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KSM (Kerr-Sulphurets-Mitchell): EXPLORATION
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Seabridge Exploration Work at KSM
There are two phases of exploration work conducted by Seabridge at KSM. During the period from 2003 to 2005 the property had been under option to Xstrata Canada, who funded and performed the work. From 2006 to the present, Seabridge funded and undertook its own work following negotiations to terminate Xstrata’s option.
Xstrata (previously Noranda Inc. and Falconbridge Ltd.) undertook a staged exploration program to systematically evaluate the potential for a large Cu dominated Cu-Au porphyry system at KSM based on the geological similarities to other major Cu-Au porphyry deposits in the Pacific Rim, the existing mineral resource and undeveloped exploration targets. The program advanced from compilation and digitalization of the existing database, delineation of under-evaluated targets, confirmation and prioritizing of target models with prospecting, geological mapping, soil and rock geochemistry, induced polarization geophysical surveys, and finally first stage drilling of numerous, widely separated areas. Although every drill hole intersected strong alteration and variably mineralized rock, the results indicated the system at KSM was gold dominated, that is, the largest economic contribution to a potential minable resource would be gold rather than copper. As this was not in line with Xstrata’s corporate objectives, the company was considering a non-aggressive strategy to maintain the option by meeting its minimum spending commitments. Thus the work required to make a full evaluation of the potential gold resources would unlikely to have been undertaken. As this was not in the best interest of Seabridge Gold, an agreement was negotiated that satisfied both companies long term objectives, and returned a 100% ownership of KSM to Seabridge.
Mapping, prospecting and rock sampling was focused the Main Copper, Iron Cap, MacQuillan, Arbee, North Mitchell, and Mitchell zones. These areas were targeted based on results of Noranda’s preliminary work in 2003 which identified favourable targets that had not previously been drilled. The objectives of the 2004 program were to identify and delineate productive versus barren intrusives, potassic alteration assemblages and copper-gold distribution / control.
At the Main Copper zone, mineralization is associated with potassic altered, quartz vein stockworked, monzonitic porphyries which intrude quartz-chlorite-magnetite hornfelsed altered volcanics. Petrographic examination indicates chlorite is likely after biotite. Average Cu and Au values from 55 rock chip samples collected over a 1,000 m × 700 m area are 0.37% and 0.5 g/t respectively.
Immediately east of Main Copper, a new area of copper mineralization was located where melting of thin glacial ice and snowfields has exposed new outcrop. Disseminated chalcopyrite, minor pyrite, and trace molybdenite occur in intensely silicified rocks and hydrothermal breccias similar to the Sulphurets Gold zone. The zone is referred to as “ Icefield”. Ten rock chip samples collected over a 200 by 200 meter area averaged 0.41% Cu and 0.6 g/t Au, and the zone may extend under thin ice cover for several hundred meters to the north and east.
The Iron Cap Zone is a large area of well-exposed, intensely and pervasive quartz-sericite-pyrite altered intrusive and volcanic rock at the northeast corner of the claim block. It covers a roughly 500 by 1500 meter, northeast trending area between the Iron Cap glacier and Mitchell glacier. Alteration is controlled by northeast trending, near vertical structures and associated stockwork fracture and veins. Pyrite content varies from 5% to 30% and averages about 15%. Quartz-pyrite veins up to several meters thick occupy some of the structures. Forty rock chip samples collected by Noranda over an area of 1200 m × 300 m from the Iron Cap average 0.32% Cu and 1.0 g/t Au. Higher grade veins within Iron Cap zone attracted previous explorers and were the focus of trenching and three short drill holes which intersected wide intervals of low grade copper-gold mineralization (S80-15: 0.35% Cu, 0.53g/t Au / 93m, and S80-11: Cu not analyzed, 0.51g/t Au / 229 m).
To the west, an altered dioritic intrusive body intermittently exposed over 200 by 800 meters is laced with a quartz stockwork of varying intensity. Fracture coating and disseminated chalcopyrite and malachite after chalcopyrite, with minor pyrite, occurs throughout the intrusive. The west side is a transitional zone with rafts and zenoliths of strongly quartz-chlorite (biotite)-magnetite hornfelsed andesites and sediments with malachite after disseminated chalcopyrite, and minor pyrite. The nearest drillhole to this area is DDH 80-16, some 200 meters to the southeast; it intersected 129 meters of variably quartz-pyrite altered volcanics grading 0.25% Cu and 0.32 g/t Au.
The Macquillan Zone occurs on the mostly forested slope north of the Sulphurets glacier, southeast of the Sulphurets deposit. Disseminated and veinlet chalcopyrite and pyrite is associated with an altered feldspar phyric intrusive, and mineralization occurs in both the intrusive and surrounding hornfelsed sediments. The intrusive is strongly quartz-sericite altered, with variable stockwork of thin quartz veinlets. The sediments have been pervasively silicified and form massive, prominent, rusty purple weathering outcrops. Less silicified sediments are calcareous, with local thin limestone beds that have been marbleized. Rock chip sampling returned and average of 0.29% Cu, 0.23 g/t from 10 partially leached samples and outline a outlououl mineralized area of at least 600 by 300 meters.
