The b 0 value of the potassic white micas as a barometric indicator in low-grade metamorphism of pelitic schists

Sassi, Francesco; Scolari, A.

doi:10.1007/bf00371166

Cited by 155 publications

(169 citation statements)

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“…The than a pressure effect (e.g., Sassi and Scolari, 1974;Guidotti and Sassi, 1986 (Shirozu and Higashi, 1972;Meunier and Velde, 1982;Inoue et al, 1987Inoue et al, , 1988Drits et al, 1993;Inoue and Kitagawa, 1994;Drews-Armitage et al, 1996;Celik et al, 1999;Yan et al, 2001;Bove et al, 2002;Schleicher, 2006).…”

Section: Mineralogymentioning

confidence: 99%

Illite occurrences related to volcanic-hosted hydrothermal mineralization in the Biga Peninsula, NW Turkey: Implications for the age and origin of fluids

Bozkaya

Uysal

et al. 2016

Ore Geology Reviews

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Section: Mineralogymentioning

confidence: 99%

Illite occurrences related to volcanic-hosted hydrothermal mineralization in the Biga Peninsula, NW Turkey: Implications for the age and origin of fluids

Bozkaya

Uysal

et al. 2016

Ore Geology Reviews

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“…Samples containing detrital micas were avoided as far as possible and samples rich in quartz, chlorite and carbonates were avoided as they may affect the b-spacing value (Sassi & Scolari 1974). Almost all the samples contain the assemblage white mica þ chlorite þ quartz + albite, with rare detrital K-feldspar in some samples, thus meeting the compositional requirements suggested by Sassi & Scolari (1974). The samples were crushed to a powder using a ring mill and the phyllosilicate fraction (52 mm) was separated from the rock powder by incorporating it into suspension in water by the addition of sodium polyphosphate.…”

Section: Sampling and Analytical Techniquesmentioning

confidence: 99%

“…The b o spacing was determined from a digital trace after computer stripping of the CoK a2 contribution. Detailed discussions of the method and its application as a geobarometer of low-grade metamorphic rocks are found in Sassi & Scolari (1974) and Padan et al (1982).…”

Section: 'Illite Crystallinity' (Kübler Index) Determinationmentioning

confidence: 99%

“…The Tschermak substitution [(Mg,Fe 2þ ) vi Si iv ¼ Al vi Al iv ] between the ideal muscovite and celadonite end-members controlling the chemistry of phengites, is thought to be particularly sensitive to pressure at low-temperature conditions. Therefore, the celadonite content of white micas serves as a qualitative geobarometer in low-grade metamorphic rocks (Ernst 1963;Sassi & Scolari 1974;Powell & Evans 1983;Guidotti & Sassi 1986;Kü bler & Jaboyedoff 2000). Increase in celadonite contents (Fe þ Mg) of white micas is accompanied by an increase in b-spacing values (Guidotti 1984) that provide an indirect method for measuring celadonite content.…”

Section: Introductionmentioning

confidence: 99%

“…Increase in celadonite contents (Fe þ Mg) of white micas is accompanied by an increase in b-spacing values (Guidotti 1984) that provide an indirect method for measuring celadonite content. X-ray diffractometry (XRD) offers a fast and reliable way to estimate b-spacing values (Sassi & Scolari 1974;Guidotti & Sassi 1986). Offler et al (1998) have measured the b-spacing values of white micas in the western Lachlan Orogen to estimate the baric types and in conjunction with 'illite crystallinity' values identified a single metamorphic boundary between the epizone and anchizone that lies to the east of Bendigo ( Figure 1).…”

Section: Introductionmentioning

confidence: 99%

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Illite crystallinity and the b-spacing values of white micas and their implications for gold mineralisation in the Lachlan Orogen

