The Southwest zone of the Galore Creek deposit is located at the headwaters of Galore Creek, a northerly flowing tributary of the Scud River, some 85 kilometres south-southwest of Telegraph Creek.
Twelve alkalic porphyry copper-gold deposits are known to occur within the Galore Creek syenite complex. This complex comprises a series of Late Triassic to Early Jurassic orthoclase-porphyry syenitic bodies which have intruded coeval Upper Triassic Stuhini Group volcanic rocks and related sediments. Faults which offset and segment the intrusive rocks and a sub-horizontal fracture cleavage are the two main structural elements in the syenite complex. The complex is roughly 5 by 2.5 kilometres in area.
The deposits are hosted primarily by highly altered potassium- enriched volcanic rocks and pipe-like breccias adjacent to syenite dikes and stocks. Typically, the deposits are manto-shaped and have a north to northeast trend related to the syenite contacts and zones of structural weakness.
The syenite complex is made up of four intrusive phases that are most closely associated with the copper deposits. Six other phases are recognized but are peripheral to the Central zone deposit. The copper-bearing rocks near the syenite intrusion are extensively metasomatized, recrystallized and locally brecciated. These may include pyroclastic and intrusive breccia, trachyte, phonolite, lithic tuff, crystal tuff, pyroxene basalt, pyroxene andesite and minor sediments. These rocks have been converted to skarns and fenitic porphyroids so that original rock types are unclear. The term "hornfels" was frequently applied to these meta-volcanic rocks in the early stages of exploration.
Alteration and mineralization are contemporaneous and spatially overlap. The hydrothermal system was extensive and the resultant alteration led to the formation of large gossans. Potassic alteration consisting of potassium feldspar, titanium biotite and magnetite have converted the syenites and volcanic rocks to pink, white and orange rocks composed mostly of orthoclase. Alteration of pyroxene, hornblende and biotite to assemblages of chlorite and calcite plus/minus albite and epidote characterizes the propylitic zone, best developed in the syenitic rocks. Calc-silicate alteration consisting of abundant garnet, diopside, epidote, albite and anhydrite is an unusual feature of the complex. Garnet replaces up to 50 per cent of the metavolcanic rocks and infills breccias near the northern end of the Central zone breccia pipe but is generally absent from the other deposits. However unusual this metasomatic overprint is, the distribution of sulphides, precious metal and magnetite is considered consistent with the expected zoning pattern for alkalic porphyry deposits.
Barr (CIM Bulletin July 1966) describes the southwest deposit as follows: "The deposit appears to be localized at the intersection of two fracture zones which have produced a local centre of brecciation in epidotized syenite porphyry lying 760 metres west of the south end of the Central Zone. Although erratic copper mineralization, in the form of oxide copper with sparse chalcopyrite, occurs in several outcrops in the vicinity of the southwest deposit, the discovery drill holes were spotted entirely on the basis of geophysical recommendations. The main part of the zone strikes east to southeast and dips steeply to the south. Surface alteration patterns indicate a northwest trending zone of pyritic mineralization flanked by hematitic alteration which extends to the northwest of the deposit. Potash feldspar, biotite and chlorite are the dominant alteration products. The mineralization in the deposit includes chalcopyrite with minor bornite, associated partly with pyrite and magnetite. Sulphides and magnetite occur as fracture fillings, coarse replacements and disseminations.
The Southwest zone contains a mineral resource of 42,400,000 tonnes grading 0.55 per cent copper, 1.03 grams per tonne gold, and 7 grams per tonne silver (estimated), at a cut-off of 0.27 per cent copper equivalent (CIM Special Volume 46, page 642).
In 1990, Mingold Resources drilled 10 drill holes totalling 939 meters into the Southwest zone area during the 1990 program. Four of these holes (GC 377 A, B, C, GC 385) failed to reach their targeted depth because of difficult overburden conditions. GC 379 was taken to a depth of 85 meters before the hole was abandoned because of difficult ground conditions. A 61 meter intercept averaged 5.14 grams per tonne gold and 1.88 percent copper (Assessment Report 20550). Drill holes GC 381 through GC 386 tested the down dip and strike projection of the zone intersected in GC 379. All holes intersected a mottled syenite breccia which contained significant copper and gold values. Additional holes are required to determine the overall dimensions and grade of this new zone.
