Discordant calc-silicate bodies from the St. Just aureole, Cornwall

1978 ◽  
Vol 42 (324) ◽  
pp. 427-434 ◽  
Author(s):  
D. H. M. Alderton ◽  
N. J. Jackson
Keyword(s):  
Hydrothermal Fluids ◽  
Chemical Analyses ◽  
Field Evidence ◽  
Ore Mineralization ◽  
Metasomatic Replacement

SummarySeveral discordant, garnet-bearing bodies are described from the St. Just part of the Land's End granite aureole, Cornwall. It is suggested that these formed by a combination of metasomatic replacement and dilation with concomitant precipitation. Other Ca-Fe aluminosilicates (containing large amounts of Zn, Sn, B, and Be) are also present in the bodies. The chemical, petrographic, and field evidence suggests that the introduced material was transported by hydrothermal fluids. These fluids could well be related to the intrusion of the granite and the earliest phases of ore mineralization. Chemical analyses of garnets, calcic amphiboles and one apatite, epidote, diopside, and axinite are given.

scholarly journals The deformation and granitisation of Ketilidian rocks in the Nanortalik area, S. Greenland

1966 ◽  
Vol 59 ◽  
pp. 1-102
Author(s):  
A Escher
Keyword(s):  
Volcanic Rocks ◽  
Time Interval ◽  
Chemical Analyses ◽  
Intrusive Body ◽  
Major Phase ◽  
Fine Grained ◽  
Field Evidence ◽  
Rigid Mass ◽  
Metasomatic Replacement ◽  
Subsequent Replacement

The Nanortalik peninsula, situated between the fjords of Tasermiut and Sarqâ, is largely composed of Ketilidian schists, quartzites and volcanic rocks. All these rocks are more or less strongly folded. The folding took place probably in three successive phases during the Ketilidian period : A first deformation resulting in folds with NNE trending axes, was followed by a second major phase of folding with NW axes. This second folding was essentially plastic. A third deformation, acting probably on a more rigid mass, was characterised by the formation of fracturec1eavage. Third-period folds possess very long wavelengths; their axes are oriented NNE to NE. Migmatisation started probably during the second deformation period resulting in the formation of many dykes and veins of pegmatite and aplite. Four generations of Ketilidian pegmatites can be recognised. Most of them appear to have been formed by metasomatic replacement. It seems that during the Ketilidian orogeny, the evolution of the schists and gneissic schists tended to a granodioritic composition. Potassium metasomatism only became active at the end of the Ketilidian period. In the NE part of the Nanortalik peninsula, three Sanerutian granites can be observed. These granites are similar in composition (quartz-microline-biotite), but possess different ages and textures. The time interval between the last Ketilidian deformation and the emplacement of the first Sanerutian granite was marked by the intrusion of several metadoleritic dykes. The first and principal Sanerutian granite usually shows an indistinct foliation due to numerous oriented inc1usions. Field evidence indicates that this granite was formed mainly by replacement of volcanic rocks. Chemical analyses show that large amounts of K, Si and Na have been supplied to produce the granitisation of the volcanic rocks. The second Sanerutian granite is characterised by a coarse porphyroblastic texture and appears to have been emplaced partially by the intrusion of a melt and partially by a subsequent replacement of the host-rock. Finally, the last Sanerutian granite displays all the characteristics of a pure intrusive body. It is generally very fine-grained and forms many cross-cutting dykes.

scholarly journals Ag-Pb-Sb Sulfosalts and Se-rich Mineralization of Anthony of Padua Mine near Poličany—Model Example of the Mineralization of Silver Lodes in the Historic Kutná Hora Ag-Pb Ore District, Czech Republic

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 430 ◽  
Author(s):  
Pažout ◽  
Sejkora ◽  
Šrein
Keyword(s):  
Solid Solution ◽  
Czech Republic ◽  
Chemical Element ◽  
Hydrothermal Fluids ◽  
Tectonic Events ◽  
Mineral Phases ◽  
Ore Mineralization ◽  
Ore Mineralogy ◽  
Low Sulfidation ◽  
Ore District

