Some Features of the Formation of Gold Placers in the Eastern Part of the Kuznetsk Alatau
Abstract Generated abstract
This paper examines how Late Quaternary arid-climate geomorphic processes influenced the formation of gold placers in the eastern Kuznetsk Alatau. It argues that active deflation, denudation, sheet wash, and the subsequent filling of deflation hollows created distinct conditions for placer development, favoring eluvial-deluvial gold enrichment in areas of intense surface lowering while limiting gold concentration in aggrading valleys where incoming debris was poorly sorted. The study uses regional geomorphic observations and an example from the Beika River valley to identify prospective settings, including the bottoms of deep deflation hollows and, under favorable conditions, buried lacustrine placers formed in formerly water-filled depressions.
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SOME FEATURES OF THE FORMATION OF GOLD PLACERS IN THE EASTERN PART OF THE KUZNETSK ALATAU
G. A. Ivankin (TPI)
The formation of placer deposits (including gold placers) is determined by the development of the relief, in particular by the characteristics of the processes of weathering of rocks, denudation, transport, and accumulation of weathering products.
In the territory of the eastern part of the Kuznetsk Alatau, a typical arid climate prevailed in Late Quaternary time. In the foothills of the middle part of the Alatau slopes, within the entire Batenevsky Ridge and, probably, almost the whole of the Minusinsk intermontane depression, a stony desert existed at that time. Very active deflation processes led to the formation of numerous deflation hollows, varied in their morphological features, and contributed to a rapid lowering of the surface level of the part of the Earth’s crust under consideration.
The deflation field forms of relief that were produced have, in the most recent time, become sites of sediment accumulation, and their hypsometric levels have become “autonomous” base levels of erosion and denudation for most watercourses (both permanent and temporary). The rapid filling of hollows with sediments leads to a rise in the base levels of erosion and denudation—many valleys are aggrading.
The mentioned features of relief development predetermined the formation of placer deposits. In areas of intense deflation, eluvial-deluvial placers were formed, in particular gold placers. Enrichment in useful components occurred mainly in connection with winnowing and sheet wash of the weathering products of the enclosing rocks. The clastic material, which entered valleys and hollows in abundance, mainly in the form of mudflow streams, was almost not subjected to sorting because of valley aggradation. Therefore, in such cases enrichment of valley deposits with gold could not have taken place.
We have sufficient factual material confirming the noted features of placer formation. An example may be the formation of an eluvial-deluvial gold placer located on the left side of the valley of the Beika River (a left tributary of the Ninya River), above the ulus of the same name, approximately 3 km away (this deposit was named by us Karpovsky).
Conclusions
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Eluvial-deluvial placers with high concentrations of gold may be expected in cases where areas of gold-bearing zones have undergone significant denudation in the process of deflation and, in part, sheet wash. The most promising, apparently, will be the bottoms of deep deflation hollows formed in such areas. In this case, the placers will be situated beneath a loose cover directly on the eluvium.
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Alluvial gold placers formed, and are forming, through intensive reworking of loose material in river valleys that are not subject to aggradation.
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Many deflation hollows, which at present are accumulative plains, were in the recent past filled with water (were lakes). Sorting of the incoming material took place here. Under favorable conditions, now-buried gold placers of lacustrine origin could have formed.