The Source of Organic Matter and Its Role in Producing Reduced Sulfur for the Giant Sediment-Hosted Jinding Zinc-Lead Deposit, Lanping Basin, Yunnan, Southwest China

2021 ◽  
Author(s):  
Qing Lan ◽  
Ruizhong Hu ◽  
Xianwu Bi ◽  
Hu Liu ◽  
Jiafei Xiao ◽  
...  
Keyword(s):  
Organic Matter ◽  
Sulfate Reduction ◽  
Southwest China ◽  
Sulfide Minerals ◽  
Source Rocks ◽  
Late Triassic ◽  
Sulfide Mineralization ◽  
Solid Bitumen ◽  
Fine Grained ◽  
Reduced Sulfur

Abstract The Jinding deposit, located in the northern part of Lanping basin in southwest China, is the second largest Zn-Pb deposit in China and the third largest Mississippi Valley-type deposit identified globally. The deposit consists of several large tabular orebodies within the Jinding dome. Two stages of sulfide mineralization (sphalerite, galena, and pyrite) are identified, which are mainly hosted in the siliciclastic strata of Early Cretaceous and Paleocene age. The early sulfide minerals are mostly fine grained (<100 μm) and disseminated in the host rocks, whereas the late minerals are ty pically coarse grained (up to 1 mm in diameter) and colloform. It is estimated that about 3.17 × 106 m3 of reduced sulfur (H2S) was involved in the sulfide mineralization of the Jinding deposit, although its origin remains equivocal. Here, we investigate the biomarker signatures of organic matter and the mechanism of generation of the H2S. The organic matter in the Jinding deposit occurs mainly as petroleum filling fractures and cavities in the wall rocks and solid bitumen intergrown with sulfides or calcite. Abundant solid bitumen is also found on the surfaces of the carbonate rocks in the Sanhedong Formation as well as in the rock fractures associated with framboidal pyrite. The petrographic characteristics and maturity-related biomarker parameters show that the solid bitumen in the ores has higher thermal maturity than that in the Sanhedong Formation, suggesting that it was generated at different temperatures in the two settings. The source-related parameters suggest that the solid bitumen in the ores and Sanhedong Formation probably both originated in a mixed marine shale and carbonate environment and that the source rocks for the bitumen precursor were late Triassic marine strata. The δ34S values, ranging from –30 to –10‰ for the fine-grained and disseminated sulfide minerals and from –24.50 to –16.27‰ for the solid bitumen in the early (main) mineralization stage, suggest that H2S was generated by microbial sulfate reduction. We propose that this occurred in the Triassic strata prior to or during migration of hydrocarbons to the Jinding dome to form a H2S-enriched paleo-oil reservoir. This hypothesis is supported by the similarity of the δ34S values (–27.62 to –17.38‰) of solid bitumen in the Sanhedong Formation (the source rocks) to that of bitumen in the ores. The late-ore sulfide, however, displays significantly higher δ34S values, ranging from –8 to 0‰. We propose that the H2S of this stage was mainly generated by thermochemical sulfate reduction as a result of the interaction between hydrocarbons, sulfate, and hydrothermal fluid. The hydrocarbons were oxidized into bitumen that has δ34S values from –7.38 to –4.61‰.

scholarly journals The influences of sedimentary environments on organic matter enrichment in fine-grained rocks of the Paleogene Shahejie formation in Nanpu Sag, Huanghua Depression, Bohai Bay Basin

2021 ◽  
pp. 014459872110310
Author(s):  
Min Li ◽  
Xiongqi Pang ◽  
Guoyong Liu ◽  
Di Chen ◽  
Lingjian Meng ◽  
...  
Keyword(s):  
Organic Matter ◽  
Source Rocks ◽  
Bohai Bay ◽  
Bohai Bay Basin ◽  
Humid Climate ◽  
High Productivity ◽  
Fine Grained ◽  
Huanghua Depression ◽  
Shahejie Formation ◽  
Nanpu Sag

