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Actinolite, hornblende and biotite coexisting in greenschist mafic metagreywackes have been analysed with the electron microprobe to obtain information on their chemical relationship during metamorphism. As in some other parts of the world, the two calcic amphiboles coexist in the greenschist facies because of a miscibility gap between them which is observed under conditions of low-pressure regional metamorphism; it is thought that the two amphiboles are in equilibrium, or at least that the actinolite participated in hornblendeforming reactions. Contact metamorphism by granitic intrusives of these metagreywackes has converted them to hornblende hornfelses with the assemblage hornblende, andesine, quartz, biotite±cummingtonite; the hornblendes of the hornfelses are found to have compositions between actinolite and hornblende of the greenschists, and frequently show fine exsolution lamellae of cummingtonite as a result of oversaturation in this component. The distribution of Fe-Mg between hornblende and biotite changes from the greenschist to the hornblende hornfels facies, and the KD is probably dependent on AlVI in the hornblende.

Oxygen and hydrogen isotopic compositions were measured on 12 serpentine and 2 actinolite samples from the Troodos ophiolite complex, Cyprus. The single analyzed antigorite(δD= −60, δ18O= 7.1) is isotopically similar to all previously analyzed antigorites from ultramafic bodies. However, although their D/H ratios are relatively “normal”(δD= −70to−92), the δ18O values of most of the Troodos lizardite-chrysotile serpentines (+12.6 to +14.1) are much higher than the 2.0–9.3‰ range typically found in such serpentines. Such high δ18O values have previously been found only in the serpentine-like mineraloids termed “deweylites”, which apparently formed at Earth-surface temperatures, and in a single sample from Vourinos, Greece that is in contact with high-18O limestone. The Troodos lizardite-chrysotile samplescannot have formed by reaction with heated ocean waters, but instead must have formed in contact with large amounts of some type of meteoric, metamorphic, or formation water, either (1) at very low temperatures in a near-surface environment, or (2) at about 100°C from waters that were abnormally enriched in18O(δ18O ≈ +4 to +8). The latter possibility seems most plausible inasmuch as extensive evaporites were deposited throughout the Mediterranean Sea during the late Miocene, and this would have been accompanied by strong18O enrichments of the local meteoric waters. Heated ocean waters, however, probably were responsible for the formation of the actinolitic amphiboles(δ18O= 4.6 to 5.5; δD= −51to−46) from the gabbro and ultramafic zones in the Troodos complex. The amphiboles must have formed at considerably higher temperatures and at an earlier stage than the lizardite-chrysotile serpentinization.

A new graphic method for calciferous and subcalciferous amphiboles is proposed on the basis of the electric neutrality of a crystal. The nine basic types of the cation-substitutions are discussed with the diagram which is constructed by the three axes of (A1++X1+), (Y3++Z3+)/4 and (X2++Y2++Z4+)/15. The solid solution of calciferous and subcalciferous amphiboles can be derived from the triply composite substitution constructed by 2 (X2+, Y2+)_??_(A1+, X1+)+Y3+, Z4+_??_(A1+, X1+)+Z3+ and (X2+, Y2+)+Z4+_??_Y3++Z3+, mainly. In the new graphic representation, there exist compositional gaps in the actinolitehornblende solid solution and in the subcalciferous amphibole solid solution under metamorphic conditions. When X2++Y+Z=15, calciferous amphiboles with Y3++Z3+=1.34-1.50 do not appear in nature. The compositional gap does not exist between calcic and subcalcic hornblende solid solution, but the gap between calcic and subcalcic actinolite solid solution may exist. On the basis of the consideration by the new graphic method, if the host rock compositions are in isochemical, metamorphic amphiboles change the variation trend of their compositional range according to the progressive mineral facies changes.

SUMMARY. The Bratteggdalen granogabbro, a relict mass in the Caledonian amphibolites of Vestspitsbergen, shows a series of amphibole development reflecting its thermal history. A brown Ti-rich hornblende occurs as a late magmatic mantling of pyroxene. Low-grade metamorphism (greenschist facies) was accompanied by the development of actinolite from pyroxene; subsequent amphibolite facies metamorphism saw the development of an alkali-rich, blue-green hornblende. The chemical changes in the amphiboles are a succinct illustration of those found in progressive regional metamorphism. THE Pre-Cambrian volcanic and subvolcanic Eimfjellet formation, part of the Hecla Hock succession in the Hornsund area of Vestspitsbergen, was metamorphosed during the Caledonian Orogeny. The metamorphosed granogabbro of Bratteggdalen, an interesting mineralogical and textural relict within the amphibolites, was previously described by Smulikowski (I965). An ophitic texture in the rock, with oligoclase-andesine plagioclase, amphiboles, and biotite idiomorphic against the typically xenomorphic quartz and chequer-albite appears to be inherited from the original primary igneous texture. Microscopic study of relicts, reaction-rims, and other mineral interrelations has enabled the reconstruction of the metamorphic history of the rock; in fig. I this is shown in diagrammatic form. Pyroxene relicts occur in two ways: as small, generally well-preserved grains enclosed within greenish-brown hornblende (~ olive, [3 greenish-brown, 9' dirty green, low birefringence, v: [oo i ] I I o; called here brown hornblende), or as irregular pyroxene grains being replaced by aggregates of actinolite (colourless to pale green, high birefringence, ~: [ooI] I5~ Blue hornblende (blue to bluish-green, medium birefringence, ~,:[ooI] 15 ~ forms rims on both the brown hornblende and the actinolite. As shown in fig. 1 the brown hornblende is considered to be a primary, magmatic mineral, while the actinolite belongs to an early stage of metamorphism, and the blue hornblende to the main, somewhat later stage. Primary biotite is developed in form of large homogeneous, dark reddish-brown plates (2V z 12 ~ with sagenite net and sphene rims. Some of the plates display lighter colouration near the margins. Small flakes of lighter biotite also occur, most of them associated with bigger biotite plates. However, it cannot be excluded that some smallflake biotite is the result of biotitization of amphiboles.

