lode 
(lōd)
(lōd)n.
1.
a. The metalliferous ore that fills a fissure in a rock formation.
b. A vein of mineral ore deposited between clearly demarcated layers of rock. Also called lead1.
2. A rich source or supply: found a lode of important documents in the archives.
[Middle English, way, load, from Old English lād, way; see leit- in the Appendix of Indo-European roots.]