The Kemess property is located in the southern part of the Toodoggone mining district in north-central British Columbia. The Toodoggone district lies within the eastern margin of the Intermontane Belt and is underlain by a northwesterly trending belt of Paleozoic to Tertiary sediments, volcanics and intrusions covering an area of 90 by 25 kilometres. The basement rocks are Proterozoic metasedimentary equivalents of the Hadrynian Ingenika Group. These rocks are unconformably overlain by volcanic and sedimentary units of the Permian Asitka Group which are in turn overlain by Upper Triassic basaltic to andesitic flows, volcaniclastics and minor limestone of the Takla Group. Volcaniclastic rocks of the Lower Jurassic Hazelton Group and rhyolitic to dacitic flows, intrusions and volcaniclastics of the Lower Jurassic Toodoggone Formation (Hazelton Group) overlie the Takla Group. Further to the west, nonmarine sediments of the Cretaceous Sustut Group overlie the volcanic strata and form the western margin of the district.
The Early Jurassic Black Lake Suite of quartz monzonitic to granodioritic composition have intruded the older strata in the central and eastern parts of the region, and form the eastern margin of the Toodoggone district. Within the district, syenomonzonitic and quartz feldspar porphyritic dikes may by feeders to the Toodoggone Formation.
The southern part of the Kemess North occurrence area is underlain by intercalated andesitic flows and pyroclastics of the Takla Group. Augite andesite underlies the western portion of the property while feldspar porphyritic andesite flows and breccias dominate the eastern portion. The volcanic rocks are massive, but the trend of the Takla Group is indicated by local limestone lenses that strike southeasterly and dip 60 degrees southwest. Local basaltic dikes intrude these units with north-northwest and north strikes.
The central portion of the area is underlain by intermediate pyroclastic rocks of the Toodoggone Formation that dip gently southward. The major units are lithic and crystal tuffs and tuffaceous breccia.
The extreme northwest and south portions of the property are underlain by stocks of granodioritic and quartz monzonitic composition of the Black Lake Suite. These stocks intrude both the Takla and Toodoggone rocks. Locally, porphyritic stocks and dikes, comagmatic with an underlying granitic pluton, intrude volcanic rocks. The most dominant of these intrusions is a syenitic porphyry dike.
Takla Group rocks are generally comprised of the following: augite porphyry, basaltic flows and tuffs; bladed feldspar porphyry; bladed feldspar porphyry tuff breccia; and basaltic dikes.
The Black Lake Suite is comprised of quartz monzonite, granodiorite, feldspar-quartz-biotite porphyry, feldspar hornblende porphyry and crowded feldspar hornblende porphyry, quartz plagioclase porphyry, and leucocratic feldspar hornblende porphyry. The Takla rocks have undergone intense structural deformation. Brittle fracturing is the dominant structural style. Myriad small-scale fractures of many generations are evident. Earlier ones are healed by quartz, carbonates, zeolites or gypsum while some later ones are still open. Numerous faults, shears and fractures cut and displace the strata to a much greater degree than the intrusions. Based upon the distribution and trend of the lithologies and structural data, major normal and transcurrent faulting occur commonly in an east-northeasterly direction (070 degrees).
There are four recognized types of alteration, quartz-sericite- pyrite, propylitic, zeolitic and hornfelsic, which appear to occur only within the volcanic and pyroclastic rocks.
Pervasive quartz-sericite-pyrite alteration occurs as a large central zone and appears as envelopes surrounding veinlets of pyrite and microfractures. It is characterized by pale bleached rock with abundant boxworks commonly lined with jarosite after pyrite. Plagioclase is altered to quartz and muscovite, and sericite may form approximately 15 per cent of the rock. Chlorite and kaolinite form approximately 30 per cent of the rock. Rutile (?) occurs as disseminated bright orange grains. The abundance of sericite and sulphide boxworks decreases with a decrease in the intensity of alteration, and sulphides (pyrite) and goethite become increasingly more common. Only quartz-sericite-pyrite alteration is known to be directly associated with the mineralization.
Propylitic alteration occurs as an elongate east-west zone parallel to and south of the central quartz-sericite-pyrite zone. Propylitized rocks are green, and are characterized by local albitization and variable epidote, chlorite and calcite.
Zeolitic alteration is most common in an area north of the quartz-sericite-pyrite zone; however, it is found locally throughout the property. Laumontite has been identified by x-ray diffraction and often occurs as fracture fillings up to 3 millimetres thick in local shear zones. It is common in the Takla Group.
