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New basement stratigraphy, regolith and structural mapping along the southern Gawler Ranges margin

Working alongside the Mineral Systems Drilling Program (MSDP), a detailed geological mapping program was carried out at each of the three MSDP drilling areas (Six Mile Hill, Peltabinna and Mount Double) between July 2015 and April 2016.

MSDP mapping locations
Location of the three MSDP drilling and mapping areas.

The purpose of this geological mapping program was to provide a regional geological context in which the stratigraphy, alteration and mineralisation intersected in the MSDP drillholes could be interpreted. The geological mapping program comprised detailed basement, structural and regolith mapping, as well as petrological, whole rock geochemical, isotopic and geochronological studies, with a particular focus on the stratigraphy of the lower Gawler Range Volcanics. The mapping team also assisted with lithological and stratigraphic logging and interpretation of the core during the drilling program.

MSDP mapping locations
MSDP mapping locations
1. Mark Pawley, Stacey McAvaney, Tom Wise and Mario Werner mapping on Hiltaba Station, Peltabinna MSDP drilling area. 2. Carmen Krapf, Adrian Fabris, Mario Werner, John Brennan, Luke Tylkowski and Stacey McAvaney logging drillhole MSDP01, Cariewerloo Woolshed, Six Mile Hill MSDP drilling area.

Outputs of the mapping program comprise a MSDP Special Map Series which includes 1:75 000 scale surface geology and interpreted Proterozoic solid geology maps for the Six Mile Hill, Peltabinna and Mount Double drilling areas, as well as an accompanying report for each drilling area describing the stratigraphy, structural geology and geological history. The surface and solid geology maps and report for Six Mile Hill have been completed, and those for Peltabinna and Mount Double will be released in the first quarter of 2017.

Recent releases

Lithological logging of Gawler Range Volcanics in MSDP drillholes at Six Mile Hill

Three of the diamond drillholes drilled during the Mineral Systems Drilling Program in the Six Mile Hill area intersected a succession of mafic and felsic volcanics of the lower Gawler Range Volcanics in excess of 1100 m thick, which is poorly preserved at the surface, where it is overlain by Meso- to Neoproterozoic and Cenozoic cover sequences. These new drillhole intersections are critical for unravelling the stratigraphy of the Gawler Range Volcanics in this area.

The GSSA commissioned Carol Simpson, a consultant volcanologist, to produce lithological logs of the volcanic facies intersected in drillholes MSDP01, MSDP03 and MSDP04, based on detailed core logging and thin section petrography, which have been released as three report books.

A fourth report discusses the correlation of individual units between drillholes and presents a model for the depositional environment of the Gawler Range Volcanics in the Six Mile Hill area.

Download the Reports

MSDP1 thin section photomicrograph
MSDP1 core image
1. Photomicrograph in plane-polarised light of the partial jig-saw fit texture of many of the blocky to cuspate-shaped chlorite-replaced, perlitic basalt clasts in in situ hyaloclastite in the upper mafic volcanic unit.
2. Core photograph from 735 m depth of 10 cm-long hyaloclastite in lower mafic volcanic unit, featuring jig-saw fit blocky to splintery clast texture.

Surface Geology of Six Mile Hill – Mineral Systems Drilling Program Special Map Series 1:75 000 scale map

Six Mile Hill mapsheet

The Six Mile Hill surface geology map provides a detailed representation of the regolith and outcropping Proterozoic stratigraphy of the first MSDP drilling area. The map is located on northeastern Eyre Peninsula and spans the southern Stuart Shelf and eastern Gawler Craton. It contains a number of peripherals, including TMI, gravity, DEM imagery, a reliability diagram showing field observation sites, a solid geology inset and a customised legend. Simplified stratigraphic logs of the MSDP drillholes are also displayed on the map.

Highlights of the Six Mile Hill mapping include:

  • Definition of new stratigraphic units, the Wire Dam Dolerite, Proterozoic mafic sills intruding the Broadview Schist, and the Sugarloaf Dam Sandstone, a Tertiary sandstone deposited in an intermontane setting.
  • Identification of a new compressional event at c. 1775 Ma, producing northwest-striking upright folding and an axial planar fabric in the Broadview Schist, Wire Dam Dolerite and Tip Top Granite.
  • Identification of new units of the Mesoproterozoic Gawler Range Volcanics in this area, including subaerial and subaqueous basaltic lavas, rhyolitic to dacitic lavas, ignimbrites and water-lain tuffs, which have been correlated with the units intersected in drillholes MSDP01-04.
  • Discovered geological context of previously Identifiied tourmaline-silica breccia system developed in Proterozoic sedimentary basement (Wade et al. 2014: RB2014/00009), which appears to be associated with the Kimban-aged c. 1740 Ma Gluepot Granite.
  • Detail mapping of transported and in-situ regolith materials and landforms resulting in the subdivision of 24 Cenozoic units.
  • Representing weathering profiles and shallowly covered subcrops by the use of piggyback codes.

Download the map

Interpreted Proterozoic Solid Geology of Six Mile Hill – Mineral Systems Drilling Program Special Map Series 1:75 000 scale map

Six Mile Hill Solig Geology mapsheet

The Six Mile Hill solid geology map provides a detailed representation of the interpreted Proterozoic stratigraphy. These include Mesoproterozoic to Palaeoproterozoic basement units of the Gawler Craton overlain on the eastern part of the map sheet by Neoproterozoic sediments of the Stuart Shelf, and Mesoproterozoic Pandurra Formation in the north and south. The map delineates a major north-south-trending fault network, including the Roopena Fault, which is interpreted to preserve a tectonic history during Palaeoproterozoic basin development, the Kimban Orogeny (1740–1690 Ma), extrusion of the Mesoproterozoic Gawler Range Volcanics, sedimentation on the Stuart Shelf during the Neoproterozoic, as well as being active as a fault scarp in recent times.

