Notes on the Auriferous Slate Sf Granite Veins of N.S.W. 89 



Mineral veius have generally been described as open fissures 

 formed by some disruptive force, and either filled at the time 

 they were opened with minerals in a molten or pasty state 

 forced up from below, or else with minerals held in solution by 

 the water circulating in the open fissures, and slowly deposited 

 on the walls until the fissure was thus gradually closed up. 

 Under this theory the relative age of mineral veins was calcula- 

 ted from the dislocations which occur at their intersections with 

 each other, and Lyell speaks of veins being classed in series on 

 this basis alone. 



The paper referred to pointed out that mineral veins were 

 generally formed either on the cleavage, divisional, or sedi- 

 mentary planes of the rocks they traversed, and not on irregular 

 fissures ; and that when the faultings, or throws commonly seen 

 at the intersection of veins, were careful'y studied, it would 

 be found that the conclusions as to relative age would in most 

 instances have to be reversed, or else abandoned, on the ground 

 that they would only fix the relative age of the joints on which 

 the veins had formed, and not that of the veins. 



As to the filling of the veins ; the fact, that the quartz of 

 our auriferous veins has the specific gravity of aqueous-formed 

 quartz, and that numerous veins occur in such a form, and 

 under such conditions as would render it impossible for their 

 contents to have been forced into them from below, appears to 

 dispose of this hypothesis. 



Eor the vein-minerals to have been deposited from the water 

 circulating throtigh the fissures, it is necessary for the latter 

 to have remained open. Now mineral veins are found at all 

 inclinations — from a vertical to a horizontal position — and every 

 miner is aware how difiacult it is to keep even a small area of 

 the vein open until the ore is taken out ; and that for the veins 

 to have remained as open fissures for the long period of time 

 that would be required to deposit their present contents is an 

 impossibility. Neither will this explanation account for the 

 small detached leads, and bunches of quartz, so common 

 in the schistose rocks. Nor for the veins which cut out a 

 short distance from the surface, where the extent of ground 

 opened is not sufficient to allow of a current of water conveying 

 the minerals, unless the latter were derived from the adjoining 

 strata. 



The theory which appears best to accord with the phenomena 

 observed is, that the contents of the mineral veins have been 

 segregated from the rocks bounding the veins, and collected 

 atom by atom on particular Hues or joints of the rock, so as 

 gradually to replace the material previously existing there. 

 After being thus formed, many changes might occur in the 