Hornfels alteration forms an irregular zone of variable intensity primarily within a crystal tuff unit. This zone seems to parallel the quartz monzonite and granodiorite intrusive contacts. Intensely hornfelsed rocks are massive, fine grained and pale grey to brown in colour. Alteration products include quartz, andalusite (?), epidote, sericite and chlorite. Pyrite occurs locally as microveinlets and fine-grained disseminations with this alteration facies.
There is a well-developed gossanous zone capping the disseminated pyrite mineralization. This gossan forms an elongate east-west zone measuring approximately 3300 metres long by 800 metres wide.
The known mineralization, in order of abundance, includes pyrite, chalcopyrite, magnetite, hematite, molybdenite and digenite. Pyrite occurs as microveinlets and disseminations within the gossan zone. Its abundance varies from 0.5 to 10 per cent, and is directly proportional to the intensity of the fracturing and alteration. Chalcopyrite occurs in northerly trending veinlets, microveinlets, or, more commonly, as disseminations with pyrite, magnetite-hematite and gangue minerals of quartz and orthoclase. Digenite rims chalcopyrite grains where supergene mineralization occurs. Molybdenite has also been found to be spatially associated with the quartz-sericite-pyrite alteration zone as fracture fillings.
Drilling results show that there is a 10 to 20 metre leached cap over the known copper mineralization, and assay results show that beneath this cap the mineralization is enriched for a thickness of up to 30 metres (Assessment Report 19962). The deposit remains open in all lateral directions.
Preliminary estimates of reserves of the Kemess North deposit are 116,108,800 tonnes grading 0.19 per cent copper and 0.37 gram per tonne gold at a cutoff grade of 0.40 per cent copper equivalent (Northern Miner - January 20, 1992). Geological reserves are 75,363,682 tonnes grading 0.51 gram per tonne gold and 0.21 per cent copper (George Cross News Letter No. 213 (November 4), 1992).
Kemess Mines Inc. completed 12 holes totalling 4100 metres in 2000. The year 2000 drill program (incorporating previous drilling results) has defined a total of approximately 360 million tonnes grading 0.154 per cent copper and 0.299 gram per tonne gold (Northgate Exploration Ltd., News Release, January 22, 2000).
Northgate Exploration Ltd. completed a 16 hole, 8200 metre diamond-drill hole program in 2001 which has defined a significantly larger and higher grade inferred mineral resource. The inferred mineral resource is estimated to be 442 million tonnes grading 0.4 gram per tonne gold and 0.23 per cent copper using a gold equivalent cut-off grade of 0.6 gram per tonne; within this inferred resource is a higher grade core estimated to contain 170 million tonnes grading 0.5 gram per tonne gold and 0.29 per cent copper using a gold equivalent cut-off grade of 0.8 gram per tonne (Stockwatch - November, 14, 2001).
Northgate Exploration Ltd.'s 2002 drill program included drilling the Nugget porphyry target, located 1 kilometre west of the proposed Kemess North pit outline, at the Kemess East, located 750 metres southeast of Kemess North (Stockwatch, Northgate Exploration Ltd., September 17, 2002).
Northgate continued drilling in 2002 and intersected a deeper zone of mineralization in the Central Cirque area. A 206-metre intercept starting at 407 metres down-hole assayed 0.29 gram per tonne gold and 0.54 per cent copper. Drilling also occurred at the Nugget zone 1 kilometre to the west and the Kemess East, 750 metres southeast of Kemess North.
As of December 31, 2002 the indicated resource of Kemess North is 407,000,000 tonnes grading 0.409 grams per tonne gold and 0.224 per cent copper. The inferred resource is 107,000,000 tonnes grading 0.36 gram per tonne gold and 0.18 per cent copper. The inferred resource for the Nugget zone, approximately 1.2 kilometres to the west, is 87,000,000 tonnes grading 0.38 gram per tonne gold and 0.16 per cent copper (www.northgateexploration.ca, January 8, 2004).
In 2003, Northgate Exploration Ltd. continued its detailed appraisal of the bulk tonnage Kemess North (094E 021) porphyry gold-copper deposit (Photo 1) located about 5.5 kilometres north of the Kemess South open pit. Work included oriented core, geotechnical and condemnation drilling, and environmental studies (in support of pre-feasibility and feasibility studies that are required by government as the project enters the Environmental Assessment process). The advanced work identified a ‘mineable resource’ for the Kemess North deposit of 369 million tonnes grading 0.34 gram per tonne gold and 0.18 per cent copper (Exploration and Mining in British Columbia 2003, page 18). The proposed development schedule calls for infrastructure development in 2005, pre-stripping of the deposit in 2006 and mining of ore by the end of 2006. The Kemess North and Kemess South deposits would be mined concurrently until reserves at Kemess South are exhausted in 2009. Mining at Kemess North would continue until 2019.
