Column leach metallurgical tests prove good gold extractions on coarse-sized ore fractions to over 89% with recoveries still increasing when experiment was stopped at 70-days
TORONTO, Ontario, March 17, 2010 – Lydian International Ltd. (TSX: LYD) (“Lydian” or “the Company”), a diversified mineral exploration and development company, today announced the results of its 2009 metallurgical test work from its 95% owned Amulsar gold discovery in Armenia.
As part of the experiment, column leach tests on three different 19mm ore composites returned gold extractions of 89.1%, 88.6% and 76.5% over a 70 day leach period but with recovery trajectories indicating gold was still being extracted in all composites with two of them likely to exceed 90% extractions after a short period of further leaching (Figure 1 and Table 1). 140 days column leach tests on 38mm ore fractions produce similar recoveries, but over longer time periods.
Figure 1. Gold recovery profiles by column leach tests on three different composites for -19mm fraction
Table 1. Gold recovery results by column leach tests on 3 different composites at different times for -19mm fraction
The column leach tests are part of heap leach amenability test work in 2009 carried out by SGS Minerals Services UK Ltd. The test work includes the column leach tests and previously reported bottle roll tests on three different ore composites at different size fractions. The bottle roll tests applied to the same composite materials returned gold extractions in excess of 89% over a 14-day test period (Tables 2 and 3), with high levels of gold extraction reaching a minimum of 80% recovery of gold to leachate after 24-48 hours (press release November 3rd 2009)
Table 2. Gold recovery results by bottle roll tests on 3 different composites at different size fractions
The variation of gold recovery values are related to permeability differences as a function of grain size and lithology where solutions may infiltrate more slowly in homogeneous rock types leaving a residue of fine gold in the deeper levels of the mineral matrix. The permeability related leach kinetics are confirmed by gold assays of the residues at different height levels in the column confirming that the gold is least recovered in the coarsest fractions of every experiment, i.e. larger than 15mm in the -19mm experiments and larger than 25mm in the -38mm experiments.
The recovery grades reported for the column leach tests have been based on the back-calculated head assays to ensure that they are the most conservative values. This is due to the presence of small discrepancies between head grade gold assays and back-calculated gold values resulting from physical sampling errors propagated by the splitting of coarse, low-grade material.
Table 3. Back-calculated gold head assays for all tests
“We are pleased with these results which imply recoveries of around 90% and a low-cost gold leaching operation at Amulsar”, said Tim Coughlin, Lydian’s President and CEO. “Cheap processing is of course very important for bulk tonnage operations. Further column leach experimental work will be completed this year to test different parts of the expanding resource and to test recoveries from newly identified prospect areas such as Erato where we drilled 229m at 1g/t gold in the last hole of the 2009 drilling season. The next stage will be to simulate a run of-mine leaching operation which does not require crushing and can amount to cost savings in the orderof 20%. Preparations are now well underway for the 2010 drilling program which is due to start with three rigs operating on June 1st”
The 2009 test work followed an initial gold recovery test program conducted at SGS Lakefield in 2008 (press release August 13, 2008). Heap leach simulations in 2008 already indicated that the ore is highly amenable to heap leaching. Whole ore gold recoveries on half and quarter inch crush bulk samples reported to be 95-97%.
Two meter high columns were loaded with approximately 50 kilograms of ore at the two different top size fractions. Gold recovery was monitored on a weekly basis by calculating the extracted gold against the head grade of the start sample. At the end of the experiment period the column required a further 48 hours of washing with a barren solution to capture any residual gold after which the columns were dismantled and residues were dried, screened for gold and silver by size and depth, and assayed for every half meter interval of the column. The gold in residue assays were subsequently used to calibrate the final extraction percentage.
The three master composites of half drill core samples in the 2009 program were selected prior to the 2009 drilling and come from different mineralized zones of the Tigranes and Artavasdes resource areas. The composites are differentiated by rock type, alteration style, and gold and multi-element distribution. The three composites have head grades ranging from 1.09 to 1.29 g/t gold (Table 4).
* estimated in the resource model prior to the 2009 drilling
Table 4. Rock type, gold head grade and representivity of the three different composites used for column leach and bottle roll tests
As reported previously, metallic screens of the composites show that >98% of the gold has a size fraction less than 106 microns (Table 5). The results confirm the observations made in previous work indicating that a gravity concentration step is not warranted with no significant coarse gold component present.
The host rock of the ore in the three composites is either porphyritic andesite related to the domal intrusions, mineralized at its margins and in cross-cutting structures (Composite A), or undifferentiated volcanoclastic breccias which are part of the sequence in which the domal andesite was emplaced (Composite B), or again represents the contact zone with is composed of a combination of porphyritic andesite and volcanoclastics (Composite C). Resource modeling prior to the 2009 drilling estimated that the composites A and B represent approximately half and one third of the pre-2009 ore volume.
All rock types have been altered to a massive silica rock (80 to 90% quartz) with variable contents of alunite and remnant feldspar. Semi-quantitative X-ray diffraction results show that composite B contains the lowest concentrations of alunite, 2%, followed by composite C, 3.7%, and Composite A, 5.3%, probably related to the transformation of more abundant feldspar phenocrysts in the andesite. Goethite and hematite are present in all three ore types and demonstrate the oxidation of the original iron-sulphides that introduced the gold. The X-ray diffraction results and chemical head analyses demonstrate that iron-oxides are most abundant in composite A, followed by composite C and B with a presence of approximately 9%, 6%, and 5% of goethite and hematite combined respectively. Silver, copper, and sulphur concentrations are low in all composites (Table 5), as well as concentrations of arsenic and antimony (less than 0.02%), or bismuth (less than 0.009 %).
Table 5. Chemical head grades and gold metallic screen results of the 3 different composites used for column leach and bottle roll tests
About Lydian International
Lydian is a diversified mineral exploration and development company with expertise employing “first mover” strategies in emerging exploration environments. Currently Lydian is focused on Eastern Europe developing advanced precious and base metal assets in Armenia and in Kosovo (under UNSCR 1244). The two main projects are gold at Amulsar in Armenia, and zinc, lead, silver and gold at Drazhnje in Kosovo. The Amulsar group of licenses is 95% owned by Lydian’s wholly owned Armenian subsidiary (Geoteam CJSC). Lydian also has a pipeline of promising gold and base metal exploration projects in the Balkans and Caucasus regions.
Lydian’s management team has a track record of success in grassroots discovery, in acquiring and developing undervalued assets, and in building companies. Lydian has a strong social agenda and a unique understanding of the complex social and political issues that characterise emerging environments. The Company’s three largest shareholders are the International Finance Corporation (IFC), a member of the World Bank Group, Newmont Mineral Holdings B.V. (owned by Newmont Mining Corporation), and the European Bank for Reconstruction and Development (EBRD). More information can be found on Lydian’s web site at www.lydianinternational.co.uk.
Dr Tim Coughlin, MAusIMM; is the Qualified Person overseeing Lydian's exploration programs. Dr. Coughlin has supervised the preparation of the technical information contained in this press release. Lydian employees are instructed to follow standard operating and quality assurance procedures intended to ensure that all sampling techniques and sample results meet international reporting standards. Please see Lydian’s web site for more information.
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