The Journal of Agriculture.

New Zealand Journal of Agriculture, Volume X, Issue 6, 21 June 1915, Page 495

The Journal of Agriculture.

Wellington, new Zealand.

2IST JUNE, 1915.

ROCK PHOSPHATE IN NEW ZEALAND:*

ITS VALUE TO THE DOMINION.

B. C. ASTON, F.I.C.

z | A HE presence of phosphates in the soil ' is essential to the THE presence all crops, particularly root crops such as turnips, growth of all crops, particularly root crops such as turnips, mangels,, and potatoes.- Many of the soils-of .this country, especially. those of the North, are deficient in'phosphoric acid in amounts necessary for - successful . turnip-growing,, and readily respond to an application of 2 cwt. to 3 cwt. of a phosphatic manure such as Island phosphate, bones, or superphosphate. ■ ; ■- The following: results show . the value ,of phosphate fertilizers in the growth of turnips at the Moumahaki Experimental Farm : ■ . . ■ .• - - Tons cwt. qr. lb. Average crop per acre for nine years (no manure) . . 3 8 312 Average crop per acre for three years (2| cwt. Malden Island phosphate) , .. ’ . . .. .. 26 o 124

Cost of fertilizer, 12s, Bd. per acre. Malden Island phosphate contains from 60 to 72 ' per cent, of tricalcic phosphate (bone phosphate), but no nitrogen or potash. In 1899 a mixture of 1 cwt. of steamed bonedust and 2 cwt. of basic slag —an almost exclusively phosphatic fertilizer-gave a crop of 43 tons of turnips to the acre. Taking another root crop Sutton’s Prizewinner mangels —at Moumahaki in 1904 : Tons. No manure .. .. .. .. 50 Superphosphate, 3 cwt. (no lb. . Ca 3 (PO 4 ) 2 ) 70, at 17s. 3d. per acre. New Zealand ground rock phosphate, 4 cwt. (2241 b. Ca 3 (PO 4 ) 2 ) .. .. 70, at 14s. per acre. Our locally produced phosphate, which in this case ' was of low grade : (50 per cent.), with no other treatment save drying and grinding, therefore gave as good a result as superphosphate, and was 3s. 3d. per acre cheaper.

To show the need the Dominion as a whole has -for phosphates the following imports for 1905 and 1914 are quoted (see Year-book, p. 319, and Journal of .Agriculture; .November, 1914, p. 356) :

Upon the ' growth' of turnips greatly ■ depends the country’s capacity for fattening stock. The demand for phosphate is therefore likely to increase as new- lands are opened for settlement and as settlers become versed in 'the application of fertilizers, and better able to afford the necessary outlay. . . . ' ■ . c.-. The illustrations supplement the figures given. above. They are photos of the experimental plots carried out by . the = Manager at the Moumahaki Experimental Farm. . .

OCCURRENCE IN NEW ZEALAND.

.. t The greatest store of phosphate is that which occurs in the soil. Some idea of the aggregate amount distributed through the great mass of soil may be obtained by assuming that the weight of . an

acre of average soil, containing, say, 0-075 per cent, of phosphoric acid) to a depth of in., is 2,000,000 lb. Then there will •be well within the reach of plants in this acre 1,500 lb. of phosphoric acid, which is equivalent to nearly 3 tons of phosphate rock (of 50 ; per cent, phosphate-content). Most of the soil phosphate is not immediately available as a plant-food, but it should be the aim of good farming to make it available.*

In addition to being distributed in small amounts in nearly all rocks and in every soil which will grow plants, phosphates occur in masses of approximately, pure mineral.

Calcium phosphate (phosphate of lime) is the most valuable of the natural mineral phosphates for manurial purposes. It is from this that superphosphate and many of the proprietary fertilizers used in New Zealand derive the phosphate to which they , owe their chief value.

. The occurrence of two instances in which tricalcic phosphate was found may be noted. The. late Mr. Skey, Colonial Analyst, imported in 1885 on a specimen containing 20-78 per cent, of phosphoric acid (equal to 45-36 per cent, of tricalcic phosphate), forwarded by Mr. Fifield from Wangapeka, Nelson. In 1887 Mr. Skey reported on a coprolitic nodule from within a quarter of a mile of Weka Pass, discovered by Mr. McKay. This contained 17-45 per cent, phosphoric acid, equal to 38-09 per cent, tricalcic phosphate.