Electron micrographs and selected area electron diffraction patterns of all six recognized asbestos minerals (chrysotile, amosite, anthopyllite, crocidolite, tremolite and actinolite) are shown. These were all produced with the same parameters on one electron microscope and using the same sample preparative techniques. X-ray crystallographic and chemical data for the six asbestos minerals from various sources in the literature are also given. It is hoped that all the data may prove useful as a comparison to other researchers involved in identifying submicroscopic asbestos fibres.

The Miyamori ultrabasic mass in Iwate Prefecture is metamorphosed, at its western side, by intrusion of granodioritic rocks., The zone of metamorphism (maximum width about 4km) developed in the serpentine and serpentinized dunite may be divided, geologically as well as petrographically, into the following subzones from west to east; 1st zone: enstatite-cummingtonite-spinel zone and spinel-hornblende zone., 2st zone: tremolite-(actinolite)-anthophylite-chlorite zone., 3rd zone: tremolite-antigorite zone., 4th zone: antigorite zone., The rocks which characterize the 1st to 3rd subzones were probably formed simultaneously according to the differece in physice-chemical conditions depending on their distances from the granodiorite mass., This was immediately followed by retrogressive metamorphism during which the rocks of each of the three subzones were successively replased by minerels characteristic of the subzone directly on its east (lower grade one) and finally by antigorite., This mineral first appears as veins through the rocks of the 1st to 3rd subzones, but is finally collected togerther to form large masses which are designated as the 4th zone., There is no evidence to show that the rocks of these subzones were formed progressively from lower grade one.

Glaucophanitic regional metamorphic terrain in the eastern part of the Kanto Mountains can be divided into the following two parts; pale coloured actinolite zone and greenish blue actinolite zone. Though the greenish blue actinolite is only found in the highest grade part of the terrain; “spotted schist zone”, pale coloured actinolites are chiefly distributed in the non-spotted schists, phyllites or weakly metamorphosed Paleozoic formation. These two kinds of actinolite can be easily discriminated to each other by their optical properties (Figure 1). Chemical, optical and X-ray data of these two actinolites are also given in this paper.

A diverse suite of rocks has been sampled from ocean basin escarpments in the North Atlantic and the Caribbean: fresh and weathered basalts, metabasalts (zeolite and greenschist facies), gabbros, metagabbros (greenschist and amphiolite facies), serpentinized peridotites, and actinolite rocks. One hundred and three representative specimens were chosen from this diverse suite of rocks, and the natural remanent magnetization (NRM) intensity and susceptibility for each specimen were measured in the laboratory. Unaltered and unweathered basalts had the highest measured NRM intensities (geometric mean, 10.69 × 10−3 emu/cm3). The weathered basalts, metamorphosed basalts, gabbros, metagabbros, and actinolite rocks all had NRM intensities much lower than those of the fresh basalts (geometric means, 0.11–1.60 × 10−3 emu/cm3). The serpentinized peridotites, however, are strongly magnetic, the geometric mean intensity being 7.86 × 10−3 emu/cm3. The serpentinized peridotites also had high susceptibilities (geometric mean, 3.298 × 10−3 emu/cm3), whereas all the other rock types had low susceptibilities (geometric means, 0.047–0.480 × 10−3 emu/cm3). The measured magnetic parameters for the several rock types are compared with published models of the oceanic crust based on measurements of the magnetic field over the oceans. These geophysical models suggest that the upper part of the oceanic crust is a strongly magnetized layer of basalt and the majority of the crust below is weakly magnetized. The fresh basalts measured in this study have intensities and susceptibilities compatible with those in the geophysical models. The metabasalts, gabbros, metagabbros, and actinolite rocks have weak intensities and therefore could be, on the basis solely of their magnetic character, volumetrically important components of the weakly magnetized part of the oceanic crust. Serpentinized peridotite has intensities and susceptibilities too high to be an important component of the oceanic crust.

Microcline phenocrysts in a monzonite gneiss, and hornblende and actinolite crystals in a series of amphibole schists, form strong lineations of elongate crystals perpendicular to axes of small folds. The crystallographic c axes of the amphibole and microcline crystals form strong maxima parallel to the A fabric axis of the rocks; the b axes of microcline form a strong maxima parallel to the C fabric axes and the b axes of the amphiboles form maxima parallel to the B fabric axis. If the folds and foliation planes are products of inelastic shear strain, these orientations correspond to the maximum elastic strain energies per unit stress for these crystals and agree with the prediction of preferred orientation by MacDonald (1960) . A predicted effect of positive and negative shear strain was not observed in these crystals. Preferred mineral orientations and recrystallization may be interpreted by use of elastic strain theory to give additional insight into the problems of rock deformation.

