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Mineralogy of Stikine Copper's Galore Creek deposits Allen, Donald Gordon 1966

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MINERALOGY OP STIKINE COPPER'S GALORE CREEK DEPOSITS by Donald G. Allen A thesis submitted i n part ia l fulfi l lment of the requirements for the degree of Master of Applied Science in Geological Engineering We accept this thesis as confirming to the required standard THE UNIVERSITY OP BRITISH COLUMBIA A p r i l , 1966 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I furth e r agree that per-mission f o r extensive copying of t h i s t h e s i s for s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representatives„ I t i s understood that copying or p u b l i -c a t i o n of t h i s t h e s i s for f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of Geology  The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8 , Canada. Date A p r i l 2 9 , 1 9 6 6 V « ABSTRACT,1 Mineralization at Galore Creek consists mainly of disseminated chalcopyrite, bornite and pyri te . Biotite and orthoclase are the dominant alteration minerals with commonly associated anhydrite, garnet, apatite, calcite and magnetite. The mineralization occurs in altered syenites, meta-volcanics and brecciated equivalents of these along the contacts of a complex of syenite porphyries which display many character-i s t i c s of epizonal intrusions. Exsolution textures of bornite and chalcopyrite indicate a minimum temperature of deposition of 475°C. This leads to the conclusion that the deposit formed at a re lat ively high temperature and a shallow depth and there-fore may be class i f ied as xenothermal. Frontispiece. Photograph, looking north down G-alore Creek val ley, showing several d r i l l sites on the southern Central Zone. Overburden in loreground i s essentially recent e lac ia l t i l l . i i ILLUSTRATIONS Figure Caption Page Frontispiece Photograph looking southeast down Galore Creek. 1 2 3 k 5 Facing t i t l e page. Following page 1, Following page k< Location and General Geology Galore Creek Property Geology A plot of c e l l edge against index of refraction of some Galore Creek garnets. Facing page 19-Paragenesis of the Metallic Minerals 28 Suggested Paragenesis 29 i i i CONTENTS Headings Page Introduction 1 General. Geology 1 Descriptive Mineralogy 8 Paragenesis 27 The Copper Bearing Phases 27 Mineral Zoning 33 Comparison with other Deposits 35 Summary and Conclusion 38 Appendices Photographs I Specimen Descriptions II Potassium-Argon Age Determination of Biotite III X-Ray Data for Unknown Mineral IV Distribution of the Common Minerals East-West sections • V A Longitudinal Section (in pocket) V B Central Zone Sections, Geology (in pocket) VI PREFACE The following mineralogical study i s based on two summers work for Kennco (Stikine) Mining Ltd. on the Galore Creek deposits. During this time, I logged in detail about 50,000 feet of d r i l l core. About 250 samples were obtained from which kO thin sections and 90 polished sections were made. The study of these samples and 75 X-ray patterns was carried out in the winter sessions 196A--I965 and 1965-1966 at the University of Br i t i sh Columbia under the supervision of Dr. R.M. Thompson. A potassium-argon age determination was carried out under the supervision of Dr. W.H. White. I am deeply indebted to Dr. J .A. Gower and Mr. D.A. Barr for permission to use geological data obtained from d r i l l core and Kennco reports, and for their advice in planning this study. Special thanks are due to Dr. R.M. Thompson, Dr. W.H. White, and Dr. K.C. McTaggart, also Dr. A . J . S incla ir for their constructive crit icism of this report, and to Dr. W.G. Jeffrey of the B.C. Department of Mines for making available his 1965 f ie ld season work. Donald G. Allen Apr i l 30, 1966 1 MINERALOGY OP STIKINE COPPER'S GALORE CREEK DEPOSITS Introduction The Galore Creek copper deposits are located about 200 miles northwest of Prince Rupert, Br i t i sh Columbia. The deposits outcrop "between elevations 2000 feet and 5000 feet at the headwaters of Galore Creek, a tributary of the Scud River. (Refer to figure 1.) The nearest communities are Telegraph Creek, about 50 miles to the north, and Wrangell, Alaska, at the mouth of the Stikine River. General Geology Regional Geology The Galore Creek deposits are situated about five miles 57<-l5 "1\ y;r< V i f \ 1 ^ V v I / \ / \ / If I V : I \ \ \ J V IN w JSC \ <c-m f I X Figure 2 map \ •1 I -\ 57 c C O / hi ( \ \ / .8^  A L e g e r d Coast Range Intrusive Rocks Syenite Porphyry Syenite Quartz Mcrzonite , granodiorite Diorite Upoer T r iassic Voicanic and sedimertory locks Permian Limestone with minor chert, quortzite, arai i ' i tc , etc. P r e Mid P e r m i a n Pnyllit* ,QU JI tzite, g i . e i s s Glacier F i g u r e I L O C A T I O N A N D G E N E R A L G E O L O G Y S T I K I N E C O P P E R A R E A C o s s i a r D i s t r i c t , B r i t i s h C o l u m b i a A f t e r G.S.C. Map 9 - 1 9 5 7 and W.G.Jef f rey (B. C. Dept. Mines) S c a l e l " = 4 mi les 2 off the eastern edge of the Coast Range batholithic complex. In the area i l lus trated by figure 1, these rocks intrude un-corrected Upper Paleozoic and Triassic volcanic and sediment-ary assemblages. The following brief description of the region-a l geology is based largely on the work of Kerr, Barr and Jeffrey. Pre-Middle Permian rocks are the oldest i n the area and are highly metamorphosed. The lower parts are made up of f ine-grained quartzose c last ic rocks and the upper parts consist of much impure crystal l ine limestone. Kerr estimated a thickness of 7000 to 8000 feet for these highly folded and metamorphosed strata. The Permian rocks consist essentially of crystall ine limestone with minor amounts of chert, quartzite and a r g i l l i t e • which have been intensely folded and faulted in places. Middle Triassic a rg i i l i t e s and quartzites flank the Permian limestones on the western edge of the Copper Canyon syenite (the eastern-most syenite porphyry in figure I ) . Jeffrey estimated a minimum thickness of 500 feet for this uni t , but thickness estimations were d i f f i cu l t because of the presence of many small folds. The volcanic and sedimentary rocks which underly much of the map area of figure 2 have been reported by Barr as Upper Triass ic in age on the basis of fo s s i l identifications by the Geological Survey of Canada. Jeffrey reports the presence of Upper Triassic foss i l s in a narrow belt of limey a rg i i l i t e s in 3 these volcanic rocks on the ridge east of Galore Creek. The " Upper Triassic rocks i n the v i c i n i t y of Galore Creek consist mainly of pyroclastic rocks with minor andesitic and trachytic flow rocks. A pseudoleucite phonolite on the ridge southwest of the Central Zone is shown in plate 5. There appears to be a great variation in the size and shape of the fragments in these pyroclastic rocks. Jeffrey notes one occurrence of a volcanic breccia containing fragments of predominantly intrusive rocks, many of which are porphyritic. Thickness determinations of the volcanic rocks are d i f f i c u l t because of great variations of dip and much fault ing. Kerr estimates 3000 and perhaps up to 6000 feet of breccias and agglomerates overlain by about 1000 feet of a rg i l l i t e s and grey-wackes. Purple volcanic sandstones and reworked tuffs which occur above the east fork of Galore Creek may belong to this upper part or may be separate from the unit ; their relationship to the volcanic rocks higher along the ridge i s obscure. The relationship between the Upper Triassic volcanic rocks, Middle Triassic sediments and Permian limestone east of Galore Creek is debatable. The Middle Triassic rocks are con-formable with the limestones and were both apparently t ightly folded as a unit so that they are now overturned. Barr states that these rocks were then uplifted and eroded before the Upper Triassic rocks were deposited. Jeffrey, on the other hand, points out that the contact between the Middle and Upper Triassic rocks may be a fault contact. The Coast Range complex in this area, consists mainly 4 pf quartz monzonite and grandiorite. Diorite occurs in small mass generally less than a mile in diameter. The small intru-sion near, the confluence of Galore Creek with the Scud River has been classified by Jeffrey as a granite. Orthoclase porphyries, under which Kerr groups a variety of rocks, occur both north and south of the map area in a northerly-trending belt about 100 miles long and 10 miles wide. These porphyry bodies vary i n diameter from less than one half mile to about three miles. Several of these porphyries are known to contain metalliferous deposits and Kerr noted the relat ively large amount of hydrothermal alteration associated with these bodies. Kerr concluded that this group was among the earliest i n -truded i n the Stikine River area; his conclusion is supported by one potassium-argon age determination on hydrothermal biotite from Galore Creek. (Refer to Appendix III.) Around the Galore Creek syenite porphyry complex, evidence of dip i s sparse in the dominantly massive volcanic rocks but they appear to indicate an imperfect domal structure. Local Geology The copper deposits on the Galore Creek property are associated with a complex of syenite intrusions. About six different phases of syenite can be distinguished on the basis of texture. The following is a description of these phases, the names of which have been proposed by Barr. The most widespread and probably the youngest is the epidotized syenite porphyry. (Refer to figure 2.) The contact of Copper Deposit Mottled breccia phases Und iff. breccia Dndiff. porphyry Junction porphyry Buckshot porphyry Dark syenite porphyry ±2 Epi syenite porphyry Younger syenite Upper Triassic voles. & seds Metamorphosed U. Triassic rocks Bedding attitudes Fold axis G Lacier SCALE 4 0 0 0 Figure 2 STIKINE COPPER LIMITED GALORE CREEK PROPERTY GEOLOGY fct'er Kennco FEET 5 this unit with the Upper Triassic rocks on the west appears to be concordant over a distance of two miles. Apart from forming the bulk of the stock, the epidotized syenite porphyry also occurs as dykes and s i l l s cutting through the Central Zone. (Refer to Appendix V I . ) The shape of the s i l l s as shown i n the Central 2one sections suggests that intrusion was controlled by roughly concentric fractures that may have resulted from force-fu l intrusion i n the area of the central dyke. This porphyry i s characterized by large blocky to tabu-la r phenocrysts of orthoclase up to several inches long and com-prising 40 to 60$ of the rock. These phenocrysts may be strongly aligned generally para l le l to the contacts of.the rock. Two generations of phenocrysts are present; the earliest'averaging about one inch long and the youngest averaging about 0.1 inch. The large phenocrysts are grey i n color and are usually zoned. They commonly are partly or completely replaced by white or pink orthoclase which obliterates this zoning. The groundmass i s feldspathic and contains disseminated grains of biot i te or horn-blende and splotches of epidote and occasionally garnet. In thin section the mafic minerals are par t ia l ly replaced by chlor i te . Magnetite and apatite form 1 to 2$ of the rock. The phenocrysts appear as clouded masses and are d i f f i cu l t to d i s t in-guish from the groundmass. This rock i s apparently very unreceptive to copper min-eral izat ion. Copper assays are rarely over 0.5$. In places, s i l l s of this porphyry appear to have acted as a dam with copper mineralization building up against i t . Plate i in Appendix I i s .6 a photograph of an anhydrite veinlet cutting the epidotized syenite porphyry. The dark syenite porphyry occurs as a dome-shaped mass at the south central part of the complex. It has also been reported as a dyke rock. Characterizing this porphyry are blocky to short tabular phenocrysts of white orthoclase averag-ing about one-half inch i n length. The groundmass i s dark and f'eldspathic with f inely disseminated b io t i te . Rarely, large remnant phenocrysts of pseudoleucite appear. These generally show a trapezohedral or rounded outline and may be zoned. (Refer to plate 7.) Much of the copper mineralization in the southern part of the Central Zone occurs in a strongly feldspathized and biot i t ized phase similar to this syenite. The intermediate syenite porphyry occurs over a limited area in the middle part of the Central Zone. It has a texture similar to the epidotized syenite porphyry but i s darker i n color and contains much smaller phenocrysts. Occasionally i t appears as fragments In the epidotized syenite porphyry. The junction syenite porphyry occurs near the western edge of the complex. It i s dark in color and contains numerous white tabular phenocrysts of orthoclase averaging 0.5 by 0.1 inch i n a b iot i te-r ich matrix. The North Junction and Junction copper deposits occur i n a highly fractured phase of this porphyry. The younger syenite i s a medium-grained equigranular rock with an average composition of 85$ orthoclase and 15$ matic minerals. The gradational contacts and the occurrence of r e l i c t bedding in places suggest that much of this rock is a granifize.d sediment. 