On the Production of Secondary Minerals at Shear-zones in the Crystalline Rocks of the Malvern Hills

1889 ◽  
Vol 45 (1-4) ◽  
pp. 475-503 ◽  
Author(s):  
C. Callaway
Keyword(s):  
Shear Zones ◽  
Crystalline Rocks ◽  
Secondary Minerals

scholarly journals Water-free oil reservoirs: origin and morphology

Georesursy ◽  
2020 ◽  
Vol 22 (4) ◽  
pp. 15-21
Author(s):  
Tatyana A. Kireeva
Keyword(s):  
High Temperature ◽  
Crystalline Rocks ◽  
Secondary Minerals ◽  
Bazhenov Formation ◽  
Iron Aluminum ◽  
Hydrothermal Origin ◽  
South Vietnam ◽  
White Tiger ◽  
Clay Rocks ◽  
Calcium Iron

The features of the morphology and composition of secondary minerals in the reservoir zones of the White Tiger (Bach Ho) deposit (shelf of South Vietnam) and deposits in clay rocks of the Bazhenov formation of the Salym area of Western Siberia are considered. It is shown that the common for these fields is the formation of a reservoir as a result of the leaching effect of high-temperature fluids. The genesis of the reservoir is determined by a complex of secondary minerals, obviously of hydrothermal origin, partially filling caverns and cracks in the rock: native silver – zincous copper – barite – anhydrite – kaolinite – laumontite (White Tiger oilfield) and sulphates of iron, aluminum, sodium and calcium – iron-aluminum alum, alunite, jarosite, mirabilite, melanterite, gypsum (deposit in the rocks of the Bazhenov formation of the Salym area). Diagnostics of secondary minerals was established based on the results of microprobe studies of undisturbed samples and analysis of the composition of water extracts from crushed core samples.The species composition of secondary minerals indicates a high temperature of the affected solutions, which varied from 600 to 200°C in the case of the White Tiger oilfield, and in the range of 350–450°C, in the case of rocks of the Bazhenov formation. Hydrothermal alteration of crystalline rocks with the formation of secondary clay minerals (kaolinite, montmorillonite, hydromica), zeolites and minerals-sulfates, which are crystalline hydrates, occurs with the absorption of huge amounts of water by the rock (up to 4∙108 tons of water per 1 km3 of altered rock). This may be related to the waterlessness (lack of bottom water) of oilfields, the reservoir of which has a hydrothermal origin. It is possible that oil deposits in crystalline rocks with high oil-saturated zones have associated waters of hydrothermal rather than sedimentogenic origin, but they occur at considerable depths and are not penetrated by drilling. This possibility is evidenced by the discovery of hydrothermal water in the basement of the White Tiger reservoir at a depth of 4493 m, which, in terms of chemical composition and mineralization, is close to the waters of sodium chloride hydrotherms of Kamchatka.

The Patterson Lake corridor of Saskatchewan, Canada: defining crystalline rocks in a deep-seated structure that hosts a giant, high-grade Proterozoic unconformity uranium system

2020 ◽  
pp. geochem2020-007
Author(s):  
Colin D. Card
Keyword(s):  
Large Scale ◽  
Shear Zones ◽  
Crystalline Rocks ◽  
Ductile Deformation ◽  
Uranium Deposits ◽  
Content Type ◽  
Athabasca Basin ◽  
Rock Types ◽  
Host Rocks ◽  
Basin Region

The Patterson Lake corridor in the Athabasca Basin region of Saskatchewan, Canada hosts a large-scale uranium system with two major deposits already delineated. The corridor developed in crystalline rocks of the southwest Rae Province, which host all of the known uranium endowment. Orthogneisses along with voluminous pegmatites are the hosts of the uranium mineralization. These rocks, however, underwent significant open-system metasomatic – hydrothermal modification. Principal amongst these alterations is early and pervasive quartz flooding of the host rocks that resulted in the development of widespread secondary quartzites and associated rock types. These secondary quartzites and their altered host rocks suffered ductile deformation, typically focussed at silicification fronts. Late carbonatite dykes exploited the associated shear zones. Semi-brittle deformation zones nucleated near the previously developed ductile high-strain zones. Graphite and associated iron-sulphides precipitated in a semi-brittle structural regime. These graphitized zones provided the necessary structural architecture to focus the uranium system, which developed may be hundreds of millions of years younger developing at ∼1.425 Ga.Host rocks of the Patterson Lake corridor prove that metasedimentary rocks are not a requirement for development of giant Proterozoic unconformity uranium deposits. Crustal-scale fault zones with access to the mantle (i.e. carbonatites) should be considered a key parameter in the exploration model for Proterozoic unconformity uranium deposits. Given the similarity of the mineral assemblages in the crystalline basement rocks of the main exploration corridor to eastern Athabasca Basin region, it is likely that a similar, cryptic geological boundary focussed the giant uranium system in that region.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

scholarly journals Fuchsite and chrome-epidote from Fiskenæsset

1976 ◽  
Vol 73 ◽  
pp. 67-69
Author(s):  
M Ghisler
Keyword(s):  
Shear Zones ◽  
White Mica ◽  
Hydrothermal Solutions ◽  
Secondary Minerals

