冲积层或冲积矿床是通过机械作用过程形成的,其成矿物质来源于含矿岩石或矿脉的风化和分解.风化、分解造成的游离矿物,经过流水的搬运和富集而成砂矿.河流携带能力减小,造成冲积物的沉降,因此,这类矿床常位于水流速度减小的部位.沉降下来的冲积物由砂、砾石、卵石等以及一些经受住了侵蚀和风化作用的游离矿物组成.这类矿物有金、铂矿物、锡石、铌铁矿、钽铁矿、金红石、独居石、锆石以及冲积宝石等. Alluvial or alluvial deposits are formed through mechanical processes, and their metallogenic materials are derived from the weathering and decomposition of ore-bearing rocks or veins, and free minerals from weathering and decomposition are transported and enriched by flowing water to form sands. This type of deposit is often located at a point where the velocity of the water flow decreases as the carrying capacity decreases resulting in the sedimentation of alluvial deposits that are composed of sand, gravel, pebbles, etc. and some free minerals that have undergone erosion and weathering Such minerals are gold, platinum minerals, cassiterite, niobite, tantalite, rutile, monazite, zircon, and alluvial gems.