Characteristics of Ore-controlling Structures and Ore Emplacement Mechanism in the Shihu Gold Deposit,Hebei Province - A Case Study of the No.101 VeinEI北大核心CSCD

The Shihu gold deposit lies in the middle-northern Taihang Mountains and is strictly controlled by faults. The ore-controlling structures in the mining district are not well-documented. Detailed field observation and laboratory investigation of the No.101 vein indicated that the ore-controlling structures of the Shihu gold deposit are the pre-Mesozoic shear joints with SN and NW strike that reactivated during the Yanshanian emerged from. The NNW-SSE left-strike-slip stresses during the main mineralization stage led to the dilation of the NW-strike structural segments along the roof and footwall of the early quartz diorite porphyrite veins, which contributed to the extensive wall-rock alteration, intensive gold mineralization and occur as quartz-vein type ores, and consequently the formation of rich ore pillars. On the contrary, the SN-strike compressive structures correspond to the weak wall-rock alteration and gold mineralization and occur as altered-rock type ores. All the rich ore pillars laterally distributed with high-angle (70°±), and wholly pitched southward with 40° angle. According to the structural ore-controlling regularities, the location between the No.47 and the No.61 exploratory line with elevation below 150 m is an excellent ore-prospecting area. Our prospecting proposal based on the ore-controlling structural analyses in the study area has been proven by the underground works in the Shihu gold deposit. © 2017, Science Press. All right reserved.     

Geochemical characteristics and genetic types of crude oils from Qinjiatun and Qikeshu oilfields in the Lishu Fault Depression,Songliao Basin,northeastern China

The Qinjiatun and Qikeshu oilfields are new Mesozoic petroleum exploration targets in Lishu Fault Depression of Songliao Basin, northeastern China. Currently, researches on geochemistry of crude oils from Qinjiatun and Qikeshu oilfields have not been performed and the genesis of oils is still uncertain. Based on bulk analyses, the crude oils in the Qinjiatun and Qikeshu oilfields of Lishu Fault Depression from the Lower Cretaceous can be classified as three types. TypeⅠoils, from Quantou and Denglouku formations of Qikeshu oilfield, are characterized by high C24tetracyclic terpane/C26tricyclic terpanes ratios, low gammacerance/C30hopane ratios, tricyclic terpanes/hopanes ratios, C29Ts/C29norhopane ratios and 17α(H)-diahopane/17α(H)-hopane ratios, indicating a brackish lacustrine facies. TypeⅡoils, from Shahezi Formation of Qikeshu oilfield show low C24tetracyclic terpane/C26tricyclic terpanes, high gammacerance/C30hopane ratios, tricyclic terpanes/hopanes ratios, C29Ts/C29 norhopane and C30diahopane/C30hopane ratios, thus suggesting that they originated from source rocks deposited in a weak reducing brackish lacustrine environment, or clay-rich sediments. Type oilsⅢ, from some wells of Qikeshu oilfield have geochemical characteristics intermediate between those two types and may be mixture of typeⅠand Ⅱoils.     

土壤氡方法用于断层活动性研究的讨论

本文系统地分析了海河断裂、天津南断裂、天津北断裂和沧东断裂等的土壤氡测量资料,用M-M珚值的组合以及H值、An值等3种方式对天津地区4条断裂的活动性强弱进行了分析和划分,经与活断层探测中得到的4条断裂的活动性分段结果对比发现,两者具有一定的一致性。同时发现,每种方法都有其局限性,进而认为,选择合适的方法,运用土壤氡测量资料能够对断层的活动性进行初步分析和分区,从而为断层的活动性分段提供参考。通过不同断裂间上述3组指标对比发现,土壤氡测量结果不能用于判断不同断裂间的活动性强弱。从实际工作出发,为利于分析断层的活动性分区,断层气测线在布设时应在探测断层与已知断裂的交汇部位附近适当增加密度。     

