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Ding W.L.,China University of Geoscierwes | Ding W.L.,China University of Geoscienees | Li C.,China University of Geoscierwes | Li C.,China University of Geoscienees | And 2 more authors.
Acta Petrologica Sinica | Year: 2011

The comprehensive geochemical cross section in the main structures of the Qiangtang basin was established to evaluate the source rock and predict the favorable hydrocarbon generation areas, based on the data of organic abundance, type and maturity from a large number of outcrop samples in the Mesozoic marine mudstone and carbonate source. The results show that relation between TOC and hydrocarbon potential (S1 + S2), chloroform bitumen "A" and total hydrocarbon content (HC) has good correlation, generally in positive liner, of which in carbonate and oil shale is higher than that in the mudstone and coal, dependent on their lithology to some extent. Subaerial weathering has small impact on organic abundance, but has significant impact on hydrocarbon potential, chloroform bitumen "A" and total hydrocarbon content (HC). The Mesozoic marine source rocks development varies in different structural unit, for example, carbonate rocks in the Suowa Formation and Delta mudstone in the Xiaochaka Formation of Dirangbicuo-Tumen sag are of good quality source rock. Oil shale and shale in the Xiaochaka Formation of Paducuo-Najiangcuo sag are of extreme good quality source rock, deep water shelf and platform carbonate rock are middle class source rocks. And platform carbonate rock in the Buqu Formation and Suowa Formation buried deep in the Dongcuo-Huluhu and platform carbonate in the Buqu Formation and upper carbonate in Xiaochaka Formation buried deep in the Tupocuo-Baitanhu are middle class quality source rock. Organic matter, is mainly II type, with maturity various in different areas, ranging from mature to over-mature, most mature-high mature and increasing from lop to bottom in a single cross section. Sedimentary environment is the main controlling factor of source rocks quality. Middle deep marine black shale or mudstone in Upper Triassic Xiaochaka, with wide hydrocarbon generation area, are the most important source rocks. While the still water mud-carbonate rocks in water closed carbonate plateform in the Jurassic Buqu Formation (J2b) and Suowa Formation (J2s) are important source rocks, with wide carbonate hydrocarbon-generation. Further study on the source rock characteristics and major source rock has significance for future oil and gas exploration.

Yang L.,China University of Geoscienees | Deng J.,China University of Geoscienees | Zhao K.,China University of Geoscienees | Liu J.,China University of Geoscienees
Acta Petrologica Sinica | Year: 2011

Ailaoshan gold belt, one of the most important Himalayan orogenie-type gold belt in China, formed during the processes of superimposed orogenesis in Sanjiang Tethys. The relationship between mineralization events and teetono-thermochronology as well as the related geodynamic regimes has been discussed in terms of the isotope dating result of gold mineralization in Ailaoshan orogenic belt Hercynian period is considered to be the oldest mineralization concentrated time through the ages obtained, however, the real metallogenic ages deviated from the apparent ages due to the excess argon, the regional ophiolites formed synchronously to the youngest apparent age (345. 2 ± 16Ma) ; the relationship between gold contents in auriferous pyrite silicolite and hydrothermal deposition suggest the geodynamic regime of seafioor spreading and initial ocean basin forming. Indosinian period is exactly the time at which the main collision of the regional orogen happened, when large-scale magmatism, Cu-Ni-Pt-Pd sulfide deposits, VMS type Cu-Pb-Zn deposits and porphyry Cu-Au deposits happened intensively, besides Re-Os isochron age of auriferous pyrite from Laowangzhai gold ore deposit is 229 ±38Ma. Metallogenic ages during Yanshan are split up into several scattered periods ( 180Ma, 135Ma, 110Ma and 90Ma) , the apparent age of the latest age spectra (91 ± IMa) is likely the response to significant transition of geodynamic regime, besides the lagescale regional diagenesis ( porphyry ) and metallogenesis ( porphyry Cu-Mo-W-Au deposits ) during the period ( ca. 90∼ 70Ma ) corresponds the transition of tectonic regimes from accretion orogeny to collision orogeny. Himalayan period are divided into three tectonic-thermal events related to mineralization, namely the early, occurred from 63. 09 ∼ 61. 55 Ma, the main, occurred from 36. 10 ∼ 33. 76Ma, and the late, occurred from 30. 80 ∼26.40Ma, which were controlled by the strongly early convergence geodynamic regime of India-Euraisa, the early to late stage transition of geodynamic regime, and eastward escapation of the Tibetan Plateau, and pulsating uplift of asthenosphere, respectively. The metallogenic characteristics, combined with published geological and isotopic information, indicate that the large-scale gold metallogeny is closely related to the intense crust-mantle material exchange and the tectonic deformation in the transition of geodvnamic regimes.

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