Lithology and petrology of the Rover field, Warramunga Province: Selected unmineralised drill core

Abstract

This Record presents the results of detailed logging and petrographic studies of six relatively unmineralised drillholes of the Rover field in the Warramunga Province, central Northern Territory. The work is part of a Northern Territory Geological Survey-Geoscience Australia collaboration project to improve understanding of the regional geological framework and resource potential of the Rover field and more broadly, the Warramunga Province. Herein we present an updated interpretation of the basement lithology previously described as comprising largely Warramunga Formation or equivalent stratigraphy. The drillholes intersect volcanic and volcaniclastic rocks of variable composition, from dacitic-andesitic coherent volcanic rocks with lesser basaltic intervals to more fractionated rhyolitic volcanic rocks. Drillholes T3/2, RVDD0001 and RVDD0002, located in the southeastern part of the Rover field, as well as the more centrally-located R2ARD17, intersect mostly coherent flow-banded feldspar-phyric dacite, porphyritic and glomeroporphyritic dacite and andesite, interlayered with minor rhyodacitic volcaniclastic sandstones and quartz-feldspar porphyritic intrusions. In the northern part of the Rover field, drillhole WGR3D001 intersected clinopyroxene-bearing basaltic layers hosted in glomeroporphyritic dacitic coherent volcanic rocks. Located in the central part of the field, drillhole R27ARD18 (Rover 27) intersected different lithologies, mainly fine- to very coarse-grained, immature polymict rhyodacitic volcaniclastic sandstone with minor intervals of rhyolitic lavas. These rhyodacitic volcaniclastic rocks are similar in composition and texture to the rocks described in the western side of the Rover field (eg Explorer 108 drillholes and the top half of the Curiosity drillholes MXCURD001 and MXCURD002; Huston et al 2020, Farias et al 2021). In summary, the variable composition and facies of the igneous rocks in the Rover field suggest bimodal volcanism characterised by: (i) less fractionated, dacitic-andesitic coherent volcanic facies in the east and north of the Rover field; (ii) mafic volcanism to the north of the field; and (iii) a more fractionated, rhyolitic volcaniclastic facies to the centre and west of the field, in proximity to base metal mineralisation (Explorer 108 and Curiosity).