. The geology of the goldfields of British Guiana. ricts.—Veins of quartz, which are somewhat auriferous, occur ina gneissose country at Karati and at Saxacalli Points on the LowerEssequibo River. Samples from their outcrops yielded at the rateof forty grains of gold per ton of quartz. In the augite-granitite rocks exposed on Black Creek Branch of theGroete Creek, and in the gneiss exposed in cjuarries on the LowerEssequibo River, veins of pegmatite traversing them pass graduallyinto magmatic quartz veins. As far as I have examined thesequartz veins they are not gold-bearing. A great mass of q
. The geology of the goldfields of British Guiana. ricts.—Veins of quartz, which are somewhat auriferous, occur ina gneissose country at Karati and at Saxacalli Points on the LowerEssequibo River. Samples from their outcrops yielded at the rateof forty grains of gold per ton of quartz. In the augite-granitite rocks exposed on Black Creek Branch of theGroete Creek, and in the gneiss exposed in cjuarries on the LowerEssequibo River, veins of pegmatite traversing them pass graduallyinto magmatic quartz veins. As far as I have examined thesequartz veins they are not gold-bearing. A great mass of quartz,probably of this type, is exposed on a small island near the northernboundary of the Penal Settlement. The quartz is not gold-bearing. Southof Arisaru gneiss is traversed by a vein of noii-auriferous quartz. At Omai three quartz veins were discovei-ed in a laterite coveringaplite. These veins were followed for some distance from the lateriteinto the aplite, in which rock they gradually pinched out. They were To fare page 189.] , THE ARZRUNI QUARTZ REEF IN LATERITE,OMAI, ESSEQUIBO RIVER. Fhofo hij C. W. Amlcnnn. Qwntz Veinit and Mineralisnd Classes. 189 studied in detail by Dr. E. E. Lungwitz, from whose published accountsmost of the following details have been taken. The principal one—the Arzruni Reef—was about two feet inthickness, and dipped at about twelve degrees to the other veins were approximately parallel to this one. The rock ofthe Arzruni Reef was of wonderful richness in gold, but the metal wasvery irregularly distributed through it. Large samples from itexamined in the Government Laboratory in 1895-96 yielded at therate of fifty-two and a half ounces of gold to the ton of quartz. Thegold in it was coarse-grained and was accompanied by a good deal oftelluride. The minei-al seheelite occurred in places in the veins insome quantity. The gold was found in the vein in large andenormously rich ore-pockets, in which the metal was assoc
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