The i^trnctures of the Auriferous Districts. 183 



hornblende and of biotite, and approximating to a hornblende-granitite. 

 Intercalated among the schistose rocks are (luartz-diorites (pi'obably 

 epidiorites), epidiorites, and hornblende-schists. The mass of the schists 

 consists of sericite-schist and of chloritic rocks, which are traversed by 

 thin veins of epidote and zoisite, aiid of quartz with carbonates. In 

 parts the schists have, been more or less completely cluuiged into 

 epidosites. The degradation and decomposition-products of the schists 

 closely resemble those usually formed from the basic rocks of the colony. 



At Omai, these country-rocks have been broken through by a wide 

 dyke of aplite about five hundred yards in breadth, which trends to the 

 west-south-west and the east-north-east and dips towards the north. 

 The aplite has been mineralised to a very marked extent, and in parts 

 consists largely of sericitic mica and quartz, there approximating in 

 composition to a greissen or to beresite. The original ferro-magnesian 

 minerals appear to have been sparsely and irregularly distributed 

 through it, and are now represented by wisps of much-altered biotite 

 which are present in places in very small quantities, and by occasional 

 aggregates of epidote with chlorite and extruded iron-ores. In places, 

 the aplite, during its intrusion, took up and absorbed some of the basic 

 country-rocks, and there it contains small plates of a pale-blue horn- 

 blende, and large aggregates of biotite altered to patches of pale-green 

 biotite, chlorite, and epidote, with here and there much separated 

 iron-ore. 



The mass of the aplite consists essentially of quartz and plagioclase, 

 principally albite, with abundant secondary white mica or sericite, 

 which occurs in the feldspar-plates in the form of tufts and I'osettes ; 

 in places, the sericite is associated with carbonates. Scattered through 

 the mass are some grains of magnetite and of titaniferous iron-ores, 

 many patches of carbonates, and crystals of pyrite. It is traversed by 

 very numerous thin veins and layers of quartz, the ft)rnier, seldom 

 exceeding fractional parts of an inch in width, preponderating. Gold 

 occurs in small (juantity all through the aplite in connection with 

 grains of cupriferttus pyrite ; it is fairly evenly distributed through the 

 rock, but it is markedly more abundant near the veins of quartz, and 

 near those places where it is traversed by tongues of diabase, than 

 elsewhere. 



The schistose rocks, the aplite, and the great granite-dj'^ke at 

 Ivumaka and Krabbu are intersected by dykes and by great masses of 

 diabase. This rock is intrusive in them, and at Omai, the schists and 

 aplite were formerly covered by it. It is not possible to definitely state 

 whether there was only one outburst, or there were repeated intrusions 

 of diabase, but the extensive mineralisation the aplite has undergone 

 renders the latter the more probable. The aplite weathers into a 

 greyish, or, in places, a yellowish sandy clay, easily distinguishable 

 from the ochreous-red decomposition-px'oducts of the schists and the 

 deeper red ones of the diabase. 



The Omai Goldfield has yielded from the small area of about forty- 

 five acres which has been worked 58,794 ounces of gold during the 

 years 1892-1907. 



