The Saddle 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.
At least 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.
The Saddle deposit is located at the contact of what are called the Younger syenite and the Buckshot syenite porphyry intrusions. Barr (CIM Bulletin July 1966) offers the following description of the occurrence: "Observations indicate that the most strongly mineralized portion of the deposit trends east, with a 50 degrees north dip, coinciding with the strike trends of fracturing and a local deviation in the trend of the Buckshot porphyry contact. Much of the surficial portion of the deposit comprised a breccia which is composed of angular fragments of both Buckshot porphyry and Younger syenite, cemented together by magnetite. Drill-hole information indicates that copper mineralization is not restricted to the magnetite-cemented breccia, as weakly altered and highly fractured phase low in magnetite contains secondary copper oxides including cuprite, tenorite, malachite and possibly chrysocolla with associated chalcopyrite."
In 2011, the Junction zone was described in a technical report (43-101) by AMEC Americas Limited on behalf of NovaGold (Galore Creek Project by AMEC, July 17, 2011) as follows in the next 5 paragraphs:
"The Saddle deposit crops out on a steep slope, 2.6 kilometres southeast of the Central Zone. It trends easterly and dips northerly at 50 degrees along the contact between buckshot syenite and green syenite porphyry. Primary mineralization is contained within a magnetite-cemented breccia body; secondary copper minerals extend beyond the breccia. The breccia contains angular fragments of buckshot syenite and green syenite porphyry and metavolcanic rocks. Graded beds and flow textures suggest that some of the green syenite represents potassium-metasomatized volcanic extrusive rather than intrusive rocks.
A strong quartz–sericite–pyrite alteration zone extends down the north-facing flank of Saddle Ridge to Jack Wilson Creek. Discontinuous mineralized shears and narrow sigmoidal chalcopyrite–pyrite–quartz veins are exposed at upper elevations of the Saddle Ridge area.
The Spire zone is an east-trending zone of propylitic alteration and disseminated chalcopyrite cropping out at 1,065 to 1,370 metres elevation on Saddle Horn Ridge. In the creek valley, gold values are associated with sericitized, pyritized and silicified zones in andesites.
Although localized chalcopyrite mineralization is recorded in the northern portion of the Saddle ridge, copper mineralization is largely restricted to the southern end of the Saddle Zone. Here, the strongest zones of mineralization are found in the oldest rocks, the epiclastic sediments (S6), which are replaced by extensive secondary biotite and a localized texturally-destructive assemblage of secondary orthoclase-magnetite.
The main stage of mineralization correlates well with the orthoclase-magnetite plus/minus biotite plus/minus magnetite assemblage.
Near 352779 metres Easting, 6331946 metres Northing and 352885 metres Easting, 6331882 metres Northing, outcrops of epiclastic sediments, near the contact with i8, contain noticeable copper mineralization. Here, orthoclase–chalcopyrite veins have a marked east–west trend and contain 3 to 4 per cent vein-hosted and disseminated chalcopyrite. Although the younger i8 is generally less well mineralized, it contains a local zone of well mineralized magnetite breccia with the best mineralization (2 to 5 per cent chalcopyrite) occurring at 352770 metres Easting, 6332336 metres Northing. The breccia infill or matrix mineralogy consists of massive euhedral magnetite plus/minus chalcopyrite."
Work History
The deposit was investigated in the early 1990s by Mingold Resouces. At this time, the deposit was described as being comprised of a magnetite-cemented intrusive-fragment breccia containing varying amounts of chalcopyrite, malachite and bornite with associated gold values. Two diamond drill holes tested the breccia with one 12-metre interval averaging 3.98 grams per tonne gold and 2.49 per cent copper (Assessment Report 20558).
AMEC reports five zones as being modelled toward its 2011 Mineral Resource Estimate for the Galore Creek deposit: the Central zone (including the Bountiful deposit), Southwest Zone, Junction/North Junction Zone, Southwest Zone, and West Fork Zone. Refer to the Central Zone deposit (104G 090) for further details of the Galore Creek deposits. Further details of a common work history and 2011 reserves and resources are given.
