Abstract
The Hongnipo deposit, a newly discovered large copper deposit in the Kangdian copper belt, SW China, is hosted in the Paleoproterozoic Hekou Group. This deposit contains ~4200 Mt of Cu ores, with an average grade of 1.42 wt.% Cu. Orebodies occur mainly as stratiform, stratoid and lenticular forms. Mineralization consists predominantly of high grade vein-type ores and low grade laminated ores. Field relationships indicate vein-type mineralization crosscuts laminated mineralization and host rocks, indicating that there were at least two mineralization events during the formation of the deposit. Pyrite separates from the laminated ores yield a Rb-Sr isochron age of 1552 ± 80 Ma, with a highly radiogenic initial 87Sr/86Sr ratio of 0.71214 ± 0.00081, indicating a major contribution from the ore-hosting rocks. Sulfides from the laminated ores have δ34S values ranging from −1.8‰ to 11.4‰, with the vast majority in the range of 5.3‰ to 11.4‰, suggesting the mixed derivation of sulfur from seawater sulfates and magmatic fluids. Chalcopyrite separates from the vein-type ores have a Re-Os isochron age of 794.8 ± 7.9 Ma. The initial 187Os/188Os (2.8 ± 1.2) and γOs (+2202) values are slightly lower than the average values of continental crust, indicating a major metal source of the Hekou Group with minor mantle input. Sulfides from the vein-type ores have δ34S values that range from −10.3‰ to 4.0‰ and cluster between 0‰ to 2.2‰, which implies a significant contribution of magmatic-sourced sulfur with minor biogenic sulfur. Two major mineralization events have been identified. The Rb-Sr age of the laminated ores likely records a VMS mineralization event at ~1.6 Ga. The much younger Re-Os age is considered to represent the timing of an important mineralization event, which is likely related to the Neoproterozoic magmatism and/or metamorphism and represents a newly documented mineralization event to be targeted by exploration.
Highlights
The Kangdian copper belt, which extends for ~300 km in the southwest of the Yangtze Block [1,2,3,4], is one of the most important iron-copper-gold production areas in China
The much younger Re-Os age is considered to represent the timing of an important mineralization event, which is likely related to the Neoproterozoic magmatism and/or metamorphism and represents a newly documented mineralization event to be targeted by exploration
Li et al [13], Sun et al [14] and Greentree [15] reported the Re-Os model ages of molybdenite (928–1005 Model Age (Ma)), a Pb-Pb isochron age of sulfides (887 Ma), and Ar-Ar plateau ages of muscovite and biotite (848 Ma and 860 Ma), respectively, proposing that it has formed by Neoproterozoic retrograde metamorphism
Summary
The Kangdian copper belt, which extends for ~300 km in the southwest of the Yangtze Block [1,2,3,4], is one of the most important iron-copper-gold production areas in China. Li et al [13], Sun et al [14] and Greentree [15] reported the Re-Os model ages of molybdenite (928–1005 Ma), a Pb-Pb isochron age of sulfides (887 Ma), and Ar-Ar plateau ages of muscovite and biotite (848 Ma and 860 Ma), respectively, proposing that it has formed by Neoproterozoic retrograde metamorphism. Zhu and Sun [17] and Song [18] reported chalcopyrite Re-Os isochron ages of 1290 Ma and 1085 Ma, respectively They suggested that the deposit formed in a single mineralization event related to regional Mesoproterozoic magmatism (~1.1 to 1.3 Ga [19,20,21]), but was overprinted by post-ore hydrothermal events related to regional Neoproterozoic magmatism or metamorphism [22]. Zhu et al [23] reported four molybdenite Re-Os ages, ranging from 835 to
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