7 The lavender-- or buckshot porphyry occurs at the south-eastern edge of the complex. This rock generally consists of up to 80$ orthoclase phenocrysts which may form an. intergrown mesh i n a purplish feldspathic matrix. Dyke rocks at Galore Greek include hornblende-, syenite, basalt, fe l s i te and biotite lamprophyre. The Copper Deposits There are ten deposits on the Galore Creek property,, most of which are scattered along the syenite contacts i n fractured and brecciated rocks. Because the Central Zone i s the largest deposit and d r i l l hole data i s abundant, discussion of the mineralogy w i l l be largely confined to this deposit. Copper mineralization i n the Central Zone occurs i n a broad alteration zone between the epidotized syenite porphyry on the west and metavolcanics on the east. The structure of the deposit has not been fu l ly determined,, but the mineralization appears to occur i n several pa ra l l e l , northerly-trending tabular' and steeply-dipping zones"with f a i r l y sharp assay boundaries. At the northern end the zone may have a shallow dip. The mineralization occurs i n a number of feldspathized and biot i t ized rock types as v/ug and fracture f i l l i n g s and as disseminated replacements. These rock types include syenite porphyry, breccias of volcanic and cataclastic or ig in , pseudoleucite meta-volcanics, "spotted" metavolcanics,, layered metatuffs or meta-sediments, and phases that are so intensely altered that the identity of the original rock is uncertain. These altered phases -8 have 'been generally termed "mottled phase" or "mottled breccia" as shown i n figure 2 . Primary copper mineralization consists of chalcopyrite, bornite and very minor amounts of chalcocite. The chaicopyrite-bornite ratio i s approximately 10 to 1 . Supergene copper mineral-izat ion is re la t ive ly minor i n importance and occurs almost entirely on fractures to a maximum depth of about 2 0 0 feet below the surface. The secondary copper minerals include malachite, azurite, chalcocite, cuprite and native copper. Descriptive Mineralogy The following is a l i s t of a i l minerals found in the Galore Creek complex with their composition and relative abund-ances : Primary Metall ic Minerals Gold Au rare Si lver Ag rare Chalcocite Cu2S minor Bornite CuqPeS4 common Galena PbS minor Sphalerite ZnS minor Chalcopyrite CuPeS2 common Pyrite P e S 2 abundant Molybdenite M0S2 rare Tetrahedrite-tennantite Ciii2 ( S b , A s)4Si3 rare Magnetite FejjO^ common Hematite i ' ^ O ^ common Secondary Minerals Copper Cu minor Chalcocite CuoS minor Covellite CuS minor Cuprite CuO minor -9 Tenorite Limonite Manganese Malachite Azurite oxides? Cu20 FeO(OH) -nH20 0up(0H)2C03 0U3(0H)2(003)2 reported common minor minor minor Primary Igneous Minerals Apatite Orthoclase Plagioclase Biotite Hornblende Aegirine-augite Sphene Pseudoleucite CacCPOA.CO^OHWF K A l S i 30 8 IaAlSi30 8 K(Pe,Mg)3AlSi30io(OH)2 IaCa2 (Mg, Fe, (Si, Al) 8022 (OH) 2 (Na, Oa) (Fe ,Mg ,A1) S i 20 6 Cal'iSi04(0,0H,P) K A l S i 3 0 8 + ? minor abundant minor abundant common reported minor rare Pervasive Aitera.tion and Skarn Minerals Anhydrite Calcite Apatite Orthoclase Biotite Garnet Epidote Diopside Chlorite Sericite Vesuvianite Sphene Clay minerals CaSG/ CaCO-5 0a3(Fe,Al) 3 Si^0 1 2 Ca2(Fe,Al)3(SiOA730H CaMgSi20g (Mg,Fe , A l k ( S i , A l) 40 1 0(0H) 8 KA13813010(011)2 Ca 1 0 Al 4 (Mg ,Fe ) 2 SI 90 3 4(0H) 2 common common common abundant abundant common common minor common common rare rare minor Ye i n Minerals Fluorite Calcite Dolomite Anhydrite Gypsum Barite Celestite Actinol i te Biebeckite Quartz Sodalite Analcime Hatrolite CaF, CaMg(CO^)o CaSOA J CaS04.-2H20 BaSOl SrSOT Ca(Fe,Mg) 1-Si 80 2 2(0H) 2 Na(Mg,Fe)^Si8022(0H) 2 SIO2 !Ta8Il6Sig024.Cl2 NaAlSi206'H20 Na2AI2Si30]_o • 2H2O rare common minor common common rare rare rare rare rare rare rare rare 10 The common minerals i n the above l i s t were identified megascopically in hand specimen and microscopically i n thin section and polished section. Other minerals whose identit ies were uncertain were determined using X-ray powder photographs. These minerals w i l l be described in their approximate order of abundance. Primary Metall ic Minerals Pyrite - The most abundant sulfide' mineral at Galore Greek is pyrite which occurs both around and within the copper-r i ch zones except where bornite i s abundant. Pyrite appears to be one of the earl iest metallic minerals deposited as i t occurs generally as corroded disseminated grains ranging from 0.1 to 2 mm. i n diameter in various stages of replacement by most other minerals, and occasionally as euhedral cubes or cubo-octahedrons. Disseminated pyrite forming tip to 7$ of the total rock volume i s not uncommon. It also occurs i n irregular veinlets up to one-half inch wide with magnetite and chalcopyrite and occasionally occurs as small scattered grains in veinlets of anhydrite. Chalcopyrite and anhydrite are clearly later than the pyrite and magnetite because they f i l l fractures i n and par t ia l ly replace the two. Both relationships, pyrite replaced by magnetite and magnetite replaced by pyrite have been observed, but the former occurs more often than the l a t ter . (Refer to plates 16 and 17.) Chalcopyrite - Chalcopyrite i s the most important ore mineral. It occurs as disseminated grains ranging i n size from 0.1 to 3 mm. in a variety of" rock types and as breccia, vug, and vein f i l l i n g s with anhydrite. Chalcopyrite i s most common i n zones 11 r i ch i n bioti te and orthoclase. As breccia f i l l i n g s , i t occurs as coarse blebs up to one-half inch in diameter i n t e r s t i t i a l to early-formed biotite or garnet. (Refer to plates g> and 9.) , Vugs which were formed by garnet, epidote or biotite replacing other minerals ( i . e . where the volume of the metasome was less then the volume of the host) may be f i l l e d with chalcopyrite. Veinlets of anhydrite may contain disseminated blebs of chalco-pyrite thus suggesting contemporaneous deposition. However, many anhydrite veins are completely barren of chalcopyrite. Anhy-drite has also been observed as fracture f i l l i n g s cutting through chalcopyrite. Bornite - Bornite has the same relationship with other minerals as chalcopyrite with which i t i s usually associated. The distribi it ion of bornite in the Central Zone is shown i n appendix V. It occurs in three dist inct zones. At the south, i t occurs f inely disseminated in altered or brecciated dark syenite porphyry; i n the middle, i t occurs with chalcopyrite and anhydrite i n vug or breccia f i l l i n g s i n garnet-rich rocks; and at the north end, bornite occurs In feldspathized and biot i t ized with abundant mag-netite or occasionally hematite. Exsolution intergrov/ths of chalcopyrite have occasionally been observed at high magnifications but are not common. According to Edwards, such intergrowths indicate a minimum temperature of deposition of 475 °C , because above this temperature extensive sol id solution between the two minerals occurs. Bornite exsolution intergrowths in chalcocite are common and may form beautiful lamellar patterns. (Refer to plate 24.) This exsolution texture indicates a minimum temperature of deposi-12 tion of 175 to 255°C. Chaicocite - Hypogene chaicocite appears occasionally i n bornite-rich zones where chalcopyrite is sparse or absent. It has been observed only i n contact with bornite with mutual boundaries. Almost always, the chaicocite contains fine exsolved lamellae of bornite. Chaicocite also occurs to a lesser extent as a supergene mineral. It has been observed on fractures and. as coatings on bornite, chalcopyrite and pyrite . Magnetite - Magnetite is a common accessory mineral i n the syenites and occurs irregularly disseminated throughout the altered phases. It often forms veinlets with or without pyrite and chalcopyrite averaging about one-half inch wide. South of the Central Zone, magnetite forms the matrix i n breccia along with minor b io t i te . (Refer to plate 13 and appendix VI.) This breccia has been described by Davis who postulates an explosive or ig in . Magnetite breccia has also been Intersected i n a d r i l l hole in the middle part of the Central Zone. Disseminated magne-t i t e occurs generally as irregular grains, whereas massive magne-t i t e cementing breccia fragments may contain crystals up to one-half inch projecting into the vugs. Occasionally a piaty variety of vein magnetite has been observed. This type may be pseudomorphous after specular hematite. (Refer to plate 18.) Hematite - Hematite occurs mainly as reddish coatings on fracture planes and i n shear zones with gypsum and chlor i te . Reddish hematitic rims around garnet occasionally have been 13 observed. Specular hematite occurs also coating fracture planes andoon veinlets with ca lc i te , chalcopyrite and rarely anhydrite. In places in the northern part of the Central Zone, hematite occurs disseminated with chalcopyrite and bornite with or without magnetite. The magnetite in this area may have an irregular alteration rim of hematite around i t . In contact with chalco-pyrite both relationships, chalcopyrite cutting hematite and hematite cutting chalcopyrite have been observed. The above relationships suggest a considerable range of deposition for this mineral. Tetrahedrite-tennantite - This mineral has been observed i n three Central Zone samples and i n one outcrop on the North Junction deposit. In the Central Zone samples, the tetrahedrite occurs in veinlets of calcite with chalcopyrite and pyrite . Material from the North Junction occurs coarsely disseminated i n a white feldspathic'rock-with bornite and chalcopyrite. Some of the ,; tetrahedrite contains exsolved blebs of chalcopyrite and bornite.(Refer to plate 2 3 . ) A sample from this deposit was identif ied by R.M. Thompson as tennantite. Samples from both deposits were identif ied by the author as tetrahedrite-tennantite on the basis of c e l l dimensions obtained from X-ray powder photo-graphs. The c e l l dimensions were found to be: 0 Central Zone sample aa= 1 0 . 