The Frisco mine is near the city of Parral, in southern Chihuahua, Mexico. It is worked by San Francisco Mines of Mexico, Ltd., and produces daily 1,500 metric tons of ore with a grade of 0.5 gram (0.015 ounce) of gold per metric ton, 150 grams (5 ounces) of silver, 5 percent of lead, 8 percent of zinc, and 0.6 percent of copper.The ore comes from about 32 fissure veins, which occupy faults of small displacement in a calcareous shale formation of probable Cretaceous age. The veins are arranged in a complex pattern whose description and explanation is the principal aim of the paper. From their attitudes and physical characteristics, the veins can be grouped into four sets of mutually parallel veins, each set parallel to a different imaginary plane. These four sets make up two systems of veins, each composed of two sets of conjugate shears. The two systems are believed to have resulted from two stages of deformation--distinct in orientation of stress but not necessarily separated by any large amount of time.The vein matter was probably introduced by a hydrothermal fluid during the second stage of deformation, when the fractures of the second system were formed and those of the first system were reopened. The walls and breccia fragments within the veins were silicified and silicated, with the formation of quartz, diopside, actinolite, epidote, and ilvaite. During the same general epoch, but somewhat later at any one place, the sulfide minerals sphalerite, galena, chalcopyrite, pyrite, and arsenopyrite were deposited--in large part as replacements of altered shale fragments. In most places, the last minerals deposited were quartz, fluorite, and calcite. The mineralogy is like that of skarn deposits and like that of the veins at nearby Santa Barbara, which Lindgren included in his hypothermal class.

In a previous paper the chemical composition and the mineralogical properties of the Lake Superior grunerite were dealt with (American Journal of Science, Vol. XIV [1927], pp. 150 ff.). The occurrence and origin of this mineral is the subject of the present publication. In the Marquette district sideritic cherts were metamorphosed into grunerite rocks by dioritic intrusives. They contain, in addition to grunerite, magnetite, garnet, and either quartz or calcite. At the contact of uralite diabase in the eastern portion of the area no grunerite rocks, but mica-magnetite schists, were formed. In the Mesabi range the original rock consisted of chert and the hydro-ferrous silicate greenalite. In the eastern portion of the range, at the gabbro contact, these sediments developed into rocks containing grunerite, fayalite, and magnetite. Ferruginous cherts west of the Mesaba station do not contain any amphibole. The substance regarded as grunerite, cummingtonite, or actinolite is optically micalike, and it is supp...

On the eastern side of the Mount Lofty Ranges of South Australia, impure marbles and calc-silicate rocks characterized by assemblages rich in scapolite and pyroxene have been formed on a regional scale by high grade metamorphism of limestones and calcareous shales. It is suggested that this metamorphism is essentially iso-chemical and that even chlorine in the scapolite (Me 55[60) could have been derived from the original sediments.A secondary paragenesis consisting of epidote, actinolite, and calcite at Tungkillo and epidote, actinolite, calcite, and garnet at Milendella, is the result of late metasomatism and reaction associated with the formation of granites, migmatites, and veined gneisses. At Tungkillo, outside the sphere of granite activity, the secondary, retrograde assemblage is due to limited metasomatism chiefly involving the introduction of water, whereas at Milendella where marbles and calc-silicate rocks are intimately associated with granitic rocks, reaction and metasomatism giving rise to the secondary minerals has been more intense. Here garnet of the andradite-grossularite series has developed.

Metabasites of the Lesser Himalaya along the Modi Khola valley in central Nepal are the supracrustal dikes and sills of basic igneous rocks emplaced in the clastic sediments and later metamorphosed together with the host rocks. They contain almost a constant metamorphic mineral assemblage of Ca-amphiboles+plagioclase+biotite+quartz±epidote±chlorite+(Fe-Ti oxides). Amphiboles occur in the form of porphyroblast and recrystallized matrix. The porphyroblasts are zoned with actinolitic cores and hornblende rims. The recrystallized matrix ranges in composition from actinolite in chlorite zone to hornblende in biotite and garnet zones. The cores of porphyroblasts are pre-kinematic and were probably formed prior to the Tertiary Himalayan orogeny. The rims of porphyroblasts and matrix amphiboles are syn-kynematic and were formed during the Upper Main Central Thrust activity in the Tertiary. The systematic changes in amphibole compositions as well as textural characteristics of metabasites are in good agreement with the classical concept of increasing metamorphic grade and intensity of deformation structurally upwards towards the Upper Main Central Thrust in the Lesser Himalaya. doi: 10.3126/bdg.v11i0.1428 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 11, 2008, pp. 5-12

At intervals during the last 20 years I have studied the well-known garnet-actinolite schists which are exposed on the southern slope of the St. Gothard Pass from perhaps 500 to about 1600 feet above the mouth of the tunnel. They extend westward along the flank of the Val Bedretto to beyond All9acqua, with one slight interruption near this spot, and can be followed eastward to the vicinity of the Pizzo Columbe, that is, for a total distance of from 16 to 17 miles, the breadth of the outcrop, which is locally interrupted by elongated masses of more normal hornblendic schist, being at its maximum about 1¼ mile. They are intersected by the Val Tremola and the Val Canaria with its tributary glens, and are exposed on the right bank of the Val Piora. Here the lower part of the mass must be about 6700 feet above sea-level, that is to say, the outcrop rises at least 2500 feet in about 5 miles. My later visits threw some light on the origin of these rocks; but I felt that more work in the field was necessary before I could come to any conclusion. Therefore I determined to return to the district and examine more particularly the outcrops near the Val Piora, of which hitherto I had seen little, having spent my time on another group of schists, which apparently overlie them. This intention was carried out in July 1897, and I had the good fortune to be accompanied by my friend

