Black Carbonaceous Shale Research Articles

Thermal and chemical variations of the Nigerian Benue trough lead-zinc-barite-fluorite deposits

The Benue trough is an intra-continental rift initiated in the Cretaceous during the opening of the South Atlantic Ocean. Lead-zinc-barite-fluorite mineralization occurs along the 600 km axis of the trough in three discrete sub-basins which coincide with the lower, middle and upper mineral districts of the Benue Valley. Lithologically these sub-basins are dominated by black carbonaceous shale in the Lower Benue, platform carbonates in the Middle Benue and sandstones in the Upper Benue. Micro-thermometric analysis of fluid inclusions in sphalerite, fluorite, barite and quartz have shown that each mineral district has its own unique thermal and chemical imprint. For example, the temperature can be bracketed between 109 °C and 160 °C for lower Benue, 89 °C–144 °C for the Middle Benue and 176 °C–254 °C for the Upper Benue. Chemical differentiation also exists between each mineral district with the Lower Benue having 22 wt % equivalent NaCl while the Middle and Upper Benue have 18 and 16 wt % equivalent NaCl respectively. This study shows that inter-district thermal and chemical variations exist between the ore-stage sulfide and post-sulfide gangue minerals of the entire Benue Valley. Similarly, intra-district thermal and chemical variations have also been observed among all the paragenetic minerals of each district.The thermal variations may be as a result of variations in the geothermal gradient accompanying continental rifting from one district to the other. The variations in the chemistry between the Lower Benue and the Upper Benue paragenic minerals may be as a result of the distinct lithological differences across the Benue Trough.

Palaeoenvironmental interpretation of an Upper Triassic deposit in southwestern Gondwana (Argentina) based on an insect fauna, plant assemblage, and their interactions

We present a multidisciplinary study of the Potrerillos Formation at the Quebrada del Durazno locality, Cuyana Basin, central-western Argentina, providing novel information on the Upper Triassic biota and its palaeoenvironmental context. The sedimentological and palaeoecological analysis suggests that the Potrerillos Formation section at the Quebrada del Durazno locality represents deltaic plain deposits with significant development of black carbonaceous shales and coal facies formed in semi-permanent swamps and/or ponds within interdistributary bays with intermittent episodes of flooding, allowing the establishment of an abundant hydro-hygrophytic vegetation and creating environments suitable for the development of a rich fauna of insects, spinicaudatans (=‘conchostracans’) and fishes. The entomofauna is represented by hemipterans, odonatans, mecopterans, orthopterans, grylloblattids, coleopterans, dipterans and miomopterans. The plant fossils are typical of the Dicroidium Flora (represented by Corystospermales, Peltaspermales, Cycadales, Gnetales, Ginkgoales and sphenophytes). Plant-insect interactions (hole, marginal and surface feeding, piercing and sucking, and oviposition) are described for the first time from the Triassic of the Cuyana Basin, pointing to the importance of the vegetation as a food and shelter, and also providing a suitable reproduction site for several groups of herbivorous insects.

On the Genesis of the Lower Benue Valley Lead-Zinc Deposits, Southeastern Nigeria: Inferences from Carbon, Oxygen and Hydrogen Stable Isotopes Studies

The Benue Trough is a metallogenic province consisting of numerous occurrences of lead-zinc, barite-fluorite deposits distributed in three principal districts at the upper, middle and lower Benue Valley in Nigeria. Ore stage Pb and Zn sulfide and post-sulfide silicate and carbonate minerals are hosted by black carbonaceous shales in the lower Benue where the sediments locally attain a thickness of about 2000 m. Carbon, oxygen and hydrogen isotopic measurements have been carried out on the carbonates (C, O) while the δD isotopic composition of sphalerites and quartz are also determined with a view to determine the origin of the lower Benue lead- zinc mineralization. The δ 13C isotopic composition of the carbonates range from -2.0 to -5.2 per mil, and a mean of -2.8 per mil. And the δD values in post-sulfide quartz ranges from -35 to -40 per mil, with an average of -37.5 per mil which implicates derivation from the oxidation of organic matter in the black carbonaceous shale while water in the inclusions are basically meteoric in origin with possible minor sea water input.