In 1991, Kennecot drilled a total of 2,960 meters in ten holes on Group II claims during the course of the field season. Seventy percent of this total was used to test the Southwest (copper-gold) zone. The Southwest Zone is interpreted as a tabular east-west striking zone approximately 400 meters long and 100 meters wide, which dips steeply south. It is localized within a breccia zone which has characteristics of a diatreme with polylithologic fragments, unsorted and unbedded with clasts supported by a fine rock flour matrix. Sulphide mineralization comprises chalcopyrite, pyrite and traces of bornite. Pyrite is predominant beyond the copper zone and may occupy up to 10 percent by volume of the breccia in these areas. This pyrite content plus the presence of magnetite explains the strong IP response which encompasses the Southwest Zone. In 1991 Drillholes GC388, 390, 393, 393A and 396 to 398 tested the Southwest Zone along strike and down dip. Drillholes GC433 and 434 were holes designed to test an induced polarization anomaly located northwest of the Southwest Zone. Neither hole intersected any significant copper values, but both holes contained up to 3 percent pyrite and 2 percent magnetite, likely source of the anomalous IP response.
In August 2003, SpectrumGold Inc. (now NovaGold Canada Inc) entered into an option agreement to acquire a 100 per cent interest in the Galore Creek property from Stikine Copper Limited (a wholly-owned subsidiary of Rio Tinto Ltd.) and Hudson Bay. From September to October 2003, Spectrum Gold carried out a 10 hole, 2,950 metre diamond drill program on the property. The work program was directed toward confirming grades of copper and gold mineralization defined by previous drilling in the Central and Southwest Zones.
Diamond drilling by NovaGold in 2004 targeted eight different mineralized areas, the Central Zone (which includes the North Gold Lens, Central Replacement Zone, and South Gold Lens), the Copper Canyon Property, the Gap Zone, the Grace Claims, the North Junction Zone, the Saddle Zone, the Southwest Zone, and the West Fork Zone. The Southwest Zone saw the addition of six holes in 2004, targeting the east-west and down-dip trends of mineralization in the zone. Attempts at extending the mineralization to the east were largely unsuccessful, but drilling at depth proved fruitful as is displayed in the results of GC04-459 and GC04-502. These holes are expected to help expand the existing resource as well as being useful in evaluating the variability of alteration and mineralization types.
In 2005, Drill Hole GC05-628 in the Southwest deposit intersected three composite intervals totaling 183.4 meters grading 0.84 per cent copper, 1.63 grams per tonne gold and 6.4 grams per tonne silver News Release, NovaGold Resources Inc, Oct 5, 2005.
An NI-43-101 compliant resource estimate for the Southwest deposit at a 0.35 per cent copper equivalent cut-off is reported at 47,700,000 tonnes of Measured and Indicated ore grading 0.45 per cent copper, 0.82 gram per tonne gold and 3.04 grams per tonne silver and; 122,900,000 tonnes of ore in the Inferred category grading 0.31 per cent copper, 0.56 gram per tonne gold and 2.27 grams per tonne silver (Updated Preliminary Economic Assessment, NovaGold Resource Inc., www.novagold.net, October 2005).
In 2007, NovaGold completed 17 holes, totalling 4,547 metres on the Galore Creek property for the Galore Creek Mining Corporation (GCMC). Drilling focussed on the Southwest Zone, Central Replacement Zone, Butte Zone and reconnaissance targets for the purpose of extending and upgrading known mineralization, identifying grade controls, and collecting geotechnical information for engineering studies.
In 2008, Galore Creek Mining Corporation (GCMC) completed nine diamond drill holes totalling 2,049.58 metres. The main objectives of the drill program were to obtain ABA (Acid Base Accounting) data in the Central, Southwest, North Junction and Junction pits, to confirm legacy grades in the Junction pit, and to collect metallurgical data in the Central pit.
Refer to the Central Zone deposit (104G 090) for further details of the Galore Creek deposits in terms of a more complete work history and for reserves and resources which are indicated to include the Southwest zone.
