CGRG Bibliography of Canadian Geomorphology
Search Results
Author : Bond, J.D.; LeBarge, W.P; and Weston, L.H.
Date : 2001.
Title : Placer deposit exploration in glaciated terrain: understanding climate impacts on drainages in the Mayo Mining District, Central Yukon, Canada.
Publication : Canadian Quaternary Association/ Association canadienne pour l'etude du Quaternaire, Annual Meeting 2001. Whitehorse, Yukon Territory, August 20 – 24, 2001.
Issue :
Page(s) :
Abstract
Understanding drainage responses to past climate change can supplement placer gold exploration in glaciated terrain. In the Mayo mining district of central Yukon placer-bearing drainages have undergone multiple periods of glaciation, periglaciation and interglaciation. Placers that have been incorporated into glacial till or buried under thick meltout drift generally require a phase of fluvial reconcentration to reform economic grades. Late glacial outwash and post-glacial fluvial down-cutting often provide the necessary erosion, but only if adequate base-level changes occur in trunk streams. During glacial advances proglacial outwash may breach drainage divides. The result is a vigorous reworking of placers in the upper reaches of the drainage. This can also occur in a deglacial setting with differential retreat of ice from a drainage. Under periglacial climates sedimentation will increase into a drainage. Also the movement of sediment through the drainage will increase as a result of higher precipitation rates. The development of large periglacial fans during the late Wisconsinan McConnell advance is apparent in streams that remained unglaciated. Periglacial fans may host reconcentrated placers and/or effectively bury placers in trunk streams. A similar setting occurs under paraglacial conditions associated with recently deglaciated areas. During interglacial climates, streams undergo a period of incision and reconcentration in response to base-level disequilibrium following the glaciation. Placer concentration will continue at varying rates throughout an interglacial. During the Holocene the earliest stages of warming appear to have been the most active downcutting and placer reconcentration phases. Excessive overburden depths and low-grade concentrations often hinder the economics of glaciated placer deposits. The importance of base level changes in reducing overburden depths and reconcentrating placers into higher-grade deposits cannot be overemphasized. Placer deposits in glaciated terrain may be less predictable than those in unglaciated terrain but the opportunity for high grade pockets and low grade/high tonnage deposits is good.
Bibliography of Canadian Geomorphology