ENFORCE27273

• Permit No: M1988112
• IBM Index Class Name: Enforcement
• Doc Date: 4/23/1992
• Doc Name: MINERALS PROGRAM PERMITTED MINING OPERATIONS ONLY 111 & 112 PERMITS POSSIBLE VIOLATION CIVIL PENALTY
• Media Type: D
• Archive: No

~ ~ I ~xlz i b r t 2
n;,TTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT
CMLRD ADE4UACY LETTER RESPONSES
Page I of 28
EXHIBIT D, MINING PLAN
1. On page D-14, reference to a "dilute cyanide solution" is made in
discussing the carbon-in-leach method of ore processinga What is the
expected concentration of cyanide in this process solution?
RESPONSE: The expected concentration of cyanide in the carbon-in-leach process
solution is 0.5 to 0.75 lbs per ton of ore. The sollutions are
expected to have total cyanide levels of approximately 175 ppm and
free cyanide levels of approximately 60 ppm.. As described on page
D-16, these solutions are contained in sealed anks only.
Additionally, the mill design includes internal cur ing and a
solution collection system to further ensure containment. within the
mill in the unlikely event of a tank leak (see response ,to question
5).
2. On page D-16, reference is made to use of sulfuric acid in treating
the tailings slurry prior to disposal. An equilibrium diagram is
provided to indicate that 70Y> of the cyanide will be volatilized at
pH 9. What is the expected concentration of free cyanide in the
treated slurry solution?
J~
RESPONSE: Laboratory test methods currently available do not all
accurate and consistent determination of free cyanide. FI
is unstable at the pH of the slurry and difficult to meas
test method is subject to interference from other elemE
and weak acid dissociable cyanide tests provide a mor
indication of cyanide present in a solution. BMR performed
testing to evaluate total, weak acid dissociable and fi
present in the slurry solution.'The data shows total cya
of 4.4 ppm and weak acid dissociable cyanide values~of 3
data also indicated free cyanide values of 52.0 ppm, wel
of the total and weak acid dissociable values and,
physically impossible. In this case, we believe that this
causing interference in the testing. The more reliable tot
data is included as Attachment 1 and will be added to App
the permit amendment application. Humidity cell testing i
however, preliminary test results as well as test result
approved permit indicate that the San Luis ore is not ac
ow for an
ee cyanide
ire and the
nts. Total
reliable
laboratory'
ee cyanide"
ide values_"''
8 ppm. The
in excess;
therefore,"
cyanate is
tory test
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from the
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