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A mineralogical study of some granites from the east half of the Smithers map sheet McCammon, James William 1939

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ST A MIHERALOGICAL STUDY OP SOME GRANITES FROM THE EAST HALF OF THE SMITHERS MAP SHEET. is James W. UcC L £ 5 S 7 n 5 A * A MIMR/.LOGICAL STUDY OF SOME GRANITES FROM THE . EAST HALF OF THE SMITHERS MAP SHEET. 'by James William McGammon oOo A Thesis Submitted for the Degree•of MASTER OF APPLIED SCIENCE in the Department of GEOLOGY oOo The University•of B r i t i s h Columbia A p r i l , 19 39. TABLE OF CONTENTS Page. INTRODUCTION a. General Statement.... I b. Geographical D i s t r i b u t i o n of Specimens Examined... 2 L AB OR ATOR Y PR QCEDURE a. Introduction 5 b. Heavy Mineral Separation ". . . . 6 c. Microscopic Determination of Minerals 10 MINERALOGY a. Megascopic Examination of Rocks. 1. Specimen No. I II 2. Specimen No. 2 ,., II 3. Specimen No. 3 12 4. Specimen No. 2? 12 5. Specimen No. 1196 12 6 . Specimen No. 1212 13 7. Specimen No. 1213 13 b. Microscopic Examination of Thin Sections 1. Thin Section No. I 13 2. Thin Section No. 2 14 3. Thin Section No. 3 16 4. Thin Section No. 27 17 '5. Thin Section No. 1196 17 6. Thin Section No. 1212 18 7. Thin Section No. 1213 19 c. The Heavy Minerals 1. Magnetite. .... .21 2. B i o t i t e 21 3. Apatite 24 4. Zircon 24 5. T i t a n i t e 25 6. Pyrite .25 7. Ilmenite 25 8. Ru t i l e 25 9. Hornblende 26 CONTENTS (CONTINUED) 1 Page. 10. Leucoxene. 26 11. Ch l o r i t e . . . 26 12. Diallage 26 13. Epidote 27 CONCLUSIONS 28 BIBLIOGRAPHY 30 ILLUSTRATION Map to Show Geographical D i s t r i b u t i o n of Specimens 4 TABLES Table No.l To Show Perecntages by Weight of the Rocks Due to Heavy Mineral Accessories 9 Table No.2 To Show Proportions of Major Constituent Minerals of the Rocks 20 Table No.3 To Show the Relative Abundance of the. Various Accessory Heavy Minerals.......... 23 oOo INTRODUCTION General Statement In the east half of the Smithers Map Sheet of northern B r i t i s h Columbia, there are exposed several intrusive g r a n i t i c rock bodies. These rock masses are believed to have been intruded during two diff e r e n t geological periods. The older group i s da.ted as Pre-Jurassic and the younger group i s considered to be Ter t i a r y . The object of the research presented i n this thesis was to carry out a. mineralogical study of rock samples from various parts of the intrusions to discover i f the mineral contents of the rocks could be used to distinguish between the two age groups. P r i n c i p a l emphasis was pla.ced on the study of the heavy minerals present i n the rocks. Specimens 1,2 and 3 were coll e c t e d by the writer. Specimens 27, 1196, 1212 and 1213, with their corresponding -2-thi n sections were kindly lent to the writer hy Dr. A.H. Lang of the Vancouver Office of the Canadian Geological Survey. The work was carried out under the supervision of Dr. CO. Swanson of the Department of Geology of the University of B r i t i s h , Columbia.. Geographical P i s t r i b u t i p r i of^Specimens Examined Seven rock specimens were examined during the course of the research carried out in the preparation of this thesis. Two of these specimens were from intrusions which are considered to he of Te r t i a r y age. These two specimens are No.l and No.27. The other f i v e specimens, Nos.2, 3, 1196, 1212 and 1213, were from intrusions which are thought to he of Pre-Jurassic age. Specimen No.l was ta,ken from the north side of Tsa-Lit Mountain which i s situated about four miles north of Mount Nadina, i n the south-west corner of the map sheet. The rock i s considered to belong to the Mount Nadina granite body which has had i t s age set as Ter t i a r y by Pr. A.H. Lang. 1 I Lang,A.H.; Geol. Surv., Can.; Sum. Rept., 1929, Part A., Pge. 75 -3-• Specimen No. 27 was obtained from a small d i o r i t i c stock near Barrett station on the Canadian Nationa! Railway. Dr. Lang 1 thinks t h i s