Farquharson. — The Platinum Gravels of Orepuki. 473 



l)een found have been recorded. It Avill be advantageous in our investi- 

 gation to first briefly review the records hitherto noted of the principal 

 occurrences. 



Nearly all discoveries can be grouped roughly in three large classes— 

 (1) veins, (2) placers, (3) eruptive rocks. 



In veins the discoveries are few, and rather remarkable. The chief 

 one is that noted by Professor W. C. Knight, from the Rambler Mine, in 

 Wyoming. The district has a country rock of gneiss-granite, penetrated 

 in several places by large dykes of dark basic rocks. The dykes are com- 

 posed mostly of a typical diorite, and it is in the outcrop of one of the 

 dioritic intrusions that the mine is worked. It is also to be noted that, 

 so far as is known, the metal or ore does not occur at all beyond the region 

 of the intrusion. 



The second noteworthy occurrence is reported by C. F. Hartt, from 

 Brazil, in South America. The country rock here is described as a syenitic 

 gneiss cut by quartz veins. Nothing further is known about it. 



Another interesting discovery is noted from near Seville, in Spain, by 

 the French chemist Vanquelin. The metal was found in a mineral con- 

 taining copper together with antimony in an undoubted vein, which was 

 actually being worked for silver. The country rock is a mica-schist. 



Again, a remarkable occurrence, which we have already mentioned, is 

 reported from New South Wales. The metal was found near Broken Hill, 

 the seat of the great silver-mines of Australia. The localities where the 

 metal has been found are described as consisting of schists, gneisses, and 

 quartzites, all of which are highly altered sediments. Intruded into these 

 in various places are dykes and bosses of granite and very basic diorite. 

 Some serpentine occurs within a distance of seven miles. The actual lode 

 has already been described. The platinum occurs here in very minute 

 specks, incapable of being distinguished by the eye. It has been suggested 

 that the metal owes its presence to hot springs which formerly issued from 

 the lode, the metal being absorbed by the clays and kaolin round the vein. 



Lastly, attention must be directed to the New Zealand lode in the 

 Auckland Province, at the Thames goldfields. A reference to the parallel 

 drawn between the Longwood and the Coromandel Peninsula shows that 

 the lodes in this instance are also in a district penetrated by dykes of 

 diorite or dolerite, though the actual veins are of quartz. 



With regard to the third class — i.e., in eruptive rocks — since all placer 

 deposits are derived more or less from igneous rocks or mountainous sedi- 

 mentary formations, it will be sufficient to describe the most common 

 placer deposits, referring them where possible to their original mother rock 

 (igneous or otherwise). 



Platinum has been obtained in commercial quantities in connection 

 with the gold-washings of south-western British Columbia. As far as the 

 metal is concerned, the area which is of special importance is in a valley 

 of a small creek along the Tulameen River. In the neighbourhood of the 

 creek a large dyke of peridotite crosses the country, but does not extend 

 to any great distance beyond. It is cut short by a rock of pyroxenite type, 

 which in its turn is replaced by a large mass of andesite. Evidently, then, 

 the gravels are formed from either the peridotite or the pyroxenite. A 

 careful examination of some nuggets which occurred amongst the scales of 

 platinum revealed the presence of chromite, and, in a few cases, of pieces 

 of olivine. Later on a nugget was got with pieces of pyroxene adhering. 



