Abstract: In some embodiments, the present invention pertains to methods of detecting a contamination of an environment by a fracture fluid that comprises magnetic particles. In some embodiments, such methods include: (1) collecting a sample from the environment; and (2) measuring a magnetic susceptibility of the sample in order to detect the presence or absence of the magnetic particles. Further embodiments of the present invention pertain to methods of tracing fracture fluids in a mineral formation. In some embodiments, such methods include: (1) associating the fracture fluids with magnetic particles; (2) introducing the fracture fluids into the mineral formation; and (3) measuring a magnetic susceptibility of the fracture fluids. Additional embodiments of the present invention pertain to fracture fluids containing the aforementioned magnetic particles, the actual magnetic particles, and methods of making said magnetic particles.