四川盆地东部天然气地球化学特征与TSR强度对异常碳、氢同位素影响

对四川盆地东部50个天然气样品组分和碳、氢同位素组成分析结果显示,天然气以烃类气体为主,干燥系数高(C1/C1+=0.975~1.0),H2S含量变化较大(H2S=0.00%~16.89%)。利用烷烃气碳、氢同位素组成和判识油型气热演化程度图版,确定四川盆地东部天然气主要为原油裂解气,且热演化程度已处于油气裂解阶段。在四川盆地东部,烷烃气碳、氢同位素组成普遍存在局部倒转现象,即δ13C1δ13C2δ13C3和δD1δD2,这主要与研究区域不同硫酸盐热化学还原作用(TSR)强度有关,因为在该反应过程中不仅会产生大量的CH4,其碳同位素较重,同时,水参与了硫酸盐与烃类的化学还原反应使得水中的H+与烃类中H+发生同位素交换,从而引起TSR生成CH4的氢同位素分馏大于干酪根直接生烃过程造成的氢同位素分馏。异常δ13CCO2值与TSR反应过程中部分碳同位素较轻的CO2与硫酸盐中金属离子(Mg2+、Fe2+、Ca2+等)以碳酸盐的形式沉淀后,导致气藏中残余重碳同位素组成的CO2与酸性气体腐蚀碳酸盐岩储集层形成的CO2相混合有关。     

Microscale Simultaneous Measurement of Carbon and Nitrogen Isotopes on Natural Diamond

Simultaneous analysis of carbon and nitrogen isotope ratios by SIMS was applied for the first-time to a natural diamond from the Kelsey Lake kimberlite, State Line Distinct, Colorado (UWD-1). This in situ procedure is faster, reduces sample size for analysis, and measures both isotope ratios from a single ~ 10 μm diameter pit, a critical advantage for zoned diamonds. The carbon isotope ratio (expressed as δ¹³C_VPDB) of the bulk UWD-1 crystal, determined by the conventional combustion method in the present study, is -5.9‰ ± 0.2‰ (VPDB, 2s). Nitrogen mass fraction ([N]) and isotope ratio (expressed as δ¹⁵N_Air) were determined by stepwise combustion and gas-source mass-spectrometry, resulting in 553 ± 64 μg g^-1 and -6.7‰ ± 1.1‰ (Air, 2s), respectively. Secondary ions of ¹²C₂^-, ¹²C¹³C^-, ¹²C¹⁴N^-, and ¹²C¹⁵N^- were simultaneously measured by SIMS using three Faraday cups and one electron multiplier. The spot-to-spot reproducibility of δ¹³C and δ¹⁵N values for the UWD-1 (178 spots on sixteen chips, 10 μm spots), were 0.3‰ and 1.6‰, respectively (2s). While ¹²C¹⁴N^-/¹²C₂^- ratios, which are an indicator for [N], varied up to 12% among these sixteen chips, such variation did not correlate with either δ¹³C or δ¹⁵N values. We propose that UWD-1 is a suitable reference sample for microscale in situ analysis of δ¹³C and δ¹⁵N values in diamond samples.     

塔里木盆地中,上奥陶统烃源岩的碳同位素宏观证据

经过十余年的勘探,已在塔里木盆地探明１３个大、中型油气田和３３个工业性含油构造,但关于塔里木盆地的古生界主力烃源岩一直有争议。本文根据两条有代表性的地表剖面和两条钻井剖面的海相碳酸盐岩碳、氧稳定同位素分析与研究,发现了中、上向陶统碳同位素组成的大幅度正向波动,认为这是当时全球范围大陆冰川作用的结果,这一时期有利于沉积有机质的保存。结合有机质丰度、成熟度指标（Ｒo）以及沉积相等地质因素综合分析,提出     

Fluid Inclusions and Hydrogen,Oxygen, and Lead Isotopes of the Antuoling Molybdenum Deposit,Northern Taihang Mountains,China

