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The replacement at the Homestake Mine Swanson, Clarence Otto 1922

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H-o Clarence Otto  Sanson THE REPLACEilEtf T A T TH E HOL E STAKE LEEIT E by Clarence Ot t o Sv/anso n A T h e s i s submi t t e d f o r th e Degre e o f b las ter o f Sc ienc e i n t h e Departmen t of Geology. THE UNIVERSITY OP BRITISH COLUMBIA April, 1922. TABLE O F COITTEUT S Page Location and History 1 ffleneral Geology 2 Description of the Deposit 2 Lower Barite Deposit ................ . ^ Upper Barite Deposit j > Structure and Size of Deposit ....... . 3 Paragenesis of the Minerals 7 Results of Assays and Chemical Analyses ... 9 Petrography of the Barite Lodes and the Schist 1 0 Chemical Experiments 1 2 Origin of the Deposit Association of Minerals 1 6 Evidence of Epigenesis and Seplaeement. 1 8 Origin of the Mineralization 2 2 The Evidence as to the General Origin of Barite 2 4 Acknowledgments •  2 6 Bibliography 2 7 ILLUSTRATIONS Figure 1. Ke y Map. ' Figure 2. Sketc h of Mine. 3 Figure 3. Polishe d surface of Ore. 8 Figure 4. Thi n Section of Schist. " T » »*~ » » I ( 1 ) THE REPLACEiJKfi T A T TH E HOUKSTAX B H U E . Location and History. The Horaestak e min e i s s i t u a t e d i n th e Sinma x cree k va l l ey , abou t thre e mile s fro m Ska-a m Ba y o n Adam s lak e ( f i g . l ) . A t r a i l connect s th e proper t y wit h th e mai n wago n roa d runnin g between Loui e Gree k an d Ska-a m Bay . The f i r s t wor k don e o n t h i s min e wa s i n 1893- 4 whe n 20 ton s o f f a i r l y high-grad e ore , runnin g 79. 2 oz . pe r to n i n s i l v e r , wer e shippe d t o th e Brnelte r a t Evere t t , Wash . Short l y afterwards MoEvo y sa w th e p r o p e r t y . ( i ) A t th e tim e o f h i s v i s i t the openin g fro m whic h th e or e ha d bee n take n wa s f i l l e d wit h caved m a t e r i a l , bu t h e s t a t e s t h a t th e excavatio n wa s o n a n i r r e g u l a r ve in . H e a ls o mention s a  "bedde d roc k highl y impreg -nated wit h b a r i t e an d galena" . Thi s statemen t n o doub t r e f e r s to th e lowe r b a r i t e replacement , whic h ha s bee n develope d sinc e then a s th e mai n or e body . The r e s iden t engineer s r epor t fo r 191 7 ( i i ) descr ibe s the undergroun d working s a s the y e x i s t today . Jus t befor e h i s examination th e L a Ros e Minin g Co . o f Cobal t becam e in t e r e s t e d in th e mine , an d ca r r i e d o n considerabl e development . Bu t th e S i lve r value s foun d wer e apparent l y low , an d th e compan y di d no t take u p th e proper ty . Sinc e the n n o fur the r wor k ha s bee n done . ( i ) Annua l Repor t o f th e Geologica l Surve y o f Canada , I894 , P. 21A . ( i i ) Annua l Repor t o f th e . i i n i s t e r o f Iiine s fo r B r i t i s h Columbia, 191? . (2) General geology. The formation in which the mine oectirs consists of metamorphosed sediments in the form of quartzites, schists and slates, called hj  Dal y the Bastion schists .("'0 The type section of this formation is found near Salmon Arm, and the correlation with the Adams lake exposures is solely on the oasis of litho-logical characteristics* Th e Bastion formation has been traced west to the Horth Thompson river by \%,Ii,  TTglow.Civ-) Description of the Deposit. The Homestake mine is situated on the north side of the Sinmax ersek valley, roughly 800 feet above the road. Th e principal outcrops are found on the western face of a rock gully, which has been cut by a stream passing ;Just below the mouth of the main tunnel. Th e rocks dip into the mountain and strike parallel with the general attitude of the hillside. Tw o main deposits of barite are found in the formation and have the appearance of conformable stratified beds. Thi s resemblance is due to the presence of bands of white and grey barite which are parallel to the general rock structure. Th e ore outcrops are brown due to a superficial stain of limonite, but this alter-ation does not extend into the barite, and specimens from the surface contain unaltered pyrite. The country rock has a general strike of I 6o°W and dips from 25-40 HE. I t consists mostly of a sericitic schist (»0 Geological Survey of Canada, Lfemoir 68, P.19. (iv) Summary Report, G.S.G.. 1921, Part A. ~JWJW* I. - ^ \ \ \ >^ '*« > r .  . . -  - i >  '  "  ' ' i - . - K r r ' o w Sketch °5 Underc} >-o  on ,+ +  fc« . 