Onset, development, and cessation of basal Early Triassic microbialites (BETM) in the Nanpanjiang pull-apart Basin, South China Block

New investigations in the Nanpanjiang Basin indicate that the onset of the iconic microbialites associated with the Paleozoic-Mesozoic boundary was Early Triassic in age. Bathymetry (water agitation, oxygenation, light penetration) and clastic load are shown to have exerted a direct control on the growth of microbialites. Carbonate supersaturation is also required for the deposition of the microbialites. Bathymetric control is further corroborated by the inheritance of the topography of a latest Permian pull-apart basin into Early Triassic times, with a distribution of basal Early Triassic microbialites (BETM) restricted to uplifted blocks and the accumulation of carbonaceous black shales in adjacent troughs. The geographically most extensive Nanpanjiang BETM bloomed on a large NW–SE trending uplifted block exceeding 12,000km2 (Luolou Platform) centered on northwestern Guangxi. Post-Triassic displacements along the Youjiang Fault obscure the paleogeographic relation of BETM exposed west of this fault.Triassic foraminifers occur in the basal most BETM episode, which is locally bracketed by high-energy grainstones made of reworked Permian foraminifers. Therefore, the Permian-Triassic boundary (PTB) is within the unconformity that separates the Late Permian Heshan Fm. from the basal most BETM. Where accommodation space was sufficient, up to five event surfaces are associated with the unconformity. Microfacies analysis supports chemical dissolution but did not reveal evidence for subaerial erosion, although intercalated grainstone made of Permian foraminifers indicate reworking. Chemical dissolution and mechanical erosion both conceivably contributed to the genesis of the unconformity. The upward shift from tabulated to domical microbial build-ups is accompanied by accumulation of coquinoid lenses between domes, which indicates deepening of the Luolou Platform BETM. The main drowning resulting from both regional tectonic subsidence and a global sea-level rise led to the cessation of the BETM that were buried under predominant fine siliciclastics. Any concomitant change in sea water chemistry appears unlikely.

Comparative geochemistry of quaternary carbonaceous sediments from the continental slope of the Baja California and the miocene monterey formation

The geochemistry of Upper Quaternary organic-rich (Corg 3.7–10.0%) sediments recovered by the 40-m-long Core MD02-2508 from the upper continental slope of Baja California is compared to the chemical composition of sedimentary rocks from the Miocene Monterey Formation, California. It is ascertained that concentrations of most macroelements (Al, Ti, Mg, K, Fe, M, S, Corg) and many microelements, including chalcophiles Ag, As, Mo, Sb, Se, Zn, along with some others (U, Co, Ni, Y, and REE) are nearly equal in both types of sediments. In addition, concentrations of most microelements in both types of sediments are close, to the average values common for the worldwide carbonaceous black shales irrespective of their lithology and age, indicating a stable influence of organic matter on their concentration during sedimentation and early digenesis.

Critical geological characteristics and gas-bearing controlling factors in Longmaxi shales in southeastern Chongqing, China

The southeastern Chongqing area, one of the highest potential shale gas accumulation areas in China, experienced strong tectonic movements. Due to the tectonic uplift in Himalayan period, the target shale formation is characterized by shallow burial depth and abundant fractures. The Lower Silurian Longmaxi shale was deposited under deep and shallow continental shelf environments with abundant pyrites and graptolite fossils. The lithology of the formation includes black carbonaceous shale, calcareous shale, and siliceous shale. The thickness of the shale varies greatly from 40 to 200 m from southeast to northwest with obvious zonation. Total organic carbon (TOC) content ranges from 1.0 to 4.0% and decreases upward in the formation owing to the change of sedimentary facies. The organic matter reaches dry gas zone. Porosity ranges from 0.5 to 7.9%, and the permeability is measured in the microdarcy to nanodarcy range. Abundant fragile minerals exist in the shales which benefit the hydraulic stimulation. Isothermal adsorption tests show that the sorption gas content in place of the Longmaxi shale ranges from 1.0 to 4.5 m3/t and the gas content in place reaches the standard of commercial exploitation. Factors impacting gas-bearing characteristics were analyzed using a mathematical statistic method, which demonstrates that TOC is the most important factor, especially to the sorption gas content. Meanwhile, clay content, thermal maturity, porosity, and mineral components are also significant factors regarding shale gas-bearing characteristics.

