Fluoride releasing kinetics in a weathered bearing biotite gneiss

In several regions of the dry zone of Sri Lanka, excessive quantities of fluoride (F-) in groundwater have affected the water quality significantly. Apart from the well-known prevalence of dental fluorosis, Chronic Kidney Disease of uncertain etiology (CKDu) is widespread in different pockets in the dry zone of Sri Lanka [1]. Fluoride is one of the substances suspected of being causative of CKDu in the area. Since the kidneys retain more F- than in any other soft tissue and excess F- exposure can cause kidney disease. Within the same zone, the prevalence of CKDu varies by geographic area in a ground water and spatial distribution of selected trace elements in groundwater. The optimum F- level in drinking water, according to WHO guidelines, is 1.5 (mg/L); however, due to the unfavorable climatic conditions that exist in tropical countries, people ingest more water than normal intake, resulting in a high F- intake. The source of F- is geogenic. It has been found that the F- content of basement rocks ranges from 9.5×10-5 to 1.44×10-3 kg/L in the region [3]. Farmers consume about 2-3 liters of water a day to quench their thirst, resulting in a daily F- intake of 3×10-3-1×10-2 kg/L [4].

Eoarchean to Neoproterozoic Detrital Zircons from the South of Meiganga Gold-Bearing Sediments (Adamawa, Cameroon): Their Closeness with Rocks of the Pan-African Cameroon Mobile Belt and Congo Craton

The core of detrital zircons from the southern Meiganga gold-bearing placers were analyzed by Laser Ablation Split Stream analytical techniques to determine their trace element abundances and U-Pb ages. The obtained data were used to characterize each grain, determine its formation condition, and try to trace the provenance. The Hf (5980 to 12,010 ppm), Y (27–1650 ppm), U (25–954 ppm), Th (8–674 ppm), Ti (2–256 ppm), Ta, Nb, and Sr (mainly <5 ppm), Th/U (0.06–2.35), Ti zircon temperature (617–1180 °C), ∑REE (total rare earth element) (98–1030 ppm), and Eu/Eu* (0.03 to <1.35) are predominant values for igneous crustal-derived zircons, with very few from mantle sources and of metamorphic origin. Crustal igneous zircons are mainly inherited grains crystallized in granitic magmas (with some charnockitic and tonalitic affinities) and a few from syenitic melts. Mantle zircons were crystallized in trace element depleted mantle source magmatic intrusion during crustal opening. Metamorphic zircons grown in sub-solidus solution in equilibrium with garnet “syn-metamorphic zircons” and in equilibrium with anatectic melts “anatectic zircons” during crustal tectono-metamorphic events. The U-Pb (3671 ± 23–612 ± 11 Ma) ages distinguish: Eoarchean to Neoproterozoic igneous zircons; Neoarchean to Mid Paleoproterozoic anatectic zircons; and Late Neoproterozoic syn-metamorphic grains. The Mesoarchean to Middle Paleoproterozoic igneous zircons are probably inherited from pyroxene-amphibole-bearing gneiss (TTGs composition) and amphibole-biotite gneiss, whose features are similar to those of the granites, granodiorites, TTG, and charnockites found in the Congo Craton, south Cameroon. The youngest igneous zircons could be grains eroded from Pan-African intrusion(s) found locally. Anatectic and syn-metamorphic zircons could have originated from amphibole-biotite gneiss underlying the zircon-gold bearing placers and from locally found migmatized rocks that are from the Cameroon mobile belt, which could be used as proxies for tracking gold.

