KEPORT ON THE GEOLOGY OF THE THAMES GOLDFIELDS.

Wellington Independent, Volume XXII, Issue 2591, 31 October 1867, Page 4

KEPORT ON THE GEOLOGY OF THE THAMES GOLDFIELDS.

DESCRIPTION OF COUNTRY. The tract of country at present open to Europeans for gold prospecting in < lie Thames commences at the mouth of the Kaunerangii river, and runs iiorlh for about nine miles, as far as the Tuta Creek, with a breadth of about four miles ; thus making the total ami open about thirty -six square miles. The whole of the country is much broken ; rising, except at the mouths of four of the streams, into hills at from 000 to 800 fool close to tlic sea, and increasing in height, towards the eastern boundary of the block, to more than 1000 feeet. The country is for the most part covered with dense bush, except where close to the sea ; aud the streams aro all mountain torrents, with largo boulders occupying their beds. GEOLOGICAL STRUCTURE. The geological structure of the country is very simple, being almost entirely composed of a huge mass of trachytic tufa, resting on palaeozoic rocks, which are cut by numerous dykes, mostly of diorite, but occasionally of tachyte. This tufa appears generally as a softish grey coarse-grained rock, weatliering white, and sometimes much stained with, peroxide of iron. "Where cut by dykes, it is hardened for considerable distances, and much altered in appearance. As might be expected, hotvover, from its origin, it varies a good deal in character; often containing rounded blocks of diorito one or two feet in diameter; indeed, in three or four places it passes into a true conglomerate, while occasionally small angular stones are seen in it, forming a breccia. These latter, however, are very local. Near Hongilcori the rounded bloelcs of diorite aro encased with a coating of red jasper. The rode is also traversed by numerous veins of quartz, carbonate of lime, or both of these minerals mixed together, in which case it is seen that the carbonate of lime is a subsequent introduction, as it is found encrusting well formed crystals of quartz. The whole of the rock, including some-, of i the dykes is much impregnated with iron pyrites generally in the form of minute cubes, but decomposed to a grey powder near the auriferous veins GOLD VEINS. Auriferous quartz veins had been found in eight different localities on tbe 11th September. The gold is similar in character to that found at Coromaudel. hunt's beef. Hunt's " reef," as it is called, is a masß of trachytic tufa over which the water of tho K.urauui Creek falls. The face thus exposed

