Seabridge Gold

KSM (Kerr-Sulphurets-Mitchell): GEOLOGY

The Kerr-Sulphurets-Mitchell (KSM) property is located in northwest British Columbia about 950 kilometers northwest of Vancouver, and 21 kilometers south-southeast of the Eskay Creek Mine.  It lies in the rugged Coastal Mountains of northwest British Columbia, with elevations ranging from 520 meters in Sulphurets Creek valley to over 2,300 meters at the highest peaks. Valley glaciers fill the upper portions of the larger valleys and have been retreating for at least the last several decades. The climate is generally that of a temperate or northern coastal rainforest, with subarctic conditions at high elevations. Current access to the property is via helicopter. Various explorers have been attracted to this area due to the numerous large, prominent pyritic gossans that are exposed in alpine areas, however there is no recorded mineral production, nor evidence of it, from the property.

Regional Geology

The region lies within “Stikinia”, a terrane of Triassic and Jurassic volcanic arcs that were accreted onto the Paleozoic basement of the North American continental margin in the Middle Jurassic. Stikinia is the largest of several fault bounded, allochthonous terranes within the Intermontane belt, which lies between the post-accretionary, Tertiary intrusives of the Coast belt and continental margin sedimentary prisms of the Foreland (Rocky Mountain) belt. At KSM, Stikinia is dominated by variably deformed, oceanic island arc complexes of the Triassic Stuhini and Jurassic Hazelton groups. Folding and thrusting due to compressional tectonics in the late Cretaceous generated the area’s current structural features.

Triassic rocks include marine sediments and intermediate volcanics of the Stuhini Group. The lowermost Stuhini Group is dominated by turbiditic argillite and sandstone, which are overlain by volcanic pillowed flows and breccias. The upper portion consists of turbidites and graded sandstones similar to the base strata. The Stuhini Group is separated by an erosional unconformity from the overlying Jurassic sediments and volcanics of the Jack Formation and Hazelton Group. The Jack Formation is comprised of fossiliferous, limey sediments, mudstones and sandstones. The base is marked by a granodiorite and limestone cobble bearing conglomerate. Overlying the Jack Formation is the Hazelton Group, dominated by andesitic flows and breccias deposited in a volcanic chain with high paleotopographic relief. Distinct felsic welded tuff horizons in the Hazelton Group are closely associated chronologically and genetically with the Eskay Creek deposit.

A variety of dikes, sills, and plugs of diorite, monzodiorite, syenite, and granite are are of Early Jurassic age and they are collectively referred to as the “Mitchell Intrusions”.  Large, coalescing hydrothermal alteration haloes developed around nested volcanic-intrusive complexes. Below the Sulphurets and Mitchell thrust faults, pre- and intra-mineral intrusives have historically been very difficult to differentiate due to intense hydrothermal alteration. Above the faults there are a number of sills and plugs of coarse-grained feldspar porphyritic monzonite to low-silica granite that intruded siliceous hornfelsed sediments and volcanics. Copper and gold mineralization is typically best developed at the margins of these intrusions. There appear to be both pre-, intra-, and post-mineral phases of mineralization.

Mineralization at KSM is occurs within a gold-enriched copper porphyry system controlled by a series of dikes, sills and plugs rather than a single stock.  It is typically associated with quartz veinlet stockworks and sheeted quartz veinlet arrays mainly in altered host rocks adjacent to the intrusions.  Less commonly, mineralized intrusive-hydrothermal breccias cut through previously veined and mineralized rocks. Principal sulfides are pyrite and chalcopyrite, with minor molybdenite, and trace amounts of tennantite, bornite, sphalerite, and galena.  All mineralization is hypogene, except for a small remnants of preserved weak supergene at higher elevations.

Hypogene mineralization is fine grained, pervasive, homogeneous, and continuous for several hundred meters along strike and depth extents. Preliminary work indicates gold is intimately associated with chalcopyrite.  The unusually homogeneous nature of the mineralization over large extents may be the result of post-mineral metamorphism and re-distribution of metals during Early Jurassic or Cretaceous deformational events. At Sulphurets, mineralization is somewhat less continuous than Mitchell, where sharp contrasts in grade occur between structurally controlled hydrothermal breccias and alteration zones.

