PAGE 8 MARCH 2017 AUSTRALIA’S PAYDIRT T ailings retreatment is not a new con- cept and with reasonable commodity prices, the potential resources contained within tailings dams are gaining greater scrutiny as illustrated by some of the re- cent articles in John Chadwick’s Interna- tional Mining. More than one company has looked at trying to treat the tailings at Queensland’s Mount Morgan gold-copper mine that prematurely closed in July 1990 when a connecting wall between two tailings dams failed. One of the original tailings dams – Sandstone Gully – was being retreated by depositing its tailings (post retreatment), into the previous open pit. Many exploration companies have also unsuccessfully tried to find another Mount Morgan; after all its initial grades were beyond spectacular with discov- ery samples in 1882 reputedly assay- ing around 3,700oz/t (yes, ounces not grams, in metric grades around 113,120 g/t or 113 kg/t or around 11.3% gold), and ultra-high-grade gold ore shoots beneath the surface enhance- ment such as 300-471 oz/t (9.2-14.4 kg/t) be- tween the 315ft and 450ft levels when the shaft pillar at Grasstree was mined out in 1912. The copper content has often been the treat- ment issue at Mount Morgan, even the origi- nal tailings retreatment scheme (1982 to 1990) struggled with copper increasing the cyanide consumption and gold recoveries closer to 50%, but it still managed to achieve average cash costs of around $388/oz in FY1990. Carbine Resources Ltd now has con- trol of the project and the key difference to previous theoretical tailings projects at Mount Morgan is Carbine’s plans to derive revenue from copper and pyrite, while at the same time enhancing the re- covery of the main target – gold. Carbine intends to utilise an innovative simple solution that removes the copper first and produces saleable copper sul- phate to the local fertiliser industry. Then the pyrite is extracted and sold. Of course, recovering the copper first and deriving value from it is not new at Mount Morgan. Recovering copper from the water was applied when the mine first re-opened in the late 1920s, and aided the finance of the open-cut over the origi - nal flooded underground mine. And per- haps that is where the idea and concept of copper recovery from the water was first considered. The bulk of the orebody is pyrite, but not just any pyrite, instead it is capable of producing unroasted pyrite that has high-grade sulphur (more than 49.5%) with low impurities/deleterious miner- als (such as arsenic, mercury and lead), which could classify it as premium pyrite, at a time when the current main source of premium pyrite – First Quantum Minerals Ltd’s Pyhäsalmi mine in northern Finland – is expected to gradually close. Mount Morgan’s pyrite is also very dif- ferent in that it mostly does not oxidise or break down – even 20 or 30 years’ later it still looks freshly broken – possibly due to its silica/quartz content/association. The greyish lumps can be seen scat- tered throughout dumps and the mine property. Previous owners unsuccessfully at- tempted to sell Mount Morgan’s pyrite but since that period a premium pyrite category has evolved with applications in lithium batteries, stainless steel and grinding wheels, while higher sulphur pyrite may be blended with lower grades and find demand among the bulk sulphu- ric acid producers in China and Europe. Premium pyrite can sell on spot at more than $US200/t, although such prices may be based on what by-product credits the pyrite is carrying. Expressions of interest in Mount Morgan’s pyrite have been made at around $US60/t, because no track record of grades has been es- tablished. Pyhäsalmi has been selling its pyrite to China at around $US110/t, but this may be related to a historic long-term contract. The Pyhäsalmi mine’s pyrite orebody (with copper and zinc by-product cred- its) is coming to the end and is expected to close in 2019. Currently, it produces 800,000 tpa of premium pyrite of which 400,000 tpa goes to China, 100,000 tpa goes to Germany and 300,000 tpa is ap- parently used domestically in Finland. Tailings retreatment is under consid- eration after the Pyhäsalmi mine closes, and may be able to produce the 300,000 tpa required for domestic consumption. China currently only imports pyrite from two sources, the other being the Romanian Baia Mare mine stockpiles at a rate of 200,000 tpa. The Baia Mare mine closed four years ago and has been selling down its stockpiles, a process expected to finish this year. China’s im- ports were expected to increase to 800,000 tpa by 2020, although it has not been stated where it expects to source its re- quired pyrite from. After the pyrite has been extracted at Mount Morgan, gold dore is ex- pected to be produced from a standard CIL cir- cuit fed by sulphide and silicate leach streams. The tailings have been re-treated at varying stages of the mine’s life, as metallurgical processes to treat the orebody evolved and the mine’s orebody changed becom- ing increasingly copper-rich with depth (copper grades were ~11% to 12%) with 5cm to 8cm thick “seams” of chalco- pyrite. Some of the early tailings were based on gold recoveries of about 50% which resulted in tailings reputedly as- saying up to 5 oz/t gold that went into/ over the adjacent Dee River. The mine actually received tailings li- cences to deposit tailings over and into the river which apparently affects the riv- GOODE NEWS Tailings retreatment: The way of the future? “ Carbine expects to achieve a two- year payback from its Mount Morgan operation once it has been commissioned, with initial gold production of 40,000 ozpa at an AISC of less than $550/oz (ERA estimates infer that the average AISC could be closer to $450/oz). To continue reading, please go to www.paydirt.com.au/paydirt-digital
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PAGE 8 MARCH 2017 AUSTRALIA’S PAYDIRT
Tailings retreatment is not a new con-cept and with reasonable commodity
prices, the potential resources contained within tailings dams are gaining greater scrutiny as illustrated by some of the re-cent articles in John Chadwick’s Interna-tional Mining.
