Sericite Schist Research Articles

Geology of the Pyhasalmi ore deposit, Finland

The Pyhaesalmi deposit is a stratabound massive pyrite-copper-zinc deposit in a Precambrian metamorphic schist belt mainly composed of metavolcanites. The host rocks of the ore are silicic fine-grained metavolcanites, and the stratum of ore is stratigraphically overlain by mafic metavolcanites. In the close environment of the ore the silicic metavolcanites, rhyolitic in composition, and the more mafic rocks have been chemically altered; hence, they are enriched in potassium, iron, and magnesium and depleted in sodium and calcium. The metamorphic derivatives of the altered volcanites are sericite schists and cordierite-anthophyllite rocks. The ore deposit, which is syngenetic with silicic volcanites, was folded during polyphase deformation. The orebody averages 0.85 percent Cu, 2.8 percent Zn, 37 percent S, 33 percent Fe, 0.2 g/ton Au, and 14 g/ton Ag. The main gangue minerals are quartz, barite, and local carbonates. The data presented indicate a fairly constant isotope composition of sulfur with an average value of 34 S of +7.5 per mil for pyrite. Isotopic dating of intrusive and supracrustal rocks yields ages of about 1,900 m.y. for the metavolcanites but a somewhat higher age (1,932 + or - 1.5 m.y.) for the gneissic granite, east of the schist belt. The lead isotope compositions of the galena in the Pyhaesalmi ore and its silicic metavolcanite hosts lie on the same isochron within limits of experimental uncertainty. The lead isotopes applied to a plumbotectonic model yield an age of 1.970 m.y. and indicate a mantle origin.

Geology of the Raposos gold mine, Minas Gerais, Brazil

The gold ore bodies are mineralized segments of folded Precambrian iron formations separated by shear zones, diabase dikes, and barren iron formation. The type of iron formation that acts as principal host is banded siderite-quartz rock. Belts of this rock are enclosed in chlorite schist, some of which is chromium-rich. Gold-bearing hydrothermal solutions, rising along the axes of plunging folds, preferentially replaced bands of siderite in the iron formation. Early solutions altered the schist wall rock to green chromian sericite schist and deposited pyrite. Arsenopyrite, pyrrhotite, chalcopyrite, quartz, ankerite, and most of the gold were introduced during the later, principal stage of mineralization, from an unknown source or sources.

Les ensembles tectoniques betiques de la region de Lorca (Espagne meridionale)

Abstract The Betic units of the Lorca area belong to the Alpujarride domain and to the Betic of Malaga Three units, slightly affected by Alpine orogenic movements, comprise the Alpujarride. The Lajara unit consists of middle and upper(?) Triassic limestones and dolomites overlying Werfenian sandstones and sericite schists. The Simon-Torrecilla unit is composed of Permo-Carboniferous micaschists overlain successively by upper Permian phyllitic schists Werfenian sericite schists and quartzite, and middle-upper Triassic limestones and dolomites. In the Selvalejo unit, analogous to the Simon-Torrecilla, the basal mica schist overlies the Simon-Torrecilla sericite schists and is generally separated from the Permo-Werfenian which rests directly on middle-upper Triassic limestone-dolomite. Intermediate between the Alpujarride domain and the Betic of Malaga is the Pena Rubia unit, a series of argillaceous sandstones with interbedded conglomerates, similar to the Malaga Betic, overlain by dolomitic limestones of the Muschelkalk and limestone of the Alpujarride facies. In the Betic of Malaga two sub-units are defined, the lower Moroticos-Olivares, composed of Devonian-Carboniferous limestones or dolomites, Permo-Triassic conglomerates, and upper(?) Triassic dolomites. The upper sub-unit, Cimbre de la Fuensanta, is distinguished from the lower unit by the presence of dolomites and limestones containing a Liassic fauna. The characteristics of the intermediate Pena Rubia unit indicate that the two Betic elements were closely related prior to Tertiary folding.

Sur la stratigraphie et la tectonique de l'Eubee moyenne (Grece)

Abstract The stratigraphic section of Euboea island (Greece) contains Kimmeridgian limestone, a diabase-radiolarite, and a transgressive upper Cretaceous massive limestone. Cenomanian and Maestrichtian beds are recognized with flysch deposits in the Maestrichtian and younger series. The sequence is part of a southwest plunging monocline with two fault systems: a principal NW-SE and a secondary NE-SW system. The first is believed to be pre-Pliocene and the second post-Pliocene. A metamorphic zone in the northeast consists of marbles and sericite schists with some trachyandesitic volcanics.