3 3 A Central Zone sample ac = 1 0 . 2 9 A o Central Zone sample a0 = 1 0 . 3 1 A North Junction sample a0= 1 0 . 3 3 A These compare with values given by Berry and Thompson: 14 Tennantite a0 = 10.21 A Tetrahedrite a0 = 10.37 A Argentian tetrahedrite a„ =10.48 A Galena - Galena occurs as sparse disseminations in vugs and fractures i n garnet-rich zones, where i t i s generally associa-ted with sphalerite. In contact with chalcopyrite, galena v/as found to have replaced chalcopyrite in some cases and to show a mutual boundary relationship i n others. Sphalerite - Sphalerite has two main modes of occurrence; associated with galena as described above, and as microscopic grains scattered throughout chalcopyrite. In polished section about 80$ of the chalcopyrite samples contain at least the occasional bleb of sphalerite. Chalcopyrite associated with bornite rarely con-tains any sphalerite. In almost a l l cases, the sphalerite contains numerous exsolved blebs of chalcopyrite which are often aligned along the 111 planes of the sphalerite. (Refer to plates 21 and 26.) This texture indicates a minimum temperature of deposition of 350 to 400° C (Edwards). Cel l dimensions of sphalerite obtained from an X-ray o powder photograph were found to be 5.414 A. According to tables in Deer, Howie and Zussman after Skinner, Barton and Kullerud, this indicates that the sphalerite contains 10 ± 5 mol percent FeS. Determination of the composition was not considered accurate enough to use as a temperature indicator. Molybdenite - Molybdenite i s a re lat ively rare mineral. It has been observed on a few fractures, and once along the contact of a lamprophyre dyke. The mineral occurs as thin coatings on the fracture and may be f inely disseminated i n the rock adjacent to the fracture giving i t a bluish t i n t . A fracture containing molybdenite has been observed to cut across chalcopyrite. M0S2 assays over 50 feet are generally less than 0.03TO. Si lver - Low but persistent s i lver values occur through-out the Central Zone. The assays vary from a trace up to a maximum of 0.9 ounces per ton. The highest assays appear to occur i n bornite-rich zones. Native s i lver has been observed i n four hand specimens, associated with bornite and chalcopyrite or bornite and chaicocite. In one specimen taken from a depth of 800 feet, a vug l ined with garnet crystals and f i l l e d with bornite and chai-cocite v/as found. Native s i lver occurs as a thin fi lm between the copper minerals and the garnet. A polished section of this speci-men revealed s i lver irregularly scattered in the bornite and chaico-c i t e . (Refer to plate 25.) A possible silver-bearing mineral present i n the G-alore Creek deposits i s tetrahedrite-tennantite, but c e l l dimensions indicate that l i t t l e or no s i lver i s present i n this mineral. Galena may also contain s i lver but the distribution of the s i lver paral lels that of bornite rather than that of galena. Gold - Gold has been observed i n one specimen from a d r i l l hole north of the Central Zone. In this sample, the gold occurs as thin films on several closely-spaced fractures. The rock around the fractures had undergone weak a r g i l l i c alteration. Throughout the Central Zone, gold values range from zero to a maxi-mum of 0 . 1 6 ounces per ton but are generally 0 . 0 1 ounces or less . These values generally para l le l the trend of s i lver . Secondary Minerals Limonite (goethite) - Limonite occurs mainly as earthy coatings on fractures down to a depth of about 200 feet below the surface. In places, the upper few feet of bedrock may be almost entirely composed of an earthy mass of limonite with minor amounts of secondary copper minerals. Malachite - Malachite occurs as botryoidal masses and fi lms, fibrous tufts up to one-quarter inch in diameter and as earthy coatings on fracture planes with azurite and limonite. The secondary copper minerals generally do not extend to as great a depth as limonite. Azurite - Azurite occurs as microcrystalline films on fractures with limonite and malachite. In fractures malachite usually l ines the walls while azurite forms a second layer coating the malachite. Massive azurite has also been observed cementing breccia fragments i n fault zones. Cuprite - Cuprite occurs mainly as reddish masses on fractures with native copper, limonite and occasionally malachite. (Refer to plate 12.) Rarely i t forms tiny black or reddish-black octahedral crystals i n vugs. Copper - Native copper occurs as reddish specks or tiny dendritic chains of minute crystals associated with cuprite on fracture planes. Covellite - Covellite has been observed only as thin X coatings on bornite and chalcocite. Tenorite - Tenorite has been reported by D.A. Barr as thin black coatings on fracture planes in a d r i l l hole specimen from the Saddle deposit. Oxides or s i l icates? of copper, iron or manganese - Thin black coatings on fracture planes and on boulders in moraine in the Galore Creek basin are thought to be manganese oxides. Results of X-ray analysis of a fine-grained black mineral associated with azurite were indeterminate as no X-ray pattern could be obtained. The mineral gives a strong copper test, therefore i t may be a hy-drated copper-bearing manganese s i l i c a t e . A dark greenish-brown botryoidal mineral cementing breccia fragments and associated with malachite, azurite and cuprite also gave indeterminate X-ray results which are shown i n appendix IV. Strong copper and iron and only a trace of manganese were indicated by X-ray fluorescence analysis. When dissolved i n n i t r i c acid, a transparent mass of s i l i c a gel remained. Therefore the mineral may be a hydrated copper-iron s i l i c a t e . The mineral was found to be br i t t l e with a conchoidal fracture and a hardness of 3 . The specific gravity was determined as 3 . 6 9 . In thin section the miner-a l is variably anisotropic with ancapproximate index of refraction of 1 . 6 6 . Rock-forming and Alteration Minerals Orthoclase - Almost a l l rocks of the Galore Creek complex have undergone moderate to strong potash metasomatism forming the minerals orthoclase and b iot i te . Many of the rocks however may .18 have been orthoclase-rich, as many of the original rocks were phonolites, trachytes or syenites. Orthoclase alteration has con-verted some rocks, part icularly on the western side of the Central Zone, into a white, pink or grey rock consisting almost entirely of the mineral. Chalcopyrite mineralization in this phase i s not strong. Orthoclase occurs occasionally as a vein mineral forming euhedral crystals up to one-half inch long which may be surrounded by later i n t e r s t i t i a l bioti te and anhydrite. Analysis of this vein material on an X-ray diffractometer indicates a composition of Orc^Aby, using the method of O r v i l l e . Orthoclase comprises most of the phenocrysts in the syenites. Occasionally a phenocryst of plagioclase part ia l ly re-placed by orthoclase has been observed. The orthoclase phenocrysts are often zoned and may be par t ia l ly replaced by a later stage of white or pink orthoclase which par t ia l ly or completely obliterates the zoning. In thin section, almost a l l orthoclase occurs as clouded, dirty grains which may be a result of incipient a r g i l l i c alteration. Only !^some of the vein material appears clear and free from inclusions. Biotite - Fine- to coarse-grained biotite occurs dissem-inated in a l l rock types. Coarse-grained biotite forms veinlets up to one inch wide. Larger veinlets with anhydrite, chalcopyrite and/or bornite are not uncommon. In breccia, biotite occurs in vugs with magnetite or anhydrite and chalcopyrite. In contact with chalcopyrite, the biotite grains are usually bent with chalco-pyrite lying along cleavage planes. (Refer to plates 22 and 28.) In thin section, the color of biot i te i s brown or green with some I I I I I I I I I 1.74 1.76 1.78 1.80 1.82 1.84 1.86 1.88 1.90 Index of refraction Figure 3 A plot of cell edge agaist index of some Galore Creek garnets of refraction showing variation in composition 19. varieties being pleochroic brown to green. The biotite usually has a dist inct mottled appearance. Analysis of bioti te on the X-ray diffractometer using Pe the method of Gower indicates 55$ Ye'ZWg -*-n octahedral sites of the biotite structure. Garnet - Garnet occurs as irregular f inely to coarsely disseminated grains with biotite and orthoclase (plate 2) i n the Central Zone and occasionally in the epidotized syenite porphyry. It occurs also as dodecahedral crystals modified by trapezohedral faces ranging i n size from 1 to 10 mm. with i n t e r s t i t i a l anhydrite in veinlets , vugs and surrounding breccia fragments. (Refer to plates 3 and 4.) Garnet crystals are strongly zoned and may be weakly anisotropic. (Refer to plate 27.) The color generally varies from l ight brown to very dark brownish black. Figure 3 shows the range of composition of some garnets of varied colors. Their compositions l i e close to .the andradite-grossularite l i n e . In each determination, the average composition of the sample is repre-sented - the index of refraction was found to vary s l ight ly i n individual grains because of strong zoning. Indices of refraction were obtained using index l iquids and an Abbe refractometer. Cel l edge determinations were made on X-ray powder photographs corrected for shrinkage. Contact relationships between garnet and biotite are d i f f i c u l t to interpret. In only one specimen garnet definitely has replaced biotite as i t can be seen lying along cleavage planes of the b io t i te . Anhydrite - The altered phases of the Central Zone and 20 Junction deposits contain abundant anhydrite except where i t has been altered to gypsum or has been removed by ground water c i rcu la-t ion . Anhydrite occurs as pervasive replacements. It occurs to a lesser extent as veins cutting the epidotized syenite porphyry. (Refer to plate 1.) Vein anhydrite i s generally white to grey i n color and fine-to medium-grained granular. Gypsum - Gypsum appears to be mainly a supergene altera-tion product of anhydrite. Both minerals are generally absent down to depths of 100 to 200 feet below the surface. (Refer to sections showing carbonate distr ibution i n appendix V.) At this leve l gypsum appears and i s present down to about 400 to 500 feet below the surface where anhydrite appears. Below this l eve l , gypsum i s minor and occurs mainly on fractures. The gypsum generally occurs as white fine-grained masses replacing anhydrite or as films cementing fractures and s l ip planes with chlorite and hematite. Occasionally, coarse, transparent selenite i s found in fractures. Calcite - Calcite occurs as a pervasive alteration mineral and in veinlets with or without anhydrite. The distribution of calc i te appears to be rather errat ic , but may be par t ia l ly con-trol led by ground water movement. In places, calcite is abundant i n the weathered zone where i t may fluoresce a b r i l l i a n t pink under short-wave ul traviolet l i g h t . Some vein calcite has a very weak pinkish fluorescence. Dolomite - Dolomite has a re lat ively minor occurrence. It has been observed in veinlets of specular hematite and as small rhombohedral crystals on fractures. 