Significant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poličany, Kutná Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry of more than twenty silver minerals are studied here. Selenium mineralization is evidenced by a) the occurrence of selenium minerals, and b) significantly increased selenium contents in sulfosalts. Identified selenium minerals include aguilarite and selenides naumannite and clausthalite. The previously unknown sulfosalts from Kutná Hora are identified: Ag-excess fizélyite, fizélyite, andorite IV, andorite VI, unnamed Ag-poor Ag-Pb-Sb sulfosalts, semseyite, stephanite, polybasite, unnamed Ag-Cu-S mineral phases and uytenbogaardtite. Among the newly identified sulfides is argyrodite; germanium is a new chemical element in geochemistry of Kutná Hora. Three types of ore were recognized in the vein assemblage: the Pb-rich black ore (i) in quartz; the Ag-rich red ore (ii) in kutnohorite-quartz gangue; and the Ag-rich ore (iii) in milky quartz without sulfides. The general succession scheme runs for the Pb-rich black ore (i) as follows: galena – boulangerite (– jamesonite) – owyheeite – fizélyite – Ag-exces fizélyite – andorite IV – andorite VI – freieslebenite – diaphorite – miargyrite – freibergite. For the Ag-rich red ore (ii) and ore (iii) the most prominent pattern is: galena – diaphorite – freibergite – miargyrite – pyragyrite – stephanite – polybasite – acanthite. The parallel succession scheme progresses from Se-poor to Se-rich phases, i.e., galena – members of galena – clausthalite solid solution – clausthalite; miargyrite – Se-rich miargyrite; acanthite – aguilarite – naumannite. A likely source of selenium is in the serpentinized ultrabasic bodies, known in the area of “silver” lodes in the South of the ore district, which may enable to pre-concentrate selenium, released into hydrothermal fluids during tectonic events. The origin of the studied ore mineralization is primarily bound to the youngest stage of mineralization of the whole ore district, corresponding to the Ag-Sb sequence of the ´eb´ ore type of the Freiberg ore district in Saxony (Germany) and shows mineralogical and geochemical similarities to low-sulfidation epithermal-style Ag-Au mineralization.

scholarly journals Structural Controls of Ore Mineralization in a Polydeformed Basement: Field Examples from the Variscan Baccu Locci Shear Zone (SE Sardinia, Italy)

Minerals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 456 ◽  
Author(s):  
Antonio Funedda ◽  
Stefano Naitza ◽  
Cristina Buttau ◽  
Fabrizio Cocco ◽  
Andrea Dini
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Ore Deposits ◽  
Hydrothermal Fluids ◽  
Orogenic Gold ◽  
Mine Area ◽  
Structural Controls ◽  
Mylonitic Foliation ◽  
Ore Mineralization ◽  
Ore Mineralogy

The Baccu Locci mine area is located in a sector of the Variscan Nappe zone of Sardinia (the Baccu Locci shear zone) that hosts several type of ore deposits mined until the first half of the last century. The orebodies consist of lenses of Zn–Cu sulphides, once interpreted as stratabound, and Qtz–As–Pb sulphide ± gold veins; the implication of structural controls in their origin were previously misinterpreted or not considered. Detailed field mapping, structural analyses, and ore mineralogy allowed for unraveling how different ore parageneses are superimposed each other and to recognize different relationships with the Variscan structures. The sulphide lenses are parallel to the mylonitic foliation, hosted in the hinges of minor order upright antiforms that acted as traps for hydrothermal fluids. The Qtz–As–Pb sulphide veins crosscut the sulphide lenses and are hosted in large dilatational jogs developed in the hanging wall of dextral-reverse faults, whose geometry is influenced by the attitude of reverse limbs of late Variscan folds. The ores in the Baccu Locci shear zone are best interpreted as Variscan orogenic gold-type; veins display mutual crosscutting relationships with mafic dikes dated in the same district at 302 ± 0.2 Ma, a reliable age for the mineralizing events in the area.

scholarly journals On beryllite and bertrandite from the Ilímaussaq alkaline intrusion, South Greenland

1967 ◽  
Vol 68 (5) ◽  
pp. 10-29
Author(s):  
S Andersen ◽  
I Sørensen
Keyword(s):  
Water Content ◽  
Late Stage ◽  
Water Pressure ◽  
Hydrothermal Fluids ◽  
Refractive Indices ◽  
Chemical Analyses ◽  
X Ray ◽  
Alkaline Intrusion ◽  
Mode Of Occurrence ◽  
Partial Water

The two beryllium silicates beryllite and bertrandite and their mode of occurrence are described from the Ilímaussaq alkaline intrusion. Optical and X-ray data are presented for the two minerals together with chemical analyses of two beryllite samples. The data for bertrandite correspond closely to those given for bertrandite from other localities. The identification of the beryllite is based on the similarity in X-ray data with the Lovozero type mineral. Pronounced differences from the latter are found in the refractive indices which are 1.50 < n < 1.52, and in the water content which varies in different samples from Ilímaussaq. The two minerals are associated with the beryllium minerals epididymite, eudidymite, chkalovite and sorensenite. The beryllium minerals are found in analcite veins and pockets formed in a late stage of the development of the complex. It is argued that differences in the partial water pressure of hydrothermal fluids govern the formation of the two minerals.

scholarly journals The occurrence of nickel-arsenides and nickel-antimonide at Igdlúnguaq, in the Ilímaussaq alkaline massif, South Greenland

