Using mill tailings to produce paste backfill is a relatively new technique. The most important way in which paste backfilling is beneficial is through mine reclamation and elimination of adverse environmental effects of the tailings. This article includes discussions on the effectiveness of different paste mixes with varying cement contents and slump values in a paste backfilling operation in a sulphide-rich environment at a copper-zinc underground mine in northeast Turkey. The chemical composition, mineralogy, specific gravity, particle size distribution, and the index theology tests have been presented. A total of 219 paste samples prepared from mill tailings (tailings samples T1 and T2) were tested at 3, 7, 28, 90, and 180 days for uniaxial compressive strength (UCS). The objective of the study was to determine the theological properties of the mill tailings with respect to paste production and determine the strength gain of the tailings with the addition of PKC (Portland composite cement)/B-type binder currently used in the pasteplant. Additionally, PKC/A-type binder was chosen to compare the tailings in terms of strength gain. It was found that for high sulphide bearing tailings, neither binder was effective or suitable to provide adequate long-term strength for paste backfilling operations, although paste backfill samples developed high early strength at 28 days of curing. Alternatives such as sulphate-resistant-based binders or desliming of the tailings should be investigated by additional tests for improving paste backfill strength performance. (C) 2004 Elsevier Ltd. All rights reserved.