stock also belongs to the Tertiary i n t r u s i o n . Specimens No. 2 and No. 1196 were secured from a large outcrop one-half mile east of Nez Lake i n the north-eastern part of the map sheet. This outcrop i s part of the g r a n i t i c basement of the Topley map area which PheraisterU and Hanson have determined as being of Pre-Jurassic age. Specimen No. 1212 was from the same intrusion as the two preceding specimens but one mile to the east. Specimen No. 1213 was part of a small stock near the eastern edge of the map sheet, due east from Nez Lake. Specimen No. 3 was obtained from a b l u f f on the shore of Babine Lake, north-east from Nez Lake. It i s part of the Topley intrusion. I Lang, A.H.; Persons! communication. II Phemister, T.C.; Geol. Surv., Can.; Sum Rept., 1928 Part A, Pgs. 56-59. -4--5-LAB ORATORY PROCEDURE Introduction Two methods of examination were used to study the minerals i n the various rock specimens. The f i r s t method consisted of having a thin section made from each specimen, and then examining these sections i n the customary petrographic manner. A l l minerals v i s i b l e were determined, together with the estimated r e l a t i v e abunda.nce of each. The second method consisted of separating the heavy minerals from pulverized portions of ea.ch rock. These mineral grains were then placed on sli d e s and determined petrographically. In carrying out the separation and study of the heavy minerals, the routine followed was fixe d after the writer had considered various methods a s described by Boos,* I Boos,M.P.; Some Heavy Minerals of the Pront Range Granites; Jour. Geol., Nov.-Dec, 1935. -6-Leckie.I Reed* 1 and had received suggestions from Dr. CO. Swanson and Dr. H.V. Warren of the University of B r i t i s h Columbia. Hea.vy Mineral Separation A sample piece of rock from each specimen was taken. The rock was crushed to pass through a 65 mesh screen. A l l material f i n e r than 200 mesh was screened off and thrown away. The heavy minerals were then separated from each sample. This separation was effected by the use of a heavy l i q u i d , namely, tetrabromoethane. Since the s p e c i f i c gravity of the tetrabromoethane used was 3, for the purposes of t h i s experiment, any mineral with a s p e c i f i c gravity of greater than 3 i s ca l l e d a, heavy mineral. To carry out the separation, the writer used a large glass separating funnel half f i l l e d with the heavy l i q u i d . Twenty-five grams of the crushed material was then placed i n the l i q u i d and the two substances wer-e\ thoroughly mixed by shaking a.nd s t i r r i n g . The mixt.ure.%as then l\e.ft to s e t t l e . When the heavy parts I Leckie.P.G.; Mineralogy of the Beach Sands i n the V i c i n i t y of Vancouver, B.C., M.A. Thesis, U.B.C. II Reed.R.D.; Heavy Mineral.Investigation of Sediments, Sc. Geol., June-July, 1924. - 7 -were separated, they were drawn off through the bottom of the funnel. The material remaining i n the funnel was r e - s t i r r e d and again l e f t to s e t t l e . This procedure was repeated u n t i l there was no further s e t t l i n g out of heavy mat er i a l . The heavy minerals were then f i l t e r e d out of the tetrabromoethane with which they were withdrawn from the funnel. Next they were thoroughly washed, f i r s t with alcohol and then with water, and f i n a l l y they were dried. The dried heavy minera!s were next c a r e f u l l y weighed. Then they were spread out on a large sheet of white paper and a magnet was passed slowly over them to remove the magnetic parts. When a l l of the magnetic grains had been removed, these were weighed. From the weights thus determined, the proportions of the various rocks due to the t o t a l heavy mineral content and also to the magnetic heavy mineral content were calculated. These results are shown i n table No.l. From thi s table, i t i s r e a d i l y seen that the amounts vary greatly i n the rocks of both ages. Consequently, the determination of the proportions of heavy