Minerals In Granitic Rocks Research Articles

Petrogenesis of REE-mineralized granitic plutons in central Thailand, Southeast Asian tin belt: New insights from geochemistry and zircon U–Pb geochronology

Granitic rocks including biotite granite and biotite-muscovite granite exposed in the Uthai Thani area, central Thailand are located on the main eastern and central granitic belts of Southeast Asia. The biotite granites are characterized by an equigranular texture, whereas biotite-muscovite granites exhibit a porphyritic texture with K-feldspar megacrysts. Geochemically, biotite granites show metaluminous to weakly peraluminous high-K calc-alkaline affinity, whereas biotite-muscovite granite exhibits strongly peraluminous and shoshonitic. The biotite granites and biotite-muscovite granites have trace element features consistent with formation in subduction and syn-collision settings, respectively. The pressure–temperature conditions of emplacement in biotite and biotite-muscovite granite types are 1.94–2.28 kbar/676 °C–713 °C and 1.39–2.00 kbar/669 °C–698 °C, respectively, indicating solidification in upper crustal paleo-depths. Positive εHf (t) values of zircon in the biotite granites indicate similarity to I-type granite of the Sukhothai Terrane, whereas negative εHf (t) values of zircon in the biotite-muscovite granites compare well with S-type granites form in the Inthanon zone. Zircon U–Pb geochronology indicates that biotite granites might have emplaced during the Late Triassic is related to Paleo-Tethys subduction beneath the Indochina terrane, whereas biotite-muscovite granites might have emplaced during the Late Triassic to Early Jurassic period, probably as a result of collision between the Sibumasu and the Indochina Terranes. In the Uthai Thani area, the high total REE contents and the presence of primary REE minerals in granitic rocks reflect mineralization potential with respect to light REE, together with the magmatism related to Fe-Cu and Sn mineralization along the main granite belts in Thailand.

Occurrence and geochemistry of altered radioactive accessory minerals as sources of radionuclide in Mesozoic granite aquifers (Korea)

Accessory minerals in granitic rocks are unlikely significant radionuclide contributions to groundwater due to their remarkable durability. However, accessory minerals incorporating U and Th may suffer structural damages due to the radioactivity and become highly susceptible to alteration. This study investigates geochemistry coupled with textural analysis of the U–Th bearing accessory minerals using a field emission scanning electron microscope and an electron probe micro-analyzer. Altered zircons with numerous open structures related to the radioactive decay show higher contents of U and Th and low analytical totals. Some thorites show high contents of U and non-formula elements due to the hydrothermal alteration in the metamicted thorite. The cerianite including U occurs as micro-veinlet in fracture with trace of Fe and Mn oxides, which indicates secondary phase formation from the decomposed accessory minerals in an oxidizing environment. Some accessory minerals with the high content of U and Th have been found in Mesozoic granite terrain in South Korea, where high concentration levels of radionuclide in groundwater were also reported. The leaching of U may be more likely when the accessory minerals are highly metamicted or altered as found in our samples. The altered zircon and thorite of the study area could be major carriers of radioelement in Mesozoic granitic aquifers where the occurrence of soluble U-minerals has not been reported.

The Mechanism of Fluid Exsolution and Sn–W Precipitation: Example from the Hongling Pb–Zn Polymetallic Deposit and the Surrounding Area in Northern China

