Geology
The iron deposits occur in the Mesoproterozoic Carr Boyd Group, a sedimentary sequence that overlies older metamorphosed sediments and igneous rocks of the Lamboo Complex.
These iron deposits occur near the base of the Carr Boyd Group in the Hensman Sandstone. The unit occurs as a northerly trending easterly dipping outcrop faulted into two unequal portions that host the Sam and Tony deposits and as north-westerly trending outcrop that hosts the Matsu deposit. Only a minority of the Matsu deposit is within Exploration License 80/2389 and as this is the least prospective deposit it is not the subject of near term exploration plans.
The easterly dipping Hensman Sandstone occurs on a ridge top at elevations of around 600 metres, part of which is a haematitic quartz sandstone and siltstone with subordinate shale horizons. The Golden Gate Siltstone conformably overlies the Hensman Sandstone and was commonly located at the base of the western flanks of these prospects and dominates the eastern region of the project area.
The Hensman Sandstone appears to be of shallow marine to deltaic fluvial facies with a sequence of cross bedded sandstone and laminated siltstone with varying degrees of bioturbation within the ferruginous units of the sequence. The iron oxide (haematite) content increases towards the upper contact of this formation. The upper most unit of the Hensman Sandstone often contains in excess of 55% iron oxide (haematite) and is represented by a uniform medium to fine grained, cross bedded sandstone with minor bioturbation.
Scanning Electron Microscope (SEM) petrology indicates the source of the haematite was from iron rich brine solutions saturating the upper lithologies of the Hensman Sandstone during a period of reduced sedimentation, resulting in micro-oolitic and colloform textures (diagram).
Recent weathering of the haematitic units of the Hensman Sandstone has resulted in the preferential leaching of the silica to leave a porous, but sometimes massive, enriched haematite rock that occurs along much of the 9 kilometre strike length.
Enrichment ranges in depth from 12 metres on the ridge top to a few metres and extends up to 200 metres down the dip slope. The average dip of the mineralisation, concordant with the formation dip, is in the range 12 to 18 degrees to the east.
SEM petrology has also confirmed the presence of magnetite within the Hensman Sandstone. During the height of burial and under increased temperate and pressure, previously formed micro-oolitic haematite was overprinted by euhedral magnetite and the associated formation of proto grunerite.
The zones of enriched magnetite correspond to areas of high amplitude airborne magnetic responses (diagram) and associated high magnetic susceptibility readings in drill holes. Approximately 300 pulp samples were submitted for SATMAGAN analysis to determine the quantity of magnetite in zones of high magnetite susceptibility. The result from the SATMAGAN test work indicated that on average 35% magnetite was associated with zones of high magnetic susceptibility in drill holes. The corresponding average grade for these zones were 45% Fe, 28% SiO2, 1.7% AI2O3 and 0.01% P and typically average 10 – 12 metres in down hole thickness.
Davis Tube analysis on a number of magnetite samples will be carried out to determine yield and concentration ratios.
Project Geology
Other Related Links:
