Froth flotation is a common method used for the concentration of ores. It is based on the principle of preferential wetting of the ore particles by oil and water, where the ore particles are selectively attached to the air bubbles and carried to the surface of the flotation cell, while the gangue particles remain in the bulk solution. In this process, various reagents are used to modify the surface properties of the ore particles and create a froth that can be easily removed.

Among the given options, copper pyrites is the only ore that is concentrated by froth flotation. Here's why:

Copper pyrites:
- Copper pyrites, also known as chalcopyrite (CuFeS2), is a sulfide ore that contains copper, iron, and sulfur.
- The ore particles of copper pyrites are relatively large and have a high density compared to the gangue minerals.
- In froth flotation, the ore is first crushed and ground to a fine size, and then mixed with water and various reagents to create a slurry.
- The slurry is then agitated and air is blown into it to create air bubbles.
- The reagents, known as collectors, are added to the slurry to selectively adsorb on the surface of the copper pyrites particles, making them hydrophobic (water-repellent).
- Frothers are also added to stabilize the froth and enhance the attachment of the air bubbles to the hydrophobic particles.
- When air bubbles are introduced into the slurry, they attach to the hydrophobic copper pyrites particles and carry them to the surface as a froth.
- The froth is then skimmed off and the concentrated copper pyrites is obtained.
- The gangue minerals, which are hydrophilic (water-loving), remain in the bulk solution and are discarded as tailings.

Other options:
- Haematite: Haematite (Fe2O3) is an oxide ore of iron and is not concentrated by froth flotation. It is typically concentrated by magnetic separation or gravity separation methods.
- Zinc: Zinc ores, such as sphalerite (ZnS), are also not concentrated by froth flotation. They are typically concentrated by froth flotation followed by roasting to convert the zinc sulfide to zinc oxide, which is then reduced to metallic zinc.
- Magnetite: Magnetite (Fe3O4) is an oxide ore of iron and is not concentrated by froth flotation. It is typically concentrated by magnetic separation or gravity separation methods.

Therefore, among the given options, only copper pyrites is concentrated by froth flotation.