Description

Placer deposits in the Mayo area occur in a wide variety of geomorphic settings, including alluvial fans, gulch gravel, valley-bottoms (alluvial plains), and bedrock terraces (bench gravel), which have been variably buried and reworked by glaciofluvial processes. Placer gold also occurs in glacial till and glaciofluvial gravel, especially where these sediment types have intersected pre-existing placer deposits, resulting in the reconcentration of gold in a zone close to bedrock. The Yukon has been subjected to several major episodes of glaciation, which are generally referred to as the pre-Reid (oldest), the Reid (intermediate), and the McConnell (youngest) glaciations. The pre-Reid glaciation consisted of multiple episodes, the earliest being at least 2.58 Ma. Although the Mayo area was heavily glaciated during the pre-Reid episodes, limited surficial deposits remain, and evidence mainly consists of erosional features and erratics at higher elevations. The subsequent Reid (approximately 300 000 years ago) and the McConnell (approximately 20 000 years ago) glaciations reworked and buried pre-existing glacial drift and alluvium, and left extensive surficial deposits. While the timing of the interglacial prior to the Reid is uncertain, the Koy-Yukon interglacial prior to the McConnell glaciation lasted approximately 170 000 years. The modern (Holocene) interglacial began approximately 11 000 years ago. These three interglacials have been the main placer-forming periods in the Mayo area. The complex stratigraphy of placer deposits in the Mayo area reflects its glacial and periglacial history. Within the glacial limit, placer deposits are best preserved near the maximum limit or terminus, where the scouring of preexisting sediment was minimal and depositional processes were dominant. Beyond the glacial limit, periglacial climatic conditions resulted in increased slope and alluvial sedimentation that buried and reworked paleoplacers. Based on surficial mapping, stratigraphic relationships and sedimentology, several placer deposit models may be described within the Mayo area. These can be grouped into modern, interglacial, glacial or periglacial placer settings. Modern placers include alluvial fans, fan-deltas, alluvial plains and gulch deposits. Interglacial placer settings in the Mayo District include alluvial plains, alluvial fans and low terraces along second and third order streams and rivers, and gulches in first order tributary valleys. These are commonly buried and reworked by glacial drift and periglacial fan sediments. Glacial placer settings in the Mayo area include glacial till and glaciofluvial gravel in major valleys, the most significant of which are Reid age or older. Periglacial placers include alluvial fans in tributary valleys and fan-deltas along major water bodies including Mayo Lake. Placer exploration targets occur in all of the above settings, however the most significant are those that remain buried in trunk valleys, which were not post-glacially re-excavated due to base-level changes. Substantial placer gold reserves may exist in these valleys but their potential remains to be evaluated. Suggested methods include a combination of seismic surveys, overburden drilling and bulk sampling.

Resources

Name	Format	Description	Link
Bulletin	HTML		https://data.geology.gov.yk.ca/reference/42033
Appendix	HTML		https://data.geology.gov.yk.ca/reference/42033
Package	HTML		https://data.geology.gov.yk.ca/reference/42033
Appendix	HTML		https://data.geology.gov.yk.ca/reference/42033
Package	HTML		https://data.geology.gov.yk.ca/reference/42033
Bulletin	HTML		https://data.geology.gov.yk.ca/reference/42033
Bulletin	Unknown		https://data.geology.gov.yk.ca/reference/42033
Appendix	Unknown		https://data.geology.gov.yk.ca/reference/42033
Package	Unknown		https://data.geology.gov.yk.ca/reference/42033
Original metadata (https://open.yukon.ca)	HTML		https://open.yukon.ca/data/datasets/placer-gold-deposits-mayo-area-central-yukon
Original metadata (https://open.yukon.ca)	HTML		https://open.yukon.ca/data/datasets/placer-gold-deposits-mayo-area-central-yukon
Original metadata (https://open.yukon.ca)	HTML		https://open.yukon.ca/data/datasets/placer-gold-deposits-mayo-area-central-yukon

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