Metal migration and precipitation in hydrothermal fluids are important topics in economic geology. The Hongling polymetallic deposit comprises one of the most important parts of the Huanggangliang–Ganzhuermiao polymetallic metallogenic belt, which is in eastern Inner Mongolia. Except for lead–zinc skarn, minor cassiterite in the skarn and disseminated W–Sn mineralization in granitic rocks have also been found. The dominant Sn–W mineralization is in the northern part of the deposit, occurring as disseminated wolframite and cassiterite in aplite hosted in Mesozoic granite porphyry. The aplite together with pegmatite K-feldspar–quartz comprises vein dikes hosted in the granite porphyry, providing evidence for the transition from melt to fluid. The veins, dikes, and Sn–W mineralization in the aplite provide an opportunity to investigate fluid exsolution and the mechanics of metal precipitation. Based on field observations, the micrographic and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) results of the vein dikes, chronology, and the whole-rock geochemistry of the host rock, together with the fluid inclusion results, this paper discusses the characteristics of the causative magma, the mechanics of fluid exsolution and W–Sn precipitation. Our results show that the causative magma is of highly fractionated A-type granite affinity and has an intrusive age of late Mesozoic (133.3 ± 0.86 Ma). The magmatic evolution during shallow emplacement led to immiscibility between highly volatile, high-silica, and W- and Sn-enriched melts from the parent magma, followed by fluid exsolution from the water-rich melt. The alkaline-rich fluid exsolution led to a change in the redox state of the magma and the chilling of the melt. Fluid boiling occurred soon after the fluid exsolution and was accompanied by the degassing of CO2. The boiling and escape of CO2 from the fluid led to changes in fluid redox and W and Sn precipitation; thus, the W and Sn mineralization are mostly hosted in causative intrusions or peripheral wall rocks, which can be used as indicators for Sn–W exploration in the area.

Decomposition of spodumene mineral in granitic rocks from South Kalimantan - Indonesia by potassium sulphate

The decomposition behaviour of spodumene mineral in granitic rock from Kalimantan Indonesia by using potassium sulphate has been studied in this research. The granitic rock from Kalimantan is indicated to contain spodumene mineral. The sspodumene is one of the main minerals which contains lithium. The purpose of this study is to decompose the α-spodumene mineral in the granitic rock of Kalimantan to β-spodumene which is subsequently easier to be dissolved in water. In this study, the decomposition of α-spodumene was performed under variations of roasting temperatures (i.e. 350°C, 450°C, 550°C, 600°C, 700°C, 800°C, 900°C and 1000°C) and roasting times (20 min, 40 min and 60 min). The results of the decomposition products were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was identified that the granitic rock from Kalimantan consists of α-spodumene (LiAlSi2O6) with lithium content of 3.09 ppm and the other major minerals are quartz (SiO2) and albite (NaAlSiO3O8). The α-spodumene was completely converted to β-spodumene at 700°C for 60 minutes.

In situ major-, trace-elements and Sr-Nd isotopic compositions of apatite from the Luming porphyry Mo deposit, NE China: Constraints on the petrogenetic-metallogenic features

Apatite is an important accessory mineral in granitic rocks and can record important petrogenetic-metallogenic information. In particular, magmatic apatite can provide information on the volatile composition and magma source of the ore-forming rocks in porphyry deposits. This work focuses on magmatic apatite within the ore-forming intrusion of the Luming super-large porphyry Mo deposit. We use electron probe micro-analyzer (EPMA) and laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) analytical methods to analyze the major- and trace-element and Sr-Nd isotopic compositions of the apatite. The results show that the apatite grains are magmatic apatite, classified as fluorapatite. The trace-element patterns of the apatites feature clearly negative Sr, Ba, and Zr anomalies and Ba, Nb, Sr, Zr and Eu depletions that are more distinct than those in the granite porphyry and monzogranite in the Luming deposit. The apatites exhibit slight LREE enrichment and distinctly negative Eu anomalies. The positive Eu/Eu∗ (δEu)-Ga correlation and the strongly negative Eu anomaly indicate that the magma of this granite porphyry may have been in a relatively reductive state. The apatites also indicate that the granite porphyry is a non-adakitic rock, which is consistent with the whole-rock geochemical characteristics. Furthermore, the apatites feature low Sr contents and δEu values and high F/Cl ratios, similar to the characteristics of typical Mo deposits. The 87Rb/86Sr and 87Sr/86Sr ratios of the apatites are 0.012811–0.037958 and 0.710897–0.714423, respectively. The (87Sr/86Sr)i (ISr) values are 0.710865–0.721183. The 147Sm/144Nd and 143Nd/144Nd ratios are 0.132166–0.225171 and 0.512520–0.512681, respectively. The εNd(t) values are −1.78–0.21, and the two-stage Nd model ages are 949–1065 Ma. The approximately positive εNd(t) values and young Nd model ages of the apatite are similar to those of the ore-forming rocks in Early Jurassic Mo deposits in NE China, indicating that these rocks shared the same magma source, which originated from the partial melting of juvenile crust.

