G. A. Desborough
1967
<p><span>Two small bodies of Precambrian basic intrusive rock </span>in<span> southeastern </span>Missouri<span> show uninterrupted </span>differentiation<span> of </span>olivine<span> </span>diabase<span> that produced ferrogabbro. </span>Olivine<span> </span>diabase<span>, foliated gabbro and coarse gabbro constitute the major textural rock types. Gravitational settling of plagio-clase, </span>olivine<span> and Fe-Ti oxides occurred </span>in<span> both intrusives and iron enrichment is a conspicuous feature. Plagioclase ranges from An58 to An35 and </span>olivine<span> varies from Fa36 to Fa57. Because these rocks were intruded into volcanic rocks at a substantial depth and were slowly cooled </span>in<span> an apparently </span>closed<span> </span>system<span>, they afford an opportunity to trace the </span>differentiation<span> trends exhibited by the disseminated </span>sulfides<span>. Pyrrhotite, chal-copyrite, pentlandite, sphalerite and cubanite are the most abundant </span>sulfides<span> deposited initially as unmixed </span>sulfide<span> solid solutions which were essentially coprecipitates with the major silicates. Paragenesis and abundance of primary </span>sulfides<span> are directly related to the </span>differentiation<span> parameters shown by the silicates. The extreme fractionation of these intrusives did not lead to a large concentration of any of the </span>sulfides<span> at any stage during consolidation. </span></p>
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10.2113/gsecongeo.62.5.595
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Society of Economic Geologists
Closed system differentiation of sulfides in olivine Diabase, Missouri
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