3
radially from the Copper Flat porphyry are Laramide veins
hosted by many of the latite dikes.
The U.S. Bureau of Mines collected and analyzed
selected samples from the mineral deposits surrounding
the copper porphyry deposit. Chemical analyses of the
veins range from 8–64,600 ppb Au, 0.2–590 ppm Ag,
40–57,337 ppm Cu, 1–475 ppm Mo, 57–8906 ppm
Pb, and 138–17,026 ppm Zn (Geedipally et al., 2012).
Carbonate-hosted replacement deposits are found dis-
tal from the center. Chemical analyses of the carbonate-
hosted deposits range from 5–99 ppb Au, 1–50 ppm Ag,
131–173 ppm Cu, 2–140 ppm Mo, 30–10,000 ppm Pb,
and 123–20,000 ppm Zn (Geedipally, 2012). As much as
130 ppm Te and 3400 ppm Bi also are found.
The mine was operated for three months in 1981 and
mine features include mine waste rock piles (dumps), a pit
lake, acid seeps, and tailings. A low- grade stockpile, mine
waste rock pile and tailings have been sampled.
METHODOLOGY
Additional sample techniques developed by USGS staff, the
BLM (Bureau of Land Management, 2014), USGS, and
EPA standard methodologies are being used for sampling
(see McLemore et al., 2024. In order to ensure that the
necessary safety protocols are followed, a Site Health and
Safety Plan (HASP) has been prepared. This includes the
location and driving instructions to the closest hospital, the
necessary personal protective equipment, site-specific haz-
ards and how they are addressed and emergency procedures.
Data collection, general geologic mapping (GIS), sam-
pling of waste and rock piles, laboratory studies, determi-
nation of engineering qualities by using the geologic and
geochemical data to determine potential of acid production
within the wastes, estimation of the volumes and tonnages
of waste and rock piles, and general stability analyses of
structures by physical examination and particle size analysis.
PRELIMINARY RESULTS
Paste pH
The acid base account (ABA) method was used to deter-
mine the acid generating potential of samples collected.
Using the C and S concentrations and the NaGph (i.e.,
measured paste pH), the below formula was then applied:
AP (kg CaCO3/tonnes) =31.25 x S (%)
NP (total C) =83.3 x C (%),
NNP =NP – AP,
NPR =NP/AP
Paste pH conducted on the waste rock piles ranged
from 3.66 to 5.67 which indicates oxidation of fine-grained
pyrite or other sulfides. The samples collected from the tail-
ings however showed a slightly different pattern in pH,
ranging from 6.30 to 8.62, probably due to the presence of
carbonates. Figures 2 and 3 are ARD plots showing the acid
forming potential of the various samples collected from the
mine tailings and waste rock piles. Some samples from the
tailings in copper flat mine in Hillsboro falls in the “uncer-
tain” and “potential acid forming” quadrants and should be
treated with care. Most waste rock pile samples, however,
fall within the non-acid forming field and may be suitable
for backfilling. All tailing samples from Steeple Rock fall
Figure 2. Acid rock drainage (ARD) plot of tailings at
hillsboro and steeple rock
Figure 3. Acid rock drainage (ARD) plot of waste rock piles
at hillsboro and steeple rock
radially from the Copper Flat porphyry are Laramide veins
hosted by many of the latite dikes.
The U.S. Bureau of Mines collected and analyzed
selected samples from the mineral deposits surrounding
the copper porphyry deposit. Chemical analyses of the
veins range from 8–64,600 ppb Au, 0.2–590 ppm Ag,
40–57,337 ppm Cu, 1–475 ppm Mo, 57–8906 ppm
Pb, and 138–17,026 ppm Zn (Geedipally et al., 2012).
Carbonate-hosted replacement deposits are found dis-
tal from the center. Chemical analyses of the carbonate-
hosted deposits range from 5–99 ppb Au, 1–50 ppm Ag,
131–173 ppm Cu, 2–140 ppm Mo, 30–10,000 ppm Pb,
and 123–20,000 ppm Zn (Geedipally, 2012). As much as
130 ppm Te and 3400 ppm Bi also are found.
The mine was operated for three months in 1981 and
mine features include mine waste rock piles (dumps), a pit
lake, acid seeps, and tailings. A low- grade stockpile, mine
waste rock pile and tailings have been sampled.
METHODOLOGY
Additional sample techniques developed by USGS staff, the
BLM (Bureau of Land Management, 2014), USGS, and
EPA standard methodologies are being used for sampling
(see McLemore et al., 2024. In order to ensure that the
necessary safety protocols are followed, a Site Health and
Safety Plan (HASP) has been prepared. This includes the
location and driving instructions to the closest hospital, the
necessary personal protective equipment, site-specific haz-
ards and how they are addressed and emergency procedures.
Data collection, general geologic mapping (GIS), sam-
pling of waste and rock piles, laboratory studies, determi-
nation of engineering qualities by using the geologic and
geochemical data to determine potential of acid production
within the wastes, estimation of the volumes and tonnages
of waste and rock piles, and general stability analyses of
structures by physical examination and particle size analysis.
PRELIMINARY RESULTS
Paste pH
The acid base account (ABA) method was used to deter-
mine the acid generating potential of samples collected.
Using the C and S concentrations and the NaGph (i.e.,
measured paste pH), the below formula was then applied:
AP (kg CaCO3/tonnes) =31.25 x S (%)
NP (total C) =83.3 x C (%),
NNP =NP – AP,
NPR =NP/AP
Paste pH conducted on the waste rock piles ranged
from 3.66 to 5.67 which indicates oxidation of fine-grained
pyrite or other sulfides. The samples collected from the tail-
ings however showed a slightly different pattern in pH,
ranging from 6.30 to 8.62, probably due to the presence of
carbonates. Figures 2 and 3 are ARD plots showing the acid
forming potential of the various samples collected from the
mine tailings and waste rock piles. Some samples from the
tailings in copper flat mine in Hillsboro falls in the “uncer-
tain” and “potential acid forming” quadrants and should be
treated with care. Most waste rock pile samples, however,
fall within the non-acid forming field and may be suitable
for backfilling. All tailing samples from Steeple Rock fall
Figure 2. Acid rock drainage (ARD) plot of tailings at
hillsboro and steeple rock
Figure 3. Acid rock drainage (ARD) plot of waste rock piles
at hillsboro and steeple rock