Neoproterozoic Chhaosa shales of Simla Group, Lesser Himalaya, were considered for major and trace element analysis to delineate palaeo-weathering, palaeo-oxygenation, tectonic setting, sediment maturity, and provenance. The shales exhibit a significant proportion of SiO$_{2}$, Al$_{2}$O$_{3}$, K$_{2}$O, MgO, Fe$_{2}$O$_{3}$, Zr, Zn, Rb, V, Cr, Sr, Y, Co, Ga, Th, Nb, Sc, and U. Source rocks are primarily of granitic (acidic) origin, as indicated by Al$_{2}$O$_{3}$ wt.% vs. TiO$_{2}$ wt.% and Cr (ppm) vs. Ni (ppm) bivariate plots. Th/Cr, Cr/Th, Th/Sc, and Th/Co values of studied samples have been correlated with post-Archaean Australian average shale (PAAS) and upper continental crust (UCC) values, which indicate that the source rock is felsic. Palaeo-weathering condition of the source is delineated by average CIA, chemical index of weathering (CIW), and A–CN–K triangular plot values. The shales depict intermediate to strong chemical weathering and semi-arid to humid climatic conditions. V/Cr, Cu/Zn, Ni/Co, and U/Th values reveal sedimentation of Chhaosa Formation under oxic atmospheric conditions, which corroborates with the inferred oxic conditions of the Neoproterozoic. SiO$_{2}$ vs. K$_{2}$O/Na$_{2}$O discriminant diagram exhibits deposition along a passive margin field. ICV values suggest deposition of compositionally mature sediments under tectonically stable conditions. Deposition of Chhaosa delta system occurred during a relatively quiescent stage of tectonism between intermittent phases of rifting related to the Rodinia Supercontinent.

$\bf{Highlights}$

$\bullet$ This is the first geochemical work ever done for the shales of Neoproterozoic Chhaosa Formation of Simla Group, Lesser Himalaya.

$\bullet$K$_{2}$O/Na$_{2}$O vs. SiO$_{2}$/Al$_{2}$O$_{3}$, TiO$_{2}$ vs. Al$_{2}$O$_{3}$, and Zr vs. TiO$_{2}$ binary diagrams of the studied shales indicate felsic source rock.

$\bullet$ High CIA, CIW, A–CN–K and Al$_{2}$O$_{3}$ values of Chhaosa shales support intermediate to strong weathering of source rock.

$\bullet$ K$_{2}$O/Na$_{2}$O vs. SiO$_{2}$ plot, K$_{2}$O vs. Na$_{2}$O, plot and CaO–K$_{2}$O–Na$_{2}$O ternary plot represent deposition of Chhaosa deposits in a passive margin setting.

$\bullet$ Values of Ni/Co, Cu/Zn, V/Cr, authigenic U and U/Th, represent a well-oxygenated condition during the deposition of the Chhaosa delta system. This is consistent with the concept of an increase in oxygen levels during the Neoproterozoic era is favoured by many workers.

The Almora nappe in the Kumaun Lesser Himalaya (KLH) is mainly composed of Saryu Formation, Gumalikhet Formation and Cambrian felsic intrusives. Zircons from a paragneiss, exposed near Kwarab along Sualbari–Almora transect, of Saryu Formation, are subjected to U–Pb geochronology in order to delineate the timing of tectono-thermal events and its implication on pre-Himalayan orogenic cycle. Zircon rims developed over Neoarchean–Paleoproterozoic zircon cores record U–Pb ages which broadly correspond to three major pre-Himalayan tectono-thermal (metamorphic) events, early Paleozoic, late Paleozoic and early Triassic. These protracted thermal imprints likely represent the metamorphic episodes experienced by the rocks of Almora nappe. The observed early Triassic rim ages of zircons from paragneiss are very well correlatable with the opening-closure of the Palaeo-Tethys Ocean.