Study of the metamorphic manganese ores of Bharweli Mine-area, Madhya Pradesh, India, and their genesis

Manganese deposits of the Bharweli area are conformable with the enclosing Precambrian quartzites, phyllites, and sericitic and garnetiferous mica schists and were formed by metamorphism of manganiferous sediments interbedded with pelitic and psammitic rocks. Braunite (two generations) and hollandite are the most abundant minerals; bixbyite, manganite, and secondary pyrolusite and cryptomelane are also present. Braunite of the first generation crystallized earliest, under conditions of increasing metamorphism and deformation. Bixbyite crystallization apparently commenced at the peak of metamorphism and continued after deformation had ceased. Second-generation braunite, manganite, and hematite formed in waning stages of metamorphism.

Sur la serie metamorphique de Velez-Malaga (province de Malaga, Espagne)

Abstract Four major petrographic facies are distinguished along the Malaga-Motril road between Torre de Mar and Nerja (Spain)--sericite schist, mica schist, gneiss, and lenticular gneiss facies. The mechanical forces which caused the fold and boudinage structures affecting the feldspathic mica schists and the mica schists with andalusite occurred contemporaneously with, if not before, the albitization of the Velez series. The sericite schists have been correlated with certain Triassic series, leading to the proposal of a post-Triassic age for the metamorphism of the Velez series. Two phases of crystallization are recognized in the petrogenesis of the Velez-Malaga crystalline schists: transformation of an older sedimentary series by intense metamorphism, and albitization of the resultant metamorphic series related to major sodic metasomatism.

Profils geologiques en Calabre sud-occidentale

Abstract The geology of southwestern Calabria (Italy) presents certain problems that are yet to be resolved. A zone of isolated dolomite outcrops is only a convenient term to relate rocks of similar lithology but does not imply paleogeographic continuity. Triassic and Paleocene fossils have been found in the dolomites but there is no evidence of continuous sedimentation and dolomitization may have contributed the appearance of continuity to the zone. A larger quartzitic schist zone extends from the Sila mountain to the Tyrrhenian coast. These thick beds are composed of sericite schist with quartz pebbles aligned parallel to planes of schistosity. Fossils have not been found but the zone is believed to be an allochthon or a para-autochthon related to the Hercynian sedimentary cycle. East of Sila a metamorphosed zone of crystophylline gneiss, crossed by granite veins, abruptly replaces the schists.

Geology, sulfur isotopes and the origin of the Heath Steele ore deposits, Newcastle, N. B., Canada

The Heath Steele mine is located 35 miles northwest of Newcastle, New Brunswick, Canada. Middle Ordovician Tetagouche Group rocks, consisting of siliceous and basic volcanic rocks, and fine-grained quartz sericite schists and porphyry, have been folded into a steeply plunging recumbent anticline. The ore deposits of zinc, lead, and copper are associated with minor folding and/or sheared dilatent zones at or near the contact between porphyry and fine-grained senicitic schist. Mineralogically the sulfide bodies consist of early, euhedral arsenopyrite, magnetite, and pyrite, followed by interstitial pyrrhotite, sphalerite, chalcopyrite and galena. Minor minerals are ternantite-tetrahedrite, bismuthinite, marcasite, hematite, and some graphite. Supergene minerals consist of chalcocite, covellite, and marcasite with a little native silver. Little hypogene replacement has taken place between the minerals, which show a porphyritic texture. Sulfur isotope ratios were determined for over 150 sulfide and sulfate specimens from five of the seven ore bodies, and from granite, acid and basic volcanics, porphyry, and sediments. The results indicate that there is no detectable fractionation either during hypogene mineralization or supergene enrichment. The spread (21.82 to 22.02) covered by the ratios is narrow, and suggestive of a well homogenized source of mineral solutions. The enrichment of S/sup 34/ in themore » ore sulfides and the presence of graphite, evident from mineralographic studies and mass spectrometric analysis, suggests reduction of original sulfates (known to be enriched in S/sup 34/) by organic carbon at temperatures in excess of 500 deg C. A calculation based on the isotopic exchange reaction between sulfide and sulfate under equilibrium conditions and the spread of the ratios indicates a temperature of 700 to 800 deg C for the source. Finally the ratios determined for sulfides in a gneissic granite close to Heath Steele have the same ratio as the ore. These factors are considered to be diagnostic of a magmatic hydrothermal origin for the orp deposits. It is believed that an original source bed has been buried until suitable temperatures were reached to cause granitization, reduction of sulfates, and mobilization of the resulting sulfides to form ore deposits at favorable loci. (auth)« less

Geology of the Mount Lyell mines, Tasmania

The host rocks of copper sulfide ores in the Mount Lyell district, Tasmania, are quartzose sericitic and chloritic schists regarded as altered equivalents of geosynclinal sedimentary and volcanic rocks of the Cambrian Dundas group and overlying Ordovician conglomerates. The principal ore bodies occur at or near intersections of east-west- or northwest-trending faults with a major longitudinal shear along which both vertical and transcurrent movements took place during the mid-Devonian Tabberabberan orogeny. The chief ore minerals are chalcopyrite, bornite, and pyrite.

