202 Till' Geology of the Gold Fields of British Guiana. 



thickness of the gravels is from two to three feet. The gold varies 

 from fine dust to small nuggets of two to three ounces in weight, and 

 the gravel yields an average (^)f about one and a half pennyweights of 

 the metal per cuV)ic yard. 



The laterites and ironstones on the hillsides in this district are 

 auriferous. 



The gravel at the Konawak Creek Placers consisted of angular 

 fragments of quartz, and was of considerable thickness — between three 

 and four feet — and had an overburden of about two and a half feet of 

 a yellowish loamy clay. It contained a higher proportion of cla}^ and 

 relatively less quartz, than most of the placer gravels do. The yield of 

 gcjld was high, from two and a half to three penn3'weights per cubic yard. 

 The metal was usually in fine grains, but occasionally small nuggets were 

 found. 8ome diamonds of fair size and of excellent qualitv were 

 obtained from these placers. 



The Mahdia Valley, and those of its tributary streams, are filled 

 with a fluviatile dejjosit of yellowish-brown sandy clay, varying greatly 

 in thickness, but averaging from six to eight feet, which is underlaid by 

 about three and a half feet of gold-bearing quartz gravel. The gravel 

 consists principally of quartz sand, and angular quartz pebbles with 

 some small pebbles of felsite. Blocks of more or less altered quartz- 

 porphyiT also occur in it. The average yield of the gravel is about two 

 pennyweights of gold per cubic yard ; the metal is usually in very fine 

 grains, and nuggets weighing a few pennyweights occur occasionally. 

 The largest nugget found in the Mahdia District weighed a little over 

 eighty ounces. 



The ])ed-rock in the Mahdia Valley is usually alight-coloured sandy 

 cla}', crossed in places by belts of sandy clay of ochreous to dark-red 

 colour ; the bed-r(»ck thus clearly indicates that the deepest parts of the 

 valley have been eroded thi-ough a country of acidic rocks, probably 

 quai-tz-porphyry, intersected by dykes of basic rocks. 



In this district the laterites and concretionary ironstones of the 

 hillsides are auriferous, and ])ayable deposits have Ijeeii worked at 

 considerable elevations. Near the heads of some of the tributary 

 streams of the jNIahdia, and in some of the higher ravines, great blocks 

 of diabase are of conunon occurrence in the gravels. 



I'he overburden in the placei's in the Minnehaha District \aries 

 greatly in deptli. Near the junction of the Minnehaha Creek, with 

 the Konawaruk, the stripping is very deep, but as the creek head is 

 approached the depth of the overburden decreases, until at its source 

 there is none. In some of the tributary streams, near the head of the 

 Miniiehaha, the overburden is deep, and contains great blocks of 

 ^liabase, whilst the gra^'els largely consist of partially decom])osed 

 angular fragments of that rock. 



Owing to the great depth of the stripping in the lower coui-se of the 

 creek the gravels have not been worked t(» any extent. AVhere they 

 have been worked the avei-age dej»th of stripjung is about fi\e feet, and 

 it consists of a reddish-brown to yellow earthy clay. Tlie gold-bearing 

 gravel consists of fine nuai'tz frairments, with blocks <if more or less 



