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The Pamphlet Collection of Sir Robert Stout: Volume 70

(1) Antimony

(1) Antimony.

Antimony occurs widely distributed throughout the colony, from the Bay of Islands, in Auckland, to the south of Otago. In many places it is auriferous, and is worked as part of the reef, but very frequently, after extracting as much gold as can be done by crushing and amalgamation, the stibnite is allowed to flow away with the tailings. Many efforts have been made to work it, and notwithstanding several somewhat conspicuous failures the industry bids fair to become well established.

In Auckland Province antimony occurs, as already mentioned, at the Bay of Islands, and also at the Thames, Waiatohi Creek, and Coromandel.

It is, however, in Queen Charlotte Sound, Marlborough Province, that the largest deposit of stibnite has been found, and in this locality an effort has been made to work on a large scale. The discovery was made in 1873, and the analysis gave 51.12 to 69.4 per cent of antimony. At this place the country is a fine-grained, greenish, schistose rock, changing in parts to a greyer colour, and becoming more quartzose. The lodes, of which there are three, vary a good deal in thickness and quality, and contain an appreciable amount of gold. The main reef has been followed from the north-eastern corner of the lease in a northwesterly direction for about 140 chains, and in the opposite course it may be traced on the same line of strike for about 4 miles. Its structure is peculiar, in that the stibnite forms the lode, and the quartzose part is disseminated through the ore. With the antimony are found loose blocks of olivine, with chromium ore, compact hornblende rock, and white and green chert.

A small company of Wellington (New Zealand) capitalists expended £25,000 in plant and works, including a dressing plant and smelting furnaces, but the undertaking proved to be unremunerative, and the property passed into the hands of an English company who worked on a much larger scale but with no better result. The ore appears to have been plentiful, bat as is usual in such deposits was bunchy and a good deal faulted.

The dressing plant consisted, in 1890, of one Blake rock-breaker, one Marsden ore-crusher, one Lucop centrifugal pulverizer, and various page 41 other appliances. The use of the Lucop pulverizer had been discontinued, but the Marsden crasher gave great satisfaction. Still the general result of the concentrating plant appears to have been very unsatisfactory, and the first smelting-works which were erected were so inefficient that they were dismantled. During 1890, 515 tons of ore, containing from 48 to 60 per cent, of antimony, with a value of £11,121, was exported by this company, but according to the Otago Witness of March 31th, 1892, the mine was put up to auction in that month, and no bid was obtained. Advices dated June 9th, 1892, stated that a syndicate had purchased the mine, and decided to go on with the work.

Passing by Collingwood, where a complex antimoniferous ore occurs, which will be described under another heading, the next deposit is at Reefton, in Nelson Province, where stibnite occurs plentifully as a constituent of the gold-bearing reef a, and also near Black's Point where, at a distance of about 1½ miles from the lnangahua River, and at an altitude of about 800 feet above the stream, or 1,400 feet above the sea-level, a number of blocks occur, which have received some attention. The surface of the country is densely clad with forest and undergrowth, and consequently prospecting has been carried on under difficulties.

About 3 miles from Brunnerton, on the Greymouth-Reefton Railway, and 8 from Greymouth, quartz reefs had been known for many years, but had not attracted much attention until about the year 1878, when blocks of richly auriferous stibnite were found in the alluvium. The quartz reefs are about 600 feet above the river, and at 400 feet higher the lode from which the specimens were derived was discovered. It is about 9 feet in thickness, is included in hard blue cherty slate, and consists of five distinct bands, as follows:—
Ft. Ins.
No. 1, next the footwall, is quartz containing stibnite dispersed in irregular masses 2 0
No. 2, compact stibnite 2 0
No. 3, stibnite, including quartz in the form of nodules 3 0
No. 4, fine-grained mixture of quarts and stibnite 0 4
No. 5, breccia of slate 1 8
9 0

The first specimens forwarded gave the astounding result of 84 ounces of gold and 86 ounces of silver per ton, or an assay value of £830. Subsequent specimens obtained by Sir James Hector did not give anything like such a good yield, the highest being from No. 2, which assayed 32 ounces of gold to the ton. Still, the prospects were exceedingly alluring, and if the reef had maintained its thickness, the results would page 42 no doubt have been satisfactory. This was not, however, the case, and the mine was abandoned without any very decisive test of the property being made.

Other localities on the west coast, where antimony is found, are Westport, Blackball Creek, near Greymouth, and Hokitika.

In Otago, ores of this nature occur, and are now being worked, as for instance at Hindon, where a 7 feet lode occurs about 1,000 feet above the river, and has yielded 500 tons (worth £10 to £20 in London). The reefs in this locality were known in 1864, but for many years remained unworked. Recently an energetic private firm has taken up the lease, and as the lode is well-defined, and the mine within easy distance of the recently opened Otago Central Railway, the prospects should be good.

At Stony Creek, near Waipori, Otago, the antimony deposits at one time offered considerable inducement for investors, and in 1875, 60 tons of ore was sent to England to be smelted. The lode, which is composed partly of fibrous and partly of compact stibnite, is 2 feet 6 inches in thickness, and has been traced for several hundred feet. Scarcity of fuel and timber constitutes a considerable drawback to cheap working, and but little has been done.

On the Carrick Range, near Cromwell, Otago, outcrops which have been traced for upwards of a mile occur at an altitude of 3,000 feet above the sea. The reefs traverse grey foliated mica-schists, and are stated to be thin. But little has been done in this locality.

In addition to the places already named, antimony occurs widely distributed throughout the colony, as for instance in the Provinces of napier and Wellington, and at Dunedin, in Otago, and with such quantities undoubtedly existing, the fact of so little being worked seems remarkable. One reason lies in the superior attractions of gold, and the fact that, although comparatively easy to treat, antimony ores require special knowledge and also fuel, which is often absent in the locality of the find.

The export of the ore commenced in 1878, with 4 tons, valued at £102, and reached, in 1800, 515 tons, valued at £11,121; altogether £36,190 worth has been sent out of the colony. In the year 1883 a bonus of £500 was offered for the first 250 tons of antimony regulus produced in New Zealand, and sold at a fair price in a foreign market; but no application was made, and consequently the reward lapsed.