ORGANIC GEOCHEMICAL CHARACTERIZATION AND SHALE GAS POTENTIAL OF THE PERMIAN BARREN MEASURES FORMATION, WEST BOKARO SUB‐BASIN, EASTERN INDIA

This study investigates the shale gas characteristics of the Permian Barren Measures Formation (Gondwana Supergroup) in the West Bokaro sub‐basin of the Damodar Valley Basin, eastern India. A total of 23 core shale samples collected from a borehole located in the western part of the sub‐basin were analysed using organic geochemical techniques and scanning electron microscopy. The samples are black carbonaceous shales composed chiefly of quartz, mica and clay minerals.Rock‐Eval pyrolysis data show that the analysed samples contain a mixture of Type II and Type III kerogen with TOC values of 2.7 to 6.2%. Rock‐Eval Tmax values ranging from 443 to 452 °C correspond to calculated vitrinite reflectance of approximately 0.8–0.9%. A cross‐plot of hydrogen index versus Tmax indicates that the samples have reached peak oil to wet gas maturities. A pristane/n‐C17 versus phytane/n‐C18 cross‐plot, together with biomarker parameters such as the dominance of C29 over C27 and C28 steranes and high moretane/hopane ratios (0.22–0.51), demonstrate that the shale samples contain terrigenous organic matter deposited in a suboxic environment.Scanning electron microscopy images of shale samples show the presence of a complex, mostly intergranular pore network. Both micropores (>0.75μm) and nanopores (<0.75μm) were observed. Some pores are elongated and are associated with layer‐spaces in sheet silicate minerals; others are non‐elongated and irregular in shape. The organic geochemical parameters and the observed pore attributes suggest that the Barren Measures Formation has good shale gas potential.

Characteristics and origin of the heterogeneity of the Lower Silurian Longmaxi marine shale in southeastern Chongqing, SW China

The Lower Silurian Longmaxi marine shale from the productive shale gas block of southeastern Chongqing, Southern China, is one of the most important marine shale gas exploration formations in southern China; geologists have recently made significant shale gas discoveries there. However, the marine shale in southern China is noticeably heterogeneous, leading to difficulties in predicting potential productive zones in the shale formation. To better determine the “sweet spots” in the black shale formation, we carefully examined the heterogeneity of the Lower Silurian Longmaxi marine shale, which is controlled by sedimentary setting, and analyzed the macro- and micro-heterogeneity based on detailed core descriptions, optical microscopy, field emission scanning electron microscopy (FE-SEM), geostatistical analysis of well logging data, geochemical testing data and reservoir property testing data. According to our research, four sedimentary subfacies were recognized and have distinct heterogeneity features within and among them in terms of thickness, mineral composition, organic matter content, pore type and pore structure. The deep water shelf subfacies (DWS) of black carbonaceous and siliceous shale that was formed in anoxic, still water has a stable sedimentary thickness and mineral composition with an total organic carbon (TOC) content generally greater than 2 wt.%; furthermore, the DWS subfacies mainly has organic and intragranular pores, showing the least heterogeneity due to the highest pore throat homogeneity coefficient. The shallow water shelf subfacies (SWS) of gray-black siliceous and argillaceous shale was deposited in shallow water with relatively intense hydrodynamics and has a relatively stable sedimentary thickness and the lowest pore structure coefficient; however, it also comprises various shales and organic matter contents and mainly has intergranular pores showing a moderate heterogeneity that is relatively greater than the DWS subfacies heterogeneity. The tidal flat subfacies (TF) comprises gray calcareous shale with argillaceous siltstone that was greatly influenced by terrigenous sediment input. This facies mostly has a noticeably variable sedimentary thickness and mineral composition with a TOC that is generally less than 1 wt.% and well-developed microfractures, indicating high heterogeneity caused by a low homogeneity coefficient and a poor sorting coefficient of the pore throats. The lagoon subfacies (L) consists of black carbonaceous and siliceous shale formed in anoxic water between the sea and the land and has a relatively stable shale thickness and mineral composition but poor lateral and pore throat connectivity. This subfacies mainly has microfractures and intergranular pores, indicating extremely high heterogeneity. The paleotomography differences in the sedimentary environment determine the sedimentary thickness of the shale, the mineral composition, the organic matter content and other factors; these factors contribute to the macroscopic heterogeneity. Diagenesis controls the pore structure and pore type by compaction, cementation, and dissolution, combined with the generation of hydrocarbons and other phenomena. This process determines the microscopic heterogeneity.