5 ' , 5 « r i t i t i c Qu a 0 « n e t t i c O r 3 3 , Scfvi f Mrif A <^« . L (3) containing considerable pyrite. O n weathering it becomes redd-ish yellow in color and breaks into thin plates. Ther e are also several talc partings present in the schist. I n the form of small lenses, or in irregular masses associated with pyrite and quartz, barite occurs throughout the schist from a short dist-ance below to a little above the main ore bodies. Hea r the mine the mountain side is composed of rocky cliffs or slaty talus material, and is only slightly covered by trees or other vegetation. Lower Barite Deposit. The lower barite deposit contains the metallic minerals pyrite, sphalerite, galena, tetrahedrite and chaleopy-rite. Practicall y all the development done occurs in this body (fig.2). Th e outcrop is about eight feet in width and can be followed on the surface for a distance of eighty feet. T o the west it disappears under surface drift, and the eastern end is buried by creek detritus. Acros s the stream, about $0  feet from the last exposure, the deposit was not found. Howeve r the schist there exposed contains pyrite and barite. I t seems prob-able that a fault follows the creek bed at this point, although no conclusive evidence was found of its presence. The underground examination showed that faults are numerous in the mine. Ther e is usually gouge of soft laminated nature developed parallel to the fault plane. Wher e the slip is small, and where the drag is visible, as when quartz veins are cut, the direction of movement may be determined. I n all such (4) cases the faults appeared noraei* Underground it is found that the barite is out off on the west by a large fault. Thi s was not examined as the drift is tightly timbered and lagged at this point. Bu t there appear-ed to be a wide zone of gouge similar to that mentioned above. The lamination of this material strikes N 60°E and dips 40°J»# The examination of the rocks found exposed in the main tunnel showed that these consist mostly of sericitio and talcose schists. Nea r the end of the tunnel the rock is much less compact, and is probably a more schistose zone which has been altered and softened by surface waters, which drip from the faces at all points underground. One stratum found in the tunnel is characterized by a surface studded with small eyes of quartz (S3, fig.2). A  simi-lar rock was found in the drift beyond the fault. I f both exposures represent the same bed, the horizontal displace of the fault is apparent. Thi s feature was not carefully investigated in the field. Many quartz veins occur in the mine. Mos t of these appear barren, but in certain places metallic minerals and bar-ite are found in them. I n one vein, 18 inches wide, which out-crops in the creek just below the main tunnel mouth, coarsely crystalline galena appears, and in an irregular vein at the end of drift D (fig.2b), barite, pyrite and a small amount of galena were found. (5) Upper Barite Deposit* The upper outcrop of barite is 12 feet in width, and is very similar to the lower one. littl e of this deposit is exposed, as the outcrop is covered on "both sides by drift, and the only development consists of a small crosscut 10 feet in length. A t the bottom and end of this opening a large irregular mass of quartz appears. Just above this barite body is a band of rook about 12 inches thick, containing barite, bomite, chalcopyrite, sphalerite and galena. I t is also conformable to the rods structure, and is marked by the copper stain on its weathered surface. Barit e is found in diminishing amounts for about 30 feet above this zone, beyond which the rock consists of a shear-ed pebble conglomerate with some pyrite. Stil l higher on the hillside unmineralized green schists and black slates appear. These continue for about 200 feet, and above them the ridge apparently consists of the massive grey quartzite common in the Bastion formation. Structure and Size of Deposit* Y/hen the whole mineralization at the Home stake mine is considered, the shape of the baritic zone appears to be cross-cutting with respect to the country rock. Thi s statement refers to the general shape of the schists that are mineralized, as of course the two main ore bodies, as well as several small similar horizons, are conformable to the attitude of the rocks in the locality. (6) Measured perpendicular to the strata, the extent of the mineralized schist is at least 200 feet. Barit e disappears a short distance above the upper ore body, but from there down was found in varying amounts as low as 30 feet below the main adit, beyond which the rocks were not carefully examined. The main ore body, which should be as extensive in this direction as any part of the baritio zone, does not contin-ue very far along the strike of the country rock, as it outcrops for only 80 feet. I t is probable that this deposit is out off on both sides by faults, but for certain reasons it does not seem likely that the barite body ever had a great lateral ex-tent. Th e faults are obvlotisly later than the mineralization, and also of small magnitude, since barite occurs in the schist beyond them. Tha t is, the offset portions of the barite depos-it must occur near the mine and carry values. I t follows, then, that if they were of large lateral extent, they would no doubt have been discovered and developed. Sinc e there is no record of this, the inference is that the ore bodies beyond the fault are small, probably due to a rapid falling off of the mineral-ization. lo evidence was available as to the extent of the baritic zone in the direction of the dip of the country rock. However, from the indications above, it is probable that the shape of the whole mineralized mass is irregular, and not con-formable to the structure of the rock formation. ?are«aaeele e f th e Mlnerale . rel iehed epeelnen e e f