Fluid inclusion studies of the Abawso gold prospect,near the Ashanti Belt,Ghana

The major Ghanaian lode gold deposits are preferentially aligned along the western and eastern contacts of the Kumasi Basin with the Ashanti and Sefwi Belts, respectively. The investigated area of the Abawso small-scale concession, covering the workings of the old Ettadom mine, is situated 3 km west of the lithological contact of the Birimian metavolcanic rocks of the Akropong Belt in the east with the Birimian metasedimentary rocks of the Kumasi Basin in the west. The rocks of the Abawso concession represent a steeply NW-dipping limb of a SE-verging anticline with an axis plunging to the SW. Quartz veining occurs predominantly in the form of en échelon dilatational veins along NNE–SSW-striking shear zones of a few metres width and shows evidence of brittle and ductile deformation. Also stockwork-style quartz veining occurs in the vicinity of the main shaft of the old Ettadom mine. Hydrothermal alteration includes sericitisation, sulphidation and locally carbonatisation. The auriferous quartz veins mainly follow the trend of brittle to ductile deformed quartz veins; however, some occur in stockwork. Fluid inclusion studies reveal a large number of H₂O inclusions along intragranular trails in auriferous quartz vein samples, as well as an overall dominance of H₂O and H₂O-CO₂ inclusions over CO₂ inclusions. Textural observations and physico-chemical fluid inclusion properties indicate post-entrapment modifications for all quartz vein samples due to grain boundary migration recrystallisation. This process is interpreted to be responsible for the generation of the CO₂ inclusions from a H₂O-CO₂ parent fluid. In comparison with mineralisation at the Ashanti and Prestea deposits, which are characterised by CO₂±N₂ inclusions, the observed inclusion assemblage may be due to a shallower crustal level of mineralisation, or different degrees and styles of recrystallisation, or a less pronounced development of laminated quartz veins due to comparably restricted pressure fluctuations. Furthermore, the microthermometric observations allow the reconstruction of a possible retrograde P-T path, depicting near-isothermal decompression in the P-T range of the brittle/ductile transition.Editorial handling: E. Frimmel     

珠江口盆地东沙隆起的沉降史及其动力机制

根据东沙隆起及其周围钻井资料的一维构造沉降对比分析,结合前人在基底、盖层及断裂等方面的研究,将东沙隆起地区的构造演化分为5个阶段:自垩纪挤压阶段、古新世-早渐新世伸展断陷阶段、早渐新世末期抬升剥蚀阶段、晚渐新世-中新世快速的裂后沉降阶段、晚中新世以来断块升降阶段.认为下地壳高速层是促使早渐新世末期抬升剥蚀的重要因素,而...     

黄河流域气候与农业种植面积变化对径流的影响

根据黄河流域1960—2005年5个水文站逐日流量、77个气象站1959—2013年逐日降水数据,结合流域内主要农作物种植面积及大型水库资料,全面探讨气候与农业面积变化及人类活动对黄河流域径流变化的影响.研究表明:黄河流域所有流量分位数总体呈下降趋势,并于1980s中后期到1990s中期发生突变.降水变化是黄河流域径流变化的主要影响因素.在考虑不同流量分位数情况下,农作物种植面积变化对不同分位数径流变化的影响也有差异性.花园口站农作物种植面积变化对径流量量级和可变性均有显著影响;其余4站各项气候变化与农作物种植指标参数较大,虽均未达到10%的显著性水平,但仍会对径流的量级变化产生影响.对唐乃亥站,农作物耕作面积的下降减少了灌溉用水,在0.5流量分位数时有高达60%增加径流量的间接作用.对于头道拐站,农作物耕作面积的增加使得流域总蒸发量增加,灌溉用水增加,在0.3流量分位数时有高达40%减少径流量的间接作用.该研究为气候变化与人类活动影响下黄河流域水资源优化配置提供重要理论依据.     

干酪根化学降解产物的碳同位素组成研究

采用一系列温和的化学降解法对松辽盆地南部嫩江组烃源岩的干酪根进行连续的选择性化学降解，并对不同降解产物进行色谱—同位素比值质谱分析。研究表明碱性水解和脱硫产物以一元脂肪酸和正构烷烃为主，其中正构烷烃碳同位素分布曲线呈现一定的“负倾”（即随碳数增加呈现逐渐贫13C）趋势；一元脂肪酸以C16和C18为主，具有明显的偶碳优势，与同碳数的正构烷烃具有相似的碳同位素组成。氧化产物则以一元脂肪酸和α,ω 二元脂肪酸为主，一元脂肪酸低碳数部分呈现“负倾”趋势，高碳数部分则呈现“正倾”的趋势；α,ω 二元脂肪酸与低碳数的一元脂肪酸具有相似的分布，表明它们可能具有相同的母源。对比研究表明JL 30抽提物中正构烷烃可能存在混源的影响，其碳同位素组成是多源混合的结果。     

Evaluating new fault-controlled hydrothermal dolomitization models: Insights from the Cambrian Dolomite,Western Canadian Sedimentary Basin

Fault-controlled hydrothermal dolomitization in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep-seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitization. With development of new concepts in hydrothermal dolomitization, the study aims in particular to test the hypothesis that dolomitizing fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilizing the Cambrian Mount Whyte Formation as an example. Here, the large-scale dolostone bodies are fabric-destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross-cut by low amplitude stylolites, dolomitization is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitization to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ¹⁸O_water and ⁸⁷Sr/⁸⁶Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitization from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO₂-rich fluids. This study highlights that large-scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.     