The only deposit which is worked in this Dominion is that at Horse-shoe Bush Estate, Clarendon, Otago, which was originally discovered by the late Mr. Ralph Ewing, of Dunedin. That this discovery was the result of systematic search by Mr. Ewing adds to the lustre of the discovery. Shortly afterwards phosphate was discovered at the Milburn Limestone Quarries,, where boulders of it had long lain exposed to the full view of visitors (lay and scientific) to the quarry, and yet for twenty years or more the phosphate had remained undiscovered. Let no one, therefore, hesitate to send in for analysis specimens of rock having the hardness and texture of rock phosphate because of its familiarity or abundance. Trained geologists had, without doubt, seen and probably cursorily " examined the Milburn and Clarendon phosphates without suspecting their ’ true composition. In this connection it may be • noted that the mineralogical name for the

crystalline phosphate of lime is “ apatite ” t the Greek “ apatao,” to. deceive), a name which must commend itself to those who . did not discover the deposit. Indeed, the discovery of great, phosphate-fields has more than once been the result of an, accident. For some time a large piece of rock brought from a Pacific island

was . used to hold a door open in an Australian city office. One day it attracted some one’s notice, and was then found to be high-grade phosphate. This led to inquiry ; and resulted in ■ the discovery of a rich phosphate island. The large Algerian deposits were ' discovered by the accidental curiosity of an observant foreman.

Some large soft deposits in northern France were for years used to dress roads until their, phosphatic nature was discovered. Andrew narrates that a specimen of Milburn phosphate was submitted to an analyst for his opinion on its value as a source .of quicklime. He condemned it as a poor sample, without discovering its true nature story which involves one of two negations: clearly it was either no phosphate or he no analyst. Andrew says, “ The (manner in which the phosphate escaped detection now seems marvellous. . A specimen. of the phosphate was to be seen in the Otago Museum, labelled Decomposed Limestone from Clarendon.’” Lastly, there is the classic instance of the Cambridgeshire coprolites, which were used to metal roads, and were discovered by Henslow in 1854, attention having, it is said, been directed to the fertilizing action of the road-dust on the adjacent paddocks.

It will be seen, therefore, that it is easy for. a person to pass over phosphate through failing to take sufficient notice, and it is to accustom farmers and others to the appearance of the mineral that small samples have been distributed gratuitously by the Department for the last ten years, a policy which I have no doubt is appreciated and of which I cordially approve. Issued with the . information which is to be found under the heading “ External Characters of Phosphate, and Tests,” samples of rock phosphate may greatly assist prospectors in conjuring up an idea of this valuable rock’s appearance. -

Isolated boulders and fragments of calcium phosphate have been from time to time recorded from districts other than Clarendon. None of these has as yet proved to be of more than theoretical interest. It may be as well to enumerate these instances in the hope that, possibly a closer ’ search may reveal larger deposits.

The most promising of these finds was that at Whangarei. Major G. Claik-Walker, in November, 1906, forwarded me a sample of white phosphate rock which was almost pure phosphate ,of lime, containing 87 per cent. Inspector Stone, of Whangarei, about the same time sent in. a specimen which contained 77 per cent. The higher-grade . specimen was so . like - the Clarendon phosphate in appearance that I thought a mistake had been made, but; I was assured that this was not so by Major Clark-Walker, who - -was corroborated by Inspector . Stone. Referring to the high-grade Specimen and the place where -it was £ discovered, the. former gentleman writes, under date sth - November, 01906; “’I find that it was a piece of what looked like shell, out of a lump of rock . from a pit (out of which' stone 'had been taken for the road) at a place called Tikarangi, between the Mata Hill, past Mangapai and Wha-

ngarei, ■at the foot of. the road known as • the Grouse Neck. I tried the shell, and it dissolved in nitric acid altogether and gave a rich creamy-yellow deposit with an aqueous solution.'of ammonium molybdate/' Major Walker must be congratulated on being the first to prove the presence of -rock phosphate at Whangarei.

I afterwards, in the same year, visited Whangarei, making a careful examination of the locality for exposed phosphate with Major Clark-Walker, with a negative result.

