Qwn'tz Veinit and Mineralisnd Classes. 189 



studied in detail by Dr. E. E. Lungwitz, from whose published accounts 

 most of the following details have been taken. 



The principal one — the Arzruni Reef — was about two feet in 

 thickness, and dipped at about twelve degrees to the north-west. 

 The other veins were approximately parallel to this one. The rock of 

 the Arzruni Reef was of wonderful richness in gold, but the metal was 

 very irregularly distributed through it. Large samples from it 

 examined in the Government Laboratory in 1895-96 yielded at the 

 rate of fifty-two and a half ounces of gold to the ton of quartz. The 

 gold in it was coarse-grained and was accompanied by a good deal of 

 telluride. The minei-al seheelite occurred in places in the veins in 

 some quantity. The gold was found in the vein in large and 

 enormously rich ore-pockets, in which the metal was associated with 

 numerous crystals of iron pyrites. The bulk of the quartz in the vein 

 was almost free from gold. The examination of one of the rich 

 pockets was described by Lungwitz in the following words : — 



" The quartz was much cracked at the ore-pocket, and showed a good 

 deal of ' paint-gold.' . . . The specimen was broken up, and every jjiece of 

 quartz was left out which appeared to be quite free from gold and gold-ore, 

 and assays of the quartz were obtained of from two dollars to three dollars 

 (two to three pennyweights) per ton, whilst the test of the whole specimen 

 had given us a result of twelve thousand dollars (six hundred ounces) or 

 more per ton. The origin of the gold must be sought for with that of the 

 formation of the iron jiyrites, for not only at this pocket, but also at other 

 places where this vein was opened up, it was evident that the gold ore, 

 whether as pure gold or as tellurium ore, was closely connected with pyrites. 

 When the pyrites crystals out of the pocket were assayed, after having been 

 completely freed from all visible gold, the results were little better than 

 those from the pure quartz. In the same way, after removal of the pocket, 

 the adjacent parts of the lode were found to be poor." (Uber die Regionalen 

 Vernnderungen der Goldlagerstatten,1899, p. 13.) 



The aplite at Omai is traversed by very numerous thin veins of 

 quartz, all of which are auriferous. 



At the Tiger Creek Placei-s of the Garnett Syndicate there is a very 

 extensive reef, or vein, of bluish quartz, which is auriferous — in places 

 to a marked extent. This vein ti'averses a decomposed metamorphosed 

 quartz porphyry. Its contents of gold was found, upon assay, to vary 

 from two to sixty-nine pennyweights per ton of quartz. In addition 

 to quartz, the rock of the vein contains muscovite of the sericite type. 

 Some specimens from it have the appearance of a silicified pegmatite. 

 It is probably an auriferous magmatic quartz vein. 



At a small creek called Anderson Creek, a tributary of the Potaro 

 River, there is a vein of somewhat auriferous quartz traversing clay, 

 the decomposition-product of feldspar porphyrite. 



As a rule, quartz veins which are auriferous appear to be far from 

 common in the Essequibo and Potaro Goldfields, although angular 

 blocks and great masses of non-aurifei'ous quartz are of frequent 

 occurrence, as, for instance, at the mouth and along the lower parts of 

 the course of the Kuribrong River. These generally are in sericite- 

 schists and otherwise altered quartz-porphyries and porphyrites. 



