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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  15-Oct-13 by Garry J. Payie(GJP)

Summary Help Help

NMI 104B1 Cu1
Name GRANDUC, LEDUC, VAUGHN K., EDNA MAY, JK Mining Division Skeena
BCGS Map 104B029
Status Past Producer NTS Map 104B01W
Latitude 56º 12' 40" N UTM 09 (NAD 83)
Longitude 130º 20' 42" W Northing 6230390
Easting 416576
Commodities Copper, Silver, Gold, Lead, Zinc, Cobalt Deposit Types G04 : Besshi massive sulphide Cu-Zn
G01 : Algoma-type iron-formation
Tectonic Belt Intermontane Terrane Stikine
Capsule Geology

The Granduc property straddles the northerly trending South Unuk Shear Zone separating the upper greenschist to amphibolite facies metasedimentary and volcanic rocks of the Upper Triassic Stuhini Group from the lower greenschist grade metavolcanic and sedimentary rocks of the Hazelton Group. Large pretectonic to syndeformational elongate plutons and dikes of the Triassic John Peakes plutonic suite, including the Bucke Stock exposed north of the Granduc Mine, composed of hornblende diorite, monzonite, gabbro and syenite, intrude the Stuhini Group metasedimentary and metavolcanic rocks.

The Granduc ore deposit comprises a series of concordant massive sulphide lenses, localized within a complex sequence of volcanic-sedimentary rocks that have been deformed by cataclasis.

The volcanic rocks east of the Granduc orebodies are pillow lavas intercalated with graphitic siltstones, thin bedded lithic and crystal tuffs and volcanic sandstones. This sequence is overlain by the ore zone, graphitic siltstones, silty argillites, thin bedded lenticular gypsum-bearing limestones and quartz pebble and quartz cobble conglomerate lenses. These rocks underwent several periods of later deformation, intrusion, alteration, faulting and erosion, culminating in Tertiary time with Hyder plutonism. The ore deposit lies along part of the deformed, overturned west limb of a north trending anticlinal fold. The less deformed rocks to the east of the ore deposit include a complex volcanic-sedimentary sequence, which is considered to be part of the Lower-Middle Jurassic Hazelton Group.

Recrystallization of the rocks in the ore horizon has converted the fine-grained laminated rocks to compositionally banded, brown to pale grey quartz-rich biotite and sericite schists, quartzites and metacherts. Feldspathic and andesitic tuffs are converted to massive, or banded biotite, and biotite-epidote-actinolite schists. Massive rocks are more common in the lower half of the ore horizon. The upper part of the orebody occurs in the finely laminated quartz-rich brown biotite schists which are derived from silty argillites.

Several steep north trending faults cut the orebodies. The Western and Granduc graphitic fault zones are west of the ore zone. Several of the orebodies have been offset by apparent right-hand strike-slip movement.

The several ore zones, which make up the Granduc deposit, comprise pancake-like, overlapping, and commonly merging lenses, which extends vertically for 760 metres, laterally for 1200 metres and over a 120 to 240 metre lenticular width. The orebodies, designated as A to F, consist mainly of pyrite, chalcopyrite, pyrrhotite, magnetite, sphalerite, galena, arsenopyrite, bornite and cobaltite. Gangue includes blocks of brecciated country rock, quartz as lenses, stringers and blebs, recrystallized coarse-grained calcite as lenses and stringers, and apatite. Minor alteration minerals consist of calc-silicate lenses and tourmaline.

Individual ore zones, which are up to a few tens of metres thick and extend laterally up to hundreds of metres, consist of massive lenses, irregular streaks and blebs, and veinlets of sulphide. Repeated deformation of the massive sulphide lenses resulted in an irregular and feathery nature to the orebodies, which have been called stringer lodes. The magnetite-apatite-calcite assemblage occurs as thinly banded layers intercalated with calc-silicate, limestone bands up to 6 metres thick, graphitic quartzofeldspathic beds and the massive sulphide lenses.

By 2006 the copper deposit was considered part of a sulphide facies banded iron formation occurring near the top of the Hazelton Group at the stratigraphic contact between mafic pillow lava and tuff with overlying sedimentary rocks that include chert, argillite and tuff (Fieldwork 2006). The 2006 program extended the mineral horizon 770 metres with four holes intersecting, on average, 2.0 per cent copper over true widths of 3-6 metres. Two holes deviated offtarget and another that targeted a magnetic anomaly intersected gabbro rich in magnetite. Prospecting led to discovery of magnetite iron formation with minor chalcopyrite in the JK zone north of the Granduc deposit.