The Antuoling Mo deposit is a major porphyry‐type deposit in the polymetallic metallogenic belt of the northern Taihang Mountains, China. The processes of mineralization in this deposit can be divided into three stages: an early quartz–pyrite stage, a middle quartz–polymetallic sulfide stage, and a late quartz–carbonate stage. Four types of primary fluid inclusions are found in the deposit: two‐phase aqueous inclusions, daughter‐mineral‐bearing multiphase inclusions, CO₂–H₂O inclusions, and pure CO₂ inclusions. From the early to the late ore‐forming stages, the homogenization temperatures of the fluid inclusions are 300 to >500°C, 270–425°C, and 195–330°C, respectively, with salinities of up to 50.2 wt%, 5.3–47.3 wt%, and 2.2–10.4 wt% NaCl equivalent, revealing that the ore‐forming fluids changed from high temperature and high salinity to lower temperature and lower salinity. Moreover, based on the laser Raman spectra, the compositions of the fluid inclusions evolved from the NaCl–CO₂–H₂O to the NaCl–H₂O system. The δ¹⁸O_H2O and δD values of quartz in the deposit range from +3.9‰ to +7.0‰ and ?117.5‰ to ?134.2‰, respectively, reflecting the δD of local meteoric water after oxygen isotopic exchange with host rocks. The Pb isotope values of the sulfides (²⁰⁸Pb/²⁰⁴Pb, 36.320–37.428; ²⁰⁷Pb/²⁰⁴Pb, 15.210–15.495; ²⁰⁶Pb/²⁰⁴Pb, 16.366–17.822) indicate that the ore‐forming materials originated from a mixed upper mantle–lower crust source.     

水样中溶解性无机碳同位素测试前处理方法对比研究

水中溶解性无机碳(DIC)的碳同位素前处理方法由传统的BaCl2沉淀法,逐步发展到野外采样后直接通过连续流系统(GasBench-IRMS)测试.当前对于BaCl2沉淀法和连续流测试结果的差异,以及最佳DIC的前处理方法均需要开展深入研究.本文应用BaCl2沉淀法、医用无菌高密度聚乙烯瓶装样、GasBenchⅡ顶空样品瓶野外直接生成CO2气体三种前处理方法,对比研究前处理方法对采自桂林盘龙洞洞穴滴水和地下河水样中DIC碳同位素测试的影响.结果表明,由于BaCl2沉淀法使水样中游离CO2逸出,导致测定的DIC碳同位素值相对于另两种方法均偏正:地下河水样的碳同位素值最大偏正0.26‰;洞穴滴水的碳同位素值最大偏正0.33‰.因为野外水样采集环境的温度、大气压强与实验室内部环境变化较小,没有引起CO2、HCO3的溶解度改变,用医用无菌高密度聚乙烯瓶和GasBenchⅡ顶空样品瓶采集水样的碳同位素测试结果相同;相对而言,利用GasBenchⅡ顶空样品瓶直接产生CO2气体,能够避免外界环境条件变化导致CO2、HCO3-的溶解度发生变化引起碳同位素分馏,是精确测定水中DIC碳同位素最佳的前处理方法.     

Carbon and Noble Gas Isotopes in the Tengchong Volcanic Geothermal Area, Yunnan, Southwestern China

Carbon and noble gas isotope analyses are reported for bubbling gas samples from the Tengchong volcanic geothermal area near the Indo-Eurasian suture zone. All samples contain a resolvable component of mantle-derived 3He. Occurrence of mantle-derived 3He coincides with surface volcanism. However, 3He occurs over a larger geographic areathan do surface volcanics. δ13C values for CO2 and CH4 vary from -33.4‰ to 1.6 ‰ and from -52.8‰ to -2.8‰, respectively. He and C isotope systematics indicate that CO2 and CH4 in the CO2-rich gases originated predominantly from magmatic component mixed with crustal CO2 produced from carbonate. However, breakdown of organic matter and near-surface processes accounts for the CH4 and CO2 in N2-rich gases. 3He/4He ratio distribution pattern suggests that mantle-derived He and heat sources of high-temperature system in central Tengchong originate from a hidden magma reservoir at subsurface. CO2-rich gases with the highest 3He/4He ratio (5.2 Ra) may be representative of the     

