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UBC Theses and Dissertations

The magnetite occurrences of the West coast of Vancouver Island, B.C. : their contact metamorphism and.. Osborne, Freleigh Fitz 1925-07-15

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HHEBKBW.-io- * «"*,, U.B.C. LIBRARY wattmrammemi //he Mao/7ehfe Occurrences oF the West Coast of ]/ct"Couver /s-Und, •& C/ *W Contact M*i*-nnorbhism and 0r9 Genesis 0 ST •S5 -~Fi.*rf 7 QUA TiA"° ®OlO J PORT KYUQUOT @ Cfovrr/ pf//veg (2) p/}*&r A/yo So*" /Z) 0S)tD &ACAF @ co#/&/y /F/YS/P 0/y<?/*0O0 *WW t/rrt£- 0O&S J/f/tAjf v>t THE MAGNETITE OCCURRENCES OF THE WE8T COAST OF VANCOUVER ISLAND. B. 0.; THEIR CONTACT METAMORPHISM AND ORE GENESIS - By — LREL.EIGH £1X1 OSBORNE • •***. A THE3IS SUBMITTED FOR THE DEGREE OF MASTER OF APPLIED SCIENCE - In %M -DEPARTMENT OF GEOLOGY • * * * * THE UNIVERSITY OF BRITISH COLUMBIA —I—•—»—••••^^••Hlll.HI.WPH !• » I» APRIL 19 3 5 • ' • •••'• ; » * » * * + THE MAGNETITE OCCURRENCES OF THE WEST COAST OF VANCOUVER ISLAND. B.C.; THEIR CONTACT METAMORPHISM AND ORE GENESIS 1. PREFACE IS) Acknowledgments. / Bibliography of Geology of West Coast. > -J*-3. SUMMARY AND CONCLUSIONS & -JT' 3. INTRODUCTION, (a) Physical features and geology of West Coast. _ -..-.-— — ..- — -- A (b) Magnetite occurrences. -'-- 4-. (1) Situation and development. _ - - — *•• (•; Topography of occurrences. - - - *• (3) Geology. - __..-_ — - -5-. (c) Classification of deposits. __ - - -£• (1) By types. _ - _.._--_ (S) By sounds. _ _ _ _ _ -4. DEPOSITS IN LIMESTONE ft! Endotheraiio effects of intrusion. Exothermic effects of intrusion. 5. DEPOSITS IN VANCOUVER VOLOAMIOS -[a) Copper Island. - -(b) Crown Prince. ,c) Darby and Joan. _ - -*• DEPOSITS IN LIMESTONE AND VOLCANICS 7. TIDEWATER AND JUNE ._ _ _ 8. MINERALOGY w Metallic Minerals - -II) Non-Metallic Minerals. 9-- -/£>• - //• . -, J. -/ 8. - /s>. 2. -2 . " z * . 2S. ' 2 7-3 3 - + * 9. CONTACT METAMORPHISM (1) General. - ^^ (2) Formation of silicate zones on Vancouver ^ Island. (3) Relation of silicates and ore. _ _ _ - j-r 10. ORE DEPOSIT!QH -r"c5' 81 Ore precipitation by llaestone. —--*•/ Ore precipitation by other than lime-^^ stone* (5) Character of ore-bearing solutions. e'e U. gUjOUBY OF THE TYPES OF MAOHETITE OCCURRENCES OF ^a^iW* 13. BIBLIOfiBAPHY OF OOITAOT METAM0RPHI3M _ _ _ _ - 7 S - - LIST OF ILLUSTRATIONS - -Oatllne nap of West Coast. Showing location of properties. Frontpieoe. Sarita River and Sydney Inlet. To follow Page. i. Maiden Hair Fern, Elijah M.C. To follow Page ^ Magnetite - Conqueror M.C. and Head Bay. To follow Page 4-. Camera Luolda sketch from thin section. To follow Page / z. Camera Luclda drawing from polished surface. To follow Page ye. Magnetite Replacing Voloanlcs. To follow Page <r^ FORWARD AND ACKNOWLEDGMENTS During the field season of 1934, the writer had the good fortune to be employed on the iron-ore survey of the Province of British Columbia, carried on by the Geological Survey of Canada. The work, which was a continuation of that begun by Dr. G.A. Young, of the Geological Survey, was confined to the occurrences on the feet Coast ofVancouver Island. This work was under the supervision of Dr. W.L. Uglow of the University of British Columbia, and the writer wishes to ac knowledge hie indebtedness to him for assistance in all stages of the preparation of this theeio. Acknowledgment is also due to Or. V. Dolmago of the Geological Survey,for discussion of foot Coaet geology and access to unpublished maps of the shore line in the vicinity of some of the occurrences. The principal publications dealing with the general geology of the West Coast of Vancouver Island are: Dawson,G.M. - Geol. Surv., Can., Ann. Rept. 1886, pp. IB - 107B. Haveook B. And Webster. A. - Geol. Surv., Can., Ann. Rept., 19037" pp. 54-59. C^aon. C.H. - Geol. Surv*, Can., Memoir No* 13, 1912. D?]fffgf Y- - G«ol. Surv., Can., Sua. Reote. - 1918 - pp. 30B - 38B 1919 - pp. 12B - 19B 1920 - pp. 12A - 22A Information on Iron ore occurrences may be found in the Annual Reports of the Ministsr of Mines of British Columbia FORWARD AND ACKNOWLEDGMENTS BIBLIOGRAPHY from 1903. The Iron ores were the subject of a special examination by Einar Lindeman In 1907; the results were published as Canada, Department of Mines, Mines Branch Publica tinn Ho. 47, 1910. The earlier work is summarized by W.M. Brewer in British Columbia Department of Mines, Bulletin No. 3, 1917. "Iron Ores of Vancouver and Texada Islands." /// — SUMMARY AND CONCLUSIONS — the magnetic Iron-ore on the West Coast of Vancouver Island, le of the contact metamorphic type, formed by the in trusion ef rocks of Upper Jurassic-age into the rooks of the Vancouver group, consisting of limestones and volcanic flows and tuffs. The intrusive is of varying lithology from granite to diorite, hut the magnetite occurrences show a preference for the mere basic type. Following the intrusion of the plutoniee the equilibrium both within the Intrusive and within the intruded reek was disturbed. In the intrusive, this is evidenced by the formation of fine grained or perphyritic contact faoiesJF contact semes ef different composition, or the alteration of certain already formed minerals in the rook. In the Intruded rook the readjustment may take the form of re oryetal ligation, or leas noticeable alteration. Ae the igneous rook consolidates materials are given off, which enter the contact zone and form silicatee and SUMMARY /^CONCLUSIONS ore. The tarlation in the mineralizers, as shown by the minerals deposited is very marked, although there is a tendency for silicates to form before the ore, especially in limestone. the observed variations point to the concentration of the last stags product of crystallization of the magma and the mineralizers within the Intrusive; and diffusion into the contact zone. The emanations characterized by the elements of lower atomic weight reach the eontact zone first* They also, as a rule, are the mere chemically active, and can so deposit first. The heavier elements may reaeh the eontact acne and not be able to deposit because they cannot maintain their concentration. Under special conditions, especially when the intruded rook approaches the intrusive rock in composition, magnetite, even in the presence or-of the more siliceous emanations may deposit firstAsimultaneously. This mstamorphism and deposition of magnetite takes place from tenuous solutions at temperatures from 1000° to 600°0 Hematite o;. . was probably formsd close to 500° or below, and the sulphides with the possible exception of pyrrhotite at lower temperaturee still. Silicates may be just as effective in the deposition of ere as limestone. /£ ^MU». 1. THE MAGNETITE OCCURRENCES OF THE WEST COAST OF VANCOUVER ISLAND, B. CJ | THEIR CONTACT META^ORPHISM AND ORE GENESIS i ---.__-.__- — -.-._•-__--._ i j ; INTRODUCTION ! I | PHYSICAL FEATURES OF VANCOUVER ISLAND I Vancouver Island is the largest island of the West Coast of forth America, and is completely surrounded by navigable waterways. The Vest Coast is deeply indented by fiords; the principal ones of whioh ares Barkley, Clayoquot, Nootka, Kyuquot and Quatsino Sounds. Inside the sounds, deep water Is found very close to the shore and mountains rise quite abruptly to heights up to three thousand feet to form the Van couver Range, the backbone of the Island. This range has a general N.w. and 3.E. trend so the fiords cut across it almost at right angles. Below Barkley Sound, the large inlets are not present and as you go south the mountains do not rise to as I great heights, until south of Port San Juan the topography is notably more subdued and a narrow coastal plain appears. CLIMATE The climate of the West Coast is very equable. The rainfall is heavy, but snow is not common and does not remain for long periods. GEOLOGY OF VANCOUVER ISLAND LEECH RIVER SERIES The oldest known rocks on the West Coast are the Leech River Series, a highly metamorphosed set of rooks, ^^»ll II • -III Ml PUTS JL TO FOLLOW PAGE /. — Fro* the euaalt of Oopper Island. View «f Talloy of Sarita River Barkley Sound. Plain-table and alidade ueed in • deposits. ipping iron ore -— Sydney Inlet-Clayoquot Sound — Shoving oharaotor of Inlets with stoop slope to water. INTRODUCTION 2. mostly slates, of unknown age, exposed only in a narrow celt at the south end of the Island. VANCOUVER GROUP the next younger rooks belong to the Vancouver group as defined by Dawson. These rocks are of Jurassic and Triaseic age. The group includes three formations. The lowest one, known as the iritiaat formation, consists of non-fossiliferous marbles and amphibolitee. 'Overlying these a thick series of volcanic material, the Vancouver voloanics, is found, flov&, and elastic Materials predominate but sills and dykes occur. This series ie of varying basicity from rhyolites to basalts but with a marked tendency for the more basic ones to predominate, while the rhyolltio types are rare. M ; 3UTTQH FORMATION , Intercalated in the Vancouver voloanics are a number of lenses of limestone, more or less recrystallized to marble, the Sutton Formation. In places this formation contains fossils, but there is still some doubt as to the correct age. Dawson refers these limestones to the Alpine Triaseic. Olapp places them in the Jurassic and calls the fauna the Sutton Jurassic, while G.C. Martin consider them Upper Triaseic in age* 0 Dawson,CM* Geol. Surv., Can*. Sum. Rept. 1886 pp. 7B-11B. @ Dolmage V. Geol. Surv., Can., Sum. Rept. 1920 p. 15A 3. COAST RAK6E INTRUSIYES Intruding the older rocks is a complex of igneous rock, probably representing an offshoot of the Coast Range Bathollth and therefore of Upper Jurassic age* The intrusivee are of varying lithology from granite to diorite; - the most common types being quarts^: di orite, granodiorite and diorlter In general the diorite, which Clapp calls the Beale diorite, represents an earlier marginal fades of the intrusive and often it intruded by the later more acid rooks. In some cases the contacts are sharp and in others they are irregular, showing the diorite ems Intruded by the acid plutonics before it was oonsolidated completely* These rooke are the most important on the West Coast, because most of the mineralisation is due to them* Cretaceous beds are found in small areas on the west Coast, but the areas are far from continuous. As far as knownn no metallic ores are found in them. In the Tertiary, Ollgocene-Miocene sediments were deposited at the south end of the Island. Igneous activity of this time Is shown by the Metchosin volcanios and the Sooke gabbro group. The Sooke gabbro caused some mineralization , but it Is not as important as that due to the rocks of Coast Range age. 0 Schofield, S.J. Geol. Surv., Can., Memoir No. 132, p.8. INTRODUCTION 4. THE MAGNETITE OCCURRENCES SITJ3A_TJOH AND DSVEItOPMEHT Moat of the magnetite properties examined are within three miles of navigable water* The most important exceptions to this statement are the claims on Gordon River, Bugaboo Creek and Harris Creek. The claims are now reached by trails from the water; in some oases little more than blazed lines. Owing to the length of time which has elapsed since the development was done on meat of the properties* the trails are now overgrown with typical coast vegetation, salmon berry, salal and devil's club, so practically new trails must be cut. The dense growth also obscures the work done on the claims. Open cute, trenches and test pits axe overgrown and filled with surface debris. Tunnels and shafts are inaccessible due to caving or to water. The combination of dense vegetation and the heavy drift mantle makes detailed examination of the deposits difficult and in most cases impossible without further exploratory work. TOPOGRAPHY OF OC&TRREMCES The examination of the magnetite occurrences showed the influence of ore deposits on topography. , Although none of the individual deposits covered a large area, the number of observed deposits made up for this deficiency. The deposits are all of the contact metamorphlc type and therefore have a tendency to resist subsequent katamorphic processes. Of all the minerals of the deposits magnetite is the most resistant. <2> Leith, O.K. «*-Mead, w.J. "Metamorphic Geology» 1915, p. 264. PLATE iU TO FOLLOW PAGE 4-. ' Maiden-hair -- Elijah lj»-jugabgo C~reeK, * * # This illustrates the luxuriant growth found in some of the valleys. These ferns are growing on soil about four inches thick on the surface of weathered limestone at about 45°. This shows the ease with which the surface may be covered by vegetation especially in moist places. PLATS IT. TO FOLLOW PAGE 4-Sf/H/jrermF ifa/y/yef = ^J /* Magnetite In Llaeetone Hootka Sound • Falle over Magnetite — Outcrop Bugaboo Oreek. -Showing Limestone magnetite oontaot 5. INTRODUCTION on account of its hardness, homogeneity and resistance to weathering, especially when pure, so it stands out in relief against the common country rock, such as diorite and limestone. This characteristic results in the formation of prominent topographical features such as: steep bluffs, tops or caps of ridges and waterfalls in streams. The resistance of the mag netite is so noticeable that a general statement may be made, that where ore-bodies are intersected by the present surface, some prominent topographical features will be present. It can toe seen that this conclusion has an important bearing on the probable continuation, on the surface, of exposed ore bodies. APPEARANCE OF THE ORE BODIES The pure magmetite, where exposed, has a characteristic steely blue colour, and usually shows a rather smooth surface. The normal colour may be obecured by a "rusty", that is llmonite, stain due to the decomposition of iron bearing sulphides or silicates. This rustiness is an important criterion for deter mining the purity of the ore. A steely blue outcrop is not neoessarily a pure outcrop, because running water will remove the limonlte, or, in certain cases, the roots of the mosses may remove it. Under these conditions, where piteous magnetite is found, it may lie due to the removal of sulphides, silicates or calcite. 