Pegmatite Dikes Research Articles

Petrology and Structure of the Bethel Area, Maine

Sillimanite-grade metasedimentary rocks of the Lower Devonian Littleton Formation and plutonic rocks of the New Hampshire magma series underlie the Bethel quadrangle of western Maine. The exposed Littleton Formation is a series of gneisses and schists about 8500 feet thick including two units, the “pyrrhotitic gneiss” and the “inter-bedded sillimanite schists and quartz-mica schists,” separately mappable from the main quartz-biotite-sillimanite gneiss. Igneous rocks include the Songo Granodiorite, the Speckled Mountain Quartz Monzonite, and the 280-million-year old granitic pegmatite, all of the New Hampshire magma series, and mafic dikes, the youngest rocks in the quadrangle, tentatively classified with the Mississippian(?) White Mountain magma series. The writer, by measuring zircon grains and calculating hydraulic equivalents in light minerals, ascertained that the gneisses and schists were derived from coarse siltstones of a graywacke series. The structure is exceedingly complex in detail, but in general the metasedimentary rocks form a series of northeast-striking, doubly plunging anticlines and synclines. The large, domelike Albany pluton of Songo Granodiorite and countless smaller bodies of igneous rock cut the folds. The Albany pluton occupies the southeastern third of the quadrangle and is cut by pegmatite and mafic dikes. In places the metasedimentary rocks exhibit textures and structures that some ascribe to granitization. The writer believes that these features formed by metamorphic segregation. Chemical analyses of the rocks indicate that little, if any, metasomatism took place during metamorphism. The Speckled Mountain Quartz Monzonite locally exhibits a distinct layering that resembles the relict bedding of meta-sedimentary rocks. The writer considers the possibility that this rock has been metasomatized and mobilized but concludes that it probably represents the consolidation product of a highly contaminated magma.

Nature and origin of central Idaho blacksands

Fifty or more heavy minerals occur in blacksand placers adjacent to the Cretaceous Idaho batholith. They contain Nb (columbium), Ta, Y, Zr, Hf, U, Th, Ti, and the rare earths. These minerals are of present or future potential value as sources of metals characterized by versatility, including strength and resistance to heat and chemical corrosion. Natural concentrations of blacksand involve mineral hardness, texture, chemical composition, and specific gravity; mineral size, shape, and degree of subroundness; and major alterations in stream regimens affecting competency, capacity, and interruptions of transportation. The latter include climatic changes, lava damming, crustal warping, faulting, and mass-wasting phenomena. Local deep disintegration of bedrock is an important adjunct to blacksand concentration. The original source of heavy mineral elements is believed to be Precambrian placer accumulations. These concentrations were later partially dispersed by metasomatic reconversion during diastrophic maxima, and indistinct swarms of accessory minerals were produced. New placers were formed again later through the operation of erosional and depositional agents. Recent blacksand placers derived their heavy minerals from quartz monzonite, granodiorite, diorite, and metamorphic remnants of original country rock commonly found in adjacent exposures of the Idaho batholith. The batholith may appear deceptively normal in these areas. When present, pegmatite and aplite dikes provide an additional source of heavy detrital minerals. The domination of one or more minerals over others in the more recent placers, appears to be related to the domination of similar elemental constituents in earlier original placer deposits. Thus recent data on both the petrography of the Idaho batholith and the nature and origin of blacksand placers lead to the following conclusions: erosional processes concentrated the first placer ore deposits in the Precambrian; and subsequent events both geomorphic and metasomatic probably played more important roles in the genesis of all types of ore deposits, including placers, than previously has been supposed.

Note on some cassiterite-bearing pegmatites near Brandberg, South West Africa

The structural setting and other features of tin-bearing pegmatite dikes peripheral to two small masses of light-colored aplitic granite in intensely deformed Precambrian schist north of the Brandberg massif (an alkaline granite ring dike of late or post-Karroo age) suggest that both the pegmatites and related granites are metasomatic replacements formed by solutions which entered along closely spaced fractures in the schist. Cassiterite occurs with tourmaline in scattered zones of greisenization, or in quartz cores and quartz-filled cross fractures in the pegmatites.

