云南省鹅头厂含铜铁矿床的地质特征、成矿作用和找矿前景探讨

鹅头厂含铜铁矿床对位于康滇地轴中部，矿体受地层、岩性、构造、火山岩和次火山岩控制。分为三个矿群。矿石的矿物组成简单。矿石以富铁、含铜、高硫、高磷为特点。成矿地球化学研究显示出热水成矿特点，属火山热水沉积一次火山热液改造成因。矿区北部的铜厂箐一带具有很好的找矿前景。     

Syn- and post-sedimentary controls on clay mineral assemblages in a tectonically active basin,Andean Argentinean foreland

In the northern part of the Calchaquí Valley (NW Argentina), Palaeogene Andean foreland sediments are represented by a 1400-metre-thick continental succession (QLC: Quebrada de Los Colorados Formation) consisting of claystones, siltstones, sandstones, and conglomerates representing sedimentation in fluvial-alluvial plains and alluvial fan settings. To understand the main syn- and postsedimentary variables controlling the clay mineral assemblages of this succession, we have studied the fine-grained clastic sediments by X-ray diffraction and electron microscopy, along with a detailed sedimentary facies analysis, for two representative sections. In the northern section, the whole succession was sampled and analysed by XRD, whereas in the second section, a control point 15 km to the south, only the basal levels were analysed. The XRD study revealed a strong contrast in clay mineral assemblages between these two sections as well as with sections in the central Calchaquí Valley studied previously. In the northernmost part of the study area, a complete evolution from smectite at the top to R3 illite/smectite mixed-layers plus authigenic kaolinite at the bottom, through R1-type mixed-layers in between, has been recognized, indicating the attainment of late diagenesis. In contrast, the clay mineral assemblages of equivalent foreland sediments cropping out only 15 km to the south contain abundant smectite and micas, subordinate kaolinite and chlorite, and no I/S mixed-layers to the bottom of the sequence. Early diagenetic conditions were also inferred in a previous study for equivalent sediments of the QLC Formation cropping out to the south, in the central Calchaquí Valley, as smectite occurs in basal strata. Burial depths of approximately 3000 m were estimated for the QLC Formation in the central and northern Calchaquí Valley; in addition, an intermediate to slightly low geothermal gradient can be considered likely for both areas as foreland basins are regarded as hypothermal basins. Consequently, the attainment of late diagenesis in the northernmost study area cannot be explained by significant differences in burial depth nor in geothermal gradient in relation to the section 15 km to the south nor with the central Calchaquí Valley. The formation of R3 mixed-layer I/S and authigenic kaolinite in the northern study area was most likely controlled by the circulation of hot, deep fluids along the reverse faults that bounded the Calchaquí valley. These faults were active during the Cenozoic, as evidenced by the syndepositional deformation features preserved in the studied sediments. Stress could also have been a driving force in burial diagenesis at the R3 mixed-layer I/S stage in these young continental sediments.     

Lithologic characteristics and diagenesis of the Devonian Jauf sandstone at Ghawar Field, Eastern Saudi Arabia

The Lower Devonian Jauf Formation in Saudi Arabia is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Jauf Formation more specifically on the reservoir quality (including diagenesis), are very few. This study, which is based on core samples from two wells in the Ghawar Field, northeastern Saudi Arabia, reports the lithologic and diagenetic characteristics of this reservoir. The Jauf reservoir is a fine to medium-grained, moderate to well-sorted quartz arenite. The diagenetic processes recognized include compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cements and of feldspar grains. The widespread occurrences of early calcite cement suggest that the Jauf reservoir lost a significant amount of primary porosity at a very early stage of its diagenetic history. Early calcite cement, however, prevented the later compaction of the sandstone, thus preserving an unfilled part of the primary porosity. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-bridging clay cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late calcite cement occurs as isolated patches, and has little impact on reservoir quality of the sandstones.In addition to calcite, several different clay minerals including illite and chlorite occur as pore-filling and pore-lining cements. While the pore-filling illite and chlorite resulted in a considerable loss of porosity, the pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurs as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration to permeability of the reservoir. Diagenetic history of the Jauf Formation as established here is expected to help better understanding and exploitation of this reservoir.     

Fracture-aperture size—frequency,spatial distribution,and growth processes in strata-bounded and non-strata-bounded fractures,Cambrian Mesón Group,NW Argentina

In Cambrian Mesón Group, NW Argentina, small faults and three opening-mode fracture sets defined by orientation and cement texture (Sets 1–3) formed sequentially in sandstone that most likely had constant mechanical properties throughout deformation. Yet the opening-mode sets display contrasting fracture-aperture-size distributions, spacing patterns, and tendency to be bed bounded. Set 1 fractures are quartz-filled or -lined opening-mode fractures with crack-seal texture, having a wide range of opening-displacement (kinematic aperture) sizes; they are irregularly spaced and non-strata-bounded fractures. Set 1 macro and microfracture-opening-displacement sizes are well described by a power law with slope −0.8. Set 2 fractures are microscopic, mostly quartz filled and have characteristic aperture sizes, are probably not bed bounded and have either a near-random or clustered spatial distribution. Set 3 fractures are quartz-lined, opening-mode fractures with extensive open pore space, having a narrow (characteristic) opening-displacement size distribution; they are regularly spaced and stratabounded. Differences between Sets 1 and 3 can be accounted for by quartz deposition resisting fracture reopening to a greater extent for Set 1 during repeated, episodic growth, where crack-seal texture is present in fracture-spanning quartz. In contrast Set 3 fractures are nearly barren with only trace-cement deposits that did not resist opening. Power-law opening-displacement size distributions may be favored in cases where fracture growth is unequally partitioned amongst variably cemented fractures, whereas a characteristic size is favored where growth is unaffected by cementation. Results imply that thermal history and diagenesis are important for fracture-size-distribution patterning.     

