Glaciated Ground – New Insights from the Mayo District
Jeffrey Bond
Placer Settings
1. Placer deposits eroded
and deposited directly by
glaciers.
1
2. Placer deposits in glacial and
interglacial gravel
2
Mayo Placer Mining District
Dublin Gulch
Keno
Gustavus Range
Highet Ck
Duncan Ck
Mayo Lake
Mayo
Last Glaciation: 17,000 years ago
Keno
Mayo
Placer Setting #1
Erosion and deposition directly by glaciers
Placer Setting #1
Erosion and deposition directly by glaciers
Can a placer concentration survive glacier erosion/deposition?
Last Glaciation: 17,000 years ago
Keno
Mayo
Bedrock Geology and Alpine Glaciation
Keno
Thunder
Gulch
Granite
Creek
Mayo
Davies Contracting
Granite Creek
Mayo
Davies Contracting
End moraine
Till 3
Till 2
Till 1
Granite Creek
Mayo
Granite Creek
till 3
till 2
till 1
bedrock
Mayo
Granite Creek
Mayo
Granite Creek
Mayo
Davies Contracting
Granite Creek
Bedrock Geology and Alpine Glaciation
Keno
Thunder
Gulch
Mayo
Bardusen Placers Ltd.
Thunder Gulch
Mayo
Bardusen Placers Ltd
Thunder Gulch
Mayo
Bardusen Placers Ltd
Thunder Gulch
Placer Setting #1
Erosion and deposition directly by glaciers
Prospecting tips in alpine glaciated valleys
• Fluvial paleo-placers concentrations can be preserved
during the reworking process by alpine glaciers
• Alpine valleys with limited glacier extent may be more
prospective – target mouth of valley
• Glaciers can thrust bedrock slabs over till
• Stacked tills may suggest limited scouring processes at
the base of the alpine glacier (oxidation variability)
• Low grade concentrations reworked from end moraine
Placer Setting # 2
Placer gold in glacial vs interglacial gravel
Location and Bedrock Geology
Keno
Mayo
Duncan Creek Golddusters
Duncan Creek
Duncan Creek Golddusters
Duncan Creek
Duncan Creek Golddusters
Duncan Creek
16 m
Duncan Creek Golddusters
$20/yd
$45/yd
$12/yd
Duncan Creek
<$10/yd
(Ager, 1997)
Duncan Creek
100,000 years ago – warm period
Keno
Duncan Creek
60,000 years ago – cold period
Keno
Duncan Creek
30,000 years ago – warm period
Duncan Creek
interglacial
glacial
interglacial
Placer Setting # 2
Placer gold in glacial vs interglacial gravel
Prospecting tips in glaciofluvial affected drainages
• Exploring for paleo-channels on bedrock regardless of
gravel genesis
• Perched economic concentrations can occur in
glaciofluvial gravel (false bedrock of interglacial gravel)
• Look for muddy gravel, poorly sorted, large clast size
• Be wary of well-sorted sandy gravel (+/- wood)
Thank you: Jim Davies, Claus Barchen, Troy and Frank Taylor