Morphological, chemical, and mineralogical properties of soils and the effects of acid sulfate weathering in the copper basin of Tennessee

The mining and smelting operations in the Copper Basin of Tennessee have left the region almost devoid of woody vegetation. The soils have been exposed to large doses of SO₂ and H₂SO₄ which could influence the weathering of the graywacke, mica schist and phyllite parent material. A study was undertaken to evaluate the effects of increased soil acidity and acid sulfate weathering on the morphological , chemical and mineralogical properties of the soils.

Five pedons were located inside the Basin to represent sites near the old and new smelters. Two pedons were located upwind from the smelter sites outside the Basin to represent soils less affected by past smelting operations. Exchangeable bases were extracted with dilute unbuffered silver thiourea (Ag-TU) containing 0.01 M Ag⁺.

No differences in morphological characteristics were observed between soils inside and outside the Basin. The upland soils are all red (2.5YR 4/6) in color with a clayey argillic horizon. The soils inside the Basin are acid throughout the profile while the soils outside the Basin have an acid epipedon and slightly acid subsoil. All the soils have very low effective cation exchange capacity (ECEC) (<12.0 meq/100 g clay) and qualify as low activity clay (LAC) soils. Sulfate-sulfur is concentrated in the argillic horizons and, at this time, tends to be more concentrated in the Basin soils.

Vermiculite, hydroxy-interlayered vermiculite (HIV), mica, micavermiculite, kaolinite, gibbsite, and quartz are the dominant minerals in all soils. Gibbsite is the most dominant mineral beneath the argillic horizon in upland soils outside the Basin with minute quantities of kaolinite. On the other hand, kaolinite is the most dominant mineral beneath the argillic horizon in all the Basin soils including the toeslope soil outside the Basin.

There is chemical evidence to support differences in pH, Fe₂O₃ and SO₄ content between soils inside and outside the Basin. However, these are not manifested to a great degree in the present system. It is possible that regional influences due to removal of plant cover may have had a greater impact than the acid sulfate weathering.