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TMa Hmp I* fibiMd at ilw raduellon ratio ehMlnd batow / Cadoeiimante«tWre*autt«d>r*tfaie«famiiMB«j«i4^>mt^tpm lOx ■— __. 14x 18x 22x MR 30x 1 1 1^ 1 12k 1«R 20x 24x 2ax ■ . / '-^ Btpmvtmtnt of mints Hoa. MARTIN BURRBLL. Mloltter; R. G. McCONNELL. Deputy UMtUt. Hcological Savatg WILLIAM McINNES. Dtrectlni Gcoloiltt. Museum Bulletin No. 30 GEOLOGICAL SERIES, No. 37 November IS, 1919 GABBROS OF EAST SOOKE AND ROCKY POINT by H. C. Ckrake OTTAWA I. Di LABROQCERIE TACB£ PRINTER TO THE UING'S MOST EXCELLENT MAJESTY IDtt No. 1782 Canada Geological Survey Museum Bulletin No. 30 GEOLOGICAL SERIES No. 37. CONTENTS. Pa(;k IiUruUuctiun 1 General geology 2 Lithological characters and mode of occurrence 3 General description 3 Detailed descriptions 6 Olivine gahbro 6 Augite gul>liro 8 Gneissic phases *< Anorthosites 9 Granite 10 Dvkes 10 \'eins 12 Hornlilendite veins 12 Gahbro-aplitc veins 13 Aplite veins 14 Kelations to the gahbro If) Changes of composition during hornblendization and aplitization 16 Rock alterations IS Triple points 20 Internal strttctiiral relations 21 c.in tal and contact relations 21 » and faulting 24 M,: .3 26 V- .• , :<« 29 ]:•> y statement 29 uiflterentiation 30 . , jsition of the original magma. 30 Proof of movement prior to consolidation 31 Time of movement 31 Time of differentiation relative to intrusion 32 Method of diflFerentiation 33 Spatial relations 34 Proportional relations of minerals 34 Changes in composition of constituent minerals 35 Special textures and structures 36 ftCCT.'J— 1 Rale of rcHilinc nic llla^^c^ of ),'eiicral ),',ilil>ruid inin|M)siti<)n ootitr oil the soiiiluvcstein coast of \aticoiner i>!aiul, ahoiit 15 miles soittliwf^t of ilie city of \icloria. The laBj^er uiiderlic^ the greater part of l".ast "^(Mike peninsula and is elliptical in outline. Its ni."jor axis is alxiut 3 miles in Ienj;th and its minor axis ahoiit 2\ miles. It is of economic interest as it forms the country rock of the llast Sooke cop))er deposits, and of scientific interest as it alTords an excellent exanipU- of the course of ditTcrciitiation of a Kalihro majjma. 'Ihe smaller, or Kocky Point mass, lies about 3 miles to the east ; it cont.iins no ore dei>osits, and a much larger proiM)rtion of it is beneath sea-level, but in the varietx and char- acter of its rocks it is identical with the I'.ast Sooke IkkK'. A number of other misses of the same );al)bro are found through- out the Sooke map-area, and in 1912 the generic name of " Sooke K!il'l>"> " a^ applied by Clapp' to the whole proup. Clapp at that time also recojjnized and reported the pros- l)ective value of the copper deix)sits in 'vast Sooke peninsula, and recommended a detailed examination of the district to secure more definite infoimation as to its economic possibilities. Accordingly, early in the summer of 1913 the i)eninsula was mapped topographica'' v F. S. Falconer, of the Geological Survey staff, on a sea' : 2,000 feet to 1 inch, with a 20-foot contour interval. Later in the season the writer and his assist- ants, V. Dolmage and A. McLeod, spent four weeks examining the geology of the two areas. > Col, Surv., tan., Mrm. 13. 1912, p. llj. 66673—2 ■ » < Mcai^iUM m-i.i.KTiN NO Mt. The writer wixhcit to expre)«s hi* thank* to C, II. Clapp for aid in the field and information freely xupplicd a* to result* obtained in the ula is the Sooke ^ah- bro. The naturp of ihe mass, whether slock or laccolith, is unknown,' since bedding is ditlicult tu determine in the l>asnlt flows into which the fjabbro is intru. ive, and since the roof has been so completely removed that no t'oreign rock now occurs within the gabbro area, and the older basalts are present only in small, isolated patches along the shore. The gabbro intrudes the Metchosin ba.salts of upper Eocene age,* and is, therefore, post-Eocene. It is overlain on Sooke I>eninsula by the Sooke formation, a series of slightly consoli- dated sandstones and conglomerates underlying a small area on the southeast coast and filling isolated wave-cut chasms on the south coast. These sediments were deteniiined from their fossils to be of early Miocene age, or possibly middle or upper 1 A conjecture may he hazirded A% to the n.itiirc of tlie intrusive man^ea from a knuwlcilgc of the amount of granitic ilifferentiate present. 1'. E. Wright in bi« atuly of the gabhro maai of mount r>oher..ia (Mich. Stair Board (Jeol. Si rv., Rept. 190», p. 355) calculated from field evtdrnce that the amount of aplitic difTcrentiate waa about 17 per cent of the whole mass. W. II. Collinn ha* estimated that aplitic materiai formed approximately 12 per cent of the Gowganda diabase (Geol. Surv.. Can., Slem. 33, p. 75). Clapp, when examining the Sooke gahhro masses, ohservcd in the case of the Empress Mountain body, which has not been disturbed during consolidation that the granitic differentiate formed a layer ino feet thick at its summit. A« ling that this is the whole of the granitic differentiate, the gabl^ro i> determined tu ..ave a maximum thickness of SOO feet, using Collins' figures. Assuming that scfrregatinns has been impcrfcc* an>l that total amount of granitic differentiate is double that collected at the top; and in addition tliat in these gabhros the granite is only 5 per cent of the total mass instead of 12 per cent, the ludy is 4,000 feet thick as a maxi- mum. The Empress Mountain mass is <, miles long by 3 miles wide; its shape would, therefore, appear to be laccolithic rather than stock tike. Unfortunately none of the other masses in the Sooke map-arra afforded t^p:r. o this kind. »aapp, C. H., Geol. Surv., Can., Sum. Rept. I"12. ,,. U0lum1Imhiui1mi;y' ttMtutnrtf Til* iHpof fHlllt plHIlf IBji* - DnnaldMiw ^^^B ct JV MI ES is^fiz'acr Longitude We»X from Greenwich MAT EAST VANCOUV BRITISH Scal( S- <»anu«y>.' JMbCn ^ iKC /«a4» aooo pee WnlBn-nurHi'H I''r«possibIe to map the different tvpes'^even "on be argre scale map that accompanies this report. ' Au attempt i-as heen ma.le to indicate the jx^sitions of a few of the larger -.asses, but the boundaries of these are only approximate Th.s rock complex is cut by a great number of dykes and .!,M.euus vems, which vary widely in composition. The e.irrest a.e of nearly the same compf,sition as the normal gabbro, and are often porphyntic; a few of them contain olivine, but the majonty do not. In the Kocky Point mass more acid t^pes are found, jounger than some at least of the gabbroid tvpe^ Thev approximate the granite in composition, and are .iupposed to represent part of the granitic differentiate of this magnia Thev hornblende and t.tan.te. These dykes, though often large are never porphynfc. The d) kes an.I older rocks are cut by a ^re-.t number of replacement vei,.s of all sizes, from a fraction ^f an wITh" l^ "", '" ^ '"' ""'"^ ^^'"^ ^- '^"-•--d of long- laded hornblende cry.stals, without, as a rule other constituents than magnet.te Lrequently large zones of homblendite, up to 250 feet m w.dth are found. These do not appear, however t,, have been formed by the deposition of hornblendite in a sing e brge fissure but rather by the ascent of solutions througlf a mu tuude of closely spaced slip planes of a large shear zone with conse(,ueBt thorough and rapid alteration of a large mass of country rock * Still younger than the.se hornblendite veins, and cutting them are large numbers of aplite veins. They are always of small size, rarely oyer an inch in width, and form both 'replacement vems and true hssure fillings. They are composed of c,„artz and albite or ohgoclase-albite, with very little ferromag: esian mmerals. *^ 8 MUSEUM BULLETIN NO. 30. DETAILED Dr.SCRIPTIONS. Olivine Gabbro. Tlie olivine gabbro, which forms approximately 85 to 90 per cent of the exjwsed part of the intrusive mass, is a dark prej-, greenish, or black rock, composed of plagioclase, augite, and olivine, with accessory ilmenite. The colour of the rock vanes with that of the plagioclase, which ranges from pure white and greenish tints to purplish-black. When the feldspar is purplish black, it may easily be mistaken in the hand specimen, unless closely examined, for a ferromagnesian mineral, and the rock may be classified as augitite or homblendite. ihe composition of the feld.spar varies from pure anorthite to Ab«oAneo, but in the great majority of cases it is bytownite, Ab^An^ to Ab„ An,5.i The augite is almost colourless and non-pleochroic ; it is probably low in iron, and approaches diallage in composition. I'artial alteration to hornblende has taken place, and the cleavage faces of the latter are so conspicuous in the hand specimen as to give the impression in the field that the gabbro is chiefly horn- blendic. No primary hornblende was found, however, in the thin .sections. The olivine is also colourless, generally without much serpentinous alteration. Its axial angle varies about 90 degrees, so that some crystals are found to he optically positive, others in the same section optically negative. Such a behaviour, accord- ing to Rosenbusch, indicates an FeO content of about 12 per cent. The proportions of the different constituents in the average oliv.ne gabbro are 45 to 50 per cent of feldspar by .volume, about the same amount of augite, 5 per cent of olivine, and 1 per cent of ilmenite. Wide variations from these proportions are found, however. Feldspar may be present in any proportion from 35 to 100 per cent ; pyroxene from to 65 per cent, olivine from to 25 per cent. The variations, moreover, are fairly independent ■ I The composition of the felilspar in these rocks was carefully determined from extinction angles given bjr the albitc twinning lamellx on the (001) face. To obtain these values with certainty, 510 grams of each ijck specimen were crushed, sifted, washed, and examined for suitable cleavage flakes. All fragme'its were rejected in which the readings of the one set of extinction angles did not correspond within 2 degrees with those of the complementary set. CABBKOS OK EAST S(X)Ki; AND ROCKV POINT. 