The Odara pegmatite

Concludes that structural features and zonal distribution of such minerals as mica, magnetite, columbite, and beryl in a zoned pegmatite dike in gneiss of the Odara area, Travancore, India, can be attributed to progressive crystallization of a pegmatitic magma, and that there is no evidence of hydrothermal replacement.

Contribuição ao conhecimento de Estruturas Migmatíticas no Complexo Brasileiro

It is the purpose of this paper to present briefly the results of a study of the genetic relations of the migmatite structures- of the area named Praia do Tombo, ilha Santo Amaro, State of Sao Paulo, Brazil. The migmatites in the area in question present the following petrographic features: the old rock, a biotite-hornblende gneiss, was intruded by granitic material whose main constituent is microclne. The illustrations give an idea of forming process. Pegmatite dikes cutting through the migmatite rock has provoked the formation of a characteristic greisening zone by a process of metasomatic alteration

The mica-bearing pegmatites of the Harts range, central Australia

Of the several mineralogic and structural types of pegmatites in the Precambrian terrain of the Harts range, Northern Territory, the coarse-grained zoned pegmatite dikes which occupy fault or joint planes in mica-rich schist and gneiss are the principal source of commercial muscovite production.

The Emerald, Feeney and Dodger tungsten ore-bodies, Salmo, British Columbia, Canada

The scheelite ore bodies are enclosed within beds of limestone and skarn, which conformably overly argillite, and dip eastwards into intrusive granite. The resultant contact and trough structure are essential for the formation of persistent ore zones. Faulting is found along the main granite contact and minor faults that strike subparallel to the troughs have exercised a definite structural control. Mineralization arising from deep within the granite was distributed by medium of quartz-tourmaline veins and siliceous veins traversing breccia zones and faults. Tungsten solutions were also concentrated by dikes of granite and pegmatite that cut across the trough.Four distinct types of host-rock are recognized: skarn, limestone, quartz, and greisenized granite. Pyrrhotite and biotite are generally present in the first three types and a close association is shown between scheelite and quartz in all four types. Most of the scheelite is finely disseminated and distinguished only by use of the ultra-violet lamp.The ore bodies are lenticular and tend to thin and splay out on the flanks. They are contact metamorphic in origin. In close proximity to the ore zones the granite is greisenized. The concentration of scheelite in the contact zone is attributed largely to the processes of greisenization. A genetic relationship is inferred between quartz-biotite veins and scheelite.The Emerald and Dodger troughs have each been tested over a length of over 4,000 feet, and the troughs follow the general stratigraphic grain of the country.

GEOLOGY OF THE CHLORIDE QUADRANGLE, ARIZONA

Research Article| April 01, 1953 GEOLOGY OF THE CHLORIDE QUADRANGLE, ARIZONA BLAKEMORE E THOMAS BLAKEMORE E THOMAS 12426½ VENTURA BOULEVARD, NORTH HOLLYWOOD, CALIFORNIA Search for other works by this author on: GSW Google Scholar GSA Bulletin (1953) 64 (4): 391–420. https://doi.org/10.1130/0016-7606(1953)64[391:GOTCQA]2.0.CO;2 Article history received: 17 Dec 1951 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 BLAKEMORE E THOMAS; GEOLOGY OF THE CHLORIDE QUADRANGLE, ARIZONA. GSA Bulletin 1953;; 64 (4): 391–420. doi: https://doi.org/10.1130/0016-7606(1953)64[391:GOTCQA]2.0.CO;2 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 The Chloride quadrangle includes the southern two-thirds of the Cerbat Mountains, a range composed mostly of presumably Precambrian crystalline rocks. The oldest rocks are quartzite, mica schist, hornblende-diopside schist, and amphibolite. Younger and larger in amount are granite and granite gneiss. Gabbroic and dioritic gneiss, pegmatite, aplite, diabase, and mylonite also occur as part of the basement complex. The earliest rocks were strongly folded, but igneous intrusion and granitization have obliterated most of the folds. The rock types and the history of the basement complex compare closely with the Archean in the Grand Canyon.The area contains no Paleozoic rocks and probably no Mesozoic rocks. Intrusions of granite porphyry associated with mineralization are believed to be Tertiary. Dikes of granite porphyry, pegmatite, aplite, and lamprophyre are associated with these intrusions.Small areas of andesitic and rhyolitic extrusive rocks of Tertiary (?) age occur along the flanks of the range. Quaternary basalt caps these rocks in some places.Several periods of faulting and erosion are visible in the volcanic rocks. The latest faulting has produced the present mountains. The greatest displacement has been on the west side, and the Cerbat Range is an eastward-tilted fault block, modified in part into a horst. This mountain building seems to have occurred in late Tertiary and Quaternary time. Recent fault-block movement is suggested by the presence of canyon terraces and by the dissection of the pediment at the west base of the range. 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.

