Piemontite‐bearing rocks from the Olary District, South Australia

Ashley, P. M.

doi:10.1080/08120098408729292

Cited by 11 publications

(4 citation statements)

References 24 publications

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“…Mn-ore deposits related to oxidizing solutions, metarhyolites and meta-pyroclastic rocks where devitrified oxidized glasses may initiate high fo, at the onset of metamorphism, and Mn-rich chert and pelagic sediments whose precursor mineralogy may have included minerals such as Mn-oxides capable of buffering fo to high levels during metamorphism (see keskinen, 1981;Kawachi ef al., 1983;Ashley, 1984;Coombs et al, 1985;Reinecke, Okrusch & Richter, 1985), are all consistent with the experimentally suggested sensitivity of piemontite to fo2. Clearly the problem of the nature and origin of the oxidizing state and the degree to which crystallochemical controls within the epidote minerals (specifically crystal field stabilization energy gained by Mn+.l in the distorted octahedral site of all the epidote minerals) maintain that high degree of oxidation during subsequent metamorphic processes could all bear more detailed examination.…”

Section: Complicationssupporting

confidence: 85%

“…Piemontite-bearing parageneses have been described from a wide range of metamorphic environments, from greenschist (Keskinen, 1981;Yardley, 1982;Kawachi, Grapes, Coombs & Dowse, 1983;Ashley, 1984;Coombs, Dowse, Grapes, Kawachi & Roser, 1985). amphibolite (Smith & Albee, 1967;Stensrud, 1973;Grambling & Williams, 1985) and blueschist (Ernst, Seki, Onuki & Gilbert, 1970;Brown, Essene & Peacor.…”

Section: Previous Experimental Studies On Piemontitementioning

confidence: 99%

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Stability relations of Mn–Fe–Al piemontite

Keskinen

Liou

1987

Journal Metamorphic Geology

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Comparison of the stability relations of Fe-piemontite, Pm,,Ps,,Cz, (Ca2A12Mnl).S Fe,,,sSi30 I 2( OH)), with similar experimentally determined results on P~,,CZ,,~ suggests that, at moderate fo,, addition of Fe to piemontite raises its thermal stability and slightly decreases its sensitivity to oxygen fugacity. Reversal study of the reaction:Fe-piemontite + quartz = garnet at Pffuid = 2 kbar in cold-seal apparatus using solid oxygen buffers was completed. The data indicated breakdown of Pm17Ps17Czhtr at 645" t 10" C along the Cu20-CuO buffer, 477" 2 10" C along the Cu-Cu20 buffer, and 365" 5 lo" C for the hematite-magnetite buffer. Mn-free clinozoisite and epidote have been shown to be stable to much higher temperatures than piemontite at moderate fo, (< Cu-Cu20). At very high fo,, however, {he presence of Mn+3 in a distorted octahedral site may permit I persistence of piemontite to higher temperatures than Mn-poor epidote minerals.The compositional range of natural FeMn-AI piemontites supports these results. Cation partitioning from piemontite-bearing parageneses also indicates crystallization at high fo2, but application of the cited results should be made with caution. Synthetic phases were too fine-grained for optical or microprobe analysis, and reaction was often incomplete.The assumption that all Fe + Mn was contained in piemontite and garnet, respectively, in the low-and high-temperature assemblages is supported by the cell dimensions for these synthetic minerals, which are close to predicted values. The reaction is pseudo-univariant. as solid solution in garnet and piemontite would be fo2-dependent in a more complex chemical system. Although bulk rock and fluid compositions may also have a marked effect on the stability of natural epidote-piemontite, fo, is + anorthite + fluid the major control on Fe : Mn : Al in epidote minerals.

