Palygorskite-bearing fracture fills in the Kinshasa area, DR Congo – an exceptional mode of palygorskite vein development

2019 ◽  
Vol 122 (2) ◽  
pp. 173-186
Author(s):  
F. Mees ◽  
R. Adriaens ◽  
A. Delgado-Huertas ◽  
D. Delvaux ◽  
P. Lahogue ◽  
...  
Keyword(s):  
Hydrothermal Activity ◽  
Upper Jurassic ◽  
Dr Congo ◽  
Quartz Content ◽  
Clay Particles ◽  
Fine Grained ◽  
Calcite Veins ◽  
Vein Type ◽  
Authigenic Mineral ◽  
Temperature Interaction

Abstract Tectonic fractures in Palaeozoic strata of the Kinshasa area, DR Congo, locally host palygorskite-bearing veins and associated calcite occurrences. The palygorskite deposits are typically massive, with a varying degree of alignment of clay particles, a higher quartz content than the arkose substrate, and a variable amount of smectite (montmorillonite). The associated calcite occurrences are macrocrystalline coatings and infillings, and more fine-grained calcite veins with cataclastic texture. The calcite coatings and infillings formed from solution in earth surface conditions, as recorded by their stable isotope signature. The palygorskite-dominated deposits in the fractures formed at a later stage, in a setting without indications of authigenic mineral formation related to hydrothermal activity or to low-temperature interaction of solutions with the local substrate. The veins most likely formed by vertical infiltration of suspended matter in fractures that extended to a post-Palaeozoic palaeosurface, during or after deposition of palygorskite-bearing Upper Jurassic to Early Cretaceous sediments. This represents an exceptional mode of palygorskite vein development, unrelated to any form of mineral authigenesis that is typically invoked to explain vein-type occurrences of palygorskite and related minerals.

scholarly journals Magmatic-Hydrothermal Processes of Vein-Type Haman-Gunbuk-Daejang Copper Deposits in the Gyeongnam Metallogenic Belt in South Korea

2021 ◽  
Vol 9 ◽  
Author(s):  
Tong Ha Lee ◽  
Jung Hun Seo ◽  
Bong Chul Yoo ◽  
Bum Han Lee ◽  
Seung Hee Han ◽  
...  
Keyword(s):  
Fluid Inclusions ◽  
Hydrothermal Activity ◽  
Hydrothermal Conditions ◽  
Copper Deposits ◽  
Quartz Veins ◽  
Calcite Veins ◽  
Vein Type ◽  
Ore Minerals ◽  
Ore Mineralization ◽  
Shale Formation

Haman, Gunbuk, and Daejang deposits are neighboring vein-type hydrothermal Cu deposits located in the SE part of the Korean Peninsula. These three deposits are formed by magmatic-hydrothermal activity associated with a series of Cretaceous granodioritic intrusions of the Jindong Granitoids, which have created a series of veins and alterations in a hornfelsed shale formation. The copper deposits have common veining and alteration features: 1) a pervasive chlorite-epidote alteration, cut by 2) Cu-Pb-Zn-bearing quartz veins with a tourmaline-biotite alteration, and 3) the latest barren calcite veins. Chalcopyrite, pyrite, and pyrrhotite are common ore minerals in the three deposits. Whereas magnetite is a dominant mineral in the Haman and Gunbuk deposits, no magnetite is present, but sphalerite and galena are abundant in the Daejang deposit. Ore-bearing quartz veins have three types of fluid inclusions: 1) liquid-rich, 2) vapor-rich, and 3) brine inclusions. Hydrothermal temperatures obtained from the brine inclusion assemblages are about 340–600, 250–500, and 320–460°C in the Haman, Gunbuk, and Daejang deposits, respectively. The maximum temperatures (from 460 to 600°C) recorded in the fluid inclusions of the three deposits are higher than those of the Cu ore precipitating temperature of typical porphyry-like deposits (from 300 to 400°C). Raman spectroscopy of vapor inclusions showed the presence of CO2 and CH4 in the three deposits, which indicates relatively reduced hydrothermal conditions as compared with typical porphyry deposits. The Rb/Sr ratios and Cs concentrations of brine inclusions suggest that the Daejang deposit was formed by a later and more fractionated magma than the Haman and Gunbuk deposits, and the Daejang deposit has lower Fe/Mn ratios in brine inclusions than the Haman and Gunbuk deposits, which indicates contrasting redox conditions in hydrothermal fluids possibly caused by an interaction with a hosting shale formation. In brines, concentrations of base metals do not change significantly with temperature, which suggests that significant ore mineralization precipitation is unlikely below current exposure levels, especially at the Haman deposit. Ore and alteration mineral petrography and fluid inclusions suggest that the Haman deposit was formed near the top of the deep intrusion center, whereas the Gunbuk deposit was formed at a shallower intrusion periphery. The Daejang deposit was formed later at a shallow depth by relatively fractionated magma.

