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File Created: 24-Jul-85 by BC Geological Survey (BCGS)
Last Edit:  18-Apr-08 by Mandy N. Desautels(MND)

Summary Help Help

NMI 114P12 Cu7
Name WINDY CRAGGY Mining Division Atlin
BCGS Map 114P072
Status Developed Prospect NTS Map 114P12E
Latitude 59º 44' 09" N UTM 08 (NAD 83)
Longitude 137º 44' 37" W Northing 6625182
Easting 345778
Commodities Copper, Cobalt, Gold, Silver, Zinc Deposit Types G04 : Besshi massive sulphide Cu-Zn
Tectonic Belt Insular Terrane Alexander
Capsule Geology

The Windy Craggy area is within the allochthonous Alexander terrane in the extreme northwest part of British Columbia. This terrane includes a thick succession of complexly deformed Precambrian to Permian basinal and platformal carbonate and clastic rocks with a subordinate volcanic component. These rocks are of relatively low metamorphic grade and are unconformably overlain by Late Triassic calcareous turbidites and a bimodal volcanic suite.

The Upper Triassic (Norian) section in the Windy Craggy area is comprised of mafic submarine volcanics with variable amounts of interbedded calcareous argillaceous sedimentary rocks. MacIntyre (1984, Geological Survey Branch) defines a stratigraphic section for the informally-named "Tats Volcanic Complex" which is subdivided into 4 major subdivisions: (1) Upper Tats-mainly pillowed basalt (at least 1500 metres thick); (2) Middle Tats-interbedded graphitic and calcareous argillites, pillowed and massive mafic amygdaloidal to pillowed flows, tuff, agglomerate and limestone (approximately 2000 metres thick); (3) Lower Tats-mainly mafic silk and calcareous argillite (approximately 1000 metres thick); (4) Mainly calcargillite-calcareous and graphitic shale, argillite and limestone of unknown age; and (5) Limestone Unit-grey limestone of (?)Silurian-Devonian age in fault contact.

The Windy Craggy deposit is hosted by Triassic (Norian) clastic sediments and mafic flows and sills of the lower part of the Middle Tats Group. Massive sulphide mineralization occurs near the transition from predominantly clastic units to overlying volcanic rocks. Continuous massive sulphide mineralization extends a minimum strike length of 1600 metres, at least 600 vertical metres, and greater than 200 metres in width. At present, the deposit is thought to consist of two discrete sulphide bodies. Recent drilling has indicated the possible presence of a third sulphide body. The deposit remains open at depth and along strike. Windy Craggy has similarities with both Besshi-type and Cyprus-type massive sulphide deposits.

The basaltic host rocks are fine grained and are commonly amygdaloidal; less commonly, the flows are porphyritic. Flows are pervasively chloritized and carbonatized and are generally only slightly foliated. Sills are conformable with bedding, medium grained and have a diabasic texture. Dykes crosscut all lithologies, including massive mineralization. The dykes are generally lighter coloured and finer grained than sills, range from less than 10 centimetres to several metres wide and generally possess a 1 to 20-centimetre wide chloritic chilled margin.

Diabase bodies of limited extent occur spatially and stratigraphically beneath massive mineralization and are from 1 to 40 metres thick. In places, diabase is host to stockwork or stringer mineralization and predates mineralization. The diabases are medium to coarse grained and are moderately to extremely altered and contain calcite, chlorite and epidote. The diabase bodies are geochemically similar to overlying footwall and hanging wall flows and likely the feeder conduits for these overlying units.

The sedimentary host rocks comprise non-calcareous to calcareous argillites. They are indistinctly to well laminated and are dominantly fine to very fine grained. Individual argillite units vary in thickness from less than a metre to 40 metres, and on average are 10 to 15 metres thick. The argillites contain predominantly minor, very fine to coarse-grained disseminated euhedral cubes of pyrite and/or fine-grained pyrrhotite.

Major faults on the property dip steeply, strike northwesterly and trend subparallel to contacts between enclosing lithologies. Two phases of folding, isoclinal and open, occur in both massive sulphides and host rocks.