Synsedimentary to Early Diagenetic Gold in Black Shale-Hosted Pyrite Nodules at the Golden Mile Deposit, Kalgoorlie, Western Australia

Synsedimentary to Early Diagenetic Gold in Black Shale-Hosted Pyrite Nodules at the Golden Mile Deposit, Kalgoorlie, Western Australia

Experimental and Theoretical Modeling of Expansion in Pyritic Shale

Abstract Expansive pyritic shales are found in black carbonaceous shales throughout the United States as well as in other countries, including Ireland, England, Norway, Canada, and Sweden. Expansion occurs when the pyrite, which occurs either as finely disseminated syngenetic framboids, macroscopic crystals, or diagenetic replacement fossils, oxidizes to form sulfuric acid. Various hydrous sulfates could precipitate in the complex geochemical environment; however, gypsum typically precipitates as the sulfuric acid reacts with the calcareous (calcium carbonate) component of the shale. This paper explores kinetic and passive attempts at measuring the expansion of the shale and introduces a hybrid experimental testing procedure that uses hydrogen peroxide to initiate the expansion process. The normalized expansion (h/H) for the non-intact shale and intact shale core were 0.0008 and 0.0033, respectively, after 84 days. Expansion rates of 3.5 mm/year/m and 1.43 mm/year/m were calculated for the non-intact shale and intact shale core samples, respectively. A theoretical expansion model is developed that uses stoichiometric calculations to determine gypsum volume and discontinuity infilling theory to determine maximum total expansion. Input variables include shale type (intact bedrock, poorly-graded fragments, well-graded fragments), % pyritic shale (%S2), height of the expansion zone, and surcharge pressure. The theoretical model is used to predict maximum height of expansion and time to maximum expansion for the experiments studied and developed.

Neoproterozoic Age Based on Microbiotas from the Raipur Group of Baradwar Sub-basin, Chhattisgarh

Abstract: An assemblage of structurally preserved organic-walled microfossils (OWMs) from the macerated residue of black carbonaceous shale belonging to Saradih Formation, the youngest carbonate horizon of the Raipur Group, Chhattisgarh Supergroup exposed at on the right bank of Mahanadi River, NE of Sarangarh township in Raigarh district, Chhattisgarh is being reported for the first time. The assemblage is comprised of 19 taxa of 13 genera belong to eukaryotes and prokaryotes viz. Leiosphaeridia, Stictosphaeridium, Dictyotidium, Synsphaeridium, Symplassosphaeridium, Satka, Trachysphaeridium, Goniosphaeridium, Trachyhystrichosphaera, Vandalosphaeridium, Siphonophycus, Oscillatoriopsis and Polythrichoides. The comprehensive account of recovered microbiotic assemblage can be correlated with globally known Neoproterozoic (early Cryogenian) assemblages, deposited in tidal complexes of shallow sea.

Prospect Analysis of Shale Gas Resource Exploration in the Lower Silurian Longmaxi Formation, Southeastern Margin of the Sichuan Basin, China

In order to understand the sedimentary characteristics of shale and prospects of shale gas exploration in the lower Silurian Longmaxi Formation northern of Guizhou Province, outcrop and core observations, thin sections, X-ray diffraction analysis and other means are used. Studies show that the thickness of Longmaxi formation shale is generally large, range from 20m to 200m, mainly develop in the water shelf. The mineral mainly compose of detrital quartz and clay minerals, and five lithofacies can be identified: black shale, silty shale, carbonaceous shale, calcareous shale and argillaceous siltstone. Longmaxi shale kerogen type is mainlyIand II, and Ro value is average of 1.87%, mainly in the mature - over mature stage. In addition, the TOC content and gas content of Longmaxi shale is high, what’s more, these two parameters have good positive correlation. Compared with the Barnett shale, both of them have some similarities in the development environment shale, shale thickness and type of organic matter and TOC content, while, Longmaxi shale is deeply buried and post-destruction more intense. Longmaxi shale sedimentary environment is stable, high shale thickness and stable distribution, good quality source rocks and high brittle mineral content, which has meet the basic parameters of shale gas exploration and development, and has a large shale gas exploration potential in study area.