Kerr Zone

Fine disseminated, fracture and veinlet controlled chalcopyrite mineralization, with minor bornite and tennanite, is associated with intrusion of Early Jurassic monzonite porphyry into Triassic sediments and volcaniclastics, and accompanying hydrothermal alteration. There is a strong phyllic overprint with a high pyrite content, generally 5 to 20%. In many respects, the deposit bears little resemblance to a classic porphyry deposit; however it has been referred to as a porphyry-type deposit since 1987. Later studies (see bibliography) indicated that mineralization was localized around one or more previously unrecognized monzonite intrusions, and is adequately described as a modified porphyry deposit. Portions of the following description draws heavily from work by Ditson, et al, 1995 and Bridge, 2001.

The Kerr deposit is a strongly deformed copper-gold porphyry, where copper and gold grades have been upgraded due to remobilization of metals during later and/or possibly syn-intrusive deformation. Alteration is the result of a relatively shallow, long lived hydrothermal system generated by intrusion of monzonite. Subsequent regional deformation along the Sulphurets thrust was diverted into the Kerr area along pre-existing structures and altered rocks with low competency.

The mineralized area forms a mostly continuous, north-south trending and westerly dipping, irregular body at least 1700 meters long, and up to 200 meters thick.  Higher grades are associated with crackled quartz stockwork, anhydrite veining, and chlorite alteration. It is enveloped by a schistose, pyrite rich phyllic alteration with low to moderate grades. Mineralization is open at depth and along strike. 

The surface expression of the deposit is a large, strongly leached schistose, pyritic gossan. Soil geochemistry shows elevated anomalous gold values over the deposit, and a halo of anomalous copper values. Induced polarization detects high chargeability and low resistivity coincident with mineralization.

Lithology and Structure

The majority of the host volcaniclastic and sedimentary rocks belong to the Stuhini Group which is highly schistose within the deposit.  Where they are undeformed, the sedimentary rocks consist primarily of coarse conglomerate, siltstone, mudstone and minor greywacke. Undeformed volcaniclastic rocks are not present within the deposit but outcrops nearby contain well-bedded, sandy tuffs to coarse volcanic conglomerate. The presence of strongly flattened clasts was used to assign a volcaniclastic origin. Within the core of the deposit, deformation and alteration preclude assignment of protolith, and either “sericite schist” or “chlorite schist” is usually the most appropriate term.

Monzonite intrusions are plagioclase-hornblende-biotite porphyries with common apatite microphenocrysts. Primary hornblende and biotite are not observed, but are recognized as hydrothermal chlorite and sericite pseudomorphs. Plagioclase phenocrysts are variably altered to sericite and have diffuse boundaries. Where alteration and deformation are intense, identification of monzonite may hinge on the recognition of plagioclase or hornblende phenocrysts alone. Several intrusive phases appear to be present, including breccias at the margins, but cannot be distinguished clearly by their mineralogy. 

Monzonite is probably part of the “Mitchell Intrusions”, which belong to the Early Jurassic Texas Creek plutonic suite. This age is inferred by previous workers from the close relationship between monzonite and porphyritic dikes. Monzonite appears to be most abundant in the lower reaches of the deposit, but it is also the suspected protolith for much of the strongly altered material in the upper central portions.

A large area of barren plagioclase porphyry and intrusive breccia occurs in the southeastern corner of the deposit. Alteration includes pervasive chlorite, epidote, sericite and carbonate. K-feldspar is a primary component in the groundmass of some porphyries. The contact between these rocks and mineralizing monzonite is probably a fault. 

Plagioclase hornblende porphyry dikes and intrusions similar to the host monzonite are most abundant in the southern half of the deposit. They are generally massive and barren or only weakly mineralized and are inferred to be late phases of the same magma.

Meter-scale, barren albite megacrystic porphyry dikes intrude the deposit along generally north-south trends. Hyalophane megacrystic dikes intrude along east-west trends. These dikes likely correlate with “Premier porphyry” dikes of the Texas Creek plutonic suite commonly associated with copper and gold mineralization throughout the region. Aphanitic andesite dikes are common throughout the deposit, and are highly altered, massive, dark green, and composed of plagioclase, chlorite, ilmenite and sericite. These dikes generally cross-cut schistosity, but many folded dikes have been observed on the surface.

