Farquharson. — The Platifium Gravels of Orepuki. 



475 



What, now, can we gather from these discoveries ? If we look back for* 

 a little at the geology of the claim we shall see that the characteri£,tics of 

 it are — {a) beds of lignite, (h) a base of gabbro rock which is an intrusion 

 into a clay-slate formation, (c) a gravel placer or beach formation. From 

 the review just given it will be evident that any one of these masses could 

 be not only a repository, but, in the case of the gabbro at any rate, an 

 original habitat of the metal. It was therefore necessary to examine and 

 test both the lignite and the rock in a very thorough manner. 



A mass of the lignite was burned completely to an ash, and when a 

 sufficient quantity of ash remained a charge was made up as follows (crucible 

 fusion) : — 



Grains. 

 Ash .. .. .. .. .. ..100 



Soda . . 

 Borax 

 PbO .. 



Argol 



125 



20 



60 



5 



After cupellation an examination of the ciipel showed the merest speck of 

 gold, so small as to be miweighable. 



It was not thought worth while to follow up this line any further, because, 

 since the lignite is a detrital formation, and as it was brought down by 

 waters which also brought down masses of the neighbouring rock, and since 

 it was probable that more platinum would be evidenced in the rock than 

 in the lignite — for these reasons it seemed better to devote attention to the 

 rock, 



A microscopic examination of several sections failed to show the faintest 

 trace, either in reflected or polarized light, of any isotropic mineral other 

 than magnetite. Recourse was then had to assays. 



A portion of the rock was taken clean and crushed in a piece of clean 

 cloth. When fine enoiigh, two charges were made of it, as follows : — 



Rock-powder 



Soda 



Borax 



PbO 



Argol 



Grains. 



1,000 



1,250 



500 



500 



50 



B. 



Rock-powder . . . . . . . . 1,000 



Soda .. .. .. .. 1,250 



Borax . . . . . . . . 600 



PbO . . . . . . 600 



Argol . . . . . . . . . . 45 



After crucible fusion, scorification, and cupellation, the weights of the beads 

 were found to be — A, 0-003 grain ; B, 0-003 grain. Since, however, some 

 decomposed material adhered to the rock, fresh assays were run with 

 exactly the same charges. The bead of A weighed then 0-001 grain, and 

 that of B 0-0012 grain. Both beads were then put together, inquarted and 

 parted in nitric acid, dried, and the combined weight got. It amounted to 

 0-002 grain. 



From this it will be seen that the whole was practically pure gold, with 

 only a trace of silver, and that probably due to the lead-oxide used. 