minerals i s of no p r a c t i c a l use to distinguish between the two ages of rocks. -8-An attempt was made to separate the minerals on the Haultain "Super-panner" hut because of the great range i n size of the grains (65 mesh to 200 mesh) the res u l t s were not sa t i s f a c t o r y . TABLE TO SHOW PERCENTAGES BY WEIGHT OF THE ROCKS DUE TO HEAVY MINERAL ACCESSORIES Specimen T o t a l Percentage By Weight Of O r i g i n a l Rock Due To heavy Minerals Percentage By Weight Due To Magnetic Heavy Minerals In O r i g i n a l Kock In.Heavy Minerals 1 1.36 1.07 78 .74 2 0.70 0 .29 41.84 3 1.42 0.70 49.44 27 13.65 6.25 45.78 1212 5.80 2 .00 27.56 1213 1.96 0 .30 12.25 Table No.1 -104 Microscopic^ Determination of Minerals The heavy minerals were determined with the aid of a. petrographic microscope hy the "immersion" method. F i r s t , a clean glass s l i d e was sprinkled with grains of the unknown minerals. This s l i d e was examined under a medium powered objective. Several grains which looked similar were then isol a t e d from the material under the lens and were transferred to a clean s l i d e . These separated grains were next c a r e f u l l y examined and a l l properties possible were noted such as cleavage, c r y s t a l form, extinction, etc. When i t was reasonably certain that a l l of these grains were the same mineral, the index of r e f r a c t i o n was determined by immersing the grains i n o i l s of various known indices u n t i l an o i l was found whose index of r e f r a c t i o n was the same as that of the mineral. The immersed grains were then covered with a cover glass and examined under the high powered objective so that the interference figure and birefringence could be determined. From the properties thus observed, the i d e n t i f i c a t i o n of the mineral was learned by r e f e r r i n g to appropriate reference tables. - I I -MI33ERALOGY  Megascopic Examination of Rocks Specimen No.I This rock i s a medium grained, l i g h t grey, g r a n i t i c rock. B i o t i t e i s very noticeable throughout and i s quite evenly di s t r i b u t e d . Pale, opa.gue, grey to colorless quartz grains occur abundantly in the main body of the rock. The chief constituent i s , however, feldspar. This l a t t e r mineral occurs as grey to pale greenish grains with a few pinkish crystals of s l i g h t l y larger size than the other grains i n the rock. There i s a resultant s l i g h t l y p o rphyritic appearance to the rock. Specimen No.2 This rock i s a medium grained, salmon pink, g r a n i t i c rock. Quartz i s abundant as grey grains. The feldspars are mostly pink, but some few have a greenish tinge. There are a few larger feldspar crystals which give the rock a s l i g h t p orphyritic appearance. A dark, fine grained mineral occurs spread throughout the rock. -12-It i s probably a o h l o r i t i c a l t e r a t i o n product. Specimen No.3 This i s a very l i g h t grey, medium grained rock. Hornblende i s a common constituent. There i s an abundance of colorless quartz. Feldspar i s pale greenish white with a few larger, greenish crystals which make the rock decidedly p o r p h y r i t i c . Specimen Ho.27 Sample 27 i s a fine grained, dark green c r y s t a l l i n e rock. The crystals are too small to be r e a d i l y determined with the aid of a hand lens, but two d i s t i n c t types can be seen. One kind appears l i g h t green and the other, quite decidedly darker. Specimen No.II96 This rock i s a medium grained, salmon pink, g r a n i t i c rock. It i s composed predominantly of pink feldspar and glassy quartz. Some of the feldspars are rather larger than the general groundmass of the rock and so give i t a porphyritic texture which is best seen on weathered surfaces. The femic mineral appears as i f i t is altered mostly to c h l o r i t e , but some parts resemble b i o t i t e . -13-Specimen No.I2I2 This, too, i s a medium grained, pinkish, granular rock. It i s mainly composed of pink feldspar and c h l o r i t e which appears