PRELIMINARY PETROGRAPHIC STUDY OF COARSE-GRAINED PALEOCENE SANDSTONES OF THE SOUTHERN TRANSVERSE AND NORTHERN PENINSULAR RANGES, CALIFORNIA

1996 ◽  
Author(s):  
Pedro C. Ramirez
Keyword(s):  
Coarse Grained ◽  
Peninsular Ranges ◽  
Petrographic Study

Significance of diagenesis for the origin of Witwatersrand-type uraniferous conglomerates

1979 ◽  
Vol 291 (1381) ◽  
pp. 277-287 ◽  
Keyword(s):  
South Africa ◽  
Organic Matter ◽  
Coarse Grained ◽  
Uranium Deposits ◽  
Multi Stage ◽  
Ore Minerals ◽  
History Of ◽  
Diverse Origin ◽  
Reducing Bacteria ◽  
Petrographic Study

A petrographic study of pyrite may be the key to the understanding of the Witwatersrand (South Africa) gold-uranium deposits: the sediments of the Witwatersrand Supergroup contain at least nine types of pyrite, namely (1) Laminated pyrite seams; (2) pyrite nodules in shales; (3) pyrite nodules in quartzite and conglomerate; (4) pyrite as overgrowths on carbonaceous filaments; (5) pyrite filling pore spaces and replacing clasts; (6) pyrite replacing detrital magnetite; (7) allogenic fragments of laminated pyrite; (8) allogenic fragments of pyrite nodules; and (9) allogenic fragments of coarse-grained pyrite. Types 1-6 probably formed during diagenesis of the sediment due to the activity of sulphate-reducing bacteria; types 7 and 8 are transported fragments of diagentic pyrite; type 9 may be of diverse origin, but may also in part be transported fragments of diagenetic pyrite. Pyrite petrography suggests a multi-stage history of ore enrichment: diagenetic precipitation of gold, uraninite and pyrite in sediments containing organic matter, followed by erosion, transport of allogenic fragments of ore minerals for short distances, and concentration in lag gravels at channel bottoms and unconformities. Repeated cycles of weathering, diagenetic precipitation from weathering solutions, erosion, minor transport and redeposition may have caused the extraordinary enrichment of the ores on major unconformities in the Upper Witwatersrand Supergroup.

scholarly journals MICROFACIES ANALYSIS OF LATE JURASSIC SAMANA SUK FORMATION, HAZARA BASIN LESSER HIMALAYA NORTH PAKISTAN

2020 ◽  
Vol 4 (2) ◽  
pp. 102-107
Author(s):  
Yasin Rahim ◽  
Qiugen Li ◽  
Umar Farooq Jadoon ◽  
Wasiq Lutfi ◽  
Junaid Khan ◽  
...  
Keyword(s):  
Late Jurassic ◽  
Coarse Grained ◽  
Microfacies Analysis ◽  
Lesser Himalaya ◽  
Calcite Veins ◽  
North Pakistan ◽  
Petrographic Study

The detailed petrological investigation of Samana Suk Formation from Hazara Basin, Pakistan was carried out to elaborate its microfacies. The Samana Suk Formation is mostly composed of fine to coarse-grained, limestone with dolomite in parts developed as a secondary diagenetic fabric. Twenty-five samples were studied from Thandiani Section, and five microfacies with seven sub microfacies were identified. The identified microfacies include Peloidal Foraminiferal Mudstone, Ooidal Peloidal Mudstone, Bioclastic Planktonic Mudstone as Submicrofacies, Peloidal Wackstone, Ooidal Wackstone, Intraclastic Wackstone as Sub Microfacies, Peloidal-Packstone Microfacies, Ooidal Mud-Wack Microfacies and Peloidal-Ooidal Wack-Pack Submicrofacies. Diagenetic features, such as Stylolites, Calcite Veins, Fractures, Dolomitization, Cementation, Compaction and Micritization have been observed in the petrographic study of the samples. The environment of deposition as depicted from the microfacies is Outer ramp for Mudstone, Peloidal Foraminiferal Mudstone, Ooidal to Peloidal Mudstone and Bioclastic Mudstone; Middle ramp for Peloidal Wackstone; Inner ramp for Ooidal Wackstone, Intraclastic Wackstone Peloidal Packstone and Peloidal-Ooidal Wack-Packstone; Inner-Middle ramp for Ooidal-Mud-Wackstone. Based on the microfacies analysis the Samana Suk Formation was interpreted to be deposited in a shallow shelf environment.

scholarly journals Mineralogical and geochemical characteristics of graphite-bearing rocks at Chenjere Area, south-eastern Tanzania: Implications for the nature and quality of graphite mineralization

2021 ◽  
Vol 47 (2) ◽  
pp. 535-551
Author(s):  
Charles D Moye ◽  
Michael M Msabi
Keyword(s):  
Industrial Applications ◽  
Geological Mapping ◽  
Geochemical Characteristics ◽  
Coarse Grained ◽  
Field Observations ◽  
Conducting Surface ◽  
Advanced Technologies ◽  
Size Grade ◽  
Petrographic Study

