Monzonitic Composition Research Articles

Effect of pressure on ore mineral solubilities under hydrothermal conditions

Experimental studies were conducted at elevated pressures and temperatures on the combined solubilities of iron, zinc, and lead sulfides in chloride solutions buffered in pH by a silicate assemblage of quartz monzonite composition plus added muscovite, and buffered in/s2 and/o2 by the assemblage pyrite-pyrrhotite-magnetite. Major controls on base metal concentration are temperature, total chloride, and pressure. Higher temperature and higher chloride concentration favor higher metal solubilities as expected, but the pressure effect is opposite to that generally expected and is of considerable importance to the problem of ore mineral transport. At 500 °C, 0.5 kbar, and 1 m total chloride, Fe, Zn, and Pb solubilities were 8500, 4300, and 8700 ppm, respectively, whereas at 1 kbar they were 4200, 2400, and 2600 ppm, and at 2 kbar, 1700, 800, and 1200 ppm. The experimental results thus indicate that the metals could be carried over long distances on a decreasing pressure gradient so long as the temperature decreases were not sufficient to significantly offset the pressure effect. Such a condition could be approximated by a near-adiabatic transport cooling path. Such a condition is probably common geologically, especially for hydrothermal processes involving fairly deep-seated sources of heat and mineral components.

The petrology of the Mont Saint Hilaire complex, southern Quebec: An alkaline gabbro-peralkaline syenite association

The Mont Saint Hilaire complex consists of an older (133 Ma) suite of layered cumulates of titanaugite, kaersutite, plagioclase and titaniferous magnetite, and two younger (122 Ma) suites, one a thick ring dyke of nepheline-olivine diorite to monzonite, and the other a pipe or funnel-like mass of peralkaline nepheline-sodalite syenite and porphyry associated with a variety of breccias. Trace element data suggest derivation of the older suite from a garnet-bearing source. Only minor amounts of possible liquid compositions are preserved in this suite. The nepheline and olivine-bearing suite followed a course of fractionation from gabbroic to monzonitic compositions involving fractionation of pyroxene, magnetite, apatite and plagioclase. Field and trace element data suggest mixing of the evolved liquid with a saline brine at crustal depths produced the strongly nepheline-normative peralkaline magma. Rich in Na and Cl, the brine was poor in other major and trace elements, and had a high initial Sr ratio. The localization and extended time of emplacement of the complex appear to be due to upward migration of a thermal anomaly from the base of a lithosperic plate.

The trace element geochemistry of some high‐grade Bergen‐Jotun kindred gneisses from the Jotun Nappe around Gjendebu, central southern Norway

Abstract The high‐grade meta‐plutonic rocks of this study lie entirely within the Jotun Nappe of the southern Norwegian Caledonides. They are divisible on the basis of metamorphic grade and petrographic character into three units, the Storadalen Complex (SCX), the Svartdalen Gneiss (SG), and the Mjølkedøla Purple Gabbro (MPG). The SCX is a differentiated series of ultrabasic to intermediate rocks now showing only tectonite fabrics. It has been metamorphosed to spinel‐Iherzolite granulite facies grade. The broadly monzonitic SG is weakly tectonized and internally differentiated. Its metamorphic grade does not exceed plagioclase‐lherzolite granulite facies grade. The mis‐named MPG is also broadly of monzonitic composition but it retains a coarse ophitic texture, and is of amphibolite facies grade. A gradational boundary exists between the MPG and SG, but the contact between these two units and the SCX is the steeply dipping Tyin‐Gjende Fault. The three units represent a comagmatic body of mid‐Proterozoic age, metamorphosed during a Sveconorwegian event and finally dismembered and upthrust during the Caledonian Orogeny.The new trace element analyses reported here show that the three rock units have remarkably similar trace element abundances and trends. K‐Rb covariation shows increasing K/Rb ratios with increasing K. These patterns were produced by magmatic fractionation processes acting at deep crustal levels, possibly in the presence of a non‐aqueous fluid phase. With the exception of K and Sr, close similarities exist between the rocks of this study and present‐day calc‐alkaline basalts and andesites from island arcs. The high K content is regarded as a primary magmatic feature, but the available data are insufficient to indicate its origin. The Sr contents are abnormally high and are ascribed to metasomatism which occurred during either high‐grade metamorphism or post‐climactic cooling. There are no systematic geochemical variations with metamorphic grade or degree of deformation.

