太平洋海底富钴结壳中的烃类有机质及其成因意义

用气相色谱-质谱(GC-MS)联测方法测定了中西太平洋海底海山富钴结壳中的可溶有机质,对其丰度、生源构成、沉积环境、成熟度等方面进行了初步的探讨.富钴结壳的烃类生物标志化合物大多具成熟烃特征,个别具低成熟烃特点."A"/C高达9.81～21.15,显示出运移烃的特征;藿烷C31-R(S JR)为0.43～0.46,Tm/(Tm Ts)为0.40～0.59,C30αβ藿烷/(αβ藿烷 βα莫烷)为0.85～0.89,C29αβ藿烷/(αβ藿烷 βα莫烷)为0.81～0.85,c29甾烷20S/(20S 20R)为0.45～0.60,从而计算出Rsc(%)为0.73%～0.81%,个别达到1.06%;C29αββ/(αββ ααα)为0.35～0.42.甾烷丰度顺序为C29甾烷＞C27甾烷＞C28甾烷,同时检出了孕甾烷和4-甲基甾烷,重排甾烷三角图显示该有机质为Ⅱ型.Pr/Ph值介于0.35～0.82,显示植烷优势.说明烃类形成于强还原环境.链状烷烃、类异戊二烯烷烃、萜烷、甾烷化合物的组成和分布都说明茵藻类低等水生生物和陆源高等植物混合生源输入.洋底热液活动是富钴结壳中有机质热演化的重要热源.有机质在特定的海底条件下生成,并被运移到海山上,通过扩散和浸粢由外层进入结壳.     

南桐矿区煤有机显微组分特征及与油气生成关系研究

根据有机岩石学方法研究了南桐矿区煤有机显微组分的特征。在显微镜下发现了大量与煤成烃有关的有机显微组分,如渗出体,变渗出体,各向异性微粒体,各向异性沥青质体,变木栓质体等。它们与该矿区煤层的高含烃性有着密切的成因关系,并且是高含烃性煤成烃的显微光学标志。     

广西金牙金矿有机包裹体激光拉曼光谱研究

金牙金矿是桂西北微细粒浸染型金矿床具有代表意义的典型矿床。其赋矿层位为三叠系中统百蓬组的富有机碳的浊积岩系。通过对成矿过程中有机包裹体的激光拉曼分子微探针研究认为:(1)有机质在成矿过程中会发生热降解,其降解产物烃的量可衡量热的程度;(2)无机组分和CO2/CH4 参数可用于研究热液的地球化学环境。     

Gas geochemistry of the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Implications for gas hydrate exploration in the Arctic

Gases were analyzed from well cuttings, core, gas hydrate, and formation tests at the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well, drilled within the Milne Point Unit, Alaska North Slope. The well penetrated a portion of the Eileen gas hydrate deposit, which overlies the more deeply buried Prudhoe Bay, Milne Point, West Sak, and Kuparuk River oil fields. Gas sources in the upper 200 m are predominantly from microbial sources (C₁ isotopic compositions ranging from −86.4 to −80.6‰). The C₁ isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate-bearing sands at 600 m. The tested gas hydrates occur in two primary intervals, units D and C, between 614.0 m and 664.7 m, containing a total of 29.3 m of gas hydrate-bearing sands. The hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane. The isotopic composition of the methane carbon ranges from −50.1 to −43.9‰ with several outliers, generally decreasing with depth. Gas samples collected by the Modular Formation Dynamics Testing (MDT) tool in the hydrate-bearing units were similarly composed mainly of methane, with up to 284 ppm ethane. The methane isotopic composition ranged from −48.2 to −48.0‰ in the C sand and from −48.4 to −46.6‰ in the D sand. Methane hydrogen isotopic composition ranged from −238 to −230‰, with slightly more depleted values in the deeper C sand. These results are consistent with the concept that the Eileen gas hydrates contain a mixture of deep-sourced, microbially biodegraded thermogenic gas, with lesser amounts of thermogenic oil-associated gas, and coal gas. Thermal gases are likely sourced from existing oil and gas accumulations that have migrated up-dip and/or up-fault and formed gas hydrate in response to climate cooling with permafrost formation.     

Uranium mineralization in the Alum Shale Formation (Sweden): Evolution of a U-rich marine black shale from sedimentation to metamorphism

The Alum Shale Formation is a metal-rich black shale, deposited on the Baltoscandian platform between Middle Cambrian and Early Ordovician. These black shales may be of particular economic interest for their relatively high uranium content (100–300 ppm) and their wide distribution from Norway to Estonia. Scandinavian Alum Shale may thus constitute a great potential resource of uranium, as a low grade ore. The Alum Shale Formation is particularly interesting to study the mineralogical expression and content of uranium in series submitted to progressive burial and metamorphism. For this purpose, the behavior of U, P, Ti and organic matter was studied on a series of representative samples from most Alum Shale prospection zones. In southern Sweden, where Alum Shale underwent fairly shallow burial, uranium concentrations have no mineralogical expression except a rather high U content of biogenic phosphates. Calcite concretions (beefs) and fractures recorded the migration of hot overpressured hydrocarbons and brines from thermally mature areas to immature Alum Shale. However, thermal maturation and fluid migration did not allow remobilization of uranium and metals. At the opposite, in northern Sweden, where the series were folded, duplicated and submitted to low grade Greenschist metamorphism during Caledonian orogeny, phospho-silicates U-Si-Ca-P (±Ti ±Zr ±Y) and minor amounts of uraninite are identified and indicate that U, P, and Ti were mobile and precipitated as new phases. The effect of metamorphism is therefore important to consider as the leachability of U, especially during (bio)-hydrometallurgical processes, which will be by far different between the two considered areas.     