The fine-grained rocks in the Paleogene Shahejie Formation in Nanpu Sag, Huanghua Depression, Bohai Bay Basin, are extremely important source rocks. These Paleogene rocks are mainly subdivided into organic-rich black shale and gray mudstone. The average total organic carbon contents of the shale and mudstone are 11.5 wt.% and 8.4 wt.%, respectively. The average hydrocarbon (HC)-generating potentials (which is equal to the sum of free hydrocarbons (S1) and potential hydrocarbons (S2)) of the shale and mudstone are 39.3 mg HC/g rock and 28.5 mg HC/g rock, respectively, with mean vitrinite reflectance values of 0.82% and 0.81%, respectively. The higher abundance of organic matter in the shale than in the mudstone is due mainly to paleoenvironmental differences. The chemical index of alteration values and Na/Al ratios reveal a warm and humid climate during shale deposition and a cold and dry climate during mudstone deposition. The biologically derived Ba and Ba/Al ratios indicate high productivity in both the shale and mudstone, with relatively low productivity in the shale. The shale formed in fresh to brackish water, whereas the mudstone was deposited in fresh water, with the former having a higher salinity. Compared with the shale, the mudstone underwent higher detrital input, exhibiting higher Si/Al and Ti/Al ratios. Shale deposition was more dysoxic than mudstone deposition. The organic matter enrichment of the shale sediments was controlled mainly by reducing conditions followed by moderate-to-high productivity, which was promoted by a warm and humid climate and salinity stratification. The organic matter enrichment of the mudstone was less than that of the shale and was controlled by relatively oxic conditions.

Facies, rock attributes, stratigraphy, and depositional environments: Yanchang Formation, Central Ordos Basin, China

2017 ◽  
Vol 5 (2) ◽  
pp. SF15-SF29 ◽  
Author(s):  
Stephen C. Ruppel ◽  
Harry Rowe ◽  
Kitty Milliken ◽  
Chao Gao ◽  
Yongping Wan
Keyword(s):  
Organic Matter ◽  
Clay Mineral ◽  
Ordos Basin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Late Triassic ◽  
Great Promise ◽  
Yanchang Formation ◽  
X Ray ◽  
Stacking Patterns

The Late Triassic Yanchang Formation (Fm) is a major target of drilling for hydrocarbons in the Ordos Basin. Although most of the early focus on this thick succession of lacustrine rocks has been the dominant deltaic sandstones and siltstones, which act as local reservoirs of oil and gas, more recent consideration has been given to the organic-rich mudstone source rocks. We used modern chemostratigraphic analysis to define vertical facies successions in two closely spaced cores through the Chang 7 Member, the primary source rock for the Yanchang hydrocarbon system. We used integrated high-resolution X-ray fluorescence and X-ray diffraction measurements to define four dominant facies. Variations in stable carbon isotopes mimic facies stacking patterns, suggesting that terrigenous organic matter (although minor in volume) is associated with the arkoses and sandstones, whereas aquatic organic matter is dominant in the mudstones. Facies stacking patterns define three major depositional cycles and parts of two others, each defined by basal mudstone facies that document basin flooding and deepening (i.e., flooding surfaces). Unconfined compressive strength measurements correlate with clay mineral abundance and organic matter. Comparisons of core attributes with wireline logs indicate that although general variations in clay mineral volumes (i.e., mudstone abundance) can be discerned from gamma-ray logs, organic-matter distribution is best defined with density or resistivity logs. These findings, especially those established between the core and log data, provide a powerful linkage between larger scale facies patterns and smaller scale studies of key reservoir attributes, such as pore systems, mineralogy, diagenesis, rock mechanics, hydrocarbon saturation, porosity and permeability, and flow parameters. This first application of modern chemostratigraphic techniques to the Yanchang Fm reveals the great promise of applying these methods to better understand the complex facies patterns that define this lacustrine basin and the variations in key reservoir properties that each facies displays.

