BASIC CHARACTERISTICS OF YANSHANIAN MINOR INTERMEDIATE-ACID ROCK MASSES AND THEIR MINEROGENESIS IN THE QINLING-DABIE MOUNTAINS REGION,HENAN PROVINCE

In the Qinling-Dabie Mountains region, Henan province, the main exposed strata are Precambrian metamorphic series, the structures are complex and the magmatic activity was intense. In such geological settings, there widely occur more than a hundred minor intermediate-acid porphyry masses and explosion breccia pipes. The main ore-bearing rock masses mostly cover an area of less than l sq km, and their K-At ages range from 97-206 m.y., considered to be Yanshanian （Mesozoic）. The distribution of these porphyry masses is controlled by fractures and they occur in groups and zones along regional fractures. No contemporaneous volcanic rocks are associated with them. They occur beyond major granite batholiths and belong to the genetic series different from major batholiths. They have been mostly altered and mineralized. The rock types mainly include granite （or granophyre） and granodiorite （or granodiorite porphyry）. Petrochemically, they are high-silica, alkalirich, potassium-rich, low-sodium, magnesium-poor and calcium-poor as compared with calc-alkaline magmas. Mineralization is controlled by rock types and petrochemical composition, so magmatic rocks are characterized by marked metallogenic specialization, e. g. granite and granophyre with SiO₂ ＞70—72％ and K₂O≥Na₂O form molybdenum deposits, while granophyre porphyry and plagioclase granite with SiO₂＜70—72％ and K₂O≤Na₂O form copper, gold and polymetallic deposits. Hydrothermal alteration roughly corresponds to the model proposed by J. D. Lauel, but porhyry molybdenum deposits exhibit ubiquitous greiseniza- tion and fluoritization other than not strong potassification and silicifica tion. Mineralization is closely related to alteration and shows vertical and horizontal zoning. According to main ore-forming element associations and charactecistics of mineralization and alteration, 6 mineralization types and 3 porphyry orebody associations may be distinguished. On the basis of the tectonics, deep fractures and petrochemistry, the author divides the Qinling-Dabie Mountains region into 7 tectono-magmatic belts and 7 corresponding porphyry metallogenic belts of these the LushiLuanchuan-Yunyang porphyry molybdenum （tungsten） metallogenic belt and Bachang-Qiushuwan porphyry copper metallogenic belt are the most important ones in the Eastern Qinling Mountains, and molybdenum mineralization is much stronger than copper mineralization. The porphyry has δ³⁴S=0.57％, ⁸⁷Sr/⁸⁶Sr=0.707-0.710, δ¹⁸O （whole rock）=7.2-9％ and δ¹⁸O （biotite）=6.6-7.1％, which indicates that the magma was derived from a deep source and that meteoric water did not play the main role. Therefore, the author holds that the porphyry masses in the QinlingDabie Mountains region are the products of distinctive tectono-magmatic activity and were derived from the deep-level differentiated magma in the lower crust. Although they are equivalent to I-type granite （Chappell and White, 1978） or syntectic granite （Nanjing University, 1980; Yang Chaoquan, 1980）, they show distinct variations and are the products formed under special tectono-magmatic conditions and in a special geochemical background in the Qinling-Dabie Mountains region.