Petrology, geochemistry and geodynamic implications of Jurassic island arc magmatism as revealed by mafic volcanic rocks in the Mesozoic low-grade sequence, eastern Rhodope, Bulgaria

Abstract The Brucejack intermediate-sulfidation epithermal Au-Ag deposit, located 65 km north of Stewart, BC, forms part of a well-mineralized, structurally controlled, north-south gossanous trend associated with Early Jurassic intrusions straddling the Late Triassic-Early Jurassic Stuhini-Hazelton Group unconformity in the Sulphurets mineral district. Mining of the deposit commenced in mid-2017 after a long history of exploration dating back to the 1880s. Mineralization is hosted in deformed Lower Jurassic island-arc volcanic rocks of the Hazelton Group exposed on the eastern limb of the Cretaceous McTagg anticlinorium. High-grade Au-Ag mineralization was formed from ~184 to 183 Ma in association with a telescoped, multipulsed magmatic-hydrothermal system beneath an active local volcanic center. Precious metal mineralization occurs as coarse aggregates of electrum and silver sulfosalts in steeply dipping, E- to SE-trending quartz-carbonate vein stockwork zones cutting low-grade intrusion-related phyllic alteration. Epithermal vein development is interpreted to have occurred during the waning stages of Early Jurassic sinistral transpression in a compressive arc environment, followed by a limited Cretaceous deformation overprint.

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Petrology of a supra-subduction zone ophiolite (Elaz1g, Turkey)

Canadian Journal of Earth Sciences ◽

10.1139/e00-041 ◽

2000 ◽

Vol 37 (10) ◽

pp. 1411-1424 ◽

Cited By ~ 48

Author(s):

Melahat Beyarslan ◽

A Feyzi Bingöl

Keyword(s):

Upper Cretaceous ◽

Middle Eocene ◽

Volcanic Rocks ◽

Island Arc ◽

Granitic Rocks ◽

Late Triassic ◽

Geochemical Data ◽

Metamorphic Rocks ◽

Low Grade ◽

Magmatic Suite

The Elaz1g region in eastern Taurus, Turkey, exposes Paleozoic-Tertiary metamorphic, magmatic, and sedimentary units. Contacts between the different units are mostly tectonic, but there are also primary sedimentary, and intrusive contacts. The metamorphic rocks of the Elaz1g region are the Bitlis-Pütürge and Keban-Malatya massifs, which are a single tectonostratigraphic unit that has been tectonically disrupted and fragmented during the Upper Cretaceous. Magmatic rocks in the region are represented by ophiolitic units, magmatic arc products, and young volcanic rocks. The sedimentary units are represented by Upper Cretaceous - Tertiary marine and lacustrine sedimentary rocks. In the study area, the metamorphic units are represented by the Paleozoic Pütürge metamorphic rocks composed of phyllite, slate, mica schist, quartz-muscovite schist, calc-schist, and low-grade metamorphite. The ophiolite that is described in this paper is composed of wehrlite-pyroxenite, gabbro, diabase dykes, and dykes cutting gabbro. These units are cut by the granitic rocks of the Upper Cretaceous Elaz1g magmatic suite. The lithological and geochemical data on the rocks of Kömürhan ophiolite indicate that these rocks were derived from crystallization of an enriched mid-ocean ridge basalt (MORB)-type magma. The Kömürhan ophiolite formed in a supra-subduction spreading zone during the Cretaceous; related to this event is the north-dipping subduction of the southern branch of Neo-Tethys ocean, which began spreading in the Late Triassic. The crust was thickened by the development of an island arc and by the thrusting of the Pütürge metamorphic rocks onto this island arc in response to north-south compression during the Late Cretaceous. The magma formed by partial melting of the subducted slab giving rise to granitic rocks that cut the upper parts of the ophiolite. The ophiolite and the Elaz1g magmatic suite attained their present position after the Middle Eocene.

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TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100165938 ◽

1996 ◽

Vol 54 ◽

pp. 694-695

Author(s):

Gejing Li ◽

D. R. Peacor ◽

D. S. Coombs ◽

Y. Kawachi

Keyword(s):

Electron Microscopy ◽

Volcanic Rocks ◽

Analytical Electron Microscopy ◽

Metamorphic Rocks ◽

New Mineral ◽

Chemical Compositions ◽

Low Grade ◽

Fine Grained ◽

Depth Analysis ◽

Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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