A computer vision system for identification of granite-forming minerals based on RGB data and artificial neural networks

Granitic stones are widely used in the field of Cultural Heritage in the north-western Iberian Peninsula. In some activities regarding conservation, such as the laser cleaning, it is of great interest the identification of the minerals on the granitic stone surface in order to improve the treatment and to avoid damages by means of the adaption of the fluence to each different forming mineral. The aim of this work is the optimization of a back propagation artificial neural network (ANN) in order to obtain the rapid and reliable identification of forming minerals in granitic rocks by means of RGB images. Our goal is, eventually, in situ monitoring the laser cleaning of granitic stonework. The results obtained, though preliminary, led a high degree of correct identification of the forming minerals for three different granitic types.

Dispersed mineralization in granitic rocks in the Dukat ore field, the Russian Northeast: Sources and relationship with epithermal gold-silver and silver-base-metal ores

The dispersed mineralization in the Late Cretaceous leucogranite of the Dukat ore field comprises melanocratic high-sulfide epidote-feldspar, pyroxene-feldspar and low-sulfide allanite-fluorite-feldspar inclusions in greisenized intrusions. The silver-base-metal mineralization is composed of pyrite, pyrrhotite, small particles of Pb, Zn, Sn, Ag, and Sb sulfides and oxides, their native species, and intermetallic compounds; the rare-metal mineralization consists of REE, Th, U, Ti, Zr, Nb, Ta, and W oxides, silicates, and aluminosilicates. The isotopic Nd, Sr, and Pb isotopic compositions and geochemical characteristics of the mineralized inclusions, rock-forming minerals of granitoids, hydrothermal minerals of preore metasomatic propylites and orebodies at the Dukat deposit show that their components have been taken from heterogeneous domains of the Paleozoic juvenile continental crust of the Siberian Platform.

The Strel’tsovka uranium district: Isotopic geochronological (U-Pb, Rb-Sr, Sm-Nd) characterization of granitoids and their place in the formation history of uranium deposits

An isotopic geochronological study of Russia’s largest Strel’tsovka uranium district has been carried out. Polychronous granite generation, which determined the structure of the pre-Mesozoic basement, had important implications for the formation of volcanotectonic structural elements bearing economic uranium mineralization. The study of U-Pb, Rb-Sr, and Sm-Nd isotopic systems of whole-rock samples and minerals of granitic rocks allowed us to estimate the deportment of these systems in spatially conjugated granite-forming and hydrothermal processes differing in age and gave grounds for revising the age of granites pertaining to the Urulyungui Complex and refining the age of the Unda Complex.

REE Abundance and REE Minerals in Granitic Rocks in the Nanling Range, Jiangxi Province, Southern China, and Generation of the REE‐rich Weathered Crust Deposits

AbstractStudies of Mesozoic granites associated with rare earth element (REE)‐rich weathered crust deposits in southernmost Jiangxi Province indicate that they have high‐K to shoshonite compositions and belong to ilmenite‐series I‐type granites. Of the studied rocks at 59–292 ppm of bulk REE content, the highest are seen in the biotite granites of Dingnan (358, 429 ppm) and mafic biotite granite of the Wuliting Granite (344 ppm) near the Dajishan tungsten mine, both areas where weathered‐crust REE deposits occur. REE‐bearing accessory minerals in these granites are mainly zircon, apatite and allanite, and REE‐fluorocarbonates are common. REE enrichment occurs in the rims of apatite crystals, and in fluorocarbonates that occur along grain boundaries of and cracks in major silicate minerals, and in fluorocarbonates that replaced altered biotite. It is therefore thought that a major part of the REE content of these granites was concentrated during deuteric activity, rather than during magmatic crystallization. The crack‐filling REE‐fluorocarbonates could subsequently have been easily leached out and deposited in weathered crust developed during a long period of exposure.