Middle–Late Devonian radiolarians from Klaeng District, Rayong Province, southeastern Thailand: Geotectonic significance of the Rayong area as a continental margin of the Sibumasu Block

A fine clastics–siliceous succession exposed at Laem Krabang Phet, approximately 20km southwest of Klaeng, Rayong area, southeastern Thailand was examined based on lithology, radiolarian biostratigraphy, and geological correlation. In the study section, thinly bedded chert layers are intercalated with black carbonaceous shale, light-colored tuffaceous shale, brown glassy tuff, and quartz-rich sandstone layers. A horizon of the chert in the section yielded poorly preserved radiolarians, however, several forms including Palaeoscenidium cladophorum Deflandre, Stigmosphaerostylus cf. pusilla (Hinde), and Entactiniidae gen. et spp. indet. were identified. This fauna is probably referable to the Middle–Late Devonian. The study section had been assigned to various stratigraphic units, such as Silurian–Devonian or Carboniferous–Permian, due to a poor fossil occurrence. However, the occurrence of the Devonian radiolarians in this study provides concrete evidence for the sedimentary age of the succession, and supports assignment to the Silurian–Devonian. Although the study succession exposed at Laem Krabang Phet is coeval with the Devonian part of the Fang chert, northern Thailand, the lithological assemblage is dissimilar, and the post-Devonian radiolarian chert is absent. These lithological, chronological, and stratigraphic results indicate that the depositional environment of the study section was close to the continental margin, such as a continental slope or rise.

Late Paleoproterozoic to Mesoproterozoic rift successions in SW China: Implication for the Yangtze Block–North Australia–Northwest Laurentia connection in the Columbia supercontinent

The late Paleoproterozoic to Mesoproterozoic Dongchuan Group in the southwestern Yangtze Block formed in a series of fault-controlled, rift-related basins associated with the fragmentation of the Columbia supercontinent. The Dongchuan Group is composed, from the base upward, of the Yinmin, Luoxue, Etouchang and Luzhijiang formations. The Yinmin Formation has a basal layer of conglomerate and coarse sandstone, up to 2m thick, marking initiation of rifting. It is a laterally discontinuous layer, indicative of lateral variations in the accommodation space created adjacent to juvenile normal faults in the earliest stages of rifting. Fluvial to intertidal facies sedimentary rocks of the Yinmin Formation are characterized by fining-upward patterns from sandstone to interbedded carbonate and mudstone, representing syn-rifting sedimentation. Enlargement of the basin and establishment of a carbonate platform during sedimentation of the Luoxue Formation suggest that faulting and volcanism were significantly reduced, marking a transition from syn-rifting subsidence to post-rifting subsidence. Black carbonaceous shale of the Etouchang Formation likely formed in a continental slope and deep ocean basin, generated by slow thermal subsidence of heated subcrustal materials during the post-rifting stage. Subsequent shoaling led to re-establishment of a rimmed carbonate shelf, in which massive argillaceous dolostone of the Luzhijiang Formation started to accumulate. Two major igneous events marked the ca. 1710-Ma rifting climax and 1685–1660-Ma waning phase of rifting. The rift sequence in the southwestern Yangtze Block correlates with the late Paleoproterozoic to early Mesoproterozoic sequence in the Mount Isa Basin, North Australia. These successions have identical zircon age patterns and similar igneous and sedimentary assemblages. In addition, the rifting-related 1735–1663Ma Hornby Bay and ~1640–1600Ma Wernecke successions in northwestern Laurentia show similarities with those synchronous successions in the Yangtze Block and North Australia. This correlation suggests that the Yangtze Block was likely connected to northern Australia and northwestern Laurentia during the assembly of Columbia supercontinent but drifted away from these continents before ca. 1590Ma and showed tectonic evolution different from them after that.