The Giant Chalukou Porphyry Mo Deposit, Northeast China: The Product of a Short-Lived, High Flux Mineralizing Event

2021 ◽  
Author(s):  
Qingqing Zhao ◽  
Degao Zhai ◽  
Ryan Mathur ◽  
Jiajun Liu ◽  
David Selby ◽  
...  
Keyword(s):  
High Precision ◽  
Inductively Coupled Plasma ◽  
Hydrothermal Activity ◽  
Ore Deposits ◽  
Ionization Mass ◽  
Inductively Coupled ◽  
Fine Grained ◽  
Porphyry Cu ◽  
Icp Ms ◽  
Porphyry Mo Deposit

Abstract Whether giant porphyry ore deposits are the products of single, short-lived magmatic-hydrothermal events or multiple events over a prolonged interval is a topic of considerable debate. Previous studies, however, have all been devoted to porphyry Cu and Cu-Mo deposits. In this paper, we report high-precision isotope dilution-negative-thermal ionization mass spectrometric (ID-N-TIMS) molybdenite Re-Os ages for the newly discovered, world-class Chalukou porphyry Mo deposit (reserves of 2.46 Mt @ 0.087 wt % Mo) in NE China. Samples were selected based on a careful evaluation of the relative timing of the different vein types (i.e., A, B, and D veins), thereby ensuring that the suite of samples analyzed could be used to reliably determine the age and duration of mineralization. The molybdenite Re-Os geochronology reveals that hydrothermal activity at Chalukou involved two magmatic-hydrothermal events spanning an interval of 6.92 ± 0.16 m.y. The first event (153.96 ± 0.08/0.63/0.79 Ma, molybdenite ID-N-TIMS Re-Os age) was associated with the emplacement of a granite porphyry dated at 152.1 ± 2.2 Ma (zircon laser ablation-inductively coupled plasma-microscopic [LA-ICP-MS] U-Pb ages), and led to only minor Mo mineralization, accounting for <10% of the overall Mo budget. The bulk of the Mo (>90%) was deposited in less than 650 kyr, between 147.67 ± 0.10/0.60/0.76 and 147.04 ± 0.12/0.72/0.86 Ma (molybdenite ID-N-TIMS Re-Os ages), coincident with the emplacement of a fine-grained porphyry at 148.1 ± 2.6 Ma (zircon LA-ICP-MS U-Pb ages). The high-precision Re-Os age determinations presented here show, contrary to the finding of a number of studies of porphyry Cu and Cu-Mo systems, that the giant Chalukou porphyry Mo deposit primarily formed in a single, short-lived (<650 kyr) hydrothermal event, suggesting that this may also have been the case for other giant porphyry Mo deposits.

scholarly journals Microstructural Investigations on Plasticity of Lime-Treated Soils

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 386
Author(s):  
Enza Vitale ◽  
Dimitri Deneele ◽  
Giacomo Russo
Keyword(s):  
Liquid Limit ◽  
Small Scale ◽  
Plastic Behavior ◽  
Short Term ◽  
Clay Particles ◽  
Fine Grained ◽  
Surface Charge Distribution ◽  
Plastic Changes ◽  
Interparticle Repulsion

The surface charge distribution of clay particles governs the interparticle forces and their arrangement in clay-water systems. The plasticity properties are the consequences of the interaction at the microscopic scale, even if they are traditionally linked to the mechanical properties of fine-grained soils. In the paper, the plasticity modifications induced by the addition of lime were experimentally investigated for two different clays (namely kaolinite and bentonite) in order to gain microstructural insights of the mechanisms affecting their plastic behavior as a function of the lime content and curing time. Zeta potential and dynamic light scattering measurements, as well as thermogravimetric analyses, highlighted the mechanisms responsible for the plastic changes at a small scale. The increase of the interparticle attraction forces due to the addition of lime increased the liquid and plastic limits of kaolinite in the short term, without significant changes in the long term due to the low reactivity of the clay in terms of pozzolanic reactions. The addition of lime to bentonite resulted in a decrease of interparticle repulsion double layer interactions. Rearrangement of the clay particles determined a reduction of the liquid limit and an increase of the plastic limit of the treated clays in the very short term. Precipitation of the bonding compounds due to pozzolanic reactions increased both the liquid and plastic limits over the time.