Petrochemistry and petrogenesis of the Precambrian Basement Complex rocks around Akungba-Akoko, southwestern Nigeria

Field, mineralogical and petrochemical studies of the Precambrian Basement Complex rocks around Akungba-Akoko were carried out with the aim of determining their petrology, petrochemical characteristics and petrogenesis. The petrology of Akungba-Akoko area comprises migmatite, granite gneiss and biotite gneiss intruded by biotite granite, charnockite and minor felsic and basic rocks. Seventeen representative samples of the granite gneiss, biotite gneiss, biotite granite and charnockite were collected during field geological mapping of the area for petrographic and geochemical analyses. Modal mineralogy revealed that the granite gneiss, biotite gneiss and granite have assemblages of quartz + feldspar + mica + hornblende + opaques and are granitic in composition. The charnockite is characterized by anhydrous mineral assemblage of quartz + feldspar + biotite + hornblende + pyroxene + opaques. Petrochemical data of the rocks revealed that they are moderately to highly enrich in SiO2, sub-alkaline, peraluminous, magnesian to ferroan and calcic and have K/Rb < 283. The geochemical characteristics and discrimination of the rocks indicated that the granite gneiss and biotite gneiss are orthogneisses formed by metamorphism of igneous protoliths of granitic composition and the biotite granite and charnockite are of igneous/magmatic origin. The biotite granite, charnockite and the igneous protoliths of the biotite gneiss are I-type granitoids formed from crustal igneous-sourced melt(s), while the igneous protoliths of the granite gneiss is a S-type granitoid probably derived from shallow crustal or sedimentary-sourced melt(s). Tectonic discrimination of the rocks indicated that they were formed during a phase of magmatic activity related to collision and subduction.

Thermodynamic modeling of the formation of corundum-bearing rocks within the Belomorian mobile belt using Perple_x software

&lt;p&gt;More than a dozen deposits of corundum-bearing rocks are known within the Belomorian mobile belt (references in Serebryakov, Rusinov, 2004); their genesis remains debatable. Some authors consider corundum-bearing rocks to be normal metamorphic rocks (for example, Lebedev et al., 1974), others suggest the metasomatic genesis of rocks with corundum: 1 &amp;#8211; corundum-bearing rocks were formed as a result of high-temperature high-pressure (600 - 700&amp;#186;C, 7 - 8 kbar) metasomatism which was accompanied by desilification and the introduction of Ca and Na (Serebryakov, Rusinov, 2004); 2 &amp;#8211; these rocks are a product of hydrothermal alteration of gneisses by fluids associated with basic intrusions (Bindeman et al., 2014). All these assumptions were made without a detailed physicochemical analysis of the mineral parageneses of corundum-bearing rocks.&lt;br&gt;The Perple_X software package (Connolly, 2005) is discussed in some recent works as an effective tool for the thermodynamic modeling of the open systems (Goncalves et al., 2012, Manning, 2013). Using the Perple_X software package (version Perple_X 6.8.7, updated 04.07.2019) we constructed P-T, T-&amp;#956; (SiO&lt;sub&gt;2&lt;/sub&gt;), and &amp;#956;(SiO&lt;sub&gt;2&lt;/sub&gt;)-&amp;#956;(Na&lt;sub&gt;2&lt;/sub&gt;O) pseudosections for a given chemical composition of kyanite-garnet-biotite gneiss of the Chupa sequence. The hp02ver.dat thermodynamic database was used, the diagram &amp;#956;(SiO&lt;sub&gt;2&lt;/sub&gt;) - &amp;#956;(Na&lt;sub&gt;2&lt;/sub&gt;O) was calculated for P = 8 kbar, T = 650&amp;#186;C, in the presence of a carbonic-aqueous fluid with X(CO&lt;sub&gt;2&lt;/sub&gt;) = 0.3. Selected solid solution models are Ca-Amph(D) for hornblende, Gt(HP) for garnet, St(HP) for staurolite, Bi(HGP) for biotite, feldspar for feldspar, Sp(HP) for spinel.&lt;br&gt;The results show that the majority of corundum-bearing rocks varieties (amphibole-free corundum-bearing rock, amphibole-bearing rock with corundum, altered quartz-free kyanite-garnet-biotite gneiss, kyanite-garnet amphibolite) could be formed by metasomatic alteration of kyanite-garnet-biotite gneisses of the Chupa sequence. This process was characterized by a significant decrease in &amp;#181;(SiO&lt;sub&gt;2&lt;/sub&gt;) and a slight increase in &amp;#181;(Na&lt;sub&gt;2&lt;/sub&gt;O). Our conclusion is partly consistent with the hypothesis that corundum-bearing rocks were formed as a result of metasomatism, which was accompanied by desilification of Ky-Grt-Bt gneisses and the introduction of Na and Ca (Serebryakov, Rusinov, 2004).&lt;/p&gt;&lt;p&gt;The study was conducted according to the IPGG project 0153-2019-0004.&lt;/p&gt;&lt;p&gt;Bindeman I.N., Serebryakov N.S., Schmitt A.K. et al. (2014) Field and microanalytical isotopic investigation of ultradepleted in &lt;sup&gt;18&lt;/sup&gt;O Paleoproterozoic &amp;#8220;Slushball Earth&amp;#8221; rocks from Karelia, Russia. Geosphere. V. 10. P. 308-339.&lt;/p&gt;&lt;p&gt;Connolly J.A.D. (2005) Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation.&amp;#160; Earth and Planetary Science Letters, 236, p. 524&amp;#8211;541.&lt;/p&gt;&lt;p&gt;Goncalves P., Oliot E., Marquer D., Connolly J.A.D. (2012) Role of chemical processes on shear zone formation: an example from the Grimsel metagranodiorite (Aar massif, Central Alps). J. metamorphic Geol., 30, p. 703&amp;#8211;722.&lt;/p&gt;&lt;p&gt;Lebedev V.I., Kalmykova N.A. &amp; Nagaytsev Yu.V. (1976) Corundum-staurolite-hornblende schists of the Belomorskiy complex, International Geology Review, 18:6, 653-662.&lt;/p&gt;&lt;p&gt;Manning C.E. (2013) Thermodynamic modeling of fluid-rock interaction at conditions of the earth's middle crust to upper mantle. Reviews in Mineralogy &amp; Geochemistry, 76, p. 135-164.&lt;/p&gt;&lt;p&gt;Serebryakov, N.S., Rusinov, V.L. (2004) High-T high-pressure Ca, Na metasomatism and formation of corundum in the precambrian Belomorian mobile belt. Dokl. Earth Sci. 395, pp. 549&amp;#8211;533.&lt;/p&gt;