In many places in the Fiskenæsset region the anorthositic rocks show a characteristic emerald green staining. The occurrences are connected with faults and shear zones, along which hydrothermal solutions have circulated, resulting in a bleaching and alteration of the anorthositic rocks (Ghisler, 1970). The plagioclase became saussuritized to white mica and epidote, and occassionally calcite is also found. Mafic minerals were altered to chlorite and more rarely to tale. In some places such as the Majorqap qava area a green rock consisting of epidote and an emerald green mineral is found as 10-50 cm thick lenses in anorthosite. The emerald green mineral mainly occurs.in the vicinity of chromite horizons or where accessory chromite is present in the anorthosite. Chromium was extracted from these chromite grains and entered the lattice of some of the minerals formed as aresult of the breakdown of plagioclase. Some mineralogical data on these two chromium bearing secondary minerals, fuchsite and chrome-epidote, are given below.

scholarly journals Permeability variation in crystalline rocks due to low-grade solution phenomena

2021 ◽  
Vol 1 ◽  
pp. 65-66
Author(s):  
Rüdiger Kilian ◽  
Michael Stipp
Keyword(s):  
Granite Gneiss ◽  
Shear Zones ◽  
Crystalline Rocks ◽  
Low Grade ◽  
Tauern Window ◽  
Detailed Structural Analysis ◽  
Distribution Shape ◽  
Porosity And Permeability ◽  
Local Shear ◽  
Quartz Aggregates

Abstract. Permeability of crystalline rocks depends on parameters such as density and interconnectivity of fractures and pores. While in pristine crystalline rocks porosity is usually considered to be low, low-grade solution phenomena such as the formation of episyenites occur occasionally and may cause a local dramatic increase in porosity and permeability. These solution phenomena can be effective in otherwise unaltered rocks and may result in the preferential removal of certain mineral phases, especially of quartz so that porosities correspond to the spatial distribution of the previously existing mineral phase if no subsequent mineralization occurs (e.g., Pennacchioni et al., 2016). Using light-optical and scanning electron microscopy, X-ray tomography, micro-XRD, as well as digital image analysis, the differences in connectivity and hence permeability between, for example, quartz-depleted granite, gneiss, and schist can be characterized and quantified. We demonstrate that such porosities do not necessarily result in high permeabilities in an undeformed granodiorite from the Central Gneiss unit of the Tauern Window (Lago di Neves area, Italy), since former quartz aggregates are not interconnected due to their relatively late crystallization age and the preservation of the magmatic fabric; however, in the case of moderate mylonitic deformation, quartz as rheologically weak phase forms interconnected aggregates and layers. Its dissolution results in an extremely increased permeability. Therefore, not only the content and grain size but also the distribution, shape and alignment of minerals are crucial for rock permeability and need to be carefully investigated when searching for a final repository of highly radioactive waste in crystalline rocks. Especially since local shear zones may form in otherwise undeformed intrusive bodies, a detailed structural analysis beyond the exclusion of the presence of fractures is required to mitigate the risk of a long-lasting nuclear waste disposal.

Aqueous Phase Diffusion in Crystalline Rock

1981 ◽  
Vol 11 ◽  
Author(s):  
M.H. Bradbury ◽  
D. Lever ◽  
D. Kinsey
Keyword(s):  
Radioactive Waste ◽  
Aqueous Phase ◽  
Water Movement ◽  
Degradation Products ◽  
Crystalline Rock ◽  
Crystalline Rocks ◽  
Radionuclide Transport ◽  
Fracture Networks ◽  
Phase Diffusion ◽  
Main Factors

One of the options being considered for the disposal of radioactive waste is deep burial in crystalline rocks such as granite. It is generally recognised that in such rocks groundwater flows mainly through the fracture networks so that these will be the “highways” for the return of radionuclides to the biosphere. The main factors retarding the radionuclide transport have been considered to be the slow water movement in the fissures over the long distances involved together with sorption both in man-made barriers surrounding the waste, and onto rock surfaces and degradation products in the fissures.

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