Copper mineralization on the north slope of Mitchell Creek above the Mitchell thrust fault is hosted by a distinctive, reddish-purple crowded Kspar-quartz porhyritic granite. Hematite dusting is ubiquitous, and magnetite is disseminated and in veinlets with quartz. Copper occurs as disseminated and fracture filling chalcopyrite, and with quartz-magnetite veinlets. The 2004 program revealed the intrusion to underlie an area at least 600 m × 400 m. Mineralization is richest near the margins, but is widespread throughout, with analyses returning 0.2 – 0.7% Cu and about0.1 g/t Au. Quartz veins and stockworks ± chalcopyrite – magnetite are locally well developed in the intrusion, and persist about 100 m into hornfels country rock to the east. The strong hematite-magnetite association is reflected by a positive magnetic anomaly revealed in Placer Dome’s aerial magnetic survey which extends under the volcanics at least 1000 m to the northwest.
The Arbee zone is a claim group of four 2-post claims covering about 0.64 square kilometers surrounded on three sides by the KSM property, and has been owned by Mr. Donald Ross of Ketchikan, Alaska since 1960. The property is underlain by siliceous, aphanitic, pale grey, hornfelsed andesite and volcaniclastics that have been intruded by numerous dykes and small irregular or deformed bodies of monzonitic porphyry. A network of quartz stockwork veinlets of variable intensity typically cuts both the intrusive and the hornfels. Disseminated, fine-grained pyrite is ubiquitous, and late pyrite veinlets are common. Malachite staining stems from minor quantities of disseminated chalcopyrite. Rock samples of siliceous hornfels averaged 2198 ppm Cu and 159 ppb Au. One sample of porphyry contained 2502 ppm Cu and 95 ppb Au.
This property was subsequently purchased by Seabridge in 2007.
The Mitchell zone is the steep, prominent gossan immediately south of Mitchell glacier and north of the Arbee claim. It consists of a foliated, schistose zone of intensely sericite and pyrite altered rocks, with a variably abundant stockwork of deformed and flattened quartz veinlets. The schistosity generally follows an east-southeast direction, and dips steeply to moderately to the north. Pyrite content ranges from 5 to 20%, and occurs as fine disseminations, with less common fractures and veinlet fillings. The degree of alteration and deformation are such that identification of the protolith is not possible.
Low-grade copper and gold mineralization is widely distributed throughout the zone, however the controls have not been well established. Three short drill holes completed by previous owners tested the east end of the zone and cut wide intervals of schistose, sericite-pyrite altered rocks with deformed quartz veinlets, ending in mineralization. A conceptual resource estimate of 200 Mt grading 0.2% Cu and 0.8g/t Au is reported in Kirkham and Margolis, 1995. Composited assay intervals include S91-395: 0.25% Cu, 0.68g/t Au / 191m. Similar alteration has been observed in recently exposed areas previously covered by the Mitchell glacier as far as 1500 meters further east. Several hundred meters west of the intense sericite-pyrite alteration, the zone hosts strong quartz stockwork with disseminated and veinlet pyrite, chalcopyrite, with chlorite (and/or green sericite) and magnetite alteration dominant. It is distinct in that the degree of deformation is much less, and pervasive pale sericite-pyrite alteration is diminished. This area is highlighted in aerial magnetic survey as a distinct positive magnetic feature. The average of seven samples collected over a 500 x 700 meter area is 0.2% Cu and 0.7g/t Au.
Fifty-six hydrothermally-altered surface and drill-core specimens from KSM were submitted to Carson GeoMin for mineralogical study and interpretation. The most important observations provided were:
- phyllic alteration (quartzsericite-pyrite ± clay and very minor K-feldspar) dominates throughout most of the altered-mineralized surface area, affecting almost all rock-types. Sporadic occurrences of propylitized rocks occur within the phyllic-altered areas.
- an area of potassic alteration (hydrothermal biotite ±K-feldspar) occurs on the westcentral edge of the phyllic-altered area, and hydrothermal biotite is also present in the Sulphurets
deposit. Much of the biotite in the samples studied is retrograded (chloritized)
- remnants of primary K-feldspar phenocrysts are common in many of the phyllic-altered monzonitic samples
- small-scale deformation features are common
- pyrite and chalcopyrite are widespread; highly variable in abundance
- gold is also widespread; most of the gold grains observed occur as very fine inclusions and microveinlets pyrite
- the minor sulphides observed - sphalerite, galena, and proustite-pyrargyrite, as well as much of the tetrahedrite - occur as very fine inclusions in pyrite and occur mostly along the N, E and S fringes of the system
He concludes that the widely-dispersed alteration and highly-anomalous Cu-Au mineralization observed at KSM is probably due to "structural leakage" of, or from, the potassic-Cu-Au core-zone of a world-class-sized (40 sq km) quartz monzonite related porphyry system.
Thirty-four hydrothermally additional specimens from KSM were submitted to Carson GeoMin in 2004. The most important observations were:
- Twenty-five samples from Sulphurets to Iron Cap confirm that variable-intensity fine-grained phyllic-argillic alteration affects almost all rock-types and dominates in all these areas except for Main Copper (potassic), and that sporadic occurrences of propylitized rocks are present in these phyllic-argillic altered areas.
- The remaining nine samples were from the North Mitchell and exhibit hydrothermal biotite and/or chlorite-retrograded hydrothermal biotite, intergrown with chalcopyrite. Recrystallized fine-grained sedimentary or volcanic rocks probably also contain some contact metamorphic (hornfels) biotite. retrograded biotite is similar to that at the Main Copper area. These samples confirm the presence of a potentially large area of retrograded potassic alteration with associated copper mineralization at North Mitchell.
