Bog Iron Deposit

Required Geological Setting

Island arc volcanoes

Occurrence

Limonite deposits precipitated from the hot spring water. Goethite and jarosite deposit from pH 2.5-3.0 strong acidic hot spring water rich in Fe and SO₄. Jarosite precipitates near hot spring bents where the hot spring water is more acidic, and goethite precipitates in the down reaches where the hot spring water is less acidic. It is considered that Fe ions in the hot springs was deposited as goethite by the activity of Fe bacteria in the hot spring water. Some reports suggest that Fe hydroxides such as schwertmannite formed as precursor, and such Fe hydroxides change to more stable goethite afterwards. Limonite ores often produce impression fossils of mosses, leaves, or plant branches. Limonite ores may be associated with diatomite and/or various phosphate minerals.

Reported Minerals

• Goethite
• Jarosite
• Hematite
• Schwertmannite
• Diatomite