Petrology of the Gillis Mountain pluton, Cape Breton Island, Nova Scotia

1981 ◽  
Vol 18 (2) ◽  
pp. 395-404 ◽  
Author(s):  
S. M. Barr ◽  
A. M. O'Beirne
Keyword(s):  
Hydrothermal Activity ◽  
Parent Magma ◽  
Metallic Elements ◽  
Cape Breton Island ◽  
Porphyritic Granite ◽  
Fine Grained ◽  
Cape Breton ◽  
Mineralization Processes ◽  
Devonian Age ◽  
Bulk Chemistry

The Gillis Mountain pluton is a small composite granitoid intrusion in southeastern Cape Breton Island. It is one of the few plutons of known Devonian age in Cape Breton Island and is particularly significant because of the presence of Cu–Mo mineralization with porphyry affinities. The pluton consists of three main phases (quartz monzodiorite, porphyritic granite, and fine-grained granite) with minor late dykes of granite, granitic porphyry, and aplite. These phases probably represent a differentiation sequence from an 'I-type' parent magma of calc-alkalic affinity. All phases have been affected by phyllic and possibly potassic alteration, presumably related to the mineralization processes. However, this hydrothermal activity appears to be little reflected in the bulk chemistry of the pluton, except possibly in increased barium content and large standard deviations in the metallic elements and sulphur.

Stratiform sulfide and barite–fluorite mineralization of the Vulcan prospect, Northwest Territories: exhalation of basinal brines along a faulted continental margin

1984 ◽  
Vol 21 (1) ◽  
pp. 78-91 ◽  
Author(s):  
David A. Mako ◽  
Wayne C. Shanks III
Keyword(s):  
Northwest Territories ◽  
Hydrothermal Vents ◽  
Thickness Distribution ◽  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
High Potassium ◽  
The Road ◽  
Fine Grained ◽  
Bottom Waters ◽  
Brine Pools

Laminated and massive sulfide (pyrite, sphalerite, galena) mineralization and massive barite – fluorite–galena lenses occur in Upper Silurian – Lower Devonian Road River Formation shales of the Vulcan property along the eastern flank of the Selwyn Basin, Northwest Territories, Canada. The 5 km thick stratigraphic section, ranging in age from Hadrynian through Mississippian, offers insight into the nature of the Mackenzie Platform – Selwyn Basin transition. Abrupt facies changes, synsedimentary faults, debris flows, local unconformities, and the presence of high-potassium mafic flows indicate extensional tectonics during deposition of the Road River Formation. Mineralization resulted from heated, metal-rich basinal brines that vented on the sea floor up normal faults.Sulfur-isotope studies indicate that both sulfate and sulfide were derived from the exhaling metalliferous brine. Sulfur-isotope data also suggest that reduction of sulfate in the brine occurred as a result of organic decomposition, possibly during thermal maturation of hydrocarbons at temperatures greater than 80 °C. Fluid inclusion observations indicate that the brine salinity reached 26 wt.% NaCl for at least a portion of the evolution of the hydrothermal system.Cooling of the brine during venting into bottom waters caused initial rapid precipitation of fine-grained barite, resulting in a baritic buildup above vent areas. Continued percolation of the brine through the baritic mound caused recrystallization of the barite and then the deposition of interstitial fluorite and galena. In other areas the dense ore fluid collected in topographic depressions, or brine pools, in which sulfide minerals accumulated under anoxic conditions. Location of hydrothermal vents, paleotopography, and intensity of hydrothermal activity were the main controls on the thickness, distribution, and grade of Vulcan mineralization.

