Targeting VHMS mineralization at Erayinia in the Eastern Goldfields Superterrane using lithogeochemistry, soil chemistry and HyLogger data

Abstract

Exploration for volcanic-hosted massive sulfide (VHMS) deposits in the Archaean Yilgarn Craton of Western Australia is hampered by a combination of a paucity of outcrop, deep weathering, and saline groundwaters in geologically complex greenstone belts. We present a detailed account of the geology at Erayinia NW (Murrin Domain) in the southern part of the Kurnalpi Terrane, ~150 km SE of Kalgoorlie and 4 km NW of the King VHMS deposit (Edjudina Domain). We have used a combination of logging, petrography, lithogeochemical, pXRF, hyperspectral and soil datasets to help identify VHMS proximal signatures for future drill testing.Diamond drilling at Erayinia NW has identified widespread hydrothermal alteration and minor base metal mineralization across a strike length of at least 3 km. A lower package of calc-alkaline metabasalt, is overlain by intermediate volcanic and associated volcaniclastic rocks, a mixed sequence of argillaceous sedimentary rocks interbedded with FI to FII affinity dacitic rocks, and calc-alkaline metabasalt. SHRIMP UPb zircon geochronology has constrained the age of the host stratigraphy to 2685 ± 5 Ma. Hydrothermal alteration (quartz-sericite-pyrite) is most prevalent in the 50-75 m thick felsic dominated sequence interbedded with black shales, with local zones of chloritization associated with minor ZnPb mineralization. Massive pyrite was intercepted in the two southernmost holes located approximately 300 m apart.Black shales and hydrothermally altered felsic rocks contain elevated Ag, As, Bi, Cd, Cu, Hg, In, Mo, Pb, Sb, Te, Tl associated with increasing Zn concentrations. Broad halos of Sb, Tl, Eu/Eu* and normative corundum define the stratigraphy of interest. Hydrothermally altered felsic rocks are characterized by higher abundances of white mica and lesser chlorite than surrounding strata. Increased quantities of Mg-rich chlorite, muscovitic (Al-rich) white mica, and Fe‑carbonate (siderite) occur proximal to FeZn mineralization. Significant enrichments in trace elements (Ag, As, Bi, Cd, In, Mo, Ni, Sb, Sn, Te, Tl; plus Alteration Index and K2O; and lower Al, Ba, Sr) in black shales towards drillholes EC154D and EC157D suggest this area is most proximal to VHMS mineralization. Soil metal concentrations vary significantly according to underlying regolith type (e.g. colluvium, alluvium, playa lake). Geochemical data levelled by regolith type reveal several bulls-eye multi-element geochemical anomalies (e.g. Zn, Pb, Cu, As, Bi, Cd, Mo, Sn, Tl, W) over the King deposit (2.15 Mt. at 3.47 wt% Zn), King North occurrence (e.g. 1 m at 6.7 wt% Zn + Pb), with new targets identified at Erayinia NW and elsewhere for future drill testing.