The first metallurgical tests to evaluate the treatment response of Tampakan ore were carried out by WMC from 1994 through to 1998 using selected drill core samples. The WMC approach had been to test master composite samples nominally representative of the total orebody.

The ore was found to be generally amenable to beneficiation by means of froth flotation. The copper recovery varied directly with the ore grade, with a final copper recovery of 85% together with a gold recovery of 70% being predicted for an ore grade of 0.9% Cu and 0.3 g/t Au in the WMC Scoping Study prepared in 1997.

Indophil took a different direction with regard to the development of a metallurgical process. While the master composite approach taken by WMC may indicate an average orebody flotation response, it can also mask the variability which can be significant in an ore deposit the size of Tampakan. Indophil has therefore extended the metallurgical development at Tampakan by testing a full spectrum of ores covering a range of head assays and ore types, in order to identify the flotation response that would be experienced in practice as the ore feed changes over the life of the operation. While the basic WMC flotation regime was generally appropriate as an average condition, this Indophil testwork successfully extended and developed the process regime to accommodate the treatment of the full spectrum of ore types expected within the Tampakan deposit.

In excess of 300 flotation tests were completed by Indophil on samples of fresh ore obtained from the drilling campaign in a program that was designed to address the process design requirements of a Pre-Feasibility Study. The program includes confirmation of the optimum primary grind size, identification of the rougher and cleaner flotation response and a simulation of the anticipated operating response through a series of locked cycle flotation tests. The results confirmed that there is a general consistency in the metallurgical response between all the ore types present in the Tampakan deposit. A metallurgical response model was developed which shows that the copper recovery varies directly with the copper grade of the ore while the copper concentrate grade depends upon the ore mineralogy. The gold recovery to the flotation concentrate varies linearly with the copper recovery. At a head grade of 1% Cu, a copper recovery of 90% would be anticipated in an optimised operating plant with a corresponding gold recovery of circa 66%. The copper grade of the concentrate could vary from 30% Cu to 50% Cu, depending upon the ore mineralogy.

Perhaps one of the most significant elements in the Tampakan ore is arsenic which occurs in the copper-arsenic mineral enargite that is recovered together with other copper minerals in the sulphide flotation process. If the arsenic levels in the concentrate are too high then penalty charges are applied and/or marketing constraints arise. An Alkaline Sulphide Leach plant has been incorporated in the concentrator design to selectively leach the arsenic from the flotation concentrate when required. The disolved arsenic will then be precipitated as ferric asenate, a stable and environmentally acceptable product for safe disposal.

Xstrata has expanded the metallurgical program since taking management control to better understand the mineralogy and metallurgical response of the ore body. This has all confirmed that the ore responds well to simple conventional flotation.