Description: Barkley Canyon is one of the few known sites worldwide with the occurrence of thermogenic gas seepage and formation of structure-II and structure-H gas hydrate mounds on the seafloor. This site is the location of continuous seafloor monitoring as part of the Ocean Networks Canada (ONC) cabled observatory off the west coast off Vancouver Island, British Columbia, Canada. We combine repeat remotely operated vehicle (ROV) seafloor video observations, mapping with an autonomous underwater vehicle (AUV), ship-, ROV-, and AUV-based identification of gas flares, as well as seismic and Chirp data to investigate the distribution of fluid migration pathways. Geologically, the site with the prominent gas hydrate mounds and associated fluid seepage is covering an area of ∼0.15 km 2 and is situated on a remnant of a rotated fault block that had slipped off the steep flanks of the north-east facing canyon wall. The gas hydrate mounds, nearly constant in dimension over the entire observation period, are associated with gas and oil seepage and surrounded by debris of chemosynthetic communities and authigenic carbonate. The formation of gas hydrate at and near the seafloor requires additional accommodation space created by forming blisters at the seafloor that displace the regular sediments. An additional zone located centrally on the rotated fault block with more diffuse seepage (∼0.02 km 2 in extent) has been identified with no visible mounds, but with bacterial mats, small carbonate concretions, and clam beds. Gas venting is seen acoustically in the water column up to a depth of ∼300 m. However, acoustic water-column imaging during coring and ROV dives showed rising gas bubbles to much shallower depth, even 〈50 m, likely a result of degassing of rising oil droplets, which themselves cannot be seen acoustically. Combining all observations, the location of the gas hydrate mounds is controlled by a combination of fault-focused fluid migration from a deeper reservoir and fluid seepage along more permeable strata within the rotated slope block. Fluids must be provided continuously to allow the sustained presence of the gas hydrate mounds at the seafloor.

Description: Models of the three-dimensional physical property variation of the NICO Au-Co-Bi-Cu deposit, Northwest Territories, and the Southern Breccia albitite-hosted uranium occurrences and their iron oxide-alkali alteration envelopes, were derived from inversion of high-resolution aeromagnetic, gravity, and magnetotelluric (MT) data at deposit to regional scales. In turn, integration of the geophysical results with physical property measurements and geologic observations leads to a new understanding of the geometry of the deposit, adjacent mineralized and altered zones, and potential cogenetic links within the host metasomatic system. NICO, which is a variant of the magnetite group iron oxide copper-gold (IOCG) class of deposit, is spatially associated with a discrete zone of lower electrical resistivity occurring within a broader, NE-dipping zone of higher density. The high-density zone overlaps a NE-dipping zone of higher magnetic susceptibility and is truncated to the southwest by a NW-striking geophysical discontinuity interpreted as a major fault zone. This inferred fault divides the magnetite-altered metasedimentary rocks hosting the NICO deposit from the albite-altered rocks within the Southern Breccia corridor to the southwest that host the uranium mineralization. Having been active during development of the metasomatic system, this fault influenced the formation of these distinct but complementary deposit types.

Description: The Great Bear magmatic zone in the Northwest Territories of Canada contains large iron-oxide alkali alteration systems noted for having high potential for iron oxide-apatite, iron oxide-copper-gold, and affiliated ore deposits. Physical properties (density, magnetic, and electrical) were measured on 824 rocks samples selected to represent the range of metasomatic alteration types in the region. Mineralogical and geochemical classification of the prograde iron oxide and alkali alteration facies reveals large variations in physical properties through the evolution of the metasomatic systems. In particular, deep and early sodic alteration produced rocks having low densities and low magnetic susceptibilities. During calcium and iron precipitation, rocks gain extremely high density and susceptibility, due to crystallization of amphibole and especially magnetite. Subsequent hightemperature, potassic- and iron-altered rocks are marked by cocrystallization of magnetite with K-feldspar or biotite, and as the transition from magnetite to hematite takes place, K-feldspar crystallizes instead of iron oxides leading ultimately to potassic felsites having low densities and susceptibilities. Subsequent cooler, shallower, and more oxidized potassic-iron alteration produced high densities but moderate susceptibilities owing to crystallization of hematite. Understanding these major variations in physical properties of rocks enables detailed geophysical mapping of alteration zones, which builds and improves the regional context for integrated mineral exploration vectors to potential ore deposits.