scholarly journals Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

Geology ◽  
2020 ◽  
Author(s):  
Tatsuo Nozaki ◽  
Toshiro Nagase ◽  
Takayuki Ushikubo ◽  
Kenji Shimizu ◽  
Jun-ichiro Ishibashi ◽  
...  
Keyword(s):  
Sulfate Reduction ◽  
Secondary Ion Mass Spectrometry ◽  
Okinawa Trough ◽  
Sulfide Minerals ◽  
Sulfide Mineralization ◽  
Ambient Seawater ◽  
Microbial Sulfate Reduction ◽  
Framboidal Pyrite ◽  
Initial Stage ◽  
Iheya North Knoll

Seafloor hydrothermal deposits form when hydrothermal fluid mixes with ambient seawater, and constituent sulfide minerals are usually interpreted to precipitate abiogenically. Recent research drilling at Izena Hole and Iheya North Knoll in the middle Okinawa Trough (East China Sea), combined with secondary ion mass spectrometry determinations of δ34S in pyrite grains, provides compelling evidence that the initial stage of subseafloor sulfide mineralization is closely associated with microbial sulfate reduction. During the sulfide maturation process, pyrite textures progress from framboidal to colloform to euhedral. Pyrite δ34S has highly negative values (as low as –38.9‰) in framboidal pyrite, which systematically increase toward positive values in colloform and euhedral pyrite. Sulfur isotope fractionation between seawater sulfate (+21.2‰) and framboidal pyrite (–38.9‰) is as great as –60‰, which can be attained only by microbial sulfate reduction in an open system. Because framboidal pyrite is commonly replaced by chalcopyrite, galena, and sphalerite, framboidal pyrite appears to function as the starting material (nucleus) of other sulfide minerals. We conclude that framboidal pyrite, containing microbially reduced sulfur, plays an important role at the initial stage of subseafloor sulfide mineralization.

scholarly journals Hydrocarbon Potential of the Late Permian and the Late Triassic Source Rocks from the Qamdo (Changdu) Basin, Eastern Tibet and Its Linkage with the Sea Level Change

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhaolin Qi ◽  
Yalin Li ◽  
Chengshan Wang
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Upper Triassic ◽  
Source Rocks ◽  
Late Triassic ◽  
Upper Permian ◽  
Late Permian ◽  
Petroleum Potential ◽  
Eastern Tibet ◽  
Rock Eval

The Qamdo Basin in eastern Tibet has significant petroleum potential and previous studies indicate that the basin contains thick potential source rocks of the Late Permian and the Late Triassic ages. In this paper, the petroleum potential of samples from measured the Upper Permian and Upper Triassic outcrop sections was evaluated on the basis of sedimentological, organic petrographic and geochemical analyses. Initial evaluations of total organic carbon contents indicated that shale samples from the Upper Permian Tuoba Formation and the Upper Triassic Adula and Duogala Formations have major source rock potential, while carbonate rocks from the Upper Triassic Bolila Formation are comparatively lean in organic matter More detailed analyses of OM-rich shale samples from the Tuoba, Adula and Duogala Formations included Rock-eval, elemental analyses, gas chromatography and organic petrography. Maceral compositions and plots of atomic O/C versus H/C indicate that the organic matter present in the samples is primarily Type II with a mixed source. Analyses of acyclic isoprenoid biomarkers indicate the organic matter was deposited under reducing and sub-to anoxic conditions. Based on the high vitrinite reflectance (Ro>1.3%) and Rock-eval data, the samples are classified as highly to over-mature, suggesting that the Tuoba, Adula and Duogaila Formation shales may generate thermogenic gas. Source rock intervals in the three formations are interpreted to have been deposited in marginal-marine environment during transgressions and under a warm and moist climatic condition.

scholarly journals Elemental Geochemical Evidence for Depositional Conditions and Organic Matter Enrichment of Black Rock Series Strata in an Inter-Platform Basin: The Lower Carboniferous Datang Formation, Southern Guizhou, Southwest China

Minerals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 509 ◽  
Author(s):  
Jianghui Ding ◽  
Jinchuan Zhang ◽  
Xuan Tang ◽  
Zhipeng Huo ◽  
Shuangbiao Han ◽  
...  
Keyword(s):  
Organic Matter ◽  
Southwest China ◽  
Tectonic Setting ◽  
Sedimentary Environment ◽  
Active Continental Margin ◽  
Source Rocks ◽  
Guizhou Province ◽  
Dominant Factor ◽  
Rock Series ◽  
Black Rock Series

