CHAPTER XXII. 



THE STRUCTURES OF THE AURIFEROUS DISTRICTS. 



[a) The Xorth- Western District. — The North-Western district 

 extends from Koriabo on the Barima River, Hoorie Creek on the 

 Barama River, and the Turabang Creek on the Waini River, on the 

 east, to the frontier of Venezuela on the west, and has an average 

 breadth of about thirty-eight miles, whilst its area is somewhat over 

 three thousand square miles. The gold-bearing formation extends on 

 the west into Venezuela. It is probable that more extended prospection 

 will materially add to its recognised area in- British Guiana. In 

 addition to the main area of auriferous rocks in the North- Western 

 district there are small outliers of similar rocks such as the Aruka 

 Hills and the low hills, Mount Everard and Mount Terminus. 



The most north-easterly exposures are the Aruka Hills. These 

 consist of epidiorite which passes in places, as at Maburima and near 

 the Indian Portage to the Arikita, into hornblende-schist. Whilst 

 " colours " of golfl are readily found in the gravels of the small streams 

 which have their sources in these hills, as far as it has been examined 

 the range cannot be considered as likely to be the source of payable 

 alluvial deposits. The rocks which compose the range are auriferous, 

 their contents of gold varying from traces to about 34 grains of the 

 metal per ton of the rock. 



Colours of gold have also been obtained from the laterites of 

 Mounts Everard and Terminus and of Koriabo, the two former being 

 residuary deposits from hornblende-schist, the latter from diabase. 



The sources of the alluvial gold in the North-Western district are 

 the residuary deposits from epidiorite and hornblende-schist, diabase, 

 and in places, for instance, near Arakaka and near Hoorie Creek, 

 from sericite-schist. 



The best known part of the district is the Arakaka Goldfield. It is 

 here difficult to distinguish between the laterite derived from epidiorite 

 and the basic schists and that from diabase, but in places this can be 

 done. For instance, near the Government Reserve at Arakaka the red 

 clays and accompanying concretionary ironstones have been derived 

 from epidiorite and basic schists, while those near Monkey Hill have 

 l^een derived in part from them, and in part from diabase. 



The Arakaka Creek flows through a valley, the lower parts of 

 which contain gravels derived from the residua of epidiorite, horn- 

 blende-schist and diabase, and, in places, fi^om acidic rock such as 

 sericite-schist. In the Barima Mine district the higher parts of many 

 of the hills consist of diabase and its decomposition-products, while the 

 deeper parts of the numerous small valleys and ravines are cut into the 

 decomposition-products of the basic schists. In many places it is not 

 possible to ascertain which of the basic rocks were the principal sources 

 of the auriferous deposits, as the country consists of a belt of epidiorite 

 and hornblendic schists intersected by numerous great dykes of diabase. 