Surface temperature differences between minerals in crystalline rocks: Implications for granular disaggregation of granites through thermal fatigue

Thermal expansion differences between minerals within rocks under insolation have previously been assumed to drive breakdown by means of granular disaggregation. However, there have been no definitive demonstrations of the efficacy of this weathering mechanism. Different surface temperatures between minerals should magnify thermal expansion differences, and thus subject adjacent minerals to repeated stresses that might cause breakdown through fatigue failure. This work confirms the existence of surface temperature differences between minerals in granitic rocks under simulated short-term temperature fluctuations so as to discriminate their potential for initiating granular disaggregation. The influence of colour, as a surrogate for albedo, and crystal size, as a function of thermal mass are specifically identified because of their ease of quantification. Four rock types with a range of these properties were examined, and subjected to repeated short-term temperature cycles by radiative heating and cooling under laboratory conditions. Results show that while albedo is the main control for overall and individual maximum temperatures, crystal size is the main factor controlling higher temperature differences between minerals. Thus, stones with large differences of mineral sizes can undergo magnified stresses due to thermal expansion differences.

Direct evidence of late Archean to early Proterozoic anoxic atmosphere from a product of 2.5 Ga old weathering

Because Precambrian paleosols (ancient soils formed by weathering) are usually subjected to later alteration, the evidence gleaned from chemical studies has provided inconclusive evidence on the atmospheric O2 evolution. In a 2.6–2.45 Ga paleosol developed on Archean granite near Pronto mine, Canada, we found that Ce-rich rhabdophane formed directly during weathering, replaced primary apatite, and has survived for about 2.5 Ga because of its low solubility and high resistance to heat. Our data show that La, Ce, and Nd behaved similarly in both rocks and rhabdophane, i.e., most Ce existed as Ce3+ in the weathering solution, unlike the younger weathering profiles where Ce3+ oxidizes and forms cerianite, CeO2. The presence of rhabdophane with Ce3+ throughout the Pronto paleosol provides compelling evidence of an anoxic atmosphere 2.6–2.45 Ga ago. Because apatite is a common accessory mineral in granitic rocks, Ce content of the replaced rhabdophane can be a useful indicator for tracing O2 evolution in the Precambrian.

Petrographic characterization of the hydrothermal alteration zones associated with gold mineralization in granitic rocks of the Batalha gold field, Tapajos (Para) - Brazil

The granitic rocks that host gold mineralizations in the Batalha gold field (Para State, Brazil) present granophyric structures that indicate crystallization at shallow levels and the influence of alkalis- and silica-rich, post-magmatic fluids. Locally, they present weakly developed rapakivi textures and their composition is predominantly of 3a and 3b granites. Their petrographic characteristics allow correlation with the Maloquinha Suite rocks, of ages around 1.84 Ga. Petrographic studies carried out using samples from drill-holes that intersect zones mineralized in gold made the characterization of ample pervasive hydrothermal alteration zones possible, showing continuous variations of the fluid compositions from the post-magmatic stages. The oldest event is characterized by sodic alterations, followed by potassic alteration producing microcline and biotite, which confers a dark red color to the rocks; propylitic alteration is superimposed on both. Final stages may have evolved to locally pervasive sericitic alteration, but this type was better characterized as of fissure style and associated with minor shear zones. Gold mineralizations are predominantly associated with propylitic alterations, but the highest grades are observed in sericitic zones and, more specifically, as free, coarse-grained gold hosted by minor quartz veins, with associated carbonates, sulfides and fluorite.