t n n g t er e v a n examine d an d found t o oontal n s p h a l e r i t e , pyr l te , galena , tetrahedrlt e en * aaalsaajrl te * A * H M e f grai n l a M a l l , an d anaall y th e f a t a l aonten t e f • • t a l l l a mlneral e l a mnAa r 10% . Barlt a fre m the aaml l mineralize d zon e abov e th a appe r herlt e Aapaal t wa a found t o contai n b o r n l t e , cha l copyr i t e , galena , aphalarlt a an a p y r l t e , an d th e amoun t e f th e copper-bearin g aiaaral a l a ama h grea t e r tha n I n th e mai n or e bod ies . Tha me ta l l i c mineral s usua l l y ooou r i n re t icu lat a form betwee n th e g ra in s e f aar l ta , an d hav e a  ver y irregula r o u t l i n e . Separat e p a r t i c l e s d o no t appea r elongate d para l le l t o an y on e d i r e c t i o n i n th e b a r i t e . Howeve r th a ma ta l l lee a e a whole ar e concentrate d i n c e r t a i n zone s whlo h ar e eenfernahl e to th e apparen t s t r a t i f i c a t i o n o f th a ore . The paragene8l s i s har d t o determine , a a th a emai l amount o f th e me ta l l i c mineral s ha s allowe d the m t e b e widel y disseminated. Ther e i s n o evidenc e e f an y mineral , e r grem p a f minerals , havin g bee n introduce d d i s t i n c t l y l a t e r tha n th e ree t , or fro m a  d i f fe ren t source . O n th e cont ra r y th e a a t a l l l e min -e r a l s appea r r a the r evenl y d i s t r i b u t e d I n a l l th e er e examined , and n o marke d replacemen t e f on e minera l b y anothe r wa a ebeerved * However i t aaem a probabl e fro m th e axaadnatla n tha t th a mineral * were deposite d i n regula r order , probabl y fro m d i f f e r e n t phaae a of minera l iza t io n o f so lu t ion s fro m th e sam e eonree * (Th e ro F A C E W.  8 F/GURE 3 Polished Surface  o~f Bari +  ic Ore.. HAG 500  DIAM S ,  s p k a / e r i t e , (8) above statements refer only to relations between the metallic minerals, as there is evidence to show that this group as a whole is later than the barite. Thi s feature will be discuss-ed later), Th e evidence on which the succession of the metall-ic minerals is based is the occurrence of small projections of one mineral in another. On this evidence, the following order of deposition was determined, (beginning with the oldest mineral), pyrite, sphalerite, galena and tetrahedrite. Pyrit e tends to be rather equidimensional and has no distinct veinlets in the barite. Sphalerite is more irregular and in places projections of this mineral almost surround barite. Galen a is found completely enclosing barite, and is characterized by its fine reticulate structure. I t occurs in veinlets cutting the barite. Tetrahed -rite, where present, is usually found at the edges of galena grains, with small projections into that mineral. (Thes e features can be seen in the camera lucida reproduction shown in figure 3)» Chalcopyrit e in the average ore is present in amounts less than 0»3% t (calculate d from a quantitative cheraioal analysis, with allowance being made for the copper in tetrahed-rite). It s time relation to the other metallic minerals is not clear. The metallic minerals appear to be of later deposition than the barite. Thi s is shown by the description given above, and by the fact that the metallic minerals appear concentrated along certain planes inthe barite, suggesting that their if) eolmtlone working alon e ohaanel a I n tt o Cortain otte r relatione , whic h wi l l to orltoo lnto r mn&e r thei r prope r heading* , wi l l to  moo d toro to oomploto tta o statemen t o f th o pmragenesle . I n •  polloto t Motion pxrit e wa n ferns * I n a  regula r networ k o f rein s appar -ently alon g cleavag e plano a I n th e barlte . I n oertal n thi n eeotiene emart a wa o fomn 4 whloh l o o f oontoaporonoos a eepoeit -Ion witt i th o tori  t o . Howeve r nea t o f th e emart a appear e t o hnr* town  depeelte d fro n th o loo t otage o o f th o mineralisation , wins* i t i n s o oonojo n a s rein * rottin g th o or e bodlee . leering (mart s om t o f th o l i n t , th e parageneol o o f main or e mineral s 1s t torite,  pyrlte , sphalerite , galen a tetrahedrite. Results o f Assay s an d Chomloa l Analyses . The analysi s o f a  typica l speoimen t o f haritl o or e 1st J.30 Om 0*5 0 lo 1.0 0 Am 0.2 0 8% 0.1 0 8 ( i n smlphldes ) 2.4 0 SiOt 3.0 0 AlfOj 2.1 0 BaO 55.0 0 80a 2?.1 0 OaO 0.8 0 Mg© 0.4 0 0 *  mndotoradmo d 1.5 7 0.05 peroent . ( 8 os . pe r ton) . 0.70 100.00 (10) Fire assays for silver were run on several specimens. It was found that those, which, under the microscope, were seen to contain the largest amount of tetrahedrite, also carry the highest silver values. Tha t the content of galena or sphaler-ite has little relation to the amount of silver present is shown by the following comparison. kg P b Z n Tetrahedrit e (app) . Specimen- H14 1?. 8 oz. per ton 0*73 % 571%  "~ TT$% Specimen- H10 4. 