Changeable hydrothermal media as potential cradle of life on a planet

According to the elaborated systemic concept, a prebiotic microsystem has a chance to be transformed into primary living unit (probiont) only under nonequilibrium oscillating conditions. This transition proceeds through three successive kinds of transformations. First, a prebiotic microsystem must acquire the specific critical properties being at the unstable state of the bifurcate transition. Then it should be relatively stabilized due to balanced oscillations between the initial and the forward states (there appears the paradoxical state of ‘stabilized instability’). The decisive transformation to the living state is connected with the inversion of the ratio of ‘free energy to entropy contribution’ when the free energy input in the microsystem becomes higher than the entropy input. Changeable nonequilibrium conditions are most typical to hydrothermal systems in comparison with other aqueous media of the Earth. In this context the hydrothermal medium seems very suitable to be considered as a potential cradle of life on a planet. To characterize a scale of the thermodynamic and physico-chemical fluctuations some hydrothermal systems in Kamchatka peninsula were explored. The period of the pressure microoscillations in Mutnovsky and Pauzhetsky hydrothermal systems range from 10 to 30 min, and the amplitude is 0.2-0.7 bar. From time to time the amplitude of the fluctuations significantly rises due to spontaneous increase of activity of the nearest volcanoes. Similar results were obtained during the exploration of thermodynamic and chemical fluctuations in Mura hydrothermal field in Slovenia: the period of the water pressure oscillations is 60-70 min, and the average amplitude about 0.5 bar. Temperature and some chemical parameters oscillate in this field with the same period. These data can be used to conduct advanced laboratory experiments on prebiotic organic synthesis under nonequilibrium oscillating conditions. Some universal aspects of this concept may allow us to better understand the origin-of-life process in the Universe.     

Geochemical constraints on the modes of carbonate precipitation in peridotites from the Logatchev Hydrothermal Vent Field and Gakkel Ridge

The ultramafic-hosted Logatchev Hydrothermal Field (LHF) at 15°N on the Mid-Atlantic Ridge and the Arctic Gakkel Ridge (GR) feature carbonate precipitates (aragonite, calcite, and dolomite) in voids and fractures within different types of host rocks. We present chemical and Sr isotopic compositions of these different carbonates to examine the conditions that led to their formation. Our data reveal that different processes have led to the precipitation of carbonates in the various settings. Seawater-like ⁸⁷Sr/⁸⁶Sr ratios for aragonite in serpentinites (0.70909 to 0.70917) from the LHF are similar to those of aragonite from the GR (0.70912 to 0.70917) and indicate aragonite precipitation from seawater at ambient conditions at both sites. Aragonite veins in sulfide breccias from LHF also have seawater-like Sr isotope compositions (0.70909 to 0.70915), however, their rare earth element (REE) patterns show a clear positive europium (Eu) anomaly indicative of a small (< 1%) hydrothermal contribution. In contrast to aragonite, dolomite from the LHF has precipitated at much higher temperatures (~ 100 °C), and yet its ⁸⁷Sr/⁸⁶Sr ratios (0.70896 to 0.70907) are only slightly lower than those of aragonite. Even higher temperatures are calculated for the precipitation of deformed calcite veins in serpentine–talc fault schists form north of the LHF. These calcites show unradiogenic ⁸⁷Sr/⁸⁶Sr ratios (0.70460 to 0.70499) indicative of precipitation from evolved hydrothermal fluids. A simple mixing model based on Sr mass balance and enthalpy conservation indicates strongly variable conditions of fluid mixing and heat transfers involved in carbonate formation. Dolomite precipitated from a mixture of 97% seawater and 3% hydrothermal fluid that should have had a temperature of approximately 14 °C assuming that no heat was transferred. The much higher apparent precipitation temperatures based on oxygen isotopes (~ 100 °C) may be indicative of conductive heating, probably of seawater prior to mixing. The hydrothermal calcite in the fault schist has precipitated from a mixture of 67% hydrothermal fluid and 33% seawater, which should have had an isenthalpic mixing temperature of ~ 250 °C. The significantly lower temperatures calculated from oxygen isotopes are likely due to conductive cooling of hydrothermal fluid discharging along faults. Rare earth element patterns corroborate the results of the mixing model, since the hydrothermal calcite, which formed from waters with the greatest hydrothermal contribution, has REE patterns that closely resemble those of vent fluids from the LHF. Our results demonstrate, for the first time, that (1) precipitation from pure seawater, (2) conductive heating of seawater, and (3) conductive cooling of hydrothermal fluids in the sub-seafloor all can lead to carbonate precipitation within a single ultramafic-hosted hydrothermal system.     