Mise en évidence de cordiérite héritée des terrains traversés dans le pluton granitique des Oulad Ouaslam (Jebilet, Maroc)

Cordierite, a quite common mineral in granitic rocks, originates from various processes; many types of crystals can be found in a given massif. The high-level Oulad Ouaslam pluton, in Morocco, displays cordierites of three different origins. Primary magmatic crystals, as well as later ones, grown in equilibrium with a water-rich fluid phase, are readily distinguishable from inherited metamorphic cordierites. The latter, which are characterized by numerous spinel (Zn-poor hercynite) inclusions, are the most interesting. They originated from the disaggregation of peraluminous enclaves, which either represent refractory assemblages or solid products of incongruent melting reactions. Thermobarometric data indicate that these rocks equilibrated at about 750 °C and 3,5 kbar (350 MPa). These values are believed to represent the conditions under which the rocks were enclaved, and of the resulting partial melting event. Peraluminous enclaves, and thus inherited cordierite, are not derived from the source region of the granite. They are partly digested pelitic xenoliths, picked up by the ascending magma. Therefore, they represent true relicts of assimilated rocks. Among the possible mechanisms of cordierite formation, contamination of the magma by aluminous rocks is a classical one. However, no clear textural evidence of the process has ever been presented in the literature. The Oulad Ouaslam pluton provides such evidence and thus confirms, at least locally, the validity of this hypothesis.

Integration of remotely sensed and gis data for mineral exploration: Halifax Pluton area, Nova Scotia, Canada

Abstract Remote sensing and geographic information system techniques as an aid to reconnaissance mineral exploration in a vegetated, glaciated terrain is presently viable. Through the examination of a multilayer database incorporating Landsat Thematic Mapper (TM), airborne gamma‐ray spectrometric and topographic data sets, useful geologic information was extracted and integrated. A portion of the South Mountain Batholith (SMB) west of Halifax was selected as an area suitable for an integrated remote sensing investigation in a humid climate with an aim towards targeting any possible mineralization in granitic rocks. Through image analysis, TM imagery over this area was enhanced and manipulated for detailed lineament mapping and for mapping of possible outcrop distribution. Subsequent transfer of digitized topographic and gamma‐ray spectrometric data from a geographic infomnation system (GIS) to an image analysis system (IAS) provided the means for the geometric resampling of TM imagery and for the superimp...

Potassium/rubidium ratios and metallogeny of the Rautio batholith, western Finland

Abstract Potassium/rubidium ratios of the granitoids (mainly granodiorites) of the Svecokarelidic (1.8–1.9 Ga) Rautio batholith in western Finland are reported in order to evaluate the use of the ratio as an indicator of the porphyry-type Mo-Cu mineralizations associated with the batholithic rocks. The results show that, in spite of the occurrence of several minor Mo-Cu mineralizations within the batholith, the K/Rb ratios are not lowered to the values reported as critical for mineralization in granitic rocks. It is therefore concluded that the criteria of ore-bearing potential applied to granites are not applicable in batholiths which are mainly granodioritic.

Neutron activation-induced beta autoradiography as a technique for locating minor phases in thin section; application to rare earth element and platinum-group element mineral analysis

Samples which have been irradiated in a thermal neutron flux are first allowed to decay for an appropriate period. The distribution of isotopes which decay by beta emission is then detected using a specific nuclear track emulsion. Data are presented to show the relative sensitivities of all elements which emit beta particles after thermal neutron capture and to demonstrate their relative rates of decay. The technique may be used most sensitively to locate minerals containing high concentrations of Sc, Co, Y, Sb, Cs, rare earth elements, Ta, Re, Ir, Au, Th, and U. Potential applications in the systematic search for rare earth element-bearing minerals in granitic rocks and platinum-group element minerals in chromitites.--Modified journal abstract.