A review of the geochronology of the Precambrian of Saskatchewan—some clues to uranium mineralization

1981 ◽  
Vol 44 (336) ◽  
pp. 371-378 ◽  
Author(s):  
Keith Bell
Keyword(s):  
Hydrothermal Activity ◽  
Uranium Mineralization ◽  
Dyke Swarm ◽  
Thermal Activity ◽  
Late Proterozoic ◽  
Vein Type ◽  
Close Relationship ◽  
Basic Magmatism ◽  
Granitoid Rocks ◽  
Depositional Age

AbstractAssessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.

Rare metals on shatter cone surfaces from the Steinheim Basin (SW Germany) – remnants of the impacting body?

2017 ◽  
Vol 155 (6) ◽  
pp. 1205-1229 ◽  
Author(s):  
E. BUCHNER ◽  
M. SCHMIEDER
Keyword(s):  
Hydrothermal Activity ◽  
Upper Jurassic ◽  
Lower Jurassic ◽  
Iron Meteorite ◽  
Rare Metals ◽  
X Ray ◽  
Central Uplift ◽  
Post Impact ◽  
Shatter Cones ◽  
First Time

AbstractThe ~3.8 km Steinheim Basin in SW Germany is a well-preserved complex impact structure characterized by a prominent central uplift and well-developed shatter cones that occur in different shocked target lithologies. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and electron probe microanalysis have revealed, for the first time, the occurrence of rare metals on the Steinheim shatter cone surfaces. Shatter cones produced from the Middle Jurassic (Aalenian) Opalinus Claystone (‘Opalinuston’), temporarily exposed in the central uplift in spring 2010, and shatter cones in Upper Jurassic (Oxfordian) limestones from the southeastern crater rim domain are commonly covered by faint coatings. The Opalinus Claystone shatter cone surfaces carry coatings dominated by Fe, Ca, P, S and Al, and are covered by abundant small, finely dispersed microparticles and aggregates of native gold, as well as locally elevated concentrations of Pt. On several surfaces of the claystone shatter cones, additional Fe, Ni and Co was detected. The Ca–Mn-rich coatings on the limestone shatter cone surfaces locally include patches of Fe, Ni, Co, Cu and Au in variable amounts and proportions. The intriguing coatings on the Steinheim shatter cones could either stem from the impacted Lower Jurassic to Palaeogene sedimentary target rocks; from the crystalline-metamorphic Variscan crater basement; or, alternatively, these coatings might represent altered meteoritic matter from the Steinheim impactor, possibly an iron meteorite, which may have been remobilized during post-impact hydrothermal activity. We here discuss the most plausible source for the rare metals found adherent to the shatter cone surfaces.

Influences of Change of Plasma on Strength Property of Eolian Sand

2012 ◽  
Vol 170-173 ◽  
pp. 830-835
Author(s):  
Chang Ning Jin ◽  
Yu Hong Zhang
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Strength Property ◽  
Friction Angle ◽  
Clay Particles ◽  
Fine Grained ◽  
Eolian Sand ◽  
Coefficient Increase ◽  
Fine Grained Soil ◽  
Internal Friction Coefficient

The plasma in the eolian sand, included silt particle and clay particle, change easily and hugely. For studying their influences on the strength property of eolian sand, mixed silt particles and clay particles into eolian sand in different proportions to measure the internal friction angle and cohesion under different forming and testing conditions. The result indicates that: for the same kind of test specimen under different test types, the changes of cohesion and internal friction coefficient are regular. For the same test type, the changes of both cohesion and internal friction coefficient of different test specimens are regular. Generally, when the content of silt particles and clay particles is lower than a certain value, the cohesion and internal friction coefficient increase accordingly and rapidly along with the increase of silt particles and clay particles; after the content of silt particles and clay particles is larger than this value, the cohesion and internal friction coefficient increase slowly or decline along with the increase of silt particles and clay particles. The change range of this value is approximately between 45%～65%, the content of silt particles and clay particles. For the purpose of this test, as to the transition of test specimens from typical sandy soil to fine grained soil caused by the increase of silt particles and clay particles, the change point of strength is at 45％ approximately, which is basically consistent with the compacting test and CBR test, etc.

scholarly journals Lithology of the Upper Jurassic-Lower Cretaceous deposits of the eastern part of the Myrgovaam and Rauchua depressions, Western Chukotka