21 Epidote - The epidotized syenite porphyry has been named as such because of the characteristic occurrence of greenish clots of epidote occurringthroughout the rock. Epidote also occurs to a lesser extent in the altered phases of the Central Zone. The re la t ive ly high birefringence of this mineral i n thin section indicates that i t i s the i ron-r ich variety. The distr ibution of epidote i s not apparently related to the distr ibution of copper, but when i t occurs i n the copper-bearing phases of the Central Zone, i t i s generally intimately associated with chalcopyrite. In contact with chalcopyrite, epidote i s euhedral, the chalcopyrite usually being surroundd by i t . This suggests that epidote replaced some pre-existing host mineral but i t s volume was less than that of the host and formed a cavity with crystals projecting inward. Chalcopyrite later pre-cipitated in and f i l l e d up these cavit ies . Apatite - Apatite i s a common minor constituent of the syenite porphyries and the altered phases of the Central Zone. It i s rarely v i s ib le in hand specimen but is commonly seen in thin section. In the epidotized syenite porphyry, apatite occurs as scattered subhedral grains up to 0.1 inch long. This apatite has a very faint pink fluorescence under short wave ultraviolet l i g h t . In the altered phases, apatite occurs as disseminated euhedral crystals up to one-quarter inch long and occasionally forms tiny irregular veinlets which are comprised of aggregates of subhedral crystals . Cel l dimensions from an X-ray powder photograph indicate that the mineral i s fluorapatite or carbonate-apatite rather than chlorapatite or hydroxyapatite. 22 Chlorite - Chlorite i s a. common late stage alteration production of biotite and hornblende in the epidotized syenite porphyry. It also occurs on fractures with gypsum and hematite In a l l phases. The extent of chlorite as a pervasive alteration mineral i s not certain. Chlorite, identif ied i n hand specimen sometimes turns out to be green biot i te i n thin section. Chlorite was observed once i n a one inch veinlet cementing cleavage frag-ments of anhydrite, the edges of which were par t ia l ly altered to gypsum. Diopside - Diopside is found mainly i n the northern part of the Central Zone where i t occurs disseminated with biotite and garnet. Euhedral crystals of diopside and garnet are occasion-a l l y found l in ing veinlets of anhydrite. The diopside i s generailjr green to dark green i n color and has a well developed {100} parting. Coarse diopside-biotite skarns with magnetite, orthoclase, anhy-drite and chalcopyrite have been found north of the Central Zone. Sericite - Sericite occurs mainly as irregular clots and veinlets replacing orthoclase. Its distribution is uncertain because i t i s d i f f i cu l t to distinguish from fine grained pervasive anhydrite both In hand specimen and thin section. It i s common i n some strongly feldspathized phases in the northern part of the Central Zone. Pluorite - Pluorite is re lat ively minor in occurrence. It i s found in veinlets or on fractures with anhydrite, gypstim or ca lc i te . Rarely, veinlets of f luorite with anhydrite, pyri te , chalcopyrite, galena and sphalerite have been observed. Hornblende - Hornblende is a common mafic mineral i n the epidotized syenite porphyry where i t i s usually par t ia l ly altered to chlor i te . It has been observed in the Central Zone only in a few samples as subhedral crystals par t ia l ly replaced by garnet and anhydrite. Sphene - Sphene is a minor accessory mineral i n the epidotized syenite porphyry. It has been observed also as tiny wedge-shaped crystals i n vuggy veinlets of orthoclase. In the altered phases of the Central Zone, i t occurs mainly associated with diopside as irregularly disseminated subhedral grains. (Refer to plate 31.) Tiny bluish earthy clots have been occasionally observed i n ser ic i t ized feldspathic phases. These have been tentatively identi f ied by X-ray analysis as mixtures of rut i le and ca lc i te . Therefore they may be an alteration product of sphene. Plagioclase - Plagioclase occurs mainly as occasional grains i n the orthoclase-rich groundmass i n a l l rock types. It generally never constitutes greater than one or two percent of the rock. Remnant plagioclase phenocrysts which have been par-t i a l l y replaced by orthoclase have been observed i n some altered syenite porphyries. The determination of composition of these plagioclases has been d i f f i cu l t because of their small grain size or irregular twinning, however, plagioclase found i n a vein-le t of calcite has been identif ied as a lb i te . Tiny euhedral crystals of albite up to one millimeter long have been observed i n massive azurite cementing breccia fragments in a fault zone. Sodalite - Light blue sodalite has been observed in several samples from the Central Zone. The mineral appears to be .24 of metasomatic origin because i t occurs in irregular clots and veinlets with anhydrite apparently replacing orthoclase. (Refer to plate 32.) In this thin section, the sodalite occurs as equi-dimensional grains and aggregates of grains that appear to have been welded together. Cel l dimensions were calculated using an X-ray powder photograph and found to be 8.87 A . This indicates the chlorine-r i c h end member rather than the sulfur- or sulfate-rich end members of the sodalite group. Quartz - Quartz i s a very uncommon mineral i n the Galore Greek Complex. It has been reported as constituting up to five percent of some syenite porphyry samples. In the Central Zone, quartz has been observed several times as small barren vein-l e t s . A few quartz veins bearing chalcopyrite, bornite, specular hematite and traces of scheelite have been found near the south-eastern portion of the complex. Barite - Barite occurs as tiny pinkish crystals or grains on fracture planes with ca lc i te . It is found mainly at a shallow depth i n the southern part of the Central Zone. Celestite - Celestite has rarely been observed as tiny pale reddish fibrous grains with calcite on fracture planes i n the epidotized syenite porphyry. Natrolite - Zeolites are uncommon i n the Galore Creek deposits. Hatrolite and anaicite are the only two that have been ident i f ied . The natrolite occurs mainly as white radiating films on fracture planes. Analcime - Analcime has been observed in one specimen as trapezohedral crystals imbedded in a one-quarter inch veinlet of natro l i te . Riebeckite - Riebeckite, a sodic amphibole, has been observed i n a specimen from north of the Central Zone. The mineral occurs as small clusters of l ight blue fibres on a fracture plane with calcite and disseminated in the rock on either side of the fracture. In the groundmass of the rock, the riebeckite i n thin section i s pleochroic purplish to blue in color and occurs as Sndi= vidual or masses of fibres scattered throughout quartz and mainly along quartz-biotite boundaries. Act inol i te - Rare greenish fibres found lying along s l ip planes have been Identified as ac t inol i te . Yesuvianite - Yesuvianite has been found i n one specimen where i t occurs as tiny brown prismatic crystals i n a veinlet of anhydrite. Aegirine-augite - Aegirine-augite has been reported as a minor mafic mineral in the epidotized syenite porphyry where i t generally occurs as tiny euhedral prisms. Clay minerals - Clay minerals are found mainly near the surfa.ce i n weathered rock. X-ray analysis has done l i t t l e to re-solve their ident i t ies , however kaolinite and i l l i t e Irnve been tentatively identif ied by thin section study as an alteration of orthoclase. Perhaps these minerals account for the typical clouded nature of orthoclase in thin section. A- greenish-grey leathery mineral found on a fracture i n a d r i l l hole sample from the western edge of the complex was identi fied by R.M. Thompson as palygorskite. Pseudoleucite - Orbicular structures up to one inch i n diameter i n the metavolcanic rocks i n the Central Zone have been identif ied as remnant pseudoleucite. In most cases they are now composed of orthoclase. Occasionally they are outlined by a very thin rim of b io t i te . The distr ibution of the; pseudoleucite meta-volcanic rocks is shown in appendix VI. Pseudoleucite phonolites also occur on the ridge west of the Galore Creek basin. X-ray analysis indicates that the pseudoleucite in this rock i s composed largely of orthoclase. A few other lines present may be a result of the presence of ser ic i te . Rarely, large remnant zoned pseudoleucites up to two inches i n diameter have been observed in the dark syenite porphyry. X-ray analysis of this material also gave an-.orthoclase pattern. Leucite has rarely been observed i n alkaline plutonic rocks. This mineral may separate early from a wide range of undersatured potash r i c h melts but i t s f i e ld of s tab i l i ty i s greatly reduced with i n -creasing water pressure. In the system FaAlSi50s-KAlSi308-H20, the leucite f i e l d extends to 51$ NaAlSi30 8 under dry conditions. At a water pressure of 1000 bars, the f i e l d extends to 29$ and at 2000 bars to 5$. Therefore at water pressures greater than 2500 bars, i . e . , depths greater than five miles leucite is not l ike ly to form. Turner and Verhoogen also point out that some pseudo-leucites may be pseudomorphs after potash analcite, a mineral l i k e l y to crystal l ize from phonolitic magmas at depths exceeding 10 miles, or under explosive volcanic conditions. 27 Paragenesis Figure 4 i s a Robertson and Yandeveer diagram i l l u s t r a t -ing the paragenetic relations of the metallic minerals. The overall paragenesis of the commonplace minerals i s i l lustrated in figure 5 . Mineralization appears to have taken place in one continuous se-quence. However some minerals such as orthoclase, magnetite and pyrite may also have been present in the original rocks. The i n i t i a l f luids were apparently r i ch in potassium, forming ortho-clase and b io t i te . Once the f luids were somewhat depleted i n potassium, calcium metasomatism occurred, followed shortly there-after by sulfide deposition. The Copper Bearing Phases Appendix VI shows the distr ibution of the various recog-nizable rock types i n a few selected sections of the Central Zone. The longitudinal section has been taken along the copper-rich phases on the west side. The others are east-west sections at various intervals along the Central Zone. From these sections i t can be seen that copper mineralization occurs i n a number of rock types. Syenite Porphyries In the south, mineralization occurs mainly i n altered 28 Figure 4 PARAGENESIS OF THE METALLIC MINERALS Molybdenite. Magnetite Galena Hemati te Spha ler i te E xsolution chalcopyrite C halcopyrite Tetrahedr it e a E xsolution chalcopyrite bornite [7 Native silver Exsolution bornite E xsolution chalcopyri te Malachite Azurite Cuprite Native copper Covell ite Chaicocite 2 9 F i g u r e 5 S U G G E S T E D P A R A G E N E S I S M agmatJe Stag* Hydrothermal Stage Weathering Sta ge Breccia* ion Or t hoc lose  Biotite .Apatite • Gornet  Diopside Epidote  Anhydrite Gypsum Fl uorite Colcite - dolomite ^ Sericite C hlorite Pyrite Magnetite  Hematite Chalcopyrite  Bornite  Chalcocite Tetrahedrite  Sphaler it e Goleno Moly bd eni 1 e L i monite  Cuprite  Native copper  Malachite A 2 urite Mn oxides 3 0 syenite porphyries which may be brecciated near contacts of s i l l s or dykes of the epidotized syenite porphyry. The physical charac-ters of altered phase resemble those of the dark syenite porphyry, however the mineralization appears to pinch out between the epi-dotized syenite porphyry and a plug of dark syenite porphyry. Occasionally tiny remnant phenoerysts of orthoclase are vis ible in some of the strongly feldspathized phases i n the northern Central Zone, indicating that the original rock