Wei HAO¹, Xu JIUHUA¹, Zhang GUORUI^1*, Zeng QINGDONG², Liu JIANMING², Chu SHAOXIONG², & Jiang BAIFANG^3
1University of Science and Technology Beijing, 30 Xueyuan Road, Haidian District, Beijing 100083 P. R.China; ^*Corresponding Author: e-mail: ronghaiwei@163.com, Tel. (0086)18701677540
²Institute of Geology and Geophysics Chinese Academy of Sciences, No. 19, Beitucheng Western Road, Chaoyang District, 100029, Beijing, P.R.China
³Liaoning Non-ferrous Geological Exploration Institute, No. 7, Beijing Road, Shenhe District, 110013, Shenyang, P. R.China

THE SOURCE AND EVOLUTION OF METALLOGENIC FLUIDS IN THE DUOBAOSHAN-TONGSHAN PORPHYRY CU (MO) DEPOSIT, HEILONGJIANG, CHINA

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The Duobaoshan-Tongshan porphyry Cu (Mo) deposit, located in the eastern part of the Xingmeng orogenic belt, is the largest porphyry deposit in the Duobaoshan-Aershan Metallogenic belt in central and northern Daxinganling. The ore bodies are mainly hosted inside a granodiorite and at the base of the Duobaoshan Formation. Four ore-forming stages are recognized in the Duobaoshan-Tongshan deposit: (I) Potassic and silicic stage; (II) Silicification-molybdenum mineralizing stage; (III) Phyllic-copper mineralizing stage; and (IV) carbonate-quartz stage. Fluid inclusions of stage (I) are characterized by aqueous, CO₂-H₂O and pure CO₂ fluids, with homogenization temperatures of 245-400°C, salinities of 6-10 wt%NaCl eqv., and densities of 0.5-0.9 g cm^-3. However, those of stage II are dominated by aqueous, CO₂-H₂O, daughter mineral-bearing inclusions, with peak homogenization temperatures of 260-300°C and salinities of 1.7 - ~39wt%NaCl eqv., and densities of 0.3-1.1g cm^-3. Stage III is also characterized by aqueous and CO₂-H₂O inclusions, with peak homogenization temperatures of 200-280°C, salinities of 0.1-24.8% wt% NaCl eqv., and densities of 0.5-1.0g cm^-3. whereas stage IV fluids are aqueous, with homogenization temperatures of 125-170°C, salinities of 0.5-12.8 wt% NaCl eqv., and densities of 0.8-0.9g cm-3. Respective trapping pressures for stage I, II, and III are 110-160MPa, 58-80MPa, and 8-17MPa, with corresponding formation temperature of 375-650°C, 310-350°C, and 210-290°C. Laster Raman spectroscopic analysis indicates that the main components of the fluid inclusions are H₂O and CO₂. The hydrogen and oxygen isotopic compositions of the fluids responsible for alteration and mineralization are constrained by magmatic fluid and meteoric water, and indicate an evolution process from magmatic hydrothermal fluid to meteoric water-bearing fluid, and indicate the influence of the wall-rocks on the evolution process of the hydrothermal fluids. Microthermometry combined with field observations and fluid inclusion petrography suggest that the Duobaoshan porphyry deposit resulted from magmatic differentiation and the large-scale mixing of distinct fluid types. Moreover, complex structures in the mining area facilitated the transport of the hydrothermal mineralizing fluids and subsequent terminal precipitation. There is a close relationship between copper mineralization and NW-striking foliated shear zones, reflecting the control of later shear belts on the copper mineralization.