Wilson

McKnight

Dugdale

et al. 2009

Australian Journal of Earth Sciences

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Gold mineralisation in the Lachlan Orogen of western Victoria, is generally hosted in turbidites with very low-grade metamorphic assemblages. Metamorphic data from these turbidites are relatively rare because of the fine-grained nature of the pelitic component and lack of suitable assemblages for thermobarometric estimates. In this study, 'illite crystallinity' (Kü bler Index) and b-lattice spacing measurements were carried out on white micas in metapelites, collected from near the inferred western margin of the Selwyn Block, as well as three exploration targets, in an attempt to relate thermal and barometric conditions to mineralisation. Higher-grade (epizone) metamorphic conditions are recorded in sequences west of the Whitelaw Fault and lower-grade (anchizone) metamorphic conditions to the east of the fault. The change from epizonal to anchizonal grade is abrupt, resolved to a distance of a few hundred metres. The b-spacing values change adjacent to the Muckleford Fault. This is due to rocks to the east being exhumed as the edge of the Selwyn Block moved westward during the Middle Devonian Tabberabberan Orogeny at *380 Ma. We propose that the juxtaposition of rocks with contrasting thermal and barometric histories represents expression of the upper crustal location of the western margin of the Selwyn Block at the time of peak deformation, at about 440 Ma, and this crustal structure controlled the distribution of the major quartz-vein-type gold deposits. The Middle Devonian orogenic activity (*380 Ma) was accompanied by the formation of disseminated gold deposits such as Fosterville. This represents a mineralising event that overprints the earlier gold deposits in a corridor at least 50 km wide and to the west of the Whitelaw Fault, that parallels the margin of the Selwyn Block. The correlation between gold assays and 'illite crystallinity' results, from X-ray diffraction and from shortwave infrared-reflectance field-spectroscopy data, were ambiguous. Kübler Indices are not found to be effective in targeting of mineralisation as the values obtained from the alteration and the host-rock assemblages were similar and reflected the ambient P-T conditions at the time of mineralisation.KEY WORDS: b-spacing, cooling history, gold mineralisation, illite crystallinity, Kübler Index, Lachlan Orogen, metamorphism, Victoria, white micas. INTRODUCTIONThe majority of Victorian gold deposits are associated with low-metamorphic-grade turbidites that are overprinted by alteration halos (Dugdale et al. 2009). If these alteration halos are to be used as a vector to potential sites of mineralisation, it is necessary to determine in which direction the alteration or metamorphic overprint is increasing. A quantitative understanding of the P-T history of the metamorphic events preserved in the Lachlan Orogen (Figure 1) (Figure 1).In the current investigation a field-based technique, short-wave infrared reflectance (SWIR), has also been used to characterise the alteration adjacent to two gold prospects. The SWIR technique measures th...

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Palaeogene K‐Ar ages from the Kamuikotan metamorphic rocks, southern area of the Kamuikotan Gorge, central Hokkaido, northern Japan

et al. 1995

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Mica separates from 44 metamorphic rocks (mostly pelitic) from the southern area of Kamuikotan Gorge, central block of the Kamuikotan zone were dated using the K-Ar method. The ages of white micas, separated from pelitic schists, range from 51 to 74 Ma. The Palaeogene K-Ar ages are supported by 40Ar-39Ar dating. Judging from mineral paragenesis and X-ray diffraction studies (RM values) of white micas, most of the pelitic schists belong to the intermediate pressure type. In the Orowen River district, the northern part of the study area, biotite from metavolcanic rocks of a lower pressure assemblage yields the youngest K-Ar ages (45-50 Ma). Although the Kamuikotan zone was considered to have been a subduction-related metamorphic belt along a Mesozoic consuming margin, the time span of the metamorphism and the lowering of metamorphic pressure in younger rocks suggest that: (1) exhumation of the younger Kamuikotan rocks accompanied the erosion of forearc basin sediments (the Yezo Supergroup); (2) the increase in the thermal gradient was probably related to the approach of the Kula-Pacific ridge to the subduction zone; and (3) the main stage of exhumation of the Kamuikotan rocks ceased before westward movement of the Pacific plate, which induced the collision of the Hidaka-Nemuro belts (palaeo-Kurile arc-trench system) with the Kamuikotan zone.

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The b 0 value of the potassic white micas as a barometric indicator in low-grade metamorphism of pelitic schists

Cited by 155 publications

References 14 publications

Illite occurrences related to volcanic-hosted hydrothermal mineralization in the Biga Peninsula, NW Turkey: Implications for the age and origin of fluids

Illite occurrences related to volcanic-hosted hydrothermal mineralization in the Biga Peninsula, NW Turkey: Implications for the age and origin of fluids

Illite crystallinity and the b-spacing values of white micas and their implications for gold mineralisation in the Lachlan Orogen

Palaeogene K‐Ar ages from the Kamuikotan metamorphic rocks, southern area of the Kamuikotan Gorge, central Hokkaido, northern Japan

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