坑道

1. Origins, structure, and basic meaning

• Structure: 坑道, read こうどう, denotes an underground mine passage excavated for extraction and transport.
• Basic usage: It names a narrow passage used by mine workers and an old mine-tunnel structure recreated in a model.

2. Common pitfalls and similar expressions

• Mine passage rather than mineral vein
  • It is an underground passage excavated for mining and transport, not the mineral-bearing layer itself.