沉积岩总有机质碳同位素分析的前处理影响

岩石样品中的有机质稳定碳同位素地球化学已经在重建古环境和古植被等领域得到十分广泛的应用。但对样品的前处理方法的系统研究较少。由于岩石样品前处理的方法不同而对有机碳同位素的测量结果所产生的正负偏差,从而导致不能准确地反映样品中所记录的信息。笔者通过大量条件试验,分析了前处理过程中主要影响实验结果的几种因素。①样品粒度的影响：粒度100目的样品可得理想数据,而粒度在60目时两个样品同位素值均相对偏正,200目时灰岩样品也相对偏正;②不同酸浓度的影响：在1～12N浓度酸处理样品其有机质碳同位素没有明显变化,但低等级酸所含杂质明显使数据偏负,加入１５％的氢氟酸对数据没有产生明显影响;③洗除样品中残余酸和烘干温度的影响：为了避免样品中有机质的损失,而不洗除样品中残余的酸,但是样品数据明显偏负并对仪器有损坏,烘干温度100°C时样品部分有机质挥发或升华而使数据相对偏正。     

微生物降解有机物的碳氢同位素分馏研究进展

微生物降解使有机化合物的稳定碳、氢同位素发生不同程度分馏的研究在有机污染物来源和微生物环境修复等领域取得了长足进展,并对原油和天然气微生物降解研究有借鉴意义。微生物作用下的同位素分馏为动力同位素分馏,导致重同位素在残余物中富集。影响微生物降解有机物同位素分馏的主要因素有微生物的降解代谢途径、辅酶作用、降解类型与程度、同位素质量差异和有机物碳数等。不同的微生物代谢途径代表不同的生物化学反应,造成了同位素分馏的显著差异;辅酶对反应的催化作用使微生物作用造成的同位素分馏更加复杂。低碳数正构烷烃遭受微生物降解程度越高,碳、氢同位素的分馏也越大,同位素变重与降解程度之间有明显的相关性。但对于复杂化合物,由于降解的多级反应,同位素分馏与降解程度间的相关性并不明显。在同样降解程度下,氢同位素分馏大于碳同位素分馏,低碳数正构烷烃的同位素分馏大于高碳数正构烷烃的同位素分馏。     

河北张麻井铀钼矿床成矿流体特征——来自流体包裹体及氢氧同位素的证据

张麻井铀钼矿是沽源-红山子铀成矿带南段的典型矿床。矿体主要赋存于早白垩世张家口组三段中酸性火山岩中,成矿与次流纹斑岩密切相关,受北北东向F₄₅、北西向F₃断裂及西辛营破火山机构联合控制。流体包裹体研究表明,包裹体以液体类型为主,均一温度介于160～220℃,盐度介于0.5%～2.5%(NaCl),密度介于0.87～0.93 g/cm~3,成矿流体以中低温、中低盐度为主,属浅成中低温热液成矿类型。氢氧同位素特征显示,矿床主成矿热液期流体δD介于-124.9‰～-96.2‰,■介于-10.7‰～-3.3‰,表明成矿热液主要来自大气降水。     

岩溶地质碳汇的稳定性——以贵州草海地质碳汇为例

近几年来对岩溶碳汇的争论越来越多,其关键问题是岩溶作用产生的重碳酸根是否稳定.本文以贵州草海流域为研究区,基于前人研究基础,以碳同位素模型计算出岩溶作用产生的DIC((Dissolved Inorganic Carbon溶解无机碳)中58.8%为草海中为水生植物利用,草海地质碳汇量达588.67 tC/a.以此推算长江中下游湖泊沉水植物每年固碳量370602 tC/a,长江中下游湖泊中仅沉水植物稳定的地质风化CO2汇量约为75万吨.从而证明岩溶碳汇的相对稳定性和岩溶动力系统新理论的合理性.