Prospect for gold and other precious metals in meta-igneous rocks of Sri Lanka: implications from geochemistry

Abstract

This study presents some major, trace and precious metal geochemistry of some representative meta-igneous rocks from the Highland and Vijayan Complexes and Kataragama Kilippe (HC, VC, KK, respectively) of Sri Lanka. Our data show different geochemical trends in chemical-discrimination diagrams, indicating each lithological unit has distinct genetical environments. Most of the mafic samples of the HC and the KK fall geochemically in the tholiietic field. In contrast, the garnetiferrous charnockitic samples of the HC and majority of the VC samples plot in the calc-alkaline field. Rocks of the VC and KK and mafic rocks of HC, deviate from typical magmatic differentiation patterns probably due to a later interaction with secondary melts or fluids. There is a clear distinction of Pt/Pd and Au/Pt vs. MgO, in which all the samples except for the garnetiferrous charnockites of the HC show a negative correlation implying a sequestration of chalcophile melts from protolith magmas. Therefore, our data indicate that possibility of occurrence of gold (Au) and other precious metals (e.g. Pt and Pd) within the meta-igneous rock units of the HC, VC and KK is reasonable except for the garnetiferrous charnockitic rocks of the HC. The garnetiferrous charnockites of the HC do not account for any geochemical evidence sensitive to precious metal enrichments in protoliths. Our estimates show that the highest (in average) Au, Pt and Pd contents are found in the rocks of VC (8 mg/ton), KK (7 mg/ton) and HC (7 mg/ton), respectively. Although these precious metal abundances in the above prospective rock units are not as high as those present in global ore-grade rocks, yet 'hard rock mining' technique could be feasible to utilize as a small-scale industry to extract these metals, especially using rock-aggregates/rock powders dumped as wastes from rock quarries in Sri Lanka.

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

“…Although, monazite ages from Sri Lanka show bimodal distribution (Figure 14d), the older ages (peaking c. 650 Ma) are associated with prograde evolution, and the younger ages (peaking c. 480 Ma) are associated with retrograde growth Durgalakshmi et al, 2021;Sajeev et al, 2010), further indicating a prolonged late Neoproterozoic to Cambrian metamorphic cycle. Texturally controlled in situ dating of the monazite from SGT strengthens the evidence for such prolonged metamorphic cycles ($ > 100 MYr) where UHT F I G U R E 1 4 Probability density plots using compiled EPMA monazite ages from the Madurai Block (Brandt et al, 2011;Catlos et al, 2008;Dev et al, 2022;Tiwari & Sarkar, 2020), this study, Trivandrum Block (Braun et al, 1998Braun & Bröcker, 2004;Johnson et al, 2015;Kadowaki et al, 2019;Sorcar et al, 2020;Yu et al, 2019) and Sri Lanka (Malaviarachchi & Takasu, 2011;Wanniarachchi & Akasaka, 2016). Unimodal age distribution with a broad age range for the Madurai Block and the Trivandrum Block and bimodal age distribution for Sri Lanka should be noted.…”

“…Probability density plots using compiled EPMA monazite ages from the Madurai Block (Brandt et al, 2011; Catlos et al, 2008; Dev et al, 2022; Santosh et al, 2003; Tiwari & Sarkar, 2020), this study, Trivandrum Block (Braun et al, 1998; Braun & Bröcker, 2004; Johnson et al, 2015; Kadowaki et al, 2019; Santosh et al, 2003, 2006; Sorcar et al, 2020; Yu et al, 2019) and Sri Lanka (Malaviarachchi & Takasu, 2011; Wanniarachchi & Akasaka, 2016). Unimodal age distribution with a broad age range for the Madurai Block and the Trivandrum Block and bimodal age distribution for Sri Lanka should be noted.…”

“…Putting together the monazite ages from the MB (Brandt et al, 2011; Catlos et al, 2008; Dev et al, 2022; Santosh et al, 2003; Tiwari & Sarkar, 2020), Trivandrum block (Braun et al, 1998; Braun & Bröcker, 2004; Harley & Nandakumar, 2016; Johnson et al, 2015; Kadowaki et al, 2019; Santosh et al, 2003, 2006; Sorcar et al, 2020; Yu et al, 2019) and Sri Lanka (Malaviarachchi & Takasu, 2011; Wanniarachchi & Akasaka, 2016) (important East Gondwana fragments) add to the evidence that monazite growth occurred unequivocally over a prolonged period of time (Figure 14a–d). The unimodal age distribution from this study, the Madurai and Trivandrum blocks (Figure 14a–c) with ages clustered around 600–500 Ma, is suggestive of a late Neoproterozoic to Cambrian long‐lived metamorphism in both the blocks (Dev et al, 2022; Kadowaki et al, 2019; Tiwari & Sarkar, 2020).…”

Overture for the Mandara and Vasuki Plates

“…The pole was determined using just 17 VGPs from samples taken at a single site on a dolerite dyke. The dyke was not described in detail, but is likely to have been 5-10 m wide (Arachchi et al, 2017). Conductive cooling of dykes this wide is likely to be so rapid (a matter of months (Delaney, 1987)) that their magnetizations sample a tiny fraction of a single cycle (~3000-10,000 years; Kodama, 2012) of paleomagnetic secular variation.…”