Benevolent Blisters

The earth has "boils" that form in its rocky flesh, rise toward its skin, and sometimes break through. Proper appreciation of these ailments, said Geologist C. Wroe Wolfe of Boston University last week, should lead to the discovery of valuable ore deposits.

Professor Wolfe believes that radioactive elements (e.g., uranium and thorium) in the deep rocks gradually release heat. Since rocks are poor heat conductors, the heat cannot easily escape. After millions of years, the temperature rises until a vast blister of hot, expanded rock has formed. If it works its way to the surface, or if cracks appear, the hot rock may liquefy and escape as a volcanic explosion or a quiet outflow of lava.

Volcanic action is not the only solution. Sometimes the hot blister merely keeps on growing slowly without breaking out. When it reaches a new stratum, it "cooks" the rock, driving out the water contained in its crystals. Soluble materials are dissolved in the water. When the water moves, through cracks or other outlets, the minerals in it are deposited, sometimes as valuable ores.

Dr. Wolfe believes that the earth has suffered from this blister disease since its early years. The blisters have invaded all sorts of rocks, cooking out of them the minerals that they contain. He suggests that geologists look for blisters, ancient or modern, and then look for the ore deposits that their cooking has formed.

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