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The gossan of a lead deposit in limestone : Yukon territory MacDonald, Ralph Crawford 1947-03-23

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^ <- 6 (0 J THE GOSSAN OF A LEAD DEPOSIT IN LIMESTONE YUKON TERRITORY fey R.C. MAGDONALD A t h e s i s submitted i n p a r t i a l f u l f i l l m e n t o f the requirements f o r the degree of MASTER OF APPLIED SCIENCE I n the Department of GEOLOGY AND GEOGRAPHY The U n i v e r s i t y of B r i t i s h Columbia A p r i l , 1947. P R E F A C E This t h e s i s i s based on the f i e l d occurrence and l a b o r a t o r y i n v e s t i g a t i o n s of numerous m i n e r a l , rock, and l i m o n i t e specimens from the S t a r Group of claims i n south c e n t r a l Yukon. The w r i t e r supervised the p r o s p e c t i n g , s t a k i n g , and e x p l o r a t i o n of the c l a i m s , and a s s i s t e d Dr. D.R. Derry i n c o m p i l i n g the g e o l o g i c a l map. The w r i t e r wishes to thank the management of Western Ranges P r o s p e c t i n g Syndicate f o r permission to make f u l l use of the i n f o r m a t i o n and m a t e r i a l obtained d u r i n g t h i s time, and i n p a r t i c u l a r t o thank Dr. Derry f o r making a v a i l a b l e copies of h i s g e o l o g i c a l map. Thanks and a p p r e c i a t i o n are a l s o extended to Dr. H.C. Gunning, under whose d i r e c t i o n t h i s study was c a r r i e d out, f o r h i s suggestions and a s s i s t a n c e . Dr. V.J. O k u l i t c h advised i n the matter of t a k i n g photographs and Dr. K. deP. Watson a s s i s t e d i n petrography. Acknowledgement i s due t o J.A. Donan, l a b o r a t o r y t e c h n i c i a n i n the Dept. of Geology, U.B.G., f o r h i s i n t e r e s t and experimentation i n d e v i s i n g a s a t i s f a c t o r y method of p r e p a r i n g t h i n and polished- s e c t i o n s of weathered specimens, and f o r h i s a s s i s t a n c e i n making them. The r e s u l t s obtained i n t h i s study could not have been achieved without the co-operation of these people. TABLE OF CONTENTS ABSTRACT INTRODUCTION ' 1 Statement of the Problem l Lo c a t i o n 2 Pros p e c t i n g 2 GENERAL GEOLOGY 5 GEOLOGY OF THE STAR GROUP 7 Table of Formations 9 D e s c r i p t i o n of formations 10 Banded A r g i l l a c e o u s Sandstone 10 • Gray Limestone 12 F a i t h Limestone 12 C a l Gray Limestone ;...15 C h a r i t y H i l l Limestone 16 C a s s i a r Omineca B a t h o l i t h . . . 16 Quartz Feldspar Porphyry.... 17 MINERAL DEPOSITS 19 Vein No. 1 19 Vein No. 2 21 Vein No. 3 ... 21 Area of Disseminated I ' l i n e r a l i z a t i o n -2? L i m o n i t i c Areas 24 HIH^RaLOGY 24 DESCRIPTION OF LIMONITE 27 Type No. 1- Blue-black. B o t r y o i d a l Limonite 28 Type No. 2- Reddish-brov/n Hard Limonite 32 Type No. 3- Yellow-brown S o f t Limonite 34 Type No. 4- Porous brown Crumbly Limonite 36 Type No. 5- Porous Orange-yellow Limonite 39 Type No. 6- Llixed Caverno'us Limonite 44 Limonite Table 47 CONCLUSIONS 48 D e r i v a t i o n of S p e c i f i c Limonite Types 48 "Material forming the Boxworks. 50 Source of I r o n 52 Secondary Lead M i n e r a l s 53 S o l u b i l i t y of Limonite i n HC1 54 TABLE OF CONTENTS (Cont.'d.) ILLUSTRATIONS" 56 to 72 Fhotographs of Hand Specimens P l a t e s 1-4; 7,10,11,13B,21,22,25,26. • Photomicrographs of P o l i s h e d Sections P l a t e s 5*, 6,8,9,12,13A ,14 ? 14A, 17-19,23,9.7. Photomicrographs of Thin Sections P l a t e s 15,16,20,24,24A,28. BIBLIOGRAPHY 73 . APPENDIX • 74 Pr e p a r a t i o n of Thin and P o l i s h e d Sections 74 A B S T R A C T The i n t e r p r e t a t i o n of leached outcrops as guides to the s p e c i f i c minerals from which they were formed has "been developed t o a r a t h e r high degree by e a r l i e r workers, among whom Boswell and Blanchard deserve p a r t i c u l a r mention. In' the present work, a gossan t h a t l e d t o the disco v e r y of a l e a d d e p o s i t i s des c r i b e d . Since many hand specimens or the l i m o n i t e from t h i s gossan l a c k the c h a r a c t e r i s t i c boxwork s t r u c t u r e s d e s c r i b e d by the authors above, microscopic i n v e s t i g a t i o n s of t h i n and p o l i s h e d s e c t i o n s were c a r r i e d out. However, the gossan i s c l a s s i f i e d i n t o s i x types mainly on the b a s i s of i t s p h y s i c a l p r o p e r t i e s . At l e a s t three of these are c o r r e l a t e d w i t h types described by Boswell and Blanchard, one of p y r i t e d e r i v a t i o n and the others from galena. The r e l a t i v e s o l u b i l i t y of d i f f e r e n t l i m o n i t e types i n d i l u t e HC1 was not found t o be of as much value as some w r i t e r s have i n d i c a t e d . The m i n e r a l d e p o s i t s t o which the l i m o n i t e p o i n t e d the way have not been s u f f i c i e n t l y exposed t o a l l o w d e t a i l e d study, but the presence of t r e m o l i t e and phlogopite i n an area of disseminated m i n e r a l i z a t i o n i n d i c a t e s t h a t t h i s p o r t i o n a t l e a s t may be of contact metamorphic o r i g i n . THE GOSSAN OF A LEAD DEPOSIT IN LIMESTONE / YUKON TERRITORY I N T R O D U C T I O N  STATEMENT OF THE PROBLEM During the 1945-46 term at the University of Briti s h Columbia, the writer was introduced to the subject of "Leached Outcrops" i n a course in Economic Geology. While prospecting in the summer of 1946, a practical f i e l d example was encountered, which illustrates some of the problems of this subject, as well as the benefit which might be derived from i t s further study. A typical piece of "limonite float" from the surface of a leached outcrop of a mineral deposit i s shown in plate 1. A typical specimen of the part i a l l y oxidized or leached mineral deposit, which was found about 4 feet below, i s shown in Plate 2. The. former appears to give no indications as to i t s origin, while the latter contains abundant fresh galena as well as a boxwork structure reminiscent of the cubic cleavage of galena. It was therefore decided to carry out a laboratory investigation of numerous mineral specimens from this deposit in an attempt to arrive at some definite conclusions as to their origin, and the possible significance of the various limonite types. To do so, i t was deemed ad v i s a b l e t o d e s c r i b e f i r s t the environment of the l i m o n i t e , and the known mi n e r a l d e p o s i t s t o which some of the l i m o n i t e p o i n t e d the way. A c c o r d i n g l y , the f i r s t p a r t of t h i s r e p o r t covers the geology and mineralogy of the area, w h i l e the l a t t e r p o r t i o n d e als w i t h the study of the v a r i o u s types of l i m o n i t e . LOCATION The S t a r Group of claims i s s i t u a t e d i n the Dawson mining d i s t r i c t of Yukon T e r r i t o r y , about f i v e m i l e s n o r t h of the B.C. - Yukon boundary, and about 2Jjj- miles south of M i l e Post 702 on the A l a s k a highway. (See Map No.- 1, i n pocket.) The claims cover a group of low=lying h i l l s on the eastern contact of the C a s s i a r b a t h o l i t h . These h i l l s reach e l e v a t i o n s of about 4400 f e e t , w h i l e the immediately adjacent v a l l e y f l o o r has>.an e l e v a t i o n of about 3600 f e e t . The e l e v a t i o n of the Rancheria R i v e r , which flows e a s t e r l y through the C a s s i a r Mountains, i s about 2900 f e e t at mile 702. PROSPECTING These claims were staked i n the summer of 1946 by prospectors working f o r the Western Ranges Pr o s p e c t i n g Syndicate. -3- The f i r s t i n d i c a t i o n s of m i n e r a l i z a t i o n found by the prospectors c o n s i s t e d of numerous patches of " l i m o n i t e f l o a t " s c a t t e r e d over a number of the hare h i l l s i n a r e s t r i c t e d area of about 6,000 f e e t long' and 600 f e e t wide c l o s e t o the i n t r u s i v e c o n t a c t . On c l o s e r examination, some of t h i s was found t o c o n t a i n o c c a s i o n a l g r a i n s of f r e s h galena. A f t e r examination by the author, i t was decided t o explore the ground more thoroughly t o attempt to f i n d the source of the l i m o n i t e . The f o l l o w i n g p o i n t s favored t h i s d e c i s i o n : (1) Occasional specks of f r e s h r e s i d u a l galena were founuL i n some pieces' of l i m o n i t e . (2) A s m a l l amount of near s u r f a c e , l o o s e , rock d e b r i s was found t o c o n t a i n a s m a l l percentage of galena i n t i n y v e i n l e t s or as disseminated g r a i n s . (3) The source of the l i m o n i t e appeared to be l o c a l . None of t h i s f l o a t was found on the surface of the bare i n t r u s i v e mass Immediately to the west, and i t was considered t h a t i f the l i m o n i t e had been t r a n s p o r t e d and deposited by i c e , some of the l i m o n i t e should a l s o have been found on the surrounding area. F u r t h e r , a l o c a l source was p o s t u l a t e d by L o r d ( 9 ) . (4) Some of the l i m o n i t e "looked" s i m i l a r t o c e r t a i n types d e s c r i b e d by Bateman (2) as having been d e r i v e d from m e t a l l i c s u l p h i d e s . The author was not s u f f i c i e n t l y - 4 - f a m i l i a r w i t h these l i m o n i t e boxworks t o s t a t e d e f i n i t e l y t h e i r d e r i v a t i o n . (5) The d i s t r i c t was apparently f a v o r a b l e f o r the l o c a t i o n of l e a d - z i n c d e p o s i t s . M i n e r a l i z a t i o n along the eastern edge of the Cassiar-Omineca b a t h o l i t h has been known f o r some years near such l o c a l i t i e s as Manson Creek, Ingenika R i v e r , and McDame Creek. I n the v i c i n i t y of the A l a s k a highway, Lord ( 9 , p. 16-18) r e p o r t s galena and s p h a l e r i t e at three l o c a l i t i e s , one about twelve miles n o r t h of the highway and two others a t f i v e and seven miles south of the highway,' a l l c l o s e t o the i n t r u s i v e . (6) Limestone and dolomite, which underlie the l i m o n i t e f l o a t , form f a v o r a b l e host rocks f o r numerous important l e a d - z i n c d e p o s i t s i n many p a r t s of the world. -5- GENERAL GEOLOGY The f o l l o w i n g i s a summary from Lord's r e p o r t (9) of the r e g i o n a l geology c o v e r i n g a narrow s t r i p along the eastern edge of the Cassiar-omlneca b a t h o l i t h extending s e v e r a l m i l e s n o r t h and south of the A l a s k a Highway. The sedimentary rocks c o n s i s t mainly of l i g h t gray limestone ana buff-weathering dolomite, but i n c l u d e some a r g i l l i t e , s l a t e , p h y l l i t e , q u a r t z i t e , and s c h i s t . F o s s i l c o r a l s i n d i c a t e t h a t some of t h i s group i s probably of Carboniferous age. S c h i s t o s e limestone and dolomite are prominent north of the highway, but were not noted south of the highway. L o c a l l y , along the g r a n i t i c c o n t a c t , some of the rocks of t h i s group- have been conspicuously a l t e r e d by contact metamorphism across a zone which i s g e n e r a l l y l e s s than 200 f e e t wide. Most of these formations have a -strike n e a r l y p a r a l l e l t o the edge of the b a t h o l i t h and d i p about 45 degrees away from i t . However, near the highway the beds s t r i k e i n many d i r e c t i o n s and some are n e a r l y f l a t - l y i n g . The Cassiar-Omineca b a t h o l i t h i s about 14 miles wide i n t h i s r e g i o n , and has a north-northwest t r e n d . I t i s l i g h t gray, massive, medium to coarse-grained.granite to g r a n o d i o r i t e , but the common v a r i e t y i s probably b i o t i t e - q u a r t z monzonite. Numerous a p l i t e dykes, and a - 6 - few