to he an a l t e r a t i o n product from hornblende. Quartz i s very scarce. Specimen 1213 Specimen 1213 i s also a medium grained, though somewha.t porphyritic, salmon pink, g r a n i t i c rock. Quartz i s p l e n t i f u l and occurs i n patches. This l a t t e r i s greenish grey i n color. The feldspar i s pink and although most of the crystals are small, some few larger ones occur scattered through the rock. The femic minerals are fine grained and are very much spread out. Probably most of the femic mineral i s c h l o r i t e . Microscopic Examination of Thin Sections Thin Section No.l The microscopic examination of thin section No.l revealed that the rock i s a granite. It i s n o n c r y s t a l l i n e , phaneric, medium, grained and has a hypidiomorphic texture. -14-The minerals i d e n t i f i e d consist of orthoclase, oligoclase, quartz, h i o t i t e , s e r i c i t e , t i t a n i t e , apatite and iron ore. The r e l a t i v e proportions of the major constituents, based on an estimation of r e l a t i v e areas i n the t h i n section, are shown i n table No.2. The mineral c l a s s i f i e d as orthoclase i s not, s t r i c t l y speaking, orthoclase, but i t should be c a l l e d a l b i t i z e d orthoclase or pe r t h i t e . The a l b i t e i s spread through the Drthoclase i n thin p a r a l l e l veinlets, and occasionally i n small irregular patches. The plagioclase often shows good zoning and i s usually p a r t i a l l y altered to s e r i c i t e as i s , also, the orthoclase. Apatite i s quite noticeable. It occurs scattered through the b i o t i t e and i n the quartz. It i s most common in and near the b i o t i t e . The crystals are very small and r occur both as short thick prisms and as long t h i n rods. The t i t a n i t e i s l i g h t brown i n color and occurs very sparingly. Thin Section No.2. This rock i s also a granite. It i s ho l o c r y s t a l l i n e , phaneric, medium grained for the most part, and has a general hypidioraorphic texture. However, one patch of p o i k o l i t i c texture i s present in the section. -15-The minerals i d e n t i f i e d are orthoclase, a l b i t e , quartz, c h l o r i t e , apatite, leucoxene, s e r i c i t e , c a l c i t e and iron ore. For r e l a t i v e abundances of the major constituents see table No. 2. Since there has been much a l t e r a t i o n i n the rock from which this section was made, the feldspars have p a r t i a l l y changed to s e r i c i t e and an amorphous substance which i s probably kaolin; the mica (or hornblende) has changed to c h l o r i t e , and the t i t a n i t e has become leucoxene. C a l c i t e has also become quite p l e n t i f u l . In general, the plagioclase occurs as subhedral crystals and the orthoclase as larger, anhedral grains. In one or two places, the orthoclase forms a large mass around a few scattered plagioclase phenocrysts, and thus gives a p o i k o l i t i c texture. On the other hand, quite commonly there can be seen wart-like myrmekitic intergrowths extending from plagioclase c r y s t a l s out into adjoining orthoclase c r y s t a l s . The quartz has an odd intergrowth with i t s e l f . Under crossed n i c o l s , patches of the mineral w i l l extinguish at one time while other patches, intimately interspaced, w i l l extinguish at another time. The c h l o r i t e occurs as small i s o l a t e d bodies and as one very large patch. A dark opague mineral, -16-probably magnetite, i s intimately associated with the c h l o r i t e . It i s probably a "released" product from the a l t e r a t i o n action which produced the c h l o r i t e . Apatite occurs as small crystals i n scattered patches. Thin Section No.3 This rock i s very much l i k e No.2. It i s a h o l o c r y s t a l l i n e , phaneric, medium grained granite with a hypidiornorphic texture. It has present i n one place, however, a p o i k o l i t i c patch where an orthoclase c r y s t a l encircles small euhedral crystals of plagioclase, t i t a n i t e , and