To lower the concentration of a a certain mixture; in this case the concentration of any unwanted materials mixed in the mine car together with the mined ores.

To lower the concentration of unwanted materials mixed with mined ores, you can employ several methods. Here are some common techniques used in the mining and mineral processing industry:

1. Physical Separation: This includes techniques like screening (sieving), where the mixture is passed through a screen to separate particles based on size. Heavy media separation can also be used to exploit the differences in density between ores and impurities.

2. Flotation: This method relies on the surface properties of materials. By adding chemicals called flotation reagents, you can make unwanted materials hydrophobic (water-repelling) while keeping the desired ore hydrophilic (water-attracting). This allows the unwanted materials to rise to the surface and be removed.

3. Magnetic Separation: If the unwanted materials are magnetic, you can use magnetic separation techniques to attract these materials away from the ore.

4. Leaching: This chemical process can selectively dissolve unwanted minerals while leaving the desired ores intact. It often involves using acid or alkaline solutions depending on the material being processed.

5. Washing: Simple washing can also help in reducing the concentration of unwanted materials, especially if they are soluble in water.

6. Chemical Treatments: Certain reagents can be added to bind with unwanted materials so they can be separated from the ore.

These techniques can often be used in conjunction to achieve the desired purity in the mined ores. A careful analysis of the mixed materials and the characteristics of the ore will help in determining the most effective method for concentration reduction.