METAMORPHISM OF SEDIMENTARY ORES. 1041 



While some of this gold was undoubtedly transferred to the sea in solution 

 by the streams, it is believed to be probable that a major part of it was 

 transferred to the sea by the streams mechanically, and by the action of 

 the sea upon the beach deposits the gold was dissolved. 



River deposits and beach deposits may in consequence of physical 

 changes be buried under later deposits, and thus pass far down into the belt 

 of cementation or even into the zone of anamorphism. They are then 

 subject to all the metamorphosing processes of the belts in which they 

 occur. In the belt of cementation the circulating underground water will 

 superimpose its work. As illustrating - this principle may be mentioned the 

 difference of opinion which exists as to the great gold deposits of the Rand. 

 These deposits, according to Becker, are dominantly marine beach deposits/ 

 although he agrees that the gold has been rearranged to some extent by 

 underground water, 6 thus explaining the crystallized character of portions 

 of the gold and the existence of gold in cracks within the quartz pebbles." 

 But Becker holds that not more than a minute fraction of 1 per cent of the 

 gold has been introduced from an extraneous source. Others have held 

 that the Rand deposits are of alluvial origin, i. e., stream placers; and still 

 others believe that the gold was deposited from solution at the time the 

 gravels accumulated/ Upon the other hand, Curtis 6 and Hammond-'' both 

 insist that all of the gold was deposited by underground water, and there- 

 fore the deposits belong to the class produced by processes of metamorphism. 



Recently an excellent statement of facts in reference to these deposits 

 has been made b}^ de Launay. ? According to this author the gold exists 

 in pyrite contained in the siliceous cement, together with other metamorphic 

 minerals, such as chlorite and muscovite. Much of the pyrite is rounded 

 like rolled grains, but a larger part is well crystallized and presents sharp 

 angles. De Launay is unable to decide between the hypotheses (1) of 



« Becker, Geo. F., The Witwatersrand banket, with notes on other gold-bearing pudding stones: 

 Eighteenth Ann. Kept. IT. S. Geol. Survey, pt. 5, 1897, pp. 160-177. 



* Becker, cit„ p. 171. 



« Becker, cit., p. 176. 



^ Becker, cit., pp. 169-170. 



"Curtis, J. S., The banket deposits of the Witwatersrand: Eng. and Min. Jour., vol. 49, 1890, pp. 

 200-201. 



/Hammond, John Hays, Gold mining in the Transvaal, South Africa: Trans. Am. Inst. Min. Eng., 

 vol. 31, 1902, pp. 841-845. 



9~De Launay, L., Observations on the Rand conglomerate: Eng. and Min. Jour., vol. 75, No. 14, 

 1903, pp. 519-521. 



MOX XLVII — 0-i 66 