柴达木盆地盐湖锂矿床成矿过程及分布规律

柴达木盆地盐湖蕴藏230×10~4t锂,集中分布在别勒滩、东西台等4个盐湖,占我国卤水锂资源总量~80%,战略资源地位不言而喻。近年来提锂技术及工程化研究倍受重视,而对盐湖锂矿成因和分布规律的了解凸显不足,锂矿资源流失严重与之不无关联。研究查明,昆仑山高温热泉群含锂泉水长期注入洪—那河,流入终端盐湖,蒸发富集成矿;锂的年输入通量748.8 t,结合区内盐湖锂矿总储量保守估算,成矿期始于14 ka BP之后;洪—那河早期主要流向别勒滩,在山前冲积扇向北推进、扇前河改道北流后,方才形成含锂河水当前分配格局。据此,破解了别勒滩锂矿在研究区储量最大的原由。还查明了锂矿床仅存在于别勒滩,而在达布逊等3个区段不能成矿的原因。阐明了锂的来源与新生代火山喷发岩、深部岩浆房、昆仑大断裂活动有关,以及含锂热水持续远程输送至盐湖成矿的地貌和水文气候动因。企业应当根据锂的分布规律和矿床特征,迅速转变钾肥生产模式。     

A new, automatic hydrothermal fluid sampler using a shape-memory alloy

A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population density of 10⁵ to 10⁶ cells ml⁻¹, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological interest.     

Geology and Geochemistry of Maoling Gold Deposit, Gaixian, Liaoning Province

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成矿系统的结构与聚矿功能

成矿系统结构对成矿动力学条件的约束与促进,引起系统固有聚矿功能的巨大变异。成矿系统动力学包括：系统运转的动力组合、系统物质运动总方向和轨迹、矿质活动空间规模形态及单位空间中成矿微过程的频度。系统结构定性分析表明：系统结构的完善程度和成矿动力学条件的优劣与系统聚矿功能的强度正相关。系统结构完善程度可由结构紧致度（Ｉ）表征,系统聚矿功能可用标准富集量（Ｑｓ）反映,它是矿床储量（Ｑ０）经成矿难度系数（Ｃ）变换的归一化指标。经结构定性半定量分析,对成矿系统聚矿功能作出初步排序,具强烈非线性成矿特征的花岗岩浆成矿系统和环流热液成矿系统的聚矿功能最高     

深海6000 m拖曳式瞬变电磁系统及其应用

针对我国西南印度洋合同区热液硫化物矿快速、有效以及便捷地质勘探装备的要求,研发了由甲板控制系统、万米光电复合缆、仪器舱拖体和天线拖体组成的深海6000 m拖曳式瞬变电磁系统.为了便于拖体布放和快速发现异常,选择重叠回线收发装置类型;采用理论数值计算确定了在拖曳高度不大于50 m的前提下,观测1～100ms窗范围内的二次场响应,可以发现近海底深海热液硫化物矿堆;另外,通过不同拖延深度海上试验,研究了拖曳深度对瞬变电磁的影响规律及仪器性能.大洋第30航次第二航段在西南印度洋脊热液区,应用该系统发现了明显的瞬变电磁异常.印证了系统的有效性.     

