Research On The Origin Of The Yueshan Intrusion And Its Relation With Mineralization, Anhui Province

The Yueshan intrusion is one of the most important intermediate-acid rock masses, which is related to mineralization in the middle-lower reaches of Yangtze river area. Base on detail of petrology and geochemistry about the intrusion, this paper discussed the genesis and the evolution of the magma. Meanwhile, the geochemical feature of the ore and gangue rare-earth element has been researched. Finally, the relations between the rock magma evolution and mineralization have been discussed. Several conclusions have been obtained as follows:1. The petrological chemistry: This intrusion is characterized by high alkali with high K and Na contents. The intrusion should be classified as high-K calc-alkaline rock series. There is a tendency that the rock magma evolves to enrich silicon and alkali in its evolutionary process.2. The trace elements geochemistry: This intrusion is rich in LREE and LILE and depleted HREE, HFSE (Nb and Ta ), Especially, the high Sr content; Eu anomaly is not obvious; the REE abundance distribution pattern is straight-line type with strong enrich LREE.3. The genesis of Yueshan intrusion: This area situated the vulnerability position of upper crust. So, the subduction of Pacific plate caused the lithospheric extension and mantle upwelling, and resulted in the partial melting of mantle, which produced the high-K basaltic magma. The basic rock magma invades and assimilates the ancient granulites in lower crust. Simultaneously, the fractional crystallization of femic minerals made the magma to enrich more silicon and alkali. The magma suffered at least twice AFC process before they emplaced. The AFC is the dominated mechanism of its evolution.4. The geological and geochemical feature of trace element and the isotope of Yueshan intrusion indicate that the source of this magma is the metasomatic enriched mantle. Possibly, it is relates to the subduction of ancient continental plate.5. According to the geological and geochemical feature of the rare-earth element about ore and skarn minerals, it shows that the formation of the deposit has a close relation with the genesis of Yueshan intrusion. Copper and iron originate from the magma, their enrichment and mineralization are the result of the rock magma evolution. Iron enriched in the mineralized fluid, which are mainly controlled by the AFC process. In this process, the magma enriched Na step by step, and made Fe-Na separated, and form the Fe-rich mineralized fluid. The primary reason Copper enrich in mineralized fluid is that the rock magma have high content of H₂O and volatilities. With the rock magma rising rapidly, the pressure suddenly reduces. This change result in H₂O and volatilities separate from the magma, and carry the coppers form the Cu/Fe ore deposit.