Geothermometry of Some Pegmatite Minerals of Hybla, Ontario

The development of new techniques for the rapid measurement of the temperature of deposition of pyrite and the degree of filling of two-phase fluid inclusions has made it possible to determine temperatures and pressures of deposition of hydrothermal minerals. These techniques are applied to some of the minerals from a system of pegmatite dikes. Pressures existing in the solutions at the time of deposition of pyrite have been calculated and found to be of the order of 3,000 bars. Temperatures of crystallization of pyrite, quartz, fluorite, and oligoclase have been found in the range 450°-550° Anomalous decrepitation of calcite is discussed.

GEOLOGY OF THE BROKEN HILL ORE DEPOSIT, BROKEN HILL, N.S.W., AUSTRALIA

The lead-silver-zinc ore deposit of Broken Hill, New South Wales, is among the great ore deposits of the world because of its size, richness, and continuity. Up to the end of 1946 approximately £50,000,000 in dividends had been won from recoverable metals worth £210,500,000 gross contained in 63,800,000 tons of ore. The deposit is a hypothermal deposit of Precambrian age resulting from the selective replacement of two closely adjacent, tightly and complexly folded stratigraphic rock layers. The original sedimentary rocks of the area now consist of tightly folded sillimanite-garnet gneisses with subordinate thin quartzite beds. These contain numerous folded sills of augen gneiss (granite), amphibolite (gabbro), and pegmatite. Post-folding peridotite, granite, and pegmatite occur. Probably following considerable uplift and erosion, thin dikes of diabase (dolerite) were intruded, followed by pegmatite dikes and silicifying solutions, and finally by ore-bearing solutions. The folds of the region are tight, steeply inclined, and extremely complex structures resulting from plastic deformation. Individual minor folds were studied in great detail by a method of axial-plane and axial-line analysis. An angular relationship exists between minor and major folds due to strain under torsional stresses. The regional pitch is flatly south. However, sudden reversals of pitch and divergences of pitch in adjacent folds are common. “Second-order” folds or folded folds exist. Cutting and offsetting the folds are “buckles” with vertical axes and crush zones of schisted rocks resulting from post-folding but pre-ore faulting movements. The lode occurs in a “belt of attenuation” between a wide arch on the west and wide basin on the east. It consists of massive lead-zine-sulphide replacement ore bodies forming (before erosion) a long continuous, irregularly shaped, flat, curving pencil of ore, 2000–3000 feet high and 300 feet thick. In longitudinal section it describes a flat arc pitching downward at each end. The “lead lodes” resulted from the selective replacement of two closely adjacent highly folded favorable beds. Each lode is distinguishable by its gangue mineralogy and metal ratios. No. 3 Lens (the lower) has fluoritic-rhodonitic gangue and comparatively high Zn:Pb and Ag:Pb ratios. No. 2 Lens, the upper, has calcitic gangue and comparatively low Zn:Pb and Ag:Pb ratios. At least three “zinc lodes”, with similar mineralogy, occur at higher stratigraphic horizons at the south end of the field. There is little observable zoning. Ore solutions are believed to have migrated up the regional pitch from the south. Intra-mineralization fracturing helped to localize ore shoots within favorable formations.

The Form and Structural Features of Aplite and Pegmatite Dikes and Veins in the Osi Area of the Northern Provinces of Nigeria and the Criteria That Indicate a Nondilational Mode of Emplacement

Numerous dikes and veins of aplite and pegmatite in the Osi area of Nigeria were studied with a view to ascertaining the mechanism of emplacement. Offsetting of the invaded rocks of a magnitude and direction appropriate to dilation is so rare as to appear to be quite fortuitous. Where offsetting is not entirely absent, it is commonly of a different magnitude and frequently in the opposite direction from that to be expected on dilation of the invaded rocks. In such instances emplacement has evidently occurred along planes of shearing formed under compressional stress. Nondilational emplacement is also clearly indicated in the case of the irregular bodies and ramifying networks of veins. The criteria advanced are similarly of significant application in the mode of emplacement of ptygmatic folds. Processes of metasomatic replacement, conveniently termed aplitization and pegmatization, are believed to have been those responsible for the development of the bodies described, while internal evidence for th...