In 2003, Northgate completed more than 10000 metres of exploration drilling on Kemess North and several nearby prospects. Twelve holes were drilled at the Nugget porphyry gold-copper prospect, just southwest of the Kemess North deposit. Hole KN-03-12 intersected 419 metres averaging 0.38 gram per tonne gold and 0.13 per cent copper starting at a depth of just 24 metres (Exploration and Mining in BC 2004, page 43). The area of shallow mineralization will be further evaluated for its potential to be a satellite ore body. Two holes were drilled at the Kemess Centre porphyry gold-copper prospect, 3 at the Duncan Ridge silver-copper-zinc skarn and 8 in an area between Duncan Lake and Kemess Lake, referred to as the ‘Valley of the Dolls’. Hole DR-03-01 intersected 11.75 metres of garnet-diopside skarn at a down-hole depth of 312 metres that graded 0.8 per cent copper, 2.24 per cent zinc and 12.7 grams per tonne silver (Exploration and Mining in British Columbia 2003, page 19).
Northgate also conducted grassroots exploration on its claims. Prospecting late in the field season east-northeast of Kemess North located numerous angular boulders of vein material that are referred to as the Hilda showing. Grab samples from the boulders averaged 5 grams per tonne gold and 44 grams per tonne silver with anomalous copper, zinc and lead values (Exploration and Mining in British Columbia 2003, page 19). The Archie occurrence, located northwest of Duncan Ridge, is a narrow quartz-magnetite vein with visible gold. The company also staked the Bear claim group, which covers a 70 square kilometre area immediately south of and adjoining its existing tenure. Data from an airborne geophysical survey completed over the new claims will assist in guiding future exploration.
In 2004, Northgate drilled 7561 metres of drilling the Kemess North and area. The Kemess is progressing through a joint federal-provincial panel review. Seven holes were drilled into the Nugget porphyry gold-copper zone in an attempt to expand on encouraging near-surface mineralization intersected in 2003. The Kemess Centre porphyry gold-copper prospect, Duncan Ridge polymetallic skarn target and Hilda structurally-hosted gold occurrence were also drilled with mixed results. The Bear claim group covers a large area immediately south and adjoining the Kemess South property. Approximately 64 line-kilometres of IP were completed over the claims. Follow-up diamond drilling is expected in 2005.
In 2005, proven and probable resources for the Kemess North deposit was given as 414 million tonnes grading 0.307 gram per tonne gold and 0.16 per cent copper (Exploration and Mining in BC 2005, page 44).
In 2005, drilling by Northgate Minerals Corporation immediately east of the proposed Kemess North pit development (and east of the East Creek fault) identified a possible extension to the deposit. The zone, termed Kemess North Offset, was first intersected by drill hole KN-05-24 which cut 308 metres averaging 0.31 gram per tonne gold and 0.24 per cent copper (Exploration and Mining in BC 2005, page 44). Additional holes confirmed the presence of a major new bulk tonnage target and established the zone as a priority drilling target for 2006. The company also tested several other targets on claims that enclose the Kemess North area, including the Kemess East and Nugget porphyry gold-copper prospects, the Hilda structurally-controlled gold zone, and the Duncan Ridge and Nor 1 skarn prospects.
Work in 2005 delineated a resource of 720 million tonnes grading 0.15 per cent copper and 0.30 gram per tonne gold (Exploration in BC, 2010, page 4).
South of the Kemess mine Northgate continued to evaluate its Bear claims. A total of 17 core holes (totaling 5786 metres) were drilled to test anomalies suggestive of buried porphyry systems that had been defined by an earlier airborne magnetic and radiometric survey and IP survey.
In 2006, Northgate Minerals Corporation continued to explore its large tenure package that encompasses the Kemess mine. Most of the drilling was focused east of the Kemess North deposit and targeted the deep KN Offset and Kemess East zones. Drilling of the KN Offset zone, located immediately east of the East Boundary fault, followed up on a 2005 intersection in hole KN-05-24 that averaged 0.31 gram per tonne gold and 0.24 per cent copper over 307.6 metres (Exploration in BC, 2006, page 61).
The Kemess East zone is essentially a continuation of KN Offset. A deep-penetrating IP geophysical (Titan) survey was performed over the Kemess North deposit and surrounding areas. The survey outlined the known mineralized zones and identified several new targets, including an intriguing buried target east of KN Offset.
