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Crustal extension Ag-Pb-Zn veins in the Xiong'ershan district, southern North China Craton; constraints from the Shagou Deposit

Li Zhanke, Li Jianwei, Zhao Xinfu, Zhou Meifu, David Selby, Bi Shijian, Sui Jixiang and Zhao Zhenjun
Crustal extension Ag-Pb-Zn veins in the Xiong'ershan district, southern North China Craton; constraints from the Shagou Deposit
Economic Geology and the Bulletin of the Society of Economic Geologists (November 2013) 108 (7): 1703-1729

Abstract

The Shagou vein-type Ag-Pb-Zn deposit in the Xiong'ershan district, southern margin of the North China craton, is hosted within amphibolite facies metamorphic rocks of the Late Archean to early Paleoproterozoic Taihua Group. The Ag-Pb-Zn veins are localized in NE- to NNE-trending brittle faults and typically display symmetrical zoning consisting of siderite, quartz + sphalerite, galena, and quartz + calcite from the margin toward the center of each vein. Ore-related hydrothermal alteration is well developed on both sides of the veins, dominated by silicification, sericitization, chloritization, and carbonatization. Sericite separates extracted from a major Ag-Pb-Zn vein yield a (super 40) Ar/ (super 39) Ar plateau age of 140.0 + or - 1.0 Ma (1sigma ) and isochron age of 141.1 + or - 1.6 Ma (1sigma ), indicating that mineralization occurred at the beginning of Early Cretaceous. Field and textural relationships indicate four hydrothermal stages marked by assemblages of quartz + siderite (stage I), quartz + sphalerite + ankerite (stage II), quartz + galena + silver minerals + ankerite (stage III), and quartz + calcite (stage IV), respectively. Silver minerals are abundant in all veins and are composed of, in paragenetic order, argentiferous tetrahedrite, polybasite, jalpaite, argentite, and native silver. These silver minerals commonly occur as replacements of galena, chalcopyrite, and other sulfides, or as fillings of microfractures in sulfides and quartz. Microthermometric measurements of primary fluid inclusions in quartz, carbonates, and sphalerite from various hydrothermal stages indicate that ore minerals were deposited at intermediate temperatures (267 degrees -157 degrees C) from aqueous-carbonic to aqueous fluids with moderate salinities (7.2-15.9 wt % NaCl equiv). Coexisting galena-sphalerite pair yields sulfur isotope equilibrium temperatures of 205 degrees to 267 degrees C, consistent with the overall homogenization temperatures of fluid inclusions. The microthermometric data also indicate that both fluid mixing and fluid-rock interaction were important mechanisms for ore precipitation. Carbonate minerals (siderite, ankerite, calcite) spanning the entire mineralization history have delta (super 13) C (sub V-PDB) values of -5.2 to -1.4 per mil and delta (super 18) O (sub V-SMOW) of 10.9 to 15.0 per mil, corresponding to calculated values for the ore fluids of -6.5 to -1.8 per mil and 1.4 to 5.4 per mil, respectively. delta (super 34) S (sub V-CDT) values of sulfide minerals (pyrite, sphalerite, galena) range from 1.1 to 5.5 per mil, consistent with a deep-seated sulfur source. Galena separates have (super 206) Pb/ (super 204) Pb ratios of 17.472 to 17.813, (super 207) Pb/ (super 204) Pb ratios of 15.411 to 15.498, and (super 208) Pb/ (super 204) Pb ratios of 38.178 to 38.506. The isotope data, together with geological and geochronological evidence, favor a primary metamorphic source for sulfur and other components in the ore fluids. A synthesis of available data suggests that the Shagou deposit is a typical vein-type Ag-Pb-Zn deposit that formed under an extensional geodynamic setting associated with tectonic reactivation of the North China craton during the late Mesozoic, a time period that is manifested by pervasive magmatism, widespread formation of metamorphic core complexes, and development of faulted basins throughout the eastern part of the craton. Metamorphic devolatilization of the Meso-Neoproterozoic marine sedimentary rocks previously subducted beneath the Xiong'ershan district, facilitated by extensive magmatism and elevated heat flow due to lithospheric extension, could have provided large amounts of ore fluids responsible for the Ag-Pb-Zn mineralization. The NE- to NNE-trending faults affiliated with the transcrustal Machaoying fault may have acted as pathways for the upward migration of deep-seated metamorphic fluids. Mixing of the metamorphically derived fluids with meteoric waters ultimately resulted in deposition of the Ag-Pb-Zn veins in brittle extensional structures.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 108
Serial Issue: 7
Title: Crustal extension Ag-Pb-Zn veins in the Xiong'ershan district, southern North China Craton; constraints from the Shagou Deposit
Affiliation: China University of Geosciences, Wuhan, China
Pages: 1703-1729
Published: 201311
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 144
Accession Number: 2013-088736
Categories: Structural geologyEconomic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 plates, 6 tables, geol. sketch maps
N33°30'00" - N34°40'00", E110°00'00" - E112°30'00"
Secondary Affiliation: University of Hong Kong, CHN, ChinaUniversity of Durham, GBR, United KingdomBureau of Land and Resources of Luoyang, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Society of Economic Geologists. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201352
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