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Geology, mineralization and geochronology of the Conrad Zone carlin-type gold prospect, east-central Yukon Territory, Canada

University of British Columbia

The Nadaleen Trend is a recently discovered, 25 kilometer long trend of mineralization along the northern margin of the Selwyn Basin in east-central Yukon. The regional geologic framework and style of mineralization are both analogous to the Carlin trend in Nevada. The Nadaleen Trend is bound structurally to the south by the regional scale Dawson Thrust and the Kathleen Lakes Fault to the north. This structural setting marks the boundary between the dominantly Neoproterozoic to Paleozoic slope and basin facies carbonates, siltstones and clastic rocks of the Selwyn Basin and Mackenzie Platform stratigraphy. Research efforts are focused on the Conrad and Osiris Zones within the eastern Nadaleen Trend, the first Carlin-type discoveries in the area. Mineralization accompanies the process of decarbonatization of host limestone and subsequent silicification and brecciation. This is reflected in mineralized zones occurring as breccias containing jasperoid replacement of carbonate by quartz and late, open space filling calcite and realgar. Mineralization is typically shear- and breccia-hosted, reflecting a strong structural and permeability control on the development of mineralization. Principal host rocks to mineralization are variably decarbonatized silty limestones and siliciclastic rocks along with narrow gabbroic dykes. Geochemical enrichments associated with Au in the Conrad Zone are typical of Carlin-type deposits, with strong correlations between As-Hg-Sb-Tl and Au. Arsenic occurs primarily as widespread and locally abundant realgar and orpiment. Several phases of Arsenic-rich pyrite are found in mineralized zones, typically as rims around earlier pyrite cores or as <10 μm disseminations and aggregates. The highest concentrations of gold are found within fine-grained pyrite, with values up to 800 ppm. Carbon and oxygen isotopic signatures of mineralized and altered host rocks indicate a significant shift from primary lithological background values. In areas of high gold concentrations, carbonate isotopic compositions can be depleted by as much as 7 ‰ δ¹³C and 10 ‰ δ¹⁸O from background carbonate isotopic compositions. This isotopic depletion indicates areas of increased fluid flow associated with Au-mineralization at the Conrad Zone. The age of Carlin-type mineralization is constrained by mineralized mafic dykes at 74.4 ± 1 Ma and thermally re-set apatite fission tracks at ~42 Ma.

Text

2015-03-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52593

Geological Sciences

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/