Düşük Tenörlü Altın Cevherinin Zenginleştirmesinde Mineralojinin Etkisinin İncelenmesi

Abstract

Refractory gold-type ores are the mineralization where low gold recovery is obtained when subjected to direct cyanide leaching. In particular, the presence of gold in the lattice structure of sulfide/oxide minerals and very fine grains cause refractoriness. Such ores may require some pre-treatment before they can be beneficiated by cyanide leaching. Nowadays, especially for refractory gold with sulphide minerals, the bulk flotation method is becoming highly preferable considering the cost of pretreatments and the environmental impacts of cyanide. Within the scope of this thesis, detailed mineralogical characterization of samples taken from an ore deposit located in the Kırşehir massive was carried out and the gravity and flotation beneficiation behavior of the ore was investigated after the detection of gold-bearing mineralization. According to the mineralogical characterization of representative drill core samples, the ore deposit was divided into three different zones such as sulphide, transition, and oxide. In the zones, quartz and feldspar were identified as the major minerals and pyrite was the main sulphide mineral in the sulphide and transition zones. In these two zones, it was determined that the native gold was completely locked with pyrite mineral, while in the oxide zone, gold was found to be submicroscopic in size and was found associated with iron oxide minerals. In addition to mineralogy, the degree of oxidation and chemical composition of all three zones were also examined. Accordingly, it was determined that the surface oxidation of the sulfide, transition and oxide zones was low, and the Au contents were 1.13 g/t, 0.71 g/t and 0.76 g/t, respectively. Bottle-roll tests were carried out to characterize the refractoriness of the gold deposit and the average Au recovery values for the sulphide, transition and oxide zones were 38.3%, 39.6% and 56.5%, respectively. The low dissolution values, supported by the findings of mineralogical interlocking, submicroscopic occurrence and low Au content, indicate that the ore deposit can be classified as refractory. Since gold was associated with iron oxide minerals in the oxide zone, shaking table test was performed only for this zone and although gold was recovered in the concentrate with a grade of 25.9 g/t and a recovery of 52.7%, it was revealed that shaking table test alone was not sufficient due to the absence of free gold in the coarse size and the loss of 21% of the gold in the submicroscopic size with the slime fraction. The flotation method was applied under different conditions for all three zones and the results obtained were evaluated in terms of gold recovery and grade. Bulk sulfide flotation was applied for the sulfide and transition zones since the gold bearing mineral was pyrite, and flotation conditions for the oxide zone were applied for the flotation of iron oxide minerals. Different types of collectors and their synergistic effects were also investigated. According to the results, the highest gold recovery in the sulfide and transition zones could be obtained when using the Aero 8045 collector with 97% recovery, 5.7 g/t grade and 86.7% recovery, 5.4 g/t grade, respectively. According to the flotation test performed in the oxide zone using Aero 825, the recovery is 27% and the grade is 0.9 g/t. Since the sulfide and transition zones are mineralogically like each other, Blend1 sample was prepared by mixing them in proportion to their reserve ratios and another Blend2 sample was formed by mixing all zones and their flotation behavior was investigated. Accordingly, the Au recovery values for Blend1 and Blend2 were 90.9% and 89.2% for tests with KAX+Aero 407 and 95.3% and 60.6% for tests with Aero 8045, respectively. While Au grade was 8 g/t in Blend1 open circuit cleaning flotation, the highest cleaning efficiency was achieved with Aero 8045 with 50.7%. From these results, it is determined that the sulphide and transition zone can be processed together and should not be blended with the oxide zone. For the oxide zone, more detailed characterization studies are required for the gold.