REPORT OF THE DIRECTOR IQII 



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primary constituent of the sedimentary gneisses, another reason 

 appears for the concentration of the pyrite in these particular rocks, 

 they being rich in graphite. Even were the precipitating action 

 limited to the original organic matter from which the graphite is 

 derived a similar though less important effect would result, since 

 the presence of premetamorphic pyrite would favor the later deposi- 

 tion of pyrite in the samcrocks. 



But while the relation of pyrite and graphite can hardly be con- 

 sidered as other than in some way genetic, the writer is not con- 

 vinced that it is as simple as above suggested and feels that further 

 investigation may prove that the graphite, like the pyrite, has a very 

 complex history, the two minerals having grown, in part, simul- 

 taneously, but the development of the former beginning before and 

 ending after that of the latter. 



So far as the distribution of the pyrite deposits bears upon the 

 suggested hypothesis as to their origin, the lack of knowledge of the 

 areal geology of the region prevents any detailed discussion. While 

 viewing the deposits as chiefly due to magmatic agencies, the ex- 

 planation oft'ered postulates no close association in space between the 

 ores and the intrusive rocks. On the contrary, the phenomena are 

 thought to point distinctly in the opposite direction, the deposits 

 being conspicuously unlike those due to contact metamorphism. 

 The fact that igneous rocks are generally distributed throughout 

 the region, so that no point in the Grenville can be beyond the 

 reach of solutions derived from these, affords the necessary basis 

 for the explanation appealed to, and thus marked areal relations 

 between ore deposits and intrusive rocks are not to be expected. 

 The distribution of the deposits is therefore controlled primarily by 

 the distribution of the Grenville, which explains their linear 

 arrangement. 



A secondary control by large structural features, such as faults 

 and shear zones, is probable, but much further study of the whole 

 region is needed before any decision upon this point can be reached. 



With reference to the type of igneous rock with which the pyrite 

 is to be regarded as genetically associated, a tentative conclusion is 

 justified. The intimate association of the pyrite at Pyrites with 

 gabbro and the possible occurrence of the same rock at Stella mines, 

 together with the very general genetic connection between iron sulfids 

 (though as a rule pyrrhotite rather than pyrite) with basic rocks 

 strongly suggest such a connection in the present instance. But a 

 serious difficulty stands in the way of the acceptance of this view. 