More than one company has looked at trying to treat the tailings at Queensland’s Mount Morgan gold-copper mine that prematurely closed in July 1990 when a connecting wall between two tailings dams failed. One of the original tailings dams – Sandstone Gully – was being retreated by depositing its tailings (post retreatment), into the previous open pit.
Many exploration companies have also unsuccessfully tried to find another Mount Morgan; after all its initial grades were beyond spectacular with discov-ery samples in 1882 reputedly assay-ing around 3,700oz/t (yes, ounces not grams, in metric grades around 113,120 g/t or 113 kg/t or around 11.3% gold), and ultra-high-grade gold ore shoots beneath the surface enhance-ment such as 300-471 oz/t (9.2-14.4 kg/t) be-tween the 315ft and 450ft levels when the shaft pillar at Grasstree was mined out in 1912.
The copper content has often been the treat-ment issue at Mount Morgan, even the origi-nal tailings retreatment scheme (1982 to 1990) struggled with copper increasing the cyanide consumption and gold recoveries closer to 50%, but it still managed to achieve average cash costs of around $388/oz in FY1990.
Carbine Resources Ltd now has con-trol of the project and the key difference to previous theoretical tailings projects at Mount Morgan is Carbine’s plans to derive revenue from copper and pyrite, while at the same time enhancing the re-covery of the main target – gold.
Carbine intends to utilise an innovative simple solution that removes the copper first and produces saleable copper sul-phate to the local fertiliser industry. Then the pyrite is extracted and sold.
Of course, recovering the copper first
and deriving value from it is not new at Mount Morgan. Recovering copper from the water was applied when the mine first re-opened in the late 1920s, and aided the finance of the open-cut over the origi-nal flooded underground mine. And per-haps that is where the idea and concept of copper recovery from the water was first considered.
The bulk of the orebody is pyrite, but not just any pyrite, instead it is capable of producing unroasted pyrite that has high-grade sulphur (more than 49.5%) with low impurities/deleterious miner-als (such as arsenic, mercury and lead), which could classify it as premium pyrite, at a time when the current main source of premium pyrite – First Quantum Minerals Ltd’s Pyhäsalmi mine in northern Finland – is expected to gradually close.
Mount Morgan’s pyrite is also very dif-ferent in that it mostly does not oxidise or break down – even 20 or 30 years’ later it still looks freshly broken – possibly due to its silica/quartz content/association.
The greyish lumps can be seen scat-tered throughout dumps and the mine property.
Previous owners unsuccessfully at-tempted to sell Mount Morgan’s pyrite but since that period a premium pyrite category has evolved with applications in lithium batteries, stainless steel and grinding wheels, while higher sulphur pyrite may be blended with lower grades and find demand among the bulk sulphu-ric acid producers in China and Europe.
Premium pyrite can sell on spot at more than $US200/t, although such prices may be based on what by-product credits the pyrite is carrying. Expressions of interest in Mount Morgan’s pyrite have
been made at around $US60/t, because no track record of grades has been es-tablished. Pyhäsalmi has been selling its pyrite to China at around $US110/t, but this may be related to a historic long-term contract.
The Pyhäsalmi mine’s pyrite orebody (with copper and zinc by-product cred-its) is coming to the end and is expected to close in 2019. Currently, it produces 800,000 tpa of premium pyrite of which 400,000 tpa goes to China, 100,000 tpa goes to Germany and 300,000 tpa is ap-parently used domestically in Finland.
Tailings retreatment is under consid-eration after the Pyhäsalmi mine closes, and may be able to produce the 300,000 tpa required for domestic consumption.
China currently only imports pyrite from two sources, the other being the Romanian Baia Mare mine stockpiles at a rate of 200,000 tpa. The Baia Mare mine closed four years ago and has been selling down its stockpiles, a process expected to finish this year. China’s im-
ports were expected to increase to 800,000 tpa by 2020, although it has not been stated where it expects to source its re-quired pyrite from.
After the pyrite has been extracted at Mount Morgan, gold dore is ex-pected to be produced from a standard CIL cir-cuit fed by sulphide and silicate leach streams.
The tailings have been re-treated at varying
stages of the mine’s life, as metallurgical processes to treat the orebody evolved and the mine’s orebody changed becom-ing increasingly copper-rich with depth (copper grades were ~11% to 12%) with 5cm to 8cm thick “seams” of chalco-pyrite. Some of the early tailings were based on gold recoveries of about 50% which resulted in tailings reputedly as-saying up to 5 oz/t gold that went into/over the adjacent Dee River.
The mine actually received tailings li-cences to deposit tailings over and into the river which apparently affects the riv-
GOODE NEWS
Tailings retreatment: The way of the future?
“Carbine expects to achieve a two-year payback from its Mount Morgan
operation once it has been commissioned, with initial gold production of 40,000 ozpa
at an AISC of less than $550/oz (ERA estimates infer that the average AISC could
be closer to $450/oz).
To continue reading, please go towww.paydirt.com.au/paydirt-digital
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