Drag folds in sedimentary rocks hosting kimberlites, West Yakutia

2021 ◽  
pp. 82-91
Author(s):  
Petr Ignatov ◽  
Nail Zaripov ◽  
Konstantin Novikov ◽  
Alexander Tolstov
Keyword(s):  
Shear Zone ◽  
Carbonate Rocks ◽  
Sedimentary Rocks ◽  
Lower Paleozoic ◽  
Local Extension ◽  
Kimberlite Body ◽  
Local Site ◽  
Body Drag

Drag folds were revealed in Lower Paleozoic sedimentary strata of Mirny, Nakyn and Syuldyukar diamondiferous fields, West Yakutia. They consist of minor anticlinal forms (3-5 to 15-20 cm thick) and cut marl, clayey limestone and dolomite bands located between monolith seams of carbonate rocks. Some folds as monocline, flexures and S- or Z-shaped folds reflect the degree of shearrelated interlayer offset. Drag folds are among shear zone occurrences including microfaults, slickensides with slip groove horizontal planes, and schistosity zones. Drag folds reflect local extension points while schistosity zones indicate compression points. For Syuldyukar field, detailed mapping results for drag folds and schistosity zones are provided at 3 scales: across 20 × 20 m observation grid within a local 2 km2 site; across 200 × 200 m grid within 20 km2 area; across 500 × 500 m grid within ~100 km2 territory. For all scales, drag fold halos are restricted to schistosity zones. Within a local site adjacent to kimberlites, drag folds mark ore-hosting fault controlling long axes of kimberlite areal projections. Within large areas, drag fold halos are 1,2-2 km, which compares with kimberlite group areal parameters. Drag fold halos reflect shear junctions, with some of them hosting kimberlites. Local occurrences of drag folds mark a major shear hosting a kimberlite body. Drag fold analysis combined with other evidence should be used as an indirect prospecting indicator of concealed shears and local extension areas controlling kimberlites.

Structural geology of the Lardeau Group near Trout Lake, British Columbia: implications for the structural evolution of the Kootenay Arc

1992 ◽  
Vol 29 (6) ◽  
pp. 1305-1319 ◽  
Author(s):  
Moira T. Smith ◽  
George E. Gehrels
Keyword(s):  
British Columbia ◽  
Shear Zone ◽  
Structural Evolution ◽  
Strike Slip ◽  
Ductile Deformation ◽  
Lower Paleozoic ◽  
Trout Lake ◽  
Facies Metamorphism ◽  
Dextral Strike Slip ◽  
Greenschist Facies Metamorphism

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic eugeoclinal strata present in the Kootenay Arc in southeastern British Columbia. It is in fault contact with lower Paleozoic miogeoclinal strata for all or some of its length along a structure termed the Lardeau shear zone. The Lardeau Group was deformed prior to mid-Mississippian time, as manifested by layer-parallel faults, folds, and evidence for early greenschist-facies metamorphism. Regional constraints indicate probable Devono-Mississippian timing of orogeny, and possible juxtaposition of the Lardeau Group over miogeoclinal strata along the Lardeau shear zone at this time. Further ductile deformation during the Middle Jurassic Columbian orogeny produced large folds with subhorizontal axes, northwest-striking foliation and faults, and orogen-parallel stretching lineations. This deformation was apparently not everywhere synchronous, and may have continued through Late Jurassic time northeast of Trout Lake. This was followed by Cretaceous(?) dextral strike-slip and normal movement on the Lardeau shear zone and other parallel faults. While apparently the locus of several episodes of faulting, the Lardeau shear zone does not record the accretion of far-travelled tectonic fragments, as sedimentological evidence ties the Lardeau Group and other outboard units to the craton.

scholarly journals Exhumation of the Ailao Shan shear zone recorded by Cenozoic sedimentary rocks, Yunnan Province, China

Tectonics ◽  
2005 ◽  
Vol 24 (6) ◽  
pp. n/a-n/a ◽  
Author(s):  
Lindsay M. Schoenbohm ◽  
B. Clark Burchfiel ◽  
Chen Liangzhong ◽  
Yin Jiyun
Keyword(s):  
Shear Zone ◽  
Yunnan Province ◽  
Sedimentary Rocks

scholarly journals Мetasomatic rocks after shungite-bearing rocks of the Maksovo Deposit, Onega Structure, Karelia

