur in the richest modern gold-bearing countries in the world. It is not necessary, I opine, to give an extended geological disquisition on this subject in order to show in what manner a great difference exists, which, strictly speaking, prevents an anology to be drawn in the case, and as my instructions particularly enjoin me from doing so, I will proceed to give a concise description of thesa rocks and their lodes, pointing out the differences that exist between California and Victoria. The country rocks as observed in the above-mentioned counties and Nevada consist principally of highly metamorphosed sedimentary beds, in which pure slate or sandstone can only be observed in very limited areas. Besides these there are plutonic rocks, such as serpentines, diorites, as well as the older granites, and gneiss. Generally speaking, the rocks are much contorted, and during my perigrinations I have observed only one occurrence, near Castle Town, where the Silurian slates observe that vertical position and regularity so prevalent in Victoria ; so that, on the whole, a very marked difference exists here, which, in all probability, has also caused the quartz lode 3to become more detached, as it were, than in Victoria, for the intrusion of plutonic and the unheaval of numerous granitoid rocks muat have destroyed that regular continuity in strike which our Bendigo lodes, at least, have maintained hitherto. The " mother lode " of California, as already stated, can be traced for hundreds of miles ; but this vein, often gigantic in its extensions, after all consists of but an irregular sue cession of blocks of quartz of changeable value, and worked in accordance more or less extensively as the prospects warrant the miners so to do. Near Grass Valley I the principal lode, which has produced millions of dollars in dividends,, ! dips south in its strike at an angle of about 27 degrees, and in that respect resembles some of the makes of stone x>n the New Chum line. In this case, however, the levels disclose a length of the block— lsoo feet, by a height of nearly 700 feet — the lode being as strong, and just now richer, in the bottom levels 900 feet and 1000 feet— than those immediately above. The dissimilarity that exists between our Sandhurst lodes and it is found to be in what Oalifornians term a "contact lode," viz., that the vein occurs between the two kinds of rock of different age ; in this case the hanging wall consists of a "curly" black slate, very hard and very irregularly bedded* whilst the footwali is formed of a greenish serpentine (plutonic), which contains iron, pyrites, hornblends, asbestos, and which is besides traversed in all directions by friction planes. Owing to its containing lime which slacks in the atmosphere the greatest difficulty is experienced in timbering the levels and stopes, because the best fitted timber of any kind is subjected to an irresistible motion against the hanging wall, owing to the expansion of this serpentine. It will thus be seen that a great dissimilarity exists between the mother lode here and our Bendigo lodes. As regards the character of the quartz, there is, however, not any great difference, with the exception of perhaps the frequency of stains of copper and silver ores, and really in some of the Idaho Mining Company's stopes (Grass Valley) I could not see any difference whatever in that* mine and the west leg of the Great Extended Hustler's Goldmining Company's Mine, Sandhurst. The stone here was of the usual laminated description, and the gold occurred likewise in the blackish slate and pyrites veins ; iron pyrites predominent, however, and no arsenical pyrites to be observed anywhere. The geld is of a light yellow colour, owing to the admixture of silver, and not so coarse as in our local lodes ; its purity standing at 1000 the fineness would be about '936 or more' thus standing much lower than our quartz gold, because the Californian miners obtain but $19 per ounce, whereas the | Victorian gold is worth over $21. The Empire Company, in the same district, are working on an entirely different lode of rich ore, as the quartz is called here. They are down to the 1236 ft. level, and have the lode payable for a total length

