DIAMOND: OCCURRENCE IN BRITISH GUIANA 2^9 



the present limit of working — of clay, which becomes more and more gravelly and the 

 constituent fragments larger and more frequently cemented together with iron oxide, as 

 greater depths are reached. Some of the pebbles are much rounded, and have sand and 

 smaller pebbles attached to them by a felspathic cement, while others are sharp and angular. 

 Some consist of felsite and concretionary iron-stone, but most are of quartz. Associated 

 with these pebbles are grains of ilmenite and small rounded pebbles of black tourmaline and 

 pleonaste, and occasionally of topaz and corundum. When dug out, the gravel is carried in 

 wooden dishes to a little creek hard by, where it is washed in sieves of one-sixteenth inch 

 mesh, the residue being picked over while wet. The diamonds, originally found by Mr. 

 Gilkes in 1890, were obtained at the foot of the hill in the bottom of the valley. The 

 diamantiferous gravel here contains many crystals of quartz, and rests upon a bed-rock of 

 kaolin, diflFering in both these respects from that which lies on the hill-side. 



Up to 1900 diamonds had been found only over an area of country measuring 200 

 yards in length by about 100 in breadth, but it is probable that the diamantiferous gravels 

 are much more widely distributed. The mode of occurrence of the diamond in these gravels 

 and the minerals with which it is associated are very much the same as in Brazil. The 

 diamond has not yet been found here in its mother-rock ; if this should at any time be 

 discovered, British Guiana may become an important diamond-producing country. 



As yet there have been found only some few thousands of small diamonds, which have 

 the form of octahedra, and are exceptionally white and brilliant. The smallest are of very 

 small size and the largest about 1^ carats, but there are very few exceeding a carat in weight. 

 During the ten years between 1890 and 1900 between 2000 and 3000 diamonds were found, 

 while, according to custom-house returns, the total export of diamonds up to January 28, 

 1902, amounted to d&10,000. A parcel of 282 stones sent to London during the year 1900 

 was valued at ^^2 8s. per carat. During a period of six weeks in the following year, a New 

 York company obtained 8227 small diamonds with an aggregate weight of 767 carats, which 

 were valued at ,£'1920 or £S, 10s. per carat. A dozen companies have since been organised 

 and ai'e now at work, and fresh ground is constantly being opened up, so that the diamond- 

 mining industry of British Guiana is likely to develop rapidly. 



We are indebted for the above account of the occurrence of diamonds on the upper 

 Mazaruni river to Mr. G. F. Kunz's Annual Reports on Precious Stones, in which is brought 

 together much information from various sources. 



Another occurrence of diamond in British- Guiana is reported by Professor J. B. 

 Harrison, the Government Geologist of that colony. This is in the gold- washing claims of 

 the Omai creek, this stream l)einga small tributary of the Essequibo river, which it joins at a 

 spot about 130 miles above the mouth of the latter. From a part of the bed of Gilt creek, 

 one of the tributaries of this stream, measuring about 500 feet in length and 50 in breadth, 

 some 60,000 ounces of gold and some hundreds of small diamonds have been recovered by 

 the somewhat crude methods hitherto in use. The auriferous gravels of this stream consist 

 of fragments of more or less decomposed diabase, pebbles of concretionary iron-stone and 

 angular quartz. They yielded at one time hundreds of very small diamonds, the majority 

 of which were perfectly clear and colourless octahedra, the remainder being of various shades 

 of pink, green, and clear yellow. 



It is stated by Mr. G. F. Kunz that in Dutch Guiana also diamonds have been found 

 for years past in the tailings of the gold-washings. They have been for the most part small 

 and have attracted but little attention, the gold being the chief object sought for. One fine 

 stone, however, is reported to have been found about the year 1890 and to have been cut in 

 the United States, 



