Abstract
Abstract The early Cambrian is a critical interval of dramatic oceanic and biochemical changes in geological history. The black shale deposits, which are rich in Mo, Ni, V, and platinum group elements (PGE), are a reflection of that interval. Among all known Cambrian black shale deposits in South China, the vanadium deposits are poorly constrained by geochronology. The newly discovered tuff layer in the Sansui Bagong vanadium deposit in Guizhou Province can provide excellent constraints on the age of vanadium deposits. In this study, we obtain a new zircon U–Pb isotopic age, which can constrain the age of the vanadium deposit. This tuff occurs in the middle part of the ore bed, and the age of the tuff layer can reflect the mineralization age of the V deposit. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used in this study to obtain the zircon U–Pb age of the tuff and indicates that the event of volcanic activity took place at 520.9 ± 1 Ma. This age is close to the boundary between the Cambrian Terreneuvian and Series 2. This result provides a good constraint on the age of the vanadium deposits in South China and makes the vanadium deposits to be comparable with other Mo–Ni–PGE deposits. The alteration of organic carbon isotope (δ 13Corg) values can reflect changes in the marine environment and is widely used in stratigraphic correlation. The analysis of the δ 13Corg values of the ore bed in the present study reveals a positive excursion at the bottom of the deposit and a negative excursion in the V-enriched layer. The δ 13Corg values in the Bagong section are comparable to those in the Xiaotan and Longbizui sections. The ages of the Sansui vanadium deposit constrained by the U–Pb isotopic age of the tuff and the δ 13Corg values are consistent. All of the data lead us to infer that the vanadium deposit formed at approximately 521 Ma.
Highlights
South China is an ideal area for studying changes in marine environment and early biological evolution because of the wide distribution of strata and abundant fossils from the Precambrian-Cambrian Period in this region
The zircons in the tuff have variable Th and U contents; the CL images differ in intensity
Some zircons are darker; most of them are brighter in the CL images
Summary
South China is an ideal area for studying changes in marine environment and early biological evolution because of the wide distribution of strata and abundant fossils from the Precambrian-Cambrian Period in this region. Great insights into palaeontology and palaeo-marine environments have been achieved through studies of the lower Cambrian strata in this area [1,2,3,4,5,6,7,8,9,10]. Black shale vanadium deposits are widely distributed in the lower Cambrian strata of South China [10,16]. The metallogenic age of V deposit is a relatively complex and controversial issue in the study of earl Cambrian. Through division and contrast of metallogenic sequence, Li et al indicated that the age of V deposit is
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