Eocene kersantite, andesite and monzonite dikes up to 3 m wide intrude the deposit along the northerly foliation trend. These are composed of highly variable amounts of biotite, fine-grained plagioclase, chlorite, tremolite/actinolite, quartz and K-feldspar. Coarse white carbonate and possible barite occur as local amygdules, especially along contacts.

The Kerr deposit occurs within a major northerly trending structural zone with strong foliation and widespread shearing. Individual structures within the deposit are masked by pervasive alteration and deformation.

Alteration
Abundant pervasive sericite occurs throughout the deposit, which is accompanied by chlorite replacement of mafic minerals in the main monzonite intrusion. Outward from this, strong chlorite-sericite alteration contains more pervasive chlorite than sericite. 

Yellow and grey sericite alteration types occur peripheral to these two chlorite-bearing types. Sericite is commonly twice as abundant as chlorite.  In drill core, zones of pale green sericite-dominant alteration are common.  Patchy quartz is present in amounts varying from 5% to 15%.  Pyrite content is generally less than 10%. 

Dark green, pervasive chlorite-dominant alteration occurs around the margins of the main monzonite intrusion.  It most commonly occurs between sericite-chlorite and intense grey sericite zones and may represent an alteration front.  Up to 60% dark chlorite is accompanied by up to 30% sericite.  Patchy quartz (5% to 15%) may locally represent dismembered veins. Anhydrite is most visible as white to pink coarsely crystalline veins up to several centimeters wide. Pyrite content is only 1% to 7%.  Primary biotite phenocrysts have been replaced by chlorite. Apatite grains up to 15 mm are locally present in some of the most strongly altered zones.

Pervasive grey sericite alteration is characterized by 40% to 60% grey sericite with 5% to 10% quartz and 0% to 7% chlorite.  Fine-grained plagioclase is commonly present in amounts varying from 20% to 50%, but much less where quartz is dominant.  Intensity of alteration and deformation are such that the rock is best described as sericite or quartz-sericite schist. The pyrite content can be as high as 15%, especially in volcaniclastic rocks.

Pervasive yellow sericite alteration is a peripheral assemblage affecting only the Stuhini Group, primarily in the footwall below the main stockwork zone.  This has the lowest average copper grade of all the pervasive alteration types. This style typically contains 5% to 15% original plagioclase, 30% to 60% yellow sericite, 10% to 20% quartz, and 10% to 20% pyrite. Yellow sericite commonly wraps around rounded quartz fragments, giving these rocks an augen-like, granular appearance. Green sericite commonly occurs in minor amounts as a replacement of selected clasts. As alteration and deformation weaken, pervasive sericite changes from yellow to green, and gradually disappears as sedimentary textures become clear. 

Anhydrite veining is most commonly associated with chlorite bearing alteration types. It is characteristic of texturally destructive chlorite-sericite alteration and the upper portions of sericite-chlorite altered monzonite. Anhydrite veins locally carry minor chalcopyrite. During deformation, anhydrite was remobilized into irregular, crosscutting networks of veinlets that post-date all other vein types. Anhydrite has hydrated to gypsum to depths of up to 250 meters, and leaching by groundwater has produced large areas of voids and broken rock called "rubble." Core recovery in these zones is poor.

Mineralization
The most important mineralization type is quartz stockwork, which drapes over the main monzonite intrusion and extends a considerable distance down the eastern side, along the footwall of the deposit. Deformation of mineralized quartz veins has resulted in segregation of sulphides into interstices between granular recrystallized quartz, resulting in a 'crackled' texture. Chalcopyrite also occurs as fracture fillings in an earlier generation of coarse vein pyrite. Narrow veins and veinlets are commonly highly contorted. The quartz stockwork veins may contain any combination of pyrite, chalcopyrite, bornite, tetrahedrite, tennantite or rare enargite. Thin films of secondary digenite and chalcocite are also present, but are only locally significant near the surface. Small flakes of possibly primary crystalline covellite are locally abundant, especially in rubbled zones and near-surface areas.

