ox gold: its formation in our reefs. 159 



We have thus removed this anomaly of gold in the act of 

 precipitating, selecting as nuclei substances so diverse from it, 

 while refusing others which differ no more from such non-metallic 

 nuclei than do these from gold ; it appears from these results 

 that whatever gold has been reduced by organic matter in the 

 experiments quoted, would never deposit on these non-metallic 

 nuclei, surface to surface, but only upon gold already occupying 

 such surfaces, reduced by the exercise of affinities far superior 

 and swifter in their action than those involved in the decay of 

 wood or other organic substances, used by Mr. Wilkinson in the 

 experiments alluded to. 



The great deoxydizing power of sulphides generally upon most 

 gold, silver or platina salts, as manifested by the experiments just 

 described, renders them so absorbent of these metals, that any 

 solutions travei'sing even a very thin vein or reef of the common 

 metallic sulphides, would, in all probability, be completely divested 

 of these metals. 



I would state, that in regaixl to silver, the nitrate is but little 

 affected by iron pyrites ; but the chloride in alkaline chlorides, 

 as also the carbonate in carbonate of soda, is decomposed with 

 liberation of silver. This metal is easily reduced from all its 

 solutions (except the ammonical) by galena, copper pyrites, and 

 the inferior sulphides of iron and copper. From its solutions in 

 carbonate of soda, potash, or ammonia, gold is also reduced by 

 the sulphides, but not from its solutions in alkaline sulphides. 



The gold or silver, deposited upon these sulphides, is coherent 

 and smooth if the solution is weak. It bears all the signs of being 

 electro-deposited, a true voltaic pair having been formed. 



I said, in a former paper, the knowledge that metallic sulphides 

 and arsenides ai'e capable of reducing several metals from their 

 solutions, should be taken into consideration when we attempt to 

 explain the origin of these metals in the forms they have taken, 

 and in the I'ocks or veins they have selected. 



As yet, most of the theories explaining the occurence of such 

 deposits in these matrices, are based upon the reducing power of 

 organic matter ; when the fact is, that most or all of these 

 sulphides are much superior in this respect to such matters, being 

 far more rapid in their effects, and capable of reducing, weight 

 for weight, more metal ; a single grain of iron pyrites being 

 sufficient to reduce S^ grains of gold. 



Organic matter could scarcely exist in such quantity among our 

 older and more altei^ed rocks, or be carried there in such quantity 

 as to effect the reduction of gold in such quantity, and in such 

 confined spaces as it is occasionally discovei'ed in. 



While allowing that organic matter may have had a share in 

 the reduction of this and other metals, I cannot but think that 

 by far the greater portion of these deposits — especially those 

 deeper-seated oiies — have been due to the " deoxydizing effects of 

 pyritous minerals." 