To date, drilling and underground development has identified two main sulphide masses, the North and South Sulphide Bodies, each with a variably developed stockwork/stringer zone. One or more smaller massive sulphide lenses are also present. The current interpretation is that these are distinct from the main massive bodies, however, it is possible that these are faulted and displaced portions of the two main bodies.

The North Sulphide Body is about 120-150 metres thick by 500 metres in diameter (true dimensions) and has a well-developed stockwork/alteration zone within both volcanic and sedimentary rocks. The tabular to lenticular, stratiform body trends west-northwest and dips moderately steeply to the north-northeast. The South Sulphide Body is relatively more deformed. This tabular to lensoidal body plunges steeply to the southeast, and extends southeastwards as a series of 15 to 60-metre wide massive sulphide lenses (Geological Survey of Canada Open File 2169).

Stratigraphic sulphide zoning, recognized in both northern and southern bodies, passes upwards from footwall stringer mineralization to massive pyrrhotite, to massive pyrrhotite-pyrite, to massive pyrite, to massive pyrite-calcite-sphalerite, and ends in discontinuous chert-carbonate-sulphides. Zoning has been modified by subsequent mineralization and structural deformation.

Three principal types of massive sulphide mineralization exist: (1) massive pyrrhotite with lesser chalcopyrite; (2) massive pyrite with lesser chalcopyrite; and (3) massive pyrrhotite and pyrite with lesser chalcopyrite and magnetite.

A stockwork/feeder zone is present beneath both sulphide bodies and have been translated (tectonically rotated) to varying degrees. The stockwork is comprised of irregular sulphide veins within pervasively chlorite and silica altered wallrock. Sulphides within the stockwork zone consist predominantly of pyrrhotite with lesser chalcopyrite and, in places, pyrite. In general, the percentage of sulphides, and number and density of sulphide veins increases upward from the bottom or "root" to the top of the stockwork zone. Gangue minerals include quartz, carbonate, chlorite and albite.

Significant gold is associated with a chert-carbonate-sulphide exhalite consisting of finely interlaminated to interbedded (less than 1 millimetre to 5 centimetres) calcite, siderite, ankerite, chert, chlorite, sericite, hematite, magnetite, pyrrhotite, pyrite, chalcopyrite and rarely sphalerite. The unit is present in several places within the deposit. This unit is thought to be present both at the base of the South Sulphide Body as well as immediately overlying the North Sulphide Body, where several thin beds are intercalated with the hanging wall volcanic flows. Individual units are generally narrow (0.1 to about 3 metres).

A supergene zone has also been identified and is up to 90-metres thick. The zone comprises pyritic mud, chalcocite, cuprite, native copper, hematite and sphalerite. Approximately 2 million tonnes of supergene zone reserves have been delineated (Geological Survey of Canada Open File 2169).

Principal "ore" minerals of Windy Craggy mineralization include pyrrhotite, pyrite, chalcopyrite and magnetite, with lesser digenite, sphalerite and rare gold, electrum, marcasite and arsenopyrite.

The North Sulphide Body is mineralogically zoned from a pyrrhotite-rich core to a pyrite-rich outer/upper portion. Massive sulphide displaying breccia textures is common. Two generations of pyrite are recognized: 1) early, colloform to framboidal spheres and colloform layers; and 2) later, recrystallized(?) euhedral, equant cubes and pyritohedrons intergrown in a boxwork fashion. In the South Sulphide Body, pyrite is present as the latter variety.

Pyrrhotite is coeval with chalcopyrite and is predominantly later than pyrite. It commonly occurs interstitially to pyrite and as fracture fillings (with chalcopyrite) within pyrite. Marcasite is prevalent only within the South Sulphide Body. It occurs as minute, rounded blebs in pyrrhotite. Chalcopyrite displays mutual boundaries with coeval pyrrhotite and is predominantly later than pyrite. It usually occurs interstitially to pyrite and as fracture fillings together with pyrrhotite in pyrite.

