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The Fenghuangshan Skarn Copper Deposit Mineralization Process Study At Tongling, Anhui Province

Posted on:2011-10-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:H Y QuFull Text:PDF
GTID:1100360332956157Subject:Mineral prospecting and exploration
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The Fenghuangshan ore-field is the typical skarn Copper Ore-Field of the Middle-Lower River metallogenic belt at Tongling, Anhui. The tectonic movement, the magmatism and the mineralization of the ore-field are very complicated. The geotectonic evolution has been through three periods:the movement (the basement formation period), the stability (the cover) and the reprise (the intra-plate distortion). From the Middle Triassic, the intra-plate distortion period induced the large-scale intermediated-acidic magma movement.This study takes the Fenghuangshan Copper Deposit as an example adopting SHRIMP U-Pb dating on zircon, Re-Os dating, major elements, trace elements and rare earth elements, microthermometric studies, carbon, hydrogen, oxygen, sulfur and lead isotope compositions to show the spatial three-dimension metallogenic fluid trend. Moreover, combining region metallogenic background studies and utilizing the modern geological and geochemical theories of rock forming and mineralization, this thesis demonstrates the magmatism, the magma revolution, the relationship of the rock forming and mineralization, the space-time revolution of the metallogenic fluid, the metallogenic physical and chemical fields and the space-time combining of the deposit orientation.The Re-Os isochronal age is 141.1±1.4 Ma of the Fenghuangshan Copper Deposit forming Early Cretaceous The Fenghuangshan Copper Deposit is the offspring of the Late Yanshanian intermediated-acidic magma and the correlated hydrotherm intruding and locating. The metallogenin material is the crust-mantle mixed type. This deposit lies on the he Middle-Lower River metallogenic belt. The Middle-Lower River Cu-Au-Fe-Mo deposit system formed at the geodynamical adjusting period, the second large-scale metallogenic period of Mesozoic. The geodynamical background is the tectonic system transition. The Fenghuangshan Copper Deposit lies at this period.The Fenghuangshan quartz monzodiorite and granodiorite in Tongling, Anhui Province are spatially and temporally associated with Cu mineralization. Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb zircon dating of quartz monzodiorite is from (136.0±2.0) to (143.0±2.4)Ma, and the weighted mean age is (139.4±1.2)Ma (n=15, MSWD=0.76). SHRIMP U-Pb zircon dating of granodiorite is from (136.7±2.0) to (145.3±2.4)Ma, and the weighted mean age is (141.0±1.1)Ma (n=17, MSWD=1.5). The intrusive age is the Late Jurassic, the Late Yanshanian. The molybdenite Re-Os isochronal age is the same to the intrusive age of granodiorite and elder than the age of quartz monzodiorite. The mineralization has the relationship with granodiorite. Isotope compositions indicate that the mineralization relates to deep fluids of mantle magma differentiation. The extensional process which is resulted from the pluton emplacement and the whole thickening of the lithosphere has the relationship with the basaltic magma underplating which is resulted from the aesthenosphere mantle and the upper crust decompression.The Xinwuli pluton is the Late Yanshanian high-K, calc-alkaline intrution (144 Ma, U-Pb zircons age), which is composed by quartz monzodiorite envelope and granodiorite inner. Geochemical characteristics of the Xinwuli quartz monzodiorite indicate that the original magma is upper mantle alkli basalt, which is contaminated by crust materials during intrusion. Curst material contamination could be happened during partial melting or magma moving upwards. The Cu mineralization has closed spatial, temporal and genesis relations with the Xinwuli pluton. Orebodies are hosted by both quartz monzodiorite and marble along the contact zone, and endoskarn orebodies are dominanted. Similar trace element features of ore samples and quartz monzodiotite indicate that copper comes from the monzodiorite intrusion. Fluids bimetasomatism between quartz monzodiorite and carbonate rocks cause Cu precipitation. Orebodies are jointly controlled by bimetasomatism and structural deformation on the three dimension distribution, resulting in breccia ores distributed along the contact zones. The whole mineralization history can be classified as high temperature skarn stage and middle-low temperature hydrothermal stage.This study takes the Fenghuangshan Copper Deposit as an example to examine the metallogenic mechanism, the nature and origin of ore-forming fluid using the characteristics of metallogenic fluid and C, H and O isotope analysis. The Fenghuangshan deposit contains garnet, quartz and calcite in which fluid inclusions were well developed. Most of the fluid inclusions in garnet, diopside, quartz and calcite are concentrated mainly in three zones and the temperatures and salinity ranges of fluid inclusions represent three different phases of ore-forming fluid evolution, indicating that the fluid experienced a continuous process of evolution, which was well coupled with metellogenic phases of the Fenghuangshan deposit. Temperature decreasing and fluid boiling resulted in the discharge of a large amount of copper from Cu-bearing fluid. Furthermore, H and O isotopic analysis indicates that the ore-forming fluid consisted mainly of magmatic water, with minor meteoric water at the late stage of mineralization of the Fenghuangshan deposit. The value of Isotope S is 1.8%o to 2.9%o. S comes from the mantle. Isotope Pb constitutes show that Pb has the character of the magma material sources and Pb of the metallogenic fluid comes from the upper mantle.
Keywords/Search Tags:magmatism, mineralization fluid evolution, isotope, SHRIMP U-Pb zircon dating, Re-Os dating, skarn Copper Deposit, Fenghuangshan, Tongling, Anhui Province
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