THE IRON ORES OF NEW ZEALAND

Wellington Independent, Volume XXIX, Issue 3995, 7 January 1874, Page 3

THE IRON ORES OF NEW ZEALAND

« . Mbmobandum by Db Heotoe. Almost everj' known variety of iron oro has been discovered in the colony, but uone have yet been successfully worked, chiefly owing to j the want of enterprise and practical acquaintance with the subjeot. Until lately, the amount of iron required in the colony has also been limited, and imported iron has been cheap ; bat the recent riao in price, and the demand for roils and other ironworks required iv connection with the public works now in progress, are causing attention to be directed to thia branch ot our natural resources. For the purposes of classification the iron oro may be divided into Granular and Massive, the former group including all the varieties of iron sand (which have always had great, and, I think, undue, prominence given to them in New Zealand); and the latter including all the ordinary ironstones, occurring either as stratified masses or aa veinstones. GBANULAE OEES OE IRON SAND: Iron sand, or black sand as it is usually termed, is found in every park of New Zealand, there being few soils or stream gravels that will not yield a considerable quantity when washed in a pan in the same manner that the gold diggers prospect for gold. Tho chief deposits are, however, to be found on the sea shore of tho west coast of both ialande, tho beat known deposit being that at Taranuki, . where the shore between tide marks is, for many miles, almost wholly formed of this black ; iron sand, to the depth of several feet. Several companies have been formed, both , in Kngland and in the colony, to manufacture ; steel from this iron sand, and very oonsider- ■ able sum.B have been spent, but aa yet with-