Base Metal Distribution in Granitic Rocks; data from the Rocky Hill and Lights Creek Stocks, California

Significant systematic areal variation patterns in copper and zinc contents exist in rocks of the Rocky Hill (Tulare County) and Lights Creek (Plumas County) stocks, California. Significant areal variation patterns in copper contents of biotite and sulfide phases, total sulfide contents and other properties also exist in the Rocky Hill stock. These patterns are related, and an increase in the content of copper-bearing sulfides is commonly accompanied by a decrease in the copper content of the associated ferro-magnesian silicate phases. This relationship is usually independent of the total copper content of the rock and of the fractionation trends shown by other metals. The distribution patterns of total sulfides and the intensity of deuteric alteration, however, are related, with both increasing in content or intensity towards the core of the stock. Some copper may have been extracted from the silicate phases and fixed in sulfides during alteration. In spite of a low overall content of copper in the Rocky Hill stock, considerable concentration has occurred in a small area. The distribution of zinc in this stock does not appear to be significantly related to any of the above factors.Transfer or migration of copper within the rocks of the Rocky Hill stock is indicated by comparisons of the frequency distributions of copper and zinc and by other data. Consideration of these distribution patterns in relation to models of mineralization in granitic rocks points out that structural level and other aspects of the local geologic setting can have an important influence on the nature of such patterns. Interpretations in regard to metallogenesis and exploration should take this influence into account.Calculated activities of Cu, Zn, and annite molecule in biotite for estimated conditions of late crystallization at Rocky Hill appear to be in satisfactory agreement with observed analysis data. The total content of sulfur in the rock, including the vapor phase coexisting with it during crystallization, then becomes the critical factor in controlling sulfide-silicate partitioning of copper. Under the crystallization conditions estimated for Rocky Hill, a separate zinc sulfide phase is not stable.An analysis of the variation data for Cu and Zn in these stocks provides estimates of local scale or outcrop variation and establishes the significance of large scale (regional) variations occurring in both. It also provides a limited basis for an estimation of the type of distribution involved at the local or outcrop scale. As a result of fracture-controlled sulfide distribution in the Lights Creek stock, local scale variation is much larger than that at Rocky Hill and more dependent on sampling configuration; highly significant large scale variation in Cu and Zn is nonetheless present.

Zircon and Other Accessory Minerals, Coast Range Batholith, California

By heavy-mineral analyses and statistical studies of zircon morphology the author has tried to correlate a series of granitic plutons in the Coast Ranges of central California and the Farallon Islands. Zircon-elongation data, analyzed by reduced major axis and elongation-frequency studies, are interpreted to be indicative of two distinct crystallization histories for quartz diorite. Intrusions forming segments of the separate areas can possibly be correlated. A distinctive elongation trend for zircon in granite represents crystallization under different conditions and suggests that true granites are not simple differentiates of the quartz diorite magma. Zircon in gabbro and in mafic xenoliths in quartz diorite is predominantly anhedral, whereas in granitic rocks it is euhedral. Zircon morphology and mineralogy of other accessory minerals suggest that the dark xenoliths are fragments of mafic igneous rocks, possibly cognate. Characteristic accessory-mineral assemblages for the major rock types are as follows: apatite-sphene-epidote-clinozoisite-allanite-zircon in quartz diorite, the most abundant rock type, and in closely associated granodiorite and adamellite; garnet-zircon-monazite-xenotime in granite; and brown hornblende-ilmenite-cummingtonite-apatite in gabbro. Heavy minerals from the large quartz diorite bodies show general similarity but wide variations in total and relative amounts. The mineral assemblages indicate similar sources for the quartz diorite, but definite correlations based on accessory mineralogy are uncertain because the suites are not unique compared to accessory minerals of granitic rocks in general.