0 "  n  •  7.0 % 15.0 % ver y little. A small piece of more or less pure tetrahedrite broken from a speeimen ran 160 oz. per ton in silver. Galen a similarly anal-ysed only carried 30 oz. Th e conclusion is, therefore, that the silver value of the ore is determined by the amount of tetrahedrite present* Petrography of the Barite Lodes and the Schist. Both ealcite and quartz were present in all the specimens of sericitie schist examined in thin section. I n general there is an arrangement into areas of almost pure eal-cite and those of dominant quartz. Calcit e occurs mostly in zones of large interlocking grains with secondary twinning well developed. Th e quartz grains show the same pattern but are individually much smaller. Wit h them can be seen a little cal-cite and a large amount of sericite, (which is poorly developed in the zones of ealcite). A  few crystals of ox'thoclase, of about the same size as the calcite grains, are associated with the quartz. Thes e are considerably altered to sericite, but j 0  i  •  .  *  r  i i FIGURE 4 -Tf i / n vScctio n o f SERICITIC 5CH/5T t*l«2 IZS dt*m (11) their outline is still distinct, and the Carlsbad twinning plane can be clearly seen, A  few grains of plagioclase were  al -so seen in the rock, and are fresh in appearance. Pyrite is present in considerable quantity and is distinctly a replacement of the schist, Squar e and triangular sections are common, and these truncate indifferently grains of calcite, quartz and sericite. figur e 4 shows a crystal of pyrite in the schist which contains a quarts remnant at its center. The schists were probably formed from beds of sand-stone containing imptirities of clay and calcareous material. The amount of original ferruginous matter was probably small, since the metamorphism produced sericite and talc, both of which are deficient in iron. Th e difference in size between the grains of calcite and quartz is to be expected, since under deformation quartz granulates whereas calcite takes up the strain by intern-al, molecular rearrangement, and also since reerystallization is more marked with calcite than with quartz. A  comparison of the average texture of quartzites and marbles that have been sub-jected to the same stress shows the effect of this difference in development. Th e metamcrphism that produced the schistosity was of such a nature as to form sericite from the clay and sand, but not severe enough to cause the formation of lime silicates. In the thin sections of the baritie ore only a few grains of calcite were found, and these are all in one slide. Quartz occurs in all the specimens examined, but in small amounts. (12). The grains are small, about the same size as those of quartz in the schist, and occur in little groups, with sometimes a few shreds of sericite in close association. Wher e there was suffic-ient mica to get two particles near enough to one another for comparison, they were found to be in more or less parallel orientation. The barite is in medium-sized grains, which are well interlocked and show no twinning. Th e size of the barite grains is very nearly the same as those of the calcite in the schist. The grains of barite are of very uniform size, and show no zonal distribution, either according to size or crystallographic orientation. A  few minute inclusions were found in the barite. Their interference color is usually high, and they are similar to calcite in many ways. The y are therefore thought to consist of that mineral. In several slides quartz was noticed of larger size than the ordinary grains of that mineral found in the ore. Moreover it is not found associated with them in the little groups in whibh they usually appear. Th e outline of this vein guartz, as it is considei-ed to be, is very irregular, and it was found intergrown with several small barite grains, which exting-uished at the same time, giving the appearance d>f micropegmatitic structure. Thi s quartz was therefore probably deposited simultaneously with the barite. Ghemioal Experiments. An effort was made to find some method of different-ially (13) staining or marking barite and quartz, which are the principal gangue minerals in the mine, Th e object of this endeavor was to learn the time relationship existing between these minerals. By treating a precipitate of barium sulphate, the following facts were learned, 1, Barium sulphate is practically insolubl* i n all the common acids, including hydrofluoric. 2, In a hot, concentrated solution of potassium carbonate, barium sulphate is completely changed to barium carbonate in a few hours, 3, Under similar conditions, silica remains unchanged, 4» A hot, concentrated solution of potassium chromate does not attack barite to any appreciable extent. Two methods of selectively treating barite in the presence of quartz follow from the above facts* 1, Since hydrofluoric acid attacks quartz and not barite, the surface of the former mineral can be roughened without marring the polish of the barite. Th e reaction proceeds at the most desirable rate when the specimen is just warm. Th e acid may be dropped on the surface directly, if it is not too large, and can easily be made to form a thin film over the specimen. After a certain time, usually about 30 seconds but depending on the temperature of the specimen, the surface can be washed free from the acid, and will be found to ba etched over the quartz. If the dried