In addition to crackled quartz stockwork, mineralization is hosted by several other types of veinlets. Ditson et al, suggest the following vein classification for Kerr:

• pyrite±quartz, sericite, minor chalcopyrite (predeformation)
• quartz±pyrite, carbonate, anhydrite, sericite, chlorite, chalcopyrite (predeformation)
• anhydrite±chalcopyrite (predeformation)
• carbonate±minor chalcopyrite, bornite (syn/postdeformation)
• quartz+carbonate, chlorite, chalcopyrite (postdeformation)

Chlorite-bearing alteration types host the greatest variety of vein types. Mineralization grading over 0.4% Cu is generally located within or adjacent to crackled quartz stockwork, however there are significant tonnages in non-stockwork mineralization grading over 0.4% Cu in the northern sector in monzonite below the stockwork. All mineralization grading over 1% Cu occurs within stockwork. The Au:Cu ratio (g/t:%) for all rocks grading over 0.4% Cu averages 0.4.

Molybdenum values were analyzed are most commonly less than 100 ppm, but range up to 423 ppm. Molybdenite is associated with chloritic alteration, and in the northern sector yellow sericite altered rocks below monzonite.

Structure
The Kerr deposit occurs within a major northerly trending structural zone with strong foliation and widespread shearing. Individual structures within the deposit are masked by pervasive alteration and deformation.

Sulphurets Zone

The deposit is comprised of two distinct zones, Raewyn and Breccia Gold. The Raewyn Copper-Gold zone hosts mostly porphyry style disseminated chalcopyrite and associated gold mineralization in moderately quartz stockworked, chlorite-biotite-sericite-magnetite altered volcanics. The alteration and mineralization are centered on a narrow, apparently conformable body of porphyritic quartz monzonite. It has an apparent northeasterly strike and dips about 45 degrees to the north. It may be offset in en echelon style by several north-northeasterly trending vertical structures. The mineralization is open at depth and to the northeast. The Breccia Gold zone hosts mostly gold bearing pyritic mineralization with minor chalcopyrite and sulfosalts in a K-feldspar-siliceous hydrothermal breccia that apparently crosscuts the Raewyn porphyry copper-gold deposit. It comprises altered intrusive clasts in a matrix of mainly silica and sulfides. Both zones have an intense phyllic overprint that nearly masks all earlier alteration phases.  Portions of the following description draw heavily from Fowler and Wells, 1995.

Lithology and Structure

The Sulphurets deposit (or Sulphurets Gold zone) formed in a high level, transitional porphyry copper-gold system that was thrust over the deeper levels of a syenite-centered porphyry copper-gold deposit (Main Copper zone) along the Sulphurets Thrust Fault (STF). Volcanic sequences on either side of the thrust have been assigned to Hazelton Group. Generally, in areas of intense alteration and mineralization, the protolith cannot be assigned accurately. Late hornblende phyric monzonite to monzogabbro dikes and sills intrude the area. 

The Sulphurets Gold zone is centered along a zone of strong faulting and phyllic-quartz-sericite-pyrite, intermediate argillic, and potassium silicate alteration. Copper-gold mineralization is usually coincident with areas of strongest fracturing and potassium silicate alteration. Late, auriferous hydrothermal breccias constitute the Breccia Gold zone.

Above the STF in the Main Copper Zone, intermediate volcanics are intruded by feldspar porphyry quartz syenites and potassic monzonite dikes. Rocks in the periphery of the dikes are K-feldspar altered and contain disseminated and fracture controlled chalcopyrite with lower Cu and Au grades than the Sulphurets Zone. The dikes are grouped with the Mitchell intrusions that correlate with late Jurassic Texas Creek intrusions common throughout the region.

Alteration/Mineralization - Raewyn Copper-Gold Zone
Gold and copper mineralization here is associated with an altered porphyritic monzonite dike. Average copper and gold values from the mineralized zones are fairly consistent. Copper values range from 0.3% to 0.7% and gold values are 0.4 g/t to 1.2 g/t. Strong quartz-sericite-pyrite (phyllic) alteration largely overprints pre-existing assemblages, however a considerable amount.

