Spruce Ridge
near North Bend, King County, Washington, USA

LOCALITY IMAGES


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.

Minerals at the Spruce Claim record a complex mineralization history, including late sedimentary precipitation of barite, and carbonate minerals such as ankerite. The Spruce Claim has been a source for aesthetic museum quality quartz and pyrite specimens. The Spuce Claim is a private claim owned by Spruce Collectors, LLC, a membership organization that exists to provide collecting opportunities for its members. Visit Geology Adventures for more information.

MINERALS (complete list, pers. comm., Bob Jackson) CLICK for PHOTOGRAPHED
*Ankerite- Ca(Fe,Mg)(CO3)2
*Barite- BaSO4
   Bravoite- (Fe,Ni,Co)S2
   Calcite- CaCO3
*Chalcopyrite- (Cu,Fe)S2
   Chlorite- (Fe,Mg,Al)6(Si,Al)4O10(OH)8
   Cosalite- Pb2Bi2S5
   Epidote- Ca2(Al,Fe)3(SiO4)3(OH)
   Galena- PbS
   Gold- Au
   Malachite- Cu2(CO3)(OH)2
*Pyrite- FeS2
*Quartz- SiO2
   Siderite- FeCO3
*Sphalerite- ZnS
   Tenorite- CuO

* photographed
 
Stacked ANKERITE crystals on QUARTZ
 
ANKERITE on QUARTZ
 
ANKERITE "rose" on QUARTZ
 
BARITE with QUARTZ and PYRITE
 
BARITE on QUARTZ
 
CHALCOPYRITE
epitactic on
PYRITE
 
PYRITE and QUARTZ cluster
 
Octahedral PYRITE
 
QUARTZ cluster
with amethyst scepter
 
Light amethystine QUARTZ cluster
with scepters
 
QUARTZ cluster
with amethyst scepters
 
Rehealed and sceptered
QUARTZ
splay

 
SPHALERITE crystal on ANKERITE




REFERENCES

Lasmanis, Raymond (July/August 1991) Minerals of the Spruce 16 Claim, King County, Washington. Rocks & Minerals.
     66(04)
, 25-30.

Livingston, Vaughn E., (1971) Geology and Mineral Resources of King County, Washington. Bulletin - Division of Mines
     and Geology (State of Washington)
63, Pages 200.