Marine Oil Shale Research Articles

A comparison of the thermal conversion behaviour of marine kerogens isolated from oil shales by NaOH-HCl and HCl-HF methods

The inherent reactivity of kerogens isolated from marine oil shales has not been extensively studied. Determining the conversion and products of demineralized oil shales simplifies modelling of oil shale pyrolysis because the complications introduced by the mineral matter are removed. Accordingly, the reactive behaviour of demineralized products (kerogens) isolated from two marine oil shales (type II kerogen) by NaOH-HCl and HCl-HF methods have been compared with each other and with those of untreated shales. Pyrolysis experiments have been carried out under N2 and H2 in a sealed system, and also in a flow through autoclave system, which is closer to practical pyrolysis conditions, at temperatures in the range 355 °C to 425 °C. The two isolation methods gave a similar conversion in sealed autoclaves and the only major difference was the higher asphaltol yield for the NaOH-HCl kerogens, so that asphaltol yield cannot be used to characterize the intrinsic reactivity of the shale organic matter. The El-Lajjun shale gave higher conversion to organic materials than the kerogens but the opposite was noted for Julia Creek, especially for pyrolysis under N2.Pyrolysis experiments in a flow through system gave similar overall conversion for the kerogens and their untreated shales but the yields of condensates for the Julia Creek shale were significantly lower for the oil shales than for the kerogens. The chemical complexity of the condensates from the flow through experiments was much greater than that for the CH2Cl2 soluble samples from the sealed autoclave pyrolysis experiments.The product compositions for the NaOH-HCl and HCl-HF kerogens were, as for the total yields, very similar, suggesting that the NaOH-HCl method is a valuable alternative in countries where the use of HF is severely restricted. Further, determining the reactive behaviour of kerogens isolated by two different methods makes it likely that features of the reactivity common to both types of kerogens are features of organic matter reactivity rather than of the isolation method and thus provides a firm foundation for future work. The isolated kerogen could also be considered as a source material for the production of fine chemicals and other applications.

Structural Characteristics of Low-Aromaticity Marine and Lacustrine Oil Shales and their NaOH-HCl Kerogens Determined Using 13C NMR and XPS

Few comparisons have been made between low-aromaticity marine and lacustrine oil shales and their kerogens, because the reliability of structural analyses has been limited by a reliance on only one method of kerogen isolation, HCl-HF. Therefore, a detailed analysis by 13C NMR and X-ray photoelectron spectroscopy (XPS) was made for Attrat marine oil shale (Jordan) and Colorado (Green River) lacustrine oil shale (USA) and their NaOH-HCl kerogens. Some differences between oil shales and their kerogens were noted, but many structural features were considered to be true characteristics of the organic matter. The results emphasise the importance of comparing the analyses of kerogens isolated by different methods to ensure that features of the organic matter are not an artefact of the method of kerogen isolation. For both oil shales, the predominantly aliphatic character of the organic part was confirmed and the long average chain length of the aliphatic hydrocarbons was established. All shales and their kerogens showed a small cluster size for the aromatic rings. The elemental analysis obtained by XPS, compared with the bulk elemental analysis, indicated major differences between the near-surface region sampled by XPS and the bulk. The organic S was determined to be aliphatic and aromatic S with possibly small amounts of sulfoxide. Most of the N was pyrrolic with smaller amounts in pyridinic or quaternary form. Nearly all of the surface organic C in both kerogens was bonded to C and H. Two major forms of organic O were distinguishable. A good correlation between the proportion of aliphatic S and pyrolysis reactivity is suggested.

