地底下那條主礦脈
這一族就是畫面本身，還沒有比喻。
noun · C1
The main, richest vein of gold, silver, or another valuable metal in one area — the thick one that all the smaller veins branch off from. The word is also used for the mine that is dug on such a vein.
主礦脈
核心畫面
Deep inside a hill there is one thick vein of gold, and every thin little vein around it runs back to that one. A miner who reaches it does not get a bit more gold; he gets the whole hill's gold at once, all in one place.
可以想成地底下有一條最粗、最富的礦脈。四周那些細細的小脈，都像是從它身上分出去的。淘金的人在溪裡撿到金沙，就沿著細脈…更多收起
可以想成地底下有一條最粗、最富的礦脈。四周那些細細的小脈，都像是從它身上分出去的。淘金的人在溪裡撿到金沙，就沿著細脈一路往回追，追的就是這一條。挖到它，不是多挖到一點，而是一次拿到整座山的金子。所以這個畫面裡有兩件事：量很大，而且全集中在同一處，一挖就全有了。後來這個詞離開礦坑，用在一整櫃老照片、一整架二手書上，靠的還是同一個畫面。From the word’s history
Wiktionary records the compound as probably a calque of Spanish veta madre, literally mother vein: the vein the smaller ones are treated as coming from.
Wiktionary 記載這個組合可能是西班牙文 veta madre 的直譯，字面就是「母親礦脈」——細脈被看成從它身上分出去的。這條線索正好對上今天的用法：mother 標的是「最大、最源頭的那一條」。
Wiktionary entry supplied in evidence packet (source_ref kaikki:3f6f69a190036ae4:1301526887:5549); the source itself hedges with probably.
Two branches
借畫面來講日常：一挖就全有了
把「一鎬敲進主脈、整批金子到手」這個畫面，原封不動搬到日常的東西上：重點不是那樣東西值錢，而是「量大而且集中在一處」。
noun · C1
A place, a collection, or a single source that holds a very large amount of one kind of thing you want, all gathered together, so that finding it means you do not have to look anywhere else.
寶庫