SONORA PALEOCHANNEL
retreat), and 3) McConnell (10.3 Ka retreat). The northerly advance of the pre-Reid sheet extended further than the Reid sheet itself, which in turn extended further than the McConnell sheet. Each retreat left a blanket of coarse and fine outwash sedimentary facies, with the coarse material at the base.
The ice sheets in the glaciated terrain
(Figure 1) were two miles or more in thick- ness. The weight of the ice was enough to force the solid crust downwards as much as a few hundred feet in elevation. Melting and retreat of each ice sheet triggered slow isostatic crustal rebound during interglacial periods. Glacial gravels and overlying finer organic muds and debris eroded as the crust slowly rebounded and hydrologic base levels slowly dropped. Crustal rebound resulting from the McConnell retreat is still in progress and has dropped local erosional base levels.
Prospect Geology
flows of the late Cretaceous Mount Nansen Group, and mafic flows and pyroclastics of the late Cretaceous Carmacks Group (Schulze 2009, Bennett 2010).
Regional and District Bedrock Structure
The Hoocheekoo Fault and the Big Creek
Fault strike northwest at the southern end of the Dawson Range. At this point, they are parallel and 25 km apart (Figure 3). They both continue northwest for 75 km, the Hoocheekoo passing near the large Carmacks and Minto mines, and the Big Creek in the vicinity of the Revenue, Nucleus, Tad Toro and Sonora deposits. Numerous smaller porphyry deposits and showings are also in this southern part of the Dawson Range (Figure 3).
At the latitude of the Sonora Au-Cu por-
phyry deposits and the Hayes Creek placer district, the strike of the Hoocheekoo Fault is mapped almost due west, having gradu- ally changed strike between the Minto Mine and the Hayes Creek district (Figure 3). The Big Creek Fault extends northwest from Freegold Mountain (Nucleus-Revenue, Figure 3) past the Selkirk First Nation’s Cash and Dawson Gold’s Tad Toro deposit and other showings, then through the center of Northern Tiger’s Sonora depos- its. The east-west Hoocheekoo Fault and the northwesterly Big Creek fault con- verge in the immediate area of the Hayes Creek placer district and the Sonora Au-Cu deposits (Figure 4). The combined fault zone, mapped as the continued Big Creek Fault, continues northwest and then west- northwest past Western Copper’s Casino
www.aipg.org
and Kaminak Gold’s Coffee deposit (Figure 2). Copper porphyry and structurally hosted gold deposits, and associated placer gold deposits, occur ubiquitously along these northwest to north-northwest-trending fault systems (Bennett, 2010).
Regional and District Bedrock Mineralization
Repeated superposition of Cretaceous
mineralizing events is an important charac- teristic of the higher-grade metal deposits throughout the Dawson Range. Early phase mineralization seems to be remobilized, re-precipitated, and significantly enriched along active structural corridors (Big Creek- Hoocheekoo systems and subsidiaries). Nucleus-Revenue and Sonora are excellent examples of multiply-mineralized deposits, each having examples of multiple mesother- mal and epithermal events. Pleistocene and modern gold-tetradymite placer deposits are present in drainages and surround each of these examples. The Te component of Casino’s placers is presently unknown to this author, as are those of White Gold, Coffee, Cash, and Tad Toro (Figure 2).
Quaternary Glacial Lithologies, Extents, Erosional Events
The Quaternary glacial geology of the
Yukon, including the Dawson Range, is shown generally in Figure 1, described by LeBarge (2009), and summarized in this section. At least three separate, successive Cordilleran ice sheets advanced and then retreated. Their scientific names and ages are as follows: 1) pre-Reid (1.5 Ma advance, unknown age of retreat), 2) Reid (200 Ka
Bedrock Lithologies The Sonora Au-Cu property, and the
Hayes Creek Au placer district are underlain by gneissic to schistose Paleozoic bedrock. The Paleozoics are intruded by at least three serpentinized and listwanitic ultramafic lenses or sills followed by the west-north- west margin of the mid-Cretaceous Dawson Range granitic batholith. A Late Cretaceous quartz monzonite porphyry stock up to 250 meters wide intrudes the northern batholithic margin south of Sonora Gulch. The monzonite porphyry has been mapped and drilled on both sides of the north- flowing portion of Hayes Creek (Figure 5 and Bennett, 2010).
Quaternary Lithologies An isolated remnant of unconsolidated
sediments rests on a channelized, pre-Reid glacial unconformity at Sonora Gulch in the Hayes Creek placer district. This paleochan- nel appears to trend west-northwest, sub- parallel to a local splay of the Big Creek Fault that also passes through the Sonora porphyry deposit (Figure 5). Bedrock out- crops in the gulch just below the mammoth tusk discovered in 2010 (Photo #3, Figures 5 and 6). Bedrock does not show up in the gulch banks again for another 700 meters downstream to the north from the mam- moth tusk site. The axis of the paleochannel lies somewhere between bedrock upstream from the mammoth tusk and the schist observed by George Wilson.
The remnant stratigraphic section in the
Sonora paleochannel consists of fluvial con- glomerate capped by thick, black, organic, permafrosted swamp mud. Clasts are well rounded, pebble to boulder-sized, and do
Jul.Aug.Sep 2024 • TPG 13
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
