338 Transactions.— Geology. 



formed which destroyed the lustre of the specimen. The 

 reason of this probably is that the iron and manganese salts, 

 which I found present in small quantities in the mine-water, 

 formed a thin coating of these salts on the crystals. On 

 bringing the copper to the surface this thin film, exposing a 

 large surface to the air, would quickly oxidize to oxide of 

 iron and manganese. These substances would then give up 

 their oxygen to the copper, which would form a layer of black 

 oxide of copper. This iron and manganese therefore appear 

 to act as carriers of oxygen to the copper. 



The explanation that one would naturally jump to with 

 regard to these deposits is — (1) That the iron- and copper- 

 pyrites have oxidized, producing sulphuric acid and soluble 

 iron- and copper-sulphates ; (2) that iron has been present in 

 the mine-timbers in the form of bolts and nails, and that this 

 iron has replaced the copper in the soluble copper-sulphate, 

 thus forming deposits of metallic copper. But, with regard to 

 the presence of metallic iron, I ascertained that no bolts were 

 used to suspend the frame-sets in the shaft, and the amount 

 of iron present as nails would not by any means account for 

 the large deposit of copper. 



From the fact of the sea being in almost constant com- 

 munication with the mine for so many years, it appeared that 

 the sodium-chloride of the sea-water would affect the solution 

 of the copper from the pyrites, as it was highly probable that 

 during the oxidation of the copper-pyrites the sodium-chloride 

 would cause a concurrent action, resulting in the formation 

 of copper-chloride and copper-sulphate. To verify this I 

 weighed out two equal portions of copper- pyrites and partly 

 oxidized them under exactly similar conditions, and while still 

 hot, and therefore still oxidizing, I plunged one into pure 

 water and the other into a solution of common salt. In each 

 case a blue solution of copper was obtained, but the brine- 

 solution was found to contain 5 per cent, more copper than 

 the other. 



I was unable to obtain an accurate sample of the mine- 

 water for quantitative analysis, but a sample I had showed 

 the presence of sulphates and chlorides of sodium, copper, 

 iron, and manganese, and from the above experiment it seems 

 likely that the copper is present as chloride and sulphate of 

 copper. 



As previously stated, the metallic iron is not in sufficient 

 quantity to account for the amount of copper produced ; but I 

 think the following explanation accounts for the quantity and 

 also for the crystalline form : As the mine- water was con- 

 nected with the sea the solution of copper could not become 

 very strong, as the salts of copper and the sea-water would 

 diffuse into each other, thus weakening the copper- solution 