surface is now rubbed with a cloth on which some rouge, yellow ochre, or other colored powder has been placed, the quartz will become colored, whereas the smooth surface of (14) the barite is unchanged. By heating a speeiijjen in a hot, concentrated solution of potassium carbonate, barite will "be attacked and not quartz. The barium carbonate formed can then be removed with hydro-chloric acid, leaving a roughened surface on the barite. O r the barium carbonate can be changed to yellow barium chromate by placing the specimen in a solution of potassium chromate to which a few drops of hydrochloric acid have oeen  added . Th e difficulty here is that the carbon dioxide formed may shift the barium chromate, which does not adhere to the surface of the specimen. Th e disadvantage of the whole method is that, where-as the reaction between a hot solution of potassium carbonate and a finely-divided precipitate of barium sulphate proceeds rapidly, a polished surface of barite is decomposed slowly and unevenly. Howeve r as barite is attacked with great violence by molten potassium carbonate, it would no doubt be possible to change that mineral to any required extent by placing the spec-imen in a solution of potassium carbonate at high temperature* This temperature could be obtained by heating the solution under pressure, and by increasing the concentration of the potassium carbonate• A method of staining, the possibilities of which were drawn to the attention of the writer by Br. V'inchell of the University of Wisconsin, involves the use of selenium oxychlor-ide, which is said to have the property of preferentially wett-ing barite. Thi s substance is a yellow liquid, which fumes on exposure to air, and is decomposed by water. I t crystallizes (15) at 10 C. and boils at 179.5°C. Selenium oxyehloride was prepared by the writer according to the method introduced by Cameron and Macallan, (v) A large glass tube with three down-bends in it was used. I n the first two of these were placed selenium and salt, respectively, in the ratio given by the equation: 2Se02 f  2Ha0 1 «  SeOCl g IfegSeO ^ The bend containing the selenium was connected to an oxygen tank through a drier of pumice and sulphuric acid. Th e other end of the glass opened to the air through a drier of calcium chloride. On being intensely heated in the stream of oxygen, the selenium burned with a blue flame to selenium oxide, which deposited as slender white crystals in the cool part of the tube. Afte r all the selenium had been converted to the oxide, this was driven over into the salt with the flame. O n heating the mixture in the second down-bend selenium oxychloride was formed, which was distilled from the sodium selenate into the third down-bend of the glass tube. T o keep the selenium oxyehloride absolutely dry, the part of the tube containing it was cut off with the flame, sealing the ends at the same time. Of the three schemes, two for etching and one for staining, the treatment with hydrofluoric acid was found most satisfactory. Specimen s of the vein material and of the mineral-ized schist were examined by use of this method. I t was found that in certain places quartz surrounds barite, and occurs as (v) Chemica l Hews, Vol. 59*  I859 , P. 267. email veinlets cutting through masses in the rock whioh consist largely of barite and pyrite. Howeve r in other specimens the intergrowth between barite and quarts suggests contemporaneous deposition. I n one specimen of the mineralized sohist pyrite appears in a regular network of relnlets whioh appear %• foll-ow the cleavage planes in the barite. These facts indicate that pyrite is later than the barite, and also show that quartz was present in probably all the stapes of the mineralization. Fo r quartz was found whioh was apparently deposited at the same time as the barite, both in slides and polished surfaces, and in other places quarts appears with pyrite in veinlets cutting barite. Ther e is also a large amount of quartz in veins which cut all the other introduced minerals. Origin of the Deposit. Association of Minerals. The relations found seem to show that all the minerals of the ore came from the same immediate source. Th e evidence is as follows. 1* Barite, quartz and pyrite appear together all through the schist. Quartz , in different places, appears contemporane-ous in deposition with both pyrite and barite. Als o in the ore pyrite is closely associated with the other metallic minerals, and in certain veins barite, quartz, pyrite and galena all appear closely intergrown. Althoug h there appears to be a gen-eral order of deposition such as mentioned under paragenesis. CM the minerals, especially quartz, seem to overlap one another in their time relations. Thi s suggests a common source for all the minerals. 2. All the baritic ore contains the metallic minerals in very even distribution, and no barite was found which did not contain some of them. Thi s indicates that all of the mineraliz-ation came from the same center of distribution. 3. The V7sy in which the metallic minerals are uniformly scattered among one another shows their close relationship. 