of 2750 ft. from north to south. The underlay of this narrow lode is to the south, whilst its cap at the 400 ft. level appears to be north, and as the country rock has a strike east and west, the vein resembles the cross lodes at Staweli in some reapects ; the character of the stone is of the ordinary kind of "ribbon" quartz, and for some years past its value has fluctuated from $25 to $40 per ton of 20001b. And I may here remark that in all the mines I have inspected in that district, as well as in others, the returns shown me exhibited, if anything, higher yields of gold from the deeper level than what they used to obtain at less depth. Whether this is owing to the really admirable reduction processes' in vogue, and continually perfected on, I find it difficult to ascertain, but the quartz I have seen at the bottom of these mines was certainly richer than what I found in situ in the higher workings. This vein occurs in metamorphic sandstone exclusively, without the intervention of serpentine or any kindred rock. Turning to ,the more southern parts of California, the croppings and deep workings on and adjacent to the "mother vein," it is found that the wall rocks differ in many respects from those in Nevada County, inasmuch as nodular schists, coarse grained sandstones and extensive beds of breccias alternate with each other, observing a strike of N. 10° W., whilst the lodes maintain a general course of N. 20° E. These rocks are very nearly vertical in position, and the numerous veins traversing same are frequently exposed to a depth of from 1500 ft. to 1800 ft. beneath their outcrops, by means of the deep valleys that empty themselves into the Merced, Sugar Pine, Tuolumne, and other rivers, thus exposing the character and value of the lodes to a corresponding depth in a very unmistakable manner, and highly satisfactory to the mining community. Many of theße lodes remain unworked, though their value has been ascertained by a systematic series of careful assays, and this' state of things may be ascribed to causes not at all dissimilar to those which operate elsewhere, and by means of which the mining interest, instead of flourishing as it should do, gradually but surely decays. The mining laws of California, or rather of the United States of California, provide amongst other things that the claimant of a piece of ground shall expend in labour or appliances a certain annual amount of money, in order to secure such holding, and this leads frequently to systematic " shepherding." ,On " the. other hand, the Lands Department grants a perpetual "patent" or fee-simple to such parties or corporations as- have proved before the district or county judge that they have made the discovery, developed same, and are working, in a bona fide manner. This " patent " • frees .the owners of all restrictions for all time to come, though recently it has been decided in the State of Nevada, on the Comstock lode, that that State has a right to proportionately tax the outcomes of those mines. ASSAYING OF OBES.. With^ this digression from the subject in' hand, I will now, before concluding, advert to the question, or rather the somewhat imperative custom, of " assaying of ores," forming aa it does a'guide for mine, mill-owners, and prospectors that is never omitted. And after careful investigation, I am convinced that many valuable discoveries are made by those means, much loss is prevented, and that a great impetus is given to teat mines previous to actual work being started therein. Ore or quartz that one would not look at in victoria is frequently brought to these assayers (and I have never missed an opportunity of watching results), but the microscopical tests or assays in the wet way or in the fire prove often the contrary; so the same with tailings ; substances of doubtful character are thus properly tested, and their respective values made known. Here it is well known that the battery, blankets, tyes, buddies, &c, do not satisfactorily prove the perfection of any process of collection of gold or silver, because assays made at every stage of the process, and ultimately of thewasste residues or tailings, disclose, especially where pyrites prevail, a very considerable loss. • In j order to avoid "such loss, the " milling " of the ore, most appropriately so termed, has undergone, and is still undergoing a very great change, and superintendents as well as owners of mines are continually experimenting with new apparatus, or devising others to intercept the more valuable metals, no matter how difficult that may be at times. ' I Have already noticed and obtained particulars' of some appliances that will doubtless save gold much better than those we have now in use, and my drawings of these will be found useful in that respect. Ores, i. c., quartz, that I have myself broken out in various mines, are now, at my instance, being sampled, and, if need be, assayed, in order to show why similar quartz in Victoria could not be made to pay as well there as here ; for the Californian treatment of the quartz from the time it leaves the stonebreaker until it issues from the tailings shoot is very different to ours on. Bendigo ; and I deem it necessary that some expense should be gone into to conduct experiments, which, if successful— of which there cannot be much doubt ■ would materially increase our yields from quartz considered and proved with, our present appliances as unprofitable to work.

The Governor has appointed Dr Skae to b*> Inspector of the Lunatic Asylums at Auckland, New Plymouth, Napier, Welling, ton, Nelaon, Hokitika, Christchurch, and Dunedin,