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Minerals 2017, 7(9), 174; https://doi.org/10.3390/min7090174

Quartz-Amethyst Hosted Hydrocarbon-Bearing Fluid Inclusions from the Green Ridge Breccia in the Snoqualmie Granite, North Cascades, WA, USA

1
Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway H91 TK33, Ireland
2
Cascade Scepters, P.O. Box 1001, Maple Valley, WA 98038, USA
3
School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK
4
Centre for Microscopy & Imaging, National University of Ireland, Galway H91 TK33, Ireland
*
Author to whom correspondence should be addressed.
Received: 14 July 2017 / Revised: 24 July 2017 / Accepted: 4 September 2017 / Published: 19 September 2017
(This article belongs to the Special Issue Fluid Inclusions: Study Methods, Applications and Case Histories)
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Abstract

The Green Ridge Breccia cuts the composite Miocene Snoqualmie Batholith in King County, WA, USA. The granite was emplaced at ~5 km depth between ~17 and 20 Ma and the crosscutting NW trending breccia contains large angular blocks of the host granite (<1 m in longest dimension). The brecciated granite blocks are cemented by quartz-amethyst euhedra (<10 cm in longest dimension) bearing vugs. A notable feature is the presence of centimetric scale amber coloured oil inclusions within the quartz-amethyst crystals. Fluid inclusion studies using Transmitted Light Petrography, UV Microscopy, Microthermometry, Laser Raman Microspectroscopy and Gas Chromatography-Mass Spectrometry record the presence and the fluid composition of three fluid inclusion types hosted by the euhedra: primary Type 1 (liquid rich two-phase (L + V) aqueous inclusions) and secondary Type 2 bituminous two-phase (S + L) inclusions and Type 3 amber coloured oil bearing two-phase immiscible liquid inclusions. The Green Ridge Breccia was the locus for convective hydrothermal fluid flow that formed the quartz-amethyst vugs formed at T~390 °C assuming a trapping pressure of ~1.65 kb. Later, hydrocarbon fluids migrated downwards from the roof source rock (e.g., the Guye Sedimentary Member) and were trapped in the euhedra. This was followed by unroofing of the batholith and exposure of the Green Ridge Breccia. This study highlights the potential for other oil migrations into the Snoqualmie Batholith in areas where it forms the basement capped by the Guye Sedimentary Member. View Full-Text
Keywords: hydrocarbon-bearing fluid inclusions; quartz-amethyst euhedra; Snoqualmie Granite; North Cascade hydrocarbon-bearing fluid inclusions; quartz-amethyst euhedra; Snoqualmie Granite; North Cascade
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Feely, M.; Costanzo, A.; Lindner, F.; George, J.; Parnell, J.; Bowden, S.; Baba, M.; Owens, P. Quartz-Amethyst Hosted Hydrocarbon-Bearing Fluid Inclusions from the Green Ridge Breccia in the Snoqualmie Granite, North Cascades, WA, USA. Minerals 2017, 7, 174.

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