Spruce Ridge
near North Bend, Washington
GEOLOGY
Snoqualmie Batholith - Miocene (20 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 Bob Jackson. Collecting is only allowed during fee-based field trips lead by Bob at Geology Adventures.

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

PYRITE and QUARTZ cluster

QUARTZ cluster
with amethyst scepters

ANKERITE on QUARTZ

Rehealed and sceptered
QUARTZ splay

PYRITE

BARITE on QUARTZ



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