Geochemical Features and Geological Processes Timescale of the Achaean TTG Complexes of the Ingozero Massif and the Pechenga Frame (NE Baltic Shield)

This article provides a geological review and results of the structural, metamorphic, and geochronological studies of the Pechenga frame outcrops located in the NW part of the Central-Kola terrain and the Ingozero massif outcrops situated in the northeastern part of the Belomorian mobile belt of the Kola Region (NW Baltic Shield). As a result of the work, the deformation scales and ages of the geological processes at the Neo-Archaean–Paleoproterozoic stage of the area’s development were compiled, and the reference rocks were dated. The petrochemical and geochemical characteristics of the Ingozero rocks are similar to those of tonalite–trondhjemite–granodiorite (TTG) complexes established on other Archaean shields. The isotope U–Pb dating of individual zircon grains from the biotite gneisses provided the oldest age for magmatic protolith of the Ingozero gneisses, which is 3149 ± 46 Ma. Sm–Nd model ages showed that the gneisses protolite initial melt formed at 3.1–2.8 Ga. Ages of metamorphic processes were determined by using isotope U–Pb dating ID TIMS (isotope dilution thermal ionization mass spectrometry): Biotite gneisses—2697 ± 9 Ma; amphibole–biotite gneisses—2725 ± 2 Ma and 2667 ± 7 Ma; and biotite–amphibole gneisses 2727 ± 5 Ma. Ages of granitoids, which cut the deformed gneisses, are 2615 ± 8 Ma and 2549 ± 31 Ma for plagiogranites and pegmatoid veins in gneisses, respectively. The following age sequence of geological processes was established by using U–Pb zircon dating: 2.8 Ga—The time of the garnet–biotite gneiss metamorphism; 2722 ± 9 Ma—The granodiorite crystallization time; 2636 ± 41 Ma—The aplite emplacement age and 2620 ± 16 Ma—The age of pegmatites origin, which marked final stages of the Archaean evolution; 2587 ± 5 Ma—The age of gabbros emplacement and 2507 ± 7 Ma—The age of gabbros metamorphism; 2522–2503 Ma—The origin time of the iron quartzite interpreted as the age of gabbros and biotite gneiss metamorphism.

