836 



MR. J. H, COLLI]SrS ON THE SUDBURY COPPER-DEPOSITS. 



As at the Copper Cliff, a very large proportion of the ore has to 

 be rejected, being of too low a grade to bear the expense of transport 

 to the smelting- works. At first an annual output of at least 



Fig. 2. — Section of Ore-deposit at Stohie Mine. 

 (Scale about 130 feet to 1 inch.) 



N.W 



8.E. 



Huronian strata, b. Diorite. c. Ore-body. s. Shaft, xx. Bore-holes. 



30,000 tons was confidently anticipated ; but up to the present time 

 the total production of two seasons has not amounted to 10,000 tons. 



Some small workings have also been made at the " 6 in 6," the 

 McConnell, the Eyre, and other places ; but none of them of any 

 extent, and none have as yet yielded saleable ore. These various 

 works, although so far not at all profitable to their owners, have 

 yet sufficed to demonstrate several important facts. 



The ore exists in three distinct forms as follows : — 



1. As local impregnations of certain siliceous and felspathic beds 

 or belts of rock of clastic or fragmentary origin, in the form of spots, 

 patches, and strings of cupreous pyrrhotite, or magnetic pyrites. 



2. As contact- deposits of the same mineral lying between the 

 impregnated beds just mentioned and certain large interbedded or 

 intrusive masses of diorite. 



3. As segregated veins of copper-pyrites and of highly nickeli- 

 ferous pyrrhotite of secondary formation filling fissures and shrink- 

 age-cracks in the ore-masses of the second class. 



There is much in this mode of occurrence to suggest that the 

 copper occurring in the first mode was an original, or at least a 

 very ancient, constituent of the beds, while the richer masses of 

 the second and third modes of occurrence have resulted from later 

 segregations into openings produced either by the intrusion of the 

 diorites or by internal movements of the rocks. 



A comparison is at once suggested with the cupreous pjTites of 

 the Sierra Morena, and especially of Eio Tinto, described by me in 

 1885*. Although the containing rocks at Sudbury, and the de- 



* "On the Geology of the Rio Tinto Mines, 

 vol. xli. p. 245. 



Quart. Journ. Geol. Soc, 