This study confirms the widespread presence of small-scale deformation and recrystallization features. These probably formed during the emplacement of multiple intrusions along active major faults during on-going pre- to post-intrusive/mineralization movements on the faults and their related smaller-scale faults, folds and fractures. Some degree of foliation is exhibited by nearly all of the hand specimens, and microscopic examination reveals the widespread occurrence of pressure-shadow grains of quartz and sericite. Some of these features indicate intrusion and mineralization were at least partly contemporaneous with deformation. Due to the structural in place during its evolution, the KSM system was relatively "open" and permeable, allowing for the outward dispersion of the hydrothermal fluids for considerable distances, resulting in the widespread and diffuse zoning of the alteration and mineralization including the widespread retrograde chloritization of hydrothermal biotite.
The results of this study support the previous interpretation. By this interpretation, the economic potential of the property is dependant upon having a major part of the copper core-zone still physically intact, and still of economic grade.
A total of 533 rock samples were collected from exposures throughout the targets selected for evaluation in 2004 and 2003. The results are presented in the following maps and confirm the widespread, district scale, disseminated and vein controlled mineralization consistent with world class Au-Cu porphyry systems.
Soil samples were collected at 100m intervals along widely spaced lines which were also used for geophysical surveys. Line directions were dictated by topography and thus are not linear. A total of 333 samples were collected, however Xstrata chose not to analyze the soils for gold. Copper results, however, even at the wide line spacings utilized, demonstrate a very large anomaly, still open north and south, and confirm the large size of the mineralizing system at KSM.
Induced polarization surveying was utilized as final confirmation, prior to drilling, that the sulfide or mineralizing system at KSM was of a world class scale and could satisfy Noranda’s minimum exploration criteria. A pole – dipole IP survey was conducted on 7 widely spaced lines and was designed for the best combination of depth penetration and resolution. It employed an “expander array”, consisting of four 100m receiver dipoles, two 200 m receiver dipoles and finally two 300 m receiver dipoles for a total array length of 1500 m. The widespread strong chargeability and low resistivity responses detected in rocks beneath the Sulphurets thrust fault satisfactorily demonstrate the extent of sulfide bearing, altered rocks. However, as is typical of the IP method, it does not differentiate between areas of strong pyrite but weak chalcopyrite (copper sulfide) mineralization or those with both pyrite and chalcopyrite.
Five drill holes totaling 1,246.6 metres were completed at Iron Cap. All holes cut long intervals of very fine grained chalcopyrite mineralization in intensely phyllic altered monzonite. Silicification and hydrothermal breccia textures are common. There is a general trend moving east to west where late stage epithermal veins in intense phyllic alteration overprint porphyry quartz stockwork veining with potassic. Potassic alteration also increases with depth towards northwest edge of drilled area. The epithermal style veins are decimeter scale, with a crude cockscomb banded texture, and polymetallic with pyrite, chalcopyrite, sphalerite, galena, and tetrahedrite or tennantite.
Three holes totaling 914.4 meters were drilled at North Mitchell. NM-05-01 tested the northern contact area and encountered weak Cu-Mo mineralization in hornfels before passing into granite at 132.4 m. The granite is extensively veined (qtz, py, qtz-py, and qtz-magnetite) and locally brecciated, but contains only traces of chalcopyrite. Veining and mineralization diminish downhole, away from the north contact. Dykes of the granite in the hornfels are barren, but the hornfels is preferentially mineralized adjacent to them. The hornfels returned 0.18% Cu and 0.10 g/t Au over 127.5 m, from 4.9 to 132.4 m. NM-05-02 tested the south margin of the granite and encountered a glassy, aphyric felsite with abundant intrusion breccia zones and magnetite cemented hydrothermal breccias. Both of these contain locally impressive splashes of chalcopyrite, but the overall content was only 0.14% Cu and 0.08 g/t Au over 114.6 m from 205.0 to 319.6 m. Exotic fragments show strong potassic alteration, and locally contain abundant disseminated chalcopyrite (2 - 10%). NM-05-03 tested the eastern end of the granite, and intersected barren porphyry and ended in phyllic rocks of the Mitchell zone beneath the Mitchell thrust fault which returned an interval grading 0.26% Cu and 0.25 g/t Au over 66.3 m, from 190.6 to 256.9 m.
WM-05-01 tested a positive magnetic anomaly approximately 800 meters west of the previously drilled portion of the Mitchell Zone. It collared in schistose, foliated sericite-chlorite altered rock with deformed quartz veins. Anomalous copper grades are attributed to fine disseminated chalcopyrite. From 13 to 58.1 metres, the rock is highly schistose and breaks easily along foliation planes. The fissile nature abruptly ends at 58.1 metres, and the intensity of quartz stockwork veinlets gradually increases with depth. Copper and gold grades also gradually increase, but tend to level off towards the bottom of the hole. Increasing grades also appear to correlate with magnetite content and appearance of k-feldspar flooding. The interval from 171.6 to 237.6 assays 0.24% Cu and 1.10 g/t Au over 66 metres. As elsewhere on the property, there is a late set of ragged calcite veinlets which is likely related to regional deformation.
Two holes, inclined towards each other on the same section were collared to test the zone, which lies along strike of the Sulphurets zone several hundred meters to the northeast. In hole IF-05-01, fine disseminated chalcopyrite occurs in variably silicified and brecciated rocks down to 121 metres, with grades averaging on the order of 0.2% Cu and 0.2 g/t Au. Below this depth, there is a sharp change in mineral tenor, with copper falling and gold increasing as indicated in the following table. Hole IF-05-02 intersected a phyllic altered, mylonitized tuff below oxidized till of the same lithology. Low copper and gold grades are associated with silicification along veins, crackle breccias and hydrothermal breccias. Below a depth of 34.4 metres anomalous copper and gold values are accompanied by anomalous arsenic, lead, and zinc concentrations.
