52 Tlip Geology of the Gold Fields of BritUIi Guiana. 



Hornblende-scliist, Mazanini-Puruni district ... ... Auvergnose. 



Hornblende-chlorite-schist, Arawaka Matope, Cuyuni River ,, 



Zoisite-amphibolite, Cuyuni River ... ... ... ... Hessose. 



Amphibulite, Cuyuni River ... ... .. .. ... Auvergnose. 



„ (altering), Cuyuni River ... ... .. Cecilose. 



Talcose serpentine, Cuyuni River ... ... ... Minnesotiase. 



Epidiorite, Essequibo River district ... ... ... ... Auvergnose. 



Hornblende-schist, Essequibo River district ... ... „ 



As a j^eneral rule wherever epidiorites, amphibolites or hornblende- 

 schists occur in the colony, the products of their decomposition — which 

 are similar to those of diabase — yield gold in greater or less quantity ; 

 and the gold found in parts of the North-west district, in the Puruni 

 district, in the Cuyuni district, and in the Groete Creek district is 

 mainly derived from them. Their contents of the precious metal has 

 been determined in average samples from various districts and places 

 as follows : — ■ 



Issorora, Aruka River ... 8 grains per ton of the rock. 



Maburima Landing, Aruka River ... 32 „ ,, „ „ 



Maburima Hill, Aruka River ... ... 7 „ „ „ „ 



Youpu, Aruka River ... ... ... 4 „ „ „ „ 



Araua Hill, Aruka River ... ... ... 3 „ „ „ „ 



Mazaruni River district ... ... ... 8 ,, „ „ „ 



Puruni River district ... .. ... 5 „ „ „ ,, 



Essequibo River district ... ... ... 12 „ „ ,, 



Konawaruk River ... ... ... ... 32 „ „ „ „ 



Konawaruk River, No. 2 ... ... 48 ,, „ „ „ 



Amphibolite, Cuyuni River .. ... 3 „ „ ,, „ 



Hornblende-chlorite-schist, Cuyuni River 4 ,, „ „ „ 



These show that in the epidiorites and hornblende-schists gold 

 occurs in sufficiently high proportions for them to become the sources 

 of gold in payable quantities when the metal has been set free and 

 concentrated by the decomposition of the rock and subsequent 

 detrition of the latei'ite resulting from it. 



The gold in part accompanies the heavy minerals of the meta- 

 morphosed rocks ; but in some of them it is present in the numerous 

 tongues and veinlets of quartz which traverse them, filling cracks and 

 spaces between, or crossing the folia of the schists. 



Black sands were separated by panning from the gravelly contents 

 of pot-holes in the Wariri belt of amphibolite, and were freed from 

 quartz and feldspar by treatment with Sonstadt solution. They 

 were free from gold in the form of visible specks, but the}^ yielded upon 

 assay gold and silver at the rates respectively of 118 and 150 grains 

 per ton of the sand. 



Where the epidiorites and hornblende-schists are intersected by 

 later dykes of diabase, as in parts of the Arakaka district in the 

 JSIorth-west, we find quartz veins and alluvial deposits containing the 

 metal in exceptionally high proportions. 



Quartz veins traversing amphibolites, epidiorites or hornblende- 

 schist may be expected to be more or less auriferous. 



The very rich mass of quartz at the Peter's Mine in the Puruni 

 River has epidiorite and hornblende-schist for its country-rocks. 