In the same month Captain J. Sinclair, Harbourmaster at Port Robinson, Cheviot, Canterbury, forwarded a bag of greenish-looking specimens which he stated appeared as a layer on top of the limestone. These contained 35 per cent, of tricalcic phosphate.

In January, 1907, Mr. H. R. Holman, of Kamo, Whangarei, sent me a large greyish-white boulder, differing in appearance from anything previously found in New Zealand, and containing 62-3 per cent, of phosphate of lime.

In February, 1907, Messrs. J. Harrison and Sons, Whangarei, sent me a piece of phosphate rock found in that district, which contained 50-73 per cent, phosphate of lime.

In June, 1909, Mr. J. S. Wilson sent me from the limestone rocks . at Hikurangi, near Whangarei, a specimen containing 58-35 per cent, phosphate of . lime and much carbonate; and in July of the same year Mr. A. F. Buckland sent a ; piece of phosphate from Fairfield, Oamaru, containing 37-9 per cent, of phosphate of lime.

The bonus offered by the Government. in 1906 for the discovery of phosphates resulted in the receipt in ’ 1907 of 539 specimens of various rocks, most of which were proved by analysis to be of no value. The following year many more specimens were tested, with similar results. In 1909 the interest in the subject continued, 107 specimens being sent in for analysis, the following being of interest:— .

K 2407, a shelly conglomerate, containing teeth and fossil bones, forwarded by Mr. J. T. Armitage, Ponsonby, Auckland, contained 4-48 per cent, of phosphoric acid. ' -

K 2159 was a phosphate rock from Mr. T. Mitchell, Whakapara, Hokianga, but the sample was too small for quantitative analysis. Further samples of rocks from the same correspondent revealed no trace of phosphate. ■ . ■ . , . . ' .* .

' K 1560 was a phosphate rock- of high grade said to have been found in the Waimate. district, and forwarded by Mr. George Pitcaithly,- of the District High School. Only a small .piece. was received, and nothing further has been heard, of the matter. '

A . most interesting discovery was made by me .at the Antipodes Islands (the: nearest land to the antipodes of Greenwich, lat. 49 0 42' S., long. 178° 43' E.). These are a few. tussockcovered islands (12,960 acres) belonging to New Zealand, and leased /to Captain Tucker, of Gisborne; lying about 458 miles in • a :south-easterly . direction , from Port Chalmers. The rocks on the islands are purely volcanic. . Large beds of ashes and ferruginous scoria abound, the cliffs under which we anchored being apparently built up of beds of scoria, successively deposited, giving the cliff the- appearance of a sedimentary rock.

. The analyses of the red scoria (K 3001 basalt (K 3002 and red earth (K 2675 derived from the red scoria, are given below. The • rocks contain an abnormal proportion of phosphoric acid, while the red earth contains about 30 per cent, of phosphates, 8-4 per cent, of which is titanium phosphate. This resisted the action of six successive fusings with bisulphate of potash.. It is thus in this state probably one of the most ’refractory phosphates known. :

ANALYSES. Antipodes Islands -Deposits.

K3OOI. Red Scoria.

K 2675Red' Earth.

K 3002. Basalt;

Silica (SiO 2 ) .. ... .. 41-95 27-68 43-15 Alumina ’ . . .. .. . 13'4° 10-48 15'45 Ferrous and ferric oxides . . . 1575 . 27-40 14’85 Phosphoric anhydride (P 205 0 5 ) .... 2-55 10-70 1-08 Lime (CaO) . . . . . . 9-10 1-50 • 8-8 o Magnesia (MgO) .. .. 5'58 0-79 7-10 Manganese oxide (Mn 2 O 3) .... 0-25 Trace. . . 0-13 Titanium oxide (TiO 2 ) . . '. . 2-25 0-46 3-44 Sodium oxide (Na 2 o) •. . ' .. 7-74 2-25 . , . 4-10 Potassium oxide (K 2 O) .. .. 1-56 ‘ . o-6o , 1-25 Moisture at no 0 ’ " .. .. 0-36 ■ . - 4-35 1-13 Loss on ignition• . . ; .. .. .. s’ oo •• Titanium phosphate (insoluble) .. ' .. ; 8-40- ■ .. ■ Zirconium oxide .. .. .. . - 0-41

• The matter insoluble, after treating with HCI and HNO 3 , was evaporated to dryness, treated with HF and H 2 SO 4 , dissolved in HCI, and fused with KHSO 4 . It then equalled 8-4 per cent., and was found to consist of titanium phosphate. I brought the matter under the notice of Mr. •A. Hutchinson, of Pembroke College, Cambridge, the well-known mineralogist, and he is at present investigating the mineralogical aspect of this curious occurrence.