Sphalerite is rarely present in the South Sulphide Body; where it occurs as small, isolated, anhedral grains within carbonate and as narrow veinlets crosscutting other sulphides. In the North Sulphide Body, sphalerite is much more common, occurring as anhedral crystals that are interstitial to euhedral pyrite.

Digenite has only been observed in the North Sulphide Body. It occurs as irregular, anhedral blebs with chalcopyrite and sphalerite, with which it displays mutual boundaries interstitial to, and as overgrowths on pyrite. It is also found as inclusions within chalcopyrite.

Arsenopyrite is exceedingly rare, and has only been identified in the North Sulphide Body. It occurs as euhedral rhombohedral or lozenge-shaped crystals that have chalcopyrite and pyrrhotite overgrowths.

Graphite is present as very fine folia and disseminations deflected around sulphides, quartz and plagioclase grains with semimassive to massive sulphide, particularly in stockwork mineralization developed in argillite.

Native gold and electrum occur not only in the gold-enriched zone, but are also present in the North and South Sulphide Bodies. Gold and electrum occur as: (1) blebs associated with chalcopyrite and pyrrhotite fracture fillings in pyrite within massive sulphides; (2) anhedral inclusions within recrystallized, euhedral pyrite in massive sulphides; and (3) as inclusions within, and intergrowths with calcite in the gold-enriched portions of the chert-carbonate-sulphide exhalite unit.

Bismuth telluride occurs as very small rounded blebs included in pyrrhotite and may be one of the following minerals (wehrlite, hedleyite or tellurobismuthinite).

In the North Sulphide Body, magnetite occurs as euhedral dodecahedrons and octahedrons included within pyrite, pyrrhotite, chalcopyrite, carbonate and rarely sphalerite. In the South Sulphide Body, bifurcating veinlets of magnetite crosscut massive pyrrhotite+ pyrite+chalcopyrite.

Quartz occurs as discrete grains interstitial to sulphides and commonly intergrown with carbonate. Hisingerite is present in anastomosing or horsetail veins and veinlets crosscutting massive sulphides in the South Sulphide Body. Stilpnomelane occurs as fibres intergrown with pyrrhotite, chalcopyrite, chlorite and quartz, and is also interstitial to sulphides within mineralization.

Exploration at Windy Craggy has included 4139 metres of underground development, extensive underground and surface drilling and bulk sampling. Reserve delineation, environmental studies, metallurgical testing, mine and infrastructure design are continuing with a view toward development.

Measured geological reserves at Windy Craggy are:

Tonnes Copper grade (per cent) Cutoff grade (per cent)
297,439,000 1.38 0.5
230,202,000 1.63 0.75
198,020,000 1.75 1.00
139,190,000 1.96 1.50

(George Cross News Letter No.227 (November), 1991.

In 1991, the Windy Craggy project, operated by Geddes Resources Ltd., completed Stage I of the Mine Development Assessment Process. In 1992, review of the project was suspended in deference to a newly initiated land and water use evaluation of the area by the provincial Commission on Resources and the Environment (CORE). The overall reserves of the deposit stand at 297 440 000 million tonnes grading 1.38 per cent copper (applying a 0.5 per cent copper cut-off), 0.2 gram per tonne gold, 3.83 grams per tonne silver and 0.069 per cent cobalt (Geddes Resources Ltd. Annual Report 1991).