7 thus from a type made up of 60 per cem feldspar, 15 per cent P>roxene. and 25 per cent olivine, the rock may pass, without change in pyroxene content, througii types with decreasing ohvnie and increasing feldspar, into a rock with 35 per cent feld- spar and little or no olivine; or with conF*ant olivine content, by decrease of feldspar and increase of augite, into a basic type carrying not more than 40 per cent feldspar with 35 per cent pyroxene; or the olivine content may become small or zero, and augite gabbros result, varying all the way from anorthosites 100 per cent feldspar to basic types with 60 per cent of pyroxene. Singularly enough, the composition of the individual minerals remain uniform, or approximately so; during these variations in proportion. A single example may be cited. On Bentinck island, south of Rocky point, four parallel gneissic bands of gab- bro occur. The proportion of feldspar varies from about 50 per cent in the most basic band to about 90 per cent in the most feldspathic, but its composition in all four bands is AbjoAn,o. The common olivine gabbro is equigranular, with an average grain of 1 to 2 mm. The feldspar in it tends to form squarish or rectangular crystals whose length is rarely more than twice the breadth. The augite is interstitial to the feldspar, and of much the same general shape. Three types varying from the noi-mal texture are found frequently enough to be worthy of separate description. Type A, termed pegmatite in the field because of its coarse grain, possesses the same equigranular texture and mineral com- iwsition as the common olivine gabbro, but the component min- erals attain a diameter of 4 to 5 mm. on the average. In addi- tion, the feldspars as a rule are zonally banded. Another, less common, and much more coarsely crystalline rqck which may be classed with these " pegmatites " is occasionally found in rounded masses 6 fee - more in diameter included in rock of ordinary grain, -into which it grades rapidly. In these masses the average grain approximates IS to 25 mm. Type n is a rock of ordinary grain, but is characterized bv rather long prisms of augite and long laths of feldspar. The ■ MISIIM HI l.l.KTl\ NO. 30. feldspar is usually very white, the au),Mte more diopsidic in api»earance than ordinariK. In some varieties there exists a suh- parallel arrangement hetween the feldspars and the augites, which i;ives the nKk a |>eculiar and conspicuous columnar tex- ture, but in others this is absent and the two minerals fomi an interlacing network. Type C is characterized by the occurrence of the augite in large crystals and crystal agcregales, which enclose the feldspars |K>ikilitically. These clumjis of ferroniagnesian mineral are more resistant to erosion than the surrounding more feldspathic parts, so that the weathered surtace acquires an uncommon, embossed ap()earance. In one variety the clumps of ferromagnesian min- eral have an average diameter of 4 to 5 mm., in a second variety of from 2 to 3 cm. Auiiitc Gahbro. The augite gabbro contains no olivine, but is otherwise identical, macroscopically and microscopically, with the normal olivine gabbro. The unusual columnar texture, type B, that distinguishes some of the varieties of olivine gabbro, was not found in any of the augite gabbros ; but otherwise most of the variations in grain and coni])ositi()n found in the one can be duplicated in the other. The composition of the constituent minerals is also much the same in both. Most of the feldspar is bytownite, near .■\b.„An„,„ but whereas in the olivine gabbros the range of comjMisition extends only to Ab,„.\n,„„ in the augite gabbros it attains Ab„„Anj„. The augite, so far as could lie delerniined by microscopic means, is the same in both rocks. iini'issic Phases. Ilotl) the olivine and augite g.'ibhros frequentU- assume gneissic structures and textures. These may be found here and there over the whole surface of the intrusive, but are much' more numerous near the perii)liery than towards the centre. Alto- gether, gneissic rocks may form 2 or 3 per cent of the whole sur- face. The most common structure of this sort is primary gneissic GABBMOS l)F FAST SmiKK AND HIXTKY 11IINT. S bandinK. in which Rabbros of widely differing Krain and com;>osi- tion are arranged in lon^ parallel ribUms or ban.ls. These bands vary from 1 to 6 feet in thickness; the contacts between them are always jjradational, but the gradation alwavs verv rajjid. usually not over an inch or two in width. The Kabi)ros comjMJs- iuK these bands are fresh and unsheared; they occasionallx are characterized by flow textures arran^'ed parallel to the long axis of the band. The grain of the different bands may vary from rather line (average 1 mm. or less) to quite coarse (average 4 or 5 mm.) ; the comiMjsition, from a rather basic olivine gabbro with perhaps (O jier cent of ferromagnesian mineral to a highly feld- spathic gabbro almost anorthosile. The compf)si ;> of the feld- spar, however, rarely varies from one band to anothet. Flow textures are also frequently found in th-se rocks. They occur at times, as mentioned, in the bands of primary gneiss just de.scrilwd ; they may lie observed occasionally in one variety of rock at its contact with another ; although "in some places near the periphery of the intrusive they affect the whole rock mass. 'Ihey are alwa\s of the same tjjie. The p)roxene forms narrow laths or needles which have been arranged with their long axes parallel to (me another and at the same time a certain amount of parallelisni of the feld.spars has also been induced. Anorlhosites. The anorthosites consist usually of bytownite, .Ab..„An, , with less than 5 per cent of ferromagnesian ccmstituents. ' They are equigranular and medium to coarse-grained, with an average grain of 2-3 mm. They are chiefly remarkable on account of their manner of occurrence in small isolated masses. A few large masses are found in the East Sooke body, one, several hundred feet long, on the top of mount Maguire, a .smaller one on the east shore of the peninsula, near P.eechey head, a third on the west coast ; but large masses are uncommon and are apt to contain in places considerable quantities of pyroxene and olivine. The remainder of the anorthosite is .scattered throughout the CCt'.T:!— ,T 10 iiu»KL'M m-i.i.r.TiN So. 30. Rabbro in small, rounded lumjis, 6 inches to a foot in diameter, which >;rade rapidly into tlie gnbbro. The impression gained from field observation was that these feldspathic patches were apophjsal in their nature, produced by the action of aplitic solutions on the normal gaiibro. However, under the microscope it is clearly seen that the feldspar is highly calcic, insteaccted under the latter hyjiothesis, and the component minerals show no sign of being other than primary crystallizations, so the conclusion is inevitable that these bodies are really small segregations of anoithositc which were in process of separation from the molten magma when solidification trok place. Granite. Granite is relatively very sir.all in amount, and, as men- tioned, is found only on Possession ixsint, at the southwest cor- ner of the peninsula. The main mass lies almost horizontal, with a low dip to the north, and is some 30 feet in thickness. It is very clearly intrusive into the complex of gabbro and Metchosin basalt that occurs here, which is penetrated and brecciated by long strings of granite. The granite is a light, greenish-white rock, weathering to a brownish-white, with an average grain of less than 1 mm. It is composed of approximate/} 20 i)er cent quartz, 70 per cent olign- clase feldspar, Ab„An,„ 6 per cent hornblende, and accessory amounts of magnetite and titanite. Many of the feldspars show- zonal banding. Dykes. As already mentioned, the dxkes are of two main types, gnbbroid and granitic, although there are many sub-types, flue to minor variations of composition and texture. The dvkes usually have wide chilled edges, indicating that the gabbros into which they were intruded had become fairly cold. The gabbroid dykes may be subdivided into the porphyritic and non-por])hyntic types. The latter are of a basaltic compo- sition, equigranular, and basaltic to galjroid in texture accord- liABBWW or KA8T SIXINK AND MICKY lUINT. 11 ing to size, and almost identical in composition so far as can be determined microscopically, with the gabbro which they cut. They are composed of 45 to 55 per cent bytownite, varying in different specimens from Ab,„An„ to Ab,oAn,o. but averaging about AbjnAn.o. The only other essential mineral is a colourless augite, but olivine is almost constantly accessory. T. , porphy- ritic dykes vary somewhat from the non-porphyritic, both in composition and texture. They are distinguished by the presence of phcnocrysts of feldspar which, in a dyke 6 feet or more in width, may attain a diameter of ^ to 1 inch. These phcnocrysts were invariably develo|)ed in place, as they do not appear in the chilled edge of the dyke for a distance of an inch or two from the marpin, and from this point inward they become progress- ively larger until their full sue is reached about 2 feet from the border. So far as could be determined, the composition of the phenocrysts was approximately that of the feldspar of the groundmass, although in some of the sections they were zoned.' The feldspar is uniformly a bytownite, about Ab,jAn„„ as in the non-porphyritic dykes, and is present in approximately the same proportion, 45 to 55 per cent. The ferromagnesian mineral is the usual colourless augite, frequently altered to a greenish amphil)ole, but, unlike the non-porphyritic dykes, olivine was not identified. The granite dykes, a'' .ough few in number, form a fairly complete series, characterized by the presence of free quartz, in amounts varying from 2 to 3 per cent in the most basic, to 35 per cent in the most siliceous. The nature of the feldspar varies with the quartz content; in the dykes low in quartz the feldspar is andesine, AhjoAn^o, and as the proportion of quartz increases, the feldspar becomes progressively nifire sodic uiilil in the most acid it becomes Ab„„An,„. The fcrroniagnesian min- eral undergoes a corresponding change. In the L..sic types a little pyroxene may be present, but hornblende predominates in all; a small amount of biotite, up to 4 or 5 per cent, is always 1 One case w.