0 7We {v v ; , 6 IHTRODiJCTION All the ore occurrences examined belong to the con tact metamorphic type, that is, they are due to the intrusion of the rocks of the Coast Range age into the rocks of the Vancouver group with consequent mineralization along the con tact , usually confined to the intruded, but in some cases ex tending into the intrusive reek as well. In most oases observed, the intrusive is a hornblende diorite. The deposits are divided Into a number of elaeeee which will be discussed la detail later. BOW TBS CONDITIONS OB VANCOUVER ISLAND AFFECT THE VALUE OF THE ORE A brief review of how the conditions on Vancouver Island affeet the value of the iron properties of the West Coast will be given. The first problem to be met is that of transportation; as stated before, most of the deposits are within three miles of navigable water, so if a short railroad or tramway were built to the shore, shipments oould be made by water* In order that the ore could be loaded, a harbour is necessary so the deposit must be on one of the sounds rather than on the open coast. Outside of the sounds severe storms are common from October to March, so it is doubtful if at all regular shipments oould be made by scow. Special barges might be used, but even then shipments might be hazardous and uncer tain. Berkley Sound is the only sound at present connected to the East Coast by railroad, so ore mined on It might be shipped to Port Alberni, the railroad terminate, and then ?. mmmm transhipped. The ore from Gordon Elver, Bugaboo and Harris Creeks, might be shipped directly to Victoria, If a projected railroad were built. Zf ore were mined from any known occurrence on the West Coast, it would be a very expensive matter to market It due to its isolation* If a smelter were established there, essentially the same transportation problem would have to be met In taking in coal and taking out the manu factured product* Sarkley Sound appears to be the only location which, at the present time, is at all feasible for such an undertaking* The climate Is such that mining operations could be carried on all the year around* The next condition to be considered is the geology. The deposits are all of the contact metamorphic type, one that Is noted for its Irregularity* This irregularity combined with the heavy soil mantle makes exploration difficult and expensive* Measurement of magnetic properties by the dip needle or magnetometer may be of value where the drift is thick, but they tell nothing of the quality Of the ore* The ore may be less valuable for a number of reasons. It may contain ex cessive amounts of sulphides necessitating roasting, or sllloeons impurities may be present which makes special furnace treatment necessary. In some occurrences, copper minerals are found with the iron, where these are present in sufficient quantity it may pay to concentrate the ore and smelt the iron and copper separately. 8. 9LA39srt<OT0ff oy DEPOSIT^ CLASSIFICATION OF MAGNETITE OCCURRENCES The occurrences examined are in the rooks of the Vanoourer group where they have been intruded by the rooks of Coast Bangs Batholith ago* The iron ores are found in all too forsmtions of the Vancouver group, and in sons oases, in two types in the same deposit. The type of country rook mineralized is used as ths basis of classification. Under these headings they fall into three groups; deposits in limestone, deposits in volcanics, and deposits in limestone and voloanioo. The table given below ohowo the distribution of the types and the claims belonging to each. In the in-Q trusiTSs a marked tendency for diorite to be responsible for mineralisation of the magnetite occurrences was noted, but this rule had exceptions. More sold phases of the plutonlos were represented by granites, monzonitee, quarts monzonitee granodioritee and quarts diorites. 0Olapp G. H. loo. city. Mem. Ho. 13. p. 190. CLASSIFICATION BY TYPE CLAIMS SfflSM INTRUSIVE REMARKS Conqueror Little Bobs Baden Powell Rose Sirdar Elijah Harris Crk.Claims Sarita RT. Rob Roy Prince Charley Glengarry Storaont Hitinat Limestone Beale Dlorite N M N N tt Sutton (?) Hitinat Sutton H H « M H tt tt tt tt tt II II tt H Quartz Beale it H tt I tt tt II II tt tt N tt tt II tt N N Copper Island Crown Prince, Seenart Darby & Joan Vancouver Volcanics * N tt tt ia Cascade Crk* Kokebittle Arm Bandy Creek Old Sport Bald Eagle Limestone M N N II Volcanics N H H H (?) Diorite * (?) ti H H / CuFeS, Fe $ (?) Tidewater June M tt Granodlorite Diorite *(?) °VFel CLASSIFICATION! BY 3QUUDS 10. Gordon RT. Bugabook Crk. Harris Ork. Barkley Sound Clayoquot Sound loetka Sound Quatsino Sound Claim Conqueror Little Boos ' Baden Powell ' ' Rose Sirdar | Elijah J 1 Dawid Harris Ork. Claims Sarita Rv. 1 Copper Is. 1 Crown Prince 1 Darby A Joan 1 Cascade Crk. 1 Han^Jy Crk. 1 Bald Eagle | Tidewater > Head Bay 1 June '* OldSport 6LASS A A A | A 1 A A A A ' A 1 B 1 B 1 B 1 C ! c ! ° ! °> A ; o, ' C MAGNETITE DEVELOPED IN LIMESTONE 11. The oontact metamorphic deposits in limestone are the most common type and the one most noted in the literature* In general , the statement may be made that deposits in this rock have a tendency to be purer and more regular than those in other country rook* On the West Coast of Vancouver Island the claims that belong to this group are: Those on Gordon River, Bugaboo - Greek in the HiUnat limestone including; Rose, Little Bobs, 0 Baden Powell, Conqueror, Elijah and David; The Sarlta River claims also belong to the Nitinat limestone. The magnetite at Head Bay, Nootka Sound, occurs in the Sutton limestone and it le probable that the limestone of the claims on Harris Creek belong in it, but this is not certain. The intrusive responsible for mineralisation in this group is, in all cases observed, the Beale diorlte. The effects of the intrusion are of two kinds, the endothermic or changes in the intrusive; and the exothermic or changes in the limestone, due to the intrusive. 0 Clapp C.H. Geol. Surv. Can., Mem. 13, p. 189. ENDOTHERMIO EFFECTS In many oases, pronounced endothermlc changes are noted in the Intrusive. This effect is not confined to contacts with3 limestone, but is also found along contacts* with other rocks, although it is usually most markedly developed along the limestone oontacts. The most common change is a decrease in size of grain in the intrusive olose to the oontact. This is often, but not necessarily, accompanied by darker colour In the diorlte, due to 12 MAGNETITE IK LIMESTONE Endothermic EffectB a large increase in the content of dark ferromagneeian minerals. In some oases porphyritlo phases may represent the intrusive at the contact, and it is only by a consideration of the mineralogical composition and its field relations that its true nature can be ascertained. "Solutions* derived from the magma of the diorite itself may cause an alteration of the intrusive* These can be divided inte two types, those which act before the magma is completely consolidated, and those acting after consolidation. The first case has not yet been fully worked out, so all the effects have not been described, but it seems probable that the formation of alteration products in feldspars, of "injection perthites* and of typical contact metamorphlc minerals, as^ primary constituents of an igneous rock may be due to this. The alteration of plagioclase to more acid feldspars along the margins is probably also due to this action. To what extent this last stage alteration may be governed by the position of the contact is difficult to say, but it seems to have a marked influence in many cases. A detailed petrographical study of a suite of specimens from the intrusive close to a contact would probably throw some light, not only on theee last stage phenomena, but else on the nature of the magma and seae of the causes of contact metamorphism. The alteration after consolidation is represented by epldotization and sillcifloation in the diorite, often along joint oraoka. Occasionally garnet may be developed and magnetite may occur in the intrusive* 0 Pcflre £ A-PLATE V. TO FOLLOW PAGE /2 Fig. A. Diorite^Conqueror M.O. showing formation of new plagioolaae (P) along the margins and within old altered feldspars (F). Where the new feldspar is close to the old <me or within it, they are in parallel orientation, but against the hornblende and pyrocene (M) this is not so. This is a common alteration close to the contact but not to this extent* Fig. B. A thin section showing the pronounced schistosity developed by the parallel orientation of diallage formed at the Tidewater under conditions of contact metamorphisau 13. MAGSETITE IN LIMESTONE EXOTHERMIC EFFECTS i ummmm* In all eases near the ore occurrence the limestone has recrystallised. This alteration may be either regional or contact, because the limestone is now a series of roof pendants in the plutonics and no field evidence is at hand to .-. show whether the limestone was marmorlzed before the intrusion. In its recryetallized form the limestone Is of varying texture from grains of almost lithographic fineness to some over one inch across, showing pronounced pelysynthetic twinning. Some sllloates were formed including garnet, (grossularite) diopside and tremolite, probably by recrystalligation of impurities. Variation In the alteration of the limestone seems, to a large extent, to have been governed by variation in the properties ef certain beds, although it is very difficult , at present, to ascertain original bedding. SILICATE 20KB The zones of contact metamorphic silicates on the Vest Coast are relatively narrow, none of them are more than a few feet thick. The commonest product of metamorphism is a mixture of garnet, epidote and quartz, with minor amounts of • ether silicates as tremolite and diopside. The distribution of the silicate zone is governedby several factors: original I bedding, attitude of the contact and breooiatlon of the lime stone. In many oases the distribution of the silicate zone MAGNETITE IK LIME8T0HE EXOTHERMIC EFFECTS — SILICATION Is parallel to the original beds of the limestone, suggesting a preferential replacement of certain zones due to texture or composition. Another important feature is the attitude of the contact. A vertical contact does not seem favourable for silication or ore deposition; one exposed on the ELIJAH M.C., Bugaboo Creek, showed silicates only where an apophysis of the diorite cut the limestone and so formed a trap for the contact metamorphosing agents. Bo very general statement can be made from the field observations that a flat contact favours the formation of large silicates zone, but this would appear to be a favourable place for mineral!sere to escape. The breociation of the limestone also to a large extent influences the distribution of the contact silicates. Where the breocia tion in the limestone was widespread the silication seems to have followed it enclosing blocks of the country rock. In a number of oases, the deposition of the magnetite was, in part, contemporaneous with the slllcatlon, although it had a tendency to extend beyond the time of formation of the garnet zone. The contemporary time of formation of silicate and ore may to large extent account for the banding observed in some deposits although preferential replacement of original beds by silicate and magnetite in most cases was present. If limestone with 40£ Oa 0 and a density of 2.6 is acted on by minerallzers 15. MAQHETITS IN LIMESTONE EXOTHERMIC EFFE0S3-. METALLIZATION which remove C0Z and OaO, and introduce Fe^Q,, Fe 0 , SiO^ to form a contact rock of density 3.0 containing 25$ OaO, depending on amount of OaO removed, there will be a contraction of volume, and magnetite may be deposited to make up for it. This may account for the irregular banding of some of the silicates and ere observed in some of the occurrences. The later magnetite may In part replace the earlier silicates so the relation of contemporaneously deposited magnetite may be obscured. The occurrence of blebe of silicatee in the magnetite may be explained as due to this replacement, or they may represent impurities in the limestone, which wae being replaced, reorystallized under the influence of the solutions depositing the ore. Olapppostulates the formation of the magnetite of the Gordon River Bugaboo Greek claims as due to concentrated magnetite solutionst "virtually magnetite magmas " which brecciate the limestone as a dyke would. If the nature of magnetite is considered, it seems difficult to see how magnetite can exist in a monominerallio magna, as magnetite. To the writer it would seem that these "apophyses" of magnetite represent replacement of limestone following, rather than causing, brecciation. The way the magnetite is formed is shown clearly at Head Bay, Nootka Sound. It is found in dyke-like or vein-like masses in the limsstone. Aotinolite in lenses parallel to the wall, with fibres running from wall to wall, is found in the magnetite. The silicatee probably represent impurities In the limestone which during the interaction of the iron bearing solutions with the 0 Olapp C.H.^ Geol. Surv., Oan. Mem. 13 p. 193. 18. MAGNETITE IN LIMESTONE EXOTHERMIC EFFECTS—METALLIZAgION oaloite, were deposited as silicates. In a section across the magnetite vein a banding can be seen with corresponding similar bands on each side, suggesting that as the magnetite was intro duced as some soluble iron salt, it interacted with the limestone along the vela and was deposited. From the distance it had travelled, It must have been very thin or gaseous. III the contact deposits, beside the silicates and mag netite, sulphides, especially those of Iron and copper iron, are developed, the principal sulphide minerals are: pyrrhotlte, pyrite and chalcopyrite. all these are developed later than the M- in magnetite with the exception of phrrhotite, which in some/stances, may have been formed contemporaneously with the magnetite. The conditions that control the distribution of the minerals along the contact cculd not be worked out. An example of this is at Sarita River. Here marble forms the top of a l*w ridge with a general East and West trend. This has been intruded by the Beale diorite so an undulating, almost flat contact Is partially exposed. At the West end of this ridge, a body of high grade magnetite with little sulphide is found, but as the deposit is followed east, pyrite and pyrrhotlte appear, with a corresponding decrease in mag netite. These sulphides seem to have a greater tendency than the magnetite to replace the silicated zone of the limestone. Another property is situated about one half mile east of the large magnetite body, apparently on the same limestone-dlorlte contact, although it is separated by an area of drift. Here pyrrhotlte, chalcopyrite ... 17. MAGNETITE IK LIMESTONE EXOTHERMIC EFFECTS and pyrite are developed but no trace of magnetite is to be seen* The only explanation that can be made seems to be that the sul phides are formed,under suitable condition,when the sulphur is present in the mineral!zers in some form. L4?E SAMQpg MMEBALJ? Fallowing the metallization some reins of quartz were formed. Calcite veins also occur in the ore, a few are mineralized by ohalcopyrite and pyrite but the majority are not mineralised, some of them probably being duo to meteoric water. Some veins of hydrous silicates are also found cutting the ore, of these serpentine and chlorite have been identified and probably others are present. MflHOR .imDftlVjB, Minor intrusives are found in the vicinity of these occurrences, at the Conqueror M.C. a porphyrite dyke occurs cutting the ore. Small dykes and sills are found at Head Bay, but they are earlier than the mineralization, because they confine the ore and are themselves mineralized. These minor intrusives are probably from the same magma that produced the mineralization. In certain oases, the diorites are themselves intruded by apophyses of more acid plutonics so possibly some of the mineral!zers from them may have caused alteration in the dlorite. WWW Mq, The Sirdar M.C. does not strictly belong in this class, but Its location in the Bugaboo Creek group make this the best '•"•-•••-• .