pegmatite and lamprophyre dykes cut the i n t r u s i v e . G n e i s s i c phases w i t h f o l i a t i o n and handing s t r i k i n g p a r a l l e l to the border were noted along the western edge of the i n t r u s i v e . L o c a l l y along the ea^ern edge, the rock w i t h i n s e v e r a l f e e t of the c o n t a c t i s f i n e - g r a i n e d , and contains very l i t t l e dark m i n e r a l s . Under the heading of " M e t a l l i c M i n e r a l Deposits", Lord (9, p.17) r e p o r t s : " B o t r y o i d a l l i m o n i t e f l o a t i s abundant about 2 m i l e s south of the highway at m i l e 702. I t occurs i n d r i f t o v e r l y i n g dense, white, buff-weathering dolomite or limestone, or both, w i t h i n a few hundred f e e t of the edge of the g r a n i t i c b a t h o l i t h and has probably not been t r a n s p o r t e d more than a few f e e t . The area of l i m o n i t e f l o a t p a r a l l e l s the g r a n i t e contact f o r more than 1,000 fe,et. One specimen of n e a r l y s o l i d , dark brown l i m o n i t e assayed; g o l d , 0.005 ounce a ton; s i l v e r , 0.79 ounce a ton; tungsten, n i l . " No mention was made of the presence of galena here, . but on p. 19 Lord (9) f u r t h e r s t a t e s : "Most known mi n e r a l d e p o s i t s i n the map area l i e w i t h i n the limestones, dolomites, and a s s o c i a t e d rocks of Group C c l o s e t o the eastern edge of the C a s s i a r b a t h o l i t h , t h a t i s n o r t h and south of the highway at about mi l e 701. T h i s s e c t i o n contains^ g o l d , s i l v e r , copper, l e a d , z i n c , tungsten, and t i n , and c l e a r l y warrants f u r t h e r p r o s p e c t i n g . " -7- GEOLOGY OF THE STAR GROUP In the area covered by the S t a r c l a i m s , P a l e o z o i c sediments of c l a s t i c and chemical d e p o s i t i o n are f o l d e d or domed t o form a sou t h e r l y - p l u n g i n g a n t i c l i n a l s t r u c t u r e ^ M a p No. 1) These.are Intruded by the C a s s i a r - Omineca b a t h o l i t h which i s considered by Lord(9) t o be of J u r a s s i c or l a t e r age. An i r r e g u l a r mass of quartz- f e l d s p a r porphyry a l s o i n t r u d e s some of the sediments, but the r e l a t i o n of t h i s t o the main b a t h o l i t h i c i n t r u s i o n i s not known. I t i s assumed by the w r i t e r , however, t h a t t h i s may be a l a t e r o f f - s h o o t g e n e t i c a l l y r e l a t e d t o the main i n t r u s i v e . The contact of the b a t h o l i t h w i t h the sedimentary s t r a t a , coinc^es f a i r l y c l o s e l y w i t h , and i s l o c a l l y d efined by a continuous depression or v a l l e y . S e v e r a l summits i n t h i s t r ench d i r e c t the l o c a l drainage i n the two opposite d i r e c t i o n s . Since the sediments d i p towards the b a t h o l i t h , and contact metamorphic minerals were not noted i n t h i s v i c i n i t y , Dr. Derry considered t h a t the contact t r e n c h might be the surface expression of a f a u l t between the b a t h o l i t h and the sediments, along which m i n e r a l i z i n g s o l u t i o n s may have penetrated or deposited. The c o l o r and t a s t e o f the water, and the brown r u s t on p l a n t s i n the upper reaches of I r o n Creek, are f u r t h e r evidence t h a t a mi n e r a l d e p o s i t may be lo c a t e d i n a p o s s i b l e f a u l t zone below the pond from which the creek i s f e d . Outcrops are numerous above the t r e e l i n e , which i s a t an e l e v a t i o n of about 3900-4000 f e e t i n t h i s area. •The overburden c o n s i s t s of s o i l ana grass i n p l a c e s , •but mainly or r e s i a u a l rock fragments and p a r t i c l e s broken ana weatherea from the u n d e r l y i n g s t r a t a . G l a c i a l e r r a t i c s c o n s i s t i n g p r i n c i p a l l y of g r a n i t i c boulders, which were probably xransportea from the C a s s i a r b a t h o l i t h , are present to the tops of the h i l l s . However, there i s no general mantle of g l a c i a l d e b r i s , and most of these e r r a t i c boulders are above the s i z e or pebbles. ' Appar e n t l y, the smaller p a r t i c l e s or g l a c i a l d r i f t , which may have been spread over the area'.at one time, have been washed o f f these h i l l s i n t o the v a l l e y . Short v e i n s of pure, white t o transparent c a l c i t e are exbosea i n some of the limestone outcrops. I n two l o c a l i t i e s near the t r e e l i n e , narrow barren quartz v e i n s cut a lower sandstone member. - 9 - T A B L E OF F O R M A T I O N S (1) J u r a s s i c o r l a t e r Q u a r t z F e l d s p a r P o r p h y r y C a s s i a r B a t h o l i t h C a r b o n i f e r o u s o r D e v o n i a n / " C h a r i t y H i l l L i m e s t o n e C a l G r a y L i m e s t o n e \ F a i t h L i m e s t o n e . S h a l e G r a y L i m e s t o n e B a n d e d A r g i l l a c e o u s S a n d s t o n e . I n t h e v a l l e y o f t h e R a n c h e r i a R i v e r , o u t c r o p s o f m i c a s c h i s t a r e w i d e s p r e a d , a n d t h e s e s t r a t a p r e s u m a b l y u n d e r l i e t h e s e r i e s l i s t e d a b o v e . (1) M a p p e d a n a c o m p i l e d b y D . R . D e r r y , G e o l o g i s t f o r V e n t u r e s L i m i t e d . . -10- DESCRIPTION OF FORMATIONS BANDED ARGILLACEOUS SANDSTONE These s t r a t a were o r i g i n a l l y mapped as limestone, hut f u r t h e r examination of the s i n g l e r e p r e s e n t a t i v e sample a v a i l a b l e , c o l l e c t e d from Claim 4, p o i n t Y, proves i t t o be an impure sandstone. The rock i s dark gray i n c o l o r and exposed surfaces show bands or laminae t h a t weather d i f f e r e n t i a l l y t o produce r i d g e s up t o \ i n . t h i c k . The f i n e l y laminated nature of t h i s rock i s q u i t e d i s t i n c t i v e even m f r e s h l y broken specimens. I n some pl a c e s where the contact between t h i s and the Gray limestone above i s . , exposed, the sandstone member i s seen t o be l o c a l l y f o l d e d and t w i s t e d whereas the gray limestone I s not. Such a r e l a t i o n s h i p suggests a l o c a l nonconformity. However, since t h e i r a t t i t u d e s are g e n e r a l l y s i m i l a r throughout the mapped area, i t may be t h a t no unconformity e x i s t s here. P o s s i b l y the Gray limestone was l e s s competent at the time of f o l d i n g , and was deformed by flowage. I n t h i n s e c t i o n , the laminated s t r u c t u r e i s seen t o be due t o the v a r i a t i o n I n composition of the d i f f e r e n t laminae, as w e l l as g r a i n s i z e v a r i a t i o n s . Anhedral quartz g r a i n s about .1 mm. diameter predominate, but some are as larg e as .5 mm. These have been h i g h l y r e - c r y s t a l l i z e d , as proven by t h e i r compaction and -11- interpenetratmg contacts. An unknown mineral (Cordierite? or Anorthoclase?) which appears very similar to quartz and also forms tight interpenetrating contacts with i t , forms possibly 10% of this specimen. It- has a pale pinkish tinge, i s slightly sericitized, and apparently lacks good cleavage. Other optical properties are: n=1.53; 2V=40°; negative; B-.006; Occasional grains resemble Carlsbad twins, and in these the optic plane i s normal to the twinning.plane. Most grains are slightly larger than the quartz grains, some are rimmed with quartz, and some contain tiny inclusions of actinolite? Brown biotite and green actinolite make up about 20% of the rock, and diopside i s present in smaller amounts. Since these minerals would not normally be found to such an extent in a fine-grained sandstone or quartzite, i t i s li k e l y that locally, at least, this member has been highly altered during the intrusion of either the Cassiar batholith, or the quartz feldspar porphyry stock, or both, ana that the introauction of most of these minerals was due to metasomatic replacement at f a i r l y high temperatures. Pyrite and magnetite form more than 3% of the thin section, and a slight amount of brown iron stain may be attributed to them. Irregular grains of pyrite are more or less concentrated along certain bands or veinlets, and This a l s o c o n t r i b u t e s to the l a m i n a t i o n . A p a t i t e , t i t a n i t e and c h l o r i t e are present i n minor amounts, the l a t t e r near areas of p y r i t e . GRAY u H 5 5 3 T O N E This i s a l i g h t - g r a y rock which weathers to a darker gray. VThen f r e s h l y broken i t has a mottled appearance. Occasional coarse c a l c i t e g r a i n s , sometimes resembling phenoerysts i n an.igneous rock, may be seen i n the f i n e  grained dense "groundmass" which shows vague bedding or f o l i a t i o n . I n t h i n s e c t i o n , f i n e - g r a i n e d ( l e s s than .1mm) compact c a l c i t e gra.ins form a matrix f o r l a r g e r c r y s t a l g r a i n s or o o l i t i c - a p p e a r i n g areas -of coarser' grained c a l c i t e . A P l a n a r s t r u c t u r e i s apparent i n the "groundmass" as w e l l as i n the e l l i p t i c a l shapes and l i n e a l arrangements of the l a r g e r g r a i n s . This may be due to f o l i a t i o n , or i t may represent bedding since the l i n e a t i o n tends to f l o w around some of the l a r g e r g r a i n s . A minor amount of c l a s t i c quartz i s present as small i r r e g u l a r g r a i n s . FAITH LIMESTONE This i s a dense, f i n e - g r a i n e d grayish-white rock th a t weathers on a l l exposed surfaces t o a b u f f or r u s t y c o l o r . The rock appears massive, w i t h a l a c k of bedding -13- f o l i a t i o n i n the hand, specimen. Even i n w e l l exposed outcrops, i t i s of t e n d i f f i c u l t t o d i s t i n g u i s h between bedding and f r a c t u r e systems. A t h i n s e c t i o n showed f i n e - g r a i n e d ( l e s s than .1 mm. compact carbonate g r a i n s , w i t h an o c c a s i o n a l v e i n l e t of l a t e r (?) coarser ( . 5 mm.) c a l c i t e . These s t r a t a u n d e r l i e most of the h i l l s covered by the c l a i m s , and form the host rock f.or a l l the known m i n e r a l i z a t i o n . While outcrops are numerous, most of t h i s area i s covered w i t h a f o o t or two of loose fragments and p a r t i c l e s c o n s i s t i n g mainly of the under l y i n g F a i t h limestone. I n view of the p o s s i b i l i t y t h a t the composition of t h i s member-may have been more f a v o r a b l e than the un d e r l y i n g Gray limestone f o r the p r e c i p i t a t i o n of the ore m i n e r a l s , comparative t e s t s were made t o determine what d i f f e r e n c e s d i d e x i s t . I n HC1, and HN0 3, the Gray limestone e f f e r v e s c e d f r e e l y and d i s s o l v e d r e a d i l y , while the F a i t h limestone e f f e r v e s c e d s l o w l y and d i s s o l v e d w i t h d i f f i c u l t y . An equal amount of each was d i s s o l v e d i n a c i d , and.after f i l t e r i n g o f f the p r e c i p i t a t e s caused by the a d d i t i o n of ammonia, the f i l t r a t e s were t e s t e d under s i m i l a r c o n d i t i o n s f o r the presence of calcium and magnesium. Ammonium oxalate gave two successive p r e c i p i t a t e s " i n the Gray limestone, -14- and only one i n the F a i t h limestone, p r o v i n g the presence of more calc i u m i n the former. Sodium ammonium phosphate gave no p r e c i p i t a t e i n the former, but d i d i n the l a t t e r , which proves the absence of magnesium i n the Gray limestone and i t s presence i n the F a i t h limestone. Three s p e c i f i c g r a v i t y t e s t s on each gave c o n s i s t e n t values of 2.70 f o r the former and S.82 f o r the l a t t e r . These r e s u l t s , combined w i t h the t y p i c a l b u f f