Epigenetic deposition

The largest and highest-grade epigenetic deposits are those in sandstone, but other types are important in a few areas. Epigenetic uranium deposits contain about 32% of the Western world s reasonably assured 30 uranium resources. 

Fluorspar deposits ate commonly epigenetic, ie, the elements moved from elsewhere into the country rock. For this reason, fluorine mineral deposits ate closely associated with fault 2ones. In the United States, significant fluorspar deposits occur in the Appalachian Mountains and in the mountainous regions of the West, but the only reported commercial production in 1993 was from the faulted carbonate rocks of Illinois. 

Kuroko deposits are strata-bound and massive in form (Fig. 1.7) and syngenetically formed on the seafloor and/or sub-seafloor environment. Vein-type deposits are fissure-filling and epigenetically formed (Fig. 1.8). 

While some histone variants can become deposited during DNA replication, certain variants also are assembled into chromatin in a replication-independent manner (reviewed in Jin et al. 2005). This allows the incorporation of histone variant into chromosomal regions with high levels of histone turnover. Histone variants can distinguish the affected nucleosomes from their canonical counterparts and are likely to have important function in the specialization of chromatin domains and their epigenetic maintenance. 

Abstract strong commodity prices in the last few years have led to a remarkable renaissance of uranium exploration in Labrador, focused in a complex and geologically diverse region known as the Central Mineral Belt (CMB). Potentially economic epigenetic U deposits are mostly hosted by supracrustal rocks of Paleoproterozoic and Mesoproterozoic age, and are difficult to place in the traditional pantheon of uranium deposit types. Recent exploration work implies that structural controls are important in some examples, but the relationships between mineralization and deformation remain far from clear. Geochronological data imply at least three periods of uranium mineralization between 1900 and 1650 Ma. It seems likely that the Labrador CMB represents a region in which U (and other lithophile elements) were repeatedly and sequentially concentrated by hydrothermal processes. The current exploration boom lends impetus for systematic research studies that may ultimately lead to refined genetic models that may be applicable elsewhere. 

The Mississippi Valley Type (MVT) deposits are epigenetic Zn-Pb deposits which mainly occnr in carbonates from continental settings (Ohmoto 1986). 

Basinal Brines as a Source of Sulfur in High-Sulfur Coals. Sulfide minerals, such as pyrite and sphalerite, in coal seams may be deposited from basinal hydrothermal fluids. The occurrence of epigenetic sphalerite in Illinois Basin coals has been described by Hatch et al. (119) and Cobb (120). Whelan et al. (121) studied the isotopic composition of pyrite and sphalerite in coal beds from the Illinois Basin and the Forest City Basin, and suggested that some of the coals were affected by Mississippi Valley-type hydrothermal solutions. 

Finch, W.I., 1967. Geology of epigenetic uranium deposits in sandstone in the United States. U.S. Geol. Surv. Prof. Pap., 538, 121 pp. 

The distributions of minerals within the Lower Kittanning seam can be related to depositional environment. Pyrite content is highest in areas which may have experienced brackish conditions. This distribution reflects the availability of iron and sulfur, and pH conditions within the swamp. Whereas much of the pyrite formed syngenetically, observations of sulfide modes of occurrence suggest that marcasite formed epigenetically. 

Inorganic elanents can be included in coal as minerals or as elanents incorporated in the organic structure (Chapters 3, 7, and 10). The most common example of the latter is the incorporation of sulfur into macerals as organic sulfur. Minerals can be incorporated into the peat during deposition, result from epigenetic processes, or be the consequence of metamorphic changes within the coal. 

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