Quartz Veins and Mineralised Masses. 195 



The granopliyre consists of a ground mass of micropegmatite, con- 

 taining much quartz, in which are numerous broad plates of labradorite 

 generally much clouded and containing sericite, a very few granules of 

 augite with biotite, epidote and chlorite (delessite) in patches, some 

 grains of titauiferous iron, much leucoxene in small aggregates, a few 

 prisms of apatite and some patches of carbonates with man}^ gi'ains of 

 pyrite. It is tra^•ersed by the veins of secondary quartz containing 

 numerous small cubes of jjyrites. 



Tlie granopliyre has the following composition : — 



iSilica ... ... ... ... ... ... 75"62 



Alumina 14-05 



Iron peroxide ... ... ... ... ... '33 



Iron protoxide ... ... ... ... ... 2"82 



Magnesium oxide ... ... ... ... '40 



Calcium oxide ... ... ... ... ... 2'79 



Sodium oxide ... ... ... ... ... 1"97 



Potassiiim oxide ... ... ... ... ... '44 



Water -26 



Carbonic anhydride ... ... ... ... '93 



Titanium oxide ... ... ... ... ... traces 



Phosphoric anhydride ... ... ... ... '009 



Iron sulphide ... ... ... ... ... "06 



Manganese oxide... ... ... ... ... trace 



99-679 



The sample analysed yielded at the rate of fifty-one grains of gold 

 to the ton of rock. 



Near Hope Placer and on the Potaro-Konawaruk Road, near the 

 hospital, masses of coarse-grained granopliyre occur. These contain 

 veins of carbonates, with many crystals of iron and copper pyrites and 

 of galena. Specimens from near the hospital were found to yield gold 

 at the rate of thirty-three grains per ton. 



The granophyre is a dark-coloured compact rock, having a specific 

 gravity of 2-72. It is made up of large and broad plates, and smaller 

 laths of plagioclase, in a ground mass of micropegmatite and interstitial 

 quartz. The larger jDlates of feldspar are, in parts, sericitised, and are, 

 in many places, deeply corroded into by the micropegmatite, whilst the 

 smaller ones are of later origin and have crystallised out from it. As 

 accessories, it contains j^atches of delessite, some grains of titaniferous 

 iron-ore, small aggregates of leucoxene, a few prisms of apatite, and, 

 in places, many small cubes of pyrites. It is traversed by thin veins 

 of carbonates, which mineral occurs also in patches. 



The mineralised masses at Inflexible and near Hope Placer, in the 

 valley of the Mahdia, show evidence of the intrusion of quartz and 

 feldspar after the partial solidification and alteration of the feldspar 

 of the original pasty mass. These rocks are now granophyres, with 

 clouded sericitised crystals of plagioclase-feldspar, surrounded by 

 clear micropegmatite. The gold which is diiiused through them 

 was probably brought into them b}^ the magma of highly quartziferous 

 micropegmatite. The carbonates of calcium and magnesium present in 



