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2-6 Reynolds, S. J., Lingrey, S. H., Kluth, C. F., Ferris, D. C., and Keith, S. B., 1980, Geology, uranium favorability, uranium occurrences and tectonic maps of individual Cordilleran metamorphic core complexes, in Coney, P. J., Reynolds, S. J., Cordilleran metamorphic core complexes and their uranium favorability; final report: U. S. Dept. of Energy, Grand Junction, CO, Report GJBX-258-80, p. 509-510.
2-6 Reynolds, S. J., Lingrey, S. H., Kluth, C. F., Ferris, D. C., and Keith, S. B., 1980, Geology, uranium favorability, uranium occurrences and tectonic maps of individual Cordilleran metamorphic core complexes, in Coney, P. J., Reynolds, S. J., Cordilleran metamorphic core complexes and their uranium favorability; final report: U. S. Dept. of Energy, Grand Junction, CO, Report GJBX-258-80, p. 509-510.
ABS
Cordilleran metamorphic core complexes are unique centers of plutonism, metamorphism, and deformation that are distributed in a discontinuous zone through the interior of the western United States. They are characterized by a distinctive assemblage of rocks and structures which occur in broad• arch-like or domal features. They exhibit a central crystalline core of plutonic and high-grade metamorphic rocks. In high structural levels, these rocks are overprinted by a gently inclined mylonitic folia-tion containing a distinctive lineation. This lineation is typically consistent in trend over an entire mountain range or region. Near the margins of the crystalline core, the mylonitic rocks have been converted into a chloritic breccia via jointing, brecciation, faulting and hydrothermal alteration or retrograde metamorphism. The chloritic breccia is accompanied and overlain by a curvi-planar dislocation surface or decollement. Above the dislocation surface are an assortment of tilted and rotated rocks which generally lack any mylonitic fabric or metamorphic texture. These upper-plate rocks range in age from Precambrian to middle Tertiary and are cut by numerous low-angle structures which are inferred to be listric-normal faults that merge with or terminate against the underlying dislocation surface. A variation on this general theme occurs in several complexes where a zone of highly tectonized metasedimentary rocks (commonly marble) occupies the footwall of the dislocation surface.
Available geochronologic studies indicate a prolonged geological history for plutonic and metamorphic rocks of the crystalline core. However, it can generally be documented that final cooling of the crystalline core and movement on the dis-location surface are Tertiary! A Tertiary age for mylonitization is demonstrated for some complexes and can be inferred for many others. The genetic relationship between plutonism, metamorphism, mylonitization, and dislocation is currently controversial.
The uranium favorability of Cordilleran metamorphic core complexes is a function of processes that are either intrinsic or extrinsic to evolution of the complexes. Intrinsic processes include plutonism, metamorphism, mylonitization and formation of the dislocation surface (brecciation, hydrothermal alteration, tilting, etc.). Extrinsic processes such as weathering and sed-imentation might have operated on rocks of the complexes before, during, or after the main phases of development of the complexes. Under favorable circumstances, both intrinsic and extrinsic processes are able to concentrate uranium into economically viable deposits.
The uranium favorability of Cordilleran metamorphic core complexes, as a group, is low. However, the favorability of individual complexes is as variable as their internal geology and regional tectonic setting. The Kettle, Selkirk and Albion complexes have the highest uranium favorability, while the remainder of the complexes have very low to moderate favorability.
Cordilleran metamorphic core complexes are in general most favorable for pegmatitic, metamorphic, hydrothermal, authigenic, allogenic, and peripheral lacustrine uranium occurrences. The complexes may be significant sources of uranium for later redistri-bution and concentration. Of particular importance in this regard are dislocation zones on the flanks of the complexes which may have been permeable channels or depositional sites for ascending (hydrothermal) or descending (meteoric) uraniferous fluids. The uranium potential of such zones is unknown and will only be revealed by exploratory drilling down-dip from uraniferous core rocks. Additional detailed study is needed to further document the uranium favorability of individual metamorphic core complexes.
2-6 Reynolds, S. J., Lingrey, S. H., Kluth, C. F., Ferris, D. C., and Keith, S. B., 1980, Geology, uranium favorability, uranium occurrences and tectonic maps of individual Cordilleran metamorphic core complexes, in Coney, P. J., Reynolds, S. J., Cordilleran metamorphic core complexes and their uranium favorability; final report: U. S. Dept. of Energy, Grand Junction, CO, Report GJBX-258-80, p. 509-510.
ABS
Cordilleran metamorphic core complexes are unique centers of plutonism, metamorphism, and deformation that are distributed in a discontinuous zone through the interior of the western United States. They are characterized by a distinctive assemblage of rocks and structures which occur in broad• arch-like or domal features. They exhibit a central crystalline core of plutonic and high-grade metamorphic rocks. In high structural levels, these rocks are overprinted by a gently inclined mylonitic folia-tion containing a distinctive lineation. This lineation is typically consistent in trend over an entire mountain range or region. Near the margins of the crystalline core, the mylonitic rocks have been converted into a chloritic breccia via jointing, brecciation, faulting and hydrothermal alteration or retrograde metamorphism. The chloritic breccia is accompanied and overlain by a curvi-planar dislocation surface or decollement. Above the dislocation surface are an assortment of tilted and rotated rocks which generally lack any mylonitic fabric or metamorphic texture. These upper-plate rocks range in age from Precambrian to middle Tertiary and are cut by numerous low-angle structures which are inferred to be listric-normal faults that merge with or terminate against the underlying dislocation surface. A variation on this general theme occurs in several complexes where a zone of highly tectonized metasedimentary rocks (commonly marble) occupies the footwall of the dislocation surface.
Available geochronologic studies indicate a prolonged geological history for plutonic and metamorphic rocks of the crystalline core. However, it can generally be documented that final cooling of the crystalline core and movement on the dis-location surface are Tertiary! A Tertiary age for mylonitization is demonstrated for some complexes and can be inferred for many others. The genetic relationship between plutonism, metamorphism, mylonitization, and dislocation is currently controversial.
The uranium favorability of Cordilleran metamorphic core complexes is a function of processes that are either intrinsic or extrinsic to evolution of the complexes. Intrinsic processes include plutonism, metamorphism, mylonitization and formation of the dislocation surface (brecciation, hydrothermal alteration, tilting, etc.). Extrinsic processes such as weathering and sed-imentation might have operated on rocks of the complexes before, during, or after the main phases of development of the complexes. Under favorable circumstances, both intrinsic and extrinsic processes are able to concentrate uranium into economically viable deposits.
The uranium favorability of Cordilleran metamorphic core complexes, as a group, is low. However, the favorability of individual complexes is as variable as their internal geology and regional tectonic setting. The Kettle, Selkirk and Albion complexes have the highest uranium favorability, while the remainder of the complexes have very low to moderate favorability.
Cordilleran metamorphic core complexes are in general most favorable for pegmatitic, metamorphic, hydrothermal, authigenic, allogenic, and peripheral lacustrine uranium occurrences. The complexes may be significant sources of uranium for later redistri-bution and concentration. Of particular importance in this regard are dislocation zones on the flanks of the complexes which may have been permeable channels or depositional sites for ascending (hydrothermal) or descending (meteoric) uraniferous fluids. The uranium potential of such zones is unknown and will only be revealed by exploratory drilling down-dip from uraniferous core rocks. Additional detailed study is needed to further document the uranium favorability of individual metamorphic core complexes.
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