Abstract

The Redwell Basin complex is a composite intrusive breccia pipe developed over a forcibly intruded molybdenite-bearing, rhyolite porphyry stock, of possible Miocene age. The complex is located within the Colorado mineral belt at the juncture of the north-western border of the belt and the eastern edge of the West Elk Mountains.Deep drilling intersects telescoped mineralized zones containing copper, lead, and zinc within the breccia pipes, and two overlapping zones containing tungsten and molybdenum in the lower part of the pipes and the upper part of the main stock. The upper tungsten molybdenum zone overlaps the junction of the breccia pipes and forms an inverted cup-like shell over the rhyolite cupola. The lower zone has a similar form and appears to be located within the rhyolite stock, peripheral to a late-phase, pluglike intrusion of porphyritic granite. The spatial arrangement of the tungsten molybdenum zones, intrusive styles, rock compositions, and composite nature of the rhyolite porphyry stock suggest that this deposit is of the Climax type.Brecciating fluids emanating from the stock were regulated by a highly metamorphosed layer of shale, now preserved as a hornfels. This hornfels layer lies between the breccia pipe floor and the top of the underlying rhyolite cupola. The layer served to partition this system into two genetically related, yet physically separated, intrusive masses. Drilling evidence suggests that this partition acted as an "expanded bed" underlying a fluidized column. The hornfels partition, although now metamorphosed and interlayered with layers and dikelets of felsite, has maintained its original stratigraphic position and structural integrity.

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