Catalytic hydropyrolysis of El-Lajjun and Julia Creek shale oils using flow-through and sealed autoclaves

High-sulfur shale oils from two marine oil shales, El-Lajjun (Jordan) and Julia Creek (Australia) were subjected to hydropyrolysis using NiMo catalysts deposited on Al-SBA-15 with Si/Al ratios ranging from 10 to 75, i.e. with decreasing acidity, both in a flow-through system at 0.1 MPa H2 pressure and in sealed autoclaves at varying H2 pressure (1–6 MPa (cold, i.e., at room temperature)). For autoclave pyrolysis of El-Lajjun shale oil catalysed by NiMo-Al-SBA-15 (Si:Al = 10:1), sulfur content of oil decreased with H2 pressure, catalyst:oil ratio and temperature, pyrolysis time having little effect. Coking decreased with increasing H2 pressure, but increased with increasing temperature and catalyst:oil ratio. Time had little effect on coking. The conditions finally adopted were 400 °C, 6 MPa (cold) H2 pressure, 30 min pyrolysis time and (0.1:1.0) catalyst:oil ratio. Lower Si/Al ratios (≤50) all gave the same hydrodesulphurization (HDS) activity, but coking declined with decreasing Si/Al ratio, so that the optimum ratio was 10. The Julia Creek shale oil also showed good HDS, but was more susceptible to coking at high Si/Al ratio. The oil obtained in catalysed pyrolysis contained almost no thiophenes or benzothiophenes and had more high-boiling point material than oil from non-catalysed pyrolysis. The catalyst was successfully regenerated after use and was also effective in HDS of both raw oil shales. For the flow-through experiments, no significant hydrodesulphurization (HDS) was observed for either shale oil, but some hydrodenitrogenation (HDN) occurred for the Julia Creek shale oils.

Geochemical characteristics of Early Cretaceous marine oil shale from the Changshe Mountain area in the northern Qiangtang Basin, Tibet: Implications for palaeoweathering, provenance, tectonic setting, and organic matter accumulation

The Early Cretaceous Shengli River–Changshe Mountain marine oil shale belt, located in the northern Qiangtang Basin, Tibet, is estimated to be the largest marine oil shale resource in China. However, its palaeoweathering, provenance, and tectonic setting during the depositional history have received little interest. In this paper, 19 outcrop marine oil shale samples from the ChangsheMountain (CSM) area were studied to investigate the provenance, palaeoclimate, palaeoweathering, and tectonic setting during the marine oil shale deposition. The total organic carbon and organic sulphur contents of the CSM oil shales range from 2.2% to 13.44% and 0.19% to 1.08%, respectively. The CSM oil shale samples contain abundant carbonate (e.g., calcite and dolomite), quartz, and clay minerals. The clay minerals of the CSM oil shale samples is dominated by illite and then by smectite. Other minerals, including haematite, apatite, pyrite, baryte, and celestite, were also identified by scanning electron microscope–energy‐dispersive X‐ray spectrometer. The total rare earth element (∑REE) contents of the oil shales range from 9.01 to 105.96 ppm (average 57.56 ppm), close to the average REE contents of U.S. coals. The REE contents in oil shale samples are mainly controlled by terrigenous input. The CSM oil shales show LREE‐enriched, HREE‐depleted, with the LREE/HREE ratios ranging from 5.12 to 10.18, negative Eu anomalies (0.56–0.84) and slightly negative Ce anomalies (0.87–1.05). The chemical index of alteration values of the CSM oil shales range from 67 to 76 (average 73), indicating a moderate chemical weathering condition. Sr/Cu and Rb/Sr ratios suggest the CSM oil shales were mainly deposited under a warm and humid climate regime. Sr/Ba ratios, ranging from 0.54 to 7.84, suggest a palaeoenvironment with fluctuant salinity. Major element, trace element, and REE relationships indicate that the CSM oil shales are mainly from the felsic and intermediate igneous rocks. The REE distribution patterns of the CSM oil shales are similar to the Late Triassic Nadi Kangri felsic volcanic rocks in the Qiangtang Basin, indicating that the CSM oil shale may be derived from the Late Triassic volcanic rocks and the oil shales were mainly formed in rift tectonic setting. Favourable preservation condition (e.g., warmer palaeoclimate, higher palaeosalinity, and dysoxic to anoxic water column environment) could be the main controlling factor for organic matter accumulation.