A proven and probable mineable reserve was reported of 424 million tonnes (Kemess North) grading 0.30 gram per tonne gold and 0.155 per cent copper (Exploration and Mining in BC, 2006, page 61).
In September 2007 the Canada-BC Joint Review Panel concluded that “development of the...Kemess North Project in its present form would not be in the public interest.” Northgate had proposed to dispose of tailings from Kemess North in nearby Duncan (Amazay) Lake, and this the panel had found especially problematic even though it met the formal environmental requirements. Subsequently, and without waiting for a Ministerial response to the recommendation, Northgate suspended exploration activity and wrote down its investment in the project. Kemess North proven and probable reserves, as of the end of 2006, were 423.9 million tonnes grading 0.30 gram per tonne gold and 0.16 per cent copper (Exploration in British Columbia 2007, page 4).
In 2010, Northgate Minerals Corp reactivated work on the Kemess North deposit to evaluate potential for a block-cave underground mine. More closely-spaced drilling in a part of the deposit identified higher gold and copper grades. The core of the Kemess North was estimated to comprise 70 million tonnes containing 0.65 gram per tonne gold and 0.3 to 0.4 per cent copper (Exploration in BC 2010, page 4). This area was targeted in 16 439 metre drill program to define the resource block and to assess its geotechnical characteristics for possible block-cave mining. Results indicated the deposit was higher grade in the northeast quadrant than predicted.
Northgate Minerals Corp. released updated resource amounts following the 2010 diamond drill program (Stockwatch News Release February 15, 2011)
Classification Amount Au Cu Ag
(tonnes) (g/t) (%) (g/t)
Indicated 136,500,000 0.558 0.29 2.105
Inferred 6,000,000 0.42 0.22 1.65
In 2011, the Kemess Underground (formerly “Kemess North”) project was in the permitting process leading to production. Kemess Underground will use the same concentrator and tailings facility as Kemess South, and ore will be extracted by a block/panel cave operation over an approximate 12-year mine life. A preliminary economic assessment for the project was completed in 2011 and based on its positive recommendation a full feasibility study is to be completed in 2012. Over 6000 metres of drilling were completed as part of the engineering, geotechnical and environmental phases of the project.
Indicated Resources at Kemess Underground are 136.5 million tonnes containing 73,710 kilograms gold and 390.4 million kilograms of copper. Within this is located a 10.3 million tonne “highgrade sector” containing 12,760 kilograms of gold and 54 million kilograms of copper (Exploration and Mining BC 2011, page 3). Mining by Aurico Gold Inc would use the existing facilities from the Kemess Mine to process ore and impound tailings.
In 2012 AuRico Gold Inc awaited results of a Feasibility Study for a decision on the Kemess Underground project. In 2012, AuRico Gold Inc. released NI-43-101 compliant resource and mineral reserve estimates. The mineral reserve estimate showed probable reserves of 100,373,000 tonnes grading 0.28 per cent copper, 0.56 gram per tonne gold and 2.05 grams per tonne silver. The mineral resources estimate showed an indicated resource of 65,432,000 tonnes grading 0.24 per cent copper, 0.41 gram per tonne gold and 1.81 grams per tonne silver and an inferred resource of 9,969,000 tonnes grading 0.21 per cent copper, 0.39 gram per tonne gold and 1.57 grams per tonne silver (Press Release, AuRico Gold Inc., March 25, 2013).
At the end of March 2013, intermediate gold producer AuRico Gold Inc reported the results of a positive Feasibility Study on the Kemess Underground deposit. Reserves are reported at: 100.4 million tonnes grading 0.28 per cent copper, 0.56 gram per tonne gold and 2.05 grams per tonne silver - containing 280,900,000 kilograms of copper, 51,029 kilograms of gold, and 187 106 kilograms of silver (Proven and Probable) (Exploration and Mining in British Columbia, 2013, page 12).
The resource exclusive of reserves is reported as 65.4 million tonnes grading 0.24 per cent copper, 0.41 grams per tonne gold, and 1.81 grams per tonne silver, containing 157,200,000 kilograms copper, 24,210 kilograms gold and 107,728 kilograms of silver (Measured and Indicated); and 10.0 million tonnes at 0.21 per cent copper, 0.39 gram per tonne gold, and 1.57 grams per tonne silver - containing 20,900,000 kilograms copper, 3544 kilograms gold and 14,260 kilograms silver (Inferred) (Exploration and Mining in British Columbia 2013, page 12).
In 2013, this included a 9-hole program using two drill rigs that targeted the Kemess offset area east of Kemess North, and also the Kemess East target to follow up 2007 exploration drilling there.
Refer to Kemess (094E 094) for related details.