4. The metallic minerals occur in certain zones parallel to the banding in the barite, which shows that they were deposit ed from solutions that worked along one set of channels. I t does not seem probable that the metallics replaced impurities in the barite, as the shape of the minerals and the occurence of small grains of quartz in the zones of metallic minerals suggests that the solutions had followed the paths provided by the presence of unreplaced sandy laminae in the original strat-um. I f any one of the metallic minerals were from a different source than the rest, a relative concentration of this mineral would be expected in some locality. Sinc e this is not the case it seems clear that the same conditions must have prevailed while all were being deposited, which suggests their common source . Opposed to this evidence is the occurrence of the relatively pure barite bodies that compose the main ore deposits, and the numerous barren quarts vein3 which cut these deposits and the country rock. Bu t these facts are not incapable of an 0») explanation* by am hypothesis whisk postwlates only saa aowroo of minermlisatism. fs r it is knows that, im roplaooaamt, ths walls of ths channels mayAte ams substance and not ta another. moreover, silisa appears ts bs one af tha sobstanoas largely ssmflmsd ts ths walls sf ths twin, (wi) Tha t ia, im ths sass sf ths Hsasstaks mine, tha first mineralising solmtloms may haws bssm psor im silisa, whioh was mostly kept within ths flssare* late r the eolutions aontainad mash quarts, as showm by the ooomrrenoa of para reins of that mineral, Howeve r a 11ttls galena, pyrite and barita wars still present, aa they are found in some of these wains* Sna h an hypothesis weald aooowmt for ths traces of vein quarto im tha barltle ere, and also fsr ths large aaswmt of smarts imtargrown with barita and pyrite im tha sohiet, where deposition was probably mot so much by metaeomatic action as by the filling of fissures and formation Of lenticular masses in the schist through the foroe of crystall-ization and the pressure of the solutions* Evidence of Epicenesis and Replacement. The foregoing discussion has presumed that ths minor-als sf ths srs have been introduced into the position they mow occupy since the rocks were formed, and also that tha maim ore bodies are replacements. Th e evidence leading to this assumpt-ion will mow be given. Concerning the epicenetic nature of the deposit little proof seems necessary. Th e field examination showed that the (vi) W . Lindgren*Mineral Deposits. P. 168. (1?) mineralized zone as a whole iB irregular, and does not corres-pond to any broad baritic horizon in the rock formation. Thi s of course indicates that the barite is not epigenetic. Th e facts given below to show that barite is a replacement will also prove it is epigenetic. A s pyrite is clearly a replace-ment of the schist, its introduction is obvious, and there can be no doubt about the epigenetic ori I > of the rest of the metallic minerals* The facts showing that the barite ore bodies are replacements are as follows:-1* The mere fact that certain relations can be readily explained by presuming that replacement has occurred is in it-self evidence 6f the truth of the supposition. 2. The texture of the barite, which consists of cryst-alline grains perfectly interlocked, is typical of metasomatic action. Ther e is no tendency to the crustification common in cavity fillings. 3. The stratified appearance of the ore, which is most-ly due to the banding of the barite into white and grey layers parallel to the bedding of the country rock, is no doubt a structure preserved by replacement, since the barite of the veins is white. Th e even size and uniform distribution of the grains of barite shows that the banding is not due to the crystallisation of that mineral, but to a difference in color which is independent of the texture of the ore. Thi s fact confirms the supposition that the banding is a preserved structure. (20) 4. The occurrence of isolated grains of quartz and sericite indicates replacement, since these remnants would ob-viously be unsupported under any other form of deposition. Th e orientation of the shreds of mica, and the size and grouping of the quartz grains show a pattern very similar to that displayed by these minerals in the country rock. 5. Particles occur in some of the barite grains which are probably unreplaced kernels. Conclusive evidence on the matter of replacement would result from the examination of a suite of specimens show-ing the gradation from ore to country rook. Unfortunatel y such a perfectly graded set of samples was not obtained. Hoi^ eve r one of the ore specimens seems to represent an intermediate stage. Thi s shows a few grains of calcite in the areas charact-erized by the presence of quartz and sericite. B y a further replacement of the calcite, the texture would become that of the ordinary baritic ore. This occurrence, and the relations set forth above, make it reasonably certain that the main ore bodies are replace-ments. Concerning the probable character of the stratum in which the deposition occurred, the following facts are of importance• 