BY LEO A. COTTON. 221 



With a view to investigating in detail the processes, as com- 

 pared with the criteria for metasomatism laid down by Lindgren,J 

 the following work was undertaken. In June of this year, 

 accompanied by my brother, Mr. M. Cotton, I visited the southern 

 portion of the New England tin- bearing area, and made some 

 observations at Tingha, Howell, Newstead, Gilgai and Elsmore. 

 About a fortnight was spent in field-work, at a spot 6 miles to 

 the south-west of Inverell. Here a number of cassiterite veins 

 were examined. 



Among these were the lodes of the Leviathian and Hill Cliff 

 Tin Mines. At the former mine, the lode consists of a number 

 of somewhat irregularly disposed veins, having a general north 

 and south direction. To the west of this lode are a number of 

 smaller veins, having the same general direction. One of these 

 was selected for the purposes of analysis and microscopic investi- 

 gation. This vein was one of the smaller ones, being about 10 to 

 11 inches wide where the sample was selected. Towards the 

 northern end there seemed to be, as far as could be determined 

 by hand-specimens, a progressive increase in molybdenite. 

 Towards the southern end the vein became much more irregular, 

 and exhibited a progressive increase in cassiterite. The molyb- 

 denite occurs in small flakes up to 2 mm. in diameter, and the 

 cassiterite in grains and crystals of similar dimensions. 



The vein at the north end is fairly regular in width, but widens 

 greatly at the south end, where it becomes some 3-4 feet in width, 

 with no well defined walls. A few crosscuts have been made at 

 this end, but the cassiterite-content is too low for economic work- 

 ing under existing conditions. Where the lode is best defined a 

 marked differentiation was observed. 



The central portion of the vein is a band of almost pure quartz 

 (see Analysis A, p. 225), varying from 1-3 inches in width. On 

 either side of this band the vein-material gradually merges into 

 the normal granite constituting the country-rock. Where this- 

 band attains a maximum thickness, large, well developed crystals 

 of quartz, from 1-2 inches in length, are developed. These crystals- 



X " Metasomatic Processes in Fissure-Veins." Trans. American Inst. 

 Mining Engineers, Vol. xxiv., 1900. 