__ 18. MAGNSTITS IH LIMESTONE EXOTHERMIC EFFECTS place for it* The magnetite here is a complete replacement, except for a few fragments in the ore, of a roof pendant or block of the Nitinat limestone by a quartz-diorite. ORE gBPQSITS ASSOCIATED WITH THE VABOOUVER VQLCAHIG3 The deposits associated with the Vancouver voloanics and apparently not related to liaestone, are much less important than those in limestone, both on account of the larger amount of impurities and because of smaller size and greater Irregularity of the distribution of the ore. These deposits are of great scientific interest because they show the variable effects of contact metamorphism. The volcanic rocks are of two types; flows sad tuffs. Some small beds of limestone may have been included in the voloanics and also, possibly, some intergrading types such as calcareous tuffs, which are known to oocur on Vancouver Island. The tendency of rock types to approach one another and the intru sive in composition during oontact metamorphism made it difficult to identify the original character of the oontact metamorphosed rook. The difficulty encountered under the microscopeMias even greater, therefore the rocks had to be named on the basis of limited field observation adjacent to the deposits. 0 Dolmage 7. Geol. Surv. Can. Sum. Rept. 1920 p. 15A. (2) Van Hiss O.R. V.S.G.S. lion. Mo. 47 - "A Treatise on Metamorphism* p. 713. Q) Plr8son fc.V. Am. Jour, of Science 4 Series vol. 40. "The Microscopic Character of Volcanic Tuffs* pp. 191-311 (1915) 19. MAGNETITE IS VOLCANIC3 The prlnoipal deposits belonging to this class are: The claims on Copper or Tzaartooa Island; the Crovn Prince Mining Claim, Sechart; The Darby and Joan M.O.,Albsrni Canal. All these occurrences are on Barkley Sound. They all show different obaraotere so it Is necessary to describe them separately. POPPf? I8LAJD On Copper Island, magnetite in the Vancouver volcanics is exposed oloee to the summit. The deposits are apparently related to the Beale diorite, bat the Saanich granodiorite passee very oloee to the deposit so contact effoots of it may be super imposed on theee due to the earlier diorite. The contact effecte obserred were various and will be dieoussed separately. It is impossible to disease theee prooeesee in the order in which they took place, because the evidence,is lacking. 3ILICATIQS WITH OQMTEttPORABV aAOIETITK DEPOSITION One of the moot Interesting contact effects observed was found at the very top of the island; here magnetite and * garnetlte rock are found in a banded structure. Observed in detail the thick ness of ths bands of magnetite and the garnetlte was from one quarter to four inches. Ths bands of silicates were far from continuous, but rather consisted of a series of Irregular parallel lenses having the general dip of the volcanic rooks of the island, with com plementary lenses of magnetite between them. The garnetlte was found to consist of a mixture of andradite and groesularlte with miner amounts of quarts and epidote. The original character of the volcanics oould not be determined but it was either a flow or MAGNETITE IN VOLOAKIOS - OQPPEH ISLAND a tuff. If it were a tuff, the handing might be accounted for ae a relic of an original bedding structure; even in a flow it is poaslble that metasomatism might take this form. The following is the origin that suggests itself to the writer* Whatever the nature of the original rock it probably had a density very close to 3.6. The density of the garnet!te lenses, as determined, was about 3.6. If the constituents of a rock •f density 2.S recomblne to form a rock of density 3.6 the loss of volume is equal to ?*ft T.frft ©* about one-third. This is 3.6 about the ratio of the exposed magnetite in the banded structure to the total mass suggesting, that in this case, the formation of the silicates took place under the influence of solutions which contemporaneously deposited magnetite to make up for the volume contraction • That the formation of the magnetite took place simultaneously with, rather than later than the garnet, Is shown under the microscope and ale© by the intinate intergrowth of garnet and magnetite. A further point in support of this mods of origin is found if the chemical analysis of an andesite, the average volcanic rook of the Vancouver group, is compared with analysis of grossularlte and andradite. A mixture of the two garnets with the exception of CaO, 9iOzand Fez 03 corresponds almost exactly to that of the volcanic. The excess of silica * forms the quarts of the contact rock while lime and ferric oxide have been introduced. The Iron was derived from the solutions which caused the metamorphlsm and Introduced the magnetite. The lime, that was being introduced at the same time, was probably also derived from the minerailsere,which had obtained it from 21. MAGNETITE IT. YOLGANICS s POPPER ISLAND limestones occurring elsewhere in the series on Copper Island* This absorption of limestone has been noted in a number of cases and introduced to account for arontaet silicates in non calcareous rooks* This case seems to show very definitely the effects of the solution where ere is deposited simultaneously*^ ' ^ * *'/'*+''* BANDED STRUCTURE DUE TO REPLACEMENT OF BEDS A banded structure of magnetite and the silicates was commonly observed in the deposits replacing volcanics. The bands were much thicker and more regular than those described as due to silication and contemporary formation of the magnetite. These are apparently due/to metasomatic action on bands in the volcanics so some are replaced by garnet, epidote, quartz, diopside and others by magnetite. It is possible that, in part, the action described as taking place in the case where the narrow banding occurs may have been active here, but although the for mation of the magnetite was in part contemporaneous with the silicates, some of It replaced earlier silicate minerals and formed veins in the silicated bands. Some of the ore also shews veins of quarts and epidote cutting it. BANDED CONTACT ROOK Beside the banded silicates and magnetite, banding of " the silicates alone was observed. One exposure on Copper Island showed a reck apparently of volcanic origin in bands six inches 0 Olapp, C.H. "Geology of Victoria and Saanich Map-Areas, Vancouver Island.* Oeol. Surv., Can. Memoir 36, p. 50, Bossier Trans. A.I.M.E. Vol. 61, 1913. p. 101. MAGHETITE IM votcMica g POPPER ISUSP thick, epidotized and apparently bleached, alternating with bands of similar thickness, consisting of epldote and quarts with snail amounts of garnet and vesuvianlte. The volcanic was apparently a tuff because it is difficult to see how a flow could be so uniformly banded with such even thickness. The adjacent bands must have been of very dissimilar composition er texture to yield such different metamorphlc products. It is conceivable that the series might represent a 1it-par-lit in jection ef a basic magma with a large amount of mineralizers late tuffs* after the injection the mineral! zers might escape late the porous rock and form the bands of silicates* The notable absence of amygdules is against this mode of formation. qjfflcp QQ^ACT, g£Hgg§ Besides the banded structures other contact effects were found. In some cases the andesites were altered to epldote along irregular lines and then replaced by magnetite. In other oases, they are feldspathized and siliclfled, with fragments ef original feldspars remaining. The new feldspars were in all cases more acid than the old showing the addition ef sodium in some form and the removal of calcium* The general features of the Crown Prince Claim are essentially the same as those of Oepoer Island except that in this case the intrusive is not visible, unless small dykes of granite cutting the ere belong to it. The banding ef silicates SAGJTSTIE IS ¥0LgAil03 - GROTS PRISC1 23. and gutgue found at Cop~er Island is also f«md "serf. r&iiDS?AtaizATicai OP inrre Froa their appeereace la the field, the rocks of tbe Cresn Prtace data •era originally toffs. Oader eonditicme of contact aetaaerpblsa a rock resexbling a Motita gneiss la pro-daeed. la thin section the rock la seen to hare suffered sarted feldsp&thisatloa and seas* coatespcraaeooB eilietfi cation. The original feldspar pbeaocryets , aear aadealne-X^bradorite, are deeply altered to aa iadetersiaate mixture of probably, ?aragfisiite aad xolsite so they bawe a sarked cloudy appearance. These paeaocryste bate besa altered to or replaced by acre acid plagiaclases, aear oI##pcl»*e-*nss*iB* mad probably sore acid. Tae aee feldepars occur irregularly la the old aad ef tea cos-pletely replace thee so all tbat caa be eeea of tbea is tbeir •gboat* foreed by tae rolsite-peragoalte. Is several cases the aee feldepars were fo-oasd is alternate twinning laaellae of tae old. This pro****again shewe the sarked introduction of soda. Hornblende aad pyrejwme occur is the feldspatMsed tuffs, probably one. ef tbese pes aa original constituent of tie rock* Several ef tbe pyrosenes observed bad cores of hornblende, aad also bernebleade rtas suggesting tbat pvr^&pt, under ce&diticus » •f c-cntact setawerpaiee, hornblende amy be altered to pyroxene aad tbat following this tbe pyroxene nay be aralitized. aetiaolite le ef later iatreduction, and veias the aoealc formed by tbe new feldspars aad tbe quart*. Snail aassee of garnet are alee found la tbe feldepathised reek aad. la isolated cases, seall stringers ef garnet eat it suggesting tbat tbe feldspethlsa-K&GH1T1TS I a l^ZAillQZ - CROSS FRIKOB tioa represented an earlier stage of the contact metajBorphism, but this is not certain. DABBY MB JQftS Tn* Darby and Jean claim on Alberxd Canal is totally different fro* the teo previously described occurrences in this class. Toe magnetite occurs In a garnetized and epidotized acne la the roeette pKjrphyrlte ©f the Vancouver vole&nics. It is possible that tae ainsralized area may represent a completely replaced lense of limestone. I© intrusive is visible close to the claim, bmt the extensive alteration of the porphyrlte to greenstones suggests, that the mineralization may be due to a concealed intrusive, although it is not impossible that the metaaorphism may be due to the porphyrlte Itself. Material frtm the garnet!zed zone under the microscope shews idiemorphic gurnet with interstitial isagnetite and quartz s© no definite conclusion as tc the relative age of them can be drawn but some of the magnetite apparently has a tendency to replace garnet, suggesting that, at least in part, the magnetite is of later formation* The alteration of the porphyrite is difficult to work out becwtfse of the fine grain of the minerals. The feldspar phenocrysts are altered to paragon!te-zoisite, the groundmaas is now a felted mass of actinolite and epidote with a few grains of some mineral of high relief and low interference colour, probably zoisite ar clinozoislte. Small garnets are also found. DEPOSITS DEVELOPED IN BOTH VOLCANICS AND LIMESTONE In several cases, both rocks of the Vancouver volcanics and the Sutton limestone have been mineralized and replaced. Various of the deposits described in limestone and in volcanics may belong here, but the occurrence of the other type of reck can net be recognized due to contact metamorphiem. The Tidewater Copper Company's mine, Clayoquot, and the June mine, .. really belong in this class, but due to several exceptional features they will be described later. The deposits which belong here are: the Sunshine group; Cascade Creek, Berkley Sounds the Defiance M.O., Handy Creek, Berkley Bound; Waterloo M.O., Kokahittle Arm, Kyuquot Sound; the Old Sport Mine, $uatslno Sound. Where the intrusive Is visible, it is a dierite, and in the ease of the Waterloo M.C. dlorite Is exposed a short distance from the occurrence. In all these deposits the contact metamorphic effects extended into both reeks. In the deposits on Bar&ey and Kyuquot Sounds, there is a marked tendency for the contact effects to be more noticeable and far reaching in the volcanics than in the limestone, probably due to the difference in composition and permeability to solutions. The Old Sport group was not visited but from Dolmages^description it appears that sllioatlon is more intense In the limestone next to the volcanics than in the volcanics <b Dolmage V. Geol. Surv. Can* Sum. Kept. 1920 p. 21A ($) Dolmage V. Geol. Surv. Can. Sum. Hept. 1930 pp. 33B-35B 26. MAGHETITS IB LIMESTONE I YOLCAHIC8 In the deposits the commonest metallic mineral Is magnetite. Hematite later than tha magnetite was found in ths Barker and Kyuquot Sound localities. In all ths cases, ohaloopyrite occurs which is younger than the hematite. Pyrlte la also found but Its relation to the hematite la not clear. It the Old Sport pyrrhotite occurs, •specially close to tha dlorlte contact, and la more or leas complementary to the ohal oopyrite. A dapaait which probably should be in this claaa la the Bald Sagle M.O., Sechart, Berkley 8ound. On this claim aa reloanioe are axpaaad next tha ore, but they are found close ta It. Tha texture of tha ore, tha impuritlee in it, and a banding closely resembling that found in ere replacing volcanics euggest that It may be a nearly complete replacement of rolcanioe near limestone. The limestone, expaaad near the ore, baa a sone of silica tee consisting of trsmollte with minor amounts of garnet and ebrine along lta contact with the dlorlte but no magnetite derel-©ped In it. In tha aaaa dapaait a mass of coarse granite er pegmatite consisting of quarts and feldapar, extenelrely garnetized, la found next tha are, but lta praolaa ralationahlp to tha ore-body la nat olaar. Due ta tha common association of the magnetite with diorite obeerred In the other depoelte it ie probable that the mineralisation hare amy be due ta It. TIDEWATER U.C. The geology of the Tidewater Copper Company*e mine at Sydney Inlet, Clayoquot Sound is rather complex, and there are unusual features so it is made, with the June Claims, Quateino Sound, a separate type. The geology is described by Dolmage and, in part, the following brief description of the general features ef the deposit is from his description. To quote from his deecriptlon -"The mountain on which the ore-bodies are situated is composed ef light grey granodiorite up to about the 1500-foot contour." Slides ef this rook show it to vary from a granite te a granodiorite in