THE FORMATION OF QUARTZ REEFS.

Inangahua Times, Volume X, Issue 1503, 30 January 1885, Page 2

THE FORMATION OF QUARTZ REEFS.

[Lake Wakatip Mati, Jax. 1. ] j On Friday evening (Boxing Night), ■ Pi-oftasor Black gave the first lecture j of the course to over 50 students or i hearers. H^ sai:> h- regretted that lie was obliged to cL'li\e<- his lectures here dining the holidays; luit he con Id not m-tke any other arrangements and, as miners geu. rally took a great interest in the sul>jects to l.c dealt j with, lie intended to go to Skip- [ i pers for a few days and then to i ! Arrowtown and Cromwell. Nm-«t » j 'Ju-less, the time at his disposal was so short tluit his discourses won'd only * lip, as it were, skeletons of the soli- | { jects whi.-h would In- dealt with. The main subject that evening would be , that of the origin of the formation • of quartz reefs, aid the introduction of gold and other ores into them. i The If.-tnied gentleman Maid that 20 years a.:o comparatively nothing was known of this formation. Some . geologists Imd said that it was owing , j to molten massess Iteing forced up from . j bo low through the npeuiu<rg of earth's ; cnist; and others asserted that the deposits were made during the glacial period. They had (irst to get over the difficulty of the theory of crevices in the earth's crust, and then the rest r would be eapy. When a hot matter ' cooled down it generally shrunk, as it also did when drying. The direction of these crevices was usually in a , straight line for miles— oftentimes, as ' it weie, a line or chain in the forms of pentagons and hexagons. Still, there was the question how were these crevices kept open aftei the shrinkage of surrounding ground, and that was ' the real difficulty to solve. Still, if r mica schist were to form, it might : solidify so strongly as to maintain the s crevices — and it was quite possiMe » that while it shrunk it mi^ht open up - such crevioes. However assuming 1 that these crevices were kept open, t the lecturer went on to explain the . theory of the formation of quartz [ reefs. &C., now universally received S>y s such geologists as have a thorough ■ knowledge, of chemistry. According ! to this theory the quartz — whi.-h was another name for silica or silicic acid — now formed in the reefs previously , existed in the mica schists in the form i of silirates — that is, it existed not as quirtz, '>ut was combined with metal lie oxides, of silicate of iron, silicate of maganesp, silicate of lim<*. I,i tl t j s coir -try we had little else than mica, its base being sili.-ic acid, although it was composed of various oxides. When two acids came into contact the stxonj ger Ht-id, got the l>ase. That supe ior { acid, in the present instances, was ! carbonic acid, of which ev<-ry 10,000 gallons of water contained four gallons, — in tact it existed more or less in onr outward broathing, in all animals, in coal, &o. In the process of quartz formation the carbonic water j dissolved the water percolating through these mica sdiist ro>:ks, and decomposed the silicates as it travelled -along, then formed carbonates aiid liberated free silica or quartz. The free gilica thus produced was to some extent, soluble in water, and was canif d for ward in solution, till the water arrived 1 at the walls of some previously existing ' crevice formed by the shrinkage { alluded to, of the wet rock drying, or, * more probably, of the heated rock { slowly cooling. Here the water stopped ( nntil slowly dried up or otherwise disap ] peared, leaving a contri'mtion of silica on one of the walls of the crevice. s This silica hardened, and by the f gradual process mentioned ultimately * accumulated into the quartz reef* we r now tit id. This was the chemical c theory of the formation of quarts reefs c universally acknowledged. 8 The learned lecturer then went on i F to explained tin !uW»t theory fteoepfte^ .

as to how gold came into the quarts and qnartz reef* will oi.lv dissolve — or is \p\f salable in water containing chlorine in solution, *nd it then l»ecomes chlorine of gold! If, therefore, cli'orine be assumed to liavf existed in the five stat« ia the water percolating through the inici schist it \vi>nld dissolve anyrrold forttnl there, and the water would carry it lons w 'th the dissolve. i »ilic--i into th i reefs. There were only two processes^ ky which gold came into the reefs." Firstly, it required' table salt, or chloride of sodium, ami saltpetre. Tlte enormous quantity of salt in th« sea— which was becoming salter every day— was proof that chloride of sod inn. existed in abundance in the rorks at some previous period in the. earth's history, and had been carried dovn to the sea by streams, fcjnlphar was also found in consideruMt. quantities in the rocks that contained sold, aud sulpunr when oxididisedkrmedsulphurine acid, which again acted on the chtorido of sodium (table salt) to form muriatic acid. This acid, acting o>i the higtu.* oxides of manganese, it »as well know i fonii.-d chlorine, and chlorine, as aHov* sut.d, dissolved «oU TUv?**r!ie<l hjetutyr said he beliewd thai h* wai Mi? fiist who Jiti] pn.j.otvdod th» latter p.n-tio'i f.f this th-o;-y, and. if a-k.'iJ i?i .\ mi.. a sohis; country, abont th«« probabilitii-s of tlie existence of gold, he would docid d!y say if mang.mcse wen* piesnut there'would be. g-»ld. The existence, therefore, ot oxides of m mj,M!ies« and ofs.ilphidrs m qou-rz ixcfa in a mica schist country was ;\ st on:; i;i<lic»tijn of g>ld in such r^%-fs. This view was strongly eon-HriiM-d by his recent experience of the mini's at tlicßtue S;) -ir, Tia ; >eka,. and at Nasel.y, for every claim there contained oxides of iii:vga3eße. Tba qiestion was— ls tliis maujjinejie to Iv fruind oxer th** rest of the country ? It was of a violator bountiful pink tint. Nevertheless, rhe louitry was full of manganese, which made i-hlm-iue. He saw it on the top of Ben Lomond that day, i"d had little .i.nbt it was to ba found in the rocks all over the Wak«tipn. Pratic.il miners generally asser-t«-d that where there was sulphnr there would he found gold ; hut sulphur wa< a link which dragged or precipitated the gold into the rerfs— althongh th* •nica s.hist rock only contained, the hundredth part of a grain of gold, (interesting experiments were here made showing the effeit of sulphate of iron on a pinCH of lraf-gold ; also showing the properties of oxygon, of which nearly one half of the whole earth "*aß composed ; also experiments with silicic acid, hydrogen gas, sod nm. «fee,, and demonstration of the cause aud efft-ct of fire-damp in mines.) The a'-ove is a brief report of ihe lecture, during the delivery of which the lecturer whs repeateily applaadtd.