SLIP OFFSET ALONG STRIKE-SLIP FAULT DETERMINED FROM STREAM TERRACES FORMATION

Slip rate is one of the most important parameters in quantitative research of active faults. It is an average rate of fault dislocation during a particular period, which can reflect the strain energy accumulation rate of a fault. Thus it is often directly used in the evaluation of seismic hazard. Tectonic activities significantly influence regional geomorphic characteristics. Therefore, river evolution characteristics can be used to study tectonic activities characteristics, which is a relatively reliable method to determine slip rate of fault. Based on the study of the river geomorphology evolution process model and considering the influence of topographic and geomorphic factors, this paper established the river terrace dislocation model and put forward that the accurate measurement of the displacement caused by the fault should focus on the erosion of the terrace caused by river migration under the influence of topography. Through the analysis of the different cases in detail, it was found that the evolution of rivers is often affected by the topography, and rivers tend to migrate to the lower side of the terrain and erode the terraces on this side. However, terraces on the higher side of the terrain can usually be preserved, and the displacement caused by faulting can be accumulated relatively completely. Though it is reliable to calculate the slip rate of faults through the terrace dislocation on this side, a detailed analysis should be carried out in the field in order to select the appropriate terraces to measure the displacement under the comprehensive effects of topography, landform and other factors, if the terraces on both sides of the river are preserved. In order to obtain the results more objectively, we used Monte Carlo method to estimate the fault displacement and displacement error range. We used the linear equation to fit the position of terrace scarps and faults, and then calculate the terrace displacement. After 100, 000 times of simulation, the fault displacement and its error range could be obtained with 95%confidence interval. We selected the Gaoyan River in the eastern Altyn Tagh Fault as the research object, and used the unmanned air vehicle aerial photography technology to obtain the high-resolution DEM of this area. Based on the terrace evolution model proposed in this paper, we analyzed the terrace evolution with the detailed interpretation of the topography and landform of the DEM, and inferred that the right bank of the river was higher than the left bank, which led to the continuous erosion of the river to the left bank, while the terraces on the right bank were preserved. In addition, four stages of fault displacements and their error ranges were obtained by Monte Carlo method. By integrating the dating results of previous researches in this area, we got the fault slip rate of(1.80±0.51)mm/a. After comparing this result with the slip rates of each section of Altyn Tagh Fault studied by predecessors, it was found that the slip rate obtained in this paper is in line with the variation trend of the slip rate summarized by predecessors, namely, the slip rate gradually decreases from west to east, from 10~12mm/a in the middle section to about 2mm/a at the end.     

永平水泄铜钴矿控矿因素

水泄铜钴矿区地质条件较为复杂,控矿因素较多,通过分析认为主要受断层及岩性控制,地层初始富集,构造及区域变质作用提供通道及热源。水的循环、溶解作用形成热卤水成矿。     

下二门油田H2Ⅲ油组交联聚合物驱后油藏剩余油分布特征

微观驱油试验表明,交联聚合物驱后剩余油进一步减少,主要以斑块状、小油滴状等形态分布于微孔隙中;数值模拟显示,下二门油田H2Ⅲ油组交联聚合物驱后80.8%的面积已为中强水淹,纵向上79.7%的剩余油分布于主力油层.受构造、储层物性及井网因素控制,未淹、弱水淹剩余油平面上主要分布在断层附近、断层破碎带、微构造高点和砂体上倾尖灭区等部位;纵向上主要分布于低渗透层段.针对剩余油分布特征,通过完善注采关系、优化注采结构,单元含水量的上升速度和产量递减幅度得到控制,采收率在交联聚合物驱的基础上进一步提高了2.01%.     

湘乡东山天然饮用含锌矿泉的地质特征及形成机理

湘乡市东山天然饮用矿泉水,是我省首次发现的大型含锌矿泉。它发育在北东向东台山含水断层带上,该断层长60km以上,倾向北西,斜贯湘乡境内,向西南通过歇马花岗岩体。在泉区,沿断层带发育一条硅化破碎带,最厚处达150m。断层上盘为白垩—第三系红层,下盘为板溪群,均为不透水层,对矿泉起遮挡保护作用。本矿泉水量丰富,每昼夜可取水2000t。泉水中锌和偏硅酸含量,已达到国家天然饮用矿泉水标准,另含10种人体必需的微量元素,属少见的优质矿泉。     

Geomorphic expression of neotectonic activity in a low relief area in an Airborne Laser Scanning DTM: A case study of the Little Hungarian Plain (Pannonian Basin)