Introduction. —Ever since the publication of Mr. Harris Teall's description of the Scourie dyke, and its passage from a true basic igneous rock into a highly foliated schist by the ordinary processes of regional metamorphism, petrologists have turned their researches in that direction for a solution as to the origin of the hitherto little understood group of basic schistose rocks, such as hornblende schist, actinolite schist, or schists strong in some pyroxenic mineral. Having lately paid some attention to these schists as they are developed in the Southern Grampians of Scotland, and more especially in that remarkable sill seen underlying the Loch Tay limestone, I thought I could not do better than bring before the members of this Society the observations I had already been enabled to make, and which I hope, in the course of next summer, to be able to considerably amplify. Lately, while arranging the rock-specimens in the Museum of the Perthshire Society of Natural Science, I had occasion to pass through my hands a large series of these hornblende schists, from many different horizons in the Highland rocks. The strong external resemblance of these metamorphosed basic rocks to one another undoubtedly pointed to a community of origin; and while they mostly occur as sills intruded into different horizons of the Highland rocks, the probability is that the source from which they have all been derived is the same, and the sill underlying the Loch Tay limestone may therefore be taken as typical of the whole series. Originally This 250-word extract was created in the absence of an abstract

Reaction zone is observed between amphibolite and gneiss. It is about 16cm in width. Chemical compositions of plagioclases and biotites vary gradually from amphibolite to gneiss. The rate process of the formation of the reaction zone is not the diffusional process of K+, Ca++ and Mg++. Basic reaction is the formation of biotite in amphibolite, and K+, Mg++ and Al+++ of biotite are mainly derived from K-feldspar, actinolite and anorthite respectively.

Based on detailed analyses of parageneses of greenstone and greenschist containing actinolite, it is concluded that the defining reactions of actinolite isograds are different in different metamorphic terranes, each representing particular physical conditions. In one district, a decomposition reaction of pumpellyite into epidote-actinolite is important in defining the actinolite isograd. In another area, a reaction of chlorite, calcite and quartz which also produces epidote-actinolite is essential in marking the actinolite isograd. In several other areas prehnite is decomposed into epidote-actinolite at the actinolite isograds. Replacement of relic augite by actinolite is a separate reaction which does not define an actinolite isograd.

SummaryIn the south-eastern part of the Khetri copper belt, actinolite occurs in association with alteration assemblages resulting from the Fe-Mg metasomatism that accompanied sulphide mineralization, and more commonly with albite-bearing rocks formed by albitization of quartzites and schists near granitic rocks. Within the latter occur many coarse, massive, and unoriented aggregates of actinolite crystals, individuals being commonly more than 10 cm long. Locally fluorite-bearing veins oecur within granitic and albite-quartz rocks. The actinolite is pleochroic from pale pink to green; γ: [001] = 26°; γ = 1·642 ± 0·003; 2Vα = 80°. The composition of the analysed actinolite closely compares with those published in the literature excepting in (OH), which is low. The mineral assemblages, formed by metasomatic replacement of pre-existing rocks, are equivalent to those of albite-epidote-amphibolite facies. The metasomatic fluid was apparently rich in Ca, F (indicated by fluorite), and oxygen (indicated by magnetite, ilmenite, and hematite).

Rare earth element (REE) abundances are reported for ten whole rock and eight mineral samples from the Preacher Creek ultramafic intrusion of southeastern Wyoming. Chondrite-normalized distribution patterns for the whole rocks exhibit a broad maximum between Sm and Gd and reflect the REE pattern of clinopyroxene, the major REE-bearing phase. Alteration of the primary mineral assemblages to actinolite and chlorite, which is generally minor, does not appear to have significantly affected the REE distributions. Absolute abundances of the REE in the rocks and constituent minerals increase as a function of differentiation, and relative abundances suggest an accompanying light REE enrichment. Trapped-liquid phases, which may be relatively enriched in REE, possibly account for some or all of the observed REE trends. The REE data, interpreted in terms of crystal-melt fractionation, suggest derivation of the intrusion by crystallization from a gabbroic magma having a REE distribution pattern similar to the parent magma of the Skaergaard stratiform complex. The results of this study are in accord with and complement a previous proposal that the Preacher Creek body formed in a manner analogous to major stratiform intrusions.

Actinolite, anthophyllite, amosite, chrysotile and tremolite varieties of asbestos from Indian mines were analysed for their chemical composition. Significant differences were found as compared with the composition of corresponding foreign varieties. The significance of this in relation to their possible toxic effects and the need for toxicological work with Indian varieties are discussed.

The Preacher Creek ultramafic body is a small, lenticular-shaped intrusion of peridotite exposed in an ancient (2400–2500 m.y.), regionally metamorphosed terrane in southeastern Wyoming, U.S.A. The central core of the body consists of clinopyroxene-olivine peridotite and is surrounded by a marginal rim of peridotite in which orthopyroxene and plagioclase also occur as primary minerals. Alteration of primary minerals is relatively minor. However, at the contact with the country rock progressive alteration of the peridotite to actinolite and chlorite is locally severe. Chemical study of the effect of this alteration indicates that no more than minor changes from the primary composition of the peridotite have occurred. Petrographic studies reveal accumulative textures characteristic of stratiform complexes. Cryptic layering in the body is indicated by partial chemical analyses of the two major primary minerals, olivine and clinopyroxene.

The paper discusses the field relations, petrography, and chemical compositions of a group of igneous rocks characteristic of geosynclinal belts: namely, greenstone, ultramafics, and gabbro, which occurs in the northeastern extremity of the Appalachians in the vicinity of Baie Verte, Newfoundland. The prevalent mineral assemblages of the greenstone are: 1. Actinolite-(chlorite)-albite-epidote-quartz 2. Chlorite-(actinolite)-albite-epidote-quartz 3. Chlorite-calcite-albite-epidote-quartz Adjacent to a large quartz-diorite intrusive, the greenstone has been metamorphosed to the amphibolite facies characterized by hornblende, oligoclase, and biotite. Concentric structures in chert lenses associated with the greenstone suggest colloidal origin. The molecular ratio of Mg /Fe of the serpentinized harzburgite is within the range typical of the primary ultramafic magma series of Hess. The alterations and problems of correlation of the ultramafics are briefly considered. Discussion of pseudostratified metagabbro, ...