type may have been a porphyritic trachyte. Breccias The copper bearing rocks i n the middle part of the Central Zone are mainly breccia on the west and metavolcanics on the east. Often, breccia fragments of syenite porphyry or meta-volcanics can be recognized, but in.most cases the fragments are so strongly altered that the original rock type i s unknown. The breccia, fragments may even be completely obliterated. Streaks of orthoclase and biotite alteration appear to give rise to a pseudobreccia which i s d i f f i cu l t or impossible to distinguish from a true altered breccia. In general, the breccias seem to occur close to the contacts of the epidotized syenite porphyry. Therefore, intrusion of this porphyry may have caused brecciation along i t s boundaries. When emplaced, the syenite magma may have been essentially a viscous mush of orthoclase crystals . Pulsations of this material, along with associated hydrothermal f lu ids , may have been able to brecciate the surrounding rocks. Kents postulates a similar origin for many hydrothermal .31 developments in the Andes that may be applicable to most porphyry copper deposits. It i s suggested that magmatic pulsations result i n hydraulic ramming of hydrothermal fluids into overlying rocks, causing brecciation. It i s possible that the f lu ids , during the ebbing phase of magmatic pulsation, because of their lesser density and viscos i ty , gather at the top of the intrusion where they may form a wet cap r i ch in vo la t i l e s . As a result of the next mag-matic onrush, the f luids become rammed into the rocks surrounding the intrusion forming a rupture breccia or wedging open pre-existing fractures. Subsequent magmatic pulsations may cause heaving up or subsidence of this breccia and resulting i n the frag-ments becoming rotated and kneaded. Kents describes a burst breccia as one "composed of angu-lar fragments packed so loosely that they barely touch one another, or they may appear to be suspended i n a matrix of f inely granular quartz and tourmaline" and i s confined to pipe-like structures. The magnetite breccia at the southern end of the Central Zone (shown i n the longitudinal sections i n appendices V and VI and plate 1 3 ; also described by Davis.) may be of this type. Kents states that "burst breccias were apparently formed by jets or streams of hydrothermal solutions that forged their way upward toward the surface. As they rose, they encountered decreasing pressure, and eventually reached a c r i t i c a l stage at which the super-heated aqueous solutions turned into steam, which then blew off the rocks above i t with explosive violence. Beyond the i n i -t i a l blast, the shaping of vent walls was accomplished by burst-ing and spal l ing, that i s , hydrothermal solutions rammed ear l ier from the conduit l a tera l ly into the walls and expanded there when 32 the steam "blast had reduced the pressure in the conduit". Many of the fragments i n the magnetite breccia are of intermediate syenite porphyry which does not outcrop nor has been encountered i n d r i l l holes i n this area. Such fragments may have been carried up from depth. Metavolcanic rocks In the northern part of the Central Zone, metavolcanic rocks are the dominant copper-bearing phases, although some of the strongly feldspathized phases to the west may be syenites. Feldspathized orbicular structures are common i n these metavol-canic rocks and have been identif ied as remnant pseudoleucites. (Refer to plate 6.) Pseudoleucite phonolites outcrop approxim-ately 8000 feet southwest of the Central Zone. In this area these phonolites occur interlayered with volcanic breccias and well-bedded tuffs. This indicates that the layered phases of the Central Zone are probably metatuffs and that some breccias were pyroclastic in or ig in . Plates 3 and 4 are photographs of garnet-r i c h layered; phases. The textures of orthoclase in thin section suggest that some rocks in the northern Central Zone may have or ig inal ly been trachytes. Plates 10 and 11 are photographs of the spotted meta-volcanic phase. This is an easily recognizable phase in that i t contains disseminated grains of biotite which appear to be pseudo-morphous after augite. Occasionally the rock is strongly garnet-ized asr. shown i n plate 10. This rock may have or ig inal ly been an augite basalt or andesite. It can be correlated readily from one 33 d r i l l hole to another as seen i n appendix VI, indicating a strike of N30°W and a dip of about 4 5 ° S E . If this represents the attitude of a i l :the metayolcanic phases, then i t appears that copper mineral izat ion i s not controlled particularly by i i thology. (ihe attitude of this phase contradicts Barr's idea that the syenite intrusions have domed the surrounding country rocks so that they dip away from the complex as i l lus trated by most strike and dip symbols on figure 2.) The copper-rich zones appear to strike N30°E to ET30°W and dip steeply east and west; however, the zone seems to flatten out i n the north. The bornite distr ibution also does not appear to be obviously related to Iithology. Mineral Zoning High grade copper sections have been observed to weaken rapidly within the space of a few feet with no apparent change i n rock type or mineral assemblage. This suggests that the main con-trols of copper mineralization are physical, or else the control may be one of heat as indicated by the parallelism of the deposit with the epidotized syenite porphyry. Perhaps alteration accom-panied by fracturing made the rocks more permeable and susceptible to mineralization. Massive rocks such as the epidotized syenite porphyry appear to have been unreceptive to copper mineralization. The copper assays increase i n some places as an epidotized syenite porphyry s t i l l i s approached. This indicates that the s i l l " acted as a "dam" against mineralizing f lu ids . Some rock types which are more susceptible to replacement may have a minor control on the distr ibution of copper, but much more work is required to prove i f 3 4 this i s so. The distr ibution of the major alteration minerals i s complex. An attempt to i l lus t ra te this distr ibution is shown i n appendix V as a dot density function. Biotite and orthoclase occur almost everywhere. Chalco-pyrite appears to be most abundant where orthoclase i s moderate and biotite i s strong. Perhaps this is because b iot i te-r ich rocks are more easily crushed and fractured, making the rocks more permeable. In contact with chalcopyrite, biot i te grains are usually bent. Bornite mineralization occurs in three separate zones. (Refer to chalcopyrite mineral distr ibution sections in appendix V.) The control of this distr ibution is not apparent, part icularly in the northern Central Zone where i t occurs disseminated with magne-t i te and b io t i t e . In the middle part, i t occurs disseminated with bioti te and garnet and as vug f i l l i n g s i n t e r s t i t i a l to garnet. In the southern part, i t occurs mainly as fine-grained dissemina^ tions i n b iot i t ized and feldspathized syenites. In this area, the bornite zone appears to para l le l the contact of the epidotized syenite porphyry. C-alena occurs along the eastern edge of the Central Zone, i c e . , farther away from the eastern side of the syenite than most of the copper minera-lization. This suggests that i t s distribution may have been controlled by heat flow outward from the syenite intrusions. The original composition of the volcanic rocks may have 35 had some control on the distr ibution of a few minerals. Diopside occurs only i n the northern part of the Central Zone. Dissemina-ted magnetite and hematite are more abundant i n this area. This may be a result of the volcanic rocks being or iginal ly more basic in composition. For example, the spotted metavolcanic phase appears to have been or ig inal ly an augite-bearing basalt or andesite. Comparison with Other Deposits The disseminated nature of copper mineralization over a wide area and i t s close association with breccias, porphyries and intense alteration suggest comparison with the porphyry copper deposits. The geologic environment i s similar - the Galore Creek syenite porphyries have many characteristics of epizonal intru-sions such as the relative small size,succession of s l ight ly different material, concordant intrusive relat ions, miarol i t ic cavities and associated breccias of cataclastic and possibly ex-plosive or ig in . The presence of remnant pseudoleucite i n the dark syenite porphyry indicates that i t crystal l ized under subvolcanic conditions. This assumes that the porphyry i s indeed an intrusive rock formed at approximately the same time as the other syenites rather than being a volcanic rock. However, the dark syenite porphyry appears to be dome-shaped and has been reported as a dyke rock. In places, i t has been observed to grade into the epidotized syenite porphyry. These features, plus the large phenocrysts i t contains suggest that 36 i t i s an intrusive rock probably related to the other syenites i n space and time. The presence of anhydrite as a common gangue mineral i s a unique feature of the Galore Creek deposits. This mineral i s not uncommon i n some South American porphyry copper deposits such as Braden, Potrer i l los and E l Salvador. At Braden i t s abundance, second only to quartz, i s ascribed to the presence of thick gypsum beds i n a portion of the stratigraphic column that may underly the Braden orebody. In North America, anhydrite has been reported i n small amounts i n copper deposits such as Ajo, Arizona; San Francisco, Utah; and Bully H i l l , Cal i fornia . Anhydrite i s a f a i r l y common mineral i n the Britannia Copper Mine, B.C. (a lode-type copper deposit), where i t occurs as post-ore veins up to five feet wide. The occurrence of anhydrite at Galore Creek may have been a result of the magmas and associated hydrothermal f luids passing through the underlying Permian limestones. The magmas may have been suff ic iently desilicated by becoming contaminated with limestone to form syenite and the hydrothermal f lu ids , apparently being sul fur-r ich, picked up much calcium. The amount of sulfur may have been i n excess of that required by iron and copper so i t combined with the abundant calcium to form anhydrite. Quartz is an abundant mineral in most porphyry copper deposits, but i t is rare at Galore Creek. Any excess s i l i c a may have com-bined with calcium to form the minerals garnet and epidote. Widespread propyl i t i c , a r g i l l i c or potash and s i l i c a 37 alteration are characteristic of most porphyry coppers. Altera-t ion i s also widespread at G-alore Creek but appears to be of a higher temperature assemblage. Bornite-chalcopyrite exsolution textures indicate that these sulfides were deposited at tempera-tures greater than 4 7 5 ° C . Minerals such as garnet, diopside, apatite, magnetite and hematite are more characteristic of high temperature deposits. Other mineralogical differences are the relative scarcity of molybdenum and the higher gold and s i lver values at Galore Creek. The absence of an extensive leached capping and under-lying supergene sulfide enrichment i s an important difference between this and many other porphyry copper deposits. Pleistocene and Recent alpine glaciation probably removed any capping that may have been present. The skarn phases of the Central Zone and the fact that the mineral deposit approximately paral lels the epidotized syenite porphyry contact, suggests comparison with the contact metasomatic deposits. The garnet distr ibution i s widespread but appears to be more concentrated i n the middle part of the Central Zone close to the large dyke of epidotized syenite porphyry. (Refer to appen-dix 7.) Plate 2 shows coarse garnet that has replaced the matrix around breccia fragments and disseminated with biotite i n the feldspathic phases. However, large masses of garnet as wholesale replacement of calcareous rocks do not occur to the same extent as in.the contact metasomatic deposits. Magnetite occurs i n the disseminated form and in veinlets rather than as massive. 