77<f Orifjui of the Fli(rer Gold of Giiuui'i. 205 



In a paper ])y Dr. Lungwitz on "The Placers of British Guiana," 

 published \\\ Tlw, Mhiing Journal, Railway and Covime^cial Gazette, 

 1900, he stated, as the result of "years of experience in British 

 Guiana," that "the greater j^art of its placer gold owes its existence to 

 chemical concentration." 



Dr. G. C. Du Bois, in his work dealing with the goldfields of 

 Surinam (Dutch Guiana), entitled " Geologisch-bergmannische Skizzen 

 aus Surinam," and published in 1901, points out that there are well- 

 marked proportions of gold in the laterites which have originated from 

 amphibolite and augite-plagioclase rocks, and remarks that in them 

 there is a concentration of the gold of the original rock. 



In the reports of the geology and petrography of the Cuyuni and 

 Mazaruni Districts, published in 1900, 1903 and 1905, I produced 

 further proofs of the derivation of placer gold by concentration of the 

 minute amounts present in the rocks during their degradation into laterite 

 and concretionary ironstone, or to more or less ferruginous gravelly clays. 



It is evident from the foregoing that there is a general consensus of 

 opinion, among those who have studied the geology of the Guianas 

 whilst residing in them, as to the origin of and the mode in which the 

 |)laeer gold has been concentrated in the so-called alluvial deposits of 

 those countries. They consider that the gold has been derived either 

 from mineralised masses of acidic rocks, from that disseminated through 

 the mass of metamorphosed basic rocks, now amphibolites, epidiorites 

 and hornblende-schists, and in part contained in thin veins or threads 

 of quartz, which in places are more or less abundant in them, or from 

 the minute amounts of the metal which are disseminated through 

 unaltered gabbro and diabase. 



Mr. E. G. Braddon, in his article on "British Guiana and its Mining 

 Development," contributed to T/i,e Mining Jonrnal in May and June, 

 1904, does not recognise the distribution of minute amounts of gold in 

 the unaltered basic rocks, and argues that " the gold depositions follow 

 the weakened or ruptured zones of certain pressure planes in the basic 

 dykes, in their contact with the older acidic rocks, or in common 

 through both," thus adopting Dr. Lungwitz's view already quoted. 

 He, however, alludes as follows to " some of the great diabase dykes 

 and masses of the Mahdia and Konawaruk, to which the origin of the 

 rich alluvial gold of these river basins can be traced." As neither 

 in hand-specimens nor in thin slices does this diabase, which is ideallv 

 fi'esh, show any traces of metamorphic effects, the " pressure planes ' 

 essential to his theory can only be existent in them at their contacts. 



Levat lays stress in his work on the position of the placers in 

 French Guiana with relation to the intrusive granite masses. I doubt 

 whether in British Guiana there is any actual relationship between the 

 great majority of the granitic inclusions and the occurrence of auriferous 

 rocks. Certainly there is a broad belt of an intrusive granitite to the 

 south-west of Omai at Kumaka and Ivuratoka, abroad belt of a similar 

 rock at Temple Bar to the north-eastward of the Konawaruk Placers, a 

 very broad one at Pakatuk Falls north-west of the Potaro Placers, and a 

 wide one at Mekoreusa or Eclipse Falls north of the Arakaka Placers, 

 which appear to lend support to Levat's theory, but there are far more 



