PRACTICAL MINING.

Inangahua Times, Volume II, 17 September 1880, Page 2

PRACTICAL MINING.

I — Lode Mining fob Gold. ♦ (Prom tlie Sydney Mail, July 17, 1880.) Regarding the formation of gold itj lodes {titce alt oilier metallic lodes) there is great diversity of opinion ; and no theory yet advanced has been able to explain all the phenomena met with in lode miuing. Precipitation, Infiltration, -Segregation, Galvanism, Sublimation, Plutonic action have all been ably handled, fiufc the generality of cases point to t>nb;> li:n-ition and pluton ; c actiou- That Ga'«. r:ini?tn TnQ' ; ration, Segregation, amf L Precipitation may each have foiraed "• mineral deposits will be readily admitted, but a large shaie (if not the largest) of (he lodes must be allowed to +.lie former at the present state of our knowledge, ! , and it will not matter here materially 1 how Ihey have been formed, but how we find them and Low, to treat them. In some lodes the gold is found as« gociated with oilier ores, sucU as silver,

copper, lead, and antimony, while in Australia, California, &c, what may be termed true gold lodes are most prevalent, matrices being qusr'z; yet there are cases where the gold is found in. slafe dis« jointed from quartz,— in granite, serpen* tine, and sandstone, also in calcspar, bat this occurs as an ingredient of a qaarfz lode* The instances in which the sold is associated with slafe may be noticed at Murray Creek, Inangabua District. New Z .-aland,— at Roomeruka, Sandhurst District, Victoria, and several other places, but in the two places above-mentioned it is of such prevalence and so remarkable in its occurrence as to be cnlled a para* dox, making those place? noteworthy for the study of its formation. In serpen* rice, it his been found in Queensland some years ago. on the Hn(phk?n?on, in Victoria, and also in New Soulh "Wales (at Gundagi) near the Murray. In ser« pcnlinous slate it has been met with in (he Serpentine and Molyneux River, Otago, and Collm^wood, Cook's Straits, New Zealand. It occurs in grnn'te in Brazil. Queensland, New Soulh "Wale?, and other places. In these latter rocks it is comparatively free from sulphides, but oxides and peroxides prevail in them, especially of iron. In the case of " Mur« ray Creek/ the auriferous rocks which contain the quar'z reefs rest on granite, and are lower Silurian, and some of the upper members of the Upper Silurian, the lower members of the Upper Silurian beiDg " warning." Those are overlaid br "oullayers" of Tertiary formation, t'e lower Bfrafum of which is invariably " Arcose." For several inches, and even ia places for several feet, spangled gold pervades this, but does Dot rise to any height in it ; this has usua'lv been called cement by the miner, and from it n 11 Cement Town " sprung up. The slate on which \hh rests stands on*edge, and lips been proven to be auriferous to some depth. A trinl crushing has given 8 dwts. of gold to the ton. with good specimens where obtained, but no decidpd course being visib'e all the sla'e had to be taken, which brought the yield down to 4 dwts. to the ton ; the crushing being expensive, and the workmen uninitiated in such work with nothing to guide them, it was abandoned. At Ecomeruka, Sandbar?*, Hie gold is identical wi'h that at Murray Creek, being found in flikes in the jointa of the slate, especially when oxide of iron veins run through the latter. The ser« penline, in Queensland, has been wrought by the alluvial miner with good results ; and so long as the serpentine wis decomposed it could be manipulated wilh the *' pan," and to no greater depth hag it been proven here. Whether the serpentine of Hew South Wates will prove productive the future will tell, but there are hopss of its doing so, a3 well a3 quartz lodes, if once understood. The granite ha? not yet been wrought by milling either in Br.izil or these colonies; there can be scarcely any doubt but that come of the gran'fe? ia tbe ,New England and Clarence districts will eventually give satisfactory returns if properly taken in band. Our present attention has to be directed to tbe lodes or quartz reefs, which are our present known stores ; therefore, prospecting for reefs will be the first nolicsd. To prospect for " re rfs "it must be the first asprtained, what nre aur-ferous rocks ? where are they situated— and how ate tbey to be distinguished from those which are not gold bearing ? Tbe first question may be summarily answered thus :■— Srranite i 3 in certain countries and in certain localities auriferoai, bufc tbe older or inferior stratified rooks, especially the Siluran formations, are the most predominant in gold bearing ; yet there are Ciises where secondary rocks are auriferous, ns in Virgl i Unifrd States, America, both in Jurassic rnJd Triassic. In all cases they are resting on granite, no auriferous rock* intervening between the gold-bearing and tbe ennite. Micaceous, Ferruginous, Aluminous slates are most promisiug, while Talcose* Cwboiiaceous, Calcareous and Felapathi© slates have not proven so. The second question is more didlcalt to answer, for their occurrence is often most abrupt and isolated : but as a general rule they are principally found flanking the western slope of any chain of mountains wlio.'e course is north and south : or nearly so. If branches are " thrown off" from any bucu mountains, tbey are, as a rule, more productive tb:m when the main chain is goldbearing strrta ; consequently, more likely to contain more auriferous lodes, thus giving an idea, that tbe " cross " disturbing force ha* exerted some influence on the productiveness, Tbe third question is partly answered by the first, provided it i? understood what these rocliS are ; that porphyry grit or arcose are not laken for granite, and one class of elates confounded with the other. If fully under* stood tl eir position is a feature of cote, If they are titled at a high angle, almost vertical, or even virtical, it is favourable to the formation of lodes. Not so if they are resting at a low angle, in which case the lodes are ;as a rule, very irregular and confined, while in the first case the best defined lodes are met with. Nest, observation must be directed whether quartz is present, either in fragments or whether the rocta are permeated by it and ulso the nature of the quartz. An ac« cuistomed eye will easily distinguish '• noblo " >fioin " barren " quartz, for there is not only a chemical but also an optical dii Terence. Barrou quartz is, as a rule, highly crystalline often transparent or seuii-tr.-iiisparent, devoid o fsulphidps and their productive oxide?, is tnosth' hoinegfneous, not seldom impregnated by mica or talc fluxes, the former foi'rning " Aventurine," the latter givinw the quartz a silky spotted appearance. The " noble "quartz is generally (near the surface) charged, with oxides, especially of iroD, bafc