-..« observed in which the outer zone> of the fehlspar phenocrysts were more calcic than the inner. fiCG73— 3i If HtllKDM •l'U.».TtN Ml. Jll. present, indiratinK lliat water was lieinj,' cotuentratecl in ihcsc acid niaKnian, IhU not necessarily in tar(;e aniuuiit. Ihc total fer- roiuaKiiesian mineral niav amount to 10 or 45 |ier cent in tlie more basic t>|>es, l)Ut rapiiliy decreases with increasini; acidity, until in the very .siliceous dykes there is less than 5 |ier cent. Titanium, which n the ordinary (jahhros is always comhined with iron as titaniferous nia(,'netite, in the granite dykes always take- the form of titanite. Only hve of the granite dykes v.c>e found. conCined to the Kocky Point mass. This fact, coupled with .le petronraphic resemblance to the >;ranitcs of Ilast Ske and other iMulies, strongly su^Kesis that the dykes are the Rrani- tic dilTerenliatc which in this mass has Iwen forced into more definitely intru.sive relations with the ^ahhro than in the other fx)dies. 'Ihe se(|uence of irruption of the dykes has not l)een deter- mined satisfactorily owing to lack of sutlicient data. Only in two cases were dykes observed to cut one another. On Heniinck island a d\ke of the granitic t) [« cuts one of the non-porphyritic gahhroid ty|)e. On Possession {wint a dyke of the |)orphyritic gabbroid tyjw cuts the intrusive granitic differentiate. Assum- ing the equivalence of the granite of I'os.session point with the granite dykes of Kocky jKiint, the sequence is as follows : Por|)hyritir Kal)l>n>trphyritu' Kal>l>ri>id dyki's Olivini' anl)ru!i. P'eitts. Hornhlenditc I'cins. The hornblendite veins are repi.ice- nient veins fomied by the action on the gabbro of solutions rich in iron and magnesia rising through joint cracks and other fissures. The majority of the veins are onl> a few inches in width, but some are very large, .SO to 250 feet wide. Like most replacement veins, they are characterized by great variabil- ity in width along their strike, and have no clean and definite vein wall, but grade into the unaltered wall rock. Lnder the microscoije, the replacement of the various constituents of the LABVIMMt ur rAlT MnKr ANP WXKY ntINT 1« wall rf>ck In liiimltlende can l>c oh-crvcd in nil ilt stages. When it i-i iiiin|i!ete, »ti»lhin),' but a felled m ■ -; i»f li)nj;-hladed cryslal-i of sition, but differ from them in two im|).>!t;mt respects. They have l)een alTected liy faulting movements, and the cupjier ores have hcen deposited within them. The faulting had granulated the large-hladed hornhlemie crystals, so that much of the hornblende of these zones is now lu) more tli.m cemented dust, and has pnxluced numerous slickcnsided cracks and llssures, while at the same time nuicli of the hornblende has l)cen converted into chlorite. The solutions which carried the copjKjr ap|)ear to have ascen be oliser\cd to eMcnd .inly a few inches from the central joint crack. It seenis equally unlikely that these zones could originalls have been wide, open fissures, since, as will lie next described, fissures originally only 2 or .^ feet in width, have been filled, not with solid hornblendite, but with coarse gabbro, grading into aplite at the centre. The most prob- able hyi)othesis appears to be, that these zones represent pre- existent, sheeted fault zones which afforded the solutions a mul- titude of closely s|)aced planes of slip through which to rise, and thus gave them power to alter broad bands of country rock. Cahbro-aplilc / 'cihs. Three or four veins, I to ^ feet in width, which can be described only as gabbro-aplite veins, were 14 MUSEUM I'JLLKTIN NO. 30. full. ; !•'! : c course of the field work. One of these was obseiv..v. uu Bentinck island, a second. and third on the Race rocks by the writer, and the fourth was found by his assistant, V. Dolmage, in the interior of East Sooke peninsula. These veins are characterized in three of the cases ob.served by a very basic edge, the width of which is about one-third that of the whole vein, grading into .m aplitic centre. The composition of the edge in each case is that of a very coarse-grained basic gab- bro: 60 to 75 per cent of pyroxene approximately, the remain- der b) townite feldspar. From edge to centre a gradual decrease m the proportion of pyroxene takes place, with increase in tlie proportion and alkalinity of the feldspar, until near the centre the !>> roxene alters to hornblende and becomes small in quantity, quartz begins to crystallize out, and the feldspar becomes oligo- clase-albite, about AbgoAnm. The whole of the Bentinck Island vein is exceedingly coarse-grained and many of the crystals are more than an inch in diameter. The change from a basic edge to an aplitic centre is not nearly so marked as in the other veins, but nevertheless the change in composition is seen under the microscope to have been similar. The ferromagnesian mineral is hornblende, which may be primary or secondary ; the feldspars are zonally banded, with a kernel of composition AbaoAn^, and outermost bands AbgjAnjs; and, as the last product of crystalli- zation, some 5 per cent of quartz has l^een deposited in intersti- tial spaces. Aplitc Veins. The aplites are found both as fissure fillings and as replacement veins and apophyses. The fissure fillings are rarely more than an inch or two in width, and commonly only a fraction of an inch, with cle;m-cut walls very slightly altered by the solutions. The alteration of the gabbro has been much more intense where the aplitic solutions have been forced through minute cracks and the intermineral spaces, instead of into open fissures. The aplite of the veins is equigranular, with an averap-- grain of less than 1 mm., and is nearly pure white in colour. Free quartz is always present, and has l)een observed to constitute as GABBROS OF KAST S(X>Ki: AMI KOCKY POINT. 16 much as 60 per cent of the total mass, and proportions of 35 to ^0 per cent are common. V'ery sodic feldspar, about Abg-./Vnij, often graphically intergrown with the (juartz, is the other prin- cipal component; '... : .'.•" ferromagnesian elements are repre- .■^ented hy a fe hreds, r,.!f!> '.'iiounting to mftre than 2 or 3 per cent, of hi . nbl.T.de, i:l!lorii\ or mica. A little titanite is conmionly pres nf. i'he qiuiri • is usually concentrated towards the centre of the . t'.-..-, :r- I occasionally the centre of a vein or apophysis is composed almost wholly of it. Aplite replacements genetally take the form of rounded apophy.ses rtither than veins. They are not nearly so numerous as the aplite veins or the hornblendite replacements, but numer- ous enough to .show that the aplitic solutions attack and alter the gabbro when forced into intimate contact with it. The ten- dency of the alteration -s to convert tlie gabbro into aplite of the vein type. Under the micro.scope the augite of the gabbro is seen to have been changed to hornblende and biotite, calcic feldspar to more sodic, and ilmenite to titanite and magnetite ; and quartz has been deposited in intermineral spaces. The aphtes are younger than all the rocks previously described, as they cut them all indifferently. The)' are probably older than the copper ores and the faulting which preceded the deposition of the latter. The evidence on these points is, how- ever, largely inferential and ma_\- be summarized as follows : No copper ores or ore minerals of any kind, with the excep- tion of occasional grains of magnetite, have been found in any aplite vein. Aplites are everywhere found cutting the hornblendite veins, except the large hornblendite zones which were faulted before ore deposition took place. Whitish fragments of sodic feldspar are fairlj- common in these big zones. The probability seems strong that the aplite veinlets must once have cut them also, but were destroyed by the later faulting, and that the feld- spar fragments are all that now remain. Ore veins are generally a later product of differentiation than igneous veins. IS MUSKIM IIII.I.ITJN XO. 30. Relations to the iiahhrn. That the aphtes and homhlendites are jjcneiically connected with the ),'ahl)ro, and are i)e),miatitic vein dei)(>sits formed as tlie V.'M exiialations of the coohnj,' niajjma. is clearly shown h\ their internal and external relations. They cut all varieties of rocks found in the stocks, inclndinjj the later d\ke^. and in the case of the ai>lites fre(|uentlv till well- defined fissures; hence they nui-^t not only he younijer than all the other rocks, hut must have heen intruded after the complete solidification of all. Their mineralogy, especially that of the later, aplitic veins, is that of a pegmatite, i.e., a rock de]H)sited from a magma highly charged with water and other volatile con- stituents. In occurrence they are entirely confined to the gabhro bodies, and rarelv extend l)eyond their edges for even a few feet ; so that they must have originated within it and probably at .some depth. Changes of Composition Dnriiuj Hornhlendization and . \pli- tization. To determine the effects of the hornblendizing and aplitizing solutions on the gabbro, and at the same time arrive at the com])osition of the .solutions which produced them, chemi- cal analyses were made by M. F. Connor of a typical oli\ ine gab- bro, a hornblendite, and an aplite. The results of the analvses, given Itelow. were then plotted on t'le straight-line diagram described by Mead' in which the jioini- on the curves are deter- mined by dividing the percentage of each oxide in the fresh rock — in this case the galibrn — by its percentage in the altered rock —the hornblendite and aplite resjjectivelw The results (I'igure 1) ... the hornblendic alteration are shown by the solid line, the aplitic alteration l)y the broken line. They are discussed in detail in another part of the bulletin. The straight line diagram (Figure 1) is a convenient means of exi)ressing gra]>hicall\ the character of the changes that have taken place during a rosk alteration of any kind. The diagram is made up of a number of horizontal lines, which are sul>divided by vertical lines according to an\ convenient method. The dia- 1 Mcail, W. J., Some geologic short cuts; Econ. Geol. 7, 1912, p. 136. GABBROS OF EAST SCXlKK AM) IdHKY POINT. 