Characterization of Jordanian oil shale and variation in oil properties with pyrolysis temperature

Marine oil shale from the Sultani mine was characterized (ultimate and proximate analysis, 13C NMR, differential thermogravimetry (DTG)). The 13C NMR indicated that the shale is highly aliphatic, and the concentration of carbonyl carbon is small. DTG indicated a total weight loss of 21 wt% to 550 °C. The shale was pyrolysed to different final temperatures in the range 360–540 °C under N2 and the shale oils produced characterized by utilization parameters (API, heating value, boiling point distribution) and by chemical properties (1H-NMR and gas chromatography-mass spectrometry GC–MS) as a function of final pyrolysis temperature. Previous studies have only investigated the utilization properties of marine-shale oil at one temperature. The average oil yield increased with pyrolysis temperature to a maximum at 520 °C, and then fell. The oil density was higher at 440–520 °C than at 360–400 °C (0.99–1.00, 0.96−0.97 g/cm3 respectively). Unexpectedly, oil heating value (39.7–40.0 MJ/kg in 360–540 °C) and sulfur content (11.25 wt% in 360–520 °C) were independent of pyrolysis temperature. Oil distillation indicated that up to 90 vol% was in the diesel fraction.1H-NMR implied that the oil produced at all temperatures was highly aliphatic. GC/MS for the oil indicated the presence of long chain hydrocarbons (C11-C32), both normal and branched, some substituted benzenes, and high concentrations of sulfur compounds, mainly substituted thiophenes with same benzothiophenes. The average molecular weight of the sulfur compounds and proportion of heavier oil were higher at 520 °C than at 460 °C, so that the increased yield of oil at higher temperatures would have to be balanced against the lower quality of the crude shale oil produced. The results emphasized the importance of studying oil properties as a function of pyrolysis temperature, as differences which could be important in practice were noted.

Evolution characteristics and model of nanopore structure and adsorption capacity in organic-rich shale during artificial thermal maturation: A pyrolysis study of the Mesoproterozoic Xiamaling marine shale with type II kerogen from Zhangjiakou, Hebei, China

Thermal maturity has a considerable impact on hydrocarbon generation, mineral conversion, nanopore structure, and adsorption capacity evolution of shale, but that impact on organic-rich marine shales containing type II kerogen has been rarely subjected to explicit and quantitative characterization. This study aims to obtain information regarding the effects of thermal maturation on organic matter, mineral content, pore structure, and adsorption capacity evolution of marine shale. Mesoproterozoic Xiamaling immaturity marine oil shale with type II kerogen in Zhangjiakou of Hebei, China, was chosen for anhydrous pyrolysis to simulate the maturation process. With increasing simulation temperature, hydrocarbon generation and mineral transformation promote the formation, development, and evolution of pores in the shale. The original and simulated samples consist of closed microspores and one-end closed pores of the slit throat, all-opened wedge-shaped capillaries, and fractured or lamellar pores, which are related to the plate particles of clay. The increase in maturity can promote the formation and development of pores in the shale. Heating can also promote the accumulation, formation, and development of pores, leading to a large pore volume and surface area. The temperature increase can promote the development of pore volume and surface area of 1–10 and 40-nm diameter pores. The formation and development of pore volume and surface area of 1–10 nm diameter pores are more substantial than that of 40-nm diameter pores. The pore structure evolution of the sample can be divided into pore adjustment (T < 350°C, EqRo < 0.86%), development (350°C < T < 650°C, 0.86% < EqRo < 3.28%), and conversion or destruction stages (T > 650°C, EqRo > 3.28%). Along with the increase in maturity, the methane adsorption content decreases in the initial simulation stage, increases in the middle simulation stage, and reaches the maximum value at 650°C, after which it gradually decreases. A general evolution model is proposed by combining the nanopore structure and the adsorption capacity evolution characteristics of the oil shale.

