CHAPTER XXV. 



THE ORIGIN OF THE PLACER GOLD OF GUIANA. 



In his work entitled "Contribution a I'etude des gites metalliferes," 

 published in Paris in 1897, De Launay stated that in French (iuiana 

 gold is often associated with diorites Mdiich, in places, have decomposed, 

 forming auriferous earth, and that in the contested territory ])etween 

 French Guiana and Brazil, accoi'ding to M. Bernard, gold is found in 

 veins of quartz in diorites traversed by veins of granulite. The 

 dioi'ites are intrusive in gneiss and in hornblende-schist. 



In a joint report with Mr. Perkins, then acting as Commissioner of 

 Mines, pulilished in 1897, dealing with the geology of the North- 

 western district, I pointed out that the source of the placer gold, and of 

 much of the precious metal in the auriferous quartz reefs in that 

 district was, in my opinion, the minute amounts of gold diffused 

 in the basic rocks, to which I applied the field-term " greenstone." In 

 March, April and May, 1898, M. Levat published in the " Annales des 

 Mines" a work entitled "Recherche et Exploitation de L'Or en 

 Guyane Frangaise " in which he pointed out that the placer gold of 

 that country has been derived from the decomj)osition of the diorites or 

 greenstones, which rocks had been shown as far back as 1873, by 

 analyses made in I'Ecole des Mines, to contain " une petite quantity '' 

 of gold. (M. Barveaux, " L'Or a la Guyane Francaise," " Annales des 

 Mines," Annee 1873, Nos. 30 a 3.\) 



Dr. E. R. Lungwitz in 1899 in his pamphlet " Uber die Regionalen 

 Yeranderungen der Goldlagerstatten," produced proofs of great 

 importaiice in connection with the hyjiothesis of the derivation of the 

 gold of the placers from that of the country rock (aplite) at Omai. 



In the report on the geology of the Essequibo, Potaro, Konawaruk 

 and Demerara Rivers Goldfields, dated March 24th, 1900, I pointed 

 out that the source of gold in these districts is, as a general rule, the 

 intrusiAe diabase, although in places it has also been derived from 

 hornblende-schist, or from epidiorite. I did not lay in this report as 

 much stress as I ought to have done on the occurrence of gold in 

 mineralised masses of acidic rock. 



In a paper published in the " Zeitschrift fiir Praktische Geologie," in. 

 July, 1900, on p. 217, Dr. Lungwitz wrote "There is no gold district 

 in Guiana without diabase, and the richest portions of the Guiana 

 gravels are characterised by the fact that the fissures in their neigli- 

 bourhood which have been filled by diabase have been again occupie<l 

 by aplite or diabase intrusions. The result of this was a thorough 

 shattering of the hanging and foot walls of these dykes, the filling of 

 the adjacent fissures by (juartz, and enrichment of the soilbands by 

 gold ores." 