38 Summary and Conclusion The geologic environment of the Galore Creek deposits i s similar to that of other porphyry coppers, i . e . , subvolcanic, however, mineral associations and textures indicate a re lat ively high temperature of formation. The deposit contains many features characteristic of porphyry coppers plus some features found i n contact metasomatic deposits. Therefore the deposits may he c lass i f ied as a high temperature porphyry copper type or as a combination porphyry copper and contact metasomatic deposit. In order to avoid such ambiguity, perhaps the best c lass i f icat ion is xenothermal, using Buddington's modification of Lindgren's c las s i -f icat ion for high temperature mineral associations at shallow depth. 39 REFERENCES Barr, D.A. The Galore Creek Copper Deposits, Stikine River, B.C. A paper presented at the Annual Western Meeting of the Canadian Institute of Mining and Metallurgy, (196.5), to be published in the C.I.M.M. Bul let in . Annual Reports 1962-64. Kennco (Stikine) Mining Ltd. Davis, R .E .G . A Magnetite Breccia, Galore Creek, B.C. Unpublished B.A.Sc. thesis, University of Br i t i sh Columbia, (1962). Deer, W.A.; Howie, R.A. and Zussman, J . Rock Forming Minerals. Volumes 1 to 5, (1962). Edwards, A.B. Textures of the Ore Minerals, Australasian Institute of Mining and Metallurgy, (i960). G i l l u l y , J . The A.jo Mining Di s t r i c t , Arizona. U.S.G.S. Professional Paper 209, (19^6). Gower, J .A. X-ray Measurement of the Iron-Magnesium Ratio in  Biotites . American Journal of Science, vo l . 225, (1957). Howell, F .H. and Molloy, J.S. Geology of the Braden Orebody, Chile, South America. Economic Geology, vo l . 55, no. 5, (i960). James, H.T. Britannia Beach Map Area. G.S.C. Memoir 158, (1929). Jeffrey, W.G. Geology of Upper Galore Creek. B.C. Department of Mines Annual Report, (1965). Kents, P. Kerr, F.A. Lower Stikine and Western Iskut River Areas, B.C. Geological Survey of Canada Memoir 2^6, (19^8). Berry, 40 Orvi l l e , P.M. Feldspar Investigations. Carnegie Institute of Washington Year Book 57. Palache, C ; Berman, H. and Frondel, C. Dana's System of Mineralogy, Volumes 1 and 2 . Robertson, F. and Vandeveer, P.C. A New Digrammatic Scheme of Paragenetic Relations of the  Ore Minerals. Economic Geology, vo l . 1+7, no. 1, (1957). Turner and Verhoogen Igneous and Metamorphic Petrology. International Series in the Earth Sciences. McGraw-Hill Book Co. Inc. , (I960). White, W.H.; Thompson, R.M. and McTaggart, K.C. The Geology and Mineral Deposits of Highland Valley, B.C. C.I.M.M. Transactions, vo l . LX, (1957). Winchell, H. The Composition and. Physical Properties of Garnet. American Mineralogist, vo l . 43, (1958). Graton, L .C. The Occurrence of Copper in Shasta County, California. U.S.G.S. Bulletin if36, (1910). APPENDIX I PHOTOGRAPHS To. face 41 Plate 1. A ten inch veinlet of anhydrite cutting the epidotized syenite porphyry near i t s contact (about 3 inches from right in top row). Chalcopyrite blebs occur disseminated throughout the anhydrite. Note also the strong alignment of the orthoclase phenoerysts approxi-mately paral le l to the conta.ct of the dyke wal l . NX core, diameter 2i inches. 'Plate 2. Mottled skarn phase showing occasional breccia fragment. Fragment in third row contains remnant pseudolucite. Brown mineral i s garnet, the white i s orthoclase and black is b io t i te . Anhydrite occurs i n stringers. 41 To face 42 Plate 3. Skarn layered phases - strongly disseminated garnet and biotite i n feldspathic groundmass. A breccia fragment i n the le f t hand corner i s surrounded by garnet crystals with i n t e r s t i t i a l anhydrite. Plate 4 . Layered phase - l a y e r s defined by i n c r e a s e in d i s s e m i n a t e d g a r n e t and b io t i te . Disseminated c h a l c o p j T i t e appears to be r i c h e r i n the garnet and biotite r i c h l a y e r s . 42 face 43 Plate 5. Pseudoieucite phonoiite interlayered with volcanic breccias and tuff's south west of the Galore Creek deposits. /plate 6 . Feldspathized remnant "pse;udoIeucite phase containing chalcopyrite and pyrite from Central ^ 2one. Magnetite and biotite occur in the stringer. Plate 7. Dark syenite porphyry containing large remnant pseudoieucite Note how orthoclase phenocrysts i n f i r s t row are almost completely obliterated by orthoclase alteration. BX core, diameter 1£ inches. 43 D face 44 Plate S. Coarse c h a l c o p y r i t e w i t h b i o t i t e and a n h y d r i t e cementing D r e c c i a f r a g m e n t s . Plate 9. Skarn phase - euhedral garnets with i n t e r s t i t i a l anhydrit and chalcopyrite. 44 face 45 Plate 10. Spotted metavolcanic phase with biotite pseudomorphous after augite. Garnet tends to surround these pseudomorphs and the biot i t ized volcanic? breccia fragments on the r ight . Plate I i . Similar spotted metavolcanic rock. Chalcopyrite (opaque) occurs in stringer and par t ia l ly replaces feldspathic groundmass. large e qui dimensional grain in lower right hand corner i s biotite •> apparently pseudomorphous after augite. Gypsum occurs in fracture i i upper l e f t hand corner. Garnet is the irregular dark brown mineral' \^ith high r e l i e f . Thin section, plane polarized l i g h t . To face 46 ! n f L t L l o p p e d P l a n S ° ° a t e a W " h l i m o n « s ' malachite, cuprite Plate 13. Magnetite breccia from southern part of Central Zone. 46 To face 47 Plate 14. Pyrite crystals corroded and par t ia l ly replaced by orthoclase and epidote (dark minerals). Polished section, reflected l i g h t . ' Plate 15. Pyrite fractured and veined by specular hematite and chalcopyrxte. Polished section, reflected l i g h t . 47 To face 48 f iate 16. Pyrite rimmed and part ia l ly replaced by magnetite. JSon-reflecTjing minerals are orthoclase and. epidote. Polished section, reflected l i g h t . Plate 17. Magnetite part ia l ly replaced along parting planes by pyri-ce and a trace of chalcopyrite. Polished section, reflected 48 J 0.5 mm. face 49 Plate 18. Piaty magnetite (pseudomorphous after specular hematite?) part ia l ly replaced by chalcopyrite and anhydrite (non-reflecting). Polished section, reflected l i gh t . Plate 19. Magnetite (grey with pinkish tinge) irregularly rimmed and" par t ia l ly replaced by hematite (lighter grey). Sulfides are bornite , and chalcopyrite. Non-reflecting mineral i s orthoclase. Polished section, reflected l i gh t . face 50 Plate 20 . Specular hematite-veined "by chalcopyrite. Anhydrite veinlet cuts across both minerals. Polished section, reflected l ip-nt. Plate 2 1 . Veinlets of specular hematite and anhydrite cutting chalcopyrite and sphalerite. Note exsolved blebs of chalcopyrite in the sphalerite. Polished section, reflected l i gh t . 50 02 m m . To face 51 Plate 22. Crushed and "bent "biotite fractured and part ia l ly replaced by chalcopyrite and bornite. Polished section, reflected l i gh t . Plate 23. Tetrahedrite, chalcopyrite and bornite. The tetrahedrite. contains numerous exBoIved blebs of chalcopyrite and bornite. Under high power lens, tiny exsolved lamellae of chalcopyrite i n the borni* ' can be seen. Polished section, reflected l i g h t . 51 face 52 IPlate 24. Bornite, chalcocite and exsolution intergrowths between the two. Bornite is the exsolved mineral. Polished section, reflected l i g h t . Plate 25. Photomicrograph of bornite, chalcocite and native s i lver . The s i lver i s the brighter colored mineral occurring as scattered blebs throughout the bornite and chalcocite. The distribution of the s i lver forms a pattern suggesting exsolution. Polished section, reflected l i g h t . 52 To face 53 Plate 26. Chalcopyrite, sphalerite and garnet par t ia l ly replaced by galena. The sphalerite contains numerous exsolved blebs and lamellae of chalcopyrite. Polished section, reflected l i g h t . Plate 27. Strongly zoned and birefringent garnet. Anhydrite occurs in the interst ices . Thin section, plane polarized l i g h t . 53 J 1 0.5 mm . i i 0.5 mm. face 54-Plate 28. Fractured garnet and bent biotite grains par t ia l ly replaced by chalcopyrite (opaque). A few white subhedral crystals of apatite are v i s i b l e . The dirty greyish brown mineral i s largely orthoclase. Thin section, plane polarized l i g h t . Plate 29. Sericite (moderate birefringent mineral) par t ia l ly replaced by hematite (opaque). A veinlet of gypsum (low birefringent mineral) cuts across the lower l e f t of the photograph. Thin section, crossed nicol s . i 1 0.2 mm . face55 Plate 30 A. Subhedral to euhedral epidote crystals (moderate r e l i e f , moderate birefringence) l in ing a vug which i s : „ i n f i l l e d with chalcopyrite and bornite (opaque). Dirty brownish grey groundmass is largely orthoclase. Thin section, plane polarized l i g h t . Plate 30 B:. Same as above. Crossed n ico l s . 55 face 56 Plate 31 A . Subhedral grains of sphene and diopside with garnet (irregular grain on l e f t ) , orthoclase and gypsum. Gypsum i s the low birefringent mineral i n upper right hand corner and i n the corroded portions of the sphene. The rest of the groundmass is largely orthoclase. Thin section, plane polarized l i gh t . Plate 31 B. Same as above. Crossed n ico l s . 56 To face - 57 Plate 32 A. Soda,lite (isotropic) i n an irregular veinlet of anhydrite (moderate birefringence). Biotite occurs as brown ragged grains with moderate birefringe. Orthoclase occurs in the dirty groundmass in the lower right hand corner and on the le f t of the photo. The mineral with high r e l i e f i s garnet?; i t shows a low birefringence. The opaque minerals are chalcopyrite and/or pyri te . Plate 32 B!. Same as above. Grossed nicol s . 57 . APPENDIX I I .SPECIMEN DESCRIPTIONS 58 •SPECIMEN NO. 63-558 l o c a l i t y : Southern Central Zone Megascopic Description 'This specimen i s dark grey i n color and contains several par t i a l ly obliterated feldspar phenocrysts. Pine grained b io t i te , chalcopyrite and bornite occur disseminated throughout the rock. Microscopic Description In thin section, two phenocrysts par t ia l ly replaced by a number of other minerals can be seen. They consist of remnant plagioclase i n streaks and patches a l l i n optical continuity surrounded by orthoclase also i n optical continuity. B iot i te , chalcopyrite, bornite and minor epidote occur disseminated throughout the phenocrysts and goundmass which consists essen-t i a l l y of an aggregate of dirty interlocking grains of orthoclase. Apatite occurs as re lat ively large subhedral to anhedral grains. One grain occurs within a feldspar phenocryst and contains numerous tiny inclusions lying para l le l to i t s C-axis. This suggests that the apatite may be metasomatic in origin rather than being p o i k i i i t i c a l l y included i n the phenocryst. Epidote forms irregular grains and aggregates of grains and i s most abundant i n the phenocrysts. The largest grains of chalcopyrite and bornite are associated with and par t ia l ly replace biotite and epidote. Composition Orthoclase Biotite Plagioclase Apatite Epidote Carbonate Bornite Chalcopyrite Name Altered syenite porphyry. 