The possibility of titanium phosphate being formed-during the progress of the assay must be remembered, but the' large amount of phosphoric acid in these rocks is unusual and difficult to account for.

Bounty Islands Granite.

K2996A. Exterior polished bv Sea-birds.

K 2996. Interior.

Loss on ignition ... .. .. s’ oo I ' l s Silica .. . . ... ... . .. 48-25 66-95 Lime ... .'. .. . . •• 9'7° ■ 3’ 2 5 Alumina' .. . . .. ... 13’3° I2 ’s° Ferric oxide . . . . ■ : .. , • ■ 44 : 4’60 Phosphoric anhydride* .. .. . .. 11- 77 ■ I '9° Magnesic oxide ' .. .. . . 0-83 0-43 Titanic oxide ... . . . . ■ . • 0-35 o-6o Potassic oxide . . . . . . ■ • 2-76 4-18 Sodic oxide . . ... . . . . • 4-42 ■ • 4-60 100-52 100-16 * Equal to tricalcic phosphate .. . - .. 25-69 44

Iron phosphate, called by mineralogists “vivianite,” has been recorded from many localities, including Campbell Island, North-east Valley,. Dunedin, Timaru, Pohangina River, Port Chalmers, Taranaki, Thames, Mercer, and Huntly. (Waikato). It is easily distinguished by its fine blue colour. Crystals of vivianite have been found in moabones. - • ‘ ' . ' Aluminium phosphate is said to occur on Green Island, off the coast at St. Clair,' near Dunedin. ’ Both iron and aluminium phosphates are of doubtful value as fertilizers on ordinary land.

. ‘ WHERE TO LOOK FOR PHOSPHATES. The deposits at Clarendon occur in limestone pockets. ■ Search should therefore be made in those districts where limestone occurs, either •as pure compact ■ limestone or as calcareous sandstone; Deposits of coprolites, or phosphatic nodules, .having a. corrugated Surface, and being often black in colour, may be looked for in greensands. I have specimens of these coprolites from Oamaru and from Flagstaff Hill near Dunedin.. . c c.

EXTERNAL CHARACTER OF PHOSPHATES, AND TESTS. . . : . New Zealand mineral phosphate, which has hitherto been ? found in workable quantities only at Milburn and Clarendon, Otago, has a dirty yellowish - white or light - grey colour. Some specimens exhibit a decided pink tinge in patches; It is usually amorphous (non-crystalline), but thin veins of crystalline apatite have been

found at Clarendon, and there is no reason why large quantities of crystalline phosphate should not be found, .In general aspect Otago phosphate resembles the harder amorphous limestones (lithographic limestone), but may easily be distinguished by not effervescing to any extent when brought into contact with a drop ;of dilute, hydrochloric (muriatic), sulphuric (vitriol), or nitric (aqua fortis) acid.. It is, moreover, harder and heavier than any limestone, but it is quite possible that .soft specimens may be found. It is softer than feldspar and than most silicate rocks likely to be. mistaken for phosphate. Some specimens .have a tendency to exfoliate or shed their fragments in layers when struck with a hammer. To sum up : . 6 7. c-

(i.) Phosphate of lime has almost any colour—usually whitish, yellowish, greyish, greenish, pink, or black. (2.) Hardness: Usually softer than feldspar or than > quartz, but harder than limestone. 0 / ■ ' (3.} Specific gravity: Heavier than limestone or quartz. : ■ ’ (4.) Usually non-crystalline, but may be crystalline. (5.) Does not perceptibly effervesce with acid. A good test that may be applied by those who have the necessary materials is to grind the rock to a fine powder, -. and place ’ about as much as will lie on a threepenny-bit, with . about | in. of magnesium ribbon, in a glass tube which has been drawn out and closed at. one end in ’.the flame. The tube is then heated to redness.’ over a .lamp or candle or with a mouthblowpipe until the magnesium kindles, and then plunged into cold water. If any phosphate is present ,in quantity, a few bubbles of gas, consisting .of . hydrides . of phosphorus, will be formed,, and will communicate to the water and air a putrid metallic smell, which is most characteristic, and recalls the odour of decaying fish. A similar smell may . often be noticed near an acetylene-generating plant. .'. • .. . .