Lts having been decomposed, whne below thesurface.especially the • water leveU wta* theaclionofcorrononisnotßorapdtboße sulphides .re in the* normal ■ tato. Its badness seems to be less than the ba on, . owiixr to the molecular arrangement of \ crystlllisation having been impeded by those ingredients of which the «■ barren "is void, hence it is more friable. The above are general rules, but there are local rules, where a " set" of productive lodes differ among themselves ; only cevtam of tbetn proving fit for working 00 the levels yet obtained, while others may in depth prove r equally productive. Yet, oa ilia surf ace, the the miner acquainted rith tbe field, will condemn a reef by certain peculiar features "observable in the locality, in which he may be correct, but when he comes to a new field may prove fallacious; what Ins former experience taught him "no goo<l " may here be as " good." Therefore, he hai to study the local peculiarities. To move fully illustrate this, it need only be mentioned that reefs found in Victoria, West Coast and Otago, * New Zealand, •• capped" by sulphide of antimony, are invariably parable, wbJlein New South Wales such favourable indications have not been met with as in the foregoing localises. If a belt of " country "as above described is found to exist, ihe next thing to be done before actual worts are initiated »lo prospect, is to prove tbe existence of gold in it, wbich is performed by using the hammer, usiug it well,— on all quartz or quartzose rocirs, and carefully examining with the ere and glass, awd should Ibat not give satisfaction the " pnn " should be resorted to 5 and not only the pounded quartz but also the coil should be carefully tested, and each rebowever snuv 1 !, be taten noteof, whether tbe gold bns bran subjected to auv abrasion whatsoever, whether it is raved, or flat rough slabs, or combined with quartz (specimen). If the latter is the case (he nature of the quaWz ha 3to be taten notice of. If tbe gold is in Ibe least abraded, it is „ evidence of i<9 having been movod, and the greater tbe abrasion the greater the distance from its present position to the place of its original site. i-