K-feldspar is present from an early widespread potassic alteration event. Outboard from the quartz-sericite-pyrite alteration the volcanic rocks are chlorite-altered and locally contain epidote, magnetite and variable carbonate (propylitic).

Multiphase brecciation, alteration, veining and widespread recrystallization characterize the zone. Vein assemblages include:

1) chalcopyrite, quartz, chlorite, sericite ± albite and carbonate, 
2) chalcopyrite, quartz, pyrite, biotite, sericite, minor chlorite and molybdenite, 
3) milky quartz veins with coarse blebby chalcopyrite, minor pyrite and chlorite

Biotite alteration with chalcopyrite may extend for ten or more meters from the intrusion into the wallrocks, and overprints earlier K-silicate assemblages. Locally, siliceous-biotite hydrothermal breccias occur within the panel. Heterolithic, siliceous hydrothermal breccias have significant gold values and little copper and may have associated dark tourmaline. Late high-angle quartz veins, up to 3 m wide, occur throughout most commonly close to faults and cross-cut all alteration domains. They contain coarse chalcopyrite, elevated gold grades, pyrite, and rare tetrahedrite ± arsenopyrite and molybdenite.

Alteration/Mineralization -The Breccia Gold Zone
The following sequence of events has been established in the Breccia zone area:

1) intrusion of monzonite followed by
2) main phase of hydrothermal breccias with K-feldspar alteration and 
3) late-stage siliceous hydrothermal activity with local breccia pipes.

The K-feldspar hydrothermal breccias are characterized by numerous, mm scale, subangular to rounded, groundmass supported mono to heterolithic fragments in a K-feldspar rich groundmass. Pyrite content ranges from 5% to 20%, and gold content ranges from 0.12 g/t to 5.6 g/t, averaging about 1.1 g/t; avg. copper content 0.10%. The siliceous breccias are dominated by aphanitic, siliceous and pyritic groundmass, rare chalcopyrite, and variable gold content ranging from 0.10 g/t to 21.20 g/t, averaging 1.52 g/t. Both breccias locally contain significant amounts of dark coloured tourmaline aggregates and rosettes.

Mitchell Zone

The Mitchell zone is exposed in Mitchell Creek valley through an erosional window exposing the footwall of the Mitchell Thrust Fault.  The zone is a moderately dipping, roughly tabular gold-copper deposit measuring approximately 1,600 meters along strike, 400 to 900 meters down dip, and at least 300 to 600 meters thick. It consists of a foliated, schistose or mylonitic zone of intensely altered and sulfide bearing rocks, with a variably distributed stockwork of deformed and flattened quartz veinlets.  The schistosity generally follows an east-southeast direction, and dips moderately steep to the north.  In general, the core area of mineralization has a moderate plunge to the north or northwest, and is lineated in a east-southeast direction.

Recent glacial meltback has provided exceptional surface exposure of a relatively fresh gold-copper porphyry system.  A zone of intense quartz and sulfide veining (“High Quartz”) forms resistant bluffs in Mitchell valley.  However, the higher grade core area is mostly covered by talus and moraine west of the bluffs. Active oxidation and leaching of sulfides has produced prominent gossans and extensive copper sulfate precipitates at the surface.

The Mitchell zone is considered to lie within the spectrum of the gold-enriched copper porphyry environment. Metals, chiefly gold and copper (in terms of economic value), are generally at low concentrations, finely disseminated, stockwork or sheeted veinlet controlled, and pervasively dispersed over dimensions of hundreds of meters.  Grades diminish slowly over large distances; sub-economic grades are encountered at distances of several hundreds of meters beyond the interpreted centre of the system.  This is distinct from the Sulphurets and Kerr zones, where there are more abrupt breaks in grade due to higher structural complexity and juxtaposition of weak and moderate grade domains by faulting, both syn-mineral structures controlling breccia contacts, and post-mineral faulting and displacements.