The following chemical test for phosphate may be- practised by .those who have any knowledge, of chemical manipulation.: —- /

A suspected rock is ground finely in a mortar and pounder, and dissolved in., nitric acid in a glass vessel with the aid of heat. The solution is then filtered, and the f molybdate/. solution, made as directed below, is added. On standing in a warm place at a temperature not exceeding 70 O C. a dense yellow precipitate separates out if any phosphate is present. .- c ./-/..A.'

Another very ’ good. .' test,? perhaps : the best,' is ; . to put ■ a’. . few drops of the' molybdate solution (which any druggist will . make up) on the suspected, phosphate, y A brisk effervescence indicates that the rock is a carbonate, probably carbonate ... of lime; no

reaction, that it is a siliceous insoluble rock such as basalt, quartz, or greywacke. If in a minute or two a yellow colour appears where the solution rests, the rock is probably phosphatic.

If a rock answering to the above description and tests be found, a small specimen should in the first instance be sent per sample-post, addressed to . the Chemist, Department of Agriculture, Sydney Street, Wellington, by whom it will be tested and reported on free of charge. • '

Reagents for the Molybdate —Molybdic Solution.

Prepared by dissolving 100 grams of finely powdered molybdic acid with heat in 400 grams of 8-per-cent. ammonia of 0-967 specific gravity, and pouring the solution into 1,500 grams of nitric acid of 1-2 specific gravity ; or else by dissolving 150 grams ammonium molybdate in one litre of hot water, and pouring the solution into one litre of nitric acid of 1-2 specific gravity. Prepared in this way the molybdic solution- will contain in the former case 5 per cent., in the latter case from 5 to 6 per cent., of molybdic acid, and 100 cubic centimetres of it are required for precipitating one-tenth gram of phosphorus pentoxide.

MANUFACTURE. The processes involved in converting the phosphate as quarried into a marketable article are: (1) Grading according to quality; (2) drying to expel the moisture (this is done by placing the selected rock upon bundles of faggots or logs, of wood, which are then ignited) ; (3) grinding to a fine powder. The product is now ready for the market, and may be used for many soils in this state. For some soils, however, it is best converted into superphosphate by the action of. sulphuric acid (vitriol), in which form it is soluble in water and makes a valuable fertilizer. For soils or crops that require nitrogen or potash these ingredients may be added either to the ground rock or the superphosphate. It is thus seen that the industry is one of the. simplest to work successfully and employs a very large proportion of unskilled labour.

NEW ZEALAND PHOSPHATE ROCK. . Professor Park, in the “ Transactions of the New Zealand Institute,” Vol. xxxv, p. 397, thus describes the rock phosphates of Otago : > “ This was first found at Discovery Point, at the head of the bend, where it rests on the upper surface of the limestone. Here it forms a massive outcrop, from 12 ft. to 18 ft. high and from

4to 5 chains long. It consists of. a very dense grey or yellowishgrey rock phosphate, very rich, in calcium phosphates. . In places it is nearly pure phosphorite, occurring in narrow-banded paleyellow and grey concretionary masses, possessing a tendency to exfoliate in layers when struck with a hammer. Cavities. in this rock were found to be encrusted with apatite possessing a mammillary structure. The extent of the deposit at this place has , not yet been determined. . . : ■ •

Another outcrop of rock phosphate crops out on the side of a valley opposite Discovery Point, and near it several large. masses of this mineral occur in a small depression in the hill about 20 ft. above this outcrop. Recent excavations show that the phosphatedeposit here is of considerable extent. It has been exposed by open trenches for a distance of 4 chains along the side of the hill, and is found to rest on an eroded surface of the greensands. Loose masses of rock phosphate lying on the slopes to the north of this point to the presence of another deposit in that direction.

