1922] Whitman: Genesis of the Ores of the Cobalt District 297 



of the diabase, leave them and diffuse to the nearest cleavage, crystal 

 boundary, or fracture, where they enter into the composition of the 

 highly dissociated equivalent of such complex molecules as :' 20 



Co 2 8 2 3 . Na,S,O a . ELO and 

 Ag 2 S 2 3 . Na 2 S 2 3 . H 2 0. 



Migration. — At this point the mechanism of diffusion may be 

 supposed to begin in its general geological manner. It must be 

 recalled here that whatever may have been the span of geological time 

 in which these operations were going on, they began with a tempera- 

 ture in the diabase and its immediate neighborhood but little below 

 the temperature of solidification ; and the heat emanated was not only 

 the superheat of the magma, but also the specific heat of the minerals 

 which crystallized from it ; while there was a molar pressure due to 

 several thousand feet of overburden and the cooling contraction of 

 the igneous mass and its wall rocks. There must also have been a 

 slow-acting but none the less effective hydrostatic pressure upon all 

 free water in fractures and pore spaces, due to a head of several 

 thousand feet and to a high vapor pressure due to the temperature. 

 The solvent was probably highly superheated either as liquid or gas, 

 and had extreme power of penetration. It was not only saturated 

 with all substances with which it came in contact, but was probably 

 heavily charged with them, and carried also the ore materials in fairly 

 strong concentration. All its solutes were highly dissociated and 

 reduced in valency to their lowest terms, and at the same time highly 

 charged with free energy. This was the result not only of high tem- 

 perature and pressure, but also results of the catalytic influence of 

 such solvent agencies as thiosulphates and alkaline carbonates, or 

 sulphides. 



Since the solvent in which the ore ions tend to diffuse is not en 

 masse but is disposed in films, the ions would have to travel far in 

 order to attain an appreciable attenuation. This form of the medium 

 of diffusion would therefore greatly increase the distance traveled by 

 an ion in a given time, the diffusion gradient being in no way affected, 

 since the gradient refers to the amount of solution traversed for a 

 given change in concentration. 



As pointed out by Daly 21 the heat conductivity of rocks is very 

 low. The rate of radiation from an intrusive mass must fall off 

 rapidly after the first extreme differences have been dissipated by 



2 ° Abegg, Handbueh der anorganisehen Chemie, Ableitung 1, p. 714. 

 21 Igneous rocks and their origin, p. 198. 



