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Several maps which show cretaceous to tertiary magmatism and associated mineralization in the Lime Hills C-1 quadrangle of the Western Alaska range by the Alaska Miners Association Annual Convention on November 5, 2014 are presented.

Ni-Cu-Co-PGE mineralization occurs as magmatic sulfides in Late Triassic mafic-ultramafic intrusions of the Wrangellia terrane in Alaska and the Yukon. Parts of this metallogenic system have seen detailed study and exploration, notably at the Quill Creek Complex and Wellgreen deposit in the Yukon Territory, and at several prospects in the Eastern Alaska Range, including the Alpha Complex. Recent mapping in the Talkeetna Mountains showed that these mafic-ultramafic intrusions and their extrusive equivalent, the Nikolai Greenstone Large Igneous Province (LIP), continue at least 60 km to the southwest of the previously recognized extent. This opens up geologic potential for magmatic Ni-Cu-Co-PGE deposits to occur in the Talkeetna Mountains of central Alaska. As part of its ongoing Airborne Geophysical/Geological Mineral Inventory and Strategic and Critical Minerals Assessment programs, the Alaska Division of Geological and Geophysical Surveys (DGGS) initiated a multi-year project to improve the understanding of mineral potential in western Wrangellia. The project began in 2013 with acquisition of magnetic and electromagnetic (EM) geophysical data over unsurveyed portions of the terrane in the Clearwater and Talkeetna Mountains. DGGS geologists completed a three week field program of geologic mapping, rock, and stream sediment sampling in 2013, and followed up with 1:50,000-scale mapping of the Talkeetna Mountains C-4 Quadrangle during the 2014 field season. Gabbroic and ultramafic rocks of probable Late Triassic age were sampled across the project area. Previous work divides the Nikolai Greenstone into a stratigraphically lower, depleted mantle-derived, low TiO2 group and an upper, enriched mantle-derived, high TiO2 group. Both intrusive and extrusive members of this earlier petrogenetic suite occur throughout western Wrangellia. DGGS investigations indicate that PGE enrichment is associated only with the earlier, low TiO2 suite. Outside of the Mount Hayes Quadrangle, the most prominent low-TiO2 type mafic-ultramafic complex is the 16 km long, up to 700m-thick sill-form body in the northeastern Talkeetna Mountains south of Butte Creek. Mapping and analytical work indicate that this is a multiphase intrusive complex dominated by gabbro to olivine gabbro, with texture varying from fine-grained to pegmatitic. The thickest, most mafic section shows large-scale gradational variation in mineralogy from olivine-rich troctolite at the center to olivine gabbro above and below, apparent differentiation which is similar to that seen at the Quill Creek Complex. Microprobe results show that olivine grains near the base of this intrusive complex have Ni concentrations around 2900 ppm, whereas olivine in the center of the complex average 1100 ppm Ni. This apparent Ni depletion is comparable to that observed at Wellgreen. Sulfide grains, including intergrown pyrrhotite and pentlandite, were found to occur at grain interstices and as rare inclusions in Ni-depleted olivine. Analyses from the northeastern half of the study area yield values of PGE per 100 percent sulfide that are on par with values for the Wellgreen deposit. These data, along with the olivine Ni depletion, imply an early separation of a sulfide melt and a high degree of sulfide-silicate melt interaction, indicating that this part of Wrangellia has completed important prerequisites for the formation of Ni-Cu-Co-PGE deposits. [ABSTRACT FROM AUTHOR]