Testing the plagioclase discriminator on the GEOROC database to identify porphyry-fertile magmatic systems in Japan
Williamson, BJ; Hodgkinson, M; Imai, A; et al.Takahashi, R; Armstrong, R; Herrington, R
Date: 23 February 2018
Article
Journal
Resource Geology
Publisher
Wiley / Society of Resource Geology
Publisher DOI
Abstract
Despite showing favourable geology, there are no known porphyry-type
deposits in Japan. This, therefore, provides an ideal porphyry-‘barren’ case area on
which to test the recently developed plagioclase-based discriminator for porphyry‘fertile’
calc-alkaline systems. The discriminator was applied to plagioclase data for
Japan in ...
Despite showing favourable geology, there are no known porphyry-type
deposits in Japan. This, therefore, provides an ideal porphyry-‘barren’ case area on
which to test the recently developed plagioclase-based discriminator for porphyry‘fertile’
calc-alkaline systems. The discriminator was applied to plagioclase data for
Japan in the online GEOROC database for convergent margin settings. Of the 3933
data points available, and considered reliable, 91% fall in the ‘barren’ field which
compares with 73% for equivalent data worldwide. ‘Fertile’ signatures in certain parts of
Kyushu and central Honshu should be further investigated, as well as areas where
there are magnetite-series magmatic systems with elevated whole-rock Sr/Y, but for
which there are currently little or no plagioclase data (SW-, N-central- and NE-Honshu).
Why the Japanese arcs appear to show anomalously poor potential for porphyry
deposits compared with other arcs worldwide, including Western Luzon, is as yet
unclear, but possibly relates to tectonic factors or the nature of the magmatic source, or
because melt PH2O in many of the magmatic systems was too low, as suggested from
low average excess Al in plagioclase.
Camborne School of Mines
Collections of Former Colleges
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