Black Schist Research Articles

Base-metal-rich metamorphosed black shales associated with Proterozoic ophiolites in the Kainuu schist belt, Finland: a genetic link with the Outokumpu rock assemblage

Metamorphosed black shale is an essential component of the Early Proterozoic Outokumpu rock assemblage, together with serpentinite, calc-silicate rock and quartz rock. This rock assemblage, hosting the major Cu-Co-Zn deposits of Outokumpu and considered ophiolitic in origin, has also been encountered to the northwest in the Kainuu schist belt. The rift basin encompassing the two areas was intruded by ophiolite complexes 1.96–1.97 billion years ago. Remnants of ultramafites are met as serpentinite and talc-carbonate rock lenses bounded by faults along the western margin of the Kainuu schist belt. The black schist formations range in thickness from tens of metres to 400 m. Metal-rich layers occur close to the serpentinite bodies. The most extensive formations of metal-rich black schist (300 Mt, 0.26% Ni, 0.14% Cu, 0.53% Zn) have been encountered at Talvivaara. The lithological, mineralogical and geochemical results indicate a genetic link between the Jormua, Talvivaara, Alanen and Pappilanmaki prospects in the Kainuu schist belt and the Outokumpu rock assemblage.

Hydrothermal syntheses of graphite from bituminous coal at 0.5-5 kbar water vapor pressure and 300-600.DEG.C.

Hydrothermal experiments were carried out to synthesize graphite from bituminous coal at water vapor pressure of 0.5-5 kbar using 1% Li2CO3 or 2% Ni metal as a catalyst. Oxygen fugacities were controlled by hematite+magnetite (HM), nickel+nickel oxide (NNO) or quartz+ fayalite +magnetite (QFM) buffers during six runs at 1 kbar. Graphite crystallized from bituminous coal at about 375°C, 0.5 kbar; 405°C, 1 kbar; 390°C, 2 kbar and 320°C, 5 kbar under uncontrolled fo2 conditions. The transition boudary from bituminous coal to graphite has a positive inclination below 1 kbar and a negative inclination over 1 kbar under uncontrolled fo2 conditions. The negative inclination of the transition boundary was probably due to the experiments that the oxygen fugacity was incompletely buffered by the escape of hydrogen gas from the system through the Ag-Pd capsule-wall. Under the foe controlled conditions by NNO buffers, graphite crystallized between 400°C and 420°C at 1 kbar. When fo2 were controlled by NNO or QFM, the crystallinity of graphite increased abruptly to reach a fully-ordered state at 420°C. The experimental results were compared with graphitization of carbonaceous material in black schists from some metamorphic districts, and also with oxygen isotope geothermometry. In natural systems, graphitization depends on metamorphic temperature and oxygen fugacity, but not on metamorphic pressure to a great extent.

Las unidades de la Zona Bética en la región de Aguilas-Mazarrón (prov. de Murcia)

Three geographic domains are defined in the region: Northern, Central and Southern, separated by vertical fractures trending originally ENE-WSW. Different sets of tectonic units outcrop in each of them. In the Northern Domain over the materials of the Mulhacen Nappe, three alpujarrides units have been distinguished; they are composed of a metapelitic sequence and a carbonate formation which are judged to be Pennotriassic and Triassic, respectively, in age. relative autochthon of the units appearing in the Central Domain is constituted by a tick serie of black schists and quartzites defined here as a new unit of the Veleta Group which has been named The Lomo de Bas This unit is overridden by an alpujarride unit of similar characteristics to the alpujarrides units appearing in the Northern Domain and another unit belonging to the Malaguide Complex. At the contact between these latter and the Lomo de Bas three are remnants of a sedimentary formation similar to the Conglomerate Marble Formation, and of an unit different to hose observed overriding he Veleta Group, which named Minarros Unit. From bottom to top, the Southern Domain displays two alpujarride units composed of a metapelitio sequence of micaschists, phyllites and quartzites with green schist facies metamorphisrn and carbonate formation attributed to the Triassic, Over these appears an alpujarrides unit fonned of micaschists and quartzites, presumibly of Paleozoic age, exhibiting medium-grade metamorphism. Above all this there is a malaguides unit formed of a Triassic and Jurassic series essentially composed of carbonates. Recent wrench faults trending NE-SW and NNE-s5W, are responsible for the present arc-shapped disposition of the structures.

