 | near North Bend, King County, Washington, USA |
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GEOLOGY
Snoqualmie Batholith - late Oligocene to early Miocene (28 Ma[million years ago] to 22 Ma). Uplift and erosion of the Old Cascade Volcanic Arc exposed plutonic rock of the Snoqualmie Batholith near Snoqualmie Pass. Intrusive rock types found within the Snoqualmie Batholith range in composition from granite to gabbro. Granodiorite is the most prevalent exposed rock type. Other lithologies within the batholith include porphyritic dacite, andesite, aplite, and intrusive breccia (Livingston, 1971).
Intrusive breccias can be the host for metallic ore deposits and aesthetic mineral specimens. An intrusive breccia is a cylindrical structure that is formed by the violent ascent of volatiles near the top of a shallow intrusion as it cools. The force of volatiles escaping to the surface causes the rock to fracture and fault, providing open spaces for subsequent mineralization by hydrothermal fluids. These high temperature acidic fluids are responsible for the alteration of plagioclase to muscovite and clay within the adjacent granodiorite breccia blocks and for the precipitation of quartz and metallic ore (usually as sulfides) on the walls of the blocks. Most intrusive breccia metallic mineral deposits within the Snoqualmie region are currently uneconomic due to poor accesibility and/or the low tenor of the ore (Cu, Au, Ag), but many mining claims are still active that produce some of the finest quartz and sulfide mineral specimens in the world.
Mineral localities within the Hansen Creek area are either breccia exposure or slump zones derived from breccia. There are a number of collecting areas existing within a relatively small area that comprise the Hansen Creek locality. Some are privately claimed. The claim owners do not allow collecting without permission. The Northwest Mineral Collective is a team of dedicated miners that is currently working one of the private claims to produce quartz specimens; visit their Instagram page for more information.
MINERALS (incomplete list)
| TiO2 - Occurs as honey-colored mm-sized crystals with complex terminations exhibiting alternating sets of tetragonal bipyramidal faces. | |
| Fe-endmember chlorite - (Fe,Mg)3Fe3(Si,Al)4O10(OH)8 - Occures as mm-scale dark green books of micaceous crystals and as micro-inclusions in quartz crystals. | |
| Cu2H2Si2O5(OH)4 - Occurs within oxidized (supergene) zone as bright blue to green botryoidal fillings within small cavities. | |
| Ca3(PO4)3F - Occurs as millimeter- to centimeter-scale clear to transluscent white hexagonal crystals, often elongated. | |
| HFeO2 - Goethite pseudomorphs after pyrite to several inches. Most pseudomorphs are incomplete with pyrite cores. Also goethite pseudomorphs after bladed siderite over 1-inch in diameter have been found. | |
| FeS2 - As cores within goethite pseudomorphs and as small inclusions in quartz. | |
| SiO2 - Colorless quartz, amethyst scepters (to several inches), doubly terminated crystals including rare dumb-bells, and rare Japan-law twin quartz crystals can be found. Some crystals exhibit stacked short-wave fluorescent phantoms. | |
| TiO2 - mm-scale sprays of acicular crystals embedded in calcite. |
* photographed
ANATASE Photo Copyright © Rick Dillhoff |
QUARTZ (Var: Amethyst) scepter Photo Copyright © Eli Hess |
Amethyst QUARTZ scepter Photo Copyright © Rick Dillhoff |
RUTILE with dark green CLINOCHLORE Photo Copyright © Douglas Merson 2018 |
Japan-law twin QUARTZ cluster |
gemmy CHRYSOCOLLA |
Amethyst QUARTZ scepters |
Amethyst QUARTZ scepter with zoning Photo Copyright © Eric He 2019 |
QUARTZ crystal with fluorescent phantoms Photo Copyright © Michael Bailey 2022 |
QUARTZ crystal with fluorescent phantoms Photo Copyright © Max Larsen 2023 |
Japan-law twin QUARTZ Photo Copyright © Jesse Hoffman |
GOETHITE pseudomorph after PYRITE |
CHRYSOCOLLA Photo Copyright © Rick Dillfoff |
PYRITE . |
High-quality amethyst QUARTZ scepter Photo Copyright © Eric He 2019 |
Rare "Dumbbell" sceptered QUARTZ (Var: Amethyst) Photo Copyright © Eric He 2019 |
QUARTZ with euhedral PYRITE inclusions Photo Copyright © Eli Hess 2023 |
FLUORAPATITE with black CLINOCHLORE and QUARTZ Photo Copyright © Douglas Merson 2018 |
Livingston, Vaughn E., (1971) Geology and Mineral Resources of King County, Washington, USA. Bulletin - Division of Mines and Geology (State of Washington) 63, Pages 200.