Geophysical Hunt for Chromite in Ophiolite

摘要

Ophiolite of Oman are famous world over, and are favorite for exploring chromite, which is a source of chromium that isused widely in steel, nichrome, and plating and painting industries. The best known chromite deposits are found in the Bushveldcomplex of South africa, however countries like Pakistan and Oman are also contributing but less than 2%of the world production.Chromite is found in the mantle rocks such as peridotite and its altered products. Large economic deposits are generally found instratiform structure and the smaller ones in pod-like or tabular lenses. In Oman the chromite deposits occur in Oman ophiolite(Semile), mainly in the mantle sequence comprising harzburgite and dunite. The mining efforts for chromite in Oman are inprogress but not on scientific grounds. On a site called Izki (670 m asl) the chromite was expected on the top of a hill in a small area(150x50 m) of ophiolite, and mining through pitting procedure was tried over there but remained unsuccessful. Geophysicalmethods were applied in the same area to search out the possibility of the existence of the ore. Since chromite is denser, moreconductive and magnetically less susceptible deposit as compared to the host rocks harzburgite and serpentinite, it is expected thatthe existence of a shallow sizable ore body would generate favorable gravity, magnetic, and resistivity signals. The integratedgeophysical study (gravity, magnetic and resistivity) reveals the probability of chromite within 30 m depth. For confirmation thedrilling was recommended on a point upto a depth of 35 meters. The drilling could not be continued beyond 12 meters depth due toreasons known to the lease owner. The drilling showed harzburgite up to 8 meters depth, then a chromite layer of 0.7 meterthickness, after that harzburgite started for the next 3 meters depth. This state of affairs confirms not only the presence of chromitebut also the revealing power of geophysics.