A comparison of the NaOH-HCl and HCl-HF methods of extracting kerogen from two different marine oil shales

The organic matter (kerogen, defined as including the organic material soluble and insoluble in organic solvents at room temperature) from two marine oil shales, El-Lajjun (Jordan) and Julia Creek (Queensland, Australia), has been extracted by the commonly used HCl-HF method and the resulting products compared with those obtained using the NaOH-HCl method, i.e. with initial strong alkali extraction. The elemental analyses on a dry ash-free basis of the solids obtained by the two methods were similar to each other and to that of the original oil shale. The pyrolysis-gas chromatography–total ion chromatograms were also similar for the kerogens obtained by the two methods and for the original oil shale, showing regular n-alkene/alkane series, as would be expected from the high atomic H/C ratio, and series of alkyl substituted thiophenes and benzothiophenes. The solid state 13C NMR spectra showed similar trends. The Fe contents of the solids obtained by the HCl-HF treatment were much higher than for the solids from NaOH-HCl treatment, which could have implications for reactivity studies. XPS showed depletion of the sulfur and oxidation near the surface and confirmed that some aliphatic sulfur was present. However, in general, both methods gave organic products with similar characteristics, allowing isolation of organic matter by a method not involving HF, whose use is restricted in many countries.

The micropaleontological record of marine early Eocene oil shales from Jordan

Core OS-28 located in central Jordan offers an expanded record of calcareous nannofossils and benthic foraminifera for the early Eocene of the southern Tethys. The oil shale succession of the studied interval covers calcareous nannofossil biozones NP10, NP11, NP12 and NP13. Microfossils document the biotic response of calcareous nannofossils and benthic foraminifera to short and long term warming trends of the early Eocene following the Paleocene-Eocene Thermal Maximum (PETM). On a global scale, two early Eocene short term shifts to higher atmospheric CO2 concentration are recorded by negative δ13C excursions. These are known as Eocene Thermal Maximum 2 and 3 (ETM2, ETM3). Stable isotope records (δ13Corg, δ13Ccarb, δ18Ocarb) from the study area do not show these negative excursions, which elsewhere can be correlated with the two hyperthermal events known from early Eocene successions. The absence of negative δ13C signals otherwise typical for ETM2 and ETM3 is explained by a diagenetic alteration of the isotope signal after deposition.High abundances of the nannofossil taxon Sphenolithus spp. in biozone NP10 indicate less fertile conditions for this interval than for the overlying biozone NP11. Throughout biozones NP11 to NP13 Coccolithus pelagicus and Toweius spp. are the dominant taxa of the assemblages, suggesting a mesotrophic environment. Surface waters experienced a temperature change from warm to moderate-warm. The benthic foraminifera in calcareous nannofossils biozone NP10 and in the lower part of NP11 reflect oligo-mesotrophic and moderate to well oxygenated bottom water conditions. Throughout the upper part of biozones NP11, NP12 and NP13, the benthic foraminifera are characterized by an increasing abundance of Anomalinoides zitteli, Lenticulina spp. and Valvulineria scrobiculata. This coincides with enriched total organic matter content (TOC), indicating a shift to mesotrophic conditions and a moderate oxygen supply of the bottom waters. Based on the micropaleontological observations made in core OS-28 the early Eocene is first characterized by an increase and subsequently by a decrease of nutrients and oxygen. The composition of both, benthic and planktic communities was rather controlled by variations of regional environmental parameters than by global ones. These include strong runoff, climatic variability and the architecture of the basin.

Elemental characteristics and paleoenvironment reconstruction: a case study of the Triassic lacustrine Zhangjiatan oil shale, southern Ordos Basin, China

Using trace elements to reconstruct paleoenvironment is a current hot topic in geochemistry. Through analytical tests of oil yield, ash yield, calorific value, total sulfur, major elements, trace elements, and X-ray diffraction, the quality, mineral content, occurrence mode of elements, and paleoenvironment of the Zhangjiatan oil shale of the Triassic Yanchang Formation in the southern Ordos Basin were studied. The analyses revealed relatively high oil yield (average 6.63%) and medium quality. The mineral content in the oil shale was mainly clay minerals, quartz, feldspar, and pyrite; an illite–smectite mixed layer comprised the major proportion of clay minerals. Compared with marine oil shale in China, the Zhangjiatan oil shale had higher contents of quartz, feldspar, and clay minerals, and lower calcite content. Silica was mainly in quartz and Fe was associated with organic matter, which is different from marine oil shale. The form of calcium varied. Cluster analyses indicated that Fe, Cu, U, V, Zn, As, Cs, Cd, Mo, Ga, Pb, Co, Ni, Cr, Sc, P, and Mn are associated with organic matter while Ca, Na, Sr, Ba, Si, Zr, K, Al, B, Mg, and Ti are mostly terrigenous. Sr/Cu, Ba/Al, V/(V + Ni), U/Th, AU, and δU of oil shale samples suggest the paleoclimate was warm and humid, paleoproductivity of the lake was relatively high during deposition of the shale—which mainly occurred in fresh water—and the paleo-redox condition was dominated by reducing conditions. Fe/Ti ratios of the oil shale samples suggest clear hydrothermal influence in the eastern portion of the study area and less conspicuous hydrothermal influence in the western portion.

