T288 Gemological Research in the 21st Century—Gem Minerals and Localities

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 132ABC, North Building

HOT LAVAS – COOL GEMSTONES – OREGON SUNSTONE GEOLOGIC HISTORY

Paper number: T288-12
Program: Technical Sessions
Time: 4:15 PM – 4:30 PM

Authors

Abstract

Upper Miocene (5 -16 million years old) high alumina olivine basalt flows were sampled at (3) locations in SE Oregon. Samples were thin-sectioned, element analyzed, (LA-ICP) radiometric age dated and isotope analyzed, Microprobe).

The Oregon State Gemstone (Oregon Sunstone) has only been found in three, geologically related, mine pits in Lake County Oregon. All locations have been sampled. All samples present evidence for the following conclusions: (1) all Sunstone basalt flows are the same age (8.2mya), (2) all sunstone crystals occur in cavities (vesicles) in the basalt, (3) all sunstone crystals are the same age (15mya), (4) native copper metals were introduced into the ascending magma, (5) crystalized labradorite feldspar poly-cores were surround by copper-bearing fluids, (6) the most rapidly cooled copper fluids crystallized first, producing the smallest copper particles in the smallest cleavage openings near crystal edges (a clear colorless outermost zone with no copper platelets), (7) the polycrystal core (thickest and best developed cleavage planes) contained the slowest cooled and largest copper crystals (platelets), (8) the Sunstone basalt flows ascended, captured inclusions of older magma, erupted by encountering a geothermal water table, producing boiling, highly vesicular, porous basalts. The basalts moved upward along recurrent fault zones. All Sunstone basalt flows are contemporaneous, but may not be coincident.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-330946

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