weathering c o l o r of the F a i t h limestone, would seem t o i n d i c a t e t h a t i t i s f a i r l y pure dolomite, w h i l e the Gray limestone i s f a i r l y pure c a l c i t e . A s s o c i a t e d w i t h some of the surface patches of l i m o n i t e f l o a t , and i n some cases without any l i m o n i t e , are patches of l i g h t brown pi e c e s of F a i t h limestone d e b r i s . T h i s m a t e r i a l i s h i g h l y f r a c t u r e d , and c r i s s  crossed w i t h t i n y dark brown v e i n l e t s . (See P l a t e 3 ) . This rock has been designated "Fractured F a i t h limestone." Thin and p o l i s h e d secxions prove t h a t the veinle'ts are due t o euhedral g r a i n s of p y r i t e disseminated along t i n y f r a c t u r e s . The p y r i t e has been almost wholly a l t e r e d t o m e t a l l i c l i m o n i t e , and a brown i r o n s t a i n permeates the carbonate along the f r a c t u r e s . Very s l i g h t movement along some of the f r a c t u r e s i s i n d i c a t e d by o f f s e t s of cross v e i n l e t s . No quartz was found i n the t h i n s e c t i o n of t h i s m a t e r i a l . -15- A n o t h e r r o c k t y p e i n c l u d e d h e r e h a s b e e n t e r m e d " E r e c c i a t e d F a i t h l i m e s t o n e " . I t c o n s i s t s o f a n g u l a r f r a g m e n t s o f n o r m a l g r a y i s h - w h i t e F a i t h l i m e s t o n e u p t o a b o u t -| i n c h i n maximum d i m e n s i o n , e m b e d d e d i n a f i n e  g r a i n e d m a t r i x w h i c h i s s t a i n e d s l i g h t l y y e l l o w i s h b u t a l s o c o n t a i n s s m a l l , m o r e o r l e s s c i r c u l a r a r e a s o f w h i t e c a l c i t e . ( S e e P l a t e 4). O n e x p o s e d s u r f a c e s , d i f f e r e n t i a l w e a t h e r i n g h a s c a u s e d g r e a t e r e r o s i o n o f t h e m a t r i x s o t h a t t h e b r e c c i a f r a g m e n t s s t a n d o u t i n r e l i e f . T h i s r o c k o c c u r s i n l o o s e d e b r i s a s w e l l a s i n p l a c e , a n d was f o u n d t o b e g e n e r a l l y c l o s e l y a s s o c i a t e d w i t h a r e a s o f l i m o n i t e f l o a t , o r a d j a c e n t t o c a l c i t e v e i n s . I n t h i n s e c t i o n , t h e b r e c c i a f r a g m e n t s a r e s e e n t o c o n s i s t o f a l a r g e n u m b e r o f t i n y , c l o s e l y p a c k e d g r a i n s , w h i c h a r e a c t u a l l y c o n s i d e r a b l y s m a l l e r o n t h e a v e r a g e t h a n t h o s e i n t h e g r o u n d m a s s . T h e b o r d e r s o f t h e f r a g m e n t s a r e q u i t e d e f i n i t e , a n d a s l i g h t c o n c e n t r a t i o n o f a l i g h t b r o w n s t a i n may b e s e e n j u s t o u t s i d e t h e i r b o u n d a r i e s . No q u a r t z was s e e n m t h i s r o c k . C A L GRAY L I M E S T O N E T h i s i s a d a r k g r a y r o c k w h i c h i s c u t b y f a i r l y n u m e r o u s c a l c i t e v e i n l e t s . N o s p e c i m e n was a v a i l a b l e f o r f u r t h e r s t u d y . -16- CHARITY HILL LIMESTONE This i s a gray c r y s t a l l i n e limestone or dolomite t h a t weathers p i n k i s h b u f f . I t contains at l e a s t t w o f o s s i l i f e r o u s bands t h a t weather t o a r u s t y red-brown c o l o r . Thin s e c t i o n s of the f o s s i l i f e r o u s m a t e r i a l c o n t a i n f i n e - t o medium-grained carbonate mixed w i t h q u a r t z , b l a c k carbonaceous and k a o l i n i c m a t e r i a l , and smaller amounts of t i n y mica f l a k e s . The quartz forms about 5%' of the rock and c o n s i s t s of angular t o rounded c l a s t i c g r a i n s between ,1mm. and .3mm. diameter. The r u s t y weathering'is confined t o a f a i r l y s h a r p l y d e f i n e d surface l a y e r l e s s than 2 mm. t h i c k . A f t e r examination of the t h i n s e c t i o n , Dr. O k u l i t c h of t h i s U n i v e r s i t y s t a t e d t h a t the s t r u c t u r e was too g r e a t l y a l t e r e d by r e c r y s t a l l i z a t i o n to determine the genus. Dr. M.A. F r i t z of the. Royal Ontario Museum t e n t a t i v e l y c l a s s i f i e d other specimens from t h i s band as Ordovi c i a n c o r a l s . CASSIAR/OMINECA BATHOLITH In the v i c i n i t y of the S t a r Group, the b a t h o l i t h i s a medium- t o coarse-grained g r a y i s h rock, and i s cut by numerous s m a l l , white t o p i n k i s h a p l i t e dykes. No specimen of t h i s m a t e r i a l was a v a i l a b l e f o r t h i n s e c t i o n examination, but Lord ( 9, p.13) s t a t e s t h a t i t v a r i e s from a g r a n i t e t o g r a n o d i o r i t e , and i s predominantly a -17- b i o t i t e - q u a r t z monzonite. Trench 3-13 (See Map 1) was dug i n an attempt t o expose the contact of the b a x h o l i t h and the F a i t h limestone, but the d r i f t - f i l l e d depression proved too deep. However, a small specimen of loose rock, which showed a contact between two rock types, was c o l l e c t e d here and st u d i e d i n t h i n s e c t i o n . I t appears t o be the contact between a f i n e - g r a i n e d a p l i t e dyke, and a border phase of the b a t h o l i t h which contains very l i t t l e dark m i n e r a l s . The dyke contains extremely f i n e - g r a i n e d quartz, a l b i t e , and m i c r o c l i n e , w i t h o c c a s i o n a l a l b i t e and m i c r o c l i n e phenocrysts l e s s than 1 mm. across. At the contact there i s a sudden change i n t e x t u r e t o medium- t o coarse grained a l b i t e , o r t h o c l a s e , m i c r o c l i n e , and quartz. Much of the f e l d s p a r i s clouded w i t h k a o l i n , and a sm a l l amount of s e r i c i t e i s present. Muscovite forms about 2% of t h i s p o r t i o n , and a very minor q u a n t i t y of magnetite was noted. I t i s l i k e l y t h a t t h i s loose specimen had been t r a n s p o r t e d only a few f e e t from the b a t h o l i t h . QUARTZ FELDSPAR PORPHYRY This i s a grayish-white rock c o n t a i n i n g prominent quartz phenocrysts from about l-^ t o 3 mm. diameter i n a f i n e - g r a i n e d groundmass. Numerous smaller f e l d s p a r phenocrysts, up t o about 1-| mm, lo n g , show up r e a d i l y i n t h i n s e c t i o n , but are r a t h e r d i f f i c u l t t o d i s c e r n i n hand specimens. -18- Th i n s e c t i o n s show two main"sizes of quartz phenoerysts, the l a r g e s t group v a r y i n g between about 1-^  to 3 mms., whi l e another group seems to be about .3 mms. diameter. There appears t o be very l i t t l e g r a d a t i o n between these two main s i z e s , and i t i s p o s s i b l e t h e r e f o r e t h a t f o l l o w i n g the f i r s t quiescent p e r i o d d u r i n g which the l a r g e r phenoerysts formed, there was a f u r t h e r upward i n t r u s i o n of t h i s m a t e r i a l , f o l l o w e d by another p o s s i b l y s h o r t e r p e r i o d of quiescence" d u r i n g which the smaller quartz phenoerysts formed. The f e l d s p a r phenoerysts are predominantly a l b i t e but a s m a l l number are o r t h o c l a s e . K a o l i n i z a t i o n i s q u i t e pronounced i n these f e l d s p a r phenoerysts, e s p e c i a l l y near t h e i r borders, while the f e l d s p a r i n the f i n e - g r a i n e d groundmass i s r e l a t i v e l y c l e a r . However, the reverse i s t r u e of s e r i c i t e , which i s much more f u l l y developed i n the groundmass. A c o l o r l e s s m i n e r a l t h a t may he hydromuscovite (damourite) forms about 3% of the s l i d e . I t occurs i n t a b u l a r to lath-shaped c r y s t a l s from about .1mm. t o 1^ -mm. long. Other o p t i c a l p r o p e r t i e s are: u n i a x i a l ; negative; n=1.58; B=.033; one cleavage; p a r a l l e l e x t i n c t i o n ; length-slow. Euhedral p y r i t e c r y s t a l s make up l e s s than 1% of the rock, and are always contained i n s i d e the damourite? The p y r i t e i s p a r t i a l l y o x i d i z e d t o a red -19- semi-transparent limonite, and a light yellow stain invariably extends outwards to color part of the otherwise colorless damourite? These light yellow areas are then slightly pleochroic, and the addition of iron has apparently changed, the composition to another unknown mineral with a slightly higher index and a more twisted mat appearance. MINERAL DEPOSITS Surface trenching exposed three widely separated veins or mineralized shears containing massive, coarsely crystalline galena. VEIN NO. 1 (See Map No. 1) The largest vein was exposed by trench 6-3 on the N.S. side of Faith H i l l . Here, fresh massive galena was found in places within 3 feet of the surface. The vein zone was traced for a length of 160 feet along i t s strike of N 25°W that more or less parallels the batholith contact. The average dip i s about 70° easterly, i.e. away from the contact. The vein zone i t s e l f pinches and swells, and the galena occurs in lens-like bodies,' up to about 12 inches thick. Where the galena lenses out, the vein zone continues and i s readily traced by a soft sooty, brownish, or bluish-black material that crumbles like a soft s o i l in the central portion of the zone. In some cases this s o i l - l i k e material contains a few tiny specks and grains of - 2 0 - f r e s h galena. The w a l l s on e i t h e r s ide of the narrow zones are r e l a t i v e l y s o l i d hut are more or l e s s completely permeated w i t h the b l a c k m i n e r a l . Blowpipe and chemical analyses confirmed the presence of manganese, i r o n , C 0 o , and water i n t h i s b l a c k m a t e r i a l . I t I s probably a mixture of hydrated manganese and i r o n oxides r e p l a c i n g the o r i g i n a l F a i t h limestone. Continuing outwards from the v e i n , the country rock passes from t h i s b l a c k rock t o a brownish rock and grades i n t o normal F a i t h limestone. The manganiferous m a t e r i a l i s c o n siderably l e s s evident i n the w a l l s adjacent t o the galena l e n s e s . Thin s e c t i o n s were s u c c e s s f u l l y made t h a t show the b l a c k opaque m a t e r i a l r e p l a c i n g the carbonate. Trenching at t h i s l o c a l i t y was suggested because of the presence of surface l i m o n i t e f l o a t . No r e s i d u a l galena was seen i n any of t h i s f l o a t , nor was there a very l a r g e q u a n t i t y or patch of i t i n evidence. However, when the f i r s t t e s t p i t showed the b l a c k s o i l - l i k e m a t e r i a l , t h i s was f o l l o w e d and the whole m i n e r a l i z e d v e i n zone exposed. The overburden here, as over most of the t r e e l e s s h i l l s c o n s i s t s p r i n c i p a l l y of r e s i d u a l products of weathering of the immediately u n d e r l y i n g s t r a t a , which produces a c e r t a i n amount of s o i l mixed w i t h loose country rock fragments. Occasional g r a n i t i c boulders g r e a t e r than -21- s i x ' inches i n diameter seem to be a l l t h a t remains of any- e a r l i e r g l a c i a l d e b r i s . VEIN NO. 2 This v e i n , s t r i k i n g N 13°W and d i p p i n g 68°W, was exposed i n trench 1-1 near the top of Guy H i l l about 2,000 f e e t north-west of V e i n No, 1. The v e i n zone i s t r a c e a b l e over a length of 65 f e e t by the same b l a c k menganiferous m a t e r i a l as exposed i n V e i n No. 1. T h i s trench was again prompted by the presence of surface l i m o n i t e f l o a t , which i n t h i s case showed an o c c a s i o n a l speck of r e s i d u a l f r e s h galena. When the top 12s- f e e t had been removed, the b l a c k manganiferous m a t e r i a l showed up, and f u r t h e r d i g g i n g exposed galena i n place about 3 f e e t below the s u r f a c e . The t r a n s i t i o n from surface l i m o n i t e through l i m o n i t e i n place t