so limited that the potentialities of these mountains can hardly be gauged at present.

Further south-east are the two old gold Reward sections, granted to Messrs. Brakespeare and Brice, but indications of mineral upon them are not known.

CONCLUSION.

Reviewing the district as a whole, there is no doubt that its present value is due to the output of tin ore, which is proceeding steadily on a limited scale. With respect to this mineral, the field is not likely ever to be one of more than moderate dimensions, as the exposure of granite is not large. The extent of terrace-ground fringing the base of the mountains is known and easily measured, and the area of lagoon and swamp ground is clearly defined. The nature of these areas has been outlined in this report. The sections taken up by the various associations cover, approximately, the tin-bearing ground at the Bight, so that we have there a compact proposition parcelled out among a few owners, some of whom, with proper management and adequate capital, will probably find their venture payable. The Cox's Bight Tin Mines Company ought certainly to do so, for the extensive tests made in different parts of the area by Messrs. Castle and Heise indicate a valuable property. The Kent Tin P.A. has not yet proved its property sufficiently to enable a forecast to be made.

Meanwhile much interest attaches to the work going on there, for success means the extension of exploration northwards and eastwards into practically virgin mineral. country. If granite is found further north, tin will most probably accompany it; but irrespective of granite exposures, the ancient schists of this part of the island are likely depositories of copper and antimony ores, and from the scattered indications which have been found hitherto it is possible that when the country is better known discoveries of value will be made.

REPORT ON THE RENISON BELL TINFIELD.

SIR,

Government Geologist's Office,

Launceston, 18th December, 1906.

I HAVE the honour to submit the report of a brief visit to the Renison Bell Tin Mine, in accordance with your instructions, on the 23rd to 27th of last month. The present report will not extend beyond a preliminary statement of the geological and mining problems met with at the northern or Renison Bell end of the Dundas tin-bearing belt, leaving a more extended report on the whole belt till a further visit to the district is made.

Deposits of tin ore occur in the North-East Dundas district, within a zone of country roughly estimated at about a mile in width, and coursing in a persistent line from N.W. to S.E. for about 3 miles in length.

Though some of the lodes strike north and south, or to the east of north, their bearing for the most part is northwesterly, which is the direction of the cleavage planes of the country rock.

This linear direction of the metalliferous belt must not be ignored. The lode occurrences have not been haphazard, but have been in obedience to some orderly physical process, which not only serves to indicate the directions in which prospecting may be carried on usefully, but also very strongly suggests that a good deal about the ore occurrences remains to be learned.

Acid eruptives being the true source of tin, the origin of the Dundas tin deposits may quite naturally be ascribed to neighbouring granite. Examination of the various lodes of this part of the West Coast leads irresistibly to the belief that underlying granite is responsible for much of the ore-deposition which has taken place. Most of the country rock at the northern end of the belt under review is slate or crystalline sandstone, or quartzite, the geological age of which has not been defined precisely, but it is nearly certain that it is Lower Silurian or Ordovician. Prof. T. S. Hall, of Melbourne, has identified some graptolites in slates from the North-East Dundas Railway, near the Ring River, and also at 12 miles from Zeehan on the

same railway line, but he pronounced the discovery of no great value for determining the age of the containing rocks. We have, however, good reason to believe that the Dundas series of stratified rocks are older than those at Zeehan, which are known to belong to the Upper and Middle Silurian.

In various parts of the North-East Dundas district the sedimentaries are penetrated by basic eruptives, such as gabbro and serpentinised olivine and pyroxene rock, e.g., on the Penzance and Goldstraw's sections. With these basics may be connected concentrations of copper, lead, nickel, and iridosmine, as regards the former epigenetically, and the latter by a magmatic process, but tin-deposition evidently took place subsequently to their consolidation, and accompanied the intrusion of tourmaline quartzporphyry dykes. These dykes have pierced both the serpentinous rocks and the sedimentary strata, but tin has not been found, and is not likely to be found, in the former, for this metal appears all over the world to be associated genetically with only acid eruptives (granitic plutonics or their geological equivalents).

My attention during this visit was confined to the country immediately contiguous to the Renison Bell Mine, and I first endeavoured to learn all that could be ascertained about the occurrence of igneous rocks in the neighbourhood.

Isaacson's Creek is a small creek which rises in a vacant section north of 1215-м, C. Brumby, and flows for a mile north-easterly by the side of the Emu Bay railway line, eventually emptying into the Ring River. Mr. Gilham took me to this creek, the sand of which gave prospects of gold, tin, and iridosmine (osmiridium). I was informed that about -dwt. or 1 dwt. of the latter mineral is present in each cwt. of tin ore from the creek. The chocolatecoloured slate on the banks of the creek hows a development of serpentine (sometimes slightly asbestiform) in the joint or cleavage planes, and it is highly probable that serpentine rock exists somewhere in the hill situate to the south-east. In the creek bed I also saw a greenish granitoid rock, the precise nature of which needs microscopical identification; but it was not fully exposed, and I could not say positively whether it is in sitú or not. Search for granite should be made in the hill above this creek.

