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Chapter XIII. The Alluvial Goldfields of Westlajtd.

Although it is beyond the scope of this Eeport to give an exhaustive account of the goldfields of Westland, I wish to offer at least some remarks upon the formation of those beds in which the principal worlds are situated. They are of various character, and may be classed as alluvial, glacier, and littoral deposits. The alluvial beds from which the largest amount of gold has been, and is still being derived, have been formed during, or at least immediately after, the termination of the Pareora formation (Captain Hutton's Kanieri Group.) In previous chapters I have already pointed out that before the advent of that formation, and during the time the Oamaru series was deposited— the land having sunk several thousand feet below its present level-calcareous strata, finely grained, from the nature o£ the deposited material were thrown down. These deposits, partly by raising the bed of the oc'ean, but, and principally by the upheaval of the Islands, assumed gradually a shallow-water or littoral character. It is at the same time evident that many oscillations occurred, judging from the strata under review although a gradual rising was predominant. Thus we find, to pive the general features, that the lower finer grained limestones were' followed by claymarls and clays, the latter becoming more and more arenaceous, till the uppermost beds, consisting of a loose ferruginous sandstone, are reached. These last form the uppermost marine bed, as they are everywhere succeeded by others of a very different character, to which we may assign the name of the Great or Lower gold-drift of New Zealand. Instead of marine strata, deltaic and fiuviatile beds appear, page 362consisting of boulders, shingle, gravel, sand, and loam (silt), where the precious metal has been retained which has been brought down from the ranges. For an enormous lapse of time these ranges have been subjected, first to marine and afterwards to subærial denudation Thus, where this lower gold-drift has been preserved, which, owing to its peculiarly loose character, could only happen under very favourable circumstances, it is obvious that the precious metal contained in it must be abundant. To this conclusion we must arrive, if we consider that during the gradual rise of the land, great denudation of the rocky surfaces of the Island went on continually, in which the gigantic glaciers took a considerable share, and that the rivers becoming larger were able to destroy not only greater masses of rocks, either by undermining their banks and rolling boulders of greater size along, but also by carrying the gold derived from the destruction of those sources farther with them towards the sea. As soon as rivers of any size reached the rather shallow sea, deltas of large dimensions were formed, where the gold was ultimately deposited.

In my Report on the formation of the Canterbury plains, I have shown how such fanlike beds are formed, and how they are liable to be destroyed, or to be covered by fluviatile deposits of more recent origin. That also the marine young miocene or older pliocene beds, immediately underlying the great gold-drift, underwent considerable denudation in many localities, is well exhibited by ranges consisting of these rocks, situated from four to eight miles from the coast line, and 600 to 800 feet high, falling steeply in many places towards the east. They often form true razorback ridges, running parallel with the direction of the central chain. Remains of the great gold-drift are still preserved on the summit of these ridges, thus showing that these older alluvial beds, in many instances assuming the texture of a conglomerate of considerable hardness, covered uniformly the whole zone, and that since their deposition remarkable denudation has there taken place. In this older alluvium the principal goldfields of Westland are situated, of which the Greenstone, Kumara, Waimea, Kanieri, and Ross diggings are the most important. It is especially in those localities that favourable circumstances have existed for a preservation of these deposits. If we examine these beds with care, and follow them a considerable distance, we find that they consist mainly of the alluvial deposits of a large river, coming from the north-east through the present Grey valley, skirting the western foot of the Hohonu range where the Greenstone diggings are situated. This river was joined by several tributaries as far south as the Totara page 363river, their deltaic deposits having considerably raised its bed. The auriferous alluvium, forming a plateau washed by the sea, and reaching to the western foot of the Southern Alps, was afterwards to a considerable extent preserved from destruction by the outrunning ridge between the last-mentioned river and the Mikonui. The lithological character of the boulders, of which this alluvium consists, gives us at once an insight into the nature of the beds from which they are derived. There are associated with them, dioritic sandstones, graywacke, conglomerate and breccia, clay, graywacke, and silicious slates, and diabasic rocks all of which are found near the summits of the Southern Alps, together with the fine-grained, light-coloured schists, characteristic to that formation. But a very considerable part of the alluvium consists of metamorphic and plutonic rocks too numerous to mention, but clearly indicating that the longest course of the river went through rocks of that description, and that the greatest denudation has taken place amongst them. It is evident, therefore, that the boulders, gravel, and sand, of which those alluvial deposits are mostly composed, must contain a great deal of gold, which, however, would not be worth extracting, had not nature herself concentrated the precious metal in numerous localities by sluicing the original accumulations on such a gigantic scale as can only be effected by natural physical forces. This West Coast plateau, besides being intersected by a number of large rivers, is nearly separated from the higher mountains forming the out-running spurs of the Southern Alps by small streams running generally in a northern or southern direction, before joining the main river. The consequence is, that for a long period it has remained almost intact, till smaller water-courses, derived from the surface drainage, began to form channels, taking their source on the plateau itself, which has the character of a swampy plain covered with manuka scrub and other vegetation peculiar to moist localities. I have already stated that the older alluvium covers the highest young tertiary ranges, which are of an altitude of about 800 feet, and repose unconformably upon the cretaceo-tertiary strata near the Grey. Of these facts I met numerous instances during my various journeys across these goldfields, where sharp razorback ridges have been formed, still bearing a distinct capping of sub-angular boulders on their summit. It is thus evident that when we meet with the original deep channels or leads, where during a long lapse of time the gold could concentrate, a rich harvest may be expected by the gold miners. To such old channels of concentration some of the goldfields of the Greenstone, Waimea, Kanieri, Ross, and the lately discovered Kumara diggings belong,