1* The examination of thin sections showed that the bar* ite grains are of approximately the same size as the calcite constituents of the country rock. I n the metasomatism of fossils the organic structure is often preserved by a variation in the (21) dimensions of the replacing grains, which show that it is poss-ible for the size of the replaced grains to affect that of the metasoiaes. Wher e the replacement has taken the form of a disseminated deposit, this is not the ease, as the pyrite cryst-als in the rook are often much larger than the original constit-uents of the rock. Bu t where replacement advances more or less as a wave, as was probably the case with the barite, the number of centers of crystallization would no doubt be considerably-affected by the texture of the stibstance replaced. Th e fact that the texture of the barite resembles that of the calcite found in the country rock, and not that of the quartz, is there-fore an indication that a bed of limestone has been replaced. 2. The small amount of serieite in the ore suggests that a relatively pure stratum was the host, as it is hardly likely that this mineral was replaced to any great extent. 3. The kernels found in certain grains of barite resembled calcite and not quartz. 4. The specimen of ore, mentioned above as being a case of incomplete replacement, will only constitute an intermediate stage to the typical ore on the hypothesis of a preferential replacement of calcite with regard to quartz. Th e adoption of an hypothesis that posulates the replacement of quartz in such a sample would develop an ore containing calcite and no quartz. As just the opposite is true, the preferential replacement of calciie is indicated. Again the absence of a gradational set of specimens renders the ease inconclusive. I t is of interest, however, to (22) note that the outward appearance of the baritle ore greatly resembles the grey limestone found elsewhere in this formation. On the whole it seems most likely that a relatively pure bed of crystalline limestone was replaced. Th e well known suscept-ibility of this type of rock to metasomatic action makes this supposition probable. Als o such an hypothesis readily accounts for the bedded appearance of the main ore bodies and the smaller highly mineralized horizons. Origin of the Mineralization. The origin of the mineralizing solutions is not clear. It has been stated above that all the minerals seem to have come from the same immediate sotxrce, but certain facts discovered are hard to reconcile to the hypothesis of a common ultimate origin. No field relaions were found that would indicate the source of the mineralizing solutions. Howeve r two general feat-ures may serve as suggestions. Certai n structural relations show the possibility of a younger granite underlying the district Also there is not known in the locality any deposit of pure bariter or baritic sediments, from which that mineral might have been dissolved by surface waters. The nature of the ore itself suggests deposition at moderately high temperature and pressure. Th e absence of erust-ification or any open cavities, the even texture of the ore, and extent of metasomatic action all Indicate that the deposit was not formed by meteoric waters at low pressure. The mindral composition of the ore gives evidence of (23) Beth Bypegene end sapergene origin, A  comparison of the lead •res sf the Slocan distriet with those of Missouri and Wisconsin shews that In hjrpogvne deposits of this type high silver values sad black sphalerite arc common, whereas in ore bodies formed by meteoric waters the galena is very low in silver and light-colored resin sine blende is the role. Henc e the presence of galena and tetrahedrite, both rich in silver, and black sphal-erite suggests deposition from solutions of magnetic origin* Bat, en the other hand, barite is considered by most authors to be only of sapergene origin* Szoept for the presence of barite, all the indicat-ions point to the hypogeno origin of the deposits* Sh e exist-ence cf this mineral In the ere could be explained by two hypotheses which dc not require its origin to be hypogene* Barlts might have been leached by the ascending solutions in their journey through the rocks, or a mingling cf barite-bearlng surface waters with the magmatic solutions might have occurred. Since barite is appreciably soluble only in solutions containing a large amount of alkaline carbonates and an excess of carbon dioxide, the leaching by ascending solutions is more probable, as their composition is more commonly cf the alkaline nature required for the reaction* Howeve r this hypothesis must be considered unlikely, as there are no beds of barite known In the distriet which would provide the source for such leaching* (Such a supposition would require a more or less concentrated deposit of barite in the path ex* the magmatic solutions, as these arc not thought tc wander very far in their Journey upwards, but te (24) be rather confined to the channel walls). Th e possibility of the mingling of different solutions from above and below is also to be dispensed with, since, in addition to reducing the