This study focused on the mineralogical and geochemical characteristics of graphite-bearing rocks at Chenjere area by conducting surface geological mapping, geochemical and petrographical analyses with the intention of characterizing the nature of graphite occurrence in these lithological units. This paper presents results of the flake size, grade and mineralization extension of graphite in the graphitic gneiss. Field observations, petrographic investigation and comparison with other studies indicate that graphite occurrence at the Chenjere area is of sedimentary origin which fall under syngenetic type. The petrographic study revealed that nature of metamorphism of rocks in the Chenjere area is of high grade (amphibolite facies). Both field observations and petrographic studies indicate that minerals in the rock associated with graphite include quartz, feldspar (mostly K-feldspar) and biotite. Further, the mineralized zones are concordant to the rest of the lithologies of the area and biotite gneiss is forming the hangingwall and footwall. The rocks’ foliation is generally NE striking and dipping SE with the dip amount ranging from 30 to 60 degrees. The graphite mineralization at the study area occurs as medium to coarse grained crystalline, flake type graphite with long axis of up to 1000 micrometres in size. Graphite flakes are disseminated and oriented in the host rock that represents a normal metamorphic fabric. Geochemical results indicate that graphite contents in the host graphitic gneiss range from 3.03 wt.% to 16.00 wt.%. Mineralogy and texture of the graphite at Chenjere area meet the standards required for industrial applications in various advanced technologies. Keywords: Graphite Mineralization, Flake Graphite, Chenjere Area

The Alteration of the Pore Spaces in Sandstones

1973 ◽  
Vol 31 ◽  
pp. 210-211
Author(s):  
R. E. Ferrell ◽  
G. G. Paulson
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
The Other ◽  
Coarse Grained ◽  
Depositional Fabric ◽  
Soluble Components ◽  
Scanning Electron ◽  
Shape And Size

The pore spaces in sandstones are the result of the original depositional fabric and the degree of post-depositional alteration that the rock has experienced. The largest pore volumes are present in coarse-grained, well-sorted materials with high sphericity. The chief mechanisms which alter the shape and size of the pores are precipitation of cementing agents and the dissolution of soluble components. Each process may operate alone or in combination with the other, or there may be several generations of cementation and solution.The scanning electron microscope has ‘been used in this study to reveal the morphology of the pore spaces in a variety of moderate porosity, orthoquartzites.

On the Origin of the Microscystalline Structure in Rapidly Solidified IN-100 Powder

1977 ◽  
Vol 35 ◽  
pp. 260-261
Author(s):  
J. M. Walsh ◽  
K. P. Gumz ◽  
J. C. Whittles ◽  
B. H. Kear
Keyword(s):  
The Other ◽  
Coarse Grained ◽  
Microcrystalline Structure ◽  
Routine Examination ◽  
Atomization Process ◽  
Centrifugal Atomization ◽  
Splat Quenching ◽  
Powder Particles ◽  
Dendritic Microstructures ◽  
Rapidly Solidified

During a routine examination of the microstructure of rapidly solidified IN-100 powder, produced by a newly-developed centrifugal atomization process1, essentially two distinct types of microstructure were identified. When a high melt superheat is maintained during atomization, the powder particles are predominantly coarse-grained, equiaxed or columnar, with distinctly dendritic microstructures, Figs, la and 4a. On the other hand, when the melt superheat is reduced by increasing the heat flow to the disc of the rotary atomizer, the powder particles are predominantly microcrystalline in character, with typically one dendrite per grain, Figs, lb and 4b. In what follows, evidence is presented that strongly supports the view that the unusual microcrystalline structure has its origin in dendrite erosion occurring in a 'mushy zone' of dynamic solidification on the disc of the rotary atomizer.The critical observations were made on atomized material that had undergone 'splat-quenching' on previously solidified, chilled substrate particles.

Correlation between dislocation, grain boundary and interface of duplex SS in stress corrosion cracking(SCC)

1990 ◽  
Vol 48 (4) ◽  
pp. 928-929
Author(s):  
Wang Zheng-fang ◽  
Z.F. Wang
Keyword(s):  
Stainless Steel ◽  
Thermal Cycle ◽  
Secondary Phase ◽  
Corrosion Cracking ◽  
Coarse Grained ◽  
Test Environment ◽  
Fine Grained ◽  
Evaluation Test ◽  
Welding Thermal Cycle ◽  
Micro Analysis

The main purpose of this study highlights on the evaluation of chloride SCC resistance of the material,duplex stainless steel,OOCr18Ni5Mo3Si2 (18-5Mo) and its welded coarse grained zone(CGZ).18-5Mo is a dual phases (A+F) stainless steel with yield strength:512N/mm2 .The proportion of secondary Phase(A phase) accounts for 30-35% of the total with fine grained and homogeneously distributed A and F phases(Fig.1).After being welded by a specific welding thermal cycle to the material,i.e. Tmax=1350°C and t8/5=20s,microstructure may change from fine grained morphology to coarse grained morphology and from homogeneously distributed of A phase to a concentration of A phase(Fig.2).Meanwhile,the proportion of A phase reduced from 35% to 5-10°o.For this reason it is known as welded coarse grained zone(CGZ).In association with difference of microstructure between base metal and welded CGZ,so chloride SCC resistance also differ from each other.Test procedures:Constant load tensile test(CLTT) were performed for recording Esce-t curve by which corrosion cracking growth can be described, tf,fractured time,can also be recorded by the test which is taken as a electrochemical behavior and mechanical property for SCC resistance evaluation. Test environment:143°C boiling 42%MgCl2 solution is used.Besides, micro analysis were conducted with light microscopy(LM),SEM,TEM,and Auger energy spectrum(AES) so as to reveal the correlation between the data generated by the CLTT results and micro analysis.

Input of coarse-grained siliciclastics into the Pyrenean Basin during the PETM (1): overview

2014 ◽  
Vol 31 ◽  
pp. 177-178
Author(s):  
Victoriano Pujalte ◽  
Juan Ignacio Baceta ◽  
Birger Schmitz
Keyword(s):  
Coarse Grained
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