A glacial boulder found at the village of Norsjovallen, 80 km WNW of the town of Skelleftea in Vasterbotten County, contains orbicules characterized by plagioclase (oligoclase) cores, which are surrounded by shells containing amphibole (actinolite), plagioclase and biotite. The grain size decreases outwards, accompanied by a greater degree of preferred orientation in the minerals. Amphibole, plagioclase and biotite are arranged so that their c-axes are aligned towards the centre of the orbicules. The matrix is much more granitic than the orbicules. In the matrix, microcline, plagioclase, quartz and biotite are the major phases. A deeply etched boulder of orbiculite from Smaland's Anneberg, 10 km NE of the town of Nassjo, also shows orbicules with plagioclase (oligoclase) cores, although in this case the cores have been affected by secondary microcline mineralization. Outer shells show contrasting proportions between plagioclase, hornblende and biotite. The outermost shells are characterized by an...

This investigation was undertaken to find the typical conditions for the formation of low-grade metamorphic rocks in which prehnite and/or pumpellyite (± actinolite, chlorite, epidote, and quartz) occur as characteristic minerals. In the p, t diagram the slope of the equilibrium curve prehnite + chlorite + H2O=pumpellyite + actinolite + quartz is negative; the slope of the equilibrium curve pumpellyite + chlorite + quartz=epidote + actinolite + H2O is positive. The point of intersection of the two equilibrium curves is an invariant point. The relative positions of the six equilibrium curves surrounding the invariant point were found by applying Schreinemakers's analysis. Experimental results show that the paragenesis prehnite-pumpellyite-chlorite-quartz is stable at 2 kb up to 345±20 °C, and at 7 Kb up to 260±20 °C. The paragenesis actinolitechlorite-pumpellyite-quartz occurs only at pressures greater than 2.5±1 kb. It is stable at 7 kb in the strongly pressure-dependent temperature range 260±20 °C to 370±20 °C. The paragenesis actinolite-chlorite-epidote-quartz, typical of the greenschist facies, may occur at pressures of 2–3 kb at temperatures of at least 350±20 °C. This temperature limit is only slightly changed with increasing pressure.

The Sanbagawa metamorphic terrain of the Yawatahama district in western Shikoku is divided into three zones (I, II and II') on the basis of systematic variation of rock-forming minerals.Zone I: This comprises the area of Paleozoic and also Mesozoic formations. Zone I is characterized by the occurrence of prehnite and pumpellyite. But actinolite is rarely observed. This zone is corresponds to the prehnite-pumpellyite metagreywacke facies.Zone II: Prehnite and pumpellyite are not stable. The common minerals of basic rocks are glaucophane, actinolite, epidote, chlorite, white mica, albite and quartz. The physical conditions of this zone are intermediate between those of the glaucophane schist and greenschist facies.Zone II': The hornblende-oligoclase assemblage is characteristic of zone II'. Garnet and/or clinopyroxene are often associated with hornblende. This zone is restricted the area where the Kawamai tectonic mass is exposed. Probably zone II' is correlated to the epidote amphibolite facies. The meatamorphism of zones I, II and II' is progressive one, and then the metamorphic grade increases northwards. The retrogressive metamorphism, however, is observed in zone II'. In many basic rocks of zone II' the primary metamorphic constitures are replaced by chlorite, actinolite, glaucophane and epidote. The retrogressive metamorphism would have been caused by the change of the physical conditions owing to the upheaval movement of the Kawamai mass. It seems that the Sanbagawa metamorphism continued in the Lower Cretaceous age in the Yawatahama district.

The Precambrian iron formation near Atlantic City, Wyoming, lies within a large southwestward-plunging syncline of metasedimentary and metavolcanic rocks. The ore is at least 2,400 million years old, and may have been deposited more than 2,680 million years ago, in which case it is roughly equivalent in age to the older iron formation deposits of the Canadian Shield. The geology of the Atlantic City deposit is similar to that of Precambrian iron formations of the Shield. Magnetite is the chief ore mineral at Atlantic City, and the gangue consists of quartz, actinolite and actinolitic hornblende.Chemical analyses of drill core material average in weight percent: total iron, 33.45; Fe 2 O 3 , 30.75; FeO, 15.49; Al 2 O 3 , 3.85; CaO, 1.31; MgO, 2.80; MnO, 0.09; Na 2 O, 1.22; K 2 O, 0.36; and SiO 2 , 44.13. The values are similar to published averages for Precambrian iron formations from the Canadian Shield.Comparisons of Ca/Mg, Ca/Na, Ca/K, Mg/Na, Mg/K and Na/K ratios from the Atlantic City deposit with various present-day geologic environments and with average crustal percentages has provided chemical information which may help in establishing a mode of origin for the Atlantic City iron formation. Analyses of fumarolic gases, of certain acidic volcanic waters, and of Dead Sea water samples are shown to be statistically similar to analyses of the Atlantic City iron formation. Close similarities in terms of these ratios with average crustal percentages also add significantly to an understanding of the possible genesis of the deposit.It is suggested that the iron formation at Atlantic City, Wyoming, may have been derived through subaerial weathering of moderately low-lying crustal rocks in an atmosphere low in oxygen, and that the leachate was then carried to and concentrated in a closed basin, where it may have received additional contributions from volcanic emanations. The question of whether the basin of deposition was marine or continental remains unanswered.

