I suppose it's possible, it could have happened eons and eons ago. Subduction is a part of Plate Tectonics. (You can find more subduction entries. At the top left in your browser menu, select Edit and then Find on this page. A small window will appear. Type in the word subduction)

This page has some animations illustrating Plate Tectonics. Maybe it happened during the Continental Drift (refresh the page to see it again).

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Perhaps I used the wrong term. FDN is not on the plate boundary, correct? I was thinking of a more localized event. Something caused by volcanic action, or by the folding of the mountain range we're in. I'm also curious as to the age of the deposit. Has this been determined, and was it a single event, or a series of events?

ebear