“ At Kiln Point a considerable amount of stripping and trenching has been effected, and here much interesting information was obtained concerning the mode of occurrence of the rock phosphate. At this place the outcrop has been stripped, for a distance of nearly 2 chains, exposing a very clear vertical section of the phos-phate-deposit and underlying limestone. The phosphate varies from ■3 ft. to 12 ft. in thickness, and rests in r a series -of pockets in aodeeply eroded surface of the limestone. In the face behind the old limekiln there are three shallow pockets, the most - southerly being 45 ft. wide, . the second 18 ft., and the third about 22 ft., varying in depth from 2 ft. to 6 ft. The pockets are separated from each other by. ridges of limestone," averaging 3 ft. . or. 4 ft. wide, as shown in the following diagram : .

• “ The phosphate fills the pockets and rises above the level of the dividing ridge of limestone to a height varying from 3 ft. to 10 ft., the greatest depth occurring at the north-east end of the section. •

“The phosphate rock exposed 1 in the face of. the open cutting is much broken and crushed, . and sometimes- shows slickenside surfaces. It is yellowish-brown in colour, with irregular seams and patches of whitish-grey. The presence of sand , renders it soft and friable and of lower grade than that exposed at Discovery Point.

At the most easterly point of the open cut, masses of fairly pure phosphate rock contain inclusions of ; basalt, occurring in small angular or nodular fragments, which are seldom over 4 in. in diameter. In a deep, narrow trench above the open cutting the phosphate is mixed with glauconitic greensands, which are said to be highly phosphatic. .

The rock phosphate has been exposed; by a long trench some 12, chains north of Kiln Point, but no feature of special interest is disclosed in this direction. i.L

“At Milburn Lime-quarry the surface ,of the Eocene limestone presents the most marked irregularity. Under. the influence of both chemical’ and physical erosion it has been formed, into wide basins and deep well-like holes, surmounted by overhanging knobs and spires of limestone. The basins are filled with yellowish-brown sands, as shown in Section 111, below: — • .

“ On the right side of the present quarry-face the upper horizon of limestone has been eroded down to the ■ lower, more sandy, and glauconitic horizon, on the irregular surface of which there rest two small patches of rock phosphate, as shown in Section IV.

“On the right bank of a small stream near . Sutherland’s limestone . quarry. there, is a . high face of rock phosphate . resting in a basin in the lower horizon of limestone, and a few hundred yards south-west of Milburn Quarry . there is a similar, but smaller, outcrop, which also appears to lie on the higher.part of the lower horizon. .. . The surface contours and the presence .of basalt fragments in the phosphates at Kiln Point . tend to show that the formation of the deposits took place in comparatively . recent times probably in the Pliocene period and obviously since the present contours of the district were determined Hence it seems probable that the phosphate-deposits will be marginal and follow the line of limestone outcrop, contouring around the slopes of the hills bounding the valleys and shallow basins.” . ' Professor Park adds . “ The evidence available from a surface examination shows that a large quantity of phosphate -rock exists in -this district, but until the deposits have been fully developed by trenching it would be obviously impossible, to express the tonnage numerically. The discovery will doubtless be followed by other discoveries in -different parts of the colony in districts; where similar geological conditions exist, the most likely localities being in Southland, North and South Otago, North and South Canterbury, Marlborough, Raglan, and North Auckland districts.” . ■

Dairying.— now has nine cow-testing associations, the largest of which is the Ferndale Cow-testing Association. More than four thousand cows are on its list, and it is the largest association in the .world. Pacific Rural Press.

* It is extremely desirable that the term “guano” should be restricted to the genuine article. Its use as a synonym of rock phosphate or phosphate containing little or no organic matter is misleading and should be discouraged.

* How this may be done, with details of the average phosphate-content of New' Zealand soils, and further information on the economic aspect of phosphate, may be found in the author’s Bulletin No. 48 (new series), or in this Journal for July and August, 1913 (“ Phosphates : Their Importance to the New Zealand Farmer”). ‘ ■

* ■1905. 1914. — 1905. 1914. Tons. Value. Tons. Value. Bonedust .. .. .. ■ it -* £ •. £ II,088 ' z 58,208 6,578 z 41,870 Island phosphate /. ' 5,523 . i 15,204 - 22,093 56,169 Unenumerated (mostly phosphatic) 22,071 74,583 Basic slag . . . . . 3°,35° 97,589 Superphosphate . . . . 4 1 ,582 151,780 Bone char 665 2,219 Phosphate mo.e," . . . . . . 54° 1843