Architecture of the Neoarchaean Jaguar VHMS deposit, Western Australia: Implications for prospectivity and the presence of depositional breaks

Abstract

The duration and nature of breaks in Archaean volcanosedimentary packages, recently re-evaluated in the Abitibi Greenstone Belt, has been assessed at Jaguar, an Archaean Cu–Zn-rich volcanic-hosted massive sulphide (VHMS) deposit in the Teutonic Bore volcanic complex (TBVC), the Eastern Goldfields of the Yilgarn Craton, Western Australia. The deposit is hosted by coherent volcanic facies and associated volcaniclastic facies, with minor non-volcanic facies.The hypothesis that VHMS ore lies on the intersection of volcanic centres and depositional breaks is found to be valid for the Jaguar deposit, with the site being an active volcanic complex at footwall time, with further dome development close to the final ore location at Mineralised Package time, and then reoccurring volcanic complexes (andesitic and basaltic) at several points in the hangingwall succession broadly tied into the ore position.At Jaguar the entire stratigraphic sequence faces west, with no major structural complications, making it ideal for stratigraphic analysis. The footwall evidences prolific volcanism with no intervening sedimentation. The Mineralised Package (MP) consists of intercalated dacite, breccia, conglomerate, sandstone and mudstone. The footwall volcanic rocks and the MP Dacite appear to be differentiation products from the same magma chamber. A major volcanic geochemical boundary is identified between the footwall/MP (tholeiitic to transitional affinities), and the immediate hangingwall succession (calc-alkaline). The hangingwall package includes four distinct volcanic units intercalated with mass flow deposits and graphitic argillites.VHMS mineralisation occurred across a distinct change in the geochemistry of erupted volcanic facies at a time of increased volcaniclastic sedimentation and extension. This break is comparable to Member level hiatuses seen in the Abitibi GB, i.e. the most brief of breaks, because there is no silicification of sedimentary unit-tops by silicic seawater exposure, and there is minimal development of black shales. A third time-sensitive criteria was the development of peperite on the base of Hanging Wall (HW) andesite lavas. The MP closely resembles breaks within interpreted deeper water domains of the Abitibi GB, for instance, the Deloro-Tisdale assemblage interface south of Timmins.The recognition of the change in the rate of emplacement of volcanic units and particularly the change in chemistry of volcanic rocks, are critical exploration lithologic guides to use in the absence of chemical sediment deposits (exhalites). Although crustal extension and basin subsidence were factors in the shaping of the succession, their effects were too subtle to use as an exploration tool. A corollary of the recognition of a Member-level VHMS-bearing interval in the Teutonic Bore volcanic complex is that, like the Kidd-Munro assemblage stratigraphy (Abitibi GB), where several ore-bearing depositional breaks are known below the great Kidd Creek deposit, there is scope for the discovery of further (potentially larger) deposits on higher Formation or Group-level breaks in the TBVC.