Chemo‐ and Biostratigraphy of the Jurassic Oil Shales from the Qiangtang Basin, Northern Tibet, China: A Case Study of the Toarcian Oceanic Anoxic Event

AbstractThe marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17± (relative to PDB), which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events (T‐OAE) in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic‐anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox‐sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo‐ and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea‐level rise and an increase of surface water productivity.

The geochemistry of trace elements in marine oil shales and their combustion residues: Occurrence and environmental aspects

ABSTRACTWith the aim of better understanding geochemistry of trace elements in marine oil shale and its combustion residues, 23 raw samples, 17 oil shale combustion residues, and 18 selected minerals from Bilong Co oil shale are studied. Potentially hazardous trace elements in raw samples include As, B, Cd, Mo, and Se, while Se, Mo, Cd, As, Bi, and U are potentially hazardous trace elements in combustion residues. As is controlled mainly by Fe-bearing minerals. B occurs mainly in clay minerals. Cd is enriched mainly in calcite. Mo is controlled mainly by organic matter. Se is mainly controlled by P-bearing minerals.

Mineralogy and geochemical anomalies of Lower Cretaceous marine oil shale from Changshe Mountain West, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone in northern Tibet represents a large marine oil shale resource in China. Thirty-four samples of oil shale were collected from the Changshe Mountain West oil shale, a new oil shale deposit discovered in this oil shale zone, to evaluate the minerals and geochemical anomalies in the oil shale. Minerals identified in the oil shale include calcite, dolomite, quartz, illite, and trace amounts of siderite, hematite, feldspar, apatite, zinc oxide, pyrite, sphalerite, barite, celestite, and Fe(Si, Al)-oxysulfate minerals. The oil shale samples are rich in trace elements compared to post-Archean average shales including Co (up to 15.8μg/g), Ni (up to 83.6μg/g), Cu (up to 101μg/g), Zn (up to 775μg/g), As (up to 255μg/g), Se (up to 6.91μg/g), Sr (up to 738μg/g), Mo (up to 87.9μg/g), Pb (up to 17.4μg/g), Cd (up to 13.0μg/g), Bi (up to 0.38μg/g), and U (up to 7.10μg/g), and to a lesser extent, Li, F, Sc, V, Cr, Ga, Sn, Hg, and rare earth elements. Trace elements of probable terrigenous origin in the oil shale were derived from two possible sources: a felsic volcanic rock source and a limestone source. High concentrations of lithophile elements (e.g., Li, Sc, Ga, and REEs) were derived from these provenances. However, the enrichment factor for these elements also is low. In addition, seawater and hydrothermal activity may have influenced the geological and geochemical compositions of the oil shale. Minerals such as calcite, dolomite, and a large proportion of pyrite are of marine origin, and the enrichment of V, Cr, Co, Ni, Cu, Se, Sr, Mo, Pb, and U in the oil shales was probably due to marine influence. Barite, celestite, sphalerite, Fe(Si, Al)-oxysulfate minerals, and fracture-filling pyrite are of hydrothermal origin, and F, Zn, and Cd were derived from hydrothermal fluids.