Lithology and Structure

Due to the intensity of hydrothermal alteration and strong post-mineral shearing, especially at Mitchell Creek, it is difficult to impossible to determine the original protolith. This is especially true in phyllic-argillic or quartz-sericite (illite)-pyrite altered rocks.  In chlorite-sericite and propylitic altered rocks, a homogeneous, tuffaceous texture is often observed, and the host is believed to be intermediate volcanic tuffs or volcaniclastics.  However, these textures may in part be shear related. Petrographic studies indicate the host was possibly a sequence of fine grained andesitic volcaniclastics, crystal tuffs, and porphyritic flows with  coeval, fine dioritic dykes and sills throughout.  Diffuse, ghost porphyritic textures may reflect dikes of the Mitchell intrusions.  Rare, meter-scale, aphanitic intermediate dykes are post-alteration and unmineralized. Rarer monzonitic intrusives have been recognized as well.

Where not obliterated by alteration, fine to coarse, lithic to cystal, tuffaceous, intermediate volcanics are dominant, followed by vaguely bedded, fine grained volcaniclastics and argillites, more common to the west.  Government mappers have assigned the stratigraphy under the Mitchell fault to the Jurassic Hazelton Group, however in many ways it more closely resembles descriptions of the Triassic Stuhini Group.  Within the central and eastern portions of the drilled area, intervals of bleached, vaguely coarse porphyritic textured rocks may be altered dikes of the Mitchell intrusive suite.  

Above the Mitchell thrust fault, alteration is mainly confined to siliceous hornfelsed zones adjacent to porphyritic monzonite and granitic Mitchell intrusions.  The host rocks are mostly dark, fine grained volcaniclastics, argillites and vaguely porphyritic andesites and basaltic flows assigned to the Triassic Stuhini Group. The intrusions appear to have thick, sill-like geometries, with thin, anastomizing dykes in the contact zones.  Similar intrusives and surrounding siliceous alteration zones have been mapped above the Mitchell Thrust Fault on both sides of Mitchell Creek Valley.

Alteration and Mineralization
Alteration and mineral zoning patterns have been modified by syn- and post-mineral deformation, however logging and petrographic examinations have been able to demonstrate the system generally follows established models observed at other gold-copper porphyry districts. 

PRIMARY HYPOGENE ASSEMBLAGES
The dominant primary hypogene alteration mineral assemblage is propylitic, with quartz-chlorite-pyrite-chalcopyrite, often with magnetite and carbonate, and more rarely with anhydrite and molybdenite, and very rarely with bornite.  It is characterized by pervasive chloritization of mafics, and quartz-pyrite alteration of most other silicates. This mineralogy is found in stockwork veins and the altered host rocks.  Microscopic examination suggest much of the chlorite is replacing original hornblende, and to a lesser extent biotite. Occasionally there is textural evidence that suggesst some of the replaced biotite may have been hydrothermal and related to earlier potassic alteration. Chalcopyrite precipitated after most of the pyrite.

There are occasional remnants of an earlier core potassic alteration.  The geometry is uncertain, and it appears that a large portion of potassic alteration has been propylitized to some degree.  It is found in stockwork veins, wall rocks, and early hydrothermal breccias.  Some of the veins have a remnant wormy, pegmatitic texture.  It is characterized by the presence of brownish-pink orthoclase and adularia typically in veins or vein haloes.  Magnetite and very dark chlorite or biotite are usually present, rarely anhydrite.  Quartz, pyrite, and chalcopyrite are ubiquitous. 

Mainly peripheral to these assemblages is a distal propylitic assemblage in andesitic and dioritic host rocks characterized by the presence of epidote, chlorite, calcite and ubiquitous quartz and pyrite.  Veining and associated chalcopyrite and molybdenite are lower in abundance.  Where the host is a sedimentary rock, the distal propylitic assemblage is similar but the rock commonly shows a banded and spotted (“diseased”) hornfelsic.  Often silica and pyrite are the only alteration minerals present, indicating the absence of a mafic component in the original sediment.  Rare calcareous sediments have typical hornfelsic magnetite skarn assemblages. 

SECONDARY HYPOGENE ASSEMBLAGES
The propylitic and potassic assemblages are overprinted by secondary phyllic assemblages.  Towards the east and higher areas of the Mitchell zone, the overprint is intense and pervasive, but is variable and intermittent to the west and at depth.  The phyllic assemblage is characterized by complete loss of mafics, introduction of mm to cm scale, deformed quartz veinlets in stockwork and sheeted arrays, with mostly creamy white to grey sericite and/or illite and pyrite as the interstitial vein component.  The phyllic assemblages may reflect a type of high sulphidation, downward penetrating, structurally controlled overprint where fluids in the upper portion of the hydrothermal cell reacted with acidic meteoric water.