2020 ◽  
Vol 65 (4) ◽  
Author(s):  
Elena V. Vatrushkina ◽  
◽  
Marianna I. Tuchkova ◽  
Keyword(s):  
Lower Cretaceous ◽  
Upper Jurassic ◽  
Coarse Grained ◽  
Fine Grained ◽  
Tectonic Environment ◽  
The Matrix ◽  
Siliciclastic Rocks ◽  
Facies Variation ◽  
Felsic Volcanic ◽  
Cretaceous Deposits

Upper Jurassic-Lower Cretaceous deposits were formed on the South-Western margin of the Chukotka terrane in active tectonic environment. Their stratigraphic units characterized by sedimentary structures and lithology similarities, facies variation and scarcity of reliable fauna findings. Detailed lithological studies are necessary due to the absence of a unified approach to the stratigraphic division of deposits. The paper presents petrographic, geochemical, and isotope-geochemical characteristics of Upper Jurassic-Lower Cretaceous rocks. The stages of changing the sedimentation conditions and sources, which determined the differences in sedimentological features and the composition of the studied strata, are reconstructed. The Oxford-Kimmeridgian section is composed of sandy debris flow deposits with an arcosic composition of psammitic differences. Among their sources, ancient granitoids dominated, while siliciclastic rocks, volcanites and metamorphic complexes were secondary. Volgian-valanginian interval is characterized by the accumulation of sediments in various parts of the submarine fan. In Volgian sequences fine -, medium - and coarse-grained turbidites with lenses of small-pebble conglomerates are identified. A large number of simultaneous pyroclastic material in the Volgian deposits indicates the synchronous volcanic activity. In the Volgian period, the province was dominated by volcanites, mainly of the basaltic and andesitic composition, siliciclastic rocks were present in smaller amount. The Berriasin section is composed of fine-grained turbidites with single horizons of medium-grained turbidites and gravelitic lenses, as well as slope deposits in the form of rhythmically interbedded sandstones and mudstones with slump structures. Sandstones have greywacke composition and contain an admixture of ash material in the matrix. The main sources for Berriasian deposits were siliciclastic rocks and felsic volcanic complexes. The Valanginian section is represented by fine and medium-grained turbidites with horizons of amalgamated sandstones. Sandstones are classified as arkoses by the ratio of rock-forming components. The dominant source in the Valanginian time was ancient granitoids, while siliciclastic rocks and volcanites were secondary.

scholarly journals Jurassic dinoflagellate cyst stratigraphy of Store Koldewey, North-East Greenland

2004 ◽  
Vol 5 ◽  
pp. 99-112 ◽  
Author(s):  
Stefan Piasecki ◽  
John H. Callomon ◽  
Lars Stemmerik
Keyword(s):  
Middle Jurassic ◽  
Upper Jurassic ◽  
Dinoflagellate Cysts ◽  
The South ◽  
Important Species ◽  
East Greenland ◽  
Sequence Stratigraphic ◽  
Fine Grained ◽  
North East ◽  
The North

The Jurassic of Store Koldewey comprises a Middle Jurassic succession towards the south and an Upper Jurassic succession towards the north. Both successions onlap crystalline basement and coarse sediments dominate. Three main lithostratigraphical units are recognised: the Pelion Formation, including the Spath Plateau Member, the Payer Dal Formation and the Bernbjerg Formation. Rich marine macrofaunas include Boreal ammonites and the successions are dated as Late Bathonian – Early Callovian and Late Oxfordian – Early Kimmeridgian on the basis of new collections combined with material in earlier collections. Fine-grained horizons and units have been analysed for dinoflagellate cysts and the stratigraphy of the diverse and well-preserved flora has been integrated with the Boreal ammonite stratigraphy. The dinoflagellate floras correlate with contemporaneous floras from Milne Land, Jameson Land and Hold with Hope farther to the south in East Greenland, and with Peary Land in North Greenland and Svalbard towards the north. The Middle Jurassic flora shows local variations in East Greenland whereas the Upper Jurassic flora gradually changes northwards in East Greenland. A Boreal flora occurs in Peary Land and Svalbard. The characteristic and stratigraphically important species Perisseiasphaeridium pannosum and Oligosphaeridium patulum have their northernmost occurrence on Store Koldewey, whereas Taeniophora iunctispina and Adnatosphaeridium sp. extend as far north as Peary Land. Assemblages of dinoflagellate cysts are used to characterise significant regional flooding events and extensive sequence stratigraphic units.

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