Speciation of Heavy Metals in Finnish Lake Ores; Selective Extraction Analysis

Abstract The speciation of Fe, Mn, Co, Cu, Ni, and Zn are studied in Finnish lake ores from areas where weathering of black schists and mica schists, containing abundant sulphide minerals, causes natural pollution by heavy metals.

Chemical characteristics of thermal waters in the Central Range of Taiwan, R.O.C.

There are 70 hot-spring areas in the Central Range metamorphic terrane of Taiwan, where argillite, slate, phyllite and black schist predominate. The chief mineral constituents of these metapelites are quartz (Qtz), K-mica (Km), chlorite and albite (Ab), with a minor amount of calcite (Cc) but without K-feldspar (Kf). P CO 2 in subsurface water is high, ranging from a few atmospheres at ∼ 150°C to nearly 100 atm. at ∼ 220°C in the Chingshui and Tuchang geothermal fields. The carbonic acid in water reacts with Ab to produce NaHCO 3-type water in the Central Range. The Na, K, Mg and Ca concentrations of these waters are controlled by solubilities of Ab, Km, chlorite and Cc, respectively. These waters have comparatively higher Na/K ratios than waters in equilibrium with Ab and Kf, and the estimated subsurface water temperatures by the NaKCa geothermometer of R.O. Fournier and A.H. Truesdell are generally 15–40°C lower than t SiO 2(Qtz) . Analytical data of thermal waters in the Chingshui, Tuchang and Chihpen geothermal fields are sufficient to define a relationship between Na/K ratio and the reciprocal of absolute temperature, which can be expressed empirically as log( Na K ) = 1670 T − 1.73 , and from which the maximum water temperature can be estimated by the following formula with an uncertainty of less than 15°C: t Na/K(Ab−Musc)( °C) = 1670/[log(Na/K) + 1.73] −273.15 The formula is valid for 350°C > t > 130°C. Since the dissolved SiO 2 in thermal water is more easily re-equilibrated with Qtz than Na + and K + re-equilibrated with Ab and Km and/or Kf in a flowing hydrothermal system, ( t Na K - t SiO 2 ) is small (< 15°C) in deep water but large (up to 50°C or more) in shallow water, and t Na K ( deep water) - t Na K ( shallow water) seldom exceeds 10°C. If thermal water is in equilibrium with Ab, muscovite (Musc) and Qtz according to the reaction 3Ab + 2H + + K + ag 3Na + + Musc + 6Qtz, then: K Ab−Musc = α 3 Na/α Kα 2 H and pH= 1 2 (log K Ab−Musc + log α K−3 log α Na) Calculated pH-values for waters in the Central Range range from 6.4 at ∼ 220°C to 8.4 at ∼ 100°C, which probably have an uncertainty of 0.2–0.5 pH unit. The equation: log(α Na/α K = log K Ab−Musc − 2 log(α Na/α H) indicates decreasing Na/K ratio with increasing pH-value, which probably accounts for the abnormally low Na/K ratios of some low-temperature waters. The reaction CaCO 3 + 2H + ag Ca 2+ + H 2O + CO 2 (g) gives m Ca = a 2 H K Cc − H γ Caf CO 2 . A plot of calculated log(√Ca/NA) vs. 1000 T for the Chingshui and Tuchang thermal waters exhibits a trend similar to that published by Fournier and Truesdell, implying that the √ Ca Na ratio of natural water may be controlled by solubilities of calcite and Ab, and that the NaKCa geothermometer is probably based on solubilities of Cc, Ab, Kf and Km. If only Ab, Kf and Km are considered and at same P- T conditions, waters in equilibrium with Ab and Kf should have lower Na/K ratios than waters in equilibrium with Ab and Km, whereas waters reacting with Ab, Kf and Km may have intermediate Na/K ratios.

