Summary:
The Hope Bay Property is located within the Hope Bay volcanic belt which is part of a massive structural-geological complex called the Slave Structural Province.
The Hope Bay deposits (Doris, Madrid, and Boston), as well as a large number of other prospects, are considered to be typical of orogenic-type mesothermal lode gold deposits, greenstone-hosted quartz carbonate vein deposits.
• The Doris gold deposit is a typical Archean lode deposit which occurs within an over 3 km long, steeply dipping quartz vein system, in folded and metamorphosed pillow basaltic rocks.
• The Madrid deposit area lies within a north-south striking package of mafic volcanic rocks, comprising a sequence of Fe-Ti tholeiitics, Mg tholeiitics, komatiitic basaltic, synvolcanic to late gabbroic, and ultramafic rocks.
• The geology in the area of the Boston deposit is a bimodal assemblage of mafic and felsic volcanic rocks in contact with sedimentary rocks, all of which are complexly folded about a large-scale synformal-anticline. The core of the anticline is occupied by mafic volcanic rocks that host the Boston deposit and these are in turn overlain by sedimentary rocks.
The Doris Area
The Doris Deposit is located at the north end of the north-south trending Hope Bay greenstone belt of Archean age near Cambridge Bay in Nunavut. Gold mineralization is contained within predominantly sub vertical quartz veins hosted within mafic volcanic rocks.
Mineralization
The Doris Vein system is characterized by a series of north–south striking, sub vertical, goldbearing, brittle-ductile structures that commonly host wide, stylolitic, ribboned, or bull quartz veins.
Within the veins, gold is commonly associated with narrow tourmaline chlorite septa oriented parallel to and along the vein margins. Veins are not consistently mineralized along strike. Gold is distributed throughout vein structure but is usually concentrated near the footwall side of the vein, where visible gold is relatively common. Gold mineralization includes visible and disseminated gold occurring primarily with quartz veins ranging from a few centimetres to approximately 10 m in scale. Visible gold includes coarse leafy free milling grains located along vein margins, tourmaline septa, and wallrock fragments which are commonly associated with pyrite. Gold is also associated with disseminated sulphides at the margins of the quartz veins, or with sulphide clusters within the vein. Occasionally, gold is present within brecciated zones adjacent to the quartz veins. Sulphide mineralization consists of trace to 2% pyrite, trace chalcopyrite, rare sphalerite, and pyrrhotite.
The Madrid Area
The Madrid deposit area is located in the northern area of the Hope Bay volcanic belt, south of the Doris deposit. It includes the Wolverine-Madrid corridor which is defined as the belt of rocks extending from the southern end of Wolverine Lake to the northwest end of Patch Lake (Sherlock et al., 2002).
The Madrid deposit area includes the Naartok East, Naartok West, Rand, Spur, Suluk, Wolverine and Patch 14 deposits. The Madrid trend also includes the Suluk T3, and Patch 7 prospects.
The style of mineralization at Madrid is different from the Doris or Boston deposits and can be generally characterized by sulphidation and replacement of favourable stratigraphic units. The most favorable lithologies are Fe-rich tholeiitic mafic volcanics which have been extensively brecciated. Hydrothermal alteration at Madrid is characterized by an early assemblage of sericite micas and carbonate alteration, consisting of magnesite and ankerite with quartz-carbonate stockwork veinlets. The main gold-bearing alteration assemblage consists of secondary albite and paragonite with lesser carbonate as ankerite and quartz-ankerite stockwork veinlets. The higher gold tenor is associated with over 10% fine grained pyrite, intense albite flooding and hematite discoloration (Sherlock et al., 2012).
The gold mineralization within Naartok West, Naartok East, Rand, Suluk, and Patch 7 consists of quartz-carbonate stockwork veining, which overprints dolomite-sericite-albite-pyrite altered mafic volcanic rocks of the Patch Group. The gold mineralization is characterized by multi-stage brecciation and alteration with at least two separate gold mineralization events. Gold occurs within north-northeast, east, southeast, and north-northwest trending brecciated and carbonate altered zones and is associated with disseminated pyrite which has replaced brecciated mafic fragments
The Boston Area
Boston mineralization has been subdivided into the B2, B3, B4, and B5 zones.
The strongest mineralization in the Boston deposit is found within the B2 zone, particularly the section investigated by the underground workings. The B2 zone has been intersected to a depth of 1,000 m, with the highest grades located in the central part of the zone.
Compared with the B2 zone, mineralization in the B3 zone is less continuous and lower grade. The B4 and B5 zones are the smallest of the three main Boston ore zones. The B4 zone is a relatively small zone hosted on the eastern contact of the volcanic core, while the B5 zone comprises several mineralized horizons located south of the Newton Deformation Zone.
Fingas (2018) recognizes at least 6 styles of mineralization in the Boston deposit, which include: vein stringer sets hosted in transition breccia; discrete veins at geological contacts; fault-hosted veins; shear-hosted mineralization; vein domains at picrite contacts; internal picrite-hosted mineralization.
Vein stringer sets hosted in transition breccia is the most important mineralization style in the B2 zone and has been exposed in underground drifts. Mineralization consists of sulphide-bearing quartz-carbonate veins, typically hosted in both volcanic- and sediment-dominated transition breccia. Zones are typically planar, from 2 to 10 metre wide, with ore shoots plunging steeply to the southwest (e.g. ore shoots within the B2 zone with an apparent plunge of 77° to 225°).