Drilling in 2005 focused in areas of highest geochemistry, potassic alteration, and strong magnetics. Three holes totaling 956.5 metres were completed; a fourth was abandoned at 25.7 metres due to hole conditions. Long intervals of low grade copper-gold mineralization were intersected in each hole, including 0.33% Cu, 0.32 g/t Au over 70 metres in hole MC-05-01, 0.24% Cu, 0.17 g/t Au over 234 metres in hole MC-05-02, 0.17% Cu, 0.30 g/t Au and 0.16% Cu, 0.58 g/t Au over 25.7 metres in hole MC-05-03.
Mineralization occurs as fine grained chalcopyrite, best developed in siliceous, hornfelsed andesites and transitional contact breccias of monzonite porphyry. Magnetite is commonly associated with chalcopyrite. There is a weak stockwork of millimeter scale quartz veins in the andesites and contact areas of the monzonite. Coarser chalcopyrite is often developed at vein and fracture intersects. There is a late set of ragged calcite veinlets which is likely related to regional deformation, however it may in part be a component of a propylitic assemblage that includes chlorite and epidote . Chalcopyrite is occasionally remobilized and reprecipitated in calcite veinlets.
Minor native Cu and chalcocite were observed from 170.45 to 171.45 metres in hole MC-05-02 beneath an incompletely oxidized horizon with malachite on weathered fractures. This is probably a thin, supergene enriched horizon developed during an earlier period of aridity and lower water tables.
MC-05-03 intersected the Sulphurets zone beneath the Sulphurets fault at 227m. Here, the alteration is dominantly phyllic, and higher gold grades are accompanied by higher arsenic, antimony, lead and zinc concentrations, indicative of a shallower epithermal environment or high sulphidation overprint. The fault zone is marked by a zone of clayey gouge and strongly foliated, schistose, mylonitic rock.
Grades are lower in the porphyry than in the andesites and breccias developed at the contacts, and the source of hydrothermal fluids and metals may originate from a deeper intrusive phase remains. The fluids ascended along fracture networks preferentially developed in the brittle, brecciated transitional contact areas between the hornfelsed andesites and porphyry intrusions.
Hole MQ-05-01 was designed to test a strong chargeability anomaly near exposures with fine disseminated chalcopyrite associated with strong silica flooding, stockwork veining, and hydrothermal breccias. Host rocks are finely porphyritic, massive diorite or andesitic intrusive. Disseminated and veinlet pyrite content ranges from a few up to ten percent and increases with intensity of silicification. High arsenic values are due to fine arsenopyrite. These features suggests a deeper, higher temperature environment peripheral to porphyry a gold-copper setting. There is a late set of ragged calcite veinlets which is likely related to regional deformation.
In September 2006. Seabridge commissioned Geosciences de Mexico SA de CV to undertake an evaluation of the Mitchell and Sulphurets zones with the goal of identifying the principal controls of metal distributions the potential size of the mineralized system. A pair of geologists spent 5 field days examining the zones and drill core. The principal conclusions were:
- KSM comprises the major portion of a mineralized district of minimum aerial extent of 40 sq km. The western extension of the district is interpreted to lie beneath a thrust sheet comprised of unmineralized sedimentary strata.
- The size, alteration assemblages, and metal content of the exposed mineralized area are consistent with those of a large porphyry copper system, however alteration assemblages associated with Cu and Au distributions at the Mitchell deposit differ from typical porphyry related systems.
- Regional metamorphism has probably modified original alteration and metal distribution characteristics of a porphyry system.
- Lithology does not appear to be an important factor and megascopically identified alteration mineral assemblages cannot be readily correlated with metal distributions.
- At Mitchell, structural controls are probably the most important control of metal distributions, It may be controlled by a large-scale shear zone exposed in Mitchell Creek.
- Cu and Au contents similar to those already identified may extend to vertical depths far beyond those tested by current drilling.
- It is probable that additional concealed deposits are present beneath the hanging wall rocks of the Sulphurets and Mitchell thrusts.
- The size of the district and of the deposits thus far drill tested indicates that the system has produced in excess of 1Gt of mineralized material (as defined by an 0.1% Cu “ore shell”).
Seabridge submitted a suite of 37 core samples from throughout the Mitchell deposit for polished thin section mineralogical and petrographic analysis to Petrographic Consultants International in 2007. The observations basically concur with earlier studies. PCI notes the strong deformation and mylonitization, episodic vein development, very fine grained habit of gold associated with sulfides, main lithologies of dioritic intrusives and andesitic tuffs, retrograde alteration of secondary biotite alteration to chlorite, and rare, late stage, fine sulphosalts in the peripheral areas.
Upon re-acquisition of a 100% interest in KSM from Xstrata, Seabridge undertook a diamond drilling program which was executed by personnel of Falconbridge Ltd. under terms of the agreement, with some assistance provided by Seabridge. Between July and October, 2006, a total of 7,505.8 metres was drilled in 24 holes on the Mitchell zone. The updated geological model of January 2010 incorporates all of Seabridge’s drilling from 2006 to 2009, and has already been described in the section covering KSM geology. All holes were targeted to delineate the Mitchell zone and provide data to enable a resource estimate. The table below provides the composited assay results.
Resource Modeling Inc. was contracted to provide an estimate of resources and calculated the following inferred resource for the Mitchell Zone:
At Sulphurets, five holes totaling 1,623 meters were drilled in a program designed to extend the known strike extents to the northeast and southwest. This objective was achieved, however a new resource estimate was not commissioned at this time.
