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Late Mesozoic Ore‐forming Events in the Ningwu Ore District, Middle‐Lower Yangtze River Polymetallic Ore Belt, East China: Evidence from Zircon U‐Pb Geochronology and Hf Isotopic Compositions of the Granodioritic Stocks
Author(s) -
Chao DUAN,
Yanhe LI,
Kejun HOU,
Shunda YUAN,
Jialin LIU,
Cheng ZHANG
Publication year - 2012
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.2012.00698.x
Subject(s) - zircon , geology , geochemistry , geochronology , cretaceous , mesozoic , mineralization (soil science) , ore genesis , structural basin , volcanic rock , volcano , fluid inclusions , paleontology , quartz , soil science , soil water
Late Mesozoic volcanic‐subvolcanic rocks and related iron deposits, known as porphyry iron deposits in China, are widespread in the Ningwu ore district (Cretaceous basin) of the middle—lower Yangtze River polymetallic ore belt, East China. Two types of Late Mesozoic magmatic rocks are exposed: one is dioritic rocks closely related to iron mineralization as the hosted rock, and the other one is granodioritic (‐granitic) rocks that cut the ore bodies. To understand the age of the iron mineralization and the ore‐forming event, detailed zircon U‐Pb dating and Hf isotope measurement were performed on granodioritic stocks in the Washan, Gaocun‐Nanshan, Dongshan and Heshangqiao iron deposits in the basin. Four emplacement and crystallization (typically for zircons) ages of granodioritic rocks were measured as 126.1±0.5 Ma, 126.8±0.5 Ma, 127.3±0.5 Ma and 126.3±0.4 Ma, respectively in these four deposits, with the LA‐MC‐ICP‐MS zircon U‐Pb method. Based on the above results combined with previous dating, it is inferred that the iron deposits in the Ningwu Cretaceous basin occurred in a very short period of 131–127 Ma. In situ zircon Hf compositions of ε Hf ( t ) of the granodiorite are mainly from –3 to –8 and their corresponding 176 Hf/ 177 Hf ratio are from 0.28245 to 0.28265, indicating similar characteristics of dioritic rocks in the basin. We infer that granodioritic rocks occurring in the Ningwu ore district have an original relationship with dioritic rocks. These new results provide significant evidence for further study of this ore district so as to understand the ore‐forming event in the study area.