o galena i n place was q u i t e evident here. VEIN NO. 3 I n t r e n c h 1-6 near the bottom of Guy H i l l on i t s N.VJ. corner, a short v e i n , c o n t a i n i n g a 2-4 i n c h width of f r e s h to o x i d i z e d galena along .a 4-6 i n c h band of l i m o n i t e , d i p s f l a t l y t o the south-west. The surface l i m o n i t e here showed only a very o c c a s i o n a l speck of galena, and the galena i n place was found about 3 f e e t below the s u r f a c e . -22- AR3A OF DISSEMINATED MINERALIZATION Limonite f l o a t c o n t a i n i n g a few g r a i n s of f r e s h galena, d i r e c t e d a t t e n t i o n t o the area between trenches 3-6 t o 3-8 near the bottom of F a i t h K i l l on i t s north-west corner. Trenching exposed p o o r l y - d e f i n e d areas c o n t a i n i n g disseminated galena i n f a i r l y f r e s h country r o c k s . I n some cases a sma l l amount of s p h a l e r i t e accompanies the galena, as w e l l as minor amounts of p y r i t e . Some of t h i s galena occurs as small g r a i n s i n . f r a c t u r e cleavage j o i n t s i n the F a i t h limestone, and i t i s a l s o common i n t i n y . v e i n l e t s . I n trench 3-6, f r e s h , disseminated p y r i t e w i t h no other m e t a l l i c s forms up to about 10% of the rock i n a small area. Specimens were obtained about 7 f e e t below the o r i g i n a l surface where the host rock was a l s o q u i t e f r e s h . I n hand specimens, t h i s rock i s more c o a r s e l y c r y s t a l l i n e and l i g h t e r c o l o r e d than the normal b u f f — weathering F a i t h limestone. Thin s e c t i o n s of t h i s m a t e r i a l c o n s i s t predominantly of medium-grained (about .3mm.) carbonate, but a l s o c o n t a i n a p p r e c i a b l e amounts ( p o s s i b l y 10%) of very p a l e phlogopite and almost c o l o r l e s s t r e m o l i t e , and smaller amounts of almost c o l o r l e s s c h l o r i t e . Quartz i s a minor c o n s t i t u e n t , but since some g r a i n s are long (about .2mm.) and narrow and have i r r e g u l a r o u t l i n e s , i t i s probably hypogene. The p y r i t e i s euhedral t o anhedral, and i s un i f o r m l y disseminated throughout. P h l o g o p i t e contains numerous -23- carbonate inclusions, indicating replacement. Kaolinic material i s sometimes associated with phlogopite and chlorite, indicating that the original rock was somewhat argillaceous. The apparent lack of typical contact metamorphic silicates along the batholith contact (See page 7) i s not surprising, since the tremolite and phlogopite are about the same color as the carbonate and are not recognized in an ordinary hand specimen. They do show, however, on a flattened or ground surface. These minerals were probably formed by contact metasomatism when heated solutions or vapors reacted with the host dolomite during or following the intrusion of the Cassiar batholith. Possibly the pyrite and quartz were also introduced at this time. Probably this whole area of disseminated mineralization represents an ill-defined contact metamorphic deposit. It is about 500 feet from the closest exposure of the batholith. No definite mineralized zone could be outlined in this area, and no gradation from the limonite to mineralization in place could be noted. Within a foot or two of the surface, in the loose weathered mantle, fresh country rock fragments.were found to contain small percentages of disseminated fresh galena. - 2 4 - LlMONITIC AREAS Numerous trenches and pits were dug on or near other areas of limonite float, but no further mineralization in place was found. In some of these, such as trenches 3-10 and 3-11, a small amount of the black manganese oxide material was found in place with limonite in vein zones with relatively solid walls. About 50 feet east of trench 3-10 an occasional piece of country rock float contains a minor amount of disseminated fresh galena. MINERALOGY Assays of the massive galena, from the three veins indicated values in silver averaging about one-third of an ounce per unit of lead. Polished sections were prepared in an attempt to determine the source of this silver, since i t i s unlikely that this amount of silver could be held in the galena in solid solution. A mineral that may be a silver sulpho-salt was found in very minor amounts and in such small areas that i t could not be dug out for micro chemical tests. (Plate 5.) It i s light gray m color, i s slightly harder (about C-) than galena, and i s Isotropic or very weakly anisotropic. Oblique illumination did not show any internal reflection, but the small size of the mineral renders such tests unreliable. The following etch tests were obtained: HN03 HCL KCN FeCL 3 KOH HgCLg Pos. Neg. Pos. Neg. Neg. Pos. -25- No other sulphides or primary minerals were found with the fresh massive galena from No. 1 Vein. There was not a great deal of limonite here, but a polished section containing a small amount of weathered material in contact with fresh galena shows the alteration in this case to have been f i r s t anglesite, and then a brown, powdery limonitic material (Plate 6.) The band of anglesite i s about -4- inch wide end was proven by blowpipe tests for lead and sulphur. The limonitic material gave positive iron and sulphate tests, but no lead. It may be that this i s Jarosite. In the par t i a l l y weathered galena from Vein No. 2 a small amount of pyrite was found in polished section. The galena here i s also surrounded by anglesite. Sphalerite has been found in small amounts in fresh rock only, from the area of disseminated mineralization. It i s associated with galena in tiny veinlets or fractures. (Plate 7.) Pyrite could also be detected in hand specimens.in the fresh Faith limesxone only, where i t occurs as disseminated grains and euhedral crystals up to about ^  inch across. Some or these crystals have been almost completely altered to metallic limonlxe, while the rock i s only very slightly iron stained, '(plates § & 9). Polished sections of numerous specimens or limonite revealed occasional small residual areas of pyrite, but these could not be seen with a hand.lens. -26- Q u a r t z w a s c o n s p i c u o u s b y i t s a b s e n c e i n a l l o i ' t h e m i n e r a l d e p o s i t s a s f a r a s e x p l o r e d i n t h e f i e l d . H o w e v e r , t h i n s e c t i o n s o f s p e c i m e n s f r o m t h e a r e a o f d i s s e m i n a t e d m i n e r a l i z a t i o n p r o v e d t h e p r e s e n c e o f a s m a l l a m o u n t o f h y p o g e n e q u a r t z . Some o f t h e l i m o n i t e f r o m t h e g o s s a n s o f t h e d e p o s i t s a l s o c o n t a i n h y p o g e n e q u a r t z . P o l i s h e d s e c t i o n s o f t h e b l a c k m a n g a n i f e r o u s m a t e r i a l f r o m V e i n ITo, 1, r e v e a l e d a w h i t e m e t a l l i c m i n e r a l f o r m i n g narrow, i r r e g u l a r v e i n l e t s i n t h e s o f t , b l a c k , n o n - m e t a l l i c w a d . ( F l a t e 1 0 ) . T h e m e t a l l i c m i n e r a l i s a l s o w i d e l y d i s s e m i n a t e d t h r o u g h o u t t h e w a d i n m i c r o s c o p i c g r a i n s . U n d e r t h e b i n o c u l a r s , i t i s s e e n t o b e a c o h e r e n t , p o w d e r y m i x t u r e o f m e t a l l i c g r a i n s . I t may r e p r e s e n t m o r e t h a n o n e m i n e r a l , s i n c e p o s i t i v e t e s t s w e r e o b t a i n e d f o r i r o n , m a n g a n e s e , a n d s u l p h u r . - 2 7 - D5GCRIPTI0N O F LIMONITE The discovery of mineralization in place beneath or very close, to four separate areas of surface limonite float indicates that the majority of the other widely scattered areas of limonite were also formed very close to their present position from pre-existing metallic sulphides. It i s not the purpose of this work to hazard an opinion as to whether this limonite indicates a commercial orebody, but i t i s f e l t that further mineralization could be reasonably expected beneath some of the other areas. In examining the limonite, both in the f i e l d and in the laboratory, i t became evident that the limonite was not a l l of one kind. Therefore i t was f e l t that laboratory investigations of the various types, coupled with their occurrences in the f i e l d , might form a v/orthwhile study. The remainder of this report i s directed to that end. -28- TYPE NO. .1, BLUE-BLACK 30TRY0IDAL LIMONITE This i s a d u l l , "bluish-black m a t e r i a l , which has a burned or c l i n k e r y appearance. (See P l a t e 11 A, & P l a t e 1 ) . Smooth, shiny, b l a c k b o t r y o i d a l surfaces are g e n e r a l l y s mall i n extent and o f t e n r e s t r i c t e d t o holes or pockets i n the s u r f a c e , so t h a t they may not be seen r e a d i l y without c l o s e examination. The protruberances are i n most cases q u i t e s m a l l , and are formed on t h i n e n c r u s t i n g bands, but one specimen contains protruberances almost -g i n c h across on an e n c r u s t i n g band about £ i n c h t h i c k . When l a r g e r p i e ces are broken, b o t r y o i d a l l a y e r s e n c r u s t i n g c a v i t i e s are o f t e n present, but these are u s u a l l y d u l l u nless connected through an opening t o the surface. T h i s m a t e r i a l , when pure,-does not s t a i n the hands, but i t i s o f t e n p a r t i a l l y contaminated w i t h other types of s o f t e r l i m o n i t e . A l l occurrences of t h i s type were r e s t r i c t e d t o s t r i c t l y surface exposures, although t h i s i s not the only type t o be found on the s u r f a c e . R e s i d u a l specks of galena seem to be e n t i r e l y l a c k i n g when t h i s type i s r e l a t i v e l y pure. The bands have a f i b r o u s r a d i a t i n g s t r u c t u r e w i t h the f i b r e s p e rpendicular t o the s u r f a c e . I t has a y e l l o w i s h - brown streak, a hardness of about 4-^-5, and a uniform s p e c i f i c g r a v i t y of 3.93. I t g i v e s o f f water i n the -29- closed tube, becomes magnetic on heating, and gives blowpipe and chemical tests for iron. Since no r e l i c t sulphides or boxwork structure were evident in the hand specimens, polished and thin sections were prepared. Plate 12 i s a photomicrograph of a polished section,• which shows the typical limonite veinlets forming an irregular and indefinite pattern. A small amount of pyrite was detected in the polished sections, and some of this i s shown in the photo. It i s quite evident that this pyrite i s being replaced or altered to limonite. Another small 'area of residual pyrite was seen that appears quite similar to that seen in Plate 8. Therefore, i t i s thought that this type of. limonite has been derived largely from pyrite. In polished sections, the encrusting layers of limonite are seen to form colloform bands on the outside edges of other limonitic areas. This material appears white, has a very smooth surface, and shows a fibrous radiating structure perpendicular to the banding. It i s isotropic and has a hardness of about S. Aqua regia stains i t light brown, but a l l the other reagents, as used by- Short (11), give a negative etch test. On the inside of the smooth surfaced banded limonite, the limonite has a pitted white surface, i s slightly softer, and i s negative to a l l etch reagents. Under -30- crossed N i c o l s i t shows r e d i n t e r n a l r e f l e c t i o n s , a n l sotropism from l i g h t blue-gray to b l a c k , and appears as i r r e g u l a r .jagged p l a t e s w i t h one cleavage. Thin s e c t i o n s of t h i s m a t e r i a l are l a r g e l y opaque when pure, but most specimens c o n t a i n other minerals. Authigenic a l b i t e was noted i n one of these i n very s m a l l amounts and i n g r a i n s about .1mm. long. Angular t o rounded quartz g r a i n s up to about .1mm. diameter are a l s o present i n some s e c t i o n s . This quartz appears t o be of hydrothermal o r i g i n since some g r a i n s show euhedral shapes. Carbonate i s present i n g r e a t e r q u a n t i t y and t h i s probably represents m a t e r i a l from the o r i g i n a l host rock. A minor amount of phlogopite was a l s o noted i n one t h i n s e c t i o n . The non-opaque l i m o n i t e v a r i e s from brown t o orange t o orange-red t o b r i g h t - r e d , and forms i r r e g u l a r p a t t e r n s i n the opaque l i m o n i t e . Some of these c o l o r s are a f u n c t i o n of the t h i c k n e s s , v a r y i n g from orange near the t h i n edges t o orange-red i n the t h i c k e r p o r t i o n s . A small amount of r e s i d u a l p y r i t e was seen i n c e r t a i n s e c t i o n s , and one area showed d e f i n i t e a l t e r a t i o n from f r e s h p y r i t e t o r e d semi- transparent l i m o n i t e . Other areas of s i m i l a r l i m o n i t e had square o u t l i n e s and were probably d e r i v e d from euhedral p y r i t e cubes. A very minor amount of t i n y g r a i n s of f r e s h galena was seen i n one t h i n s e c t i o n . TYPE 1 A A s l i g h t l y m odified form of t h i s b o t r y o i d a l type was found i n s m a l l q u a n t i t y only, near the surface i n Trench 1-1 where Ve i n No. 2 was exposed. I t i s hard, heavy, and tough, and appears t o be almost pure m e t a l l i c i r o n oxide. F l a t , t h i c k bands i n t e r s e c t each other at angles of about 75°, l e a v i n g spaces or c a v i t i e s which are rounded or f i l l e t e d at t h e i r corners. C o l l o f o r m •banding and b o t r y o i d a l s t r u c t u r e i s q u i t e apparent. (See P l a t e s 13 A, and 13 3.) The b o t r y o i d a l surfaces are not smooth and shiny as i n the main type, but are rough, and d u l l brownish-black. No r e s i d u a l sulphides were found i n t h i s m a t e r i a l , and as i t appears t o be of minor importance, l i t t l e study was g i v e n t o i t . -32- TYPE NO. 2 REDDISH-BROITN HARD LIMONITE This i s a. dull, dark reddish-brown, hard and heavy- massive material, which contains numerous irregular cavities, some of which are f i l l e d or partly coated with soft powdery material. (See plate 11 C.) Most of the cavities are smaller than those shown in the photograph. The powdery material i s principally yellow, but some is a very definite brick red. This latter powdery material forms a thin dull coating on parts of the surface. Many of the cavities that are f i l l e d with the yellow material show a fragile boxwork structure formed of very fine narrow walled partitions. Some of the smaller unfilled cavities have a few thick walled partitions formed of the main hard material, and these appear to be pseudo or r e l i c t boxworks. The brick red powder i s generally lacking in boxworks. This material Is also restricted to surface occurrences and was found mainly on Hope H i l l . (See Map #1). • It has a dark brown streak and. a hardness of about 4^- to 5. The average of four specific gravity tests was 3.71, hut these varied from 3.65 to 3.77 probably as a result of impurities of the yellow.powdery limonite. In polished sections, white, smooth surfaced, metallic limonite may form most of the f i e l d , or may occur as irregular areas or tiny veinlets in a background of -33- • light gray limonite. (See Plate 14, & 14 A). This latter material appears non-metallic, and gives orange to red internal reflections under crossed ITicols. This is the yellow powdery material mentioned above as f i l l i n g some of the cavities. The fragile boxwork structures were found to be formed by very narrow veinlets of the white metallic limonite, but do not seem to have any definite pattern. A small amount of pyrite was also detected, none of which could be noted in hand specimens. Thin sections contain only a very minor amount of carbonate, and no quartz. Semi-transparent orange-colored veinlets form indefinite boxwork patterns in the black opaque to reddish semi-opaque metallic limonite. (See Plates 15, and 16.) The red limonite appears similar to that noted as forming after pyrite In a thin section of Type 1 limonite, and many of these red areas again show square outlines. One fresh pyrite cube was seen in one section, and a minor amount in other sections. It appears that Type 2 limonite has also been largely of pyrite derivation. -34- TYPE NO. 3 YELLOW BROWN SOFT LIMONITE This i s a soft, rusty or light yellowish-brown material, with a smooth or velvety f e e l . Usually i t does not form large masses alone, but i s often associated with one of the previous types. When scratched with a knife this fine powdery material i s readily grooved. In two l o c a l i t i e s , hard limonite containing this powdery material also has a small amount of malachite as an encrusting coating, and also disseminated in tiny areas throughout the limonite. Malachite was proven by i t s green color, adamantine luster, hardness of about 3.5, encrusting form with botryoidal surface and divergent fibrous rosettes, and also by chemical and blowpipe tests that proved the presence of copper, carbon*dioxide and water. This limonite type, when pure, seems to occur in small •oieces only and boxwork structure appears to be lacking in these hand specimens. However, when associated with Type No. 2 hard limonite, a very fine-walled cellular boxwork of this powdery material may be preserved. In polished sections this material does not present a smooth f l a t surface under the microscope, but shows a cellular boxwork of grayish-white metallic-appearing' veinlets surrounding small irregular polygonal ce l l s that may'he empty or f i l l e d with a non-metallic powdery -35- limonite. (See Plates 17 and 18.) Some of these polygonal cells have double wails.(See Plate 19.) The metallic veinlets are not the same hard limonite previously described, but have a hardness of about C . The whole f i e l d as seen in the microscope has an orange to dark red internal reflection under crossed Hicols. A considerable quantity of malachite i s present in one polished section, and i t s fibrous re.diating structure i s readily seen. (See Plate 18.) The xhin section of the limonite containing malachite shows the typical cellular pattern (Plate 20) of this type. Most or the cel l s are empty, but some contain powdery limonite and others contain malachite. -36- TYP5 TO. 4 POROUS iSROW CRUMBLY LIlQNITE " This i s a d u l l , dark brov/n, porous, l i g h t - w e i g h t l i m o n i t e t h a t has a f r o t h y appearance due t o i t s l i n e c e l l u l a r boxwork s t r u c t u r e . (See P l a t e 11B.) On surfaces exposed t o weathering the d e t a i l of the boxworks i s not u s u a l l y w e l l preserved, but i t may r e a d i l y be observed by breaking the specimen. The f u l l d e t a i l of t h i s boxwork however, i s best obtained by sawing or rough g r i n d i n g to a f l a t s u r f a c e , and examining w i t h a hand lens or 20 power b i n o c u l a r s . (See P l a t e s 21, end 22.) Small areas of shiny b l a c k b o t r y o i d a l surfaces ( s i m i l a r to those described i n Type No. 1) may be seen o c c a s i o n a l l y i n more or l e s s p r o t e c t e d hollows or c a v i t i e s . l e a t h e r e d surfaces are somewhat darker brown, while f r e s h surfaces show numerous brownish y e l l o w and o c c a s i o n a l b r i c k r ed areas of s o f t powdery l i m o n i t e ( s i m i l a r t o t h a t d e s c r i b e d i n Type No. 3) which f i l l some of the boxwork c e l l s . I n t h i s case, however, n e i t h e r of these powdery l i m o n i t e s form c e l l w a l l s or show any boxwork s t r u c t u r e i n themselves. This m a t e r i a l contains appreciable percentages of quartz, some as i r r e g u l a r g r a i n s , but most of i t i n slender, well-formed, euhedral, doubly-terminated c r y s t a l s up t o \ i n . long. Occurrences of t h i s type were not r e s t r i c t e d e n t i r e l y to the s u r f a c e , but were found down t o depths of about one -37- f o o t , on the northwest side of Hope H i l l . ' P o l i s h e d s e c t i o n s r e v e a l a f a i r l y d e f i n i t e c e l l u l a r p a t t e r n formed by white, m e t a l l i c l i m o n i t e v e i n l e t s . The p a t t e r n c o n s i s t s of one strong set of f a i r l y l o ng, s t r a i g h t , p a r a l l e l c e l l w a l l s , w i t h one or more other minor sets a t 90° or about 45° to the f i r s t . Many of the i n d i v i d u a l v e i n l e t s are seen t o c o n s i s t of two narrow l i m o n i t i c w a l l s separated by a space about twice t h e i r t h i c k n e s s which r e s u l t s i n a "double-walled" c e l l p a r t i t i o n . ( P l a t e 23.) ITo p y r i t e was found i n t h i s type, although a l l the l i m o n i t e i s the hard, white, m e t a l l i c v a r i e t y . I n t h i n s e c t i o n s , the l i m o n i t e v a r i e s from l i g h t to dark brown opaque and orange red. A small amount of carbonate was noted, and one t h i n s e c t i o n contains a small amount of a l b i t e which i s s l i g h t l y s e r i c i t i z e d . This same s e c t i o n contained only very minor quartz i n t i n y g r a i n s , but another t h i n s e c t i o n , t h a t was cut from the specimen a. shown i n P l a t e 21, c o n t a i n s A c o n s i d e r a b l e q u a n t i t y of coarse grained v e i n quartz w i t h some euhedral c r y s t a l s up t o 2 mm. long. The boxwork i n t h i s s e c t i o n c o n s i s t s predominately 0 f l i m o n i t e v e i n l e t s forming f a i r l y s t r a i g h t w a l l s i n c l o s i n g square, r e c t a n g u l a r , and polygonal c e l l s . T h i s boxwork resembles somewhat the galena "cleavage boxwork" described by Blanchard and Bo s w e l l , ( 8 , p.675.) However, i n t h i s t h i n s e c t i o n , there i s considerable evidence of the l i m o n i t e growing and e a t i n g i t s way along the quartz -38- grain boundaries. (See Plates 24 and 2 4 A . ) Some hexagonal quartz grains ere more or less rimmed with narrow limonite veinlets. The straight walls of some euhedral quartz crystals show a f a i r l y uniform depth of penetration (or replacement) by limonite, but i t i s more lik e l y that the limonite has replaced galena that had previously partially replaced and veined the quartz. - 3 9 - TYPS NO, 5 POROUS ORANGE-YELLOW LIMONITE This i s a light orange-yellow to light brown colored 'limonite with a fine porous structure and a somewhat sandy appearing surface when examined with a hand lens or binoculars. Residual galena i s present but most has been oxidized. The boxwork structure i s somewhat masked by numerous •tiny -grains of limonite and carbonate coating the c e l l walls, and i t i s this that gives the sandy appearance. (Plate 25). As in type No. 4, the structure of the boxwork is best demonstrated by cutting or grinding to a f l a t surface, though i t may be detected on a freshly broken surface in small isolated areas. Individual cells are quite small (less than 1mm.) and are cubical, rectangular, and triangular in shape. C e l l walls are invariably straight, and show practically no f i l l e t i n g or enlarging at their lines of intersection, thereby forming sharply defined corners. Most of these partitions are quite thin, and appear fragile; but large, stronger,'and more continuous partitions take the place of fragile partitions about every third or fourth c e l l . Flat surfaces show thick (.5mm. to 2mm.) intersecting veinlets, quite widely spaced (5mm. or more), forming a more or less rectangular to triangular major pattern. These veinlets proved to be cerussite. The fine cellular pattern could readily be formed by the incipient alteration of galena proceeding along i