摘要
研究了湘西黔东地区下寒武统有机地球化学特征 ,包括三个富含有机质的层位 :底部牛蹄塘组黑色页岩 ;清虚洞组下部泥质条带灰岩和中部泥质灰岩 ,其中的泥质灰岩层是花垣MVT铅锌矿床的矿化围岩之一。这些层位中有机质的正构烷烃、类异戊二烯烃类、甾烷和萜烷的生物标志化合物特征表明 ,它们的先质来源与寒武纪海中的菌藻类有关。这些有机质都具有较高的演化程度 ,均已进入生油门限 ,以黑色页岩的演化程度最高 ,但仍未达演化的终点阶段。泥质岩的演化程度不仅与成岩作用有关 ,而且受到成矿热流体的影响 ,造成有机质的族组成、生物标志化合物和最高热解温度 (Tmax)等与矿化强度成正比关系的变化。
The paper have studied the characteristics of organic geochimestry of Lower Cambrian and relavant mineralization of Lead-Zinc ore deposits in western Hunan and eastern Guizhou province.The lower Cambrian is located at the passive continental margin of Yangtze landmass in southeast,and divided into three units from lower to upper,i.e.,Niutitang Formation,Balong Formation and Qingxudong Formation,which belong to basin,shelf and ramp to margin reef-band facies of carbonate platform respectively.Algal limestone,grey-dark muddy limestone and overlying oolite limestone are host rocks of Huayuan MVT Lead-Zinc ore deposits in Qingxudong Formation. There are three beds richin organic matter:black shale in lower part of Niutitang Formation,zebra muddy limestone in lower part and grey-dark muddy limeston in middle part of Qingxudong Formation,and the black shale is much higher (75%) than other beds (0.2%～0.4%).On the basis of the GC-MS of organic matter tracts and Rock-Eval Py,Py-GC analysis,their characteristics of normal paraffin is higher carbon number range,single peak at the back,higher carbon number of main peak (27～31),weak odd-even predominance ,and Pr/Ph<1,but the characteristics of biomarker of sterane and terpane are different between them.Ischolestane is predominant in sterane of black shale(C 29 is main(=34.33%),C 29 αββ/ααα=2.18) and in grey-dark muddy limestone,cholestane is predominant(C 29 =42.2%,C 29 αββ/ααα=0.42).Tricycline terpane is predomenant in terpane of black shale(65.65%),Tm/Ts=1.14,and in grey-dark muddy limestone,hopane is predominant(=66.2%),Tm/Ts=1.22.Above mentioned characteristics suggest that the precursor origin of organic matter among all beds is blue algal and bacteria in Cambrian sea,and deposited on the reduction to weakly redaction environments.The evolution level of organic matter is different among them,they have passed oil-window and the black shale is higher than other,but it is still not beyond the end stage of evolution. Some data evidence that the evolution level of altered grey-dark muddy limestone is not only related to diagenisis but also to hot ore-forming fluid.Therefore,they can result in obvious change of group composits,biomarker,pyrolysis T max and pyrolysis parameters.In massive muddy limestone,chloroform bitumen “A”=0.004%,saturated hydrocarbon=11.80%～41.1%,aromatic hydrocarbon=15.07% ～5.45%,asphaltene=31.00%～50.94%,Zn<0.1%,but in interbedded rocks,Zn>1.0%,chloroform bitumen “A”increased to 0.0112%,saturated hydrocarbon rise to 42.18%～57.06%,aromatic hydrocarbon to 9.7%～21.47%,and asphaltene decrease to 7.36%～14.55%,pyrolysis T max from massive rock′s 397℃ increase to interbedded rock′s 510℃,and with increase of mineralization there occur the decrease in free hydrocarbon (S 1),pyrolysis hydrocarbon (S 2),hydrogen index (HI),oxygen index (OI) and hydrocarbon index (S 1/TOC) of grey-dark muddy limestone,All these suggest that there are close relationship between the organic composition and mineralization,and some organic composition may be directly precipitate during mineralization.
出处
《沉积学报》
CAS
CSCD
北大核心
2000年第2期290-296,共7页
Acta Sedimentologica Sinica
基金
国家自然科学基金资助项目 !(批准号 :4 9572 12 1)