Geomorphology and sedimentary sequence evolution during the buried stage of paleo-uplift in the Lower Cretaceous Qingshuihe Formation,Junggar Basin,northwestern China: Implications for reservoir lithofacies and hydrocarbon distribution

The evolution of large-scale paleo-uplifts within sedimentary basins controls the sedimentary provenance, depositional systems and hydrocarbon distributions. This study aims to unravel changes in paleo-geomorphology, interpret sedimentary sequence evolution, and investigate favourable reservoir types and the hydrocarbon distribution during the buried stage of a long-term eroded paleo-uplift, taking the Lower Cretaceous Qingshuihe Formation (K₁q) in the Junggar Basin as an example. These research topics have rarely been studied or are poorly understood. This study integrates current drilling production data with outcrop and core analyses, drilling well logs, 3D seismic data interpretations, grading data, physical property comparisons and identified hydrocarbon distributions.After more than 20 million years of differential river erosion and weathering in arid conditions, the large-scale Chemo paleo-uplift within the hinterland area of the basin formed a distinctive valley–monadnock paleo-geomorphology prior to the deposition of K₁q. Since the Early Cretaceous, tectonic subsidence and humid conditions have caused the base level (lake level) to rise, leading to backfilling of valleys and burial processes. Two systems tracts in the target strata of K₁q, consisting of distinctive depositional systems, can be identified: (1) a lowstand systems tract (LST), which is confined within incised valleys and is mainly composed of gravelly braided rivers and rarely occurring debris flows and (2) an extensive transgressive systems tract (TST), which developed into an almost flat landform and consists of braided river delta to lacustrine depositional systems. Overall, the physical properties of braided river reservoirs in the LST are better than those of the braided river delta reservoirs in the TST. However, the inhomogeneous distributions of carbonate cements cause differences in the physical properties of conglomerate reservoirs in the LST. However, for sandstones in both the LST and TST, coarser grain sizes and better sorting result in better physical properties. Altogether, four types of reservoir can be identified in the study area: Jurassic inner monadnock reservoirs, K₁q LST stratigraphic onlap reservoirs, LST structural reservoirs and TST structural reservoirs.     

An autochthonous geological model for the eastern Andes of Ecuador

We describe a traverse across the Cordillera Real and sub-Andean Zone of Ecuador, poorly known areas with very little detailed mapping and very little age control. The spine of the Cordillera comprises deeply eroded Triassic and Jurassic plutons, the roots of a major arc, emplaced into probable Palaeozoic pelites and metamorphosed volcanic rocks. The W flank comprises a Jurassic (?) submarine basaltic–andesitic volcanic sequence, which grades up into mixed Jurassic/Cretaceous volcanic and sedimentary rocks of the Inter-Andean Valley. The sub-Andean Zone, on the E flank of the Cordillera, comprises a newly recognized Cretaceous basin of cleaved mudrocks, quartz arenites and limestones. East of the syndepositional Cosanga Fault, the Cretaceous basin thins into a condensed sequence that is indistinguishable from the rocks of the adjacent hydrocarbon-bearing Oriente Basin. The principal penetrative deformation of the Cordillera Real was probably latest Cretaceous/Palaeocene. It telescoped the magmatic belts, but shortening was largely partitioned into the pelites between plutons. The plutons suffered inhomogenous deformation; some portions completely escaped tectonism. The pelites conserve two foliations. The earliest comprises slaty cleavage formed under low- or sub-greenschist conditions. The later is a strong schistosity defined by new mica growth. It largely transposed and obliterated the first. Both foliations may have developed during a single progressive deformation. We find inappropriate recent terrane models for the Cordillera Real and sub-Andean Zone of Ecuador. Instead we find remarkable similarities from one side of the Cordillera to the other, including a common structural history. In place of sutures, we find mostly intrusive contacts between major plutons and pelites. Triassic to Cretaceous events occurred on the autochthonous western edge of the Archaean Guyana Shield. The latest Cretaceous–Paleocene deformation is interpreted as the progressive collision of an oceanic terrane(s) with the South American continent. Young fault movements have subsequently juxtaposed different structural levels through the Cordillera Real orogen.     