t s -40- cleavage planes. The commencement of such an a l t e r a t i o n vras noted i n a p o l i s h e d s e c t i o n of f r e s h galena from V e i n I7o. 1, i n which a n g l e s i t e .veinlets f o l l o w the c r y s t a l boundaries and cleavage planes of galena. I n t h i s Type 5 m a t e r i a l , nowever, the v e i n l e t s are c e r u s s i t e , and no a n g l e s i t e was found. This m a t e r i a l occurred as one l a r g e p i e c e ana numerous smaller p i e c e s i n one l o c a l i t y only, at p o i n t X on the west side of Guy H i l l . I t was not a s s o c l a t e a w i t h any other type, and there was no F r a c t u r e d F a i t h limestone (the " i n d i c a t o r " ) nearby. A s m a l l amount of d i g g i n g proved t h a t t h i s m a t e r i a l had been t r a n s p o r t e d , and had probably been r o l l e d or moved down the slope from i t s o r i g i n a l p l a c e of formation, and then subjected t o f u r t h e r weathering under d i f f e r e n t environ mental c o n d i t i o n s . P o l i s h e d s e c t i o n s of 'this type show very l i t t l e m e t a l l i c l i m o n i t e , and hence no boxwork p a t t e r n . The l i m o n i t e i s predominantly the n o n - m e t a l l i c powdery m a t e r i a l t h a t g i v e s a reddish-brown i n t e r n a l r e f l e c t i o n under crossed N i c o l s . A small amount of f r e s h galena i s surrounded by an a l t e r a t i o n product, which e f f e r v e s c e s w i t h n i t r i c a c i d , and was proven i n t h i n s e c t i o n t o be c e r u s s i t e . A small amount of fresh, p y r i t e remains i n centers of s m a l l areas of m e t a l l i c l i m o n i t e . I n t h i n s e c t i o n s , the boxwork i n t h i s case i s seen -41- to be formed by semirtransparent, non-metallic, orsnge to brownish-stained carbonate which i s probably mainly calcite or dolomite. There i s a definite lack of metallic limonite- in the c e l l walls. Pine grained euhedral to anhedral pyrite i s disseminated throughout the sections, and i t s partial oxidation accounts for the staining of the carbonate. Large areas of galena have been more or less altered to, and are contained in, a transparent mineral determined to be cerussite. The cerussite i s mainly white to gray, but some is lavender colored. It has an extremely high birefringence and index of refraction, and under high power the surface has a very crinkled appearance and shows considerable change of r e l i e f as the stage i s rotated. It i s uniaxial negative •to biaxial negative with 2 V less than 10°. The ortho- rhombic crystal form was detected by crushing some of the material and observing i t under the binoculars. These crystals effervesced with n i t r i c acid, but they are ©o small that a positive blowpipe test for lead could not be relied upon as i t was d i f f i c u l t to ensure that a pure sample had been used. The fact that most of the original carbonate of the limestone has been stained by the oxidation of the pyrite, while the cerussite i s clear, may he due to the earlier and easier oxidation of pyrite preceding the alteration of galena to cerussite. This agrees with the well known -42- comparative rates of oxidation of various metallic minerals. An argument against this explanation becomes obvious when one considers the electro-potential series of sulphides as determined by Gottschalk and Buehler (12). They found that when two sulphides such as pyrite and galena were in . mutual contact, a small electric current was set up that flowed from the high potential pyrite to the lower potential galena. This accelerates oxidation of galena and retards oxidation of pyrite. Under perfect conditions, galena sould be completely oxidized before pyrite. What usually happens, of course, i s that the early oxidation forms a layer of anglesite or cerussite around the galena, thus nullifying the action of the electric c e l l , and oxidation of each mineral then proceeds more or less individually. In this case i t may be that cerussite was less susceptible to replacement or staining by iron oxides than was the original carbonate of the limestone. Albite was not detected in these thin sections. Only an occasional tiny grain of quartz i s present, but whether this i s clasic or hypogene i s not known. A colorless mineral, that occurs in very small tabular plates, and radiating rosettes or stellated masses has been determined as barite. Its most distinguishing feature as seen under crossed ITico-ls in the aggregated crystals i s the dark cross caused by their radial uniformity of orientation. IT has perfect cleavage in one direction, and appears to have two other cleavages intersecting at about 78°. Other optical properties are: n -1.63; 2Vs40°; positive; length-slow; axial plane perpendicular to the length of the crystals ( i . e . perpendicular to the best cleavage.) An Estimation of the birefringence i s rendered inaccurate by the d i f f i c u l t y in determining the correct thickness of these thin sections. A positive barium flame test could not be obtained from the crushed limonite, possibly because the barite i s present in such small amounts and i s too small to be recognized in the hand specimen. Barite has not been found in any of the ho.st dolomite, and i t i s considered that the barite in this limonite was introduced by the hydrothermal solutions along1 with the metallic sulphides. It i s not closely a l l i e d with the large areas of galena and cerussite,. but occurs in small scattered areas in the iron-stained carbonate. -44- TYPE 170, 6 MIXED CAVERNOUS LEJOIflTE This material has a very dull bluish-black surface with large areas of yellow brown soft limonite (Type No. 3). The latter, combined with relatively large depressions or surface cavities, gives this type a rather coarse appearance. Locally, botryoidal surfaces are developed in the cavities. The a u l l bluish-black surface i s merely a soft, weathered coating above a hard metallic limonite. In some of the softer material, cubical to rectangular cells form a coarse boxwork pattern. (Plate 26.) Fresh galena i s present in some of the specimens in f a i r l y large areas rather than as scattered grains.. This limonite was found about 2 feet to 3 feet below the surface in Trench 1-1, where Vein No. 2 of massive galena was exposed. The surface limonite float here was mainly Type No. 1, blue-black botryoidal limonite, in which only an occasional grain of fresh galena could be found. Type No. 6 appears to be a gradation between Type No. 1, ana f a i r l y fresh, but part i a l l y oxidized galena. The.cubical to rectangular boxwork (Plate 26) was not seen in the hand specimens to grade into galena, but i t s form and proximity to galena strongly suggest such an origin* It appears to be quite similar to the "cleavage boxwork" of galena derivation aescribed by Blanchard and Boswell (S, p. 675.) However, the cel l s are larger, with -45- the distance between parallel plates up to Q mm. In polished sections, the c e l l walls were found to be formed of metallic limonite. They ?.re straight and parallel over small areas, end are crossed obliquely or at right angles by other partitions. (Plate 27.) Double c e l l walls are not uncommon. The boxwork pattern occurs in a back ground of non-metallic powdery limonite, that gives a dull reddish-brown internal reflection under crossed Nicols. In the large areas of massive metallic limonite, no boxwork- structure i s present. The residual galena i s surrounded with anglesite that grades outward to non-metallic and then to metallic limonite. The typical boxwork (Plate 27) was not seen to grade into the anglesite or galena, although possibly this could be found by further polished section study. The pattern formed in pa r t i a l l y weathered galena by the replacing anglesite appears quite similar to the limonitic boxwork seen in Plate 27. The limonitic c e l l walls are obviously occupying the former position of anglesite noted previously as having formed along the cubic cleavage planes of galena during the latter's incipient alteration. (See p. 40.) Thin sections show the four distinct colors of limonite; orange, brown, red, and opaque black. The f i r s t three are semi-transparent, and the f i r s t two are non--46- metallic as seen under oblique illumination. Each of the f i r s t three colors may occupy large separate areas or may form a network of tiny veinlets through the black opaque ' metallic limonite. This network also suggests the "cleavage boxwork" pattern of galena, (Plate 28.) However, in the polished section, the boxwork pattern i s formed by a metallic limonite network (Plate 27), whereas, in thin section the network i s due to semi-transparent, non-metallic orange colored veinlets in the black metallic opaque limonite. This apparent discrepancy could be explained by proving: (1) that the portions showing the boxwork in thin sections were equivalent to the massive metallic limonite areas in the polished sections where no boxwork pattern i s evident, and (2) that the portions showing the metallic limonite boxwork in polished sections were too delicate to preserye in thin sections since their background consists of non-metallic powdery limonite. Accordingly, an attempt was made to prepare thinned polished sections but the technique was not successfully mastered in time for this work. One area of fresh residual pyrite i s partially altered to red metallic limonite in the same manner as shown in Plate 9 and numerous rectangular areas of similar red limonite suggest the former presence of pyrite. The f i e l d relations, and the abundance of residual galena l e f t l i t t l e doubt as to the origin of this type of limonite, but i t was studied as a guide to the meaning of microscopic and physical features of other types. -47- LIMONITE TABLE This t a b l e summarizes the important f e a t u r e s of s i x types of l i m o n i t e . Typs No. Name & D e s c r i p t i o n Occurrence Structure ,'Iaicjrfl^c.Qpic) A s s o c i a t e d M i n e r a l s the Probable Source 1. Blue-Black B o t r y o i d a l D u l l , c l i n k e r y . Surface Widespread I n d e f i n i t e C o l l o f o r m banding. P y r i t e . Carbonate Authigenic a l b i t e . Hypogene quartz. Minor galena P y r i t e & Galena 2JReddish-Brown Hard D u l l , massive; s m a l l c a v i t i e s . Surface. Hope H i l l Massive. C i r c u l a r to p o l y g o n a l c e l l s .  P y r i t e . Carbonate. P y r i t e . 3. Yellow-brown S o f t Widespread i n other types. Polygonal c e l l s . Double w a l l s are c ommon. Mala c h i t e P y r i t e & Chalco p y r i t e ? 4. Porous Brown Crumbly C e l l u l a r Boxwork; l i g h t - w e i g h t ; f r o t h y . Down t o 1. f o o t on Hope H i l l 'Cleavage Boxwork" Coarse Vein quartz c r y s t a l s . Carbonate. Authigenic a l b i t e . Galena w i t h a u a r t z . 5. Porous Orange- Yell o w . Boxwork masked by sandy appearance. West side Guy H i l l on surface N i l , because of l a c k of m e t a l l i c l i m o n i t e . Galena. C e r u s s i t e . Carbonate. B a r i t e . Minor p y r i t e & Hypogene? quartz. Galena & P y r i t e 6. Mixed Cavernous. D u l l , b l a c k & brown; coarse boxwork. 