17 gram tii,'iired, which has been contrived by Mead, is so divided that a fniile Hne represents any quantity up to infinity. One of the horizontal lines is allotted to each of the component oxides of the rock. The position of the jwint on each line, which repre- sents the change of that oxide during alteration, is obtained by dividing the percentage of that component in the chemical analysis of the fresh rock by its percentage in the altered rock, and multiplying the result by 100. The points so obtained on the various horizontals may then be connected by lines. The result shows at a glance the relative gains and losses during alteration, dr the absolute gains and losses if any factor is known to have remained constant. Thus, if any constituent has remained constant, then all of the constituents whose points fall to the right of the known point have decreased in absolute amount, and the constituents whose points fall to the left have increased. If weight has remained constant, i.e., if 100 grams of fresh has yielded 100 grams of altered rock, then all consti- tuents whose points lie to the right of the vertical 100-line have decreased in absolute amount, tiiose whose points lie to the left of this line have increased. If an absolute change in weight can be determined, i.e., if 100 grams of fresh are known to have yielded 90 grams of altered rock, then the vertical line 90 is the zero line, a" ' 'nts to the right or left of this represent abso- lute losses i respectively. When lack of information renders it ii. e to fix any point as constant, the relative gains and losses of the different constituents are all that can be determined. eet!?.-}— 4 18 MISI I M mi.Ll.IlN N' .y\ 1 o 3 Sit). 47-58 18 03 1-10 3 -34 (.5-37) 10-88 16-92 0-32 1-04 0-60 06 0-20 01 45-42 10-64 3 03 10-22 (10-08) 13-82 11-84 0-45 2-17 2-20 0-08 o-3g 0-01 03 77-86 .\l,l«, |-\...( )3 11-96 0-21 K.-( ) 0-32 (l-".-l (0-40) \!.,'() ( lO 0-29 1-92 K;<) N.i.() : HO 31 5-67 0-60 MuO 0-02 TiO, 0-25 iM): 0-04 10008 100-21 99-45 1. Frosh, rather fine-grained olivine kji')!""". eontaining approximately 5 [xr cent of olivine, the remainder pyroxene and feldspar in al)out equal proportions. 2. Hornblendite, from one of the larfjo zones, observed under the mirros- coiK- to be eonij)osjd almost wholly of fresh, jjraniilated hornblende. 3. Aplite, a fresh sfK'cimen of medium composition, eontainin); perhaps .somewhat more than the average of ferromagnesian mineral. Rock . Iltcralioii. The jjahbros are on the whole onW sli,L,'htly altered. They have, however, been atTected, sul)se(iuent to consolidation, by shearing movements, juvenile solutions, and meteoric solutions. .\s rej;ai"ds the first, refjional stresses ha\e caused a certain amount of faultinj,', with production of wide sheai zones. Granii- lalion of the f;abbro and its jiartial conversion into .schist undoubiedlx took place along these zones, but these effects have been ohscmed by the action of the hornblendite-forminjj solu- tit)ns, which flowed through the fault channels depositing horn- blendite. A later faulting has sheared the h-)rnblendite with formation |.>osilive evidence that still e.xists to indicate the supposed previous condition is the occasional occurrence alon(,' the shores of Sooke peninsula of vertical dyVe-!:ke bands of gnbbro .'^ to 10 feet in width, now comi)leteIy altered to soft kaolinic material, but still preserving the original texture of the gabbro and con- taining unaltered nodules of it. These seem to have been formed by seepage of meteoric water along joint cracks. Weathering since glaeialion extend.s only a fraction of an inch from the surface in massive rock, and a few incl?s where joint- ing has allowed rain and air to penetrate more rapidly and easily. The feldspar has been partlv kaoiinized, the augite uralitl/ed, the olivine converted to serijentine, and the ilmenite to leucoxene. Some of the aplite veins have been epidotized. This is believed to be due to meteoric waters and the localization in these veins is probably due io the good channels afforded the .solutions, and perhaps also to the composition and fineness of grain of tlie veins. The feldspars have been completely converted in some places to iron-iMK)r varieties of epidote, such as zoisite and clino- zoisite, and in i)laces to an iron-poor pistacite. Kaolin has usually been formed at the same time, and proliabty also quartz, although any quartz thus formed cannot be separated from the quartz originally present. Some aplite dykes were founvi con- sisting wholly of quartz, kaolin, and epidotes, a>H nearly all have undergone this change to " greater or less degree. CCfVr.S— 4J 20 MUSKUM BULLKTIN NO. 30. Triple Points. It is of interest to note the occurrence in the gal)l)ro of two fairly definite limits, which may l)e termed " triple points " for want of a letter name. As already de.scril)cd, the gabbro is \w* of uniform composition throughout, but includes types ranging from highly basic to extremely siliceous. This change is accom- panied by a corresponding change in the composition of the feld- spar from anorthite in the most basic varieties to albite in the most siliceous. In the most basic types olivine forms approxi- mately 25 per cent of the rock, and is accompanied by pyroxene and anorthite or bytownite. The proportion of olivine becomes less and less in the rocks characterized by progressively more sodic feldspar, until it disappears altogether when the feldspar becomes Ab„An„o. The point at which olivine ceases to appear is the first "triple point," so called because it apparently marks the limit of the equilibrium of olivine, pyroxene, and feldspar in an increasingly sodic series of magmas. It is true that many rocks with feldspar more calcic than Ab4oAna„ do not contain olivine, but this is ascribed to the removal from such rocks of the olivine crystals, by sinking, after the partial crystallization of the rocks. The second " triple point " observed is identical or nearly so with that found by W. H. Collins in the Gowganda diaiiases.* At this point feldspar, pyroxene, hornblende or biotite, and free quartz are in equilibiium, and the feldspar has the composition AbejAnj,. Rocks containing feldspar more calcic than this are composed of n) roxene and feldspar with accessory titanium and iron combined as titaniferous magnetite. Rocks with more sodic feldspar contain in addition hornblende and biotite (Collins found biotite only), with free quartz, and accessory iron and titanium take the forms of titanite and magnetite. Emphasis may be laid on the fact that the sudden mineralo- gical changes at the " triple points " are not accompanied by any sudden change in chemical composition. On the contrary, all the evidence indicates that the chemical changes are gradual and smoothly progressive. Collins found a similar condition to pre- vail. 1 Collins. W. H., Geol. Sur»., Can., Mtm. 33, 1913, p. 80. GABBROS OF FAST StxiKF. AND ROCKY POINT. 21 INTERNAL STRUCTURAL RELATIONS. Spatial and Contact Relations. The relations Ijetween the different rocks of the mass are c. two cl.isses ; general arrangement in space, and contact relations. Although both of these have been taken up to some extent, tiie previous statements are here recapitulated and somewhat enlarged. In space, the olivine gabbro occupies the whole central part of the intrusive. If its upper horizons were originally of other comix)sition, all trace of this condition, except the anorthosite remnant on the summit of mount Maguire, has been removed by erosion. Erosion has also eaten deeply into^the edges of the mass locally, especially on the western and southeastern coasts, and there the olivine gabbro outcrops directly on the seashore. The augite gabbro is found over the remainder of the coast-line, occupying a position peripheral to the olivine gabbro and form- ing a partly removed shell around it. It is found in a narrow strip around the southwestern end of the peninsula, and as a wider band along the north coast. Anorthosite does not occur in any continuous mass, but small bodies of it are scattered throughout the strip of augite gabbro, and larger bodies at oi near the contact i' the olivine and augite gabbros. Thus the largest mass on mount Maguire is directly underlain by olivine gabbro, and the moderately large masses on the western coast and near Reechey head lie fairly close to the contact of the oli- vine and augite gabbros. The only granite mass found on Sooke peninsula occurs at the extreme southwestern tip, on Possession point, intruding the augite gabbro there ; this point is supposed to be very near the original periphery of the body, as the augite gabbro here forms an extensive contact breccia with the Metcho- sin basalt, and such bands of contact breccia are nowhere else fognd to be more than 200 or 300 feet in width. Turning now to the relations between the different rock varieties as found at their contacts, it is necessary to consider those lietwjen the different varieties of each principal rock type » MLSI.l'M mi-t.KTIN NO. .VI. and nlso those l)et\veen the different tvi)es. The varieties of oh- vine ),'al>l)ro de.scril)ed on pajje 'f, are nsnaiiy found to possess gradational relationships with one another so that although the zone in which gahliro of one texture passes