Scope

This project deals with the metallic ore bodies of the southwest portion of the Index Mining District, Snohomish County, Washington.

Location

The area is bound to the west by the city of Gold Bar, the east by the city of Reiter, the north by the Skykomish River, and the south by the King County line.

Geologic Section

The oldest rocks in this area are interbeded quartizites, marbles, cherts, slates and schists which have been intruded by granodiorite.  At the time of the intrusion the older metamorphic rocks were tilted from 90 degrees to 75 degrees in the Gold Bar area, to as little as 6 degrees in the Reiter area.  The youngest material is glacial deposits with stream sediments.

Ore Deposits

The granodiorite and the metamorphic series are cut by nearly vertical shear zones with an average strike of N 45 E.  The majority of the shear zones are found in the granodiorite.  The granodiorite is the predominant rock of the Index Mining District.

These shear zones range from a fraction of an inch to over twenty feet in width.  As a rule the narrow portions are void of ore bodies, where as teh wider portions of the shear zones contain lens shaped ore bodies dispersed along the country rock.  Quartz and calcite are common associates with these ore bodies.  Lens size varies from slight impregnations to large sulphide masses along the shear zones.

Ore Minerals

Within the shear zones chalcopyrite and bornite are the major minerals.  Associates include pyrite, azurite, malachite, chalcocite and hematite.

Major minerals within the schists are chalcopyrite, arseno-pyrite and bornite.  Associates include pyrite and hematite; assays would also suggest sperrylite and cooperite, both platinum ores.

Ores

The shear sones have historically yielded copper in great abundance with minor traces of gold and silver.  Todate, no exploration has exposed either the granodiorite intrusion or one of the numerous shear zones with the area.

The schists have no history of having been used as an ore body.  Exploration has shown traces of copper, silver, gold, and platinum present.

Percentage of these metals varies greatly with the highest concentration being found in a layer of green schist.  The green schists overlay a blue schist inwhich the ore concentration tends to disappear the closer one gets to the granodiorite intrusion.

Commercial Aspects

As with the whole of the Index Mining District, the major ore values were found within the granodiorite intrusion.  These values were for teh most part due to the abundance of copper within the shear zones.  The occurence of gold and silver with in the schists needs further exploration to determine if a commerical sized deposit does exist.  The platinum found in concentrations of 1/10 ounces per ton is of geologic interest, but again further exploration is required.

The abundance of timber and water are excellent for power generation and construction, but will require several settling ponds above Crystal Creek's enterance to Proctor Creek.

In the late 1880's, gold was found on the Skykomish River at a site now known as Gold Bar.  The placers produced roughly 1,000 ounces of gold and platinum.  These finds eventually lead to the establishment of lode mines 12 miles to the northeast of Gold Bar.  These mines produced for several decades high grade silver ore with traces of gold, platinum and copper.  The major ore of these mines was arseno-pyrite.

Four years ago a mining company purchased the claims south of Gold Bar and started exploration.  This led to a thirty foot audit and then development was abandoned due to low grade assays.  Work resumed last year with a twenty-five foot audit and again abandoned due to low grade assays.

With continued gold prices, and desire for further development, outside help was contracted to locate the ore body if any .  Extensive drilling and assay work was conducted during the spring of 1980.  Highest assay results were from surface samples showing per ton: .175 platinum, .085 gold.  At depth, the average assays ran per ton: .07 silver, .035 platinum and .001 gold.

Conclusions

In conclusion, the source of the Skykomish gold bar was found but due to transportation problems, low smelter prices and settling pond problems - the ores' richness is not great enough for economic feasibility, unless ore is retrieved at a greater rate than 1,000 tons or ore per day.  However at this mining rate, the size of the ore body is insufficent for commercial development; unless the batholith itself can be found to contain gold or platinum in sufficent quantities to rate further development.

Bibliography

Bennison, A.P. - Geologic Highway Map, Pacific Northwest Region, 1973
Cannon, Bart - Minerals of Washington, 1975
Huston, Richard - Unpublished correspondence, 1980
Ray Lasmanis - for x-ray defraction of extremely small samples and microscopic work.