2-3 f e e t below surfac e i n v e i n . "Cleavage^ boxwork." Double - w a l l s . Galena. A n g e l s i t e , T y r i t e . Galena & P y r i t e . V -48- CONCLUSIONS Before s t a r t i n g these i n v e s t i g a t i o n s , the w r i t e r perused the l i t e r a t u r e , i n c l u d i n g the references l i s t e d i n the b i b l i o g r a p h y , and e s p e c i a l l y those papers by Boswell and Blanchard (3 to 8) who have emphasized the p h y s i c a l c h a r a c t e r i s t i c s t h a t d i s t i n g u i s h l i m o n i t e types d e r i v e d from s p e c i f i c s u l p h i d e s . A f t e r studying each l i m o n i t e type and forming an o p i n i o n as to i t s source, the author r e f e r r e d back to the works l i s t e d i n the b i b l i o g r a p h y to p i c k out the most important f e a t u r e s of c o r r o b o r a t i o n or disagreement. DERIVATION OF SPECIFIC LIMONITE TYPES Type No 1, b l u e - b l a c k b o t r y o i d a l l i m o n i t e , which the author has a t t r i b u t e d t o p y r i t e and galena, appears t© be q u i t e s i m i l a r t o the " B o t r y o i d a l l i m o n i t e c r u s t s d e r i v e d from massive p y r i t e i n limestone gangue" i l l u s t r a t e d and described by B o s w e l l and Blanchard ( 5 , p. 373). They s t a t e : "The a c i d s o l u t i o n s from the o x i d i z i n g p y r i t e were so strong t h a t they over- 'whelmed the n e u t r a l i z i n g power of the limestone." In Trench 1-1, t h i s l i m o n i t e was found on the surface and contained only very o c c a s i o n a l specks of r e s i d u a l galena. Type No. 6 l i m o n i t e c o n t a i n i n g abundant galena was found 2-3 f e e t below the s u r f a c e , immediately -49- above o x i d i z i n g massive galena. I n t h i s case at l e a s t , i t appears t h a t as o x i d a t i o n proceeds the c h a r a c t e r i s t i c cleavage boxwork of galena (as seen' i n Type 6, P l a t e 26) i s l o s t , and Type ITo.'l l i m o n i t e i s formed. Therefore, i t i s q u i t e l i k e l y t h a t t h i s l i m o n i t e developed i t s f i n a l c h a r a c t e r i s t i c s from the minor r e s i d u a l p y r i t e noted, but t h a t galena may a l s o have been present o r i g i n a l l y . The s i m i l a r i t y between Type No.s 4,5,6, and the "cleavage boxwork" of galena d e r i v a t i o n has been mentioned p r e v i o u s l y . Type ITo. 5 may be a combination of "cleavage boxwork" l a r g e l y masked b y " p a r t i a l l y s i n t e r e d l i m o n i t e c r u s t s " of c e r u s s i t e d e r i v a t i o n . (8, p. 678.) The r o l e of f e r r i c sulphate i n the o x i d a t i o n of m e t a l l i c s u l p h i d e s , and the r a p i d n e u t r a l i z i n g a c t i o n of limestone or dolomite on sulphate s o l u t i o n s , are too w e l l known to be d e a l t w i t h here. Boswell and Blanchard (4, p. 424, 438-9) found t h a t the s i g n i f i c a n t types of o x i d a t i o n products of s p h a l e r i t e and galena were be s t developed i n environments of moderately slow n e u t r a l i z e r s , such as f e l d s p a t h i c rock. I n environments of r a p i d n e u t r a l i z e r s , the d i s t i n g u i s h i n g c h a r a c t e r i s t i c s are o f t e n p a r t i a l l y masked by a f i n e , f l u f f y type of p u l v e r u l e n t l i m o n i t e . They consider t h a t the only reason f o r any p r e s e r v a t i o n whatsoever of s i g n i f i c a n t types i n limestone l i e s i n the f a c t t h a t galena and s p h a l e r i t e u s u a l l y occur i n massive form, and t h a t the e f f e c t s of the CaC0 3 do not -50- r e a d i l y penetrate to the centers of large nodules of the sulphides. On the Star Group, the occurrence of massive galena i n dolomite, and Type no. 3 sof t , powdery limonite p a r t i a l l y obscuring the c h a r a c t e r i s t i c cleavage boxwork, agrees with the findings stated above. MATERIAL FORiu'llJG THE BOXWORKS The i l l u s t r a t i o n s by Boswell and Blanchard are hand specimen photographs, or s l i g h t l y magnified sketches of boxwork patterns as seen with a hand lens or binoculars. L i t t l e mention i s made of microscopic investigations of polished or t h i n sections, except when explaining boxwork structure and i t s r i g i d i t y , suchas t h e i r description of the "Coarse C e l l u l a r Boxwork" of sphalerite 1 derivation (4, p. 434.) Here they state that microscopic observations prove that p a r a l l e l quartz v e i n l e t s forming the boxwork i n the oxidized products are si m i l a r to quartz- v e i n l e t s i n the fresh sulphide, and that t h i s quartz i s c l e a r l y hypogene. " I t was further observed that as oxidation of the sulphide mass proceeds, the v e i n l e t s gradually advance t h e i r front and "eat" t h e i r way into the less coarsely fractured portions of the sulphide mass.... These extensions of the white to glassy v e i n l e t s consist, not of pure s i l i c a , but of l i m o n i t i c jasper, - and are c l e a r l y supergene." In a l a t e r paper (6, p. 793-4) i t i s stated that the SiOg content of some of the supergene limonite boxworks i s as high as 55%, but that those derived from galena and bornite -51- are generally low in s i l i c a . They found that the s i l i c a content of the boxwork varies also with-the type of gangue (the most siliceous was derived from oxidation of pyrite in limestone), the d i s t r i c t concerned, and physico- chemical laws. They consider that circulating ground waters, containing s i l i c a in solution or in colloidal form, may i n f i l t r a t e along fractures in the fresh sulphide, and thus provide a source of limonitic jasper even when no vein quartz or sil i c a t e minerals were originally present. The c e l l walls of the limonite boxworks from the Star Group contain ho quartz or limonitic jasper, but consist of undetermined metallic iron oxides. The difference between these findings and those of Boswell and Blanchard may be explained by: (a) the general lack of quartz in the veins and the limonite (except in Type No.. 4), (b) the improbability of circulating ground waters containing silica, reaching the present relatively high elevations at which the veins and limonite are found. It i s conceivable that during some earlier geological period the topographic and other conditions may have existed that allowed s i l i c a - bearing ground waters to i n f i l t r a t e the sulphides and- produce limonitic jasper boxworks. However, these would have been destroyed by erosion long before now. If The boxwork in Type 6 limonite contained limonitic jasper in the c e l l walls, i t i s not li k e l y that this structure would be destroyed in i t s alteration to Type 1 -52- l i m o n i t e . (See p. 4??.) Type No.- 4 l i m o n i t e contains considerable hypogene quartz. Nevertheless, the c e l l w a l l s oi' the boxwork s t r u c t u r e (which appears q u i t e s i m i l a r t o the "cleavage boxwork" of galena d e r i v a t i o n ) c o n s i s t of m e t a l l i c i r o n oxide, and not s i l i c a . At l e a s t some of the s t r u c t u r e was- found i n t h i n s e c t i o n s to be patterned a f t e r the shapes of the euhedral quartz c r y s t a l s . However, i t i s considered t h a t most of the boxwork i n t h i s type i s patterned a f t e r the cubic cleavage planes of galena. SOURCE OF IRON During the e a r l y p a r t o f the e x p l o r a t i o n of the S t a r Group, the author was not sure of the o r i g i n of the i r o n i n the l i m o n i t e f l o a t . I t became apparent t h a t the l i m o n i t e had formed very c l o s e t o where i t ' was found (See p.3), and t h i s was corroborated by the di s c o v e r y of the mi n e r a l d e p o s i t s . However, the p o s s i b i l i t y s t i l l e x i s t e d t h a t the i r o n had been introduced i n s o l u t i o n i n c i r c u l a t i n g ground waters and had been p r e c i p i t a t e d as l i m o n i t e by the n e u t r a l i z i n g a c t i o n of the limestone. The only p y r i t e found i n the f i e l d was i n the area of disseminated m i n e r a l i z a t i o n , and there was l i t t l e evidence of i t s a l t e r a t i o n to l i m o n i t e . The-minor s p h a l e r i t e i n the same l o c a l i t y suggested another p o s s i b l e source of i r o n , but i t again was q u i t e f r e s h . M i c r o s c o p i c study of p o l i s h e d and -53- thin sections has revealed residual- pyrite in many of the limonites, and the author now considers that a l l the iron in the numerous areas of limonite float was derived locally from pyrite or other primary iron-bearing sulphides. SECONDARY LEAD MINERALS Most authors seem to agree that galena, when subjected to weathering processes, usually alters to anglesite or cerussite, both of which are quite insoluble in aqueous solutions. Anderson (1, p. 531) states that anglesite always forms f i r s t and that sny cerussite that may be present is due to replacement of the sulphate and not the sulphide. Boswell end Blanchard, while favoring the formation of limonite by the reaction of fer r i c sulphate on cerussite, suggest (4, p. 445) that cerussite i s formed from anglesite, although they also state (4, p. 443) that ".... sphalerite or galena.... may oxidize to the sulphate or carbonate state by ordinary air-water oxidation processes," The author considers that thin sections of Type No, 5 limonite prove that cerussite may form directly from galena (See p.41), and suggests the following as a possible reaction: PbS E 20 + C0 2 -> PbC03+H23 It was noted (See p. 40) that this limonite had been weathered in an environment remote from i t s place of formation. The oxidizing solutions here probably carried more COp and less sulphate than those in the mineral deposits. -54- SOLUBILITY OF LIEIONITS IN HC1 Bateman(2, p. 251) states that limonite derived from iron-hearing sulphides i s readily soluble in dilute HCl, while that derived from iron-bearing gangue or rock silicates i s not. He makes no attempt to substantiate this statement, but i t probably originated with Morse & Locke (10, p. 25°), who state: "the sulphide iron, having gone to limonite, may be approximated as that easily soluble in dilute HCl", and further (p. 258): "that the capping iron soluble in five minutes in 3 or 4% HCl was in fact approximately the same as the sulphide iron content of what we regarded as typical ore vertically below the capping." Boswell and Blanchard (3, p. 617) state: "as the chalcopyrite approaches purity, the iron of the indigenous limonite, though variable, approaches one-quarter to one-third that of the sulphide, the rest being removed." A discrepancy i s apparent in the above findings. Solubility tests were made on some of the limonites from the Star Group, in an attempt to substantiate' the former authors. In a l l cases i t was found that the acid required heating to dissolve even the powdered material. The table following shows some of the results. -55- Type ¥.0. Q u a l i t y Condition Solution Solubility 1. 50 mg. 50 mg. 50 mg. 50 mg. 30 mg. Solid Solid Powdered Powdered Solid Cold 1:1 HCl Hot 1:1 HCl Cold 1:1 HCl Hot 1:1 HCl • 6cc. Hot 1:5HC1 Slight D i f f i c u l t 15 mins. Slight D i f f i c u l t 10 mins. D i f f i c u l t . Xot 2. 20 mg. Powdered 2 c.c Cold 1:1 HCl Very l i t t l e . 20 mg. powdered 2 c.c Hot 1:1 HCl Most in 5 mins. 3. 20 mg. Powdered Cold 1:1 HCl Some solution. 20 mg. Powdered Hot 1:1 HCl Rapid solution. 