Research On Yanshanian Magmatism And Poly Metallic Metallogenic Series In The Luzong Area,Anhui Province

Luzong region is an important ore concentration area of middle to lower Yangtze Fe-Cu-Au mineralizing belt in Anhui province, which is holded between Tan-Lu fault and Yangtze fault, including the volcanic basin and uplift of the boundary. Mineralization is closely related to the Yanshanian magmatic outbreak, characteristics of magmatism and mineralization are significantly. This article selects ore-forming magmatic rocks and different types of ore diposits in Luzong region as the research object, on the basis of the collection and second development of massive data, field geological investigation, collection and test of key samples, we deal with petrology, mineralogy, mineragraphy, elements-isotope geochemistry, electron microprobe analysis and high-precision chronology, complete the ore-forming magmatism, systematically analyse the relation of the magmatism and mineralization and the metallogenic regularity, and summarize the magma-metallogenic dynamic model. Then we obtain the understandings of the full text are as follows:1. Petrological and geochemical results of magmatic rocks related to mineralization showed that the igneous rocks in Luzong area include shoshonitic series in the basin and calc-alkaline intrusion series in the uplift of it. The shoshonitic series cover early monzonite-diorite intrusions related to Longmenyuan-Zhuanqiao volcanic rocks and later syenites related to Shuangmiao-Fushan volcanic rocks, magmatic crystallization gradually enhanced from the early to later period, and have the characteristic of enrich Si and K. While the calc-alkaline intrusion series has the characteristic of low magmatic crystallization and typical adakites.2. By using the zircon U-Pb dating technology, we get the age of the ore-forming magmatic rocks in mainr mines is between135～130Ma, combining previous geochronologydata and relationships of the fieid outcrops, we consider the age of monzonite-diorite intrusions is135～129Ma, the syenite intrusions is129～124Ma, the calc-alkaline intrusion series is136～133Ma. The ages of two series are quite close, combining the high precision seismic detection sections recently; we question the opinion of existence of calc-alkaline intrusion series underneath the Luzong basin.3. Element and isotope geochemistry study shows that, the isotopic characteristics of the two magmatic series have a remarkably general similarity, indicating they are belong to a same deep process, while the source regions are different. The magmatic origin, evolution and geniese of the volcanic and intrusive rocks of shoshonitic series are consistent, is mainly derived from EMI enriched mantle, exieting the Yangtze crust material contamination in the process of magma rising. Calc-alkaline intrusion series represented by Shaxi intrusion formed from the basaltic lower crust material partial melting.4. Metallogenic types in Luzong region are divided into porphyritic type Fe-Cu deposit, sediment-reformation epithermal type Fe-Cu deposit, hydrothermal vein type Cu-Au deposit and porphyry Cu-Au deposit. Mineralization age is between147-129Ma, of which, mineralization age of Longqiao sediment-reformation epithermal type Fe-Cu deposit is-147Ma, Shaxi porphyry Cu-Au deposit is between135～132Ma, porphyritic type Fe-Cu deposit is132-131Ma and hydrothermal vein type Cu-Au deposit is133-129Ma.5. Ectron microprobe analysis, trace elements and isotope geochemistry study show that, the vast majority of metallogenic materials of the four metallogenic types are drived from the deep magma source, the ore-forming fluid is given priority to magmatic water mixed with some meteoric water. The salt layer in middle Triassic series provides part sulfur source for the mineralization, sedimentary strata also provide some metallogenic materials in Longqiao deposit.6. By analyzing the magmatism and mineralization in Luzong region, we conclude the two Yanshanian magmatism series control the two metallogenic series respectively, that is, the porphyritic type Fe-Cu deposit, hydrothermal vein type Cu-Au deposit releted to the mantle-derived shoshonitic series, the porphyritic type Fe-Cu deposit releted to the basaltic lower crust material partial melting. The sediment-reformation epithermal type Fe-Cu deposit is related to the magmatism of～147Ma, isn’t controlled by the shoshonitic series as predecessors thought before. Because of no intrusions are temporarily found in this area, we can’t establish the relationship of the mineralization to magmatism.7. On the basis of comprehensive study of time and space frame, ore-controlling geological factors and metallogenic regularity, we sumerise the metal metallogenic model and earth dynamics process is as follows:after146Ma, Luzong area and neighborhood turn into the Pacific tectonic regime, regional extension is enhanced and lithosphere delamination and mantle up welling, magma formed form the metasomatism of asthenosphere mantle rised along the Luohe crust cutting deep fault, then formed the porphyritic type and hydrothermal vein type deposit in the different places in the basin. While calc-alkaline adakite magma derived from the basaltic lower crust material partial melting formed the porphyry deposit in the uplift area aroud the volcanic basin.