is traversed by four email, nearly vertical, veins oi quartz with gold running N. by E. babkt's beef. Barry's " reef," about 100 yards higher up iht> creek, is a vein i>f mulloi-k about a foot thick, dipping 70 degrees W. The gold occurs generally ia more or Jess rounded uodules (like flints in chalk), of quart;;, some of which are very rich. This vein is exposed on the right bank of the creek for a distance of about 15 feet. TOOKEY's BISEE. Tookey's " reef" consists of a series of small veins of auriferous quartz dipping 60 degrees N.W. Ib is situated about 220 feet above the level of the sea, on the side of a hill of traehytic tufa, between the Kuranui and Moanaturi Circles. COPPER. A little north of Wainui a lode of copper occurs, below high water mark, running N.JN'.E. into the hills, where, however, owing to the vegetation, it cannot now be seen. The ore appears to be a mixture of iron and copper pyrites, like that at Kawau, with some red oxide. The specimens sent have been lying on the beach for some time. This lode also occurs in tho tufa. Small specks of copper pyrites often occur together with iron pyrites ia tho quartz veins traversing the tufa. LEAD. About 2g- miles up the Tararu Creek, in the tufa, hardened by its proximity to a dyke of diorite, a quartz vein occurs with crystals of galena, dipping 70 degrees N.N.E., and in one of the claims novy being worked in the Waitohi Creek, crystals more than an inch, long, of stibnite (sulphide of antimony), has been found embedded in the tufa. AGU OF TUFA. This tufa is probably of tertiary age, and not older than tho Waitamata veins. BTBUCTUBES. There are no marks of bedding nor stratification to be seen, but from the extent of country that it covers, and tho general vertical direction of the dykes, I think that it is not Jar from horizontal, dipping probably slightly to tho west or north-west. The absence of slate boulders in the streams and on the coast, seems to show that this tufa extends over much more ground than that visited by me, and I can see no reason why auriferous veins should not be found in any part of it. These veins, being thin and vari- > able, must always render gold mining in this district highly speculative, and if, as I believe, the stratification is nearly horizontal, deop siuking will be useless, and in order to enable a company to make a profit, it will require more ground than that usually allotted to a gold claim. PAI/iEOZOIC FO3MATIONS. In one locality only, between the Tararu and the Waiohanga Creeks, are palteozoio rooks seen in the district. They here consist of blue arenaceous slates covered by a fine grained felsifco tufa, the whole dipping 35 degrees S.W. TERTIARY TBACHYTIC TUFA. Lying on the tops of the old tufaceous hills, between Shorfcland and Tararua, a deposit of fine red and white trachjtic tufa is seen of a much later "date than the old one on which it rest3. This does not cover much extent of country, and is probably of pleisto» ceno age, and formed by the former eruptions of Aroka mountain. i alluvium. The largest quantity of alluvium in tho ' district is that between the Kauaeranga and Kuranui streams. This I estimate to cover an area of 700 acres, out of which 100 acres must be deducted for the township of Shortland, and 200 more for tapu burial grounds, leaving 400 available for diggers. This tract may be considered as an incline sloping up from the sea to a height of 40 feet at the foofc of the hills. Ib is an old sea beach covered, where the creeks debouch into it by recent lluviatile accumulations. SLUICING. These latter, at the Karaka, have been worked by sluicing pretty systematically for the last three weeks, and the results have not been satisfactory. The gold is of the same description as that found in tho veins, but ■isriociated with, minute grains of cinnabar uud magnutic iron sand ; it appears to be greatest in quantity in the upper three feet of the deposit, and but little has been found unoug the larger boulders below this depth. RESULTS, KAKAKA CBEEK. The best resu!t3 that I heard of in the Knraka were half-an-ounce in three days with one sluice box. WAIOTAHI CBEEK. Since then better prospects have been obVmed in the Waiotahi Creek, but not, I think, sufficient to justify the opinion that payable alluvial gold exists there in any quautity. BRITISH CLAIM. A shaft, the British claim, is now being dunk by subscription, in the flat at the em boiiehure of the Karnka, with the intention of bottoming the alluvial deposits. No gold has been found as yet during the sinking, ami as the bottom when reached, will be an old coast line sloping propably seawards, there ia no reason i'or hoping that gold will reward their labors. TARARU. The alluvial deposit at the mouth of the Turin u is about 150 acres, one-third of which, is Maori cultivation, and could not bo touched. At tho mouth of the Maerocro 300 acres, 100 of which are tapu ; and at tho mouth of lint Whnkatcte about 300 acres, two-thirds of which are burial grounds and tapu. Thus tho whole of the alluvial deposits in the district available for gold mining purposes areAcres. Khvaka -400 Tararu ... 100 Maeroero „. , 200 Wliakatete ... [ ... 100 Total 800 This, of course, does not include the small quantity of alluvium up the beds of each of the crooks. Judging from the smallncss of tho particles of gold found, and that it occurs most plentifully in the upper portion of tho allu» vium, I am of opinion that the greater part of the gold broken oil from the veins by the streams, is carried out to sea before it has had time to cleru 1 itself from the quarts matrix ; that fine projecting particles of gold are rubbed off during the passage of the quartz down to the sea, in the ordinary state ot the stream, and are deposited in the upper , part of the alluvium ; but the first considerable fresh clears out all these deposits and '. takes them out to sea, and on the subsidence of the water to its ordinary flow they haveto begin again to accumulate, until they are- . again swept away. Gold is reported to havo been also found in the Puru, "Wbakntete, Wnikangs, andi Tararu streams. ; ft-W/Hvxxov..