GEOLOGY OF THAMES.

Thames Star, Volume LXIII, Issue 17663, 14 August 1929, Page 5

GEOLOGY OF THAMES.

A VOLCANIC UPHEAVAL

EVIDENCES OF MOVEMENT,

CONTRIBUTED BY “AURIFEROUS"

From a point at the head of the Shellback Creek and Tinker’s Gully, in a south-westerly direction, there is ample evidence to prove that one time —aeons of ages ago—a volcanic upheaval must have taken place in tne locality of Look-out Rock, thus causing the Punga Flat faulting. The evidence is conclusive in regard to an eruption in the fact that the country rock .in the vicinity is a substratum of ancient andesite, whereas to the west of the fault the andesite rock is more of a recent flow. Another prominent feature in the vicinity greatly supports the upheaval assumption, that being the huge well-defined quartz reef forming a scarp end on. The upheaval side of it corresponds with the Waiotahi, Cambria, Fortunia reef. The attitude of the scarped reef is fully 100 feet higher than the point where the latter line pf reef intersects the fault. There is a. lateral movement to the north of fully 200 ft. by the eruptive matter, as shown by the displacement of the continuation of the aforestated reef at the point of intersection with the fault.

No Subsidence.

In the writer’s opinion, no subsidence took place west of the fault. The upheaval merely tilted the surface slightly. This accounted partially for the forming of the Punga Flat plateau. Had a subsidence of the country taken place similar to the Aloanataiari, the scarpe on the end of the big quartz reef would show a smooth surface, whereas it is very rugged, whilst the scarpes or slicken sides on the hillsides of the Moanataiari fault show out very smooth in places, denoting the fact that at one time a heavy overburden had a slow subsidiary movement. The country rock west of the Punga Flat fault to the Moanataiari and from the Shellback to the Hape Creek is a very much altered andesite. A Geological Problem.

A decided geological problem in . this area is that no less than six wellknown dioritic andesite intrusions show up. Two of them are on the surface and known as the Hape and Waiotahi quarries. Another was penetrated in the Una Hill, and it proved to be 250 ft., but it did not show : on the surface or on the scarpe of the hill not more than 200 ft away, neither in a drive immediately underneath.

A second one was penetrated in

the Moanataiari Union mine, 'where a small vein of quartz carrying filch specimens was discovered in it. The intrusion was of no great extent. The surrounding country Avas of the best description of andesite, containing numerous small leads of exceeding richness. A third intrusion Avas met .with in the late Durham Ox. claim, situated on the left side of the Moanataiari Creek, about 300 ft further up the creek from the junction of the Canadian gully. This intrusion also contained a vein of quartz impregnated Avith the precious metal. . Another one was obser\ r able in a driA r e situated on the main ridge that divides the Moanataiari and Shellback Creeks. It is of an exceedingly hard nature, and AA'ould he suitable for road metal. The several intrusions vary in size and shape, some being more elongated than others and in no way connected with each other.

Other Peculiarities. Several other peculiar classes of rock ave noticeable in this area, more particularly in that portion lying at the south side of the Lord Nelson peak on the Hape Creek side. The country rock is of a embracing quartz of an opaline appearance. 'Pieces of this, after being polished, have a beautiful lustre well worthy of having a place in the School of Mines museum. A Barren Strata.

Another geological feature, and not conducive to the gold welfare of the field, is that Aoav of barren andesite commencing at a point Avhere the Waiotahi-Cambria reef intersects the Moanataiari fault. It forms the thin end of a Avedge. The eastern line takes in the front of Messenger’s Hill, drops into the Moanataiari Creek a little to the east of Canadian Gully, thence over the ridge into the Shellback Creek, and continues on its course to Tararu Creek.

The other line skirts the Moanataiari fault to the Eureka Flat, and it then takes a decided turn, hugs the hangingAvall of Barry’s reef to the sea beach, thence along the foreshore to the Shellback Creek, and joins up with that portion already commented on that extends to Tararu Creek. The country rock is very much altered. Take, for instance, the scarpes on the face of Messenger’s Hill and again on the Bluff on the east side of the track leading up to the Eureka from the Moanataiari Creek. In both instances they are coarse in the grain, more particularly the bluff. The latter is more solid and composed principally of quartzite, whereas the Messenger’s Hill rock is very much broken.