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岩石学报 2012
Genetic types and the relationship between alkali-rich intrusion and mineralization of Beiya gold-polymetallic ore field, western Yunnan Province, China
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Abstract:
The Beiya gold-polymetallic ore field is one of the typical deposits related to the Jinshajiang-Ailaoshan alkali-rich intrusion of the Cenozoic Period, and it is also a magmatic-hydrothermal metallogenesis system related to alkali-rich intrusion during the Himalaya epoch. Based on the recent extensive researches and field investigations, this article systematically studies and concludes the genetic of various ore types, the relationship between mineralization, alkali-rich porphyries and the genesis of iron ore. In the ore field, four types of gold-polymetallic deposits have been recognized, there are porphyry-type Cu-Au mineralization, skarn-type Fe-Au-Cu-Pb-Zn mineralization, breccia-type Fe-Au-Pb-Zn deposits and hydrothermal Au-Ag-Pb-Zn mineralization in wallrock. Among the fours type of gold-polymetallic deposits, skarn and hydrothermal type are the most important metallogenesis. The whole-rock geochemical dating of quartz syenite porphyry shows that it belongs to potassic alkali-rock. And the LA-ICP-MS U-Pb age are defined as sample WDS-1 (31.5±1.1Ma), sample HNT-1 (31.34±0.73Ma). The quartz syenite porphyry which is shoshonitic series, not only provides a rising force and heat, but also acts as the main source and carrier for the ore-forming material and mineralization fluid. As a result, it builds a porphyry body-centered continuous porphyry-hydrothermal system, which is made of porphyry-type, skarn-type, hydrothermal-type, and various weathered-sedimentary-type deposits. The progress of forming the quartz syenite porphyry and ores was accompanied by the strong magmatic activity in the Sanjiang metallogenic belt, and the crust-mantle reaction made an important contribution to the mineralization and diagenesis in Beiya area. A large number of iron ore are produced along the contact between the alkali-rich porphyry and surrounding rock. It is found that the native iron ore accounts for 30.08% of magnetite and siderite accounts for 24.68%. Most of the magnetites which assume tabular forms and polysynthetic twin are the illusion of hematite. According to research, magnetite and siderite is the metasomatism product of the iron-bearing skarn in the alkaline environment. When the H+ concentration in Hydrothermal is decreases, hematite will be reduced to magnetite. It is the illusion of hematite when magnetite retains the crystal forms of hematite. The analyses show that the ore-forming fluids and the skarn mineralization last for a long time, which may be one the most important reason for the accumulation of that abundant metal.