Lower down the Argent River, north-west of the Renison Bell, and also on the line of McKimmie's tramway

towards the Tasmanian Smelting Company's lease, serpentine is also reported to be present. From the latter direction Mr. Gilham brought to me some stones of granitoid rock found by him in prospecting. All this shows that the northern end of the metalliferous line connected with the eruptive rocks has not yet been seen.

At 140 feet from the south-west angle of the Renison Bell Section 2536, Porphyry Creek crosses the boundary line. Its bed is quartz-porphyry, containing scattered needles of tourmaline, a little iron pyrites, and fluor stains. The apparent direction of this quartz-porphyry dyke is northwesterly, consequently parallel to the general trend of the lode-belt. Going south-easterly a similar rock outcrops on the boundary line between Section 165-93м and Section 1963-м, 1000 feet above the railway line, intrusive into slate. The distances between the exposures are so great that I could not satisfy myself whether this is the same dyke or not. Tourmaline quartz-porphyry and tourmalinized slates are intimately associated with tin ore deposits in other parts of the district, and consequently it is not surprising that the tin lodes on the Renison Bell ground should be accompanied by this intrusion. It would appear that the dyke forms an intrusion extending along the western side of the tin-bearing belt all through that ground. At the same time, it is not the only occurrence of quartzporphyry in the district. I noticed a small quartz-porphyry dyke 3 feet wide in the centre of a 50-feet pyritic formation in the south-east angle of Section 1342-м, 75 acres, in the name of J. Craze, which was discovered a few weeks ago. The formation with the dyke has a bearing N. 350 W. Further south on the Penzance and Goldstraw's sections there is a good deal of quartz tourmaline porphyry, and there can be little doubt that its intrusion all through was an integral part of the process which introduced the tin into this area.

A further indication of the granitic source of the tin present in this district is in the well-known vein of axinite in the Cornwall (New Dalcouth) and Commonwealth sections. The question whether this vein has faulted the lode there or has been the channel of mineralisation is of interest, and even of some importance, to the owners. Different views exist, but in the short time at my disposal I was unable to arrive at any definite opinion in the matter. It seemed to me, however, that the direction in which the ore-body should be developed is along the line of lode, notwithstanding that the bearing of the axinite

vein corresponds more with the general trend of the other lode outcrops in this belt. I could not, however, investigate the whole of the data bearing on this point.

I have been informed that as far as can be ascertained fully 200 tons of tin ore have been sent out from the North-East Dundas district during the last fifteen years from alluvial and detrital deposits. In some parts of the field much of the ore has been found as large nuggets, 7 lbs. to 14 lbs. in weight; sometimes boulders of pure tin ore a hundredweight each have been met with in sluicing, and one large boulder weighing nearly a ton of ore is in the Tasmanian Museum, Hobart. These boulders indicate the existence of rich tin veins up to a couple of feet or more in width.

The tin is invariably in the form of oxide (cassiterite), but apart from that found in connection with quartz-porphyry, it is in the majority of instances associated with sulphidic gangues (pyrite, arsenopyrite, or pyrrhotite). It is this that has probably mainly contributed to the stagnation of lode-mining in this field. The treatment of ore stuff from which pure oxide of tin, as on the East Coast, can be easily removed is so simple and inexpensive that the separation of tin stone from these contaminating sulphides has been a bogey which has frightened adventurers.

The exact metallurgical treatment cannot be settled offhand, but there is no inherent difficulty about it (comparable, say, with the zinciferous sulphides of Mt. Read, &c.). Mr. J. D. Millen of the Mt. Bischoff Smelting Works states that he has made several experiments on the sulphide ore at the Renison Bell, and is satisfied with the result.

Mr. Donald Clark, in his Australian Mining and Metallurgy" (p. 224), seems to think that the ore at the Cornwall Mine, which is mainly pyrrhotite with a little pyrite and arsenopyrite, could be roasted and concentrated for 15s. per ton. Mining costs would probably be between 8s. and 10s. per ton; development 4s. to 5s. Altogether, with tin at its present price, sulphidic ore of 1 per cent. quality might be expected to pay working expenses. If these properties are ever to be exploited seriously, it is manifest that the present is a highly favourable time.

I paid a visit to the Commonwealth section, now E. Flight, 271-м, 77 acres, where the tunnel has been driven into the Cornwall (New Dalcouth) property to the south. The tin-bearing pyrites in this tunnel appears to have a