The Obduro AP Coated OMEGA-BOLT^®: Load-bearing Capacity in highly acidic Environments

Barrick Gold Corporation is one of the world’s largest gold producers operating gold, silver and copper mines on four continents. The Goldstrike mining complex, which is also operated by Barrick, is located on the Carlin Trend, one of the most abundant gold deposits in the USA approx. 60km south-west of the town of Elko in Nevada. This is also where the Rodeo Mine, an extension of the Goldstrike Complex, is located.

Because of the highly corrosive environment at both the Goldstrike Complex and the Rodeo Mine, Barrick approached DSI for a solution. The aggressive environment had largely dissolved the previously installed mesh after only 6 days. A competitor’s rock bolt with acid resistant coating could be pulled out by hand after only 30 days and was greatly damaged.

Barrick mining Engineers provided DSI with underground water samples from these mines, both of which were highly acidic and electronegative at pH values around 1.5. For 72 days, DSI tested OMEGA-BOLT^® samples with a special Obduro AP Coating in the first solution with a pH value of 1.5 – this contained, but was not limited to a sulfuric acid concentration of 14%. In contrast to the competitor’s product, which began to corrode after one day, the Obduro AP coated OMEGA-BOLT^® did not show any reaction at all to the highly acidic sample.

The second sample solution contained pH levels of 1.8, had other acids in addition to a sulfuric acid concentration of 13% and was highly electronegative. The Obduro AP Coating did not show any reaction after 15 days in the second sample solution. Even a fully coated washer that sat in the solution for 400 days did not show any damage at all. In contrast to this, the competitor’s bolt that was tested reacted violently with the second mine sample only a few minutes after exposure.

The tests were conclusive and clearly demonstrated that the competitor’s product does not protect the bolt against acid corrosion. In contrast, DSI’s Obduro AP Coating withstood tests that were even more severe. The coating was neither damaged by sulfuric acid with a pH value of 0.3 at a concentration of up to 93%, nor did it show any reaction to hydrochloric acid with a pH value of 0.7 and a concentration of up to 70%. Acid solutions with concentrations above 30% are very rare in nature.

In co-operation with the mine operator, DSI installed 12 Obduro AP coated OMEGA-BOLT^® Rock Bolts alongside the competitor’s coated rock bolts in the mine. 30 days after installation, tests were carried out. The tests were completed using DSI’s equipment - an Enerpac RCH 302 cylinder. All of the pull tests performed were carried out with the required load of 12t. All of the competitor’s rock bolts pulled out by hand and were strongly corroded, whereas all of the Obduro AP coated OMEGA-BOLT^® Rock Bolts successfully passed the tests.

During the 90 day test, DSI also cored out the area around one of the bolts. The OMEGA-BOLT^® was absolutely coated in acid solution buildup, but the bolt had no surface damage, and due to the high abrasive strength of the coating, the point anchoring locations along the bolt did not cut through the coating to the steel.

Before the tests, Barrick had to install new bolts in both mines every 30 – 90 days. The coated OMEGA-BOLT^® Rock Bolts that were installed following the tests only require biannual tests. DSI has color coated the bolts so that the mine personnel know instantly when they were installed.

Since the successful conclusion of the test program, DSI has supplied 209,000 OMEGA-BOLT^® Rock Bolts and washers with Obduro AP Coating to the Goldstrike Complex and the Rodeo Mine so that the operator has been able to significantly reduce inspection and rehabilitation work.

The greatest technical challenge during the development of the Obduro AP Coating was to develop a coating that could adapt its shape to the shape of the OMEGA-BOLT^® that was to be installed in the Barrick Mines: The welded and crimped bolt expands during installation. In addition, the coating had to have a high abrasive strength, allowing the coating to withstand the pull tests with loads of 12t without suffering any damage. The Obduro Coating is an extremely high-capacity coating and has resisted all acid environments it has been exposed to up to today.