In 2007, all drilling at the KSM project was undertaken within and peripheral to the Mitchell zone. A total of 15,293.5 meters of core drilling in 37 holes were completed. The program was designed to provide greater data density and delineate mineralization to allow a new resource estimation that would demonstrate an expanded resource, as well as upgrading resource classification where data continuity and density was sufficient.
Resource Modeling Inc. was contracted to provide an updated estimate of resources using the new drill data and Seabridge’s update geological model, and calculated the following resources for the Mitchell Zone, as well as updated resource estimates for Sulphurets and Kerr.
Seabridge’s 2008 exploration efforts centered primarily around infill and step-out drilling within the Mitchell deposit in order to improve the overall confidence in the estimate of the in situ resources and to try explore for potentially higher-grade zones within the currently recognized deposit. Thirty-four core holes totaling 15,416 meters were drilled within the Mitchell zone in 2008. In addition to logging and sampling, representative samples from the 2008 drilling program were selected for metallurgical test work that is currently underway.
Once again Resource Modeling Inc. was contracted to provide an updated estimate of resources using the new drill data and Seabridge’s update geological model, and calculated the following resources for the Mitchell Zone, as well as updated resource estimates for Sulphurets incorporating results of 3 holes drilled in 2008.
Three diamond core holes totaling 1,761 meters were also drilled within the Sulphurets zone to follow up on the down-dip extension of previously defined mineralization. Like the 2008 Mitchell drilling, samples from the 2008 Sulphurets drilling program were selected for ongoing metallurgical testing.
A few holes targeted the North Mitchell zone above the Mitchell thrust fault. Weak mineralization occurs mainly in the fractured, brittle hornfelsed volcanics and sediments at the contact zone with relatively barren monzonite porphyry. This intrusive is distinct from the dioritic porphyries that are associated with the formation of the Mitchell zone.
Seabridge's 2009 exploration work concentrated on infill drilling within the Mitchell, Sulphurets, and Kerr deposits in order to upgrade resource categories within current pit designs to at least an indicated level. At Mitchell, nine of the holes totaling 3,754.6 were drilled using larger diameter HQ tools to allow detailed geotechnical data collection including down-hole digital photography. In addition, 18 shallow, large diameter holes were drilled at various locations throughout the property for geotechnical purposes.
Eighteen core holes were drilled directly targeting the Mitchell zone totaling 5,597.8 meters. The majority of these holes were drilled along the northern and southern flanks of the mineralized zone to test the north dipping extension of the system and upgrade Inferred material to indicated.
Eight diamond core holes totaling 3,297.6 meters were also drilled within the Sulphurets zone to follow up on the down-dip extension of previously defined mineralization. Like the 2008 Mitchell drilling, samples from the 2008 Sulphurets drilling program were selected for ongoing metallurgical testing. The majority of these holes were drilled along the western flank of the west dipping mineralized zone below the Sulphurets thrust fault in order to upgrade inferred resources to an indicated category. Several of holes also tested the Main Copper zone, which is located immediately above the Sulphurets thrust fault.
Five holes totaling 956.8 meters were drilled at various locations in the Kerr zone primarily do acquire geotechnical data for mine design, and core for metallurgical testing. The results are consistent with historical drilling. The holes were large diameter HQ size, which enhanced recoveries in the “rubble” zone where leaching of fine anhydrite filled fractures has produced an unconsolidated rock. Recoveries were in the 70% to 90% range in this material.
Nine additional holes were drilled for geotechnical purposes, including mine and infrastructure design at scattered areas in North Mitchell zone (M-09-097, 098) and other areas beyond the mineralized zones.
The new geological model and expanded assay data base were used to update the resource estimate at KSM. This was used in the design of an improved mine plan and mineral reserve published in the project’s PFS completed in early 2010.
The goal of exploration drilling during 2010 was to upgrade inferred resource within the preliminary pit limits to measured and indicated resources. After completing a PFS in early 2010, a diamond drilling program was designed that focused on upgrading parts of Mitchell, Sulphurets and Iron Cap. These results were part of a broader strategy to capture the maximum resource as engineering studies moved to define reserves on the KSM property.
A total of 6 holes were drilled in the Mitchell deposit in 2010. These holes concentrated on converting inferred resource blocks along the east and south west parts of the proposed Mitchell pit limits. Total drilling in Mitchell during 2010 was 2,298.0 meters. The work successfully targeted 153 M tonnes of inferred resources.
One additional drill hole was completed on the proposed Mitchell high-wall to study rock properties. It was 601.8 meters long and encountered two mineralized intervals in the area above the Mitchell deposit.
A total of 6,535.9 meters in 17 holes were completed at Sulphurets during 2010, which greatly expanded the resources in this deposit. Based on historical work, the drilling program was designed to expand the deposit up-dip to the surface and along strike to the south west into an area known as the Canyon zone. Results increased the measured and indicated resource from about 2.0M oz Au and 0.5B lbs Cu to 4.0M oz Au and 1.2B lbs of Cu, primarily by expanding the footprint of the Sulphurets deposit.
Drilling on the Kerr zone in 2010 was designed to evaluate rock properties in conjunction with mine planning. The holes were, for the most part, collared outside of the resource area to evaluate strength and stability of the surrounding rock. This goal was successfully completed and results were incorporated into an updated PFS.
Exploration drilling at Iron Cap during 2010 was designed to test the hypothesis that the shallow part of the system represented an epithermal deposit that over laid a deeper porphyry deposit. Surface indications contained a strong vein-controlled precious and base metal signature and historical drilling was not interpreted to have intersected a porphyry Cu-Au system.
