Wood-tin occurs as placer accumulations at several localities in the Black Range, southwestern New Mexico. Individual nuggets, 3 cm or less in diameter, commonly enclose fragments of porphyritic rhyolite, and contain cassiterite, hematite, cristobalite, and/or chalcedony. Color zoning is well developed in wood-tin and appears to have chemical significance; the iron content in cassiterite-rich layers, as much as 7.8 percent Fe203 by electron probe analysis, generally increases through the color sequence: tan, yellow, red, dark brown. The addition of iron is correlated with a decrease in both the c cell parameter and the cell volume of cassiterite, suggesting that Fe3+ has substituted for Sn4+ in the crystal structure. Although wood-tin is rarely found as lode deposits, it probably was deposited originally as fracture fillings in the Tertiary Taylor Creek rhyolite with which it is closely associated. A low temperature, low pressure environment of deposition is reasonable for the wood-tin.

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