MINERALS OF COLUNGWOOD DISTRICT

Nelson Evening Mail, Volume LVI, 16 August 1924, Page 7

MINERALS OF COLUNGWOOD DISTRICT

(By H. P. Washbourn) No. VI. When I come to the iron deposit at lhe Para para I have to make the bold assertion that not one of those who have made geological reports on it have been sufficiently acquainted with the data to he seen to understand or get a grasp <” the situation This will net seem so holt! when consideration is given to the advantages that 1 have had ill such a long and intimate knowledge, not only oi Inc iron deposit, hut also of the country it is situated in when compared with their .short and imperfect, inspection of only a few acres of it. . . It. is the surrounding and adjoining country that makes clear what, otherwise appears to be a chaotic jumble oi ironstone by showing cause and effect. it would be useless and take too muon time to oontravert the many absurdities that have been made in regard to the Parapara iron, but I shall have to snow that, the latest one made by Dr. Bell is founded on very "complex theory and is not supported by the facts. In Bulletin No 3 he gives two plans —one of the surface outcrops, and the other a cross section.

In tin* surface* outcrop plan lie shows certain isolated blocks of ore and then shows them as resting on the limestone with the bare bed limestone slowing between the outcrops. This shows tha' he had not grasped the position, and it is simply quite unsupported theory, lie should have shown the visible outcrops and tlieii the spaces between as being covered with soil and therefore, unknown to him instead of showing them as being bare of ironstone to the bed rock. The surface plan omitted many important outcrops, and was very nnhivourably commented on by those knowing the deposit. Tile late iUr Webb was sent to Para para, and I suggested to him that this pla t could he amended by implying that the country had been more clear since the <iryt issue and that the outcrop omitted in that could be ineluded in a second one. This was done and a. supplementary one was issued containing those omitted in the first one. The section plan could not be amended, i as it. was wrong from one end to the , other, rind until lately 1 could - not im-j agino bow be could possibly make so gioat. a mistake as placing the iron deposit. on the top of an anticline. In conversation with me at. Para para he said. "It. was very seldom that a sineline was so .deirly show i." in a lecture '■!'* i Nelson and in Wellington lie gave it. as a sineliue and yet when his cross see j lion plan came mu tie placed the ore deposit on the top of an anticline. Southward from where this section is supposed to turn th.-ie are 'caim i .* clear sections showing (lie various strata iimlerlving ill- it.m deposit, uniformly

dipping T o tho west I was over tho ' c ! ground lately and X tliink discovered t the causo of the gross < rrn- of th.-. sedition On the eastern s'Jc of the ore p deposit, and undcrly'ng it is a long lull i I descending north from Trig C to '.ho 1 I I'm a para >nu<l ,, at. betwe?i fng avd I Trig A on this line there is a fault, f tlie lower portion of the hill being turned j [over with a very high dip to the east. . I While on the couth side of the fault and t I for sevenl nil's, the .1 p ;s ro the west, although .it not so high an angle, .so that it. is quite possible for two section v lines to lie taken within a .I.am if each . ether, .n which everything would oe f 1 ftversed. Unfortunately Dr. D ll seems f to have tauon bis section from the f.wdt- , cd an i tin n o\. r , ortioru On l 1 1 (* soul hern side of this fault and ( where his section ought, to have been ( ■ taken the visible strata of rock with a , dip of about 40 per cent. from the ' horizontal to the west cn’iir in Ims or . der -tv 'l'king upwards to various schists. ( My building stone, quarry, wliicli is a , large mass of quartzite, other schists, limestone, and the iron. 'the iron me j follows the dip of the rock on the hot- ( tom and there are two places on western ( side of the deposit showing that the sur- , face of the or<> also ti ll.e the same t dip. . i “Rinopai." "Rinorui,” and the “Grey • . Knob" are undisturbed portions, the . limestone not having been eroded from j under them as in the other portions. Ihe j ore in spaces between those outcrops is | still there, only at. a lower level, the ore , having merely sunk down into the cave- j ties made by the erosion and removal of ( the underlying limestone by tne water j and the depressions made by these sub- , sidenees has been filled with alluvium ] and should have been shown as such and j not as blank spaces. . ‘ Tt is surely not ditlieult to understand that whatever is above a subsidence j i follows it down to a lower level. Ihe Takaka Range shows some good examples ( 'of limestone drops, in. and few people ( would he dense enough not. to see that j whatever vote red the surface before the , subsidence would be still there in the , j pit. A bore put down a little to tire ) 'west- of “Rigopai 1 think would pn.i bably go several hundred feet in tmclis- , turbed ironstone until it s;truck the tin- , .disturbed limestone on which the ore t rests. Gypsum or selenite is not found , 1 in the “pots” in the limcmite, but only } • where blocks of carbonate o! iron have oxidised in an alluvial overlying and t quite, independent of the limonite. , i In l)r. Bell's theory or more pro- , perlv speaking various theories of the , origin of the ore with its transmutation , ■ from quartzite and “complex carbon- , 'ate," etc., he appears to me to make , ■ihe matter much more “complex than j .is necessary. 1 shall advance a much ( ■ less complicated theory as to the origin | !of iho ore. which is a hydrous oxide of | i iron formed from the decomposition of ( ihe sulphide by water and is deposited jin the. shape of a brown curd. On tbs ' ill go of the Burn para Inlet there is a , spring of apparently clear water which, j during neap tides, deposits a quantity { of this curd to be swept away again by ihe spring tides. On the Aorere Plain ( ami in numbers of the small flat streams j 'a quantity of this curd accumulate, in f i the. summer when there are no freshes. ' This curd where protected from currents j. soon consolidate, probably partly from ilie- attraction of the molecules for each ( other and in a comparatively short- time forms soft- limonite. The many small deposits of iron ore scattered about the

