188 The Gcohxjy of the Gold Fields of Britixh Guiana. 



from the pegmatite dyke exposed in Kalacoon Bay. Like the great 

 majority of gold-bearing veins in British Guiana it occurs in the 

 immediate vicinity of hornblende-schist, a belt of which is exposed at 

 Bartika Point. 



There are two veins of quartz which run through gneiss exposed 

 in tlie channel of the river above Itaballi Rapids. The outci'op of 

 one yielded gold upon assay at the rate of ten grains, whilst that of 

 the other gave 9*5 pennyweights per ton of quartz. These auriferous 

 veins are in the neighbourhood of a complex of diabase dykes 

 intruded through the gneiss. 



For about nine miles above Turesi Cataracts to the lower end of 

 the Marabisi Channel the Mazaruni River traverses a country made up 

 of quartz-diorite, more or less schistose in character, epidiorite, amphi- 

 bolite and hornblende-schist, and traversed by numerous dykes of 

 diabase. This structure appears to extend across counti-y in a northerly 

 direction to the Puruni River, where the breadth of the belt of basic 

 rocks is about seven miles. The country is traversed by many veins 

 of quartz, — the rock of the outcrops of every one of those which I 

 examined being more or less auriferous. 



Some miles further up the river at the south-west end of Issano 

 Island there is a vein of quartz, varying from three to ten feet in 

 breadth across its outcrop, which traverses a chloritic schist. The vein 

 is auriferous, specimens from its outcrop yielding upon assay gold at 

 the rate of three pennyweights to the ton of rock. It has the typical 

 appearance of a fissure vein. 



From near the mouth of Tiger Creek to near Barnard's Landing 

 the Puruni River passes through country similar to that above Turesi 

 Cataracts on the Mazaruni. The country is traversed by veins of quartz,, 

 all of those I examined being auriferous. Towards the northern end 

 of this broad belt of basic rocks the great mass of auriferous cjuartz and 

 the extensive quartz veins now being worked as the Peters Mine occur^ 

 the country rock of the veins being a chloritised hornblende-schist. 



The Quartz Veins of the Esseqtdbo, Potaro and Demerara 

 Districts. — Veins of quartz, which are somewhat auriferous, occur in 

 a gneissose country at Karati and at Saxacalli Points on the Lower 

 Essequibo River. Samples from their outcrops yielded at the rate 

 of forty grains of gold per ton of quartz. 



In the augite-granitite rocks exposed on Black Creek Branch of the 

 Groete Creek, and in the gneiss exposed in cjuarries on the Lower 

 Essequibo River, veins of pegmatite traversing them pass gradually 

 into magmatic quartz veins. As far as I have examined these 

 quartz veins they are not gold-bearing. A great mass of quartz, 

 probably of this type, is exposed on a small island near the northern 

 boundary of the Penal Settlement. The quartz is not gold-bearing. South 

 of Arisaru gneiss is traversed by a vein of noii -auriferous quartz. 



At Omai three quartz veins were discovei-ed in a laterite covering 

 aplite. These veins were followed for some distance from the laterite 

 into the aplite, in which rock they gradually pinched out. They were 



