Laserfiche WebLink
Introduction <br />Naturally mineralized deposits of uranium were discovered in rock formations adjacent to Ralston Creek <br />in 1949 by Fred Schwartzwalder, a German immigrant and part-time prospector living in Golden, <br />Colorado (Williamson, 1983). These deposits were formed about 60 million years ago when enriched <br />hydrothermal solutions precipitated uranium, resulting in "pitchblende" mineralization along fault and <br />fissure systems associated with local geologic formations (DREGS, 2009). <br />The Denver - Golden Oil and Uranium Corporation acquired the mine in 1955 and continued development <br />with support from the Atomic Energy Commission (AEC). Shipping cutoff grades for this ore were <br />unusually high relative to typical uranium ores, at times nearly 1% uranium oxide (versus an AEC cutoff <br />grade of 0.1 %). Some ore samples from this mine were assayed to contain as much as 58% uranium <br />oxide (Paschis, 1979). <br />The majority of ore extracted from the Schwartzwalder Mine was processed at the Canon City Milling <br />Facility (CCMF) operated by Cotter Corporation (N.S.L.) (Cotter). A primary reason for high cutoff <br />grades for Schwartzwalder ore was the high cost of transport. In the early days, ore was shipped to Utah <br />or Grand Junction for processing until the CCMF was built in 1958. <br />Cotter purchased the Schwartzwalder Mine in 1965. In the late 1970's, an advanced ore sorting system <br />was installed to improve the efficiency of separating economically viable ore from lower grade waste <br />rock. In 1977, the average ore grade delivered to the CCMF was about 0.6% uranium oxide (Wright, <br />1980). Waste rock containing varying amounts of uranium remains at the Schwartzwalder Mine site. <br />Initial development of underground workings at the mine began relatively high up the hillside on the <br />south side of the valley in the vicinity of the Illinois Fault. As the upper mine workings advanced <br />downwards along various mineralized fault systems, several additional portals were developed until the <br />narrow valley floor forced constraints on the amount of space available for waste rock. <br />As the mine approached the elevation of the valley floor, the Steve portal (50 feet above the present <br />elevation of the creek) became the primary access point in support of continued downward mine <br />advancement. Beginning in the late 1970's, two engineered waste rock piles were developed on hillsides <br />above the valley floor to accommodate continued mine development as underground workings eventually <br />reached depths in excess of 2,000 feet below the Steve Level. <br />Material associated with mine disturbance along the valley floor is a mix of mine waste rock and naturally <br />occurring soils, alluvial sands and gravels. For the purposes of this report, these materials are collectively <br />referred to as "alluvial fill ". The word "pad" is sometimes used in general reference to disturbed alluvial <br />fill materials on the south side of Ralston Creek. The pad was altered as needed over the years to <br />accommodate facilities in support of mine operations. <br />Because seasonally varying amounts of groundwater associated with Ralston Creek are in contact with <br />alluvial fill, and some of these materials include mineralized waste rock, water quality in the creek is <br />subject to seasonal uranium concentrations in excess of the applicable stream standard (0.03 mg/L) from <br />1 <br />