1964 ◽  
Vol 43 ◽  
pp. 1-50
Author(s):  
O.I Soen ◽  
H Sørensen
Keyword(s):  
Fault Plane ◽  
Hydrothermal Fluids ◽  
North Coast ◽  
Fine Grained ◽  
The North ◽  
Vein Formation ◽  
Field Evidence ◽  
Ore Minerals ◽  
Main Factors ◽  
Alkaline Massif

Ore minerals are rare in the alkaline rocks of the Ilímaussaq massif in SW. Greenland. At the locality of Igdlúnguaq on the North coast of the Tunugdliarfik fjord accessory amounts of Ni-arsenides and Ni-antimonide have been found in natrolitized naujaite adjacent to an acmite-arfvedsonite vein. The latter is later than the naujaite but earlier than or contemporaneous with the neighbouring lujavrites. A brief description of the field occurrence and petrography of the ore-bearing naujaite and the acmitite-arfvedsonite vein is given. The ore minerals in the naujaite occur in very small and fine-grained aggregates, which consist of galena, skutterudite, niccolite, breithauptite, maucherite, löllingite and gudmundite. Diablastic intergrowths are common. Niccolite-maucherite network or cell textures, skutterudite-breithauptite and niccolite-breithauptite myrmekites, maucherite-breithauptite myrmekites and breithauptite-maucherite myrmekites and bladed intergrowths, breithauptite-löllingite network or cell textures, maucherite-löllingite bladed intergrowths, breithauptite-gudmundite bladed intergrowths, as well as certain zonal and other textures are described and their significance discussed. It is concluded that the observed assemblages of ore minerals and their characteristic textures have resulted from the modification at temperatures around 4000 C of earlier formed ore minerals, which are thought to have included galena, skutterudite, niccolite and breithauptite. The acmite-arfvedsonite vein is believed to have been formed by replacement of the naujaite along a fracture or fault plane. It is thought that the modifications of the earlier ore minerals in the naujaite are genetically related, in both time and space, with the formation of the acmite-arfvedsonite vein which is believed to be connected with the emplacement of the neighbouring lujavrites. It is suggested that fracturing of rocks, recementation of cracks and fractures, and the circulation of pneumatolytic or hydrothermal fluids having differential dissolving power for As, Sb, S and other components in the system of ore minerals, may have caused significant changes in the partial vapour pressures of these components. Such changes in partial vapour pressures of As, Sb and S are regarded as the main factors controlling the mineralogical and textural modifications of the ore minerals. Thezeolites and other low-temperature minerals in the acmite-arfvedsonite vein were formed at a late stage of the vein formation, when temperature had already declined appreciably. With regard to the origin of the ore minerals no conclusive arguments can be presented. Field evidence seems to favour the possibility that the components of the ore minerals have been completely or partly introduced into the naujaite as a result of hydrothermal action connected with the emplacement of the lujavrites and with the associated acmite-arfvedsonite veins. However, the possibility cannot be excluded that the ore minerals were present in the naujaite as primary magmatic minerals, which were subsequently modified during the emplacement of the lujavrite.

Metamorphic processes at high temperature and low pressure: the petrogenesis of the metasomatized and assimilated rocks of Carneal, Co. Antrim

1975 ◽  
Vol 280 (1294) ◽  
pp. 225-269 ◽  
Keyword(s):  
High Temperature ◽  
Low Pressure ◽  
Small Scale ◽  
New Mineral ◽  
Chemical Analyses ◽  
Rock Types ◽  
Silica Ratio ◽  
Rock Suite ◽  
Metasomatic Replacement ◽  
Limestone Assimilation

The Tertiary dolerite plug at Carneal cuts basalt lavas and incorporates blocks of chalk and flint from underlying Cretaceous rocks. Assimilation by the dolerite of the pure limestone and flint took place under the very rare highest-temperature, low-pressure conditions. Only about twenty-five examples of the resulting metamorphosed and metasomatized rocks are known in the world, few fully described. The rock suite enables the conditions and mechanisms of assimilation to be deduced. The pressure, about 200 x 10 5 Pa (200 bar), and the temperature, estimated as 1050-1100 °C, produced an exomorphic suite of larnite, spinel, merwinite, spurrite, scawtite and related assemblages, with wollastonite, quartz, plagioclase, hydrogrossular, xonotlite and related minerals representing flint. Complementary desilication of the igneous rocks gives the endomorphic suite of pyroxene-rich dolerite, pyroxenite, titanaugitemelilite-rock and aegirine- and nepheline-bearing types. Chemical analyses o titanaugite, sahlite, melilite, wollastonite and the main rock types are provided and optical and other properties of the minerals. Two related mechanisms of limestone assimilation occurred. Most of the rocks resulted from the incorporation of the chalk in the olivine-dolerite magma, paradoxically, the addition of 18-26 % CaO to the dolerite magma so lowers the silica ratio that 17-18% additional S i0 2 is required to produce the endomorphic hybrids, with the complementary exomorphic suite. The second mechanism, a metasomatic replacement, preserves existing mineral (and fossil) textures. Mineral textures and the preservation of a cyclostome bryozoan now composed of wollastonite (by silicification of calcite) show the metasomatism to have been a tranquil process despite the high temperature. To produce the vein assemblage of merwinite, hydrogrossular and melilite, this mechanism required 63 % CaO and 23 % H 2 0 , an addition which is only slightly more hydrous than calcium hydroxide. These mechanisms are evidence for the production of peralkaline rocks by limestone assimilation but only on a very small scale. The retrograde phase of metamorphism produced minerals in order of approximately increasing water content, including xonotlite, bicchulite (a new mineral), thomsonite, tobermorite, tacharanite and plombierite.