页岩孔隙演化及其与残留烃量的耦合关系：来自地质过程约束模拟实验的证据

加强页岩孔隙演化规律研究,特别是定量评价其与残留烃之间的关系对页岩油的勘探具有重要意义。采集鄂尔多斯盆地低成熟度湖相Ⅰ型富有机质页岩,通过地质条件约束(埋藏史、地层压力、地层水矿化度等)成岩物理模拟实验模拟页岩演化,利用压汞法、氮气吸附法和二氧化碳吸附法获得不同温压段页岩的比孔容、比表面积和孔径分布,结合氯仿沥青A抽提定量结果,确定孔隙演化规律及其与残留烃的关系。结果表明页岩大孔比孔容与残留烃含量先增加后减小,微孔和中孔的比孔容随着模拟实验温度的增加呈现先减小后增大。XRD分析显示黄铁矿含量控制大孔,有机质丰度和粘土含量控制微孔和中孔。微孔和中孔的比孔容增加为高—过成熟度阶段页岩气提供储集空间,大孔比孔容与残留烃含量变化一致,生油窗阶段大孔增加是页岩油的有利储集带。     

The Ge/Si ratio as a tool to recognize biogenic silica in chert

Germanium and silicon, dissolved in seawater, are considered to be incorporated into biogenic opal with no or little fractionation, which permitted to use diatoms as reliable recorders of seawater Ge/Si. Does some fractionation occur during diagenesis, preventing the use of Ge/Si in ancient sediments? We examined the Ge/Si ratio of fossil sponges and flint nodules of the Cretaceous Chalk Formation of northern France. Though disputed, silica in this formation is considered to originate from sponges. No fractionation is observed between sponges and diagenetic flints, which allows us to observe whether Ge/Si bears a biogenic or detrital signature. We may thus confirm that sponges were the main silica supplier during the chalk deposition. The Ge/Si ratio may be used to identify a biogenic signature in cherts where the origin of silica is dubious.     

Relating background fractures to diagenesis and rock physical properties in a platform–slope transect. Example of the Maiella Mountain (central Italy)

Fractured reservoirs are of prime interest as fracture networks control most of the fluid flow and/or accumulation. However, characterizing 3D fracture patterns from subsurface data remains challenging. Studying fractures on outcrops is a good substitution to 1D data from subsurface exploration tools. In addition, outcrops allow deciphering the nature, origin and conditions for fracture formation through the geodynamic history. In this paper, we aim at characterizing the true 3D fracture patterns and determining the genetic role of facies, diagenesis and rock physical properties. We targeted a platform–slope transect within a carbonate reservoir analog, the Maiella Mountain in central Italy, where implications for analog hydrocarbon reservoir can be discussed.Fracture patterns are sorted based on geometric and kinematic criteria from field measurements and petrographic analyzes on thin-sections. Sedimentary facies, pore types and rock physical properties have been characterized in order to establish the impact of early diagenesis on rock evolution. Diagenetic sequences have been unraveled and correlated to the fractures. Fracture sequences have been determined considering the cross-cutting relationships and compared with burial–uplift history. In the two studied formations (platform and slope carbonates), we interpret a stage of fracturing perpendicular to bedding, formed at shallow depth and occurring prior to major regional tectonic events. The studied carbonates have undergone early diagenesis during fast and shallow burial, conferring early brittle behavior. The amount of stylolites is not correlated to burial depth but to fracture density, porosity and free air P–wave velocity. It means that fracture development, mechanical and petrophysical properties are acquired during early diagenesis.Both studied formations have undergone the same geodynamic history and their brittle response is different and not related to folding but to burial and early cementation. Deciphering the close relationship between sedimentary facies, diagenetic and geodynamic history has allowed unraveling the controling factors on rock properties and therefore on fracture pattern.     

Changes in the Tropical Cyclone Genesis Potential Index over the Western North Pacific in the SRES A2 Scenario

The Tropical Cyclone Genesis Potential Index (GPI) was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific (WNP). The outputs of 20th century climate simulation by eighteen GCMs were used to evaluate the models’ ability to reproduce tropical cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial distribution of genesis. Some of the models also showed ability in capturing observed temporal vari...     

Overpressure preventing quartz cementation? - A reply

Chemical compaction and the relative importance of the pressure dissolution and illite-mica induced dissolution (IMID) models have remained a contentious issue, as is the role played by stress in chemical compaction. This paper offers further support and evidence as discussed in Stricker et al. (2016b), focusing on the reservoir quality of the Triassic Skagerrak Formation sandstones in the high pressure high temperature (HPHT) Central Graben, North Sea. The reply discusses alterative reservoir quality interpretations and comments as raised by Maast (2016). A series of theoretical and experimental studies, as well as field based evidence is presented providing strong support to the important role of stress (e.g. vertical effective stress) during chemical compaction. The evidence leads to the conclusion that the process of chemical compaction is stress and temperature driven and significantly enhanced by clay minerals, playing a catalytic role by increasing the width of diffusion pathway or by modifying the kinetics of the dissolution process.