Geochemical characteristics, redox conditions, and organic matter accumulation of marine oil shale from the Changliang Mountain area, northern Tibet, China

The organic-rich Changliang Mountain oil shale, located in the North Qiangtang depression, northern Tibet, is considered to be excellent mineral resource in China. The Changliang Mountain oil shale reported here was deposited in a tidal flat-lagoon environment and is characterized by black thin-layered oil shales intercalated with dark-gray marls. Here, we present geochemical data from the Changliang Mountain oil shale profile, in order to investigate the mechanism of organic matter (OM) accumulation and to establish the formation model for the marine oil shale deposition. Total organic carbon (TOC) values range from 2.96 to 23.47% in the oil shale samples, while the marl samples contains low TOC contents, ranging from 0.06 to 0.21%. In the organic-rich oil shale sediments, many redox indicators, including Mo/Al ratios, V/Cr ratios, Th/U ratios, Ni/Co ratios, and the relationship of Mo to TOC suggest a deposition under dysoxic to anoxic environments. Subsequently, the bottom water evolved into an oxic water body when the organic-poor marls were deposited. However, the negative and/or weak relationship between TOC and productivity indices P/Ti and Ba/Al indicates that OM accumulation was not controlled mainly by primary productivity, but dysoxic/anoxic bottom water environment. A stratified water column may be initiated by the supply of fresh water from the continent nearby, combining with warm and humid climate, which is beneficial to the reproduction of marine organisms. The death and bury of these organisms could lead to the formation of dysoxic/anoxic bottom waters and enhance the preservation of OM. In this study, a preservation model of the Changliang Mountain oil shale was established. The model implies that excellent preservation is the major controlling factor for OM enrichment in the oil shale layer. In addition, factors such as mixed deposition with clay minerals, and detrital matter input cannot be ignored for their influence on OM enrichment.

Recovery of shale oil condensate from different oil shales using a flow-through apparatus

Four oil shales from different locations and origins have been reacted in a flow-through system (425°C, with N2 or H2 as sweep gases at 1atm pressure) with a view to more closely simulating a practical process for oil shale conversion than can be achieved with a sealed autoclave system.It was observed that there was no general correlation between the yields in the two systems, nor was there a general correlation between the amount of condensate and the amount of volatiles obtained by thermogravimetric analysis.For all four oil shales, the condensate gave more complex gas chromatography–mass spectrometry total ion chromatograms (GC–MS TICs) than the CH2Cl2-solubles from sealed autoclave reactions. Surprisingly, the products from one of the Jordanian oil shales, Yarmouk, and an Australian Julia Creek oil shale were remarkably similar. The product from the lacustrine Colorado oil shale was much more similar to that from a lacustrine algal coal (torbanite) than to those from marine oil shales. The differences in yields and product characteristics between sealed autoclave and flow-through reactions suggest that yields and product distributions obtained from sealed autoclave reactions should be treated with caution.

OCCURRENCE AND ENRICHMENT OF TRACE ELEMENTS IN MARINE OIL SHALE (CHINA) AND THEIR BEHAVIOUR DURING COMBUSTION

The Shengli River-Changshe Mountain oil shale zone represents the potentially largest marine oil shale resource in China. With the aim to have better knowledge of the distribution of trace elements in oil shale, and their behaviour during oil shale combustion and gasification, 28 raw Changliang Mountain oil shale and marl samples, 19 oil shale combustion residue samples and 23 samples of minerals isolated from Changliang Mountain oil shale are studied for trace element content. The oil shale samples from the Changshe Mountain area are characterized by high ash yield (54.69-86.75%) and total organic carbon (TOC) content (2.20- 13.44%). The contents of Se, Mo, Cd, As, B, and Ni in raw oil shale samples are 3.78 to 28.44 times their upper continental crust values. The enrichment of an element in oil shale seams may be a function of that association and the origin of oil shale fractions. Some trace elements in the Changshe Mountain oil shale show susceptibility to release into the atmosphere, including about 93% Hg and 20-30% As, Ba, Be, Co, Cr, Nb, and Sc. The behaviour and migration of trace elements during oil shale combustion strongly depend on their mode of occurrence in the rock. Based on Pearson's coefficients of correlation between elements, as well as cluster and isolated mineral analyses, the main modes of occurrence of trace elements in marine oil shale are distinguished: 1) clay mineral affined - B, Ba, Be, Cr, Cs, Ga, Hf, Li, Nb, Rb, Sc, Sn, Ta, Th, V, W, Zr, REEs; 2) organic affined - As, Mo, Se; 3) Fe-bearing mineral affined - Bi, Co, Cu, Ni, Pb, U; 4) calcite affined - Cd, Sr and 5) fossil affined - Cd, Zn.