into gahbro of another is usually only a few inches in width, sometimes as narrow as one inch, still there is no sharp line of demarcation between them. I'ainlly intrusive relations are found in several places, however, and when these occur it is nearly always the com- mon t\[)e of olivine gabhro wiiich is intrudeil by the special- textured tyi>es. The relations which establish the fact of intrusion are: (1) in places, long narrow stringers of the intru- sive i)enetrate the intruded rock; (2) ver) slight decrease in the size of the grain of the component minerals of the intrusive occurs near some of the contacts; (3) flow textures in the intru- sive rocks are develojjed along many of the contacts. The relations between the olivine and augite gabbros are of nuich the same character. At several places, as on Rentinck island and the western end of Sooke peninsula, the augite gabbro is clearly equivalent in age to the olivine gabbro, as it merges into the olivine gabbro by gradual increase of olivine. Furthermore, it is interbanded with the olivine gabbro to form a primary gneiss. At several other points, notably at the southwestern corner of the peninsula and on Race rocks, the augite gabbro is distinctly later than the olivine gabbro, since it has intruded it in the manner described, and has bn.ken off fragments which are now included in the augite gabbro. At two points, however, in the olivine gabbro area around Beechey head, these relations are exactly reversed, and similar phenomena show the augite gabbro to be intruded by the olivine gabbro. The anorthosites possess similar relations tf) both olivine and augite gabbros. The gradational relations may best l)e seen on mount Maguire, where the fairly pure anorthosite merges in places into true gabbro by increase in the olivine- augite content. The same gradational relation is found along the edges of the lar-je anortho.Mte masses on the south and west coasts, as well as along tho.se of the small masses scattered through the augite gabbro. In the latter places the gradation is CABBKOS (IF KAST S'»)KK AND ROCKY WIINT. 23 .ibiiii>t, whereas on mount Majfuire the changes are much less so. In two places, near ISeccliey head, the anorthosite was seen ('elinit«fly to intrude the olivine gabbro, in the form of well- de'med dykes. 'J'he granite on I'ossession i)f)int is distinctly intrusive into the au^ite |,'abbro, am! forms an extensive contact breccia with it. However, Clapp found that in other bodies of the .'sooke gabbro the jjranite portion is clearly j,'radational into the under- lyinjj j,'abl o. It is assumed, therefore, that the (,'ranite of the East Sooke intrusive also once jKissessed a j;radational relation to the basic rocks, and that this relation was obliterated by move- ments which, as will be shown, took plac? before solidification, as the j^radational relations of the f,'abbros to each other were partly obliterated. The followinR quotation from a "cent rejiort by Clapp* makes clearer the lelations of the f;ranite and jjabbro as found by him in the other masses of the Sooke maj.-area: " At several places, in fact along all of the exposed contacts between the two, the gabbro, which greatly predominates, and the granite may be seer to grade into one ano her w-ithin a dis- tance of one to three feet. .\t most places the two rocks main- tain their nonnal character to the narrow transitional zone, though usually the gabbro is more feldspathic near the transi- tional zone than is normal elsewhere. In a few places, as to the southeast of Empress mountain, the gabbro is fine-grained and porphyritic near the transition, and even the granite is fine- grained. In the vicinity of ICmpress mountain the granite clearly overlies the ,_ libro, and grades abruptly downward into it. . . . . . . T'-e granite forms two or three small knolls about 100 feet high surmounting the gabbro ridge; and a mile to the southeast of the summit of b"mi)ress mountain the granite occtu's at the top of the intrusive stock, forming a zone f)r layer 100 feet or more in thickness capping the gabbro and inmiediately under- lying the apparently flat roof of Metchosin volcanics .... At several places the granite forms irregular masses, many of •Clapp. C. n.. kes. They evidently resulted in formation of '"•ssures into which the dykes were intra '.li and were jointing rather than faulting movements, as li ' ■• or no displacement along them has been detected. In time, the movements resulting in the intrusion of the non-porphyritic gabbroid dykes and the granitic dykes evi- dently occurred after the solidification of the gabbroid differen- tiate of the magma, and l)efore that of the granitic differentiate: the movements resulting in the intrusion of the porphyritic gab- broid (hkes occurred alter the solidification of the granitic differentiate. The fifth movement appears to have resulted in the formation of large faults, with wide shear zones, and accompanying joints. Although \ holly inferred, this movement, especially the formation of the wide shear zones, is necessary to explain satisfactorily how it was possible for the hornblend- izing solutions .vhich escaped at this time to convert bands of gabbro up to 250 feet in width into hornblendite, when the influence of the solutions when they rose through a joint crack does not appear to have extended more than 6 or 8 inches on fach side of it. nABIIRD!) (IK K.AST S<»1KK AND KrKKY PllINT as D-positinn from the liDrnhlendizing solutiuns apparently sealed most of the joint and fault fissures resuItiiiK from the fifth movement, so that it was not until the sixth movement, whicli pHwluced new joints and small fissures cutting the old, that the escain; of the nplitizinjj solution took place. The seventh movement resulted in further fauitinff. No new fault pl.ines were produced, hut the stresses were relieved by slip alonj; the fault /ones of the fifth movement, with consequent brccciation of the hornhlendite which filled them. The eighth movement resulted in further jointing. In addition, some later movements probably occurred, as two or three sets of joints cut the aplitc veins and each other ; but as it is difficult to distinpiiish betw ecu the diflferent sets, the actual number of movements producing ihem is unknown. In spite of the large number of observations of strike and dip of the v.irious joint, vein, and dyke syster.is, no regularity could be determined, even among those systems which belong rather definitely to a single set. It is possible that a regularity of arrangement might be established by a more intensive study, which might show that much of the jointing has been due to com- pressional feces; on the other hand, it is probable that many of ihem are tension joints, formed by the strains set up during the cooling of the mass, and without regularity of arrangement. A somewhat greater regularity is found in the fault.s. Their .-trikes vnr\ considerably, but in general fall into two sets, -.he one between north 10 degrees west and north 20 dein-ees east, the other between north 45 degrees east and north 6.=; degrees east. In most places the fault |)lanes have a steep or vertica; dip. The displacement in all the faults noted is nearly horizontal, as shown by the direction of the strire on slickensidcd surfaces. The dip of the stri.-e was not observed to exceed 20 degrees, and was invariably to the southwest. The amount of the displace- ment is difficult to estimate, as good horizon markers are lacking, but it is probably not much over 1,000 feet even in thc.large^t. Mt'HM'M BlIltTIN Nci .V) MFNKKAL DKPOSITS. Tlic mineral (leiM)>its of I-'.a>f St«»kc pciiiiiMila are of two t\|)es, copper and iron (lepo>il>. The former are of miicli greater economic importaiue. 'I'liev are found in tlie lar^e liornMendite yones which ha\e suffered from a second |)eri<)d of fauhiiit; with conset|uent trituration of the liornlilende cr\stal-i. '! he universal association of the ore» with the hornl>lenhow dearly that the true se<|uence of fonnation was: (I) hornhlendiie; (2) faiiU ; { ^) ore dei>osition. l'"resh, slickensided surfaces are common in the lar^e horn- blendite zones, whereas all other textures are dcstn)\ed; hence these surfaces were fonned subsequent to hornblenchzation. Small, unfaulted hornblendite zones are coarse and ) cjona- titic in texture, and the lar>;e ones arc princijially made up of fine-graince brecci.ited m.aterial. Hence, a>;ain, faulting followed hornblcnd- ization. .\l)litic strinfjers cut the small, unfaulted, hornblendite zones, but tione cut the larjje ones. Presuni.ibly such strinijers once existed, but have been destroyed by faultinj;. Xon-faulted hornblendite zones carry no chalcoj)) rite, hence deiK)sition of copi)er did not accompany hornblenchzation. The sulphides in the ores are universall '(und in distinct cracks in the hornblendite, not interKrown witU the hornblende; hence de|>osition is sul)se<|ueiit to and not conteni]»nr,meous with hornblendization. The sulphides are sometimes found dei>osited in cracks, tlie walls of which are slickensided, and sometimes ore veinlets cut across slickensides. Hence ore deposition was subse(|uent to faulting. As mentioned, the ores consist largely of chalcopyrite, dis- seminated more or less thickly in small cracks and veinlets throughout the hornblendite mass. The percentage of chalcopy- rite present may vary all the way from zero rp to 100 per cent; occasionally ore chutes occur consisting of dense, ma.ssive chal- ,\1II1HC>« or I \SI SKIKI \MI H(H KY IIIIVT i? roiHiite. 'I'lie .ivcraKC );er tent copficr. \'er> few other luinenils of aiu kind are found aaiim|>;in\ in^' the ihario|n rile. A little (|iiarl/ foldvpar, lalcite, pvrilc. inajinflile, inolUidenile, ;ind zeolites h.ive l)eeii oliservcd, hut the anioinit of tliese i> »o small as to l>c net;lii;il>le: and rc'iricit'il to the surface is a little iiali\e ropjier, ii\idl/ed <-o|i|ier niinrr.il-, .ind lininnite. I'or practical pur]M)ses it ni;i\ he s.iid thai ihc Old) >;an);ue present is the lutrnhlendite itself. .