Glaucophane Schists of Caledonian age from Spitsbergen

1972 ◽  
Vol 109 (1) ◽  
pp. 29-36 ◽  
Author(s):  
W. T. Horsfield
Keyword(s):  
Radiometric Dating ◽  
Chemical Analyses ◽  
Glaucophane Schist ◽  
Field Evidence ◽  
Mineral Assemblages ◽  
Caledonian Orogeny ◽  
First Time

SummaryGlaucophane schists from Oscar II Land in western Spitsbergen are described for the first time. Although lawsonite, aragonite and pumpellyite have not been found, the mineral assemblages correspond generally with glaucophane schist assemblages known from elsewhere. The results of three XRF chemical analyses are presented, and five K/Ar radiometric determinations. The radiometric dating and field evidence both suggest that the glaucophane schists are a result not of the Tertiary orogeny which affected this part of Spitsbergen, but of the earlier Caledonian orogeny.

Black and white waters and their possible relationship to the podzolization process

Soil Research ◽  
1983 ◽  
Vol 21 (1) ◽  
pp. 59 ◽  
Author(s):  
R Reeve ◽  
IF Fergus
Keyword(s):  
Storage System ◽  
Residual Liquid ◽  
Chemical Analyses ◽  
Black And White ◽  
Black Water ◽  
Field Evidence ◽  
Close Proximity ◽  
Leaching Experiment ◽  
Water Field ◽  
White Water

Highly coloured, organic-stained water (black water) occurs as springs, seeps and perched lakes in the Cooloola area of south-eastern Queensland (latitude 26� S.). Springs of clear, colourless water (white water) sometimes occur in close proximity to the black water. Field evidence suggests that black waters move laterally along semipermeable B horizons of humus podzols, whereas white waters are part of a much larger storage system in which the water has been decolorized by contact with the C horizons. Thus it appears that black waters are the active eluviating agent and white waters are the residual liquid phase of the podzolization process. Chemical analyses of black and white waters, and the results of a laboratory leaching experiment, support this view. Possible mechanisms and some implications for the genesis of podzol B horizons are discussed.

scholarly journals Role of Hydrothermal Fluids in the Formation of the Kamioka Skarn-Type Pb–Zn Deposits, Japan

Geosciences ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 447
Author(s):  
Yuichi Morishita ◽  
Ayaka Wada
Keyword(s):  
Oxygen Isotope ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Hydrothermal Activity ◽  
Hydrothermal Fluids ◽  
Control Factor ◽  
Oxygen Isotope Ratios ◽  
Carbon And Oxygen Isotope ◽  
Crystalline Limestone ◽  
Ore Mineralization

The Kamioka mine, located in Gifu Prefecture in Japan, is famous for the large water Cherenkov detector system, the Super-Kamiokande. The Kamioka skarn-type Pb–Zn deposits are formed in crystalline limestone and are replaced by skarn minerals within the Hida metamorphic rocks. The Kamioka deposits mainly consist of the Tochibora, Maruyama, and Mozumi deposits. The present study focuses on the ore-forming hydrothermal fluid activity in the Kamioka deposits and the peripheral exploration area based on the carbon and oxygen isotope ratios of calcite and rare earth element (REE) analyses. The carbon and oxygen isotope ratios of crystalline limestone (as the host rock) are not homogeneous, and depending on the degree of hydrothermal activity, they decreased to various degrees because of the reaction with the ore fluids. Thus, the carbon and oxygen isotope ratios of crystalline limestone can be used as an indicator of the influence of the hydrothermal fluids for the ore mineralization. The REE contents in the ores of igneous origin are one order of magnitude higher than the limestone origin. Further, depending on the formation temperatures, calcites precipitated during ore mineralization have a stable carbon isotope ratio and a widely varying oxygen isotope ratios. The Kamioka district fracture system is likely a major control factor on ore mineralization from hydrothermal activity. In addition, the skarnization-related ore-forming fluids are mostly meteoric in origin, confirming the conclusions from previous studies.

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