Definition of "lode"

The metals traditionally sought in the Bristol Bay region have been gold and copper, mostly in deposits near Lake Iliamna. An exception is a gold lode discovered about 1930 near Sleitat Mountain (4), where about $200 in gold was recovered from small quartz veins near the periphery of a small granitic intrusive body.

1967, Henry C. Berg, Edward Huntington Cobb, Metalliferous Lode Deposits of Alaska, page 14

In recent years, Jack Grieve of the department of English and linguistics at the University of Birmingham in England has embraced Twitter as a bountiful lode for looking at language-use patterns.

2019 September 25, Gary Stix, “Two Linguists Use Their Skills to Inspect 21,739 Trump Tweets”, in Scientific American‎