\.s the larjje shear /ones in which the ores are found _\iciil more readil> to erosion.il intluences than the hard, luialtereil fiahhros, they ;ire lopo^raphic;ill> t:. pressed li> the presence of small valleys nti land; and on the sea coast, where wave action is stroiijj, as on the southwest coast, hy narrow wavc-cirMled chasms. These chasms sonietimts run in for 1(X) feet or more and thus form an infallilile indicator of the presence of these /ones. The vallevs on land, however, have l>een filled in with soil, so that they .-ire now only shallow dei>ression-. diflicult or impossible to trace in the present uncleared condition of the countrv. The shear zones in whicli the ores are found are strong and iiersistenl, .'uid can usually he followed for several hundred feet. The lai>;est, th-it exposed on the Martjaret, ("opjKT Kinj^, and I'.ureka claims, is tr;icealile for at least 4,300 feel. The strike, as dcscrihcd under " {'aultinj^'," pajje 25, varies fjreatlv Iwtween the ditTerent zones. I>ut there are two principal ^cts of shear zones, one ha\ injj strikes hetween north 10 dejjrees west and north 20 dej^rees east, the other l)etween north 45 dei;rees east and north ()5 decrees east. They vary in width from a few feet to one which is at least 2.^0 feet wide. Their size and I)ersistence render these deposits of considerahle prospective value, and make it ])rohahle that they will continue to carry good values to considerahle depths. There is, hoNvever. no reason to believe that they will increase in value with depth. They will more probably decrease gradually in value, probably with fjnid'ial increase of the ])roi>ortion of pyrite. Native copper, winch is fre(|uently found in small amount at the surface, is due to surface alter.ition only, and cannot be expecled beyond depths of a few feet. 28 MUSKUM BULLETIN NO. 30. A second type of mineral deixjsit, very subordinate both as regards quantity and value, is the magnetite-pyrrhotite deposits. Under the course of differentiation as pfeviously outlined, such deposits might be formed at two periods in the history of con- solidation of the gabbro. They might have resulted from the early separation and aggregation of iron minerals from the Iwdy of the gabbro magma, as at Sudbury, and thus in age antedate the consolidation of nearly all its phases; or they might have been formed in the last stages of differentiation at the time of the formation of the homblendite veins, had the waters that formed these been laden with excess of iron. That these waters did carry iron in excess of that required for the conversion of the rock into homblendite is shown by the almost universal presence, in the middle of the small homblendite veinlets, of strings of mag- netite and pyrrhotite grains. One of the two deposits observed on the peninsula belongs without doubt to the second type, as it is found in a large shear zone, in the form of lenses, greatly cracked and cut by the later depositions of chalcopyrite. This is the deposit at Iron mountain, section 79. Here the only gangue mineral is hornblende, in bladed forms and granulated, and the metallic minerals are magnetite and pyrrhotite. The pyrrhotite is found in fairly large, comparatively pure, masses. The other body is found on section 83 ; it was not examined by the writer. These massive deposits are too low grade in copper to l)e even of prospective value. They are rich in the valueless metallic minerals, and it would be difificult and expensive to separate the chalcopyrite from them. The deposits have been exploited for iron as well as copper, but the sulphur is too high for the deposit to be a possible source of iron with the present conditions existing in the iron industry of this continent. It is possible that at some future time they may have some value as a source of sulphur for the manufacture of sulphuric acid. Their chief value has been as an iron flux in copper smelting. CABBKOS OF EAST S(X)KF. AND ROCKY WINT. 29 THEORETICAL PART. INTRODUCTOKY STATEMENT. The facts detailed in tlie preceding pages have shown that the Sooke intrusives include a large number of different petro- graphic types that fall naturally into a series of which, although the end members are widely different, the proximate members differ but slightly. The writer will endeavour to prove that these differences are due to the process of differentiation acting on an originally homogeneous magma whose composition was probably that of a rather basic basalt. The different rock types present certain irregularities, previously detailed, of distribution, shape, and inter-relations with one another; it will be shown that the most likely explanation of these irregularities is the occurrence of movement and disturbance within the masses prior to their consolidation. It is possible that the movements may have been those which accompanied the intrusion of the masses, in which case the differentiation must have taken place at greater depths ; but the bulk of the evidence seems to indicate that they were not so profound as this would imply, and that the actual sequence of events was, intrusion, differentiation, and movement. The method l>y which the differentiation appears to have taken place is that of partial crystallization and sinking of crystals, aided in the later stages by the regional movements, which strained off or squeezed out the mother liquor from partly crystallized material. Bowen* has recently shown that such an explanation of differentiation appears the only adequate and possible one; and the facts observed in the study of the Sooke intrusives bear out his theory. The records of the final stage of differentiation, the period of exhalation of aqueo-igneous solutions, are here unusually complete, for there have been two types of veins formed by these solutions, a basic and an aplitic, instead of only the usual aplitic veins. Unfortunately, owing to the smallness of the intrusive mass, cooling and consolidation overtook and ended the differentiative processes before their work was com- plete. » llowcn, N. L., Jour, of Geol., supplement to vol. 23, I91S. 30 Ml'SIlM lU'I.l.KTIN Ni). MX PROOF OF DIFFKRKNTIATION. The following facts, which have been already taken up in detail, indicate that the various rock tyi)es have been derived from a common magma by differentiation: The principal types occupy definite positions in space, the most basic at the centre, the most siliceous at the periphery. In undisturbed masses, such as the Empress ^lountain body, the siliceous part lies at the top. The different tyi>es and sub-varieties grade into one another at their contacts, where disturbance during consolidation has been small or lacking. Where disturbance has been great, the more acid types intrude the more basic. Although the end members of the series are of widelv differing chemical composition, the proximate members differ only slightly from one another. The mineralogical composition shows a similar gradation, except at two " triple points," where there are sudilen changes accompanying the appearance of a new mineral or the disappearance of one already present. COMPOSITION OF THE ORIGINAL MAl.MA. At present, olivine gabbro occupies approximately 90 per cent of the exposed area of the East Sooke intrusive, and augite gal.bro practically all of the remainder; the relative area of anorthosite and granite exposed is very small. The proportion of granite was formerly probably larger, as on account of its peripheral position it was the first to be exposed to erosion; but from the examination of the Empress Mountain and other stocks, and from the results already (|uote: the opinion that the mass was intruded to its present position '■efore differentiation took place, as the results of movement do not appear to have been sufficientl) profound to sustain the hypothesis of intrusion after differentiation. In support of this conclusion the following evidence is adduced : The main mass has been shown to have been liquid at the time of movement. It seems unlikely, if differentiation took place before intrusion, that a large, forward movement would have ended in the present spatial arrangement of acid differentiates on the periphery, basic ones in tl.e centre. More likely remi.xing would have occurred. The formation of the separate species b_\ differentiative pro- cesses which took place liefore movement began must have involved much crystallization of olivine, pyroxene, and probably also bytownite. It has already been shown from field evidence (page 31) that crystallization certainly had at least begun. It seems probable that any large advance of the magma after this had occurred would have caused crushing and biecciation of these already-formed crystals. This effect would be most evident in the more basic varieties of olivine gabbro. However, nothing of the sort has been observed. (.ABBROS or KAST SIMIKF. AXD ROCW POINT. 33 It has ;i!rea(h I)een shown on field evidence that the 1 or .S per cent of the ma(,mia whicli forms the gneissic phases, was in a very viscous condition when movement took place. Xothinjj is known as to whether the remainder was viscous or fluid. Assuni- ins a Keneral advance of the whole maj,nna after differentiation, let us consider hoth possibilities. If the greater part of the ma^jma was fluid, the rest viscous, a general advance of the whole majjina would almost certainly resuh in the complete remi.xinjj of these fluid i)ortions and the viscous parts would l)e rendered ^neissic ; so that the ijresem condition would he that of a matrix of unifonn composition surroundinjr patches of gneissic differentiates. This is not the case. If the whole or greater part of the magma was in a viscous c.p.dition at the time of a general advance, then the wliole or greater part would have been rendered gneissic. This is also not the case. It seems clear, therefore, that the movement which occurred after differentiation had died its close, or nearly so, could not have been that throug. h the magma attained its present position; so that different!; •. went on in situ. MICTlIOl) Ol- l)IIFi:i,'h are fouiul to make clear the tendency of the feldspar to lieconie more and more sodic. Out of thirty-seven sections of olivine g-'d'hro examined, six, or 1() per cent, contained feldspar whose composition varied from Ah,,uAn;„ to .