86 



crustal disturbances which tilted and folded the Carbon- 

 iferous rocks. The main intrusions may at points have 

 originally reached the surface through the Carboniferous 

 sediments and appeared as a volcano or a series of volcanoes. 

 The three principal types in order of age, commencing 

 with the oldest, are monzonite, diorite porphyrite and 

 porphyritic monzonite. In general, the coarser types are 

 younger than the fine-grained ones, and the more felds- 

 pathic younger than the basic types. 



The normal monzonite shows considerable variation 

 in different parts of the same mass. The rock varies 

 from grey to black in colour, and from granitoid to semi- 

 porphyritic in texture. The coarser types consist of black 

 prisms of pyroxene or secondary hornblende, flakes of 

 brown biotite and a light coloured plagioclase feldspar 

 which is often labradorite. The microscope discloses 

 in addition some alkali feldspar, magnetite and apatite. 

 At times local variations show an almost total disappearance 

 of the feldspar, in which case the bulk of the rock is made 

 up of augite and hornblende. In the finer grained varieties, 

 the granular white feldspathic groundmass is peppered 

 with tiny grains and small prismatic individuals of the dark 

 constituents which gives a characterisitic mottled aspect 

 to the rock. 



The following analysis of the monzonite from the 

 700-foot level of the Le Roi mine was made by the Mines 

 Branch. 



Si02 54-49, Ti02 0-70, AI2O3 16-51, Fe203 2-79, 

 FeO 5-20, MnO o-io,MgO 3-55, CaO 7-06, K204-36, 

 Na20 3-50, H2O — 0-07, H2O+ I -18, P205 0-20, S 0-23, 

 C O2 0-24. 



Diorite porphyrite. — ^The diorite porphyrite occurs 

 in oval, dyke-like forms expanding into larger masses. 

 It is probably younger than the normal monzonite but 

 field evidence is not clear on this point. It is cut by dykes 

 of porphyritic monzonite. Mineralogically the rock might 

 be regarded as a phase of the monzonite. It varies from 

 light grey to greenish black. The texture ranges from 

 porphyritic to fine granitoid. The rock consists of 

 phenocrysts of plagioclase feldspar (andesine to acid 

 labradorite), pyroxene and hornblende lying in a ground- 

 mass of feldspar, quartz and hornblende, the relative 

 amounts of these constituents fluctuating widely. 