Vein relationships suggest multiple pulses of overprinting phyllic veins, together with contemporaneous development of propylitic alteration and veining in new fractures over the development of the hydrothermal cell.

There are clearly multiple stages of veining. Later veins have abundant coarse pyrite, often with molybenite, and cm scale, near massive coarse pyrite veins are common.  The phyllic alteration has a strong foliation best manifested in sericite rich intervals.  Sheeted quartz veinlets often follow the foliation, and may indicate deformation of pre-existing veins, or perhaps contemporaneous formation of quartz veinlets and deformation. In some surface exposures, intensely deformed zones contain coarse clasts of rotated, previously veined material, and strong shear textures are noted in microscopic thin sections.  The highest concentrations of pyrite and quartz veinlets are generally strongly coincident with phyllic-argillic alteration.  These assemblages include:

Quartz-sericite-pyrite (QSP) - creamy to grey fine sericite and/or clay, strongly schistose or mylonitic.  Quartz vein stockwork usually intense, and are mostly foliation parallel or oblique.  Generally 5 to 20% fine disseminated pyrite, lesser chalcopyrite, minor molybdenite, rare tourmaline.

QSP with intense stockwork veining - similar to above with >60% quartz veinlets, in general it forms the core area of the QSP, but appears to be fragmented or dismembered.

Intermediate argillic - characterized by pale green sericite and/or chlorite (which inlarge part may be illite or other clays), abundant pyrite, common molybdenite, late pyrite only veins.  In general, it forms a crude partial halo around the east, north, and south sides of the Mitchell zone.  It has lower than average copper and gold concentrations, and higher than average molybdenum.

OTHER SECONDARY LATE VEINS and MINERALS
Coarse, centimeter scale, purple tinted anhydrite veins occasionally are found throughout the Mitchell zone, more typically at depth and along the north side or hanging wall of the deposit.  These are distinct from the sub-millimeter anhydrite filled fractures that are found in isolated parts of the propylitic altered areas.

Relatively coarse grained, sub-centimeter pyrite veins are common especially in the upper portions of the Mitchell deposit.  These tend to have a distinctly paler tone than earlier pyrite.

A variety of micron-scale silver sulfosalt occurrences have been identified in microscopic examination of polished thin sections.  These are usually found along the north side of Mitchell.  Although the core of the Mitchell zone contains elevated silver values on the range of 3 to 6 ppm, based on observations to date the silver here probably occurs as a contaminant within chalcopyrite, not as sulfosalts.

Trace amounts of galena, sphalerite, arsenopyrite, and tetrahedrite or semseyite have been observed, mostly occurring in secondary alteration phases.

Centimeter to sub-meter scale, discontinous, bulbous, boudinaged, coarse, pegmatitic, quartz-chlorite-calcite veins are common throughout the Mitchell zone.  These are almost always mineralized with chalcopyrite that is typically coarser grained than in the host rocks.  The calcite is often tinted orange when exposed and is probably ankeritic.  These veins appear to have been emplaced in dilatent zones at the last stages of the regional deformation event.

BORNITE BRECCIA
The Bornite Breccia is a late, cross-cutting pipe or dilatent structure within the Mitchell zone.  In this structure, bornite replaces earlier aggregates of pyrite and chalcopyrite which occur in the matrix of a silica and anhydrite rich mass.  The texture is chaotic and deformed, and is tentatively interpreted as a breccia vein subsequently sheared during regional deformation.  It is postulated to have formed from acidic fluids related to the high sulphidation overprint descending along fractures and precipitating in cross-cutting or dilatent structures.  Gold grades are lower than average, and there is a halo surrounding the structure from which gold and copper have been leached. The structure has dimensions of approximately 300 by 300 meters with a maximum thickness of about 50 meters, and dips steeply to the north cross-cutting the general shape of the Mitchell zone.  The leached halo is about 10 to 30 meters wide. The interpretation is tentative as it has only been intersected in a few drillholes, and has not been observed in outcrop.