In the present study, we have estimated the quality factor Coda-Q (Q$_c$) using the single backscattering model for Mainland Gujarat region of Western Deccan Volcanic Province (DVP) India. The said region comes under seismic zone III as per seismic zonation map of India and is vulnerable for earthquakes of magnitude up to 6.0. Mainland Gujarat comprises of the eastern rocky highlands and western alluvial plains. The broadband waveforms of 80 local earthquakes (Mw 2.5–4.3) having depths in the range (2.0–34.0 km) recorded at eight stations of Mainland Gujarat have been used for the analysis. The average values of Q$_c$ for the lapse time windows of 20–90 s with standard error varies respectively from 113 ± 12 to 411 ± 37 at 2 Hz and 1008 ± 150 to 3600 ± 400 at 16 Hz, respectively. This suggests that the region is more attenuative and heterogeneous than the Kachchh and Saurashtra of DVP. The increase in ‘Q$_c$’ values with lapse time displays the depth dependence of ‘Q$_c$’ because of the fact that longer lapse time windows will sample larger area. We have compared the frequency-dependent relations for ‘Q$_c$’ derived here with those of other parts of India and the World. The study is inevitable for the estimation of source parameters, thereby, evaluation of seismic hazard of the region.

This work focuses on the natural graphitic carbonaceous material (GCM) distributed in metasedimentary and crystalline rocks in and around Larji–Rampur tectonic window, Himachal Himalaya. The GCM, associated with the ore mineralization, is mostly flaky, however, it is also granular and amorphous. The micro Raman spectroscopy of representative samples confirms that the studied GCM is mostly disordered graphite and rarely poorly ordered graphite, but well crystalline ordered graphite is also present. The carbon isotope compositions reflecting the source of carbon in GCM at various locations attribute that the carbon was mostly sedimentary organic carbon which has been metamorphosed to disordered graphite, however, the ${\delta}^{13}$C of the inorganic carbon contents in metabasalts from Bhallan signify the involvement of fluid possibly derived from the mantle. Limited ${\delta}^{13}$C$_{inorganic}$ data in a range from 0 to -11%, points to the heavier carbon probably derived from the diagenetic carbonates or dissolved organic matter. Overall, the carbon isotope compositions of GCM from the Larji–Rampur window reject diversity in carbon source and mixing of carbon reservoirs, which can adequately be explained by the Proterozoic marine carbon cycling. A close linkage in the depositional processes of GCM with ore mineralization in the area is also invoked.

$\bf{Highlights}$

$\bullet$ The graphitic carbonaceous material (GCM) is present in and around Larji–Rampur tectonic window, Himachal Himalaya, at places associated with ore mineralization.

$\bullet$ Micro Raman spectroscopy confirms the presence that this GCM is mostly disordered graphite though the ordered graphite is also present uncommonly.

$\bullet$ The ${\delta}^{13}$C values vary widely from –1.5‰ to –33.5‰. The ${\delta}^{13}$C compositions are heterogeneous and complex carbon systematics is apparent. In addition to the predominant sedimentary organic carbon form Proterozoic marine carbon, it was also derived from carbonate source, carbon from the fluids, and rarely but possibly from the mantle source.

$\bullet$ A close linkage in the formation and evolution processes of the GCM with the ore mineralization is also invoked.