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Section: Complicationssupporting

confidence: 85%

Section: Previous Experimental Studies On Piemontitementioning

confidence: 99%

Stability relations of Mn–Fe–Al piemontite

Keskinen

Liou

1987

Journal Metamorphic Geology

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“…An Fe 3+beating dravite-uvite containing 1.1-1.6 wt.% MnO has also been identified in piemontite-rich rocks of the Olary district, South Australia (el. Ashley, 1984) by one of us (J.F. Slack, unpub, data, 1989).…”

Section: Discussionmentioning

confidence: 99%

Alkali-deficient tourmaline from the Sullivan Pb-Zn-Ag deposit, British Columbia

1997

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Alkali-deficient tourmalines are found in albitized rocks from the hanging-wall of the Sullivan Pb-Zn-Ag deposit (British Columbia, Canada). They approximate the Mg-equivalent of foitite with an idealized formula □(Mg2Al)Al6Si6O18(BO3)3(OH)4. Major chemical substitutions in the tourmalines are the alkali-defect type [Na*(x) + Mg*(Y) = □(x) + Al(Y)] and the uvite type [Na*(x) + Al(Y) = Ca(x) + Mg*(Y)], where Na* = Na + K, Mg* = Mg + Fe + Mn. The occurrence of these alkali-deficient tourmalines reflects a unique geochemical environment that is either alkali-depleted overall or one in which the alkalis preferentially partitioned into coexisting minerals (e.g. albite).Some of the alkali-deficient tourmalines have unusually high Mn contents (up to 1.5 wt.% MnO) compared to other Sullivan tourmalines. Manganese has a strong preference for incorporation into coexisting garnet and carbonate at Sullivan, thus many tourmalines in Mn-rich rocks are poor in Mn (<0.2 wt.% MnO). It appears that the dominant controls over the occurrence of Mn-rich tourmalines at Sullivan are the local availability of Mn and the lack of other coexisting minerals that may preferentially incorporate Mn into their structures.

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“…Asterisks indicate occurrences of stratabound Fe-Cu (-Zn-Pb) mineralisation in the sequence;filled ellipses indicate occurrences of iron formations banded iron formations and Mn-rich rocks (Ashley 1984a). Cook and Ashley (1992) proposed an evaporitic origin for the albite-and calcsilicate-rich metasediments on the basis of their textures, mineralogy and calcsilicate pseudomorphs after dolomite and gypsum.…”

Section: Geological Settingmentioning

confidence: 99%

Sulphide mineralisation in the Olary Block, South Australia

1995

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The South Australian portion of the Willyama Inliers hosts a diversity of small sulphide and uranium deposits and numerous outcropping gossans. This fact, together with geological similarities to the adjacent Broken Hill Block has led to extensive exploration. A broad classification distinguishes two main types of sulphide mineralisation: 1) stratiform iron sulphide-dominated (+Cu, Zn, Co) deposits which occur widespread within specific stratigraphic intervals, and stratabound occurrences of syn-depositional to diagenetic origin which show some structural control; 2) syn-tectonic to post-peak metamorphic replacement and vein-type deposits (Fe-Cu-Au and Cu-Zn-Pb), which are hosted by fractures and within faults and shear zones. These occurrences show no stratigraphic control and are not spatially related to type 1 mineralisation. Late-stage deposits also differ from stratiform/stratabound mineralisation in their texture, mineral assemblage and geochemical composition. Much of the sulphide mineralisation in the Olary Block has been interpreted as resulting from rift-associated syn-to diagenetic processes, such as hot spring exhalations and base metal precipitation along reduction-oxidation interfaces. Subsequent granitic intrusive, high grade metamorphic and multiphase deformation events would have induced remobilisation and redeposition of sulphides in a variety of epigenetic modes. However, a detailed petrographic and geochemical study of sulphide mineralisation in the Olary Block demonstrates that due to the lack of abundant pervasive fluids, translocation and modification of preexisting sulphides were restricted to less than a few centimetres. Instead, widespread syn-tectonic to epigenetic (i.e., post-peak metamorphic) mobilisation of ore constituents occurred to form retrograde sulphide mineralisation as well as multiple generations of late-stage vein deposits. These epigenetic deposits are genetically unrelated to synsedimentary and diagenetic occurrences, an aspect of significance for exploration in the Olary Block. Temporal separation of peak metamorphism in deeper crustal levels from its occurrence in shallow levels, periodic tectonic disturbances and repeated seismic pumping are processes believed to have resulted in intermittent mobilisation of ore constituents from a deep-seated metasedimentary reservoir.

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Piemontite‐bearing rocks from the Olary District, South Australia

Cited by 11 publications

References 24 publications

Stability relations of Mn–Fe–Al piemontite

Stability relations of Mn–Fe–Al piemontite

Alkali-deficient tourmaline from the Sullivan Pb-Zn-Ag deposit, British Columbia

Sulphide mineralisation in the Olary Block, South Australia

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