HYPOGENE LEACHING
Petrographic examination of polished thin sections from the Mitchell zone indicates that chalcopyrite accompanied all of the hypogene alteration assemblages to some degree. Also, there are indications that the secondary phyllic alteration leached some metal, including copper and gold, from earlier phases, and redistributed that metal in new veinlets.  As the system matured, re-fracturing and multiphasic primary and secondary alteration episodes would, through leaching and re-precipitation, have the effect of homogenizing metal distribution especially considering the density and homogeneity of the fracture (vein) patterns over much of the Mitchell zone.

SUPERGENE PROCESSES
Supergene processes of oxidation, leaching, and re-precipitation are essentially absent at the Mitchell zone, due to the high rate of erosion and glaciation.  Along the higher areas of the slopes of Mitchell valley, oxidation has penetrated to several 10’s of meters along a few fractures and copper oxide coatings have been observed in areas of the mineralized material above the Mitchell Thrust Fault.  Below the fault, oxidation is rare and has only been observed in fractures within a few meters of the surface in the most southerly holes. Minor chalcocite coatings on chalcopyrite and pyrite have also been observed in these holes, to a maximum depth of a few meters.

METAL DISTRIBUTION
At the property scale, gold and copper are generally coincident.  An area marking  consistent grades mostly above 0.75 g/t Au and 0.2% Cu has dimensions of about  500 x 1000m at the surface.  To the east, the gold grade tends to fall off at a lower rate than copper.   Gold and copper grades are closely related to the density of quartz stockwork veining, as sulfides are disseminated in minute “crackle” fractures within the veins, as well as coalescing vein haloes in wall rock.  Zones of intense to massive quartz stockwork and sheeted veining where veins make up more than half of the rock volume (High Quartz) are contained within the central area of the deposit, but there is no consistent correlation between vein density and gold and copper grades.  The “High Quartz” zones occur mostly within areas of intense phyllic or QSP alteration, but extend to the west and at deeper levels into propylitic altered areas.  Molybdenum occurs in distinct halo that is stronger on east side.  Analyses of molybdenite concentrates from metallurgical test sampling indicate anomalously high Rhenium concentrations.

Gold has not been observed at Mitchell except under microscopic examination of polished thin sections and metallurgical test concentrates.  When observed, gold grains are generally less than 10 microns, and occur within both pyrite and chalcopyrite grains, on sulfide grain surfaces, and as grains isolated in minute fractures in gangue.  Preliminary metallurgical testing indicates about 60% of the gold is recoverable and would report to a chalcopyrite concentrate using standard flotation methods.  Cyanide leaching of a pyrite concentrate to produce dore bars could bring total gold recovery to about 78%.

Structure and Metamorphism
Regional mapping by government geologists demonstrate that Jurassic Hazelton Group rocks exhibit overturned folds that are southeast vergent in the region of KSM. The thrusts are also southeast vergent.  The area occurs within the regional Skeena fold and thrust belt that was formed in the Cretaceous.  Triassic Stuhini Group rocks above the faults form the east side of a broad north plunging anticlinorium.  Triassic rocks were thrust over Jurassic rocks and truncated the upper portion of the Mitchell deposit.  Less competent phyllic-argillic altered rocks at Mitchell and Kerr zones appear to have provided the least resistance and were the focus of shearing and faulting during this event.

High temperature and pressure conditions during post-mineralization deformation is thought to have promoted re-mobilization of metals and contributed to the homogeneity of grades over large distances.

Petrographic examinations of polished thin sections of selected core samples show ample evidence of post-mineral deformation, including ribbon textured quartz due to shearing, crushed and sutured quartz due to strain, shear fabrics, muscovite wrapping quartz boudins and quartz-sericite crystals filling pressure shadows. Most of the core samples from within the Mitchell zone have been categorized as mylonites or mylonitic.  Primary textures are rare.

 

All disclosure of a scientific or technical nature was prepared by, or under the supervision of,
William E. Threlkeld (Licensed Registered Geologist #790 in the State of Washington), a Vice President of Seabridge. Mr. Threlkeld is a "Qualified Person" under National Instrument 43-101.