232 University of California Publications in Geology [Vol. 13 



and monoclinic pyroxenes, the olivine, mica, etc., and also the plagioclase lie 

 with idiomorphie contour within the pyrrhotite. They show, however, some- 

 what rounded edges and angles That the pyrrhotite was in fluid condi- 

 tion after the solidification of the silicate minerals is shown by the occasional 

 fine veins of pyrrhotite that bend and split them." Garnet zones were observed 

 at contacts of pyrrhotite and plagioclase. 4 3 



(2) Oftentimes fine ore veins or again thick ore dikes shoot off from the 

 sulphide mass either into the gabbro or schist. Also we find corresponding 

 veins, schlieren and dikes, in part of pyrrhotite-norite with varying sulphide 

 content, in part of pure sulphide, within the gabbro massif, or more often in 

 the peripheral part. These occur without relation to any observed regular ore 

 concentration. 44 



(3) The copper always separates as chalcopyrite (CuFeS^). It never forms 

 bornite (Cu 3 FeS 3 ) or ehalcocite (CuJS), apparently due to the mass influence of 

 the iron sulphide. Nickel concentrates in part in pyrrhotite (Fe s S 9 ) and, with 

 higher nickel content, in part also in millerite (NiS), pentlandite ([Ni, Fe]S) 

 and polydymite (R 4 S 5 ), that is, in minerals of low sulphur content. 45 



(4) Crystallisation series. Crystals of pyrite, rich in cobalt, and of ilmenite 

 are often found with good idiomorphie contour intergrown in the pyrrhotite and 

 chalcopyrite. The pentlandite, millerite, and, to all appearances, also the 

 polydymite are always of an earlier stage than the pyrrhotite. Chalcopyrite 

 appears to be earlier than the pyrrhotite. 46 



Following Vogt's paper many authors have advocated a "magmatic 

 origin" for these deposits. Some have simply contented themselves 

 with affirming a magmatic origin, not concerning themselves with the 

 details of the process. Others have followed Vogt in applying Soret's 

 principle to explain the occurrence of ore bodies along the walls of 

 the intrusive masses. For instance, Barlow, in a detailed account 47 

 of the Sudbury deposits, presents a theory for their origin much like 

 that of Vogt. 



Coleman believes that the dominant process in determining the 

 position of the deposits along the margins of the irruptive mass is 

 gravitative settling of sulphides. 48 



Hore also subscribes to the settling theory and believes that the 

 accumulation of considerable masses of the pure sulphides may be 

 explained by the limited miscibility of sulphide and silicate melts. 49 



Browne investigated nickel mattes and compared them with Sud- 

 bury ores. He concluded that 



the nickel deposits of Sudbury existed primarily as eruptions of molten sulphides 

 mixed with the constituents of the dioritic enclosures, and that by gradual cooling 



« Ibid,, p. 138. ^Ibid., p. 140. a Ibid., p. 137. 



« Ibid., p. 264. **Ibid., p. 128. 



i- Barlow, A. E., Can. Geol. Surv., Ann. Eept., vol. 14 (1901), pt. H, p. 125. 

 4 « Coleman, A. P., Out. Bur. Mines Report, vol. 12 (1903), p. 277; also in 

 later papers by same author. 



^' Hore, R. E., Can. Min. Inst. Tran., vol. 16 (1913), p. 271. 