Deposits of monazite and Nb-bearing rutile in a belt more than 10 mi. long in northern Lemhi County, Idaho, are distinguished by their notable concentrations of such elements as Th, Ti, Nb, Ba, Ca, Fe, P, S, and the rare earths, and by their abundance of carbonates, chiefly calcite. These deposits occur as structurally controlled replacements of crystalline limestones, amphibolites, and porphyroblastic gneisses which form part of the complex metamorphic border zone of the Idaho batholith. Most of the deposits, which are small and tabular, show a sporadic and irregular distribution of minerals, the most abundant of which are actinolite, allanite, apatite, monazite, calcite, barite, ilmenorutile (Nb-bearing rutile), ilmenite, and magnetite. Other minerals, some of them sparse, include biotite, phlogopite, garnet, epidote, glaucophane, ancylite, bastnaesite, sphene, rutile, chlorite, pyrite, pyrrhotite, chalcopyrite, and quartz. Silicates, except sphene, were deposited first and were followed successively by phosphates, carbonates, sulfates, oxides, and sulfides. Most of the Th entered the allanite instead of the somewhat later monazite. The deposits possess all the compositional characteristics of the carbonatites, but differ from the type carbonatites in their seeming lack of association with alkalic igneous rocks. Although the deposits were regarded by others as replacements of marble beds and as products of metamorphic differentiation, the unique association and concentration of elements so characteristic of the carbonatites, coupled with the paragenetic development, suggests that they, like the carbonatites, are of magmatic rather than of metamorphic origin.

Deposits of fibrous amphiboles which differ from previously known occurrances in the Central Caucasus in being of distinctive compositions and geologic positions. The deposit is in the top of an anticline of Devonian sediment volcanic strata. It is related to hydrothermal veins in metasomatized gabbroids. Small hypabyssal intrusions of granite-porphyry are structurally related to the asbestos veins. The petrography of the deposit and the related rocks is described in detail, as is the structure. Four generations of mineralization are recognized. Alteration shows a pronounced zonal distribution. The outer area of the zoning is well defined because of regional metamorphism. The asbestos is the result of interaction between the hydrothermal fluids and the country rock. Structurally a combination of folding with NE trending shears and NW trending tension fractures localize the ore deposits. The fibrosity of the actinolite is related to wild movement during tectonism. M. A. Klugman

The rocks are volcaniclastics, flows, and sills of a calcalkaline suite of early Paleozoic and possibly late Precambrian age, ranging from rhyolite to basalt. Glass was originally a major constituent of the units of felsic to intermediate composition. Low-rank metamorphism caused mineral assemblages that are apparently in the quartz-albite-muscovite-biotite chlorite subfacies of the Abukuma-type greenschist facies. Quartz and albite are nearly ubiquitous, and K-feldspar is near-maximum microcline. Chlorite, actinolite, and epidote are major constituents of the intermediate to mafic units. Devitrified felsic metatuffs interbedded with argillite are similar chemically to quartz keratophyres, whereas the metarhyolites are only slightly more sodic than normal calc-alkaline rhyolites which suggests that the metatuffs underwent metasomatism after deposition. Semi-quantitative and whole-rock analyses were performed.

A copper deposit about 40 miles southwest of the Coeur d9Alene district, Idaho, shows a marked structural and mineralogical resemblance to the copper deposits of the Ducktown type. It occurs as a replacement along bedding plane fractures and fissures in quartzitic beds of the Belt series and its ore consists chiefly of pyrrhotite, chalcopyrite, and lesser cubanite in a silicate and carbonate gangue. Fracturing repeated several times during mineralization caused deposition in three distinct mineral stages, shown by the partial replacement of one group of minerals by later ones. Minerals deposited during the first stage include the silicates (diopside, tremolite, actinolite, biotite, epidote, tourmaline, microcline, and muscovite), and a little quartz; during the second stage, the carbonate (ferriferous dolomite); and during the third stage, the sulphides (pyrrhotite, chalcopyrite, arsenopyrite, and cubanite), and a little quartz and calcite. Except for its mode of occurrence, the deposit possesses most of the characteristic features of a pyrometasomatic deposit but is, nevertheless, a hypothermal deposit formed probably under exceptionally intense temperature conditions.

The writer surveys the Doshinkubo ore deposits of the Chichibu mine, which belongs to the magnetite deposits of the pyrometasomatic type consisting of pyrite, pyrrhotite, chalcopyrite, and some silicate skarn minerals. At the contact between the quartz-diorite and limestone, the following zones of mineral association were recognized by megascopic and microscopic observations. Zone 1: quartz-diorite, which is composed of quartz, plagioclase (An45 Ab55_??_An55 Ab45), brown hornblende, biotite and blue actinolite. Zone 2: mixed rock zone (width; 20_??_30cm.), which is composed of quartz, plagioclase, brown hornblende, diopside, garnet, chlorite, and calcite. Zone 3: vesuvianite-xanthophyllite zone (width; about 2m), which is composed of vesuvianite, diopside, wollastonite, garnet, and xanthophyllite. Zone 4: garnet-chlorite-epidote zone (width; about 10m.), which is composed of andradite, pistacite, and chlorite. Zone 5: magnetite ore body (width; about 30m.). Zone 6: hedenbergite-ilvite zone (width; about lm.). Zone 7: limestome. The occurrence of the Zones 2 and 3 are closely related, with an intrusive body of the quartz diorite, and those of the Zones 4, 5, and 6 controlled by the formation of the ore body. From the observation mentioned above, the writer suggests that the Zones 2 and 3 were formed by the magmatic “reaction” between the quartz-diorite magma and limestone, but the Zones 4, 5, and 6 may be the products of the mineralization at the later stage.

