Asanko’s Nkran gold mine achieves 100% reconciliation through blast movement monitoring

Asanko’s Nkran gold mine achieves 100% reconciliation through blast movement monitoring

Asanko-Nkran-pit-post-blast-heave

Commodity Ore Grade Geology Powder Factor Flitches Location
Gold high* Structural 0.6 kg/m3 2 Africa

 

Asanko Gold’s Nkran mine, located in Ghana, is an open pit operation in the Kumasi Basin.
  • Mineralisation is shear-hosted in a sedimentary basin with Granitic intrusions
  • Blasts are fired in six-metre (20 ft) benches and mined in two flitches (3 m)
  • A proven reserve of 4.4 Mt at 1.85 g/t gold, the site contains high grade ores (up to 2.0 g/t)

Challenges

Ore loss and dilution negatively impacted mill feed ore grade and ounces
  • Ounces produced vs reserve model reconciliation was 18% below target
  • Mill feed ore grade was 10% below reserve model expectation
  • Blast movement, causing ore loss and dilution, was considered to be contributing factor

Solution

The BMM System accurately measured blast movement and translated post-blast dig lines
  • Blast movement monitors (BMMs) were installed in monitoring holes throughout the shot
  • Installation and detection as per site standard operating procedures
  • BMM System calculated new dig lines for each flitch, and areas of ore loss and dilution that would have occurred without monitoring

Results

100% reconciliation for ore grade and ounces produced
By accurately accounting for ore movement in production blasts, Nkran mine has achieved significant reserve model reconciliation improvements:
  • Mill feed ore grade reconciliation variance of 102% (vs 88% over the previous period)
  • Ounces produced variance of 100% (vs 96%)
Following is an example blast from Nkran that quantifies blast movement and additional value.
  • Measured horizontal blast movement ranged from 1.5 to 11.6 m (5 to 38 ft) and vertical movement was up to 9.8 m (32 ft)
In this blast, the mine site added US$237,000 of value.
  • Maximized ore yield—recovered 2,800** tonnes of additional ore at a value of US$137,000***
  • Reduced dilution—diverted 5,500 tonnes of waste from the mill, avoiding US$100,000**** of milling costs
* Average grade of ore polygons
** Numbers are rounded
*** Calculated at a gold price of US$1,250/oz
**** Based on milling costs of $18 per tonne
Accounting for blast movement added US$237,000 of value—in one blast
Asanko-Nkran-Top-flitch
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