THE ALFORD FOREST ORE.

Lyttelton Times, Volume LXIX, Issue 8395, 2 February 1888, Page 5

THE ALFORD FOREST ORE.

PEOFESSOE BICKEETON’S EEPOET. Professor Bickerton has kindly allowed our representative to copy the following report on his examination of some of the supposed tin ore from Alford Forest " Some months ago Mr Jacobsen brought me some crushed ore, which he supposed consisted of tin-stone. The density of the substance forbade such an idea, but an assay of each of the samples showed tin in small quantity. A fragment from a sample of rock which he supplied me with afterwards, also gave under the blowpipe a minute head of tin. Although we tried the sample in many different places, we could find no more tin. We consequently made an assay with potassium cyanide, with no result. It is extremely easy to get a bead of tin, if a minute fragment of tin-stone be heated with cyanide of potassium under the blowpipe, but I have been able to get no indications with any of the many samples that have been given me by different people as Alford Forest ore. The mineral which Mr Jacobsen and others especially point out in the rook as tin-stone, is really a kind of glass called pitch-stone, and has a specific gravity of 2-7, while tin-stone has a specific gravity of about 7 - . That is, tin-stone has about the same density as iron, and is nearly three times as heavy as this mineral. Practically tin-stone or cassiterite, oxide of tin, is the only ore of tin; the sulphide, or tin pyrites, a brassy-looking ore, being very rare. The value of a sample of tin ore is often roughly estimated by the density. I therefore took the specific gravity of about a dozen samples, with the mean result of about 2'7 (excepting one sample containing iron). That is, the average of the samples could not possibly contain one per cent of tin-stone. I believe several samples of the stone have been sent to Sir J. Hector, and he told me none contained tin. Probably Dr Skey assayed these, and I suppose there is hardly a chemist in the world who has a firmer reputation as an analyst than has Dr Skey. I believe also that Professor Black has made assays with like results. An assay does not pretend to be a chemical test. It is a refined commercial test, and it is well known that very poor tin ores, with an immense quantity of siliceous matter, do not yield tin in assaying unless many precautions are taken. My view of the case is that, unless tin has inadvertently or wilfully been mixed with the stone, there is tin at Alford Forest, but the prospectors are selecting the wrong stuff, in fact, are sending the gangue instead of the ore. Further search, therefore, requires to be made. On the other hand, knowing that every fryingpan, every saucepan, many shovels, and all tinware contain the metal, it is easy to see how readily some of this may get in and contaminate the sample. There is some of the samples, and in some cases beads of iron, produced by smelting in a forge, have been mistaken for tin. I have mixed pounded _ tin-stone r with ten times its weight of siand,' : and have washed out over 95 per cent of the tin-stone. This shows how easy it is to separate it from other rock. - The prospectors should pound the samples they think to be tin-stone, and wash them. ‘ | The tin-stone isnearly as easy to pan out : : as gold. When they have separated a lot, it should he as heavy as iron filings, and should have something the look of resin. Withcyanide of potassium, it is extremely i smpltituitt a clay’’ tobacoopipe,/,*

toy teacup, or a small crucible, when heated for a quarter of an hour in a hot forge. PROFESSOR BLACK’S OPINION. The following private letter from Professor Black to a gentleman in Christchurch, who sent him a sample of ore from Alford Forest, gives his opinion on the matter:— “ I cannot find any tin ore in the stone you forwarded. The chief constituents of it are angite quartz and some felspar. It also contains a very small proportion of iron in the metallic state nearly pure. This is of very rare occurrence, and is of much interest, although of no importance from a commercial point of view. One would not readily mistake tin stone for anything else, owing to its great weight. It is more than twice as heavy as anything your sample contains. It is a thousand pities the Schools of Mines are not to be supported by the present Government. If we had another term of three years of these schools we would have in the Colony 5000 men and boys who would be able in a few minutes to identify any mineral they might come across.—l am, &c., “James Black.”