Cemented Rock Fill at The Doe Run Company 1991-2006

9th International Symposium on Mining with Backfill
Lori R. Young, Harold E. McIntire, Thomas R. Yanske,
Abstract The Doe Run Company has been extracting pillars in conjunction with placing CRF (cemented rock fill) since 1991. During that time over 10.5 million short tons of pillar ore have been extracted and over 4.5 million short tons of CRF have been placed. This utilization of CRF reduces back spans, minimizing both dilution and air blasts, and where applicable increases pillar stability by trapping pillars not being extracted. Open stope areas created by pillar extraction can reach up to 160’ in width, and at times exceed 300’ in length.. The CRF being placed is comprised of ROM (run of mine) rock with a maximum dimension of 3’, containing a 2% binder by weight of cement and fly ash. Doe Run has three CRF batch plants for producing binder slurry. One is on surface at the Fletcher Mine and two are underground at the Buick Mine. CRF is placed in 3’ lifts within the backfill areas, whose perimeters are delineated by fill fences. CRF placement continues in this matter until near the back, when one of two methods of topping off are utilized, one using a slinger truck and the other using a foam grout pump. Both methods leave the CRF in tight contact with the back. CRF has been placed, ranging in heights, from 16’ up to 70’. During fiscal 2006 over 500,000 short tons of CRF will be placed at Doe Run’s Buick and Fletcher mines.
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