2019 ◽  
pp. 149-164
Author(s):  
L. V. Kuleshevich ◽  
М. М. Filippov ◽  
N. А. Goltsin ◽  
R. Sh. Krymsky ◽  
K. I. Lokhov
Keyword(s):  
Chemical Composition ◽  
Carbonate Rocks ◽  
Sedimentary Rocks ◽  
Northwestern Part ◽  
K Concentration ◽  
Qualitative Characteristics

The Maksovo metasapropelite deposit, which contains shungite matter and is called maksovite, is located in the eastern Onega structure. The deposit is a diapiric fold which formed ca. 2070±10 Ma ago. It is underlain by carbonate rocks and overlain by tuff siltstones and is cross-cut by 1956±5 Ma gabbro-dolerites. Unaltered maksovites are pelitomorphic rocks with a massive to mildly layered texture and moderate concentrations of all petrogenic components and Сorg of about 30%. Fe-Mg rich and alkaline metasomatic rocks evolve after maksovites and mafic and carbonate tuff siltstones in the northwestern part of the deposit within a multiple ridge-like fold after brecciation zones. They differ from unaltered sedimentary rocks in heterogeneous (brecciated, streaky) textures, mineral and chemical composition and are saturated with numerous sulphide, carbonate, quartz and albite veinlets. They are identified by intense biotitization, chloritization and the presence of calcite, microcline metacrystals, albite-carbonate metacrystals with apatite and carbonate-quartz metacrystals with sulphides and rutile, veinlets and disseminated mineralization. Na concentration rises to 5.67% and K concentration to 7.57%. P and Ti concentrations, accompanying alkaline metasomatism, as well as Mg-Fe and ore-bearing components (often incompatible), increase locally. Metasomatic rocks evolve heterogeneously and are represented by breccia zones. Their slightly elevated radioactivity disturbs the qualitative characteristics of primary maksovite as a useful mineral. Maksovites were dated at 1558±61 Ma by the Re-Os method from sulphides.

scholarly journals SPECIFIC FEATURES OF CLAY MINERALS IN ANCIENT CRUSTS OF WEATHERING OF VARIOUS ROCKS IN DIAMONDIFEROUS REGIONS

2019 ◽  
pp. 13-20
Author(s):  
N. N. Zinchuk
Keyword(s):  
Carbonate Rocks ◽  
Weathering Crust ◽  
Ordered Structure ◽  
Mixed Composition ◽  
Lower Paleozoic ◽  
Material Development ◽  
Structural Types ◽  
Bivalent Cations ◽  
Layered Formation ◽  
Weathering Crusts

Results of complex research of different age ancient weathering crusts in various rocks (terrigenous-carbonate rocks of Lower Paleozoic, dolerites, tuffs and tufogene formations, kimberlites) within the main diamondiferous regions of the Siberian platform indicated that complicated multicomponent composition of initial formations (with the exception of terrigenous-carbonate rocks), containing di- and trioctahedral minerals, the structure of which has tri- and bivalent rock-forming elements, stipulated decelerated transformation of the initial material. Development of incomplete weathering profiles is first of all caused by weak ejection of bivalent cations from primary minerals. That is why newly emerging phases will be dioctahedral and often preserve mixed composition of cations. The most important typomorphic indications of clay formations in the studied weathering crusts are as follows: a) omnipresent dioctahedral hydromica (2М1) in the weathering crust of terrigenouscarbonate rocks and its association in the most mature profiles with kaolinite of relatively ordered structure, than of kaolinite, having been formed at the expense of other rocks; b) constant availability of trappean formation (tuffs, tufogene rocks, dolerites) in sections of crusts of weathering together with di- and trioctahedral montmorillonite, as well as disordered vermiculite-montmorillonite mixed-layered formation, to this or that degree disordered kaolinite, associated in the weathering crust of tufogene rocks with halloysite (at complete absence of micaceous minerals in the products of weathering); c) the content in the crust of weathering of kimberlites together with polycationic montmorillonite of a significant quantity of trioctahedral chlorite (packets δ and δ'), serpentine (structural types A and B) and altered to various degree phlogopite, including related with it hydromica 1M.