H–O, S and Pb isotope geochemistry of the Awanda gold deposit in southern Tianshan, Central Asian orogenic belt: Implications for fluid regime and metallogeny

The Awanda gold deposit is located within the southern Tianshan Accretionary Complex, a late Paleozoic orogenic belt in the northern margin of Tarim block in NW China. The gold mineralization here occurs in primarily within shear zones and secondary s faults with quartz mica schist as the principal host rock. The sulfide mineral assemblage is dominated by arsenopyrite, and pyrrhotite, with minor pyrite and gudmundite. Alteration includes silicification, sericitization and rare carbonatization. The measured δ18O values for the gold-bearing quartz range from 15.9 to 20.3‰, and the estimated δ18O fluid values range from 7.8 to 12.2‰. The δD values for fluid inclusions from quartz range from −116.3 to −87.6‰. The δ34S values of gold-associated sulfide minerals range from −3.6 to +6.2‰, and the calculated δ34SH2S values of H2S for the hydrothermal fluids range from −4.8 to +5.8‰, with an average of −0.4‰. Lead isotopic compositions of sulfides from gold-bearing ores show 206Pb/204Pb ratios ranging from 17.4625 to 18.5356, 207Pb/204Pb ratios from 15.4943 to 15.6468, and 208Pb/204Pb ratios from 37.8825 to 38.8238, respectively. Collectively, the isotope (H, O, S, Pb) characteristics suggest that the ore-forming fluids were of metamorphic origin derived through dehydration of carbonaceous black shale with the sulfur sourced from crustal components, and the lead from a mixture of host rocks and ore-forming metamorphic fluids. This deposit can be classified as orogenic gold deposit and share many major characteristics with those of Muruntau-type gold deposits. During late Paleozoic, the southern Tianshan Accretionary Complex was intensely deformed into an orogenic belt by folding and thrusting, generating regional thrust faults at different scales. The ore-controlling subsidiary faults also formed subsequently, with the ore-forming fluids derived from dehydration of deeply buried carbonaceous black shale and the ore fluids channeled into shear zones leading to gold precipitation.

Preservation of Mesoproterozoic age deep burial fluid signatures, NW Scotland

Bedding-parallel fibrous calcite is a widely developed feature of mudrock successions, reflecting conditions of fluid overpressure (Stoneley, 1983; Parnell et al., 2000; Cobbold et al., 2013). The calcite preserves signatures of fluids developed during deep burial, including hydrocarbons. Most studied examples are of Phanerozoic (<540 Ma) age. This study reports well-preserved fibrous calcite in the Mesoproterozoic (∼1180 Ma) Stoer Group, NW Scotland. The fibrous calcite occurs immediately above a unit of carbonaceous black shale. If hydrocarbons were generated from the black shales, they could have contributed to the development of fluid overpressure, but there is no direct evidence for this. The calcite reflects the original deep burial fluid, rather than a later overprint, because (i) it has a distribution related to stratigraphy, (ii) the bedding-parallel fibres have not been recrystallized, and (iii) later veining is at high angles to bedding. The calcite contains fluid inclusions, and has yielded stable isotope and entrained volatile data, indicating the potential to record diagenetic processes over one billion years ago.

CARBONATE RETICULATED RIDGE STRUCTURES FROM THE LOWER MIDDLE TRIASSIC OF THE LUOPING AREA, YUNNAN, SOUTHWESTERN CHINA: GEOBIOLOGIC FEATURES AND IMPLICATIONS FOR EXCEPTIONAL PRESERVATION OF THE LUOPING BIOTA

Exceptionally preserved carbonate reticulated ridge structures are documented from the lower Middle Triassic Guanling Formation of the Luoping area, eastern Yunnan Province, southwestern China. Macrostructures suggest these reticulated ridge structures are morphologically similar to the growth-related structures in ancient and modern microbial mats. Other such features as minute load structures and pyrite crystals beneath the reticulated layers on bedding surfaces are overlain by a black carbonaceous shale layer. Clay minerals in the reticulated layers are oriented parallel to bedding at the top, and they usually form wavy laminae. These characteristics indicate that these carbonate reticulated ridge structures share a similar microstructure to their siliciclastic analogs, and are also comparable with that of wrinkle structures. SEM imaging shows that many tiny objects—coccoid spheres, rod-like structures and filamentous fibrils—are distinct within those ultra-thin, wavy laminae, suggesting similar accretion and growth models to modern microbial mats. Accordingly, the Luoping reticulated ridge structures are of biogenic origin. These microbial mats are associated with the early Middle Triassic Luoping Biota and they are thought to have played a crucial role in the preservation of the fossils through sealing and microbial coats. An SEM-EDS analysis on fossil fragments and their surrounding matrix reveals that microbial mats also played an important role in the phosphatization of Luoping fossils.