composition. On the top ef the hill over the ore-bodies limestone occurs, tn contact with it on the lower side are a series of andesites; _jfhe contact has a shallow dip, and is slightly undulating. The andeeites are, in general, openly folded but looally eteep dips are encountered. Below the andeeltee a eeries of schistose /torks, with a flat dip are found, theee were observed to grade laterally into porphyritic types similar to porphyrite dykes in the limestone and andesitss, so they are thought to repreeent contact metamorphosed dykes or sills younger than the andesites. The ore-bodies occur in the limestone, andeeites and ths sill forms,as replacements of them. •» COHTACT METAM0RPHI3M OF THE LIMESTONE AND ANDESITS The limestones are marmorized and small garnets and grains ef diopside are developed in them, apparently by recrye-i 0 Dolmage V. Geol. Surv., Can., Sum. Rept. 1980 pp. 20-21A. TIDEWATER MO. talllzation of impurities. Mica, probably near phlogoplte, Is formed In small stringers by the introduction of material. Locally, the limestone is altered to^masses of garnet and epidote. In the volcanics the commonest alteration noted is the formation of garnet, epidote, quartz and diopside, in some eases, original banding of the rook is preserved in them. It was noted that the volcanicB seened to have a greater tendency to develop con-tact silicates than the limestone, perhaps due to a greater dis-tanoe^from the intrusive. OOyTAgT METAMQRPH^Sy OF SILLS The alteration of the sills could not be worked out completely because a complete suite of specimens was not available, however the early stages are suggested by an alteration observed in a porphyrite dyke. The alteration of the porphyrite may have been, in part, or all, endothermlc. The rock has been acted on by solutions which altered pyroxene to hornblende. The basic feldspars," near andesine -labradorite, forming the phenocrysts have been, in part, altered to a mixture probably of paragon!te and zeisits and replaced by a more acid plagioclase, near ©ligoclaee. The new feldspars resemble small pegmatite masses but they are found within the basic ones, and in some cases residuals of the andesins-labradorlte are found In parallel 0 optical orientation in the collgoclase suggesting a replacement by tenuous solutions. After this alteration hornblende was introduced in parallel zones so a pronounced gneissic structure Is developed. That this stage took place in the sills is probable, (2? For a somewhat parallel case eee Foye w.V. - Sc. Oeol. Vol. 11, p. 668* RV . TIDEWATER 29. • but a thin section showing it was not available. The next stage in the alteration of the sills gives a dark green, fine grained schistose rock. Under the microscope the sohistosity is seen to bo due to elongated light green grains with prominent deavage, Showing a pleoohroism from green to light green and a high extinc tion angle. This mineral was determined as a pyroxene near Q dlallage. Minor amounts of quarts and an indeterminable feld spar wars also found* the diallage schist is altered, apparently by solutions, along channels, the majority of them parallel to the schlstosity but sons cutting across it. This alteration changes the schist to a grayk fins grained, cherty appearing reck so all traces of schistesity are lost. All intermediate stages between the schist and the shorty rook are present. Under the microscope with even the highest magnification available it is difficult to work out the mineralogy of the cherty rock. A mineral, apparently a feld spar, but its basicity could not bs determined made up the larger, mass of ths rock. A colourless pyroxene and some garnet and quarts made up the remainder. The whole rock is cut by veins of colorless pyroxene, near dispel do. The next process is a further alteration of the rock by solutions. This order is beautifully illustrated in the hand specimen. A mass of dlallage schist is altered along certain lines to the cherty material and inside this a narrow sons of andradite garnet is found, definitely later than the other al-Q> For a dsscription of dlallage occurring under somewhat similar conditions BOO -Miller, W.J. - "The Magnetic Iron-ores of Clinton Co. I.Y.* So. Geol. Vol. 14, pp. 514 - 533. See ftt*r£ ~V 0 « m: % 30. TIDEWATER teratione. . The next stage la a further formation of contact silicates so large masses of the rook are eventually replaced by garnet and epidote with miner amounts of diopside or hedenbergite. The period of metallization followed and probably to some sxtent overlapped it* The first metallic to be formed was magnetite, fol lowing it bornits was deposited. Chalcopyrite was formed later than the bornite as seen both under the microscope and in the hand specimen. The order found in the case of the Tidewater is essentially the same as that found by Dolmage at the Marble Bay Mine, Texada Island. The bornite Is commonly replaced along joints and contact with ether minerals, by oovelllte and sometimes chalcocite. The alteration is only occasionally noted in the ehalcopyrlte and In no ease observed, was the alteration found along the contact of bornite and ehalcopyrlte, which, if the oovelllte were formed later than the ehalcopyrlte, would be a favourable place for it to form. The explanation that would seem to cover the case is that the copper sulphides, In par^,were formed before the deposition of the ehalcopyrlte but that some action extended beyond this time so a little of freshly deposited ehalcopyrlte was altered. The alteration of the limestone and andesite probably followed essentially the same order of,' formation of silicates, than metallisation but the ohange could not be worked out in as grsat detail. 0 Dolmage V* "The Marble Bay Mine,Texada Island,B.O.M. So. Qeol. Vol. 16, PI. 12, p. 384. 31. TIDEWATER The complexity of the metamorphic process outlined above may be due to emanations from several intrueives below the ore-bodies. Endotheralc effects in the sills may account far some of the alteration in them. Tfg fpys finis Taa June or Jeune group of claims la about four •ilea from Quatsino Sound. Liaeetones and volcanics have been Intruded by a dierite; a mere acid intrusive oocura near the claim and it probably la reeponeible fox many of the effects observed in the diorite, volcanics and limestone. The con tact effecta on the volcanics are not extremely marked; some quarts, epidote and garnet are developed and they are miner alised by magnetite and sulphides. The way In which the mag* netite replaces the volcanics, along strlngsrs and around graina la of interest beaouae it auggssts that the iron must have been introduced in very tenuous solutions or in some fora approaching a gas. Io vary exteneive mineralisation of the limestone was observed, but it was found to be largely replaced by clear, coarse grained quarts, resembling that of pegmatite dykes or igneous reeks. REPLACEMENT OF PIORITS The mast notable feature of thia deposit was a re placement and mineralisation of the diorite. This process was noted in ether occurrences but net so extensively developed ae here. It followed some lines of weakness such as a joint oraok, so It can bs obeerved In all stages from a narrow line to one embracing large amounts of ths diorite. The first alteration JUNE GROUP is the introduction of magnetite vhloh, in most cases, replaces the ferroaagnesian constituents of the rook, although it is rarely found replacing feldspars. This replacement must have been by very tenuous solutions or by gases because of the preferential replacement of certain constituents, and due to the fact that en the polished surface no *lalbl» connection Is visible between the magnetite masses. The basic plagio-olass is largely replaced by pyrite and pyrrhotite, in some cases tills replacement seems to have chosen alternate twinning lamellae In the feldspar. Bornite followed the Iron sulphides and some quartz veins observed were probably related to it. Covelllte and ohalcoclte are found in the bornite but in this oase they were not observed at all In the chalcopyrlte, so they were judged to have formed before the chalcopyrite, whloh was later than the bernite. Fine grained quartz with pyrite, in contrast to the clear, coarse grained quartz related to the bornite, cute all the ore minerals. Other non-metallic minerals include a dark-green, fine columnar epidote which appears as an alteration of the plagioclase, apparently follow ing the formation of the pyrrhotite. Serpentine Is found in veins cutting the other minerals. It may be an alteration of the early minerals or of later introduction. The origin of the mineralizing solutions could not be worked out; whether they were from the diorlte Itself or the •ere acid intrusive. It is peculiar that the diorlte should be replaced when ten feet away a limestone occurs, but it is probable that the limestone does not extend very far below the surfsow. MINERALOGY - METALLIC Before discussing the contact metamorphism, In general, the properties of the minerals found and peculiarities in them will be described so descriptions to use in the discussion of contact metamorphism and ore-genesis may be kept together* To determine the minerals present and their ages,• polished surfaces were prepared of over twenty-five pieces of characteristic ore. The general results will be summar ised below under the particular mineral species. In the polishing of the ore, not much difficulty was experienced. The majority of the minerals in the section were hard, so that they could be ground to a good surface rapidly by means of a steel lap, using "Wellsworth Emery No. 180". It was found, that If little water were used, and the emery run until fairly dry, much better results could be obtained. After this treatment, It was put on another steel lap with "Wellworth Emory No. 303*, and ground until all the scratches were re moved. The polishing was carried on on a steel lap covered with fine linen, revolving at high speed. Chromic oxide mixed to a stiff paste with water or liquid soap was the polishing agent. The surface was held on this lap with con siderable pressure until the lap was nearly dry, then a further application of the chromic oxide made* Most of the polishing 34. MIMSRALOGY - METALLIC Of the hard minerals took place when the lap was nearly dry and in this case the soap was of advantage because it dried more quickly on the lap. The specimens were mounted on glass slides with plasticine and examined under a Leitz mineral ©graphical microscope, fitted with a prism illuminator. . An qtc lamp with condensing lease was found useful for oblique illumination to supplement the vertical illuminator under medium power ob jectives. By Means of the oblique Illumination, minerals which mould not be determined otherwise were easily made out, such as the nature of some of the gangue minerals. In the determination of the paragenesls of the minerals in the section, a constant difficulty was encountered, das to, not only the hard metallic minerals present, but also to the hard silicates, such as garnet, which tend to have idiomorphic form. VIth these minerals and softer ones in the same section there is a constant tendency for the softer ones to be called younger'. This probably accounts for the obscure time relations noted between pyrrhotite and magnetite. The commonest metallic mineral found in the deposits was magnetite. This mineral has the composition usually written T9s0f - H 5.5*6.5 G 5.2. It crystallises in the isometric system as octoheoVons and dodecahedrons. It is strongly magnetic and in some cases has polarity. In the surfaces from Vancouver Island magnetite is usually the oldest metallic mineral. In general it is slightly later than the garnet 0 Gilbert 6. vThe Relation of Hardness to the Sequence of Ore Minerals* Ec. Geol. 7©1. 19, pp. 668-673. MIHERALQGY , METALLIC? minerals. The size of grain varies from some one-half inch aoross to some toe fine to see, and vlth difficulty distinguishable under the microscope. One difficult thing to account for ob served under the microscope was the different appeamoe of grains. In the ease of the claims at Head Bay, Nootka Sound, in ons of ths small wins in limestone, the magnetite in the centre of the vein is much lighter than that at the two sides. No visible impurities oan be detected under the microscope. Adjacent grains of different oelors sight he accounted for by different optical orientation of the plane of too section, as an ootonedrar plane and a cubic plane but no apparent reason oan be found why, on opposite sides of a vein, a different orientation should hold from that In ths centre, the obvious explanation would be a slight change in the composition ef ths depositing solutions at the time of deposition. Broderiokf for a similar ease, but obssrvsd in adjacent grains of similar Orientation, comes to the conclusion that it may be due to a solid solution of Fe ZQ3 In F«3 0t . In the Nootka Sound oaee there wae not much difference in the etch figures produosd on ths surface by hot hydrochloric aoid. Unfortunately accurate chemical analyses could not bs made. In a great number of cases, adjacent magnetite grains had a different color, but their orientation oould not^be drawn from them. In some cases these grains etched very differently with hot hydrochloric aoid. Ho titanium minerals were found either by etching or blowpipe tests. O Broderick T.M. "Some of the Relations of Magnetite and Hematite." So. Oeol. Vol. XIV. 1919. p.363. 36. MINERALOGY - METALLIC In several places "geniculated* magnetite was found. This type was named because of the resemblance to the geniculated twins of rutile. Examination of specimens failed to show any simple crystal face in the isometric system, which could form the twinnlng^lane so it was concluded the structure was not due to twinning. One explanation is that it was produced by inter ference of individual crystals during growth, and the longitudinal furrows on the individual grains are due to the oscillatory com bination of thus dodecahedron and the octohedron. The magnetite with polarity, constituting the variety lodestone is of Interest, because of its relative rarity. Two occurrences were noted on the West Coast. At the Sunshine group on Cascade Creek. Berkley Sound, magnetite with a strong polarity was found. At the Black Prince claim, about one mile from the above locality, more lodestone was founds its polarity was ' relatively weak. Pieces from both localities were polished and etched. The two magnetites were of totally different character. That from the Sunshine Group polished with a pitted surface. It was relatively pure with only a small amount of quartz later than the magnetite.thWt.% __. tended to have a somewhat parallel . arrangement throughout the surface. On etching, this surface showed a parallel arrangement of etched bands w>rh/renounced cracks v•-:.