\h,„An„„; and in thirty-three sections of au>;ite gahbro, thirteen, or -10 per cent, carried feldspar between Ah,,, All;,, and Abu-An,.-,- Tint these sodic feldsi)ars are reall> products of a later crystallization than the more basic is shown by the facts: that they are found in the outer bands of zoned cr>stals where these occur; that the auj^ite j;al)bro, already proved to l>e a ditTereiitiate of the olivine gabbro and slifjhtly later than it in cr\stallizin};, contains a larj,'er proportion of types carr\ injj the more sodic feldspars; that the aujjite fjabbro carries feldspars much more sodic than tlie olivine gabbro; and that the granii proved a still later differentiate, is characterized by feldspars more «odic still. The possible chanjjes in the composition of the pyroxene could not be determined satisfactorily with the microscope. .\s for the olivine, most of the crystals show partial resorption. The mineralogical changes accompanying the appearance of quartz in the rocks have been described, and, like those of the feldsjiars and the olivine, follow exactly the lines indicated by the investigators of the geophysical laboratory. These facts indicate that as cr\stallization proceeded some agenc\ continuously re- moved the crystals from the liquid magma. Preceding sections have shown that the agent must have been gravitation. Special Textures and Structures. The structure of the anorthosites may be specially cited as most easily explicable by the hy])othesis already given. .\s previously mentioned, they are found as a rule in small isolated masses, a foot or so in diameter. These masses are usuall\ cf)arsely crystalline, and contain very little admixture of the other rock minerals. It is diflicult to account for such occur- rences, except by the theory that, as feldsjiar crystals separated from the magma, they were segregated from the olivine ami r.ABIIKIlS OF FAST SXIKK AMI K(K-KV I-OINT. 37 p.vroxene crvstals fdnninj,' at the same time by the more rapid sinking of the latter, and, as they themselves slowlv sank, they became a >;«; related together into small masses, lurther sinking would probably have resulted in apKrenation into larj-er masses, and two or three such masses are found ; but for the most part the process was brought to an end l)y tlie increasing viscositv of the coolinj; majonii. Howen's hyiK)thesis also explains easily the formation of the rounded bjdies of ver.\ coarsely crystalline " ijcymatite " de scrilied on page 7. The) ma> be supposed to represent large, loose masses of earlier-formed crystals, which have been con- solidated by a movement of the magma, with squeezing off of the interstitial li(|uor. rati; of C()oI.I.N(; OK Tin; INTRlSIVi;. Piowen has shown that by internal evidence, chiefly the zoiiary banding of mix-crystal minerals such as feldspars, an approximate estimate may lie made of the rate at which a magma has cooled and whether or not it underwent much supercooling before crystallization commenced. A very rapid loss of heat is apt to result in great undercooling of the licpiid mass before crystallization commences; crystallization once initiated, an almost instantaneous separating of mineral takes place sufficient to bring the liquid once more into stable equilibrium with the solid pha.se. The whole amount of each mineral .so separating will have the same composition. Very slow cooling of the liquid magma, with sinking of crystals prevented, would favour resorp- tion of the earlier-formed crystals and thus produce a similar rock composed of minerals of uniform composition. Such a condition, however, is almost impossible to attain in nature. An intermediate rate of cooling produces zoning in the mix-crystals present, there being a special rate which will produce maximal zoning. The feldspars seem to be particularly liable to zoning, probably because on account of their low specific gravity they sink very slowly through the magma and hence are not so apt to be removed from the scene of their formation before outer layers can be deposited on them. 98 Ml'SIUM Bl'I.I.KTlN KH. 30. Applyinn these criteria to the East Sooke gahbro, it is found that ahhou^h the feldspars in every hand specimen exhibit variations in composition, nevertheless in most of the rocks they are far from exhibiting maximal zoning. The feldspars of only a few of the coarse pegmatitic varieties are noticeably zoned. Hence it must be concluded that considvjrahlc undercooling took place, in spite of the fact that the cooling of such a large piiitonic mass was almost certainly fairly slow. In support of this con- clusion there might also be cited the uniform composition of all of the mineralr throughout a large part of the gahbro. Furthermore, the occurrence of poikilitic text, res in some of the rocks indicates a very rapid growth of the pyroxene crystals once crystallization was initiated. The rather imperfect segregation of the different minerals in the more basic rocks, as evidenced in the lack of occurrence of highly basic types such as pyroxenite, dunite, and picrite, and the incomplete segregation of the anorth- osites, also points to a crystallization dcicrred until increasing viscosity was almost able to prevent the downward movement of crystals. The fact that so much differentiation actually did take place, in spite of the relative brevitj- of the period between the commencement of crystallization and the time when viscosity ended the downward movement of crystals, throws an interesting light on the speed with which sinking, once initiated, may go on. FINAL STACKS OF DIFFf.RICNTIATlON. During the final stages of the differentiation of the ."^f .e ni.igma the homblendite and aplite veins were formed. The pro- cesses of deposition and the l)ehaviour of the components of the solution have been so different from that displayed durinj; the crystallization of the original magma as to be worthy of separate detailed description. The mineralogy of the veins, their con- nexion with the gabbro mass, ar i their metatnorphic effect on the gabbro have been detailed on pages 12-16 and shown by analyses on page 18, and t' results of these analyses have been platted graphically in Figure 1. CABBRr>» OK KAST «OOKK AND kUCKV POINT. M General Discussion of figure 1. The mode of construction and interpretation of Figure 1 have already been described, and it has been shown that to deter- mine absolute gains and losses during an alteration the weight the volume, or the amount of some one constituent nuist be known to have remained constant, or, if not constant, the extent of Its change must be known. In the present case no one constituent can be assumed to have remained constant, as all were probably very soluble in the hot solutions. If alumina, the most insoluble oxi .*>. I'lidcr till- a!.siii)'.,i!M;i, ind leavini; out of con^ideiation tlie minor coiiii>t^ient-i of ih littioi<>, such as K^' >, MnO, TiO,., and I'./)., which n ■■■'>■ make up le>^ than 1 \ter cent of tny of the hk' -, i '• -<-- ' tiiat the hornldendiie alteration resuhed in slitrlit uc". -c • f -ilica. larjfe increase of uon, maj;- nesia, soda, and v • <. - ill' uss .>f hme and aUiinina. In the aplitic ahcralion a ii..o\' ii.ii larger increase in sihca and s(kI;i took i)lace, wherea- wai-i .'.is sli(,'lit'.> lost, alumina more so, and lime, iron, ar I i', almos . '>nM))ctel\ removed. It may aIsol>€ seen fi"' ;;!"<: I V>. > fi ;■ .tin these conclusions arc correct, wheil • . I.' ' .)■ le i f constancy of volume he accepted or not, a- ■ .1 i f n- .e so far to the ri),'ht or left of the assumed zero crticai '' ' n order to alter their si);nifi- cance materially, (|ui' • inadin ■' umptions as to weijiht and volume cluin>;es vvoi ,d have to he 1 lade. Thus, for instance, to assume that majjneM-i had iiot been iildcd din-ini,' the hornhlend- izinR alteration, would lie eciuivalent lu assuming that the horn- Mendite possesses ajiproximately 30 i)er cent of ptre space, which is clace after the rock was once thorouf,'hly altereil to hornblende, althr)U){h in some cases additional ni;ij,'netite was deposited. It is reasonable to conclude, therefore. i!iai the horn- blende was in ecjuilibrium with the solutions when the alteration was complete, exce])t that the solutions were aot to lie still supersaturated with iron, .\nalysis No. 2, therefore, an example of thorou>;h alteration so far as the microscope can show, rei)re- sents the compfisition of the solid in etiuilibrium with the litpiid which ])roduced the alteration. Siich an ei|uilihriuin implies the jiresence in the solution of all the coniixment oxides indicated in the analysis, thoujjh not necessarily m the same pro;)oriions as in the hornblendite ; in fad, the solution must have been saturated l.AHIIIhlSI O^ KASI I'lKI. \\|i K(K KY hllM 4t With the cniiipmmds id wliiiti ilie>c (.sides rsi^ted in soliitiim. uiKlcr the exiMiiiK mndition^ i.f teiiii>«>t.tlure and |>re>-ure. Tlie M.liilioiis weic not, however, in e<|iiilil)iiiiMi uilli the k.iIiIho, heme the niiiieials „f the anhUu) weie iiiei.i-.oniatirallv replaced. In tliis way the (,'al>hro lieiaine enriclicd, particularly with ivoii, also with niaj:ne>ia -i.da, and prol.,ilJ> to a small extent with sihca: and knanie impoverished in aiuniiit.i and liincT 'Ihe aplitic solutions did not react s(. readily witli the pahliro as did the hortihiendizins; sohnions. and altlion(,'h the ten kiicies of Ihe alteration can l>r ohserved in many i)lacts, it mi^ht lie dilhcull to tin.i one in which alteration has lieen carried to its limit, and the jjahhio completely iransfornied to pure aplite. The evKlcTice as to the coin|K)sition of solutions drawn from a con- sidcraiion of the composition of the soiid with which Ihev are in e<|uilil,rium is not, therefore, available; Init fortunatelv this can he olilained directly, as imuh aplite is present in the form of fissure rtllmus. \naKsis .