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• The sandstones are generally fine to very fine grained, of low porosity, <br />well cemented, lenticular, discordant and crossbedded. Most sandstones <br />at the mine show a well defined system of joints at outcrops. A 25 to <br />30 foot-thick channel filled sandstone can be observed in cross sections <br />along Tuttle Draw near the county road. The "upper" sandstone unit of <br />the Dakota (Young, 1973) is absent at the mine site. <br />Conglomerates are absent in overburden strata. However, a 2 to 4 foot <br />conglomerate marks the base of the Dakota in the underburden. This <br />conglomerate is the "lower" lithologic unit of the Dakota described by <br />Young (1973). <br />E. MINERALOGY. Iron disulfides (pyrite [FeS2] and marcasite [FeS2]) <br />are commonly the most undesirable minerals present in overburden strata <br />at the Nucla Mine site. These minerals are associated with coal-bearing <br />rocks in which reducing conditions are prevalent at the time of <br />deposition. When exposed to an oxidizing environment in the presence of <br />• percolating water, iron disulfides often react to foray acid leachates. <br />According to Caruccio et al. (1977), the rate at which these acid <br />leachates are produced are dependent on the quantity and grain-size <br />distribution of pyritic material, availability of oxygen, presence of <br />iron bacteria, amount of calcareous material and relationship to the <br />ground water aquifer. <br />Another mineral commonly encountered in overburden strata at the Nucla <br />- Mine is gypsum (CaSO4-2HZ0). Gypsum is significantly soluble in water <br />and, according to Hounslow (1978), "precipitates readily from solutions <br />produced by the oxidation of pyrite coupled with the dissolution of <br />limestone". As gypsum occurs both as a primary and secondary diagenic <br />mineral in strata at the mine site, a similar cycle of solution and <br />precipitation can be expected in spoil materials. <br />Quartz, feldspar and clay minerals occur as primary detrital minerals irr <br />sandstones and shales. Clays, shales and organic residues coninionly have <br />• higher quantities of trace metals occurring as adsorbed ions than do <br />coarser grained strata. These ions may be released into solution as a <br />result of oxidation and low pH. Other less commonly occurring minerals <br />6-16 Revised 03/13/87 <br />