•:. etched deeper between them . , In one case, a radiating structure was observed, resembling that in specular!te, but no Ijematite could be found in the section. A similar structure was found in seme of the magnetite at Bead Bay even more highly dsveloped than this, but it showed no trace of polarity* The MINERALOGY * METALLIC speoimensfrom the Black Prince MUG. showed a mass of very pure magnetite consisting of grains from one-half a millimeter to one centimeter in diameter, intergrown with one another. Apparently when this magnetite was being formed, numerous centres of crystallization were set up so the equidimensional grains grew until they interfered with one another. The faces represented are, therefore, not crystal faces, but contact faces Under the microscope the grains appear different colors, and on etching the color,contrast is greater* Noganing Is observed within the grains. Specular!te or specular hematite occurs in several places. Under the microscope it shows needle like forms which are not as easily etched, by hot concentrated hydrochloric acid as the magnetite crystals. In all cases, where found, the hematite fojned later than the magnetite with needle like pro jections cutting the grains of magnetite giving angular outlines to the pieces. For a somewhat similar occurrence, BrOderIck° or /arto otto (j rc/r-q / f> rfff *J , suggest these may be replacements of magnet!te„ The relation to the sulphides is not clear, except In the case of the Waterloo M.C. where the chaleopyrlte Is younger. In all cases the specularlte was formed by magmatic solutions or alteration. of earlier magnetite under deep seated conditions. It could not be formed by weathering because ef the unoxidized condition of the sulphides near It. Some of the hematite was slightly magnetii'o but this is probably dueto included magnetite. a> Br Oder i ok T.M, "Some of the Relations of Magnetite and Hematite" Ec. Geol. Vol. 14, 1919, p. 362. 38 MINERALOGY - METALLIC Pynhotite was found to be the most common sul phide in the deposits. In certain cases it was found to son8titute practically the entire mineralization along the contact as at the small occurrence, described on Sarita River. On the polished surface, the mineral appeared as; veins in the magnetite and garnet, or as disseminated grains in them. These small grains never showed crystal boundaries and since they vera almost structureless as viewed under the microscope, it was very difficult to determine the relative ages of the pyrrhotite and the enclosing hard mineral. The hand specimens where the pyrrhotite occurred as stringers often proved mere valuable in telling the relative age than the polished surface. In general the conclusion arrived at was that the pyrrhotite was in most eases later than the magnetite. Fyrite occurred as stringers in the ore, as a 0 filling for joint cracks, and as disseminated grains with a strong idiomorphlc tendency. In some cases pyrite of several generations was found. The most usual occurrence was for it to be ;just latsr than the pyrrhotite and occurring as veins in it, however .when pyrrhotite did not occur pyrite often did, In which ease it occurred as grains or veins in the magnetite and garaetite. In some oases the pyrite occurred after ohalcapyrite associated with veins of oalolte or quarts; but It wasmjore usual for it to precede the copper iron sulphide. Chalcopyrite belonged to the last stage of sulphide mineralization, except when small amounts of pyrite appear of later formation. Under the microscope this mineral is easily recognised by its softness and color. It is almost & PL. ?}. PLATS 71. TO FOLLOW PAGE J<9 fiat A» Camera lucida drawing of section from June. Mine, showing forms of pyrite (P) replacing pyrrhotite (M). The tendency to develop idiomorphic form is noticeable. The spherical structure seen in the two grains was noted in several places, hut It could not he explained* i x 2°& Fig. B. June Mine. Magnetite (M) showing idiormorphlc form replacing calcite (C) interstitial to idiormorphlc grossularite (G). The magnetite is also replacing the garnet. MISERALOGY - METALLIC? u. 39. m\ w 4 . ,; If entirely structureless and seldom shows crystal forces, then usually against a soft mineral such ae calcite. In some eases where cut by later quarts veins the line of the veins shewed curious angular displacements suggesting a following of some structure as cleavage or parting, but since it is negative to the usual reagents, it was not etched. One peculiar Structure between magnetite and chalcopyrite was noted at the June group of claims. Here masses of magnetite were found which shewed in cress section, concentric elliptical bands of chalco pyrite. The whole structure was about four Inches across the major axis. Under the microscope the chalcopyrite was seen to toe definitely later than the magnetite. The only explanation that would seem at all feasible is,that the magnetite was formed and then subjected to stress so concentric lines cf weakness I were formed. Later copper bearing solutions came along and |§ took advantage of this to deposit. ||| m Bomite was found only in the two localities, namely |j the Tidewater and June. In both these localities it was definite ly earlier than the chalcopjprite although at the June one occurrence suggested a later generation of bomite but the !|f m evidence was not conclusivs and it was met only in one place in |i one section. * |:|j Oovelllte and chalcocite were found ae primary minerals la the bornite. They occurred as small stringers and veins in the bomite, sometimes apparently parallel to the octohedral cleavage of that mineral. The evidence would point to the formation cf the coveliite and chalcocite, before the intro duction of the chalcopyrite. > >!, *&***&*&: •'-•''•••'-''• MINERALOGY - METALLIC Galena *as found as small cubes in toe altered line-atone at the June. The above Hat constitutes the primary metallic minerals observed in the magnetite occurrences. In general the average pangenesis of the minerals for all the deposits would be magnetise, pyrrhotite, pyrite, bornite, chalcopyrite. Lsoally there might be variations, but this list, except for the bornite, corresponds to Claps's'list for Southern Vancouver Island* 0 Olapp, C.H. Osol. Surv., Can,, Mem. 13, p. 168* MIKSRALOGY - mH-ti£?klLIQ 41. In the case of the non-raetallies, the paragenesis tf mors difficult to dstannine because thin sections of the contact metamorphosed products weirs not asAlable. The identity of the transparent minerals was determined by in spection and by the examination of powder in oil using Larsen's tables, A few were determined by their optical properties in thin section,where these were available. 0 Larsen E.3. "The Microscopic Determination of the Nonopaque Minerals" 0.S.G.S. Bull 679 - 1921. MIKERALOGY - SON-METALLIC 42. Garnet is present in the deposits both in massive and in crystal forms, showing the dodecahedron, and icosltetra-dron. The commonest form that occurs is the red calcium iron garnet, andradite. The calcium aluminium garnet, grossularite, occurs quite commonly but does not form as large bodies as the andradite. <4uite often the two minerals occur together and can only be separated under the microscope, by the different indices if refraction* The garntft does not show preference for any type of intruded rock, but apparently developed squally well in any of then* In general, garnet appeared to have been formed before the metallic minerals were deposited, but probably in •est cases there was some overlapping in their time of formation. Epidote is another very common constituent in the com tact zone, occurring often intimately mixed with the magnetite. More often it occurs as an alteration of the volcanic rocks Invaded, often extending long distances from the contact. It ie quite often found as alteration of the Intrusive rook, especially almng fissures. Ho attempt was made to distinguish G> epidote formed by "contact metamorphism*, and that formed later, "as in fissure veins,n In the amphibole group actinolite and tremolite were found in some quite large crystals but they did not occur as plentifully as the epidote. Some hornblende may have been formed by contact metamorphlc process, but it was found impossible to distinguish between the product of Contact metamorphism and toe product of normal uralitization. 0 Lindgren 1. •Metasomatic Processes in Fissure Veins* Tr. A.I.M.E. Vol. 30, pp.610-611 - 1901. few 43. MIHERALOGY - SOB-KJETALLIO In the pyroxene group several individuals were found* Diopslde is of quite common occurrence in the contact metamorphosed voleanics, but it Is quite easily overlooked in the field. In several localities a dark green mineral resembling dippside was found, probably hedenbergite or an intermediate mineral. So wollaatonite was observed but Dolmage reports some from the West Coast. Some vesuvianite was found under the microscope in a •ass with epidote and quarts. Chlorite and serpentine were observed in a number of plaoes. They occurred later than the ore and in some oases are probably secondary, fotmdd by the alteration of earlier contact, silicates* Exaot relations of these were difficult to determine due to their softness and tendency to be removed during the polishing of surfaces. In several cases under the petrographlcal microscope small- grains of minerals thought to be clinosoisite or zoisite were found. On account of the high magnification required, it could not be distinguished whether the extinction was parallel or nearly so* Quarts is of very frequent occurrence in the deposits of * the Vest Coast* It is found in the masses of contact metamorphosed roes containing epidote and diopslde. It also occurs as veins cutting the ore in many of the deposits and is later than the majority of the mineralisation although it is occasionally found with pyrite. (D Dolmage f »M. G.S.C* Sum. Rept. 1920 p. 15A 44 • SfilHERALOGY s NON-METALL?0 Calcite occurs as residual fragments of limestone in the contact metamorphosed rock and ore and also as veins cutting the ore gone* Some calcite crystals found were due to recent solutions and deposition from meteoric water. Titonite was observed in several slides of both the igneous rock and the contact metamorphosed product* Plagioclase near ol^oclase and more acid was found as an alteration product in some of the slides. The new feldspars seemed to he developed in the elder more basic ones Aether by the replacement of the eld feldspars bodily by the new ones, or by the removal of lime and addition of soda to the more basic ones. qopTAgT MgSMfiSaOgB - «"»•* Before discussing the contact metamorphism of the magnetite deposits It Is as well to review the existing ideas of this process and the definitions of the word. The word metamorphism Is, Itself, a much abused term; it has been defined by various authors with various applications so now, when metamorphism Is mentioned, the exact meaning of the author has to be judged from the context or from a definition. Contact metamorphism has also suffered from the usages imposed upon It* The definition adopted by probably the majority of geologists is. "Contact metamorphism comprises all metamorphic changes due to contact with or proximity to any body of eruptive (igneous) rook, the new crystallizations not being definitely directed by dead weight stress." This definition is obviously intended to include the alteration, where materials are derived from the magma. Certain geologists would confine contact metamorphism to the effeote due to heat and mlneralisera without accession of material from the magma; , -~-~__zr55«*&»'i'*r'-'* •" • "*" —'—-•••—"""— "• * ....--this effect is usually, simply called recrystallization. The case where much material is contributed by the intrusive is oalled contact metasomatism. Barren further divides the metasomatio processes into, pneumatolytio and hydrothermal, depending whether the emanations are above or below the critical point for water" vapour. Probably one reason for the confusion in the definitions of contact metamorphism and its phases, is the difficulty in determining which process* was the one most active, and so one 0 Daly R.A. "Metamorphism and its Phases". Bull, Oeol., Soo., of Am. Vol. 28, 1917 p, 405. ,f) Barrell, J. "Geology of Marysvilie^Mining District Montana." U.S.G.S. Prof. Paper Ko. 57, pp.116-117, 1907. OOHTAOt METAMORPHISM e GENERAB term Is used to cover the several processes. In the same way, the distinction between pneumatolytic and hydrothermal alteration It very difficult to make so that, In many oases, these terms are used Interchangeably. mmsmmmm, There Is a disagreement among geologists as to the relatlTe Importance of the different processes of contact metamorphlsm. Recrystallizatlon, or the case where not much material has been Introduced from the magma, has been proved In a number of cases. By this process limestone is altered to marble and Shale to hornfels. The products of recrystallizatlon along igneous contacts are so similar to those which are due to the less severe regional metamorphlsm that It Is often difficult to separate the two effects. This may account for the overlooking of recrystallizatlon under conditions of contact metamorphlsm. Another reason for the overlooking of recrystallizatlon is that the alteration, by emanations from the intrusive, is usually much more striking and also due to the fact that they may replace or alter the recrystallized material. KAGfmq, gmmmsm The effect of Introduction of material from the magma Is usually so striking that all geologists must admit Its Importance In the formation of the contact zone. To discuss how the emanations from the magma arc given off to the contact zone, and the origin cf the mineral!zers it is necessary to follow the CONTACT METAMORPHISM » SEKERAL changee In an intrusive from the molten atate to consolidation. If a normal magma is started with, it Is thought that it has a large quantity of gases associated with it auoh as; chlorine, water vapour, carbon dioxide, fluorine, sulphur, and other volatile eonetituente, which reduoe the fusion point of the melt and the viscosity. It is wall known that in the crystallization of igneous rocks the acoessory minerals, magnetite, pyrite, pyxrhotite, rutile, titanite, ilmenlte are the flrat to form. The flrat ©ryetallization of the metallica has always been difficult to explain becauae the same magma may form ore-bodies from ita mineralisers, as a laat product. Certain geologists? against the evidence of many petrographera, would even raverae the order of accessories first, and make them of later intro duction by the mineral!zers. The processes advanced aa the moat prominent in the igneoua rook magma are; magmatic differentiation due to liquation and the principle of supersaturation abovs the amount necessary for the formation of entootles. To these may be added many minor processes which have been postulated for the formation of peculiar rook types. If the rigid principle of the formation of eutectics la hold, it la almost impossible to account for some igneoua rocks. •a an example, a chip of a rock from Oliftan Point, Copper Island, 0 Tolman,G.F., and Rogers, A.F. *A study of the Magmatic Sulphide Ores." Stanford Univ. Publication 1916. pp. 30-31. Review Ec. Oeol. Vol. 13, pp.633-637. 