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Corrosion Strategies at the Resolution Copper Project, Arizona
Louis Sandbak
Resolution Copper
Gabino Preciado
Resolution Copper
INTRODUCTION
Corrosion has long been identified as a potential risk to
the long-term ground support stability due to degradation
of internal ground support elements such as rock bolts but
also to surface support from mesh, straps, bolt plates, and
ancillary support of utilities such as hangers. The emphasis
is to understand the corrosion mechanisms on the primary
ground support elements and any supplemental steel or arch
sets. The water and chemical processes from oxidation(rust),
stress corrosion cracking, and even the electrical charge cre-
ated during these reactions contribute to the corrosion of
the steel support elements. The main goals are to mitigate
the effects of corrosion and to be able to predict those areas
of high water or high sulphide for potential rehab maps.
It is also essential to identify and classify the visible corro-
sion as part of damage mapping and provide bolt testing to
those areas of suspected internal damage from corrosion.
This is important to get an estimate of the support longev-
ity or expected life before rehab to minimize the overall cost
of the operation.
Fully encapsulated bolts using resin provide the best
protection from the low pH acids generated from oxida-
tion of pyrite as well as alkaline waters with high particu-
late solids and higher salinity that can lead to corrosion.
In addition, it can be demonstrated that pumpable resins
using hollow bolts or rebar are more effective in ensuring
the complete encapsulation of bolts than the partial encap-
sulation from resin-epoxy cartridges that must be placed in
the holes manually and bolts spun to break the cartridges
to complete the mixing. This is especially important in high
water prone areas.
Resolution Copper completed the sinking of the No
10 shaft to a depth of 6,943’ below the surface and was
ultimately connected to the number 9 shaft. The deepest
development at the mine is the second transfer pumping
station (TPL2) or 68 level at 6,780 feet below the surface.
The current 68 level and subsequent 58 level development
and lower caving levels and shafts will be dependent on the
long-term viability of the ground support given the high
sulfide environment if coupled by the presence of hot water
and associated high humidity (60%).
WATER CHEMISTRY RESEARCH
Water sampling of the #9 and #10 shaft and of the TPL2
or 68L were collected and summarized in several reports.
In a more recent study by Logsdon (2022), the kinds of
water collected from deep water flows include Montgomery
(2012) and are summarized in Table 1. The chemical con-
centrations of typical water collected vary in the number
of dissolved solids and show that underground waters at
Resolution are neutral pH and do not show evidence in
total dissolved solids or high sulfate concentrations of
high acid generation. The conceptual model is that native
groundwater is not corrosive (neutral pH, very low oxy-
gen), but where the groundwater becomes oxygenated (in
mine voids, fractured rock around excavation develop-
ment aided by ventilation), and passes through high sulfide
rock, the water becomes corrosive. The suggestion is that
if these were typical of most of the water and geology low
in sulfides, the environment of rock bolts, mesh, and other
steel-based infrastructure, there would be little or no risk
of corrosion. However, the presence of abundant hot water