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Conglomerates are absent in overburden strata. However, a 2 to 4 foot conglomerate marks <br /> the base of the Dakota in the underburden. This conglomerate is the "lower" lithologic <br /> unit of the Dakota described by Young (1973). <br /> Mineralogy. Iron disulfides (pyrite [FeS2] and marcasite [FeS2]) are commonly the most <br /> prevalent minerals present in the lower ten feet of overburden and the interburden strata <br /> at the Nucla East study area. These minerals are associated with coal-bearing rocks in <br /> which reducing conditions are prevalent at the time of deposition. When exposed to an <br /> oxidizing environment in the presence of percolating water, iron disulfides often react to <br /> form hydrous iron sulfates. These compounds commonly appear as white and yellow salt <br /> crusts on weathered rock surfaces. According to Caruccio et al . (1977), the rate at which <br /> these acid leachates are produced is dependent on the quantity and grain-size distribution <br /> of pyritic material, availability of oxygen, presence of iron bacteria, amount of <br /> calcareous material, and relationship to the ground water aquifer. According to Nordstrom <br /> (1982), framboidal pyrites are the most reactive form of pyrites, while massive pyrite or <br /> nodules react very slowly. Pyrite nodules are common within the Nucla East study area. <br /> Another mineral commonly encountered in overburden strata at the Nucla Mine is gypsum <br /> (CaSO4-2H2O). Gypsum is significantly soluble in water and, according to Hounslow et al . <br /> (1978), "precipitates readily from solutions produced by the oxidation of pyrite coupled <br /> with the dissolution of limestone". As gypsum occurs both as a primary and secondary <br /> diagenic mineral in strata within the Nucla East study area, a similar cycle of solution <br /> and precipitation can be expected in spoil materials. <br /> Quartz, feldspar, and clay minerals occur as primary detrital minerals in sandstones and <br /> shales. Clays, shales, and organic residues commonly have higher quantities of trace <br /> metals occurring as adsorbed ions than do coarser grained strata. These ions may be <br /> released into solution as a result of oxidation and low pH. Other less commonly occurring <br /> minerals found in overburden strata include calcite (CaCO3), limonite (Fe 203) and possibly <br /> siderite (FeCO3). Small accumulations of copiapite (FeO 4) and halotrichite (Fe or Mg SO4) <br /> may occur as crusts on the faces of coal seams and associated strata in abandoned open <br /> pits near the operating Nucla Mine (Caruccio et al ., 1977). <br /> Coal Seam Analysis. Table 6-1-1, Coal Seam Analysis Data, summarizes the quality of the <br /> upper Dakota and lower Dakota coal seams for exploration drill holes placed within the <br /> Nucla East permit area. <br /> 6-1-9 Revised 04/11/88 <br />