Contrasting roles of rock-forming minerals in alkaline ring complexes

Alkaline ring complexes display numerous paradoxical features. They have a mantle origin but frequently have crustal isotopic signatures. These paradoxes can be explained if one considers that the history of an alkaline complex is written in terms of both original magmatic trends followed by hydrothermal overprinting. The systematic association of strongly differentiated acid rocks with cumulative basic rocks suggests a derivation from an intermediate liquid of monzonitic composition, which may well be a mantle-derived liquid. The differentiation trends are governed by olivine, calcic clinopyroxene, calcic plagioclase and calcic amphibole, which affect respectively iron-, alkali-and silica-enrichment. Fractionation or resorption of these critical minerals controls the different evolution trends. Late iron-rich sodic (amphibole and pyroxene) and potassic (micas) minerals are the result of magmatic differentiation and they appear often as subsolidus assemblages, sensitive to oxygen fugacity and to the water content of the vapour phase. The hydrothermal fluids can be supplied either from the vesiculation of late magmatic liquids and/or by the remobilization of interstitial ground waters in a convective-type geothermal field. In this model, it is not necessary to invoke an important component of crustal fusion.

The plutonic alkaline series: the problem of their origin and differentiation, the role of their mineralogical assemblages

The plutonic alkaline ring complexes present several different trends of differentiation, the two more important being the silica-oversaturated one and the silica-undersaturated one. A hiatus appears in the silica-oversaturated association for monzonitic compositions, which may be compared with the “Galy Gap” in volcanic series. Characteristics of the plutonic series as the cumulative features of the basic rocks, the differentiated patterns of the acid rocks and the monzonites which present REE patterns of initial liquid lead one to propose the existence of a magma of monzonitic composition. Its vanishing is owing to cumulation of the early mineral phases and to consequent evolution of the residual liquid. The trends of differentiation can be explained by a multistage model where mineral phases are both controllers of the differentiation and images of this differentiation. The path from monzonites to syenites is governed by calcic plagioclase (Bowen's plagioclase effect), olivine and calcic clinopyroxene, which have effects upon iron-enrichment and increase in alkalies. Calcic amphiboles, and more modestly biotite, play a significant role for the silica level of the liquids. The path from syenites to late stage differentiates is governed by alkali feldspars and calcic amphiboles. Late iron-rich sodic (amphiboles and pyroxenes) and potassic (annite-siderophyllite) minerals are reflecting the mode of the differentiation. One must also consider opaque minerals, marks of fo 2, and zircons, marks of temperature and agpaitic index. In the alkaline plutonic series, the controls of the differentiation by minerals can explain the coexistence of silica-saturated and undersaturated series and of peralkaline and peraluminous trends. The role of calcic amphiboles seems fundamental and we suggest that their stability is controlled by the characteristics of surrounding lithosphere: water amounts, porosity and permeability. Thus can be understood differences observed between oceanic and continental alkaline series, between complexes emplaced in cratonic environments or in youthful mountain belts, and specially coexistence of granites and nephelinic syenites, subsolvus granites and albitic granites, with their features showing a crustal signature.