48. CONTACT METAMORPHISM g GENERAL showed phenocrysts of quartz which was the first rock forming mineral to crystallise. Plagioelase phenocrysts were formed next, and the quarts was corroded and embayed and then a mioropegmatite which apparently altered the feldspar made up the groundmass. This case demonstrates how an eatectic may be passed and a mineral deposited whloh is unstable in the remainder of the magma* Vegt® points out the tendency for the glass mal^Lx of a reck to approach a eutectlc composition. This oscillation about eutootle omposition demonstrates how the "enteotio* may not bo in equilibrium with the already deposited minerals whloh explains why a rook may be altered by its own "eutootle juices.• Colonjrbelleves that the last •tags residium, approaching a enteotic, may with the mineralizers produce important effects on the already formed minerals such as; the formation of "injection perthites", and the formation of aetinolite, bzotite, chlorite, at the expense of earlier ^erromagnesian minerals. Zn the case where the end stage product extends into the Intruded rock, its importance cannot be overlooked. This tendency toward the formation of eutectics would account for the rather notable tendency for the contact sones along different intruslvos to be rather similar, a faet which has boon urged by a number of supporters of the recrystalllsatlon hypothesis as a streng&rgument for similar impurities in the ® Vogt J.H.L. "The Physical Chemistry of the Crystallization and Magmatio Differentiation if Igneous Rocks* Jour, of Geol. Vol.31,1922. pp.333-252 - pp.407-419. <D Colony R.J. "The Final Consolidation Phenomena in the Crystallisation of an Igneous Rook" Jour, of (tool. Vol.31, pp.l89-l?8. J.'.'-.-1, .: 49. COfiTAGT iiETAMORPHISM a OSSERAL intruded rook so that similar silicate contact zones are formed* The changes in the magma show a tendency toward an equilibrium from the molten state until it is consolidated. The proximity to an intruded reck will have a marked influence on the processes which go fen in the magma, so variations in the intrusive may be noted. Fine grained contact fades due to rapid cooling, caused by the escape of mine rail sere or shilling because of the proximity of the intruded rook are common. Porphyritic fades or marginal facies of different composition may be due to the absorption of wall rock upsetting the equilibrium in the rook. ->.•-„ This absorption^ of wall rook, especially limestone has been noted in many cases with the resulting production of peculiar rook types. It seems probable that this interaction would modify, to a large extent, the content of the mineral!zers and also cause their emanation to be somewhat irregular. The effect of the intrusive on the country rock Is usually so much more noticeable than the endothermic effects, that contact metarnorphism is often applied to this phase alone. After the magma is in place in the intruded rock, and as •» consolidation begins, a heat wave travels out; this wave in some oases, produces a recrystallizion, and a general readjustment of the country rock. It travels out slowly and the temperature Q) Paly ft.A. "Genesis of the Alkaline Hocks. * Jour, of Geol. VOl. 26. pp.97*13*. "Origin of the Alkaline Hocks.* Jour, of Geol. Vol. 21, pp.87*118. fe'iv 50. CONTACT METAMCHPHISM «. GENERAL gradient is steep, so that before it has gravelled a long distanoe a considerable part of the intrusive haa consolidated, so there is a collecting of the last stage of crystallization product, and the miaeralisers which are released and enter the country rock. The reasons the intruded rather than the intrusive rook is attacked, are two, chemical and textural. The emanations are derived from the intrusive and as a result are more nearly in equilibrium with it, so they prefer to attack a rack of another composition. < ^ However, ae shown in the consideration of the processes in the Igneous reck, the mineralizes may not be in equilibrium with the Intrusive, and so it may be attacked. The texture of the Intrusive is usually close grained, while the country rook is relatively parous either, as an original character, or due to the heat wave from the intrusive. In individual deposits variation in the composition of the emanations may be traced by the order of deposition of the minerals. Ho rule seems to hold except that, in general the more acid emanations precede the more basic ones, but exceptions to this have bean noted raanjj: times, even in the one deposit. . On account of this variation in the contents of the emanations several authorsf especially those working on the iron-ores of Eastern United States, have postulated the differentiation of the last stage material and the mineraiizers into two poles, one aeid and one basic Aoeording to this view the more acid Q Colony R.J. 'Magnetite Iron Deposit of South Eastern New York" Saw Tork State Museum Bulls* 349-250. 193$. 51. OOHTAQT METAKQRPHI8M g OBfflSRAL pole would represent a normal pegmatite, using it as the name of a product about as acid as a/granite, and the basic one would contain the iron and other basic metals. They use pegmatite also as a nans for the basic differ^tiate, which is unfortunate because it leads to confusion. In the case of the contact metamorphic magnetite there is not the striking evidence for differentiation of the mineralizere and the last stage residium into poles; but the two types seem to ooae off together. The reason why over lapping of the solutions is common, will be discussed in connection with the contact metamorphism on Vancouver Island. 53< FORMATION OF SILICATE ZONE - VANCOUVER ISLAND OOKTACT M£TAMQRPHI3M OH VANCOUVER ISLAND > FORMATION OF iJt. jt.. ,T.„Mm.- *-iJC -TisJPl. ~IMU In considering the contact metaraorphism of the magnetite occurrences of Vancouver Island, the type of field-work done must he borne in mind. A series of isolated occur rences were examined} the purpose of the examination being mainly economic so the work was confined to a limited area close to the ore bodies* The lack of broad field work made it relative ly impossible to determine the order of some of the processes on a broad field basis. Taking the occurrences all together, it is impossible to find •widmnee of reorystalllsatloa without addition of material except In the ease of the limestone which was marmorised. this recryetalllzation may have been due to an earlier regional metamorphism, but In certain cases, a gradual increase in sise of grain as tfao intrusive contact is approached suggests, that al though It may have been altered to marble by regional metamor phism that it subsequently was recrystallised under the influence of the intruaove. The action of emanations from the magma is much more Important both as a contact metamorphosing agent and as the source of the metallic minerals of the contact zone. A noticeable feature of the deposits of the test Coast is the small size of the garnet sons formed. Xn many occurrences elsewhere, the garnet sons forms important rook unite in the contact deposits, along lntruslves of the same basicity as those of Vancouver Island. The only explanation that may be advanced ie that the magmas •IS,. 53. FORMATION OF SILICATS ZONE - VANCOUVER ISLAND which produced the contact metamorphlsm were relatively high in iron hoaxing mineral!sera so the zone due to the more acid pa*?t waa not large. That some of the more aold products were present is shown by the formation of some silicates and the alteration of the basic feldspars of the intrusive to more acid forms along the margins and craoke. These emanations are characterised by their high content of, sodiums in some form, and of si Horn* The other common elements are also present, but they arm subordinate in amount to these in their effects. In the limestone contact tones ofVanoouver Island, minerals con taining soda are relatively rare although soda lime feldspars0 are found in some oases, but in the contact zones of other form ations the albite molecule is often noted. The reason for the small amount of soda in the limestone is that more stable compounds can be formed with the lime and iron, so the soda passes out and may reach the surface as sodium chloride which is often noted in fumarollc deposits. The deposits associated with the rocks of the Vancouver volcanlcs show fairly wide sones of alteration. The volcanlcs are of about the same basicity as the rooks which intrude them, so their alteration may bs very similar to that which goes on in the 9 igneous rocks. For this reason, the formation of more acid feld spars at the expense of old ones in the contact metamorphism of the volcanlcs, is ascribed to the same cause that produces the alteration In basicity of the feldspars in the intrusive, that Is, it is the result of the end stage products of the final consolidation ©<Jlapp,C.H. Oeol. Surv., Can.Mem.13, p.49. ®Colony,R.<J. Jouro. of Oeol. Vol. 31. pp.169-178* FORMATION OF SILIOATS ZONE - VANCOUVER ISLAND 54. Of the igneous magma. During this feldepathlzation, some aillelflcation takes place, showing that the solutions must have boon rich in sodium and silicon. Later then the felds-pa thisation, and probably under more intense metamorphiem, there is a ohange in the character of the mineral!zers, so they contain mora lime and iron and the "contact silicates" are formed. the lime may hare bean derived from the magma or nerhane from limestones, through which the mineralizers passed. 8nder certain conditions, the magnetite appears to have bean introduced with the contact metamorphosing solutions, but in general the add solutions tend to be first; In the Tidewater several eyelaa were gone through. The first was under the in fluence of the add solutions when feldspars were formed. During the next stage, these materials, introduced, were removed and magnesium iron and lime added to form diallage. After the formation of the diallage, some of the components ware removed, and soda reintroduced to form feldspars again. <„ Following thie andradits which required a large accession of iron was formed. The complexity of the alterations at the Tidewater may be due to emanations from several intrueives or to reversal in the character of emanation from one. t RBLATIOH OF SILICATE3 TO MAQHETITS As noted previously, there is no fixed relationship between the time of formation of the silicates and the magnetite. In the oontaot deposits of Vancouver Island, there is no evidenoe for the differentiation of the material from the™»v~*J«*'«into two poles. According to the prevailing notion of the nature of the mineral!sers and the end stage products of crystallisation, they are characterised by their mutual soldblllty and motility. These properties seem to exclude differentiation by processes similar to those in the magma. A theoretical explanation may be given which seems to satisfy the observed irregular!tiee in the emanations. From their nature, it seems probable that the agents producing oontaot metamorphisra collect wi.thin the margin of the inatruslve. Oontaot metamorphism Is generally supposed to take place at such a depth that open fractures cannot exist In the rock, therefore the mineralizers must escape by the incipient or mlscrosopic fraoturss in the intrusive. Due to the fine charaoter of the cracks they aot simillarly to porous porcelain, that Is, the solutions must diffuse through them to reach the intruded rock. It is also probable that some diffjcLsion may take place through the massive intrusive itself, but no experimental results heaving on this point are available. All elements and oxides do not diffuse with the same speed; in general the lower the atomlo or molecular weight of the eubstanoe, the faster it diffuses. <D Fo* gases and dilute solutions this rate equals I / ! vmoleloular weight Wallace J. •Introduction to Physical Chemistry* 1919 p.89. 56. RSLATIOH OF 3ILI0ATE8 TO MAOHETITE This would apply either in a solution or in a gas. The effeot of this would he that the mineralizers containing the lighter elements as sodium and silicon would diffuse out more rapidly than the mineralizers with the heavy bases and iron, As a result the mineralizers which produoe the eilicatlon would act on one spot much before the basic emanations arrive, The time interval between the silicates and magnetite would vary with the d&stance the minerals had to diffuse and the place where they were given off so, under certain conditions, the magnetite depositing and the silieating mineralizers may be contemporaneous in their action. Besides the rate of diffusion other properties of the mineralizers will influence the formation of the contact zone. One of these is the concentration of the material in the zone of reaction,and the other is the chemical activity of the elements. Tfyft more chemically active elements are, those of lower atomic weight, and they are also the ones that diffuse fastest. These elements reaoh the zone of contact metamorphiem first, and so begin to react so theze concentration in the zone is reduced, but due to their high rate of diffusion a steep concentration gradient will be maintained and there will be a relatively rapid renewal of material. In the case where the elements of higher atomic weight are present they reach <> the zone of deposition, but duo to slower rate of diffusion the concentration cannot be maintained. So, until after the concentration of the chemically more active elements is reduced, there is no chance for the less active ones to deposit* It can be seen that with an easily A%aH*an S.Q.. U.S.G.8. Bull. #312 - pp. 7-9. :i !i! RSUTIOH gg SILIOATgg TO MAGNETITE replaced rock such as limestone,that the effect on the siliceous emanations will be most rapid so they will, in general, form the silicated zone before the magnetite is deposited. This accords with the facts because in the deposits in limestone, there was a greater tendency to have the silicate definitely earlier than the magnetite. In the yolcanics the presence of silicates already in the contact sons may allow the magnetite to deposit before or contemporaneously, with sane of the silicates. By the Mass I»aw the high concentration of silicates would tend to inhibit deposition of further silicates so even in the presence of the acid emanations magnetite might deposit. The later introduction of the magnetite may also be explained mechanically by this process. The acid emanations may i diffuse out, and then the magnetite solutions be deposited in another place or relatively wide solution channels may be established, so it could paeess out by ordinary flew. i i 58. ORB DEPOSITION The ohemistry of the deposition of magnetite is dis cussed following the discussion of the silicates, because of its general tendency to form later than they. As an intro duction, a brief discussion of the chemical properties of magnetite is glean . In composition magnetite usually conforms to the general formula Fe ?04 er ferros© ferric oxide. As represented by the formula, magna tite contains 72.4$ iron, and 27.6# oxygen. It often differs from this theoretical value even when pure, due to Its ability to form solid solutions with ferric oxide, hematite. To quote from "The Oxides of Iron," <• "Ferrlo oxide (hematite) dissociates at high temperatures, giving off oxygen and leaving a homogeneous product which may be considered as a solid solution of magnetite, Fe^ 0? , In hematite (Fe2 0 ). The proportion of magnetite in the product depends upon the temperature and oxygen pres sure above the oxides. The lower the oxygen pressure, and the higher the temperature, the more magnetite isfound in the solid solution. The reaction is strictly reversible for magnetite readily takes up oxygen at a temperature of 300° until the equilibrium proportion at the temperature in question is attained. Magnetite is therefore chemically unstable under atmospheric conditions, although it may remain unoxidized for long periods.