LUCKY STRIKE PIT (MANKE PIT)
near Shelton, Mason County, Washington, USA

LOCALITY IMAGES


GEOLOGY
Crescent Formation - Late Paleocene to middle Eocene (62-48 Ma). The Crescent Formation is comprised of a large volume of submarine/subaerial basalt. The Crescent basalts are among the oldest basalts in this region and makeup the basement of the Coastal range. Babcock et al. (1992) concluded that the Crescent Formation basalts erupted into a subsiding rift basin along the western coast approximately 60 mya. Exposure of the Crescent formation can be found as a continuous swath defining the northern, eastern, and southeastern edge of the Olympic Peninsula. Based on gravity studies, the Crescent Formation is thought to extend eastward beneath the Puget Sound to Seattle. Most of the Crescent Formation, especially on its eastern edge, is covered with Quaternary glacial till deposits.

Exposure of the Crescent Formation near Shelton is comprised of both subaerial basalt flows and submarine pillow basalts that have been altered to a low grade (sub-greenschist facies) metabasalt. Centimeter to decimeter scale zeolite filled vugs are found within the interiors of individual pillows and along planar trends parallel to flow contacts. Contact quarry operator for current collecting status.

MINERALS
*Apophyllite-
(K,Na)Ca4Si8O20(F,OH) - 8H2O - Occurs as translucent to light green crystals to a about 1 inch.
*Calcite-
CaCO3 - Occurs as beautiful tea-colored rhombohedral crystals to a few inches. Interpenetration twins are common.
*Chlorite-
(Mg,Fe)3(Si,Al)4(Mg,Fe)3O10(OH)8 - Chlorite occurs as a fine-grained coating of amygdules.
*Heulandite-
(Ca,Na)2-3Al3(Al,Si)2Si13O36 - 12H2O - Occurs as translucent white to peach-colored fan-shaped crystals to about 2 inches.
*Stilbite-
NaCa2Al5Si13O36 . 16H2O - Occurs as translucent to opaque white crystals to about 2 inches. Opaque crystals have undergone dehydration. "Bow-ties" are common.

* photographed

 
APOPHYLLITE
 
APOPHYLLITE
 
CALCITE and STILBITE

 
Pink HEULANDITE with
STILBITE
 
Light green HEULANDITE

 
HEULANDITE with
CHLORITE inclusions and
APOPHYLLITE
 
HEULANDITE on
CHLORITE
 
STILBITE on
APOPHYLLITE

 
STILBITE and
LAUMONTITE
on CHLORITE


REFERENCES

Babcock R. S., Burmester R. F., Engebretson, D. C., Warnock A., Clark K. P. (1992) A Rifted Origin for the Crescent Basalts
     and Related Rocks in the Northern Coast Range Volcanic Province, Washington and British Columbia. Journal of
     Geophysical Research, B, Solid Earth and Planets. 97(5)
, 6799-6821.