\ represents one of these, an averane aplite vein, selected hecause it reiiresents at once the solid that was in eijuilil.rium with an aplitic solution and the result of an ideally complete aplitic alteration. As detailed in the previous r)araj;rapli, the presence of each oxide in the a|)lite indicates that It iinist have ieen present in the solution. Th*. proportions were difTeient. hu..c\er fn.m th(een more concent r.iied than die aplili/inj;, at least m iron, lime, and ma),mesia ,ind perli.ii.s in afl CO!i-titii'"nts. A'(7i//ir<' Physiiiil Conditions of I ' i.iii-Dc[''^sjiwu. .\s leRanis the rcl ,tive j.hvsical c;itidiiloiis of deposition of the two tvjieN of veins, it :s ?)robable that the a|)ti)es were deposited from cooler, more dili?te solutions than were the horn- blendites The aplites were of later formation, for liefore the dc|«>sitiKK AMI MOIKY IMINT. 4S It seems probable that this control of the escajie of solutions by jointing and faultinj,' may be the explanation of the usual absence of hornblendite t> jies amonjf the igneous veins formed as the last products of diflferentiation of other magmas. If jointing was deferred until the magma had cooled to a point where the solutions could not carry lime, iron, and magnesia, except in small (|uantities, nothing but aplilic veins would be formed. Tliis migl-.t have lieen the case in the mass under discussion, had not regional faulting fissured the rocks scjon after their consolida- tion. .Iddilioiial Considerations and Conclusions. Behaviour of Lime in ilie Solnlion. From the analy.ses and Figure 1 it may be inferred tliat the concentration of lime in the hornblendizing solutions was higher than in the aplitizing. It has also been shown thai the former were hotter than the latter. Projecting this temperature-concentration curve for lime, the conclusion ma> l)e drawn that still hotter, earlier solutions than any of those which have left their record here might carry lime in still larger proportions, and deposit it in some form at an earlier date. Such deposition of lime would then have ended before that of hornblende began. Behaviour of .llumina. As shown on Figure 1, there was some loss of alumina from the wall rocks during alteration by both types of solutions. On the hypothesis of constant volume, previously- shown to he the most probable, the proportion of alumina removed is almost identical in both. It seems probable, therefore, that the solubility of alumina in these juvenile solu- tions, at whatever temperature, was never great enough to satisfy the other bases present for the formation of alumino-silicates. so that constant additions t" the supply had to l)e made by drawing on the wall rocks. .SI' M MARY. The .Sooke gabbro is found throughout the Snnke map-area, southern Vancouver island, as a number of masses of varying size intrusive into the Metchosin basalts. It is of lower Oligocene 4« MUSF.l'M Ul'I.LKTIN Nil, .K). age. Its resemblances in composition to the Metchosin basalts, and the restriction of i*.s occu lence to the areas underlain by tl em, strongly suggest the view that it represents the plutonic phase of the igneous cycle that l)egan with the extrusion of the basalts in late Eocene times. The masses examined by the writer were those underlying Fast Sooke i^tninsula and l^ocky point. The other gabbros of the Sooke map-area were studied by C. H. Clapp, and present certain differences which may he summarized as the results of quieter, less disturl)ed cr_\ stalliza- tion. The intrusion of the gabbro seems to have taken place quietly, as it lias not formed extensive shatter breccias at its contacts. Cooling then began, and evident e has been given to show that a considerable degree of undercooling probably took place before crystallizati >n was initiated. When the crystals began to form, they coinciuently began to sink through the liquid magma, on account of their greater specific gravity, and thus caused the reparation of the originally homogeneous magma into several portions of differing composition, the lighter of which occupied the upper horizons. This primary different! at ive pro- cess was not long continued, however, and did not result in any very perfect sorting of the various rock minerals, as it was brought to an end at an early date by the increasing viscosity of the cooling liquid. It resulted, however, in the production of four different rock types, of definitely different mineral com- position ; and each type groups together a series of rocks whose end members differ widely in composition, but of which any two adjacent memljers differ only slightly. Even the classification into four general types is a more or less arbitrary one, since, as might be expected from rocks so formed, the different types merge into one another by a' gradual change in mineral composi- tion. The tyiJes so formed are : olivine gabbro, made up of olivine, pyroxene, and bytownite feldspar; augite gabbro, similar to the preceding but without olivine; anorthosite, consisting of by- townite feldspar either pure or containing small quantities of pyroxene with or without olivine; and granite, made up of (.ABBKOS <)l KASr WIDKK AMI Kck KV l-OINT. 47 quartz, hornblende and mica, and oligoclase. The olivine gal.l.ro was the heaviest of the differentiates, as well as much the larjjest in quantity; it, therefore, occupies the central and lower iwrts of the mass, and covers about 'JO per cent of its present exposed area 1 he auRite gahbro occupies a peripheral position on the north and south coasts, and covers most of the remaining 10 per cent of the exiwsed area. The nnorthosite, the only monomineralic rock formed, shows the effects of the incomplete sorting that took place, as it is found in fairly large bodies in two or three instance-; only, but occurs chiefly in little bodies, a foot or so in diameter scattered throughout the augite gabbro. All of the granite that may have been formed has been removed bv erosion, with the exception of one small outcrop on Possession point, on the very periphery of the intrusive. After the formation of the various rock tvpes had been brought to an end by the increasing viscosity of the cooling liquid, regional disturbance took place, the effects of which were of great importance. The still semi-liquid mass was churned up; but as the different phases were already too viscid to remix readily and thoroughly, more especially in tiie cooler, outer parts of the stock, the result was merely the partial destruction of the earlier gravitational arrangements of the rocks, the irregular interpenetration of one by masses and streams of another, and the production of gneissic bands and flow textures. It is also probable that there was a general straining off of small masses of liquid, acid differentiate, which went to swell the main body of granitic differentiate at the upper horizons. Resides replacing regular with irregular arrangements, producing gneissic textures and assisting differentiative processes by straining off acid magma, the movements destroyed t j seme extent the gradationat relations between ihc different types that had previously existed, and in some cases forced more liquid portions into intrusive relations with the more solid. After the events described and the consolidation of the rocks now at the surface was completed, tbe\' were intruded by two series of satellitic dykes, an acid and a basic. The latter were the earlier and of much the same composition as the gabbro 48 MISKIM BII.LKTIN N(l. M. itself, and the acid varieties form a series varvinj; in composition from a (|iiartz diorite to a very siliceous granite. Then followed a period of faulting with production of larjie shear zones in the gabhro, accompanied by much jointing. Through the fissures and shear zones rose very hot solutions highly charged with mineral matter, >.vhich altered the locks with which they came in c(mtact to masses of hornblendite. Another i)eriod of jointing ensued, and through this set of fissures there again rose solutions which formed aplitic fissure and replacement veins. After these were formed, a second jjeriod of faulting took place, in which the stresses relieved themselves along the earlier-formed shear zones now filled with hornblendite, and through the brecciated and crushed hornblendites the solutions which deposited the chalcopv- rite ores ascended. Tinally, further minor jointing took i)lace. The relations of the hornblendites and aplite to each other and the main gabbro mass were studied in some detail. It was shown that these are the pcgmatitic after-effects of the intrusion, the last exhalations of the cooling magma. The hypothesis is advanced that the emission of such solutions from a magma is a continuous process throughout the whole period of cooling, but that the escape of the solutions so ff)rmed is governed by the more or less accidental occurrence of movements able to joint the intrusive and thus afford channels of flow. The load of such solutions always includes all the constituents of the rock from which it has originated ; although the amounts of these vary, and are dependent on the temperature of the solutions, and probabh also on other conditions of which we are ignorant. The composi- tion of the veins formed by them, and their metamorphic effects on the wall rocks, therefore, var\ according to the time in their history when they were enabled to make their escape. In the case under consideration, opportunity for escai)e occurred at two, or possibly three, periods, owing to the frequency with which jointing and faulting movements affected the stock, and veins of different composition thereby resulted.