Posts Tagged ‘ilmenite’

The Geological and Ecological History of the Okefenokee Swamp (part two)

November 25, 2010

How did titanium-bearing (heavy mineral) sands accumulate in Trail Ridge?

About 1.8 million years ago, a period of time that marks the boundary between the Pliocene and the Pleistocene, there existed an enormous barrier island off the coast of south Georgia and north Florida that was 130 miles long.  A high stand of the Atlantic Ocean combined with wind and wave to create this island which encroached upon and buried a freshwater marsh, then an extension of an early version of the Okefenokee Swamp.  Today, this island is a terrace standing above the surrounding lowlands. Placer deposits of titanium-bearing heavy mineral sands motivated Dupont Corporation to buy large portions of Trail Ridge from lumber companies, but as I noted in my previous blog entry, the controversy over the potential environmental damage was so great that the project was canceled.  Mining heavy mineral sands is a strip mining operation where all vegetation and topsoil is stripped from the ground.  Then big machines eat through vast areas of subsoil, the material churned through pumped-up ground water for 7 days a week and 24 hours a day–an unceasing, hellish operation.  The surrounding area suffers constant heavy truck traffic as well because the separated minerals must be transported to distant factories.  After the land is raped, reclamation efforts turn the mined areas into tree farms and ponds–the former a paltry substitute for the original forest.

Image of a titanium mine in Florida.  The water is necessary in a step that separates the minerals from the sand.  The reclaimed land becomes wetlands and tree farms.  Wetlands are resilient but monocultured tree farms are almost barren of wildlife.

It’s no wonder Dupont Corporation was pressured not to destroy Trail Ridge, but they have other environmentally detrimental projects around the world including some in nearby Florida.

Dupont mines four kinds of coumpounds from heavy mineral soils like those that exist in Trail Ridge.  Ilmenite, or titanium dioxide (FeTiO3), is used as an industrial white pigment; rutile, or titanium oxide (TiO2), is used as a metal alloy; zircon (ZnSO4) is used as a refractory for founding molds and nuclear fuel rods; and monazite ( (Ce, La, Th)PO4) is a radioactive compound consisting of rare earth elements used in high powered magnets, industrial pigment, x-ray screens, fiber optics, and color television tubes.

These heavy mineral sands are black and are usually located under several feet of regular sand, though they occasionally appear on the surface, if erosion occurs.  They are radioactive.  Dr. Gale Bishop of Georgia Southern University found that sea turtles occasionally nest in these radioactive sands (which also occur on St. Catherine’s Island), and the baby turtles suffered a high rate of mutation and mortality.

A complex geological process led to the accumulation of heavy mineral sands in Trail Ridge and other areas along the coast, such as St. Catherine’s Island.  Metamorphic rocks, those formed deep underground, are the most important source of titanium, but igneous rocks from Mesozoic-aged volcanic flood basalts, and even sedimentary rocks are contributing sources of titanium.  Rocks located from what’s now South Carolina to Canada are the original sources of titanium-bearing minerals.  Rain water weathered these rocks into a substance known as saprolite which later eroded into rivers.  Rivers carried these titanium-bearing sands into the ocean.  As the ocean transgressed, these sediments were reworked to the surface where long shore currents and winds concentrated the heavy mineral sands into specific placer deposits.  They concentrated together because they have a certain relative density (specific gravity) that differs from just plain sand, and they tend to deposit in the same places.  Rain further concentrated the minerals by leaching out iron oxides.