The Structures of the Auriferous Districts. 185 



assaying their contents of gold were found to range from about one and 

 a half to three hundred pennyweights of gold to the ton of the rock. 

 One drift was driven into a mass of mineralised granite or gneiss, and 

 samples from it yielded at the rates of from ninety-five to one hundred 

 pennyweights of gold to the ton. 



Although in the Potaro, Tiger Creek and Konawaruk Goldfields no 

 e\ idence was obtained of the existence of the older, more or less 

 schistose, basic rocks — epidiorite and hornblende-schist — their presence, 

 but in quantities subordinate to that of the more recent diabase, is 

 clearly shown in places near these goldfields ; as, for instance, in the 

 neighboui'hood of the Ekureparu and of the Oewang Creeks, west of 

 the mouth of the Mahdia Creek on the Potaro River, and near Two 

 Mouth and Willis' Landing on the Konawaruk River. The rocks 

 from these places are auriferous, those from the Konawaruk River 

 yielding upon assaying about two pennyweights of gold per ton. 



The structure of this goldfield indicates that its main source of 

 placer gold was the enormous mass of diabtise, through which have been 

 eroded the great valleys of the upper Konawaruk, Minnehaha, Mahdia, 

 and Tiger Creeks ; whilst the subordinate sources were the older basic 

 rocks, originally gabbro or diabase, and the mineralised belts of acidic 

 rocks. Probably the occurrence of the latter in places has given rise 

 to some of the very rich placer workings of this goldfield. 



The small goldfield in the neighbourhood of Akaiwanna is situated 

 in a gneissose country traversed by a belt of epidiorite, and intersected 

 by gi'eat dykes of diabase. Here the source of the placer gold was the 

 decomposition and degradation of both epidiorite and diabase. 



The unimportant auriferous area near Kumaparu Rapids, in the 

 Demerara River district, occurs in a country of gneissose rocks with, as 

 near Darina, areas of hornblende-schist and, as near Appaparu, of 

 quartz and chlorite-schist ; through this country enormous outbursts 

 of diabase have taken place, this rock being present in great abundance 

 in the forms of bosses, dykes, and sills. At Kanaimapoo, about a 

 mile north of the Great Falls on the right bank wf the river, quartz- 

 veins have been worked for gold with not very satisfactory results. The 

 principal vein ran through a dark-red clay derived from diabase or from 

 epidiorite into an epidiorite derived from a gabbro or diabase-gabbro, 

 whence the miners followed it into an altered granitite intersected 

 by quartz-porphyry, and changed in places int(j a chloritic rock. 

 The. vein where it traversed the red clay always contained gold, 

 generally in small and varying quantities, but in places in fairly rich 

 pockets ; its average contents was about two and a half pennyweights 

 of gold to the ton. But near the junction of the epidiorite with the 

 granitite the quartz was richer in auriferous pyrite and in free gold, 

 and contained as much as thirty-seven pemayweights of gold to the 

 ton. When followed into the granitite it was found to be practically 

 barren. 



On the Berbice River there is a small area of somewhat auriferous 

 nature, the country rock of which is a gabbro more or less changed to 

 epidiorite. 



O 