The Datang Formation black rock series deposited in an inter-platform basin are considered to be one of the main source rocks in Southwest China. However, their depositional conditions and organic matter enrichment in such a setting are not well understood. In this study, geochemical characteristics of total organic carbon (TOC), major, trace and rare earth elements (REEs) of thirty black rock series samples from a newly-cut roadside outcrop (Zhenning section) in Southern Guizhou, Southwest China are systematically investigated to examine provenance, paleoredox conditions, paleoclimate, paleoproductivity and sedimentary rate, and further to explore their influence on organic matter enrichment. Results show that TOC contents of the investigated samples range from 0.90% to 2.83%, with an average of 1.45%, with TOC variations being in accord with the stratigraphic cyclicity. These data also indicate that the target black rock series were deposited in a combination of continental island arc and active continental margin tectonic setting that exhibited moderate weathering, oxic/dysoxic oxygen levels, hot and arid to semiarid climate, and a higher sedimentary rate. Multiple paleoredox indicators (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni) ratios), together with slightly negative Ce anomalies and EFU-EFMo covariation, totally suggest an oxic/dysoxic water environment, which is usually considered unfavorable for organic matter preservation. Average (La/Yb)N ratios (1.41) reflect a higher sedimentary rate, resulting in shortening the exposure time of organic matter in the degradation region of aerobic bacteria under oxic/dysoxic conditions. Of the three factors that could affect organic matter enrichment, including paleoproductivity, paleoredox conditions and sedimentary rate, the relatively high paleoproductivity indicated by the relatively high TOC contents appears to be the dominant factor. In contrast, the other two factors, i.e., paleoredox conditions and the rate of sedimentation play relatively less significant roles. Based on these factors, an enrichment model of organic matter for the black rock series in Southern Guizhou Depression is established. These findings also contribute to constraining the sedimentary environment in such a setting and further deepen our understanding of the potential shale gas resources of the Southern Guizhou Province.

scholarly journals Effective source rock selection and oil–source correlation in the Western Slope of the northern Songliao Basin, China

2021 ◽  
Vol 18 (2) ◽  
pp. 398-415
Author(s):  
He Bi ◽  
Peng Li ◽  
Yun Jiang ◽  
Jing-Jing Fan ◽  
Xiao-Yue Chen
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Thermal Evolution ◽  
Songliao Basin ◽  
Source Rocks ◽  
Crude Oils ◽  
Western Slope ◽  
Geochemical Parameters ◽  
Group I ◽  
Oil Source

AbstractThis study considers the Upper Cretaceous Qingshankou Formation, Yaojia Formation, and the first member of the Nenjiang Formation in the Western Slope of the northern Songliao Basin. Dark mudstone with high abundances of organic matter of Gulong and Qijia sags are considered to be significant source rocks in the study area. To evaluate their development characteristics, differences and effectiveness, geochemical parameters are analyzed. One-dimensional basin modeling and hydrocarbon evolution are also applied to discuss the effectiveness of source rocks. Through the biomarker characteristics, the source–source, oil–oil, and oil–source correlations are assessed and the sources of crude oils in different rock units are determined. Based on the results, Gulong and Qijia source rocks have different organic matter primarily detrived from mixed sources and plankton, respectively. Gulong source rock has higher thermal evolution degree than Qijia source rock. The biomarker parameters of the source rocks are compared with 31 crude oil samples. The studied crude oils can be divided into two groups. The oil–source correlations show that group I oils from Qing II–III, Yao I, and Yao II–III members were probably derived from Gulong source rock and that only group II oils from Nen I member were derived from Qijia source rock.

scholarly journals Low Temperature Illitization through Illite-Dioctahedral Vermiculite Mixed Layers in a Tropical Saline Lake Rich in Hydrothermal Fluids (Sochagota Lake, Colombia)