hornblende. The i d e n t i f i e d minerals include quartz, orthoclase, oligoclase, t i t a n i t e , hornblende, apatite and iron ore. See table No.2 for proportions of minerals present. In general, the orthoclase and quartz show no c r y s t a l form but occur as ir r e g u l a r masses, whereas the plagioclase usually shows cry s t a l edges and sometimes complete c r y s t a l form. Wart-like myrmekitic intergrowths similar to those i n section No.2 are quite common. They appear to be outgrowths from s l i g h t l y zoned plagioclase into orthoclase. The quartz shows an intergrowth within i t s e l f which i s similar to that of section 2. Scattered grains -17-extinguish at the same time. E x t i n c t i o n i n some of the plagioclase crystals passes gradually from the center outward and thus indicates zoning. Alte r a t i o n is not very pronounced i n t h i s section although the feldspars are somewhat altered as i s , also, some of the hornblende. Thin Section Ho.27 Specimen No.27 proved to he a h o l o c r y s t a l l i n e , phaneric, fine grained d i o r i t e . The minerals i d e n t i f i e d i n the thin section were labradorite, diallage, apatite and iron ore. See table No.2 for r e l a t i v e proportions of these minerals. There wa.s nothing of very great interest i n this specimen. The plagiocla.se i s sub-hedral and usually well zoned. Al t e r a t i o n i s s l i g h t . Thin Section No.1196 Once more we have a granite. This section i s very much l i k e that of No.2. The minerals present are quartz, orthoclase, plagioclase, apatite, c h l o r i t e - b i o t i t e , leucoxene and iron ore. See table No.2 for r e l a t i v e proportions of - these minerals. -18-As i n section No.l, the orthoclase has veinlets of a l b i t e strung through i t , and so, i t i s i n r e a l i t y , micro-perthite rather than orthoclase. Wart-like myrmekitic intergrowths are found extending from the plagioclase crystals out into the orthoclase as described for sections 2 and 3. The plagioclase i s c a l l e d oligoclase but i s very near to a l b i t e and should probably be more c o r r e c t l y termed a l b i t e - o l i g o c l a s e . The a l t e r a t i o n has not been very intense. Thin Section No. 121 P. This section i s very badly altered, so much so, in fact, that the i d e n t i f i c a t i o n of the feldspars was not s a t i s f a c t o r i l y completed. Minerals i d e n t i f i e d include a l b i t e , apatite, epidote, s e r i c i t e and c h l o r i t e . Because of the large amount of a l t e r a t i o n and of the i n a b i l i t y to be sure of mineral ide n t i t y , no estimate cf mineral proportions was attempted with the result that table No.2 could not be s a t i s f a c t o r i l y f i l l e d i n . The a l b i t e i s the most prominent mineral. It occurs a.s sub-hedral crystals which are surrounded by a microcrystalline aggregate of other minerals. Prominent -19-araong these small grains are many feldspar crystals which show carlsbad twinning. These are l i k e l y to he orthoclase hut since no conclusive evidence could he recognized, i t was thought best not to name them. Epidote occurs quite abundantly as aggregates of small grains. Although no large quartz grains were recognized, under the high power, patches of what looked li.ke micro-graphic intergrowth could be quite e a s i l y seen. The rock i s doubtfully c l a s s i f i e d as a syenite. Thin Section No.1213 Al t e r a t i o n i s very pronounced i n this section as i n No.1212. The minerals i d e n t i f i e d are quartz, orthoclase, oligoclase, c h l o r i t e , s e r i c i t e , c a l c i t e , epidote, leucoxene and iron ore. Approximate r e l a t i v e proportions of the orthoclase and plagioclase are given i n table No.2. The remainder of the slid e consists of mixed grains of the other minerals. Although quartz i s very scarce i n the thin section, from the hand specimen i t can be seen that there i s s u f f i c i e n t quartz present to c l a s s i f y the rock as