Sunday, October 25, 2009

How the Iron Ore Formed

Under the right circumstances both iron and magnesium ions are capable of acting as weak acids under the influence of alkali or alkaline mineralization as exemplified by the underlying Stockbridge marble formation, or as at the time of deposition a back arc basin coral reef. The re4actions that occurred between the CaCO3 and the proposed iron and magnesium oxides found in the overlying Walloomsac formation providing the iron to form the hydrous iron oxide (limonite) at the contact between the Stockbridge and Walloomsac formations. The Walloomsac also provided the necessary magnesium ions for converting the limestone to dolostone a mixture of calcium and magnesium carbonate. Undoubtedly there were chemical reactions occurring at the beginning of the depositation of the Walloomsac on top of the Stockbridge formation.

The real transference of ions did not really become strong until the Taconic orogeny during the late Ordovician that buried both formations underneath a nappe of older Cambrian rocks that were associated with the island arc that had formed earlier off the south coast of the North American craton. The position of older rocks on top of younger rocks was a puzzle to geologists for decades that was known as the ‘Taconic Problem.” This puzzle was finally unraveled in the 1970s with the discovery of plate tectonics.

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