The Origin of Garnets in Anatectic Rocks from the Eastern Himalayan Syntaxis, Southeastern Tibet: Constraints from Major and Trace Element Zoning and Phase Equilibrium Relationships

Amphibolite- and granulite-facies metamorphic rocks are common in the eastern Himalayan syntaxis of southeastern Tibet. These rocks are composed mainly of gneiss, amphibolite and schist that underwent various degrees of migmatization to produce leucogranites, pegmatites and felsic veins. Zircon U–Pb dating of biotite gneiss, leucocratic vein and vein granite from the syntaxis yields consistent ages of ∼49 Ma, indicating crustal anatexis during continental collision between India and Asia. Garnets in these rocks are categorized into peritecitc and anatectic varieties based on their mode of occurrence, mineral inclusions and major- and trace-element zoning. The peritectic garnets mainly occur in the biotite gneiss (mesosome layer) and leucocratic veins. They are anhedral and contain abundant mineral inclusions such as high-Ti biotites and quartz, and show almost homogeneous major-element compositions (except Ca) and decreasing HREE contents from core to rim, indicating growth during the P- and T-increasing anatexis. Peak anatectic conditions at 760–800°C and 9–10·5 kbar are well constrained by phase equilibrium calculations, mineral assemblages, and garnet isopleths. In contrast, anatectic garnets only occur in the vein granite. They are round or subhedral, contain quartz inclusions, and exhibit increasing spessartine and trace-element contents from core to rim. The garnet–biotite geothermometry and the garnet–biotite–plagioclase–quartz geobarometry suggest that the anatectic garnets crystallized at ∼620–650°C and 4–5 kbar. Some garnet grains show two-stage zoning in major and trace elements, with the core similar to the peritectic garnet but the rim similar to the anatectic garnet. Mineralogy, whole-rock major- and trace-element compositions and zircon O isotopes indicate that the two types of leucosomes were produced by hydration (water-present) melting and dehydration (water-absent) melting, respectively. The leucocratic veins contain peritectic garnet but no K-feldspar, have lower whole-rock K2O contents and Rb/Sr ratios, higher whole-rock CaO contents and Sr/Ba ratios, and show homogeneous δ18O values that are lower than those of relict zircons, indicating that such veins were produced by the hydration melting. In contrast, the vein granite contains peritectic garnet and K-feldspar, has higher whole-rock K2O contents and Rb/Sr ratios, lower whole-rock CaO contents and Sr/Ba ratios, and shows comparable δ18O values with those of relict zircons, suggesting that this granite were generated by the dehydration melting. Accordingly, both hydration and dehydration melting mechanisms have occurred in the eastern Himalayan syntaxis.

Petrographic characteristics and zircon UPb geochronology of granitogneiss rocks in the Chu Lai - Kham Duc area (Quang Nam province)

The early Palaeozoic granitogneiss association in the Chu Lai - Kham Duc area (Quang Nam) is a large area of hundreds of km2, along southern of the East – West ductile deformation zones (Tam Ky – Phuoc Son fault zone), which is studied in detail in different geologic maps scales by the geologists, which is named Chu Lai complex. The five samples studied in detail are composed mainly of granitogneiss and biotite gneiss from the Chu Lai - Kham Duc area. The samples were crushed and large zircons were extracted. The in-situ zircon U–Pb geochronology was conducted on five samples (60 zircons in total) of age between 444 Ma and 426 Ma. These ages indicated the prolonged magmatic – tectonic period between the late Ordovician and middle Silurian in Kon Tum massif.