Fluid sources for the La Guitarra epithermal deposit (Temascaltepec district, Mexico): Volatile and helium isotope analyses in fluid inclusions

The La Guitarra deposit (Temascaltepec district, South-Central Mexico), belongs to the low/intermediate sulfidation epithermal type, has a polymetallic character although it is currently being mined for Ag and Au. The mineralization shows a polyphasic character and formed through several stages and sub-stages (named I, IIA, IIB, IIC, IID, and III). The previous structural, mineralogical, fluid inclusion and stable isotope studies were used to constrain the selection of samples for volatile and helium isotope analyses portrayed in this study. The N₂/Ar overall range obtained from analytical runs on fluid inclusion volatiles, by means of Quadrupole Mass Spectrometry (QMS), is 0 to 2526, and it ranges 0 to 2526 for stage I, 0 to 1264 for stage IIA, 0 to 1369 for stage IIB, 11 to 2401 for stage IIC, 19 to 324 for stage IID, and 0 to 2526 for stage III. These values, combined with the CO₂/CH₄ ratios, and N₂-He-Ar and N₂-CH₄-Ar relationships, suggest the occurrence of fluids from magmatic, crustal, and shallow meteoric sources in the forming epithermal vein deposit. The helium isotope analyses, obtained by means of Noble Gas Mass Spectrometry, display R/Ra average values between 0.5 and 2, pointing to the occurrence of mantle-derived helium that was relatively diluted or “contaminated” by crustal helium. These volatile analyses, when correlated with the stable isotope data from previous works and He isotope data, show the same distribution of data concerning sources for mineralizing fluids, especially those corresponding to magmatic and crustal sources. Thus, the overall geochemical data from mineralizing fluids are revealed as intrinsically consistent when compared to each other.The three main sources for mineralizing fluids (magmatic, and both deep and shallow meteoric fluids) are accountable at any scale, from stages of mineralization down to specific mineral associations. The volatile and helium isotope data obtained in this paper suggest that the precious metal-bearing mineral associations formed after hydrothermal pulses of predominantly oxidized magmatic fluids, and thus it is likely that precious metals were carried by fluids with such origin. Minerals from base-metal sulfide associations record both crustal and magmatic sources for mineralizing fluids, thus suggesting that base metals could be derived from deep leaching of crustal rocks. At the La Guitarra epithermal deposit there is no evidence for an evolution of mineralizing fluids towards any dominant source. Rather than that, volatile analyses in fluid inclusions suggest that this deposit formed as a pulsing hydrothermal system where each pulse or set of pulses accounts for different compositions of mineralizing fluids.The positive correlation between the relative content of magmatic fluids (high N₂/Ar ratios) and H₂S suggests that the necessary sulfur to carry mostly gold as bisulfide complexes came essentially from magmatic sources. Chlorine necessary to carry silver and base metals was found to be abundant in inclusion fluids and although there is no evidence about its source, it is plausible that it may come from magmatic sources as well.     

参量阵浅地层剖面仪在海底羽状流探测中的应用——以ATLAS P70在马克兰海域调查为例

海底渗漏的羽状流是沉积层赋存天然气水合物的重要证据之一,基于非线性水声学原理的参量阵浅地层剖面仪作为海洋探测的重要设备,对于获得羽状流在水体中的物性特征和渗漏点的浅地层信息有着重大意义.本文根据ATLAS P70浅地层剖面仪在马克兰海域调查中得到的浅地层剖面数据,结合多道地震数据、多波束数据以及地质样品等资料,刻画了研究区内羽状流形态特征,分析了羽状流区海底地层流体运移的通道以及近海底微地形地貌特征.通过研究发现在羽状流区伴随泥火山喷发,自生碳酸盐岩发育,剥蚀海底松散沉积物形成大小不一的麻坑,滋生生物群落等特征.反映在浅剖初始高频(20 kHz)数据界面上羽状流表现为柱状浑浊反射异常,形态呈火焰状,高度由80 m到1500 m不等;对应在次级低频(4 kHz)信号界面可以清晰显示流体渗漏的浅地层结构特征,从中不仅可以识别出流体的运移通道,如泥火山和管状通道等,而且揭示了流体逸散的残留地貌,如麻坑构造和海底滑坡等.本文依托参量阵浅地层剖面数据,对巴基斯坦马克兰海域羽状流有了较全面的认识,为天然气水合物的研究垫定了基础.     

核磁共振测井在天然气勘探中的应用

核磁共振测井不仅能够测得孔隙度、渗透率等岩石物理信息，为储层评价提供科学依据，而且通过采用适当的探测手段和数据处理方法，可以探测到地层中天然气的信息，并能给出储层含气饱和度，而成为天然气勘探的一个重要方法，本文论述了核磁共振测井探测天然气的基本原理和数据处理方法，并对几个实例作了分析。     

Terbuthylazine and Deethylterbuthylazine in Rain and Surface Water – Determination by Enzyme Immunoassay and Gas Chromatography/Mass Spectrometry

Rain and surface water samples from Southern Germany were investigated from 1991 to 1995 for terbuthylazine and one of its major metabolites, deethylterbuthylazine. The concentrations observed were compared to the concentrations found for atrazine and deethylatrazine in the same water samples. Concentrations ranged from < 0.02 μg/L to 0.7 μg/L for terbuthylazine and from < 0.02 μg/L to 0.6 μg/L for deethylterbuthylazine, compared to concentrations of < 0.02 μg/L to 3 μg/L and < 0.02 μg/L to 0.5 μg/L for atrazine and deethylatrazine, respectively. The ratios of metabolite concentrations to parent compound concentrations were calculated for deethylterbuthylazine to terbuthylazine (DTR) and deethylatrazine to atrazine (DAR). In rain water, DTR of 0.8…3.0 and DAR of 0.3… 1.9 were determined with mean values of 0.9… 1.7 for DTR and 0.6…0.9 for DAR in the different years. The ratios increased during summer periods. The highest ratios were observed in samples from forest stands, showing that degradation of the herbicide has occurred during transport between the source and the sampling site. The DTR in rain water were about 50… 100% higher than the DAR. This indicates a higher degradation rate of terbuthylazine during atmospheric transport. In surface water, DTR of 0.3… 1.2 with mean values of 0.5…0.8 and DAR of 0.2…2.2 with mean values of 0.2… 1.3 were observed. The ratios increased from June to September.     

