1525
The Geopyörä Index: A New Instrument for Assessing
Comminution and Rock Strength Parameters
Marcos de Paiva Bueno, Thiago Almeida, Leonardo Lara, Malcolm Powell
Geopyörä Oy, Pirrakatu 1, Oulu, Finland
ABSTRACT: The product of the A and b parameters (i.e., Axb), which are obtained through curve fitting to
drop weight test (DWT) data, has long been regarded as a fundamental metric for evaluating ore resistance to
impact breakage. This parameter also serves as the foundation for calculating the SMC test drop weight index
(DWI), a key indicator of rock strength, that in combination with the Bond ball mill work index (BWI), is
widely used in comminution modelling to predict the overall specific energy requirements of AG/SAG and ball
mills, HPGRs and Crushers.
The conventional process of fitting the A and b parameters to DWT data is complex, requiring multiple data
points and considerable effort to achieve an acceptable fit. In this paper, we present the Geopyörä Index, which
bypasses conventional practices by offering a simple formula that obviates the need for curve fitting and provides
a direct and efficient means of estimating comminution parameters.
Since the Geopyörä Breakage test utilizes a principle of controlled degree of crushing, with applied breakage
energy being a response rather than an input, the direct measurement of this response turns out to be the ideal
metric for the development of a new way to assess rock strength, being incorporated into the calculation of a
new index. Over 200 samples have been tested, proving that the Geopyörä Index can not only effectively and
accurately estimate the parameters of conventional tests, but also provide a direct measure of rock strength in
its own right.
INTRODUCTION
Aiming to improve orebody characterization, the Geopyörä
breakage test brings a solution to the industry’s current
challenges by being a fast and low-cost test that requires
a minimal quantity of material, and that measures energy
and force for every particle (Bueno et al 2021). This test
can deliver a set of the industry standard parameters of ore
characterization, but the main goal is to populate precise
orebody models that predict process performance with a
high degree of accuracy (Chavez 2020). The Geopyörä
test achieves this by using two counter-rotating wheels to
nip and crush the particles with a tightly controlled gap
between rollers, shown in Figure 1.
Unlike drop weight tests where energy is used as an
input (Napier-Munn et al 1996 Morrell 2004), the
Geopyörä uses a different approach. Energy is measured as
a response to the crushing force, making it not an input,
but a result from the test. By adjusting the “reduction
ratio” (crushing gap relative to particle diameter), the test
can achieve a range of different values of breakage ener-
gies, effectively mapping the rock’s response to both force
and resulting specific breakage energy for each particle
The Geopyörä Index: A New Instrument for Assessing
Comminution and Rock Strength Parameters
Marcos de Paiva Bueno, Thiago Almeida, Leonardo Lara, Malcolm Powell
Geopyörä Oy, Pirrakatu 1, Oulu, Finland
ABSTRACT: The product of the A and b parameters (i.e., Axb), which are obtained through curve fitting to
drop weight test (DWT) data, has long been regarded as a fundamental metric for evaluating ore resistance to
impact breakage. This parameter also serves as the foundation for calculating the SMC test drop weight index
(DWI), a key indicator of rock strength, that in combination with the Bond ball mill work index (BWI), is
widely used in comminution modelling to predict the overall specific energy requirements of AG/SAG and ball
mills, HPGRs and Crushers.
The conventional process of fitting the A and b parameters to DWT data is complex, requiring multiple data
points and considerable effort to achieve an acceptable fit. In this paper, we present the Geopyörä Index, which
bypasses conventional practices by offering a simple formula that obviates the need for curve fitting and provides
a direct and efficient means of estimating comminution parameters.
Since the Geopyörä Breakage test utilizes a principle of controlled degree of crushing, with applied breakage
energy being a response rather than an input, the direct measurement of this response turns out to be the ideal
metric for the development of a new way to assess rock strength, being incorporated into the calculation of a
new index. Over 200 samples have been tested, proving that the Geopyörä Index can not only effectively and
accurately estimate the parameters of conventional tests, but also provide a direct measure of rock strength in
its own right.
INTRODUCTION
Aiming to improve orebody characterization, the Geopyörä
breakage test brings a solution to the industry’s current
challenges by being a fast and low-cost test that requires
a minimal quantity of material, and that measures energy
and force for every particle (Bueno et al 2021). This test
can deliver a set of the industry standard parameters of ore
characterization, but the main goal is to populate precise
orebody models that predict process performance with a
high degree of accuracy (Chavez 2020). The Geopyörä
test achieves this by using two counter-rotating wheels to
nip and crush the particles with a tightly controlled gap
between rollers, shown in Figure 1.
Unlike drop weight tests where energy is used as an
input (Napier-Munn et al 1996 Morrell 2004), the
Geopyörä uses a different approach. Energy is measured as
a response to the crushing force, making it not an input,
but a result from the test. By adjusting the “reduction
ratio” (crushing gap relative to particle diameter), the test
can achieve a range of different values of breakage ener-
gies, effectively mapping the rock’s response to both force
and resulting specific breakage energy for each particle