Geochemical discrimination of volcanic rocks associated with borate deposits; an exploration tool?
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|Authors:||Floyd, P. A.; Helvaci, C.; Mittwede, S. K.|
|Author Affiliations:||Primary: |
University of Keele, Department of Earth Sciences, Keele, United Kingdom
Dokuz Eylul Universitesi, Izmir, Turkey
Muteferrika Consulting Services, Ankara, Turkey
|Volume Title:||Journal of Geochemical Exploration|
|Source:||Journal of Geochemical Exploration, 60(3), p.185-205. Publisher: Elsevier, Amsterdam-New York, International. ISSN: 0375-6742|
|Note:||In English. 64 refs.; illus., incl. 4 tables, geol. sketch map|
|Summary:||The Miocene borate deposits of western Turkey are associated with extensive medium- to high-K calc-alkali ignimbritic volcanism and a differentiated comagmatic alkaline trachybasalt-trachydacite lava suite. Ignimbritic air-fall and reworked pumiceous clastic materials are intimately associated with lake sediments that host the borate deposits. Local ignimbritic volcanism is considered the primary source of the B for the Kirka borate deposit in this area. Comparison of the geochemical composition of Turkish ignimbrites associated with borates ("fertile" ignimbrites) with those that do not ("barren" ignimbrites), exhibit a number of features that might prove useful in the exploration for borates in similar volcanic domains. In particular, "fertile" ignimbrites are (a) generally a high-K calc-alkali suite, well-evolved and fractionated (K/Rb is low, <200) with a high-silica rhyolitic bulk composition, (b) exhibit a combined high content of B, As, F, Li and Pb, with high B/La (>1) and B/K (>0.001) ratios, and (c) a mildly fractionated REE pattern (LaN/YbN∼2) and large positive Eu anomaly (Eu/Eu*∼0.1). Other apparent discriminants involving both compatible and incompatible elements (relative to major silicate phases) are largely a function of different degrees of partial melting and fractionation. It is suggested that the initial source of the B (and other associated elements) was from LIL-rich fluids released by the progressive dehydration of altered oceanic crust and pelagic sediments in a subduction zone. The absence or presence of sediments in a segmented subduction zone may influence the variable lateral distribution of borates in active margins on a global scale. Once the crust has become enriched in B via previous or contemporary subduction-related calc-alkali magmatism, the effect of tectonic environment, climate and hydrothermal activity influence the local development of the deposits. Abstract Copyright (1998) Elsevier, B.V.|
|Subjects:||Borate deposits; Boron; Calc-alkalic composition; Cenozoic; Chemical ratios; Geochemical indicators; Geochemical methods; Igneous rocks; Ignimbrite; Lithologic controls; Mineral exploration; Mineral resources; Miocene; Neogene; Pyroclastics; Rift zones; Tertiary; Volcanic rocks; Anatolia; Asia; Middle East; Turkey; Kirka Deposit; Western Turkey|
|Coordinates:||N360500 N420200 E0445000 E0261000|
|Copyright Information:||GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands|
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