LITOESTRATIGRAFIA RELAÇÕES ESTRATIGRÁFICAS E EVOLUÇÃO PALEOGEOGRÁFICA DOS GRUPOS CANASTRA E PARANOÁ (REGIÃO DE VAZANTE-LAGAMAR, MG)

This paper attemps to define the terrigenous and carbonate facies, lithostratigraphy and Middle Riphean paleogeographic evolution of the Paranoa Group. From west to east, three contemporaneous regressive zones can be recognized: the Paracatu Zone, with basal black schists, phyllites of the Western Facies and turbidites of the Eastern Facies; the Vazante Zone, a dolomitic barrier reef complex; and the State Zone on the continental platform, which contains patch reefs of the Lagamar Facies. These three zones were buried by the carbonate-pelitic psamitic sediments of the Cover Sequences. The lithostratigraphy of the Canastra Group is also defined showing the superposition of two deltaic cycles (the Lower Quartzitic Unit and the Middle Quartzitic Unit) overlain by sub-littoral to littoral deposits of the Upper Psamo-Pelitic Unit. During deposition of this sequence, an are evolued which separated the flyshoid basin of the Ibia Formation to the west from the Cover Sequence to the east. The contemporaneous zones of the Paranoa Group are stratigraphically related to the Upper Psamo-Pelitic Unit of the Canastra Group.

Cobalt as an exploration tool in the Outokumpu zone, Finland

Cobalt as an exploration tool in the Outokumpu zone, Finland

Tunnelling in Taiwan's north link railway : Chu, F H Tunn Tunnlg, V11, N8, Oct 1979, P48–49

The author describes the Taiwan railway system consisting of the unconnected 1.067 M gauge west line and the 0.762 M gauge east line. Three projects under construction include the north link line, the east line widening to 1.067 M and the south link line. The north link line will include 15 rock tunnels in a variety of geological conditions. Short tunnels are excavated by traditional hand methods while for longer tunnels US-made full-face tunnelling machines, Swiss jumbos and Japanese rail-mounted jumbos are being used. Geological conditions encountered included black schist, hornblendite, gneiss and silcified schist. The article describes excavation methods and difficulties caused by flooding and creeping of saturated topsoil causing cracking of a completed section of tunnel lining.

Origin of Precambrian copper sulfides of the Outokumpu District, Finland

The Outokumpu region is an integral part of the Precambrian formations of the Karelidic orogeny. The copper deposits discovered in the western part of Karelian mica schist area are associated with a lithologic complex that regularly consists of black schists, serpentinites, and siliceous quartz-rich rocks. This rock association makes up the coherent stratigraphic sequence, known as the Outokumpu zone, a prerequisite for the occurrence of Outokumpu-type ores.The lithological and structural setting, together with the high nickel content of the serpentinite-siliceous rock association, indicates a genetic relation between its components. The location of this rock association in a specific stratigraphic position corroborates the concept that they were emplaced concurrently with sedimentation.The copper deposits show clear stratigraphic affiliation with the enclosing metasedimentary rocks of the Outokumpu sequence. The stratified structure and systematic relationship between sulfur isotope ratios and stratigraphy in the Outokumpu ore suggest that the sulfides were deposited during sedimentation of the siliceous host rock. The conformable alteration of carbonaceous intercalations with the siliceous host and country rock of the Outokumpu ores indicates a common depositional environment. Several lithological and geochemical features of the carbonaceous schists in the Outokumpu district indicate that they were deposited under stagnant marine conditions.The simple mineralogy and high cobalt content of the ore suggest volcanic origin. Sulfur isotopic evidence and the compatibility between the radiometric ages of the Outokumpu galenas, metavolcanics resulting from Precambrian volcanic activity, and black schists support the notion that the Outokumpu stratiform copper ores were formed under conditions characterized by submarine volcanism and a restricted environment of sedimentation.The Outokumpu-type sulfide deposits seem to be the Precambrian equivalent of more recent massive pyrite deposits of sedimentary-volcanogenic origin that differ in location and geologic ages. The ores underwent regional metamorphism which modified the structure and composition of the ores and their surroundings.

Primary and secondary structures in the polymetallic ores of Rajpura-Dariba, Rajasthan, India

The Precambrian Rajpura-Dariba polymetallic deposits of Rajasthan, associated with black schists, quartzite and calcsilicate rocks, exhibit several primary structures, suggesting a syn-sedimentary origin. The secondary features of the sulphides are attributed to the effects of metamorphism.

