A mountain of = A large quality of, a huge amount of, a large number of, 大量的
You can use both 具象名詞或抽象名詞. See examples below
具象名詞: A concrete noun names something you can experience with one of your five senses; something you can see (like the moon), touch (like a blanket), smell (like a rose), hear (like laughter), or taste (like sugar).
A mountain of laundry.
A mountain of mittens.
A mountain of awards.
A mountain of letters.
A mountain of waves. 大量的波浪, 很多的波浪
抽象名詞: An abstract noun names feelings (such as jealousy and attraction), ideas (such as peace and freedom), and qualities (such as generosity and determination). Abstract nouns do not exist as physical objects in the world.
A mountain of love.
A mountain of trouble.
Myself. Went abroad at age 11. With over 32 years of experience speaking and writing English. Tutored English as an Undergrad. A project manager in the US since 1992.