Art. XLI.—On the Occurrence of some Rare Minerals in New Zealand.
[Read before the Auckland Institute, 23rd October, 1893.]
At the meeting of the Australasian Association for the Advancement of Science, held at Christchurch, in 1891, I read a paper describing a number of new and rare minerals found in New Zealand.* Since that date a number of other minerals have come under my notice, some of them new to this country, and some of them, although previously known here, yet interesting from the exceptional character of their occurrence.
Cervantite (Yellow Oxide of Antimony).
In the month of January, 1892, Mr. George Wilson, Inspector of Mines for the Hauraki Goldfields, forwarded a collection of ores from the antimony-lode at Waikari, in the Bay of Islands district, to the Thames School of Mines for examination, and the determination of their value. The principal ore in this collection was antimonite, the commonly-occurring grey sesquisulphide of antimony. In several specimens the sulphide was incrusted with a layer of the yellow oxide (SbO4) several inches thick. Its hardness was about 5, and specific gravity 4, while its colour varied from yellowish-white to sulphur-yellow. The purest example contained 76 per cent. of antimony.
Cervantite is a most valuable ore of antimony, but is seldom found in large quantities. It generally results from the alteration of the sulphide, and is most frequently found at the outcrop, or shallower parts of antimony-lodes. It is well known at Hillgrove in New South Wales, Oporto in Portugal, and many other foreign localities; but so far as I can ascertain it has not been previously described from New Zealand.
Senarmontite (the Grey Oxide of Antimony).
This mineral was also identified in the collection from Waikari. It frequently accompanies antimonite, but is even less abundant than cervantite.
In the Colonial Museum and Laboratory report for 1892,
[Footnote] * “Transactions Australasian Association for Advancement of Science,” vol. iii., pp. 150–153.
Mr. Skey, the Government Analyst, describes a mixture of this mineral and stibnite from Waikari containing 78·9 per cent. of antimony.
Pyromorphite (Phosphate and Chloride of Lead).
A small specimen of this mineral was forwarded to me from the Champion Mine, Tui Creek, Te Aroha, towards the end of 1891. It occurred as an incrusting layer of small, irregular, yellowish-green crystals, on a yellowish-brown crypto-crystalline quartz, which is found associated with the galenalode in that mine. It has not been identified in any other part of New Zealand.
Anglesite (Sulphate of Lead).
In 1889 I collected several examples of this mineral at the Champion Mine, Te Aroha, where it occurred in thin veins and small threads in the galena-lode, especially near the outcrop. Its colour was greyish-white, and it occurred in a massive form.
In a paper read before the Auckland Institute in October, 1885, Mr. J. A. Pond, F.C.S., stated that the ore-body cut in the low-level tunnel at the Surprise Mine, Te Aroha, was a sulphate of lead, containing a few enclosed grains of galena. This appears to be the first record of this mineral from this colony.
Cerussite (Carbonate of Lead).
During a visit to Te Aroha, in 1889, I collected this mineral at the Champion Mine, where it occurred in a quartz lode in large lenticular-shaped shoots. In the paper referred to above Mr. Pond described the lode in the Surprise Mine, which, near the surface, he stated was composed principally of carbonate of lead.
The lustre of the Tui Creek cerussite which I possess is vitreous or resinous, and the colour greyish-white to dark-brown. It occurs in a compact, granular or massive form, and crystals are rare.
The rocks at Te Aroha, in which the last three minerals are found, consist principally of indurated tuffs and ash-beds, with which are associated flows of solid hornblende-andesite and dacite.
Genthite (Hydrated Silicate of Nickel and Magnesia).
During the operation of clearing away a slip on the Tapu Road, in the month of September, 1891, the roadmen discovered a small vein of this rare and interesting mineral. I subsequently examined the locality, and found it situated
about a mile south of Tapu. The vein was very irregular, and less than ½in. in thickness. The matrix was rusty-coloured quartz. The strike of the vein was N.N.E. to S.S.W., and it was contained in highly-decomposed brown coloured tuffs, which are probably of pyroclastic origin judging from the occurrence in them of a thin seam of coaly shale a few chains distant from this point.
Melanterite (Ferrous Sulphate).
This mineral results from the alteration of iron-pyrites. It is found in large quantities in many of the old workings in the Kurunui Hill and Old Caledonia Mine, where it occurs in thick layers incrusting the floors and sides of the drives, and as stalactitic masses which frequently reach to the floor, and thus block up the passages. The exposed surfaces are always invested with a layer of greyish-white ferrous sulphate, which occurs in the form of fine acicular filaments possessing a beautiful silky lustre. The solid mineral possesses a bluish-green colour and a coarsely crystalline structure.
This mineral is found in metal mines in all parts of the world, but its vast development at the Thames is of an exceptional character.
Vivianite (Hydrated Phosphate of Iron).
Early in 1892 Mr. James Macky, jun., manager of the Norfolk Battery, presented the School of Mines with a large specimen of this mineral from what was described as an extensive deposit which had been discovered during the operation of sinking a well on the property of Mr. Matthew Hunter, situated near Mercer Railway-station. This vivianite occurs in the earthy form. It is soft and friable, and possesses a deep-blue colour. It is a very pure variety, and contains about 26 per cent. of phosphoric acid. I have not been able to visit, and personally examine, this deposit, but, judging from the details supplied by Mr. Macky, it would appear to be by far the largest known in New Zealand.