ountry have probably been formed in Once "a. firm nucleus lias been formed ny water containing iron passing over I. w j]l deposit most of the iron it conains on that already there and in thin [•ny build up a, large quantity. . So far rom the iron ore. being on an anticline it s the eastern edge of a very large pear. Raped rinclinc, the narrow and deep nd being at the Parapara Flat and ndeninf? and flattening out southwards. At the Parapara end the eastern and western uptununl folds of tho limcstonQ ir so clos-.» togdlior that the country rom" the old paint works northward IS mm a great number of depressions altoether sunk to a lower level. Smith of the old paint works tho Up,,,,,,.,1 jy.es of the smeline have beome sttfficiently apart to leave the round in tween undisturbed and the line if .fee.regions follow along the western mi rasii i.u edges >4 i lie sincline indepenlentls of'cinli other and always getting lift her apart. On jh,. western line there are several ,1-ge gullies hearing tlie appearance of mum 'water cut out, gullies in the orliuarv wav, but digging works have liown that they are the result of coninuous subsidences caused by the renoval of the limestone from underneath. Y, mention some, of the larger ones such S Gletigyle, Appoo's Gully, Richmond lill anil parilcidarly McGregor’s Dry lullv, nettr Gulden Gully. In this case or Vears the tailings and water from onsideiiible sluicing operations were run nto a limestone drop in on the Golden lullv side of a hill which divided it com' McGregor's Gully. Tho water and and from this sluicing came up at the over end of McGregor's Gully more ban a mile away. This was the first ign of it after it'was run into tho hole. ~At a later date, nature being assisted ,v the water from the diggings, new de,‘ressinn look place. A digger had a lam on (his line and one night the botom of tlie dam dropped down and when cow it afterwards there was a large ouiifl hole and the trees were standing ip alright with their tops where the tot tom of the dam and water had been. When the Para para Sluicing Company core sluicing in No. 1 face the bottom ; f limit ground race dropped out and heir 43 heads of water and mud was ’tinning in it for some time, hut it was tever known where it came out again. The section on the eastern side across he i,tin deposit should have shown all he focks. including the iron lode dipping it- an angle of upwards of 40 deg. from he horizontal to the westward and on he westward side about a mile distant similar series of rocks 'lipping at about lie same angle to the eastward, the iron virtg on the limestone on this side as In tlm other, hut in a lesser degree. If his does not indicate a sincline I do not mow what it docs denote. Whether lie iron ore follows the. sincline between he two outcropping edge's there is milling to show. Any one wishing to a: satisfied as to the iron deposit beng in a sincline and not on an anticline an easilv do so by starting on the outli side of the fault, near my quarry f quartzite building stone and then fol'iw along the ridge to the south, as. it utcrops above the surface and is easily ceil ami then follow it down the dip o flic westward into the. gorge of tha Ttkurua Creek bed and up again on tliQ titer side. (To he continued.)