Exploration Geologists & Prospectors
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SOUTHERN ACCRETED TERRANES
Wyoming Mineral Belt Concept: Plate II.
Plate II. A broad wedge of exotic terranes (the green band) accumulated along the southern margin of the Wyoming Province and added to the Wyoming Craton in Archean time (>2.4Ga). These are composed of meta-volcanic and meta-sedimentary rocks rich in metals. These were strongly sheared and metamorphosed during accretion and were further modified during later pulses of magmatic activity causing many of the metallic elements to be mobilized, enriched and redeposited. This broad band, known as “southern accreted terranes” is a primary source of metals, some of which are preserved as ore deposits (such as banded iron formation) while others have been remobilized and redistributed during later episodes of tectonism, intrusion, and hydrothermal activity. Across Wyoming, these exotic terranes were greatly influenced by the wave of thermal energy, magmatism, and hydrothermal fluids accompanying the progressive withdrawal of the Farallon slab. The red stars are locations of currently known mineral districts within the accretionary wedge.
Plate I. The composite crust of the southern Wyoming Craton and the central rocky Mountain region was, for a considerable time, underplated by a flat-slab ocean plate (Farallon) and was effectively sealed off from the influences of mantle heat and convection. Stresses applied to the crustal plate by the northeastward migration of the Farallon slab formed the Laramide mountain ranges and intervening basins. Later, as the Farallon plate sank and was assimilated into the mantle, a concentrated wave of thermal energy rose through the continental crust along previously formed fractures and shear zones. This produced an enormous volume of metal-pregnant magma and associated hydrothermal fluids producing numerous intrusive bodies, volcanic centers, and mineral deposits.
Several districts within the Wyoming Mineral Belt include Wharf Gold, S.D. and in Wyoming, the Bear Lodge rare earths district, Rattlesnake Hills gold, several uranium districts and our potential Granite Ridge prospect. At the southwest termination of the Belt the Bingham Canyon copper porphyry fits the Farallon Plate rollback time progression of 38 my.
Our approach uses geophysics, multispectral remote sensing, and subtle geochemical indicators as essential tools that allow us to efficiently extend our exploration into areas where fractures, intrusive bodies, and associated mineral deposits are covered by Tertiary sedimentary units. Fortunately, the geochemical signature extends far beyond the areas of ore-grade mineralization. Also, hydrothermal fluids have continued to migrate upward through buried fractures and into the overlying sedimentary cover, providing subtle evidence of the deeper mineralization. Our interpretations rely heavily on field observation, analysis of rock and soil samples, and interpretation of structural patterns relative to tectonic history. Field observations are integrated with geophysics, multispectral mapping of alteration – often with imaginative extrapolation. The work is augmented using published data and reports along with information gleaned from data archives.
Our Exploration Approach
Using spectral imagery to map alteration.
The Wyoming Mineral Belt Concept (developed by J. F. Davis & Dr. R. W. Marrs)