* The melting point of magnetite is 153S°0 ., which is different from that of Doelter^who gives 1190°- 1235°0 which is obviously too lev because magnetite formed on the lining of a copper con verter is not melted at this temperature. % 0 "The Oxides of Iron* The Carnegie Institution at Washington, Tear Book No. 15, 1916, p.137. ® Hodgeman and Large - "Handbook of Chemistry and Physios" ®"Data of Geochemistry" - U.S.O.A. Bull 695, p.287. 89. ORE PEPOSITIOg FORM OT IRON IN MINERALIZERS Just what form the iron is in in the magna is difficult 0 to say. The average composition of igneous rooks shows an excess of ferrous over ferric iron, and, therefore, probably much of the iron in the mineralixers is in the ferrous form. The for mation of magnetite as an early product of crystallization in the magma shows the presence of the ferrous as well as ferric iron. The twojfclme© ©f formation for the iron oxides may be assumed to be due to iron in two forms in the magma; one of whioh forms the rook minerals, and the other goes into the mineralisers in some form. This is probably a ferrous or ferric fluoride ©r chloride or a mixture of them. The emanations are thought to be the iron halldea because these elements show strong ©hemioal affinity and are fairly stable. The halides are known to occur in the magma by the preseno* of minerals contaln-ing them, and they are also common in volcanic emanations. From the predominance of ferrous iron in the consolidated rook, some geologists\ave argued that the iron in the mineral!sers is in the ferrous form, and that the high ferric oxide content in the contact sone, le due to oxidation by limestone. Follow. Ing this explanation, one would expect that along Intrusive contacts with non calcareous sediment® that the ratio of ferrous to ferric oxide would be greater than in the limestone contact sons. Th© composite straight-line diagrams of the changes in <D Olark© F.W. Washington, H.8. -Average Composition of Igneous Rook", national Acad, of So. Vol. 8 #5, ^ P. 10B-U5. 1923. ^"Bttta ©f Geochemistry. U.S.G.S. Bull. 696. p.256. Oxide Content ©f Umeeton© Oontact Zones," Eo.Geol.voi.iB. -ORE DEPOSITIOH -GESESI3 OF THE MAGNETITE 60. regional and contact metamorphism in "Metamorphlc Geology" by O.K. Leith, and W.J* Mead, were compared. They show that In almost all types of katamorphism ttoet* there Is an Increase in ferric oxide content, especially when there is a relative increase in total iron. The only marked exception is in the case of the contact metamorphiem of cloys and slates, Plate 10. where, when there is not much increase in total iron, the ferrous exceeds the ferric. The study of these plates shows that, in general, the conditions that obtain in contact metamorphisra, are such that ferric oxide Is formed, whether by introduction of ferrio salts from the magna, or by oxidation of ferrous •alts which would be subject to the same conditions ae the introduced iron. - 6ftS DEPOSITION -ORE PREOIPITATIQH BY LIME3T0NE The Chemistry of the formation of magnetite in con tact zones has been discussed in several places. Leith and Harder in the "Iron Ores of Iron Springs District, Utah*, W.S.G.S. Bull. #338, assume the Iron was introduced as ferrous chloride and write the following equation. 3?* 01 ^ _-#- *H ,. 0 = Fe^ 0^ -r e HOI * Hz Magnetite is soluble in the hydrochloric acid, so It could not precipitate until the concentration of the acid Is decreased by Interaction with limestone* It may also be lest by diffusion because it tends to diffuse much mere rapidly than the iron oxide through porous rock. Leith and Harder exclude ferric chloride from the reaction because they say it can only form ferric oxide, by the following reaction: 2Pe "013 * Ca 003 - Fez 0^ + 0a 01 z + 3C0Z Xt seems probable that this does not represent the only reaction that takes place in the contact tone. VIth a reducing agent such as carbon, the carbon dioxide may be reduced. 0 •*- ooz - ^co This reaction does not take place at all at temperatures below 600° 0. but at 800° 0. it proceeds rapidly. With 00 in the •» centaot soae, the ferric oxide will be altered to magnetite by the following reaction: 3 TBZ QJ+ 00 = ^Fe5 0^ i- C02 <!> SmlliTan E.G. U.8.G.8. Bull #312, P.10. ® Winohell *•»• •Petrographic Studies of Limestone Alteration at Bingham.• Trs. A.I.M.E. March, 1934. - ORE; DEPOSITION -ORE PRBCIPITATI08 BY LIMESTQHE 62. More data ie available for this reaction ae shown by the following ourve & J?/r£ff£rs &*"***»** At 806° only about 28$ 00 by volume le required to reduce the hematite. The ferric oxide would not be completely converted to the ferroue oxide, but the works of Soaman and Hosteller ehowa magnetite would form. Ae the curve shows, at 500° the maximum concentration of 00 le required to affeot the reduction of the ferrlo iron and since this le aleo below the temperature of the free formation of 00 by carbon,hematite is the most stable, so it is formed. The upper limit of temperature is more difficult to define. The critical points of many minerals in the contact sone have net been determined. One mineral which occurred In the contact deposits on Vancouver Island,tremollte3cannot form above 1000<> - noo° , so the probable temperature range ie from 1000° to 600° with a probable preference for the higher end Q Findlay - "The Phase Rule and its applications". P.309. ® 'The Oxides of Iron." "The Dissociation of Hematite in Air". Journ. Am. Oheau Soo. Vol. 38 pp.807*833»1188-1198. Q Allen A Clement. Am. Journ. of So. 4th Series. Vol.26, p. 101. 1906. - ORE DEPOSITION -ORE PRECIPITATION BY LIMESTONE beeause, there, magnetite oan form most easily. Hematite forms close to 500° or lower. An attempt was made to find the conditions under which sulphides form, but no definite information could be found. Investigation of the sulphides, as of the iron oxides, hare net been made beeause they are not so important in iron blast furnace practicev. The only conclusion that could be drawn Is that pyrrhotite ,the ferrous sulphide,, oan form at a higher temperature than the ferrio sulphide, pyrite; and that in general, pyrite forme before ehaleopyrite. 64. - ORS DEPOSITION -PRE PRECIPITATION BY SILICATES The chemistry of the precipitation of magnetite by rocks, other than limestone, la not well understood. The only work la this branoh of the subject is on the precipitation Of minerals at low temperatures as related to agricultural chemistry, and the chemistry of secondary enrishment. This application of experiments carried on at low temperature to conditions of high, temperature may give results that are mis leading. From the field evidence and the evidence of the mineralographical microsoope it is seen that iron bearing solutions do replace other than carbonate rocks and precipitate magnetite* If as before It is assumed that the iron is introduced at ferrous on ferric fluoride or chloride reactions to cause a precipitation may be worked out. Any one of thess salts is completely hydrolysed in water giving the corresponding hydroxide and the acid. The presence of a natural silicate with the alkali, or alkaline earth, metals hastens this precipitation, as shown by Sullivan^in several papers. The basts of the silicates are taken into solution and hydroxides oxides or silicates are precipitated depending on the strength of the base deposited. Sullivan's work was mainly on the copper salts but his experiments show that iron reacts similarly. ••'" 0 Sullivan E.G. - "The Interaction Between Minerals and %ter Solution." U.8.G.S. Bull 312. "The Chemistry of Ore Deposition11. Kc. Geol. Vol. 1, pp.67-76. "Experiments on theSeparation of the Constituents of a Solution by Filtration Through a Mineral Filter". Be. Geol. Vol. 3, p.750. r t * * ••#.•'# I 65. - 8RE DEPOSITION -ORE PRECIPITATION BY SILICATES Some of the minerals which gave this effect are: feldspar, amphibole, augite, biotite,garnet, veeuvianite and olivine. Even quartz has the power of taking iron from ferric acetate solutions. At the high temperature at which the formation of the magnetite takes place it may be supposed that the silicon left will be removed in solution and magnetite deposited especially if free fluorides are present. A reaction in volving twrie chloride and a simple alkali metal silicate may be written: zFe Gljtz-R* Si QJ*JEZQ s z Fe (OR)3 wSi Oz^<rMa 01. If fluorine were present a soluble salt of hydrofluosalicic aeid would be formed. From this quartz might be deposited. Under the conditions of high temperature and low oxygen pres sure the ferric oxide would easily be dehydrated and reduced. If a ferrous halide were the form of the salt it would give magnetite by dehydration of the hydroxide without reduction. So date, regarding the temperature at which the deposition In the silicates took place could be found, but it seems probable that It took plaoe at as high a temperature as in the limestone. Q {J.S.G.3. Bull, 313, p.20. gXiATE VII. TO MlMt.".-. Camera lucida eketoh of Uagnetite (M) replacing volcanics June Mine* In the sketching it was necessary to omit many fine veins of magnetite surrounding grains of the rock. - ORE DEPOSITION -PHYSICAL CONDITIONS OF THE SOLUTIONS So far the possible reactions producing the magnetite have been discussed. The physical conditions, except that the emanations were at a high temperature have not been dis cussed. At 9009 water would be well above its critical point and due to its pressure it would aet almost as a solution so tiki use of "solutions" is probably not incorrect. Clapp sug gests that the magnetite was formed from very concentrated solutions "virtually magnetite magma", which, of course, must have been very viscous. No facts in support of this view eould be seen in any of the deposits. Direct evidence in the shape of flow structure, orientation of contact silicates ©r limestone fragments, which under this hypothesis would con stitute jcanoliths, is lacking. On the other hand, there is auoh evidence that the iron bearing solutions were very tenuous. In the replacement of the diorite at the June mine the magnetite replaoed, prefsrentially, the ferromagnesian constituents of the reck without visible solution channels existing between the masses of magnetite. In the replacement of voloanics on the same claim the method of replacement of certain grains in the rock suggests the agents must have been very thin, either a* gases or a very tenuous solutions. At Head Bay, Nootka Sound, the banding of the ore and the distance it has penetrated along a Joint or bedding plane again>uggests a very tenuous solution. 0 Clapp, O.H. Geol. Surv., Can. Mem. #13. - ORE DEPOSITION -^—^———*~*m\ in •• I i • i M PHYSICAL CONDITIONS OF THE 80LUTI0NS AJ1 the polished surfaces from the different deposit* support the idea of tenuous solutions. Definite information regarding the temperature of formation of the silicates could not he found but it seems probable that they were derived from solutions the same temperature, or higher than that of the solutions producing the magnetite* The emanations producing the sllioation were juet as thin as thoee producing the magnetite as shown by their ease of diffusion, and the way in which they were observed to penetrate some of the minerals of the original rook as along oleatage planes in feldspars. 69. MAQSETITE QOOORHEHOES OF THE WORLD the writer made a brief review of some of the liter ature on the occurrences of magnetite the world over, to deter mine the position of the contact metamorphic deposits as a source of ore. A brief summary of the geology of the more im portant types and of some of the principal localities is given, magnetite may be divided into two classes, o_ji the basis of its present commercial value, the titaaiferous and the non~titaniferou« ere. the titaniferous ore is not commercially valuable at the present time, on account of the lack of an efficient method of " reduotion, so the outline will be largely confined to the non-titaniferous ore. USmm SB^EgatlO? TYPEf Magnetite is a common accessory In igneous rocks of all basicity, so it is net remarkable that the segregation of material should produce ore-bodies. These are more common from bodies ef igneous reck corresponding in basicity to a gabbro but at a rule,are titanlferous. Exceptions have been noted where non-titaniferous magnetite occurs as a segregation, or titan lferous magnetite is of contact metamorphic origin. PEGMATITE TIPS* the nojtotitaniferoue magnetite formed by the oentrla-bution of iron, in eeme form from the magma, is the most widely distributed and the commercially most valuable source ef mag-aetite as an ere of iron. Hies divides these into* — <D Rise, H. »Eoonemie Geology" 4th Edition 1916, p.604. 6a MAGNETITE OCCURRENCES OF THE WORLD "PEGMATITE TYPE" .— / . . . ; 1. Senticular deposits in metamorphic rocks. 2. As more or less lensA shaped or tabular bodies in igneous rooks. / 3. As replacement of limestone not of contact metamorphic character. 4. Contact metamorphic deposits. 