Quartz Veins and Mineralised Masses. 



193 



and ofi'er no reliable evidence as to their origin. They are traversed by- 

 thin veins of quartz and of carbonates, and by others of epidote, zoisite 

 and carbonates. They contain numerous patches of carbonates and 

 a few minute cubes of pyrites. 



In a few places the bores at Omai traversed laj^ers of sericite-rock 

 and of sericite-sehist. These appear to have been originally feldspar- 

 porphyrite, possibly apophyses from the aplite mass. 



The diabase of Omai is a normal ophitic diabase, varying in texture 

 from coarsely crystalline, approaching gabbro in structure, to fairly 

 fine-grained. Where narrow veins of diabase traverse the country rocks 

 it is either of the tholeite type or a very fine-grained augite-porphyrite. 



Assays of average samples of the difl^erent varieties of rock of the 

 cores from the holes were made in the Government Laboratory, with 

 the following results in grains of silver and gold per ton (2,240 lbs.) of 

 the rock : — 



Kind of Rock. 



Silver. 



Gold. 



Epidiorite 



Epidote-chlorite-schisl 



Sericite-sehist 



Feldspar-porphyrite 



Aplite (bore-hole No. 2) 



Aplite (bore-hole No. 1) 



Diabase 



These figures indicate that the contents of gold in the rocks near 

 Omai vary with the degree of sericitisation to which they were 

 subjected. 



While the country at Omai is in accordance with that of the 

 district generally, it differs from it in a very important respect — the 

 epidiorites and chlorite-schists, which are the country rocks, have been 

 intruded into by a mass of aplitic gi-anitite, which appears to he the 

 main soui-ce of the gold at Omai. This forms a great boss in the 

 midst of the country rocks. During its intrusion many of the already 

 formed crystals of feldspar in it were bent and broken, the mass 

 probably having then been in a pasty state. Whether or not the 

 aplite was mineralised before and during its passage through the 

 schists it is not possible to say, but the prevalence of epidote in the 

 country rocks in its vicinity points to marked metamorphism having 

 taken place in them, whilst it took up and absorbed in places more 

 or less of the country rocks. After the intrusion of the aplite the 

 district was subject to a great outburst, and probably to repeated 

 outbursts, of diabase. The aplite was underlain, intruded and covered 

 by diabase. The diabase is at present in an ideally fresh condition, 

 whilst the presence of secondary minerals, especially of white 

 mica, in the aplite points to its having undergone profound 

 metamorphism. 



