The Chemical Evolution from Older (323–318 Ma) towards Younger Highly Evolved Tin Granites (315–314 Ma)—Sources and Metal Enrichment in Variscan Granites of the Western Erzgebirge (Central European Variscides, Germany)

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts. Based on the evolution with time, we could reconstruct enrichment factors for tin and tungsten starting from the protoliths (575 Ma) that were later converted to high-grade metamorphic rocks (340 Ma) and served as sources for the older biotite granites (323–318 Ma) and the tin granites (315–314 Ma). This evolution involved a continuous enrichment of both tin and tungsten with an enrichment factor of ~15 for tin and ~7 for tungsten compared to the upper continental crust (UCC). Ore level concentrations (>10–100 times enrichment) were achieved only in the greisen bodies and dykes by subsequent hydrothermal processes.

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The chemical evolution from older (323–318 Ma) towards younger highly evolved tin granites (315–314 Ma)—sources and metal enrichment in Variscan granites of the Western Erzgebirge (Central European Variscides, Germany)

10.5194/egusphere-egu2020-3092 ◽

2020 ◽

Author(s):

Marion Tichomirowa ◽

Axel Gerdes ◽

Manuel Lapp ◽

Dietmar Leonhardt ◽

Martin Whitehouse

Keyword(s):

Granulite Facies ◽

Source Rocks ◽

Metamorphic Rocks ◽

Control Factor ◽

Basement Rocks ◽

Ore Bodies ◽

O Isotopes ◽

Variscan Granites ◽

Highly Evolved

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts.In contrast to previously published suggestions (Romer and Kroner, 2015; Wolf et al., 2018), we can exclude a substantial role of intense sedimentary weathering as an important control factor for later Sn and W enrichment in granite related ores of the Western Erzgebirge due to the remarkable homogeneous Hf and low O isotopes in granitic zircons that are extremely distinct to all pre-Devonian basement rocks of Saxothuringia. We document a source enrichment from meta-sedimentary rocks (575 Ma) towards metamorphic rocks (340 Ma) were restites from granulite-facies melts are enriched 6&#8211;7 times in Sn compared to UCC (upper continental crust). These rocks are also enriched in K, but depleted in Na and Ca, contain abundant muscovite, and are fertile for later melting. Further enrichment of Sn and W occurred during multiple melt production of the older igneous granites (323&#8211;318 Ma) leading finally to a general enrichment of Sn (15 times compared to UCC) in the tin granites (315-314 Ma). Multiple melt production did not lead to a very strong enrichment of ore metals in the granites but is probably very important for a general enrichment of Sn and W in the thick granite-rich crust of the Erzgebirge. Efficient leaching by hydrothermal fluids led to a very strong enrichment (up to several orders) of Sn and W in the greisen ore bodies.&#160;References:Romer, R.L.; Kroner, U. Sediment and weathering control on the distribution of Paleozoic magmatic tin-tungsten mineralization. Mineral. Depos. 2015, 50, 327&#8211;338, doi:10.1007/s00126-014-0540-5.Wolf, M.; Romer, R.L.; Franz, L.; Lopez-Moro, F.J. Tin in granitic melts: The role of melting temperature and protolith composition. Lithos 2018, 310&#8211;311, 20&#8211;30.

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Some supracrustal (S-type) granites of the Lachlan Fold Belt

Earth and Environmental Science Transactions of the Royal Society of Edinburgh ◽

10.1017/s026359330001419x ◽

1988 ◽

Vol 79 (2-3) ◽

pp. 169-181 ◽

Cited By ~ 149

Author(s):

A. J. R. White ◽

B. W. Chappell

Keyword(s):

Volcanic Rocks ◽

Source Rocks ◽

Crystal Fractionation ◽

Metamorphic Rocks ◽

Contact Aureole ◽

High Grade ◽

Fold Belt ◽

Fertile Window ◽

Lachlan Fold Belt ◽

Sedimentary Source

ABSTRACTS-type granites have properties that are a result of their derivation from sedimentary source rocks. Slightly more than half of the granites exposed in the Lachlan Fold Belt of southeastern Australia are of this type. These S-type rocks occur in all environments ranging from an association with migmatites and high grade regional metamorphic rocks, through an occurrence as large batholiths, to those occurring as related volcanic rocks. The association with high grade metamorphic rocks is uncommon. Most of the S-type granites were derived from deeper parts of the crust and emplaced at higher levels; hence their study provides insights into the nature of that deeper crust. Only source rocks that contain enough of the granite-forming elements (Si, Al, Na and K) to provide substantial quantities of melt can produce magmas and there is therefore a fertile window in the composition of these sedimentary rocks corresponding to feldspathic greywacke, from which granite magmas may be formed.In this paper, three contrasting S-type granite suites of the Lachlan Fold Belt are discussed. Firstly, the Cooma Granodiorite occurs within a regional metamorphic complex and is associated with migmatites. It has isotopic and chemical features matching those of the widespread Ordovician sediments that occur in the fold belt. Secondly, the S-type granites of the Bullenbalong Suite are found as voluminous contact-aureole and subvolcanic granites, with volcanic equivalents. These granites are all cordierite-bearing and have low Na2O, CaO and Sr, high Ni, strongly negative εNd and high 87Sr/86Sr, all indicative of S-type character. However, the values of these parameters are not as extreme as for the Cooma Granodiorite. Evidence is discussed to show that these granites were derived from a less mature, unexposed, deeper and older sedimentary source. Other hypotheses such as basalt mixing are discussed and can be ruled out. The Strathbogie Suite granites are more felsic but all are cordierite-bearing and have chemical and other features indicative of an immature sedimentary source. They are closely associated with cordierite-bearing volcanic rocks. The more felsic nature of the suite results in part from crystal fractionation. It is suggested that the magma may have entered this “crystal fractionation” stage of evolution because it was a slightly higher temperature magma produced from an even less mature sediment than the Bullenbalong Suite. The production of these S-type magmas is discussed in terms of vapour-absent melting of metagreywackes involving both muscovite and biotite. The production of a magma in this way is consistent with the low H2O contents and geological setting of S-type granites and volcanic rocks in the Lachlan Fold Belt.

