U.S. GOLD CORP.

Table 22.1: Grindability Test Quantities

Of note, the comminution circuit equipment selection uses primarily Bond work index data, of which there are 44 data points. A quality control problem was identified with the ball mill work index tests conducted in program BL1990, and a correction was applied based on a published procedure (Nikolić, 2022) using the comminution consultant’s database of over 5,000 ball mill work index tests.

The expected relative standard deviation of a grinding circuit design database is between 10% and 20% of the work index average value based on the comminution consultant’s global database of over 40 projects with large grindability datasets. The rod mill and ball mill work index standard deviations for the Project did not meet this expectation, which is interpreted as meaning that the full variability of the deposit may not have been captured by the current data set. The comminution equipment design criteria and resultant sizing/selection calculations therefore make allowance for greater variability in ore grindability than what is indicated in Table 22.1 via additional contingency allowances.

Values for the comminution circuit design criteria are summarized as follows:

The flowsheet design parameters are also shown in Figure 22.1.

The decision to include a pebble crusher in the flowsheet is based on the relationship between the ore’s Bond Ball Mill Work Index (BWi) and Bond Rod Mill Work Index (RWi). Figure 22.2 was provided by Alex Doll, it displays CK Gold samples (indicated in purple) relative to the red and green shaded regions. These samples, along with the selected design parameters (RWi of 19.4 kWh/t and BWi of 17.9 kWh/t), plot on the periphery of the “optional pebble crushing” zone. This suggests a pebble crusher is required to prevent the accumulation of critical-size material.