During my mapping for the Geological Survey in 1930 of the metamorphic rocks of western Unst, numerous small masses were encountered that were composed of a central part of talc followed outwards in order by zones of actinolite, chlorite, and biotite. Whilst revisiting the island in 1933 I was able to examine these associations in detail and to collect abundant material for study. As in many cases the zones are made up of a single mineral and may be a foot or so in thickness, specimens of great beauty are obtainable.

Greenstones derived from basalts, tuffs, and dolerites were dredged at two stations on the eastern slope of the median valley of the Mid-Atlantic Ridge at 22°N latitude. The rocks consist mainly of the typical greenschist assemblage albite, actinolite, chlorite, and epidote. The greenstones reflect increasing metamorphic grade and intensity of shearing with the depth at which they were recovered. Bulk chemical analyses of six greenstones give spilitic compositions characterized by high soda (maximum 5.4%) and low potash (minimum 0.05%) contents. Relics of calcic plagioclase, pseudomorphed olivine phenocrysts, and other textural features indicate derivation from abyssal basalts, which typically have soda around 2.7% and potash around 0.2%. The alkali contents of the greenstones are most likely a result of metasomatism during metamorphism, and do not indicate a primary spilitic magma, or reaction between magma and sea water. The significance of the greenstones in relation to the tectonics and structure of the Mid-Atlantic Ridge is discussed.

From the distribution of metamorphic minerals such as prehnite, chlorite, pumpellyite and actinolite, the Sanbagawa metamorphic terrin in the cental part of Kii Peninsula can be divided into the following three zones representing a progressive mineralogical changes of regional scale:Zone I; An assemblage of prehnite-chlorite-quartz-sodic plagioclase is most characteristic. Actinolite is not stable. Pumpellyite and epidote are commonly found.Zone II; An assemblage of colorless actinolite-epidote (-pumpellyite)-chlorite-sodic plagioclase can be widely found. Prehnite is not stable.Zone III; Both of pumpellyite and prehnite are not stable. Pale bluish green actinolite-epidote-chlorite-sodic plagioclase is most characteristic.Probably, the regional metamorphism in the present district was formed under relatively lower solid pressure conditions than those prevailed in other terrains such as the Kanto Mountains of the same Sanbagawa belt of Japan.

The geology of the Dalradian rocks near Tayvallich is described with a detailed geological map. 78 new chemical analyses of metamorphic rocks, each for 30 elements, are given including intrusive epidiorites, basic pillow lavas, agglomerates, grits, slates, limestones and calcareous slates. Basic volcanic glasses have been locally showered into the sediments. The epidiorites are albite-chlorite-calcite-quartz-sphene (epidote) rocks with actinolite being confined to rocks with mg in excess of 0.44. Metasomatic movement occurred between the margins and centres of the pillow lavas and is also believed to have affected the volcanic glasses. The sedimentary rocks can be distinguished from the epidiorites by a number of chemical characteristics including the high P, Ti and Nb of the epidiorites and their differing trends of variation such as Cr against Niggli mg. The Loch Awe epidiorites are characterised by high Zr and P and are less tholeiitic than epidiorites higher in the Dalradian sequence. They may be shallow intrusions and extrusions of a magma that had undergone substantial intratelluric differentiation.

The Fe formation is located in E.-central Quebec and probably is a regionally metamorphosed equivalent of the Fe-bearing sediments of the Labrador trough. Mineral assemblages are composed of select combinations of the following: quartz, talc, actinolite, Ca-pyroxene, cummingtonite, magnetite, hematite, calcite, and dolomite. Seventy-six spectrographic analyses of minerals give the following average concentration ranges for minor constituents: Al 2 O 3 , MnO, and Na 2 O

A statistical study of about 550 chemical analyses of amphiboles in the hornblende-actinolite series makes it possible to recognize their paragenetic types. The similarities or differences in the above types have been demonstrated by applying Student's t-test and Fischer's test. Typical hornblendes of regional metamorphic rocks are stable within the range 900 to 550°C. Actinolite is characteristic of greenschist facies rocks that formed at temperatures below 550°C. The contents of Al IV and alkalies decrease with decreasing temperatures and the content of Al IV increases with significant increase of pressure. The Al content also increases (due to AlvI) during the transition from clinopyroxene bearing rocks to garnet bearing rocks. Correlations revealed some peculiarities in isomorphism which confirmed the scheme Fe +3 Al IV → MgSi, but failed to confirm the replacement of AM AlIv by MgSi. The role of a glaucophane component has been shown. Curves showing the relationship of Ng and f in the various paragenetic types of amphiboles have been derived using regression equations.

The characteristic mineral assemblage in the lowest grade Dalradian slates and phyllites in quartz + albite + phengite + chlorite + calcite + dolomite + anatase. New analyses of coexisting minerals include muscovite, phengite, chlorite, biotite, and chloritoid. Muscovite-paragonite relationships in chlorite zone rocks are examined. The claim of recent workers that phengites change towards a more muscovitic composition with increase in metamorphic grade is not sustained; the composition range of phengites is believed to increase with rise in pressure and temperature, and the ratio Fe+3 : Fe+2 also increases. Greenschist facies chlorites are usually ripidolites, and those from quartz-albite-phengite-chlorite schists are richer in aluminium than chlorites from actinolite schists, and poorer in aluminium than chlorites from chloritoid schists. Reactions of the type quartz + phengite + chlorite + carbonates = products + CO2 + H2O are suggested, from which biotite, epidote, and actinolite form in the c...

