High resolution X-ray computed tomography investigations of high-grade gold ore zones in the Cripple Creek District, Colorado

Gold mineralization in the Oligocene Cripple Creek alkaline volcanic center is
characterized by high-grade veins and low-grade disseminated Au-Te deposits. Telluride
distribution and grain-scale characteristics have been evaluated using highresolution
X-ray computed tomography (HRXCT) to study samples of high-grade gold
veins. HRXCT allows for non-destructive, three-dimensional examination of geologic
specimens. The X-ray scans highlight density contrasts, providing an excellent method
to examine the distribution of mineral grains in rocks. A series of two-dimensional
X-ray scans are stacked to produce a three-dimensional data set that can be rotated,
sliced and viewed from any angle. Using custom-developed software for measurement
of volumetric data sets (BLOB3D), information about mineral grains, such as volume
and major/minor axes orientations, can be extracted for in-situ analysis.
HRXCT results from three-dimensional analyses of individual in-situ grains show
variation of grain-scale features among the high-grade Cripple Creek specimens. In
addition, volumetric data indicate a substantial percentage of the gold in the highgrade
ore samples is contained in a small percentage of grains, e.g. on average 50% of
the gold in the samples is derived from the largest 9% of grains. Conversely, the smallest
grains that comprise half of the population of grains only account for 15% of the
total gold concentration. These results could have major impacts on ore processing to
maximize economic recovery. We continue to evaluate the applications of HRXCT in
ore studies, including the relationships between grain populations and ore grade