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<br />3. Historic Impacts: Mining, Flow Augmentations, and Project
<br />Reach Land Use
<br />
<br />3.1. Mining Impacts
<br />
<br />The Leadville mining district has produced in excess of $800 million in silver, lead, zinc,
<br />gold, and copper since the mid 1800's (Collins and Collins, 1986), Smelting operations
<br />have also utilized significant quantities of manganese, bismuth, and iron, Mining in the
<br />area commenced around 1860 on California Gulch when placer gold was discovered, By
<br />1875, the gold mining had essentially ceased, in part due to the difficulty of processing a
<br />heavy gray mineral that was present in high concentrations in the placer deposits, This
<br />material was identified as cerussite (lead carbonate) in 1876, which is a common lead ore
<br />that forms upon the interaction of carbonated waters with galena (lead sulfide; Hurlbut
<br />and Klein, 1977), The cerussite ore also contained large amounts of silver. The lead-
<br />silver ore was mined extensively until about 1902, From about 1903 to after WWI, large
<br />quantities of zinc carbonate ore were mined in the Leadville district. Since about 1923,
<br />base metal complex sulfide ores have constituted the primary mining activity in the
<br />region, Between 1859 and 1966, approximately 24 million tons of ore were produced in
<br />the Leadville district (Studzinski, 1996), Some local mines have actively produced gold
<br />ore in recent years (Collins and Collins, 1986),
<br />
<br />Mining waste generated in the Leadville region over the past 150 years has been directly
<br />disposed of on the Arkansas River floodplain, and has been transported down the
<br />Arkansas River project reach via upstream tributaries including California Gulch (BOR,
<br />1999), These tailings are located along the channel margin and floodplain within the
<br />project reach, and consequently constitute a potential source of contaminants for the
<br />active channel (URS, 1977), As the channel course has shifted laterally through time,
<br />many tailing deposits are located away from the main channel in relict channel features
<br />and on the adjacent floodplain or low terrace surfaces, Additional concern has been
<br />expressed that mine tailings have been transported though irrigation ditches and
<br />deposited in broad fields in the valley bottom, Within the project reach, some of the
<br />tailings have been identified as phytotoxic, such that vegetative reinforcement of channel
<br />banks and floodplain surface is locally limited (URS, 1997),
<br />
<br />The delineation and geochemical analyses of tailings within the project reach is ongoing,
<br />To date, approximately 90,000 cubic yards of tailings have been mapped and
<br />geochemically evaluated along the project reach CURS 1997; 1998), Treatment strategies
<br />for the tailings were undergoing feasibility evaluations at the time of this investigation,
<br />
<br />Sediment control measures have been implemented on California Gulch to reduce the
<br />quantity of tailings delivered to the project reach, Whereas historic sediment loading out
<br />of California Gulch likely consisted of substantial quantities of sand and finer grained
<br />material, sediment control measures will reduce both the size and volume of sediment
<br />introduced in the future,
<br />
<br />May 7, 1999
<br />
<br />Fluvial Geomorphological Assessment
<br />Upper Arkansas River
<br />
<br />Page 8
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