a granite. -20-TABLE TO SHOW PROPORTIONS OF MAJOR CONSTITUENT. fMINEPALS IN THE ROCKS Thin Section Quartz Orthoclase Albite Oligoclase Labradorite Biotite Chlorite Hornblende Diallage / 25 SO /Q 6 2 2.2 /a 50 8 3 25 52 /e 5 27 65 26 //96 27 33 35 5 72/Z ? p 40 p /a/3 9 46 34 •? Tab/e. No. 2-Figures represent percentages and are based on an estimation of r e l a t i v e areas of minerals as observed i n t h i n sections. -21-The Heavy Minerals The heavy minerals were separated from six of the rock samples. No separation waa made from specimen No. 1196. In a l l , t h i r t een d i f f e r e n t heavy minerals were i d e n t i f i e d . Their d i s t r i b u t i o n among the six samples and their r e l a t i v e abundances are shown i n table No.3. Magnetite. Magnetite i s the most abundant accessory mineral. It occurs f r e e l y i n a l l six rocks. (See table No. I for percentage occurrence i n the t o t a l rock and in the heavy mineral concentrate.) The mineral occurs as d u l l black, opaque grains which are highly magnetic. Microchemical tests indicate iron but no titanium. B i o t i t e . B i o t i t e i s seen only i n rocks I, 2 and 3. It i s abundant only i n No. I. Since the s p e c i f i c gravity of b i o t i t e i s only 3.1 at i t s maximum, i t may be that a l l of the b i o t i t e present i n the rocks did not s e t t l e out -22-during the separation. (This point was checked and i t was found that much b i o t i t e remained with the l i g h t e r residiie.) The mineral occurs as green plates which often show pseudo-hexagonal cross sections. -23-TABLE TO SHOW THE RELATIVE ABUNDANCE OF THE  VARIOUS ACCESSORY HEAVY MINERALS PI CD CD (D fl CO CD CD CD CD CD CD CD CD CD •P •p +^  o +3 •P •P • - J >cf fl -P •P B •H •H •H o •H •H •H fl (D •H cd O •H •P •P +3 fl t-l fl -p <D .- M fc rd O <D O cd •H cd Pi CO s* r-l o O •H <D fl •H p< +3 P4 ' 3 £> o i - l cd p< P< 60 « <i •H fl .fl :o cd EH n U CD o o w / F C F VR a F C /? / ? F C 3 F /? C W ? C /? S F 27 F C >3 5 /a/2. F /? /? c VR C /a/3 F Ff F VR VR VR C F- F/ooJS C- Common 3 — Sc<f/~c& f?=/Xcrr-e Vfi?= \/ery Fo/~e. 7ajb/e A/o.3 -24-Apat it e This mineral is f a i r l y evenly di s t r i b u t e d through a l l six rocks, although i t i s present i n Nos. 1212 and 121.3 to a somewhat lesser extent than i n the others. The apatite occurs as colorless prisms which vary i n shape and size but are, for the most part, very small. Some crystals are long and thin while others are short and stout. The ch a r a c t e r i s t i c hexagonal cross section i s well developed. Usually the cr y s t a l faces are smooth but sometimes they are badly corroded and give the mineral an opaque appe arance. Zircon Zircons can be found in each specimen, but they are not common. They occur as tiny, clear (or occasionally brownish) tetragonal bi.pyra.mids. The most common form i s a. f i r s t order h i pyramid combined wi th f i r s t and second order pri.sms. Another common form i s the combination f i r s t and second order prisms, f i r s t order bipyranid, and ditetragonal hipyramid.* I Dana.S.S.; A textbook of Mineralogy; figures 912 and 914; Pge. 610. \ T i t a n i t e This mineral occurs i n a l l specimens except the d i o r i t e , No. 27. It occurs as rather large, sub-hedra! to euhedral crystals which are brownish to pale yellow in color. The grains are often i n a state of p a r t i a l a l t e r a t i o n to leucoxene so that they have the color a.nd .crystal shape of t i t a n i t e but are quite opaque. Pyrit e Pyrite occurs as c h a r a c t e r i s t i c brass yellow cubes. It i s present i n very small amounts i n a l l specimens except No. 27. Ilmenite Although present to some extent i n a l l of the rocks, ilmenite i s p l e n t i f u l only i n Nos. 2 and 1212. It occurs as i r r e g u l a r l y shaped grains which have a purplish color in r e f l e c t e d l i g h t . The grains are non-magnetic and give p o s i t i v e microchemical tests for both iron and titanium. R u t i l e R u t i l e i s present only