Audiometric Control System of Wet Semiautogenous and Autogenous Mills

The audiometric control system of commination process introduced in this paper has been developed at the concentration plant of Outokumpu Cy, Vuonos mine.The material handled in the grinding circuit a low—grade nickel ore. The high Variability of the type of ores handled (serpentinite, chlorite, talck, black schist) makes the grinding process a very fluctuating one.The control system which has been developed is based on the noise emitted by the mill. Equipment was developed for selective measurement of the noise and the information given by this equipment was found reliable enough to serve as the basis for an automatic computer control system, in which the controlled variable is the noise and the manipulated variables are the components of the feed.A mathematical process model was experimentally identified in order to tune control algorithms.In the course of long-term testing the control system developed has been found advantageous for maintaining the mill at maximum capacity.The capacity within the audiometric control system was found to be higher than with the power control system used before. The main reasons for this higher capacity are the increased throughput of the ore and the decreased number of serious disturbances.

On some geochemical features in the black schists of the Outokumpu area, Finland

On some geochemical features in the black schists of the Outokumpu area, Finland

Mantled Gneiss Domes in the Albion Range, Southern Idaho

The Albion Range, in southern Idaho east of the Antler orogenic belt and west of the Sevier orogenic belt, exposes a northeast-trending chain of four mantled gneiss domes. The Green Creek Complex (Precambrian [2.5 b.y.] gneiss and metasediments), which forms the cores of the domes, is unconformably overlain by the Paleozoic Dove Creek Group, consisting of sparsely fossiliferous metasediments approximately 22,000 feet thick. The basal quartzite and overlying schists, marbles, and thin quartzites are of probable Cambrian age. A massive quartzite and overlying schist and limestone may be Cambrian or Ordovician in age. Ordovician quartzite more than 7000 feet thick forms the middle part of the metasedimentary section, and this is overlain by massive pure dolomite, calcareous black schist, and quartzite of Ordovician through Mississippian(?) age. Devonian strata are thin or absent. At the top of the metasedimentary section are limestone, schist, and quartzite of the Pennsylvanian Oquirrh(?) Formation. Younger Paleozoic sandstone, limestone, and chert, and Triassic(?) shale occur in fault contact overlying the metasediments. Cenozoic sedimentary and volcanic rocks unconformably overlie the deformed older rocks. Metamorphic grade (greenschist and amphibolite facies) increases northwestward and downward in the area. Staurolite and kyanite occur in Cambrian rocks in the northern half of the range; cordierite, andalusite, and sillimanite occur in Precambrian rocks in the southern half of the range, but these may be due to Tertiary contact metamorphism. Deformation during Mesozoic metamorphism produced two fabric systems; locally a Precambrian metamorphic fabric survived the younger metamorphism. Early bedding foliation and northeast-trending, northwest-vergent folds and lineations predated rise of the domes. Northwest-trending folds and lineations with northeast and southwest vergence were produced during and after doming; over much of the western half of the range these structures destroyed all older fabrics. During the Oligocene (30 m.y.) a postkinematic adamellite stock—the Almo Pluton—and related granitic dikes were emplaced. Following emplacement of the pluton, uplift of the range accelerated to an average rate of .5 mm per year, bringing the gneiss domes to the surface from a depth of at least 10 km. The Albion Range is part of a belt of rocks along the western part of the Cordilleran miogeosyncline which was affected by high-grade regional metamorphism during the middle of the Mesozoic. The metamorphic rocks are part of the Cordilleran infrastructure, which can be traced from California into southern British Columbia and beyond.

