alkaline complexes
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Abstract New data on the gold mineralization related of the Late Paleozoic alkaline complexes of North Vietnam are presented. Two types of gold mineralization associated with syenites and granosyenites have been identified: gold only and gold-polymetallic. Geochemical characteristics are given for both types and the first data on the sulfur isotopic composition of ore minerals.

Phosphate rocks are a vital resource for world food supply and security. They are the primary raw material for phosphoric acid and fertilizers used in agriculture, and are increasingly considered to be a potential source of rare earth elements. Phosphate rocks occur either as sedimentary deposits or igneous ores associated with alkaline rocks. In both cases, the genesis of high-grade phosphate rocks results from complex concentration mechanisms involving several (bio)geochemical processes. Some of these ore-forming processes remain poorly understood and subject to scientific debate. Morocco holds the world’s largest deposits of sedimentary phosphate rocks, and also possesses several alkaline complexes with the potential to bear igneous phosphate ores that are still largely underexplored. This paper summarizes the main geological features and driving processes of sedimentary and igneous phosphates, and discusses their global reserve/resource situation. It also provides a comprehensive review of the published data and information on Moroccan sedimentary and igneous phosphates. It reveals significant knowledge gaps and a lack of data, inter alia, regarding the geochemistry of phosphates and basin-scale correlations. Owing to the unique situation of Moroccan phosphates on the global market, they clearly deserve more thorough studies that may, in turn, help to constrain future resources and/or reserves, and answer outstanding questions on the genesis of phosphates.

Abstract. A two-stage fuzzy inference system (FIS) is applied to prospectivity modelling and exploration-target delineation for REE deposits associated with carbonatite-alkaline complexes in western part of the state of Rajasthan in India. The design of the FIS and selection of the input predictor map are guided by a generalised conceptual model of carbonatite-alkaline-complexes-related REE mineral systems. In the first stage, three FISs are constructed to map the fertility and favourable geodynamic settings, favourable lithospheric architecture, and favourable shallow crustal (near-surface) architecture, respectively, for REE deposits in the study area. In the second stage, the outputs of the above FISs are integrated to map the prospectivity of REE deposits in the study area. Stochastic and systemic uncertainties in the output prospectivity maps are estimated to facilitate decision making regarding the selection of exploration targets. The study led to identification of prospective targets in the Kamthai-Sarnu-Dandeli and Mundwara regions, where project-scale detailed ground exploration is recommended. Low-confidence targets were identified in the south of the Siwana ring complex, north and northeast of Sarnu-Dandeli, south of Barmer, and south of Mundwara. Detailed geochemical sampling and high-resolution magnetic and radiometric surveys are recommended in these areas to increase the level of confidence in the prospectivity of these targets before undertaking project-scale ground exploration. The prospectivity-analysis workflow presented in this paper can be applied to delineation of exploration targets in geodynamically similar regions globally such as Afar province (East Africa), Paraná-Etendeka (South America and Africa), Siberian (Russia), East European Craton-Kola (Eastern Europe), Central Iapetus (North America, Greenland and the Baltic region), and the Pan-superior province (North America).

AbstractExisting geochronological information on Deccan indicates prolonged (started at 68.5 Ma) alkaline magmatism related to the Réunion mantle plume based on the 40Ar/39Ar ages from Sarnu-Dandali and Mundwara alkaline complexes. We studied in detail an alkaline lamprophyre, from the Sarnu-Dandali complex, rich in groundmass (magmatic) as well as xenocrystic phlogopites and clinopyroxenes. 40Ar/39Ar age determinations of the phlogopites from this lamprophyre, reveal two distinct ages of 65.44±1.5 Ma and 68.17±1Ma. However, paleomagnetic results show a VGP at 32.31 N and 298.52 E concordant with that of the Deccan Super Pole at 65.5 Ma and support the younger eruption age at ca. 65.44±1.5Ma. Analyzed phlogopites lack any signs of retention of excess radiogenic Ar and yield similar inverse isochron ages, which suggests that the older age of ca. 68.17±1Ma belongs to the crystallization of xenocrystic phlogopite during mantle metasomatism. Trace element compositions support derivation of lamprophyre magma from an OIB- type enriched (metasomatized) mantle source with an involvement of phlogopite.This finding suggests that the pre-Deccan ages of ca. 68-69 Ma reported previously, may reflect the timing of metasomatism of the subcratonic lithospheric mantle during the separation of Greater-Seychelles from India at ca. ∼68.5 Ma. The absence of pre-Deccan alkaline rocks therefore indicates the short-duration (occurred between 67-65 Ma) of alkaline as well as small-volume, volatile-rich magmatism directly related to the Réunion (Deccan) plume.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5490881