Metal sources for the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation, South China

Total organic carbon content (TOC), trace element and platinum-group element (PGE) concentrations were determined in the black shales of the Lower Cambrian Niutitang Formation in the Nayong area, Guizhou Province, South China, in order to study the polymetallic Ni–Mo–PGE mineralization. The results demonstrate that numerous elements are enriched in the polymetallic ores compared to those of the nearby black shale, particularly Ni, Mo, Zn, TOC and total PGE, which can reach up to 7.03wt.%, 8.49wt.%, 11.7wt.%, 11.5wt.% and 943ppb, respectively. The elemental enrichment distribution patterns are similar to those in the Zunyi and Zhangjiajie areas except that the Nayong location is exceptionally enriched in Zn. Whereas positive correlations are observed between the ore elements of the polymetallic ores, no such correlations are observed in the black shale. These positively correlated metallic elements are classified into three groups: Co–Ni–Cu–PGE, Zn–Cd–Pb and Mo–Tl–TOC. The geological and geochemical features of these elements suggest that Proterozoic and Early Palaeozoic mafic and ultramafic rocks, dolomites and/or Pb–Zn deposits of the Neoproterozoic Dengying Formation and seawater could be the principal sources for Co–Ni–Cu–PGE, Zn–Cd–Pb, and Mo–Tl–TOC, respectively. Furthermore, the chondrite-normalized patterns of PGEs with Pd/Pt, Pd/Ir and Pt/Ir indicate that PGE enrichment of the polymetallic ores is most likely related to hydrothermal processes associated with the mafic rocks. In contrast, PGE enrichment in the black shale resembles that of the marine oil shale with terrigenous and seawater contributions. Our investigations of TOC, trace elements and PGE geochemistry suggest that multiple sources along with submarine hydrothermal and biological contributions might be responsible for the formation of the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation across southern China.

The structure and reactivity of a low-sulfur lacustrine oil shale (Colorado U.S.A.) compared with those of a high-sulfur marine oil shale (Julia Creek, Queensland, Australia)

Oil shales from two different continents (Australia and North America) of different ages (100 and 40millionyears) and origins (one marine, one lacustrine) have been reacted in the range 355–425°C under H2 or N2 for 1 or 5h with or without the addition of catalyst. The shales differed in S content, and the nature of the mineral matter, but both had high atomic H/C ratios. The overall reactivity of the two shales was similar and high yields of soluble products could be obtained under relatively mild conditions with only small CO2 yields, but the temperature dependence of reactivity and the effect of potential catalysts differed markedly. Increasing the temperature and time led to increases in conversion but of different extents. Substituting H2 for N2 led to a large increase to conversion for the lower-atomic-H/C ratio marine oil shale. The CH2Cl2 solubles from the marine oil shale showed a larger range of compounds than those from the lacustrine oil shale which resembled the CH2Cl2 solubles from torbanite, a coal-like material derived from lacustrine algae.

The geochemistry of platinum group elements in marine oil shale—A case study from the Bilong Co oil shale, northern Tibet, China