云南广南县老寨湾金矿地质特征及找矿标志

广南县老寨湾金矿位于滇、黔、桂“金三角”重要成矿区带上,金矿体矿体呈似层状赋存于断层构造破碎带或层间构造破碎带中,构造控矿明显。矿体围岩均为下泥盆统坡松冲组第一段(D1ps1)硅化石英砂岩;矿床成因属中-低温热液叠加改造型金矿床,断层构造、硅化等矿化蚀变及地球化学异常是重要的找矿标志。     

Ancient deep roots for Mesozoic world-class gold deposits in the north China craton:An integrated genetic perspective

The North China Craton(NCC)hosts some of the world-class gold deposits that formed more than 2 billion years after the major orogenic cycles and cratonization.The diverse models for the genesis of these deposits remain equivocal,and mostly focused on the craton margin examples,although synchronous deposits formed in the interior domains.Here we adopt an integrated geological and geophysical perspective to evaluate the possible factors that contributed to the formation of the major gold deposits in the NCC.In the Archean tectonic framework of the NCC,the locations of the major gold deposits fall within or adjacent to greenstone belts or the margins of micro-continents.In the Paleoproterozoic framework,they are markedly aligned along two major collisional sutures-the Trans North China Orogen and the Jiao-Liao-Ji Belt.Since the Mesozoic intrusions hosting these deposits do not carry adequate signals for the source of gold,we explore the deep roots based on available geophysical data.We show that the gold deposits are preferentially distributed above zones of uplifted MOHO and shallow LAB corresponding to thinned crust and eroded sub-lithospheric mantle,and that the mineralization is located above regions of high heat flow representing mantle upwelling.The NCC was at the center of a multi-convergent regime during the Mesozoic which intensely churned the mantle and significantly en riched it.The geophysical data on Moho and LAB upwarp from the centre towards east of the craton is more consistent with paleo-Pacific slab subduction from the east exerting the dominant control on lithospheric thinning.Based on these results,and together with an evaluation of the geochemical and isotopic features of the Mesozoic magmatic intrusions hosting the gold mineralization,we propose a genetic model that invokes reworking of ancient Au archives preserved in the lower crust and metasomatised upper mantle and which were generated through multiple subduction,underplating and cumulation events associated with cratonization of the NCC as well as the subduction-collision of Yangtze Craton with the NCC.The heat and material input along zones of heterogeneously thinned lithosphere from a rising turbulent mantle triggered by Mesozoic convergent margins surrounding the craton aided in reworking the deep roots of the ancient Au reservoirs,leading to the major gold metallogeny along craton margins as well as in the interior of the NCC.     

Mechanisms of salinization in a middle Eocene lake in the Tanggu area of the Huanghua Depression

The Sha-3-5 Submember of the Shahejie Formation in the Tanggu area of the Huanghua Depression contains analcime-bearing dolomite, indicating salinization of an ancient lake during deposition. Solar evaporation and hydrothermal salinization have both been proposed as ways to generate these saline conditions. Based on a comprehensive analysis of core data, thin sections, spore and pollen data, elemental geochemistry, pyrolysis results, and vitrinite reflectance, we assessed the mechanisms driving salinization in light of provenance evolution, geothermal evolution, paleoclimate, mineral responses to evaporation, and the relationship between fluid temperature and salinity. The vertical profiles of ΣREE, Eu/*Eu, and T_max exhibit little variation, and the maximum paleotemperatures attained by organic matter are comparable to present-day drill hole temperature. No major changes in provenance or paleotemperature and no petrological fabrics that would indicate a hydrothermal input are observed in the studied section. However, evidence for a semi-humid to semi-arid climate, primary evaporitic textures and structures, and a positive relationship between fluid temperature and salinity all support evaporation as the primary mechanism driving rising salinity. Solar evaporation, rather than hydrothermal eruption, appears to have been the primary factor driving lake salinization during middle Eocene deposition of the dolomitic Sha-3-5 Submember.