<p>The Yllymakh massif is one of the Mesozoic ring intrusions of Central Aldan, Yakutia. Geological relations between rocks in this massif are enough complicated to call it multiphase. Therefore, the idea about one or different magma sources is still the topic of modern discussions. According to the previous works, there are a lot of different rocks in the Yllymakh massif. And our petrological investigation [Vasyukova et al, 2020] accepted three groups of rock that differ a lot from each other. They have not great differences in mineral composition (aegirine in all rocks, feldspars in syenites). But some critical points in their geochemical features and ages. Foid syenites containing nepheline and pseudoleucite belong to the first group. They are 140±1.9Ma old. Second group includes alkali syenites (131±2.4Ma old). And the third group of rocks are alkaline granites mostly consist of alkali pyroxene and quartz (125±1.9Ma old).</p><p>All studied rocks are divided into three groups according to the silica content and contents of the most of other elements. Points marking the composition of syenites from different groups form multidirectional trends. The alkali granite’s characteristics make an independent cluster. The REE-plots also vary. Rocks of the first group has U-shape plot and wide variations in absolute contents. Rocks of the second group have high contents of REE and gentle slope. The granites from the third group have also U-shape plot but the lowest contents.</p><p>In this work we use the LA-ICP MS to determine the contents of RE elements in minerals. There were two minerals, that have chosen – apatite and pyroxene. Usually, apatite is the main concentrator of noncoherent elements that control the form of REE-spectra and the level of REE-contents in rocks. But in the Yllymakh massif, all apatite have a similar spectra form of normalized contents. The plots of normalized REE contents have a sharp negative slope and are characterized by very insignificant Eu anomalies. Such graphs are typical for the apatite of alkaline complexes. At the same time, the REE-plots of pyroxenes are quite equal to the form of REE-plots of the corresponding rock. Pyroxenes from foid syenites and alkali granites have U-shape plot and pyroxenes from feldspar syenites have a regular negative gentle slope plot. The only difference is that the REE content in the granite pyroxenes is as high as in the syenites.</p><p>The results of the research suggest that the formation of the rock spectrum of the Yllymakh massif occurred by reactivation of geochemically similar sources in a different time in addition to others. The contents of REE in rocks were controlled by REE-contents in pyroxene and its ratio with other rock-forming minerals. Supported by RFBR grant 19-05-00788</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.a8f2a37e3c0065515141161/sdaolpUECMynit/12UGE&app=m&a=0&c=a9f448fcade7302be1a6ca5e05985168&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.ad91c58e3c0063715141161/sdaolpUECMynit/12UGE&app=m&a=0&c=61a6b8cf3e9847d9a2091f620d19fdc7&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.dbd2469e3c0060915141161/sdaolpUECMynit/12UGE&app=m&a=0&c=7fc98b6a3ce7560d19ce7158c38a4079&ct=x&pn=gnp.elif&d=1" alt=""></p>

<p>Alkaline complexes are an important target for geological exploration, with both scientific and economic interests. They are host to different types of mineral deposits, such as Rare Earths, igneous phosphates, -and K-rich minerals and rocks. In Morocco, the Central High-Atlas (CHA) hosts several transitional to alkaline complexes ranging from Upper Jurassic to Eocene and showing almost all the differentiation terms of transitional to alkaline suites. These alkaline complexes are however poorly explored and their potential in terms of mineral resources is still elusive.</p><p>The aim of this research is to use Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to discriminate different transitional to alkaline rock lithologies and their associated mineralizations. For that purpose, series of band ratios proven to be sensitive to the silica, mafic, felsic and carbonate contents of transitional to alkaline rocks were applied. Our results show that the major Upper Jurassic magmatic intrusions of Moroccan CHA, such as Anemzi, Inouzane, Tassent, and Tasraft, hold distinct igneous facies, mainly composed of Mafic to felsic rocks. Field and petrographic observations have confirmed the ASTER results and highlighted that these rocks are formed of gabbro to syenite. The later are associated with significant feldspar concentrations, but also host apatite, garnet, and magnetite vein-type ores. Thereafter, field- and petrographic-based data were used as training data to perform a supervised classification allowing to refine the geological mapping of the studied alkaline intrusions.</p>

<p>The bulk rock and geochemistry of the Kayla and Khatastyr lamproites is similar to other Aldan lamproites and lamprophyres.  The ultramafic varieties are close to cratonic Ol- lamproites and alkaline Al, Si-rich varieties are closer to orogenic type.</p><p>Trace element bulk rock trace element (TRE) spider diagrams show inclined patterns with the LILE, Sr, Pb, U, peaks and Ta, Nb minima suggesting melting of originally depleted metasomatized Phl peridotites and mixed ancient (EMII, Nd, Sr isotopes) source (low crust)  and later olivine and clinopyroxene fractionation. They are dated 132-134 Ma (Late Cretaceous plume) similar to Chompolo lamprophyres and many alkaline complexes.</p><p>Thermobarometry for the deep-seated xenocrysts gives the low temperature and Sp-Gar and Gar facies for Cr- diopsides and chromites. Low - Cr- clinopyroxenes derived from lamproites give hot 90 mw/m<sup>2</sup> advective branches. </p><p>The REE patterns for Cr-diopsides are more inclined for deeper varieties and reveal Ba, Th, U, Sr peaks and minima Ta, Nd and smaller in Zr-Hf. The `low Cr diopsides show flatter REE and HFSE minima TRE patterns of parental melts are lamproitic. Salites reveal hot crust conditions.</p><p>Lamproites melted from Phl peridotite eclogites mixture in the lithosphere base and interacted with mantle beneath Moho.</p><p>The work was supported by the Ministry of Science and Higher Education of the Russian Federation RBRF grants 19-05-00788a, 18-05-00073a;  Government tasks for Institute of Geochemistry SB RAS and Institute of Geology and Mineralogy SB RAS and the governmental assignment in terms of Project IX. 129.1.4</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.4ea3446a7a0068249921161/sdaolpUECMynit/12UGE&app=m&a=0&c=101ace07d05786aa80749a09f997276d&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.7be3a47a7a0064449921161/sdaolpUECMynit/12UGE&app=m&a=0&c=58a37dd97ea8acf0b318506645b8f918&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.911e478a7a0063649921161/sdaolpUECMynit/12UGE&app=m&a=0&c=ec045b1e85e57506c9df6f4987365dc2&ct=x&pn=gnp.elif&d=1" alt=""></p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gnp.6b2d469a7a0068749921161/sdaolpUECMynit/12UGE&app=m&a=0&c=db2505c5dc47a12bf5bbe2da42dc4538&ct=x&pn=gnp.elif&d=1" alt=""></p>