EMPR AR 1959-6; 1960-6; 1965-8
EMPR ASS RPT 5608, 8118, *10000, *10531, *10946, *11763, 13144, 15748
EMPR EXPL 1980-523; 1982-415,416; 1983-564,565; 1985-A16,17; 1987-
EMPR FIELDWORK *1983, pp. 149-170,173-184; 1985, pp. 191-196,
*pp. 197-210; 1986, pp. 191-210
EMPR GEM 1975-E196
EMPR INF CIRC 1989-1, p. 12; 1990-1, p. 28; 1991-1, pp. 26,29;
1992-1, pp. 3,6; 1993-1, pp. 7,8
EMPR MAP 65 (1989)
EMPR MER 1985, pp. 7,16,21
EMPR OF 1992-1; 1992-3; 1998-10; 1999-2
EMPR P 1991-4, pp. 108-110
EMPR PF (*Gammon, J.B. and Chandler, T.E. (1984): Exploration of
the Windy Craggy massive sulphide deposit, British Columbia,
Canada; *Geddes Resources Ltd. (1986): Summary and references
for the Windy Craggy deposit located in Northwestern British
Columbia; Geddes Resources Ltd. (1987): Windy Craggy Project;
Geddes Resources Ltd. 1987, 1988 Annual Reports; Peter,
J.M. (undated): The Windy Craggy Copper-Cobalt-Gold Massive
Sulphide Deposit, Northwestern British Columbia; Geological notes
and field notes; An Overview of Developments at the Windy Craggy
Project, Speech by Dr. Gerald Harper, President of Geddes
Resources Limited at the Whitehorse Geoscience Forum, Nov.28,
1989; Ministry of Energy, Mines and Petroleum Resources Press Release: Windy Craggy Project Road Access Study, December 7, 1989; Excerpts from Vancouver Sun Newspaper, Feb.24, Mar.24,
Apr.28, June 9,12, 1990; Geddes Resources Limited Third Quarter
Report 1991; Slide descriptions from Don's talk (undated);
Memoranda regarding Windy Craggy assessment review/alienation;
Visitor's Briefing of the Windy Craggy Deposit, Geddes Resources
Limited, Aug. 1992; British Columbia Geoscience Research Grant
Application, Genesis of the Windy Craggy Deposit: A Contribution
to the Understanding of Massive Sulphide Formation in Volcano-
sedimentary environments, submitted by J.M. Peter and S.D. Scott,
Feb.25, 1988; B.C. Geoscience Research Grant Progress Report #1,
submitted by J.M. Peter, July 28, 1988)
EMR MIN BULL MR 223 B.C. 359
EMR MP CORPFILE (Geddes Res. Ltd.)
GSC OF 926; *2169, pp. 25-67; 2191
GSC P 79-1A, pp. 17-20; 78-1A, pp. 35-41
CIM Vol. 86, No. 966, Jan. 1993, pp. 50-57
CMH 1994-95, p. 161
GCNL #17, 1982; #9,#69,#177,#197,#252, 1983; #17,#68,#233, 1984;
#60,#78,#163,#191, 1985; #29, 1986; #78,#176,#193,#202, 1988;
#36(Feb.21),#69(Apr.11),#79(Apr.25),#113(June 13),#141(Jul.24),
#164(Aug.25),#207(Oct.27),#245(Dec.21), 1989; #106(Jun.1), 1990;
#5(Jan.8),#14(Jan.21),#114(June 3),#227(Nov.26),1991
MIN REV July/August 1990
N MINER Dec.9, 1982; Jan.13, Jun.9, Jul.7,28, Sept.15, Oct.6,13,
Dec.8, 1983; Feb.9, Apr.5, 1984; Jan.31, Apr.11, May 9, Jun.20,
Jul.18, Sept.9, 1985; Feb., Mar.24, Apr.28, Nov.17, 1986; Feb.16,
Mar.23, May 18, Sept.7, 1987; Mar.7, Apr.11,18, May 9, Jul.4,
Sept.19, Oct.24, 1988; May 22, Jul.31, Aug.28, Sept.18, Oct.2,16,
23,30, Nov.6,13, Dec.4,25, 1989; Jan.29, Feb.19, Jul.2, Oct.15,
Dec.3,24, 1990; Jan.3, July 8, Dec.2,9,23, 1991; Apr.13,20, June
22, 1992
N MINER MAG Oct., 1989; Nov., 1990
NW PROSP Nov./Dec. 1989
W MINER Feb., May 1983
V STOCKWATCH Oct.26, 1989
Falconbridge File
Geddes Resources Ltd. Annual Report 1991
Times-Colonist Newspaper Jan.15, 1983; June 20, 1992
Toronto Globe and Mail Jan.19, 1983