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From: Nigel
ArtDate: 5th October 2006
Section: (FILLYABOOTS NEWS RELEASES)
Remote Name: 87.74.115.61
Date: 10/10/06
Time: 22:55
5th October 2006
Tianshan Goldfields Ltd Announces Gold Mountain Heap Leach Amenability Confirmed
News Item - Conduit PR
Tianshan is pleased to release metallurgical studies for the Gold Mountain Project.
Initial metallurgical tests on core found gold is freely leachable and is non refractory. Leach extractions from -75 micron milled ores range between 72-100% for the oxide types (average 88%) and 17-100% for the non oxide samples (average 65%). Comprehensive sampling of 14,000 tonne heap leach at Yelmand confirms Yelmand deposit is amenable to heap leaching. Metallurgical Studies
Two metallurgical studies have been completed. One based on leach testing of drill core samples, and a second on the heap leach residue and Run of Mine ore from the 20022003 leaching operation undertaken at Yelmand by Chinese partners.
Leach Testing Core Samples
A set of 66 samples from Yelmand, Jinxi and Mayituobi deposits, consisting of one metre intervals of coarsely crushed half-core (-4mm) and their corresponding milled assay sample pulps (-75 micron) were subject to leach tests.
Gold fire assays averaged 2.86g/t Au across all samples and all assay laboratories ranging from 0.5 to 17.2g/t Au; this average is considered higher than average grade of the resource, but it was seen from the results that gold dissolution is not sensitive to gold grade, with the yield increasing as gold grade increases.
Gold was found to be very amenable to recovery by leaching from the Gold Mountain ores. Leach extractions from -75 micron milled ores range between 72-100% for the oxide types (average 88%) and 17-100% for the non oxide samples (average 65%). This clearly demonstrates that gold is freely leachable and is non refractory.
The leach extractions from crushed (-4.75mm) core samples average 57% for oxide samples and 46% for non oxide samples. These results are very encouraging for three day leaches, considering leach times in practice for heap leach operations are typically 180 days, and this shows the potential for rapid heap leach kinetics.
Correlation of gold dissolution with minor elements such as mercury (Hg) and arsenic (As) is shown to be negligible, indicating that these elements have low relevance to the gold deportment and recovery.
Analysis of the leach data in conjunction with the geological and mineralogical features of the cores indicate the textural and permeability features, such as degree of brecciation and re-brecciation, vugginess, porosity, and silicification, can provide mineralogical pointers to heap leach permeability that can now be ascertained from core logging data.
Yelmand Leach Pad Study
A work programme conducted by the Company sampled and assessed a small scale heap leach that was operating on the Yelmand deposit in 2002-2003. The heap leach pad was constructed, operated and decommissioned by the former joint venture partners over the period May 2002 to October 2003, processing some 14,000 tonne of mixed oxide and non oxide ore grading an average 2.4g/t Au. It is reported that over 16kg of gold was produced, representing a recovery of 50% compared with 60% obtained in prior test work undertaken at Arxi Gold Mine laboratory.
Comprehensive sampling of the leached heap by section with a dozer showed the unleached material assayed a total gold grade of 1.14g/t Au. Further leaching of samples removed from the heap showed a further 0.76g/t Au was cyanide leachable under optimal conditions, corresponding to 78% recovery.
Four bulk composite samples were taken at different height intervals across the sections of the heap, and sent to the SGS laboratory in Tianjin, China for size-by-size gold assays. Gold by fire assay was carried out at SGS Tianjin, and bulk leach extractable gold (BLEG) assays were done on sub samples of the size fractions at SGS Welshpool in Perth, Australia.
The bulk composite samples made up from the multiple samples taken across the entire section and base of the spent heap were used to generate a leach profile for the heap and to enable calculation of actual and potential heap leach efficiencies.
Assays for the +25mm fractions (making up some 25% of the mass in the heap) are consistently higher in gold content, indicating that a finer crush size and improved control of the crushing operation would have increased the gold recovery from the operation. Leaching of the milled (-75 micron) and crushed (-1mm) fractions gave similar soluble gold results to each other, indicating that a terminal heap residue of 0.75g/t Au could be achieved from the head grade of 2.4g/t Au an extraction of 68%.
Gold assays and leach tests on the various size fractions contained within the bulk composite samples from the heap showed that the gold is finely disseminated, and follows the mass distribution. Leaching of the individual size fractions at 1mm crush size and milled -75 micron confirmed that further gold could be extracted with efficient crushing and an extended leaching period conforming to normal practice.
Some 100kg in total of samples comprising both oxide and non oxide ore types were taken for testing from the faces that were mined during the heap leach operation. These ore samples were leached to provide an overall comparison with the ore originally placed onto the heap leach operation.
Head assays of the oxide and non oxide ore samples from the mined faces are 2.23g/t Au and 2.52g/t Au respectively, which are comparable to the 2.4g/t Au reported for the head grade of the heap.
Similar recoveries were obtained for the non oxide ore both crushed to -1mm and milled to -75 micron. The oxide ore showed a more marked response to milling, with 97% leach recoveries evident from milled material.
The average leach efficiency of the 1mm crushed samples was similar to the calculated terminal leach efficiency from the Yelmand heap.
Future Work
The next phase of metallurgical work is in progress, and sources further samples from each deposit, still maintaining the oxide/non oxide distinction, but selected so that the average grade for each type is 0.8 to 1.0g/t Au. The work will focus on determining the cyanide soluble component of composites across the various deposits to more fully map the leach variability and characterisation across the project. Crushed core samples will then be subjected to column leach testing.
For further information, please contact:
Keith Liddell Tianshan Goldfields Limited +61 8 9221 7466
Dave Evans Tianshan Goldfields Limited +27 83 301 6016
David Youngman WH Ireland Limited +44 161 832 2174
Leesa Peters / Jos Simson ConduitPR +442074296666
Jos Simson Conduit PR Ltd 76 Cannon St EC4N 6AE Office: +44 (0) 20 7429 6666 Direct: +44 (0) 20 7429 6603 Fax: +44 (0) 20 7429 6699 Mob: +44 (0) 789 987 0450
www.conduitpr.com
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