APPLICATION OF BOREHOLE GEOPHYSICS AT AN EXPERIMENTAL WASTE STORAGE SITE*

AbstractA suite of electrical, radiation, and mechanical borehole probes were run in a 76‐mm‐diameter borehole drilled to a slant depth of 380 m in leptite and granite. The hole is located in Precambrian bedrock in central Sweden where a site is dedicated to in‐situ experiments pertaining to the disposal of radioactive wastes. The challenge to borehole logging methods for such site investigations is to resolve geological features and fluid flow parameters in geological sites which are initially chosen for their homogeneity, low porosity, and minimal fracturing. The Stripa borehole is characterized by high electrical resistivity values in the 20–100 kΩm range, by acoustic velocities around 5800 m s‐1 (which is close to laboratory values on intact specimens), and by total porosity of around one volume percent. In this context, probe resolution was adequate to produce interpretable information on almost all of the logs.Two principal rock types were encountered in the hole: granite, of quartz monzonitic composition, and leptite. The granite and leptite intercepts are subdivided into units characterized by mafic mineral content, sulfide mineral content, and electrical and radiation properties. Iron‐rich zones in the leptite are highly anomalous on the gamma‐gamma and neutron logs; thin mafic zones in the granite can also be distinguished. Occurrences of a few percent pyrite are detected by the electrical, gamma‐gamma, and neutron logs. Although overall porosity is quite low throughout the hole, analysis of the resistivity and neutron logs indicates the porosity increases by a few volume percent at fracture zones. The differential resistance and caliper probes detect borehole diameter roughness of less than 1 mm, helping to confirm acoustic waveform anomalies which are indicative of fracture zones. Compres‐sional wave transit time and shear‐wave interference patterns usually occur coincident with open fractures observed in core, the correlation being especially good at major fracture zones.

A synthetic model for vapor generation in tonalite magmas and its economic ramifications

The evolution of an aqueous vapor phase from a simplified tonalite (quartz diorite) magma during intrusion and crystallization has been quantitatively modeled for a stock of square cross-section using the procedure developed for a quartz monzonite composition by Whitney (1975b). Vapor generation from tonalitic compositions may continue from a significant portion of the body to greater depths than was encountered in the quartz monzonite model. In addition, higher initial temperatures in tonalites may allow intrusion and vapor generation at shallower depths than previously determined. This model suggests vapor fractionation may be a viable method of separating economic elements from tonalitic magmas over a greater pressure and depth range than was found for quartz monzonite compositions.

Petrology of Rattlesnake Mountain Sill, Big Bend National Park, Texas

The Rattlesnake Mountain intrusion in the Big Bend region of Texas is an early Tertiary analcime-bearing monzonite sill about 80 m thick that was injected at shallow depth and underwent differentiation in place. It contains sheets, lamellae, cylindroidal masses, and ocelli of syenite that show systematic distribution within the monzonite. Lamellae occur in the contact rocks, cylinders are confined to the lower central zone, and sheets are concentrated in the upper central zone. Ocelli are found only in a narrow zone near the top of the sill. All rocks of the sill display similar mineral assemblages with strong compositional zonation of individual mineral species. In particular, feldspars range from intermediate plagioclase, through anorthoclase, to Na-rich sanidine, and finally, to albite plus K-feldspar. Pyroxenes show a general trend from essentially normal augite to increasingly iron-plus-sodium–enriched varieties. Over-all crystal settling did not cause formation of syenitic rocks, but the central zone of the sill contains a relatively mafic monzonite that is complementary in composition and amount to the enclosed bodies of syenite. Border zones have little syenite (1 percent), and the monzonite composition is the same as a mixture of the more mafic central monzonite and enclosed syenitic rocks in the proportions in which they occur in the central zone. Crystal fractionation played a dominant role in generating syenitic rest liquids that could be aggregated into the structures found in the sill; rifting of a partially solid crystal mesh explains the formation of lamellae and many sheets, but the cylindroidal masses and ocelli are more enigmatic. The rocks of the Rattlesnake Mountain sill, as well as others of Big Bend, show distinct chemical similarities to alkalic oceanic suites such as those of the Azores. The syenite of the sill is typical of the undersaturated felsic rocks found in many shallow mafic intrusions in Big Bend, and it is in contrast to oversaturated quartz-bearing microsyenite, microgranite, and extrusive equivalents that occur as separate masses unconnected with more mafic rocks. There appear to be two differentiation trends related, perhaps, to undersaturated and saturated basaltic lava flows known in the area and possibly also affected by depth at which differentiation occurred.