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Petrogeochemistry of Amphibolites from Shivpura District Bhilwara, Rajasthan, India

Journal of Institute of Science and Technology ◽

10.3126/jist.v20i2.13962 ◽

2015 ◽

Vol 20 (2) ◽

pp. 103-112

Author(s):

Harel Thomas ◽

Lalu Paudel

Keyword(s):

Iron Oxide ◽

Science And Technology ◽

Parent Magma ◽

Igneous Rocks ◽

Metamorphic Rocks ◽

High Grade ◽

Probable Origin ◽

Highly Evolved

Amphibolites are frequently observed in the medium- to high-grade metamorphic rocks of Shivpura. These amphibolites are the result of the metamorphism of pre-existing mafic igneous rocks under medium to high grade P-T conditions and consist essentially of hornblende–plagioclase–garnet–clinopyroxene-epidote–iron oxide. Geochemically, these orthoamphibolites are tholeiitic, show association with non-orogenic environment and shift to subalkaline derivatives with progressive differentiation. It is also clear that the parent magma for these rocks was highly evolved in nature. Paper records the petrography, geochemical characters and a probable origin of these amphibolites.Journal of Institute of Science and Technology, 2015, 20(2): 103-112

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Rare earth elements in high-grade metamorphic rocks from the western Alps

Lithos ◽

10.1016/0024-4937(79)90061-6 ◽

1979 ◽

Vol 12 (1) ◽

pp. 41-49 ◽

Cited By ~ 28

Author(s):

J. Dostal ◽

S. Capedri

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Western Alps ◽

Metamorphic Rocks ◽

High Grade

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Geochronology of high-grade metamorphic rocks from the Anjul area, Lut block, eastern Iran

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2013.12.021 ◽

2014 ◽

Vol 82 ◽

pp. 151-162 ◽

Cited By ~ 5

Author(s):

Michael Bröcker ◽

Gholamreza Fotoohi Rad ◽

Fateme Abbaslu ◽

Nikolay Rodionov

Keyword(s):

Metamorphic Rocks ◽

High Grade ◽

Lut Block ◽

Eastern Iran

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Zircon ages and the distribution of Archaean and Proterozoic rocks in the Rauer Islands

Antarctic Science ◽

10.1017/s0954102093000252 ◽

1993 ◽

Vol 5 (2) ◽

pp. 193-206 ◽

Cited By ~ 88

Author(s):

P. D. Kinny ◽

L. P. Black ◽

J. W. Sheraton

Keyword(s):

Granulite Facies ◽

Metamorphic Rocks ◽

Low Grade ◽

High Grade ◽

Ion Microprobe ◽

Rock Interaction ◽

Mafic Rocks ◽

Grade Fluid ◽

Vestfold Hills ◽

Intrusive Suite

The application of zircon U-Pb geochronology using the SHRIMP ion microprobe to the Precambrian high-grade metamorphic rocks of the Rauer Islands on the Prydz Bay coast of East Antarctica, has resulted in major revisions to the interpreted geological history. Large tracts of granitic orthogneisses, previously considered to be mostly Proterozoic in age, are shown here to be Archaean, with crystallization ages of 3270 Ma and 2800 Ma. These rocks and associated granulite-facies mafic rocks and paragneisses account for up to 50% of exposures in the Rauer Islands. Unlike the 2500 Ma rocks in the nearby Vestfold Hills which were cratonized soon after formation, the Rauer Islands rocks were reworked at about 1000 Ma under granulite to amphibolite facies conditions, and mixed with newly generated felsic crust. Dating of components of this felsic intrusive suite indicates that this Proterozoic reworking was accomplished in about 30–40 million years. Low-grade retrogression at 500 Ma was accompanied by brittle shearing, pegmatite injection, partial resetting of U-Pb geochronometers and growth of new zircons. Minor underformed lamprophyre dykes intruded Hop and nearby islands later in the Phanerozoic. Thus, the geology of the Rauer Islands reflects reworking and juxtaposition of unrelated rocks in a Proterozoic orogenic belt, and illustrates the important influence of relatively low-grade fluid-rock interaction on zircon U-Pb systematics in high-grade terranes.

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