Mode

Copper ore consists, according to CT, of 5.2% of ore minerals, quartz grains (53.1%) and a matrix of crystallized calcite (40.9%). The distribution of copper minerals in the entire rock volume is shown in Figure 6. It can be seen that it is possible to clearly distinguish dense copper-containing minerals from quartz and calcite on the tomogram, whereas the latter two minerals are quite difficult to distinguish from each other, because of their close X-ray density.

**Figure 6.** The distribution of copper minerals (green) in the quartz-calcite matrix (gray) in sandstone.

#### Grain Size

Using the CTVox and CTan programs, it is possible to analyse in detail not only the sizes of the grains composing the rock, but also their interrelations, which is especially important for the purposes of process mineralogy. Copper minerals are fairly evenly distributed throughout the rock volume, sometimes forming individual grains with an average size of 70 μm and fine-grain aggregates 260 μm in size (Figure 7a,b), sometimes up to 2.0–4.5 mm (Figure 7c).

**Figure 7.** (**a,b**) Aggregates of copper minerals in the volume of sandstone and (**c**) aggregate distribution according to the maximum diameter.

#### Grain Shape

Copper minerals have a quite isometric shape, the coefficient of sphericity, calculated as the ratio of the short to the long axis, is 0.78 (when the shape of the grain approaches isometric, this coefficient reaches 1, Figure 8a).

**Figure 8.** (**a**) Distribution of aggregates of copper minerals according to the sphericity coefficient and (**b**) the orientation of the longest axis, grade

#### Roughness

Specific surface of copper minerals, calculated as the ratio of the total surface of minerals to their volume and representing the degree of tortuosity of the boundaries (roughness), is equal to 31.86 mm2/mm3.

#### Orientation

The orientation of copper grains and aggregates is also marked, expressed quantitatively as the deviation of the longest axis of grains from the vertical in grades (Figure 8b).

#### Porosity

One of the most important characteristics of rocks for comminution, linking the strength of the rock with a defect in its structure, is porosity. It determines the interpretation of the strength properties and behavior of the rock during comminution [30]. The total porosity of the sandstone sample is 1.4%, the open porosity is 0.68%. The pore connectivity is low. In general, the pores of the subcapillary size are less than 0.2 μm, the predominant pore size is 25–50 μm, but there are also single pores with a diameter of more than 100 μm. The pore sphericity factor is 0.62. The void density, calculated as the ratio of the number of pores per unit volume of rock, is 9.10 mm<sup>−</sup>3.

#### *3.2. Granodiorite*
