gems, spinel, Afghanistan, Tajikistan, balas ruby, Kuh-i-Lal, geology

Data on the geological structure and mineralogy of the Kuhi-lal deposit allow its red spinel genesis to be interpreted in a new way. The following points seem to be proved in the paper: 1) Red spinel and magnesium skarns developed independently of one another. 2) When red spinel occurs together with Mg-skarns, it complicates their zoning and occupies an unusual position in the exocontact zone. 3) The genesis of minerals of the magnesium skarn formation may be connected either with the input and output of substances during the desilication of acidic rocks and demagnesiation of carbonate rocks, or may occur without significant input or output of substances. In the second case, the mineral-forming process might result from metamorphic changes in the «contaminated» clayey rocks present in the carbonate formation.