30 mg. Powdered 6 c.c Hot 1:5 HCl Most in 5 mins. A l l these limonites -were probably derived from sulphides, and i t i s considered that their differences in solubility are related to the type and relative amounts of metallic limonite in each. In,any event, i t i s inconceivable that a gossan containing up to 55% SiOg in-the boxworks (See p. 50) would be readily soluble in dilute HCl. PLATE 1• A t y p i c a l specimen of surface l i m o n i t e f l o a t from the S t a r Group. X 1 . Color v a r i e s from reddish-brown to h l a c k . FLATE 2 . p a r t i a l l y weathered galena a s s o c i a t e d w i t h a l i m o n i t e boxworks s t r u c t u r e . X 84. The "boxwork grades i n t o galena (g) at the bottom of t h i s photo. -57- PLATE 4. P o l i s h e d surface of " B r e c c i a t e d F a i t h Limestone" t h a t occurs near areas of surface l i m o n i t e f l o a t and near pure c a l c i t e v e i n s . X 2. -58- PLATS 5. Photomicrograph of p o l i s h e d s e c t i o n showing unknown mineral ( s i l v e r sulpho-sa.lt? 3) i n galena ( g ) . This i s the maximum '-rain s i z e i n which t h i s mineral was found. X 570. -59--60- Photomicrograph of o o l i s h e d s e c t i o n showing almost comp a l t e r a t i o n of disseminated p y r i t e (P) to gray m e t a l l i c l i m o n i t e ( L ) , i n f r e s h rock. X 200. FLATS 9. Photomicrograph of p o l i s h e d s e c t i o n showing i n c i p i e n t a l t e r a t i o n o f * p y r i t e (F) to l i m o n i t e (L) . X 570. -61- PLATS 10. P o l i s h e d surface of wad from Ve i n No. 1, showing i r r e g u l a r masses and v e i n l e t s of a f i n e powdery m e t a l l i c mixture of iron-manganese mi n e r a l s . Ilote: double-walled tendency. X 3 FLATS 11. ( n a t u r a l Size) A - Type 1. Blue-black b o t r y o i d a l l i m o n i t e . B - Type 4. Porous brown crumbly l i m o n i t e . C - T ^ e 2. Reddish-brown hard l i m o n i t e . -62- PLATE 12. photomicrograph of p o l i s h e d s e c t i o n showing i n d e f i n i t e p a t t e r n formed by m e t a l l i c l i m o n i t e v e i n l e t s (L) i n Type 1 l i m o n i t e , of p y r i t e (P) d e r i v a t i o n . X 65. 200/< PLAT^ 13 A. Photomicrograph of p o l i s h e d s e c t i o n showing t y p i c a l c o l l o f o r m handing i n Type 1 and 1 A l i m o n i t e . X S5. Gray i n lower l e f t i s impregnating f l u i d . - 6 3 --64- PLAT3 14. photomicrograph of p o l i s h e d s e c t i o n of Type 2 l i m o n i t e showing i r r e g u l a r areas and v e i n l e t s of m e t a l l i c l i m o n i t e ( L ) i n a background of non- m e t a l l i c powdery l i m o n i t e . X 200 PLATS 14 A Photomicrograph of p o l i s h e d s e c t i o n showing the t y p i c a l c i r c u l a r t o polygonal c e l l u l a r s t r u c t u r e formed by m e t a l l i c v e i n l e t s i n Type 2 l i m o n i t e . X 65. -65- FLL; l T i _ i 15 • Photomicrograph of t h i n s e c t i o n of Type 2 l i m o n i t e , w i t h semi-transparent, n o n - m e t a l l i c , orange c o l o r e d v e i n l e t s forming a boxwork p a t t e r n i n opaque m e t a l l i c l i m o n i t e . Note the double w a l l s . X 50. T3T A TV 1 P. 1 i l ' l l J I C a S i m i l a r to above. X 60. Although type 2 i s considered to have been deri v e d mainly from p y r i t e , l o c a l areas i n some of the t h i n s e c t i o n s e x h i b i t a p a t t e r n as above t h a t resembles the "cleavage boxwork" noted i n Types 4,5, 8c 6. (See P l a t e 23.) White areas are h o l e s , and carbonate. (C). - 6 6 - PLATS IS. S i m i l a r to above. "Tote the mala c h i t e , (lt}g the larg e area shows i t s f i b r o u s r a d i a t i n g s t r u c t u r e . X 65. -67- Fhotomicrograph of p o l i s h e d s e c t i o n showing the double w a l l s of some of the t y p i c a l polygonal boxwork i n Type 3 l i m o n i t e . X 200. Photomicrograph of t h i n s e c t i o n of Type 3 l i m o n i t e showing the t y p i c a l o o l y s o n a l boxwork, and areas of malachite, (LI). X 60." - 6 8 - F l a t surface of Type 4 l i m o n i t e , showing the w e l l developed "cleavage boxwork", p o s s i b l y of galena d e r i v a t i o n . X 4. S i m i l a r to above, but wi t h the boxwork p a r t i a l l y masked by powdery l i m o n i t e . X 4. Photomicrograph of p o l i s h e d s e c t i o n of Type 4 l i m o n i t e . Note the r e g u l a r boxwork p a t t e r n formed by double-walled m e t a l l i c l i m o n i t e v e i n l e t s . Gray i s impregnating f l u i d . X S 5 . PLATS 24. photomicrograph of t h i n s e c t i o n of Type 4 l i m o n i t e . Y ellow t i n t e d areas are quartz, and white areas are hol e s . This apparently shows the galena d e r i v e d "cleavage boxwork" p a t t e r n , but also shows t h a t many of the l i m o n i t e v e i n l e t s (black) are formed around euhedral quartz c r y s t a l s , and along i r r e g u l a r f r a c t u r e s and g r a i n boundaries i n the quartz. X 12. FL^TS 24 A. Photomicrograph o i t h i n s e c t i o n o i a r e l a t i v e l y f r e s h rock showing v e i n quartz (white) surrounded D y sub-opaque l i m o n i t e . X 65. This specimen came from below trench 6-9, ana i s unusual i n th a t i t c o n s i s t s mainly of quartz, w i t h a. small amount of galena. Limonite has apparently formed around the quartz by the o x i a a t i o n of p y r i t e , a minor amount of which was noted i n the t h i n s e c t i o n . The dark area i n top center i s the t y p i c a l sub-opaque red l i m o n i t e t h a t has rep l a c e d a euhedral p y r i t e c r y s t a l . -71- PLATS 25. F l a t surface of Type 5 l i m o n i t e , showing the "cleavage boxwork" almost completely masked by powdery l i m o n i t e c e r u s s i t e g r a i n s , g i v i n g i t a sandy appearance. X 4 . (Note: two t y p i c a l photos r.re included.) PLATS 26. Type 6 l i m o n i t e , showing the "cleavage boxwork" of galena d e r i v a t i o n . The other siue of t h i s specimen contains weathered galena. X 1-2,. -72- PLATE 27. Photomicrograph or p o l i s h e d s e c t i o n of Type 6 l i m o n i t e , showing the "cleavage boxwork" of galena d e r i v a t i o n . The c e l l w a l l s ere m e t a l l i c l i m o n i t e . Note the tendency toward double w a l l s . X 65. TE 23. Photomicrograph or ohin s e c t i o n of Type 6 l i m o n i t e , w i t h semi-transparent, n o n - m e t a l l i c , orange c o l o r e d v e i n l e t s forming a "cleavage boxwork" p a t t e r n i n opaque m e t a l l i c l i m o n i t e . -73- BIBLIOGRAPHY 1. Anderson, A.L. "The I n c i p i e n t A l t e r a t i o n of Galena." -Scon. Geol., V o l . 25, Aug., 1930. 2. Bateman, A.M. "Economic M i n e r a l Deposits." John Wiley & Sons, I n c . , New York, 1942. 3. Roland Blanchard & P . P . B o s w e l l . "Notes on the O x i d a t i o n Products Derived from C h a l c o p y r i t e . " Econ. Geol. V o l . 20, Nov., 1925. 4. P.F. Boswell & Roland Blanchard. "Oxidation Products Derived from S p h a l e r i t e and Galena." Econ. Geol.,. V o l . as, Aug., 1927. - 5. Roland Blanchard & P.F. Bo s w e l l . "Status of Leached Outcrops I n v e s t i g a t i o n . " Eng. & Min. J o u r . , Feb 18 & Mar. 3, 1928.. 6. P.F. Boswell & Roland Blanchard. " C e l l u l a r S t r u c t u r e i n Limonite." Econ. Geol., V o l . 24, D e c , 1929.. 7. Rolend Blanchard & P.F. B o s w e l l . J "Limonite Types Derived from B o r n i t e and Tetfia h e d r i t e . " Econ. Geol., V o l . 25, Sept.- Oct., 1930. 8. R. Blanchard & P.F. B o s w e l l . " A d d i t i o n a l Limonite Types of Galena end S p h a l e r i t e D e r i v a t i o n . " Econ. Geol., V o l . 29, Nov., 1934. 9. Lord, C.S. " G e o l o g i c a l Reconnaissance Along the Al a s k a Highway Between Watson Lake and T e s l i n R i v e r , Yukon & B r i t i s h Columbia. G.S.C. Paper 44-25. 1944. 10. H.W. Morse & Augustus Locke. "Recent Progress w i t h Leached Ore Capping" Econ. Geol., V o l . 19. Apr. May, 1924. 11. Short, M.N. "Microscopic Determination of Ore M i n e r a l s . " U.S.G.S. B u l l . 825, 1931. 12. Gottschack, V.H. and Buelher H.A. "Oxidation of Sulphides." Econ. Geol., V o l . 7, 1912. 13. Augustus Locke. "Leached Outcrops as Guides t o Copper Ore" W i l l i a m s & Wilkina,. B a l t i m o r e , M..D, 1926. -74- APPSNDIX PREPARATION OF THIN AND POLISHED SECTIONS Due to the porous sua f r a g i l e nature of some of the specimens, d i f f i c u l t y was encountered i n attempting t o make s a t i s f a c t o r y p e l i s h e a s e c t i o n s , and i t was found almost impossible t o make t h i n s e c t i o n s i n the normal manner, attempts were made t o impregnate the specimens w i t h Canada balsam bei'ore g r i n a i n g ana p o l i s h i n g , but these were not very s u c c e s s f u l . J.A. Donari suggested end t r i e d a method t h a t proved s a t i s f a c t o r y , and t h i s method was used f o r most of the t h i n and p o l i s h e d s e c t i o n s d e s c r i b e d h e r e i n . The specimen should be heated t o about 100° C f o r a few hours t o d r i v e o f f most of the o i l taken up duri n g the sawing o p e r a t i o n . I t i s then completely immersed i n an "impregnating f l u i d " bath and the whole subjected t o a f a i r l y strong vacuum f o r 24 hours. Upon removal, the specimen should be found t o be w e l l coated and impregnated w i t h the now s t i c k y end vis c o u s impregnating f l u i d . I t i s then heated i n an oven at a c o n t r o l l e d temperature of 70° C f o r !?4 hours, f o l l o w e d by a f u r t h e r 24 hours at 100° C. (Note- Donan has since found t h a t one 24 hour p e r i o d of heating a t 100° C i s s a t i s f a c t o r y . ) At xhe ena of t h i s Lime the impregnating f l u i d has become "baked" t o a f a i r l y hard and b r i t t l e mass. The p o l i s h e d or t h i n s e c t i o n may then be f i n i s h e d i n the normal manner. - 75- Th e impregnating f l u i d used was " B a k e l i t e P l a s t i c s " , manufactured by C . I . L . , and commonly r e f e r r e d to as B a k e l i t e V a r n i s h . I t was thinned by adding methyl a l c o h o l , or a 50-50 mixture of methyl a l c o h o l and ether. This reduces the v i s c o s i t y and allows the impregnating f l u i d t o more e a s i l y penetrate the c a v i t i e s , pores and c a p i l l a r y openings. Under the vacuum the v o l a t i l e substances are " b o i l e d o f f 1 1 , l e a v i n g the remaining very v i s c o u s " P l a s t i c " f i l l i n g the spaces. I n these f i r s t few attempts, w h i l e success was achieved, i t was found t h a t some la r g e c a v i t i e s were not wholly f i l l e d , and some smaller ones h a r d l y at a l l . Nevertheless the porous s t r u c t u r e was s t i l l preserved even i n t h i n s e c t i o n s , though of course holes were l e f t . I t seems t h a t the baked p l a s t i c t h a t forms an e n c l o s i n g s h e l l around the whole border as the s e c t i o n i s being ground,, holds i t so r i g i d l y t h a t the s t r u c t u r e i s saved i n s p i t e of the imperfect impregnation. I t may be found t h a t improved impregnation would r e s u l t by u s i n g a low vacuum during the e a r l y p a r t of the immersion p e r i o d . S Y M B O L S G A L E N A V E I N S IN P L A C E , i 1 T R E N C H OR PIT. A R E A S W I T H G O S S A N F L O A T . L I M I T OF T R E E G R O W T H . U n ^ « « y of British ColumMi WESTERN RAN3ES PROSPECTING SYNDICATE V a ~ , C a n a d a S T A R G R S C A L E I" = 5 0 0 V \ \ • " ' L I T T L E V " V / j • ' U - \ - - / ^ ... % OCT. 19 4 6. C A M P A E L E V . 3 6 0 0 ' D.R. DERRY R.C. MACDONALD \ \ 6 4 c V \ y> \V.) r A' . ^ 3 7 ° * > V".' 'ii^ ' G U Y '/-0 H I L L " > < ^ . \ \ yf \ \ 4 \ 3-;/3 3 - / 5 s a 3-14 \ . .:••<• . i ; \ \ •' v > ^ . r « o»3-3,4,5 V < - . . . A \ 0 0 - \ > | • \ N ' " 3-2 / V \ \ U f N/''.\/!Hk"" * 3-7 ' \ v • / IS / s \ / .. / • • • -jy • • • •• 8 — ^ . L E G E N D 14 Q U A R T Z P O R P H Y R Y . G R A N I T E . DEVONIAN OR CARBONIFEROUS. \ Jc L ^ ± ^ V . v l " 3 T\ -\ \ • * - ^ 6 8 ° m - - r ^ .' I •• Gild /XV 6.., I / »o- \ • A \ . " F A I T H H I L L \ %'e-r, 7 C H A R I T Y H I L L C H A R I T Y H I L L L I M E S T O N E , (with foss i l i f erous shale bands . ) C A L G R E Y L I M E S T O N E . S H A L E ( rusty w e a t h e r i n g . ) FA ITH L I M E S T O N E . SH A L E . G R E Y L I M E S T O N E . B A N D E D A R G I L L A C E O U S L I M E S T O N E . e • • • • 4 2 0 0 16 V s.w. r 40' GUY HILL N.E. A X 2 0 ' \ 35C r \J V V y v v v v Vj y S.W. FAITH HILL N.E. V 400C' B 6-3 TRENCH W0 I 350C ' \ s \ HOPE HILL FAITH HILL CHARITY HILL •4CP0 / y y y VERTICAL SECTIONS. S C A L E = 5 0 0 V CASSIAR v \v \sT*0< w /' y ,\\\-'\ BATHOLITH KEY M A P SCALE f= I MILE. YUKON TERRI TORY BRITISH COLUMBIA 

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