In action underground: The state-of-the art rig working underground at the 1,225 m level.

Investment lengthens mine's life

Open pit mining was started at the Pyhäsalmi mine, which is part of the Outokumpu international metals group, in 1962. Underground operations came five years later and had reached a depth of 970 m by 1995.

Core drilling in 1998 revealed further zinc, copper and pyrite ore reserves of some 17 million tonnes - with the orebody extending to more than 1,400 m below the surface. Now investment of some FIM 300 million (around USD 50 million) to exploit these reserves is expected to lengthen the life of the mine to the year 2013.

Memory card

Playing a central role in the new operations is an Atlas Copco Diamec 264 APC (Automatic Performance Control) drill rig, equipped with greatly improved computerised capabilities. A new computer program helps to collect, store and act on data during the entire drilling operation.

The program supplies on-the-spot information about the drilling operation and rapid analysis of the geology to gain data on the rocks and strata being drilled.

This makes it possible to optimise the drilling parameters for different rock types and to test the drill bits being used. In addition, the stored data provide swift documentation of a particular drill hole and report its average values.

The APC Data Logging System (ADLS) is a measurement-while-drilling (MWD) operation which is totally integrated into the standard APC control system. ADLS is very easy to use - the operator simply inserts a memory card into a slot in the control panel, enters the hole depth and then drills.

Rapid analysis

After the hole is drilled, the card goes to the geologist for analysis by the Drill Analyser PC program, which has been designed specifically to analyse Diamec APC log files. The data are plotted as a series of graphs and are compiled as a drill report that is printed and saved on file.

Drilling parameters which can be analysed include penetration rate, bit force, water flow and pressure, rpm and system pressure as a function of hole depth or drilling time.

In a nutshell, the overall result is a rapid analysis of the geology which, while optimising drill parameters for different rocks and testing drill bits, can pinpoint and easily identify structural features such as homogenous rock and crack formations.

Longer life

The mine acquired the Diamec 264 APC drill rig last year to work alongside an older, manually operated Diamec 252 core drill. The APC uses wireline core drilling with an Atlas Copco XsafE 3 m-long core barrel (B size, 60 mm) taking a 42 mm core. KS impregnated bits for medium to hard rocks are being used.

APC drilling is giving longer life under these conditions - between 70-80 m compared to 50-60 m with conventional drilling. And Chief Mine Geologist Timo Mäki has noted that all drill operators preferred the APC rig to the older model.

Using APC, it can continue drilling in automatic mode through lunch breaks and shift changes and also improve bit life. In addition, with high rock stresses and the risk of rock bursts at depths in excess of 1,000 m, the data collected by the MWD system can be of considerable value in mine planning and operations - in the design of stopes, for example.

More valuable information on ore types is also made available to the metallurgist, enabling a reduction in the costly and time-consuming business of testing many ore samples in order to achieve a consistent blend for the grinding process.

Better rock analysis

Says Jyrki Korteniemi, Production Geologist at the Pyhäsalmi Mine: "The APC rig helps to provide a better analysis of the the rock. This means that, with the same drill bit, you can drill through different formations in the hole."

Production Geologist Jyrki Korteniemi at the Pyhäsalmi Mine. "Thanks to the APC rig, you can drill through different rock formations with the same drill bit."

The new computerised functions on the Atlas Copco Diamec APC drill rig are pointing the way towards more efficient and less costly drilling operations in the future. This text is based on an article written by Alan Kennedy in geoDrilling International magazine, December, 1999.