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 523
Author(s):  
Gabriel Ricardo Cifuentes ◽  
Juan Jiménez-Millán ◽  
Claudia Patricia Quevedo ◽  
Fernando Nieto ◽  
Javier Cuadros ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Organic Matter ◽  
Low Temperature ◽  
High Salinity ◽  
Source Rocks ◽  
Temperate Climate ◽  
Lake Basin ◽  
X Ray ◽  
Saline Waters ◽  
Mixed Layers

In this investigation, we showed that high salinity promoted by hydrothermal inputs, reducing conditions of sediments with high content in organic matter, and the occurrence of an appropriate clay mineral precursor provide a suitable framework for low-temperature illitization processes. We studied the sedimentary illitization process that occurs in carbonaceous sediments from a lake with saline waters (Sochagota Lake, Colombia) located at a tropical latitude. Water isotopic composition suggests that high salinity was produced by hydrothermal contribution. Materials accumulated in the Sochagota Lake’s southern entrance are organic matter-poor sediments that contain detrital kaolinite and quartz. On the other hand, materials formed at the central segment and near the lake exit (north portion) are enriched in organic matter and characterized by the crystallization of Fe-sulfides. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray spectrometry (EDX) data allowed for the identification of illite and illite-dioctahedral vermiculite mixed layers (I-DV), which are absent in the southern sediments. High humidity and temperate climate caused the formation of small-sized metastable intermediates of I-DV particles by the weathering of the source rocks in the Sochagota Lake Basin. These particles were deposited in the low-energy lake environments (middle and north part). The interaction of these sediments enriched in organic matter with the saline waters of the lake enriched in hydrothermal K caused a reducing environment that favored Fe mobilization processes and its incorporation to I-DV mixed layers that acted as mineral precursor for fast low temperature illitization, revealing that in geothermal areas clays in lakes favor a hydrothermal K uptake.

Geochemistry of cobalt, nickel, chromium, and vanadium in the sediments of the estuary and open Gulf of St. Lawrence

1979 ◽  
Vol 16 (6) ◽  
pp. 1196-1209 ◽  
Author(s):  
D. H. Loring
Keyword(s):  
Mineral Deposit ◽  
Source Rocks ◽  
Anthropogenic Sources ◽  
Terrestrial Organic Matter ◽  
Lawrence Estuary ◽  
Fine Grained ◽  
Hydrous Oxides ◽  
High Concentrations ◽  
St Lawrence Estuary ◽  
Local Anomalies

Total Co (3–22 ppm), Ni (4–160 ppm), V (4–168 ppm), and Cr (8–241 ppm) concentrations vary regionally and with textural differences in the sediments of the St. Lawrence estuary and Gulf of St. Lawrence. They are, except for local anomalies, at or near natural levels relative to their source rocks and other marine sediments.Chemical partition and mineralogical analyses indicate that small but biochemically significant quantities (2–24%) of the total element concentrations are potentially available to the biota and are most likely held by fine-grained organic material, hydrous iron oxides, and ion exchange positions in the sediments. In the upper estuary, nondetrital Ni, Cr, and V supplied from natural and anthropogenic (Cr) sources are apparently preferentially scavenged from solution by terrestrial organic matter and hydrous oxides and concentrated in fine-grained sediments deposited below the turbidity maximum. In the lower estuary, the fine-grained sediments are relatively enriched in nondetrital V supplied from anthropogenic sources in the Saguenay system. Elsewhere the sedimentation intensities of the nondetrital elemental contributions have remained relatively constant with fluctuations in total sediment intensity.Seventy-six to 98% of the total Co, Ni, Cr, and V is not, however, available to the biota, but held in various sulphide, oxide, and silicate minerals. The host minerals have accumulated at the same rate as other fine-grained detrital material except for some local anomalies. In the upper estuary, detrital V concentrations are highest in the sands as an apparent result of an enrichment of ilmenite and titaniferous magnetite from a nearby mineral deposit. In the open gulf, relatively high concentrations of Ni, Cr, and V occur in sediments from the Bay of Islands, Newfoundland, and probably result from the seaward dispersal of detrital Ni, Cr, and V bearing minerals from nearby ultrabasic rocks.

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