An isotopic study of lead in sedimentary pyrite

The lead in sedimentary pyrite is typical of dissolved lead in the original depositional environment, provided the isotopic composition is not changed by radioactive decay of uranium or thorium within the samples, or by recrystallization of the samples long after deposition. These conditions appear to be realized, generally, in pyrite from unmetamorphosed sedimentary rocks. In metasedimentary rocks, the origin of lead in pyrite may be quite complex, but in favorable cases the isotopic composition of such lead provides some information about the pre-metamorphic history of the samples. The lead content of thirty samples of pyrite from sedimentary and metasedimentary rocks has been determined by X-ray fluorescence spectrometry. Lead content ranges from a few ppm to several hundred ppm in both the sedimentary and metasedimentary samples. The uranium content of most of the samples was determined by isotope dilution; much of the uranium, and in some cases much of the lead, associated with the samples could be removed by leaching for several days in hot HCl. The U/Pb ratio of most of the leached samples is sufficiently low that the contribution of radiogenic lead by decay of the uranium is negligible. The isotopic abundances of lead, in the samples for which the sedimentary age is known, are related to a two-stage model for the isotopic development of oceanic lead based on the isotopic composition of lead in the modern North Pacific. This model provides reliable minimum ages for the time of deposition of the samples and in many cases this minimum age is within a few hundred million years of the known age. A few samples which show larger deviations apparently originated in restricted basins of deposition. Samples from black schists in Finland contain excess Pb 206 which probably originated in black shale environments prior to metamorphism. Other samples from Finland, and a sample from the Canadian shield, give model ages considerably greater than the latest metamorphism, suggesting intervals of at least several hundred million years between sedimentation and metamorphism.

The Leannan fault

A powerful north-east-trending fault cuts right across the north-west corner of Ireland and forms the most important member of a system of steep wrench-faults that dissect the Dalradian rocks of Donegal into parallel strips. The contrast between the rocks flanking this Leannan fault is very marked. On the north-western side the outcrops of the same succession of metasediments run parallel to the fault-line for over 60 miles; over this distance they show little change in lithology, structure, or metamorphism. On the other side the geology varies considerably along the fault, and, except in the north-east, the outcrops run at a high angle to the fault-line; as a result, several different rock-groups are brought against the fault. The metamorphism increases progressively to the south-west so that rocks of kyanite grade are finally brought against others of chlorite grade. The main movements on the fault are shown to have occurred between the deposition of red beds, presumably of Lower Old Red Sandstone age, and the deposition of Viséan marine sediments. The fault-zone generally consists of one main break accompanied by two others of lesser importance: together these fractures isolate narrow strips of metasediments in which inverted sequences are the rule. It is argued that the inversion of these strata predates the faulting, and that they were derived from the now eroded limb of a great recumbent fold. Along the main fault a total of 60 yards of intense deformation is usual, and black schist, platy siliceous mylonites, and quartzitic breccias are the result; the steep platiness is always set at an acute angle to the fault. Two separate movements are shown to have occurred; a downthrow to the south-east amounting to several thousand feet is combined with a left-handed displacement, the amount of which, though difficult to estimate, may be as much as 25 miles. The Leannan fault is directly in line with the Great Glen fault and the possibility that it is a continuation of this structure is discussed.

Gold impregnation deposits in the Moto area (central Africa)

In contrast to the vein-type deposits in the southern (Kilo) area, the economically important gold ores of the northern (Moto) sector of the Kilo-Moto district, Congo region, are impregnation deposits in Kibalian schists (Precambrian), commonly in a carbonate-quartz-albite rock and often in close association with bodies of itabirite and bands of black schist. The ore bodies do not appear to be associated with any known structural feature; their general concordance with planes of foliation or schistosity suggests that permeability resulting from a high proportion of carbonate in the country rock may have been a controlling factor in mineralization.