76$ 7 6 3 3 1 3 1 59 .SPECIMEN NO. 89-1507 Local i ty: Northern Central Zone Megascopic Description This rock is very dark i n color and contains numerous "spots" of b io t i t e , averaging about two millimeters i n diameter, disseminated in a dark grey feldspathic groundmass. The biotite occurs as four to eight sided grains suggesting that i t may be pseudomorphous after augite. Chalcopyrite and a trace of" magne-t i te irregularly disseminated and in fractures which are cut by later ones bearing gypsum. Microscopic Description Plate 11.is a photomicrograph of this specimen. The biot i te occurs f inely disseminated i n 3. feldspathic groundmass and pse-udomorphous after aiigite. The goundmass consists essen-t i a l l y of dirty orthoclase with numerous inclusions. Garnet occurs as irregular grains with biotite in some of the pseudo-morphs. Chalcopyrite occurs as irregular grains mainly par t ia l ly replacing biotite and as fracture f i l l i n g s . The veinlet of chalcopyrite is cut by a stringer of calcite with anhydrite, gypsum and a trace of f luorite Composition Biotite Orthoclase Garnet Gypsum Anhydrite Carbonate Epidote Pluorite Chalcopyrite Magnetite Name Spotted metavoicanic phase or altered basalt. 62$ 20 7 2 1 1 t r t r : ' 5 2 60 SPECIMEN NO. 107-1220 loca l i ty : Middle part of Central Zone Megascopic Description This specimen consists of several white feldspathic breccia fragments, averaging about two inches in diameter, cemented by garnet and anhydrite. One fragment contains weakly disseminated b io t i te , garnet and a trace of chalcopyrite and pyri te . It also contains a vague white phenocryst of orthoclase about one half inch by one quarter inch. The fragments are covered with/ coarse garnet crystals up to one quarter inch in diameter projecting inward into the vug. In ter s t i t i a l to the garnet and f i l l i n g np the vug is crystal l ine anhydrite containing pyrite cubes and irregular blebs of chalcopyrite. Microscopic Description The thin section cuts across a breccia fragment contain-ing a phenocryst of orthoclase that appears extremely dirt3r -d i r t i e r than the surrounding feldspathic groundmass. In reflected l i ght the phenocryst appears whitish, suggesting that i t may be par t i a l ly altered to clay minerals. Scattered throughout the groundmass are tiny-prismatic crystals of apatite. Garnet, anhydrite and minor chalcopyrite occur as irregular replacements which appear to have been controlled by a fracture plane across the fragment. Coarse garnet crystals with strong zoning and weak anomalous birefringence surround the breccia fragments. The cores of the garnet are irregular and more strongly birefringent. Surrounding the cores i s a layer of dark brownish-red garnet which grades into a l ight brown color towards the edge of the crysta l . Coa-rse anhydrite occurs i n t e r s t i t i a l to these garnets. Composition Orthoclase ( a rg i l i i c ) 65$ Garnet 24 Anhydrite 5 Biotite 1 Apatite 2 Chalcopyrite 2 Pyrite 1 Name Altered brecciated syenite porphyry. 61 SPECIMEN NO. 107-1327 loca l i ty : Middle Central Zone Megascopic Description 'The bluish-grey color of this specimen is due to scattered clots of sodalite in a grey feldspathic groundmass. B iot i te , chalcopyrite and pyrite also occur disseminated throughout. Pyrite occurs as well-formed par t ia l ly replaced cubes comprising about 2 percent of the rock. Microscopic Description In thin section sodalite occurs as granular aggregates of roughly equidimensional grains with i n t e r s t i t i a l anhydrite forming irregular clots and veinlets . Also in these veinlets an isotropic mineral with higher r e l i e f and at least three good cleavages i s found. This mineral may be f luor i te . Biotite occurs a.s ragged brownish-green grains that may be par t ia l ly replaced by sodalite and anhydrite. The groundmass is composed of typical ly clouded granular orthoclase. An unknown mineral with high r e l i e f (uniaxial?) occurs as an alteration rim on some of the opaque minerals. A veinlet of calcite and anhydrite cut across the corner of the thin section. Composition Orthoclase Sodalite Anhydrite Biot i te Carbonate Pluorite Unknown alteration mineral Apatite Pyrite Chalcopyrite Name Altered phase - original rock type unknown. 54$ 17 15 4 3 t r i t r i 2 62 SPECIMEN NO. 114-163 Locality: West Rim Megascopic Description This specimen is a tan colored feldspathic rock with prominent layering which is defined by zones containing more strongly disseminated chalcopyrite, bornite and chalcocite. Microscopic Description In thin section this specimen consists essentially of a fine-grained aggregate of dirty orthoclase. Carbonate occurs as irregular veinlets and as disseminated grains i n the groundmass. Some of the veinlets l i e para l le l to the layering out others cut across at various angles. The copper minerals varying from O . i mm.to 1 mm.in diameter appear to have part ia l ly replaced the orthoclase, or perhaps they completely replaced some pre-existing mineral that had formerly defined the layering. A relat ively large mass of bornite and chalcopyrite about 2 mm. i n diameter appears to be pseudomorphous after a corroded pyrite • crysta l . The mass is riddled with holes f u l l of orthoclase but a vague straight boundary is present on one side. This suggests that the grain may have been original ly pyrite that had been par t ia l ly replaced by orthoclase. Later, the remaining pyrite was probably replaced by bornite and chalcopyrite. Occasional grains of plagioclase are present i n the groundmass, but no grains suitable for composition determinations were found. Composition Orthoclase 70$ Carbonate 20 Plagioclase 2 Apatite 1 Chalcopyrite 3 Bornite 3 Chalcocite 1 Name Layered metatuff or metasediment phase. 6 3 SPECIMEN NO. 117-437 Locality: Northern extension of Central Zone Megascopic Description This specimen is greyish i n color, containing biotite and a few bluish clots of riebeckite disseminated throughout a feldspathic groundmass. Also v i s ib le are occasional small par-t i a l l y obliterated phenoerysts of orthoclase averaging 1 m i l l i -meter by two millimeters. One edge of the sample i s bounded by a fracture plane which contains scattered grains of calcite and riebeckite. Microscopic Description This specimen consists of an inequigranular aggregate of dirty orthoclase grains. Some of the large grains may be phenoerysts. Biotite occurs as disseminated ragged grains and aggregates of grains poikiIobla.sticaily including the odd grain of orthoclase. Some of the grains are bent and some exhibit weak zoning. Quartz occurs as clear grains with weak undulatory extinction under crossed n ico l s . The quartz usually contains randomly oriented fibres of riebeckite. Riebeckite occurs as irregular pleochroic bluish to purplish clots of fibres and individual fibres associated with b io t i te , which i t appears to have par t ia l ly replaced, and quartz. The opaque minerals tend to be associated with biotite and l i e along biotite cleavage planes. Composition Orthoclase Biotite Quartz Riebeckite Carbonate Plagioclase Opaque minerals Name Altered porphyritic trachyte? "llfo 10 5 4 2 1 1 64 SPECIMEN NO. 118-585 l o c a l i t y : Northern Central Zone Megascopic Description This rock is strongly mottled, consisting of irregu-l a r l y disseminated chalcopyrite, garnet and biotite with irregu-l a r surges of anhydrite i n a fine grained pinkish-orange feldspath-i c groundmass. One edge of the specimen is bounded by a fraction coated with gypsum. Microscopic Description In thin section, orthoclase occurs as the inequigranular groundmass of the rock. Some of the larger grains are f i l l e d with numerous tiny inclusions. Biotite occurs as greenish irregu-la r bent grains with undulatory extinction under crossed nicols . Garnet occurs as irregularly dispersed grains mainly associated with and par t ia l ly replacing? b iot i te . Anhydrite occurs as irregular surges or veinlets pervasively replacing orthoclase. Chalcopyrite appears to be mainly associated with garnet and biot i te which i t par t ia l ly replaces. One grain of hornblende, par t ia l ly replaced? by biotite was observed. An occasional tiny stringer of sodalite with anhydrite is present. Composition Orthoclase Anhydrite Biotite Garnet Sodalite Gypsum Hornblende Chalcopyrite Name Altered phase - original rock type unknown. 47$ 37 7 5 1 1 tr 2 65 SPECIMEN NO. 118-812 loca l i ty : Northern Central Zone Megascopic Description This specimen consists of b io t i te , garnet, epidote, chalcopyrite and magnetite, disseminated throughout a greyish feldspathic groundmass. Greyish irregular clots and surges of anhydrite are common. Microscopic Description In thin section, orthoclase occurs as an inequigranu-lar clouded mineral comprising much of the groundmass. Clots of coarser grained orthoclase occur i n a mass of fine-grained ortho-clase. Anhydrite occurs as irregular surges par t ia l ly replacing orthoclase. Although many grains are not continuous i n the thin section a group may be in optical continuity. This suggests a poiki loblast ic texture. Garnet occurs as scattered irregular yellowish-brown grains. Biotite occurs as ragged brownish-green grains v/hich may be bent and have a s l ight undulatory extinction. Almost a l l the chalcopyrite grains occur i n contact with euhedral epidote or par t ia l ly replacing epidote, thus suggesting that the chalcopyrite has f i l l e d cavities l ined with epidote crystals . (Refer to plate 30.) This epidote has a birefringence of about 0.030 indicating the i ron-r ich variety. Apatite occurs as the occasional euhedral crysta l . Composition Orthoclase 5 5 $ Anhydrite 27 Garnet 5 Biotite 5 Epidote 3 Apatite 1 Magnetite 1 Chalcopyrite 3 Name Altered phase - original rock type unknown. 66 .SPECIMEN NO. 120-638 Local i ty: Northern Central Zone Megascopic Description This specimen consists of disseminated chalcopyrite, bornite and magnetite in a pinkish-orange feldspathic groundmass. Irregular bluish zones of sericite give the rock a mottled appearance. Microscopic Description The orthoclase i n the groundmass i s inequigramular and a dirty grey i n color. Sericite occurs as irregular veinlets with minor carbonate replacing the orthoclase. In contact with serici te i n places, the orthoclase has a clear overgrowth on i t . Biot i te occurs as the occasional very irregular grain and is par t i a l ly replaced by orthoclase? and carbonate. Apatite occurs as groups of" euhedral crystals generally i n the feldspathic groundmass close to the sericite veinlets . Occasionally an apatite grain contains bornite or chalcopyrite lying along a cleavage plane. The opaque minerals mainly appear to have par t i a l ly replaced the orthoclase near the boundary of these veinlets . Magnetite i s occasionally fractured by the sericite but chalcopyrite and bornite appear to have par t ia l ly replaced the ser ic i te i n places. Composition Sericite 50$ Orthoclase 35 Plagioclase 1 Apatite 3 Biotite 2 Magnetite 5 Chalcopyrite 3 Bornite 2 Name Altered trachyte? (A sample taken about 15 feet from this one contains tiny phenoerysts of orthoclase i n a f ine-grained feldspathic groundmass.) 67 SPECIMEN NO. 161-479 Local i ty : Northern Central Zone Megascopic Description This specimen is l ight grey in color. Clots of epidote and pyrite with tiny black specks of magnetite occur disseminated throughout a groundmass of a dirty-white mottled feldspar. Occasional greenish s e r i c i t i c clots have a hexagonal outline suggesting remnant pseudoleucite. The pyrite grains are pit ted, corroded and appear to be par t ia l ly replaced by orthoclase. The fracture cleavage planes (about 4 fractures per inch) are cemented with gypsum. Microscopic Description \ In thin section the rock consists essentially of f ine-grained clouded orthoclase par t ia l ly replaced by clay minerals anhydrite and ser ic i te . Two clay minerals are present: 1. a very low birefringent variety - kaolinite? 