206 SYSTEiMATIC DESCRIPTION OF PRECIOUS STONES 



market at Kimberley. The first of the above three tables gives the total yearly production 

 for the whole of South Africa, from the discovery of diamonds in 1867 up to the year 1892. 

 Details connected with the production in certain years of individual mines are collected 

 together in the second and third tables. 



Formerly, when the claims were in the possession of single individuals or small companies, 

 the aim of the owners was to obtain and sell as many stones as possible. Now, however, the 

 output is controlled by the " De Beers Consolidated Mines," and only a certain number of 

 stones are placed on the market, in order to keep up the price. Experience has shown that 

 the annual demand for diamonds, both for jewellery and for technical purposes, amounts in 

 value to about d£'4,000,000. Taking the average value of rough stones at 21«. per carat, this 

 corresponds to a weight of rather over 3,800,000 carats, or about 15^ cwts. ; the yearly 

 production of Cape diamonds is rather over 3,000,000 carats, and the difference between 

 these weights represents the amount supplied by Brazil, India, Australia, and Borneo. 



Although the total weight of stones collected is so enormous, yet the relative amount 

 of diamond in the "blue ground" is extremely small. The proportion which this 

 constituent bears to the whole mass varies both in different mines and in different parts of 

 the same mine. Thus in some mines the " blue ground " excavated from successively lower 

 depths has shown a maj-ked increase in richness. It would be naturally of great importance 

 to those interested, were it possible to foretell whether such an improvement in yield would 

 be maintained or not ; this, however, is not possible, and it is equally impossible to give any 

 explanation of the variation. 



The Kimberley mine, since its discovery in July 1871, up to the present day, has 

 been the richest of all the deposits. Many of the original miners made their fortunes in less 

 than a month, and one case is quoted in which diamonds to the value of over ^£"10,000 were 

 found in the short space of a fortnight. A cubic yard of " blue ground " from the Kimberley 

 mine contains more diamonds than a mass of equal size from any other district ; this being 

 so, mining operations were here prosecuted with great vigour, all the other mines being at 

 one time forsaken. Owing to the want of reliable statistical reports dealing with early times, 

 it is not possible to determine with certainty whether the deposit increases in richness as 

 greater depths are reached, or not. Probably it does not, and if this be so, the Kimberley 

 mine differs in this respect from the others. 



Boutan has collected statistics dealing with the content of diamonds in the " blue ground " 

 excavated from the Kimberley mine by certain companies. From the year 1881 to 1884, 

 this varied between 3'04 and 7"17 carats per cubic metre (about 1-3 cubic yards), an amount 

 corresponding to two- to five-millionths of a per cent. This yield, however, applies only to 

 the richest parts of the " blue ground," the mean yield for that part of the deposit which is 

 worked, taking rich and poor together, is about 4t-55 carats per cubic metre (3'5 carats per 

 cubic yard). If, however, the material of the western side of the mine, which on account of 

 its poverty is not worked, is also included, the mean yield for the whole deposit will be 

 4-20 carats per cubic metre of "blue ground," or on the average three-millionths of a 

 per cent. 



TTie dimensions of the portion of the deposit which is worked being known, it can be 

 calculated that the excavation of " blue ground " to a depth of one metre would result in the 

 production of 88,000 carats of diamonds, which at £1 per carat would be of the aggregate 

 value of ^88,000. From the same part of the deposit, a cubic metre of worked material 

 would contain on an average ^£"4 11*. worth of diamonds. 



The De Beer's mine is li times the size of the Kimberley mine ; the central point of 

 the former is situated 1771 yards to the east of the central point of the latter. The deposit 