Existing data on the distribution of Mg, Fe and Mn among coexisting metamorphic aotinolites, cummingtonites, Ca-pyroxenes, and orthopyroxenes, are examined in terms of theoretical solution models applicable to binary and ternary solid solutions. Analysis indicates that the data on the distribution of the major components Mg and Fe may be satisfactorily approximated by functions derived on the assumption that actinolite, Ca-pyroxene and orthopyroxene are ideal binary solutions of their Mg and Fe end members and that cummingtonite is of the general type of regular solution, at least with respect to composition. Although the distribution of Mg and Fe may be regarded as governed by the laws of binary solutions, thus disregarding the minor element Mn, the distribution of Mn can be explained only with reference to the ternary system. One predictable ternary effect is the increase in the atomic fraction Mn/(Mg + Fe 2+ + Mn) of cummingtonite and orthopyroxene relative to the same fraction of actinolite and Capyroxene as these minerals increase in Mg relative to Fe content. Certain observed invariant relations of the distribution functions are also interpreted in terms of the multicomponent systems. The data are also examined with a view of detecting the elemental source of certain deviations in the atomic fractions which might be attributed to errors in the chemical analyses or to failure of a given element to attain equilibrium. In addition, the structural-energetic basis for the thermodynamic functions is discussed in terms of the crystal structure of cummingtonite.

"Galena is uncommon in pyrometasomatic deposits but does occur in Precambrian sulfide deposits of this type in central Sweden, in what were almost pure carbonate rocks. Associated minerals are in one deposit andradite and fluorite, but mostly magnesium-fluosilicates with tremolite or actinolite. Two contrasting deposits are associated with the same granite body; one is dominantly galena and other quite minor sulfides, the other is dominantly copper sulfides and galena is essentially absent. Thus, strong fractionation of sulfides must have occurred."

The 40K/40Ar ages of crossite and phengite from blueschists and actinolite and white mica-chlorite concentrates from intercalated greenschists in a metamorphic terrane near Seldovia, Alaska, indicate that metamorphism occurred in Late Triassic or Early Jurassic time. The Seldovia blueschist terrane is associated with cherts, mafic volcanics, and serpentinites, which are interpreted to be parts of a dismembered ophiolite. The terrane may be a segment of a fossil subduction zone.

Igneous rocks in the Carr Fork area include the Bingham stock (granite followed by granite porphyry, gradational granite porphyry, Type A porphyry, and quartz-latite porphyry), the Last Chance stock (same age as granite of Bingham stock), and Carr Fork dikes (three types correlative with porphyries of Bingham stock). A zonal pattern of hornblende-augite alteration products and of magnetite and sulfide minerals is related to distance from the center of the Bingham orebody. The sequence of alteration minerals, inward, is calcite, chlorite, quartz, actinolite, sericite, biotite, and orthoclase, and the sequence of metallic minerals is magnetite, pyrite, chalcopyrite, and bornite.

The King Island Scheelite Mine lies in the contact aureole of a granodiorite stock. Its open cut and numerous drill cores expose a contact metamorphosed and metasomatized series of finely interbedded argillaceous and calcareous sediments, with interleaved flows of picrite‐basalt and basic pyroclastics, the scheelite ore being limited to two limestone horizons. The range and gradation in composition of the original rocks has resulted in an unusual variety of metamorphic rocks, including forsterite‐phlogopite‐spinel‐tremolite hornfels, antho‐phyllite‐cordierite hornfels, biotite hornfels, actinolite hornfels, a variety of calc‐flinta, and marbles. The original sedimentation gave rise to a rapid alternation of limestone and shale, many times repeated, and during metamorphism these rocks reacted with each other to produce narrow bands of calc‐flinta.Subsequent pyrometasomatism selectively converted the greater part of the marble beds to scheelite‐bearing andradite skarn, leaving the various hornfels and calc‐flinta very little affected. The replacement of the marble was a volume for volume process, and the conversion of 1,000,000 tons of marble to average grade ore involved the introduction of about 350,000 tons of SiO2, 250,000 tons of Fe2O3, 55,000 tons A12O3, 30,000 tons of H2O and 82,500 tons of CaO.The temperature of the contact metamorphism attained over 500° C., and the rocks cooled to about 400° C. before the pyrometasomatism occurred. The rocks giving rise to the various hornfels underwent varying degrees of contraction during metamorphism, whereas the limestones probably expanded during metamorphism, and became more permeable to solutions.

Reaction zones are observed between amphibolites and quartzo-feldspathic veins. They are formed under upper amphibolite facies. Typical reaction zone is as follow: Actinolite+anorthite+quartz/ Biotite+actinolite+plagioclase+quartz/ Biotite+plagioclase+quartz// Biotite+plagioclase+quartz/ Biotite±cordierite+oligoclase+quartz±orthoclase. The boundary of the original rocks is represented by the abrupt change of the amount of ferro-magnesian minerals. An contents of plagioclases decrease from amphibolite to quartzo-feldspathic vein. Changes of mineral assemblages and chemical compositions of plagioclases in the reaction zone demonstrate that there are chemical potential gradients of K2O, CaO and Al2O3. μK2O is highest and μCaO is lowest at the core of the vein. The scale of reaction zone is referred to the initial amount of Kfeldspar in the quartzo-feldspathic vein, and the rate of the fomation of the reaction zone is controled by the rate of decomposition of K-feldspar. Main components transferred during the reaction are CaO and K2O. Migrations of other components are very small in amount.

Detailed chemical, optical and X-ray study of the green accicular amphibole occurring at the contact of the ultrabasic rocks with the granite gneiss is presented. It is shown that the mineral is a magnesium rich actinolite. The mode of occurrence and the chemistry of the mineral suggest that it has formed in the ultrabasic rock through a process of metasomatism deriving the required silica, alumina and lime for its formation from the bordering granite gneiss.