Ore metal redistribution by hydrocarbon–brine and hydrocarbon–halide melt phases, North Range footwall of the Sudbury Igneous Complex, Ontario, Canada

We report methane-dominant hydrocarbon (fluid) inclusions (CH₄±C₂H₆–C₂H₂, C₃H₈) coexisting with primary brine inclusions and secondary halide melt (solid NaCl) inclusions in Au–Pt-rich quartz-sulfide-epidote alteration veins associated with the footwall-style Cu–PGE (platinum-group element)–Au deposits at the Fraser Mine (North Range of the Sudbury Igneous Complex). Evidence for coentrapment of immiscible hydrocarbon–brine, and hydrocarbon–halide melt mixtures is demonstrated. A primary CH₄–brine assemblage was trapped during quartz growth at relatively low T (min. T _trapping∼145–315°C) and P (max. P _trapping∼500 bar), prior to the crystallization of sulfide minerals in the veins. Secondary inclusions contain solid halite and a mixture of CH₄, C₂H₆–C₂H₂ and C₃H₈ and were trapped at a minimum T of ∼710°C. The halite inclusions may represent halide melt that exsolved from crystallizing sulfide ores that texturally postdate (by replacement) early alteration quartz hosting the primary, lower T brine–CH₄ assemblage. Laser ablation ICP-MS analyses show that the brine, hydrocarbon and halide melt inclusions contain significant concentrations of Cu (0.1–1 wt% range), Au, Bi, Ag and Pt (all 0.1–10 ppm range). Cu:Pt and Cu:Au ratios in the inclusions are significantly (up to 4 log units) lower than in the host alteration veins and adjacent massive sulfide ore veins, suggesting either (1) early Cu loss from the volatiles by chalcopyrite precipitation or (2) enhanced Au and Pt solubilities relative to Cu at the temperatures of entrapment. Concentration ratios between coexisting brine and CH₄ inclusions are lower for Cu, Au, Bi and Ag than for other elements (Na, Ca, Fe, Mn, Zn, Pb) indicating that during interaction with the brine, the hydrocarbon phase was enriched in ore metals. The high concentrations of ore metals in hydrocarbon, brine and halide melt phases confirm that both aqueous and non-aqueous volatiles were carriers of precious metals in the Sudbury environment over a wide range of temperatures. Volatile evolution and magmatic sulfide differentiation were clearly part of a single, continuous process in the Sudbury footwall. The exsolution of H₂O-poor volatiles from fractionated sulfide liquid may have been a principal mechanism controlling the final distribution of PGE and Au in the footwall ore systems. The study reports the first measurements of precious metal concentrations in fluid inclusions from a magmatic Ni–Cu–PGE environment (the Sudbury district). Electronic Supplementary Material Supplementary material is available for this article at     

Abiogenic Fischer–Tropsch synthesis of hydrocarbons in alkaline igneous rocks; fluid inclusion, textural and isotopic evidence from the Lovozero complex, N.W. Russia

A detailed fluid inclusion study has been carried out on the hydrocarbon-bearing fluids found in the peralkaline complex, Lovozero. Petrographic, microthermometric, laser Raman and bulk gas data are presented and discussed in context with previously published data from Lovozero and similar hydrocarbon-bearing alkaline complexes in order to further understand the processes which have generated these hydrocarbons. CH₄-dominated inclusions have been identified in all Lovozero samples. They occur predominantly as secondary inclusions trapped along cleavage planes and healed fractures together with rare H₂O-dominant inclusions. They are consistently observed in close association with either arfvedsonite crystals, partially replaced by aegirine, aegirine crystals or areas of zeolitization. The majority of inclusions consist of a low-density fluid with CH₄ homogenisation temperatures between −25 and −120 °C. Those in near-surface hand specimens contain CH₄+H₂ (up to 40 mol%)±higher hydrocarbons. However, inclusions in borehole samples contain CH₄+higher hydrocarbons±H₂ indicating that, at depth, higher hydrocarbons are more likely to form. Estimated entrapment temperatures and pressures for these inclusions are 350 °C and 0.2–0.7 kbar. A population of high-density, liquid, CH₄-dominant inclusions have also been recorded, mainly in the borehole samples, homogenising between −78 and −99 °C. These consist of pure CH₄, trapped between 1.2 and 2.1 kbar and may represent an early CH₄-bearing fluid overprinted by the low-density population. The microthermometric and laser Raman data are in agreement with bulk gas data, which have recorded significant concentrations of H₂ and higher hydrocarbons up to C₆H₁₂ in these samples. These data, combined with published isotopic data for the gases CH₄, C₂H₆, H₂, He and Ar indicate that these hydrocarbons have an abiogenic, crustal origin and were generated during postmagmatic, low temperature, alteration reactions of the mineral assemblage. This would suggest that these data favour a model for formation of hydrocarbons through Fischer–Tropsch type reactions involving an early CO₂-rich fluid and H₂ derived from alteration reactions. This is in contrast to the late-magmatic model suggested for the formation of hydrocarbons in the similar peralkaline intrusion, Ilímaussaq, at temperatures between 400 and 500 °C.