BY SYDNEY B. J. SKERTCHLY. XXI 



(8.) Dioritc. — The diorite of this district is ahnost in- 

 variably of the quartzose variety. It occurs in masses, as at Sun 

 Eise, south of the Tate, in sheets fed by dykes, as at the Pirate 

 Mine, on the Tate Eiver, but generally occurs as dykes. These 

 dykes around Herberton and Watsonville are the principal 

 carriers of tin, and have been much altered into chloritic and 

 serpentinous rock at the time they were charged with mineral. 



The diorite dykes are certainly in many cases newer than 

 the granite, but I have not yet found them traversing the 

 Chillagoe Limestones. 



(4.) ]'!rl(i(/i/ti'. — This peculiar rock is essentially the ore- 

 bearing gangue of the true Chillagoe deposits. It is essentially 

 a siliceous rock charged with lime garnet. It varies from a rock 

 almost indistinguishable from quartzite to a pure garnet rock, 

 with crystals half an inch in length. 



It traverses alike the Herberton Beds, the Chillagoe Lime- 

 stone, and the granite. Where it is ore-bearing it is nearly 

 always highly ferruginous. It occurs at or near the line of 

 contact of the sedimentary rocks and the granite. 



(IV). ( 'his.sirJcatt'on. of ()rc-I>i-j)i).sitft. — No system of classifi- 

 cation of ore-deposits is quite satisfactory, but the following 

 scheme seems to be best suited for the district under considera- 

 tion. Intermediate varieties are of common occurrence which 

 might with almost equal propriety be placed in either of two 

 divisions. 



(1). True Fissnri' Lodes. — These are characterised by well 

 defined walls, often showing zones of crushed rock, and with 

 flucans or clayey selvages. Both walls and tlucans generally 

 show one or more sets of slickensides. Their course is generally 

 more or less sinuous, and they generally pitch or hade at a steep 

 angle. The ore occurs either in bands or shoots, and seldom 

 occupies the Avhole width of the lode. Where they are of any 

 size they may be deemed absolutely permanent. They are 

 principally confined to the district between Watsonville and 

 Montalbion. An excellent example of a tin fissure lode is the 

 Stewart's T Claim, at Watsonville, which is down 4-iO feet, and 

 has averaged 28% of tin from top to bottom in a lode averaging 



