In the present paper, influence of a lignin-based biopolymer in improving gold and silver recoveries during cyanidation leaching is discussed. Series of laboratory cyanidation leaching testworks at the absences and the presences of the biopolymer were performed under variations of the biopolymer concentration, NaCN concentration, slurry density and particle size distribution. The ore samples used were from Pongkor Gold Mine of PT. Antam, Tbk. in Indonesia. The biopolymer additive was found to reduce slurry viscosity that leads to a higher dissolved oxygen concentration in the leach solution. The testwork results show that the use of biopolymer improves gold and silver recoveries as well as leaching kinetics. At biopolymer dosage of 800 mg/L, the increases of gold and silver recoveries were 4.5% and 6.4%, respectively. The lignin-based biopolymer is able to disperse fine solid particles and stabilizes the ore suspension in the leach-slurry that results in a better contact between the ore and the leaching agents. The effect of biopolymer on the gold and silver recoveries was found to be more significant at lower cyanide dosages. The addition of biopolymer resulted in the increase of cyanide consumption, lowering final pH and higher dissolved iron which is associated with gold-bearing pyrite dissolution. Enhanced dissolution of gold-bearing pyrite at higher dissolved oxygen concentration was found as the major factor that improves gold recovery at the presences of the biopolymer in addition to lowering slurry viscosity that leads to higher dissolved oxygen concentration and effect of fine particles dispersion. (C) 2015 Elsevier Ltd. All rights reserved.