Mechanical behaviour of deep rock core samples from a seismically active gas field

This study concerns the laboratory testing of core samples from massive sedimentary rocks from an oil and gas field. The depth of extraction of the samples analysed varies between 1000 and 5000 metres. In all, 65 tests were performed, most of which included systematic measurement of acoustic activity during loading. The aim of the testing was to determine which types of fracture could occur in the rock matrix under field-stress conditions by examining in particular the relationship between confining pressure and the transition from brittle to ductile behaviour. The results of the laboratory tests are used to predict the occurrence of seismic activity resulting from the depletion of the gas reservoir which has been monitored during the last twenty years.     

连县小带铅锌铁锰矿床特征与喷流沉积机制浅析

连县小带是粤北近几年发现的又一喷流沉积铅锌矿床。简要介绍其成矿环境、地质特征,讨论喷流(喷气)沉积(成矿)作用及成矿分带的主要地球化学机制,如因脉动喷流(喷气)造成盆地内地球化学性质的周期变化,引起矿石组构的周期变化等。     

用气体地球化学方法探讨活断层的有关问题

探讨了以氡为主的断层气测量结果与断层活动性的关系;并讨论了土质、土壤、含水量、取样深度等对断层气氡测量的影响。     

On the scavenging of gaseous nitrogen compounds by large and small rain drops I. A wind tunnel and theoretical study of the uptake and desorption of NH3 in the presence of CO2

An experimental study has been carried out in the Mainz vertical wind tunnel to determine the rate at which NH₃ in the presence of CO₂ is absorbed by freely suspended water drops. The experimental uptake rates were found to be in good agreement with the rates predicted by the Kronig-Brink convective diffusion model and, for gas concentrations in the ppbv range also by the model in which it is assumed that the absorbed gas is well mixed inside the drop (henceforth called well mixed model). The same conclusion was shown to apply also to the desorption of NH₃ from a drop previously exposed to NH₃. The latter result is in contrast to the desorption of SO₂ which must be described by a model which accounts for the diffusion of the species inside the drop. Comparison of our experimental results with theory show further that the uptake of NH₃ in presence of CO₂ is significantly overestimated if the slow reaction CO_2(aq)+H₂OHCO ₃ ^– +H⁺ is neglected in the theoretical computation.     

North Atlantic climatic events recorded in Aptian Naskapi Member cores,Scotian Basin

Early Aptian black laminated organic mudstones, including the Selli Level, are recognized over large areas of Tethys and western European basins. This interval was investigated in a 75 m-thick continuously cored section of varicoloured shale in the lower Naskapi Member from the Panuke B-90 well in the Scotian Basin, offshore eastern Canada. This study complements the palaeogeographic range of correlatable Selli black shales and provides information on their relationship to sea-level change and palaeoclimate. Total organic carbon (TOC) was measured on 127 discrete samples, chemical environmental proxies (Th/K, Mn/Ti, K/Ti, Th/Ti, V/Ti) were measured with a portable X-ray fluorescence (pXRF) spectrometer, and colour parameters L*a*b* were measured by spectrophotometer. Several black shale levels are recognized and correlated with similar shales in Europe between the Barremian–Aptian boundary and the Selli Level. The Th/K ratio proxy for hinterland humid or arid climate conditions shows no systematic variation with black shale levels. Several sea-level lowstands are inferred from condensed sandy intervals with some brackish water biota and tidal sedimentary structures. Black shale intervals are found in highstand intervals, with no systematic relationship to inferred transgressions. The formation of black shales is related to palaeoceanographic changes that may be driven by conditions remote from the Scotian Basin.     

鄂尔多斯盆地东部二叠系山西组页岩气成藏条件与有利区筛选

鄂尔多斯盆地东部榆106井区山西组页岩沉积在三角洲平原分流河道间沼泽、天然堤、决口扇远端与洼地环境。根据有机地球化学、物性、含气性、岩性实验分析,结合钻井、录井、测井资料与沉积相研究,开展了该区山西组页岩气成藏条件与有利区分布研究。山西组页岩有机碳含量较高,山二段平均5.28%,山一段平均3.02%,有机质类型以Ⅱ_2、Ⅲ型干酪根为主,有机质成熟度较高,R_o平均1.89%,生气条件优越。页岩孔隙度平均1.7%,渗透率平均0.0415×10~(-3)μm~2,平均含气量0.64 m~3/t,页岩单层厚度小,垂向上普遍与致密砂岩、煤层组成互层,累计厚度较大(平均达75 m),页岩渗透性较好而储集性能稍差。页岩脆性矿物含量平均49.9%,黏土矿物含量平均50.1%,黏土矿物含量较高,资源丰度普遍较低,但是页岩埋深小于3000 m,试气产能较高(0.64×10~4m~3/d),商业开发潜力较好。山二段有机质含量比山一段更高,含气性比山一段更好。主要基于页岩厚度与沉积相展布预测的山二段页岩气有利区呈北东向、南北向条带状展布,受分流河道间沼泽微相的控制。