in specimen No. I where i t occurs as brownish orange prisms which have very pronounced s t r i a t i o n s p a r a l l e l to the prism faces. A -26-geniculated twin was? seen i n a quartz grain. Hornblende This mineral occurs abundantly i n rock No. 3 and very sparingly i n Nos. 2 and 1213. It i s present as dark, sea-green prisms which have the c h a r a c t e r i s t i c a,mphibole cleavage. Leucoxene Leucoxene i s common in specimens 2 and 1213 but i s occasionally seen i n No. 3 and i s absent from the others. It seems to have been formed mostly from t i t a n i t e , but can sometimes be recognized on and with ilmenite. Chlorite Although the s p e c i f i c gravity of c h l o r i t e i s less than that of the heavy l i q u i d used for the mineral sep-aration, a few grains were distinguished in the residue of specimen No. 2. Diallage. Diallage occurs only i n the d i o r i t e , No. 27. In t h i s rock i t i s very abundant. It i s pale bottle green, of a lamellar -habit and shows good parting. The extinction angle is usually around f o r t y degrees but in some grains i t i s zero. Epidote This mineral i s present only i n the much altered specimens Nos. 1212 and 1213. The epidote occurs as pale, apple green grains. Some grains show s t r i a t i o n s p a r a l l e l to the crys t a l edges. -28-CONCLUSION r The material here presented has shown that i n the d i s t r i c t where the rocks which were examined were obtained, the mineral composition of these rocks cannot be used to any advantage to distinguish between the dif f e r e n t aged in t r u s i v e s . From table No. I i t i s seen that the proportions of heavy minerals i n the rocks vary greatly i n both the T e r t i a r y and the Pre-Jurassic groups. There i s an overlapping of values between the two groups and so no dividing l i n e can be set. • Table No. 2 likewise gives no clue to an age d i s t i n c t i o n between the rocks. The composition o f the Ter t i a r y specimen No. I i s closer to that of the Pre-Jurassic specimen No. 3 than i s the composition of the Pre-Jurassic specimen No. 2 to No. 3. S i m i l a r l y , there i s a very great difference between the two T e r t i a r y specimens Nos. I and 27. F i n a l l y , turning to table No. 3, we see once more that there i s no i n d i c a t i o n of any s t r i c t s i m i l a r i t y between the members of one group which i s not also i n -29-evidence in the other group. A l l of the minerals common to "both T e r t i a r y rocks (Nos. I and 27) are also present in almost i d e n t i c a l proportions in a l l of the Pre-Jurassic ones. Hornblende was i d e n t i f i e d i n most of the Pre-Jurassic specimens and not i n either of the T e r t i a r y ones. This, however, could possibly he due to the fa.ct that the samples were a l l grab samples and not t r u l y representative of their respective outcrops. In any event, a single mineral does not seem s u f f i c i e n t for a conclusive d i s t i n c t i o n . Admittedly the study of six specimens seem inadequate evidence upon which to form an opinion as to the value of a heavy mineral study. However, i t does seem to the writer that i f there were any minera! peculiar-i t i e s c h a r a c t e r i s t i c of either age of intrusion, they would show up even with the a.mount of work herewith completed. -30-BIBLIOGRAPHY Boos,M.F.: Some Heavy Minerals of the Front Range Granites; The Journal of Geology, November-December, 1935. A Textbook of Mineralogy,Fourth E d i t i o n , 1.932. Owen Lake Mining Camp, B.C.; Summary Report, 1929, Part A; Geological Survey of Canada. The Mineralogy of the Beach Sands in the V i c i n i t y of Vancouver, B.C.; Master of Arts Thesis, 1936; University of B r i t i s h Columbia.. Phemister,T.C.: Topley Map Area, B.C.; Summary Report, 1928, Part A; Geological Survey of Canada. Reed,R.D.: Heavy Mineral Investigations of Sediments; Economic Geology, June-July, 1924. Dana,E.S.:  Lang,A.H.: Leckie, P.G.: 

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