MSDP01 is one of four diamond drillholes drilled during 2015 in the Six Mile Hill area as part of the Mineral Systems Drilling Program (MSDP). The hole was drilled vertically to 1116.8 m depth over the period 31/7/2015-15/9/2015, and intersected six units from the lower part of the Mesoproterozoic Gawler Range Volcanics, comprising an ‘upper felsic volcanic unit’ (30.5-66.46 m), an ‘upper mafic volcanic unit’ (66.46-368.97 m), a ‘middle felsic volcanic unit’ (368.97-665.15 m), a ‘lower mafic volcanic unit’ (665.15-964.2 m), a ‘quartz- and feldspar-phyric felsic unit’ (964.2-1095.95 m), and a lower felsic volcanic unit’ (1095-1116.8 m). This report includes a graphic log, description and interpretation of the main geological features of the lower GRV units in MSDP01, based on detailed logging of both the physical drill core and high resolution core images, as well as thin section petrological observations. The ‘upper felsic volcanic unit’ is a massive, homogeneous dacite. It is moderately crystal-rich (~20 modal %), and contains abundant plagioclase and minor ex-ferromagnesian mineral phenocrysts and up to 1 modal % quartz phenocrysts, set in an originally glassy groundmass, which retains a micropoikilitic texture. A flow foliation is faint in the lower half of the unit and the base is brecciated, amygdaloidal and contains small fine-grained sediment rafts, which have undergone minor peperitic mixing with the host dacite. The unit lacks evidence of a fragmental origin and is interpreted as a coherent body, emplaced either as a lava over-riding wet sediment or a shallow sill intruding them. The ‘upper mafic volcanic unit’ consists of 27 basalt flow units, ranging in thickness from 2-25 m, but also contains a small volume of autoclastic rocks and volcaniclastic sedimentary rocks toward the base. The flow units are characterised by a conspicuously amygdaloidal and oxidised top and some with patchy vesicular texture, which may indicate a flow-top breccia. Four packages of flow units were observed (from top to bottom); (i) 6 aphyric to very sparsely plagioclase-phyric flow units, (ii) 5 moderately plagioclase-phyric units which also contain scattered plagioclase megacrysts, (iii) 9 almost aphyric flow units, several of which contain convincing pillow texture, and (iv) 7 aphyric basalt flow units which are intercalated towards the base with more voluminous hyaloclastite and volcaniclastic breccia and minor normally graded sandstone intervals. The ‘middle felsic volcanic unit’ is a homogeneous, coarse-grained, relatively crystal-rich (25-30 modal %) dacite. This unit contains abundant phenocrysts of plagioclase and minor replaced ferromagnesian phenocrysts with inconspicuous trace quartz phenocrysts. The groundmass has a micropoikilitic texture indicative of its original glassy texture. A faint flow texture in the groundmass is mainly observed close to the base. The upper contact of the unit is sharp and planar, with tiny flames of the mafic material extending into the dacite at mm scale, and the lower contact with the lower mafic volcanic sequence is sharp. The base of the dacite is finely amygdaloidal, perlitic and spherulitic and contains slightly more conspicuous quartz as well as a small amount of alkali feldspar phenocrysts. The ‘lower mafic volcanic unit’ comprises a sequence of 15 flow units, which range in thickness from almost 5-43 m and which are all either aphyric (mainly upper half) or very sparsely plagioclase-phyric (mainly lower half). At the top of the highest basalt flow unit, the basalt has a quenched texture and includes small (sub-mm) peperitic lenses of fine, quartz-bearing sediment, which were unconsolidated when incorporated. Apart from these tiny sediment lenses, there are only a few metres of volcaniclastic sandstone in this thick sequence, and one of these was found to contain conspicuous quartz and felsic lithic grains. The majority of the basalt flow units display the same systematic internal structure, which involves an amygdaloidal top, in places with flow-top breccia texture and minor incorporated sediment, and a massive, weakly amygdaloidal interior. Probable pillow margins and hyaloclastite are less common than in the upper interval of mafic volcanic rocks in this hole, and mainly occur in the first two flow units below the crystal-rich dacite. The ‘quartz- and feldspar-phyric rhyolite’ is a massive, crystal-rich (~30 modal %) rhyolite, which is distinguished from all other logged units in the 3 MSDP holes by the presence of relatively abundant quartz phenocrysts (12-15 modal %). The feldspar phenocrysts include both alkali feldspar > plagioclase, and there is a small number of highly altered probable ferromagnesian phenocrysts. There is sporadic development of a diffuse flow-banding, and a 4 m-wide band of brecciated rhyolite is either an autobreccia separating two units of the same rhyolite or, possibly more likely, a zone of brittle deformation. The phenocrysts in the rhyolite are unbroken and the groundmass was originally glassy. Based on the observed core and thin section textures, the rhyolite is considered more likely to be a coherent lava rather than a densely welded ignimbrite. The ‘lower felsic volcanic unit’ is an altered dacite, which has a slightly oblique, possibly erosional contact with the overlying rhyolite. This unit is finer grained than the overlying rhyolite and is also distinguished by a moderately crystal-rich (20-25 modal %), plagioclase-rich, quartz-poor composition, the presence of ex-biotite phenocrysts, and a lenticular groundmass foliation. The intense sericite-quartz-hematite alteration prevents distinction of this unit as a coherent lava or ignimbrite.