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.,

Stratigraphy, structure, and petrology of the Mt. Cube area, New Hampshire

Research Article| January 01, 1942 Stratigraphy, structure, and petrology of the Mt. Cube area, New Hampshire JARVIS B. HADLEY JARVIS B. HADLEY Search for other works by this author on: GSW Google Scholar Author and Article Information JARVIS B. HADLEY Publisher: Geological Society of America Received: 04 Feb 1941 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1942 Geological Society of America GSA Bulletin (1942) 53 (1): 113–176. https://doi.org/10.1130/GSAB-53-113 Article history Received: 04 Feb 1941 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JARVIS B. HADLEY; Stratigraphy, structure, and petrology of the Mt. Cube area, New Hampshire. GSA Bulletin 1942;; 53 (1): 113–176. doi: https://doi.org/10.1130/GSAB-53-113 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Seventy per cent of the bedrock in the Mt. Cube area consists of metamorphic rocks of sedimentary and volcanic origin, ranging from middle Ordovician (?) to early Devonian. The total thickness is about 16,000 feet. Two of the oldest stratigraphic units, the Orfordville formation and the Piermont member of the Albee formation, are described in detail because this is the type locality.The Orfordville formation, presumably middle Ordovician, is 5000 feet thick, and consists of interbedded black schist and volcanic rocks. The schist represents carbonaceous marine mud and sand. The volcanics represent metamorphosed basalt flows and pyroclastics (now amphibolite) with some rhyolite, quartz latite, and dacite (now biotite gneiss). The Piermont member, 1000 feet thick at maximum and locally absent, comprises most of the lower part of the Albee formation, and consists of aluminous, carbonaceous schist interbedded with noncarbonaceous quartzmica schist, quartzite, and fine conglomerate.About 30 per cent of the bedrock consists of gneissic igneous rocks, ranging from granite to quartz diorite. Most of them belong to the late Devonian Oliverian and New Hampshire magma series.The stratified rocks were severely folded, broken by thrust faults, and metamorphosed during the late Devonian. Thrusting and overturning of folds is toward the east-southeast, except in the southeastern part of the area, where it is toward the west. The concordant, domical intrusives of the Oliverian magma series were active during the later stages of the folding, and represent the tops of syntectonic phacoliths, rather than pretectonic laccoliths.The metamorphic and tectonic relationships of minerals in the middle-grade zone of metamorphism are briefly discussed, and an area of wholesale retrograde metamorphism associated with a major thrust fault is described. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

VI.— The Marginal Intrusions of Ben Nevis; the Coille Lianachain Complex; and the Ben Nevis Dyke Swarm

I. INTRODUCTION. Subject of Paper. —The igneous complex of Ben Nevis is one of many intruded into the metamorphic rocks of the Highlands in Lower Old Red Sandstone times. It consists of a central core of volcanic rocks resting upon schist which has subsided into, and is now completely surrounded by, the Inner Granite. This in its turn is two-thirds encircled by a slightly more basic, and earlier, intrusion known as the Outer Granite (Fig. 1). The two main schist formations into which the Ben Nevis complex is exteriorly intruded are the Leven Schists and the Ballachulish Limestone. On the north-west side, however, the igneous rock also comes in contact with the Eilde Flags and on the north side with black schist grouped with the Ballachulish Slates. The Outer Granite is in the main a strikingly porphyritic pink rock, but around seven-eights of its periphery there is a non-porphyritic margin of varying breadth (Fig. 2). Very similar rock types to those found in this non-porphyritic margin also occur in the small plutonic mass (with an outcrop of a little under one square mile) lying half a mile to the east of the extreme north-east corner of the Ben Nevis complex and about three miles south of Spean Bridge (Fig. 7). No detailed account of this intrusion has yet been published, and from the wood which covers part of its outcrop it is proposed to refer to it as the Coille Lianachain mass. It is with the latter, and with the non-porphyritic This 250-word extract was created in the absence of an abstract The author wishes to acknowledge the invaluable help rendered by Professor E. B. Bailey, Mr. A. G. MacGregor and Dr. G. W. Tyrrell in the preparation of the paper. Acknowledgement is also due to the Controller of H.M. Stationery Office for permission to reproduce Fig. 1 from the Geological Survey Memoir on Ben Nevis and Glen Coe (1916) and for the loan of the block, and to the Institute of Quarrying for permission to reproduce two illustrations from the “Quarry Managers’ Journal” (March, 1934). He wishes also to express his thanks to the Geological Survey for offering every facility to examine maps, sections and other material. The cost of analyses and part of the cost of publication has been defrayed by a generous grant from the Carnegie Trustees for the Universities of Scotland.

A NEW LEPIDOLITE DEPOSIT IN COLORADO*

ABSTRACTA newly discovered pegmatite deposit near Ohio City, Colorado, is chiefly lepidolite, massive topaz, beryl, and albite, with some samarskite and columbitc. Three parallel pegmatite dikes, cach about 11 fect thick and 300 feet long, cut black schist. The minerals arc banded parallel to walls, with the following succession from walls to center; fine‐grained albite and quartz, large plates of lcpidolite with crystals of topaz and beryl, fine‐grained lcpidolitc, and lamellar albite. An estimate of the bulk percentage of the various constituents heads to the belief that at least several thousand tons of each of the commercially vdluahle minerals await mining.