2. a moderate birefringent variety - i l l i t e ? These minerals also l i e on fracture planes cutting the pyrite . The;,; pyrite occurs as corroded grains par t ia l ly replaced by orthoclase. Epidote occurs as scattered dirty grains. Composition Orthoclase Kaolinite, I l l i t e j Sericite Anhydrite Epidote Pyrite Name 45$ 40 7 5 3 Pseudoleucite metayolcanic phase? 68 .SPECIMEN NO. 176-756 Local i ty : Northern Central Zone Megascopic Description This specimen is pinkish grey in color with a weak layered appearance as a result of biotite being more strongly disseminated i n zones. Epidote, b io t i te , pyrite and magnetite are strongly disseminated throughout the pinkish feldspathic groundmass. Microscopic Description In thin section, euhedral crystals of apatite and irregular grains of b io t i te , epidote and opaque minerals occur scattered throughout a dirty fine grained orthoclase-rich groundmass. The only minerals that have a tendency to occur together are epidote and b iot i te , with epidote par t ia l ly replac-ing b io t i te . Composition Orthoclase 48$ Epidote 20 Biotite 15 Apatite 3 Garnet 2 Chalcopyrite 5 Magnetite 4 Pyrite 3 Name Layered metatuff or metasediment phase. 6 9 SPECIMEN NO. 182-483 Local i ty: Southern Central Zone Megascopic Description This specimen consists of f inely disseminated b io t i te , bornite and chalcopyrite i n a greyish mottled feldspathic ground-mass . Microscopic Description In thin section, the groundmass consists of inequi-granular clouded orthoclase. Some of the larger grains may be phenocrysts, suggesting that the rock i s an altered porphyry. Disseminated throughout this groundmass are ragged grains of biot i te and opaque minerals along with euhedral to subhedral crystals or aggregates of crystals of apatite. The chalcopyrite occurs along intergranular boundaries par t ia l ly replacing both orthoclase and b io t i te . Sericite occurs as irregular surges with carbonate replacing the feldspathic groundmass. Composition Apatite Bornite Orthoclase Sericite Biotite Carbonate Chalcopyrite 46$ 25 15 5 4 3 2 Name Altered syenite porphyry. 70 SPECIMEN NO. 186-852 Local i ty : Northeastern Central Zone Megascopic Description This specimen contains strongly disseminated irregular masses of b io t i te , garnet and chalcopyrite i n a grey feldspathic groundmass. Microscopic Description - In thin section, ragged grains and aggregates of grains of bioti te and garnet occur scattered throughout a d i r ty , inc lu-sion f i l l e d groundmass of orthoclase with minor anhydrite. The biot i te is greenish-brown i n color and is often bent, having undulatory extinction under crossed n ico l s . Numerous euhedral to subhedral crystals of varying size of apatite are disseminated throughout. A couple of ragged grains of hornblende are present. These are par t i a l ly replaced by anhydrite and orthoclase. Pyrite occurs as corroded cubes par t ia l ly replaced by orthoclase. In contact with a grain of pyri te , a few grains of orthoclase exhi-bi t zoning which is distinguished by variable extinction under crossed n ico l s . Chalcopyrite occurs as very irregular grains scattered throughout the groundmass and par t ia l ly replacing aggregates of biot i te or garnet. (Refer to plate 28.) Composition Orthoclase 53% Bioti te 20 Garnet 10 Apatite 4 Anhydrite 4 Hornblende <r 1 Epidote * 1 Plagioclase < 1 Magnetite 1 Pyrite 1 Chalcopyrite 5 Name Altered phase - original rock type unknown. 71 SPECIMEN NO. 189-978 Locality: Northern Central Zone Megascopic Description This specimen i s a dark rock consisting of irregular clots of medium-grained biotite and garnet surrounded by dark greenish fine-grained biot i te . Anhydrite occurs as a pervasive alteration throughout the specimen and i s also present in fractures. Chalcopyrite i s weakly and irregularly disseminated with a trace of bornite and magnetite. Microscopic Description In thin section, this specimen consists almost entirely of anhydrite, garnet and b iot i te . The biotite i s fine to medium-grained. Fine-grained biotite occurs In zones as a granular aggregate with orthoclase which are barren of garnet. Garnet occurs as disseminated aggregates of irregular grains. It generally appears to have part ia l ly replaced the coarser biotite along intergranular boundaries. Anhydrite surrounds and cuts through both biotite and garnet. Chalcopyrite occurs mainly in contact with and part ia l ly replaces b iot i te . Composition Biotite 50% Garnet 22 Anhydrite 20 Orthoclase 5 Chalcopyrite 2 Bornite * 1 Magnetite < 1 Name Altered phase - original rock type unknown 72 SPECIMEN NO. 189-979 Locality: Northern Central Zone Megascopic Description This specimen i s greenish in color due to the abundance of diopside which occurs as irregular masses in a matrix of orthoclase and some biot i te . Disseminated throughout the rock are tiny subhedral to euhedral grains of sphene. Gypsum occurs on fractures. Microscopic Description In thin section, this specimen consists mainly of a granular aggregate and occasional individual grains of diopside with minor sphene, b iot i te , garnet and orthoclase. (Refer to plate 31.) Orthoclase appears to occur i n t e r s t i t i a l to the diopside. Several one sixteenth inch veinlets of gypsum with ' carbonate also occur as a replacement of the groundmass. Composition Carbonate Garnet Plagioclase Apatite Gypsum Sphene Biotite Diopside Orthoclase 6 6 % 8 6 5 5 k 3 2 < 1 Name Altered phase - original rock type unknown. 73 APPENDIX" III POTASSIUM-ARGON AGE DETERMINATION OP BIOTITE Sample Description The bioti te sample was obtained from d r i l l core at a depth of about 300 feet below the surface, i n the northern part of the Central Zone. The biotite occurs as large grains up to 3/4 inch in diameter in a coarse biotite-diopside skarn. Associated with these minerals i s magnetite as occasional i r reg-ular blebs varying from i inch to i inch i n diameter, and chalco-pyrite and anhydrite in veinlets and as cavity f i l l i n g s inter-s t i t i a l to euhedral diopside. No secondary alterations of these minerals were observed. Data and Calculation Kfo = 8.22 ± 0.04 Constants: 1.181 x 10" 4 K 0 . 5 8 5 x 10" / y r . 4.72 x 10~'° / y r . If the above result is significant (further work i s necessary to prove that this i s so) i t should indicate the mini-mum age of the Galore Creek syenite porphyries. Biotite i s an abundant alteration mineral in the complex. Coarse biotite has been observed in stringers up to one inch wide cutting some of the porphyries. Biotite also occurs i n veinlets of chalcopyrite and anhydrite indicating that copper mineralization occurred approximately at this time. The age obtained confirms Kerr's ideas that the ortho-clase porphyries i n the Stikine River area are among the oldest intrusions. Pew age determinations on the main part of the Coast Range complex are available but the age i s believed to vary from Jurassic to Cretaceous or Early Tertiary. A r f ° =0.74 Ar*° Ar Ar K** 4 0 K 10 6.786 x I0's c ^ n . v r P -0.01220 Age = 198 ±- 10 mi l l ion years. Possible Significance of Results 74 An age of 1 9 8 mi l l ion years indicates that the syenite porphyries are' approximately the same age as the en-closing volcanic and sedimentary rocks and thus confirms the conclusion that the syenite porphyries formed under subvolcanic conditions. Perhaps the plug of dark syenite porphyry at the southern part of the G-alore Creek Complex i s a remnant volcanic neck. Both the dark porphyry and the phonolites southwest of Galore Creek contain pseudoleucite. 75 APPENDIX IV X-RAY DATA FOR UNKNOWN MINERAL The followningis the X-ray data for the unknown mineral described under Secondary Minerals: A» X-ray powder photograph. Iron radiation, I 3B? 6 4B IB IB IB dm 7.32 4.21 2.^ -6 2.23 1.71 1.49 Some of the above lines correspond to the strongest l ines of goethite which are 4.21 (10), 2.69 (8) and 2.44 (7). However, 2.69 does not appear in the above data. The pattern suggests the presence of poorly crystall ized goethite. B. X-ray diffractometer data. Copper radiation. I dm M 5.06 Malachite? W 4.57 W 3.87 W 3.67 Malachite? W 3.35 Quartz? W 2.86 M 2.44 Goethite? W 2.33 W 2.24 W 2.13 W 1.82 M 1.67 W 1.59 W 1.56 W 1.51 w 1.44 Many peaks on the above pattern were d i f f i cu l t to pick out because of a very high background in places. Some of the l ines correspond to malachite and goethite but the others cannot be determined. 76 Prom the above'data and chemical tests, i t can only be concluded that the mineral i s poorly crystal l ized unknown hydrated iron-bearing s i l i c a t e . The weak X-ray patterns -obtained may be a result of admixed malachite and goethite with which the unknown was associated. The X-ray fluorescence pattern indicated strong copper which may be a constituent of the unknown or of the malachite which may have been present. 7 7 DISTRIBUTION OP THE COMMON MINERALS IN THE CENTRAL ZONE APPENDIX V A EAST-WEST SECTIONS APPENDIX T B LONGITUDINAL SECTION (in pocket) Explanation The distr ibution of minerals i s plotted as a dot density function, i . e . where the mineral is most abundant the stippling is heaviest. The data has been obtained from visual estimates of d r i l l core. The dashed lines on the section showing the carbonate distr ibution indicate the zones where gypsum and anhydrite are present. The upper l ine indicates the appearance of gypsum and the lower l ine indicates the appearance of anhydrite. The dashed l ines on the chalcopyrite section outline the zones i n which bornite i s the main associate of chalcopyrite. Elsewhere, pyrite i s the main associate. The distr ibution of orthoclase outlines the area where data i s available because weak to strong orthoclase is ubiquitous. Red stippling on the epidote sections i l lustrates diopside distr ibution. Red st ippling on the hematite sections: i l lus trates galena distr ibution. SECTION C w Orthoclase E Chlorite Biotite S E C T I O N E Epidote Garnet ! Biotite Carbonate Chalcopyrite SECTION Orthoclose Chlorite Biotite Epidote Magnetite Hematite Chalcopyr i te S E C T I O N K Chlorite Biotite Garnet Carbonate Hematite Chalcopyr i te S E C T I O N M Orthoclase Chlor i te Biot i te fl pidote Garnet Carbonate Magnetite Hemoti te Chalcopyrite 3.".' Bornite S E C T I O N P / . . N ^ ' G ypsum -L O N G I T U D I N A L s 1 1 jk. .•: '••.' M* i j.-1';jjj I Biotite M a g n e t i t e , • • ' . • • • • trj yt', Bornite . , -/ S E C T I O N Chlorite RED STIPPLING I DIOPSIDE Hematite GALENA Mineral Abundances Strong Moderate Weak Trace APPENDIX V B ONGITUDINAL SECTION MINERAL DISTRIBUTION FOR EXPLANATION SEE APPENDIX V IN T E X T FOR LEGEND SEE APPENDIX VI SCALE : I = 500 Longituainal Section .V S e c t i o n I W Section K 2! / / s s o s s 5. ft... . Volcanic breccia 7 CENTRAL ZONE SECTIONS SKETCHES SHOWING GEOLOGY AS I N T E R P R E T E D FROM DRILL HOLE DATA SCALE I = 5 0 0 [ S 3 • ra APPENDIX VI Legend Epidotized syenite porpnyry Da'K sycti+e porphyry Brecc io Loyered met a tufts, or me*asedir'ients Pseudoleuc i te meta </oicopic«: Spotted metavolcanics Strongly a l t e r e d phases o* unknown or ig in Overburden Position of longitudinal sections relotive to east-west sections 


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