out success. Lately, a largo extent (about fire miles) of the bench bus been leased to a now company, and they are now erecting furnaces. At the Manukau Heads, near Auckland, a similar deposit of iron sand has also been worked, but the company failed. Samples from twenty-six different localities have been analysed. The iron they contain is present as magnetito, hematite, or as titaniferous oxide. The acidic rocks, such as the granite of the South Island and trachytes of the North, have been the chief source of the magnetite. The metamorphic schists afford the drifts abounding in hematites or specular ores, while the titanic oxides are derived from the diorites and basaltic rocks. These observations give a fair indication of the formations where, in future, the different ores may be looked for in the massive form.' MASSIVE OEEB. The massive iron ores have not yet been applied to the manufacture of iron in New Zealand on a large scale ; but, in one case pig or cast iron of excellent quality has b"en manufactured on a small scale, as an experiment, from a brown ore at Parapara, near Oollingwood. The same ere is also used in Nelsou for the manufacture of iron minium, or ochre pigment. No 1 (Manukau), though placed with the massive ores, is really the common black sand, whioh in certain localities becomes cemented by oxidation, so as to form a very compact stratum, which can be broken up and worked like an ordinar) ironstone. This form of ore I intolerably abundant south of the Manukau Heads, and might be obtained for admixture with other varieties. No 2 (Dunstan Gorge) is from a vein of loadstone that occurs in chlorite schist in the interior of Otago. The rock at this pluce is a very compact, foliated diorate, having crystals of magnetite dispersed in the same way that garnets occur in mica schist. No attempt; lias been made to ascertain the thickness of this lode, as its position is at present too inaccessible to permit of its being worked. No 3 (Dunstan) is from a lode of hematite, or specular iron, six foet in thickness, that occurs in mica schist in the vicinity of the Wukatipu Luke. Other veins of a similar nature, and also lodes yielding 20 per cent of copper, have been found in this district. Limestone also occurs in the vicinity, and as charcoal can be obtained in abundance from the extensive forests, there is a fair prospect of metallurgical operations being commenced when the railway now in course of construction, to connect the Lake with the Bluff harbor, is completed. No 4 is from a vein from the serpentine series of the Dun Mountain, or what is known as the mineral belt of Nelson. This series forms a range along the east side of Blind Bay, which is singular in having a barren appearance, due to the large amount of magneeia mixed with the soil. The sections of these hills show them to consist of slates, I limestones, and indurated sandstones, consisting of triaesic fossils, that puss in ascending series to diabase breccias, aspociated with diorite, and a peculiar form of compact olivine rook known aB dunite. The rock appears at the surface as large masses, several miles in extent, and is speckled with grains of chromic iron ; but the principal deposits of ore are in j a band of serpentine lying between the dunite and a limestone formation. The serpentine is traversed by dykes of felstone, diallage, and a variety of other minerals ; the district being one of the most interesting in New Zealand to a mineralogist. It was here that the hematite vein was found in 1853, along with red, grey, and blue oxides of copper. The thickness was not ascertained at the time, and the works have now fallen in. This sample of hematite i& interesting on account of its containing an appreciable amount of gold. No 5 (Maranaraa, Auckland) is a sample of mixed hematite and magnetite, containing a marked percentage of manganese, and is found in brecciated sandstones and slates, probably of Iriassie age, on the west side of the Gulf of Thames. Pure manganese ores are very common in this formation, and have been worked on the Island of Pakibi, and also near the Bay of Islands. The occurrence of copper lodes at Kawau and the Great Barrier, in connection with the same formation, affords an indication of its being worthy of a more thorough mineral exploration than it has yet received. The above are only a few of the many anhydrous massive iron ores whioh exist in New Zealand ; and the next group consists of those ores whioh contain a large proportion of combined water, and are generally known as brown or hydrous ores. No 6 (Spring Swamps, Auckland) may be taken as a type of the bog iron ore which forms in swampy localities, generally near the outcrop of the brown coal formation. From the quantity of the sulphur generally contained in this ore, it is not adapted formating good iron ; but it could be obtained in considerable abundance, and undor favorable circumstances for working, being generally close to supplies of coal and limestone. No 7, from Raglan, may be taken as an average sample of the brown iron ores from the tertiary coal formation, which occur generally as ball-Btones or concretionary masses dispersed through the shale, and can generally . be obtained in large quantities wherever that formation prevails. This ironstone is of great practical importance. No 8 (Eawau) is a hydrous hematite, formed by the decomposition of the hematite ore associated with the manganese veins alluded to under No 5. This particular sample is from the Island of Kuwau, but this ore is generally to be four d in thin, irregular veins wherever the sandstone formation has undergone decomposition into a form of laterite, which takes place to a very great depth in some places. As an iron ore, however, it would be very difficult and expensive to collect, unless to supplement a supply derived from hotter defined deposits of ore. No 9 is from a deposit of hydrous hematite that occurs in the upper tertiary drifts at Parapara, in the Province of Nelson, but is also not infrequent in many other localities. The ore occurs as the matrix of a quartz conglomerate, but Often containing large masses of nearly pure ore, of several hundred pounds weight. On breaking these there is frequently a kernel of undecomposed Bulphide of iron, showing the origin of the ore to be probably from the denudation of a mineral vein. The deposit at this place covers about fifty acres in oxtenfc, and is 100 feet thick, and, as previ- \ ously mentioned, is worked on a small scalo for the preparation of pigment. SPATHIC IRON OBES. Taking the foregoing aa typical samples of the different varieties of hydrous iron ore it now remains to notice the occurrence, in the ' upper secondary coal formation, of iron ores containing a sufficient percentage of carbonate of iron to enable them to be classed with the black banrlß or Bpathio iron ores, which are generally considered the moat favourable for ■ the purposes of a blaßt furnace. Nos 10 and 11 are samples of this ore, taken from two veins that occur along with coal seamß at the Collingwood Coalmine. These ores occur at Collingwood under circumstances very favourable for their being worked, as they can be mined along with coal of the very finest quulity that occurs in New Zealand, the only drawback being that the coal seams are not more than three feet thick, while the ore is from ten to twenty inches. The coal measures are now being explored by a tunnel 700 feet in length, and so far aa it has gone, they show an iraptovement from what was anticipated from the examination of the outcrop. Close to the coalmine there is abundance of fine crystalline limestone, belonging to an older formation ; and deposits of graphite and also micaceous hematite, that might be useful in working puddling furnaces, are found in the same district, The area of country near Collingwood occupied by a similar formation, is about ten or twelve square miles ; and as Golden Bay offers very favorable conditions for the erection of deep-sea wharves, I think ifc likely that this locality will be the first in New Zealand where the mineral resources will lead to the establishment of a manufacturing industry,