Gold Deposits of the ~15-Moz Ahafo South Camp, Sefwi Granite-Greenstone Belt, Ghana: Insights into the Anatomy of an Orogenic Gold Plumbing System

2021 ◽  
Author(s):  
Quentin Masurel ◽  
Paul Morley ◽  
Nicolas Thébaud ◽  
Helen McFarlane
Keyword(s):  
Rock Mass ◽  
Shear Zone ◽  
Gold Mineralization ◽  
Hanging Wall ◽  
Spatial Association ◽  
Sedimentary Rocks ◽  
Shear Zones ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Plutonic Rocks

Abstract The ~15-Moz Ahafo South gold camp is located in southwest Ghana, the world’s premier Paleoproterozoic gold subprovince. Major orogenic gold deposits in the camp include Subika, Apensu, Awonsu, and Amoma. These deposits occur along an ~15-km strike length of the Kenyase-Yamfo shear zone, a major tectonostratigraphic boundary juxtaposing metamorphosed volcano-plutonic rocks of the Sefwi belt against metamorphosed volcano-sedimentary rocks of the Sunyani-Comoé basin. In this study, we document the geologic setting, structural geometry, and rheological architecture of the Ahafo South gold deposits based on the integration of field mapping, diamond drill core logging, 3-D geologic modeling, and the geologic interpretation of aeromagnetic data. At the camp scale, the Awonsu, Apensu, and Amoma deposits lie along strike from one another and share similar hanging-wall plutonic rocks and footwall volcano-sedimentary rocks. In contrast, the Subika gold deposit is hosted entirely in hanging-wall plutonic rocks. Steeper-dipping segments (e.g., Apensu, Awonsu, Subika) and right-hand flexures (e.g., Amoma, Apensu) in the Kenyase-Yamfo shear zone and subsidiary structures appear to have represented sites of enhanced damage and fluid flux (i.e., restraining bends). All gold deposits occur within structural domains bounded by discontinuous, low-displacement, sinistral N-striking tear faults oblique to the orogen-parallel Kenyase-Yamfo shear zone. At the deposit scale, ore-related hydrothermal alteration is zoned, with distal chlorite-sericite grading into proximal silica-albite-Fe-carbonate mineral assemblages. Alteration halos are restricted to narrow selvages around quartz-carbonate vein arrays in multiple stacked ore shoots at Subika, whereas these halos extend 30 to 100 m away from the ore zones at Apensu and Awonsu. There is a clear spatial association between shallow-dipping mafic dikes, mafic chonoliths, shear zones, and economic gold mineralization. The abundance of mafic dikes and chonoliths within intermediate to felsic hanging-wall plutonic host rocks provided rheological heterogeneity that favored the formation of enhanced fracture permeability, promoting the tapping of ore fluid(s). Our interpretation is that these stacked shallow-dipping mafic dike arrays also acted as aquitards, impeding upward fluid flow within the wider intrusive rock mass until a failure threshold was episodically reached due to fluid overpressure, resulting in transient fracture-controlled upward propagation of the ore-fluid(s). Our results indicate that high-grade ore shoots at Ahafo South form part of vertically extensive fluid conduit systems that are primarily controlled by the rheological architecture of the rock mass.

Observations geologiques en Sierra de Lujar (cordilleres Betiques internes, Espagne)

1966 ◽  
Vol S7-VIII (4) ◽  
pp. 585-591
Author(s):  
Jean Boulin ◽  
Patrick Dimpault Darcy ◽  
Henry Leroy
Keyword(s):  
Host Rock ◽  
Carbonate Rocks ◽  
Sedimentary Rocks

Abstract The Sierra de Lujar is composed of Triassic sedimentary rocks, mostly limestones and dolomites, in a reversed series. This unit seems to be the inverted flank of a recumbent fold of which the Lanjaron nappe is the normal flank, the fold being inclined toward the inner zones of the range. A lead deposit is associated with the carbonate rocks. It is of the stratiform type and appears to be related to a shoal zone that existed during the sedimentation of the ore host rock, and perhaps also to reworking and concentration of the latter, in which case it would be synsedimentary. These Triassic shoals, which have probably shifted somewhat, lie parallel to the northeast-southwest direction of the minor alpine (Cenozoic) folds that make up the Sierra. These minor folds are themselves parallel to the general alignment of the range.

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