Esquisse geologique de l'Arabie seoudite

Abstract An outline of the geology of Saudi Arabia. The Precambrian basement consists of two distinct series. The Medina series, the older, includes rocks metamorphosed to different stages (sericite schists, gneisses, and migmatites), with numerous lava flows, particularly in the western part. Various granites and dike rocks intrude the Medina but not the Wadi Fatima series lying discordantly above it. The Wadi Fatima is folded and contains three local stromatolitic zones. The Paleozoic is represented in the north by rocks exhibiting a typical Saharan facies. Marine Muschelkalk (Triassic) beds and Jurassic formations (beginning with Toarcian) cover a large area. The most important Cretaceous transgression occurred in the Maestrichtian, when a gulf extended to the Djeddah region. The grabens of central Arabia appear to be related to the formation of the Red Sea depression during Mio-Pliocene time.

日立鉱山の採鉱法

The ore deposits of Hitachi Mine are cupriferous pyrite ore, belonging to the “Kieslager type”. The veins extend over two thousand meters along the strike from east to west. The country rock of these ore deposits are chiefly chlorite schist, sericite schist and biotite schist with hardness varying in various degrees.This necessitates the use of mine timbers not only in the stopes but also in the drifts. For this reason overhand horizontal cut-and-fill method has been, adopted in most of the stopes.In 1952, we have succeeded in filling the stopes with sand slime from the milling plant. Since then, we have introduced under-hand horizontal cut.and-fill method with sand slime as back filling on top of the top slicing method and thereby, greatly improved the method of mining. This method has been adopted together with the overhand horizontal cut-and-fill method in our mine, but the production of the former method alone amounts to about half of the whole production at present.

Paragenesis of the zinc-lead-copper deposits at the Mindamar Mine, Nova Scotia

The Mindamar mine is in Richmond County on Cape Breton Island, Nova Scotia. The ore bodies are irregular lenses that lie within a persistent, wide, steeply dipping shear zone cutting mainly sericite schist. The schist was derived principally from siliceous siltstone of probable Middle Cambrian age.The deposits consist of extremely fine-grained pyrite and sphalerite with minor chalcopyrite, galena, and tennantite with a little gold, silver, and realgar in gangue composed mainly of dolomite, magnesite, quartz, sericite, talc, and chlorite. They were formed chiefly in the following overlapping stages:(1) Deposition of most of the fine-grained pyrite and sphalerite by replacement of sericite schist. (2) Deposition of most of the dolomite and magnesite and some of the quartz, partly in fractures and partly by replacement. (3) Deposition of most of the galena, chalcopyrite, and tennantite and some of the pyrite and sphalerite both in the carbonates and in the fine-grained pyrite- and sphalerite-bearing ore.Dolomite and magnesite, in part, appear from their textures to be meta-colloidal. Talc occurs chiefly as randomly oriented flakes which originated by replacement of dolomite and magnesite without recognizable change in volume.Most of the numerous diabase dikes were intruded after deposition of the carbonates and ore minerals. Several, however, were emplaced before completion of carbonate and ore deposition and their margins are intensely carbonatized and locally mineralized.Much of the fine-grained ore shows thin layers differing from one another in the proportions of ore minerals to gangue minerals or of individual ore minerals to each other. This structure may be attributable mainly to selective replacement of relic lamination in sericite schist and partly to replacement controlled by closely spaced parallel fractures.

Stratigraphy and Geological Structure of the Sanbagawa Crystalline Schist in the Northern Part of the Tenryu River District

