Antimony
High-grade gold mineralization along the Blue Spec Shear (and the Red Ribbon Shear) is variously associated with the presence of antimony (in its sulphide form of stibnite). In production, as part of the process for extracting gold from the auro-stibnite (gold-antimony) ore, antimony concentrate can be produced.
The price for antimony metal is currently at a 20 year high ranging between US$5000-6000 per tonne and as a result, the production of antimony concentrate as a by-product of gold production has the potential to be a valuable source of additional revenue for the Blue Spec Shear Project.
There is currently robust demand for antimony concentrate from a number of Chinese and Indian smelters as a result of historically low stockpiles of antimony concentrates. Northwest has had preliminary discussions with a number of parties interested in securing rights with respect to Northwest’s prospective antimony by-production from the Blue Spec Shear Project.
What is antimony
Antimony (Sb) is a silvery brittle metalloid which has wide variety of both industrial and domestic applications and is present in many products in everyday use
Antimony ores are processed to produce antimony concentrates which typically grade between 40-60% antimony. The concentrates are then smelted to produce antimony metal (99.9% antimony) which can be subsequently converted simply into antimony trioxide which commands a price premium to antimony metal.
Non-metallurgical markets for antimony (antimony trioxide) include flame retardants, PET catalysts for the PET containers, glass, ceramics. Minor non-metallurgical markets include rubber, ammunition, fireworks, pharmaceuticals, pesticides and fluorescent light bulbs.
Metallurgical markets for antimony (antimony metal) include lead-acid batteries and lead and copper alloys. Antimony metal is also increasingly being used by the electronics industry in the production of semiconductors, diodes, infra-red detectors and Hall-effect devices. A newly discovered alloy of antimony and tellurium has been developed by Intel and Philips in the production of phase-change memory chips to replace the flash memory chips used in cameras, phones and computers.
Value to Northwest
Past production and current drilling results from the Blue Spec Shear indicate that the auro-stibnite (gold-antimony) ore from the shear variably grades between 2-4% antimony with higher grades of antimony associated with higher grades of gold. The antimony concentrate produced during previous treatment of Blue Spec Shear ore graded approximately 60% antimony with very low impurities.
Based on the high quality of Blue Spec Shear antimony concentrate, Northwest would expect to receive around 35% of the antimony metal price for its concentrates (around US$1,800 per tonne based on an antimony metal price of US$5,000 per tonne).
Northwest will evaluate the economics of producing a higher value antimony metal from antimony concentrate by employing conventional electrowinning of the antimony concentrate in the treatment process. The outcome of such an evaluation will largely depend upon the Blue Spec Shear gold project’s ultimate mineral resource, incremental capital expenditure and the relative revenues from producing a concentrate and metal.
Antimony price
Antimony prices have risen from a 40 year low of around US$1,000 per tonne in August 2001 to the US$5-6000 level in 2008. Antimony prices are quoted daily in the Australian Financial Review.
A number of factors not present during past buoyant price periods indicate that the recovery will endure. China is now the largest importer of antimony ores and concentrates and its own domestic demand has also become the world’s largest.
Analysts expect antimony prices to rise to US$6,000 per tonne and to remain at or around this level to 2010.
World supply and demand
China has historically been the largest producer of antimony. However, decades of unregulated mining practices have resulted in Chinese resources, primarily located in the Nandan province, being exhausted through over-exploitation, high-grading and damage to mine workings in particular through flooding.
In addition, wide ranging policy reforms by the Chinese government aimed at resource conservation, orderly development, mine safety, environmental protection and value-added further processing, all controlled by quotas and licensing of mining, smelting and exporting have combined to reduce production and exports.
World consumption of antimony has increased significantly over the last 20 years, a trend which is set to continue.
Flame retardants account for about 70% of primary antimony demand and 90% of the demand for antimony trioxide. More stringent flammability standards and safety legislation, together with increased demand for plastics and IT-related products, will result in higher demand for flame-retardants. World demand for antimony trioxide in this market is forecast to rise by 7.5% annually from an estimated 106,000 tonnes in 2004 to 152,000 tonnes by 2009.
PET catalysts provide a further area of growth for antimony trioxide, with growth again concentrated in new industrialising countries where markets for PET containers for carbonated soft drinks, beer and mineral water are less mature. Asian demand for bottle-grade PET is forecast to grow at over 10% per year to the end of the decade.
In addition, the growing demand for digital household appliances has resulted in increased sales of antimony metal for semiconductors and electronic components.
Impact on ore processing
The metallurgy and processing of auro-stibnite ores (gold-antimony ores) is well understood and the presence of antimony will not materially affect gold recoveries from the treatment of Blue Spec Shear ore.
This is demonstrated by the recovery rate for gold from the most recent processing of ore from the Golden Spec deposit which ranged between 89-91%. Northwest expects recoveries to exceed 90% for gold and 60% for antimony in concentrate (in line with average industry recovery rates for antimony) in production from the project.
Auro-stibnite ore can be treated with a conventional process flow comprising gravity gold recovery, flotation of antimony to a bulk concentrate and sequential leaching of gold and antimony. An additional step of electrowinning both the gold and antimony concentrate results in even higher recoveries and produces a higher-value antimony metal rather than an antimony concentrate.
Please follow this link for more information on Metallurgy and Processing .
Links for more information on antimony
Roskill Information Services: The Economics of Antimony (Tenth Edition)
United States Geological Survey: Antimony statistics and information
China Antimony Chemicals Co Limited: Market news
Chemico Chemicals Pvt. Ltd: Indian smelter group
Page last updated: 04.03.2008
