Geochemical systematics and precious metal content of the sedimentary horizons of Lower Gondwanas from the Sattupalli coal field, Godavari Valley, India

Abstract

Abstract Major, trace, rare earth (REE) and platinum group elements (PGE) have been analysed from the carbonaceous horizons of Permian Barakar Formation of Sattupalli coal field of Godavari Valley to understand the provenance and depositional environment. Barakar Formation of coal field consists of sandstone, siltstone, carbonaceous shale and coal seams. Coal is enriched in trace elements compared with the Clarke's background values. Ferromagnesian trace elements (Ni, Cr and Co) are similar in range in both coal and carbonaceous shales along with Large ion lithophile elements (LILE; Rb, Sr, Cs and Ba), High field strength elements (HFSE; Nb, Ta, Zr and Ti), Light REE (LREE; La-Sm) and Ag. Archean Upper Crust (AUC) normalized REE and multielement variation patterns of the coal show a flat REE with a slight depletion in Ce and Eu contents in most of the samples. Their multielement patterns exhibit enrichment of Th and U; negative Ta, Zr, Hf and positive Ti anomalies. Pronounced positive anomaly occurs at Zr, Hf and Ti that are combined with both positive and negative Nb and Ta anomalies in carbonaceous shales and clay. Sandstones have a high SiO 2 (50–80 wt.%), low Fe 2 O 3 , Al 2 O 3 and moderately high K 2 O contents. AUC normalized REE patterns are almost flat with slight negative to no Eu anomalies followed by small negative Ce anomalies (Ce/Ce* = 0.87–0.95 with one exception). Their multielement patterns exhibit positive U, small negative Nb-Ta, a pronounced positive Zr-Hf anomaly followed by negative Ti and V anomalies. Enrichment of both Zr and TiO 2 in some samples reflects on the mafic and felsic sources at the source region. The fractionated REE patterns, HREE enrichment and negative Eu anomalies are consistent with contribution of zircon through felsic source. Nb/Ta troughs endorse their inheritance from schistose rocks of Eastern Ghats complex. The high Al 2 O 3 /Yb and Th/Yb ratios along with negative Eu anomalies reflect on the TTG/felsic rocks of provenance. Based on the geochemical, available petrological and paleocurrent analysis indicate the source rocks of the Barakar Formation were granite, granitic gneiss, high grade metamorphic rocks from Eastern Ghats, and basic rocks. The provenance is located west and south east (i.e. partly Peninsular gneiss and partly Eastern Ghat Complex). The Au-PGE contents of Sattupalli coalfield have been deposited through NE–SW trending post depositional transverse faults that have affected all the Gondwana Formations during the early Cretaceous. The mafic rocks present within the basement could have been the source of these elements.