This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 垽 is uncertain. It visually combines 沂 and 土, but the original semantic and phonetic roles are unclear.
The top 沂 suggests water, and the bottom 土 is earth. Imagine muddy sediment settling at the bottom of a river—a possible meaning hinted by its components, but treat this as a mnemonic only.
For ギン, picture a silver (銀, ぎん) coin buried in the mud (垽): 銀 -> ギン, and the coin is stuck in the sediment.