5. As veins. Only the last two divisions, under this scheme are definitely defined, and it seems easier to regard them all of the same types, and the defined types, contact metamorphic deposits and veins as only a special case of it. The problem atical forms will be discussed first followed by the specific case, o on tact metamorphic The non-titaniferous magnetites of the Eastern United States have long formed a puzzle for the geologists and various origins have been postulated for them. They are associated with Pre Cambrian rocks which have been highly metamorphosed so their origin Is not clear until the relations of the recks are worked out. Probably a good many of them are of contact metamorphic origin, but since contact deposits are not common in that district, and the wide alteration often accompanying contact metamorphisra may obecure the true nature of the rook this origin may be overlooked. The explanation that receives the most support, at present, is that the mag-9 netite was formed from solutions allied to pegmatites and con taining the iron in the mineralisers. The character of the gangue minerals feldspar, quartz, amphiboles and apatite is urged In support of this view, but precisely the same minerals may be developed under conditions of contact metamorphism, a* shown on Vancouver Island, *» **« Adirondack magnetite 70. MAGNETITE OCCURRENCES OF THE WORLD "PEGMATITE TYPE* Hewland comes to the conclusion that some of the ore may be a segreajation from a granite, similar to those in the gabbro, out that the magma had a sufficient concentration of silica for the titanium to form.titanite. However, a large part of the ore body was formed by the introduction df iron by later "pegmatite" solutions. Miller in discussing the origin of the magnetite of Clinton Co., Hew York, comes to the conclusion that diallage was formed by the leaching of iron from hyper-sthene and hornblende by the action of "pegmatite" solutions. The iron deposited as magnetite later. The similarity of the procees in this ease t© that observed in some deposits on Vancouver Island, under conditions of contact metamorphism is i noticeable. For the magnetite of Horth Carolina, including the Cranberry magnetite, W.S. Bayley postulates a similar origin to those of Hew Jersey, which he says are of pegmatitio origin, although in this case the feldspars are altered to epidote, another analogue to the processes in contact deposits. Grout comes to the conclusion that the magnetite of Horthem Minnesota is a direct contribution from the magma as "pegmatites." ©HewUad, D.H. "On the Association and Origin of the Non-titaniferous Magnetites in the Adirondack Region." Ec. Geol. Vol. II, pp. 763*773. ^Miller, f.J. "Magnetic Iron-Ore of Clinton County, Hew York.* E©. Qool. X4, pp.&>9~S3S. ®Batt«»» W.8. "The Magnetites of Horth Carolina - Their Origin." BO. Cool. Vol. 14 pp.509-635. ™4„**.ftt. * ® Of out F.F. "Mag****** lir^oUB * ** * Mina0iota-It. CteOl* Vol. 18, pp.2S3V269. 71. MAGNETITE OQCURREKOES QF THE WORLD "PEGMATITE TYPE" Leith provisionally classified the Atikokan magnetite and the deposit near Bathhurst N.B., in this group. Throughout the whole group the resemblance to oontact metamorphlc ore bodies Is noticeable* The huge magnetite deposits of Lapland; Kiirunavaara, Luossavaara, Tolluvaara and Gelllvare are very difficult to explain both on account of their huge size and their apparently unique features. Per Gel;}er%elieves the ore bodies represent a magmatlc product somewhat similar to the pegmatite type of Eastern United States. Daly believes the deposit is a differ entiation In situ of a quartz porphyry. Gei^er's theory of the origin seems to be better able to account for the facte especially the presence of apatite in large amounts. Other occurrences havd been classed with these by Geijer including* Grangeberg la Central Sweden, Solberg and Lyngrot in Southern Norway, and the Blagodat type of the Eastern Ural Mountains. The deposits of this group are few in number, and no fully satisfactory ex planation of their origin has yet been given. Oontact raetamorphio deposits, or the specific ease where the mineralising solutions eome from an intrusive mass a and extend into and ••place another rock type with perhaps some replacement of the intrusive, as well, are common. The deposits 0Leita, O.K. "The ir«s* Ores of Panada*. - Jour. Canadian Mining Institute. Vol. 11, 1908, pp.94-95. ©Geijer Per. *®ome Problems in Iron Ore Geology in Sweden and AmsJtoa." Bo. Geol. Vol. 10, BP-fJ-saj. ^^ , fl s . ©Daly,R.A. "Origin of Iron-Ores at Klra*ma, Sweden. O.s.A. Traao. Vol. 26, p.99, 1915. 72. mmMMjmmmm s& ™ WORLD V COKTAOT METAMORPHIG nay be developed at the con tacts of rook with intrdsives of any basicity but in the deposits important for their iron content there is a tendency for the intrusive to be of medium basioity. Due to lack of uniformity in rock nomenclature and to the use of "granite* for any, light colored, plutonie rook an exact comparison of the basicity in the intruslves could not be made. According to the literature contact, deposits may be found along rocks such as granite, monzonite, quartz-monzonite, but there la a tendency for more of the iron ores to be found along contacts of granodiorite, quartz dierite, diorite and their porpbyritlc equivalents* All the contact metamorphic ore-bodies are noted for their irregularity, both in the dis tribution of ere and the gangue contact silioatee. The ore ie commonly mixed with eueh amounts of Iron or copper iron sulphides that it often requires roasting before use. These ©res are of such wide distribution that all the occurrences cannot be listed but a few of the more important type looalitiee will be mentioned. The distribution of the contact metamorphic deposits in America is so striking that Eckel ®says; "We might summarise the matter by saying that almost every known Iron deposit along the Pacific Coast, from Alaska to Soutbem Chile, and from the coast back to* the eastern-most mountain range, falls into the class of deposits." eSekel, B.C. "Iron Ores Their Occurrence Valuation and CentrelS 19** P»87. MAGNETITE 0CCURRSM0S8 Of THE WORLD CONTACT METAMORPHIO Theee relatione are true in general, but exoeptlone say be noted. The more important localities in the United Statee are: Iron Springe /Utah; The Barth IroiPoree; The magnet!tee of Shasta Co., California; and the occurrenoe near Fairvlew I.lf., and Dillsbux?, York Co?, Pa. Many smaller depoelte might be added to the liet. In Canada many contact meteporphio depoelte are found eepeoially in the feet. Among the best known ones are thoee of Texada Island. In Eastern Canada, eepeoially Ontario contaot deposits are commonly found. Outside of United Statee and Canada, many contact metamorphio iron ore depoelte are known. In the following oo-eurenoee noted the information wae obtained from "Iron Ore Re-eouroee of the World", publiehed by the International Oeologioal 4Leith,O.K. a Harder, E.O. U.3.G.3. Bull 338. z Jones, J.O. "The Barth Iron Ore Occurrenoe" Ec. Oeol.VOL. 8, pp.247. 3 Presoott Baeil - "Mgte ore of Shaota Co. Calif." So. Oeol. Vol. 3, p.465. L* Smythe, D.D. - "A contaot metamorphic Iron Ore Depoeit Near Fairrlew I.M." Ec.Ocol. Vol. 16, pp.410. ^Harder,K.O. - "Structure and origin of the Magnetite Depoelte near Oillabuxy York Co. Pa." So. Gaol. Yoli.8, pp. 599-623, 1910. <£ MoOonnell, R.O. "Oeol. 3urr. Can. Mem. #58, 1914. d*epe S.J. - "InTeetigntion of «*g»otic Iron oree froaEeetern Ontario". A.I.M.S. Tr. Vol. 29, pp.373-405 - 1900. "Report of Ontario Iron Ore Committee! Toronto 1923 Appendix. 74. MAGNETITE , OCTREES PESf OF JHE WORLD CONTACT METAMQRPHIC Congress of 1910, Stockholm. Magnetite occurs in a zone apparently extending south from Mexico into Peru* In Mexico the deposits are in limestone, where it has been intruded by diorite, monsenite, porphyrite, and granite. In Cuba, impor tant deposits are found in limestone due to the intrusion of diorite. Outside of America, important occurrences of contact metamorphic ore bodies are known in Sweden, Russia, Hungary. Japan,Australia, and China. Many other countries have this type of deposit, indeed they seem to occur almost anywhere where there is extensive igneous intrusion and not too great a removal of the contact zone by erosion. •MM* ,yoM»Mq|«, * Magnetite formed by the contact metamorphism of iron formation in the Pre Cambrian rocks is of rather M common occurrence in areas of extensive igneous intrusive". It is possible that some magnetite may be formed by regional meta-morphism, but it is more common under conditions of contact metamorphlam. The ore of thie type is, as a rule, rather impure due to an excessive amount of eliiceous impuritiee in the form of quartz, amphibole and other silicates. In Eastern North ^ America there are a large number of deposits belonging to thie type. They are found in Sweden, Norway, Brazil and South Africa, 0Papers by Xepp, Lindgren, Ross and others. A.I.M.S. ?*jns. 56. 1916 • 78. MAGNETITE OCCURRENCES OF THE WORLD IRQK FORMATION Grout®comes to the conclusion that due to the Intrusion of a gabbro, the magnetite formed in the Gunflint formation was fused; hut his melting point is two to three hundred degrees too low* Occurrences of black sand are fairly common but not, at present, of commercial value* These deposits are derived by the concentration of accessory minerals, or of other raag-netite occurrences. Often where the magnetite^fcrmf large bodies, they are titaniferous. An occurrence of interest from its peculiarity rather than Its commercial importance is that found about a fumarole^ the magnatite occurs as octohedra, lining a vent in the pumice. The purity of the.pumice precludes the possibility of the derivation of the iron from it so the magnetite must have been deposited by emanation from the fumarole under conditions of low oxygen pressure and rather high temperature. A notable feature was the occurrence of halite on the faces of, and intergrown with the octohedra of magnetite. Floor!te was also found in considerable quantities by analysis. Magnetite in all Its occurrences is formed at high tem perature either as a direct product of the magma or due to the aetamorphic effects of the magna on previously existing iron minerals. The wide areas of igneous activity favour the production & Grout, F.F. Be. Geol. Vol. 18, p. 353. ^"ramarolio Incrustations in the Valley of Ten Thousand Smokes." Geophysical Laboratory- Wash. #541, by E.G. Zies. 76. MAGNETITE 00CURREHCE3 OF THE WORLD IRON FQRMA.TIOy of magnetite, while conditions of weathering favour the pro duction of the higher oxides and hydrates. OOMMEROIAL VALUE OF MAGNETITE An attempt was made to determine the proportion of magnetite, used as a source of iron, derived from contact metaraorphic deposits. More than general results could not be obtained because if the statistics are available, the ore is not separated In to the types, or if the amount of magnetite la listed theloealitlee where It was mined are not given, so the geology of the deposits cannot be found. Figures for United States^show that of a total production |>f Iron-ore, for the year 1923, of 09,351,442 tons, that 2,190,624 tons, or 3.16$ ©f the total ore produced was magnetite. Of mines producing over 100,000,,tons,*r 1.2> of the total ^ frem contact metamorphic deposits, the remainder being from the magnetite type of the Eastern U.S. From the rem/alnder of the smaller producers^, no figures are available, but from the distribution of the localities it seems probable that about 11$ Is from contaot metamorphic deposits, and thai part of this production is iised as flux. In Canada? the iron ore produced in 1933 was 20,739 tons, and the principal part of this was magnetite from Moose Mountain? Ontario. O "Mineral Resources of the United States 1923." Pt. 1 pp.295-329. Advance chapter. ® "Mineral Production of Canada 1933* Bureau of Statistics 1924. MAGNET!T3? OCCUKRSHCSS OF THE WORLD COMMERCIAL VAOT OF MAGBSHTE In Sweden with a production of 5,597,707 tons of iron ©re in 1933 the larger part • probably 85$, is magnetite produced from the Lapland type of deposit and a small amount of ere from the contact deposits. Among $he smaller producers of Iron ore, it is probable that contact metamorphic magnetite is more important than in the tin!ted States. An instances of this is Japan, where magnetite from contact deposits is mined for use in the blast furnace. The tendency at present seems to be *ft use easily available hematite as an ore, and to only use magnetite to form a mixture with the other ore. Doubtless, as the easily available high grade hematite bodes become depleted, the smaller contact metamorphic ore bodies will become more valuable as • source of iron, but at presentt they are rather minor producers• •Skandinavlska Kre&itacktiebolaget.* Stockholm, Quarterly Rept. Jan. 1985. The following is a short bibliography of contact metamorphism. In many places, references to contact metamor-phism may be found, but in those given below, a general treat* ment of the subject is given, or some feature is emphasised. Bain, G.W. "Almandite and its significanee in the contact Zones of the Grenville Limestone.1* Jour, of Geol. Vol. 31, 1933. pp.650-668. (Gneisses formed by the contact metamorphism of limestone) jjggtyUJU "Pbysieal Effects of Contact Metamorphism.* Am. Jour. 8c. 1902. pp. 279-296. Barrel!, J. "Geology of the Marysville Mining District, Montana.* U.3.G.S. Prof. Paper 57. Brocfc. R.W. "A British Columbia Example of the Contact Metamorphism of a Granite to a Garnet." R. Soc. Can., Tr. (3) 9. IV. pp.175-180, Butler. B.S. »A Suggested Explanation of the High Ferrio Oxide content of Limestone Contact Zones." Eo. Geol. Vol. 18, pp. 398-405. Clements. J.M. "A Contribution to the Study of Contact Me tamorphlsm•" Am. Jr. So. (4), Vol. 7. pp.81-91. 1899. (Suggests transfer of Na silicate from intrusive to contact zone.) BIBLIOGRAPHY ismJhh "Ore Deposits at the Contact of Intrusive Rocks and Limestone.* So. Geol. Vol. 3. p. 1. 1907. ujk£« * Contact Deposits" Mining Scientific Press 103. pp.678-681. 1911. Harder. E.G. "The Iron Ores of Western and Central California.* U.3.G.3. Bull 430. 1909. "3hap Granite and Associated Rooks.• Jhap Quat. Jour* of Geol* Boo. of Lon. Vol. 47 * 1891. p. 268. ftflth, q.K. & Harder.S.q. "The Iron Ores of the Iron Springs District, Utah.* U.S.G.S. Bull 338, 1908. Llnderen. W. "The Character and Genesis ofOertaln Con tact Deposits." Trans* A.I.M.E. Vol. 31, 1902. p. 698. hiMm&JL "Copper Deposits of Clifton Morenci Dis trict Arizona,". U.S.G.S. Prof. Paper 43, 1905. ?TfSOO^t B. "Boats Observations on Contact Hetamorphic Ore Deposits.* So* Geol.Vol. 10, 1915. p.55. !I§.kLO£RAPHY 8purrt Qarr,eyand Fenner "Study of a contact metamorphic Ore Deposit. The Dolores Mine at Matehuala Srt.P. Mexico. Ic. Geol.Vol. 7. p. 444. "The Copper Deposits e£ the Velardena District, Durango, Mexico. '• Ec Geol. Vol. Ill* p. 688. teed. W«H» "Ore Deposits near Igneous Contacts." Trans.A.I .M.S. Vol. 33, 1903. pp. 715*746. Geology and Ore Deposits of the MaoXay Region Idaho". Prof. Paper 97. (Reviews questions to be answered in a contact net. deposit development of garnet in growth.) Uglow. W.L. "A Review of theExiating Hypotheses on the Origin of the Secondary Silicate Zonee at the Contact of Limestone with the Intrusive." Be. Geol. Vol. 8, pp. 19.50. » 315-234. 


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