4 University of California Publications in Geology. [Vol. 7 



sulphates of the alkalies, leached from the surface material and, 

 acting on the abundant pyrite and manganese minerals of the 

 rocks, they became charged with iron and manganese salts. 

 Probably more or less free acid and free gas were formed in the 

 mixed solutions, and the decomposing and oxidizing effect of 

 these solutions on the sulphides of the veins and on the gangue 

 must have been comparatively rapid. The solutions which 

 percolated downward through the ore body were essentially 

 sulphated waters of the alkalies, iron, manganese, and silver, with 

 potassium and sodium chlorides, bromides, and iodides. 



The alkali chlorides predominated over the bromides and 

 iodides in the upper zone of oxidation and it is safe to say that 

 chlorine was greatly in excess of bromine or iodine in this zone. 

 The dilute solutions moved slowly downward through main 

 channels and narrow fissures, thoroughly saturating portions of 

 the vein, leaching out the potash of the feldspar and converting 

 the silver sulphides to sulphates. With sufficient silver present 

 the evaporation in this zone would have caused the precipitation 

 of the main deposit of the cerargerite even if the bromide and 

 iodide of silver had also been thrown out previously or with it. 

 These two haloids, however, would not have existed in the alkali 

 chloride solution but would have been completely transposed 

 into cerargerite, while the bromine and iodine would have been 

 absorbed in the cold solutions and carried down possibly as 

 sodium and potassium salts. 



The solutions passing downward became more concentrated 

 in bulk, stronger relatively in bromine, iodine, and alkalies, and 

 at the same time depleted in chlorides, until a stage was reached 

 where the almost constant associate and natural successor of 

 cerargerite, the double salt embolite, crystallized. Bromine and 

 chlorine are alike and usually accompany and replace each other, 

 so that cerargerite and embolite are typically associated. As the 

 chlorine diminished in the solutions, bromine replaced it in 

 cerargerite as shown by tests, and probably a gradation from 

 cerargerite to embolite occurs in the mines. The embolite zone 

 represents a proportionate increase of bromine to chlorine in the 

 solutions, yet sufficient chlorine was still present to prevent the 

 formation of bromyrite and to form considerable cerargerite in 



