The Pamphlet Collection of Sir Robert Stout: Volume 66

Alluvial Mining

Alluvial Mining.

Alluvial gold is chiefly found in the South Island, in the Districts of Otago, Westland, and Nelson, in which mining operations are carried on over an area of about 20,000 square miles.

The auriferous sand, or gold drift, as it is usually termed, is of three distinct kinds.

Firstly, that which is found in the beds of rivers, and which is worked by small parties of miners, as the process requires no large expenditure of capital to effect the separation of the gold.

Secondly, immensely thick deposits of gravel of more ancient date occupy the wider valleys and the flat country, from which the gold can only be obtained by means of considerable expenditure and large engineering works for the purpose of bringing a supply of water for undermining and working the auriferous deposits. This description of mining is of a more permanent character than the former, and provision has been made by the Colonial Government for assisting the miners by the construction of water-races, which will supply the means of profitable employment to a much larger number of persons than at present gain a livelihood by it.

Some of these deposits are of considerable age, the cements of Tuapeka being certainly not younger than the lowest Tertiary deposits of the colony. They occur in beds from 300ft. to 500ft. thick, and cover a considerable area of country. These cements are treated in a different way from ordinary alluvial deposits, being crushed and washed in the same manner that a quartz reef is worked; but in consequence of the nature of the deposit as much as 150 tons of stone is put through the batteries in one day. They consist of coarse gravels and silts cemented together, carrying variable quantities of gold, and were first found at the Blue Spur in Otago, and subsequently at a number of other places in the same district. At Charleston also, and elsewhere on the West Coast, auriferous cements are worked, but the localities first cited are those which to the present time have received the greatest attention. The yield of gold from these cement claims is small, but, in consequence of the large amount of material which can be operated upon, the value of the deposits is considerable, and their extent guarantees that they will afford a remunerative return for some time to come.

Thirdly, along the sea-coast the continued wash of the waves produces a shifting action on the sands which are brought down by the rivers and drifted along the shore, thus producing fine deposits of gold, the extraction of which, by the aid of simple mechanical contrivances, affords employment to a large number of diggers, who can labour without incurring the hardships and privations which attend the occupations of miners in the more inland districts.

The alluvial diggings at Collingwood were discovered in 1858; those of Otago in 1861; and in 1864 the goldfields near Hokitika proved a great attraction to the mining population of New Zealand. In Otago the gold drifts rest on the denuded surface of their parent rocks. The auriferous gravels in the western district, on the other hand, as a general rule, rest on the surface of Tertiary rocks of marine origin, and they have a general distribution parallel to whatever was the western shore of the Island at the time of their deposit.

The richest alluvial diggings in Westland usually occur in places very inaccessible for water supply, the streams having cut their channels much below the surface of the country, so that an organized system of irrigation is necessary to obtain the required amount of water for the gold-washing.

The following is the composition of New Zealand gold as exported from various districts:—

Melted gold from West Coast, Hokitika, Westland :
Assay—Gold .9627
Silver .0363
Copper .0010
Melted gold from Thames District, Auckland :
Assay—Gold .6565
Silver .3390
Copper .0045

Refined gold, as extracted by the chlorine refining process, and as exported by the Bank of New Zealand, Auckland :
Assay—Gold .9942
Silver .0058

The total quantity of gold entered for exportation from New Zealand up to the 31st December, 1885, amounted to 10,789,650oz., valued at £42,327,907.

The quantity exported in 1884 amounted to 246,393oz., valued at £988,953.