PETROGRAPHY, STRUCTURES, AND PETROFABRICS OF THE PINCKNEYVILLE QUARTZ DIORITE, ALABAMA

The Pinckneyville quartz diorite complex underlies an area in eastern Alabama extending from the Coosa River in northwest Elmore County northeast through Coosa and Tallapoosa counties into Clay County. Dark-gray, coarse-grained quartz diorite gneiss constitutes the major part of the complex, but there are smaller amounts of granodiorite and granite gneiss. Hornblende-biotite gneisses also occur and are considered to represent metamorphosed basic sills and dikes intruded before the quartz diorite complex. Schist septa lie within the complex and are usually parallel to the regional strike. The sequence of intrusion as interpreted from inclusions and petrographic data is (1) quartz diorite, (2) granodiorite, (3) granite. Small but persistent amounts of allanite and epidote are characteristic of the rocks of the complex. The texture is subporphyritic and shows evidence of protoclastic deformation. A northeast-southwest trend of inclusions, foliation, lineation, and contacts dominates. Primary flow structures are shown in the orientation of inclusions and micas. Secondary structures were superposed on the original flow structures shortly after intrusion and prior to complete consolidation. A prominent secondary structure is a lineation in b. Stretching in b is indicated by boudinage structures, the lineation, and small displacements of dikes. The intensity of the planar structures in the gneiss grades from strong to indistinct or lacking from east to west. Structures in schist inclusions indicate that some folding had taken place prior to intrusion. Thin pegmatite, granodiorite, and granite dikes are common. Most of them are essentially parallel to the regional strike. The petrographic boundary between gneiss and schist is always sharp. On a large scale, the gneiss structures are essentially parallel to the contacts, but slight to marked discordant relations occur at many localities. The schist structures usually parallel the contacts. Petrofabric analysis confirms the structural field observations. The mica fabrics are ac -girdles and are most complete where the foliation is weakest. Microscopic s -planes do not always coincide with the observed foliation. The quartz fabrics are also ac -girdles but are not so well developed as the mica girdles. Quartz orientations cannot always be related to known s -planes. It is concluded that the Pinckneyville quartz diorite complex represents a syntectonic intrusion—that is, that intrusion took place while external or regional forces were still active. The shape of the intrusion was controlled largely by the wall-rock structures which had developed earlier. The rocks show both igneous and metamorphic characteristics because the intrusion took place under regional metamorphic conditions.

Mt. Waldo batholith and associated igneous rocks, Waldo County, Maine

The central part of the Bucksport, Maine, topographic map area is underlain by a medium-textured, porphyritic, biotite granite, termed here the Mt. Waldo batholith. The age of the granite has not been determined but is probably either Devonian or Carboniferous. The pluton is roughly circular in plan, with a diameter of approximately 10 miles. Planar flow structures in the granite tending to curve parallel to the margins of the intrusion about the northern end stand steep to vertical. Within the intrusion, the planar flow structure averages about north in strike and vertical in dip. Linear structure is not developed. On the north, northeast, and south, the older metamorphic wall rocks, probably Paleozoic, are crosscut by the granite; elsewhere, the structure of the wall rocks tends to conform to the outlines of the intrusion. Close to the intrusion, the axes of the minor folds in the wall rocks are steeply inclined or vertical; farther from the margins, the pitch of minor folds decreases. The overlying rocks were perhaps pushed bodily upward by the intrusion. Intrusives older than the granites of the Mt. Waldo batholith are both granitic and more basic. Both groups are of undetermined age. The earlier gneissic granites are foliated and locally show linear structure consisting of biotite streaking on the foliation planes. This type outcrops in small masses. Pegmatite and aplite dikes are present, some older and others younger than the batholith granites. Diabase dikes are the latest intrusions in the area.