Initial drilling was used to evaluate if a porphyry mineral system was preserved below the Iron Cap target. These first 8 drill holes totaled 3,212.4 meters and successfully demonstrated that Iron Cap is a porphyry Cu-Au deposit with a remnant epithermal deposit superimposed on the mineralized zone. Pursuing that interpretation, the program was expanded to an additional 33 diamond drill holes. Total drilling at Iron Cap during 2010 was 15,400.7 meters that led to the estimation of a resource.
In 2011, the original KSM program was focused on continuing the conversion of inferred resources at Sulphurets and Kerr. Our first attempts at testing a deep core zone weres also undertaken on the Mitchell deposit; this drilling primarily served to evaluate the potential for underground mining. A geophysical survey was included in the 2011 program with the goal of refining potential for deep core targets.
Drilling on the Mitchell deposit during 2011 included 5 diamond holes totaling 3,400 meters. These holes all exceeded 600 meters in depth and at the time were the deepest holes in the deposit. The drill core was extensively surveyed for geotechnical characteristics as part of the evaluation of underground mining potential. These holes were very useful in confirming the resource estimation as significant parts of the holes were within measured and indicated resource blocks. They also demonstrated the great depth continuity of the Mitchell deposit.
Results from 2010 prompted an aggressive drilling campaign at Sulphurets in 2011, totaling 11,480 meters in 34 drill holes. These holes continued the process of refining the mineralized zone in Sulphurets. During this program, the limits of the deposit were not greatly expanded, however, both inferred resources and waste material were converted to measured and indicated resource blocks by increasing the density of drill intersections.
Nine holes totaling 2,630 meters completed at Kerr in 2011 intersected mineralization. The drilling converted both inferred and waste blocks within the resource and expanded the deposit down dip. Gold and copper grades increased down dip in the deposit, giving us an early clue that a high grade core zone was buried below Kerr.
During the year a large magnetotelluric geophysical survey was conducted on the KSM property. A total of 145 data sites were collected in a rough grid pattern using a 500 meter off-set in both the north-south and east-west directions. The goal of this work was to detect porphyry style mineralization at depth, understand the fluid pathways that created the KSM deposits and integrate geological models and electrical properties models into a 3-dimentional representation. Several target zones were identified from this work and were best represented as:
- Low resistivity zones that had potentially detected porphyry sulfide mineralization.
- High resistivity zones that had potentially detected intense hydrothermal alteration.
Since the discovery of Mitchell in 2006, our exploration focus has been on defining and delineating a resource base that would support capitalization of the KSM project. In the pursuit of this goal information was accumulated that built a working hypothesis for the source, transportation and deposition of the metals in the mining camp. Our data pointed to an undiscovered central core zone to the porphyry Au/Cu deposits in the KSM mining district that would be expected to contain significantly higher Cu and Au grades in a deposit of similar scale to what has been discovered. A central core zone to this style of porphyry system is an essential component of the fluid processes that formed those parts of the KSM mineral system defined to date. The program in 2012 was designed to utilize the accumulated knowledge to test the concept of a preserved central bornite-core zone on the KSM land holdings.
The erosional level and structural displacement in the KSM Mining Camp preserved the entire vertical mineralized column of a porphyry Au/Cu system. Analysis of translation along thrust faults strongly supports the idea that a high grade core zone is preserved on Seabridge claims. Initially, four separate targets were identified as potential deep core zones that were supported by the results of the magnetotelluric geophysical survey (MT) including:
- Dip projection of the Sulphurets deposit.
- Lateral projections to the Mitchell/Iron Cap deposits.
- Lateral projections to the Sulphurets deposit.
- Dip projection of the Kerr deposit.
Two deep drill holes were completed testing an MT low resistivity anomaly between Mitchell and Iron Cap. The holes were collared above the Sulphurets Thrust Fault (STF) and penetrated through the Mitchell Thrust Fault (MTF). In the panel between the STF and MTF intense hydrothermal alteration was encountered indicative of the margins to a porphyry system. This alteration is not consistent with either Mitchell or Iron Cap and is interpreted as a blind, unexplored porphyry mineral system.
A low resistivity MT anomaly along the dip projection of the Sulphurets deposit was tested with 3 drill holes totaling 2,306 meters. These holes encountered extensive thermally metamorphosed or hornsfeld rock. The hornsfeld did not provide an immediate vector toward a core zone target, which reduced the priority of this effort.
The lateral projection to the north east of Sulphurets is known as the Ice Field target. Several previous drill holes designed to extend the Sulphurets deposit encountered intensive alteration with gold grades. A low resistivity MT anomaly corresponded to this target area prompting two drill holes, totaling 1,410 meters, to test this target. Results indicate a high level or epithermal style occurrence rather than the core zone to a porphyry system.
The lateral projection to the south west of Sulphurets is now known as the Camp Zone. Drilling in the Camp Zone demonstrated a preserved portion of an epithermal Au-Ag occurrence associated with the upper parts of the KSM mineral system. Argillic alteration was dominant in this zone, which also contained high gold, silver, lead and zinc concentrations particularly within veins and structures. We had interpreted Pretium Gold’s high grade Brucejack deposit as the epithermal or top portion of the very large gold-copper porphyry system we see at KSM and that our property contained only the deeper parts of this complex. However, the new Camp zone appears to be part of the epithermal system preserved in the bottom of Sulphurets Valley.
The dip projection of the Kerr deposit returned a very discrete and high amplitude low resistivity anomaly in the MT survey. The Kerr resource was open at depth and this anomaly provided good support for the dip continuity of the deposit. Initially, the drill core showed intense hydrothermal alteration characteristic of the Kerr deposit and abundant sulfide minerals with better than average copper grades. These first three drill holes were suggestive of a high grade core zone to the Kerr Porphyry Au-Cu deposit.
