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LYNDHURST OCHRE CLIFFS

LYNDURST - SOUTH AUSTRALIA

AUG 28TH 2020

OCHRE MINE & QUARRY

GEOLOGY

Northern Flinders Ranges

 

 

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Lyndhurst Ochre

Burra Group: Siltstone, laminated; shale; sandstone, heavy mineral lamination, quartzose to feldspathic, cross-bedding; dolomite, blue-grey to pale pink, lenticular. 

ADELAIDE GEOSYNCLINE

 

NEOPROTEROZOIC, Sturtian to Torrensian

The colours in the claystone have a more dull and earthy appearance, this is due to a low amount of iron-bearing oxides, the yellow ochre is mainly coloured by goethite. 

Ochre Sample, Red (RHSCC No. 173 B):

 1.8% Hematite

 40.0% Quartz

 17.7% Kaolinite

-  23.7% Muscovite

-  0.2% Anatase

 3.4% Halite

13.3% Amorphous 

Ochre Sample, Yellow (RHSCC No. 163 A):

- 5.7% Goethite

- 0.3% Bassanite

- 57.46% - 65.85% - Quartz

Data on the ochre is from a study accepted in 1998, only 2 samples were taken for the sample size.  

The two specimens analysed here, one red, the other yellow, were collected by P.  Horton in November 1994 (SAM R1710 and R1709). The ochres are dull and earthy in appearance and the dullness of  the  colour  (RHSCC no.173  B  (red)  and  163 A (yellow)) is  due  to  the  low concentration of iron-bearing oxides.

 

In the yellow ochre goethite is the iron-bearing mineral (5.7%) and is responsible for the colour. The other minerals present are the same as in the red ochre except for a small amount (0.3%) of bassanite (see Mount Howden, below) and mineral proportions are similar to the red ochre (Table 2). XRF analyses confirm the high amount of silicates in the ochres. The quartz figures are very high  (57.46% and 65.85%) and  also the amount of A1203  (13.87% and  14.91%) due to the presence of kaolinite and muscovite in the sample. The trace element concentrations for the Lyndhurst ochres are similar to the Port Noarlunga ochres, showing high Zr, Ga, Ba and Rb. The Lyndhurst ochres are, however, richer in Sr. The physical appearance, mineralogy and chemistry of these Moana, Port Noarlunga and Lyndhurst ochres are overall very similar and as such suggest a common mode of formation; in fact, they are all Pleistocene claystones formed by deep weathering of Precambrian sediments even though they  are  some  600km apart. The trace  element fingerprints distinguish between the  three deposits based on the limited sampling so far undertaken.

 

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Pooraka Formation

Clay, sand and carbonate earth, silty, with gravel lenses.

Pleistocene alluvial/fluvial sediments

Pleistocene, Late

ST VINCENT BASIN

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Telford Gravel

Polymict gravel, well rounded, includes boulders. Alluvial fan deposits.

Pleistocene

    TELFORD BASIN

 

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Ochre Mining and Quarrying

The Ochre Cliffs are located around 2 km north of Lyndhurst, the main pit is 20 by 15 meters long and 6 meters deep. Four colours of ochres are visible in vertical bands, these have been eroding out for some time before the trade of ochre from this location. Ochre from Lyndhurst formed from claystones which were deposited during the Pleistocene and most likely have been formed from deep weathering of the blow basement sediments. 

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REFEreNCES

South Australian Government. (n.d.). SARIG geological map. SARIG. 

Jercher, M., Pring, A., Jones, P. G., & Raven, M. D. (1998). Rietveld X-Ray Diffraction and X-Ray Fluorecence Analysis of Australian Aboriginal Ochres. Archaeometry, 40(2), 383–401. https://doi.org/10.1111/j.1475-4754.1998.tb00845.x

K. W. A. Summers. (1953, March). Report on [the] Spring Creek copper mine. (Report Book 35/35). South Australia Department of Mines, Mineral Resources Branch, Uranium Section. 

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