Origin of coastal placer

Coastal placers are placers enriched in the loose sediments of modern coastal zones and ancient coastal zones, mostly surface deposits. In terms of definition, it is different from the surface sedimentary minerals collected in the loose sediments of the shallow seabed and the shallow sea placers which are buried under the modern sediments [1].

The main mineralization process of seaside placer can be divided into five stages: primary occurrence stage, activation stage, transportation stage, enriched ore stage and post-generation change stage of placer.

(1) Primary occurrence stage: In this stage, industrial minerals are distributed or enriched in magmatic rocks, metamorphic rocks, sedimentary rocks and other major rock types or primary ore bodies. The abundance of industrial minerals contained in rocks is very important to the supply of sand minerals and is a prerequisite for the formation of industrial placer deposits. The higher the abundance of industrial minerals in the rock and the larger the exposed area, the more likely it is to form a large-scale placer deposit.

(2) Activation stage: Due to the weathering and erosion of rocks, weathering crusts of different thicknesses are formed, which loosens industrial minerals. The thickness of the weathering crust is often different due to the difference in lithology, the degree of development of geological structures and the climate in which it is located. The formation of the weathering crust marks the beginning of the formation of placer deposits, sometimes forming residual deposits and residual slope deposits on the rock surface or slope The formation of placer often requires sufficient cutting depth, and structural uplift is a necessary prerequisite for the formation of weathering crust. Climatic conditions are the necessary conditions for the formation of such placer, and the nature of bedrock determines the intensity of weathering.

(3) Transportation stage: The transportation and differentiation of substances are closely related to the effects of surface water systems. Rivers are the main way to transport weathered products to the coastal zone; the differentiation depends on the intensity of the dynamic conditions; the distance to be transported depends on the slope of the terrain and the specific gravity, hardness, hydraulics, and particle size of heavy minerals. Minerals such as gold and cassiterite with a larger specific gravity are first precipitated and deposited during the initial transport stage, while lighter heavy minerals such as zircon and monazite can be transported farther, while gold with strong wear resistance is It can be transported for hundreds of kilometers. At this stage, some alluvial placer deposits can be formed in the coastal area.