The Sanbagawa crystalline schist of this district can be divided lithologically into the following formations., Yosizawa formation Black schist of pelitic origin, interbedded with some beds of green schist., Thickness : 350∼650m., Zihati formation Alternating beds of green schist (albite spotted and nones-potted) and black schist (albite spotted and nonspotted)., Thickness: 300∼700m., Wasanma formation Quartz schist; limestone schist; alternation of sericite schist, black schist and green schist beds., Thickness: 300∼400m., Sinkai formation Black schist., Thickness: 500∼600m., Hunayo formation Black schist., Thickness: 700m+., The Yosizaya and the Zihati formations are characterized by a folded structure which strikes east-west., Linear structures can be seen aligned east-west in the cleavage plane which is parallel to the bedding of the Yosizawa formation., The linear structures of the Zihati formation are aligned both east-west and north-south and are formed to the plane or cleavage which is parallel to the bedding plane., Parts of the wasanma and the Sinkai formation are characterized by east-west intraformational folding formed by slip movement in the cleavage plane, S1 parallel to the bedding plane., Linear structures can be seen aligned east-west on the cleavage plane S1, and parallel to the axis of the intraformational folds., In addition, north-south linear structures can be seen on the cleavage plane S2 which can b3 found in a position corresponding to that of the axial plane of the intraformational folds., The Hunayo formation and the lower Sinkai formation are characterized by a north-south structure., Linear structures are found oriented north-south within cleavage planes which are parallel to the bedding plane., Analysis of the linear structures in the crystalline schist formation of this area infers that the orogenic movement can be divided into the following two stages., 1st stage: A north-south differential movement or formations above the lower Sinkai formation and an east-west differential movement of formations below the lower Sinkai formation., Intrusion of the Tatuyama metadiabase sill into spaces between formations which had suffered separate differential movements., 2nd stage: An east-west differential movement throughout the whole Sanbagawa crystalline schist formation in this region.,

GEOLOGICAL RECONNAISSANCE OF THE ISLAND OF MARGARITA, PART I*

The Island of Margarita, Venezuela, is largely composed of crystalline rocks, mainly garnetiferous and graphitic schist and gneiss, greenstone and amphibolite, intruded by peridotite and serpentinite. A belt of graphitic sericite schist with interbedded marble lies south and east of the higher-grade metamorphics. Small bodies of pyroxene diorite or gabbro intrude the sericite schist. The large mass of coarse-grained soda granite porphyry forming Cerro Mata Siete is believed to underlie the sericite schist unconformably. For the most part the metamorphics strike northeast and dip steeply southeast. Along the south and southeast margin of the island Eocene sandstone, shale, and conglomerate are folded in a general synclinal structure and overlain unconformably by patches of gently dipping Miocene sediments. Pebbles and cobbles of volcanic rocks are abundant in the lower beds of the Eocene section, though no source for such rocks is known on the island. Major deformation and metamorphism in Margarita presumably occurred before the end of the Cretaceous, with renewed folding after the Eocene sediments were deposited and prior to the Miocene.

Alteration of a Colorado Granite to Sericite Schist

Petrographic and chemical study of fresh granite, sericitized granite, and sericite schist shows the changes characteristic of this type of alteration. The principal chemical changes were a large loss of soda and a gain of water. The difference between the sericitized granite and the sericite schist is principally in texture and structure.

III.—The Contact-Zone of the Alps and the Apennines in Western Liguria

In a paper on the Permian formation in the Maritime Alps, etc. (Geol.Mag., 1916, pp. 7–17), I mentioned incidentally that it extends from those Alps, viz. from the Montgioie range east into Liguria as far as the Savona Hills. As in the former so also in the latter region, that formation is composed of essentially gneissic schists known as apenninites or besimaudites belonging to the Lower Permian or Permo-Carboniferous, and of sericitic schists, quartzites, and clastic rocks or ‘anagenites’ which constitute the Upper Permian or Verrucano proper, forming a transition to the Lower Trias. The geological limit of the Permian in the Savona Hills coincides more or less with the geographical line of division of the Alps and Apennines at the Colle or saddle—also called Bocchetta—d'Altare; but another geological line of division exists still further east, at the junction of the Triassic and Eocene formations in the Chiaravagna Valley near Sestri Ponente, immediately west of Genoa. In reality the geological division is marked, not by either of those lines but by a contact-zone between them. This contact-zone occupies the whole of Western Liguria and comprises two distinct and dissimilar parts: one, the Triassic calc-schists and pietre verdi area or Voltri group, which extends for about 25 kilometres along the Riviera littoral west of Genoa from Sestri Ponente to Voltri, Varazze, and Celle Ligure, and the other or Savona group, which skirts the littoral for about 15 kilometres from Celle to Savona and Zinola, and is composed for the greater part of a crystalline massif of granitic, gneissic, and amphibolic rocks.

IV.—The Altered Clastic Rocks of the Southern Highlands, their Structure and Succession

I Have not been able to trace the exact relationships of this zone, with its bands of limestone, to those already given, as underlying it. Certain grits and quartzites occurring on the top of the Ben Lawers ridge may possibly belong to it, and it is certain that many of the quartzites and grits of Glenlyon, Blair Athole, and Ben Y Ghloe belong to a horizon higher than the upper argillaceous series just described. Leaving the matter thus in the meantime, until further research shall explain their true relationship, it is certain that an arenaceous band of grits and quartzites succeeds the sericite and graphite schists of the upper argillaceous zone, thus completing the whole cycle of deposits, though no evidence has yet been forthcoming to show what or where the top of this series may be.