Geological and geochemical characteristics in the paleo-weathering crust sedimentary type REE deposits, western Guizhou, China

A supergene REE deposit closely interrelated with the weathering of the Emeishan basalt formation was produced in the Xuanwei formation, the overlying stratum of the late Permian Emeishan basalt formation in West Guizhou, China. The host strata consist primarily of offwhite kaolinite clay rock and/or grayish black carbonaceous shale. Mineralogical analyses reveal that kaolinites are the major minerals in REE ores with small amounts of smectite, illite, boehmite, hornblende, pyrophyllite, calcite, dolomite and/or iron-bearing minerals, with a certain proportion of feldspar, quartz crystal debris and noncrystal debris. Geochemical analyses reveal high enrichment of trace elements like Cu, Nb, Ta, Zr and Hf. The host strata feature considerable lithological variability, close interrelation of the REE grade with the lithology and uneven spatial distribution of the REE ores, which are mostly found in Lufang, Maojiaping and Zhangsigou profiles of Weining County and can be as thick as 20m. Of the five stratigraphic profiles, 48% have their whole-rock ∑REE higher than 1000ppm. The REE in this framework consists primarily of ion adsorbed phases and REE-rich residual independent mineral phases. Comprehensive analyses suggest that the source may not only include the Emeishan basalt, but the intermediate acid volcanic rocks evolved from the Emeishan basalt in the later periods; the hydrothermal alteration subsequently imposed on the host strata might have boosted the mineralization of the rare earth. The preliminary genetic model should have been: the denudation product from the weathering of the parent rock was migrated to the sea-continental margin at the continent side carrying huge quantities of REE with it and was preserved by the quick marine transgression. The host strata consist primarily of kaolinite clay rock and/or carbonaceous shale, which are so far believed to be a sedimentary type REE deposit closely interrelated with weathering effect.

Age, origin and significance of nodular sulfides in 2680 Ma carbonaceous black shale of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia

Sulfide nodules composed of pyrite occur within black shales in the Lucky Bay area of the Bulong Domain, Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia that correlate with the Neoarchean Black Flag Group. Detailed petrography reveals a variety of shapes and textures, from spherical to ovoid and zoned to uniform. Some nodules have recrystallized, resulting in a later generation of pyrite. All have been affected by post-depositional metamorphism, as evidenced by pressure shadows containing quartz±mica±carbonate assemblages. LA-ICP-MS analyses show that these nodules are enriched in a range of trace elements, including Co, Ni, Cu, Ag, Sb, Te, Au, Tl, Pb, and Bi. Gold and Te concentrations range from 0.3 to 1ppm and 10 to 50ppm, respectively. The Black Flag Group equivalents stratigraphically and structurally underlie a younger basin east of Lucky Bay that contains turbidites, sandy debris flows and BIF, the latter of which hosts several gold deposits at Randalls, 60km SE of Kalgoorlie. It is likely that the lateral equivalents of the nodular sulfide-bearing black shale originally occurred stratigraphically beneath what is now the ore horizon at Randalls. Given its anomalous Au and Te content, this lithology is a potential contributor of gold to the BIF-hosted gold deposits of the Randalls Goldfield, as well as other similar gold resources elsewhere in the Eastern Goldfields Superterrane.

Early Devonian graptolites and tentaculitids in northwest Peninsular Malaysia and a revision of the Devonian–Carboniferous stratigraphy of the region

Meor Hakif Amir Hassan, Erdtmann, B.D., Wang X.-F. & Lee C.P., Early Devonian graptolites and tentaculitids in northwest Peninsular Malaysia and a revision of the Devonian–Carboniferous stratigraphy of the region. Alcheringa 37, 1–16. ISSN 0311-5518. Early Devonian tentaculitids are described from new outcrops in northwestern Peninsular Malaysia. The fossils occur in black carbonaceous shales of the Timah Tasoh Formation exposed in the state of Perlis. The occurrences of the graptolite Monograptus langgunensis and the tentaculitid Nowakia (Turkestanella) acuaria acuaria give an Early Devonian (Pragian or Emsian) age for the black shales. The tentaculitid subspecies Nowakia (Turkestanella) acuaria posterior is reported for the first time from Peninsular Malaysia.