1985-11-25_ENFORCEMENT - M1977378 (2)

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el STANDARD METALS CORPORATION P.O. Box 247 Silverton, Colorado 81433 (303) 387-5533 STANDARD METALS CORPORATION MILL TAILINGS REVEGETATION PROJECT Site History The Mayflower Mill , originally owned and operated by Shenandoah-Dives Mining Company of Kansas City, Missouri , began production in January 1930, on ores removed from the Mayflower Mill . Initial milling capa- city was 350 tons per day. In 1934 mill capacity was increased to 700 tpd and remained at that level until 1953, when the mine and mill closed due to depressed metal market prices. Major products produced at the mill between 1930 and 1953 were concen- trates of lead (galena) and zinc (sphalerite) ores, utilizing a dif- ferential flotation process. Of the 700 tons of ore produced per day, approximately 5% was recovered as merchantable product. The remaining 95%, primarily ground-up host rock, was diverted to the mill waste or tailings circuit at the final stage of the flotation process. The mill tailings, stripped of desirable mineral content, was then combined with mill process wastewater forming a slurry which was pumped to the tail- ings disposal sites. During the Mayflower Mill operating period, 1930 to 1953, tailings pond No. 1 (directly northeast) and No. 2 (currently being revegetated) were constructed employing a gravity launder and decant system. Tail- ings slurry was pumped from the mill into wooden launders set on a downhill grade, following the disposal site perimeter. The slurry was then discharged from the launders and onto the disposal site through spigots placed at periodic intervals in the launder. Variation in specific gravities of slurry particles was used in engineering pond construction, with the heaviest particles (+200 mesh) being deposited first, forming the tailings retention dam or berm; the smaller particles (-200 mesh) and slurry water were then deposited in sequence toward the pond interior. Decant towers were constructed at locations farthest from tailings slurry entry points, and were used to decant clarified water from the pond interior, allowing maintenance of specified berm freeboard as the pond increased in height. In 1959 Standard Metals Corporation reopened the Sunnyside Mine, acquired the Mayflower Mill and installed a new crushing plant and rod mill , which increased milling capacity from 700 to 1000 tpd. In addition to lead and zinc products, a gold-silver amalgam product was also produced from the Sunnyside Mine ores, which possessed high gold heads. The mill oper-