From: "Barbanell, Melissa (Salt Lake City)" <mbarbanell@barrick.com>

To: Chuck French/RTP/USEPA/US@EPA

Date: 02/15/2010 07:42 PM

Subject: Ore and Carbon Metrics M o nitoring.docx

Chuck,

This is the information that we have been able to gather on measuring carbon and

ore.

Thanks and we will see you on Wednesday.

Melissa(See attached file: Ore and Carbon Metrics Monitoring.docx)Ore Metric

– Ore Pre

‐ Treatment Group

1. Monitoring Equipment

a. Roasters

– The throughput is measured by a densitometer and flow meter. The

densitometer measures the density of the calcine (oxidized ore slurry) exiting the

roaster oxidation circuit and the flow meter measures the slurry volumetric flow rate.

This equipment is located after the roaster oxidation circuit and before the Carbon

‐ In

‐

Leach (CIL) tanks.

b. Autoclaves

– The throughput is measured by a densitometer and flow meter. The

densitometer measures the density of the slurry autoclave feed and the flow meter

measures the slurry volumetric flow rate. This equipment may be located upstream or

downstream of the autoclaves. In some cases, there are separate meters for each

autoclave. In other cases, the meters are located at a common feed point for all

autoclaves.

2. Monitoring Frequency and Recording

a. Roasters and Autoclaves

– At least one reading of density and flow is collected every 5

minutes. The readings are totaled at least daily, and then compiled into monthly and

12

‐ month rolling total throughput values (tons).

3. Monitoring Equipment QA/QC/Accuracy

a. Roasters and Autoclaves

1. Densitometers

– Calibration occurs by one of two methods:

i. Side

‐ by

‐ side redundant densitometers

– A consistent difference

between readings of greater than 5% (or less) requires a calibration.

ii. Single densitometer

– On a quarterly basis, the densitometer reading is

compared to a laboratory density analysis of a slurry sample. A

difference of greater than 5% (or less) requires a calibration.

2. Flow meters

– A zero flow check is performed at least annually during down

time.

Carbon Metric

– Carbon Group

1. Monitoring Method/Frequency

– The volume of carbon loaded into the carbon vessel is

measured for each batch. A record of the vessel volumetric capacity is maintained on site. The

date and the vessel fill level (i.e., volume size) of each batch are maintained in a log. This

volume data is combined with the carbon density (a typical value is 0.6 g/ml) to calculate total

tons of carbon. Batch weights are compiled into monthly and 12

‐ month rolling total throughput

values (tons).

2. Monitoring QA/QC/Accuracy

– The capacity of the carbon vessel is maintained on site. The

vessels are typically loaded to a pre

‐ defined full batch size level. If a mine needs to occasionally

run partial batches, then the dimensions of the carbon vessel must be maintained on site along

with a calculation of batch volume/weight per length of head or dead space. The measurement

of dead space length is accurate to within 5%.For example, Figure 1 shows the carbon vessel at Goldstrike. The full batch fill level represents

15 tons of carbon (256" carbon depth, 82.5" interior diameter, 793 ft 3 of carbon, 0.60645 g/ml

carbon density). For this vessel, a plum line is used to measure the dead space of the partial

batch to the nearest half foot. One half foot is equal to 0.35 tons, which is 2.3% of a 15

‐ ton

batch.

Figure 2: Goldstrike Carbon Vessel

255"

245"

80" 256" 15 tons of carbon 79"

ID 82.5"

OD 83.75" head space or dead

bed Acid Wash Vessel Dimensions

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