temper-ature, the presence of meteoric waters would necessitate low pressure at the time of deposition. Fo r it is clear that in surface waters, (which usually contain no great amount of alkal-ine carbonates nor a big excess of carbon dioxide), the solubil-ity of barite is small, and free channels would therefore be necessary for the rapid circulation of the large amount of meteoric water required to provide the barite. T o put the case briefly, it is hard to reconcile deposition at high pressure, which seems to be the condition at the Home stake mine, with the presence of a large supply of circulating meteoric water. The Evidence as to the General Origin of Barite. lindgren states that barite is not a mineral of igneous origin, and that it is not found in contact metamorphie deposits, (vii) Sinc e the relations at the Homestake mine seem to show that it is there of hypogene origin, it might be advisable to carefully examine the evidence advanced to show that barite can-not be of igneous origin. This evidence may be said to consist of two general arguments. On e is based on field relations, the other on chemical data. The field relations in the majority of the barite deposits described in the literature, show that this mineral is (vii) Minera l Deposits, l?!?, P* 377. (25) of supergene origin* Howeve r it is probable that the greater part of the reports are concerned with commercial deposits, which must necessarily be very pure. Th e amount of the barite which occurs as gangue in metallic ores is no doubt greater than that of the valuable deposits, hut because of its contamination with sulphides, its usual occurrence away from industrial cent-ers, and a variety of other reasons, it is not commonly of commercial value. Owin g to the wide distribution of this type of barite, it seems unlikely that all if it could have been derived from the strata traversed by the solutions, A  few specific instances may be given in which the barite appears to be definitely of igneous origin. S.J . Sehofield found barite apparently as a replacement of part of a mass of slate that had been engulfed in an igneous intrusive at the Britannia mines. (viii) T.C . Holland describes a network of veins of quartz and barite which he regards as magmatie differentiates, (ix) Hanson, of the Geological Survey of Canada, believes that the barite at the Dolly Varden mine is hypogene. (x) The cheraieal evidence put forward to show that barite cannot be of magmatie origin is the fact that barite and quartz cannot exist together in a rock melt, as barium silicate and sulphuric oxides are formed,, (xi) I t seems clear that barite (viii) Persona l Communication. (ix) T*C . Holland, Rec. Geol. Survey of India, 1897, Vol, 30. "(x) Persona l Communication. (xi) G.F . Clarke, Bulletin 6?.5, U.S.G-.3. P. $84. (26) and quartz can exist together in solutions at fairly high tem-perature, and also that the elements composing these minerals do occur in magmas. Th e chemical composition of the magma would largely determine the order of crystallization of the minerals. If conditions were such that part of the barium content would remain in the unsolidified portion of the magma, the nature of the minerals in this liquid remnant would be greatly affected by the conditions of temperature and pressure, and the presence of mineral^J-zers, especially water, since silica appears to be not as active in aqueous solutions as in dry melts, and the ordinary acids are not effective without the presence of water. I t seems probable that results found from experiments with rock melts cannot be directly applied to magmas, as it is known that sider-ite, for instance, occurs in veins of igneous origin, and yet if iron carbonate is melted with silica, iron silicate and carbon dioxide will be formed. The above discussion shows that there is no definite grounds on which the hypogene origin of barite can be excluded. Since the relations at the Homestake mine strongly suggest a deep seated source for all the mineralization, there appears to be no cause for not accepting this interpretation. Acknowledgments. The writer wishes to acknowledge the help rendered in the preparation of this paper. Especiall y is he indebted to the Geological Survey of Canada, for the aid rendered in the field examination and the permission to have this paper published; to (27) the Geological Staff of the University, particularly Dr. W.L. Uglow whose many suggestions and careful criticism have heen invaluable; and to Prof. Thomson of the mining department and Dr. Archibald and Dr. Clark of the ohemistry department for their assistance. Bibliography. Heferenees in Text. (l) Annua l Report of the Geological Survey of Canada, 1894, P. 21A. (ii) Annua l Report of the Liinister of Mines for B.C. 1917". (Hi) Memoir 68, R.A. Daly, G.S.C* (IT) W.L . Uglow, Summary Report, 0.S.C., 1921, Part A. ( • ) Clismlca l Hews , Vol , 59 , 1859 , P . 267 . (v i ) v; . Lindgren , Minera l Deposi t s . ( v i i ) do . do . do . (Ix) T.C . Holland, Rec. Geol. Survey of India, I897. Vol. 30. (x i ) G.P . Clarice , Bu l l e t i n 69 5 U.S.G.S . 


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