The Arghash gold ore sample treatment

Abstract

The Arghash gold deposit includes two oxidized and sulfide zones. In this work, separate samples from mineralogical zones and drilling cores of both oxidized and sulfide zones were taken, in which the gold head grades were 2.5ppm and 0.8ppm, respectively. Microscopic studies of polished and thin sections of the samples showed that the Arghash mineralization was simple and composed of pyrite, iron oxide and hydroxide. To process the Arghash oxidized sample, the gravity separation treatment with a jig and shaking table were employed and different experiments were performed. The results obtained from these experiments were not acceptable as the gold particles were disseminated in fine sizes. The grade of the gold in the jig concentrate using feed size fractions of -2360+500 microns was 3.4ppm and in the shaking table using two feed size fractions of -500+75 and -300+75 microns was 3.8ppm and 2.4ppm respectively. The gold recovery in the jig test was 34% and for the shaking table test were 20.7% and 25.88% for the two size fractions. Because of the very low recovery obtained from gravity concentrations, cyanidation tests were carried out using an oxidized sample. Based on these experiments, the optimum value for size (d80), cyanide concentration, pH and cyanidation time were determined as 75 microns, 1000ppm, 10.5 and 24 hours, respectively, which yielded 90% recovery. The sulfide sample was used in the cyanidation process. The recovery of direct cyanidation on the sulfide sample was relatively low (about 66%); therefore, the sulfide zone of Arghash belongs to the "refractory gold" type. Thus as pretreatment, the sulfide part of the sample was separated by flotation. The optimum parameters for separation including the feed size (80% passing), collector dosage, frother dosage, pulp density and conditioning time were defined as 74 microns, 100g/t, 40g/t, 30% and 5 minutes, respectively. Roasting and ultrafine grinding procedures were also used for the sample pretreatment. The cyanidation test was then done using a flotation tail and roasted and very fine ground flotation concentrate. The maximum gold recovery (approximately 90%) was obtained by cyanidation of the roasted flotation concentrate.