CHAPTER XXIII. 



QUARTZ VEINS AND MINERALISED MASSES. 



Quartz Veins or Reefs. — The auriferous quartz veins, or so-called 

 reefs, of the colony occur in the majority of cases where the country 

 consists of gneiss traversed by belts of epidiorite, or of hornblende or 

 chloritic schists, through which numerous intrusions and outbursts of 

 diabase have taken place. 



North- Western District. — Quartz veins are of common occurrence in 

 the neighbourhood of Arakaka, in the North- Western district. This 

 district consists of more or less acidic schists of very varying 

 character, but generally sericitic, which are bounded on the north-west, 

 at Mekoreusa or Eclipse Falls, by a great roll of gneissose granite, and 

 are traversed by belts of epidiorite changed in places to hornblende 

 and to chlorite schist, through which numerous dykes and sills of 

 diabase have been intruded. No quartz veins occur in the diabase 

 whilst in the unaltered epidiorite and hornblende-schist, only, as a 

 rule, narrow veins and stringers of quartz are found. But veins and 

 lenticular masses of quartz which are, not unfrequently, rich in gold 

 are of common occurrence in tlie decomposition-products of the 

 epidiorite, hornblende-schist and diabase. 



Veins of quartz occur in the granitic-gneiss and acidic schists, but 

 where they are seen in the unaltered rock they are either practically 

 barren or are auriferous only to a slight extent. 



B(»th the structure of the district and the petrographical examina- 

 tions of its rocks indicate that the schists are of earlier origin than is 

 the granitite of the district, and that the diabase was intruded later 

 thi-ough them. The older basic intrusions, represented by the belts of 

 epidiorite and hornblende-schist, are more or less auriferous. The gold 

 is present in part in the numerous threads and narrow veins of 

 pyritiferous quartz which traverse them, but it is also present diffused 

 through the rock. Whether the gold was an original constituent of 

 the rock, or whether it was introduced into it during and after the 

 granitic intrusions in the neighbourhood, it will not be possible to say 

 until more extended examinations of the district have been made. 



The quartz veins which occur in the granitite-gneiss and sericite- 

 schist of the district are either usually magmatic quartz veins, due to 

 granitic intrusions, or are fissure-veins. Some of the larger veins, 

 traversing epidiorite and hornblende-schist, may be magmatic quartz 

 veins, whilst others are fissure-veins which have been subjected to 

 secondary enrichment. Where the country rock traversed by these 

 veins has decomposed to a great depth their size has been largely 