Download the map

Geology of the Six Mile Hill 1:75 000 Map Sheet – Mineral Systems Drilling Program Special Map Report Book 2016/00014

Cover of Report Book 2016/00014

The report accompanying the Six Mile Hill surface geology and solid geology map sheets describes the physiography, regional geology, stratigraphy, structural geology and geological history of the Six Mile Hill area. For each stratigraphic unit the distribution, lithology, contact relationships, thickness, emplacement, depositional environment and age are described, accompanied by outcrop photographs and rock sample photomicrographs. This also includes a detailed description of the newly established regolith material and landform units, as well as brecciation and veining observed during mapping. The structural geology section contains a description of the morphology, sense of movement and timing of the major faults and shear zones, as well as a stereographic analysis of the bedding and tectonic structures observed in each of the stratigraphic units.

Download RB 2016/00014

Cover of Report Book 2016/00024

Mineral Systems Drilling Program Rock Shack - Outcrop sample collection for the Mineral Systems Drilling Program, Southern Gawler Ranges Margin

During the mapping program rock samples were collected for petrology, geochemistry and geochronology as well as hand specimen, to compare with the lithologies intersected in the MSDP drill holes. This report comprises a photographic collection of nearly 100 selected rock samples collected during the geological mapping program as displayed during the MSDP Open Day on 11 August 2016.

Download RB 2016/00024

Cover of Report Book 2015/00030

Stratigraphy of the Gawler Range Volcanics in DDH RC 1, south-eastern Gawler Ranges.

As part of a geological study supporting the MSDP, the stratigraphic drill hole DDH RC1, drilled by the Department of Mines in 1978, has been reanalysed. This drill hole occurs within the Cariewerloo MSDP drilling area and contains a sequence of lower GRV equivalent to that intersected in MSDP drilling.

Report book 2015/00030 ‘Stratigraphy of the Gawler Range Volcanics in DDH RC 1, south-eastern Gawler Ranges’ contains a new lithology and stratigraphic log of the drill hole, as well as new petrology and geochemistry data.

Download RB 2015/00030

Cover of Report Book 2015/00021

Stratigraphy of the lower Gawler Range Volcanics in the Roopena area, north-eastern Eyre Peninsula.

The lower Gawler Range Volcanics exposed in the Roopena area provide a rare example of mafic and felsic volcanism synchronous with sedimentation in a lacustrine setting. In the subsurface this volcanic sequence extends northwards to the MSDP Cariewerloo drilling area, and is bound by a N-S-trending fault system which appears to have been active during volcanism.

Report book 2015/00021 ‘Stratigraphy of the lower Gawler Range Volcanics in the Roopena area, northeastern Eyre Peninsula’ contains detailed  petrological descriptions of the Roopena Basalt, Angle Dam Volcanics and Fresh Well Formation, as well as lithological and stratigraphic logs of 25 drill holes in the Roopena area. By identifying sedimentary and volcanic time markers across the basin system, a model for the spatial and temporal evolution of the volcanosedimentary sequence has been constructed which discusses the interactions between volcanism, sedimentation and tectonism.

Regolith map of the Southern Gawler Ranges Margin (YARDEA and PORT AUGUSTA 1:250 000 map sheets)

The regolith map of the Southern Gawler Ranges Margin geoscience product provides a valuable regional overview of the main regolith types and their associated landforms, a general outline of the major areas of bedrock or regolith dominated terrain as well as the occurrence of in-situ versus transported regolith of this emerging mineral province.

Mapping was based on the 1:100 000-scale geology layer (SARIG) using the RTMAP scheme (after Pain et al., 2007). The regolith polygon linework was newly compiled for the YARDEA and PORT AUGUSTA 1:250,000 scale map sheets using ArcGIS 10.1. For each regolith polygon ten attributes were captured during the mapping process including regolith materials and landforms name, description, RTMAP code and map symbol, as well as the TI (transported or in-situ) and RED (residual-erosional-depositional) scheme. Mapping and map compilation was based on a variety of data, with the 1:100,000 State geology dataset, Landsat TM5 and ETM7 images, 1sec and 3sec DEM, radiometrics, Google Earth (3D view) and existing CRCLEME regolith maps for the area representing the key datasets. Spatial accuracy and linework detail was in parts improved in comparison to the 100k State geology dataset, due to the availability of higher resolution images. It should be noted that the SGRV regolith map represents the surface distribution and expression of the regolith and it does not include any information about regolith thickness, stratigraphy and age. Very limited information about bedrock weathering intensity was available from existing datasets. Therefore, outcropping bedrocks has only been subdivided into several map units based on their geological province, lithology and stratigraphy. Material that has a close association with the underlying bedrock and has not experienced a large degree of transport has been mapped as residual material. Piggyback codes have been used for some polygons where it was known that different regolith overlies other regolith material.

As mineralisation in regolith is often related to intense induration, e.g. uranium and gold in calcretes, induration of regolith material has also been mapped on the SGRV Regolith Map. Information about induration has been extracted from the existing 1:100 000-scale geology data layer in SARIG.

The SGRV regolith map aims to provide a broad-scale framework for guiding geochemical prospecting for a wide range of minerals and materials, as a basis for guiding mineral exploration, and to provide a useful dataset for addressing other land use issues like groundwater.

Download the Regolith map of the southern Gawler Ranges margin

The Regolith SGRV map layers (located in the Geology layer group) are available for download via SARIG

SGRV Regolith map

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For more information, contact:

Stacey Curtis
Senior Geologist
+61 8 8429 2577