Focal Mechanism and Focal Depth of the May 22, 2016 MS4.6 Earthquake in Chaoyang, Liaoning

An earthquake with M_S4.6 occurred at 17:08 p.m., May 22, 2016 in Chaoyang County, Liaoning Province. We used the P-wave first motion method, TDMT method, and CAP method to determine the focal mechanisms and the PTD method and sPn-Pn method to determine the focal depth. The focal mechanism results of the three methods are consistent. The depth results of the CAP method, PTD method and sPn-Pn method are close. We used the double difference location method to relocate earthquakes in 2009-2016, and obtained the strikes and dip angles of the small earthquake distributions with the help of simulated annealing algorithm and gauss Newton algorithm fitting. According to the focal mechanism results, the depth results, the characteristics of small earthquake distributions and the structural characteristics of the source area, the seismogenic fault strike is NEE and the main pressure force direction is NNW. The earthquake focal mechanism is for a normal fault type with a little left-lateral strike slip motion.     

江汉盆地大型富锂卤水矿床成因与资源勘查进展:综述

古近纪时期,华南江汉盆地的潜江凹陷和江陵凹陷发育盐湖,沉积了巨厚的蒸发岩,并形成和储藏了富锂、钾、铷、铯、溴、碘等元素的卤水资源,这些元素含量达到工业品位或综合利用品位;富锂卤水属于深层地下卤水型锂矿资源,镁锂比值低,是非常优质的锂资源。本文总结了江汉盆地大地构造特征、火成岩及古气候背景,论述了古盐湖沉积岩相特征、富锂卤水水化学、分布及储层特征、卤水中锂的来源与富集机理、卤水型锂矿成矿模式以及富锂卤水勘查与开采技术进展,提出了卤水开发利用中存在的问题和解决途径。江汉盆地富锂卤水成因包括:古盐湖锂可能主要来自高温水岩反应产生的富锂热液流体的补给;在干旱的气候下,古湖水不断蒸发浓缩,导致卤水中锂浓缩富集;在盐湖演化末期,逐渐埋藏的盐类晶间富锂卤水被转移至裂隙、砂岩及玄武岩储层中储集;在较高的地热背景值下,埋藏卤水与储层岩石可能发生水岩反应,进一步促进了卤水中锂的富集。江汉盆地深层卤水初步勘查显示,氯化锂资源量已达到大型工业规模,展示了巨大的资源潜力。此外,卤水锂开采技术已基本形成,建议进一步加强富锂卤水的绿色开发技术研究,制定相关勘查开发规范。     

吐哈盆地台北凹陷侏罗系煤系源岩地球化学分类及意义

烃源岩的沉积环境、母源输入与有机质性质有着密切联系,吐哈盆地台北凹陷不同层系、不同地区侏罗系煤系烃源岩由于其沉积环境、母源输入的不同,导致其地球化学指标差异;通过对源岩地球化学指标相关性分析表明,姥植比（Pr/Ph）是反映源岩沉积氧化还原环境和水体盐度的重要指标;C29ααα20R在C27～C29规则甾烷ααα20R中的相对含量也是反映沉积水体盐度的重要指标。同时发现源岩类型划分的主控指标是族组成中芳烃、沥青质组分含量及饱芳比、非沥比等四项指标,姥植比、伽马蜡烷指数为源岩类型划分的次控指标,据此将台北凹陷侏罗系煤系烃源岩划分为三类。     

松辽盆地昌德地区营城组火成岩气藏储层特征及其控制因素

松辽盆地昌德地区火山岩储层以酸性岩为主,主要岩石类型为熔结凝灰岩和凝灰岩,与国内其他含油气盆地的火山岩储层明显不同。宏观上岩性较致密,岩心观察仅见构造裂缝和溶蚀孔,局部见溶蚀洞,显微镜下观察储集空间类型多样,发育粒内溶孔、晶内熔孔、晶间微孔、构造微裂缝、炸裂缝和收缩缝等。火山岩厚度普遍较薄,其中芳深9井区火山岩厚度最大,最厚仅为75m。从岩相类型看,芳深9井附近为爆发相,其他地区为溢流相。研究区火山岩为低孔低渗储层,岩性和岩相与物性关系密切,同时控制着原生孔隙的形成。后期的成岩改造,包括构造活动、溶蚀作用等决定了次生孔隙的发育程度,构造运动产生的裂缝是该区储层得以改善的主要因素,而后期充填作用破坏了储层的储集性能。火山口附近爆发相与溢流相的叠合区是天然气勘探的有利目标。     

Magnetostratigraphy of the Red Beds in the Hengyang Basin

Abstract This paper discusses the Cretaceous-Tertiary magnetic polarity sequence of the the Hengyang Basin on the basis of magnetostratigraphic study. The age of each stratigraphic unit has been determined with the magnetic polarity time scale combined with ³⁹Ar/⁴⁰Ar dating, thus providing evidence for determining the geological ages of different formations. The authors assign the age of the Dongjing Formation of the Hengyang Basin to Early Cretaceous, the Shenhuangshan Formation to Early-Late Cretaceous, the Daijiaping Formation to Late Cretaceous, and the Dongtang and Xialiushi formations to Palaeocene.