Felsic magmatic rocks of Askot and Chiplakot regions in the inner segment of the Kumaun Lesser Himalaya are represented by the Paleoproterozoic two-mica (biotite–muscovite) granite gneisses (ca. 1850 Ma), which are referred herein as Askot (AGGn) and Chiplakot (CGGn) granite gneisses, respectively. They are invariably metamorphosed, giving rise to augen bearing or augen free gneissose texture exhibited mainly by micaceous minerals. They bear a common bt-ms-pl-qz-Kf-zrn-ap-ttn±mag assemblage. The magnetic susceptibility (MS) mapping, phase petrology of biotite and muscovite from AGGn and CGGn are employed to assess the granite series, nature and crystallization condition of their respective granitic magmas. Although the observed average MS values of the AGGn (0.019–0.028${\times}$10$^{–3}$ SI) and CGGn (0.051–0.098${\times}$10$^{–3}$ SI) are slightly distinct, both typically belong to ilmenite series (reduced) granites. The AGGn and CGGn biotites are primary, siderophyllite, belonging to ferri-siderophyllite transition and ferri biotites, respectively, which crystallized with muscovite unaccompanied with other mafic minerals. The AGGn and CGGn muscovites are primary in nature, belonging to celadonite and paragonite solid solution series, which evolved in peraluminous (S-type) granite melt under reduced conditions.The AGGn and CGGn biotite and muscovite thus represent primary liquidus phases, not the secondary or restite or metamorphic products except a few tiny muscovites. The observed FeO$^t$/MgO ratio of AGGn (5.47–10.72; av. 7.78) and CGGn (2.44–3.69; av. 2.90) biotites dictate anorogenic alkaline (A-type) and syn-collisional peraluminous (S-type) host granite magmas, respectively. However, siderophyllite (aluminous) nature and vital 3Fe ${\Leftrightarrow}$2Al substitution of AGGn and CGGn biotites strongly propound their evolution in peraluminous (S-type) granite magmas. The CGGn biotites are enriched in phlogopite (Mg$_{apfu}$ = 1.75) as compared to AGGn(Mg$_{apfu}$=0.88) biotites,which probably reflect derivation of CGGn melt from crustal source with slightly more mafic as compared to the crustal source of AGGn melt. The estimated physico-chemical conditions of AGGn (P=3.6–4.21 kbar,T=690–780°C, f O$_2$=10$^{–16.29}$ to 10$^{–15.72}$ bars, Fe$^{3+}$/Fe$^{2+}$=0.12–0.16, H$_2$O${\thickapprox}$4 wt.%) and CGGn (P = 3.03–6.63 kbar, T = 750–840°C, f O$_2$ = 10$^{–16.54}$ to 10$^{–14.22}$ bars, F$^{3+}$/Fe$^{2+}$ = 0.04–0.11, H$_2$O${\thickapprox}$3 wt.%) point to strongly reduced and moderately reduced nature of respective host magma, that prevailed at mid-crustal depths. The differential reducing conditions of host magma evolution are unequivocally demonstrated by the stability of AGGn and CGGn biotites from the Fayalite–Magnetite–Quartz (FMQ) to the above Nickel-Nickel Oxide (NNO) buffers and observed MS values.

Rare earths and Yttrium (REY) are a group of critical metals essential for this electronic and digital era. China is the leading producer of REY with more than 90% of global export. Mines of REY are limited and the need for green and efficient energies have augmented the demand of REY and it is putting enormous pressure on global production. REY market is predicted to grow from USD 5.3 billion in 2021 to 9.6 billion by 2026, at a CAGR (Compound Annual Growth Rate) of 12.3%. The need for permanent magnets is propelling the demand of the critical group REY and is expected to rise gradually in the coming years. In the present review, we have summarized the minable REY resources and their applications. The requirement for alternative resource is pivotal to meet our future needs. We have extensively reviewed the studies of REY in coal Cy ash (CFA). A comprehensive analysis has been done for the REY resources worldwide for the last several decades in coal ash (CFA and bottom ash) and divulged into the application, speciation and distribution for major coal-consuming countries like China, India, USA, Russia, UK, Poland, etc., individually. We have also made a comparative global study and inferred potential extractable coal ash resources using various parameters such as global average, critical percentage ($C_p$), outlook coefficient ($C_{out}$), etc., for a better understanding of economic exploitation.

$\bf{Highlights}$

$\bullet$ We have put up enormous effort to synthesize rare earth elemental data of coal ash from different coal-consuming countries. Following are the major highlights of this review article.

$\bullet$ We have compiled data on occurrence of Rare Earths and Yttrium (REY) in coal ash from 13 countries such as China, India, USA, UK, Poland, etc.

$\bullet$ Up-to-date global data of mined REY resources and reserves have been compiled.

$\bullet$ Broad characterization and classifications of REY have been introduced.

$\bullet$ Comprehensive analysis of application, speciation and environmental impact of REY in coal ash have also been compiled.

$\bullet$ Comparative study has been done using parameters such as global average, critical percentage, outlook coefficient, etc. These parameters would help in determining ideal candidates for beneficial extraction of REY.

$\bullet$ This study would serve as a knowledge resource centre for new research related to REY.