Middle English spelling of load (n.) "a burden," it keeps most of the word's original meaning "a way, a course, something to be followed." The differentiation in sense took place 16c., that of spelling somewhat later. Mining sense of "vein of metal ore" is from c. 1600, from the notion of miners "following" it through the rock. Also found in lodestone, lodestar, and, somewhat disguised, livelihood. Middle English also had lodesman (c. 1300) "leader, guide; pilot, steersman."