Composition and Time Relations of Plutonic and Associated Volcanic Rocks, Boulder Batholith Region, Montana

Research Article| December 01, 1974 Composition and Time Relations of Plutonic and Associated Volcanic Rocks, Boulder Batholith Region, Montana ROBERT I. TILLING ROBERT I. TILLING 1U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT I. TILLING 1U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, Hawaii 96718 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (12): 1925–1930. https://doi.org/10.1130/0016-7606(1974)85<1925:CATROP>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ROBERT I. TILLING; Composition and Time Relations of Plutonic and Associated Volcanic Rocks, Boulder Batholith Region, Montana. GSA Bulletin 1974;; 85 (12): 1925–1930. doi: https://doi.org/10.1130/0016-7606(1974)85<1925:CATROP>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 Comparison of areally weighted bulk compositions for the Boulder batholith and prebatholith volcanic rocks (Elkhorn Mountains Volcanics) shows a close match in terms of K2O-Na2O-CaO-SiO2 variations. Detailed examination of available chemical data suggests, however, that the constituent units of the volcanic rocks differ among themselves, as well as from many of the batholith units. Most sampled volcanic rocks are chemically and isotopically similar to the volumetrically minor mafic members of the putonic main series of Tilling (1973). The sodic-series plutonic rocks, which form about 15 percent of the exposed batholith, apparently have no compositionally similar counterparts in the Elkhorn Mountains Volcanics in terms of bulk composition.The Butte Quartz Monzonite, which makes up about three-quarters of the batholith in terms of individual samples and bulk composition, is chemically distinct from most volcanic rocks. This relation suggests that only small amounts of magma of Butte Quartz Monzonite composition erupted onto the surface. The voluminous silicic ash flows of the middle member of the volcanic rocks were probably derived from the same magma that mostly crystallized subsurface to form the Butte Quartz Monzonite. Field, chemical, K-Ar age, and paleomagnetic evidence, however, strongly suggest that a time gap separated the extrusion of the middle-member volcanic rocks from the intrusion of the Butte Quartz Monzonite and related younger silicic variants.Compositional and time relations between the plutonic and genetically associated volcanic rocks are generally compatible with the concept that the volcanic rocks are eruptive equivalents of a shallow evolving batholith but seem incompatible with some specific aspects of the “extrusive complex” or “floored sheet” hypothesis as applied to the Boulder batholith by Hamilton and Myers (1967, 1974). 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.

The jacupirangite at Kodal, Vestfold, Norway

The large jacupirangite dyke at Kodal was first found by W.C. Brogger (1933) who published one chemical analysis of the rock. Recent investigations of the dyke as a potential ore body, including diamond-drilling operations, have shown that it is about 20 m wide and 2 km long. It strikes approximately E–W and has a general dip of 80 °S, cutting through larvikite and nordmarkite of the Oslo Permian Igneous Province. The jacupirangite has an average modal composition (volume percent): apatite 24, magnetite 37, ilmenite 9, pyroxene 25, amphibole and biotite 5. The iron-titanium oxides and apatite cement the pyroxene in a typical igneous texture. The Kodal dyke and other jacupirangites in adjoining areas of the Oslo Igneous Province all show a eutectic mixture of iron-titanium oxides and apatite which is assumed to form an immiscible liquid with silicate melts of monzonitic composition. This is assumed to be a possible explanation for the formation of the jacupirangites in the Oslo region.

Experimental Studies of Igneous Rock Series: Felsic Body Suite from the Needle Point Pluton, Wallowa Batholith, Oregon

The phase relationships of four analyzed granitic rocks which comprise a late-stage felsic body sequence intruding the Mesozoic granodiorites and tonalites of the Needle Point pluton, Wallowa Batholith, Oregon, have been determined in the presence of 15 wt percent water at pressures to 3 kbar. Pressure-temperature curves were located for the beginning of melting, and for the disappearance of K-feldspar, quartz, plagio-clase, biotite, and hornblende in granodiorite no. 678, quartz monzonites nos. 685 and 774, and granite no. 705. Compositions and structural states of plagioclases from the granitic rocks, basic masses intruding the batholith, and mafic inclusions, as well as the compositions of coexisting feldspars, were determined using the electron microprobe analyzer. Variations in each of these parameters throughout the melting interval of each granitic rock were measured at 2 kbar pressure. Although experimental conditions (excess H_2O present; fO_2 regulated but not controlled) forbid detailed comparison with natural occurrences, the results indicate that, at 2 kbar pressure, temperatures of at least 730° C and 780° C are required to generate liquids of granite and quartz monzonite composition. Several factors suggest that the normal product of partial fusion of many crustal rock types is a H_2O-undersaturated granite liquid; crystal mushes with this type of liquid are probably involved if intermediate magmas are derived from crustal sources.