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Another class of goldfields owes its existence to the destruction of the old alluvial beds, when the gold disseminated through them has become concentrated in the present water-courses or on those narrow terraces fringing them, which were formed when the river stood at a higher level. The broader and more numerous the terraces, the less are the chances of the existence of rich leads. In illustration I have copied from my note-books a few sections from the Waimea district on plate 5. No. 5 gives a section near Waimea township, where the high banks on both sides consist of somewhat micaceous claymarls belonging to the Kanieri formation, topped by alluvium. The river flows here in two branches with a large island in the centre formed of newer alluvium. The working of this bed, although only two feet thick, has proved very remunerative. Ascending the Waimea Creek we find that its channel gradually narrows, and that a mile above the township it runs in a deep gorge cut into the Kanieri beds (Section No. 6.) The alluvial beds along the river are here about 15 feet wide, reaching only a few feet above the present level of the water; they have proved to be exceedingly rich in gold; whilst the terraces on both sides, about 20 feet above the water, have been remunerative only when several favourable conditions united. The third section (No. 7) is from the lower course of the Kopitea, a small water-course reaching the sea north of the Waimea. The old river bed is here very wide, the tertiary cliffs standing a considerable distance from each other, and the low terraces between them being of considerable breadth. This valley was thoroughly prospected in 1865, but no payable ground could be detected, although everywhere very fine scaly gold in minute quantities was to be obtained. Some of its small tributaries proved, however, of considerable richness. In some instances this auriferous drift occurs either amongst the morainic accumulations, as, for instance, on the Kanieri river about six miles above the township of that name, or the lower beds containing the precious metal have been preserved by them from destruction. This is well shown in the cliffs at the junction of the Kanieri with the Hokitika river, where old preglacier alluvium is immediately covered by silt, over which again an ancient moraine has been accumulating. This alluvium, without doubt brought down in the bed of a large torrent issuing from a glacier then not far distant, often contains a considerable quantity of gold, generally scaly and waterworn. On the Kanieri flat these alluvial deposits have also yielded a considerable quantity of gold. After sinking 30 to 35 feet, where the boulders, having always their edges somewhat rounded, became of large size, a bed of rather incoherent page 365sandstone is reached, forming the bottom of the auriferous deposits. Here amongst blocks of eight feet in diameter coarse gold was found, and often in such large quantities that it was well visible to the naked eye. Nos. 8 and 9, on plate 5, give some details of these interesting sections. It is thus clear that the huge torrent issuing from the glacier not far away, deposited a considerable amount of coarse gold amongst the large boulders; the greatest portion, however, became so finely divided, or was washed to such distances, that at present it is inaccessible to mining operations.

In the descriptive part of this publication I have already alluded to the black sand beachers, who watch the coast principally in such localities where small indentations favour the preservation of magnetic or titaniferous ironsands. These sands always contain a certain amount of fine gold, derived from the enormous destruction of auriferous rocks going on without interruption: first in the rivers draining the Southern Alps, and afterwards along the sea coast. I may here observe that some of the quartz conglomerates belonging to the Grey Coal Measures, on prospecting, have been found to yield a certain amount of gold. If these operations should prove to be of a payable nature, a great deal of additional ground for mining enterprise will no doubt be opened up.