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for a copy of this paper please contact the Yukon Geological Survey; geology@gov.yk.ca.

Galena and pyrrhotite occur in manganese-stained quartz-carbonate breccia beneath rusty limestone. Surface geology of the area suggests that the mineralization is a replacement of brecciated limestone in the footwall of a low-angle fault. Results from previous exploration have proved disappointing but the host structure is probably regional in extent and larger deposits may exist along strike.

Quantitative mineralogy, U-Pb geochronology of zircon and monazite, 40Ar/39Ar geochronology of muscovite and sericite, and Pb isotopes from galena in veins and feldspar in plutons provide insight into the age of metamorphism, mineralization, intrusion emplacement and the sources of metals at the Plateau South (MINFILE 105N 034, 035, 036) occurrences in central Yukon. Orogenic mineralization and metamorphism is ca. 110 Ma to 100 Ma, and possibly as old as ca. 130 Ma. Following deformation and regional metamorphism, two biotite-muscovite plutons, the Russell stock and Armstrong pluton, were emplaced at 95.39 ± 0.03 Ma and 95.51 ± 0.03 Ma, respectively. These plutons are here reassigned to the Tungsten suite based on mineralogy, chemistry and age. Coeval with these plutons are contact metamorphism and possibly intrusion-related mineralization. Lead isotopic data from galena cluster into two groups: Group 1 is enriched in thorogenic Pb with 206Pb/204Pb values between 18.31 and 18.14, 207Pb/204Pb between 15.62 and 15.55 and 208Pb/204Pb between 38.77 and 38.30. Group 2 is isotopically evolved with 206Pb/204Pb values between 19.13 nd 18.91, 207Pb/204Pb between 15.78 and 15.63 and 208Pb/204Pb between 39.24 and 39.07. We suggest that late Early Cretaceous mineralization is related to large-scale orogenic fluids that tapped primitive (deep?) metal sources and early Late Cretaceous mineralization, coeval with local intrusions, sourced isotopically distinct metals from the intrusions. Alternatively, all mineralization could relate to Early Cretaceous orogenic fluids but with heterogeneous, locally derived metal sources and thermal resetting of Ar ages near the intrusions.

Detailed vertical-face mapping of 'Slab Creek' was carried out in the summer of 2001 to evaluate the relations of Wernecke Breccia bodies with alteration, veining and iron oxide-copper-gold mineralization. Slab Creek is situated near the 'Slab' mineral occurrence in the Bonnet Plume River district of the Wernecke Mountains. Meta-sedimentary rocks in the area consist of meta-siltstone, meta-silty dolomite and phyllite of the lower succession of the Early Proterozoic Wernecke Supergroup, known as the Fairchild Lake Group. These rocks were folded and metamorphosed to lower greenschist facies, and were subsequently intruded by the Wernecke Breccias during the Mid Proterozoic. Three alteration zones can be recognized within Slab Creek, an inner feldspar zone coinciding with the large breccia bodies, surrounded by a chlorite-quartz-carbonate zone, grading outward into a sericite-chlorite zone. Alteration, veining and mineralization is most intense within the albite alteration zone where iron oxide-copper-gold (cobalt-uranium) mineralization is disseminated and occurs as vein infill.

New mapping and drilling associated with gold exploration has elucidated the structural and lithological controls on hydrothermal gold systems in the White River area. The Paleozoic basement consists of a sequence of amphibolite facies clastic metasedimentary and meta-igneous rocks that host lower grade ultramafic rocks, some magmatically and some tectonically emplaced during the Late Triassic – Early Jurassic. Mapped ultramafic bodies show close congruence with published airborne magnetic anomalies. All of these rocks are cut by brittle normal faults and fractures, and dykes correlated with middle Cretaceous to early Tertiary extension-related intrusive rocks. Gold mineralization associated with these fractures is strongly controlled by host rock types. Two main rock types, felsic gneiss and quartzite, are preferentially fractured and hydrothermally altered. Other rock types are only weakly fractured and locally altered. In particular, ultramafic bodies and micaceous lithologies locally impeded fluid flow.

This report releases whole-rock geochemical assay results of 102 samples collected by the Geological Survey of Canada (GSC) and Yukon Geological Survey (YGS) from four Carlin-type gold zones (Conrad, Sunrise, Osiris and Anubis) in the Nadaleen Trend, Yukon.

The Rau deposit in central Yukon is a gold-rich carbonate replacement deposit hosted in mid-Paleozoic carbonate rocks of the Mackenzie Platform in the footwall of the Dawson thrust. Gold-bearing sulphide mineralization is peripheral to a zone of hornfels and local tungsten-bearing skarn that is associated with several small bodies of granitic aplite and pegmatite that have yielded 40Ar/39Ar muscovite ages of 62.3 ± 0.7 Ma, 62.4 ± 1.8 Ma and 59.1 ± 2.0 Ma. These intrusions are geochemically different and slightly younger than the 65.2 ± 2.0 Ma McQuesten plutonic suite farther to the south. Most Pb isotopic analyses of sulphides from the Rau deposit cluster within compositions of igneous feldspars from the associated intrusions; however, some analyses fall on a trend toward more radiogenic compositions that were determined for the host carbonate rocks. The data are consistent with the Rau sulphide mineralization being genetically related to the early Paleocene felsic intrusions, and forming peripheral to more proximal zones of hornfelsing and tungsten-bearing skarns.