The NW corner of the Little Hungarian Plain, which lies at the junction of the Eastern Alps, the Pannonian Basin and the Western Carpathians, is a neotectonically active region linking the extrusional tectonics of the Eastern Alps with the partly subsiding Little Hungarian Plain. The on-going deformation is verified by the earthquake activity in the region. An extremely flat part of the area, east of Neusiedlersee, the so-called Seewinkel, has been investigated with Airborne Laser Scanning (ALS, also known as airborne LiDAR) techniques, resulting in a digital terrain model (DTM) with a 1 m grid resolution and vertical precision of better than 10 cm. The DTM has been compared with known and inferred neotectonic features.Potential neotectonic structures of the DTM have been evaluated, together with geological maps, regional tectono-geomorphic studies, geophysical data, earthquake foci, as well as geomorphological features and the Quaternary sediment thickness values of the Seewinkel and the adjacent Parndorfer plateau. A combined evaluation of these data allows several tectonic features with a relief of < 2 m to be recognized in the DTM. The length of these linear geomorphological structures ranges from several hundred meters up to several kilometers. The most prominent feature forms a 15 km long, linear, 2 m high NE–SW trending ridge with gravel occurrences having an average grain size of ca. 5 cm on its top. We conclude this feature to represent the surface expression of the previously recognized Mönchhof Fault. In general, this multi-disciplinary case study shows that ALS DTMs are extremely important for tectono-geomorphic investigations, as they can detect and accurately locate neotectonic structures, especially in low-relief areas.     

Seal integrity and feasibility of CO<Subscript>2</Subscript> sequestration in the Teapot Dome EOR pilot: geomechanical site characterization

This paper reports a preliminary investigation of CO₂ sequestration and seal integrity at Teapot Dome oil field, Wyoming, USA, with the objective of predicting the potential risk of CO₂ leakage along reservoir-bounding faults. CO₂ injection into reservoirs creates anomalously high pore pressure at the top of the reservoir that could potentially hydraulically fracture the caprock or trigger slip on reservoir-bounding faults. The Tensleep Formation, a Pennsylvanian age eolian sandstone is evaluated as the target horizon for a pilot CO₂ EOR-carbon storage experiment, in a three-way closure trap against a bounding fault, termed the S1 fault. A preliminary geomechanical model of the Tensleep Formation has been developed to evaluate the potential for CO₂ injection inducing slip on the S1 fault and thus threatening seal integrity. Uncertainties in the stress tensor and fault geometry have been incorporated into the analysis using Monte Carlo simulation. The authors find that even the most pessimistic risk scenario would require ∼10 MPa of excess pressure to cause the S1 fault to reactivate and provide a potential leakage pathway. This would correspond to a CO₂ column height of ∼1,500 m, whereas the structural closure of the Tensleep Formation in the pilot injection area does not exceed 100 m. It is therefore apparent that CO₂ injection is not likely to compromise the S1 fault stability. Better constraint of the least principal stress is needed to establish a more reliable estimate of the maximum reservoir pressure required to hydrofracture the caprock.     

黄骅坳陷埕北断坡不整合特征与油气成藏

黄骅坳陷埕北断坡处于歧口凹陷向埕宁隆起过渡的斜坡带上,发育多个不整合,这些不整合对该区的油气成藏起重要作用。利用地震资料,在剖面上将不整合划分为5种类型：褶皱不整合、断褶不整合、削截不整合、超覆不整合、平行不整合。其中平行不整合分布在凹陷区,褶皱不整合分布在基底,断褶不整合分布在大断裂下降盘,削截不整合分布在大断裂上升盘,而超覆不整合多分布在隆起斜坡区;利用测井资料,在纵向上将不整合划分为3层结构：不整合面之上岩石、风化粘土层及半风化岩石,由于每层结构的岩性与厚度不同,形成ACE型、ADE型、BCE型和BDF型4种岩性配置模式。不整合构成埕北断坡油气侧向运移的重要通道,同时在其之上形成超覆不整合油气藏,在其之下依靠风化粘土层遮挡形成削截不整合与褶皱不整合油气藏。勘探证实,研究区众多油气显示或油气藏均位于不整合面上、下50 m范围内。开展不整合与油气成藏关系研究,将拓宽黄骅坳陷隐蔽油气藏的勘探空间,对我国东部油气资源挖潜具有重要的理论与实践意义。