The Bilong Co oil shale zone is located in the South Qiangtang depression. This zone, together with the Shengli River-Changshe Mountain oil shale zone in the North Qiangtang depression, northern Tibet plateau, represents the potentially largest marine oil shale resource in China. Seventeen samples including oil shale and micritic limestone were collected from the Bilong Co oil shale area to determine the concentrations, distribution patterns, occurrences and origins of platinum group elements (PGEs) in marine oil shale. The oil shale samples from the Bilong Co area exhibit very low total PGE contents ranging from 1.04 to 2.96ng/g with a weighted mean value of 1.686ng/g, while the micritic limestone samples from the Bilong Co area exhibit a little lower PGE value ranging from 0.413 to 1.11ng/g. PGEs in oil shale samples are characterized by high contents in Pd (average 0.79ng/g), Os (average 0.123ng/g) and Pt (average 0.644ng/g) compared with Ru (average 0.068ng/g), Rh (average 0.033ng/g) and Ir (average 0.026ng/g). The highest values for individual PGEs are not uniformly distributed in the section. Clearly, the PGEs are generally enriched in the oil shale samples near the boundary between micritic limestone and oil shale.The individual PGEs in oil shale samples from the Bilong Co area exhibit various modes of occurrence. Ruthenium and Pt occur mainly in pyrite, while Pd is associated mainly with organic matter and Mg-minerals. Rhodium and Os are controlled mainly by pyrite and organic matter. Iridium is present mainly in other Fe-bearing minerals, rather than pyrite. The PGEs in the Bilong Co oil shale are mainly of seawater origin and possibly influenced by terrigenous supply.

Minerals and potentially hazardous trace elements in marine oil shale: new insights from the Shengli River North surface mine, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone, including the Changliang Mountain–Shengli River oil shale, the Shengli River North oil shale, and the Changshe Mountain oil shale, represents potentially the largest marine oil shale resource in China. New geochemical data from the Shengli River North oil shale are presented to evaluate potentially hazardous trace elements in oil shale and to discuss possible factors controlling the geochemical anomalies. Oil shale samples from the Shengli River North area are characterized by high ash yield (59.25–66.27 %) and TOC content (4.77–9.35 %) with low total sulfur content (0.1–1.56 %) and intermediate shale oil content (3.60–16.30 %). Minerals in the Shengli River North oil shale include calcite, clay minerals, quartz, dolomite, and Fe-bearing minerals (e.g., pyrite, limonite, and hematite), and trace amounts of zeolite, apatite, and barite. Potentially hazardous trace elements in oil shale samples include As, Se, Mo, F, Ni, Cd, and Hg. Arsenic is present probably in both organic and inorganic matter. Selenium is controlled mainly by Fe-bearing (probably pyrite), while F and Cd occur mainly as apatite. The organically bound Mo and Ni are dominant, and Hg probably occurs as a substitution in the structure of pyrite, apatite and calcite. The elevated concentrations of F and Cd in the Shengli River North oil shale may be related to sediment source. Water chemistry may have played an important role for Ni and Mo enrichments, while the enrichment of Se in the oil shale samples is possibly related to hydrothermal fluids. Other elements including Hg and As are probably related to several factors.

Trace elements and their behaviour during the combustion of marine oil shale from Changliang Mountain, northern Tibet, China

The Shengli River–Changshe Mountain oil shale zone represents a potentially large marine oil shale resource in China. With the aim of better understanding the geochemistry of trace elements in marine oil shale and its combustion residues, 40 raw samples, 27 oil shale combustion residues and 29 selected minerals from Changliang Mountain oil shale are studied for geochemical analyses. The contents of Se, Cd, Mo, As, Cs, Pb, Sr and U in the oil shale samples are enriched from 1.47 to 33.91 times as compared with the Clarke values, whereas the concentrations of other elements are slightly higher/lower than the respective worldwide means. The most enriched elements in oil shale combustion residues are Se, Cd, Mo, As and U with enrichment values from 4.78 to 50.92. Trace elements with high volatile behaviour such as As, Co, Ni, Sc, Sn and V occur predominantly in organic matter and/or sulphides. Other non-volatile or slightly volatile trace elements (e.g., Be, Bi, Cs, Cu, Ga, Hf, Li, Nb, Rb, Ta, Th, W, Zr and REEs) may occur mainly in original and relatively refractory minerals in raw oil shale. The potentially hazardous trace elements in Changliang Mountain oil shale include As, Cd, Mo and Se. Arsenic and Se are controlled mainly by Fe-bearing minerals (probably pyrite) in Changliang Mountain oil shale. Cadmium is present mainly in dolomite, while Mo occurs mainly in organic matter.