The McQuillan Zone targeted a discrete magnetic anomaly down dip of surface alteration and mineralization in the Sulphurets and McQuillan prospect area. Below the Mitchell Thrust Fault alteration intensity increases significantly and is characterized by potassium feldspar, biotite and magnetite with chalcopyrite and pyrite. This alteration mineral assemblages indicates that the McQuillan target zone is within a high temperature and high pressure environment, potentially the location of a core zone.
Exploration in 2013 was designed to accomplish three goals. First, a program was completed to confirm and define a porphyry core zone that was envisioned on the Deep Kerr target. That program began with wide spaced drilling on the target, which established the presence of higher grade copper and gold intervals in the deep parts of the Kerr deposit. Once that concept had been confirmed, drilling was stepped up to complete sufficient holes so that an initial resource estimation could be completed.
Second, an assessment was conducted on additional deep core targets within the property. The potential of this effort became obvious with the success at Kerr. The targets were evaluated principally by drilling, and detailed geology. Those preliminary results provided a prioritization for subsequent geophysical surveys and more aggressive drill testing.
The final goal for 2013 was an appraisal of the Camp Zone. Defining the mineral controls, geological limits of the system and size potential of the target was required to understanding how this target will fit into the KSM project.
Three drill holes in 2012 provided a strong indication that the dip projection of the Kerr deposit could provide a large and higher grade ore zone as conceived in our exploration model. Geophysical surveys showed a discrete high amplitude low resistivity anomaly below the surface exposure of the Kerr deposit. Part of this anomaly corresponded with the Deep Kerr zone and was interpreted to indicate abundant sulfide minerals in altered rocks producing a resistivity contrast.
The first drill holes in 2013 immediately confirmed the concept and showed that, sitting down dip and in part continuous from the Kerr deposit, the Deep Kerr reported significant mineralized intervals containing total metal values per tonne that are approximately two times KSM’s proven and probable reserve average, with some intervals exceeding 1.0% copper and gold grades as high as 1.7 grams per tonne (g/T). Five large core drilling rigs were quickly moved on to the project in order to expedite the drilling.
The drilling concentrated on about 1,000 meters of strike of the projected Deep Kerr target. Within the Deep Kerr several intervals of bornite-bearing (Cu5FeS4) rocks were intersected, indicating higher temperature ore forming processes were being encountered in the drilling. As the drilling progressed the Deep Kerr zone became recognizable as:
- A wide continuous alteration zone characterized by anhydrite, potassium feldspar and magnetite as minerals.
- Abundant chalcopyrite and locally bornite with an observable decrease in pyrite content.
- An increase in the abundance of quartz veins with copper minerals both internal to and at the margins of the veins.
During the 2013 program, 29 diamond drill holes were attempted, 25 holes were completed through the Deep Kerr target, two were lost due to significant hole deviation and two were terminated due to weather and made ready for re-entry. Of the 25 holes completed, 23 encountered significant gold and copper grades over extensive widths. The weighted average of the drill intercepts from the Deep Kerr zone yields a grade of 0.46 g/T gold and 0.71% copper over a width of 220 meters. These results represent a substantial increase in copper grades over previous drilling at KSM and generated a NI 43-101-compliant inferred resource estimate of 514 million tonnes of 0.36 g/T gold, 0.53% copper, 1.8 g/T silver and 28 ppm molybdenum.
Iron Cap was the first new target zone in 2013 to be evaluated for deep higher-grade potential. Iron Cap had been explored since 1991 by previous owners, focusing on surface showings and shallow drilling they concluded it is the expression of a small epithermal vein system. Ongoing exploration since 2010 by Seabridge determined that the epithermal system was superimposed on the upper portion of a much larger gold-copper porphyry deposit. With success at Kerr and a district-scale deposit theory the highest priority target for a second magmatic core discovery at KSM became Iron Cap.
During 2013, drill holes confirmed the existing resource model at Iron Cap down to about 200 meters. Below that point, the holes entered volcanic and intrusive rocks as well as chaotic breccia zones with variable intensity of veining and alteration. Discrete intervals containing orthoclase and magnetite alteration, intense stockwork veining and concentrations of chalcopyrite with minor bornite characteristics of a core zone were encountered. Evidence strongly suggested that the Iron Cap deposit sits above and is displaced to the south-southeast of a near-magmatic high-grade core zone. Additional work was undertaken during the winter season to refine the target with the plan to aggressively drill the Iron Cap core zone in 2014.
The McQuillan Zone is targeting the down dip projection of surface alteration and mineralization in the Sulphurets and McQuillan prospect areas. Alteration intensity generally increases down hole at McQuillan and is characterized by a progression from chlorite and sericite to potassium feldspar, biotite and magnetite with localized chalcopyrite. The hole completed in 2013 shows a homogenous alteration pattern down hole, indicating it could be oblique to the Cu-Au target zone. Modeling of previous drill holes and downhole geophysical surveys was employed to refine the target.
Four additional drill holes were completed in the Camp Zone in 2013. These holes were designed to evaluate alternative orientations to the structural controls on this target area. Results indicated that structures are oriented northwest-southeast and control the distribution of argillic alteration and gold concentrations. Although results indicated potential to expand the Camp Zone, the target did not appear to match the potential for discovery of additional deep core zones and it was therefore relegated to a lower priority.