Total production from 1971 to 1978 and from 1981 to 1984 included mining of 15.5 million tonnes of ore from which 124,048,961 grams of silver, 2,000,061 grams of gold and 190,143,710 kilograms of copper were recovered.

Ore reserves before production began in 1971 were 39,316,435 tonnes grading 1.73 per cent copper (Granduc Mines Ltd. Annual Report 1969). Inventory in 1986 was reported as 9.89 million tonnes grading 1.79 per cent copper with minor gold and silver (Open File 1992-1).

WORK HISTORY (from H. Wasteneys (Assessment Report 28912)
Icefield barriers delayed discovery of the well-exposed mineralization around Granduc Mountain until 1931 when prospectors Dawson and Fromholz hiked into the Leduc Valley from the Unuk River in Alaska. However, the copper showings were not staked until 1951 when Kvale and McQuillan staked them for the Helicopter Exploration Company Ltd. The Granby Mining company did the first systematic surface and underground exploration in 1952, but development did not take place until a joint venture by ASARCO and Newmont Mining Corporation Ltd were able to finance the challenging work needed to put the deposit into production. Mine development commenced in the early 1960s punctuated by the February 18, 1965 avalanche disaster in the Leduc camp. Production began in 1968 utilizing the 18 km Tide tunnel connecting the mine workings to the upper Salmon River valley to produce 2000 ton per day of copper ore. Production ceased in 1977 because of low metal prices. In 1979 the mine was acquired by Esso Minerals Canada Ltd and operated until closure in May 1984. Following the closure in 1984 the property remained dormant and the mill structure at Tide Lake was removed after heavy snow collapsed the roof.

No other major mining or exploration activities were conducted after 1984 although efforts were focused on finding extensions of the known mineralization along strike to the north and south adjacent to the Granduc fault, an understanding of which has been elusive. The discovery of the North Zone, located about 3 km north of the main mine workings, was the last significant development and no copper mineralization has been discovered west of the Granduc fault on Granduc Mountain. In the 90s various localized exploration efforts by Hecla Mining Company coincided with academic studies by the Mineral Deposits Research Unit (MDRU) of the University of BC. The discovery of the rich Eskay Creek precious metal deposit some 40 km north of Granduc prompted a significant geological reassessment of the region starting with the MDRUs Iskut River study involving mineral deposit studies, regional structural mapping, geochronology and lithogeochemistry extending south to the Granduc property.

In 2004 the patented mining claims covering the Granduc mine property were purchased by Glenn Zinn and transferred to Bell Resources Corp. Subsequent staking by Teuton Resources surrounded the crown grants and their claims were in turn enclosed partially by Bell Resources claims. The Teuton Resources claims were optioned by Bell in 2005 and exploration work began. In the spring of 2005 an airborne EM and magnetometer survey revealed extensions of the deposit magnetic anomalies to the south under the South Leduc glacier. This was followed up with a diamond drilling program during September and October of 2005 on the margin of the South Leduc glacier, which confirmed that the magnetic anomalies were related to magnetite-iron-formation – hosted copper mineralization.

Exploration work in 2006 by Bell Resources Corp on the patented Granduc claims and surrounding, contiguous Silver Leduc claims optioned from Teuton Resources included a spring season drilling program south of the Granduc deposit, a prospecting program during the summer over the north side of Granduc Mountain and a fall drilling program on mineral occurrences found during the summer.

A 1206 kilometres airborne electromagnetic and magnetic geophysical survey was conducted by Bell in 2006 (Assessment Report 28167). The 2006 drilling totalled 4053 metres in 12 NQ2 diamond-drill holes (Assessment Report 28912).

Bibliography
EMPR AR 1931-47,49; *1953-82-86; 1954-80-83; 1955-14-16; 1956-15-17;
1957-6; 1958-6; 1959-6; 1960-6; 1961-8; 1962-8; 1964-18-20; 1965-
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University of British Columbia, (in Property File: 104B 054)
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unpublished M.A.Sc. Thesis, University of British Columbia
Equity Preservation Corp. Stewart-Iskut-Sulphurets Compilation, Dec.
1988, Showing No. B71)
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Placer Dome File

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