GEOLOGICAL CHARACTERISTICS OF MOLYBDENUM DEPOSITS FROM A CERTAIN DISTRICT, CHINA, WITH SPECIAL REFERENCE TO PLATINUM METALS IN MOLYBDENUM ORE MINERALS

The two episodes of molybdenum deposition in this district are distinct from eachother in geological setting, relation with magmatic rocks, the type of ore deposit, wall-rock alteration, as well as mineral and element assemblages. Geological and geoche-mical evidence indicates that the two episodes of molybdenum mineralization andrelated acid-intermediate magmatic rocks resulted from a common source deep in thecrust and were accompanied by the north-east striking deep fault activity during theYenshanian cycle. Osium, platinum and palladium have all been detected in molybdenite. Highercontents of these metals are found in three mineral associations (molybdenite-chalco-pyrite-magnetite, molybdenite-bornite-chalcopyrite, and scheelite-molybdenite). The or-der of enrichment of platinum metals in various molybdenum ore associations are:OsPtPdRuRhIr. Variation in platinum and palladium contents inmolybdenite is found to be related to the type of ore deposit and to ore assemblages.Osmium content in molybdenite is a function of the age of molybdenite (the older themolybdenite, the higher its osmium content) and the Os/Re ratio may serve as an indi-cater for geological age. Three polytypes of molybdenite [2H_1, 2H(?), and 2H_1 + 3R] have been recogniz-ed, each of which is characterized by crystal structure, occurrence, physical and chem-ical properties. The molybdenite polymorphism is attributed to temperature of forma-tion and to the rate at which crystallization took place and can therefore be regardedas an indicater for the ore-forming environments.