In 2014, the exploration program was designed to accomplish three goals. First, the initial focus was to expand on the strike and dip potential of the Deep Kerr deposit. Drilling in 2013 did not define the limits of the Deep Kerr deposit. In an effort to identify those limits, the program intended to step out to the north and at depth to define the scale of the deposit.
Second, working off results in 2013, exploration drilling was expanded on the Lower Iron Cap zone to test continuity and extent of another potential core zone target. Historical drilling on the Iron Cap deposit indicated plunge continuity to the northwest. Using the understanding developed from Deep Kerr, a program was developed to extend the Iron Cap deposit down plunge to the northwest where a core zone target was postulated.
The final goal for 2014 was to complete an appraisal of two additional core zone targets (which subsequently became three). Integrating geophysical surveys across the property with the understanding from Deep Kerr, suggested additional untested higher grade target zones remained to be discovered. The aim in this program was to determine which of these targets held the greatest potential for additional discoveries.
Work on the Deep Kerr zone in 2014 began by focusing on confirmation of the resource block model and then the extension of the deposit to the north and down dip. Results from the 2014 drilling campaign are being integrated into the resource model which will permit expansions of the 2013 inferred resource estimate.
Two holes (K-14-25D and 28C) were drilled into the existing resource to evaluate the performance of the model by determining how well the new data matched up against the model’s predicted block grades. In order to expedite this work, daughter holes were completed from two widely spaced parent drill holes that were begun in 2013. In each case, the results showed mineralized intervals consistent with those predicted by the model; there was little difference in the bulk grade of the mineralized interval, with individual copper grades ranging from -12% to +30%. These results are within the acceptable ranges for an inferred resource classification and they are consistent with the expectation for a predictive geological model.
The north strike projection of the Deep Kerr deposit was a primary target at the end of 2013. The northernmost drill holes in the 2013 program intersected well mineralized intrusive rocks. Three additional sections were drilled in 2014 at 140 meter intervals stepping north from the 2013 data. Mineralized zones consistent with the Deep Kerr deposit model were encountered in the first two cross sectional step-outs (holes K-14-39, 43, 44 and 48), 280 meters north of previous drilling. On the northern most section (holes K-14-41 and 41A), a large interval of post mineral intrusive rock was intersected. The projection of the high-grade Deep Kerr intervals was coincident with fault structures. It is not known at this time if the Deep Kerr mineralization continues farther north along these faults and beyond the post mineral intrusion.
Three drill holes (K-14-34A, 40 and 45) were targeted to provide mineralogical zoning indicators and extend the depth projection of the Deep Kerr zone. Holes K-14-34A and 45 were set up to drill down the interpreted Deep Kerr zone and encountered long sections of the mineralized zone; however, this orientation was difficult to maintain and technical limitations terminated the holes before reaching the limits of the deposit. These two holes therefore bottomed in mineralization. Hole K-14-40 was drilled perpendicular to the zone. These tests confirm that the Deep Kerr zone plunges west-northwest and continues to at least 1350 meters below surface.
In 2013, the south limit of the Deep Kerr deposit was provisionally established at the southernmost drill hole (K-13-26) in the zone at that time. As the 2014 program progressed, it became clear the southern boundary was arbitrary. Two drill holes were completed to confirm a southern extension-- one hole (K-14-42) at the southern limit of the 2013 resource model and one hole (K-14-46) 550 meters beyond the 2013 model. These holes confirm significant strike potential but additional drilling is required to extend the resource model and establish the grade distribution.
The Iron Cap Lower zone is interpreted as a northwest plunging, northeast-southwest striking tabular body below the existing reserves. Following the zone down plunge intercepted higher grade Cu-Au consistent with a core zone. A total of 10,429 meters in 10 drill holes tested this Lower Iron Cap target in 2014. Work is ongoing to estimate an initial resource for the Lower Iron Cap zone.
The Lower Iron Cap Zone is a series of related, intermediate-composition intrusions, each with extensive and intensive hydrothermal alteration including potassic, phyllic, and silicic alteration, all of which contain copper, gold and silver. Drill holes that targeted the southwestern strike projections of the target zone penetrated numerous intrusive events with variable grade distribution enhanced in the contact zones between these intrusions. The holes drilled along the northern strike projection encountered more consistent intrusive rock with much less grade variability, like hole IC-14-59 with 592.7 meters of 1.14 g/T Au and 0.37% Cu. Hydrothermal alteration in these holes to the north exhibit vertical continuity over 1,000 meters tested so far, indicating significant potential at depth, particularly down the apparent north-northwest plunge.
Drill hole IC-14-61 approaches to within 1,000 meters of the proposed trace of the Mitchell-Teigan Twin Tunnel alignment, potentially making the Iron Cap Lower Zone an attractive early development option with lower capital and operating costs than other deposits at KSM which are further from key infrastructure.
Three additional deep target concepts were drill tested during 2014. Initial results were inconsistent. Along the east-side of the Kerr deposit, drilling revealed a thick package of thermally metamorphosed sedimentary rocks with numerous pyrite veins. This package of rocks contains alteration and chemical characteristics interpreted to represent the margin of the intrusive mineral system at Kerr. Drilling to the northwest of the Sulphurets deposit encountered intensely metamorphosed sedimentary and volcanic rocks with extensive fracture and vein controlled phyllic and potassic alteration. Long intervals of highly anomalous gold concentrations are reported in these drill holes, indicating proximity to the dip projection of the Sulphurets deposit. Two drill holes were also completed into the McQuillan target. These holes encountered intrusive rocks similar to other mineralized intrusion at KSM, however the alteration style and intensity is indicative of a post or inter mineral rock.
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.