Concentric patterns in the granites of the Llano-Burnet region, Texas

The larger bodies of pre-Cambrian coarse-grained granites in the Llano-Burnet uplift of central Texas have been studied with special attention to structure and texture. They are steep-walled, roughly circular massifs averaging 12 miles in diameter. Flow layers or schlieren with parallel schist xenoliths are well developed near the borders. Lineation within the flow layers was not detected. The flow layers follow the outlines of the massifs and usually dip outward at angles of 70 degrees or more. Vertical joints normal to the strike of the flow layers are characteristic of the outer portions of the massifs. Pegmatite and aplite dikes near the borders dip toward the centers of the massifs, suggesting marginal fissure fillings. The granites exhibit a concentric arrangement of three textural varieties. These are, in order of their solidification, an outer coarse-grained granite, an intermediate zone of porphyritic coarse-grained granite, and a core of medium-grained granite. The adjacent textural varieties are mutually gradational indicating simultaneous intrusion. Chemical and petrographic analyses show that the three textural varieties are similar. At a later stage small bodies of fine-grained granite were intruded into the centers of the massifs, around the margins, and in radial dikes.

An Occurrence of Tinstone in the Pre-Cambrian of Western Ontario

At Eagle Lake in western Ontario are early pre-Cambrian metamorphic rocks intruded by two different granites. The earlier, a gray granite, has dikes of light-colored pegmatite, which in one locality take the form of a tinstone-bearing pegmatitic greisen. A tinstone-bearing greisen has also been reported from eastern Manitoba, and a reddish pegmatite at Shatford Lake in eastern Manitoba also carries tinstone. The several occurrences indicate a tin-bearing area of about 150 miles in length.

Metamorphism of a Granitic Dike at Franklin, New Jersey

A body of rock occurring near the Franklin Furnace ore body has been variously interpreted by writers on the local geology. This paper is a further study, leading to the view that the rock, hitherto considered of sedimentary origin, is an altered pegmatite dike.

Tungsten mineralization at Oreana, Nevada

The Oreana tungsten deposit is unique among American tungsten deposits in that the scheelite mineralization is considered pegmatitic. Beryl, oligoclase, albite and phlogopite are associated with it; fluorite and quartz form adjacent masses. The customary garnet and epidote are virtually absent. This mineralization differs considerably from the western quartz-vein type.Two forms of scheelite deposition occur: (1), in complex pegmatite dikes that cut metadiorite; (2), in lens-like masses along an inclined contact between limestone and metadiorite.Zones of silicification and alteration lead downward from the limestone-metadiorite contact within the limestone, but contain only traces of scheelite. It is believed, however, that such zones represent channelways leading to ore deposition above and are pegmatitic in character.

A brief description of the pegmatites southwest of Custer, South Dakota

This paper describes a recently opened soda-rich feldspar deposit, the Big Tom, five miles south of Custer, South Dakota. The associated rocks consist of pre-Cambrian schists cut by pegmatite and granite dikes. The minerals found are albite, cleave-landite, microcline-perthite, quartz, muscovite, tourmaline, beryl, amblygonite and columbite. Other commercial feldspar deposits in the vicinity are Tin Mountain, Tricky Claims, and the White Elephant. The dikes in the region are probably genetically related to the Harney Peak granite batholith. Evidence for a hydrothermal phase appears absent, and therefore the pegmatite, as exposed, may have originated from the fractionation of a soda-rich magma.

Rare chemical constituents of amelia (Virginia) pegmatite dikes, and their mineral sources

Students of Igneous phenomena have long since become familiar with the occurrence of rare minerals in pegmatitic bodies. The great local concentration of rare elements in pegmatite minerals provides a remarkably good opportunity for the Investigation of deep‐seated rock constituents, for it is reasonable to suppose that these same elements are widely distributed in minute amounts through the parent rocks to which they are genetically related; but their concentration in pegmatite bodies affords a record of their presence that is lacking in other rocks.The unusual number of rare minerals of the Amelia, Virginia, pegmatites has long attracted attention, and the rare elements of the more abundant minerals which have been investigated in the laboratories of the United States Geological Survey afford an unusual opportunity to study the rare constituents of a pegmatite. This famous locality for rare minerals is situated 38 miles southwest of Richmond, just south of Appomattox River, on the Piedmont plateau.

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.