202 Becker — Auriferous Conglomerate of the Transvaal. 



Even if the ore-bearing currents were so rapid as to per- 

 meate the pebbly beds more freely than sandstones possessing 

 the same interstitial space, the smaller resistance of the former 

 would not confine ore deposition to the coarser mass. Permea- 

 tion would take place in any direction in inverse proportion to 

 the resistance in that direction, and the auriferous fluid would 

 escape from the pebble-layer as sewage does from porous 

 underground distributing pipes. It follows, then, that the 

 sandstones as well as the conglomerates should have been 

 impregnated when soaked in an auriferous solution, and to 

 approximately an equal extent, while as a fact the sandstone 

 does not contain one one-thousandth part of the gold. The 

 impregnation theory would, furthermore, seem to involve the 

 presence and the prevalence of chutes in the banket. TheVe 

 is no doubt that most of the gold occurs in patches which are 

 distinctly different from chutes, and many engineers are confi- 

 dent that real chutes are absent. Much of the pyrite is in the 

 form of minute waterworn pebbles, and much of the gold is 

 inclosed in the pyrite, indicating a common origin for the two 

 minerals. This fact is regarded by De Launay as fatal to the 

 impregnation theory, and, indeed, it seems impossible to recon- 

 cile this mode of occurrence with the hypothesis. 



Had the gold been deposited from solution one or another 

 of the characteristics of various deposits might well have been 

 absent or obscure. It is difficult to believe that all should 

 have been obscure if not totally absent. The evidence in such 

 a case must be considered cumulatively. 



The strength of the impregnation theory lies in the fact that 

 some of the gold and of the pyrite appears to be crystallized, 

 as if deposited in place. A portion of the observed phenom- 

 ena seem certainly secondary. Below water level, or "in the 

 blue," visible gold is very rare* on the Rand. In the oxidized 

 upper levels it was much more frequent, and free gold was 

 often found in the cavities from which pyrite had disappeared 

 by oxidation. This is, of course, a very common phenomenon 

 at the croppings of auriferous deposits, and can be accounted 

 for only by the recrystallization of gold attending the oxidation 

 of pyrite. The modus operandi is also pretty clear. Ferric 

 sulphate is a weak solvent for gold, and iron sulphate is one of 



* " "Very rare " is a relative term. Mr. Hammond takes exception to my state- 

 ment, which he probably interprets in a more superlative sense than I intended 

 it. Hatch and Chalmers, who were certainly thoroughly familiar with the 

 ore, assert that, as a rule, the gold "is disseminated through the ore in finely 

 divided particles which are rarely of sufficient size to be visible to the eye " 

 unless the ore is first panned. I am quite aware that in most of the mines a 

 speck of gold is seen from time to time and that there are some specimens in 

 which it is abundant. The point of the statement in the text is that more visible 

 gold occurred in the oxidized zone than beneath it. 



