Characteristics Of Mafic-Untralmafic Intrusion And Mineralization In Chaqin Area, Inner Mongolia

Mafic-ultramafic intrusion in Chaqin region, locates in western section of Inner Mongolia axis, neighboring Bayan Obo axis marginal depression towards north, and Jining-Linhe deep fault passed through. This region belongs to high-grade metamorphic belt in northern margin of North China block. Main ideas are as follows:1.Mafic-ultramafic intrusion in Chaqin region, intrudes in late-Caledonian gnesis-plagiogranite and hornblende plagiogneiss of upper-Archaean Seertenshan group, and the intrusion is cutted by granite-dikes or diabase-dikes. Main lithofacies is bistagite-facies, including epidote bistagite, biotite bistagite, garnet bistagite, and minor gabbro. Major rock minerals are bistagite-baicalite, and hornblende, plagioclase, biotite, epidote, apatite, titanite, etc. Hydrotheraml alternation and skarnization are clear and significant.2. SiO₂, MgO, Al₂O₃, Na₂O of rock from Chaqin intrusion is extremely high. TiO₂ of rock is low. In oxide-SiO₂ and oxide-MgO digram, correlations between oxides and SiO₂, MgO are weak or unobvious. However in ACM digram, geochemical data fall into ca- area, and it indicates rocks from Chaqin intrusion belong to transition section of mafic-ultramafic rock. These suggest there have being serious assimilation and contamination in crystallization process. In magmatic evolution process, it gives priority to accumulation and fractional crystallization is secondary. Rocks from Chaqin intrusion show a characteristic of tholeiite series. Diopside crystallization temperature calculated by Mercier single pyroxene thermometer is 800℃, and paragenetic temperature between garnet and diopside is 301℃.3. The zircon SHRIMP age of bistagite is 399±4Ma （n=8, MSWD=1.7）, belonging to Neopaleozoic early-Devonian, in which eight grains of tatal 15 zircons are upon concordia ages, and this dating result indicates the age of intrusion forming.4.Chaqin Cu-Pt-Pd ore deposits located in main metallogenic belt in Inner Mongolian Province, and available minerals include PGM （sperrylite, mertieite, etc）, metal sulfide （chalcopyrite, pyrite, pyrrhotite, bornite, etc） and minor oxide （magnetite, malachite, limonite, etc）. The major metallogenic epochs can be divided into: cumulus pile period, metal minerals are magnetite, pyrite, chalcopyrite, etc; post-magmatic hydrothermal fluids period, metal minerals are pyrite, chalcopyrite and minor PGM; alteration period, metal minerals are chalcopyrite, pyrite and PGM.