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Abstract: Deep weathering profiles and associated supergene Mn-oxides deposits are widely distributed in South China. However, data on their ages are not available until most recently. 40Ar/39Ar laser incremental heating analysis of potassium-bearing supergene Mn-oxides collected from four weathering profiles in the Qinzhou–Fangcheng Mn belt, Guangxi Province, South China, provides, for the first time, numerical constraints on timing of weathering and supergene Mn enrichment. Thirty-eight of 42 cryptomelane grains yield well-defined plateau (36 grains) or pseudo plateau (2 grains) ages ranging from 17.6±0.5 Ma to 4.71±0.08 Ma (2σ). The results, when combined with data from Mn-oxides deposits from the adjacent Guangdong and Hunan Provinces, document a protracted history of weathering and supergene Mn enrichment, spanning from the earliest Miocene to the latest Pliocene in South China. This indicates that warm and humid climatic conditions conducive to intense weathering and secondary mineralization prevailed across South China during the whole Neogene. The climatic conditions inferred from weathering geochronology are consistent with sedimentary records and fossil floral and fauna associations from Cenozoic inland and marginal sea basins of South China. The weathering geochronology data also provide temporal constraints on the initiation and intensification of the East Asian monsoon that has been the cause for the South China''s humid climate. [Copyright &y& Elsevier]

The Jiaodong gold province, the largest gold-producing district in China, is located in the Jiaodong peninsula at the eastern margin of the North China craton and bounded by the continental scale Tan-Lu fault, 40 km to the west. Previous geochronological studies suggest that pervasive gold deposition took place in the westem part of the province between 122 and 119 Ma. Here we report high-quality, 40Ar/39Ar ages of the Pengjiakuang and Rushan deposits from the eastern part of the Jiaodong gold province, placing additional chronological constraints on the timing of regional mineralization. Seven sericite grains extracted from auriferous alteration assemblages at the Pengjiakuang deposit yielded well-defined plateau ages between 120.9 ± 0.4 and 119.1 ± 0.2 Ma (2σ). Three separates of igneous biotite from a sample of the Queshan gneissic granite, adjacent to the Pengjiakuang deposit, gave reproducible plateau ages of 124.6 ± 0.6 to 123.9 ± 0.4 Ma (2σ). Six sericite separates from two samples in the Rushan deposit yielded 40Ar/39Ar plateau ages at 109.3 ± 0.3 to 107.7 ± 0.5 Ma (2σ), whereas biotite from the Kunyushan monzogranite that hosts the Rushan deposit had plateau ages ranging from 129.0 ± 0.6 to 126.9 ± 0.6 Ma (3 separates from one sample). The apparent age gap between hydrothermal sericite and magmtic biotite from both deposits, together with the similar argon closure temperatures for these mica minerals, suggest that gold mineralization had no direct relationship to the granitoid magmatism. Instead, gold deposition coincided with the emplacement of mafic to intermediate dikes widespread in the Jiaodong gold province, which have been dated at ca. 122 to 119 Ma and, less commonly, at 110 to 102 Ma. The new 40Ar/39Ar ages from the eastern Jiaodong peninsula, when combined with published data from the western part suggest that gold mineralization was broadly contemporaneous throughout the district. The Early Cretaceous gold mineralization also is widely developed in four other major gold districts along the Tan-Lu fault. The temporal and spatial correlation of these gold deposits with mafic to intermediate dikes commonly found in most mineralized areas, the presence of well-documented metamorphic core complexes and halfgraben basins along the Tan-Lu fault, and voluminous basalts therein, snggest that the Early Cretaceous was an important period of lithospheric extension, possibly caused by the late Mesozoic lithospheric thinning beneath the eastern block of the North China craton. Lithospheric thinning and extension could have resulted in abnormally high heat and fluid fluxes necessary for large-scaled gold mineralization. [ABSTRACT FROM AUTHOR]